Tolga Akova

Comparison of the bond strength of laser-sintered and cast base metal dental alloys to porcelain

OBJECTIVE The purpose of this study was to compare shear bond strengths of cast Ni-Cr and Co-Cr alloys and the laser-sintered Co-Cr alloy to dental porcelain. METHODS Dental porcelain was applied on two cast and one laser-sintered base metal alloy. Ten specimens were prepared for each group for bond strength comparison. ANOVA followed by Tukey HSD multiple comparison test (alpha=0.05) was used for statistical analysis. Fractured specimens were observed with a stereomicroscope to classify the type of failure after shear bond testing. RESULTS While the mean shear bond strength was highest for the cast Ni-Cr metal-ceramic specimens (81.6+/-14.6 MPa), the bond strength was not significantly different (P>0.05) from that for the cast Co-Cr metal-ceramic specimens (72.9+/-14.3 MPa) and the laser-sintered Co-Cr metal-ceramic specimens (67.0+/-14.9 MPa). All metal-ceramic specimens prepared from cast Ni-Cr and Co-Cr alloys exhibit a mixed mode of cohesive and adhesive failure, whereas five of the metal-ceramic specimens prepared from the laser-sintered Co-Cr alloy exhibited the mixed failure mode and five specimens exhibited adhesive failure in the porcelain. CONCLUSIONS The new laser-sintering technique for Co-Cr alloy appears promising for dental applications, but additional studies of properties of the laser-sintered alloy and fit of castings prepared by this new technique are needed before its acceptance into dental laboratory practice. SIGNIFICANCE Laser sintering of Co-Cr alloy seems to be an alternative technique to conventional casting of dental alloys for porcelain fused to metal restorations.

Internal fit evaluation of crowns prepared using a new dental crown fabrication technique: Laser-sintered Co-Cr crowns

STATEMENT OF PROBLEM Difficulties encountered during casting of base metal dental alloys limit their use. Application of these alloys might be enhanced if new techniques are used. PURPOSE The purpose of this study was to compare the internal fit of laser-sintered Co-Cr alloy crowns with base metal restorations prepared from another Co-Cr alloy and a Ni-Cr alloy using conventional casting techniques. MATERIAL AND METHODS Internal fit of laser-sintered Co-Cr crowns was compared with the fit of conventionally cast Ni-Cr and Co-Cr alloy crowns. Twelve crown-shaped specimens were prepared on a stainless steel die representing a prepared maxillary right central incisor for each group. Fit of crowns was evaluated using 2 different techniques: (1) weighing the light-body addition silicone that simulated a cement material, and (2) measuring the internal gap width on a die for longitudinally sectioned specimens. One-way ANOVA followed by Tukey multiple comparison test was used for statistical analysis (alpha=.05). RESULTS Significantly higher mean (SD) light-body silicone weights (P<.001) were observed in the laser-sintered Co-Cr alloy group (14.34 (1.67) mg) compared to the conventionally cast Ni-Cr alloy group (9.36 (1.97) mg) and Co-Cr alloy group (7.85 (1.19) mg). Mean internal gap widths (SDs) were 58.21 (19.92) microm, 50.55 (25.1) microm, and 62.57 (21.62) microm, respectively, for the cast Ni-Cr and Co-Cr alloy groups and the laser-sintered Co-Cr alloy group. No significant difference was observed between the 3 groups for internal gap widths (P=.42). CONCLUSIONS Weighing the light-body addition silicone is a convenient method for evaluating the 3-dimensional internal fit of dental crowns. However, no significant difference was found among the 3 alloy groups evaluated for the internal gap width of sectioned crown specimens.

Effect of zoledronic acid on osseointegration of titanium implants: an experimental study in an ovariectomized rabbit model.

