Prosthodontic treatment can improve the ingestible food profile in Japanese adult outpatients.

PURPOSE: To investigate the effect of prosthodontic treatment on the ingestible food profile in adult Japanese outpatients, and to identify the related risk factors that can deteriorate the profile. METHODS: The participants were 277 outpatients who visited university-based specialty clinics in Japan for prosthodontic treatment. The demographic data, number of present teeth assessed via intraoral examination, and oral health-related quality of life assessed by the total Oral Health Impact Profile (OHIP-J54) scores of all participants were recorded before treatment. Ingestible food profile score (IFS) was recorded using a validated food intake questionnaire. Eligible participants who answered the questionnaire before and after treatment were categorized into five groups based on the prosthodontic treatments they received (i.e., crowns, bridges, removable partial dentures, removable complete dentures, and removable complete and partial dentures). RESULTS: Multivariate analysis of covariance revealed a statistically significant main effect of prosthodontic intervention (time course: before and after treatment) on mean IFS (P=0.035, F=4.526), even after adjusting for covariates (age, number of present teeth, and treatment modality). Multiple linear regression analysis revealed that the low number of present teeth (r=0.427, P<0.001) and a high OHIP-J54 total score (r=-0.519, P<0.001) of the patients at the baseline were significantly associated with their baseline IFSs, even after adjusting for confounding variables. CONCLUSIONS: The findings of this multicenter follow-up study indicate the importance of prosthodontic rehabilitation in improving patients' ingestible food profiles.

Development of Innovative Contra-angle Handpiece Device with Piston Movement for Root Canal Preparation.

INTRODUCTION: The purpose of this study was to assess the optimal amplitude and weight of the newly developed contra-angle handpiece. The handpiece uses piston movement without using an endodontic motor and enables a safe, quick, and reliable canal preparation. METHODS: A prototype handpiece was designed. Instrumentation was performed on root canal resin blocks by 20 operators in 3 groups: the prototype handpiece with an H file (a stainless steel #25 manual H file, the piston group), a manually standardized technique with a K file (stainless steel #15-25 K files, the manual group), and a nickel-titanium (NiTi) reciprocating file with an endodontic motor (Reciproc Blue R25 [VDW, Munich, Germany], the NiTi group). Transportation of the canal center line and the time required for preparation were measured and statistically analyzed. RESULTS: The optimal condition was an amplitude of 1.35 mm and a weight of 61.0 g. Transportation of the canal center was observed in all groups. A statistically significant difference was found at 2.0-3.0 mm from the apical foramen between the piston or NiTi group and the manual group, but no significant difference was found between the piston and NiTi groups. The least transportation was found in the NiTi and piston groups. The handpiece with a #25 H file demonstrated a good centering ability, similar to the NiTi file, which enabled speedy preparation. The time required for preparation between the piston or NiTi group and the manual group was statistically different. No significant difference was observed between the piston and NiTi groups (P < .05). CONCLUSIONS: We concluded that the newly designed handpiece achieved efficient canal preparation and negotiation. The handpiece could avoid endodontic accidents, including ledge formation, instrument separation, and perforation.

In vitro wear behavior of restorative resin composites against bovine enamel.

The purpose of this study was to clarify the effects of fabrication method of restorative resin-based composites on its wear using enamel as antagonist teeth. Wear evaluation was performed via two-body wear test using hemispherical samples of restorative resin-based composite (abrader specimen) fabricated through direct restoration method, indirect restoration method, and CAD/CAM, and bovine enamel (substrate specimen). As a result, there was a difference in wear volume between resin-based composite and bovine enamel depending on the fabrication method. Resin composite used for indirect restoration method showed more wear in both the abrader and substrate specimens. Resin composite used for CAD/CAM crowns showed greater wear volume in the abrader specimen. In conclusion, results clarified that fabrication method of restorative resin-based composite has an influence on the wear of the resin composite itself and enamel as antagonist teeth.

A multi-centered epidemiological study evaluating the validity of the treatment difficulty indices developed by the Japan Prosthodontic Society.

