Fumihiko Watanabe

Finite element analysis of the influence of implant inclination, loading position, and load direction on stress distribution

The selection of the appropriate alignment of an implant and the position of implantation are vital for its longterm success. Excessive load is generated around inclined implants, causing microcracks in the bone, which result in implant loosening and eventual failure. This study was designed to analyze the stress distribution caused by varying the degree of inclination of an implant body and varying the loading position and direction, using the finite-element method of stress analysis. Buccal and lingual two-dimensional simulation models of a cylinder implant, embedded in the first molar edentulous cross-section of the mandible, were prepared, and the stress distribution and maximum principal stresses were recorded. Regardless of the point and direction of loading, compressive stresses were relatively greater when the implant was inclined. This tendency became more pronounced when a 45° loading direction and eccentric loading were tested. For the inclined model, with a 45° loading direction, the compressive stress was observed on the cortical bone adjacent to the direction of inclination, while tensile stress was observed on the opposite side.

Hard and soft tissue responses to three different implant materials in a dog model.

The aim of this study was to assess hard and soft tissue responses using three dental implants made of different materials. Implants made of titanium (Ti), yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and ceria partially stabilized zirconia/alumina nanocomposite (Ce-TZP/Al2O3) were used in a dog model. Five male beagles were sacrificed at three months after implantation, and harvested mandible were observed and analyzed. Histological observations were similar in all groups. There were no significant differences in any histomorphometric parameters. Our results suggested the possibility of Ce-TZP/Al2O3 as a dental implant material, similar to Ti and Y-TZP.

The change in retentive force of magnetic attachment by abrasion

Magnets are frequently applied to removable dentures as retentive attachments. A magnet-retained removable overdenture might be slightly shifted from side to side by eccentric movement in the mouth, and the surface of magnetic attachment may be worn as a result. However, the relationship between the retentive force of magnetic attachment and its surface abrasion has not been reported. The purpose of this research is to investigate this relationship. Ten Mgfit DX 400 magnetic attachments for natural tooth roots were used for this experiment. The magnetic attachments were embedded in autopolymerizing acrylic resin, and ten pairs of specimens were fabricated. A 5-mm repeated gliding motion was applied on each pair of specimens until 30 000, 50 000, or 90 000 cycles had been achieved. The abrasion machine was under 5 kg loading, and the slide speed was 60 times/min. The retentive force of magnetic attachment was measured with a tension gauge at (1) before gliding; (2) after 30 000 gliding cycles; (3)after 50 000 gliding cycles; or (4) after 90 000 gliding cycles. The average change of retentive force of ten magnetic attachments after 30 000, 50 000, and 90 000 gliding cycles was 0.016 N, 0.003 N, and −0.008 N, respectively. The change was statistically analyzed using a paired-sample t test, which showed that the number of gliding cycles did not affect the retentive force of magnetic attachment significantly. The surface of magnetic attachment after gliding was observed by a microscope, and the abrasion of this attachment surface is clearly seen.

A preliminary report on dental implant condition among dependent elderly based on the survey among Japanese dental practitioners

BackgroundThe objective of this study was to ascertain the situation relevant to implants, the status of oral self-care, the status of aftercare provided by the dentist who placed the implant, and the usage status of the implant card, in homebound or institutionalized older adults who are receiving home-visit dental care due to the inability to visit a dental clinic on their own.MethodsA survey questionnaire was sent by post mail to 2339 people who are representative members or dental specialists belonging to any of the following three academic societies: Japanese Society of Oral Implantology, Japanese Society of Gerodontology, and Japan Prosthodontic Society. The survey questions asked were about provision/no provision of implant treatment, provision/no provision of home-visit dental care, the situation of patients after implant treatment, the situation of implants in the context of home-visit dental care, and the usage status and recognition of the implant card.ResultsNo less than 30% of the dentists had patients who were admitted to the hospital or became homebound after receiving implant treatment at their clinic. Twenty-two percent of the dentists had been consulted about the implants. Dentists who continued to provide post-operative implant care through home-visit dental care accounted for approximately 80%. On the other hand, however, 40% of the dentists did not know the post-implantation status of their implant patients. Of the patients receiving home-visit dental care, approximately 3% had implants (identified mainly by visual inspection). It was found that more than 50% of the dentists offering implant treatment did not use the implant card, and even in cases where it was used, most of the cards were not in the standardized format.ConclusionsWithin the limitation of low response rate to the questionnaire in this preliminary study, we concluded that many of practitioners including specialists indicated the need of universal record of implant for dependent elderly cares.

