PROJECT SUMMARY After nearly seven decades of research, dental composites restorations continue to show limited clinical service, with more than 50% of placed bonded restorations failing in less than ten years. Pathogenic bacteria and human salivary enzymes produce detrimental products that degrade dental resins and adhesives. As a result, the bond strength is debilitated, which increases the progression of secondary caries, premature failure of restoration, and tooth loss. Current approaches to evaluate the effects of biodegradation sources on bond strength are failing to replicate clinical conditions in a laboratory setting. Our goal is to develop an experimental approach for accurately predicting composite restorations' lifetime using realistic environments. Our innovative approach significantly improves existing methods by challenging bonded interfaces to different degradative sources simultaneously. In this study, we proposed to find the specific contribution of the main degradative sources (salivary enzymes, bacteria enzymes and acids, and cyclic mechanical loading) after working in synergy on bond strength reduction (aim 1). We will also evaluate the bond strength durability of dentin/resin composites interfaces within a clinically relevant microbiome environment. This project will assess the degradation of the tooth-restoration interface under representative oral conditions and will help elucidate the individual and synergistic effects of the primary degradative sources on bond strength durability. The application of this novel approach will help improve the prediction of the durability of composite restorations, thereby rendering the restorative treatment more predictable