Four-year clinical evaluation of a self-adhesive luting agent for ceramic inlays.

OBJECTIVES: The aim of this randomized controlled clinical trial was to evaluate the 4-year clinical performance of a self-adhesive resin cement, RelyX Unicem (3M ESPE), used for cementation of ceramic inlays. In addition, the influence of selectively acid-etching enamel prior to luting on the clinical performance of the restorations was assessed. METHODS: Sixty-two IPS Empress 2 inlays/onlays were placed in 31 patients by two experienced clinicians. The restorations were luted with RelyX Unicem with (=experimental group: E) or without (=control group: NE) prior enamel etching with phosphoric acid. At baseline, 6 months, and 1, 2, and 4 years after placement, the restorations were assessed by two calibrated investigators using modified USPHS criteria. Ten selected samples of each group were investigated under SEM regarding morphological changes at the cement-inlay interface. RESULTS: The recall rate at 4 years was 97%. Two restorations (1 E, 1 NE) were lost, and one (E) had to be replaced due to inlay and tooth fracture resulting in a survival rate of 95%. No significant differences between the experimental and control group were noticed regarding all criteria (McNemar, p < 0.05). An obvious deterioration in marginal integrity was observed after 4 years as only 5% (E = 7%; NE = 3%) of the restorations exhibited an excellent marginal adaptation. In 90% of the restorations small, still clinically acceptable marginal deficiencies were observed. SEM of the luting gap showed an increased wear of the RelyX Unicem cement over the 4-year period. CONCLUSIONS: The self-adhesive luting cement RelyX Unicem can be recommended for bonding of ceramic inlays/onlays. Additional selective enamel etching does not improve the clinical performance of the restorations within the 4-year period. CLINICAL RELEVANCE: The self-adhesive resin composite RelyX Unicem showed acceptable clinical performance after 4 years of clinical service.

Microtensile Bond Strength of Composite Cement to Novel CAD/CAM Materials as a Function of Surface Treatment and Aging.

OBJECTIVES: To evaluate the effect of different surface treatments on the bond strength to a composite and a polymer-infiltrated ceramic CAD/CAM block after six-month artificial aging. METHODS AND MATERIALS: Two types of CAD/CAM blocks (Cerasmart, GC; Enamic, Vita Zahnfabrik) were cut in slabs of 4-mm thickness, divided into six groups, and subjected to the following surface treatments: group 1: no treatment; group 2: sandblasting (SB); group 3: SB + silane (Si); group 4: SB + Si + flowable composite (see below); group 5: 5% hydrofluoric acid etching (HF) + Si; and group 6: 37% phosphoric acid etching (H3PO4) + Si. Sections of the same group were luted together (n=3: 3 sandwich specimens/group) using a dual-cure self-adhesive cement for all groups, except for the sections of group 4 that were luted using a light-curing flowable composite. After three weeks of storage in 0.5% chloramine at 37°C, the sandwich specimens were sectioned in rectangular microspecimens and trimmed at the interface to a dumbbell shape (1.1-mm diameter). One half of the specimens was subjected to a microtensile bond strength (µTBS) test, and the other half was tested after six months of water storage (aging). Data were statistically analyzed with a linear mixed-effects model for the factors surface treatment, material type, and aging, together with their first-degree interactions (α=0.05). RESULTS: The lowest bond strengths were obtained in the absence of any surface treatment (group 1), while the highest µTBSs were obtained when the surface was roughened by either SB or HF, this in combination with chemical adhesion through Si. Loss in bond strength was observed after six-month aging when either surface roughening or silanization, or both, were omitted. CONCLUSIONS: Both the composite and polymer-infiltrated ceramic CAD/CAM blocks appeared equally bonding-receptive regardless of the surface treatment used. Creating a microretentive surface by either SB or HF, followed by chemical adhesion using Si, is mandatory to maintain the bond strength after six months.

Dentin Bonding Testing Using a Mini-interfacial Fracture Toughness Approach.

Measurement of interfacial fracture toughness (iFT) is considered a more valid method to assess bonding effectiveness as compared with conventional bond strength testing. Common fracture toughness tests are, however, laborious and require a relatively bulky specimen size. This study aimed to evaluate a new simplified and miniaturized iFT (mini-iFT) test. Four dentin adhesives, representing the main adhesive classes, and 1 glass ionomer cement were applied onto flat dentin. Mini-iFT (1.5 × 2.0 × 16 to 18 mm) and microtensile bond strength (µTBS; 1.5 × 1.5 × 16 to 18 mm) specimens were prepared from the same tooth. For the mini-iFT specimens, a single notch was cut at the adhesive-dentin interface with a 150-µm diamond blade under water cooling; the specimens were loaded until failure in a 4-point bending test setup. Finite element analysis was used to analyze stress distribution during mini-iFT testing. The correlation between the mean mini-iFT and µTBS was examined and found to be significant; a strong positive correlation was found (r(2) = 0.94, P = 0.004). Weibull data analysis suggested the mini-iFT to vary less than the µTBS. Both the mini-iFT and the µTBS revealed the same performance order, with the 3-step etch-and-rinse adhesive outperforming the 2-step self-etch and 2-step etch-and-rinse adhesive, followed by the 1-step SE adhesive and, finally, the glass ionomer cement. Scanning electron microscopy failure analysis revealed the adhesive-dentin interface to fail more at the actual interface with the mini-iFT test, while µTBS specimens failed more within dentin and composite. This finding was corroborated by finite element analysis showing stress to concentrate at the interface during mini-iFT loading and crack propagation. In conclusion, the new mini-iFT test appeared more discriminative and valid than the µTBS to assess bonding effectiveness; the latter test nevertheless remains more versatile. Specimen size and workload were alike, making the mini-iFT test a valid alternative for the popular µTBS test.

