Effect of fatigue loading on the screw joint stability of zirconium abutment.

PURPOSE: This study evaluated the effect of fatigue loading on the screw joint stability of a zirconium abutment connected to an external hexagon implant in vitro. MATERIALS AND METHODS: Fifteen titanium and 15 zirconia abutments of 3 different heights (5, 8, and 11 mm) were connected to external titanium implants with titanium screws. A torque gauge was used to measure the reverse torque values before and after loading. An air cylindrical loading device was used to simulate mastication at a 45-degree angle to the longitudinal axis of the implant. RESULTS: There were significant differences (P<0.05) before and after the loading of titanium (5mm) and zirconia (5, 8, and 11 mm) abutments. CONCLUSION: Zirconia abutments for external hexagon implants had durability rates similar to those of titanium abutments after repeating load on the reverse torque of the abutment screw, indicating that the zirconia abutment could be reliably used instead of the titanium abutment.

Long-term clinical evaluation of implant over denture.

PURPOSE: The use of implants to treat edentulous jaws has become a well-established and accepted contemporary clinical method. The aim of this study was to analyze information about the implants used, patients, denture modality, and complications after denture insertion in partially and fully edentulous patients with implant overdentures placed. METHODS: A survey was performed about patients rehabilitated using implant dentures at the Tsurumi University Dental Hospital during 8 years. A total of 201 implants were placed: 112 in the maxilla and 89 in the mandible. Descriptive statistics were used for each patient, such as the implant positions and numbers, retainer designs, denture modalities, implant survival rate and prosthetic complications. RESULTS: The positions of implant placement were: incisor (44%); canine (26%); premolar (18%); and molar (12%). Approximately 70% of the retainers were bar attachments and magnet attachments. The majority of the prostheses were metal-based dentures (84%) compared to only 10 acrylic dentures (16%). Fully edentulous, fourteen (12 maxillary, 2 mandibular) of 171 implants failed. Partially edentulous, three (3 maxillary, 0 mandibular) of 30 implants failed. The denture complications observed during maintenance were denture fracture, retainer breakage and artificial tooth fracture. CONCLUSION: Although the mandibular implant dentures placed were exceedingly reliable for rehabilitation with a high survival rate, the maxillary implant dentures exhibited a low survival rate and more frequent complications. Significantly higher implant failures and prosthetic complications were observed in the initial period after placement than in the following years.

The influence of zirconia coping designs on the fracture load of all-ceramic molar crowns.

This study investigated the influence of zirconia coping designs on the fracture load of all-ceramic crown. Four kinds of zirconia copings were designed (a: Conventional zirconia coping with flat occlusal surface: thickness of the each coping is 0.6 mm evenly, and at the cervical margin area, the coping is adjusted sharply so as to fit preparation margin, b: Conventional zirconia coping with shoulder collar of 1 mm: thickness of the each coping is 0.6 mm evenly, and there is a collar of 0.6 mm from the margin, c: Zirconia coping with following original cuspal configuration (concave): two inclined cusp planes, and at the cervical margin area, the coping is adjusted sharply so as to fit preparation margin, and d: Zirconia coping with supporting configuration on the occlusal area: supporting configuration against the occlusal force, and at the cervical margin area, the coping is adjusted sharply so as to fit preparation margin) and porcelain was fired. Vertical and lateral load were conducted until fracture. Coping design affected the fracture load; conventional uniform thickness coping design showed the lowest load (a), whereas cuspal configuration to perform even thickness of porcelain showed the highest fracture load both load directions (c).

Clinical marginal and internal gaps of zirconia all-ceramic crowns.

