Effects of different factors on the development of wall lesions adjacent to resin -matrix composite

Secondary caries is the most common reason for restoration replacement, regardless of the type of materials. It has been suggested that the development of secondary caries wall lesion is associated with the gap at the tooth/restoration interface, leading to my hypothesis that different gap widths could alter the dynamics inside this microspace, thus affecting the wall lesion development. Objectives. The first objective was to develop a new in vitro microbial model in which varying distances between tooth and restoration specimens could be controlled and the demineralization level along the cavity wall could be evaluated. The second objective was to investigate the individual effect of gap size, sugar, and fluoride toothpaste as well as their interaction on secondary caries development. Methods. Several pilot projects were conducted to develop the new model. In this model, specimens are incubated with Streptococcus mutans (TH16) with a daily regimen of 4x1-h-incubation with culture media, and 20-h incubation with a buffer solution. Consequently, tooth specimens are sectioned and analyzed under a confocal microscope for the presence and size of the outer lesions (OL) and wall lesions (WL). Using this model, three main experiments were performed to investigate the hypothesis proposed previously. Results. The results showed that this new model could be used to study secondary caries progression adjacent to different gap sizes. Gap size was found to affect dentin WL development, with bigger lesions being observed with wider gaps. Sucrose was found to produce deeper OL and bigger dentin WL compared to glucose. It also appeared to enhance more demineralization of dentin WL inside bigger gaps. Fluoride toothpaste was found to reduce the size of dentin WL. In addition, marginally significant interaction effect between toothpaste and gap size suggested that fluoride toothpaste was more effective in inhibiting dentin WL in specimens with wider gaps. Conclusion. From these in vitro studies, it was concluded that gap size is an important factor affecting secondary caries development on the dentin cavity wall. It also appears to alter the effect of sugar and toothpaste, with the effect of sucrose and fluoride toothpaste being more notable inside wider gaps.