PURPOSE: The Japan Prosthodontic Society developed a multi-axis assessment protocol to evaluate the complex variations in patients who need prosthodontic care, and to classify the level of treatment difficulty. A previous report found the protocol to be sufficiently reliable. The purpose of this multi-center cohort study was to evaluate the validity of this multi-axis assessment protocol. METHODS: The treatment difficulty was evaluated using the multi-axis assessment protocol before starting prosthodontic treatment. The time required for active prosthodontic treatment, medical resources such as treatment cost, and changes in the oral health-related QOL before and after treatment, were evaluated after treatment completion. The construct validity of this protocol was assessed by the correlation between the dentist's pre-operative subjective assessment of the treatment difficulty, and the level of difficulty determined by this protocol. The predictive validity was assessed estimating the correlations between a "comprehensive level of treatment difficulty" based on the four axes of this protocol and total treatment cost, total treatment time, and changes in the oral health-related QOL before and after treatment. RESULTS: The construct validity of this protocol was well documented except for psychological assessment. Regarding the predictive validity, the comprehensive level of treatment difficulty assessed before treatment was significantly correlated with the three surrogate endpoints known to be related to the treatment difficulty (total treatment cost, treatment time, and improvement in the oral health-related QOL). To further clarify the validity of the protocol according to patients' oral condition, a subgroup analysis by defects was performed. Analyses revealed that treatment difficulty assessment before treatment was significantly related to one or two surrogate endpoints in the fully edentulous patients and the partially edentulous patients. No significant relationship was observed in the patients with mixture of full/partial edentulism and the patients with teeth problems, possibly due to the small sample size in these groups. CONCLUSION: This study revealed that the multi-axis assessment protocol was sufficiently valid to predict the level of treatment difficulty in prosthodontic care in patients with fully edentulous defects and with partially edentulous defects.

Effects of polymerization shrinkage on the interfacial stress at resin-metal joint in denture-base: a non-linear FE stress analysis.

OBJECTIVES: The purpose of this study was to investigate the effects of polymerization shrinkage on stress at the interface between resin and metal in removable dentures. METHODS: Three-dimensional finite element models of a denture-base were studied, which consisted of acrylic occlusal rims with different heights and metal frameworks. A relaxation modulus of 1.5 GPa for the resin and a Young's modulus of 220 GPa for the metal were used as the material properties. Each model was constrained at the edge of the framework on the palatal vault. Surface-to-surface contact elements were used to calculate the interfacial stress in a direction perpendicular to the bond surface under a linear shrinkage ranging from 0.41 to 0.65%. The principal stress within the resin was also calculated. RESULTS: The maximum interfacial and principal stresses within the denture-base increased with resin shrinkage. Under the lowest linear shrinkage, the mean area percentages in the resin-metal joint that showed interfacial tensile stresses over 10 and 20 MPa were 63.4 and 0%, respectively. While under the highest linear shrinkage, these mean area percentages were 98.8 and 38.1%, respectively. Negligible differences in the stresses were shown by occlusal heights. SIGNIFICANCE: The polymerization shrinkage level has a significant influence on the residual stress at the resin-metal interface. Enhancement of the bond strength on the interface can reduce the failure probability at a resin-metal joint.

Do patients have a preference for major connector designs?

AIM: The aim of this research was to evaluate patients' preferences for resin analogs of four major connector designs formulated to have equal rigidity once fabricated in the same alloy. METHODS AND MATERIALS: Nineteen Kennedy Class I or II partially edentulous patients participated at two centers. The four major connector analogs (MCAs) were fabricated for each subject using light-polymerizing acrylic resin. The subjects were asked to wear each of them in the mouth for 30 seconds in six pairs in random order, and to report their preference for each pair. Based on these data, the four analogs were ranked in a descending preference order for each patient. Within-subject comparisons preferences were performed with the Friedman test, and the multiple comparisons were performed with the Wilcoxon Signed Ranks test for data of each sample independently. RESULTS: Statistically significant and consistent preference orders were revealed for both samples, and the thin and wide design was significantly preferred to the thick and narrow design. However, a higher variation was observed for the first preference of each subject. CONCLUSIONS: Subjects demonstrated a tendency to prefer thinner MCAs. However, the individual predilections of patients may not be an appropriate basis for an attempt to find a 'best design' applicable to all patients.

