The Influence of Cement Layer Thickness on the Stress State of Metal Inlay Restorations—Photoelastic Analysis

Abstract

The successful restoration of teeth requires a good connection between the inlay and natural tissue. A strong bond may improve retention and reinforce tooth structure. The purpose of this study was to evaluate the influence of cement layer thickness on contraction stress generated during photopolymerization, and to determine the changes in stress state of the cement occurring during aging in water (over 84 days). Two cements were used: resin composite cement (NX3) and self-adhesive resin cement (Maxcem Elite Chroma). A cylindrical sample made of CuZn alloy was used to imitate the inlay. The stress state was measured by photoelastic analysis. The contraction stress of the inlay restoration was calculated for cement layer thicknesses of 25 µm, 100 µm, 200 µm, and 400 µm. For both tested materials, the lowest contraction stress was observed for the thinnest layer (25 µm), and this increased with thickness. Following water immersion, a significant reduction in contraction stress was observed due to hygroscopic expansion. Applying a thin layer (approximately 25 µm) of composite and self-adhesive resin cements resulted in high levels of expansion stresses (over −6 MPa) after water aging.

Influence of Cement Thickness on the Polymerization Shrinkage Stress of Adhesively Cemented Composite Inlays: Photoelastic and Finite Element Analysis

“…This leads to shrinkage stresses at the adhesive interface [39]. The result of present study is in agreement with the study conducted by Sokolowski et al (2021) [40], which reported that higher shrinkage stresses are associated with thicker cement layers.…”

“…Studies showed that the vector resulting from volumetric shrinkage occurs in the central direction of the material volume, and the stress distribution is predominantly controlled by the free surface, adhesion resistance, and interface cracks [40][41][42][43]. This indicates that the pattern of isochromatic fringes formed in the photoelastic resin (Figure 2) was the result of the strain generated in the photoelastic resin, being superior in the group with higher cement thickness due to the more accentuated shrinkage during polymerization.…”

Effect of Cement Layer Thickness on the Immediate and Long-Term Bond Strength and Residual Stress between Lithium Disilicate Glass-Ceramic and Human Dentin

“…The literature has reported that the lowest shrinkage stress (photoelastic analysis) was observed for the thinnest layer (25 µm) and proportionally increased with higher thicknesses (100 µm, 200 µm, and 400 µm) [ 30 ]. However, after the aging simulation, the authors reported that the use of thicker cement layers might have a positive clinical effect, resulting in the creation of expansion stress that could potentially influence the sealing of the marginal gap and enhance restoration-tooth retention [ 30 ]. This assumption was based on the expansion stresses found in the thinner cement layer group.…”

A Model of Damage for Brittle and Ductile Adhesives in Glued Butt Joints

“…Within the last decades, adhesive bonding became a very common assembly technique in many industrial sectors, such as aeronautical (e.g., in composite aircraft to bond the stringers to fuselage and wing skins to stiffen the structures against buckling [1]), civil (e.g., in glass-fiber-reinforced polymer pultruded beams [2] or in carbon-fiber-reinforced polymer beams [3]), automotive (e.g., in both closures and structural modules [4]), and biomedical engineering (to fix implants in bone tissue in orthopedic or dentistry surgery [5]), as an alternative to conventional joining techniques, such as welding and riveting [6]. Adhesive bonding provides several advantages, including reduced stress concentrations, higher corrosion resistance, water tightness, and the ability to join materials with dissimilar properties.…”