PURPOSE: Marginal and internal gaps of NobelProcera crown zirconia were clinically evaluated using silicone materials. MATERIALS AND METHODS: Ninety-one crowns were examined before final cementation, and white and black silicone materials were used to record the marginal and internal fit. The silicone materials were sectioned bucco-lingually and mesio-distally, and the thickness of the silicone layers was measured using a microscope. Sixteen reference points were measured on each specimen, and mean marginal and internal gaps were obtained. Mean marginal gaps among anterior, premolar, and molar tooth groups, in addition to mean gaps at the reference points within the groups, were compared using two-way ANOVA and Games-Howell analysis. RESULTS: The marginal mean values were the smallest among all tooth groups, and the largest were at the rounded shoulders. There were no significant differences in the mean marginal gaps among the three tooth groups, while there were significant differences in the mean marginal and internal gaps of each tooth group. CONCLUSIONS: The mean marginal gap of the NobelProcera crown zirconia was 44.2 µm, which is within clinically accepted standards.

Clinical evaluation of posterior all-ceramic FPDs (Cercon): a prospective clinical pilot study.

PURPOSE: This study prospectively evaluated the clinical performance of posterior zirconium-oxide-based all-ceramic fixed partial dentures (FPDs). METHODS: Forty-two abutments of 21 Cercon FPDs were fitted in 20 patients at the Tsurumi University Dental Hospital from August 2005 to August 2006. The performance of these FPDs was evaluated using the California Dental Association (CDA) quality assessment system at baseline and at all follow-up examinations. RESULTS: All FPDs were examined after a mean observation period of 28.1 (+/-3.4) months. During the observation period, no fracturing of FPDs was seen. All of the FPDs examined were rated as satisfactory with regard to all factors at the follow-up examinations based on the CDA quality assessment criteria. CONCLUSION: Within the limitations of this short-term clinical study, no core framework fractures were seen. According to the CDA criteria, 100% of the FPDs were rated as satisfactory during this observation period.

Effect of framework shape on the fracture strength of implant-supported all-ceramic fixed partial dentures in the molar region.

PURPOSE: The aim of the present study was to clarify the effects of the shape of the zirconium framework of implant-supported, all-ceramic fixed partial dentures (FPDs) on the fracture strength and fracture mode. MATERIALS AND METHODS: This study consisted of mechanical strength testing and 3D finite element analysis (FEA). The three framework shapes used in this study were: (1) conventional shape (control); (2) convex shape: 1.0-mm curve in the direction of the occlusal surface; and (3) concave shape: 1.0-mm curve in the direction of the gingival surface. Five frameworks were made for each condition (total: 15). A load (N) was applied until the FPD fractured. For FEA, a 3D model consisting of cortical bone, cancellous bone, implant bodies, and superstructure was constructed. RESULTS: The results of the mechanical strength test showed that fracture load was 916.0 +/- 150.1 N for the conventional shape, 1690.5 +/- 205.3 N for the convex shape, and 1515.5 +/- 137.0 N for the concave shape. The mean final fracture load for the FPDs with frameworks was the highest for the convex shape; however, a critical crack in the veneer porcelain (736.5 +/- 145.2 N) was confirmed during loading for the convex shape. Stress distribution maps for all conditions showed that tensile stress was generated at the veneer porcelain on the gingival side of the mesial and distal connectors of the pontic; however, there were differences in the maximum value and stress distribution within the framework. CONCLUSION: The shape of the framework, particularly the shape of the pontic-connector interface, affects the stress distribution, fracture strength, and fracture mode of all-ceramic FPDs, and stress concentration inside a framework may induce cracking of layering porcelain.

Validity and reliability of patient satisfaction questionnaires in a dental school in Japan.

PURPOSE: The purpose of this study was to construct questionnaires for the dental school setting from freely given patient answers with the aid of text mining, and to confirm the structure, reliability and validity of the questionnaires. METHODS: Using these questionnaires, we carried out a survey of the satisfaction of patients treated at the Dental Hospital of the Tsurumi University School of Dental Medicine. A total of 3394 patients participated in the study. To confirm the reliability of inter-item correlations and construct validity, factor analysis was carried out, and items belonging to each factor and Cronbach's alpha coefficients were calculated. RESULTS: Four factors were extracted and 64.0% of the variance was explained by these four factors. All correlation coefficients were >0.85. These four factors were: 'Treatment', 'Communication', 'Facilities' and 'Appearances'. From structural equation modelling, we determined that overall satisfaction was >0.75 and was statistically significant. CONCLUSION: The questionnaires used in this study are useful for measuring patient satisfaction in the dental school hospital setting.

