Comparative analysis of bonding strength between enamel and overlay of varying thicknesses following an aging test

Abstract

Background/purpose: Overlay restorations can be used clinically as a treatment option to preserve natural dentine. However, whether the residual enamel thickness and overlay thickness affect the adhesion between the restoration and tooth is still unknown. This study was to investigate effects of the overlay thickness and residual enamel thickness on bonding strength.

Materials and methods

Overlays of different thicknesses were prepared with natural teeth which had 2, 4, and 6 mm of occlusal reduction (n = 10). Specimens were subjected to 10,000 cycles in water at 5-55 °C, and finally compressive strength tests were used to evaluate the bonding strength.

Results

All groups showed good bond strength (P > 0.05). The overlay restorations of different thicknesses reduced the preparation amount by 30.3%-7.2% and significantly preserved more of the tooth structure (P < 0.005). Compared to the control group, the overlay restoration increased the marginal fitness by about 0.67-0.88 times. The thermal cycling indicated that the decrease in the maximum bearing stress was due to the aging of the ceramic itself. Therefore, the thickness of the overlay had a greater influence on the compressive strength than the bond strength.

Conclusion

Based on the above this study recommends an overlay thickness of at least 2 mm in clinical practice. The aging test confirmed that adhesion between the overlay and teeth was quite firm and stable. This shows that a stable adhesive effect of the overlay can be used as a treatment option for preserving a greater amount of a tooth's structure.

Bonding stability of universal adhesives to feldspathic ceramic with or without prior silane application

PURPOSE

This study aimed to assess the bonding stability of three universal adhesives to a CAD-CAM feldspathic ceramic with or without prior silane application.

MATERIALS AND METHODS

The universal adhesives tested were Ambar Universal (FGM), Single Bond Universal (3M), and Ybond Universal (Yller). Scotchbond Multipurpose Plus (3M) was used as a control. The silane used was RelyX Ceramic Primer (3M). Microtensile bond strength (μTBS) to Vitablocs Mark II was measured after 24 h or 6 months of water aging (n = 20). Failure modes were observed through scanning electron microscopy, and pH and degree of C=C conversion (DC) of the adhesives were measured (n = 3). Data were analyzed using one-, two-, and three-way ANOVA.

RESULTS

The pH values differed significantly among the adhesives (p < 0.001), while the DC was similar (p = 0.141). The universal adhesives showed significant differences in μTBS, with higher immediate results when using silane and lower results after aging. Notably, a significant decrease in μTBS was observed after 6 months when silane was applied. In contrast, the control adhesive exhibited consistent results between the 24-h and 6-month storage periods. The universal adhesives showed a decrease in μTBS ranging from 25.5% to 40.1% after prolonged storage. Adhesive failures were predominant in all groups. The presence or absence of silane in the adhesive composition did not affect the bonding performance.

CONCLUSIONS

The application of a separate silane coupling agent improved the immediate bond strength of universal adhesives to CAD-CAM feldspathic ceramic. However, this bond strength significantly decreased after 6 months of water aging. The bond strength remained stable for universal adhesives when applied without silane after 6 months of aging.

Effectiveness and safety of bleaching agents on lithium disilicate glass ceramics

Background

Aesthetic expectations have increased the use of aesthetic materials in dentistry. Lithium disilicates are frequently used materials for these expectations. Bleaching is another method used to provide aesthetics. Bleaching processes on restorative materials are not fully known. This study investigated the effect of at-home and in-office bleaching methods on the color change, surface roughness, and topography of lithium disilicate glass-ceramic materials produced with two different techniques and subjected to different polishing procedures.

Methods

A total of 144 disc-shaped pressed and computer-aided design (CAD) lithium disilicate glass-ceramic specimens were randomly divided into four groups. Glazing and three different chair-side polishing procedures were performed. The specimens in each group were randomly divided into two groups and subjected to at-home and in-office bleaching processes (n=9). The home bleaching process was repeated with 16% carbamide peroxide agent for six hours for seven days, while the in-office bleaching process was applied with 40% hydrogen peroxide agent for two sessions of 20 minutes. After the bleaching processes, the final color and surface roughness experiments of the specimens were carried out, and the results were recorded. ANOVA and Tukey multiple comparison tests were used FOR the statistical analysis of the data (α=0.05).

Results

The material*polish*bleaching, polish*bleaching, material*bleaching, and material*polishing interactions were not statistically significant regarding color and roughness changes of both specimens (P>0.05).

Conclusion

Both bleaching processes can be safely applied to lithium disilicate glass-ceramic materials.

Impact of in vitro findings on clinical protocols for the adhesion of CAD-CAM blocks: A systematic integrative review and meta-analysis

STATEMENT OF PROBLEM

Computer-aided design and computer-aided manufacturing (CAD-CAM) blocks have evolved rapidly, making it difficult to establish the best clinical protocol for bonding a given block and whether an established protocol is appropriate for a newly introduced product.

