Purpose : The purpose of this study was to investigate the influence of the cross section shape of a metal strengthener on stress distribution and deflection in acrylic denture bases under loading.
Materials and Methods : Thirteen 3-D finite element models of acrylic palatal straps with embedded metal strengtheners of different section shapes (square, rectangle, inverted concave, concave, inverted convex, convex, inverted triangle, triangle, flat top half round, flat bottom half round, inverted horseshoe, horseshoe, and round) having an equal area size were created. The thickness and anterior-posterior width of each strap were 2 mm and 11.2 mm, respectively. One end of each strap was fixed on the ridge, and the median line on the deepest palatal vault of each model was fixed vertically. A vertical or 30 degree distally oblique force of 10 N was loaded on the other end of each strap.
Results : The straps with the triangular and square cross section-shaped strengtheners had lower maximum stresses and deflections, while higher values were found in the straps with the round, half round and horseshoe section strengtheners. The straps with the round and half round section strengtheners demonstrated sharp stress concentrations at the interface between the metal and the acrylic denture base under oblique loads.
Conclusion : The use of triangular or square section-shaped metal strengtheners effectively minimized both the maximum stress in the acrylic denture base and deflection of the saddle.

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Purpose : Magnetic attachments are available for various prosthodontic applications. However, several problems have been noted over the past few years as their use has increased. In this study, the challenges associated with magnetic attachments in prosthodontics are summarized, based on data collected over an 8-year period.
Materials and Methods : Seventy-seven patients with overdentures and magnetic attachments were observed from November 1992 to August 2000 at Osaka Dental University Hospital. The relationship between the occurrence of problems and time was analyzed through the use of the Kaplan-Meier survival analysis. The prognostic factors were classified into two categories : complete vs. partial dentures, and conventional dentures vs. dentures for resected jaws, which were the compared using the Log rank test at a significance level of 0.05.
Results : Problems were noted for 37.1% of the abutment teeth and 30.6% of denture bases. The overdentures placed in cases where jaws had been resected for tumor removal performed significantly worse than conventional overdentures.
Conclusion : Magnetic attachments might help to improve denture retention, except for cases where jaws have been resected.

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Purpose : The purpose of this study was to examine the change in spinal cord excitability in a leg muscle during maximal voluntary clenching on a stabilization appliance.
Materials and Methods : The H reflex of the soleus muscle was elicited in five healthy male volunteers by electrical stimulation of the tibial nerve under the following five dental occlusal conditions : mandibular rest position (RP : control), maximum voluntary clenching in the intercuspal position (IP), maximum voluntary clenching on a hard acrylic stabilization appliance (H-SA), maximum voluntary clenching on a soft stabilization appliance (S-SA) and maximum voluntary clenching on a very soft stabilization appliance (VS-SA).
Results : The soleus H reflex modulations in the IP, H-SA, S-SA and VS-SA conditions were 117.6%, 119.5%, 126.2% and 133.6%, respectively. There was a significant difference between IP and S-SA, and IP and VS-SA (p=0.0001-0.0226) ; however, there was no significant difference between IP and H-SA (p=0.3412-0.9940). Significant positive correlations between the magnitude of the soleus H reflex and the masseter electromyogram activity were found in each subject (r=0.670-0.862, p<0.05).
Conclusion : This study demonstrated that the spinal cord excitability in the motor pathway of a leg muscle was considerably raised during clenching on a soft stabilization appliance compared to a hard stabilization appliance, suggesting that a powerful biting action on a resilient intraoral appliance strongly influences the motor system in humans.

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Purpose : The purpose of this study was to examine the characteristics of the shape of a denture-supporting area and their relationship to masticatory ability. The correlation among the shape of the denture-supporting area, maximum biting force, and the masticatory ability of the wearers of maxillary and mandibular complete dentures was investigated.
Materials and Methods : Duplicate casts were made from the master casts of 28 complete denture wearers. The surface area (S) and projected area (P) of the maxillary and mandibular denture-supporting areas were measured ; the volume (V) was measured using a duplicate of the mucosal surface of the denture base made with the duplicate cast. In addition, V/P, S/P, and V/S were calculated from the factors of V, S, and P. The correlation among these measurements and ratings, the maximum biting force and the masticatory ability of the subjects were analyzed using Pearson's correlation coefficient.
Results : Maximum biting force significantly correlated with mandibular volume (V), surface area (S), projected area (P), and V/S, which indicates the average height of the residual ridge. No significant correlation was observed between the shape of the denture-supporting area of the maxilla and the maximum biting force. Masticatory ability significantly correlated only with the mandibular surface area (S).
Conclusion : The height and surface area of the mandibular denture-supporting area can help predict the recovery of function in complete denture wearers before treatment.