Association between masseter muscle activity levels recorded during sleep and signs and symptoms of temporomandibular disorders in healthy young adults.

AIMS: To examine whether any signs and symptoms of temporomandibular disorders were significantly associated with masseter muscle activity levels during sleep. METHODS: One hundred three healthy adult subjects (age range, 22 to 32 years) participated in the study. They were asked to fill out questionnaires, undergo a calibrated clinical examination of their jaws and teeth, and perform 6 consecutive nightly masseter electromyographic (EMG) recordings with a portable EMG recording system in their home. The EMG data were considered dependent variables, while the questionnaire and examination data were considered independent variables. Multiple stepwise linear regression analysis was utilized to assess possible associations between these variables. RESULTS: Both gender and joint sound scores were significantly related to the duration of EMG activity. None of the other independent variables were found to be related to any of the muscle activity variables. CONCLUSION: The results suggest that both gender and clicking are significantly related to duration of masseter EMG activity during sleep.

Stress analysis in edentulous mandibular bone supporting implant-retained 1-piece or multiple superstructures.

PURPOSE: The aim of this study was to investigate the stress distribution in mandibular bone supporting a single or separate multiple implant-retained superstructures. MATERIALS AND METHODS: Three-dimensional finite element models consisting of the mandibular bone, 8 implants, and 1 or more superstructures were created. Vertical and oblique loads were directed onto the occlusal areas of the superstructures to simulate the maximum intercuspal contacts and working contacts, such as the canine-protected and group function occlusion. RESULTS: The unseparated 1-piece superstructure generated the lowest maximum equivalent stresses in the peri-implant bone, followed by the 2-piece superstructure separated at the midline. For the 3-piece superstructure, which was separated between the canine and the premolar, the maximum stress was lower when the canine on the working side was loaded than when the posterior teeth were loaded. DISCUSSION: Separating the 1-piece superstructure into 2- to 4-piece superstructures increased the mechanical stress around supporting implants. Canine load on the working side is distributed well in 1-piece and 3-piece superstructures. CONCLUSION: Based on the results of this finite element model study, canine protected occlusion is recommended for 1-piece and 3-piece superstructures. The unseparated superstructure was more effective in relieving stress concentration in the edentulous mandibular bone than the separated superstructures.

Patients' preference for acrylic resin major connector analogues formulated for titanium alloy removable partial dentures.

PURPOSE: Aim of this study was to determine patients' preference to acrylic resin major connector analogues (MCA) that simulated strengthened major connector designs formulated for Ti-6Al-7Nb alloy. MATERIALS AND METHODS: Four MCA namely wide design (Wide), design with 2 strengthening ridges (2SR), design with 1 strengthening ridge (1SR), and thick design (Thick) were fabricated using light-polymerizing acrylic resin for 10 patients with Kennedy Class I or II partially edentulous maxillary arches. They were asked to wear each MCA in the mouth for 30 seconds in 6 pairs, and to report their preference for each pair. Using these data the 4 MCA were ranked in a descending preference order for each patient. A within-subject comparison of preferences was performed with the Friedman test and multiple comparisons with Wilcoxon Signed Ranks test. RESULTS: A statistically significant preference order was revealed: Wide, 1SR, 2SR, and Thick (P < 0.008). The wide design (P < 0.004) and the 1SR (P < 0.01) were significantly preferred to the thick design. However, individual data showed that the first preference varied depending upon the subject. CONCLUSION: Thinner designs tended to be preferred to the thicker design by the subjects, while none of the designs tested were consistently selected as the best design.

Masticatory function after unilateral distal extension removable partial denture treatment: intra-individual comparison with opposite dentulous side.

