The effect of cooling procedures on monomer elution from heat-cured polymethyl methacrylate denture base materials.

OBJECTIVE: To evaluate the amount of methyl methacrylate (MMA) released in water from heat-cured polymethyl methacrylate (PMMA) denture base materials subjected to different cooling procedures. METHODOLOGY: Disk-shaped specimens (Ø:17 mm, h:2 mm) were fabricated from Paladon 65 (PA), ProBase Hot (PB), Stellon QC-20 (QC) and Vertex Rapid Simplified (VE) denture materials using five different cooling procedures (n=3/procedure): A) Bench-cooling for 10 min and then under running water for 15 min; B) Cooling in water-bath until room temperature; C) Cooling under running water for 15 min; D) Bench-cooling, and E) Bench-cooling for 30 min and under running water for 15 min. A, B, D, E procedures were proposed by the manufacturers, while the C was selected as the fastest one. Control specimens (n=3/material) were fabricated using a long polymerization cycle and bench-cooling. After deflasking, the specimens were ground, polished and stored in individual containers with 10 ml of distilled water for seven days (37oC). The amount of water-eluted MMA was measured per container using isocratic ultra-fast liquid chromatography (UFLC). Data were analyzed using Student's and Welch's t-test (α=0.05). RESULTS: MMA values below the lower quantification limit (LoQ=5.9 ppm) were registered in B, C, E (PA); E (PB) and B, D, E (QC) procedures, whereas values below the detection limit (LoD=1.96 ppm) were registered in A, D (PA); A, B, C, D (PB); C, D, E (VE) and in all specimens of the control group. A, B (VE) and A, C (QC) procedures yielded values ranging from 6.4 to 13.2 ppm with insignificant differences in material and procedure factors (p>0.05). CONCLUSIONS: The cooling procedures may affect the monomer elution from denture base materials. The Ε procedure may be considered a universal cooling procedure compared to the ones proposed by the manufacturers, with the lowest residual monomer elution in water.

Rehabilitation Considerations for Very Young Children with Severe Oligodontia due to Ectodermal Dysplasia: Report of Three Clinical Cases with a 2-Year Follow-Up.

Introduction: Management of oligodontia can be complicated and requires multidiscipline care, involving a wide spectrum of interventions. The aim of this report is to describe the challenges of oral rehabilitation of three very young children with oligodontia. Report. Three preschool aged Caucasian males, diagnosed with ectodermal dysplasia, were treated with interim removable dentures in order to replace missing teeth, reclaim vertical dimension, and improve function and aesthetics. The main challenges faced were patient cooperation, dental and skeletal characteristics, and parental expectations. Two years post-treatment, both patients and parents reported excellent adaptation to prosthesis and satisfaction with aesthetics. Conclusion: Rehabilitation of oligodontia may be challenging due to accompanying oral findings, dentofacial growth considerations, and behavioral issues. Establishment of good rapport between patients, parents, and clinician is the key for the success of the treatment even with the use of nonpharmacological behavioral management techniques.

Illuminant metameric effects on interbrand and intrabrand color differences of direct composite resins.

STATEMENT OF PROBLEM: Information on the illuminant metameric effects on the intrabrand and interbrand differences in color of direct composite resins is lacking. PURPOSE: The purpose of this in vitro study was to evaluate the effects of different illuminations on the color differences of the same or different brands of composite resins. MATERIAL AND METHODS: Sixty-four disks were prepared from 8 different direct dental composite resins of A3 shade, and, after polymerization and hydration for 48 hours, their color coordinates were measured in the Commission Internationale de I'Eclairage (CIE) L∗a∗b∗ color space with a portable colorimeter on a black and white background under D65 (daylight), F2 (cool white fluorescence), and A (incandescence) illuminations. Translucency parameters (TP) and fluorescence intensities (FI) of the brands were also measured to assist in the interpretation of brand behavior under the illuminations. The Kruskal-Wallis and Friedman nonparametric tests with post hoc multiple comparisons tests were applied to analyze the data for differences within and between brands under all illuminations (α=.05), while regression analysis was used to estimate the relationship between D65 and F2 or A illumination data. RESULTS: Statistical analysis showed significant differences among brands (P<.05) for all color coordinates under all illuminations, with a strong linear relationship between them (R2=0.72-0.97). Intrabrand differences were significantly different across brands (P<.05) and ranged from 0.06 to 3.1 across illuminations in ΔE∗ab units (0.05 to 2.4 in ΔΕ00 units). Interbrand differences were also significantly different (P<.05), with a range of 0.15 to 8.7 ΔE∗ab units or 0.14 to 5.7 ΔΕ00 units. CONCLUSIONS: Primary color coordinates of composite resins were affected by A or F2 illumination and were strongly associated with D65 values. Redder or yellower composite resins were affected more under A or F2 illumination. Intrabrand differences, although small, may contribute to clinical mismatches under A or F2 illuminations. Clinicians should be aware that certain brand pairs may present acceptable differences under D65 illumination but could become unacceptable under A or F2 illumination.

