Purpose: The purpose of this study was to compare the stress transfer from a fixed restoration, supported by an implant restored with either a segmented or non-segmented implant abutment, connected to a simulated tooth with decreased foundational support by photoelastic evaluation.
Methods: A photoelastic model of a human left mandible, edentulous posterior to the first premolar, was fabricated, with a 3.75×13 mm screw-type implant embedded within the edentulous area. The edentulous areas were restored with a three-unit fixed prosthetic restoration with the distal implant abutment connected to the simulated tooth abutment. The implant abutments consisted of either a segmented conical abutment or a non-segmented UCLA abutment. A hemiseptal periodontal defect was created by the removal of buccal and disto-buccal tissues to simulate decreased support caused by a 4 mm infrabony defect. Vertical occlusal loads were applied at fixed locations on the restorations for the simulated periodontal condition. The stresses which developed in the mandible were monitored photoelastically and recorded photographically.
Results: Decrease of the foundational support of the tooth resulted in higher stresses transferred to the mesial and apical aspects of the implant as compared with those in the non-defect control condition. Similar results were obtained for both segmented and nonsegmented abutment restorations.
Conclusion: Within the limitations of this study, application of load to the simulated abutment teeth with decreased periodontal support resulted in higher stresses around the supporting implant structure for both abutment designs. The distribution and intensity of the stresses were similar for segmented and nonsegmented abutments.

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Purpose: The purpose of this study was to evaluate the feasibility of formation of thin film coatings of bioactive ceramics, such as β-tricalcium phosphate (β-TCP), by radio frequency (RF) sputtering. In this paper, we report the results of our preliminary attempts, as a trial of this concept, to use radio frequency sputtering for obtaining thin film coatings of a ceramic substance on a quartz glass substrate.
Methods: We attempted to obtain a thin film coating of β-TCP on a quartz glass surface using an RF sputtering deposition system (L-332S-5FHS, ANELVA, Japan). We examined the thickness of the films deposited on the quartz glass substrate with a confocal laser scanning microscope and characterized the films by electron probe microanalysis (EPMA), scanning electron microscopy (SEM), X ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analysis.
Results: The films were found to be about 0.51 μm in thickness. Although our attempt was directed at obtaining a β-TCP coating on the quartz glass surface, the resultant film consisted of Ca and P in the ratio of 3:1, and was almost amorphous. However, the Ca and P were uniformly distributed on the surface of the films, confirming the feasibility of using an RF sputtering system to obtain a homogeneous film coating.
Conclusion: Our results suggest that RF sputtering may be a feasible technique for the preparation of ceramic coatings.

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Purpose: The purpose of this study was to elucidate the influence of teeth clenching on the head posture and body sway during an impact lord to the greater trochanter of the femur.
Methods: The sternocleidomastoid muscle activities, head posture, and the total locus length of head movement and body sway during and in the absence of a striking weight impact under the resting position of the mandible and during 50% and 100% voluntary maximal clenching were analyzed.
Results: 1) The activity of the sternocleidomastoid muscles increased with the teeth clenching force, and the increase was greater during a striking weight impact than that in the absence of a striking weight impact. 2) The decrease in the lateral bending and rotation angles of the neck observed during a striking weight impact was greater under the voluntary teeth clenching conditions as compared with that under the resting position of the mandible. 3) The total locus length of the head movement and body sway were shorter under the voluntary teeth clenching conditions as compared with that under the resting position of the mandible. 4) In contrast to the observations under the resting position of the mandible during a striking weight impact, the ratio of the total locus length of the head movement to that of the body sway under the voluntary teeth clenching during a striking weight impact decreased to the level noted under the resting position of the mandible in the absence of a striking weight impact.
Conclusion: The results of this study suggest that teeth clenching stabilizes the head in cooperation with the activities of the sternocleidomastoid muscles, and prevents excessive head movement and body sway during a striking weight impact.

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Purpose: This study was conducted to determine the esthetically acceptable range of deviation of the midline position and incisal inclination of complete dentures, based on the results of esthetic evaluation conducted under various midline positions and degrees of incisal inclination in complete denture wearers. In addition, the influence of anatomic landmarks of the face in the evaluation of the midline position was also examined.
Methods: Frontal pictures of each of 10 complete maxillomandibular denture wearers were taken, with the lips opened in the intercuspal position. Each image was processed to yield 21 images with varying midline positions (±2.5 mm at 0.5-mm intervals) and varying degrees of incisal inclination (±2.5 degrees at 0.5-degree intervals) for evaluation. These images were presented to the examiners (20 dentists and 20 dental students), who gave a score of 0 to the images that appeared esthetically unacceptable, 1 to those that appeared neutral, and 2 to those that appeared esthetically acceptable. The scores of each image were totalled to yield the natural appearance score. We checked for significant differences in the natural appearance score between control images and each of the images evaluated in this study.
Results: No significant difference in the natural appearance score was noted when the midline deviation was within ±1 mm (in the evaluation by dentists) or ± 1.5 mm (in the evaluation by students) (P>0.05). In addition, no significant difference in the score was noted when the incisal inclination was between −2 and +1.5 degrees (in the evaluation by dentists) or between −2.5 and +2 degrees (in the evaluation by students) (P>0.05).
Conclusion: The results suggest that in complete denture wearers, midline deviation within ±1 mm and incisal inclination within ±1.5 degrees are esthetically acceptable.

