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Original Article

Korean J Orthod 2021; 51(1): 55-74

Published online January 25, 2021 https://doi.org/10.4041/kjod.2021.51.1.55

Copyright © The Korean Association of Orthodontists.

The global distribution of permanent canine hypodontia: A systematic review

Saritha Sivarajana , Shani Ann Mania, Jacob Johnb, Mona M. Salah Fayedc, Yoon-Ah Kookd, Mang Chek Weya

aDepartment of Pediatric Dentistry and Orthodontics, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia
bDepartment of Restorative Dentistry, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia
cDepartment of Orthodontics, Faculty of Dentistry, Cairo University, Cairo, Egypt
dDepartment of Dentistry, College of Medicine, The Catholic University of Korea, Seoul, Korea

Correspondence to:Wey Mang Chek.
Associate Professor, Department of Pediatric Dentistry and Orthodontics, Faculty of Dentistry, University of Malaya, Lembah Pantai, Kuala Lumpur 50603, Malaysia.
Tel +0176355746 e-mail weymc@um.edu.my

Received: April 29, 2020; Revised: September 13, 2020; Accepted: September 16, 2020

Objective: To systematically review studies on canine agenesis prevalence in different populations and continents, based on the jaw, sex, location, and associated dental anomalies. Methods: Electronic and hand searches of English literature in PubMed, Web of Science, Scopus, OpenGrey, and Science Direct were conducted, and the authors were contacted when necessary. Observational studies (population-based, hospital/clinic-based, and cross-sectional) were included. For study appraisal and synthesis, duplicate selection was performed independently by two reviewers. Study quality was assessed using a modified Strengthening the Reporting of Observational Studies in Epidemiology checklist, with main outcome of prevalence of canine agenesis. Results: The global population prevalence of canine agenesis was 0.30% (0.0−4.7%), highest in Asia (0.54%), followed by Africa (0.33%), and the least in Europe and South America (0.19% in both continents). Canine agenesis was more common in the maxilla (88.57%), followed by both maxilla and mandible (8.57%), and the least common was mandible-only presentation (2.86%). The condition was more common in females (female:male ratio = 1.23), except in Asia (female:male ratio = 0.88) and Africa (female:male ratio = 1). In Asia, unilateral agenesis was almost twice as prevalent as bilateral, but in Europe, the bilateral form was more common. Conclusions: The overall prevalence of canine agenesis is 0.30%, with the highest prevalence in Asia, followed by Africa, Europe, and South America. The condition is more common in the maxilla than the mandible, and in females than males (except in Asia and Africa), with unilateral agenesis being more common in Asia and the bilateral form showing a greater prevalence in Europe.

Keywords: Canine agenesis, Prevalence, Continents

Congenital absence of teeth, hypodontia,1 is the most prevalent craniofacial malformation and dental anomaly.2 Its reported prevalence varies across studies, continents, racial groups, dentitions, sexes, and jaws. The prevalence ranges widely among Caucasians (3.9% to 11.3%)3 and is higher among African populations (13.4%), followed by European (7%), Asian (6.3%), and Australian (6.3%) populations.4 Female subjects are more likely to show hypodontia than male.3-6 The occurrence of this condition can be classified as common, less common, and rare.3 Canine agenesis refers to failure of canine formation, which are considered to be the most stable teeth; agenesis of maxillary canines is less common, while that of mandibular canines is rarely observed.7 Nevertheless, the absence of canines complicates orthodontic treatment planning because of their esthetic and functional importance.8

Information regarding the global and regional distribution of canine agenesis is of paramount importance since it can elucidate the treatment need, complexity of treatment, and the resources required to manage these cases. Early detection may facilitate interventions to ameliorate the disease process, such as early primary tooth removal to enhance space closure or maintenance of the predecessor to ensure adequate alveolar bone for future replacement.9 Some degree of multidisciplinary combined management may be required, especially in cases of unilateral agenesis. Furthermore, the assessment of agenesis prevalence by continents can reflect the comparative frequency of missing teeth in different regions of the world. There is a paucity of studies on the prevalence of canine agenesis, with very few studies reporting the prevalence of agenesis exclusively, and most only superficially referring to individual studies without analyzing the combined prevalence, and instead only focused on the prevalence of hypodontia in general.

The aim of the current review was to summarize the available worldwide data on canine agenesis. The primary objective was to systematically evaluate the available evidence related to its prevalence in different general populations and continents. The secondary objectives were to report the prevalence by jaw (maxilla and mandible), sex (male and female), and location (unilateral or bilateral), and to report the associated dental anomalies. Identifying the overall prevalence and pattern can enhance management and better treatment planning of this condition.

Protocol and registration

This systematic review was conducted and reported in accordance with the Cochrane Handbook for Systematic Reviews of Interventions and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).10 The review protocol was registered in the National Institute of Health Research database (https://www.crd.york.ac.uk/prospero/; protocol no: CRD42019120204; registration Date: March 14, 2019). Ethical approval was unnecessary since we retrieved data from previously published studies in which informed consent had been obtained by the primary investigators.

Eligibility criteria

Inclusion criteria
  • 1. Participants: Male and female subjects with no age restriction; sample size of 50 participants or more

  • 2. Outcome measures

    • a. Primary outcome: Overall prevalence of canine agenesis

    • b. Secondary outcomes: Prevalence of canine agenesis in the maxilla and mandible, female:male ratio, ratio of unilateral to bilateral cases, dental anomalies associated with canine agenesis

  • 3. Study design: Observational studies (population-based studies, hospital/clinic-based studies, and cross-sectional studies), studies supported by radiographic imaging of the teeth or relevant history and records

  • 4. Published English studies with no publication-year restriction

Exclusion criteria
  • 1. Studies on syndromic patients (e.g., patients with a cleft involving the alveolus or those with Down’s syndrome)

  • 2. Case reports, case series, systematic reviews, or meta-analyses

  • 3. Studies that reported canine agenesis in specific samples of patients with teeth agenesis that cannot be generalized to the general population, e.g., canine agenesis in hypodontia patients with no relevance to the general population.

Information sources, search strategy, and study selection

Comprehensive electronic database searches without publication-year restrictions were conducted for literature published until May 4, 2019 (Table 1 and Figure 1). Only articles in English were included from relevant databases such as PubMed, Web of Science, Scopus, OpenGrey, and Science Direct. In addition, hand searches of relevant journals, such as those listed in relevant systematic reviews, was performed. Articles and reference lists of the included studies were individually screened for additional relevant studies. The corresponding authors were contacted for obtaining clarifications or additional information when necessary.

Table 1 . Search engines, keywords, dates of searches, and the data retrieved

Search enginesKeywordsDateResultsDuplicatesExclusion by titleExclusion by abstractExclusion by full textFinal
PubMed‘Canine Or Cuspid’ AND ‘Agenesis OR missing OR hypodontia’ AND ‘Prevalence Or Incidence Or Association’ AND ‘Maxillary Or Mandibular’ AND ‘Population or Hospital’ AND ‘Dental anomalies’2.5.19322,49020601
Web of Science‘Canine Or Cuspid’ AND ‘Agenesis OR missing OR hypodontia’ AND ‘Prevalence Or Incidence Or Association’ AND ‘Maxillary Or Mandibular’ AND ‘Population or Hospital’ AND {Dental anomalies}2.5.193620412
ScopusSame as above2.5.194964135419
OpenGreySame as above2.5.196,1152,6951,00111
Science Direct'canine' AND 'agenesis' AND 'prevalence' AND 'maxillary or mandibular' AND 'population' AND 'dental anomalies'2.5.1923963
Hand-searched articles680033
Total6,7702,4904,2801,1235249

The process of exclusion that led to the final list of included studies is presented.


Figure 1. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart of the study selection process.

The search strategy was implemented using a combination of Medical Subject Headings (MeSH) and free-text words for PubMed and optimized for each database (Table 1). Literature search, study inclusion, methodology quality assessment, and data extraction were carried out independently and in duplicate by two pairs of reviewers (S.S. & M.C.W. and S.A.M. & J.J.) who were not blinded to the authors, and the results were revised by the fifth author (M.M.S.F.).

Eligible articles were assessed in two phases. In the first phase, only titles and abstracts were screened. Full-text assessment was then conducted in the second phase to determine final eligibility. Articles were excluded when they did not meet one or more of the inclusion criteria. Any disagreements were resolved by discussion and consultation with the fifth author (M.M.S.F.) for consensus.

Data items

A standardized data extraction sheet was designed for data extraction by the two pairs of independent reviewers in duplicate (S.S. & M.C.W. and S.A.M. & J.J.). Data extraction included general information (the names of the authors, the year of publication, and the study setting), data pertaining to methods (study design), participant data (sample size, age, sex, country, region, race, and population) and outcome data (primary and secondary outcomes mentioned). Race referred to a group of people who shared similar physical characteristics.

Risk of bias across studies

Critical appraisal of the study was performed using a modified version of Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) checklist11 consisting of seven items related to (1) study design, (2) study setting, (3) participant criteria, (4) sample size, (5) variable description, (6) outcome measurements, and (7) statistical analysis. The quality of the studies was categorized as weak (3 and less), moderate (4 or 5), or high (6 or more) by two pairs of independent reviewers in duplicate (S.S. & M.C.W. and S.A.M. & J.J.). Any disagreements were resolved by discussion and consultation with the fifth author for consensus (M.M.S.F.).

Summary measures and synthesis of results

Relevant prevalences from every study were recalculated and summed to be reported as overall percentages across all studies (Tables 2 and 3) and in terms of agenesis in the maxilla and mandible, female:male ratio, and unilateral and bilateral agenesis.

Table 2 . Population prevalence of canine agenesis among the assessed individuals

No.StudyNumber of individuals with canine agenesisStudy size (n)Prevalence of agenesis by individual (%)
1Mani et al.17 (2014)58340.60
2Alsoleihat and Khraisat35 (2014)4854.71
3Patil et al.19 (2013)184,1330.44
4Afify and Zawawi47 (2012)58780.57
5Rózsa et al.16 (2009)134,4170.29
6Kazanci et al.20 (2011)13,1650.03
7Bäckman and Wahlin36 (2001)07390.00
8Locht41 (1980)17040.14
9Bernadette et al.34 (2013)29470.21
10Gomes et al.15 (2010)21,0490.19
11Ng’ang’a and Ng’ang’a25 (2001)26150.33
Total5317,5660.30

Table 3 . Prevalence of canine agenesis based on the total number of missing teeth

No.StudyNumber of cases of canine agenesisNumber of cases of tooth agenesisPrevalence of agenesis by number of teeth (%)
1Mani et al.17 (2014)85081.57
2Alsoleihat and Khraisat35 (2014)41428.57
3Endo et al.5 (2006)566968.05
4Abu-Hussein et al.24 (2015)31671.80
5Nik-Hussein48 (1989)2812.47
6Sisman et al.26 (2007)91824.95
7Sheikhi et al.29 (2012)274545.95
8Chung et al.44 (2008)253297.60
9Vahid-Dastjerdi et al.32 (2010)101975.08
10Zhang et al.45 (2015)10694111.26
11Al-Abdallah46 (2015)215843.60
12Kazanci et al.20 (2011)21531.31
13Aktan et al.21 (2010)873,1472.76
14Bäckman and Wahlin36 (2001)0890.00
15Magnússon38 (1977)31671.80
16Nordgarden et al.40 (2002)148341.68
17Locht41 (1980)1931.08
18Rølling and Poulsen43 (2009)171,0701.59
19Behr et al.30 (2011)426936.06
20González-Allo et al.31 (2012)32981.01
21Topkara and Sari33 (2011)93752.40
22Bernadette et al.34 (2013)21361.47
23Gomes et al.15 (2010)21081.85
24Souza-Silva et al.18 (2018)91147.90
25Küchler et al.22 (2008)4994.04
26Calvano Küchler et al.27 (2008)3783.85
27Tavajohi-Kermani et al.23 (2002)22260.88
28Muller et al.39 (1970)189401.91
29Lai and Seow28 (1989)263148.28
30Lynham37 (1990)3923.26
31Ng’ang’a and Ng’ang’a25 (2001)3793.80
Total39713,2582.99


Additional analyses

No subgroup analysis was performed.

Study selection

Initial database and hand searches yielded a total of 6,770 studies, of which 2,490 duplicates were excluded (Figure 1). Subsequent exclusion by title (3,157) and abstract (1,071) yielded 52 remaining articles, which were considered for this review. This included 18 articles identified from database searches and 34 articles identified with hand searches.

Study characteristics

Full texts of all 52 articles were assessed for eligibility. Two studies12,13 were excluded since they did not report actual prevalence data or data that can be used to calculate the prevalence for their populations, and another study excluded samples with canine agenesis in both arches,14 which affected the accuracy of the overall prevalence estimation.

