Effect of firing temperature on the interface between 3Y-TZP zirconia and porcelain.

PURPOSE: The purpose of this study is to clarify the porcelain firing temperature conditions that give strongest bonding strength of porcelain to zirconia to manufacture all-ceramic fixed dental prostheses (FDPs) with excellent long-term stability. METHODS: Opaque porcelain samples (8.0 × 3.0 × 1.2 mm) were placed in the center of zirconia plates (25.0 × 3.0 × 0.5 mm) and fired at temperatures of 950°C, 1,050°C, 1,100°C, and 1,150°C. Schwickerath crack initiation tests, elemental analyses, and morphological changes of the samples were compared. RESULTS: There was no difference in the bonding strength among all the groups of porcelain fired at different temperatures. Elemental analysis of Si and O2 at the interface between the zirconia and porcelain were observed in the 950°C, 1,050°C, and 1,100°C groups. No silicon was found in the 1,150°C group by elemental analysis, and the zirconia plate where the porcelain sample was placed had irregular shape changes. CONCLUSION: It is suggested that silicon is also involved in chemical bonds due to firing at high temperatures.

Peri-implant tissue augmentation by volume-stable collagen matrix transplantation: a study of dog mandibles.

The aim of this study was to investigate histologically the amount of peri-implant tissue augmentation after volume-stable porcine collagen matrix transplantation. Six male beagle dogs were used in the experiment. P2, P4, and M1 distal roots were extracted under general anesthesia. After 6 months, implants were placed in the same sites, and volume-stable porcine collagen matrix transplantation was performed. Impressions were taken at 1 and 2 weeks and at 1, 2, and 3 months after transplantation. The dogs were euthanized at 3 months, and their mandibles were removed and scanned using micro-computed tomography. Standard Triangulated Language data were also obtained. Using preoperative models as a reference, the data for all time points were compared, and changes in the thickness of the cross-section of the implant sites were measured. The model created at 3 months was then compared with the mandible data, and the thickness of collected peri-implant soft tissue was measured under optical microscopy. Increased thickness was found at some of the sites on the buccal side. Regarding the peri-implant soft tissue, the thickness of the measured sites on the buccal side was significantly increased at 3 months in the experimental group. Histological observations of the internal structures of the tissue in the experimental group revealed irregular collagen fibers and a remnant collagen matrix. Endogenous tissue was observed within the collagen matrix, indicating good fusion with the surrounding autologous tissue. These results suggest that volume-stable porcine collagen matrix transplantation promotes peri-implant tissue augmentation on the buccal side.

Marginal and internal fit of three-unit fixed dental prostheses fabricated from translucent multicolored zirconia: Framework versus complete contour design.

STATEMENT OF PROBLEM: Translucent multicolored zirconia materials enable more esthetic complete contour zirconia fixed dental prostheses (FDPs) than conventional zirconia, which exhibits low translucency and high opacity and is monochromatic. However, how the marginal and internal fit of translucent multicolored zirconia FDPs compare with those of traditional frameworks that require veneering is unclear. PURPOSE: The purpose of this in vitro study was to compare the marginal and internal fit of frameworks and complete contour 3-unit FDPs fabricated from translucent multicolored zirconia. MATERIAL AND METHODS: Frameworks with a thickness of 0.5 mm and complete contour FDPs with a thickness of 0.8 to 1.5 mm were manufactured by using a workflow similar to one from a zirconia master model (mandibular left second premolar-mandibular left second molar). Two polyvinyl siloxane replicas were made for each specimen to measure the marginal and internal fit. Measurement locations were mesial, lingual, buccal, and distal for each abutment. In these locations, the marginal opening (MO), chamfer area (CA), axial wall (AW), and occlusal area (OC) were measured. The data were analyzed with 2-way ANOVA and the Bonferroni post hoc test (α=.05). RESULTS: Frameworks showed significantly better mean ±standard deviation fit values than complete contour 3-unit FDPs at measurement areas MO (frameworks: 112 ±22 µm, complete contour FDPs: 144 ±37 µm) (P=.013), CA (frameworks: 89 ±12 µm, complete contour FDPs: 110 ±22 µm) (P=.006), and OC (frameworks: 182 ±36 µm, complete contour FDPs: 244 ±64 µm) (P=.008). At the measurement area AW (frameworks: 47 ±7 µm, complete contour FDPs: 50 ±9 µm of each location, no significant difference was observed between frameworks and complete contour FDPs (P=.361). CONCLUSIONS: Design differences in 3-unit FDPs fabricated from translucent multicolored zirconia influenced the marginal and internal fit. Frameworks had smaller marginal fit than complete contour FDPs for translucent multicolored zirconia.

