Omar Zidan

The retention of complete crowns prepared with three different tapers and luted with four different cements

STATEMENT OF PROBLEM The role of adhesive properties of cements on the retentive strength of crowns with different degrees of taper is not clear. PURPOSE This study evaluated the retention of full crowns prepared with 3 different tapers and cemented with 2 conventional and 2 adhesive resin cements. MATERIAL AND METHODS One hundred twenty sound human molar teeth were assigned randomly to 1 of 12 groups, (n=10). The groups represented the 4 cements: zinc phosphate (Flecks), a conventional glass ionomer (Ketac-Cem); 2 adhesive resin cements (C&B Metabond and Panavia); and 3 tapers of 6-degrees, 12-degrees, and 24-degrees within each cement. Crowns were cast with a high noble alloy. The 6-degree taper was considered the control within each cement group. Retention was measured (MPa) by separating the metal crowns from the prepared teeth under tension on a universal testing machine. Analysis of variance was used to test the main effects on the retentive strength of full crowns, namely cements, tapers, and failure modes. The Fishers multiple comparison test was used to evaluate the source of the differences. The chi(2) analyses were used to examine the relationships between failure types, cements, and tapers. All statistical tests were conducted at alpha=.05. RESULTS There was a significant difference in the main effect cement (P<.0001) and taper (P=.0002). The mean retentive strength values of both Flecks and Ketac-Cem were significantly lower than the mean retentive strength values of both C&B Metabond and Panavia (P<.0001). The retention of crowns prepared with 6-degree taper was not significant from the 12-degree taper (P=.0666). The difference in retention was significant between the 6-degree taper and the 24-degree taper (P<.0001) and between 12-degree taper and 24-degree taper (P=.0178). The types of failure were adhesive in the cement (65%), cohesive in the tooth (31%), and assembly failure (fracture of embedding resin) (4%). The type of failure was dependent on the degree of taper (P<.0001) and on the type of cement (P<.0042). CONCLUSION Within the limitations of this study, the retentive values of the adhesive resins at 24-degree taper were 20% higher than the retentive values of the conventional cements at 6-degree taper. The use of resin luting agents yielded retention values that were double the values of zinc phosphate or conventional glass ionomer cement.

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 use of a dentinal bonding agent as a root canal sealer

The quality of the apical seal obtained with laterally condensed gutta-percha and an experimental sealer (Scotchbond) as compared with a commonly used sealer (Tubliseal) was assessed in 40 recently extracted maxillary canines. By using 2% methylene blue dye as a tracer, the quality of the apical seals was assessed by measuring the linear dye penetration. Canals obturated with gutta-percha and Scotchbond leaked significantly less than when gutta-percha and Tubliseal were used.

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 (DBAs) 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 DBAs but independent of the particular technique used. In dentin, there was significant difference in gap occurrence between DBAs 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 GlumalClearfil.

Bond strengths of etched base metals: Effects of errors in surface area estimation

T he technique of bonding electrolytically etched, cast base metal retainers to acid-etched enamel with resin cements has recently been introduced as a conservative method for replacing missing teeth in selected situations.’ Electrolytic etching of base metal alloys creates a relief pattern that improves the retention of resins applied to metal surfaces in the same manner that acid etching improves the resin bond to enamel surfaces. The metals used for this technique are base metal alloys that may be categorized as beryllium-containing nickel-chromium (Ni-Cr) alloys, nonberyllium Ni-Cr alloys, or cobalt-chromium (Co-Cr) alloys. Acid types, concentrations, etching times, and current densities have been recommended by manufacturers and investigators.2’x Zidan” found that different base metal alloys etched under the different recommended etching conditions yielded different bond strengths. The framework for the retainers used in the etched, cast metal, resin-bonded prosthesis will vary in geometric configuration and consequently surface area. Calculation of the current density setting for attaining an optimal etch and therefore maximum retention of the metal framework is based on the surface area of the framework.‘” No convenient method presently exists for accurately determining the surface area of the framework, and an estimate of surface area must be relied on to determine the current density setting. Since an infinite variety of shapes and surface areas of retainers is possible for each clinical situation, the introduction of errors in the calculation of the milliamperage is inevitable. The purpose of this study was to investigate the effect of errors in estimating the surface area on the bond strength of eight base metal alloys used for the etched, cast metal, resin-bonded technique. Another objective was to compare these values with the mean bond strengths reported by Zidan’ for the same metals etched as recommended.