Due to large individual differences of masticatory function, an inter-individual comparison between denture patients and complete dentate people would be insufficient. This cross-sectional study aimed to evaluate patients' masticatory performance (determined by Mixing Ability Index, MAI) and bite force (determined by maximum bite force, MBF) after removable partial denture (RPD) treatment by comparing those of the RPD replaced side with those of their own opposite dentulous side, and to evaluate influence of bite force on masticatory performance in different dentitions. Subjects included patients with unilateral distal extension RPDs (n=28). Apart from the RPD replaced area on one-side, all subjects had intact dentitions. Both masticatory parameters were evaluated separately on each chewing side. MAls and MBFs obtained from the RPD replaced side (0.65 +/- 0.50 and 220 +/- 155 N, mean +/- SD) were significantly lower than those from the dentulous side (1.06 +/- 0.64 and 450 +/- 268 N; Wilcoxon signed-ranks, P < 0.001). MBF significantly influenced MAI in both RPD replaced (Univariate linear regression; R2 = 0.17, P < -0.001) and dentulous sides (R2 = 0.51, P < 0.001). After RPD treatment, masticatory performance and bite force of RPD replaced side were lower than those of their own dentulous side. The influence of the bite force on masticatory performance in RPD replaced side was less significant than that in the dentulous side.

[Sensory perceptive and discriminative abilities of patients with occlusal dysesthesia].

PURPOSE: It is not rare for dentists to come across patients who complain of several uncomfortable feelings of occlusion despite the absence of any observable occlusal anomaly or discrepancy. These kinds of symptoms are well defined by the term "occlusal dysesthesia" (OD). This study evaluated the occlusal perceptive and discriminative abilities in OD patients. METHODS: The sensory perceptive and discriminative abilities were tested in 8 OD patients and 31 healthy subjects as controls. All of these subjects went through three types of tests: 1) thickness discrimination test by using occlusal registration foils, 2) thickness discrimination test by using bite block, and 3) mouth opening reproducibility test. RESULTS: The median of the foil thickness discrimination ability of the control group was 14 microm and that of the patient group was 8 microm. In the bite block thickness discrimination test, both groups showed less than +/- 1mm thickness discrimination ability on average and were able to reproduce pre-indicated mouth opening with less than 10% error. There was no significant difference in these study results between the two groups. CONCLUSIONS: Sensory perceptive and discriminative abilities of OD patients were not significantly different from those of the healthy subjects in this study sample.

Bruxism force detection by a piezoelectric film-based recording device in sleeping humans.

AIMS: To test the reliability and utility of a force-based bruxism detection system (Intra-Splint Force Detector [ISFD]) for multiple night recordings of forceful tooth-to-splint contacts in sleeping human subjects in their home environment. METHODS: Bruxism-type forces, i.e., forceful tooth-to-splint contacts, during the night were recorded with this system in 12 subjects (6 bruxers and 6 controls) for 5 nights in their home environment; a laboratory-based nocturnal polysomnogram (NPSG) study was also performed on 1 of these subjects. RESULTS: All 12 subjects were able to use the device without substantial difficulty on a nightly basis. The bruxer group exhibited bruxism events of significantly longer duration than the control group (27 seconds/hour versus 7.4 seconds/hour, P < .01). A NPSG study performed on 1 subject revealed that, when the masseter muscle electromyogram (EMG) was used as a "gold standard," the ISFD had a sensitivity of 0.89. The correlation coefficient between the duration of events detected by the ISFD and the EMG was also 0.89. CONCLUSION: These results suggest that the ISFD is a system that can be used easily by the subjects and that has a reasonable reliability for bruxism detection as reflected in forceful tooth-to-splint contacts during sleep.

Influence of length of food platform on masticatory performance in patients missing unilateral mandibular molars with distal extension removable partial dentures.

