MicroShear Bond Strenght (µSBS) test of a self-adhesive cement on three different restorative materials, with or without the use of an adhesive, before and after thermocycling

Objective The objective of this study was to evaluate the micro-shear bond strength of a self-adhesive resin cement, with and without the use of a universal adhesive, applied to dentin and three different indirect restorative materials (zirconia, lithium disilicate, and feldspathic ceramic). Testing was performed either 24 hours after cementation or following artificial aging. Materials and Methods A self-adhesive resin cement (BeautiCem SA, Shofu) was tested for the cementation of indirect restorations materials such as Zirconia (ZR Lucent Supra, Shofu), Lithium Disilicate (Vintage Prime Press, Shofu), and Feldspathic Ceramic (Vintage PRO, Shofu). Dentin and the three restorative materials were embedded in acrylic resin (Probase Cold, Ivoclar, Schaan, Liechtenstein) to ensure proper positioning during testing. A total of 240 composite cylinders (Beautifill II, Shofu; 1.84 mm diameter × 2.5 mm height) were fabricated and light-cured for 20 seconds using a LED curing light (Elipar™ DeepCure-L, 3M). These were divided into 4 groups (n=60) for cementation onto dentin (D), zirconia (ZR), feldspathic ceramic (FC), and lithium disilicate (LD). Each group was further subdivided into two subgroups (n=30) for testing either at 24 hours (T0) or after artificial aging in a thermocycler (T1) for 10,000 cycles between 5°C and 55°C (THE100; SD Mechatronik, Westeham, Germany). Each subgroup was then divided once more (n=15) into samples cemented with the use of the adhesive (BeautiBond Xtreme, Shofu) or without it. Bond strength was evaluated via microShear Bond Strenght (µSBS) test using the UltraTester (Ultradent Products, South Jordan, UT, USA). The load was applied at a crosshead speed of 0.5 mm/min in a direction perpendicular to the cylinder/cement interface until failure occurred. Bond strength was recorded in MegaPascals (MPa). Following debonding, a failure mode analysis was conducted on both the cylinders and the bonding substrates. Failure modes were classified as: adhesive (A; at the cement/composite, cement/dentin, or cement/material interface), cohesive (C; within the material or the cylinder), or mixed (M; simultaneous presence of A and C). Results Statistical analysis using a three-way ANOVA revealed a highly significant interaction among material, adhesive, and aging (P<0.001). At T0, in the absence of adhesive, LD exhibited the highest µSBS values, followed by FC, ZR, and D (P<0.001). The application of the adhesive eliminated the significant differences among the restorative materials, increasing bond strength exclusively in ZR and D (P<0.001). Following artificial aging (T1), among the specimens treated with adhesive, D recorded significantly superior performance compared to all ceramic materials (P<0.001), with an increase in mean SBS from 19.8 to 28.5 MPa. Conversely, aging caused a drastic drop in adhesion for ZR and FC, whereas LD maintained the highest stability values in the absence of adhesive. Conclusions The results indicate that the effectiveness of bonding protocols is not uniform but depends strictly on the combination of the specific material and temporal stress. LD proved to be the intrinsically most stable and best-performing prosthetic material, showing remarkable resistance to aging degradation even without the use of an adhesive. On the other hand, the application of an adhesive represents a critical and essential factor for stabilizing materials with lower natural affinity, such as ZR. The behavior of dentin constitutes the most significant finding: its synergy with the adhesive not only shields against the negative effects of aging but also suggests a potential maturation or stabilization process of the adhesive interface over time, offering crucial clinical insights for the longevity of direct and indirect restorations.