Effect of Conventional and Acid-modified Casein Phosphopeptide-Amorphous Calcium Phosphate Crèmes on Dentin Permeability Before and After Acid Challenge.

This study investigated the effect of conventional and acidified casein phosphopeptide-amorphous calcium phosphate-containing crèmes (CPP-ACP and ACPP-ACP) on dentin permeability (DP) before and after acid challenge, using a fluid-flow measuring device and scanning electron microscopic (SEM) examination. Fifty dentin discs were prepared from intact human third molars. Each tooth was sectioned 3 mm above and below the cementoenamel junction. The smear layer was removed to expose the dentin and dentinal tubules. For fluid-flow measurement, 20 specimens were used and divided into two groups: (a) CPP-ACP (pH=7) and (b) ACPP-ACP (pH=2). The dentin surfaces were treated with the crème for five minutes daily for two weeks, and then an acid challenge was performed using 6% citric acid. Under simulated pulpal pressure, DP was measured at baseline, five minutes, two weeks, and after acid challenge. The remaining specimens were prepared and examined using SEM to investigate dentinal tubule occlusion. DP was not significantly different between the two CPP-ACP-containing crèmes at any test period (p≥0.05). DP after two weeks or acid challenge was significantly lower than that at five minutes (p<0.05). The results were consistent with the SEM micrographs that presented patent dentinal tubules after a five-minute application and partial blockage of dentinal tubules after the two-week application. The dentinal tubules remained partially occluded after acid challenge. Using conventional and acid-modified CPP-ACP-containing crèmes for two weeks decreased DP and partially occluded the dentinal tubules, which resisted acid challenge.

Effect of bleaching agents on bonding to pulp chamber dentine.

AIM: To determine the effect of intracoronal bleaching agents on adhesion of bonding agents to pulp chamber dentine. METHODOLOGY: Forty extracted human maxillary anterior teeth were randomly divided into four groups of 10 teeth each. Bleaching agents were sealed in pulp chambers for 7 days, as in clinical use. Group 1 (control): distilled water, group 2: 35% hydrogen peroxide, group 3: sodium perborate mixed with water, and group 4: sodium perborate mixed with 35% hydrogen peroxide. Teeth were stored in saline at 37 degrees C for 7 days. After the bleaching agent was removed, teeth were leached in water for a further 7 days prior to bonding. The crown was cut vertically from mesial to distal and the labial pulp chamber dentine was prepared for bonding with Clearfil SE-Bond and filled with resin composite (Clearfil AP-X). The bonded specimens were kept moist at 37 degrees C for 24 h. Microtensile bond strengths were determined using a universal testing machine. Additional teeth were prepared using the same bleaching procedures to investigate the scanning electron microscopic appearance of the dentine surface. RESULTS: Mean values (+/-SD) of microtensile bond strength for the experimental groups were: group 1: 5.29 +/- 2.21 MPa, group 2: 5.99 +/- 1.51 MPa, group 3: 9.17 +/- 1.65 MPa and group 4: 3.99 +/- 1.31 MPa. Dentine treated with sodium perborate in water (group 3) had significantly higher mean bond strength when compared with the other three groups (P < 0.05, Tukey's test). Mean bond strength was lowest when dentine was treated with sodium perborate plus hydrogen peroxide (group 4). CONCLUSIONS: In terms of subsequent bond strength during restoration, sodium perborate mixed with distilled water appears to be the best intracoronal bleaching agent.

Micro-tensile bond strengths of bonding agents to pulpal floor dentine.

AIM: The purpose of this study was to characterize the dentine surface of the pulpal floor and to determine the micro-tensile bond strengths of two dentine adhesive systems used in conjunction with a resin composite core material to pulpal floor dentine. METHODOLOGY: Thirty-six extracted human molars were cut horizontally with a slow-speed diamond saw to expose the pulp chamber and the pulp tissue was removed. Eight teeth were used to investigate characteristics of untreated and etched dentine surfaces of the pulpal floor using SEM. Twenty-eight teeth were randomly allocated to two groups, each of 14 teeth. In group 1, a 'one-bottle' system (Prime & Bond NT) was used as dentine bonding agent and in group 2, a self-etching-priming system (Clearfil SE Bond) was applied. Pulp chambers of both groups were then filled with resin composite core buildup (FluoroCore) and kept moist in tap water at 37 degrees C for 24 h. Samples were prepared for micro-tensile bond testing by sectioning each tooth vertically in the mid-pulpal floor region and shaped to an hour-glass form of 1 +/- 0.2 mm(2) area at the bonded interface. Micro-tensile bond strengths were determined using a universal testing machine at a crosshead speed of 1 mm min-1. Fractured surfaces were examined by SEM. RESULTS: The intact pulpal floor showed numerous calcospherites with variable tubule density and few accessory canals. Etching the pulpal floor with 34% phosphoric acid gel resulted in an irregular surface with patent dentinal tubules and the dome-shaped calcospherites mostly lost. With self-etching primer, the superficial dentine surface was less demineralized and little peritubular dentine matrix was removed. Mean bond strength for the self-etching-priming (Clearfil SE Bond) specimens was significantly greater than for 'one-bottle' (Prime & Bond NT) specimens (P< 0.05, Student's t-test). The fracture mode of Clearfil SE Bond specimens was mostly partial cohesive failure within dentine, whilst Prime & Bond NT specimens mostly showed partial cohesive failure in bonding resin/composite. CONCLUSIONS: Despite an irregular surface morphology and absence of a smear layer, bonding to pulpal floor dentine was weaker than previously reported for cut coronal dentine. The self-etching-priming system bonded more strongly than the 'one-bottle' system.