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Background and aim To perform a systematic review of anatomical studies using cone beam computed tomography (CBCT) to assess the influence of demographic factors (age, gender and geographic region) on the prevalence of C-shaped canal anatomy in maxillary molars, mandibular premolars and molars. Data sources A search was conducted between May and August 2018 in four electronic databases and five peer-reviewed journals. The authors of included articles were also contacted for additional studies and the bibliographic references hand-searched. Study eligibility criteria, participants and interventions The research protocol was previously registered in the International Prospective Register of Ongoing Systematic Reviews (CRD42018095201) and included defined inclusion/exclusion criteria. Prevalence studies on C-shaped canal anatomy in maxillary molars, mandibular premolars and molars were searched. Study appraisal and synthesis methods The selected studies were submitted to full-text analysis and critical appraisal by two evaluators using the Joanna Briggs Institute Critical Appraisal tool. The final group of papers (n = 25) were pooled and forest plots with proportions and odds ratio with a 95% confidence interval performed. Meta-regression was undertaken to evaluate possible sources of heterogeneity and funnel plot visual analysis to assess publication bias. Results The included studies reported data on 25 445 teeth of 13 142 patients. A significant difference in the average prevalence proportion of C-shaped configuration was observed between mandibular first (0.3%; 0.1–0.6%) and second (12%; 10.3–13.7%) molars (P < 0.05). No significant difference in the prevalence of C-shaped configurations was observed comparing males (13.5%; 8.8–18.3%) and females (20.5%; 13.7–27.4%) in mandibular second molars (P > 0.05), although males were associated with significantly lower odds (0.573; 0.511–0.641) (P < 0.05). The pooled proportion of C-shaped anatomy in mandibular second molars in East Asian countries (39.6%; 36.0–43.1%) was significantly higher compared with other regions. Limitations Because of the limited number of studies, no statistical analysis was performed for maxillary molars and mandibular premolars. Conclusion Meta-analysis revealed that gender and geographic region may act as a confounding factor for the prevalence of C-shaped anatomy in mandibular second molars, whilst age did not influence the prevalence of C-shaped configurations in this tooth group. Knowing these preoperative factors would help to anticipate complex morphologies in clinics.

The aim of this study was to conduct a systematic review to compare the clinical out- comes of two different resorbable collagen membranes in terms of regenerated bone volume, postoperative complications and membrane degradation during bone regen- eration procedures. Randomized controlled trials (RCT) or controlled trials (CT) that compared both techniques were reviewed on four electronic databases up to December 2015, a manual search was performed on the bibliography of the collected articles and the authors were contacted for additional references if undetected on the electronic and manual search. Membrane exposure was evaluated as a dichotomous outcome and the statistical unit was the membrane. The results were presented as relative risk (RR) with a 95% confidence interval. Eight RCTs and one CT were in- cluded in this study. The majority of the studies depicted a bone augmentation area, which ranged from 46.15% to 94.6% for the non-cross-link membranes and from 44% to 92.6% for the cross-link membranes at the 4-6 month re-entry surgery. From a total of 289 patients, a forest plot concerning the membrane exposure was con- structed using the obtained RR of the included studies. The overall RR was 1.43 (95% CI: 0.85-2.39) with no statistically significant differences between the two groups, although with a marginal tendency towards higher exposure in the cross-link mem- brane group. This systematic review suggests the different membranes present them- selves as appropriate for bone regeneration procedures, although cross-link membranes present higher rates of postoperative complications. However, more RCT with higher sample sizes are needed to evaluate the different membranes. The sug- gested lack of clinical differences between the compared membranes suggest that further cost-benefit ratio, tissue integration and postoperative complication oriented studies should be performed so that clinicians can take a patient-centred, evidence- based decision.