The need for polishing and occlusal adjustment of zirconia prostheses for wear on antagonist teeth.

The attrition of enamel when opposed by ceramics is of great concern. The purpose of this study was to evaluate enamel wear against high translucent zirconia (Zr), lithium disilicate (LD), gold (Au), and enamel (E) with different surface and contact conditions. The materials were divided into two groups: polished and ground (n=8 each). Two-body wear tests were performed against human enamel with vertical and horizontal, horizontal, and vertical repetitive movements as experiments 1 to 3 respectively. The surface roughness of all materials except Zr changed throughout the experiments. In experiment 1, Zr and Au showed less antagonist wear when polished than when ground. In experiment 2, polished groups showed less antagonist wear than ground groups in all materials. In experiment 3, Zr and LD exerted greater antagonist wear than E, regardless of Ra. These findings confirm the importance of polishing and occlusal adjustment of zirconia.

Factors associated with discontinuation and resumption of implant maintenance therapy.

Discontinuation of implant maintenance is the main risk factor for implant failure. The purpose of this study was to identify factors associated with previous discontinuation and resumption of maintenance among implant patients. A questionnaire survey was sent to 171 patients receiving implant maintenance at a university hospital; 169 patients responded. To assess the effect of job status, 26 patients (15.4%) with a history of maintenance discontinuation were classified as employed and nonemployed. The main reasons for previously discontinuing maintenance were work issues (in employed respondents) and dissatisfaction with treatment skill or chairside manner (in nonemployed respondents). The main reasons for resuming maintenance were those related to dental treatment (in employed respondents) and awareness of the importance of maintenance (in nonemployed respondents). There were significant differences in relation to job status in the reasons reported for discontinuing and resuming maintenance (both P < 0.05). The present findings suggest that oral health professionals should consider these factors when assisting patients in reducing the risk of implant failure.

Reliability and validity of the patient disability-oriented diagnostic nomenclature system for prosthetic dentistry.

PURPOSE: The Japan Prosthodontic Society (JPS) has proposed a new diagnostic nomenclature system (DNS), based on pathogenesis and etiology, to facilitate and improve prosthodontic treatment. This system specifies patient disability and the causative factor (i.e. "B (disability) caused by A (causative factor)"). The purpose of this study was to examine the reliability and validity of this DNS. STUDY SELECTION: The JPS Clinical Guideline Committee assessed mock patient charts and formulated disease names using the new DNS. Fifty validators, comprising prosthodontic specialists and dental residents, made diagnoses using the same patient charts. Reliability was evaluated as the consistency of the disease names among the validators, and validity was evaluated using the concordance rate of the disease names with the reference disease names. RESULTS: Krippendorff's α was 0.378 among all validators, 0.370 among prosthodontic specialists, and 0.401 among dental hospital residents. Krippendorff's α for 10 validators (3 specialists and 7 residents) with higher concordance rates was 0.524. Two validators (1 specialist and 1 resident) with the highest concordance rates had a Krippendorff's α of 0.648. Common disease names had higher concordance rates, while uncommon disease names showed lower concordance rates. These rates did not show correlation with clinical experience of the validator or time taken to devise the disease name. CONCLUSIONS: High reliability was not found among all validators; however, validators with higher concordance rates showed better reliability. Furthermore, common disease names had higher concordance rates. These findings indicate that the new DNS for prosthodontic dentistry exhibits clinically acceptable reliability and validity.

Fit of e.max Crowns Fabricated Using Conventional and CAD/CAM Technology: A Comparative Study.