Reduction of the size of food platform of a distal extension removable partial denture has been recommended to decrease functional load on the abutment teeth and residual ridges. The purpose of this study was to investigate the influence of shortening food platform on masticatory performance. Eight subjects unilaterally missing mandibular molars participated in the study. A unilateral design was used for the denture framework. The length of the food platform was changed as follows. Initially, (A) was adjusted so that the distal end of the platform was in accordance with the distal end of maxillary second molar. Next, the platform was shortened successively to 15 mm (B) and 10 mm (C). Subjects were asked to masticate 2-colored wax cubes to evaluate masticatory performance. Mixing Ability Index was calculated from the color mixture and the form of masticated cubes. Repeated measures one-way ANOVA indicated significant difference of Mixing Ability Index among platforms (P < 0.0001). The Dunnett's test indicated no significant difference between A (1.27 +/- 0.29) and B (1.36 +/- 0.29), and a significant difference between A and C (0.89 +/- 0.30), (P < 0.001). Masticatory performance decreased significantly when the length of food platform was shortened to 10 mm.

Reproducibility of interocclusal recording for mandibular removable partial denture in bilateral distal extension cases.

Interocclusal recording for removable partial denture in bilateral mandibular distal extension were evaluated for the differences of the interocclusal recording material utilized during different impression techniques. The purpose of this study is to develop interocclusal recording utilizing occlusion rims with high accuracy. The intraoral model with urethane rubber mucosa with 3 metallic spheres as measuring points was utilized. With the applied pressure (functional) and minimum pressure (anatomical) impression techniques, working casts were fabricated. Interocclusal recording was registered with the occlusion rim on the intraoral model unto the articulator by applying the interocclusal materials; paraffin wax (PW), ALUWAX (AW), impression paste (IP) and Exabite II (EB). Analyses were conducted with the three-dimensional analyzer and calculated for the amount of vertical and antero-posterior displacement between the intraoral model and the working cast. The results were that PW had the greatest displacement, especially with the functional impression technique, while AW had minimum displacement especially in the posterior direction. With the functional impression technique utilizing AW was revealed to minimize the amount of interocclusal displacement.

Influence of loading positions of mandibular unilateral distal extension removable partial dentures on movements of abutment tooth and denture base.

PURPOSE: The aim of our study was to explore the effects of different loading positions on the movements of the abutment tooth and denture base of removable partial denture with unilaterally designed framework (RPD-U). MATERIALS AND METHODS: The experiment was carried out with a simulation model of a mandible without left molars. The movements of abutment tooth and denture base of the unilateral and bilateral designs were due to 30N vertical load on 12 loading positions determined with a strain gauge circuitry. The effects of loading positions on the movements of the abutment tooth and denture base were compared between two designs. RESULTS: During the loading on buccal, lingual positions, and the most disto-central position the movements of the abutment tooth and denture base of the unilateral design were significantly greater than those of the bilateral design (P < 0.01). During the loading on the three mesio-central positions the movements of the abutment tooth and denture base were equal between designs, and were significantly lower than during the loading on the other positions (P < 0.01). CONCLUSION: Ending the denture teeth at the mesial cusp of second molar and positioning the occlusal contacts over the ridge crest adequately stabilize the abutment tooth and denture base of RPD-U.

Electromyographic evaluation of masticatory function in denture wearers in related to existing occlusal support.

The aim of this study was to clarify the relationship between partially edentulous pattern and the masticatory function in removable partial denture wearers. Eighty eight removable partial denture wearers and 7 subjects with intact dentition volunteered for this study. Using the Eichner's index, all subjects were divided into 6 groups. Electromyographic (EMG) activities of the masticatory muscle were recorded during chewing a piece of raw carrot. The masticatory function was analyzed by using the variation coefficient (VC) of the time parameter of EMG interval recorded during mastication. The association of the VC with group classification based on Eichner's index was analyzed using analysis of covariance with gender and age as the covariates. The result of the analysis revealed that the VC was significantly associated with group classification and the patients in groups without posterior occlusal supports exhibited significantly higher VC values than those in groups with posterior occlusal supports. These findings suggested that the reduced function in patients without the posterior occlusal contacts was difficult to attain improved and satisfactory outcome with removable partial dentures and that there is a significant need for posterior occlusal support for the preservation of masticatory function.

Study on the effects of shortening the distal end of a mouthguard using modal analysis.

