Kazumichi Wakabayashi

Mechanical properties of new self-adhesive resin-based cement

PURPOSE The aim of this study was to compare the bonding strength, flexural strength, elastic modulus, water absorption and the expansion after water storage of new self-adhesive resin cements to commercially available dental cements. METHODS Two types (hand-mix and auto-mix) of new self-adhesive resin cements (SAC-H and SAC-A, Kuraray Medical), one conventional resin cement (Panavia F2.0), three self-adhesive resin cements (Relyx Unicem, Maxcem and G-Cem), and two resin-modified glass-ionomer cements (Fuji Luting S and Vitremer) were used. Shear bond strengths, flexural strengths and elastic moduli (ISO 4049), water absorption (ISO 4049), and the expansion rate after water storage were investigated. RESULTS Both SAC-H and SAC-A provided adhesion to enamel and dentin, and had the same bond strength to gold alloy and zirconia as conventional resin cements. SAC-H and SAC-A had greater flexural strengths (86.4-93.5MPa) than commercial self-adhesive resin cements or glass-ionomer cements. The elastic moduli of self-adhesive and glass-ionomer cements were 5.2-7.4GPa and 2.3-3.4GPa, respectively. The water absorption of SAC-H and SAC-A (26.3-27.7microg/mm(3)) were significantly lower than commercial self-adhesive resin cements. SAC-H and SAC-A showed significantly lower expansion rates (0.17-0.26%) than commercial self-adhesive cements and glass-ionomer cements after 4 weeks water storage. CONCLUSIONS It is suggested that the new self-adhesive resin cements exhibited a favorable bonding capability and mechanical properties.

Effects of multiple firings on the mechanical properties and microstructure of veneering ceramics for zirconia frameworks

OBJECTIVES The purpose of this study is to evaluate the effects of multiple firings on the mechanical properties and microstructure of veneering ceramics used with zirconia frameworks. METHODS Five different veneering ceramics for zirconia frameworks were used: Vintage ZR (ZR), Cerabien ZR (CZR), Vita VM9 (VM9), Cercon ceram KISS (KISS), IPS e.max ceram (e.max), and one veneering ceramic used for PFM frameworks: Vintage MP (MP). Twenty specimens were fabricated of each veneering ceramic. Ten specimens were fired twice and another ten specimens were fired ten times. Three-point flexural strength following the ISO 6872 and Vickers hardness were measured, and fracture toughness (K(IC)) was calculated. Density and porosity were determined. Specimens were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). RESULTS For all materials, density increased and porosity decreased after 10 firings. Significant differences in density and porosity were observed between 2 and 10 firings, with the exception of VM9 (P<0.05). There were no significant differences in flexural strength between 2 and 10 firings except for MP. The Vickers hardness of ZR, VM9, KISS and MP increased significantly after 10 firings (P<0.001). There were no significant differences in fracture toughness for ZR, CZR, VM9 and MP between 2 and 10 firings. However, e.max underwent a significant increase in fracture toughness (P=0.000), and there was a significant decrease in the toughness of KISS after 10 firings (P=0.007). CONCLUSION Multiple firings could be effective for improving the densification and the hardness of veneering ceramics for zirconia restorations. CLINICAL SIGNIFICANCE By 10 firings, the density and hardness of the veneering ceramics used with zirconia frameworks were raised, and porosity was reduced. However, no significant changes occurred in flexural strength, fracture toughness or microstructure.

Tensile bond strength between tooth-colored porcelain and sandblasted zirconia framework

PURPOSE The purpose of this study was to examine the bond strength between tooth-colored porcelain and sandblasted zirconia framework. METHODS The surfaces of zirconia specimens that had been cut into a size suitable for a bending test were sandblasted at three different pressures (0.2, 0.4 and 0.6MPa). The surface roughness of each specimen was measured and then a 3-point bending test was performed. After that, other zirconia specimens simulating a crown framework were fabricated and their surfaces were sandblasted. Three types of tooth-colored porcelain were fired onto the surface of those zirconia specimens, and the tensile bond strength between the two substances was examined. RESULTS When the sandblasting pressure was increased, the surface roughness of zirconia specimens tended to become, but the flexural strength remained unchanged. The specimens simulating a zirconia framework had a higher strength of bond when sandblasted at 0.4 or 0.6MPa than when blasted at 0.2MPa. The zirconia specimens sandblasted at a pressure of 0.4MPa had a bond strength to tooth-colored porcelain of 37.7-49.5MPa. CONCLUSION When sandblasted at a pressure of 0.4MPa, the zirconia specimens developed a strong bond with the tooth-colored porcelain, regardless of the type of porcelain.