Risk of bias within studies

Critical appraisal of the remaining 49 articles was performed using the modified STROBE checklist (Table 4). After excluding 14 studies (28.6%) that were of moderate quality (modified STROBE score of 4 or 5), 35 (71.4%) high-quality studies5,15-48 (modified STROBE score of 6 or 7) were included in this systematic review.

Table 4 . Quality analysis of the 49 studies based on a modified STROBE checklist

No.AuthorStudy designSettingParticipant criteriaSample sizeVariable descriptionOutcome measurementStatistical testTotal score
1Gomes et al.15 (2010)7
2Rózsa et al.16 (2009)7
3Finkelstein et al.6 (2018)XX5
4Mani et al.17 (2014)7
5Alsoleihat and Khraisat35 (2014)X6
6Souza-Silva et al.18 (2018)7
7Patil et al.19 (2013)X6
8Kazanci et al.20 (2011)7
9Aktan et al.21 (2010)7
10Edward et al. (2008)XX5
11Küchler et al.22 (2008)X6
12Tavajohi-Kermani et al.23 (2002)7
13Shafi et al. (2008)XX5
14Endo et al.5 (2006)7
15Aasheim and Ogaard (1993)XX5
16Abu-Hussein et al.24 (2015)7
17Afify and Zawawi47 (2012)7
18Altug-Atac and Erdem (2007)XXX4
19Bäckman and Wahlin36 (2001)7
20Bergstnou (1977)XX5
21Davis (1987)XXX4
22Fekonja (2005)XX5
23Fukuta et al. (2004)XXX4
24Nik-Hussein48 (1989)X6
25Ng’ang’a and Ng’ang’a25 (2001)7
26Sisman et al.26 (2007)X6
27Calvano Küchler et al.27 (2008)X6
28Lai and Seow28 (1989)X6
29Lynham37 (1990)X6
30Magnússon38 (1977)X6
31Muller et al.39 (1970)X6
32Nordgarden et al.40 (2002)X6
33Locht41 (1980)X6
34da Cunha Coelho et al. (2012)XX5
35Gokkaya et al.42 (2016)X6
36Sheikhi et al.29 (2012)7
37Rølling and Poulsen43 (2009)X6
38Rose (1966)XXX4
39Behr et al.30 (2011)7
40Chung et al.44 (2008)X6
41González-Allo et al.31 (2012)7
42Vahid-Dastjerdi et al.32 (2010)7
43Zhang et al.45 (2015)X6
44Topkara and Sari33 (2011)7
45Shetty et al. (2012)XX5
46Bernadette et al.34 (2013)7
47Al-Abdallah46 (2015)7
48Raju et al. (2011)XX5
49O'Dowling and McNamara (1990)XX5

STROBE, Strengthening the Reporting of Observational Studies in Epidemiology.



Results of individual studies

Description of the studies

A total of 35 studies were included in this review. The demographic data are summarized in Table 5. Slightly less than two-thirds15-34 (57.1%) of the selected studies were retrospective, about a third35-46 (34.3%) were cross-sectional, while two studies29,47 were both retrospective and cross-sectional. Almost half (48.6%)17-21,24,29-35,42,45-47 of the studies were published after the year 2010. The sample size varied from 85 to 100,577, with a median of 1,622 participants. The study participants, aged 5–46 years, were recruited equally from orthodontic (36.1%) and dental clinics (36.1%), followed by the pediatric clinic (13.9%). One study45 recruited patients from both orthodontic and pediatric clinics, another44 recruited them from dental and orthodontic clinics, while another37 recruited participants from the Australian defense force. Only two studies39,43 were epidemiological surveys. Almost an equal number of studies were from Asia (n = 14, 40.0%) and Europe (n = 12, 34.3%), followed by South America (n = 4, 11.4%), North America (n = 2, 5.7%), Australia (n = 2, 5.7%), and Africa (n = 1, 2.9%). The global reported population prevalence of canine agenesis ranged from 0.0% to 4.7% (Table 6), with high variations among studies, and the median prevalence was 0.29%. The term population refers to the people living in a particular country. The prevalence of canine agenesis in the maxilla (between 0.03% and 4.7%) was higher than that in the mandible (between 0% and 1.12%).

Table 5 . Demographic characteristics of the high-quality studies

No.AuthorYear of studyStudy designStudy settingsSample sizeAge (yr)Sex (M:F)CountryRegionRacePopulation
1Endo et al.5 (2006)NARetrospective studyPediatric and orthodontic clinics of Nippon Dental University3,3585–151:1.3JapanNiigataJapaneseOrthodontic patients
2Gomes et al.15 (2010)1998–2000Retrospective studyOrthodontic patient at the Federal District Brazil (16 orthodontic clinics)1,04910–151:1.07BrazilBrasíliaNAOrthodontic patients
3Rózsa et al.16 (2009)NARetrospective studyDepartment of Pediatric Dentistry and Orthodontics, University Budapest4,4176–181:1HungaryBudapestHungarianOrthodontic and pediatric patients
4Mani et al.17 (2014)2004–2010Retrospective studyRadiology department of the dental clinic of the University Sains Malaysia83412–161:1.32MalaysiaKelantanMalayDental patients
5Souza-Silva et al.18 (2018)2014–2016Retrospective studyRadiographic centre3,4008–301:1.17BrazilNortheast regionNAOrthodontic patients
6Patil et al.19 (2013)2008–2012Retrospective studyDepartment of Oral Medicine and Radiology, Jodhpur Dental College General Hospital4,13313–381:0.93IndiaJodhpurIndianDental patients
7Kazanci et al.20 (2011)1996–2008Retrospective studyDepartment of Orthodontics, Faculty of Dentistry, Ataturk University3,1659–251:1.58TurkeyNATurkishOrthodontic patients
8Aktan et al.21 (2010)NARetrospective studyEight clinics100,5775–371:2.37Turkey6 regions- Samsun, Gaziantep, Kayseri, Tokat, Konya, BoluTurkishDental patients
9Küchler et al.22 (2008)1999–2007Retrospective studyFederal University of Rio de Janeiro’s Continuing Education Clinical Program in Pediatric Dentistry1,1676–121:1.24BrazilNorthern Rio de JaneiroNAPediatric patients
10Tavajohi-Kermani et al.23 (2002)NARetrospective studyDepartment of Orthodontics, University of Tennessee, and orthodontic practices in Memphis1,0168–181:2.3USAPittsburghNAOrthodontic patients
11Abu-Hussein et al.24 (2015)2006–2013Retrospective studyHypodontia patients to Center for Dentistry, Research & Aesthetics2,20010.2–39.51:1.6IsraelJatt, AlmothalatArabOrthodontic patients
12Ng’ang’a and Ng’ang’a25 (2001)2001Retrospective case studyPrivate orthodontic practice6158–151:0.86KenyaNairobi 30% from other parts of thecountryKenyans of African descentOrthodontic patients
13Sisman et al.26 (2007)2007Retrospective studyOrthodontic patient files Department of Orthodontics of Erciyes University, Kayseri and Kırıkkale University2,4139–361:1.82TurkeyKirikkaleNAOrthodontic patients
14Calvano Küchler et al.27 (2008)2008Retrospective studyThose attending the Federal University of Rio De Janeiro’s continuing Education Clinical program in Pediatric Dentistry975 patients6–121:1.01BrazilRio de JaneiroNAPediatric patients
15Lai and Seow28 (1989)1989Retrospective studyCurrent patient records kept at the Pediatric Dentistry Unit of the Dental School, University of Queensland1,032 patients obtained after screening6–191:0.95AustraliaQueensland, dental schoolCaucasianPediatric patients
16Sheikhi et al.29 (2012)2012Retrospective and cross-sectionalFaculty of dentistry and dental clinics2,4227–351:1.74Iran8provincesIraniansDental patients
17Behr et al.30 (2011)1994– 2006Retrospective studyRegensburg University Medical Centre1,4421,353 final5–441:1.13GermanyEastern BavariaCaucasianOrthodontic patients
18González-Allo et al.31 (2012)2005– 2009Retrospective studyClinical files from dental clinic2,888 panoramic radiographs7–211:1.06PortugalNAPortugueseDental patients
19Vahid-Dastjerdi et al.32 (2010)2010Retrospective studyRecords of Iranian orthodontic patients treated at two schools1,7519–271:0.99IranTehranIraniansOrthodontic patients
20Topkara and Sari33 (2011)2011Retrospective studyDepartment of Orthodontics of the Faculty of Dentistry of the Selcuk University2,761 patients9–461:1.55TurkeyKonyaCaucasian patientsOrthodontic patients
21Bernadetteet al.34 (2013)2004– 2012Retrospective studyPatient’s dental records from belonging to a Pediatric dental office9479–341:1.54RomaniaTîrgu MureșNAPediatric patients
22Alsoleihat and Khraisat35 (2014)2011Cross-sectionalUn-admixed Druze school children (schoolchildren of two schools)8514–181:0.89Jordan (East Jordan)Al-AzraqDruze practising consanguin eous marriages and endogamySchool children
23Bäckman and Wahlin36 (2001)1976Cross-sectionalDepartment of Odontology/Pedodontics, UmeaÊ University73971:1SwedenUmeå, northern SwedenSwedishDental patients
24Lynham37 (1990)1990Cross-sectionalAustralian defense force recruits662 obtained after screening16–261:0.24AustraliaNANAAustralian defense force
25Magnússon38 (1977)1977Cross-sectionalSchool children1,116 final sample8–161:1.14IcelandReykjavikNASchool children
26Muller et al.39 (1970)1970Cross-sectionalChildren part of a large survey14,9401. White – 13,4592. African American – 1,48111–15Overall 1:1.01White 1:1.01African American1:0.91USAIllinoisWhite and African AmericanEpidemiological study
27Nordgarden et al.40 (2002)2002Cross-sectional97 public clinics9,532181:0.95NorwayOslo and Akershus countiesNorwegiansDental patients
28Locht41 (1980)1980Cross-sectionalOne school district7049–101:0.88DenmarkArhus municipalityDanishDental patients
29Gokkaya and Kargul42 (2016)2016Cross-sectionalDepartment of Pediatric Dentistry, Dental School of Marmara University1,6587–121:1.11TurkeyIstanbulTurkishDental patients
30Rølling and Poulsen43 (2009)2009Cross-sectionalOne district, all children examined as part of a systematic oral health care8,1389–121:1DenmarkArhus municipalityDanishAll children, epidemiological
31Chung et al.44 (2008)2008Cross-sectionalDepartment of Orthodontics, Yongdong Severance Dental Hospital, Yonsei University8831:1.65KoreaSeoulKoreansOrthodontic patients
32Zhang et al.45 (2015)2008Cross-sectionalGeneral group enrolled in three university in Hebei provinceOrthodontic group visiting the Department of Orthodontics, Peking University6,015 -general3,481 -orthodontic10–26General 1:0.89Orthodontic1:1.5ChinaHebei provinceHan originDental and orthodontic patients
33Al-Abdallah46 (2015)2011Cross-sectionalDepartment of Oral Medicine and Radiology, Institute of Dental Sciences8,22512–181:1.19IndiaBareilly, UPNorth IndianDental patients
34Afify and Zawawi47 (2012)2002–2011Retrospective and cross-sectional studyFaculty of Dentistry, King Abdul Aziz University87812–301:1.04Saudi ArabiaWestern regionSaudi patientsDental patients
35Nik-Hussein48 (1989)1989NAPatients attending Faculty of Dentistry, University of Malaya1,5836–151:1.01MalaysiaKuala LumpurNADental patients

M, male; F, female; NA, not available.


Table 6 . Overall prevalence of canine agenesis in different geographic locations

Studies/continentsPrevalence of canine agenesis (%)Prevalence of canine agenesis by individual (%)Prevalence of canine agenesis by number of teeth (%)Prevalence of canine agenesis in the general population, excluding the orthodontic group (%)Prevalence of canine agenesis in the orthodontic group (%)
Overall
Based on studies which reported the outcome of interest0.302.990.380.10
Asia
Endo et al.5 (2006)NA*0.547.40--
Mani et al.17 (2014)0.6
Patil et al.19 (2013)0.44
Abu-Hussein et al.24 (2015)NA*
Sisman et al.26 (2007)NA*
Sheikhi et al.29 (2012)NA*
Vahid-Dastjerdi et al.32 (2010)NA*
Alsoleihat and Khraisat35 (2014)4.7
Gokkaya and Kargul42 (2016)NA
Chung et al.44 (2008)NA*
Zhang et al.45 (2015)NA*
Al-Abdallah46 (2015)NA*
Afify and Zawawi47 (2012)0.57
Nik-Hussein48 (1989)NA*
Europe
Rózsa et al.16 (2009)0.290.192.55--
Kazanci et al.20 (2011)0.03
Aktan et al.21 (2010)NA*
Behr et al.30 (2011)NA*
González-Allo et al.31 (2012)NA*
Topkara and Sari33 (2011)NA*
Bernadette et al.34 (2013)0.21
Bäckman and Wahlin36 (2001)0
Magnússon38 (1977)0.27
Nordgarden et al.40 (2002)0.10
Locht41 (1980)0.14
Rølling and Poulsen43 (2009)NA*
South America
Gomes et al.15 (2010)0.190.194.51--
Souza-Silva et al.18 (2018)NA*
Küchler et al.22 (2008)NA
Calvano Küchler et al.27 (2008)NA*
North America
Tavajohi-Kermani et al.23 (2002)NA*NA*1.85--
Muller et al.39 (1970)NA*
Australia
Lai and Seow28 (1989)NA*NA*7.14--
Lynham37 (1990)NA*
Africa
Ng’ang’a and Ng’ang’a25 (2001)0.330.333.80--

NA, not available.

