Evaluation of interface pressure and temperature management in five wheelchair seat cushions and their effects on user satisfaction.

BACKGROUND: Factors such as the manufacturing materials, shape or even the mechanical and thermal response of sitting Pressure Redistribution Support Surfaces (PRSS) can be potential contributors to pressure ulcers. However, few studies have compared a number of characteristics of the most frequently used devices. OBJECTIVE: To compare three potential contributors to pressure ulcers in five commercial PRSS: pressure redistribution, temperature and perceived comfort. METHOD: Study with a cross-over randomized design in healthy volunteer participants. Data was collected in a temperature and relative humidity controlled environment. To assess thermal response, the temperature (Flir-E60) of the region of interest was captured before and after use of each PRSS for further analysis. The region of interest was the gluteal zone. To assess the pressure redistribution a pressure mat (XSensor®) was used between the 5 cushion and each study participant using a standardized method. Finally, a subjective perception questionnaire recorded comfort, adaptability and thermal sensation parameters. Data analysis levels of significance were set at 0.05. RESULTS: A total of 22 participants completed the assessments. There were no statistically significant differences in baseline temperatures between PRSS (>0.05). Pressure redistribution analysis showed significant differences between all PRSS in all variables evaluated except in the maximum and peak pressure index al sacrum. The subjective assessment suggested no major user-perceived differences between PRSS. CONCLUSION: Seat cushions made of open cell polyurethane foam blocks of variable hardness and the horseshoe cushion (also open cell polyurethane foam) seem to provide a more effective pressure relief characteristic than those injected with polyurethane foam and gel in most of the studied pressure variables. However, the cushions provide similar thermal response and perceived comfort.

Survival analysis of mandibular complete dentures with acrylic-based resilient liners.

OBJECTIVE: The purpose of this long-term randomised controlled trial was to compare the longevity of dentures constructed using a conventional acrylic resin (CAR) to that of dentures constructed using an acrylic-based resilient liner (ARL). MATERIALS AND METHODS: The follow-up study was essentially carried out by annual telephone calls to each of the 67 participants. The Kaplan-Meier method and life-table analysis were used for univariate analyses. The Cox proportional-hazards test was used as a final model for statistically adjusting predictor variables such as sex, clinician type, mandibular denture type and age at denture delivery. RESULTS: The denture type was likely to affect the survival time of the dentures, while the sex and clinician type were not. The group using acrylic-based resilient denture liners had twice the risk of having shorter denture-survival times than those using conventional acrylic resin dentures. Younger participants were likely to have a reduced risk of having shorter denture-survival times than older participants. CONCLUSION: We conclude that mandibular complete dentures constructed using ARL are twice as likely as dentures constructed using CAR to have shorter denture survival times, mainly because of material deterioration.

Long-term prosthetic aftercare of direct vs. indirect attachment incorporation techniques to mandibular implant-supported overdenture.

OBJECTIVE: The aim of this long-term study was to compare the need for prosthetic aftercare of direct vs. indirect attachment incorporation techniques to mandibular implant-supported overdenture. MATERIALS AND METHODS: Forty-five consecutive patients were included (130 implants were placed). Treatment was randomly allocated, resulting in 22 patients (group A) to be treated with direct ball attachment incorporation and 23 patients (group B) to be treated with indirect ball attachment incorporation. All patients were treated by experienced oral-maxillofacial surgeons/periodontists and experienced prosthodontists/residents. From the first day that the patients visited the clinic up to 20 years after the first treatment session, all surgical or prosthetic therapeutic interventions were recorded. The recorded data for the present study included the number of aftercare visits and dental treatment received (pressure sores relieve, liner changes due to loss of retention and attachment replacement due to wear). RESULTS: The mean follow-up was 93±57 months. No implants were lost. Statistical analysis revealed a statistically significantly (P<0.001) greater need for prosthetic interventions in group B vs. group A. The mean number of visits dedicated to - pressure sores relieve (7.04±1.4 vs. 3.63±0.84); liner exchange due to loss of retention (3.6±1.3 vs. 1.09±1.06) was significantly higher in group B. Attachment replacement due to wear occurred only in group B (11/23 - 47.8%). CONCLUSION: The direct technique for attachment incorporation in mandibular implant-supported overdentures using ball attachments is superior to the indirect technique from the aftercare perspective during a long-term evaluation period.

Interactions between thermal cycled resilient denture lining materials, salivary and serum pellicles and Candida albicans in vitro. Part I. Effects on fungal growth.

In the present study, the growth of a single isolate of Candida albicans on seven saliva-, serum-coated or protein free (uncoated), thermocycled (4-70 degrees C for 1 min, respectively; 0, 1000 and 10 000 times) commercial resilient lining materials was investigated by monitoring pH changes in growth media. The inhibitory effect of the tissue conditioners on fungal growth was observed using three parameters, i.e. (i) the delay in the onset of the rapid decline in pH, (ii) the reduction in the rate of pH change and (iii) the pH minima reached. In the case of control soft liners (not thermocycled and uncoated), the antifungal effect appeared to depend upon the type of commercial soft liner used. Thus, an initial delay in pH decline and a very high pH minima were observed with fluoric and heat-cured silicone materials. High pH minima were also observed with cold-cured acrylic soft liners, whereas cold-cured silicone materials did not significantly differ from heat-cured acrylic resin (P>0.05). However, the antifungal effect of the materials was significantly reduced both by thermal cycling (ANOVA, P<0.01) and a layer of protein coating (saliva, P<0.05; serum, P<0.01). These results, taken together, suggest that the ageing of the materials and the biological fluids of the host, particularly serum, promote yeast growth on soft lining materials.