The effect of cooling procedures on monomer elution from heat-cured polymethyl methacrylate denture base materials

Abstract Objective To evaluate the amount of methyl methacrylate (MMA) released in water from heat-cured polymethyl methacrylate (PMMA) denture base materials subjected to different cooling procedures. Methodology Disk-shaped specimens (Ø:17 mm, h:2 mm) were fabricated from Paladon 65 (PA), ProBase Hot (PB), Stellon QC-20 (QC) and Vertex Rapid Simplified (VE) denture materials using five different cooling procedures (n=3/procedure): A) Bench-cooling for 10 min and then under running water for 15 min; B) Cooling in water-bath until room temperature; C) Cooling under running water for 15 min; D) Bench-cooling, and E) Bench-cooling for 30 min and under running water for 15 min. A, B, D, E procedures were proposed by the manufacturers, while the C was selected as the fastest one. Control specimens (n=3/material) were fabricated using a long polymerization cycle and bench-cooling. After deflasking, the specimens were ground, polished and stored in individual containers with 10 ml of distilled water for seven days (37oC). The amount of water-eluted MMA was measured per container using isocratic ultra-fast liquid chromatography (UFLC). Data were analyzed using Student's and Welch's t-test (α=0.05). Results MMA values below the lower quantification limit (LoQ=5.9 ppm) were registered in B, C, E (PA); E (PB) and B, D, E (QC) procedures, whereas values below the detection limit (LoD=1.96 ppm) were registered in A, D (PA); A, B, C, D (PB); C, D, E (VE) and in all specimens of the control group. A, B (VE) and A, C (QC) procedures yielded values ranging from 6.4 to 13.2 ppm with insignificant differences in material and procedure factors (p>0.05). Conclusions The cooling procedures may affect the monomer elution from denture base materials. The Ε procedure may be considered a universal cooling procedure compared to the ones proposed by the manufacturers, with the lowest residual monomer elution in water.

Removal of denture adhesives from PMMA and Polyamide denture base materials.

OBJECTIVE: Denture adhesives need complete removal due to their frequent replacement. Our study investigates the removal of denture adhesives from denture base materials, using different methods. METHODOLOGY: PMMA and Polyamide denture base materials were used to fabricate 120 samples (15×15×1.5mm). One side of the samples was left as processed and the other polished with a usual procedure, hydrated for 24 h, dried, and weighted. They received 0.2 g of three adhesive creams on their unpolished surface (Corega, Olivafix, Fittydent), pressed on polysulfide material, stored under 37°C and 95% rel. humidity for 1 h and 60 of them, following their separation from polysulfide base, brushed under running water, whereas the rest inserted in a cleanser bath (Fittydent Super) for 5 min. The samples were dried and inserted in the oven (37°C) for additional 10 min and weighted again. Roughness tests of denture materials and light microscopy of adhesives creams were also used to evaluate the materials. Time lapse images of spayed with water adhesives on PMMA base were also taken to evaluate the volumetric changes of adhesives. Weight data before and after adhesive removal, indicating the amount of remaining adhesive, were statistically analyzed using Welch's ANOVA and Games-Howell multiple comparisons tests at α=0.05 level of significance. RESULTS: Roughness of Polyamide was higher than PMMA and Fittydent showed greater volumetric changes than the others. Significant differences (p<0.05), were found between PMMA and Polyamide bases, between Olivafix and Fittydent adhesives, and between brushing and cleansing methods but only for PMMA-Olivafix combination. CONCLUSIONS: Adhesives showed a stronger adherence to PMMA surface, and Fittydent was the most difficult to be removed. Removal methods were not effective for all adhesives or denture base materials. These indicate that removal methods, adhesive type and denture base material are all playing a significant role in the removal of adhesives from denture surfaces.