*Study reported the number of cases of canine agenesis, but did not report the number of individuals with canine agenesis.



Synthesis of results

Primary outcomes

Due to the high variation, the overall prevalence was calculated from studies that reported canine agenesis data either by individual (population prevalence based on the number of assessed individuals) or by the number of missing teeth (prevalence of canine agenesis based on the number of missing teeth). The overall prevalence of canine agenesis based on the total number of missing teeth (2.99%) (Table 3) was higher than the population prevalence based on the number of assessed individuals (0.30%) (Table 2). The prevalence in the general population excluding the orthodontic population was higher (0.38%) than that investigated among the orthodontic population (0.10%). The overall population prevalence was the highest in Asia (0.54%), followed by Africa (0.33%),23 and was the least in Europe and South America (0.19% in both continents). Similarly, the prevalence of agenesis as a percentage of missing teeth was the highest in Asia (7.40%), followed by Oceania (Australia) (7.14%), South America (4.51%), Africa (3.80%), and Europe (2.55%), with the lowest prevalence in North America (1.85%) (Table 6).

Secondary outcomes

Pooled prevalence based on studies that reported the prevalence in the maxilla and mandible using data for individuals revealed the same findings, with the maxilla-only prevalence being the highest (88.57%), followed by the prevalence in both the maxilla and mandible (8.57%), and the mandible-only prevalence being the least (2.86%) (Table 7). Similarly, the overall prevalence by teeth was greater in the maxilla (73.73%) than the mandible (26.27%). By continent, the prevalence in the maxilla was the highest in Asia (0.78%), followed by Africa (0.33%) based on one study,25 South America (0.19%) based on one study,14 and the least in Europe (0.13%) based on five studies.16,20,34,36,41 Meanwhile, the prevalence of agenesis in the mandible only and in both maxilla and mandible was only reported in Europe (0.01% and 0.03%, respectively; Table 7). Among all forms of canine agenesis, the overall prevalence of missing maxillary permanent canines was almost similar (35.60% and 39.63%, respectively). Likewise, in the mandible, the prevalence of missing mandibular permanent canines was almost similar (12.07% and 12.69%, respectively).

Table 7 . Prevalence of canine agenesis by jaw in different geographic locations

Studies/continentsPrevalence in maxilla alone (%)Prevalence in mandible alone (%)Prevalence in both maxilla and mandible (%)Continentprevalence in maxilla alone (%)Continentprevalence in mandible alone (%)Prevalence in both maxilla and mandible in the same individuals (%)
Overall
Based on studies which reported the outcome of interest88.572.868.57
Asia
Endo et al.5 (2006)NA*NA*NA*0.780.000.00
Mani et al.17 (2014)0.600
Patil et al.19 (2013)NANANA
Abu-Hussein et al.24 (2015)NA*NA*NA
Sisman et al.26 (2007)NANA*NA
Sheikhi et al.29 (2012)0.580.25NA
Vahid-Dastjerdi et al.32 (2010)NA*NA*NA*
Alsoleihat and Khraisat35 (2014)4.700
Gokkaya and Kargul42 (2016)NA00
Chung et al.44 (2008)NA*NA*NA*
Zhang et al.45 (2015)NA*NA*NA*
Al-Abdallah46 (2015)NA*NA*NA
Afify and Zawawi47 (2012)0.570NA
Nik-Hussein48 (1989)NA*0NA*
Europe
Rózsa et al.16 (2009)0.200.020.070.130.010.03
Kazanci et al.20 (2011)0.0300
Aktan et al.21 (2010)NA*NA*NA
Behr et al.30 (2011)NA*NA*NA*
González-Allo et al.31 (2012)NA*NA*NA*
Topkara and Sari33 (2011)NA*NA*NA*
Bernadette et al.34 (2013)0.210.00%0.00%
Bäckman and Wahlin36 (2001)0%00
Magnússon38 (1977)0.270NA
Nordgarden et al.40 (2002)0.090.01NA
Locht41 (1980)0.1400.14
Rølling and Poulsen43 (2009)NA*NA*NA*
South America
Gomes et al.15 (2010)0.19000.1900
Souza-Silva et al.18 (2018)NA*NA*NA
Küchler et al.22 (2008)NANANA
Calvano Küchler et al.27 (2008)NANANA
North America
Tavajohi-Kermani et al.23 (2002)NANANANANANA
Muller et al.39 (1970)0.060.01NA
Australia
Lai and Seow28 (1989)NA*NA*NANA*NA*NA*
Lynham37 (1990)NANA*NA
Africa
Ng’ang’a and Ng’ang’a25 (2001)0.33000.3300

NA, not available.

*Study reported the number of cases of canine agenesis, but did not report the number of individuals with canine agenesis.



By sex, the overall ratio of canine agenesis was higher in females than in males, with a female:male ratio of 1.23. However, this was only true in Europe and South America, wherein females were twice as much affected than males. In Asia, the ratio was higher among males (ratio = 0.88), while the prevalence was the same for both sexes (ratio = 1) in Africa (Table 8). The overall bilateral:unilateral agenesis ratio was 1.13. The worldwide prevalence of unilateral agenesis was almost similar to that of the bilateral form (50.0% and 46.7%, respectively). However, in Asia, the prevalence of unilateral agenesis was almost double that of bilateral agenesis (66.7% and 33.3%, respectively). In Europe, the prevalence of bilateral (58.8%) agenesis was higher than that of unilateral agenesis (35.3%) (Table 9).

Table 8 . Prevalence of canine agenesis by sex

ContinentsMale:femaleOverall male:female ratio
Overall
Based on studies which reported the outcome of interest1:1.23
Asia
Endo et al.5 (2006)NA1:0.88
Mani et al.17 (2014)1:0.67
Patil et al.19 (2013)1:0.8
Abu-Hussein et al.24 (2015)NA
Sisman et al.26 (2007)NA
Sheikhi et al.29 (2012)NA
Vahid-Dastjerdi et al.32 (2010)NA
Alsoleihat and Khraisat35 (2014)1:3
Gokkaya and Kargul42 (2016)NA
Chung et al.44 (2008)NA
Zhang et al.45 (2015)NA
Al-Abdallah46 (2015)NA
Afify and Zawawi47 (2012)1:0.67
Nik-Hussein48 (1989)NA
Europe
Rózsa et al.16 (2009)1:2.251:2.25
Kazanci et al.20 (2011)NA
Aktan et al.21 (2010)NA
Behr et al.30 (2011)NA
González-Allo et al.31 (2012)NA
Topkara and Sari33 (2011)NA
Bernadette et al.34 (2013)NA
Bäckman and Wahlin36 (2001)0:0
Europe
Magnusson38 (1977)NA
Nordgarden et al.40 (2002)NA
Locht41 (1980)NA
Rølling and Poulsen43 (2009)NA
South America
Gomes et al.15 (2010)0:20:2
Souza-Silva et al.18 (2018)NA
Küchler et al.22 (2008)NA
Calvano Küchler et al.27 (2008)NA
North America
Tavajohi-Kermani et al.23 (2002)NANA
Muller et al.39 (1970)NA
Australia
Lai and Seow28 (1989)NANA
Lynham37 (1990)NA
Africa
Ng’ang’a and Ng’ang’a25 (2001)1:11:1

NA, not available.


Table 9 . Prevalence of canine agenesis by location

ContinentsUnilateral:bilateralPrevalence of individuals with unilateral missing canine only (Individuals with unilateral missing canine only, excluding combined unilateral + bilateral in same individual/all individuals with missing canines) (%)Prevalence of individuals with bilateral missing canine only (Individual with bilateral missing canine only, excluding combined unilateral + bilateral in same individual/all individuals with missing canines) (%)Prevalence of individuals with combined unilateral and bilateral missing canines in the maxilla and mandible (%)
Overall
Based on studies which reported the outcome of interest1:1.1350.046.73.3
Asia
Endo et al.5 (2006)NA66.733.30.0
Mani et al.17 (2014)1:1.5
Patil et al.19 (2013)NA
Abu-Hussein et al.24 (2015)NA
Sisman et al.26 (2007)NA
Sheikhi et al.29 (2012)NA
Vahid-Dastjerdi et al.32 (2010)NA
Alsoleihat and Khraisat35 (2014)4:0
Gokkaya and Kargul42 (2016)NA
Chung et al.44 (2008)NA
Zhang et al.45 (2015)NA
Al-Abdallah46 (2015)NA
Afify and Zawawi47 (2012)NA
Nik-Hussein48 (1989)NA
Europe
Rózsa et al.16 (2009)1:335.358.85.9
Kazanci et al.20 (2011)0:1
Aktan et al.21 (2010)NA
Behr et al.30 (2011)NA
González-Allo et al.31 (2012)NA
Topkara and Sari33 (2011)NA
Bernadette et al.34 (2013)2:0
Bäckman and Wahlin36 (2001)0:0
Magnusson38 (1977)N
Nordgarden et al.40 (2002)NA
Locht41 (1980)1:0
Rølling and Poulsen43 (2009)NA
South America
Gomes et al.15 (2010)2:0100.00.00.0
Souza-Silva et al.18 (2018)NA
Küchler et al.22 (2008)1:0.5
Calvano Küchler et al.27 (2008)NA
North America
Tavajohi-Kermani et al.23 (2002)NANANANA
Muller et al.39 (1970)NA
Australia
Lai and Seow28 (1989)NANANANA
Lynham37 (1990)NA
Africa
Ng’ang’a and Ng’ang’a25 (2001)1:150.050.00

NA, not available.



Common dental anomalies associated with canine agenesis were retained primary canines,16,30 agenesis of other permanent teeth,16,30 agenesis of the third molar,31,32,45,46 supernumerary teeth,16 ankylosis,28 taurodontism,28 enamel hypoplasia and conical incisor,28 and Class III malocclusion.31,45

This systematic review attempted to evaluate the global distribution of canine agenesis in isolation.3,49 We presented the population prevalence of canine agenesis in terms of individuals, which better reflected the actual treatment need, unlike another review4 that reported the prevalence in terms of the number of missing teeth. Reports based on individual prevalence without considering the population sample can be biased, since the bigger quantity of smaller-sized studies may overwhelm the smaller quantity of bigger-sized studies and distort the final summary. Therefore, we recalculated the prevalence in every included study to generate an overall prevalence.

In this review, an almost equal proportion of the included studies were conducted in Asia (37.1%) and Europe (37.1%); this was in contrast to the review on the overall prevalence of hypodontia, in which most studies were conducted in European countries (43.0%), followed by the Asian region (32.0%).4 The global distribution in this review ranged from 0.0% to 4.7%, with a pooled overall prevalence of 0.30%, which is much lower than that of hypodontia (6.4%).4 Polder et al.3 reported that canines are one of the rarely missing teeth after the first and the second molars.

In this review, the prevalence of canine agenesis was higher in the Asian region than in the African, European, and South American regions. In contrast, the overall prevalence of hypodontia was the highest in Africa (13.4%, 95% confidence interval [CI]: 9.7, 18.0), followed by Europe (7% CI: 6.0, 8.0%) and Asia (6.3% CI: 4.4, 9.1).4 This suggests that canine agenesis per se is more common in the Asian region than in the European region, possibly due to the racial differences between the two continents.

Our findings showing that canine agenesis was more common in the maxilla than the mandible are in agreement with the general pattern of hypodontia reported in two other systematic reviews addressing hypodontia, both of which reported marked differences between the jaws in relation to the frequency of agenesis of various tooth types.3,4 Similarly, the greater prevalence in females is in agreement with the findings of these two systematic reviews.3,4 However, in Asia, the higher prevalence in males may indicate a genetic inheritance of this trait among males. Bilateral agenesis was more prevalent than unilateral agenesis in Europe, similar to the general pattern of hypodontia except for the maxillary lateral incisors.3 However, in Asia, the prevalence of unilateral agenesis was double that of the bilateral form, indicating a genetic inheritance pattern among Asians. The overall information presented in this review could provide valuable guidance to clinicians for treatment planning and managing patients with canine agenesis.

