[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

The retention of maxillary complete dentures can be affected by physical factors such as adhesion, cohesion, interfacial surface tension and atmospheric pressure. These physical factors operate in the fluid film between the denture base and the mucosa. Denture adhesives change the viscosity of the intervening saliva in the retention of complete dentures. Several reports have shown that denture adhesives improve denture retention. Due to the increase of dry mouth, the need for denture adhesives is increasing. In this paper, physical factors concerning upper complete denture retention and the role of denture adhesives are reviewed.

View full abstract

Purpose: Many reports have described the influence of wearing an oral appliance that is used for dental treatment of obstructive sleep apnea syndrome. However, the morphological change in the oropharyngeal region by wearing a mandibular advancement device has not been fully studied. In this study, the influence of posture and respiratory phases during cephalometric radiograms were investigated, as to the morphological change of the oropharyngeal region in normal subjects.
Methods: Twelve nonsnoring normal subjects (ten males and two females; mean age 27.3 years;body mass index 21.9kg/m²) participated in this study. Cephalometric radiograms were carried out with the subjects either by inspiration or expiration depending on whether in the upright or supine position. Repeated-measures ANOVA was used for comparing the measurement values for the two factors, posture and respiration.
Results: There was no significant difference between the inspiration and the expiration in the oropharynx. However, the area of the pharyngeal cavity and the antero-posterior widths of the middle and the inferior regions of the upper airway significantly decreased by change of body posture from upright to supine. The distance between the hyoid bone and mandibular were significantly decreased from upright to supine position.
Conclusions: The present results clearly indicate that the morphological assessment of the oropharyngeal region by cephalometric radiograms is influenced by posture.

View full abstract

Purpose: To identify the intrinsic factors affecting masticatory functions, parameters associated with clinical oral findings together with bite force and questionnaires were investigated. Methods: Cross-sectional data were derived from clinical examinations, periodontal pocket probes, bite force recordings, masticatory satisfaction scores and eatable food scores. Two hundred and thirty-five subjects in their 40's and 50's (94 males and 141 females; mean age of 49.3±5.5 years old) who were under care of dental clinics were administered in this survey.
Results: The results showed that eatable food score was 92.4±12.4 (Mean±SD), masticatory satisfaction score 7.0±2.7, number of residual teeth 24.5±3.9, number of occlusal supporting zone 3.3±1.0, bite force 1, 376.4±830.1 N, and occlusal contact area 39.2±29.4 mm2. Multiple regression analysis showed that eatable food score was associated with the number of residual teeth and the bite force, while masticatory satisfaction score was associated with periodontal pocket depth in the posterior region in addition to the number of residual teeth, and with occlusal supporting zone.
Conclusions: From the results of this study, the number of residual teeth and bite force are related to the function of eating foods, while periodontal status can play an important role in the satisfaction of eating.

View full abstract

Purpose: This study investigated the influence of saliva secretion on masticatory function.
Methods: Experimental hypo-salivation was produced by the oral administration of atropine sulfate presenting an anti-cholinergic effect in 20 healthy subjects with full dentates (average age: 27.2±3.9years old). The unstimulated whole salivary secretion rate during ten minutes (whole salivary secretion rate) and masticatory efficiency using the sieving method were measured before and after medication. In 76 elderly denture wearers (average age: 78.6±5.2 years old), the salivary secretion rate was measured and the presence of self-awareness of dry-mouth was inquired. For the denture wearers who became conscious of dry-mouth, the masticatory efficiency was evaluated using the sieving method.
Results: In 15 dentates out of 20, the oral administration of atropine sulfate led to experimental dry-mouth. In 15 dentates, whole saliva secretion rates were 3.9±2.6 and 1.5±1.0 g before and after medication. The masticatory efficiencies were 62.7±9.4% and 58.3±9.2% before and after medication. The salivary secretion rate was decreased significantly by the administration of atropine sulfate (p<0.01). The masticatory efficiency after atropine sulfate was significantly lower than that before medication (p<0.01). In denture wearers, 20 patients became conscious of dry-mouth (dry-mouth group) and 53 patients did not become conscious of dry-mouth (non dry-mouth group). There was no significant difference between mean age of the dry-mouth group and non dry-mouth group. The whole saliva secretion rates were 0.35±0.26 g (dry-mouth group) and 1.20±1.58 g (non dry-mouth group). The masticatory efficiency was 21.0±15.8% in the dry-mouth group and the value was significantly lower compared to the value of 43.0% used by us as the standard value of masticatory efficiency of complete denture wearers.
Conclusion: The understanding that saliva plays an important role in masticatory function was supported objectively.

View full abstract

Purpose: This study investigated the relation between masticatory functions and occlusal contact area (OCA) under two different bite forces [10 and 50% maximum voluntary contraction (MVC)].Methods: Bite impression registrations of 12 healthy subjects were usud to determine the OCA of less than 50um thickness. Five mandibular positions, intercuspal position (IP), 1 and 2mm lateral positions from IP, were regulated by an altered extraoral Gothic arch tracer.
Mandibular movement and massetter and temporal muscle activity were recorded during mastication in order to analyze bilateral muscle activity ratio.
Results: 1. The OCA significantly decreased according to the lateral deviation from the IP. 2. The OCA increased according to the bite force in each position but the degree of increase of the OCA decreased according to the lateral deviation from the IP. 3. There was a significant correlation between the degree of increase of the OCA and bilateral massetter muscle activity ratio but no correlation was found between the OCA and the temporal muscle activity.
Conclusions: The OCAs in IP, working and balancing sides of lateral occlusal positions increased according to clench in each position. On the working side of the lateral occlusal positions, as the OCA in 10% MVC was wider, the OCA showed a greater increase according to clench in only the working side of lateral occlusal positions. The amount of OCA increase according to clench in the balancing side of the lateral occlusal positions influenced the massetter muscle activity ratio of the working and balancing sides of the lateral occlusal positions.

