Effect of the denture adhesive for dry mouth on the retentive force of the experimental palatal plates: a pilot controlled clinical trial.

BACKGROUND: A denture adhesive for dry mouth with good cleaning properties has recently been developed. While previous studies on models have shown the effectiveness of denture adhesives in terms of retention and cleanability, no reports have evaluated their effectiveness in the oral cavity. The aim of this study was to compare and investigate the retention and usability of an experimental palatal plate in the dentulous jaw using a denture adhesive for dry mouth, a conventional cream-type denture adhesive, an oral moisturizer, and a denture moisturizer. METHODS: Ten healthy dentulous participants (mean age 27.2 ± 1.6 years) were included in the study. Palatal plates were fabricated. Four test samples were used: denture adhesive for dry mouth, conventional denture adhesive (cream type), oral moisturizer, and denture moisturizer. The sample was applied to the inner surface of the palatal plates, and the retentive force of the palatal plate was measured every 10 min for 30 min. After the measurements, the study participants were asked to rinse the palatal plate with water and subjectively evaluate the samples used. RESULTS: The conventional denture adhesive (cream type) showed increased retentive force over time, with the maximum retentive force obtained after 10 min of application. However, its washability was rated second lowest. The denture adhesive for dry mouth showed the highest retentive force immediately after application. Its washability was also good. CONCLUSIONS: The results suggest that the denture adhesive for dry mouth has reasonable retentive force in the oral cavity and cleaning properties compared to the conventional cream-type denture adhesive.

Effect of traction direction and pressure load on the palatal plate on retentive force.

BACKGROUND: Recently, a denture adhesive that is easy to clean and contain moisturizing ingredients have been developed for patients with dry mouth. Although the retentive force produced by conventional denture adhesives and oral moisturizers have been compared on models, no study has reported their comparison in the oral cavity. In this study, we aimed to clarify the effects of different directions of traction and loads at the time of pressure contact on the retentive force on a palatal plate made from a dentulous jaw model. METHODS: A palatal plate was fabricated with thermoplastic resin on a dentulous jaw model, and a loop-shaped traction device was attached to the centre of the palate. The test samples were a cream-type denture adhesive, a denture adhesive for dry mouth, an oral moisturizer, and a denture moisturizer. The specimens were applied to the inner surface of the plate, which was then mounted under vertical pressure. Then, the retentive force was measured, using a digital force gauge, while the plate was pulled in different directions and with different loads. RESULTS: No significant difference in retentive force was observed in any of the test samples when the direction of traction was between 45° and 60°. The retentive force of the denture adhesive for dry mouth was significantly higher with a direction of traction of 90° than that of 45° or 60°. The retentive force when oral moisturizer was used was significantly higher in the 90° traction direction than in the 45° direction. There was no significant difference between a force of 4.0 kgf or 5.5 kgf when using a denture adhesive for dry mouth. Comparing the four load size conditions, the larger the load, the higher was the retentive force. Similar results were obtained for the cream-type denture adhesive and denture moisturizer. Significantly higher retentive force was observed for larger loads when oral moisturizer was used. CONCLUSIONS: The results suggest that the direction of traction and the pressure load affect the retentive force on a palatal plate.

Development of an optimal relief method for the palatal plate by stress analysis.

BACKGROUND: Plate dentures cannot be easily modified after fabrication; therefore, the sites and magnitude of relief must be effectively assessed at the time of fabrication. However, a considerable variation exists in the magnitude of optimal relief and relief range, and there are no guidelines that present these clearly, leading the dentists to decide subjectively. Thus, this study aims to develop an optimal relief method to improve the stress bearing capacity of the palatal mucosa. METHODS: The objective of this study, namely, the borderline, was set in steps. A three-dimensional finite element model for the pseudopalatal plate was created and used to evaluate the changes in stress distribution in the palatal mucosa due to the selective relief of stresses above the borderline. The resulting data were used to develop the optimal relief method. RESULTS: In the relief model with a borderline of 0.04 MPa or higher, the distribution volume at which a high stress of 0.20 MPa or higher is generated was approximately 800% of that with the no-relief model, and in the relief model with a borderline of 0.06 MPa or higher, the respective ratio was approximately 280%. On the other hand, the relief models with a borderline of 0.14 MPa or higher were approximately 60%. In the mid-palatal relief model, the distribution volume at which a stress of 0.20 MPa or higher was generated was 180% of that in the relief model. CONCLUSIONS: The supportive strength of plates can be increased by selectively applying optimal relief rather than standard relief, allowing for easier and more effective plate-denture treatment.

Changes in denture retention with denture adhesives and oral moisturizers for the oral cavity: an in vitro study.

BACKGROUND: It is difficult to maintain complete dentures during meals in place. This in vitro study aimed to assess changes in denture retention between rest and function using denture adhesives and oral moisturizers in an oral cavity model. METHODS: The following test samples were applied between the palatal plate and the edentulous jaw ridge model: denture adhesive, denture adhesive for dry mouth, oral moisturizer, and denture moisturizer. The retentive force was measured under two conditions: at rest while immersed in water and during function with a 2.5-kg load applied. The plate was pulled perpendicular to the occlusal plane and the retentive force was measured using a digital force gauge. RESULTS: Under dry conditions, denture adhesive for dry mouth and oral moisturizer had a significantly higher retentive force than denture adhesive and denture moisturizer. After 30 min of immersion in water, the retentive force of the denture adhesive increased while that of the oral moisturizer decreased. After 30 min of function, the retentive force of the denture adhesive and denture adhesive for dry mouth remained high, while that of the oral moisturizer and denture moisturizer significantly decreased. Between rest and function, the retentive force of the denture adhesive and denture adhesive for dry mouth was high, and that of the oral moisturizer was low. CONCLUSIONS: Immediately after use, denture adhesive for dry mouth exhibited high retentive force, but retention gradually decreased due to its water content.