Microshear Bond Strength of Resin Cements to Lithium Disilicate Substrates as a Function of Surface Preparation.

OBJECTIVES: To investigate the effect of hydrofluoric acid (HF) etching, silane solution, and adhesive system application on the microshear bond strength (µSBS) of lithium disilicate glass-ceramic (LD) to three resin cements. MATERIALS AND METHODS: Circular bonding areas were delimited on the lithium disilicate surfaces using a perforated adhesive tape. Specimens were assigned to 18 subgroups (n=12) according to surface treatment: NT = no treatment; HF = 4.8% HF for 20 seconds; silane solution: (1) no silane; (2) Monobond Plus, a silane/10-methacryloyloxydecyl dihydrogen phosphate solution for 60 seconds; (3) Monobond Plus+ExciTE F DSC, a dual-cure adhesive; and resin cement: (1) Variolink II, a bisphenol A diglycidyl ether dimethacrylate (bis-GMA)-based, hand-mixed, dual-cure resin cement; (2) Multilink Automix, a bis-GMA-based, auto-mixed, dual-cure resin cement; (3) RelyX Unicem 2, a self-adhesive, auto-mixed, dual-cure resin cement. Tygon tubes (Ø=0.8 mm) were used as cylinder matrices for resin cement application. After 24 hours of water storage, the specimens were submitted to the µSBS test. Mode of failure was evaluated under an optical microscope and classified as adhesive, mixed, cohesive in resin cement, or cohesive in ceramic. Data were statistically analyzed with three-way analysis of variance and Dunnett test (p<0.05). RESULTS: When means were pooled for the factor surface treatment, HF resulted in a significantly higher µSBS than did NT (p<0.0001). Regarding the use of a silane solution, the mean µSBS values obtained with Monobond Plus and Monobond Plus+ExciTE F DSC were not significantly different but were higher than those obtained with no silane (p<0.001). Considering the factor resin cement, Variolink II resulted in a significantly higher mean µSBS than did RelyX Unicem 2 (p<0.03). The mean µSBS for Multilink Automix was not significantly different from those of Variolink II and RelyX Unicem 2. According to Dunnett post hoc test (p<0.05), there was no significant difference in µSBS between the different resin cements for HF-etched and silanized (with or without adhesive application) LD surfaces. CONCLUSION: LD may benefit from pretreatment of the inner surface with HF and silanization, regardless of the resin cement used.

Bonding of low-shrinking composites in high C-factor cavities.

OBJECTIVES: Polymerization shrinkage causes stress at the tooth-restoration interface. The magnitude of the stress depends upon several factors, such as the configuration factor (C-factor) of the cavity, the polymerization-conversion rate and filling technique. The aim of this study was to investigate the effect of curing time and filling method when high C-factor cavities were filled with low-shrinking composites. METHODS: Three low-shrinking (Filtek Silorane, 3M ESPE: FS; N'Durance, Septodont: N'D; Kalore, GC: Ka) and one conventional composite (Z100, 3M ESPE) were bonded into standardized occlusal Class-I cavities using either a two-step self-etch adhesive (Silorane System Adhesive, 3M ESPE: SSA) or a one-step self-etch adhesive (G-Bond, GC: GB). Five experimental groups were formed according to the employed adhesive/composite combination (SSA/FS, SSA/Z100, GB/N'D, GB/Ka, GB/Z100), and further divided into three subgroups conforming to curing time and filling technique (20 s/bulk; 80 s/bulk; 80 s/layered). For each subgroup, non-trimmed 1 mm×1 mm sticks were prepared from five teeth to measure the micro-tensile bond strength (µTBS) to cavity-bottom dentine. RESULTS: The two-step self-etch adhesive SSA generated higher bond strengths than the one-step self-etch adhesive GB, irrespective of the filling method. When GB was used, bulk filling with a low-shrinking composite revealed the highest bond strengths. For all composites, the layering method provided the highest bond strengths. SIGNIFICANCE: The two-step self-etch adhesive Silorane System Adhesive (3M ESPE) performed better than the one-step self-etch adhesive G-Bond (GC), regardless of the composite used. When the latter all-in-one adhesive was used, effects of shrinkage stress became more apparent.

Meta-analytical review of parameters involved in dentin bonding.

Bond-strength testing is the method most used for the assessment of bonding effectiveness to enamel and dentin. We aimed to disclose general trends in adhesive performance by collecting dentin bond-strength data systematically. The PubMed and EMBASE databases were used to identify 2,157 bond-strength tests in 298 papers. Most used was the micro-tensile test, which appeared to have a larger discriminative power than the traditional macro-shear test. Because of the huge variability in dentin bond-strength data and the high number of co-variables, a neural network statistical model was constructed. Variables like 'research group' and 'adhesive brand' appeared most determining. Weighted means derived from this analysis confirmed the high sensitivity of current adhesive approaches (especially of all-in-one adhesives) to long-term water-storage and substrate variability.

Relationship between bond-strength tests and clinical outcomes.

One often alleges that laboratory bond-strength testing cannot predict clinical effectiveness of adhesives. Major argument to sustain this claim is the wide variation in bond-strength values recorded for one specific adhesive among different research institutes worldwide. The main reason for these inconsistent bond-strength measurements is supposedly the current lack of a standard bond-strength testing protocol. This paper (and presentation) aimed to report on an extensive literature review with regard to the different laboratory bond-strength test methods and their data provided, along with a second extensive literature review on clinical effectiveness data of adhesives in terms of retention rates of adhesive Class-V restorations. Combining both systematic reviews, we have subsequently searched for a potential relationship between bond-strength data and clinical outcomes.