Evaluation of heat-cured resin bases following the addition of denture teeth using a second heat cure

The Effect of Microwave Disinfection on Denture Base Polymers, Liners and Teeth: A Basic Overview

The aim of this paper was to overview the current scientific knowledge concerning the effect of microwave disinfection on denture related material properties. Cross-infection control in dentistry is a significant issue in everyday clinical practice due to the recent increase in some infectious diseases such as hepatitis B, C and AIDS and therefore numerous methods of disinfection have been used. The most widespread method of disinfection used in everyday practice is chemical, however, studies have suggested that chemical disinfectants alter the physical and mechanical properties of the acrylic resins and enable the growth and proliferation of certain bacteria. Therefore, microwaves were introduced as an easy to use-and-access, low cost, chemical free alternative. The question that arose was if and in what way the microwave irradiation affected the denture related material properties. Microwaving affects the denture resin bases, liners and teeth in different ways. The results showed that microwave disinfection could be a safe alternative for the disinfection of denture bases and liners compared to the chemical one, when the procedure is carried out in dry conditions, but could possibly cause dimensional changes of clinical significance on them when the irradiation takes place in wet environment. It also seems to have no detrimental effects of clinical importance on the flexural properties, impact strength and hardness of denture resins and the bond, flexural strength, porosity and hardness of denture liners. The effects of microwave disinfection on the hardness of denture teeth and teeth/denture bond strength are still controversial and no safe conclusions can be drawn.

Effect of the processing cycle on dimensional changes of heat-polymerized denture base resins

Background:

The second processing cycle for adding the artificial teeth to heat-polymerized acrylic resin denture bases may result in dimensional changes of the denture bases. The aim of this study was to evaluate the dimensional changes of the heat-polymerized acrylic resin denture bases with one and two-cycle processing methods.

Materials and Methods:

A metal edentulous maxillary arch was used for making 40 stone casts. Maxillary complete dentures were made with heat-polymerized acrylic resins (Meliodent and Acropars) with one and two stage processing methods (n = 10 for each group). Linear dimensional changes in anteroposterior and mediolateral distances and vertical changes in the first molar region were measured following each processing cycle, using a digital caliper. Mean percentage of the dimensional changes were subjected to two-way analysis of variance and Tukey honest significant difference tests (α = 0.05).

Results:

Postpolymerization contraction occurred in both anteroposterior and mediolateral directions in all studied groups; however, the vertical dimension was increased. Acropars acrylic resin showed the highest dimensional changes and the second processing cycle significantly affected the measured distances (P < 0.05). Meliodent acrylic resin was not significantly influenced by the processing method.

Conclusion:

Reheating of the acrylic resin denture bases for the addition of denture teeth result in linear dimensional changes, which can be clinically significant based on the acrylic resin used.

In vitro adhesion of Candida glabrata to denture base acrylic resin modified by glow-discharge plasma treatment

This study evaluated the potential of plasma treatments to modify the surface chemistry and hydrophobicity of a denture base acrylic resin to reduce the Candida glabrata adhesion. Specimens (n = 54) with smooth surfaces were made and divided into three groups (n = 18): control - non-treated; experimental groups - submitted to plasma treatment (Ar/50 W; AAt/130 W). The effects of these treatments on chemical composition and surface topography of the acrylic resin were evaluated. Surface free energy measurements (SFE) were performed after the treatments and after 48 h of immersion in water. For each group, half (n = 9) of the specimens were preconditionated with saliva before the adhesion assay. The number of adhered C. glabrata was evaluated by cell counting after crystal violet staining. The Ar/50 W and AAt/130 W treatments altered the chemistry composition, hydrophobicity and topography of acrylic surface. The Ar/50 W group showed significantly lower C. glabrata adherence than the control group, in the absence of saliva. After preconditioning with saliva, C. glabrata adherence in experimental and control groups did not differ significantly. There were significant changes in the SFE after immersion in water. The results demonstrated that Ar/50 W treated surfaces have potential for reducing C. glabrata adhesion to denture base resins and deserve further investigation, especially to tailor the parameters to prolong the increased wettability.

Influence of microwave disinfection on the dimensional stability of intact and relined acrylic resin denture bases

STATEMENT OF PROBLEM

Microwave irradiation has been suggested as a method to disinfect denture bases. However, the effect of microwave heating on the dimensional stability of the relined denture bases is unknown.

PURPOSE

The purpose of this study was to evaluate the dimensional stability of intact and relined acrylic resin denture bases after microwave disinfection.

MATERIAL AND METHODS

A standard brass cast simulating an edentulous maxillary arch was machined and used to fabricate 2- and 4-mm-thick denture bases (n=200), which were processed with heat-polymerized acrylic resin (Lucitone 550). The 2-mm thick-specimens (n=160) were relined with 2 mm of autopolymerizing resin (Tokuso Rebase Fast, Ufi Gel Hard, Kooliner, or New Truliner). Distances between 5 removable pins on the standard brass cast were measured with a Nikon optical comparator, and the area (mm) formed by the distance between 5 pins was calculated and served as baseline. During fabrication, the pins were transferred to the intaglio surface of the specimens. Differences between the baseline area and those subsequently determined for the specimens were used to calculate the percent dimensional changes. The intact and relined denture bases were divided into 4 groups (n=10) and evaluated after: polymerization (control group P); 1 cycle of microwave disinfection (MW); daily microwave disinfection for 7 days (control group MW7); water storage for 7 days (WS7). Microwave irradiation was performed for 6 minutes at 650 W. Data were analyzed using 2-way ANOVA followed by Tukey's test (alpha=.05).

