title: Meta-analysis and systematic review of the number of non-syndromic congenitally missing permanent teeth per affected individual and its influencing factors.
abstract: OBJECTIVE
  Dental aplasia (or hypodontia) is a frequent and challenging anomaly and thus of interest to many dental fields. Although the number of missing teeth (NMT) in each person is a major clinical determinant of treatment need, there is no meta-analysis on this subject. Therefore, we aimed to investigate the relevant literature, including epidemiological studies and research on dental/orthodontic patients.
  
  
  METHODS
  Among 50 reports, the effects of ethnicities, regions, sample sizes/types, subjects' minimum ages, journals' scientific credit, publication year, and gender composition of samples on the number of missing permanent teeth (except the third molars) per person were statistically analysed (α = 0.05, 0.025, 0.01).
  
  
  CONCLUSIONS
  The inclusion of small studies and second-hand information might reduce the reliability. Nevertheless, these strategies increased the meta-sample size and favoured the generalisability. Moreover, data weighting was carried out to account for the effect of study sizes/precisions.
  
  
  RESULTS
  The NMT per affected person was 1.675 [95% confidence interval (CI) = 1.621-1.728], 1.987 (95% CI = 1.949-2.024), and 1.893 (95% CI = 1.864-1.923), in randomly selected subjects, dental/orthodontic patients, and both groups combined, respectively. The effects of ethnicities (P > 0.9), continents (P > 0.3), and time (adjusting for the population type, P = 0.7) were not significant. Dental/orthodontic patients exhibited a significantly greater NMT compared to randomly selected subjects (P < 0.012). Larger samples (P = 0.000) and enrolling younger individuals (P = 0.000) might inflate the observed NMT per person.
  
  
  CONCLUSIONS
  Time, ethnic backgrounds, and continents seem unlikely influencing factors. Subjects younger than 13 years should be excluded. Larger samples should be investigated by more observers.
authors.affiliation: *Iranian Tissue Bank and Research Centre, Tehran University of Medical Sciences, **Department of Dental Anatomy and Morphology, Dental Branch, Islamic Azad University, Tehran, Iran and vahid.rakhshan@gmail.com.
authors.forename: Vahid
authors.initials: V
authors.lastname: Rakhshan
authors.affiliation: ***Private Practice, Tehran, Iran.
authors.forename: Hamid
authors.initials: H
authors.lastname: Rakhshan
mesh_terms: D000367:Age Factors; D000848:Anodontia / Q000453:epidemiology*; D001208:Asia / Q000453:epidemiology; D019229:Dentition, Permanent; D005060:Europe / Q000453:epidemiology; D006801:Humans; D008310:Malocclusion / Q000453:epidemiology; D009656:North America / Q000453:epidemiology; D015203:Reproducibility of Results
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