The effect of amalgam bonding on the stiffness of teeth weakened by cavity preparation

OBJECTIVE The objective of this study is to evaluate the effect of amalgam bonding on the stiffness of teeth weakened by cavity preparation. METHODS Strain gages were bonded to maxillary premolars. The rigidity was tested by applying a load to a sequence of sound, prepared and restored teeth as follows: sound tooth, MOD preparation, amalgam restoration, amalgam removed recovering the MOD preparation, bonded amalgam restoration, bonded amalgam removed recovering the MOD preparation, bonded composite restoration. The relative stiffness (RS) and relative deformation (RD) of each condition for each cusp to that of the sound tooth was determined. RESULTS The premolar cusps were deformed 1.80, 2.14, and 2.32 times more than the cusps of the sound tooth for the three succeeding MOD preparations. For these three preparations, the stiffness of the premolar cusps was 0.58, 0.48, and 0.46 relative to a stiffness of 1.00 for the sound tooth. The deformation was 1.77, 1.27, and 1.16 for the non-bonded amalgam, the bonded amalgam, and the bonded composite, respectively, corresponding to a mean RS of 0.59, 0.80, and 0.88. The calculated mean stiffness parameter C (standard deviation) was 2.6% (6.9) for the amalgam restoration, 62.5% (12.8) for the bonded amalgam restoration, and 77.8% (15.8) for the bonded composite restoration. The stiffness parameter C measured the extent to which the procedure returned the stiffness of the restored tooth to the original stiffness of the intact tooth (100%). SIGNIFICANCE Cavity preparation reduced the stiffness and weakened the tooth. Restoring the prepared tooth with unbonded amalgam did not restore the lost tooth stiffness. Restoring the prepared tooth with bonded amalgam or with bonded composite recovered a significant portion of the lost tooth stiffness. It was concluded that bonding amalgam to tooth structure could partly restore the strength and rigidity lost by the cavity preparation. This might lead to a reduction in cuspal flexure and the incidence of tooth fracture due to fatigue.

Etched base-metal alloys: comparison of relief patterns, bond strengths and fracture modes.

Abstract The relief patterns, the bond strength and the fracture modes of 8 base-metal alloys were evaluated. Resin-etched metal bonds were established between a pair of etched metal surfaces. The bonds were tested under tension. The relief patterns and the fracture modes were evaluated by SEM. The relief patterns were related to the composition, microstructure and the preferential dissolution of the various phases. The relief patterns appeared retentive for 7 of the eight alloys evaluated. The differences in the bond were statistically significant. Four modes of fracture were identified. The fracture was mainly located in the resin among the alloys with high bond strength. Interfacial debonding occurred in areas lacking three-dimensional relief.

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.

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 (DBAs) to both dentin and acid-etched enamel was measured after one hour and the results compared. For all the DBAs tested, the bonding strength to enamel was higher than that to dentin. These differences were significant for all DBAs 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 DBAs 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 DBAs, namely, retention of the restoration and prevention of marginal gaps. The Gluma/Clearfil combination should be recommended for clinical trials.

Marginal gap formation in the composite resin/glass ionomer cement Class V restoration

The purpose of this study was to assess marginal gap formation in Class V restorations using 2 dentin bonding agents (DBA) and 7 different cavity filling methods. Two glass ionomer cements (GIC) were used: Ketac-Bond (KB) and Ketac-Fil (KF). Class V cavities were prepared, one-half in enamel and one-half in dentin, in extracted human teeth. There were 2 control (no GIC used) and 12 experimental groups with 10 restortions each. Seven groups were evaluated with Scotchbond Lightcure (S) and 7 with Prisma Universal Bond (P). For each DBA the KB was applied as a 0.5 mm layer in 2 of the groups. In one of these the cement was etched with 35% H3PO4 for 30 s. For each DBA the KF was applied either in bulk, leaving the margins exposed (2 groups), or the cavities were filled, and then cut back after 24 h, exposing the margins (2 groups). The KF was etched in 2 of these 4 groups with 35% H3PO4 for 30 s. In all cases the enamel was beveled and etched. All cavities were filled with Silux. Basic fuchsin dye was used to detect marginal gaps. Each restoration was photographed, traced, and scored for marginal gaps as 0 or 1 at 5 enamel and 5 dentin locations. Gaps were present in 6.6% of all enamel locations and in 92% of all dentin locations. The effect of methods and DBA on marginal leakage at the enamel and dentin locations was assessed by two-way analysis of variance. There were significant differences between methods for enamel (p<0.01) and for dentin (p<0.005). The leakage scores for S were significantly greater than P in enamel (p<0.005) and in dentin (p<0.025). Although there were statistically significant differences among methods and between DBA, these differences are considered to be of little or no clinical significance because there were so few enamel marginal gaps while dentin marginal gaps were present in almost all the cases.