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.

Retentive strength, disintegration, and marginal quality of luting cements.

This study evaluated the retention of complete crowns by using five different methods of cementation. Complete crowns were prepared with standardized dimensions on extracted human molars. Metal crowns were cast with a high noble gold ceramic alloy and were cemented with zinc phosphate cement, glass ionomer cement, composite resin cement, composite resin cement with a dentinal bonding agent, and adhesive resin cement. The retention was measured by subjecting the specimens to tensile load until fracture occurred. The disintegration was measured according to American Dental Association Specification No. 8, and the condition of the cements at the margins of crowns was analyzed by use of a scanning electron microscope. Kruskal-Wallis one-way analysis of variance revealed statistically significant differences between the mean retentive strengths. The retention of the zinc phosphate and the glass ionomer groups was significantly different from that of the adhesive resin group. The retention of the adhesive resin cement was 65% greater than the retention of the composite resin and the composite resin/dentinal bonding agent group, but the Mann-Whitney Wilcoxon rank sum test did not depict this difference as significant. The mean +/- SD of the disintegration for the zinc phosphate, the glass ionomer cement, and the composite resin cement was 0.025 +/- 0.013, 0.023 +/- 0.011, and 0.017 +/- 0.001, respectively. The scanning electron microscope analysis of the margins revealed that the composite resin cement was almost intact, the zinc phosphate was subjected to limited disintegration, and the glass ionomer displayed the worst marginal integrity.

The effect of dentin pre-treatment and heat-augmented cure on marginal gap formation of a dentin bonding agent.

This study evaluated the effect of enhancing the cure of a DBA and the effect of dentin surface pre-treatment on marginal gap formation. Dentin cavities were prepared on extracted teeth and were pre-treated either with EDTA or phosphoric acid. Marginal leakage was expressed as percent length of margins with gaps. The mean percent length of margins with gaps for the chemically cured groups ranged from a maximum of 97% to a minimum of 85%. For the chemical/thermal-cured group, the mean percent length of margins with gaps was 95%, 95%, 73%, 35%, and 65%, corresponding to the following: pretreatment, no pre-treatment, EDTA, and phosphoric acid for 60, 15, or five s, respectively. SEM micrographs showed partial removal of one smear layer with EDTA and total removal of the smear layers with phosphoric acid. It is concluded that dentin pre-treatment methods have an effect on the percent length of margins with gaps when the DBA used had its cure supplemented with heat.

Resin-bonded fixed partial dentures: a recall study.

A clinical recall program was initiated at the University of Minnesota to evaluate the longevity and factors affecting longevity of resin-bonded fixed partial dentures (FPDs). Of the 49 resin-bonded FPDs evaluated in the clinic, 43 were acid-etched metal, resin-bonded FPDs, four were combinations of resin-bonded and conventional FPDs, and two were composite resin pontics. None of the combination FPDs and one of the two composite resin pontics were judged as failed at the examination. Of the 43 acid-etched metal resin-bonded FPDs, 15 were found to be debonded (failure rate = 34.9%). The average length of service for the 43 FPDs was 47.3 months. The average time of placement to debondment was 33 months for the 15 debonded FPDs. The failure rate for maxillary FPDs and FPDs with two retainers were significantly lower than the failure rate for mandibular FPDs and FPDs with more than two retainers (p greater than 0.05). The clinical significance of the present study was discussed.

Restorative and endodontic management of an anomalous mandibular molar.

Morphologic variations of dental hard tissue should be recognized and considered during restorative procedures. Overlooking anomalies increases the potential for clinical complications. Amalgam was used erroneously in a patient when the presence of a paramolar structure was overlooked. The clinical complications that resulted from overlooking the anomaly led to restorative, endodontic, and periodontal failures. The present report describes the use of conservative endodontics and a cast restoration, taking into account the presence of the paramolar structure, to correct the case.

Evaluation of the bond mediated by eight DBA's to enamel and dentin.

It is well-established that the bonding strength between resin and acid-etched enamel is considered clinically adequate. The tensile bonding strength mediated by a group of dentinal bonding agents (DBA's) to both dentin and acid-etched enamel was measured after one hour and the results compared. For all the DBA's tested, the bonding strength to enamel was higher than that to dentin. These differences were significant for all DBA's except for Gluma/Clearfil F-II. Analysis of variance revealed significant differences between material-specific means to either enamel or dentin. For enamel, the significant differences were due to the relatively low bonding strength value measured with the Prisma Bond. The bonding strength of all DBA's tested to acid-etched enamel would secure clinically high retention rate and adequate marginal quality. For dentin, these differences were due mainly to the high mean values for strength of bonds when the Gluma/Clearfil F-II combination was used. The low values and the large variations of the bonds to dentin measured with the commercial systems would affect the two major functions of DBA's, namely, retention of the restoration and prevention of marginal gaps. The Gluma/Clearfil combination should be recommended for clinical trials.

A comparative study of the effects of dentinal bonding agents and application techniques on marginal gaps in Class V cavities.

The effectiveness of eight dentinal bonding agents (DBA's) and four of their combinations in eliminating marginal gaps in class V cavities was evaluated by the bulk method of composite application and two different incrementation techniques. The cavities were prepared one-half in enamel and one-half in dentin. Basic fuchsin 0.5% in propylene glycol was used for detection of the presence of gaps. For each cavity, the presence of gaps was scored as 0 or 1, at five enamel and five dentin locations. Marginal gaps were present in 6% of all enamel locations and in 75% of all dentin locations investigated. The gap frequency was lowest at the enamel occlusal locations, it increased gradually toward the dentin, and attained the highest value at the gingival locations. In enamel, the occurrence of gaps was dependent on the DBA's but independent of the particular technique used. In dentin, there was significant difference in gap occurrence between DBA's with any of the incrementation techniques. The frequency of gap occurrence was not significantly changed by the incrementation techniques. The most effective single agent in producing gap-free restorations was the Gluma, and the most effective combination was the Gluma/Clearfil.

Microscopical analysis of fractured restorative resin/etched enamel bonds.

The purpose of the present work was to analyze the boundary structures of fractured restorative resin/etched enamel bonds. The fracture patterns were studied by scanning electron and optical microscopy. The three main types of failure observed were classified as: apparent interfacial failure, failure in the bulk of the restorative resin and failure in the bulk of the enamel. The fracture of the resin/etched enamel bond in the case of the apparent interfacial failure was located in the resin very near the interface. No true interfacial debonding occurred in any of the bonds studied.

Correlation between tensile and bond strength of composite resins.

The purpose of the present work was to measure the bond strength of five composite resins (two microfilled and three conventional) to human etched enamel and to correlate the findings with previously published results on the tensile strength of the same resins. The two microfilled composites showed a significantly lower bond strength than the three conventional products. The coefficient of correlation between tensile and bond strength was 0.74.

Tensile strength of restorative resins.

The purpose of the present work was to measure the tensile strength of restorative resins and to study the effect of the method of measurement on the recorded results. A direct pull method using dumb-bell shaped specimens was used. The tensile strength of the resins was also tested using the diametral compression method suggested by the A.D.A. It was found that the method of testing affects the results. Although the diametral compression method is a simple method, it cannot be considered reliable for all types of material. The tensile strength of the conventional composites was significantly higher than the tensile strength of the microfilled composites.