PURPOSE

This integrative systematic review and meta-analysis aimed to clarify whether the clinician can select the most efficient adhesion protocols for CAD-CAM blocks by reading published in vitro studies and implementing them in daily practice.

MATERIAL AND METHODS

Based on the population, intervention, comparison, and outcome (PICO) strategy, 3 databases were searched for in vitro studies, randomized clinical trials, prospective or retrospective studies, and case reports from January 1, 2015, to July 31, 2021. A meta-analysis analyzed 28 studies to calculate the mean difference between best and worst protocols for each author and block with a random-effects model (α=.05).

RESULTS

From 508 relevant studies, 37 in vitro studies, 2 clinical studies, and 1 clinical report were selected for data extraction and qualitative analysis. Vita Enamic, IPS e.max CAD, LAVA Ultimate, and Vita Mark II blocks were the most studied, and RelyX Ultimate was the most used luting cement. The meta-analysis confirmed the null hypothesis that the evidence-based efficacy of clinical protocols to bond CAD-CAM blocks is still controversial (P<.05).

CONCLUSIONS

There are objective standards for individual in vitro tests, but the studies lack standardization. Some tested protocols were more efficient than others. Randomized clinical trials and well-documented clinical situations were almost nonexistent, making direct application of in vitro findings in clinical practice impossible.

Effects of surface treatments on the bonding properties of polyetherketoneketone to dentin: An in vitro study

STATEMENT OF PROBLEM

Polyetherketoneketone (PEKK) has been recently introduced as a dental material for fixed dental prostheses. However, how surface treatments affect the bonding of PEKK to dentin is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effects of airborne-particle abrasion and acid etching on the bonding of PEKK to dentin.

MATERIAL AND METHODS

Eighty-four PEKK specimens were fabricated, polished, and divided into 6 groups (n=14): no treatment (group NT), airborne-particle abrasion with 110-μm alumina particles (group Al), 98% sulfuric acid etching for 5 seconds (group SA5), 98% sulfuric acid etching for 30 seconds (group SA30), 98% sulfuric acid etching for 60 seconds (group SA60), and airborne-particle abrasion plus 98% sulfuric acid for 5 seconds (group AlSA5). Sixty PEKK specimens (n=10) were fabricated for the shear bond test. Another 24 PEKK specimens (n=4) were fabricated for surface element analysis and morphological observations. For each group, 2 specimens after surface treatments were randomly selected to examine scanning electron microscope (SEM) observations and surface element analysis. Another 2 specimens after bonding were randomly selected to examine cross-sectional observations. Airborne-particle abrasion with 110-μm alumina particles was performed to cobalt-chromium (Co-Cr) specimens (group Co-Cr, n=10). A light-polymerizing polymethylmethacrylate and composite resin primer (visio.link) was applied to the treated PEKK specimens and bonded with a resin cement (RelyX Ultimate) to dentin. The Co-Cr specimens were bonded with the resin cement to dentin. The shear bond strengths of all groups were tested by using a universal testing machine, and fracture analysis was performed. A statistical analysis was performed by using 1-way ANOVA, followed by the Student-Newman-Keuls-q post hoc test (α=.05).

RESULTS

The shear bond strengths of groups SA5 and AlSA5 were higher than those of groups NT, Al, SA30, SA60, and Co-Cr (P＜.05). Group SA5 achieved the highest shear bond strength (16.84 ±1.84 MPa). The SEM observations showed that after surface treatments, groups SA5 and AlSA5 had a uniform sponge shape with small pores, while groups SA30 and SA60 had a collapsed shape with large pits and pores. The sulfur element content and H₂SO₄-etched thicknesses of groups SA30 and SA60 were higher than those of groups SA5 and AlSA5. The cross-sectional SEM observations of groups SA30 and SA60 after bonding revealed that H₂SO₄-etched pores were deeper and not filled with the bonding material.

CONCLUSIONS

Compared with airborne-particle abrasion, the 98% sulfuric acid etching significantly improved the shear bond strength of PEKK to dentin. The surface treatment of 98% sulfuric acid etching for 5 seconds led to the high bond strength of PEKK to dentin, which meets the requirements for clinical use.

