Direct versus indirect inlay/onlay composite restorations in posterior teeth. A systematic review and meta-analysis.

Objective: To evaluate the long-term clinical performance of direct versus indirect composite inlays/onlays in posterior teeth.

Data: Screening for inclusion eligibility, quality assessment of studies and data extraction was performed independently by two authors.

Sources: The electronic databases MEDLINE, EMBASE, Cochrane Oral Health Group's Trials Register and CENTRAL were searched (14.12.2015), with no restriction to publication date or language. We included only randomised controlled trials (RCTs) and evaluated them according to Cochrane risk of bias tool. The main outcome assessed was the restoration failure, determined by several clinical parameters.

Study Selection: Two studies concerning direct and indirect inlays (82 patients with 248 restorations) and one study for onlays (157 patients with 176 restorations) satisfied the inclusion criteria. Two trials, one of unclear and one of high risk of bias, could be mathematically combined. The meta-analysis indicated no statistically significant difference in the risk failure between direct and indirect inlays, after 5 years (RR: 1.54; 95% Cl: 0.42, 5.58; p=0.52) or 11 years of function (RR: 0.95; 95% Cl: 0.34, 2.63; p=0.92). Only one parameter, the marginal discoloration, slightly favored direct inlays after 11 years (RR: 0.41; 95% Cl: 0.17, 0.96; p=0.04). Only one study dealt with onlays; an overall 5-year survival of 87% (95% CI: 81-93%) was reported.

Conclusion: The difference of the two techniques did not reach statistical significance in order to recommend one technique over the other. The scarcity of primary studies support the need for further well-designed long-term studies in order to reach firm conclusions about both techniques.

Clinical Significance: Resin composite materials, placed directly or indirectly, exhibit a promising long-term clinical performance when rehabilitation of posterior teeth is needed. Although many years in clinical practice, the selection of the best treatment protocol still remains subjective. The available studies, and their synthesis, cannot provide reliable evidence in this field.