Masayuki Takaba

Oral health-related quality of life in patients treated by implant-supported fixed dentures and removable partial dentures.

OBJECTIVES This study investigated the association between denture status [implant-supported fixed dentures (IDs) and removable partial dentures (RPDs)] and oral health-related quality of life (OHRQoL). MATERIALS AND METHODS Consecutive patients with IDs and RPDs were recruited from the Prosthodontics Departments at Showa University and Tokyo Medical and Dental University. The Japanese version of the Oral Health Impact Profile (OHIP-J-49) was administered to each subject. For each OHIP-J-49 question, the subjects were asked to indicate the frequency with which they had experienced a dental problem during the last month. Responses were recorded on a 5 point Likert rating scale, with 0 being never and 4, very often. Summary scores were calculated and regression analyses conducted to investigate the association between denture status and OHIP-J-49 summary score. RESULTS In total 79 ID subjects (mean age±SD of 51.7±12.4 years, 44.3% men) and 109 RPD subjects (mean age of 66.5±8.6 years, 30% men) participated after giving informed consent. The regression analysis between the type of treatment and the OHIP-J-49 summary score revealed a significant association with a coefficient of 17.0 (Confidence interval, CI: 10.9-23.1). When age and duration of denture usage, which had significant associations with OHIP-J-49, were included in this model, the regression coefficient remained virtually unchanged at 17.4 (CI: 9.75-25.0), thus indicating little potential confounding by them. CONCLUSIONS OHRQoL in patients with implant-supported fixed dentures is generally less impaired than it is in those patients with RPDs.

A 3-year follow-up of ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) frameworks for fixed dental prostheses

PURPOSE Zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/A) shows significantly higher mechanical strength than yttrium-oxide-partially-stabilized zirconia (Y-TZP) and allows post-sintered machining that does not require any subsequent treatment. The aim of this prospective study was to assess the clinical performance of veneered Ce-TZP/A frameworks for fixed dental prostheses. METHODS Fifteen patients with 22 Ce-TZP/A fixed prostheses were included in this study. The fixed dental prostheses were cemented with resin cement (baseline) and were evaluated at baseline and at 1, 6, 12, 24 and 36 months after cementation. Clinical events, including fracture and loss of retention, secondary caries, and marginal integrity, were recorded. The biologic outcome was judged by comparing the pre-treatment and post-treatment bleeding on probing (BOP), and probing pocket depth (PPD) of the abutment teeth. Radiographic examination was also performed at 12, 24 and 36 months. RESULTS The mean observation period was 35.9±5.5 months. During this period, one abutment tooth was extracted due to root fracture and the survival rate was 95.2%. No significant change in BOP, PPD, and radiographic image was found during the 36-month follow-up period. CONCLUSION Within the limitations of this study, Ce-TZP/A was found to provide sufficient stability as a framework material in all regions. Special attention, however, must be paid to designing framework that provides sufficient support for the veneer. Furthermore, studies with longer observation periods and more patients are needed.

Implant‐Supported Fixed Dental Prostheses with CAD/CAM‐Fabricated Porcelain Crown and Zirconia‐Based Framework

Recently, fixed dental prostheses (FDPs) with a hybrid structure of CAD/CAM porcelain crowns adhered to a CAD/CAM zirconia framework (PAZ) have been developed. The aim of this report was to describe the clinical application of a newly developed implant-supported FDP fabrication system, which uses PAZ, and to evaluate the outcome after a maximum application period of 36 months. Implants were placed in three patients with edentulous areas in either the maxilla or mandible. After the implant fixtures had successfully integrated with bone, gold-platinum alloy or zirconia custom abutments were first fabricated. Zirconia framework wax-up was performed on the custom abutments, and the CAD/CAM zirconia framework was prepared using the CAD/CAM system. Next, wax-up was performed on working models for porcelain crown fabrication, and CAD/CAM porcelain crowns were fabricated. The CAD/CAM zirconia frameworks and CAD/CAM porcelain crowns were bonded using adhesive resin cement, and the PAZ was cemented. Cementation of the implant superstructure improved the esthetics and masticatory efficiency in all patients. No undesirable outcomes, such as superstructure chipping, stomatognathic dysfunction, or periimplant bone resorption, were observed in any of the patients. PAZ may be a potential solution for ceramic-related clinical problems such as chipping and fracture and associated complicated repair procedures in implant-supported FDPs.

Effect of clonazepam and clonidine on primary sleep bruxism: a double-blind, crossover, placebo-controlled trial

The aim of this study was to assess the acute effects of clonazepam and clonidine on rhythmic masticatory muscle activity in young adults with primary sleep bruxism, as well as accompanying effects on sleep architecture and cardiac activity. This study used a double‐blind, crossover, placebo‐controlled design. Polysomnography was performed on 19 subjects [nine men and 10 women; mean age (±SE): 25.4 ± 2.7 years] for 5 nights. The first 2 nights were used for the habituation and diagnosis of sleep bruxism. The other 3 nights were randomly assigned for clonazepam (1.0 mg), clonidine (0.15 mg) or placebo (all administered 30 min before bedtime). Sleep, oromotor activity and cardiac activity variables were assessed and compared among the three drug conditions. Clonidine significantly reduced the median percentage of time spent in the rapid eye movement sleep stage compared with placebo and clonazepam. The number of rhythmic masticatory muscle activity episodes was reduced with clonidine by >30% compared with placebo and clonazepam. The reduction of rhythmic masticatory muscle activity index by clonidine was associated with an increase of mean RR intervals (slower heart rate) during quiet sleep periods and during a 70‐s period before the onset of rhythmic masticatory muscle activity episodes. However, no changes in cardiac activity variables were observed for clonazepam. In young adults with primary sleep bruxism, clonidine was significantly more effective in suppressing sleep bruxism than clonazepam. The acute effects of clonidine on rhythmic masticatory muscle activity episodes may be mediated by suppression of autonomic nervous system activity and non‐rapid eye movement–rapid eye movement sleep processes.