CAD/CAM fabrication and clinical application of surgical template and bone model in oral implant surgery.

OBJECTIVES A novel implant surgery support system with computer simulation for implant insertion and fabrication of a surgical template that helps in drilling bone was developed. A virtual reality haptic device that gives the sense of touch was used for simulation and a surgical template was fabricated by CAD/CAM method. Surgical guides were applied for two clinical cases. MATERIAL AND METHODS Three-dimensional (3D) jaw bone images transferred from DICOM data filmed by CT scanner were fed to the software and manipulated using the haptic device. The site for implant insertion was determined after evaluating the quality of bone and position of the mandibular canal. The surgical template was designed with ease using the free design CAD function of haptic device. The surgical template and bone model were fabricated by a fused deposit modeling machine. Two clinical cases were applied using the present system. RESULTS Simulation to determine the site of implant insertion and fabrication of the surgical bone templates were successfully done in two clinical cases, one for three implant insertion in lower right jaw and the other is for seven implant insertion in lower edentulous jaw, respectively. During surgery, the templates could be firmly adapted on the bone and drilling was successfully performed in both cases. CONCLUSION The present simulation and drilling support using the surgical template may help to perform safe and accurate implant surgery.

High-resolution 3-D shape integration of dentition and face measured by new laser scanner

Face and dentition were measured using a high-resolution three-dimensional laser scanner to circumvent problems of radiation exposure and metal-streak artifacts associated with X-ray computed tomography. The resulting range data were integrated in order to visualize the dentition relative to the face. The acquisition interval for dentition by laser scanner was 0.18 mm, and complicated morphologies of the occlusal surface could be sufficiently reproduced. Reproduction of occlusal condition of upper and lower dentitions was conducted by matching the surface of the occlusal impression record with upper dentition data. To integrate dentition and face, a marker plate interface was devised and adopted on the lower dental cast or by the subject directly. Integration was performed by matching both sets of interface data. Reproduction of the occlusal condition and integration of the dentition and face were accomplished and visualized satisfactorily by computer graphics. The integration accuracy was examined by changing the attachment angle of the marker plate, and the marker plate attached at 45/spl deg/ showed the smallest error of 0.2 mm. The current noninvasive method is applicable to clinical examination, diagnosis and explanation to the patient when dealing with the physical relationship between face and dentition.

Influence of abutment tooth geometry on the accuracy of conventional and digital methods of obtaining dental impressions

Statement of problem. Direct (intraoral) and indirect (desktop) digital scanning can record abutment tooth preparations despite their geometry. However, little peer‐reviewed information is available regarding the influence of abutment tooth geometry on the accuracy of digital methods of obtaining dental impressions. Purpose. The purpose of this in vitro study was to evaluate the influence of abutment tooth geometry on the accuracy of conventional and digital methods of obtaining dental impressions in terms of trueness and precision. Material and methods. Crown preparations with known total occlusal convergence (TOC) angles (−8, −6, −4, 0, 4, 8, 12, 16, and 22 degrees) were digitally created from a maxillary left central incisor and printed in acrylic resin. Each of these 9 reference models was scanned with a highly accurate reference scanner and saved in standard tessellation language (STL) format. Then, 5 conventional polyvinyl siloxane (PVS) impressions were made from each reference model, which was poured with Type IV dental stone scanned using both the reference scanner (group PVS) and the desktop scanner and exported as STL files. Additionally, direct digital impressions (intraoral group) of the reference models were made, and the STL files were exported. The STL files from the impressions obtained were compared with the original geometry of the reference model (trueness) and within each test group (precision). Data were analyzed using 2‐way ANOVA with the post hoc least significant difference test (&agr;=.05). Results. Overall trueness values were 19.1 &mgr;m (intraoral scanner group), 23.5 &mgr;m (desktop group), and 26.2 &mgr;m (PVS group), whereas overall precision values were 11.9 &mgr;m (intraoral), 18.0 &mgr;m (PVS), and 20.7 &mgr;m (desktop). Simple main effects analysis showed that impressions made with the intraoral scanner were significantly more accurate than those of the PVS and desktop groups when the TOC angle was less than 8 degrees (P<.05). Also, a statistically significant interaction was found between the effects of the type of impression and the TOC angle on the precision of single‐tooth dental impressions (F=2.43, P=.002). Visual analysis revealed that the intraoral scanner group showed a homogeneous deviation pattern across all TOC angles tested, whereas scans from the PVS and desktop scanner groups showed marked local deviations when undercuts (negative angles) were present. Conclusions. Conventional dental impressions alone or those further digitized with an extraoral digital scanner cannot reliably reproduce abutment tooth preparations when the TOC angle is close to 0 degrees. In contrast, digital impressions made with intraoral scanning can accurately record abutment tooth preparations independently of their geometry.