Using a modal analysis system, we carried out a comparative assessment of the vibratory properties of the maxillary dentition of a human dry skull with a different distal end of a mouthguard. Mouthguards used in this study were: 1. a mouthguard covering up to the third molar (8MG), 2. the second molar (7MG), 3. the first molar (6MG), and 4. the second premolar (5MG). To identify the modal shape, the frequency response functions were recorded on a fast Fourier transform analyzer from the force signal impacted with a vibration generator and the response signal picked up using a laser-doppler vibrometer. The transient response waves were obtained throughout the transient response simulation procedures after curve-fitting procedures. Mean decay rates (sec(-1)) of the transient response waves were calculated for the anteriors, premolars and molars, and compared among different sets of experimental conditions. The decay rates became lower as the distal end of a mouthguard was short. The decay rates with 8MG, 7MG and 6MG (anteriors) exceeded the no mouthguard's decay rate + 2S.D. values. These results imply that a mouthguard should distally cover up to the second molar at least to ensure efficient absorption and/or dispersion of a traumatic force.

The effects of loading locations and direct retainers on the movements of the abutment tooth and denture base of removable partial dentures.

The purpose of this study was to evaluate the degree and amount of movement of the abutment tooth and denture base influenced by the direct retainer of distal extension removable partial denture and the location of functional loading, then to suggest direct retainer design with minimal adverse effect and with optimum functional loading location for residual tissue. The displacement of the abutment tooth and inclination of the denture base were determined, with 30 N as work load utilizing simulation model and strain gauge system, about two types of direct retainers with mesial or distal rest and nine loading points on denture base. Displacement and inclination was determined with the one-way analysis of variance and Scheffe's multiple test was performed. The results revealed that type of direct retainer influenced on the magnitude rather than direction of the abutment tooth displacement. The distal displacement of abutment tooth was significantly less in Type M clasp (with mesial rest and connection) than in Type D clasp (with distal rest and connection) (p<0.05). The location of loading points influenced both of the magnitude and direction of the abutment tooth and denture base movement. Posterior and lingual loading resulted in significantly distal displacement of abutment tooth (p < 0.05).

Vibration analysis of obturator prostheses with different bulb height designs.

The purpose of this study was to investigate the effect on the vibratory characteristics of a cast hollow obturator prosthesis retainer when varying its bulb height. Bulb parts with high (H), middle (M), and low (L) lateral walls were prepared. A Vibration Generator was used to excite the three obturators, while a Laser-Doppler Vibrometer was employed to detect the vibrations at specified measurement points. The frequency response functions of each obturator were recorded on an FFT analyzer to enable their modal shapes to be identified. In addition, transient response simulations were carried out and the decay rate (DR) and the maximum amplitude (MA) of the rest and clasp parts of each obturator were obtained. These were statistically analyzed by ANOVA and Fisher's PLSD test (p < 0.01). The modal shapes were almost the same in all obturators. Significant differences were found in DR in all pairs among the three obturator prostheses, with the DR of the L type being the highest. On the other hand, there were no significant differences in MA. We conclude that the L type is preferable from the standpoint of its vibratory characteristics.

Complete denture treatments for a cerebral palsy patient by using a treatment denture. A case report.

This article describes the prosthodontic treatment for a patient with cerebral palsy, in which complete dentures were successfully stabilized using treatment dentures. A 69-year-old edentulous male with no medical complications or mental retardation presented to our clinic. Opening movement of the jaw was possible, but a conspicuous mandibular shift towards the right was observed. He had never received any prosthodontic treatment. Initially, treatment dentures with flat tables were fabricated to rectify his erratic mandibular movements. During the first 3 weeks, the treatment dentures functioned poorly. Eventually, the patient could make tapping movement to some degree and have a meal with less effort. Indentation marks from the cusps of the opposing maxillary denture could be clearly seen on the flat tables. After six weeks, as he did not complain of any pain, definitive dentures were fabricated. When flat table treatment dentures are used, it is considered that the mucosa provides information regarding the vertical stop and bite force. In addition, it is speculated that there is an increase in the response from masseter muscle. In the present case, flat tables were effective for rehabilitation of the mandibular movement.