Bond strength of resin cement to ceramic with simplified primers and pretreatment solutions.

Manufacturers have recently introduced surface primers and pretreatment solutions that reportedly simplify the bonding process of resin cements to ceramics through various combinations of etchant and coupling agents. This study evaluated the shear bond strength (SBS) of a resin cement to a lithium disilicate glass-ceramic material pretreated with various new surface treatment solutions and compared the results to those of a control group prepared with the traditional application of hydrofluoric acid (HF) and silane. Resin cement was bonded to pretreated glass-ceramic surfaces, and specimens were tested for SBS after 24 hours of storage in water. Traditional surface treatment of lithium disilicate glass ceramic with HF and silane resulted in a significantly greater mean SBS than did simplified primer solutions. There were no statistically significant differences among the simplified pretreatment groups. In the control group, the majority of failures were due to mixed adhesive-cohesive fracture, while in the simplified treatment groups the failure mode was usually adhesive, suggesting a weaker interface.

Fracture resistance of bonded CAD/CAM restorations with standard or extended preparations.

The purpose of this study was to evaluate the fracture resistance of teeth with standard or extended mesio-occlusodistal (MOD) preparations after restoration with bonded computer-aided design/computer-aided manufacturing (CAD/CAM) materials. Standard or extended MOD cavities were prepared in 60 of 70 extracted, caries-free third molars. In the standard MOD preparations (n = 30), 4.5- mm buccal and lingual/palatal wall thickness remained, and proximal boxes extended 1.0 mm coronal to the cementoenamel junction. In the extended MOD preparations (n = 30), the buccal and lingual/palatal walls were reduced to a thickness of 3.0 mm. A CAD/CAM acquisition unit was used to scan 20 standard and 20 extended preparations. Subsequently, 10 standard and 10 extended preparations were restored with milled lithium disilicate, and 10 of each type were restored with resin nanoceramic. Ten of each preparation type were left unrestored (negative control). An additional 10 third molars were neither prepared nor restored (positive control). After thermocycling and cyclic loading, specimens were fractured in a material testing device. Although bonded CAD/CAM restorations reinforced the tooth structure, the mean fracture loads were significantly lower (P < 0.05) in teeth with restored extended preparations (2642.4 [SD 479.4] N) than in teeth with restored standard preparations (3376.6 [SD 817.9] N). The type of CAD/CAM restorative material did not significantly affect the fracture load. Practitioners should consider covering the cusps with a CAD/CAM restorative material to reduce the potential for fracture in preparations with reduced cuspal thickness, especially in patients with heavier occlusion or functional loads.

Fracture Resistance of Titanium-Based Lithium Disilicate and Zirconia Implant Restorations.

PURPOSE: To evaluate the fracture resistance of a newer lithium disilicate abutment material. MATERIALS AND METHODS: A premolar-shaped implant crown was designed using CAD/CAM software, and four groups of implant and crown combinations were milled: (1) lithium-disilicate hybrid-abutment crown; (2) "screwmentable" lithium-disilicate hybrid abutment/lithium-disilicate crown with screw channel; (3) lithium-disilicate hybrid abutment/lithium-disilicate crown; and (4) zirconia hybrid abutment/lithium-disilicate crown (control). The specimens were cemented to a titanium-base implant system, subjected to thermocycling and cyclic loading, and fractured in a material testing device. RESULTS: The lithium-disilicate hybrid-abutment crown had significantly greater fracture load than all the other groups, which were not significantly different from each other. CONCLUSIONS: Based on fracture load, the new lithium-disilicate hybrid-abutment material may serve as a viable alternative to the use of zirconia as a hybrid-abutment material.

Microleakage and shear bond strength of a new sealant containing prereacted glass ionomer particles.

A new fluoride-releasing sealant system is claimed to allow easier and faster placement while providing high bond strengths without the need for phosphoric acid etching. A study was designed to compare the microleakage and shear bond strength of a self-etching, Giomer-based sealant system with those of a traditional resin sealant. Group 1 received traditional sealant applied after use of a 35% phosphoric acid etchant; group 2 received Giomer sealant after use of a self-etching primer; and group 3 received Giomer sealant after the addition of an initial phosphoric acid etching step and placement of the primer. The sealants were placed in the occlusal pits and fissures of extracted human third molars, thermocycled, placed in dye, and sectioned. The extent of microleakage (dye penetration) was expressed as a percentage of the cross-sectional length of the sealed interface. The sealants were also bonded to the facial enamel of bovine incisors. Specimens were thermocycled and tested in shear mode in a universal testing machine. The new self-etching sealant demonstrated significantly greater microleakage (P < 0.017) and lower bond strength (P < 0.05) than both the traditional sealant system and the new system when placed with phosphoric acid etchant. Phosphoric acid etching significantly improved the shear bond strength and reduced the microleakage of the new sealant.

Microtensile bond strength of lithium disilicate to zirconia with the CAD-on technique.

PURPOSE: Recently, a novel technique was introduced to combine lithium disilicate and zirconia into one restoration. The purpose of this study was to compare the microtensile bond strength of veneering ceramic to a zirconia core in two techniques: the e.max® CAD-on technique and the Press-on technique. MATERIALS AND METHODS: Group A was prepared by veneering sintered zirconia blocks (e.max® ZirCAD) with lithium disilicate blocks (e.max® CAD) using the CAD-on technique according to manufacturer's instructions. Group B was prepared by taking sintered e.max® ZirCAD blocks and veneering them with fluorapatite glass-ceramic (e.max® ZirPress) using the Press-on technique according to manufacturer's instructions. Each block was loaded in a dynamic cyclic loading machine. The blocks were then sectioned into 1 × 1 mm(2) beams (n = 43) using a precision saw, thermocycled, and loaded in tension until failure on a universal testing machine. A mean and standard deviation were determined per group. Data were analyzed using an unpaired t-test (α = 0.05). RESULTS: The mean microtensile bond strengths were 44.0 ± 13.8 MPa for the CAD-on technique and 14.9 ± 8.8 MPa for the Press-on technique. Significant differences were found between the two groups (p = 2.7E-19). CONCLUSIONS: The CAD-on technique (lithium disilicate/zirconia) resulted in greater microtensile bond strength than the Press-on technique (fluorapatite glass-ceramic/zirconia).

Effect of imaging powders on the bond strength of resin cement.

The application and incomplete removal of a computer-aided design/computer-aided manufacture imaging powder may affect the dentin surface prior to bonding a ceramic restoration. The purpose of this study was to compare the effect of imaging powder residue on the shear bond strength of a self-adhesive resin cement to dentin. Mounted human third molars were sectioned coronally with a diamond saw to expose the dentin, which was then prepared with a diamond bur mounted in a custom jig. The dentin surface was sprayed with 3 different imaging powders. The 3 powder groups were then divided into 3 subgroups based on the method of powder removal: no rinse, 1-second rinse, and 10-second rinse. A control group was created that had no application of imaging powder. A self-adhesive resin cement was bonded to the surfaces and loaded to failure in a universal testing machine after 24 hours of storage. Data was analyzed with Kruskal-Wallis and Mann-Whitney nonparametric tests. The bonding to dentin surfaces of the powder groups that were rinsed for 1 or 10 seconds were not significantly different from each other or the nonpowdered control. The type of imaging powder did not significantly affect the bond strength. The nonrinsed powdered dentin surface had a significant reduction in bond strength compared to both the control and the rinsed powdered surfaces.