Fabrication of removable palatal augmentation prosthesis on a complete denture to reduce weight and maintain hygiene.

A removable veneer-type palatal augmentation prosthesis (PAP) was attached to a complete denture to reduce weight and maintain good hygiene. As a result, the weight of the PAP was reduced from 27.1 g at the time of palatal augmentation, by using the tissue conditioner, to 16.6 g, with the definitive removable veneer-type prosthesis. This method can also be applied to removable partial dentures when the impression of the palatal augmentation is properly positioned on the definitive cast after the removal of the tissue conditioner.

Fabrication of a customized tray for preventing fracture of isolated abutment teeth in definitive casts.

Isolated abutment teeth with advanced bone resorption on definitive casts for a partial removable dental prosthesis can fracture when the definitive cast is removed from the impression or during subsequent laboratory procedures. This report describes a technique that avoids fracture of the definitive cast during its fabrication. A separating line is formed on the custom tray, which enables removal of the definitive cast without fracturing the isolated tooth. In addition, if the cervical line is sharp and appears compromised, then the impression can be trimmed at the clinical cervical line to enlarge the abutment diameter and increase its resistance to fracture without altering the shape of critical areas.

Influence of denture supporting tissue properties on pressure-pain threshold--measurement in dentate subjects.

PURPOSE: The present study was designed to clarify the relationship between the properties of the palatal mucosa and the pressure-pain threshold. METHODS: Three parts of the palatal mucosa of 17 dentate subjects were measured: the median part of the palate, the lateral part of the first molar, and the midpoint between these two parts. The subjects were instructed to press a pushbutton when he or she felt pressure-pain. The probe pressure was gradually increased (1N/s). The thickness (T) (mm) and elasticity (E) (MPa) were used as the parameters of the properties of the palatal mucosa, whereas pressure (P) (MPa), compressibility (C) (%), and subsidence (S) (mm) were used as the parameters of the pressure-pain threshold. The Shapiro-Wilk test was used to consider the data of distribution of normality for each measurement point, as obtained from the 17 subjects. A Kruskal-Wallis test and a Wilcoxon signed rank test were performed for multiple comparisons, the Bonferroni method was used to compensate for the P-value. Spearman's rank correlation coefficient was calculated. RESULTS: T correlated with the values of S at the median points (P=0.001) and midpoints (P=0.011). CONCLUSION: Thickness can be an index of the amount of relief where pain is caused easily. In addition, modulus of elasticity is important as an indicator of the bearing ability of denture support tissues, it is necessary to consider how to evaluate the modulus of elasticity and to evaluate the relationship between the parameters of the pain threshold.

Systematic clinical evaluation and correction procedures for support of removable partial dentures.

Support, retention, and bracing are the three main functions of a direct retainer in removable partial dentures (RPDs). RPDs must have sufficient supporting ability for proper occlusal rehabilitation. Support ability depends on the fit, size, shape, and location of the occlusal rest. Support cannot be adjusted chairside in most cases. The purpose of this article is to present systematic evaluation criteria for support in an RPD and to describe methods for adjusting cast clasps with improper support. Appropriate design of RPDs and preparation of abutments are also described.

[Prediction of mandibular movement by observation of facial skin markers].

PURPOSE: Various methods have been used for observation of mandibular movement. However, many methods disturb physiological movement as the subject must wear a sensor. Therefore, to predict mandibular movement from the motion of facial skin, the correlation between the movements of mandibular incisor-tooth point and facial skin markers was evaluated by multiple regression analysis. METHODS: Nine retro-reflective markers were placed on the lower facial skin of 8 dentulous subjects and three markers on the wire frame attached to the mandibular tooth, respectively. Movement of markers was repeatedly recorded by 6 video cameras from centric occlusion to maximal opening position. Data was analyzed and the movements were constructed in 3D. In order to predict movement (opening, vertical, anterior-posterior) at an incisor-tooth point, multiple regression analysis was performed by making the 27 amounts of 3D movements (X, Y, Z components) of nine facial skin markers as explanatory variables. The difference between the actual value and the predicted value by multiple regressions was calculated, and compared in the 5 ranges of analysis (0-5 mm, 0-10 mm, 0-15 mm, 5-10 mm, 10-15 mm). RESULTS: The movements of mouth opening and vertical direction could be predicted with the accuracy of 0.76 mm (3.7%)and 0.69 mm (4.9%) in the range of 0-15 mm with nine variables, respectively. However, the accuracy of movements in the anterior-posterior direction was 0.40 mm (9.7%) with ten variables. The ratio was larger than these in the movements of mouth opening and vertical direction. CONCLUSIONS: It was suggested that movement of mandibular incisor-tooth point in mouth opening and vertical direction to 15 mm could be predicted from the facial skin markers.