Repair of Bulk-Fill and Nanohybrid Resin Composites: Effect of Surface Conditioning, Adhesive Promoters, and Long-Term Aging

Effect of brushing simulation on the wear behavior of repaired CAD-CAM restorations

OBJECTIVE

The aim of the present study was to evaluate the influence of multidirectional brushing on the surface roughness, morphology, and bonding interface of resin-repaired CAD-CAM ceramic and composite restorations.

MATERIALS AND METHODS

Twelve (N = 12) blocks (4 mm × 4 mm × 2 mm for parallel axis; 5 mm × 4 mm × 2 mm for perpendicular axis) of lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar AG) and CAD-CAM resin composite (Tetric CAD, Ivoclar AG) were obtained and repaired with direct resin composite (Clearfil AP-X, Kuraray). An abrasive slurry was prepared and the brushing was performed according to each restorative material and axis of brushing (n = 6; perpendicular to repair interface and parallel to repair interface) during 3,650 cycles (240 strokes per minute) to simulate 3 years of brushing. The surface roughness (Ra) and the profile variation for each material (restoration and direct repair resin composite) were measured at the baseline condition and after brushing, and the mean roughness and presence of steps at the repair interface were evaluated through factorial analysis of Variance (ANOVA). Scanning Electron Microscopy (SEM) images were taken to evaluate the surface topography of the repaired materials after brushing.

RESULTS

The mean roughness of the repaired CAD-CAM restorations was affected by the brushing (P < .05), mainly when evaluating the repair material and the interface (P < .05), while the restorative CAD-CAM materials presented more stable values. The profile evaluation showed higher steps at the interface when repairing lithium disilicate than for CAD-CAM resin composite.

CONCLUSION

Repaired CAD-CAM restorations were susceptible to wear after brushing simulation. The surface roughness of the direct resin composite was the most affected leading to step development at the interface, particularly in the repaired lithium disilicate samples. Cinical maintenance recalls and polishing protocols must be considered to enhance the longevity of such restorations.

The efficacy of Er,Cr:YSGG laser and contemporary universal adhesive systems on composite resin repair bond strength: an in vitro study

The aim of this study is to investigate the repair bond strength of composite resin following three different surface treatments (bur-grinding, silanization, and Er,Cr:YSGG laser irradiation) using various universal adhesives. A total of 160 resin composite specimens, produced in cylindrical form (6 × 2 mm) with a nanohybrid composite resin within metal molds, were subjected to 5000 cycles of aging in a thermocycler. The aged samples were categorized into four groups based on surface treatments: control, bur, silane, and Er,Cr:YSGG laser. Following surface treatments, the specimens underwent repair using the same resin composite and four different adhesive systems: Tokuyama Universal Bond (TUB), Prime Bond Universal (PBU), Gluma Bond Universal (GBU), and Clearfil SE Bond (CSB). Subsequently, the specimens were subjected to shear forces, and statistical analysis was performed using two-way ANOVA and Tukey tests (p < 0.05). The failure modes were examined using a stereomicroscope, and the surface topography of the roughened resin composite was assessed through scanning electron microscopy (SEM). Results indicated that silane + GBU exhibited the highest shear bond strength (SBS) (15.61 MPa) while control + TUB showed the lowest SBS (7.63 MPa). Silane demonstrated significantly higher SBS values (p ≤ 0.05), with no significant difference observed between bur and laser methods (p = 0.998). It is recommended to include an additional silanization step before applying universal adhesive, as it effectively enhances the bond strength of the repaired composite.

The Effect of Mechanical Alteration on Repair Bond Strength of S-PRG-Filler-Based Resin Composite Materials

This study investigates the impact of mechanical alteration on resin composite surfaces and its subsequent effect on repair bond strength. A total of 100 resin composite disks were prepared and were allocated for 24 h or 1 year of artificial aging. Specimens were embedded in epoxy resin, and the composite surfaces were mechanically altered using either diamond burs or air abrasion with aluminum oxide or glass beads. A universal bonding material was applied and a 2 mm circular and 3 mm high repair composite cylinder were prepared using a Teflon mold. Then, the specimens were tested for their shear bond strength, and the de-bonded specimens were observed under a scanning electron microscope to determine the failure pattern. SPSS 26.0 statistical software was used to analyze the data. Two-way ANOVA showed a statistically significant effect of mechanical alteration and aging on the shear bond strength of S-PRG-filler-based resin composite (p < 0.05). Surface modification with a fine diamond bur showed a significantly higher bond strength in both 24-h- and 1-year-aged specimens. Surface modification with alumina significantly increased the bond strength of 1-year-aged specimens; however, it was statistically insignificant for 24 h-aged specimens. Mechanical alteration with a fine diamond bur and 50-micron alumina can improve the repair bond strength of the composite.

Scoping review: Effect of surface treatments on bond strength of resin composite repair

OBJECTIVE

to evaluate the existing evidence on surface treatment techniques employed in resin composite repair and their effect on the repair short- and long-term bond strength.

DATA AND SOURCE

This scoping review was performed under the PRISMA-ScR guidelines for scoping reviews and registered on the Open Science Framework platform.

STUDY SELECTION

A systematic search was conducted in PubMed, Embase, and Scopus and grey literature up to September 2022 without language or date restriction. In vitro studies comparing mechanical surface and/or chemical treatments on repair bond strength of resin composite were included. Studies evaluating experimental adhesive systems or resin composites were excluded. Selection of studies and data extraction were performed. Data from selected studies was qualitatively analyzed.

