Studies of Akt/mTOR–Autophagy–Apoptosis Crosstalk in Human Gingival Fibroblasts Around New Digital Processed Dental Composites

Introduction: Incomplete polymerization of in vivo composite resins (CR) poses a significant problem, with monomer-to-polymer conversion rates ranging from around 60 to 75%. Furthermore, oxygen exposure hampers polymerization in the surface layers. This research aims to evaluate the autophagy-inducing potential of three types of CRS and to explore the role of the Akt/mTOR–autophagy–apoptosis crosstalk in composite resin-induced autophagy. The study uses human gingival fibroblasts and three composite materials (M1 and M2, which are 3D printed, and M3, which is milled). Materials and Methods: SEM analysis was performed on the dental materials, and cells kept in contact for 24 h were subjected to tests including the following: MTT, LDH, NO, immunological detection of proteins involved in autophagy and apoptosis, as well as immunofluorescence tests (Annexin V and nucleus; mitochondria and caspase 3/7; detection of autophagosomes). Results: The results showed statistically significant decreases in cell viability with M1 and M2, linked to increases in cytotoxicity and oxidative stress (LDH and NO). Using multiplex techniques, significant increases in glycogen synthase kinase 3 beta (GSK3b) protein were observed in both M1 and M2; a decrease in mTOR (mechanistic target of rapamycin) expression was noted in M1 and M3. Immunofluorescence tests revealed an increase in Annexin V across all materials studied, and an increase in autophagosomes in M1 and M2, whereas a decrease was observed in M3. Conclusions: The relationship between apoptosis and autophagy is highly complex, indicating they may occur sequentially, coexist, or be mutually exclusive. Understanding this complex interplay can help in designing new 3D-printing protocols and monomer compositions to prevent autophagy imbalance.