Fatigue properties of hollow zirconia implants.

The objective of this study was to clarify the fatigue behavior of hollow yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) specimens assuming its use for two-piece implants. The fatigue properties of a solid specimen (which simulated a one-piece implant) and 3 types of hollow specimens (which simulated two-piece implants) were evaluated. Specimens were either solid with a diameter of 4.0 mm (S) or hollow with an inner diameter of 3.0 mm and outer diameters of 4.0 mm (H0.5), 4.5 mm (H0.75), or 5.0 mm (H1.0). For each group, 25 specimens were prepared followed by blast and acid etch treatment. Static fracture and cyclic fatigue tests were conducted by modifying the methods provided in ISO6872. Fracture modes were determined by observing the surfaces under a scanning electron microscope. As a result, the cyclic fatigue load of S and H1.0 were similar, and hollow specimens with outer diameters greater than 0.75 mm displayed the ability to withstand molar occlusal forces.

Influence of eccentric cyclic loading on implant components: Comparison between titanium and zirconia abutments.

The objective of this study was to investigate the effects of eccentric cyclic loading on implant components using the internal joint system with titanium and zirconia abutments. Abutments were made of either pure titanium (Ti group) or zirconia (TZP group). Cyclic loading test was conducted according to the specifications of ISO 14801. Loading condition was at 2 points assuming axial load and eccentric load. The reverse torque value reduced after the eccentric load and reduced more in the TZP group than the Ti group. Marginal gap changed after eccentric loading, and was greater in the TZP group. In the TZP group, changes in configuration were observed in the implant body, and Ti was detected on the abutment surface. From the above, the eccentric load may have worse effects than axial loads. It was suggested that the TZP group was clinically disadvantageous compared to the Ti group.

Applying intraoral scanner to residual ridge in edentulous regions: in vitro evaluation of inter-operator validity to confirm trueness.

BACKGROUND: The 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. METHODS: Both 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. RESULTS: In 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. CONCLUSIONS: The present study demonstrated satisfactory trueness of intraoral scanning of the residual ridge in edentulous regions during in vitro evaluation of inter-operator validity.

Maxillary reconstruction using tunneling flap technique with 3D custom-made titanium mesh plate and particulate cancellous bone and marrow graft: a case report.

BACKGROUND: Reconstructive surgery is often required for tumors of the oral and maxillofacial region, irrespective of whether they are benign or malignant, the area involved, and the tumor size. Recently, three-dimensional (3D) models are increasingly used in reconstructive surgery. However, these models have rarely been adapted for the fabrication of custom-made reconstruction materials. In this report, we present a case of maxillary reconstruction using a laboratory-engineered, custom-made mesh plate from a 3D model. CASE PRESENTATION: The patient was a 56-year-old female, who had undergone maxillary resection in 2011 for intraoral squamous cell carcinoma that presented as a swelling of the anterior maxillary gingiva. Five years later, there was no recurrence of the malignant tumor and a maxillary reconstruction was planned. Computed tomography (CT) revealed a large bony defect in the dental-alveolar area of the anterior maxilla. Using the CT data, a 3D model of the maxilla was prepared, and the site of reconstruction determined. A custom-made mesh plate was fabricated using the 3D model (Okada Medical Supply, Tokyo, Japan). We performed the reconstruction using the custom-made titanium mesh plate and the particulate cancellous bone and marrow graft from her iliac bone. We employed the tunneling flap technique without alveolar crest incision, to prevent surgical wound dehiscence, mesh exposure, and alveolar bone loss. Ten months later, three dental implants were inserted in the graft. Before the final crown setting, we performed a gingivoplasty with palate mucosal graft. The patient has expressed total satisfaction with both the functional and esthetic outcomes of the procedure. CONCLUSION: We have successfully performed a maxillary and dental reconstruction using a custom-made, pre-bent titanium mesh plate.

Wear properties of esthetic dental materials against translucent zirconia.

To clarify the influence of translucent tetragonal zirconia polycrystals (TZP) on wear properties of esthetic dental materials, two-body 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.

Prospective multicenter non-randomized controlled study on intraosseous stability and healing period for dental implants in the posterior region.

BACKGROUND: A current implant body surface was treated with "rough processing" by sandblasting and acid etching for the purposes of obtaining more reliable osseointegration and shortening the treatment period. Various reports have examined the healing period with the use of these implant bodies, but a consensus opinion has not yet been obtained. The purpose of this study is to evaluate the relationship between insertion torque (IT) and implant stability quotient (ISQ) at implant treatment using the current rough-surfaced implant. We evaluated the implant treatment sites with ISQ values, IT values, and voxel values. METHODS: Participants in this study comprised 26 patients (10 males, 16 females; mean age, 55.5 years) who received posterior region dental implants at Tokyo Dental College Hospital or Fukuoka Dental College Hospital. For all participants, pretreatment computed tomography and determination of bone quality from voxel values were performed. Thirty-two implant bodies were inserted into the posterior region, and insertion torque was measured. ISQ was also measured at 0, 2, 4, 6, 8, and 12 weeks postoperatively. RESULTS: Eight implant bodies in the maxilla and 24 in the mandible were inserted. All ISQ values increased, exceeding 60 by 6 weeks postoperatively. For insertion torque < 30 N cm, ISQ increased significantly after 8 weeks. For ≥ 30 N cm, the ratio at which high ISQ values appeared increased significantly after 6 weeks. Compared with the treatment area with insertion torque < 40 N cm, the treatment area ≥ 40 N cm showed a significantly higher voxel value. CONCLUSIONS: No significant relationship was found between the insertion torque value and the ISQ value. Also, it was suggested that the ISQ value was considered to be an important indicator for observing the treatment state of the implant.

Influence of eccentric cyclic loading on implant components: Comparison between external joint system and internal joint system.

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.

Current State of Undergraduate Education in Oral Implantology in Japan.

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.

Wear behavior between zirconia and titanium as an antagonist on fixed dental prostheses.

The aim of this in vitro study was to investigate the wear behavior of the abrader when tetragonal zirconia polycrystal (TZP), cp-titanium (CpTi) and Ti-6Al-4V alloy (TiAlV) were used as the antagonist on fixed dental prostheses (FDPs). Both hemisphere abrader and flat substrate specimens were prepared using TZP, CpTi and TiAlV. Two-body wear tests were performed in distilled water, and the wear volume of the abrader specimen was measured to evaluate the wear behavior. In addition, scanning microscopic observation and an electron probe micro-analysis were performed to elucidate the underlying mechanism of the wear. The wear volume of CpTi and TiAlV abrader specimens was approximately 20 times larger than that of TZP abrader specimen against all substrate specimens. This is due to the differences in hardness between the ultra-hardness of TZP and the comparatively low hardness of CpTi and TiAlV. The wear volume of CpTi and TiAlV abrader specimens against the TZP substrate was significantly smaller than for the CpTi and TiAlV substrates despite the hardness of TZP being much larger than those of CpTi and TiAlV. This phenomenon may be based on the adhesive wear mechanism. Elements of Ti, Al and V originating in the TiAlV substrate were detected adhering to the abrader CpTi specimen. These results suggest that FDPs of CpTi and TiAlV are susceptible to wear against not only TZP but also CpTi and TiAlV in contrast to TZP FDPs.

Influence of surface treatment of yttria-stabilized tetragonal zirconia polycrystal with hot isostatic pressing on cyclic fatigue strength.

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.