Secondary caries lesions next to direct restorations are associated with the restoration material and the integrity of the tooth-restoration-interface (presence of interfacial gaps) as well as the application of masticatory forces. It remains unclear if this is true for indirect restorations. We aimed to evaluate secondary lesions next to conventionally-cemented partial gold (PG) and adhesively-cemented partial ceramic (PC) restorations, placed with or without interfacial gaps.

In human molars, standardized two-surfaced cavities were prepared. Four groups (restoration material + cementation strategy) were compared: (1) gold + glass ionomer cement (Degudent/Ketac Cem), (2) lithium disilicate ceramic + self-adhesive resin cement (IPS e.max Press/RelyX Unicem 2), (3) lithium disilicate ceramic + self-etch adhesive + resin cement (IPS e.max Press/Adhese Universal/Variolink Esthetic DC), (4) lithium disilicate ceramic + etch-and-rinse adhesive + resin cement (IPS e.max Press/Syntac/Variolink Esthetic DC). Half of the restorations received a simulated interfacial gap (mean gap height was 237 μm), while the other half did not (n = 12/group). Specimens were submitted to a Lactobacillus rhamnosus-monospecies-biofilm-model with concomitant cyclic loading for 10 days. Mineral loss (ΔZ) of enamel-surface-lesions (ESL) and dentin-wall-lesions (DWL) was analyzed using transversal microradiography.

For ESL, neither the presence of an interfacial gap nor the restoration material nor the cementation strategy had a significant influence on ΔZ (p > 0.05/Generalized Linear Modelling). For DWL, ΔZ was significantly higher beneath restorations with interfacial gaps (p = 0.003/GLM); the restoration material and cementation strategy did not have a significant influence (p > 0.05).

The presence of interfacial gaps, but not the restoration material or cementation strategy determined secondary caries lesions next to indirect restorations in vitro.