Penetration pattern of rhodamine dyes into enamel and dentin: confocal laser microscopy observation.

Enamel and dentin are susceptible to extrinsic and intrinsic stains. The purposes of this study were to determine the penetration pattern of Rhodamine B and dextran-conjugated Rhodamine B into the enamel and dentin as observed by confocal laser microscopy and to relate it to the penetration pattern of hydrogen peroxide commonly used as an active ingredient in tooth-whitening agents and high-molecular-weight staining molecules. Eighteen recently extracted human maxillary anterior teeth were used. Teeth were cleaned and painted with nail varnish except for the crown area above the cemento-enamel junction (CEJ). The painted teeth were then immersed in Rhodamine B and dextran-conjugated Rhodamine B (70 000 MW) for 4, 7, 10 and 15 days. Teeth were sliced to 3 mm thickness in transverse plane and mounted on a glass slide just prior to observation with confocal laser microscopy. Rhodamine B and dextran-conjugated Rhodamine B readily penetrated into the enamel and dentin when exposed for 4 and 7 days, respectively. Rhodamine B penetrated along the interprismatic spaces of the enamel into the dentin. The penetration was accentuated in sections with existing crack lines in the enamel. Rhodamine B was readily absorbed into the dentinal tubules at the dentino-enamel junction and continued to penetrate through the dentin via the dentinal tubules into the pre-dentin. Within the limitations of this study, it is concluded that Rhodamine B and dextran-conjugated Rhodamine B when applied to the external surface of the tooth readily penetrate into the enamel and dentin via the interprismatic spaces in the enamel and dentinal tubules in the dentin, suggesting that stain molecules and bleaching agents possibly exhibit similar penetration pathways.

The accuracy of optical scanning: influence of convergence and die preparation.

The purpose of this study was to determine the reliability of the data acquisition and modeling process of laser and white light scanners by evaluating the reproducibility of digitized simulated crowns with different convergences. A secondary purpose was to analyze the influence of die preparation by testing this hypothesis with a set of dies without ditching compared with a set with well-defined margins. Ditching or trimming the die defines the position of the margin and acts as a guide to gingival contour when the restoration is being waxed. Two light scanners (a white light optical scanner [Steinbichler Gmbh, Neubeuern, Germany] and red laser light scanner [TurboDent System, Taichung, Taiwan]) were evaluated. Two sets of simulated crowns were fabricated as cone frustrum models with a total occlusal convergence (TOC) of 0°, 5°, 10°, 15°, 20°, and 25° and a 9-mm base and 3-mm height using a precision milling machine and computer-aided design/computer-aided manufacturing (CAD/CAM) technique. One set of the dies was ditched immediately below the finish line to enhance marginal definition. Each die was optically digitized five times directly with the two different measuring systems. The area of each triangle in the scan that is occlusal to the margin line was calculated and summed to produce the final surface area measurement provided. The digitizing error was compared with the computed surface area of the original master die sets and compared with a paired t-test (df=4; 95% CI). There was no difference in accuracy of the untrimmed dies between the two systems evaluated. We also did not find any difference in the 0° (p=0.12) and 5° degree (p=0.21) groups among the ditched dies. However, when the TOC exceeded 5°, there was a significant difference between the two groups, with the laser groups having a smaller error percentage. Three-dimensional light scanning was not affected by the convergence angle except in the 0°-5° range. Trimming the dies greatly affected the accuracy of scanning.

The effects of repeated heat-pressing on properties of pressable glass-ceramics.

The aim of this study was to evaluate the properties of four heat-pressed glass-ceramic materials after repeated heat-pressing. Two commercially available heat-pressed glass-ceramic systems [Optimal pressable glass-ceramics (OPC and 3G) and Empress pressable glass-ceramics (Empress and Empress2)] were selected. Disc samples (14 mm x 1.4 mm) of each tested material were heat-pressed and used as controls. Sprue and button parts of the pressed groups were retrieved and used for repeated heat-pressing to construct specimens of re-pressed group. All the heat-pressed casting procedures were performed according to the manufacturers' instructions. A biaxial flexural strength (BFS) test (ISO 6872) was performed to determine the strength of pressed and re-pressed glass-ceramic disc specimens (n = 10) at a crosshead speed of 0.5 mm min(-1). Ions eluted from etching procedure were collected and examined using inductively coupled plasma mass spectrometer. Surface characteristics were examined with electron probe microanalysis, X-ray diffraction and secondary electron imaging (SEI). The data were analysed statistically (ANOVA + Tukey's HSD post hoc test, P < 0.05). The BFS values obtained ranged from 123.5 +/- 18.5 to 365.9 +/- 35.5 MPa. The re-pressed Empress2 group had a statistically significant higher BFS mean than the pressed control group (P < 0.05). The SEI micrographs of the lithium disilicate-reinforced glass-ceramic material (Empress2) showed a densely packed, interlocking microstructure and an increase in size with preferred orientation of the lithium disilicate crystals after repeated heat-pressing. Repeated heat-pressing treatment produced a statistically significant increase in the flexural strength of Empress2 glass-ceramic material.

Changes in resin-infiltrated dentin stiffness after water storage.

