Hot isostatic pressing processed yttria-stabilized tetragonal zirconia polycrystal (HIP Y-TZP) has the potential for application to implants due to its high mechanical performance. The aim of this study was to investigate the influence of surface treatment of HIP Y-TZP on cyclic fatigue strength. HIP Y-TZP specimens were subjected to different surface treatments. Biaxial flexural strength was determined by both static and cyclic fatigue testing. In the cyclic fatigue test, the load was applied at a frequency of 10 Hz for 10 6 cycles in distilled water at 37°C. The surface morphology, roughness, and crystal phase of the surfaces were also evaluated. The cyclic fatigue strength (888 MPa) of HIP Y-TZP with sandblasting and acid-etching was more than twice that of Y-TZP as specified in ISO 13356 for surgical implants (320 MPa), indicating the clinical potential of this material.

BackgroundThe purpose of this study was to investigate the trueness of intraoral scanning of residual ridge in edentulous regions during in vitro evaluation of inter-operator validity.MethodsBoth edentulous maxillary and partially edentulous mandibular models were selected as a simulation model. As reference data, scanning of two models was performed using a dental laboratory scanner (D900, 3Shape A/S). Five dentists used an intraoral scanner (TRIOS 2, 3Shape A/S) five times to capture intraoral scanner data, and the “zig-zag” scanning technique was used. They did not have experience with using intraoral scanners in clinical treatment. The intraoral scanner data was overlapped with the reference data (Dental System, 3Shape A/S). Regarding differences that occurred between the reference and intraoral scanner data, the vertical maximum distance of the difference and the integral value obtained by integrating the total distance were analyzed.ResultsIn terms of the maximum distances of the difference on the maxillary model, the means of five operators were as follows: premolar region, 0.30 mm; molar region, 0.18 mm; and midline region, 0.18 mm. The integral values were as follows: premolar region, 4.17 mm2; molar region, 6.82 mm2; and midline region, 4.70 mm2. Significant inter-operator differences were observed with regard to the integral values of the distance in the premolar and midline regions and with regard to the maximum distance in the premolar region, respectively. The maximum distances of the difference in the free end saddles on mandibular model were as follows: right side, 0.05 mm; and left side, 0.08 mm. The areas were as follows: right side, 0.78 mm2; and left side, 1.60 mm2. No significant inter-operator differences were observed in either region.ConclusionsThe present study demonstrated satisfactory trueness of intraoral scanning of the residual ridge in edentulous regions during in vitro evaluation of inter-operator validity.

To clarify the influence of translucent tetragonal zirconia polycrystals (TZP) on wear properties of esthetic dental materials, twobody wear test was performed using translucent TZP as abrader specimen, and bovine tooth enamel (BTE), two resin composites including hybrid filler (CRH) and nano filler (CRN), two glass ceramics including leucite reinforced feldspar porcelain (POR) and lithium disilicate (LDC), or translucent TZP as substrate specimen. After the wear test, wear volume were determined from substrate specimen and surface roughness were measured from abrader specimen. In addition, Vickers hardness was measured and surface morphologies were observed after wear test using a scanning electron microscope. The wear volume of the esthetic dental material against translucent TZP was greater in glass ceramics (POR, LDC), smaller in resin composite (CRH, CRN) and BTE, and no wear in translucent TZP. Microstructures of the esthetic dental material may play a crucial role for wear behavior against translucent TZP.

The purpose of this in vitro study was to investigate the influence of eccentric loading on implant components by measuring screw loosening and observing these components under several load positions and magnitudes. The external and internal joint system implants with butt joint connection were subjected to cyclic loading tests according to the specifications of ISO 14801. Load position was set at 0, 4, or 8 mm, and load was set at 100 or 300 N. On the external joint system, the reverse torque values decreased with distal shift in the loading position and an increase in magnitude of load, and abrasion and deformation on the anti-rotation device were observed. On the internal joint system, no large decrease in reverse torque was observed even though increasing the load position and load, however, abrasion and deformation on the anti-rotation device as well as fracture at implant/abutment connection were observed.

An anonymous questionnaire-based survey was used to determine the current state of and issues involved in undergraduate education in oral implantology at Tokyo Dental College. The participants comprised 139 students who had received lectures on and practical training in oral implantology in 2013. The results indicate that the overall level of student comprehension was high for both lectures and practical training content; the level of difficulty was appropriate for practical training, but the amount of practice time given requires reconsideration. Over 80% of the students gave positive responses in their overall evaluation of lectures and practical training, and the number of students who had an interest in oral implantology after finishing the course and who wanted to be involved in oral implantology as dentists increased. These results indicate that this undergraduate education program is effective in improving understanding of oral implantology. Improvement is required, however, in lecture methodology and practical training content. It is also suggested that the curriculum should be evaluated by students regularly and that the courses be subject to updating as required.