Restoration gaps needed to exceed a threshold size to impede sealed lesion arrest in vitro

After selective excavation, bacteria are sealed beneath restorations. Leaking restorations could maintain carbohydrate-supply, leading to lesion progression and pulp damage. It is unclear if fluid (and thereby carbohydrate) exchange occurs through any interfacial gaps, or if such exchange only occurs in case gaps exceed a certain threshold size. We investigated how different restoration gap sizes impact on survival of sealed bacterial in vitro.

Bacterially contaminated artificial residual lesions were induced on the pulpo-axial walls of standardized dentin micro-cavities using acetic-acid demineralization and a continuous-culture Lactobacillus rhamnosus biofilm-model. Adhesive restorations with different gap sizes (0/100/200/400 μm) were placed (n=24/group). Restorations were submitted to cyclic loading (42 g/0.2 Hz) under highly cariogenic conditions in a mastication-simulating artificial mouth. After 25 days, the number of sealed viable bacteria was determined as colony-forming units.

After 25 days, CFU were significantly reduced in all groups (-99.99%, p<0.001/Mann-Whitney). Significantly more viable bacteria remained in restorations with gaps ≥ 200 μm (p<0.001).

Restoration gaps needed to exceed a threshold size to impede lesion arrest in vitro. There is great need to better understand why such threshold exists and which factors (mastication forces, restoration material, lesion location) could moderate the observed association.

A certain gap sizes was necessary to allow sufficient fluid exchange for bacterial survival in vitro. It is not possible to deduct clinical recommendations at present.