Measurement of submucosal forces transmitted to dental implants.

Early loading of dental implants after placement is believed to be a major cause for premature implant failure. If a transitional denture or partial denture is used during the healing period, occlusal forces may be transmitted to the submerged implant, leading to poorly differentiated growth of bone cells and/or potential inhibition of osseointegration at the bone-implant interface. The objective of this study was to develop an experimental model to measure the force transmission and to characterize the effect of selected loading conditions and relief methods on the forces transmitted to the implant. The loading conditions studied included unilateral and bilateral loading of the prosthesis. Forces were measured at two different relief conditions (relief with and without soft liner) and were compared against a control with no relief. The results show that fabrication of the prosthesis with a proper relief at the implant-denture junction can eliminate the submucosal force transmission to the implant on loading the denture both under unilateral and bilateral loading conditions. When a soft liner is used at the relief site, the transmitted force is small, but a finite value is reproducibly recorded. With no relief, the submucosal force transmission is high and may adversely affect the healing process or osseointegration. The experimental model is valuable in measuring and understanding the submucosal forces that are transmitted to the implant by loading the transitional prosthesis, and such measurement may assist in the proper design of the prosthesis for improved clinical durability and for other uses.

Color stability of heat-polymerized and autopolymerized soft denture liners.

STATEMENT OF PROBLEM: The physical and mechanical properties of soft denture liners are influenced by a number of factors. Aging is one factor that has an effect on the characteristics of polymers. The resistance of denture liners to aging can potentially influence the color stability of these liners. PURPOSE: This study attempted to determine the color stability of soft liners by subjecting them to an in vitro accelerated aging test. MATERIAL AND METHODS: Two autopolymerizing and 3 heat polymerizing commercially available soft denture lining materials were tested. Seven sample disks were made of each material according to manufacturers' instructions. Color measurements were recorded before and after the accelerated aging process. Color changes (DeltaE) were calculated by measuring tristimulus values at several wavelengths in the visual spectrum with the use of Commission International de l'Eclairge Lab (CIE-LAB) uniform color scale. RESULTS: Kruskall-Wallis variance analysis and Mann-Whitney U-Wilcoxon rank sum W tests were performed for statistical comparison of the DeltaE values. Ufigel P and Simpa liner materials showed significantly greater color changes than the other tested materials. There were no significant differences in color change among Ufigel L-Molloplast B, Ufigel L-Flexor, and Molloplast B-Flexor liner materials. However, a significant difference in color change was found between Ufigel P and Simpa liners. CONCLUSION: Heat-polymerized soft liners were more color stable than autopolymerized soft liners. No significant differences were found among heat polymerized materials; however, significant differences in color change were found between the 2 autopolymerized liners.

Setting and stress relaxation behavior of resilient denture liners.

STATEMENT OF PROBLEM: Resilient denture liners are widely used for the patients who are not comfortable with correctly made conventional hard-based dentures because of thin and relatively nonresilient mucosa or severe alveolar resorption. There are several materials used for denture liners and the efficacy in their use is influenced by their viscoelastic properties. PURPOSE: This study evaluated the setting behavior and viscoelastic properties of various types of resilient denture liners and the changes in viscoelasticity with the passage of time. MATERIAL AND METHODS: Four types of resilient denture liners were used. Setting behavior of 5 autopolymerizing materials was evaluated with an oscillating rheometer. Stress relaxation tests were conducted to evaluate the viscoelastic properties of 9 materials and changes that occurred over time by means of Maxwell model analogies. RESULTS: Significant differences were found in the setting behavior of the autopolymerizing materials. The acrylic resin and fluoroethylene materials demonstrated viscoelastic properties and the silicone and polyolephin materials were found to be elastic. The acrylic resin materials exhibited the greatest changes in viscoelastic properties over time when compared with silicone, polyolephin, and fluoroethylene materials. CONCLUSIONS: The results suggest that it is important to select denture liner materials according to clinical situations because of the wide ranges of setting behavior, viscoelastic properties, and durability over time.

Effect of addition antimicrobial agents to denture reliners.

This study aimed at evaluating the incorporation of two antimicrobial drugs (nystatin and polynoxylin) as regards: the effect of the liner on the activity of the drug, determination of the least effective concentration of each drug and its duration of action, as well as assessment of the effect of the drug on the mechanical properties and the chemical composition of the liner. Results showed that nystatin added to denture liners in three different concentrations by weight (3%, 5%, 10%) acted effectively against Candida albicans, and that there was a direct relationship between concentration of Nystatin and its duration of action. The inhibitory effect of nystatin (10%) lasted for at least 32 weeks (end of study period). Furthermore, this concentration did not affect the strength properties of the liner. On the other hand, polynoxylin inhibited a number of strains of bacteria and Candida only in high concentrations (40-60%), and these concentrations adversely affected the strength properties of the liner.