Fracture force for veneered materials on restorations measured by torsion testing

The torsional fracture strength at the interface between a base plate and veneering material was evaluated for three kinds of veneered restoration: porcelain fused to zirconia (PFZ), porcelain fused to metal (PFM), and composite resin veneered metal (CRVM). The metal and zirconia base plate (30×4×0.4 mm) were prepared and these plates were veneered as test specimens using each material to a total thickness of 1.2 mm. Torsional force was applied to each specimen using a rotational speed of 1.0 deg/min until the veneering material underwent fracture or exfoliation. The torsional fracture values were measured and the data were statistically analyzed using one-way ANOVA. The torsional fracture strength for PFZ, PFM, and CRVM was 3.0, 3.1, and 11.1 N•cm, respectively.

Hard and soft tissue responses to implant made of three different materials with microgrooved collar in a dog model

The objective of the present study was to assess hard and soft tissue around dental implants made of three different materials with microgrooves on the collar surface. Microgrooved implants were inserted in the mandibles of five male beagles. Implants were made of three kinds of material; titanium (Ti), yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and ceria partially stabilized zirconia/alumina nanocomposite (Ce-TZP/Al2O3). The animals were euthanatized at three months after implantation, and harvested tissue was analyzed by means of histology. All kinds of implant were osseointegrated, and there were no significant differences in any histomorphometric parameters among the three groups of microgrooved implants made of different materials. Within the limitations of this study, implants with microgrooves integrated into the surrounding bone tissue, without statistically significant differences among the three tested materials, Ti, Y-TZP, and Ce-TZP/Al2O3.

Abutment screw loosening of endosseous dental implant body/abutment joint by cyclic torsional loading test at the initial stage.

Cyclic torsional loading tests were carried out in the laboratory using various implant systems, in order to clarify differences between the systems in loosening of abutment screws. Six samples from six commercially available abutment systems were used, giving a total of 36 samples. Four of the systems used internal connections, and two used external connections. The abutment screw for each system was tightened to a torque value specified by the manufacturer, and after 5 min, the loosening torque was measured using a digital torque meter. Measurements were taken twice, and a second measurement was taken as a reference value. A cyclic torsional loading test with 100,000 cycles was performed on the sample, and the loosening torque was again measured after the test. In conclusion, loosening of the abutment screw occurred as a result of cyclic torsional loading, and the degree of loosening varied with each implant system.

Comparison of diameters at the cementoenamel junction between South Asians and Japanese

Previously, sex differences among the various tooth types in Japanese skulls were examined to facilitate choosing an implant diameter similar to the cervical diameter of each tooth, and it was found that mesiodistal diameters at the cementoenamel junction were narrower in women than in men. Also interesting and relevant to the selection of implant diameter is the possible existence of racial differences in diameters at the cementoenamel junction. The purpose of this research was to test the hypothesis that the diameter at the cementoenamel junction of the tooth differs in humans of different races. We compared 106 skulls of unknown sex collected from South Asia with the skulls of Japanese women. Our conclusions are as follows: (1) Except for the lower canine, no significant racial differences were found in the labiolingual diameter of any teeth. (2) Except for the upper canine, upper central incisor, lower second premolar, and lower first premolar, a significant racial difference was found in the mesiodistal diameter. In all teeth in which this value differed, the mesiodistal diameters of South Asians were narrower than those of Japanese women, except for the lower canine. (3) The labiolingual and mesiodistal diameters of the lower canine were significantly larger in South Asians than in Japanese women. (4) Among South Asians, no significant left/right differences were found in the diameter at the cementoenamel junction of any tooth.

Prognostic Research Related to Survival of IMZ Implants at Two Institutes.

目的: 本研究は, 日本歯科大学新潟歯学部附属病院および三条市榎本歯科医院の2施設で過去13年間に行われた271症例, 972本のIMZインプラント13年間にわたる症例の予後評価である.方法: 972本のインプラントのうち, 2年間に254人において臨床的に913本のインプラントが検査された (リコール率93.7%). 主に生存率, 上下顎の生存率, サイズ別生存率の項目について, Life Table AnalysisとKaplan-Meier法を用いて比較検討した.結果: 検討の結果, 以下の結論が得られた. 1.両施設での累積生存率は5年目で96.3%, 10年目で92.6%, 13年目で89.9%であった.2.インプラントと天然歯との連結症例において, 施設1で12.1%, 施設2で6.8%に連結歯の破折が認められ, そのいずれも失活歯であった. 3.両施設のインプラントの生存率を, Kaplan-Meier法で解析した結果, 上下顎の生存率に有意差が認められなかった (Breslow-Gehan-Wilcoxonの検定, p=0.61). 4.また, インプラント体の直径3.3mmと4.0mm間 (Logrankの検定, p=0.51) およびそれぞれの長径間 (Logrankの検定, p=0.45) で生存率に差はなかったが, インプラント体のサイズ別の除去率をみると, 2施設で直径別では直径3.3mmが6.9%, 直径4.0mmが3.4%と, 径の太いほど低く, また長径では, 長径8mmが13.0%, 10, 11mmは4.4%, 13mmは2.0%, 15mmは0%であり, 短いほど高い傾向を示した.結論: IMZインプラントの長期生存率は高く, 同インプラントが臨床的に有用であることが示された.