It is thought that loosening of the abutment influences fracture of the abutment and the implant body, and that this phenomenon influences bone resorption. Therefore, in this study, in a test piece without abutment loosening, an abutment was fitted to an implant body at 20 Ncm. In the test pieces with abutment loosening, the loosening was established by rotating it by 90°(1/4 rotating the abutment), 180°(1/2 rotating the abutment), and 360°(1 rotating the abutment). Each test piece with established loosening was set in a universal testing machine, the load until fracture of the tablet was measured, and strain occurring in the implant collar area was measured using a strain gauge. The relationship between abutment loosening and strain in the implant collar area was evaluated. Furthermore, the relationship between abutment loosening and the maximum bending load and amount of implant deformation was evaluated.

The following conclusions were obtained.

The fracture load of the tablet was 85.1±4.0 N, and the relationship between the fractured load and loosening of each abutment showed no significant difference.

When the tablet fractured, the strain in the collar area of test pieces with loosening of 1/2 and 1 rotation was more than 0.1%. This measurement value suggests the risk of bone resorption. Furthermore, the value of strain in the collar area of test pieces of loosened abutments was similar to that occurring when a load of 200-300 N was applied to the test piece fitted at 20 Ncm. Both the maximum bending load and the amount of deformation of the test piece with loosening of 1 rotation showed decreases of approximately 23% in comparison with those of the test piece without loosening. It is suggested that regular examination to detect the presence of abutment loosening is necessary after the setting of superstructures.

Various types of multi-purpose adhesion system with easy manipulation, in which universal surface treatment is possible by systematically combining treatment materials that can bind to adherends, such as metals, ceramics, and resin composite, have been commercialized and clinically used.

However, because their compositions are comparatively complicated, there are many unclear points. Therefore, in this study, regarding the various types of multi-purpose adhesion system, to precisely investigate the relationship between differ ences in adherends and the effectiveness of adhesion to resin composite, we performed a tensile bond strength test and evalu ated the characteristics of failure mode after the test. Furthermore, to investigate the improvement of the bond strength of resin composite due to ultraviolet irradiation to each adherend, we also evaluated the contact angle of distilled water on each adherend surface, and the tensile bond strength of the multi-purpose adhesion system, using a low-pressure mercury lamp to irradiate with ultraviolet light at wavelengths of 185 and 254 nm, and an excimer lamp to irradiate with ultraviolet light at a single wavelength of 172 nm.

As a result, for adherends (12%Au-Ag-Pd alloy, Clearfil AP-X, CEREC Blocs, and Nano-Zirconia) after sand-blast treat ment, various types of multi-purpose adhesion system showed bond strengths equal to or greater than those of the conven tional surface treatment materials applied to each different adherend. In particular, regarding three types of adherend (12%Au-Ag-Pd alloy, Clearfil AP-X, and CEREC Blocs), a multi-purpose adhesion system (UNIVERSAL PRIMER) showed a significantly greater adhesive strength, in comparison with the two other types of multi-purpose adhesion system and conven tional application methods in which the surface treatment material is applied to each different adherend. The contact angle of distilled water on every adherend decreased after ultraviolet irradiation, and the hydrophilicity more markedly increased us ing the excimer lamp with stronger light energy. Furthermore, in the evaluation of the improvement of bond strength by changing the adherend surface to being more hydrophilic using the UNIVERSAL PRIMER, the bond strength was similar to that of the specimen without ultraviolet treatment, showing no significant differences. However, in the Weibull analysis of the reliability of the bond strength, the dispersion of the bond strength decreased with 12%Au-Ag-Pd alloy, Clearfil AP-X, and Nano-Zirconia, excluding CEREC Blocs; therefore, decreases in the bond strength could be prevented by ultraviolet treatment.

Zirconia used in dental materials has an elastic modulus of 200 to 250 Gpa, which is about twice that of titanium. Therefore, if zirconia is used as an implant body material, the concentration of stress on peripheral tissue is expected to be greater than with titanium implants.

In this study, we mounted superstructures on zirconia implants in beagles, subjected the implants to mechanical loads such as chewing, and then performed a morpho-histological evaluation of peri-implant bone tissue.

We fabricated φ3.0×15.5 mm (threads 9.5 mm, collar 2.0 mm, abutment 4 mm) one-piece zirconia implants for the experi ment. Experimental implants with a machined surface and a laser-treated surface were prepared. Two adult female beagles were used as the experimental animals. Mandibular bilateral molars were extracted, and after 6 months, 3 machined surface implants and 3 laser-treated surface implants were placed in the right sides and the left sides, respectively. Immediately after implantation, a metal protector was attached on adjacent teeth over the implants to prevent loading on the implants for 3 months.

Three months after implantation, the protector was removed. Samples were collected from one beagle as a no loading mod el. Metal superstructures were placed on the zirconia implants and a metal table was attached to the opposing maxillary pre molar area to make occlusal contact in the other beagle. Samples were collected 12 months after the start of occlusal loading. The bone-implant contact ratio (BIC) and bone area (BA) were measured on both the cortical and cancellous sides of the bone tissue samples. Marginal bone levels (MBL) were observed with X-rays before and after the occlusal load.