Since we aimed to report the prevalence based on the number of individuals with missing canines, we could not include studies reporting the number of missing canines instead of the number of individuals with missing canines; this limited our ability to present the data in terms of combined prevalence by number of teeth. Most studies assessed either orthodontic patients,5,14,17,19,22-25,29,31,32,43 pediatric patients,21,26,27,33 both orthodontic and pediatric patients,15 both orthodontic and dental patients,44 or dental patients.16,18,20,28,30,35,39-41,45-47 Three studies were epidemiological surveys of school children,34,37,42 one enrolled defense force recruits,36 while only one study was a truly epidemiological study on a general population.38

  • 1. The global distribution of canine agenesis ranged from 0.0% to 4.7%, with a pooled overall population prevalence of 0.30%.

  • 2. The population prevalence of canine agenesis was the highest in Asia (0.54%), followed by Africa (0.33%); the least prevalence was observed in Europe and South America (0.19% for both continents).

  • 3. The highest prevalence was of the maxilla-only form (88.57%), followed by the presentation in both maxilla and mandible (8.57%), while the mandible-only form showed the lowest prevalence (2.86%).

  • 4. Canine agenesis was more common in females, with an overall female:male ratio of 1.23, except in Asia (0.88) and Africa (1).

  • 5. In Asia, the prevalence of unilateral agenesis was almost double that of bilateral agenesis, but in Europe, bilateral agenesis was more common.

With a clearer picture of the occurrence of canine agenesis and its accompanying predilection, management of the condition can be better predicted and planned. Future research on prevalence is suggested to report both in terms of missing teeth and individuals, also moving forward, research linked to its aetiology and genetic-based treatment can be considered.

No potential conflict of interest relevant to this article was reported.

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Article

Original Article

Korean J Orthod 2021; 51(1): 55-74

Published online January 25, 2021 https://doi.org/10.4041/kjod.2021.51.1.55

Copyright © The Korean Association of Orthodontists.

The global distribution of permanent canine hypodontia: A systematic review

Saritha Sivarajana , Shani Ann Mania, Jacob Johnb, Mona M. Salah Fayedc, Yoon-Ah Kookd, Mang Chek Weya

aDepartment of Pediatric Dentistry and Orthodontics, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia
bDepartment of Restorative Dentistry, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia
cDepartment of Orthodontics, Faculty of Dentistry, Cairo University, Cairo, Egypt
dDepartment of Dentistry, College of Medicine, The Catholic University of Korea, Seoul, Korea

Correspondence to:Wey Mang Chek.
Associate Professor, Department of Pediatric Dentistry and Orthodontics, Faculty of Dentistry, University of Malaya, Lembah Pantai, Kuala Lumpur 50603, Malaysia.
Tel +0176355746 e-mail weymc@um.edu.my

Received: April 29, 2020; Revised: September 13, 2020; Accepted: September 16, 2020

Abstract

Objective: To systematically review studies on canine agenesis prevalence in different populations and continents, based on the jaw, sex, location, and associated dental anomalies. Methods: Electronic and hand searches of English literature in PubMed, Web of Science, Scopus, OpenGrey, and Science Direct were conducted, and the authors were contacted when necessary. Observational studies (population-based, hospital/clinic-based, and cross-sectional) were included. For study appraisal and synthesis, duplicate selection was performed independently by two reviewers. Study quality was assessed using a modified Strengthening the Reporting of Observational Studies in Epidemiology checklist, with main outcome of prevalence of canine agenesis. Results: The global population prevalence of canine agenesis was 0.30% (0.0−4.7%), highest in Asia (0.54%), followed by Africa (0.33%), and the least in Europe and South America (0.19% in both continents). Canine agenesis was more common in the maxilla (88.57%), followed by both maxilla and mandible (8.57%), and the least common was mandible-only presentation (2.86%). The condition was more common in females (female:male ratio = 1.23), except in Asia (female:male ratio = 0.88) and Africa (female:male ratio = 1). In Asia, unilateral agenesis was almost twice as prevalent as bilateral, but in Europe, the bilateral form was more common. Conclusions: The overall prevalence of canine agenesis is 0.30%, with the highest prevalence in Asia, followed by Africa, Europe, and South America. The condition is more common in the maxilla than the mandible, and in females than males (except in Asia and Africa), with unilateral agenesis being more common in Asia and the bilateral form showing a greater prevalence in Europe.

Keywords: Canine agenesis, Prevalence, Continents

INTRODUCTION

Congenital absence of teeth, hypodontia,1 is the most prevalent craniofacial malformation and dental anomaly.2 Its reported prevalence varies across studies, continents, racial groups, dentitions, sexes, and jaws. The prevalence ranges widely among Caucasians (3.9% to 11.3%)3 and is higher among African populations (13.4%), followed by European (7%), Asian (6.3%), and Australian (6.3%) populations.4 Female subjects are more likely to show hypodontia than male.3-6 The occurrence of this condition can be classified as common, less common, and rare.3 Canine agenesis refers to failure of canine formation, which are considered to be the most stable teeth; agenesis of maxillary canines is less common, while that of mandibular canines is rarely observed.7 Nevertheless, the absence of canines complicates orthodontic treatment planning because of their esthetic and functional importance.8

Information regarding the global and regional distribution of canine agenesis is of paramount importance since it can elucidate the treatment need, complexity of treatment, and the resources required to manage these cases. Early detection may facilitate interventions to ameliorate the disease process, such as early primary tooth removal to enhance space closure or maintenance of the predecessor to ensure adequate alveolar bone for future replacement.9 Some degree of multidisciplinary combined management may be required, especially in cases of unilateral agenesis. Furthermore, the assessment of agenesis prevalence by continents can reflect the comparative frequency of missing teeth in different regions of the world. There is a paucity of studies on the prevalence of canine agenesis, with very few studies reporting the prevalence of agenesis exclusively, and most only superficially referring to individual studies without analyzing the combined prevalence, and instead only focused on the prevalence of hypodontia in general.

The aim of the current review was to summarize the available worldwide data on canine agenesis. The primary objective was to systematically evaluate the available evidence related to its prevalence in different general populations and continents. The secondary objectives were to report the prevalence by jaw (maxilla and mandible), sex (male and female), and location (unilateral or bilateral), and to report the associated dental anomalies. Identifying the overall prevalence and pattern can enhance management and better treatment planning of this condition.

MATERIALS AND METHODS

Protocol and registration

This systematic review was conducted and reported in accordance with the Cochrane Handbook for Systematic Reviews of Interventions and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).10 The review protocol was registered in the National Institute of Health Research database (https://www.crd.york.ac.uk/prospero/; protocol no: CRD42019120204; registration Date: March 14, 2019). Ethical approval was unnecessary since we retrieved data from previously published studies in which informed consent had been obtained by the primary investigators.

Eligibility criteria

Inclusion criteria
  • 1. Participants: Male and female subjects with no age restriction; sample size of 50 participants or more

  • 2. Outcome measures

    • a. Primary outcome: Overall prevalence of canine agenesis

    • b. Secondary outcomes: Prevalence of canine agenesis in the maxilla and mandible, female:male ratio, ratio of unilateral to bilateral cases, dental anomalies associated with canine agenesis

  • 3. Study design: Observational studies (population-based studies, hospital/clinic-based studies, and cross-sectional studies), studies supported by radiographic imaging of the teeth or relevant history and records

  • 4. Published English studies with no publication-year restriction

Exclusion criteria
  • 1. Studies on syndromic patients (e.g., patients with a cleft involving the alveolus or those with Down’s syndrome)

  • 2. Case reports, case series, systematic reviews, or meta-analyses

  • 3. Studies that reported canine agenesis in specific samples of patients with teeth agenesis that cannot be generalized to the general population, e.g., canine agenesis in hypodontia patients with no relevance to the general population.

Information sources, search strategy, and study selection

Comprehensive electronic database searches without publication-year restrictions were conducted for literature published until May 4, 2019 (Table 1 and Figure 1). Only articles in English were included from relevant databases such as PubMed, Web of Science, Scopus, OpenGrey, and Science Direct. In addition, hand searches of relevant journals, such as those listed in relevant systematic reviews, was performed. Articles and reference lists of the included studies were individually screened for additional relevant studies. The corresponding authors were contacted for obtaining clarifications or additional information when necessary.

Table 1 . Search engines, keywords, dates of searches, and the data retrieved.

Search enginesKeywordsDateResultsDuplicatesExclusion by titleExclusion by abstractExclusion by full textFinal
PubMed‘Canine Or Cuspid’ AND ‘Agenesis OR missing OR hypodontia’ AND ‘Prevalence Or Incidence Or Association’ AND ‘Maxillary Or Mandibular’ AND ‘Population or Hospital’ AND ‘Dental anomalies’2.5.19322,49020601
Web of Science‘Canine Or Cuspid’ AND ‘Agenesis OR missing OR hypodontia’ AND ‘Prevalence Or Incidence Or Association’ AND ‘Maxillary Or Mandibular’ AND ‘Population or Hospital’ AND {Dental anomalies}2.5.193620412
ScopusSame as above2.5.194964135419
OpenGreySame as above2.5.196,1152,6951,00111
Science Direct'canine' AND 'agenesis' AND 'prevalence' AND 'maxillary or mandibular' AND 'population' AND 'dental anomalies'2.5.1923963
Hand-searched articles680033
Total6,7702,4904,2801,1235249

The process of exclusion that led to the final list of included studies is presented..


Figure 1. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart of the study selection process.

The search strategy was implemented using a combination of Medical Subject Headings (MeSH) and free-text words for PubMed and optimized for each database (Table 1). Literature search, study inclusion, methodology quality assessment, and data extraction were carried out independently and in duplicate by two pairs of reviewers (S.S. & M.C.W. and S.A.M. & J.J.) who were not blinded to the authors, and the results were revised by the fifth author (M.M.S.F.).

Eligible articles were assessed in two phases. In the first phase, only titles and abstracts were screened. Full-text assessment was then conducted in the second phase to determine final eligibility. Articles were excluded when they did not meet one or more of the inclusion criteria. Any disagreements were resolved by discussion and consultation with the fifth author (M.M.S.F.) for consensus.

Data items

A standardized data extraction sheet was designed for data extraction by the two pairs of independent reviewers in duplicate (S.S. & M.C.W. and S.A.M. & J.J.). Data extraction included general information (the names of the authors, the year of publication, and the study setting), data pertaining to methods (study design), participant data (sample size, age, sex, country, region, race, and population) and outcome data (primary and secondary outcomes mentioned). Race referred to a group of people who shared similar physical characteristics.

Risk of bias across studies

Critical appraisal of the study was performed using a modified version of Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) checklist11 consisting of seven items related to (1) study design, (2) study setting, (3) participant criteria, (4) sample size, (5) variable description, (6) outcome measurements, and (7) statistical analysis. The quality of the studies was categorized as weak (3 and less), moderate (4 or 5), or high (6 or more) by two pairs of independent reviewers in duplicate (S.S. & M.C.W. and S.A.M. & J.J.). Any disagreements were resolved by discussion and consultation with the fifth author for consensus (M.M.S.F.).

Summary measures and synthesis of results

Relevant prevalences from every study were recalculated and summed to be reported as overall percentages across all studies (Tables 2 and 3) and in terms of agenesis in the maxilla and mandible, female:male ratio, and unilateral and bilateral agenesis.

Table 2 . Population prevalence of canine agenesis among the assessed individuals.

No.StudyNumber of individuals with canine agenesisStudy size (n)Prevalence of agenesis by individual (%)
1Mani et al.17 (2014)58340.60
2Alsoleihat and Khraisat35 (2014)4854.71
3Patil et al.19 (2013)184,1330.44
4Afify and Zawawi47 (2012)58780.57
5Rózsa et al.16 (2009)134,4170.29
6Kazanci et al.20 (2011)13,1650.03
7Bäckman and Wahlin36 (2001)07390.00
8Locht41 (1980)17040.14
9Bernadette et al.34 (2013)29470.21
10Gomes et al.15 (2010)21,0490.19
11Ng’ang’a and Ng’ang’a25 (2001)26150.33
Total5317,5660.30

Table 3 . Prevalence of canine agenesis based on the total number of missing teeth.

No.StudyNumber of cases of canine agenesisNumber of cases of tooth agenesisPrevalence of agenesis by number of teeth (%)
1Mani et al.17 (2014)85081.57
2Alsoleihat and Khraisat35 (2014)41428.57
3Endo et al.5 (2006)566968.05
4Abu-Hussein et al.24 (2015)31671.80
5Nik-Hussein48 (1989)2812.47
6Sisman et al.26 (2007)91824.95
7Sheikhi et al.29 (2012)274545.95
8Chung et al.44 (2008)253297.60
9Vahid-Dastjerdi et al.32 (2010)101975.08
10Zhang et al.45 (2015)10694111.26
11Al-Abdallah46 (2015)215843.60
12Kazanci et al.20 (2011)21531.31
13Aktan et al.21 (2010)873,1472.76
14Bäckman and Wahlin36 (2001)0890.00
15Magnússon38 (1977)31671.80
16Nordgarden et al.40 (2002)148341.68
17Locht41 (1980)1931.08
18Rølling and Poulsen43 (2009)171,0701.59
19Behr et al.30 (2011)426936.06
20González-Allo et al.31 (2012)32981.01
21Topkara and Sari33 (2011)93752.40
22Bernadette et al.34 (2013)21361.47
23Gomes et al.15 (2010)21081.85
24Souza-Silva et al.18 (2018)91147.90
25Küchler et al.22 (2008)4994.04
26Calvano Küchler et al.27 (2008)3783.85
27Tavajohi-Kermani et al.23 (2002)22260.88
28Muller et al.39 (1970)189401.91
29Lai and Seow28 (1989)263148.28
30Lynham37 (1990)3923.26
31Ng’ang’a and Ng’ang’a25 (2001)3793.80
Total39713,2582.99


Additional analyses

No subgroup analysis was performed.