PURPOSE Zoledronic acid (ZA), a new-generation intravenous bisphosphonate, exhibits the greatest affinity for bone mineral with the longest retention, thereby leading to its ability to be dosed at annual intervals in the treatment of osteoporosis. The purpose of this preliminary study was to evaluate the effects of systemic administration of a single dose of ZA on osseointegration and bone healing around titanium dental implants. MATERIALS AND METHODS Thirty-six female New Zealand rabbits (aged 6-12 months) were used in this study. Rabbits were randomly assigned to 1 of 3 groups: sham control group (SH), ovariectomy group (OVX), and OVX and ZA group (OVX + ZA). Animals in the OVX and OVX + ZA groups were subjected to bilateral ovariectomy, whereas animals in the SH group were sham operated. Eight weeks later, 1 implant was placed in each tibia of the animals. ZA was administered in the OVX + ZA group during the implantation, whereas the OVX and SH groups received saline solution infusions. All of the subjects were sacrificed 8 weeks after the implantation, and tibial specimens were harvested. Histomorphometric bone-to-implant contact analysis, resonance frequency analysis, removal torque testing, and digital radiographic absorptiometry were administered, and the data were statistically analyzed. RESULTS Histomorphometric, resonance frequency, and radiodensitometric analyses showed significant improvement in osseointegration of implants in the OVX + ZA group compared with the OVX group. However, the differences in removal torque results between the groups were not statistically significant. CONCLUSIONS The results of this study suggest that systemic ZA administration may improve osseointegration of titanium implants placed in estrogen-deficient states of bone.

Mechanical Properties of Polyamide Versus Different PMMA Denture Base Materials

PURPOSE Polymethyl methacrylate (PMMA) resins are the most commonly used denture materials; however, they do not have a high flexural strength (FS). This study aimed to compare the mechanical properties of a polyamide-based, injection-molded denture material (Deflex) with another injection-molded PMMA base material (SR-Ivocap) and a conventional compression-molded PMMA (Meliodent). MATERIALS AND METHODS Flexural properties (deflection, bending strength, and bending modulus) of denture base materials were evaluated (n = 10). Specimens meeting International Standards Organization (ISO) specification number 20795-1 requirements were prepared (65 × 10 × 3 mm(3)). A three-point bending test was carried out on an Instron testing machine at a 5 mm/min crosshead speed. The Knoop hardness test was used to compare microhardness values. Data were analyzed using ANOVA, followed by REGWQ. RESULTS The group results, standard deviations, and statistical differences (p < 0.01) for Deflex, SR-Ivocap, and Meliodent were (A) flexural strength (MPa: 78.3 ± 1.0,(a) 69.8 ± 1.4,(b) 81.1 ± 1(a)), (B) flexural modulus (GPa: 0.70 ± 0.13,(a) 0.85 ± 0.27,(a) 1.70 ± 0.23(b)), (C) Knoop Hardness (kg/cm(2) : 7.5 ± 1.0,(a) 13.5 ± 1.4,(b) 16.9 ± 1.0(c)). Different superscript letters indicate significant difference. All Meliodent specimens fractured during flexural testing, but no Deflex specimens did. CONCLUSIONS While polyamide denture material produced good fracture resistance, its modulus is not yet sufficiently high to be equal to standard PMMA materials. Clinical Implications. Polyamide has some attractive advantages, but will require modification to produce consistently better properties than current PMMA materials.

Influence of different indentation load and dwell time on Knoop microhardness tests for composite materials

Abstract Various microhardness test methods with different indentation loads and dwell times have been used to evaluate the hardness of composite materials. However, there is still no agreement on the ideal test method for composites. The aim of this study was to determine the influence of different indentation load and dwell time on Knoop Hardness Number (KHN) of three different kinds of light-cured composites. A mold was fabricated to make cylindrical specimens of three different composite resins (TPH, Tetric Ceram, Surefil), and 45 cylindrical composite discs were prepared. Hardness tests on the materials were performed with three different loads at two different dwell times. One-way analysis of variance and LSD did not reveal a statistically significant difference between TPH and Surefil with 50 gf at both dwell times. However, on the other matched load and time groups, Surefil exhibited higher KHN than TPH and Tetric Ceram. Our results suggest that the indentation load is critical for micro-indentation hardness tests and as the results are directly affected, further studies are needed to standardize the micro-indentation test load.

