Purpose: This study aimed to compare the survival rates of remaining teeth between implant-supported fixed dentures (IFDs) and removable partial dentures (RPDs) in patients with large edentulous cases. The second goal was to assess the risk factors for remaining tooth loss.
Materials and methods: The study subjects were selected among those who received prosthodontic treatment at Okayama University Dental Hospital for their edentulous space exceeding at least four continuous missing teeth. Twenty-one patients were included in the IFD group and 82 patients were included in the RPD group. Survival rates of remaining teeth were calculated in three subcategories: (1) whole remaining teeth, (2) adjacent teeth to intended edentulous space, and (3) opposing teeth to intended edentulous space.
Results: The ten-year cumulative survival rate of the whole remaining teeth was significantly higher in the IFD group (40.0%) than in the RPD group (24.4%). On the other hand, there was no significant difference between two groups in the survival rate of teeth adjacent or opposing to intended edentulous space. A Cox proportional hazard analysis revealed that RPD restoration and gender (male) were the significant risk factors for remaining tooth loss (whole remaining teeth).
Conclusions: These results suggest that IFD treatment can reduce the incidence of remaining tooth loss in large edentulous cases.

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Purpose: This study aimed to evaluate the effects of thymosin β4 (TB4) on bone formation.
Methods: A 5 mm diameter bone defect was created in the skulls of Wistar rats. Two types of experimental models were prepared: one with atelocollagen sponges used to fill the bone defect and one without. In each experimental model, bone formation in calvarial defects was compared between the group receiving synthetic partial peptides of TB4 intraperitoneally (TB group) and the control group, which received an equivalent amount of phosphate-buffered saline. Calvarial defect sections collected on postoperative days 5, 10, and 20 were analyzed, and the area of newly formed bone was measured. Furthermore, the sections on postoprerative day 5 were immunostained with anti-osterix antibody and the osterix-positive cells were counted. The total RNA extracted from granulation tissue obtained on postoperative day 10 was analyzed using reverse transcriptase–polymerase chain reaction (RT–PCR).
Results: In both models, with or without atelocollagen sponges, new bone formation was significantly greater in the TB4 group than in the control group. In some TB4 group individuals, the entire bone defect region of diameter 5 mm was almost covered with newly formed bone by postoperative day 20. Immunostaining revealed a significant number of osterix-positive cells in the TB4 group. On postoperative day 10, the expression levels of bone-related genes were analyzed by RT–PCR, which showed no statistically significant differences between the two groups.
Conclusion: The osteogenesis-promoting effects of TB4 observed in critical-sized defects could be of practical use in bone regeneration therapy.

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Purpose: To investigate the form of mouthguard sheets that best retains its thickness.
Methods: Mouthguards were molded using ethylene-vinyl-acetate (EVA) sheets and a suction-type molding device. Five sheet conditions were compared. These were I-N (Incisal part of the cast positioned at the center – Normal sheet), I-H (Incisal part positioned at the center – Horizontal v-shaped groove 30 mm from the anterior end), I-C (Incisal part positioned at the center – Convexing v-shaped groove toward the back 10–40 mm from the anterior end), C-N (Center part positioned at the center – Normal sheet), and C-C (Center part positioned at the center – Convexing v-shaped groove toward the back 10–30 mm from the anterior end). Post-molding thickness was determined for the incisal (incisal edge and labial surface) and molar portion (cusp, central groove, and buccal surface). Sheets were heated until they sagged 15-mm below the clamp. Scheffé multivariate comparison was performed to compare changes in post-molding thickness among sheet conditions.
Results: Post-molding thickness of mouthguard material differed significantly between the two portions; rates of thickness reduction were smaller for I-C and C-C compared with other conditions. There were no significant differences between I-C and C-C at any measurement points.
Conclusion: The present results suggested that thickness reduction of the EVA sheet material after vacuum-forming may be decreased at both incisal and molar portions if the v-shaped groove with a v-shaped cross section was given in the frontal teeth region of the sheet at the apparatus and materials for this study used.