Removal of denture adhesives from PMMA and Polyamide denture base materials

Abstract Denture adhesives need complete removal due to their frequent replacement. Objective Our study investigates the removal of denture adhesives from denture base materials, using different methods. Methodology PMMA and Polyamide denture base materials were used to fabricate 120 samples (15×15×1.5mm). One side of the samples was left as processed and the other polished with a usual procedure, hydrated for 24 h, dried, and weighted. They received 0.2 g of three adhesive creams on their unpolished surface (Corega, Olivafix, Fittydent), pressed on polysulfide material, stored under 37°C and 95% rel. humidity for 1 h and 60 of them, following their separation from polysulfide base, brushed under running water, whereas the rest inserted in a cleanser bath (Fittydent Super) for 5 min. The samples were dried and inserted in the oven (37°C) for additional 10 min and weighted again. Roughness tests of denture materials and light microscopy of adhesives creams were also used to evaluate the materials. Time lapse images of spayed with water adhesives on PMMA base were also taken to evaluate the volumetric changes of adhesives. Weight data before and after adhesive removal, indicating the amount of remaining adhesive, were statistically analyzed using Welch's ANOVA and Games-Howell multiple comparisons tests at α=0.05 level of significance. Results Roughness of Polyamide was higher than PMMA and Fittydent showed greater volumetric changes than the others. Significant differences (p<0.05), were found between PMMA and Polyamide bases, between Olivafix and Fittydent adhesives, and between brushing and cleansing methods but only for PMMA-Olivafix combination. Conclusions Adhesives showed a stronger adherence to PMMA surface, and Fittydent was the most difficult to be removed. Removal methods were not effective for all adhesives or denture base materials. These indicate that removal methods, adhesive type and denture base material are all playing a significant role in the removal of adhesives from denture surfaces.

Intra- and inter-brand color differences of denture teeth under different illuminations.

Debonding, staining and wear are usually the reasons for denture teeth replacement by new ones from same or different brands. Objective This study investigates the possible differences in color of denture teeth of the same or different brands under different illuminations, since their metameric behavior in color under specific illumination may become unacceptable. Methodology For the purpose of this study, 10 denture teeth (#11), shade A3, of 4 different brands were selected (Creopal/KlemaDental Pro, Executive/DeguDent, Cosmo HXL/DeguDent, Ivostar/Ivoclar-Vivadent). Teeth stabilized in white silicone mold and the CIELAB color coordinates of their labial surface under 3 different illumination lights (D65, F2, A) were recorded, using a portable colorimeter (FRU/WR-18, Wave Inc). ΔE*ab values of all possible pairs of teeth of the same brand (n=45) or pair combinations of different brands (n=100) under each illumination light, in a dry and wet state were calculated. Data were analyzed statistically using 3-way ANOVA, Friedman's and Wilcoxon's tests at a significance level of α=0.05. Results The results showed that brand type affected significantly L*, a* and b* coordinates (p<0.0001), illumination a* and b* coordinates (p<0.0001), but none of them was affected by the hydration state of teeth (p>0.05). Intra-brand color differences ranged between 0.21-0.78ΔΕ* units with significant differences among brands (p<0.0001), among illumination lights (p<0.0001) and between hydration states (p=0.0001). Inter-brand differences ranged between 2.29-6.29ΔΕ* units with significant differences among pairs of brands (p<0.0001), illumination lights (p<0.0001) and hydration states (p<0.0001). Conclusions Differences were found between and within brands under D65 illumination which increased under F2 or A illumination affected by brand type and hydration status. Executive was the most stable brand than the others under different illuminations or wet states and for this reason its difference from other brands is the lowest. In clinical practice, there should be no blending of teeth of different brands but if we must, we should select those that are more stable under different illuminations.

The effect of different cooling procedures on mechanical properties of denture base materials measured by instrumented indentation testing.

