Clinical Trial for Evaluating the Effectiveness and Safety of a New Dental Plaque Removal Device: Microscale Mist Unit.

This study evaluates the effectiveness and safety of a microscale mist unit (MSM-UNIT) that sprays high-speed fine water droplets to remove dental plaque adhering to the oral mucosa (tongue and palate) and tooth surface. Fifteen patients who had difficulty self-managing sufficient oral care were included in this study. Effectiveness was evaluated for at least five patients' tongues, palate mucosas, and tooth surfaces, and safety evaluation was conducted at all three sites for all patients. Effectiveness was evaluated using the rate of degree of dental plaque removal. Safety was evaluated using a numerical rating scale (NRS) for pain and symptoms of inflammation. An operator who performed treatment and an evaluator who evaluated effectiveness and safety were designated. In addition, an image judgment committee judged effectiveness. Although evaluation of the tongue varied between the evaluators and the image judgment committee, the rates of degree for all plaque removal increased in all regions. In addition, low pain NRS results and minimal symptoms of inflammation were observed and within an acceptable range. The MSM-UNIT can be used effectively and safely for removing oral plaque not only from teeth, but also from the oral mucosa.

Morphological comparison of masseter muscle fibres in the mandibular rest and open positions using diffusion tensor imaging.

BACKGROUND: The masseter muscle has a complicated multipennate internal structure and exhibits functional differentiation when performing various stomatognathic functions. It is important to understand the internal structural changes of the muscle during functioning to elucidate characteristic muscle disorders such as local myalgia. Diffusion tensor imaging (DTI) may be useful for investigating the internal structural features of muscle. OBJECTIVES: To evaluate the features of masseter muscle fibres in human participants using DTI fibre tractography, and to elucidate the structural differences in the masseter muscle between the mandibular rest and open positions. METHODS: Five healthy men (age 31 ± 7 years) underwent DTI and T1-weighted MRI of the right masseter muscle in the mandibular rest and open positions. MR images were used as a reference for muscle layer segmentation (superficial, intermediate, and deep). DTI fibre tractography of the masseter muscle was performed and the orientation of the DTI fibres was analysed in each layer using coordinates based on the Frankfurt horizontal plane. RESULTS: The DTI fibre orientation of the deep layer significantly changed between the mandibular rest and open positions in the frontal plane (p < 0.05, Wilcoxon rank sum test). However, no significant change was found in the superficial and intermediate layers. CONCLUSION: DTI fibre tractography confirmed regional differences in the orientation change of the masseter muscle fibres between different mandibular positions. The results may support the existence of functional partitioning inside the masseter muscle and suggest that DTI may be useful for the evaluation of muscle fibres in multipennate muscles.

Application of Diffusion Tensor Imaging Fiber Tractography for Human Masseter Muscle.

Diffusion tensor imaging (DTI) has been used to indicate the direction of nerve and muscle fibers by using the characteristics that water molecules preferentially diffuse along the fibrous structure. However, DTI fiber tractography for multipennate muscles, such as the masseter muscle, is challenging due to a lack of data regarding the imaging parameters. This study aimed to determine the optimal DTI parameters for masseter muscle fiber tractography. A 27-year-old healthy man voluntarily underwent DTI and T1-weighted magnetic resonance imaging of the right masseter muscle. Four imaging parameter settings were created by combining the following parameters that particularly affect the signal-to-noise ratio: b-value, number of excitations (NEX), and number of motion probing gradient (MPG) directions. DTI fiber tractography was performed using specific software for each parameter setting. The length and orientation of the muscle fibers in each layer were calculated. As a result, the masseter muscle fibers of each layer were identified on DTI. Although the detected fiber length was affected significantly by the imaging parameters, the fiber orientation was insignificantly affected. The appropriate combination of the b-value, NEX, and the number of MPG directions for masseter muscle fiber tractography could be determined based on previously reported anatomical data of the masseter muscle fibers. DTI may enable the non-invasive evaluation of masseter muscle fiber length and orientation. Elucidation of the details of masseter muscle fiber orientation is useful in evaluating stomatognathic biomechanics and muscle disorders.

Osteogenic effect of low-intensity pulsed ultrasound and whole-body vibration on peri-implant bone. An experimental in vivo study.

OBJECTIVES: The aims of this study were (i) to compare the osteogenic impact of low-intensity pulsed ultrasound (LIPUS) and low-magnitude high-frequency (LMHF) loading achieved with whole-body vibration (WBV) on peri-implant bone healing and implant osseointegration in rat tibiae, and (ii) to examine their combined effect on these processes. MATERIAL AND METHODS: Titanium implants were inserted in the bilateral tibiae of 28 Wistar rats. Rats were randomly divided into four groups: LIPUS + WBV, LIPUS, WBV, and control. LIPUS was applied to the implant placement site for 20 min/day on 5 days/week (1.5 MHz and 30 mW/cm2 ). WBV was applied for 15 min/day on 5 days/week (50 Hz and 0.5 g). In the LIPUS + WBV group, both stimuli were applied under the same stimulation conditions as in the LIPUS and WBV groups. After 4 weeks of treatment, peri-implant bone healing and implant osseointegration were assessed using removal torque (RT) tests, micro-CT analyses of relative gray (RG) value, and histomorphometrical analyses of bone-to-implant contact (BIC) and peri-implant bone formation (BV/TV). RESULTS: The LIPUS + WBV group had significantly greater BIC than the WBV and control groups. Although there were no significant intergroup differences in RT, RG value, and BV/TV, these variables tended to be greater in the LIPUS + WBV group than the other groups. CONCLUSIONS: The combination of LIPUS and LMHF loading may promote osteogenic activity around the implant. However, further study of the stimulation conditions of LIPUS and LMHF loading is necessary to better understand the osteogenic effects and the relationship between the two stimuli.

