Data sourcesPubMed, Scopus, Web of Science and Google Scholar databases. Websites of scientific societies of dental traumatology, paediatric dentistry, endodontics, oral-maxillofacial surgery and World Health Organization and the US Centres for Disease Control and Prevention were searched. There were no language restrictions, but the search was limited to the years 1996-2016.Study selectionObservational studies reporting proportions of individuals with at least one TDI (prevalence) and who developed TDI (incidence rate) were considered. Data from any setting were eligible but those from emergency and traumatology services, where TDI frequency could be artificially higher, were excluded.Data extraction and synthesisData were extracted or calculated by one author and checked by the remaining authors. Study quality was assessed with an adapted version of the Newcastle-Ottawa scale (NOS) for disease frequency studies. Poor quality studies (scores 0-2) were excluded from the analysis. Prevalence rates for the permanent dentition, primary dentition and in 12-year-olds, incidence rate to any tooth for any age, male-to-female prevalence ratio (PR) in 12-year-olds, with 95% confidence intervals (95 CIs), were extracted/calculated. Study quality, Z-score distribution, funnel plot symmetry analysis, between-study heterogeneity, sensitivity and subgroup analyses were performed.ResultsNo disease registries of population surveys covering at least 10,000 people were identified. One hundred and fifty-two studies were included covering more than one purpose, 102 related to TDI prevalence in permanent teeth and 46 to prevalence in primary teeth, with 42 for TDI prevalence among 12-year-olds while 11 considered TDI incidence rate. Based on data from 268,755 individuals (age range 7-98 yrs; median 13.8yrs) the global estimate of pooled prevalence for TDI in permanent teeth = 15.2% (95% CI, 13.0%-17.4%). For primary teeth the global TDI prevalence = 22.7% (95 % CI, 17.3%-28.7%) based on 59,436 individuals. The prevalence in 12-year-old children = 18.1% (95% CI 15.3%-21.0%) based on 33,829 individuals. There was no difference between the incidence rates between permanent and primary teeth, with the global TDI rate being estimated at 2.82 events per 100 persons per year (95% CI, 2.28-3.42) based on 233,480 individuals. Using the 2016 World population approximately 900 million people had at least one TDI and approximately 180 million children had at least one TDI in their primary teeth.ConclusionsThis study shows that more than one billion living people have had TDI. TDI is a neglected condition which could rank fifth if it was included in the list of the world's most frequent acute/chronic diseases and injuries.