View full abstract

Purpose: Recently, the excellent mandibular movement analyzer, ARCUS digma (KaVo), was developed. It is very compact and operation is simple compared to the conventional types. It is also quite a new technique that the kinematic axis is used as a reference axis to analyze mandibular movements. This study evaluated the possibility of clinical application of this new instrument.
Methods: Ten healthy dentate subjects were selected. The inclination of the sagittal condyle path and the angle of the lateral condyle path were obtained in two different ways for each subject: one was measured at the adjusted condylar guidance of the articulator through the check bite method with parafin wax in the usual manner, and the other was derived using this analyzer. The accuracy and the reproducibility of this analyzer were also examined by measuring the inclinations of the sagittal condyle path and the angles of the lateral condyle path several times for each.
Results: The inclination of the sagittal condyle path and the angle of the lateralcondyle path obtained by the two different methods showed no significant difference. The accuracy and reproducibility of this analyzer were clinically acceptable.
Conclusions: It was concluded that this newly developed mandibular movement analyzer, ARCUS digma, is very useful for clinical application as it can solve many on-the-spot problems which are unavoidable with traditional analyzers.

View full abstract

Since few clinical trials have been carried out for permanent soft denture liners, clinicians do not have sufficient evidence of their use. This study investigated the efficacy of applying a permanent soft lining material in a clinical setting.
Methods: Twenty-eight edentulous patients who visited the Nihon University School of Dentistry at Matsudo Affiliated Dental Hospital and who fulfilled the selection criteria and accepted informed consent were enrolled in this trial. The study design was a randomized controlled clinical trial with two-period cross-over. Intervention was conventional denture treatment for both maxilla and mandible in one arm, and conventional denture for maxilla and mandible denture with soft lining material (Sofreliner MS, Tokuyama) in the other arm. The random-permuted-block-within-strata method was used for allocating the subjects into two groups. One group received a conventional denture in both jaws followed by maxilla conventional denture and mandible soft-lined denture, and the other received two sets of denture in contrary order. Outcomes were masticatory performance, number of visits for denture adjustment and preference of fabricated denture. Statistical as well as ITT (Intention to treat) analyses were performed.
Results: 1. Masticatory performance with soft-lined denture was significantly higher than the conventional denture at two and three months after completing adjustments of the denture. 2. The number of visits for denture adjustment with the soft-lined denture was significantly lower than that with the conventional denture. 3. Seventy-two percent of subjects selected the soft-lined denture.
Conclusions: Application of a permanent soft lining material to mandible complete dentures resulted in an improvement in masticatory performance and fewer visits for denture adjustment. Moreover, the majority of subjects selected the soft-lined denture.

View full abstract

Purpose: This study examined the effect of the phosphate-bonded dental investment in relation to the manufacturers' recommended ratio in two different concentrations (50 and 100wt%) of liquid.
Methods: Fluidity, setting time, compressive strength, setting expansion and thermal expansion of the investments were measured. The fitness of gold alloy for metal-ceramics made in each of the investments was measured.
Results: A new phosphate-bonded dental investment for quick heating showed significantly greater fluidity and longer setting time than did the other phosphate-bonded dental investments tested. The compressive strength, setting expansion and thermal expansion of the new investment was similar to the properties of the other phosphate-bonded dental investments. The setting expansion of all the phosphate-bonded dental investments appeared to be more influenced by differences in the liquid concentration rather than by the thermal expansion. The fitness of gold alloy for metal-ceramics cast in the recently developed phosphate-bonded dental investment was similar to the other phosphatebonded dental investments.
Conclusions: The use of a new phosphate-bonded dental investment for quick heating can improve the results of porcelain-fused-to-metal crowns because its fluidity and setting time were greater than those of the other phosphate-bonded dental investments tested.

View full abstract

Purpose: Recently, laser welding has gained wide acceptance as a dental laboratory technique for bonding metals. We have previously reported a new technique for installing a magnetic keeper in the overdenture abutment coping using laser welding. In the present study, the influence of this technique on the attractive force and corrosion were evaluated.
Methods: A commercially-available magnetic keeper and dental casting Au-Ag-Pd alloy were used. Specimens were prepared by one of the following procedures: original magnetic keeper only, conventional cast-on technique and laser welding technique. Attractive force between thedental magnetic assembly and magnetic keeper was measured using a self-made measuring device. The results were analyzed using the one-way ANOVA test. The external and inner surface of magnetic keepers and cross sections of specimens were observed using metal and stereoscopic microscopes before and after immersion of the specimens in 0.9% NaCl solution for 21 days.
Results: There was no significant difference of attractive force between the conventional cast-on technique and laser welding technique. All of the specimens using the cast-on technique rusted in the corrosion test. Half of the specimens using the laser welding technique changed less, and no oxidized layer or corrosion was observed on the surface.
Conclusions: Installation of magnetic keepers using laser welding is useful for increasing both attractive force and corrosion resistance.

View full abstract