Translucency and low-temperature degradation of silica-doped zirconia: A pilot study

The purpose of this study was to examine the translucency and low-temperature degradation of silica-doped experimental Y-TZP (Yttria-stabilized tetragonal zirconia polycrystal) containing almost no alumina. The experimental Y-TZP samples were sintered at either 1,450 or 1,500°C. The samples of commercially available translucent Y-TZP and conventional Y-TZP were used as controls. The contrast ratio (CR) and translucency parameter (TP) were obtained to compare the translucencies. In addition, the specimens were also subjected to an accelerated aging test. The results showed that the experimental Y-TZP sintered at 1,500°C and translucent Y-TZP exhibited almost the same level of translucency. During the accelerated aging test, the translucent Y-TZP underwent a substantial increase in monoclinic content, an index of degradation after the aging test. However, neither the experimental Y-TZP nor the conventional Y-TZP exhibited any appreciable change. It was concluded that the silica-doped Y-TZP will develop translucency and resistance to degradation when sintered at 1,500°C.

Fitting accuracy and fracture resistance of crowns using a hybrid zirconia frame made of both porous and dense zirconia

The purpose of this study is to evaluate the fitting accuracy and fracture resistance of crowns using a hybrid zirconia frame made of both porous and dense zirconia. Commercial semi-sintered zirconia, sintered dense zirconia and sintered hybrid zirconia were used. Sintered zirconia was milled using the CAD/CAM system, and semi-sintered zirconia was milled and sintered to fabricate molar crown frames. Completed frames were veneered with tooth-colored porcelain. The marginal and internal gaps between frames/crowns and abutments were measured. Each crown specimen was subjected to a fracture test. There were no significant differences in marginal and internal gap among all the frames and crowns. The crown with the hybrid zirconia frame had a 31-35% greater fracture load than that with the commercial or dense zirconia frame (p<0.01). This suggests that the all-ceramic crowns with a hybrid zirconia frame have a high fracture resistance.

Fracture Resistance of Computer-Aided Design/Computer-Assisted Manufactured Glass-Ceramic Incisor Crowns Fabricated on Reverse-Tapered Preparations

PURPOSE To evaluate the fracture resistance of computer-aided design/computer-assisted manufactured (CAD/CAM) glass-ceramic incisor crowns fabricated on reverse-tapered preparations. MATERIALS AND METHODS Resin abutments with known total occlusal convergence angles (-8, 0, and 12 degrees; n = 20) were scanned with the TRIOS scanner, and glass-ceramic crowns were fabricated with KaVo Arctica, stored in water for either 1 or 30 days, and submitted to fracture test. RESULTS The fracture resistance of crowns made on reverse-tapered preparations was not significantly different (P = .471) from crowns fabricated over abutments with 0- or 12-degree tapers, irrespective of the water storage period. CONCLUSION The fracture resistance of anterior glass-ceramic crowns fabricated over reverse-tapered preparations was similar to that of crowns made on abutments with 0- or 12-degree tapers.

Fluorescence of thulium-doped translucent zirconia

The fluorescence and physical properties of thulium-doped zirconia were investigated. A standard grade of zirconia (TZ-3Y-E) and two translucent dental zirconia materials (Zpex and Zpex Smile) were examined. The specimens were prepared by addition of 0-1.5 wt% Tm2O3 and then sintering. When exposed to UV light, the Tm2O3-doped zirconia exhibited blue fluorescence with a peak wavelength of 460 nm. The fluorescence intensity of Zpex and Zpex Smile was higher than that of TZ-3Y-E, with Zpex being more intense than Zpex Smile. Zpex exhibited maximum fluorescence intensity when doped with 0.8 wt% Tm2O3. XRD analysis revealed that TZ-3Y-E and Zpex contained primarily tetragonal zirconia, while Zpex Smile contained largely cubic phase zirconia. There were no changes observed in the microstructure or physical properties of the zirconia specimens when doped with Tm2O3.