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Purpose : This paper focuses on reviewing the methodologies available for evaluating masticatory performance. The objective of this article was to identify various reported methods and reveal consensus and controversies that are clinically relevant and strategically applicable for future studies.
Materials and Methods : Articles in the PUBMED database were located using four phrases as keywords : “masticatory performance, ” “masticatory efficiency, ” “masticatory ability, ” and “masticatory efficacy.” We then categorized the papers according to their prevalence by decade of publication, their topics, and their methodological variation. We conducted an in-depth review of the selected articles and their methodological characteristics.
Results : The amount of published literature about masticatory performance continues to increase. Although objective methods were predominantly used, studies using subjective measurements are increasing. Specific methodologies offer certain advantages for evaluating mastication in terms of their availability, reliability, and sensitivity. However, there appears to be no validated method of assessment available for clinicians to use routinely.
Conclusion : A reliable means of assessment of masticatory performance is needed as a resource in the practice of evidenced-based dentistry. One reason for evaluating masticatory performance is to promote an increase in studies of functional and psychological outcomes of prosthodontics treatment. Methodologies for testing masticatory performance continue to be introduced at a steady rate, and researchers and clinicians still seek the best methods of gathering information, depending on the specific purpose. The significance of assessing masticatory performance in a routine dental practice needs to be addressed.

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Purpose : The aim of this study was to investigate the EMG biofeedback threshold suitable for patients having masticatory muscle pain due to clenching behavior.
Materials and Methods : EMGs from the unilateral anterior area of the temporal muscle in 18 subjects suffering masticatory muscle pain or stiffness were recorded by a one-channel portable EMG biofeedback apparatus.
Results : Sixteen of the subjects (88.8%) were found to have valid thresholds. The threshold of 30% maximum voluntary contraction (MVC) EMG level for 2s provided the highest accuracy rate at 81.3%.
Conclusion : EMG biofeedback training with the threshold utilizing combined EMG amplitude and burst duration is thought to be useful as a therapeutic strategy for patients with clenching behavior.

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Purpose : This study investigated the effect of the cross-sectional dimensions on the deflection of the lingual bars in Ti-6 Al-7 Nb and Co-Cr removable partial denture frameworks and of the stress distributions in the frameworks and the underlying oral mucosa.
Materials and Methods : Three-dimensional finite element models (FEM) of nine lingual bars with different dimensions (thickness : 1.5, 2.0, or 2.5 mm ; height : 4, 5, or 6 mm) including the underlying mucosa were produced for a Kennedy Class II case. Each framework included occlusal rests on the first premolars of both arch sides. The bottom surface of the mucosa and the rest on the edentulous side were fixed in a vertical direction. The rest on the tooth-supported side was fixed in all directions. Elastic moduli of 200 and 123 GPa were input into the program as values for the Co-Cr and Ti-6 Al-7 Nb alloys, respectively. A 30° buccally oblique biting force of 20 N was directed toward each of the three missing tooth locations.
Results : The Ti-6 Al-7 Nb frameworks resulted approximately 1.2 times the maximum stress in the mucosa compared to the Co-Cr frameworks with the same cross-sectional dimensions. The framework displacement and stress in the mucosa decreased as the thickness or the height of the bars increased. The maximum principal compressive stress within the mucosa was estimated to be 1.84 MPa at the posterior ridge crest when the smallest cross-sectional Ti-6 Al-7 Nb bar was used.
Conclusion : The rigidity of the Ti-6 Al-7 Nb lingual bars was comparable to that of the Co-Cr lingual bars when the cross-sectional dimensions of the former were 0.5 mm thicker or 2.0 mm higher than the latter.

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Purpose : To obtain maximum attractive force for magnetic attachments, the degree of flatness of the keeper surface is very important. This study evaluated the flatness of keeper surfaces fabricated on copings using the cast-bonding and the direct-bonding techniques.
Materials and Methods : Specimens were made with keepers from the Hyper Slim 3513 magnetic attachment system (Hitachi Metals, Tokyo, Japan) using both the cast-bonding and the direct-bonding techniques. In the cast-bonding technique, the coping with the keeper was waxed up and cast according to conventional laboratory procedures. In the direct-bonding technique, the keeper was cemented on the cast housing with resin cement. The 3-dimensional shape of the keepers was measured using non-contact laser beam equipment (NH-4N, Mitaka Kohki, Tokyo, Japan), and the flatness was statistically analyzed with the Mann-Whitney U-test at a significance level of α=0.05.
Results : The keepers fabricated with the cast-bonding technique had a convex curvature, whereas the direct-bonding technique produced a flatter keeper surface. There was a significant difference (p<0.01) in the flatness between the two techniques.
Conclusion : The direct-bonding keepers were significantly flatter than the cast-bonding keepers, whose surfaces bulged in the center. The direct-bonding technique thus allowed optimal retentive force for the magnetic attachment.