Adhesion to a Lithium Disilicate Glass Ceramic Etched with Hydrofluoric Acid at Distinct Concentrations

This study evaluated the effect of different hydrofluoric acid (HF) concentrations on the bond strength between a lithium disilicate-based glass ceramic and a resin cement. Eighty ceramic-blocks (12×7×2 mm) of IPS e.Max CAD (Ivoclar Vivadent) were produced and randomly assigned to 8 groups, considering 2 study factors: HF concentration in 4 levels, i.e., 1% (HF1), 3% (HF3), 5% (HF5), and 10% (HF10), and storage in 2 levels, i.e., baseline (tests were performed 24 h after cementation), and aged (storage for 150 days + 12,000 thermal-cycles at 5°C and 55°C). Acid etching (20 s) was performed, followed by washing, drying, and silanization. Four resin cement cylinders (ϕ= 0.96 mm) were built-up from starch matrices on each ceramic sample (n= 40). Additional ceramic samples were etched and analyzed for contact angle, micro-morphology, and roughness. In baseline condition (without aging), the HF3, HF5, and HF10 groups showed similar bond strength values (13.9 - 15.9 MPa), and HF1 (11.2 MPa) presented lower values than HF5, being that statistically different (p= 0.012). After aging, all the mean bond strengths statistically decreased, being that HF3, HF5, and HF10 (7.8 - 11 MPa) were similar and higher than HF1 (1.8 MPa) (p= 0.0001). For contact angle, HF3, HF5, and HF10 presented similar values (7.8 - 10.4°), lower than HF1 and CTRL groups. HF5 and HF10 presented rougher surfaces than other conditions. For better bond strength results, the tested ceramic may be etched by HF acid in concentrations of 3%, 5%, and 10%.

Survival rate and load to failure of premolars restored with inlays: An evaluation of different inlay fabrication methods

STATEMENT OF PROBLEM

Studies that evaluate the survival rate and load to fracture of premolars restored with inlays produced using different methods are lacking.

PURPOSE

The purpose of this in vitro study was to compare the survival rate and fracture load of premolars restored with inlays fabricated using different methods.

MATERIAL AND METHODS

Thirty maxillary premolars were selected, embedded, and prepared to receive inlays fabricated using different methods (n=10): LaCom-digital scanning with Lava C.O.S. scanner (3M ESPE), followed by milling of composite resin block (Lava Ultimate; 3M ESPE) in a milling unit; CeCom-digital scanning with Cerec 3D Bluecam scanner (Dentsply Sirona), followed by milling of a Lava Ultimate block in Cerec (Dentsply Sirona); PresDis-impression with polyvinyl siloxane, inlay made using the lost wax technique, and IPS e.max Press (Ivoclar Vivadent AG) pressed ceramic (lithium disilicate). A dual-polymerizing resin cement system was used to lute the inlays. Inlays were mechanically cycled (2 Hz, 10⁶ mechanical pulses, 80 N) after 24 hours, and the specimens were stored in distilled water at 37°C for 11 months. Then, a fatigue test was conducted using a 10-Hz frequency and 400-N load on the inner inclines of the cusps. The test was complete when the specimen fractured or when the specimen reached 1.5×10⁶ cycles. The specimens that survived fatigue testing were submitted to a single-load fracture test in a universal testing machine and analyzed using a stereoscope for failure classification. Survival rates were estimated using the Kaplan-Meier method and log-rank test (Mantel-Cox). Fracture load data were analyzed using 1-way ANOVA (α=.05).

RESULTS

No significant differences were detected among the groups for the survival rate (P=.87) or for the load to fracture (P=.78). Most failures were longitudinal, catastrophic fractures.

CONCLUSIONS

Premolars restored with inlays fabricated using the tested methods had similar survival rates and loads to fracture.

Fatigue Failure Load of Restored Premolars: Effect of Etching the Intaglio Surface of Ceramic Inlays With Hydrofluoric Acid at Different Concentrations

The aim of this study was to evaluate the effect of etching, with different hydrofluoric acid concentrations at the intaglio surface of feldspathic ceramic inlays, on the fatigue failure load of restored premolars. A total of 60 upper premolars were embedded in plastic cylinders with acrylic resin (up to 3 mm below the cement-enamel junction) and prepared using a device specially designed for that purpose. Teeth were randomly assigned to three groups (n=20): HF1, HF5, and HF10 (etching with hydrofluoric acid for 60 seconds at concentrations of 1%, 5%, and 10%, respectively). Preparations were scanned and restorations were milled by a computer-aided design / computer-aided manufacturing system. The inner surfaces of the inlays were etched and received an application of a silane coupling agent; the dentin and enamel were treated appropriately for the luting system (RelyX ARC, 3M-ESPE). The restorations were cemented and the fatigue failure load (in N) was determined using the staircase method (10 Hz; 10⁵ cycles in each step). The initial load (585.5 N) was applied on the slopes of the cusps (labial and palatal/lingual, simultaneously) through a cylinder attached to the test machine (Instron ElectroPuls E3000). The tested samples were analyzed under a stereomicroscope for failure analysis. Fatigue data were analyzed by one-way analysis of variance. There was no statistical difference among the fatigue failure loads (in N): HF1 (448.5±79.1), HF5 (360.7±55.4), and HF10 (409.5±121.1). Regarding the fracture mode, there was a predominance of interfacial fracture (50%), followed by cusp fracture (34.6%). It may be concluded that the etching with hydrofluoric acid at the tested concentrations (1%, 5%, and 10%) does not influence the fatigue failure load of feldspathic ceramic inlays cemented on premolars.