RESULTS

Study selection

Initial database and hand searches yielded a total of 6,770 studies, of which 2,490 duplicates were excluded (Figure 1). Subsequent exclusion by title (3,157) and abstract (1,071) yielded 52 remaining articles, which were considered for this review. This included 18 articles identified from database searches and 34 articles identified with hand searches.

Study characteristics

Full texts of all 52 articles were assessed for eligibility. Two studies12,13 were excluded since they did not report actual prevalence data or data that can be used to calculate the prevalence for their populations, and another study excluded samples with canine agenesis in both arches,14 which affected the accuracy of the overall prevalence estimation.

Risk of bias within studies

Critical appraisal of the remaining 49 articles was performed using the modified STROBE checklist (Table 4). After excluding 14 studies (28.6%) that were of moderate quality (modified STROBE score of 4 or 5), 35 (71.4%) high-quality studies5,15-48 (modified STROBE score of 6 or 7) were included in this systematic review.

Table 4 . Quality analysis of the 49 studies based on a modified STROBE checklist.

No.AuthorStudy designSettingParticipant criteriaSample sizeVariable descriptionOutcome measurementStatistical testTotal score
1Gomes et al.15 (2010)7
2Rózsa et al.16 (2009)7
3Finkelstein et al.6 (2018)XX5
4Mani et al.17 (2014)7
5Alsoleihat and Khraisat35 (2014)X6
6Souza-Silva et al.18 (2018)7
7Patil et al.19 (2013)X6
8Kazanci et al.20 (2011)7
9Aktan et al.21 (2010)7
10Edward et al. (2008)XX5
11Küchler et al.22 (2008)X6
12Tavajohi-Kermani et al.23 (2002)7
13Shafi et al. (2008)XX5
14Endo et al.5 (2006)7
15Aasheim and Ogaard (1993)XX5
16Abu-Hussein et al.24 (2015)7
17Afify and Zawawi47 (2012)7
18Altug-Atac and Erdem (2007)XXX4
19Bäckman and Wahlin36 (2001)7
20Bergstnou (1977)XX5
21Davis (1987)XXX4
22Fekonja (2005)XX5
23Fukuta et al. (2004)XXX4
24Nik-Hussein48 (1989)X6
25Ng’ang’a and Ng’ang’a25 (2001)7
26Sisman et al.26 (2007)X6
27Calvano Küchler et al.27 (2008)X6
28Lai and Seow28 (1989)X6
29Lynham37 (1990)X6
30Magnússon38 (1977)X6
31Muller et al.39 (1970)X6
32Nordgarden et al.40 (2002)X6
33Locht41 (1980)X6
34da Cunha Coelho et al. (2012)XX5
35Gokkaya et al.42 (2016)X6
36Sheikhi et al.29 (2012)7
37Rølling and Poulsen43 (2009)X6
38Rose (1966)XXX4
39Behr et al.30 (2011)7
40Chung et al.44 (2008)X6
41González-Allo et al.31 (2012)7
42Vahid-Dastjerdi et al.32 (2010)7
43Zhang et al.45 (2015)X6
44Topkara and Sari33 (2011)7
45Shetty et al. (2012)XX5
46Bernadette et al.34 (2013)7
47Al-Abdallah46 (2015)7
48Raju et al. (2011)XX5
49O'Dowling and McNamara (1990)XX5

STROBE, Strengthening the Reporting of Observational Studies in Epidemiology..



Results of individual studies

Description of the studies

A total of 35 studies were included in this review. The demographic data are summarized in Table 5. Slightly less than two-thirds15-34 (57.1%) of the selected studies were retrospective, about a third35-46 (34.3%) were cross-sectional, while two studies29,47 were both retrospective and cross-sectional. Almost half (48.6%)17-21,24,29-35,42,45-47 of the studies were published after the year 2010. The sample size varied from 85 to 100,577, with a median of 1,622 participants. The study participants, aged 5–46 years, were recruited equally from orthodontic (36.1%) and dental clinics (36.1%), followed by the pediatric clinic (13.9%). One study45 recruited patients from both orthodontic and pediatric clinics, another44 recruited them from dental and orthodontic clinics, while another37 recruited participants from the Australian defense force. Only two studies39,43 were epidemiological surveys. Almost an equal number of studies were from Asia (n = 14, 40.0%) and Europe (n = 12, 34.3%), followed by South America (n = 4, 11.4%), North America (n = 2, 5.7%), Australia (n = 2, 5.7%), and Africa (n = 1, 2.9%). The global reported population prevalence of canine agenesis ranged from 0.0% to 4.7% (Table 6), with high variations among studies, and the median prevalence was 0.29%. The term population refers to the people living in a particular country. The prevalence of canine agenesis in the maxilla (between 0.03% and 4.7%) was higher than that in the mandible (between 0% and 1.12%).

Table 5 . Demographic characteristics of the high-quality studies.

No.AuthorYear of studyStudy designStudy settingsSample sizeAge (yr)Sex (M:F)CountryRegionRacePopulation
1Endo et al.5 (2006)NARetrospective studyPediatric and orthodontic clinics of Nippon Dental University3,3585–151:1.3JapanNiigataJapaneseOrthodontic patients
2Gomes et al.15 (2010)1998–2000Retrospective studyOrthodontic patient at the Federal District Brazil (16 orthodontic clinics)1,04910–151:1.07BrazilBrasíliaNAOrthodontic patients
3Rózsa et al.16 (2009)NARetrospective studyDepartment of Pediatric Dentistry and Orthodontics, University Budapest4,4176–181:1HungaryBudapestHungarianOrthodontic and pediatric patients
4Mani et al.17 (2014)2004–2010Retrospective studyRadiology department of the dental clinic of the University Sains Malaysia83412–161:1.32MalaysiaKelantanMalayDental patients
5Souza-Silva et al.18 (2018)2014–2016Retrospective studyRadiographic centre3,4008–301:1.17BrazilNortheast regionNAOrthodontic patients
6Patil et al.19 (2013)2008–2012Retrospective studyDepartment of Oral Medicine and Radiology, Jodhpur Dental College General Hospital4,13313–381:0.93IndiaJodhpurIndianDental patients
7Kazanci et al.20 (2011)1996–2008Retrospective studyDepartment of Orthodontics, Faculty of Dentistry, Ataturk University3,1659–251:1.58TurkeyNATurkishOrthodontic patients
8Aktan et al.21 (2010)NARetrospective studyEight clinics100,5775–371:2.37Turkey6 regions- Samsun, Gaziantep, Kayseri, Tokat, Konya, BoluTurkishDental patients
9Küchler et al.22 (2008)1999–2007Retrospective studyFederal University of Rio de Janeiro’s Continuing Education Clinical Program in Pediatric Dentistry1,1676–121:1.24BrazilNorthern Rio de JaneiroNAPediatric patients
10Tavajohi-Kermani et al.23 (2002)NARetrospective studyDepartment of Orthodontics, University of Tennessee, and orthodontic practices in Memphis1,0168–181:2.3USAPittsburghNAOrthodontic patients
11Abu-Hussein et al.24 (2015)2006–2013Retrospective studyHypodontia patients to Center for Dentistry, Research & Aesthetics2,20010.2–39.51:1.6IsraelJatt, AlmothalatArabOrthodontic patients
12Ng’ang’a and Ng’ang’a25 (2001)2001Retrospective case studyPrivate orthodontic practice6158–151:0.86KenyaNairobi 30% from other parts of thecountryKenyans of African descentOrthodontic patients
13Sisman et al.26 (2007)2007Retrospective studyOrthodontic patient files Department of Orthodontics of Erciyes University, Kayseri and Kırıkkale University2,4139–361:1.82TurkeyKirikkaleNAOrthodontic patients
14Calvano Küchler et al.27 (2008)2008Retrospective studyThose attending the Federal University of Rio De Janeiro’s continuing Education Clinical program in Pediatric Dentistry975 patients6–121:1.01BrazilRio de JaneiroNAPediatric patients
15Lai and Seow28 (1989)1989Retrospective studyCurrent patient records kept at the Pediatric Dentistry Unit of the Dental School, University of Queensland1,032 patients obtained after screening6–191:0.95AustraliaQueensland, dental schoolCaucasianPediatric patients
16Sheikhi et al.29 (2012)2012Retrospective and cross-sectionalFaculty of dentistry and dental clinics2,4227–351:1.74Iran8provincesIraniansDental patients
17Behr et al.30 (2011)1994– 2006Retrospective studyRegensburg University Medical Centre1,4421,353 final5–441:1.13GermanyEastern BavariaCaucasianOrthodontic patients
18González-Allo et al.31 (2012)2005– 2009Retrospective studyClinical files from dental clinic2,888 panoramic radiographs7–211:1.06PortugalNAPortugueseDental patients
19Vahid-Dastjerdi et al.32 (2010)2010Retrospective studyRecords of Iranian orthodontic patients treated at two schools1,7519–271:0.99IranTehranIraniansOrthodontic patients
20Topkara and Sari33 (2011)2011Retrospective studyDepartment of Orthodontics of the Faculty of Dentistry of the Selcuk University2,761 patients9–461:1.55TurkeyKonyaCaucasian patientsOrthodontic patients
21Bernadetteet al.34 (2013)2004– 2012Retrospective studyPatient’s dental records from belonging to a Pediatric dental office9479–341:1.54RomaniaTîrgu MureșNAPediatric patients
22Alsoleihat and Khraisat35 (2014)2011Cross-sectionalUn-admixed Druze school children (schoolchildren of two schools)8514–181:0.89Jordan (East Jordan)Al-AzraqDruze practising consanguin eous marriages and endogamySchool children
23Bäckman and Wahlin36 (2001)1976Cross-sectionalDepartment of Odontology/Pedodontics, UmeaÊ University73971:1SwedenUmeå, northern SwedenSwedishDental patients
24Lynham37 (1990)1990Cross-sectionalAustralian defense force recruits662 obtained after screening16–261:0.24AustraliaNANAAustralian defense force
25Magnússon38 (1977)1977Cross-sectionalSchool children1,116 final sample8–161:1.14IcelandReykjavikNASchool children
26Muller et al.39 (1970)1970Cross-sectionalChildren part of a large survey14,9401. White – 13,4592. African American – 1,48111–15Overall 1:1.01White 1:1.01African American1:0.91USAIllinoisWhite and African AmericanEpidemiological study
27Nordgarden et al.40 (2002)2002Cross-sectional97 public clinics9,532181:0.95NorwayOslo and Akershus countiesNorwegiansDental patients
28Locht41 (1980)1980Cross-sectionalOne school district7049–101:0.88DenmarkArhus municipalityDanishDental patients
29Gokkaya and Kargul42 (2016)2016Cross-sectionalDepartment of Pediatric Dentistry, Dental School of Marmara University1,6587–121:1.11TurkeyIstanbulTurkishDental patients
30Rølling and Poulsen43 (2009)2009Cross-sectionalOne district, all children examined as part of a systematic oral health care8,1389–121:1DenmarkArhus municipalityDanishAll children, epidemiological
31Chung et al.44 (2008)2008Cross-sectionalDepartment of Orthodontics, Yongdong Severance Dental Hospital, Yonsei University8831:1.65KoreaSeoulKoreansOrthodontic patients
32Zhang et al.45 (2015)2008Cross-sectionalGeneral group enrolled in three university in Hebei provinceOrthodontic group visiting the Department of Orthodontics, Peking University6,015 -general3,481 -orthodontic10–26General 1:0.89Orthodontic1:1.5ChinaHebei provinceHan originDental and orthodontic patients
33Al-Abdallah46 (2015)2011Cross-sectionalDepartment of Oral Medicine and Radiology, Institute of Dental Sciences8,22512–181:1.19IndiaBareilly, UPNorth IndianDental patients
34Afify and Zawawi47 (2012)2002–2011Retrospective and cross-sectional studyFaculty of Dentistry, King Abdul Aziz University87812–301:1.04Saudi ArabiaWestern regionSaudi patientsDental patients
35Nik-Hussein48 (1989)1989NAPatients attending Faculty of Dentistry, University of Malaya1,5836–151:1.01MalaysiaKuala LumpurNADental patients

M, male; F, female; NA, not available..


