Haluk Baris Kara

The Effect of Bleaching Agents on the Color Stability of Ceromer and Porcelain Restorative Materials In Vitro

PURPOSE The aim of this in vitro study was to determine the color changes of five different restorative materials after exposing these materials to two different home bleaching agents. METHODS This study applied bleaching agents to an ultralow-fusing porcelain, a low-fusing porcelain, two types of heat-pressed glass ceramics, and a ceromer. A total of 24 disc-shaped specimens were fabricated (with a diameter of 10 mm and a thickness of 2 mm) from each material (n=12). The initial color measurements were taken with a spectrophotometer. The first set of specimens were bleached with 10% hydrogen peroxide (HP) for one hour daily for 10 days. The other set of specimens were bleached with 10% carbamide peroxide (CP) bleaching gel for eight hours daily for 14 days. Data were analyzed with the one-way analysis of variance and Kruskal-Wallis statistical test. The difference in the prebleaching and postbleaching color of each material was considered to be statistically significant at p < 0.05. RESULTS The study found a statistically significant difference among the color changes of the test groups after exposing them to both bleaching agents (p<0.05). Appreciable color change was observed in the Estenia (ΔE=3.99) specimens that were bleached with the HP, and noticeable color changes were observed in the Estenia (ΔE=1.89) and IPS Empress 2 (ΔE=1.66) groups when they were treated with the CP. CONCLUSIONS Restorations (especially polymer-containing restorative materials) should be protected before any bleaching procedure due to the high risk of color change.

Effects of different concentrations of hydrogen peroxide on the color stability of various esthetic restorative materials in vitro

Purpose: The aim of this in vitro study was to determine the color changes of four different restorative materials after exposing these materials to two different bleaching agents. Materials and Methods: In this study, bleaching agents were applied to a low-fusing porcelain (VITA VM9), heat-pressed glass ceramics (IPS Empress Esthetic), and two types of composites (Clearfil Majesty Esthetic and Clearfil Photo Posterior). Twenty disc-shaped specimens were fabricated (with a diameter of 10 mm and a thickness of 2 mm) from each material (n0 = 10). The initial color changes were measured using a spectrophotometer. The first set of specimens were bleached with 10% hydrogen peroxide (HP) for 1 h daily for 10 days. Another set of specimens were bleached with 40% HP bleaching gel for two consecutive applications for 20 min each. The data were analyzed statistically by using two-way analysis of variance (ANOVA) and post hoc Tamhane′s T2 tests ( P < 0.05). Results: The mean color change value (ΔE) for Clearfil Majesty Esthetic was significantly higher than the value for VITA VM9 groups, treated with the 10% HP. In addition, the values for Clearfil Photo Posterior were significantly higher than the values for Clearfil Majesty Esthetic, IPS Empress Esthetic, and VITA VM9 groups treated with the 40% HP (P < 0.05). The comparative evaluation of bleaching agents on the color change of materials revealed that the differences between the bleaching agents were significant for the Clearfil Photo Posterior groups (P < 0.05). Conclusion: The effects of bleaching agents should be known and applied consciously when restorative materials (especially polymer-containing restorative materials) are present.

Custom Cast Post Treatment on an Implant Platform in 2 Patients

T he use of implant-supported prostheses to replace missing natural teeth has become an accepted treatment approach in dentistry. Although implant prostheses have a high overall success rate, numerous complications have been reported, and the device sometimes fails. The biological complications associated with the use of the device include peri-implant radiolucency, peri-implantitis, and loss of osseointegration radiographically. Mechanical failure of implant components can manifest in the form of loosened screws, loss of retention, screw or fixture fracture, and porcelain or framework fracture. Screw complications are caused by screw-joint instability, which may occur due to bruxism, unfavorable superstructure, overloading, malfunction, interceptive occlusal contact, metal fatigue after screw loosening, and component misfit. While several factors may affect screw complications, the most important are (1) adequate preload, (2) a precise fit of the mating implant components, and (3) basic antirotational characteristics of the implant and abutment interface. To avoid screw loosening, a precise fit between the mating implant components is very important; once a screw is loosened, the resulting metal fatigue may lead to screw fracture. The most catastrophic mechanical complication is fixture fracture, which is usually caused by loss of the implant. The causes of fixture fractures in the posterior region include cantilevers, bruxism, and heavy occlusal forces; all lead to bending overload. To avoid fixture fracture, the manufacturer currently recommends the use of a wider diameter fixture and a third fixture, and offsetting the fixtures to achieve a tripod effect. When an abutment screw is fractured or deformed, it must be removed without damaging the implant body for the new abutment. Location of the fracture along the abutment screw dictates the removal method of the broken fragments. If a fracture occurs above the implant head, an explorer, hemostat forceps, or straight probe may be successful in removing the fractured fragments. When the fracture occurs below the implant head, other specialized removal systems are required, such as retrieval instruments (Nobel Biocare, Zurich, Switzerland), the Neo Screw Remover Kit (Neobiotech, Seoul, Korea), and the Implant Repair Kit (ITI Dental Implant System. Institute Straumann, AG, Waldenburg, Switzerland). Removal and replacement of the fractured fragment with a new abutment is the appropriate option for most patients, but in some patients, an alternative solution may be required. The present clinical report presents an alternative method for removal of a deformed abutment screw and trapped healing cup without damaging the implant components.