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Purpose: The purpose of this study was to evaluate the influence of a vent hole on the retentive force of a cement-retained superstructure to an abutment.
Methods: The retentive force of superstructures with/without a vent hole, retained using one of two luting cements, was measured using a universal testing machine both before and after thermocycling
Results: The retentive force of the cement-retained superstructure with the vent hole was greater than that of the cement-retained superstructure without the vent hole. While the retentive force decreased significantly after thermocycling, the size of the vent hole had little influence on the retentive force.
Conclusion: It was concluded that placement of a vent hole in the superstructure is useful, with little adverse effect on the retentive force of the restoration.

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Purpose: The purpose of this study was to investigate the influence of immersion in warm water and the timing of the immersion on bonding strength between a built-up self-curing resin and a heat-cured denture base resin.
Methods: In this study, self-curing resins (Unifast II or Unifast Trad) were built up on denture base resins after surface treatment of the latter with or without primer. The specimens were cured under three conditions (immersion in warm water for 10 s after build-up (E), immersion in warm water for 210 s after build-up (L), and without immersion in warm water (N)), and shear bond strength and failure patterns were measured.
Results: For Unifast II without primer, there were significant differences in shear bonding strength between conditions E and L, or conditions E and N. A cohesion failure rate of 70% was noted under condition E. Bonding strength of Unifast II with primer also differed significantly between conditions E and L. There were no correlations between the failure patterns and the curing conditions. For the case of Unifast Trad without primer, no significant difference was in the bonding strength were observed under the different conditions, whereas for that with primer, significant differences in bonding strength were observed between conditions L and N. Since the failure pattern in all cases was represented by cohesion failure, there was no statistically significant relationship between the curing conditions and the failure pattern.
Conclusion: Immersion in warm water at the beginning of the polymerization response enhances the bonding strength of Unifast II to denture base resin without primer. On the other hand, for the cases of both Unifast II with primer and that of Unifast Trad with and without primer, there was no correlation between immersion in warm water during polymerization of the resin and bonding strength.

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Purpose: The aim of the present study was to record the electromyographic (EMG) activity of the mentalis muscle (Ment) during various jaw functions in healthy young subjects.
Methods: Twelve healthy males were enrolled for the study. A portable EMG recording device was used to record the EMG activity from the Ment, anterior belly of the digastric muscle (Dig), and the masseter (Mm) muscles. The EMG activities of these muscles were recorded during maximal voluntary clenching (MVC), maximal voluntary jaw opening (MVO), and the masticatory process. The EMG activity of Ment was compared with the EMG activities of Dig and Mm during various jaw functions.
Results: (1) The EMG activities of Ment and Dig were significantly greater during MVO than during MVC (P<0.05). A strong correlation was found between the activities of Ment and Mm during MVO (r=0.739, P<0.01), and between those of Ment and Dig during MVC (r=0.664, P<0.05). (2) It was observed that during mastication of peanuts, Ment showed synchronous activity with that of Dig and reciprocal activity with that of Mm.
Conclusion: These results indicate that Ment acts in coordination with the actions of Dig and Mm during various jaw functions.

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Purpose: The purpose of this study was to investigate the relationship between the intelligibility of the /S/ sound and the incisal overjet of the anterior teeth of in a maxillary denture.
Methods: Five subjects who were fitted with maxillary dentures participated in this study. Using a speech recognition system for the evaluation of phonetic functions, the correct and incorrect ratios of the intelligibility of the sound of the monosyllable [Si] in five subjects were determined in relation to increases in the degree of incisal overjet of the anterior teeth in a maxillary denture by +0, +1, +2 and +4 mm relative to that of the dentures already in use.
Results: In association with increase in the degree of incisal overjet in experimental dentures from +0 to +4 mm, while the appearance ratio of the correct [Si] sound decreased from 73.0±8.6% at +0 mm to 48.5±7.8% at +4 mm, that of the incorrect [Si] sound increased from 17.4±4.7% at +0 mm to 36.0±10.6% at +4 mm.
Conclusion: Increasing distance between the incisal edges of the maxillary and mandibular incisors make correct pronunciation of [Si] progressively more difficult.

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