Table 6 . Overall prevalence of canine agenesis in different geographic locations.

Studies/continentsPrevalence of canine agenesis (%)Prevalence of canine agenesis by individual (%)Prevalence of canine agenesis by number of teeth (%)Prevalence of canine agenesis in the general population, excluding the orthodontic group (%)Prevalence of canine agenesis in the orthodontic group (%)
Overall
Based on studies which reported the outcome of interest0.302.990.380.10
Asia
Endo et al.5 (2006)NA*0.547.40--
Mani et al.17 (2014)0.6
Patil et al.19 (2013)0.44
Abu-Hussein et al.24 (2015)NA*
Sisman et al.26 (2007)NA*
Sheikhi et al.29 (2012)NA*
Vahid-Dastjerdi et al.32 (2010)NA*
Alsoleihat and Khraisat35 (2014)4.7
Gokkaya and Kargul42 (2016)NA
Chung et al.44 (2008)NA*
Zhang et al.45 (2015)NA*
Al-Abdallah46 (2015)NA*
Afify and Zawawi47 (2012)0.57
Nik-Hussein48 (1989)NA*
Europe
Rózsa et al.16 (2009)0.290.192.55--
Kazanci et al.20 (2011)0.03
Aktan et al.21 (2010)NA*
Behr et al.30 (2011)NA*
González-Allo et al.31 (2012)NA*
Topkara and Sari33 (2011)NA*
Bernadette et al.34 (2013)0.21
Bäckman and Wahlin36 (2001)0
Magnússon38 (1977)0.27
Nordgarden et al.40 (2002)0.10
Locht41 (1980)0.14
Rølling and Poulsen43 (2009)NA*
South America
Gomes et al.15 (2010)0.190.194.51--
Souza-Silva et al.18 (2018)NA*
Küchler et al.22 (2008)NA
Calvano Küchler et al.27 (2008)NA*
North America
Tavajohi-Kermani et al.23 (2002)NA*NA*1.85--
Muller et al.39 (1970)NA*
Australia
Lai and Seow28 (1989)NA*NA*7.14--
Lynham37 (1990)NA*
Africa
Ng’ang’a and Ng’ang’a25 (2001)0.330.333.80--

NA, not available..

*Study reported the number of cases of canine agenesis, but did not report the number of individuals with canine agenesis..



Synthesis of results

Primary outcomes

Due to the high variation, the overall prevalence was calculated from studies that reported canine agenesis data either by individual (population prevalence based on the number of assessed individuals) or by the number of missing teeth (prevalence of canine agenesis based on the number of missing teeth). The overall prevalence of canine agenesis based on the total number of missing teeth (2.99%) (Table 3) was higher than the population prevalence based on the number of assessed individuals (0.30%) (Table 2). The prevalence in the general population excluding the orthodontic population was higher (0.38%) than that investigated among the orthodontic population (0.10%). The overall population prevalence was the highest in Asia (0.54%), followed by Africa (0.33%),23 and was the least in Europe and South America (0.19% in both continents). Similarly, the prevalence of agenesis as a percentage of missing teeth was the highest in Asia (7.40%), followed by Oceania (Australia) (7.14%), South America (4.51%), Africa (3.80%), and Europe (2.55%), with the lowest prevalence in North America (1.85%) (Table 6).

Secondary outcomes

Pooled prevalence based on studies that reported the prevalence in the maxilla and mandible using data for individuals revealed the same findings, with the maxilla-only prevalence being the highest (88.57%), followed by the prevalence in both the maxilla and mandible (8.57%), and the mandible-only prevalence being the least (2.86%) (Table 7). Similarly, the overall prevalence by teeth was greater in the maxilla (73.73%) than the mandible (26.27%). By continent, the prevalence in the maxilla was the highest in Asia (0.78%), followed by Africa (0.33%) based on one study,25 South America (0.19%) based on one study,14 and the least in Europe (0.13%) based on five studies.16,20,34,36,41 Meanwhile, the prevalence of agenesis in the mandible only and in both maxilla and mandible was only reported in Europe (0.01% and 0.03%, respectively; Table 7). Among all forms of canine agenesis, the overall prevalence of missing maxillary permanent canines was almost similar (35.60% and 39.63%, respectively). Likewise, in the mandible, the prevalence of missing mandibular permanent canines was almost similar (12.07% and 12.69%, respectively).

Table 7 . Prevalence of canine agenesis by jaw in different geographic locations.

Studies/continentsPrevalence in maxilla alone (%)Prevalence in mandible alone (%)Prevalence in both maxilla and mandible (%)Continentprevalence in maxilla alone (%)Continentprevalence in mandible alone (%)Prevalence in both maxilla and mandible in the same individuals (%)
Overall
Based on studies which reported the outcome of interest88.572.868.57
Asia
Endo et al.5 (2006)NA*NA*NA*0.780.000.00
Mani et al.17 (2014)0.600
Patil et al.19 (2013)NANANA
Abu-Hussein et al.24 (2015)NA*NA*NA
Sisman et al.26 (2007)NANA*NA
Sheikhi et al.29 (2012)0.580.25NA
Vahid-Dastjerdi et al.32 (2010)NA*NA*NA*
Alsoleihat and Khraisat35 (2014)4.700
Gokkaya and Kargul42 (2016)NA00
Chung et al.44 (2008)NA*NA*NA*
Zhang et al.45 (2015)NA*NA*NA*
Al-Abdallah46 (2015)NA*NA*NA
Afify and Zawawi47 (2012)0.570NA
Nik-Hussein48 (1989)NA*0NA*
Europe
Rózsa et al.16 (2009)0.200.020.070.130.010.03
Kazanci et al.20 (2011)0.0300
Aktan et al.21 (2010)NA*NA*NA
Behr et al.30 (2011)NA*NA*NA*
González-Allo et al.31 (2012)NA*NA*NA*
Topkara and Sari33 (2011)NA*NA*NA*
Bernadette et al.34 (2013)0.210.00%0.00%
Bäckman and Wahlin36 (2001)0%00
Magnússon38 (1977)0.270NA
Nordgarden et al.40 (2002)0.090.01NA
Locht41 (1980)0.1400.14
Rølling and Poulsen43 (2009)NA*NA*NA*
South America
Gomes et al.15 (2010)0.19000.1900
Souza-Silva et al.18 (2018)NA*NA*NA
Küchler et al.22 (2008)NANANA
Calvano Küchler et al.27 (2008)NANANA
North America
Tavajohi-Kermani et al.23 (2002)NANANANANANA
Muller et al.39 (1970)0.060.01NA
Australia
Lai and Seow28 (1989)NA*NA*NANA*NA*NA*
Lynham37 (1990)NANA*NA
Africa
Ng’ang’a and Ng’ang’a25 (2001)0.33000.3300

NA, not available..

*Study reported the number of cases of canine agenesis, but did not report the number of individuals with canine agenesis..



By sex, the overall ratio of canine agenesis was higher in females than in males, with a female:male ratio of 1.23. However, this was only true in Europe and South America, wherein females were twice as much affected than males. In Asia, the ratio was higher among males (ratio = 0.88), while the prevalence was the same for both sexes (ratio = 1) in Africa (Table 8). The overall bilateral:unilateral agenesis ratio was 1.13. The worldwide prevalence of unilateral agenesis was almost similar to that of the bilateral form (50.0% and 46.7%, respectively). However, in Asia, the prevalence of unilateral agenesis was almost double that of bilateral agenesis (66.7% and 33.3%, respectively). In Europe, the prevalence of bilateral (58.8%) agenesis was higher than that of unilateral agenesis (35.3%) (Table 9).

Table 8 . Prevalence of canine agenesis by sex.

ContinentsMale:femaleOverall male:female ratio
Overall
Based on studies which reported the outcome of interest1:1.23
Asia
Endo et al.5 (2006)NA1:0.88
Mani et al.17 (2014)1:0.67
Patil et al.19 (2013)1:0.8
Abu-Hussein et al.24 (2015)NA
Sisman et al.26 (2007)NA
Sheikhi et al.29 (2012)NA
Vahid-Dastjerdi et al.32 (2010)NA
Alsoleihat and Khraisat35 (2014)1:3
Gokkaya and Kargul42 (2016)NA
Chung et al.44 (2008)NA
Zhang et al.45 (2015)NA
Al-Abdallah46 (2015)NA
Afify and Zawawi47 (2012)1:0.67
Nik-Hussein48 (1989)NA
Europe
Rózsa et al.16 (2009)1:2.251:2.25
Kazanci et al.20 (2011)NA
Aktan et al.21 (2010)NA
Behr et al.30 (2011)NA
González-Allo et al.31 (2012)NA
Topkara and Sari33 (2011)NA
Bernadette et al.34 (2013)NA
Bäckman and Wahlin36 (2001)0:0
Europe
Magnusson38 (1977)NA
Nordgarden et al.40 (2002)NA
Locht41 (1980)NA
Rølling and Poulsen43 (2009)NA
South America
Gomes et al.15 (2010)0:20:2
Souza-Silva et al.18 (2018)NA
Küchler et al.22 (2008)NA
Calvano Küchler et al.27 (2008)NA
North America
Tavajohi-Kermani et al.23 (2002)NANA
Muller et al.39 (1970)NA
Australia
Lai and Seow28 (1989)NANA
Lynham37 (1990)NA
Africa
Ng’ang’a and Ng’ang’a25 (2001)1:11:1

NA, not available..


Table 9 . Prevalence of canine agenesis by location.

ContinentsUnilateral:bilateralPrevalence of individuals with unilateral missing canine only (Individuals with unilateral missing canine only, excluding combined unilateral + bilateral in same individual/all individuals with missing canines) (%)Prevalence of individuals with bilateral missing canine only (Individual with bilateral missing canine only, excluding combined unilateral + bilateral in same individual/all individuals with missing canines) (%)Prevalence of individuals with combined unilateral and bilateral missing canines in the maxilla and mandible (%)
Overall
Based on studies which reported the outcome of interest1:1.1350.046.73.3
Asia
Endo et al.5 (2006)NA66.733.30.0
Mani et al.17 (2014)1:1.5
Patil et al.19 (2013)NA
Abu-Hussein et al.24 (2015)NA
Sisman et al.26 (2007)NA
Sheikhi et al.29 (2012)NA
Vahid-Dastjerdi et al.32 (2010)NA
Alsoleihat and Khraisat35 (2014)4:0
Gokkaya and Kargul42 (2016)NA
Chung et al.44 (2008)NA
Zhang et al.45 (2015)NA
Al-Abdallah46 (2015)NA
Afify and Zawawi47 (2012)NA
Nik-Hussein48 (1989)NA
Europe
Rózsa et al.16 (2009)1:335.358.85.9
Kazanci et al.20 (2011)0:1
Aktan et al.21 (2010)NA
Behr et al.30 (2011)NA
González-Allo et al.31 (2012)NA
Topkara and Sari33 (2011)NA
Bernadette et al.34 (2013)2:0
Bäckman and Wahlin36 (2001)0:0
Magnusson38 (1977)N
Nordgarden et al.40 (2002)NA
Locht41 (1980)1:0
Rølling and Poulsen43 (2009)NA
South America
Gomes et al.15 (2010)2:0100.00.00.0
Souza-Silva et al.18 (2018)NA
Küchler et al.22 (2008)1:0.5
Calvano Küchler et al.27 (2008)NA
North America
Tavajohi-Kermani et al.23 (2002)NANANANA
Muller et al.39 (1970)NA
Australia
Lai and Seow28 (1989)NANANANA
Lynham37 (1990)NA
Africa
Ng’ang’a and Ng’ang’a25 (2001)1:150.050.00

NA, not available..



Common dental anomalies associated with canine agenesis were retained primary canines,16,30 agenesis of other permanent teeth,16,30 agenesis of the third molar,31,32,45,46 supernumerary teeth,16 ankylosis,28 taurodontism,28 enamel hypoplasia and conical incisor,28 and Class III malocclusion.31,45

DISCUSSION

This systematic review attempted to evaluate the global distribution of canine agenesis in isolation.3,49 We presented the population prevalence of canine agenesis in terms of individuals, which better reflected the actual treatment need, unlike another review4 that reported the prevalence in terms of the number of missing teeth. Reports based on individual prevalence without considering the population sample can be biased, since the bigger quantity of smaller-sized studies may overwhelm the smaller quantity of bigger-sized studies and distort the final summary. Therefore, we recalculated the prevalence in every included study to generate an overall prevalence.

In this review, an almost equal proportion of the included studies were conducted in Asia (37.1%) and Europe (37.1%); this was in contrast to the review on the overall prevalence of hypodontia, in which most studies were conducted in European countries (43.0%), followed by the Asian region (32.0%).4 The global distribution in this review ranged from 0.0% to 4.7%, with a pooled overall prevalence of 0.30%, which is much lower than that of hypodontia (6.4%).4 Polder et al.3 reported that canines are one of the rarely missing teeth after the first and the second molars.