Intrapulpal Heat Generation during Provisionalization: Effect of Desensitizer and Matrix Type

PURPOSE This study investigated the effect of different matrices and application of a desensitizer on pulpal temperature rise during direct provisionalization. MATERIALS AND METHODS The apical third of a second premolar was resected and pulpal tissue was removed. Silicone heat-conducting medium was injected, and a J-type thermocouple was inserted into the pulp chamber and sealed. The tooth was embedded in acrylic resin with its cervical line 1 mm higher than the base. Addition and condensation silicone impression materials were mixed and placed inside plastic molds. Impressions were taken before tooth preparation. The tooth was then prepared with a 1.5-mm shoulder finish line. The experimental model was kept in a 36 degrees C water bath. Four provisional materials were applied in sequence onto the prepared tooth using matrices. Each provisional resin was used in combination with each matrix (n = 12). Then a dentin desensitizer was coated on the prepared tooth and provisionalizations were made in the same manner. The thermocouple was connected to the data-logger. During setting of the resins, pulp temperatures were recorded and transferred to the computer. Measurements were conducted for each test group by calculating the temperature rise as the difference between the start and highest temperature reading. RESULTS The type of the silicone matrix used and the use of desensitizer did not affect the intrapulpal heat generation during direct provisionalization. CONCLUSION Application of a desensitizer and different type of matrix seems to be noneffective on intrapulpal heat rise, although the type of provisional material used may be effective.

Diamondlike carbon coating as a galvanic corrosion barrier between dental implant abutments and nickel-chromium superstructures.

PURPOSE The objectives of this study were to evaluate the galvanic corrosion behavior between titanium and nickel-chromium (Ni-Cr) alloy, to investigate the effect of diamondlike carbon (DLC) coating over titanium on galvanic corrosion behavior between titanium and Ni-Cr alloy, and to evaluate the effect of DLC coating over titanium abutments on the fit and integrity of prosthetic assemblies by scanning electron microcopy (SEM). MATERIALS AND METHODS Five Ni-Cr and 10 titanium disks with a diameter of 5 mm and thickness of 3 mm were prepared. DLC coating was applied to five titanium disks. Electrode samples were prepared, and open circuit potential measurements, galvanic current measurements over platinum electrodes, and potentiodynamic polarization tests were carried out. For the SEM evaluation, 20 Ni-Cr alloy and 10 gold alloy superstructures were cast and prepared over 30 abutments. DLC coating was applied to 10 of the abutments. Following the fixation of prosthetic assemblies, the samples were embedded in acrylic resin and cross sectioned longitudinally. Internal fit evaluations were carried out through examination of the SEM images. RESULTS Titanium showed more noble and electrochemically stable properties than Ni-Cr alloy. DLC coating over the cathode electrode served as an insulating film layer over the surface and prevented galvanic coupling. Results of the SEM evaluations indicated that the DLC-coated and titanium abutments showed no statistically significant difference in fit. Hence, no adverse effects on the adaptation of prosthetic components were found with the application of DLC coating over abutment surfaces. CONCLUSIONS DLC coating might serve as a galvanic corrosion barrier between titanium abutments and Ni-Cr superstructures.

Effects of Hard Thin-Film Coatings on Adhesion of Early Colonizer Bacteria Over Titanium Surfaces.

Purpose:The purpose of this in vitro study was to evaluate the effect of diamond-like carbon (DLC) and titanium (Ti) nitride coatings over Ti surfaces on the adhesion of early colonizer bacteria. Materials and Methods:Specimens were divided into 3 groups (n = 10) according to different surface modifications: titanium nitride (TiN)-coated Ti discs (experimental group 1), DLC-coated Ti discs (experimental group 2), and uncoated polished Ti discs (control group). Discs were incubated in bacterial cell suspension (Streptococcus mutans and Streptococcus sanguis) for 1 hour, and the single colonies formed by adhering bacteria were counted by fluorescence microscopy. Surface roughness and topography were examined by atomic force microscopy. Results:The surface roughness of DLC was lower than TiN coating and the control group. Statistically significant reduction of the number of adherent bacteria was observed on DLC-coated surfaces. Conclusions:DLC coating over Ti surfaces strongly inhibits the adhesion of early colonizer oral bacteria.