RESULTS

A total of 76 studies were included in the qualitative analysis. Among the mechanical treatments, alumina blasting was the most frequently used, followed by silica coating and diamond bur. As for chemical treatments, dentin bonding systems were the most frequently evaluated, followed by universal adhesive systems and silane/ceramic primer. The combination of mechanical and chemical pre-treatments increased the repair bond strength of resin composite in both short- and long-term simulated aging scenarios. The evidence obtained from the included studies was classified as moderate quality, mainly due to the medium risk of bias observed across most of the studies.

CONCLUSION

The techniques used to treat the surface of resin composites for repair are diverse. Incorporating a combination of mechanical and chemical pre-treatments resulted in superior repair bond strength of resin composite materials under both short- and long-term simulated aging conditions.

CLINICAL SIGNIFICANCE

The analysis of evidence revealed significant variability among protocols for repairing resin composites. Utilizing both mechanical and chemical pre-treatment methods is important for enhancing the bond strength of resin composites during both short- and long-term simulated aging situations.

Mechanical Behavior of Repaired Monolithic Crowns: A 3D Finite Element Analysis

This study evaluated the mechanical behavior and risk of failure of three CAD-CAM crowns repaired with different resin composites through a three-dimensional (3D) finite element analysis. Three-dimensional models of different cusp-repaired (conventional nanohybrid, bulk-fill, and flowable resin composites) crowns made of zirconia, lithium disilicate, and CAD-CAM resin composite were designed, fixed at the cervical level, and loaded in 100 N at the working cusps, including the repaired one. The models were analyzed to determine the Maximum Principal and Maximum Shear stresses (MPa). Complementary, an in vitro shear bond strength test (n = 10) was performed to calculate the risk of failure for each experimental group. The stress distribution among the models was similar when considering the same restorative material. The crown material affected the stress concentration, which was higher for the ceramic models (±9 MPa for shear stress; ±3 MPa for tensile stress) than for the CAD-CAM composite (±7 MPa for shear stress; ±2 MPa for tensile stress). The shear bond strength was higher for the repaired CAD-CAM resin composite (±17 MPa) when compared to the ceramics (below 12 MPa for all groups), while the repair materials showed similar behavior for each substrate. The stress distribution is more homogenous for repaired resin composite crowns, and a flowable direct resin composite seems suitable to repair ceramic crowns with less risk of failure.

Repair bond strength of bulk-fill composites: influence of different primers and direction of debonding stress

Background

The purpose of this in vitro study was to evaluate the effect of different adhesion primers on the repair bond strength of bulk-fill resin composite and short-term hydrolytic stability of the repair interface before and after accelerated aging. In addition, direction of debonding stress was examined.

Materials and methods

Bulk-fill substrates were aged in water for 14 days at 37 °C. Smooth resin composite surfaces were prepared for the substrates with a superfine grinding paper (FEPA #500, #1200, #2000). Test specimens were produced by attaching bulk-fill composite to the substrate surfaces, using three different primer/bonding systems. Specimens were aged 24 h at 37 °C in water, or thermal cycled (5-55 °C/5,000 cycles). Subsequently, shear bond strength and micro-tensile bond strength were evaluated. In total there were 60 specimens for the shear bond strength and 60 specimens for the micro-tensile bond strength measurements (30 stored in water 24 h, 30 thermal cycled, n = 10 in each primer/bonding mode).

Results

The mean shear bond strength was 9.1-13.1 MPa after 24 h water storage and 6.9-10.7 MPa after thermal cycling. The mean micro-tensile bond strength was 28.7-45.8 MPa after 24 h water storage and 22.7-37.9 MPa after thermal cycling.

Conclusion

The Ceramic primer (silane containing) seems to perform better than the three-step etch and rinse adhesive or the Composite primer. Shear-type stress had an adverse effect on the repair bond strength of bulk-fill resin composites.

Effect of Different Surface Treatments on the Long-Term Repair Bond Strength of Aged Methacrylate-Based Resin Composite Restorations: A Systematic Review and Network Meta-analysis

This systematic review and network meta-analysis is aimed at investigating the effect of common surface treatments on the long-term repair bond strength of aged resin composite restorations and to rank and compare these surface treatments. In vitro studies evaluating the methacrylate-based resin composites subjected to rigorous aging protocols before and after being repaired with a new composite were included. A frequentist network meta-analysis was carried out using a random effects model. P scores were used to rank the efficacy of the surface treatments. Also, the global and node-split inconsistencies were evaluated. Web of Science, PubMed/Medline, Scopus, and Embase databases were searched until July 07, 2022. Twenty-six studies were included in the meta-analysis. The results showed that the application of silane and a total-etch (shear MD 32.35 MPa, 95% CI: 18.25 to 46.40, P score 0.95; tensile MD 33.25 MPa, 95% CI: 25.07 to 41.44; P score 0.77) or a self-etch (shear MD 38.87 MPa, 95% CI: 21.60 to 56.14, P score 0.99; tensile MD 32.52 MPa, 95% CI: 23.74 to 41.29; P score 0.73) adhesion protocol subsequent to the roughening with diamond bur produced the highest (micro)tensile and (micro)shear bond strengths compared to diamond bur alone as the control group. There was no difference between self- and total-etch adhesive protocols. Mechanical surface treatments yielded greater bond strength when used alongside the chemical adhesive agents. Further, it is possible to achieve acceptable repair bond strength using common dental clinic equipment. Therefore, clinicians could consider repairing old resin composites rather than replacing them.