Effect of Combined Application of Hydrofluoric and Phosphoric Acids and Active Irrigation with a Microbrush on Shear Bond Strength of Lithium Disilicate Ceramics to Enamel.

Background: This study assessed the effect of combined application of hydrofluoric (HF) acid and phosphoric acid (PA) and active irrigation (AI) with a microbrush on shear bond strength (SBS) of lithium disilicate (LDS) ceramics to enamel. Materials and Methods: This in vitro study was conducted on 40 extracted teeth that received enamel preparation with a #12 cylindrical bur. Forty IPS e.max LT rods (3mm diameter, 6mm height) were fabricated and randomly assigned to four groups (n = 10) for surface treatment with 5% HF (group 1), 5% HF and AI with a microbrush for 20 seconds (group 2), 5% HF and 32% PA (group 3), and 5% HF and 32% PA plus AI with a microbrush for 20 seconds (group 4). Silane and Choice 2 cement were used for bonding rods to enamel. The SBS was measured by a universal testing machine. Data were analyzed by two-way analysis of variance (ANOVA), Bonferroni, and Chi-square tests (alpha = 0.05). Results: Group 4 had the highest SBS, and group 1 had the lowest SBS (P < 0.05). Group 2 had a significantly higher SBS than group 1, and group 4 had a significantly higher SBS than group 3. AI with a microbrush significantly increased the SBS (P < 0.05), but the application of PA caused no significant change in SBS (P > 0.05). The interaction effect of PA and AI on SBS was not significant (P > 0.05). Conclusion: The application of PA in addition to 5% HF acid caused no significant change in the SBS of LDS ceramic to enamel. However, AI with a microbrush significantly increased the SBS.

Heat Caused by Dental Implant Fixture Seating: Temperature In Vitro and Software Simulation.

Surgical implant procedures and insertions can result in mechanical and thermal damage to the involved bone. When dental implants are inserted, thermal injury can exponentially increase with augmented temperatures that may be caused by friction between fixture and drilled bone. Excessive heat induces delayed regeneration due to bone cell necrosis and implant mobility, resulting in dislocation of the hydroxyapatite structure. These are considered to be key factors in early failure of implant therapy. The current in vitro experimental study measures heat that is generated by implant placement in adjacent mandibular bovine bone. Research is conducted in two stages: first, using in vitro tests and second, with Abaqus software computer simulations. Bovine ramus is used as osseous model. We place a thermocouple ~ 2 mm from the rim of an osteotomy during seating of each dental implant. Finite-elements analysis models assess seven BioHorizons Laser-Lok implants with different diameters. We find that average temperatures increase from 0.2°C to 7.8°C. With heat indeed generated, a low-temperature rise is produced by implant surface friction against freshly cut bone surface. Although bone is a poor thermal conductor, implant titanium and the steel shank of the handpiece bur are better at heat conduction. Larger diameter and implant displacement may act as a heat sink to draw away generated heat that is caused by friction of seating the implant at the bone-implant interface. During in vitro experiments and simulated modeling, we find that none of the implants, regardless of diameter/length, reach an eccentric temperature range necessary for bone necrosis.

Evaluation of the Effect of Buccolingual and Apicocoronal Positions of Dental Implants on Stress and Strain in Alveolar Bone by Finite Element Analysis.

OBJECTIVES: The position of dental implants in the alveolar bone can affect the surrounding bone from biomechanical and biological aspects. The purpose of this study was to evaluate the effect of implant position on stress and strain distribution in the surrounding bone by using finite element analysis (FEA). MATERIALS AND METHODS: Thirteen computerized models of a 3.8-mm-diameter XiVE implant with the abutment and crown of a mandibular second premolar in a mandibular bone segment were designed. In the reference model, the implant was placed at the center of the alveolar ridge with its crest module located above the alveolar crest. In the other models, the implants were positioned buccally, lingually, coronally or apically by 0.5, 1 or 1.5mm. By using the ANSYS software program, a 100-N load was applied to the buccal cusp parallel to and at a 30-degree angle relative to the longitudinal axis of the fixture. The models were analyzed in terms of the distribution of stress and strain in the bone. RESULTS: The different implant positions induced nonlinear stress and strain changes in the bone. The central, 1.5-mm apical, and 1.5-mm coronal implant positions induced high amounts of stress and strain under off-axial loads. CONCLUSIONS: Within the limitations of this study, the results showed that the stress and strain in the bone around the implant undergo small nonlinear changes with buccolingual and apicocoronal shifting of the implant and can be affected by the configuration of the implant in contact with the bone.

The color masking ability of a zirconia ceramic on the substrates with different values.

Background. The color masking ability of a restoration plays a significant role in coveringa discolored substructure; however, this optical property of zirconia ceramics has not been clearly determined yet. The aim of this in vitro study was to evaluate the color masking ability of a zirconia ceramic on substrates with different values. Methods. Ten zirconia disk specimens,0.5 mm in thickness and 10 mm in diameter, were fabricated by a CAD/CAM system. Four substrates with different values were prepared, including: white (control), light grey, dark grey, and black. The disk specimens were placed over the substratesfor spectrophotometric measurements. A spectrophotometer measured the L*, a*, and b* color attributes of the specimens. Additionally, ΔE values were calculated to determine the color differences between each group and the control,and were then compared with the perceptional threshold of ΔE=2.6. Repeated-measures ANOVA, Bonferroni, and one-sample t-test were used to analyze data. All the tests were carried out at 0.05 level of significance. Results. The means and standard deviations of ΔE values for the three groups of light grey, dark grey and black were 9.94±2.11, 10.40±2.09, and 13.34±1.77 units, respectively.Significant differences were detected between the groups in the ΔE values (P<0.0001).The ΔE values in all the groups were more than the predetermined perceptional threshold(ΔE>2.6) (P<0.0001). Conclusion. Within the limitations of this study, it was concluded that the tested zirconia ceramic did not exhibit sufficient color masking ability to hide the grey and black substrates.

Rhinorrhea triggered by an obturator prosthesis: a clinical report.

This clinical report describes an unusual cause of nasal leakage in a patient with an obturator prosthesis who had previously undergone a maxillectomy. The diagnosis of gustatory rhinorrhea was determined by eliminating other possible causes of rhinitis. Gustatory rhinorrhea has been described as a complication of a maxillectomy.