In this review, the prevalence of canine agenesis was higher in the Asian region than in the African, European, and South American regions. In contrast, the overall prevalence of hypodontia was the highest in Africa (13.4%, 95% confidence interval [CI]: 9.7, 18.0), followed by Europe (7% CI: 6.0, 8.0%) and Asia (6.3% CI: 4.4, 9.1).4 This suggests that canine agenesis per se is more common in the Asian region than in the European region, possibly due to the racial differences between the two continents.

Our findings showing that canine agenesis was more common in the maxilla than the mandible are in agreement with the general pattern of hypodontia reported in two other systematic reviews addressing hypodontia, both of which reported marked differences between the jaws in relation to the frequency of agenesis of various tooth types.3,4 Similarly, the greater prevalence in females is in agreement with the findings of these two systematic reviews.3,4 However, in Asia, the higher prevalence in males may indicate a genetic inheritance of this trait among males. Bilateral agenesis was more prevalent than unilateral agenesis in Europe, similar to the general pattern of hypodontia except for the maxillary lateral incisors.3 However, in Asia, the prevalence of unilateral agenesis was double that of the bilateral form, indicating a genetic inheritance pattern among Asians. The overall information presented in this review could provide valuable guidance to clinicians for treatment planning and managing patients with canine agenesis.

Since we aimed to report the prevalence based on the number of individuals with missing canines, we could not include studies reporting the number of missing canines instead of the number of individuals with missing canines; this limited our ability to present the data in terms of combined prevalence by number of teeth. Most studies assessed either orthodontic patients,5,14,17,19,22-25,29,31,32,43 pediatric patients,21,26,27,33 both orthodontic and pediatric patients,15 both orthodontic and dental patients,44 or dental patients.16,18,20,28,30,35,39-41,45-47 Three studies were epidemiological surveys of school children,34,37,42 one enrolled defense force recruits,36 while only one study was a truly epidemiological study on a general population.38

CONCLUSION

  • 1. The global distribution of canine agenesis ranged from 0.0% to 4.7%, with a pooled overall population prevalence of 0.30%.

  • 2. The population prevalence of canine agenesis was the highest in Asia (0.54%), followed by Africa (0.33%); the least prevalence was observed in Europe and South America (0.19% for both continents).

  • 3. The highest prevalence was of the maxilla-only form (88.57%), followed by the presentation in both maxilla and mandible (8.57%), while the mandible-only form showed the lowest prevalence (2.86%).

  • 4. Canine agenesis was more common in females, with an overall female:male ratio of 1.23, except in Asia (0.88) and Africa (1).

  • 5. In Asia, the prevalence of unilateral agenesis was almost double that of bilateral agenesis, but in Europe, bilateral agenesis was more common.

With a clearer picture of the occurrence of canine agenesis and its accompanying predilection, management of the condition can be better predicted and planned. Future research on prevalence is suggested to report both in terms of missing teeth and individuals, also moving forward, research linked to its aetiology and genetic-based treatment can be considered.

CONFLICTS OF INTEREST

No potential conflict of interest relevant to this article was reported.

Fig 1.

Figure 1.Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart of the study selection process.
Korean Journal of Orthodontics 2021; 51: 55-74https://doi.org/10.4041/kjod.2021.51.1.55

Table 1 . Search engines, keywords, dates of searches, and the data retrieved.

Search enginesKeywordsDateResultsDuplicatesExclusion by titleExclusion by abstractExclusion by full textFinal
PubMed‘Canine Or Cuspid’ AND ‘Agenesis OR missing OR hypodontia’ AND ‘Prevalence Or Incidence Or Association’ AND ‘Maxillary Or Mandibular’ AND ‘Population or Hospital’ AND ‘Dental anomalies’2.5.19322,49020601
Web of Science‘Canine Or Cuspid’ AND ‘Agenesis OR missing OR hypodontia’ AND ‘Prevalence Or Incidence Or Association’ AND ‘Maxillary Or Mandibular’ AND ‘Population or Hospital’ AND {Dental anomalies}2.5.193620412
ScopusSame as above2.5.194964135419
OpenGreySame as above2.5.196,1152,6951,00111
Science Direct'canine' AND 'agenesis' AND 'prevalence' AND 'maxillary or mandibular' AND 'population' AND 'dental anomalies'2.5.1923963
Hand-searched articles680033
Total6,7702,4904,2801,1235249

The process of exclusion that led to the final list of included studies is presented..


Table 2 . Population prevalence of canine agenesis among the assessed individuals.

No.StudyNumber of individuals with canine agenesisStudy size (n)Prevalence of agenesis by individual (%)
1Mani et al.17 (2014)58340.60
2Alsoleihat and Khraisat35 (2014)4854.71
3Patil et al.19 (2013)184,1330.44
4Afify and Zawawi47 (2012)58780.57
5Rózsa et al.16 (2009)134,4170.29
6Kazanci et al.20 (2011)13,1650.03
7Bäckman and Wahlin36 (2001)07390.00
8Locht41 (1980)17040.14
9Bernadette et al.34 (2013)29470.21
10Gomes et al.15 (2010)21,0490.19
11Ng’ang’a and Ng’ang’a25 (2001)26150.33
Total5317,5660.30

Table 3 . Prevalence of canine agenesis based on the total number of missing teeth.

No.StudyNumber of cases of canine agenesisNumber of cases of tooth agenesisPrevalence of agenesis by number of teeth (%)
1Mani et al.17 (2014)85081.57
2Alsoleihat and Khraisat35 (2014)41428.57
3Endo et al.5 (2006)566968.05
4Abu-Hussein et al.24 (2015)31671.80
5Nik-Hussein48 (1989)2812.47
6Sisman et al.26 (2007)91824.95
7Sheikhi et al.29 (2012)274545.95
8Chung et al.44 (2008)253297.60
9Vahid-Dastjerdi et al.32 (2010)101975.08
10Zhang et al.45 (2015)10694111.26
11Al-Abdallah46 (2015)215843.60
12Kazanci et al.20 (2011)21531.31
13Aktan et al.21 (2010)873,1472.76
14Bäckman and Wahlin36 (2001)0890.00
15Magnússon38 (1977)31671.80
16Nordgarden et al.40 (2002)148341.68
17Locht41 (1980)1931.08
18Rølling and Poulsen43 (2009)171,0701.59
19Behr et al.30 (2011)426936.06
20González-Allo et al.31 (2012)32981.01
21Topkara and Sari33 (2011)93752.40
22Bernadette et al.34 (2013)21361.47
23Gomes et al.15 (2010)21081.85
24Souza-Silva et al.18 (2018)91147.90
25Küchler et al.22 (2008)4994.04
26Calvano Küchler et al.27 (2008)3783.85
27Tavajohi-Kermani et al.23 (2002)22260.88
28Muller et al.39 (1970)189401.91
29Lai and Seow28 (1989)263148.28
30Lynham37 (1990)3923.26
31Ng’ang’a and Ng’ang’a25 (2001)3793.80
Total39713,2582.99

Table 4 . Quality analysis of the 49 studies based on a modified STROBE checklist.

No.AuthorStudy designSettingParticipant criteriaSample sizeVariable descriptionOutcome measurementStatistical testTotal score
1Gomes et al.15 (2010)7
2Rózsa et al.16 (2009)7
3Finkelstein et al.6 (2018)XX5
4Mani et al.17 (2014)7
5Alsoleihat and Khraisat35 (2014)X6
6Souza-Silva et al.18 (2018)7
7Patil et al.19 (2013)X6
8Kazanci et al.20 (2011)7
9Aktan et al.21 (2010)7
10Edward et al. (2008)XX5
11Küchler et al.22 (2008)X6
12Tavajohi-Kermani et al.23 (2002)7
13Shafi et al. (2008)XX5
14Endo et al.5 (2006)7
15Aasheim and Ogaard (1993)XX5
16Abu-Hussein et al.24 (2015)7
17Afify and Zawawi47 (2012)7
18Altug-Atac and Erdem (2007)XXX4
19Bäckman and Wahlin36 (2001)7
20Bergstnou (1977)XX5
21Davis (1987)XXX4
22Fekonja (2005)XX5
23Fukuta et al. (2004)XXX4
24Nik-Hussein48 (1989)X6
25Ng’ang’a and Ng’ang’a25 (2001)7
26Sisman et al.26 (2007)X6
27Calvano Küchler et al.27 (2008)X6
28Lai and Seow28 (1989)X6
29Lynham37 (1990)X6
30Magnússon38 (1977)X6
31Muller et al.39 (1970)X6
32Nordgarden et al.40 (2002)X6
33Locht41 (1980)X6
34da Cunha Coelho et al. (2012)XX5
35Gokkaya et al.42 (2016)X6
36Sheikhi et al.29 (2012)7
37Rølling and Poulsen43 (2009)X6
38Rose (1966)XXX4
39Behr et al.30 (2011)7
40Chung et al.44 (2008)X6
41González-Allo et al.31 (2012)7
42Vahid-Dastjerdi et al.32 (2010)7
43Zhang et al.45 (2015)X6
44Topkara and Sari33 (2011)7
45Shetty et al. (2012)XX5
46Bernadette et al.34 (2013)7
47Al-Abdallah46 (2015)7
48Raju et al. (2011)XX5
49O'Dowling and McNamara (1990)XX5

STROBE, Strengthening the Reporting of Observational Studies in Epidemiology..


Table 5 . Demographic characteristics of the high-quality studies.