PURPOSE: The aim of this study was to examine the fit accuracy of e.max crowns by investigating marginal and internal gaps. MATERIALS AND METHODS: In experiment 1, 60 e.max computer-aided design/computer-assisted manufacture (CAD/CAM) crowns were manufactured. The crowns were fabricated using optical scanning of artificial teeth (Op group) or scanning of a plaster model following a silicone impression (M group). Cement space settings of 90, 120, and 150 µm were applied. Marginal and internal crown gaps were compared among six conditions (Op90, Op120, Op150, M90, M120, M150). In experiment 2, e.max CAD crowns from the Op group (CADop group) and the M group (CADm group) were compared with e.max Press crowns (Press group) by measuring marginal and internal gaps of the crowns using Scheffe multiple comparison test. The level of significance was set at .05. RESULTS: In experiment 1, the marginal gap of the Op90 group was significantly higher than that of the Op120 and Op150 groups. The marginal gap of the M90 group was significantly higher than those of the M120 and M150 groups, and the internal gap of the M90 group was significantly lower than that of the M150 group. Although there was no statistically significant difference in marginal gap among the three groups, the internal gap of the CADm group was significantly higher than the Press group. CONCLUSION: Although the variation in cement space settings and fabrication techniques affected accuracy, e.max CAD crowns fabricated using optical scanning of melamine teeth achieved a clinically acceptable fit.

Objective assessment of actual chewing side by measurement of bilateral masseter muscle electromyography.

OBJECTIVE: The aim of this study was to examine the validity of objective assessment of actual chewing side by measurement of electromyographic (EMG) activity of the bilateral masseter muscles upon chewing test foods. DESIGN: The sample consisted of 19 healthy, dentate individuals. The subjects were asked to chew three types of test foods (peanuts, beef jerky, and chewing gum) for 10 strokes on the right side and then on the left side, and instructed to perform maximum voluntary clenching for 3s, three times. EMG activity from the bilateral masseter muscles was recorded. The data were collected in three different days. The root mean square EMG amplitude obtained from the maximum clenching task was used as the maximum voluntary contraction (MVC). Then, the level of amplitude against the MVC (%MVC) was calculated for the right and left sides on each stroke. The side with the larger %MVC value was judged as the chewing side, and the concordance rates (CRs) for the instructed chewing side (ICS) and the judged chewing side (JCS) were calculated. Intraclass correlation coefficients (ICCs) of the CRs were calculated to evaluate the reproducibility of the method. RESULTS: High CRs between the ICS and JCS for each test food were recognized. There were significant ICCs for beef jerky (R=0.761, P<0.001) and chewing gum (R=0.785, P<0.001). CONCLUSIONS: The results suggested that the measurement of EMG activity from the bilateral masseter muscles may be a useful method for the objective determination of the actual chewing side during mastication.

Comparative cross-sectional study of masticatory performance and mastication predominance for patients with missing posterior teeth.

PURPOSE: Missing posterior teeth can decrease masticatory function and cause horizontal mastication deviation, i.e., mastication predominance. Mastication predominance may lead to abnormal tooth attrition and temporomandibular disorders. This study evaluated masticatory performance and mastication predominance in patients with missing posterior teeth to investigate effects of missing posterior teeth on masticatory performance and mastication predominance. METHODS: Thirty volunteers with normal dentition (control group), 30 patients with unilateral missing posterior teeth (unilateral group), and 23 patients with bilateral missing posterior teeth (bilateral group) participated. Gummy jellies were used to evaluate participants' masticatory performance, and electromyography was used to assess the degree of mastication predominance. Chewing gums, gummy jellies, and peanuts were used as foods of various hardnesses for evaluating mastication predominance. RESULTS: Compared with the control group, masticatory performance did not differ in the unilateral group but was significantly decreased in the bilateral group. With chewing gum and gummy jellies, the degree of mastication predominance was significantly increased in both unilateral and bilateral groups than the control group. With peanuts, the degree of mastication predominance was significantly increased in the unilateral group than the control group. CONCLUSIONS: Although masticatory performance was not decreased in the unilateral group, the degree of mastication predominance was increased. Decreased masticatory performance was observed in the bilateral group, and for foods with normal hardness and soft foods, the degree of mastication predominance was increased. These results suggested that mastication predominance should be considered in the recovery of masticatory performance in patients with missing posterior teeth.