Summary
Prevalence studies using CBCT technology on MB2 canal were searched between May and September 2019. 83 studies were submitted to full text analysis and scientific merit evaluation by 2 evaluators and 26 studies were pooled into a meta-analysis. The included studies reported data of 23,926 maxillary molars (15,285 maxillary first molars and 8,641 maxillary second molars) from at least 12,456 patients, comprising 5,541 males and 6,915 females (2 studies did not report the number of patients). The average age of the patients was 40.9 years and was calculated based on 20 studies that reported this information. The included studies were published in English (n=24), Chinese (n=1) and Portuguese (n=1) and represented data from 24 countries.
Overall prevalence of MB2 canal
In the present study, prevalence of MB2 canal in maxillary first molars ranged from 96.7% (Belgium sub-population) to 30.9% (Chinese sub-population) while in second molars, the highest and lowest prevalence were reported in the Brazilian (83.2%) and Chinese (13.4%) sub-populations. Overall, mean prevalence of MB2 was higher in maxillary first molars (69.6%) than in second molars (39.0%). The presence of MB2 canal in maxillary first molars were addressed in 22 studies (41 population groups) with a high heterogeneity values for both maxillary first and second molars.
MB2 canal and gender
Influence of gender on the prevalence of MB2 canal in maxillary first molars was compared in 16 studies (35 population groups). Statistical comparison of untransformed proportions of MB2 for males (71.9%; 66.5%-77.4%) and females (66.8%; 60.4%-73.2%) was not significant. Meta-analysis calculation of 11 studies (12 population groups) on MB2 canal in maxillary second molars showed a high heterogeneity value and no statistical difference in its prevalence when comparing males (38.6%; 30.7%-46.5%) with females (32.1%; 23.9%-40.2%).
MB2 canal and age
The influence of age on the prevalence of the MB2 canal in maxillary first and second molars was assessed in 11 (30 population groups) and 8 (9 population groups) studies, respectively. Meta-regression calculation depicted a constant MB2 prevalence over the years and omnibus p-value excluded age as a source variance of heterogeneity.
MB2 canal and geographic region
Geographic region meta-analysis on MB2 prevalence in maxillary first and second molars were performed in 22 (41 population groups) and 16 (17 population groups) studies, respectively. In maxillary first molars, the highest proportion of MB2 canal was observed in Africa (80.9%; 67.7%-93.8%) (4 population groups combined) and the lowest in Oceania (53.1%; 46.6%-59.7%) (1 single population group), with statistical difference among a few regions. Regarding maxillary second molars, Africa showed also the highest MB2 prevalence (62.4%; 53.5%-71.3%) (2 population groups combined), while the lowest was observed in West Asia (21.6%; 18.4%-24.8%) (1 single population group), with statistical significant differences between regions.