No.AuthorYear of studyStudy designStudy settingsSample sizeAge (yr)Sex (M:F)CountryRegionRacePopulation
1Endo et al.5 (2006)NARetrospective studyPediatric and orthodontic clinics of Nippon Dental University3,3585–151:1.3JapanNiigataJapaneseOrthodontic patients
2Gomes et al.15 (2010)1998–2000Retrospective studyOrthodontic patient at the Federal District Brazil (16 orthodontic clinics)1,04910–151:1.07BrazilBrasíliaNAOrthodontic patients
3Rózsa et al.16 (2009)NARetrospective studyDepartment of Pediatric Dentistry and Orthodontics, University Budapest4,4176–181:1HungaryBudapestHungarianOrthodontic and pediatric patients
4Mani et al.17 (2014)2004–2010Retrospective studyRadiology department of the dental clinic of the University Sains Malaysia83412–161:1.32MalaysiaKelantanMalayDental patients
5Souza-Silva et al.18 (2018)2014–2016Retrospective studyRadiographic centre3,4008–301:1.17BrazilNortheast regionNAOrthodontic patients
6Patil et al.19 (2013)2008–2012Retrospective studyDepartment of Oral Medicine and Radiology, Jodhpur Dental College General Hospital4,13313–381:0.93IndiaJodhpurIndianDental patients
7Kazanci et al.20 (2011)1996–2008Retrospective studyDepartment of Orthodontics, Faculty of Dentistry, Ataturk University3,1659–251:1.58TurkeyNATurkishOrthodontic patients
8Aktan et al.21 (2010)NARetrospective studyEight clinics100,5775–371:2.37Turkey6 regions- Samsun, Gaziantep, Kayseri, Tokat, Konya, BoluTurkishDental patients
9Küchler et al.22 (2008)1999–2007Retrospective studyFederal University of Rio de Janeiro’s Continuing Education Clinical Program in Pediatric Dentistry1,1676–121:1.24BrazilNorthern Rio de JaneiroNAPediatric patients
10Tavajohi-Kermani et al.23 (2002)NARetrospective studyDepartment of Orthodontics, University of Tennessee, and orthodontic practices in Memphis1,0168–181:2.3USAPittsburghNAOrthodontic patients
11Abu-Hussein et al.24 (2015)2006–2013Retrospective studyHypodontia patients to Center for Dentistry, Research & Aesthetics2,20010.2–39.51:1.6IsraelJatt, AlmothalatArabOrthodontic patients
12Ng’ang’a and Ng’ang’a25 (2001)2001Retrospective case studyPrivate orthodontic practice6158–151:0.86KenyaNairobi 30% from other parts of thecountryKenyans of African descentOrthodontic patients
13Sisman et al.26 (2007)2007Retrospective studyOrthodontic patient files Department of Orthodontics of Erciyes University, Kayseri and Kırıkkale University2,4139–361:1.82TurkeyKirikkaleNAOrthodontic patients
14Calvano Küchler et al.27 (2008)2008Retrospective studyThose attending the Federal University of Rio De Janeiro’s continuing Education Clinical program in Pediatric Dentistry975 patients6–121:1.01BrazilRio de JaneiroNAPediatric patients
15Lai and Seow28 (1989)1989Retrospective studyCurrent patient records kept at the Pediatric Dentistry Unit of the Dental School, University of Queensland1,032 patients obtained after screening6–191:0.95AustraliaQueensland, dental schoolCaucasianPediatric patients
16Sheikhi et al.29 (2012)2012Retrospective and cross-sectionalFaculty of dentistry and dental clinics2,4227–351:1.74Iran8provincesIraniansDental patients
17Behr et al.30 (2011)1994– 2006Retrospective studyRegensburg University Medical Centre1,4421,353 final5–441:1.13GermanyEastern BavariaCaucasianOrthodontic patients
18González-Allo et al.31 (2012)2005– 2009Retrospective studyClinical files from dental clinic2,888 panoramic radiographs7–211:1.06PortugalNAPortugueseDental patients
19Vahid-Dastjerdi et al.32 (2010)2010Retrospective studyRecords of Iranian orthodontic patients treated at two schools1,7519–271:0.99IranTehranIraniansOrthodontic patients
20Topkara and Sari33 (2011)2011Retrospective studyDepartment of Orthodontics of the Faculty of Dentistry of the Selcuk University2,761 patients9–461:1.55TurkeyKonyaCaucasian patientsOrthodontic patients
21Bernadetteet al.34 (2013)2004– 2012Retrospective studyPatient’s dental records from belonging to a Pediatric dental office9479–341:1.54RomaniaTîrgu MureșNAPediatric patients
22Alsoleihat and Khraisat35 (2014)2011Cross-sectionalUn-admixed Druze school children (schoolchildren of two schools)8514–181:0.89Jordan (East Jordan)Al-AzraqDruze practising consanguin eous marriages and endogamySchool children
23Bäckman and Wahlin36 (2001)1976Cross-sectionalDepartment of Odontology/Pedodontics, UmeaÊ University73971:1SwedenUmeå, northern SwedenSwedishDental patients
24Lynham37 (1990)1990Cross-sectionalAustralian defense force recruits662 obtained after screening16–261:0.24AustraliaNANAAustralian defense force
25Magnússon38 (1977)1977Cross-sectionalSchool children1,116 final sample8–161:1.14IcelandReykjavikNASchool children
26Muller et al.39 (1970)1970Cross-sectionalChildren part of a large survey14,9401. White – 13,4592. African American – 1,48111–15Overall 1:1.01White 1:1.01African American1:0.91USAIllinoisWhite and African AmericanEpidemiological study
27Nordgarden et al.40 (2002)2002Cross-sectional97 public clinics9,532181:0.95NorwayOslo and Akershus countiesNorwegiansDental patients
28Locht41 (1980)1980Cross-sectionalOne school district7049–101:0.88DenmarkArhus municipalityDanishDental patients
29Gokkaya and Kargul42 (2016)2016Cross-sectionalDepartment of Pediatric Dentistry, Dental School of Marmara University1,6587–121:1.11TurkeyIstanbulTurkishDental patients
30Rølling and Poulsen43 (2009)2009Cross-sectionalOne district, all children examined as part of a systematic oral health care8,1389–121:1DenmarkArhus municipalityDanishAll children, epidemiological
31Chung et al.44 (2008)2008Cross-sectionalDepartment of Orthodontics, Yongdong Severance Dental Hospital, Yonsei University8831:1.65KoreaSeoulKoreansOrthodontic patients
32Zhang et al.45 (2015)2008Cross-sectionalGeneral group enrolled in three university in Hebei provinceOrthodontic group visiting the Department of Orthodontics, Peking University6,015 -general3,481 -orthodontic10–26General 1:0.89Orthodontic1:1.5ChinaHebei provinceHan originDental and orthodontic patients
33Al-Abdallah46 (2015)2011Cross-sectionalDepartment of Oral Medicine and Radiology, Institute of Dental Sciences8,22512–181:1.19IndiaBareilly, UPNorth IndianDental patients
34Afify and Zawawi47 (2012)2002–2011Retrospective and cross-sectional studyFaculty of Dentistry, King Abdul Aziz University87812–301:1.04Saudi ArabiaWestern regionSaudi patientsDental patients
35Nik-Hussein48 (1989)1989NAPatients attending Faculty of Dentistry, University of Malaya1,5836–151:1.01MalaysiaKuala LumpurNADental patients

M, male; F, female; NA, not available..


Table 6 . Overall prevalence of canine agenesis in different geographic locations.

Studies/continentsPrevalence of canine agenesis (%)Prevalence of canine agenesis by individual (%)Prevalence of canine agenesis by number of teeth (%)Prevalence of canine agenesis in the general population, excluding the orthodontic group (%)Prevalence of canine agenesis in the orthodontic group (%)
Overall
Based on studies which reported the outcome of interest0.302.990.380.10
Asia
Endo et al.5 (2006)NA*0.547.40--
Mani et al.17 (2014)0.6
Patil et al.19 (2013)0.44
Abu-Hussein et al.24 (2015)NA*
Sisman et al.26 (2007)NA*
Sheikhi et al.29 (2012)NA*
Vahid-Dastjerdi et al.32 (2010)NA*
Alsoleihat and Khraisat35 (2014)4.7
Gokkaya and Kargul42 (2016)NA
Chung et al.44 (2008)NA*
Zhang et al.45 (2015)NA*
Al-Abdallah46 (2015)NA*
Afify and Zawawi47 (2012)0.57
Nik-Hussein48 (1989)NA*
Europe
Rózsa et al.16 (2009)0.290.192.55--
Kazanci et al.20 (2011)0.03
Aktan et al.21 (2010)NA*
Behr et al.30 (2011)NA*
González-Allo et al.31 (2012)NA*
Topkara and Sari33 (2011)NA*
Bernadette et al.34 (2013)0.21
Bäckman and Wahlin36 (2001)0
Magnússon38 (1977)0.27
Nordgarden et al.40 (2002)0.10
Locht41 (1980)0.14
Rølling and Poulsen43 (2009)NA*
South America
Gomes et al.15 (2010)0.190.194.51--
Souza-Silva et al.18 (2018)NA*
Küchler et al.22 (2008)NA
Calvano Küchler et al.27 (2008)NA*
North America
Tavajohi-Kermani et al.23 (2002)NA*NA*1.85--
Muller et al.39 (1970)NA*
Australia
Lai and Seow28 (1989)NA*NA*7.14--
Lynham37 (1990)NA*
Africa
Ng’ang’a and Ng’ang’a25 (2001)0.330.333.80--

NA, not available..

*Study reported the number of cases of canine agenesis, but did not report the number of individuals with canine agenesis..


Table 7 . Prevalence of canine agenesis by jaw in different geographic locations.

Studies/continentsPrevalence in maxilla alone (%)Prevalence in mandible alone (%)Prevalence in both maxilla and mandible (%)Continentprevalence in maxilla alone (%)Continentprevalence in mandible alone (%)Prevalence in both maxilla and mandible in the same individuals (%)
Overall
Based on studies which reported the outcome of interest88.572.868.57
Asia
Endo et al.5 (2006)NA*NA*NA*0.780.000.00
Mani et al.17 (2014)0.600
Patil et al.19 (2013)NANANA
Abu-Hussein et al.24 (2015)NA*NA*NA
Sisman et al.26 (2007)NANA*NA
Sheikhi et al.29 (2012)0.580.25NA
Vahid-Dastjerdi et al.32 (2010)NA*NA*NA*
Alsoleihat and Khraisat35 (2014)4.700
Gokkaya and Kargul42 (2016)NA00
Chung et al.44 (2008)NA*NA*NA*
Zhang et al.45 (2015)NA*NA*NA*
Al-Abdallah46 (2015)NA*NA*NA
Afify and Zawawi47 (2012)0.570NA
Nik-Hussein48 (1989)NA*0NA*
Europe
Rózsa et al.16 (2009)0.200.020.070.130.010.03
Kazanci et al.20 (2011)0.0300
Aktan et al.21 (2010)NA*NA*NA
Behr et al.30 (2011)NA*NA*NA*
González-Allo et al.31 (2012)NA*NA*NA*
Topkara and Sari33 (2011)NA*NA*NA*
Bernadette et al.34 (2013)0.210.00%0.00%
Bäckman and Wahlin36 (2001)0%00
Magnússon38 (1977)0.270NA
Nordgarden et al.40 (2002)0.090.01NA
Locht41 (1980)0.1400.14
Rølling and Poulsen43 (2009)NA*NA*NA*
South America
Gomes et al.15 (2010)0.19000.1900
Souza-Silva et al.18 (2018)NA*NA*NA
Küchler et al.22 (2008)NANANA
Calvano Küchler et al.27 (2008)NANANA
North America
Tavajohi-Kermani et al.23 (2002)NANANANANANA
Muller et al.39 (1970)0.060.01NA
Australia
Lai and Seow28 (1989)NA*NA*NANA*NA*NA*
Lynham37 (1990)NANA*NA
Africa
Ng’ang’a and Ng’ang’a25 (2001)0.33000.3300

NA, not available..

*Study reported the number of cases of canine agenesis, but did not report the number of individuals with canine agenesis..


Table 8 . Prevalence of canine agenesis by sex.

ContinentsMale:femaleOverall male:female ratio
Overall
Based on studies which reported the outcome of interest1:1.23
Asia
Endo et al.5 (2006)NA1:0.88
Mani et al.17 (2014)1:0.67
Patil et al.19 (2013)1:0.8
Abu-Hussein et al.24 (2015)NA
Sisman et al.26 (2007)NA
Sheikhi et al.29 (2012)NA
Vahid-Dastjerdi et al.32 (2010)NA
Alsoleihat and Khraisat35 (2014)1:3
Gokkaya and Kargul42 (2016)NA
Chung et al.44 (2008)NA
Zhang et al.45 (2015)NA
Al-Abdallah46 (2015)NA
Afify and Zawawi47 (2012)1:0.67
Nik-Hussein48 (1989)NA
Europe
Rózsa et al.16 (2009)1:2.251:2.25
Kazanci et al.20 (2011)NA
Aktan et al.21 (2010)NA
Behr et al.30 (2011)NA
González-Allo et al.31 (2012)NA
Topkara and Sari33 (2011)NA
Bernadette et al.34 (2013)NA
Bäckman and Wahlin36 (2001)0:0
Europe
Magnusson38 (1977)NA
Nordgarden et al.40 (2002)NA
Locht41 (1980)NA
Rølling and Poulsen43 (2009)NA
South America
Gomes et al.15 (2010)0:20:2
Souza-Silva et al.18 (2018)NA
Küchler et al.22 (2008)NA
Calvano Küchler et al.27 (2008)NA
North America
Tavajohi-Kermani et al.23 (2002)NANA
Muller et al.39 (1970)NA
Australia
Lai and Seow28 (1989)NANA
Lynham37 (1990)NA
Africa
Ng’ang’a and Ng’ang’a25 (2001)1:11:1

NA, not available..


Table 9 . Prevalence of canine agenesis by location.

ContinentsUnilateral:bilateralPrevalence of individuals with unilateral missing canine only (Individuals with unilateral missing canine only, excluding combined unilateral + bilateral in same individual/all individuals with missing canines) (%)Prevalence of individuals with bilateral missing canine only (Individual with bilateral missing canine only, excluding combined unilateral + bilateral in same individual/all individuals with missing canines) (%)Prevalence of individuals with combined unilateral and bilateral missing canines in the maxilla and mandible (%)
Overall
Based on studies which reported the outcome of interest1:1.1350.046.73.3
Asia
Endo et al.5 (2006)NA66.733.30.0
Mani et al.17 (2014)1:1.5
Patil et al.19 (2013)NA
Abu-Hussein et al.24 (2015)NA
Sisman et al.26 (2007)NA
Sheikhi et al.29 (2012)NA
Vahid-Dastjerdi et al.32 (2010)NA
Alsoleihat and Khraisat35 (2014)4:0
Gokkaya and Kargul42 (2016)NA
Chung et al.44 (2008)NA
Zhang et al.45 (2015)NA
Al-Abdallah46 (2015)NA
Afify and Zawawi47 (2012)NA
Nik-Hussein48 (1989)NA
Europe
Rózsa et al.16 (2009)1:335.358.85.9
Kazanci et al.20 (2011)0:1
Aktan et al.21 (2010)NA
Behr et al.30 (2011)NA
González-Allo et al.31 (2012)NA
Topkara and Sari33 (2011)NA
Bernadette et al.34 (2013)2:0
Bäckman and Wahlin36 (2001)0:0
Magnusson38 (1977)N
Nordgarden et al.40 (2002)NA
Locht41 (1980)1:0
Rølling and Poulsen43 (2009)NA
South America
Gomes et al.15 (2010)2:0100.00.00.0
Souza-Silva et al.18 (2018)NA
Küchler et al.22 (2008)1:0.5
Calvano Küchler et al.27 (2008)NA
North America
Tavajohi-Kermani et al.23 (2002)NANANANA
Muller et al.39 (1970)NA
Australia
Lai and Seow28 (1989)NANANANA
Lynham37 (1990)NA
Africa
Ng’ang’a and Ng’ang’a25 (2001)1:150.050.00

NA, not available..


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