Plasticization of polymers by water sorption lowers their mechanical properties in a manner that is predictable by the polarity of their component resins. This study tested the hypothesis that when adhesive resins were used to create resin-infiltrated dentin, the reductions in their flexural moduli after water storage would be lowered proportional to their hydrophilic characteristics. Three increasingly hydrophilic resin blends were used to fabricate polymer beams and macro-hybrid layer models of resin-infiltrated dentin for testing with a miniature three-point flexure device, before and after 1-4 weeks of water storage. Flexural modulus reductions in macro-hybrid layers were related to, and more extensive than, reductions in the corresponding polymer beams. Macro-hybrid layers that were more hydrophilic exhibited higher percent reductions in flexural modulus, with the rate of reduction proportional to the Hoy's solubility parameters for total intermolecular attraction forces (delta(t)) and polar forces (delta(p)) of the macro-hybrid layers.

Effect of pre-processing surface treatments of acrylic teeth on bonding to the denture base.

The aim of this study was to examine the bond strength between acrylic teeth after various surface treatments and processing with either a heat- or microwave-polymerized denture base material. Specimens were prepared and tested according to the methods described in American National Standard/American Dental Association Specification No.15 (Synthetic Polymer Teeth) using a special assembly. Three brands of acrylic teeth were used with the following treatments: control (no treatment), grinding and grinding plus sandblasting. Treatment groups were further divided into two denture base processing subgroups: heat-polymerized and microwave-polymerized methods. Denture base processing to the acrylic teeth was performed according to the manufacturer's recommendations. Bond strength test was performed using a universal testing machine with five specimens and each specimen is composed of six anterior teeth per experimental group. Data were analysed using a three-way anova and the Scheffe'F-test post hoc pair wise comparison at the 95% significance level. The mean bond strength values ranged from 33.1 +/- 4.1 to 51.6 +/- 2.5 MPa. The bond strength values of sandblasted surfaces were significantly higher than those of the ground surface and the control (P < 0.05). Combined (acrylic tooth and denture base resin) cohesive failures were disclosed in all tested samples. Acrylic tooth surface pre-processed surface treatment with grinding plus sandblasting and processed with a heat-polymerized denture base provided the greatest bond strength between acrylic tooth and denture base.

Measurement of clinical wear of two packable composites after 6 months in service.

Original large-particle composites exhibited poor wear characteristics. With the packable composites, there has been a reintroduction of large particles. The clinical wear characteristics of such packable composites are relatively unknown. The purpose of this study was to compare wear between two types of packable composites: Alert (Jeneric Pentron) and Surefil (Dentsply Caulk). Each material was compared with and without a surface sealant. Fifty-two subjects were included. Subjects had to have two to four eligible teeth, be 21 years of age, in good health and in need of moderate to large class 2 restorations on molars, and/or a two-surface class 1 on molars. Wear was assessed, using the Moffa-Lugassy (ML) scale, by evaluating stone models made from polyvinyl siloxane (PVS) impressions taken at baseline and 6 months. Rating was done by four calibrated examiners using a forced consensus model. The use of a surface sealant with Alert significantly reduced the median wear rate at 6 months compared with that of the SureFil restorations.

Effect of preparation convergence on retention and seating discrepancy of complete veneer crowns.

The purpose of this study was to evaluate the retention and marginal seating discrepancy of complete veneer crown cemented with zinc phosphate cement using various preparation convergence designs. The method employed was that of cementing cast metal crowns onto 46 metal dies fabricated as complete veneer crown preparations with various convergence angles ranging from 0 degrees to 70 degrees and a shoulder finish line. The marginal discrepancy was calculated by measuring the change in crown height before and after cementation using an optical measuring microscope. The force required to remove the crowns from the dies in a vertical direction was determined using an Instron universal testing machine and recorded as retention. The increase in preparation convergence exhibited a wide variation of seating discrepancy between specimens, ranging from 4.58 +/- 1.13 to 73.13 +/- 78.32 microm. Significant tilting of crown was observed as the convergence angle of preparation increased. The retention values ranged from 4.03 +/- 0.61 to 12.12 +/- 0.33 MPa. The Pearson analysis revealed statistically significant correlations between preparation convergence and marginal discrepancy (r = +0.62), and retention (r = -0.91). Crown retention and marginal discrepancy were influenced by the preparation convergence design.

Effect of preparation convergence on retention and seating discrepancy of complete veneer crowns.

The purpose of this study was to evaluate the retention and marginal seating discrepancy of complete veneer crown cemented with zinc phosphate using various preparation convergence designs. The method employed was that of cementing cast metal crowns onto 46 metal dies fabricated as complete veneer crown preparations with various convergence angles ranging from 0 degrees to 70 degrees and a shoulder finish line. The marginal discrepancy was calculated by measuring the change in crown height before and after cementation using an optical measuring microscope. The force required to remove the crowns from the dies in a vertical direction was determined using an Instron universal testing machine and recorded as retention. The increase in preparation convergence exhibited a wide variation of seating discrepancy between specimens, ranging from 4.58 +/- 1.13 to 73.13 +/- 78.32 microm. Significant tilting of crown was observed as the convergence angle of preparation increased. The retention values ranged from 4.03 +/- 0.61 to 12.12 +/- 0.33 MPa. The Pearson analysis revealed statistically significant correlations between preparation convergence and marginal discrepancy (r = +0.62), and retention (r = -0.91). Complete veneer crown retention and marginal discrepancy were influenced by the preparation convergence design.