The direct contact between bone tissue and implant surface was confirmed with all specimens. No marginal bone losses were observed in all histological specimens and X-rays. No differences between the BIC ratio and BA were found between the machined and laser-treated surface types. In both surface types, the BIC ratio and BA after a 12-month occlusal load were higher than before starting the occlusal load.

Zirconia has a higher elastic modulus than titanium, and is predicted to be disadvantageous in terms of stress dispersion when used as an implant body material. However, no abnormal resorption of bone tissue peripheral to the zirconia implants under 12 months of occlusal loading was found in beagles, and these findings suggest that zirconia will be useful as an implant body material.

The indications and methodology of implant treatment for young patients are dependent on individual growth and development, and so the planning of endosseous implant treatment in younger individuals should be based on both careful diagnosis and established growth predictors. Here, we report a case of a 16-year-old female treated with an implant in the maxillary esthetic zone, with long-term observational follow-up for over 20 years. The patient has reported both functional and esthetic satisfaction.

In over 20 years of function, a step of approximately 2.1 mm at the incisal edge between the single tooth implant restorative superstructure and the adjacent central incisor tooth has developed. This change in spatial position may have been influenced by various factors, specifically: growth of the pre-maxilla and mandible, eruption of the third molars, and sequential development and eruption of the permanent dentition. Indeed, it seems better to wait for growth to be completed prior to initiating implant treatment. However, early implant intervention may be required for a variety of reasons in younger patients. Reasons include medical conditions such as partial or total edentulism or specific cases of trauma. In such cases, we have to consider the growth curve of each patient, the bone age, the influence of eruption forces of the third molar teeth, and orthodontic analysis facilitated with a lateral cephalogram. Additionally, it is important to confirm the position of the adjacent tooth CEJ and incisal edge positions, followed by careful implant insertion with palatal placement to limit the depth and preserve the buccal plate.

With the arrival of the super-aging society, there is growing interest in implant overdentures (IODs), which provide favorable outcomes while minimizing the number of implants required, for persons with an edentulous jaw or few remaining teeth. Particular attention is being paid to magnetic attachments (MAs), since they are easy to remove and maintain, and are thus well suited for a society with high longevity. With various types of MAs having various levels of performance, it is essential to know the performance of each MA for exploring the most appropriate MA. We procured seven different MAs fabricated within and outside of Japan and compared their basic performance. The results showed substantial variations in their attractive forces, varying from 1.29 to 7.68 N, and volumes, from 8.6 to 41.3 mm³. Up to a 10-fold difference was observed in the attractive force per unit volume, ranging from 0.04 to 0.44 N/mm³. Two types of magnetic circuits are used for magnetic attachments, open and closed circuits. We found that open-circuit MAs had a substantially lower attractive force and a substantially higher stray magnetic field than closed-circuit MAs. An anticorrosion test revealed no problems, except for the slight corrosion affecting tin-brazed products. Some MAs had a nickel-plated adsorption surface with a magnet not coated with stainless steel etc., while others were simply assembled by pressing. For these products, there was concern over the possibility of corrosion induced by physical stimuli during practical use. Many previous studies, comparing MAs with bar- and ball-type attachments, employed open-circuit MAs with inferior basic performance, which might have resulted in underestimations of the performance of MAs. Further comparative studies are warranted using closed-circuit MAs with superior basic performance features including durability.

Purpose : The aim of this study is to evaluate the long-term prognosis and clinical performance of implant-supported lithium disilicate (LS2) single crowns in the molar region.

Materials and Methods:173 patients, 55 males, 118 females, received 383 implant-supported LS2 single crowns. All the subjects had received single implant treatment in the molar region from June 2008 to March 2014 in one private clinic. All the molars were restored by LS2 single crowns retained by cement. The cumulative survival rate of implants, change of superstructures and mechanical complications were retrospectively assessed.

Results : No implants failed. Seven crowns had to be reproduced due to fractures. Three crowns showed small ceramic chipping, but recovered by polishing. The cumulative survival rates of implants and crowns were 100% and 97.2%, respectively, at 5 years after restoration. The mechanical complication rate was 2.6%. There was a statistically significant difference in the mechanical complication rate between the premolar and molar region.

Conclusion : Implant-supported LS2 single crowns in the molar region showed good, long prognosis and high clinical performances during a 5-year follow-up.

Since the launch of the Dental Implant Clinic in the Dental Hospital of Tokyo Medical and Dental University in 1995, we have conducted a periodic retrospective study of new patients every five years to investigate the trend among new patients and the reasons behind it. The total number of new patients, gender distribution, age distribution and reasons for their visit were studied at five-year intervals from April 1996 to March 2017.

The number of new patients increased from 275 in 1996 to 1643 in 2011, but decreased to 1164 in 2016. The male : female ratio was 1 : 2 almost every year. The peak of new patients' age changed gradually from 40s and 50s in 1996 to 60s in 2011, but that in 2016 was the same as in 2011. About 80% of the reason for visit was the request for dental implant treatment. The number of patients who had complaints about implant treatments at other clinics increased from that in 1996 to 2011, although in 2016, it was almost the same as in 2011.

Furthermore, the number of dental implant surgeries between 2001 and 2016 was proportional to that of new patients who requested dental implant treatment. On the other hand, the number of other surgeries related to dental implants increased every year. The total number of surgeries in 2016 was almost the same as in 2011.