Amerigo Cantoro

The effect of different surface treatments on bond strength between leucite reinforced feldspathic ceramic and composite resin.

OBJECTIVES The aim of this study was to evaluate the effect of different surface treatments on the microtensile bond strength between a leucite reinforced glass-ceramic and composite resin. METHODS Leucite reinforced ceramic blocks (n=24) were constructed using the hot pressing technique. The blocks were assigned to 4 groups, which received the following surface treatments: G1: hydrofluoric (HF) acid and silane; G2: silane alone; G3: HF acid and silane then dried with warm air (100 degrees C); G4: silane alone then dried with warm air (100 degrees C). Unfilled resin was applied, followed by composite resin. Specimens were prepared and loaded in tension to determine the microtensile bond strength. Failure modes were classified by stereo- and scanning electron microscopy (SEM). Data was analysed using Kruskal-Wallis test followed by the Dunns multiple range test. RESULTS The groups including the warm air step (G3 and G4) achieved a significantly stronger adhesion than G1 and G2. Pre-treatment of the surface with hydrofluoric acid in G1 resulted in significantly higher bond strength than G2. Failures were mostly cohesive in the luting resin for G1, G3 and G4 and mainly adhesive at the ceramic-resin interface in G2. CONCLUSIONS The method of application of silane to the ceramic surface can have a significant influence on the adhesion between the ceramic restoration and the resin cement. Enhancing the condensation reaction by drying the silane with a 100C warm air stream significantly improved the microtensile bond strength, possibly eliminating the need for the hydrofluoric acid etching step.

Effect of surface pre-treatments on the zirconia ceramic–resin cement microtensile bond strength

OBJECTIVE To evaluate the influence of different surface treatments on the microtensile bond strength of resin cement to zirconia ceramic. MATERIALS AND METHODS Twelve cylinder-shaped (∅ 12×5.25 mm high) blocks of a commercial zirconium-oxide ceramic (Cercon® Zirconia, DENTSPLY) were randomly divided into 4 groups (n=3), based on the surface treatment to be performed: (1) airborne particle abrasion with 125 μm Al₂O₃ particles (S); (2) selective infiltration etching (SIE); (3) experimental hot etching solution applied for 30 min (ST) and (4) no treatment (C). Paradigm MZ100 blocks (3M ESPE) were cut into twelve cylinders of 4mm in thickness. Composite cylinders were bonded to conditioned ceramics using a resin cement (Calibra®, DENTSPLY), in combination with the proprietary adhesive system. After 24h bonded specimens were cut into microtensile sticks and loaded in tension until failure. Bond strength data were analyzed with Kruskall-Wallis and Dunns Multiple Range test for multiple comparisons (p < 0.05). Failure mode distribution was recorded and the interfacial morphology of debonded specimens was analyzed using a scanning electron microscope (SEM). RESULTS Bond strength values achieved after SIE and ST treatment were significantly higher than after S treatment and without any treatment (p < 0.05). Premature failures were mostly recorded in the S group. SIGNIFICANCE Conditioning the high-strength ceramic surface with SIE and ST treatments yielded higher bond strengths of the resin cement than when zirconia ceramic was treated with airborne particle abrasion or left untreated.

Bonding potential of self-adhesive luting agents used at different temperatures to lute composite onlays

OBJECTIVES To assess whether the bonding potential to dentin of self-adhesive resin cements was affected by their pre-cure temperature. METHODS Composite overlays (Paradigm MZ100, 3M ESPE) were luted on 100 extracted molars with G-Cem (GC Corp.), BisCem (Bisco), Multilink Sprint (Ivoclar Vivadent), SAC-A (Kuraray Co.), XP Bond/Calibra (Detrey Dentsply). The cements were used at pre-cure temperatures that recur in their handling (4 degrees C refrigerator, 24 degrees C room and 37 degrees C intraoral), as well as following pre-heating up to 60 degrees C. Microtensile bond strengths to dentin were measured and compared with statistical tests. Scanning electron microscope observations of cement-dentin interfaces were performed. RESULTS The bond strength of G-Cem and Calibra was not significantly affected by temperature changes from refrigerator storage to intraoral application. At any assessed pre-cure temperature the total-etch luting agent Calibra achieved a significantly stronger adhesion than the auto-adhesive cements. Limited to null adhesion was yielded by BisCem and SAC-A. The procedure of 60 degrees C pre-heating, proposed in previous studies for restorative resin composites, was of no use for the tested luting agents. Only the total-etch luting agent Calibra developed a distinct hybrid layer. The self-adhesive cements exhibited a more superficial interaction with dentin. CONCLUSIONS Regardless of the pre-cure temperature, the bonding potential of the self-adhesive resin cements was inferior to that of the total-etch luting agent tested as control. The adhesive properties of the BisCem and SAC-A were extremely scarce.

Microleakage in class II restorations: open vs closed centripetal build-up technique.

PURPOSE This study evaluated whether a Class II restoration in a flowable resin composite has to be placed prior to (open-sandwich technique) or after (closed-sandwich technique) construction of the interproximal wall in the centripetal build-up technique in order to reduce microleakage. METHODS AND MATERIALS Thirty non-carious molars were selected and randomly divided into two groups (n = 15). A standardized Class H preparation was made with the cervical margin 1 mm below the cementum-enamel junction. In Group 1, flowable resin composite was applied as a 1 mm base, remaining exposed at the cervical margin. In Group 2, the hybrid resin composite was applied to the interproximal wall, followed by a layer of flowable composite on the pulpal floor, away from the margins. The restorations were then subjected to 500 thermal cycles, each with a dwell time of 20 seconds at 5 degrees C and 55 degrees C. Adaptation at the cervical margin was evaluated by dye penetration and SEM analysis using the replica technique. The data were statistically analyzed using the Mann-Whitney U-test (p < 0.05). RESULTS The centripetal open-sandwich technique led to significantly lower dye penetration than the centripetal closed-sandwich technique (p < 0.001). CONCLUSION Flowable resin composite placed under hybrid resin composites in Group 1 provided better marginal adaptation and fewer voids. However, neither Group 1 nor Group 2 was able to completely prevent microleakage.

Post space debridement in oval-shaped canals: the use of a new ultrasonic tip with oval section.

This study evaluates the effect on post space debridement in oval-shaped canals of an experimental ultrasonic tip with oval section (Satelec) compared with a circular ultrasonic tip (KaVo). Thirty teeth with an oval-shaped canal were endodontically treated and obturated and then randomly divided into 3 groups (n = 10) according to the procedure used for post space debridement: Satelec tip, Largo #2 drill + KaVo file, and Largo #2 drill + water. Debris and dentin tubules were evaluated by assigning scores to scanning electron microscope post spaces images; lower scores corresponded to fewer debris and higher number of open tubules. The Satelec group showed significantly lower debris and open tubules scores than KaVo group (p < .05) and control group (p < .05), which differed significantly between each other (p < .05). Also the debris and open tubules scores in different post space regions differed significantly among the experimental groups (p < .001). The oval ultrasonic tip resulted in a better post space debridement than a circular ultrasonic tip in oval-shaped canals.