RESULTS

Intact specimens and those relined with Kooliner and New Truliner showed increased shrinkage after 1 (P=.05, .018, and .001, respectively) and 7 (P <.001, .003, and <.001, respectively) cycles of microwave disinfection. With the exception of specimens relined with Kooliner, intact specimens showed greater shrinkage than the relined specimens after 7 cycles of microwave disinfection.

CONCLUSIONS

Microwave disinfection produced increased shrinkage of intact specimens and those relined with New Truliner and Kooliner.

The effect of cyclic drying on dimensional changes of acrylic resin maxillary complete dentures

Poly(methyl methacrylate) dentures may exhibit dimensional changes when drying. Drying has been shown to destroy Candida albicans. This study investigates the effect of simulating overnight cyclic drying on dimensional changes of four complete denture base materials. Denture specimens used in this study had been prepared for a previous study. All dentures had been kept hydrated at room temperature for 2 years. The materials used were, group 1, conventionally packed and cured Trevalon, group 2 was injection moulded and conventionally cured (Trevalon Success), group 3 (Acron MC) and group 4 was Microbase, which is injection moulded and microwave cured. The measurements of the inter-molar and inter-premolar width, and anterior posterior dimension between the premolars and molars were recorded after 8 h drying and then after four cycles of dehydration and rehydration. The dentures were more dimensionally stable in the anterior posterior than the cross arch dimension. There was a statistically significant (P < 0.02) increase in the intermolar width for Trevalon, Trevalon Success and Acron after 8 h drying and after four cycles. There was a statistically significantly difference between Microbase and the other materials after 8 h drying and there was a significant difference between the injection moulded groups in the interpremolar width (Trevalon Success versus Acron, Trevalon Success versus Microbase) after cyclic drying. Although statistically significant dimensional changes were observed for all materials these were small and were considered not to be clinically significant. Microbase was the least dimensionally stable material during air-drying.

Teaching an abbreviated impression technique for complete dentures in an undergraduate dental curriculum

STATEMENT OF PROBLEM

Traditional methods for teaching complete denture fabrication are time-consuming, difficult to master, and not used by many general practitioners.

PURPOSE

This study compared the efficacy of traditional denture fabrication techniques with a more abbreviated method in a dental school setting.

MATERIAL AND METHODS

A retrospective record review of 80 completely edentulous patients treated by predoctoral dental students was completed. Forty patients were treated with traditional denture techniques; the other 40 patients were treated with an abbreviated method. The data abstracted included the number of visits to completion and the number of postinsertion visits and relines required within the first 3 months after delivery. A Wilcoxon rank sum test was performed to determine statistical significance between the groups with regard to number of visits for fabrication and postinsertion adjustments. A test for a difference in proportions by using the normal approximation to the binomial distribution was performed for statistical analysis of the incidence of relines.

RESULTS

The abbreviated denture technique resulted in a statistically significant difference in the number of visits for fabrication (P<.01) and postinsertion adjustments (P<.05.) There was no difference (P=.39) in the number of relines between the 2 groups.

CONCLUSION

Teaching the abbreviated complete denture technique in an undergraduate dental clinic decreased the number of appointments necessary to complete denture therapy without increasing the number of adjustments or reline procedures.

Linear dimensional change of heat-cured acrylic resin complete dentures after reline and rebase

STATEMENT OF PROBLEM

Relining and rebasing of complete dentures are common procedures to improve the fit of the prostheses. After relining or rebasing, adjustments may be required because of dimensional change that occurs during reprocessing of the denture when new denture base material is polymerized.

PURPOSE

This study analyzed the linear dimensional change of heat cured acrylic resin that occurs during reline and rebase procedures for complete dentures.

MATERIAL AND METHODS

Twenty-two maxillary and mandibular complete denture bases with artificial teeth were saturated by immersion in distilled water at 37 degrees C +/- 1 degree C. Fine crosses were marked on the incisal edges of the central incisors and the supporting cusps of the second molar teeth. Distances between the marks were measured with a high resolution traveling microscope. Heat-cured acrylic resin was processed by a long curing cycle of 72 degrees C for 6.5 hours, then heated to 100 degrees C for over 30 minutes and kept at 100 degrees C for 1 hour. The relined or rebased denture was allowed to cool slowly in the water bath for 48 hours to reach ambient temperature. The reference-crosses were measured immediately after careful deflasking.

RESULTS

In the relining procedure, all incisor-molar and intermolar distances exhibited shrinkage of 0.3%, despite different shapes of maxillary and mandibular dentures. Results of the rebasing procedure were similar to that of the reline expect that only 0.1% intermolar shrinkage was found on the maxillary denture.

CONCLUSION

Shrinkage was approximately 0.15 mm for an interarch distance of 50 mm. This degree of change is both clinically undetectable and insignificant. Using this processing cycle for acrylic resin in reline or rebase procedures did not cause clinically significant dimensional changes to complete dentures.

Temperature and dimensional changes in the two-stage processing technique for complete dentures

OBJECTIVES

This study concerned the temperature and linear dimensional change of heat-cured acrylic resin in the two-stage processing technique for complete dentures.

METHODS

Thermocouples were incorporated in the acrylic resin for recording temperatures. Measurements between reference marks were made by a high-resolution digital measuring microscope.

RESULTS

No increase in temperature associated with the exothermic nature of the polymerization reaction was recorded. The temperature of the resin followed the waterbath temperature closely. The temperatures recorded at various regions were in phase with each other. The total linear shrinkage of the base after two processing cycles was less than 1% and compares favourably with studies on the single-stage processing technique.

CONCLUSIONS

Temperature differential is excluded as a reason for the warpage of dentures. The dimensional changes of the denture base resulting from the two-stage processing technique cannot be considered to be of any clinical significance.