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Purpose: The aim of this study was to evaluate the change in thickness of the mouthguard sheet due to different heating conditions during fabrication.
Methods: Mouthguards were fabricated with ethylene vinyl acetate (EVA) sheets (4.0-mm thick) using a vacuum-forming machine, and six conditions which varied the height of the frame above the surface, reversing the sheet while heating, and controlled power on–off of the heater when a specified level of sagging had been attained were used to determine optimal conditions. The working model was trimmed to a height of 20-mm at the incisor and 15-mm at the first molar. Post-molding thickness was determined for the incisal portion (incisal edge and labial surface) and molar portion (cusp, central groove, and buccal surface). Differences in the change in thickness due to heating condition were analyzed using Scheffé's multiple comparison tests.
Results: The heating condition which the sheet frame was lowered to and heated at 50 mm below the top of the post, the heater was turned off when the sheet sagged by 10 mm, and the sheet was molded when the sagging reached 15 mm showed the thickest, what the decrease in the thickness reduction was approximately 0.40–0.44 mm at the incisal, and that was 0.35–0.40 mm at the molar portions.
Conclusion: When molding a mouthguard using an EVA sheet, the thickness of the incisal and molar portions of the mouthguard can be maintained by adjusting the height of the sheet frame and heating conditions, which may be clinically useful.

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Purpose: The fatigue failure of denture clasps has often been observed in removable partial denture rehabilitation. To increase their fatigue strength, shot peening was evaluated as a surface treatment. In this study, we evaluated the fatigue resistance and retention of cast clasps by using a shot peening treatment.
Methods: A cobalt–chromium (Co–Cr) alloy, commercial pure titanium (CP Ti), silver–palladium–gold (Ag–Pd–Au), and a gold–platinum (Au–Pt) alloy were cast and then treated with shot peening. The retentive forces of the clasps were measured up to a repetition of 10,000 insertion/removal cycles in distilled water at 37 °C. A fatigue test was also performed using a 15-mm cantilever. Specimens were loaded with a constant deflection of 2.0 mm with 20 Hz. A shot peening treatment indicated a better stability of retentive forces than that without shot peening. The retentive force of Co–Cr clasps without shot peening was remarkably decreased at 500 cycles of insertion/removal repetition.
Results: The clasps with a shot peening treatment provided approximately 1.4–3.6 times higher fatigue strengths than those without a shot peening treatment.
Conclusion: To prevent the fatigue failure of the denture clasps and use the dentures for long term, a shot peening treatment would be recommended.

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Purpose: The present study was designed to assess the potential of oral myofunctional therapy (OMFT) for improving respiration parameters, Apnea-Hypopnea Index (AHI), and saturation of peripheral oxygen (SpO₂) during sleep.
Methods: The Epworth Sleepiness Scale (ESS) was administered to 92 students in class time at the Nihon University School of Dentistry at Matsudo. The results showed that 15 students had a high ESS. Of the 15 students who had learnt about their excessive sleepiness, six students expressed their intention to receive treatment for their sleep condition. They volunteered as subjects for the study. The Lip Trainer Patakara^® was used for labial closure force (LCF) training for 2 months. LCF, AHI and SPO₂ during sleep were measured before training and after 2 months training. The paired t-test was applied for statistical analyses.
Result: LCFs before and 2 months after training were 8.8 ± 1.6 and 12.9 ± 0.6 N, respectively. LCF significantly increased after training compared to that before training. SpO₂ before training and after training were 90.0 ± 2.9% and 96.8 ± 0.8%, respectively. SpO₂ after training was significantly increased compared to that before training. AHI before and after training were 15.1 ± 3.4 and 9.2 ± 1.5 events/h, respectively. AHI after training was significantly decreased compared to that before training.
Conclusion: From this study, the following conclusions were made: (1) OMFT significantly increases LCF; and (2) the AHI and SpO₂ during sleep are significantly improved after OMFT.

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Purpose: To evaluate the effect of bulb height of hollow bulb obturator prosthesis on articulation and nasalance.
Method: A total of 10 patients, who were to undergo maxillectomy falling under Aramany class-I and II, with normal speech and hearing pattern were selected for the study. They were provided 2 maxillary obturators, one extending full height of the defect and other with bulb height approximately up to inferior nasal concha. The patients were asked to wear each obturator for 6 weeks and the speech analysis was done to measure changes in articulation and nasalance at 6 different stages of treatment i.e. preoperative, postoperative (after complete healing), 24 h and 6 weeks after providing full bulb height obturator and reduced bulb height obturator. Articulation was measured objectively for distortion, addition, substitution and omission by speech pathologist and nasalance was measured by Dr. SPEECH software.
Result: Comparison between full and reduced bulb height for nasalance and articulation, showed that there was no statistical significant difference (P > 0.05) between the two for both the parametres.
Conclusion: Articulation and nasality improves after providing obturator. Articulation and nasalance both are independent of bulb height.