Association between patterns of jaw motor activity during sleep and clinical signs and symptoms of sleep bruxism.

The aim of this study was to investigate the association between patterns of jaw motor activity during sleep and clinical signs and symptoms of sleep bruxism. A total of 35 university students and staff members participated in this study after providing informed consent. All participants were divided into either a sleep bruxism group (n = 21) or a control group (n = 14), based on the following clinical diagnostic criteria: (1) reports of tooth‐grinding sounds for at least two nights a week during the preceding 6 months by their sleep partner; (2) presence of tooth attrition with exposed dentin; (3) reports of morning masticatory muscle fatigue or tenderness; and (4) presence of masseter muscle hypertrophy. Video‐polysomnography was performed in the sleep laboratory for two nights. Sleep bruxism episodes were measured using masseter electromyography, visually inspected and then categorized into phasic or tonic episodes. Phasic episodes were categorized further into episodes with or without grinding sounds as evaluated by audio signals. Sleep bruxism subjects with reported grinding sounds had a significantly higher total number of phasic episodes with grinding sounds than subjects without reported grinding sounds or controls (Kruskal–Wallis/Steel–Dwass tests; P < 0.05). Similarly, sleep bruxism subjects with tooth attrition exhibited significantly longer phasic burst durations than those without or controls (Kruskal–Wallis/Steel–Dwass tests; P < 0.05). Furthermore, sleep bruxism subjects with morning masticatory muscle fatigue or tenderness exhibited significantly longer tonic burst durations than those without or controls (Kruskal–Wallis/Steel–Dwass tests; P < 0.05). These results suggest that each clinical sign and symptom of sleep bruxism represents different aspects of jaw motor activity during sleep.

In Vivo Evaluation of Inter-operator Reproducibility of Digital Dental and Conventional Impression Techniques

Purpose The aim of this study was to evaluate and compare the inter-operator reproducibility of three-dimensional (3D) images of teeth captured by a digital impression technique to a conventional impression technique in vivo. Materials and methods Twelve participants with complete natural dentition were included in this study. A digital impression of the mandibular molars of these participants was made by two operators with different levels of clinical experience, 3 or 16 years, using an intra-oral scanner (Lava COS, 3M ESPE). A silicone impression also was made by the same operators using the double mix impression technique (Imprint3, 3M ESPE). Stereolithography (STL) data were directly exported from the Lava COS system, while STL data of a plaster model made from silicone impression were captured by a three-dimensional (3D) laboratory scanner (D810, 3shape). The STL datasets recorded by two different operators were compared using 3D evaluation software and superimposed using the best-fit-algorithm method (least-squares method, PolyWorks, InnovMetric Software) for each impression technique. Inter-operator reproducibility as evaluated by average discrepancies of corresponding 3D data was compared between the two techniques (Wilcoxon signed-rank test). Results The visual inspection of superimposed datasets revealed that discrepancies between repeated digital impression were smaller than observed with silicone impression. Confirmation was forthcoming from statistical analysis revealing significantly smaller average inter-operator reproducibility using a digital impression technique (0.014± 0.02 mm) than when using a conventional impression technique (0.023 ± 0.01 mm). Conclusion The results of this in vivo study suggest that inter-operator reproducibility with a digital impression technique may be better than that of a conventional impression technique and is independent of the clinical experience of the operator.

The Effect of Bite Force on Occlusal Contact and Masticatory Functions

目的: 咬頭嵌合位付近の側方咬合位において, 咬合力による咬合接触面積の変化と咀嚼機能との関係について検討する.方法: 正常有歯顎者12名について, 咬頭嵌合位および顎位規定装置で規定した1, 2mmの左右側方咬合位の咬合接触を, 軽い咬合時と強い咬合時において, 咬合印象法によって記録した. 咬合接触領域は50μm以下の近接領域とした. また, ガム咀嚼時の咬筋, 側頭筋の筋活動と咀嚼運動を同時に測定し, 咬合接触面積と咀嚼筋の筋活動比の関係を検討した.結果: 1. 咬頭嵌合位から側方咬合位に移動することで, 咬合接触面積は有意に減少し, それぞれの側方咬合位において咬合力を大きくすることにより, 増加した咬合接触面積も有意に減少した. 2. 平衡側2mmの咬合接触面積の増加量と咬筋の筋活動比は, 有意な負の相関関係が認められたが, 側頭筋の筋活動比との相関関係は認められなかった.結論: 咬頭嵌合位および側方咬合位の作業側と平衡側の咬合接触面積は, 強く咬合することで増加した. また, 側方咬合位の作業側では, 軽い咬合時の咬合接触面積が大きいほど, 咬合力負荷に伴う咬合接触面積の増加量も大きいという関係が認められ, 平衡側では, 咬合力が加わった場合の咬合接触面積の増加量が大きいと, 作業側と平衡側の筋活動比に影響があることが示された.