The fracture strength by a torsion test at the implant-abutment interface.

BACKGROUND: Fractured connections between implants and implant abutments or abutment screws are frequently encountered in a clinical setting. The purpose of this study was to investigate fracture strength using a torsion test at the interface between the implant and the abutment. METHODS: Thirty screw-type implant with diameters of 3.3, 3.8, 4.3, 5.0, and 6.0 mm were submitted to a torsion test. Implants of each size were connected to abutments with abutment screws tightened to 20 N · cm. Mechanical stress was applied with a rotational speed of 3.6 °/min until fracture occurred, and maximum torque (fracture torque) and torsional yield strength were measured. The mean values were calculated and then compared using Tukey's test. The abutments were then removed, and the implant-abutment interfaces were examined using a scanning electron microscope (SEM). RESULT: No significant differences in mean fracture torque were found among 3.3, 3.8, and 4.3 mm-diameter implants, but significant differences were found between these sizes and 5.0 and 6.0 mm-diameter implants (p < 0.01). Concerning mean torsional yield strength, significant differences were found between 3.3, 3.8, and 4.3 mm-diameter and 5.0 and 6.0 mm-diameter implants (p < 0.01). Observations under the SEM showed that all the projections of the abutment corresponding to the internal notches of the implant body had been destroyed. CONCLUSIONS: Smaller diameter implants demonstrated lower fracture torque and torsional yield strength than implants with larger diameters. In internal tube-in-tube connections, three abutment projections corresponding to rotation-prevention notches were destroyed in each implant.

Embryological study of the development of the rat temporomandibular joint: highlighting the development of the glenoid fossa.

Basic embryological findings on the development of the temporomandibular joint have yet to be elucidated sufficiently. This experiment, was undertaken to find the standard time course of the development of the temporomandibular joint in rat fetuses. Serial frontal and sagittal sections of rat fetal heads (between 13.5 and 20.5 days post-conception [p.c.]) were examined microscopically. The condyle was recognized as a mesenchymal condensation at 14.5 days p.c., while the glenoid fossa was recognized at 15.5 days p.c. The mesenchymal condensation of the condyle had differentiated into chondrocytes by 16.5 days p.c., and endochondral ossification was recognized at 17.5 days p.c. The intramembranous ossification of the glenoid fossa was already recognized by 16.5 days p.c.; this started in the posterior region and progressed anteriorly between the zygomatic arch and the squamous part of the temporal bone. Ossification of the condyle had not been completed by 20.5 days p.c., a mass of hypertrophic chondrocytes remained in the center of the condylar head. The glenoid fossa was almost completely ossified by 19.5 days p.c. A coarse region of cells, reminiscent of apoptosis, was recognized in the region of the prospective superior joint space at 17.5 days p.c., and an actual joint space had formed by 18.5 days p.c. The inferior joint space was recognized at 19.5 days p.c. as a fissural cavity, but it was much narrower than its superior counterpart. The prospective meniscus was distinguished on the condylar surface at 17.5 days p.c. by the difference in the shape of its constituent cells. The results obtained here seem to be useful for further experiments and molecular biological studies.