Tightening and Loosening of the Abutment Screw Negatively Affects Implant Osseointegration in the Early Healing Stage in Rat Tibiae.

PURPOSE: To examine the effect of tightening and loosening the dental implant screw on implant osseointegration in an elderly rat model. MATERIALS AND METHODS: Titanium dental implants were inserted in the bilateral tibiae of 34 elderly Wistar rats (1 year and 3 months old). Rats were randomly divided into five groups: control (no loading); immediate loading (IL) (vertical load [3 Hz for 15 minutes/day] immediately after implantation); early loading (EL) (load started on postoperative day 7); five times abutment removal (R5) (tightening and loosening of the abutment screw once per day for 5 days each week); and two times abutment screw removal (R2) (tightening and loosening of the abutment screw once per day for 2 days each week). After 4 weeks, the rats were euthanized, and the bone structure surrounding the dental implants was evaluated using microcomputed tomography analysis. RESULTS: Osseointegration failed more frequently in the EL, R2, and R5 groups than in the control and IL groups (P = .06). The EL, R2, and R5 groups also tended to have lower relative gray values than the control and IL groups. CONCLUSION: Tightening and loosening the abutment screw might negatively affect dental implant osseointegration in the early healing stage in older adults.

Evaluation of implant screw loosening by resonance frequency analysis with triaxial piezoelectric pick-up: in vitro model and in vivo animal study.

OBJECTIVE: The aim of this study was to evaluate implant screw loosening using resonance frequency (RF) analysis with triaxial piezoelectric pick-up in vitro and in vivo. METHODS: For the in vitro experiment, a titanium implant was inserted into a mandibular model. The abutment screws were tightened to 10 N torque and loosened from 0 to 90° for RF measurement using 13 different screw conditions. In the in vivo experiment, three titanium implants were installed in each tibia of a New Zealand white rabbit, and the RF values were recorded after 8 weeks. For the RF analyses, a small 3D accelerometer was mounted rigidly onto the implant abutment, and impulsive vibration was directly applied to the abutment to vibrate the implant in a direction perpendicular to the tibia and implant (x-axis). The y-axis was defined as parallel to the tibia. The RF values of the x- and y-axis directions (RF-X and RF-Y) were used for evaluation. RESULTS: The RF values significantly decreased according to the degree of screw loosening (p < 0.05, ANOVA). In the in vitro model, RF-Y with x- and y-axis vibrations (RF-Yx and RF-Yy) significantly differed from the initial value at 10 and 15°, respectively (p < 0.05, Dunnett's test). In the in vivo experiment, the RF-Yy significantly differed from the initial value between 5 and 20° (p < 0.05). CONCLUSION: The results suggest that RF analysis with triaxial piezoelectric pick-up can be used to detect implant screw loosening. CLINICAL RELEVANCE: RF analysis with the triaxial piezoelectric pick-up can be used to detect screw loosening after mounting the superstructure.

Na18F accumulates on the compressive side of peri-implant bone under immediate loading.

This study aimed to examine the dynamic change in bone metabolism by immediate loading in several sites around implants using high-resolution Na18F-PET scan. Two titanium implants (Ø 1.2 mm) were inserted parallel to each other in the right tibiae of Wistar rats (n = 4). The left tibia was set as control side. One day after insertion, closed coil springs of 4.0 N were attached to the expose superior portions of the implants to apply a continuous mechanical stress. The rats with fluorine-18 (18F) ion (5 mCi/rat) intravenously injected were scanned by PET scanner at 4, 7, 14, 28 days after load application. Round region of interests (ROIs) were set around the distal implant of the right tibia (loaded side) and same site (control) of the left tibia. Furthermore, four rectangular ROIs were set at the superior and inferior parts of traction side (mesial) and opposite side (distal) of the distal implant. Longitudinal dynamic changes in bone metabolism were evaluated by examination of the accumulation count of 18F ion at each ROI. The uptake values of ROIs (loaded side) initially increased until 7 days, and they gradually decreased from the peak level to the pre-loading level despite a static force being applied to the implants. In cancellous bone, the uptake values at the superior part of traction side and inferior part of opposite side showed significantly high value compared with those at other parts. In conclusion, immediate loading to the implant initially enhanced bone metabolism around it, especially at the part with compressive stress. Peri-implant bone metabolism varies according to different loading conditions.