Limited evidence on the best position for prosthetic margins

The Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Database of Systematic reviews, Medline, Google Scholar and Scopus databases were searched along with handsearching of the Journal of Prosthetic Dentistry, International Journal of Prosthodontics, Journal of Dentistry and Caries Research.

Randomised controlled clinical trials, prospective or retrospective studies or case-control observational studies reporting on caries susceptibility of teeth serving as abutments for prosthetic restorations were included. Only English language studies were included.

Study selection and quality assessment was carried out by two reviewers. Trials were compared by grouping abutments teeth/abutment surfaces with subgingival margins. Caries incidence was evaluated as a dichotomous variable. The risk ratio (RR) for caries incidence of prosthetic margins was calculated for the direct comparisons and pooled using a random-effects model. The overall quality of evidence supporting the association between secondary caries and margin placement was assessed using the GRADE system.

Twenty-two studies were included, representing 2,648 prosthetic restorations placed in 1,242 patients with mean follow-up time ranging from two to 11.4 years. A random effects meta-analysis was performed on two studies. This found a pooled risk ratio (RR) for secondary caries of sub-gingival margins at up to five years of 1.25 (95% CI: 0.70 to 2.22). At ten years of follow-up, the RR was1.22 (95% CI: 0.81 to 1.83) and at 15 years 0.67 (95% CI: 0.45 to 1.00).

This systematic review and meta-analysis failed to detect a significantly different secondary caries rate of subgingivally located prosthetic margins in the short to mid-term (10 years). Due to the small number and the limitations of the included studies the results do not provide conclusive evidence as to the effect of prosthetic margin placement on the incidence of secondary caries.