Clinical marginal gap of porcelain fused to electro-formed gold coping crowns.

This study evaluated the marginal and internal gaps of Auro Galvano Crowns (AGC) in vivo. One hundred AGC crowns were examined using white and black silicone materials; the thickness of the silicone layer was measured at 16 reference points using a microscope. The mean marginal gaps among anterior, premolar and molar teeth, and the mean gaps within the groups were compared by analysis of variance and Dunnett T3 test. The results showed that at the margins, there were no significant differences among the four measuring points within each group, and there were no significant differences in the mean marginal gaps among the three groups. The mean marginal gaps in all groups were within the limits of clinical acceptability.

Use of abutment-teeth vs. dental implants to support all-ceramic fixed partial dentures: an in-vitro study on fracture strength.

The aim of the present in-vitro study was to compare the fracture strength of all-ceramic Fixed Partial Dentures supported by tooth-analogues and periodontal membrane with the same supported by dental implants. As ceramics are highly brittle, they cannot withstand deformations of more than 0.1% without fracturing. Hence, when planning an all-ceramic FPD, it is essential to evaluate abutment support, as the fracture strength of all-ceramic constructions depends on the stability of the support to reduce strain in the beam of the prosthesis. The support provided by implants differs, however, from the support provided by natural teeth as the implants are anchored directly in the bone with no intermediate tissue. One question that arises is whether strain and stress in the prosthesis are lower when the prosthesis is loaded on implants compared to natural teeth and hence if all-ceramic FPDs benefit from implant support. Twenty-four three-unit all-ceramic FPDs-12 supported by two dental implants and 12 by two tooth-analogues serving as end abutments-were made. All FPDs were subjected to preloading in a preloading procedure and subsequently subjected to load until fracture occurred. Load at fracture were registered and comparisons between the two groups were made. The loads at fracture were statistically significant higher in the group supported by implants compared to the group supported by tooth-analogues (p = 0.003). Within the limitations of this in-vitro study, the following conclusions can be drawn: All-ceramic fixed partial dentures can be used in combination with dental implants. The solid support gained from implants might thus be beneficial for the outcome of such treatment due to decreased strain and stress levels in the prosthesis when loaded on implants compared to when loaded on natural teeth. Clinical studies are, however, needed to confirm these findings as there are more factors that influence the final clinical outcome.

Magnetic attachment for esthetic management of an overdenture.

Magnetic attachments are a popular means of retaining removable overdentures and maxillofacial prostheses.(1) When used in anterior regions, these attachments often are not esthetic because the metallic color of the cast coping or attachment can be seen directly or through the denture base. An esthetic magnetic attachment with a composite facing can be fabricated to overcome this problem.

Arrangement of artificial teeth in the neutral zone after surgical reconstruction of the mandible: a clinical report.

This clinical report describes the fabrication of a fixed partial denture, supported and retained by implants, for a patient with unfavorable tongue movement caused by movable grafted skin on the floor of the mouth after surgical reconstruction of the mandible. The neutral zone technique was used, and successful results were obtained.

The reconstruction of bilateral clefts using endosseous implants after bone grafting.

This article presents the orthodontic reconstruction of an adult bilateral cleft patient with a severe Class III malocclusion in which endosseous implants were inserted after secondary alveolar bone grafting. The patient was a 21-year-old Japanese male whose lateral incisors were congenitally missing and whose premaxilla was inclined lingually. The occlusion was classified as Angle Class III with an overjet of -8 mm. Orthodontic alignment was initiated to correct the position of the maxillary incisors before bone grafting. After the anterior occlusal relationship was corrected, bilateral alveolar clefts were reconstructed by bone grafting with autogenous particulate marrow and cancellous bone harvested from the iliac crest. ITI-SLA fixtures (Institute Straumann, Waldenburg, Switzerland) (length, 10 mm; diameter, 4.1 mm) were placed into the grafted bone for prosthetic restoration of the missing lateral incisors. The results illustrate that this protocol can be expected to provide an acceptable occlusion and good dentoalveolar stability in adult cleft patients.