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Purpose : The purpose of this study was to histologically examine the hydroxyapatite (HA)-coated layer of endodontic endosseous implants after clinical application. The HA was applied using a high-velocity flame-spraying technique (HVFST).
Materials and Methods : Two implants placed six years earlier in two different patients were studied. The first patient was a 24-year-old man who received implant therapy to improve the crown : root ratio after removal of a radicular cyst. The second patient was a 15-year-old boy in whom an implant was placed to restore the dentition after dental root breakage. The extracted materials were fixed in a 10% formalin solution and examined with light microscopy and scanning electron microscopy (SEM).
Results : Because the implants adhered tightly to the bone, it was necessary to remove both the implant and the surrounding bone. Histological examination using toluidine blue staining in an SEM indicated some remaining HA coating that directly contacted the bone in the first patient. In the second patient, SEM showed that the HA coating had been resorbed, and the bone had bound directly to the titanium.
Conclusion : Although each of the implants had been in use for six years, the coated HA layers displayed completely different phenomena. We concluded that the causes for this difference were related to the limitations of the HA coating technique and various long-term clinical conditions.

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Purpose : This study evaluated the accuracy of a sectional stock tray for making impressions.
Materials and Methods : A sectional stock tray is a full arch tray sectioned into right and left halves that can be reconnected with a tray handle. An impression of a maxillary model (500A, Nissin, Japan) with four reference points was made with two types of silicone impression material (Injection and Hard types, Exafine, GC, Japan). Five casts (Vel-mix stone, Whipmix, KY) were fabricated for each tray (total of 10 casts). Impression accuracy was evaluated by measuring the four distances between the reference points (mm) using a Profile projector (x50, V-16E, Nikon, Japan). The results (n=5) were analyzed by ANOVA/Duncan's test (α=0.10)
Results : Making impressions should be easier with this sectional stock tray. There were no significant differences (p>0.10) between the sectional stock tray and a conventional stock tray.
Conclusion : Impression accuracy of the sectional stock tray with dowel-plug holes was confirmed.

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Purpose : This in vitro study investigated the influence of implant splinting on stress distribution in two experimental implant-bone models.
Materials and Methods : Two experimental implant-bone models simulated the original Brånemark model with four implants between the mental foramina and one additional implant placed on each side posterior to the mental foramen. The stress distribution on each implant in the models was examined by applying a static load to the superstructure. Three types of superstructures were studied to determine the effect of additional implants in the posterior region : 1) a metal superstructure supported by all six implants (Full dental arch ; Metal FDA) ; 2) the same type of superstructure made of resin instead of metal (Resin FDA) ; and 3) the metal superstructure supported by four anterior implants, with the conical abutments removed from the two posterior implants (Short dental arch ; Metal SDA).
Results : Regardless of the type of superstructure tested, high stress was observed around each loaded implant. The highest stress was concentrated on the distal implants of the FDA compared to the stress on the anterior implants.
Conclusion : The elevated stress concentration around the implants found in the present in vitro study is considered to be one of the reasons for the high failure rate of additional posterior mandibular implants.

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Purpose : This article introduces the procedure for fabricating CAD/CAM all-ceramic crowns using the DECSY system in combination with the DECSY Scan and ProCAD blocks.
Materials and Methods : A working model is manufactured after preparing the abutment tooth in the usual manner. Occlusal data are obtained using soft resin occlusal registration material. By using the DECSY Scan, the abutment tooth and occlusal record are measured, and the design of the crown is calculated. Data for the completed crown are transferred to the DECSY unit, and the ProCAD ceramic block is milled. After the milling is finished, the crown is polished, and the stain porcelain fired.
Results : The CAD/CAM all-ceramic crowns were fabricated and luted. The patients were satisfied with their crowns.
Conclusion : The use of both the DECSY Scan and ProCAD blocks is recommended for the fabrication of CAD/CAM all-ceramic crowns with the DECSY system.

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Objective : The methods of connecting dentures and abutment teeth, and of supporting and bracing by retainers play an important role in limiting the mobility of partial dentures during function. Bracing is more important than the retention of dentures for supporting and stabilizing occlusion. An appropriate retainer for this purpose is the riegel. Clinical consideration must be given to the type of supporting and bracing forms for retainers on abutment teeth for Suginaka riegel^® dentures.
Methods : Modified extended arm clasps and extended-arm ring clasps were fabricated for the Suginaka riegel^® dentures since they are considered to be more effective at supporting and bracing. Telescopic crowns, 4/5 outer crown-type double crowns without retention, and Konus crown-type double crowns without retention by eliminating friction were fabricated. These retainers were first considered for use in support and bracing. Then ideal retainers for a free end saddle were considered.
Results : Ring clasps had a greater bracing effect. Extended-arm ring clasps were the most appropriate for a unilateral free end saddle. Good results were also found for modified extended arm clasps. Of the telescopic forms, the Konus crown-type double crowns were the most effective at supporting and bracing, and they produced good results in all cases. The 4/5 outer crown-type double crowns were effective for cases that did not require buccal bracing.
Conclusion : Clasp forms are available for unilateral free end saddles treated on one side under the appropriate conditions for each abutment tooth and residual ridge. Konus crown-type telescopic forms provide the greatest stability for free end saddle dentures.

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