Vincenzo Spinelli

Background and Objectives: To evaluate the influence of proximal box design on primary stability and adhesive bond strength of indirect partial bonded restorations (IPBR) in posterior teeth. Materials and Methods: Thirty extracted human third upper molars were randomly assigned to three groups (n = 10 each): Group A, butt joint overlay-type restorations with proximal box (height-to-depth ratio 1:2–1:3); Group B, proximal box with height-to-depth ratio 1:1; and Group C, flat bevel preparation as control. Specimens underwent standardized preparation: immediate dentin sealing, restoration with overlays, and cementation with Panavia V5 adhesive resin cement. Mechanical measurements were performed to assess the tensile bond strength 48 h post-cementation using a universal testing machine. Finite element analysis (FEA) was also carried out to evaluate stress distribution at the adhesive interface. Data were analyzed by ANOVA with the Bonferroni post hoc tests. Results: Group A exhibited significantly higher bond strength values (403.7 ± 37.5 N) compared with Group B (340.4 ± 32.7 N; p < 0.01) and Group C (324.8 ± 33.3 N; p < 0.01). No significant difference was observed between Groups B and C. FEA corroborated the experimental findings, showing more homogeneous stress distribution for Group A and higher stress concentrations in Groups B and C. Conclusions: Proximal box design significantly affects the primary stability and bond strength of IPBR in vitro. A deeper proximal box with favourable geometric features enhances adhesive performance and stress distribution. Within the limitations of this study, these findings suggest potential clinical benefits, although further in vivo studies under dynamic conditions are needed to confirm long-term restoration performance.

Mineralized connective tissues represent the hardest materials of human tissues, and polymer based composite materials are widely used to restore damaged tissues. In particular, light activated resins and composites are generally considered as the most popular choice in the restorative dental practice. The first purpose of this study is to investigate novel highly reinforced light activated particulate dental composites. An innovative additive manufacturing technique, based on the extrusion of particle reinforced photo-polymers, has been recently developed for processing composites with a filler fraction (w/w) only up to 10%. The second purpose of this study is to explore the feasibility of 3D printing highly reinforced composites. A variety of composites based on 2,2-bis(acryloyloxymethyl)butyl acrylate and trimethylolpropane triacrylate reinforced with silica, titanium dioxide, and zirconia nanoparticles were designed and investigated through compression tests. The composite showing the highest mechanical properties was processed through the 3D bioplotter AK12 equipped with the Enfis Uno Air LED Engine. The composite showing the highest stiffness and strength was successfully processed through 3D printing, and a four-layer composite scaffold was realized. Mechanical properties of particulate composites can be tailored by modifying the type and amount of the filler fraction. It is possible to process highly reinforced photopolymerizable composite materials using additive manufacturing technologies consisting of 3D fiber deposition through extrusion in conjunction with photo-polymerization.