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Purpose: This finite element analysis (FEA) compared stress distribution on external surface of different morse taper implants, varying implant bodies length and dimensions of metal-ceramic crowns in order to maintain the occlusal alignment.
Methods: Three-dimensional finite element (FE) models were designed representing a posterior left side segment of the mandible: group 0, 3 implants of 11 mm length; group 1, implants of 13 mm, 11 mm and 5 mm length; group 2, 1 implant of 11 mm and 2 implants of 5 mm length; group 3, 3 implants of 5 mm length. The abutments heights were 3.5 mm for 13 mm and 11 mm implants (regular) and 0.8 mm for 5 mm implants (short). Evaluation was performed on a computer program (Ansys software), with oblique loads of 365 N for molars and 200 N for premolars, applied on ridges of cusps and grooves.
Results: Abutments with 0.8 mm height generated less von Mises stresses compared with 3.5 mm height. The use of short implants associated with bigger crowns concentrated higher stress distribution and stress values on the surface implants, principally on the vestibular side (oblique direction of the loads). The more distal implant concentrated higher stress.
Conclusions: Moreover, these 5 mm implants were positioned at the cortical bone level, which has higher elastic modulus and may have influenced at the stress distribution. However, despite the higher stresses, these implants were well able to withstand the applied forces.

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Purpose: To evaluate the influence of different metallic flask systems for acrylic resin denture processing on tooth displacement and framework misfit of mandibular fixed implant-supported complete dentures.
Methods: Standard mandibular implant-supported complete dentures in five implants were waxed and randomly assigned to three groups: G1 – conventional flask, G2 – double flask, and G3 – occlusion flask. Framework misfit in all the implants and the linear distances between teeth (I-I – incisor-to-incisor; P-P – premolar-to-premolar; M-M – molar-to-molar; RI-RM – right-incisor-to-right-molar; and LI-LM – left-incisor-to-left-molar) were measured before and after denture processing using an optical microscope. Dentures were processed by hot water curing cycle (9 h/74 °C). Collected data were analyzed by paired Student's t-test and one-way ANOVA (α = 0.05).
Results: All the measured distances presented changes in tooth displacement after denture processing. However, the M-M distance for G1 (p = 0.003) and the P-P (p = 0.042) and LI-LM (p = 0.044) distances for G3 showed statistically significant differences. Differences between the flask systems were not statistically significant. Statistically significant differences in the framework misfit due to denture processing were found for all the implants and groups, with the exception of right median implant for G2 and right distal implant for G3. A comparison of the flask systems found statistically significant differences in which G1 presented an increase in the misfit values and G2 and G3 a decrease.
Conclusions: Different flask systems did not cause significant changes in tooth displacement. Frameworks misfit values were influenced by the different flask systems. The conventional flask presented an increase in the framework misfit, while the experimental flasks showed a decrease.

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Purpose: This study evaluated the effect of fatigue loading on the screw joint stability of a zirconium abutment connected to an external hexagon implant in vitro.
Materials and methods: Fifteen titanium and 15 zirconia abutments of 3 different heights (5, 8, and 11 mm) were connected to external titanium implants with titanium screws. A torque gauge was used to measure the reverse torque values before and after loading. An air cylindrical loading device was used to simulate mastication at a 45-degree angle to the longitudinal axis of the implant.
Results: There were significant differences (P < 0.05) before and after the loading of titanium (5 mm) and zirconia (5, 8, and 11 mm) abutments.
Conclusion: Zirconia abutments for external hexagon implants had durability rates similar to those of titanium abutments after repeating load on the reverse torque of the abutment screw, indicating that the zirconia abutment could be reliably used instead of the titanium abutment.

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Patient: A 2-day-old female infant with complete unilateral cleft lip, alveolus, and palate (left side) was presented to the Department of Prosthodontics, Government Dental College and Hospital, Nagpur for evaluation and treatment with presurgical nasoalveolar molding (PNAM) prior to surgical intervention.
Discussion: The alignment of the alveolar segments creates the foundation upon which excellent results of primary lip and nasal surgery are dependent in the repair of the cleft lip, alveolus, and palate patient. Presurgical infant orthopedics has been employed since the 1950s as an adjunctive neonatal therapy for the correction of cleft lip and palate. One of the problems that the traditional approach failed to address was the deformity of the nasal cartilages and the deficiency of columella tissue in infants with unilateral and bilateral cleft lip and palate. The purpose of this article is to illustrate the step-by-step fabrication process of the PNAM prosthesis used to direct growth of the alveolar segments, lips, and nose in the presurgical treatment of cleft lip and palate.
Conclusion: As a result, the primary surgical repair of the lip and nose heals under minimal tension, thereby reducing scar formation and improving the esthetic result. Frequent surgical intervention to achieve the desired esthetic results can be avoided by PNAM.

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DOI of original article: http://dx.doi.org/10.1016/j.jpor.2013.01.002

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