PURPOSE: To evaluate the different cooling procedures on the mechanical properties of five heat-cured polymethyl methacrylate (PMMA) denture materials. METHODS: 250 specimens were made equally from Meliodent (ME), Paladon 65 (PA), Probase Hot (PB), Stellon QC-20 (QC) and Vertex Rapid Simplified (VE) implementing five different cooling procedures (n=10/procedure): A) removal from water bath, bench-cooling (10min) and cooling under water (15min), B) remain in water bath till room temperature, C) removal from water bath and cooling in water for 15min, D) removal from water bath and bench cooling till room temperature and E) removal from water bath, bench cooling for 30min and cooling under water for 15min. The specimens were immersed in distilled water (15 days/37ºC) and then subjected to Instrumented Indentation Testing for Martens Hardness (HM), indentation modulus (EIT) and elastic index (ηΙΤ). Results were statistically analyzed by two- and one-way Analysis of variance (ANOVA) plus Tukey post hoc tests (α=0.05). RESULTS: The highest values for HM were recorded for QC, PA, VE with B cooling procedure, PB with A and ME with E, for EΙΤ for QC, PB with A, for PA, VE with B and ME with E, and for ηIT for QC, PB with B, PB with E, ME with C and VE with D. CONCLUSIONS: The cooling procedures recommended for PB resulted in the lowest mechanical properties. A and B may be considered as universal short- and long-cooling procedures respectively providing the highest mechanical properties for the materials tested.

Color changes of polyetheretherketone (PEEK) and polyoxymethelene (POM) denture resins on single and combined staining/cleansing action by CIELab and CIEDE2000 formulas.

PURPOSE: The purpose of study was to investigate the long-term effect of staining and/or cleansing solutions on the color stability of two non-metal removable partial denture materials. METHODS: One hundred disks (25×3mm) of polyoxymethylene (POM) and polyetheretherketone (PEEK) were immersed in water, wine, coffee, cleanser and combo bath, simulating normal daily use. Color parameters in the CIELAB system was measured every 30 cycles up to 240 using a contact colorimeter and color differences estimated using ΔEab and ΔE00 formulas. Two-way repeated measures ANOVAs and regression analyses were performed at α=0.05. RESULTS: Regression analysis indicated a strong R2 between color changes and number of cycles, for both materials. Tests of within-subjects effects for the ΔEab revealed significant differences among cycles and between the materials in the wine and coffee baths (p<0.001). Significant materialXcycles interactions were also recorded with all staining baths. ΔE00 values were lower than ΔEab up to 63.6%. Tests within and between-subjects effects for the ΔE00 gave similar but not the same with ΔEab results. CONCLUSIONS: ΔE00 found to correlate well with ΔEab. Long term exposure of both materials showed a progressive discoloration in all except control baths. POM discolored more than PEEK in coffee, and combo baths but not in cleanser. Discoloration was smaller in combo bath (where a cleanser was also used) indicating the effectiveness of a cleanser to prevent long term discoloration of both materials.

Intra- and inter-brand color differences of denture teeth under different illuminations

Abstract Debonding, staining and wear are usually the reasons for denture teeth replacement by new ones from same or different brands. Objective This study investigates the possible differences in color of denture teeth of the same or different brands under different illuminations, since their metameric behavior in color under specific illumination may become unacceptable. Methodology For the purpose of this study, 10 denture teeth (#11), shade A3, of 4 different brands were selected (Creopal/KlemaDental Pro, Executive/DeguDent, Cosmo HXL/DeguDent, Ivostar/Ivoclar-Vivadent). Teeth stabilized in white silicone mold and the CIELAB color coordinates of their labial surface under 3 different illumination lights (D65, F2, A) were recorded, using a portable colorimeter (FRU/WR-18, Wave Inc). ΔE*ab values of all possible pairs of teeth of the same brand (n=45) or pair combinations of different brands (n=100) under each illumination light, in a dry and wet state were calculated. Data were analyzed statistically using 3-way ANOVA, Friedman's and Wilcoxon's tests at a significance level of α=0.05. Results The results showed that brand type affected significantly L*, a* and b* coordinates (p<0.0001), illumination a* and b* coordinates (p<0.0001), but none of them was affected by the hydration state of teeth (p>0.05). Intra-brand color differences ranged between 0.21-0.78ΔΕ* units with significant differences among brands (p<0.0001), among illumination lights (p<0.0001) and between hydration states (p=0.0001). Inter-brand differences ranged between 2.29-6.29ΔΕ* units with significant differences among pairs of brands (p<0.0001), illumination lights (p<0.0001) and hydration states (p<0.0001). Conclusions Differences were found between and within brands under D65 illumination which increased under F2 or A illumination affected by brand type and hydration status. Executive was the most stable brand than the others under different illuminations or wet states and for this reason its difference from other brands is the lowest. In clinical practice, there should be no blending of teeth of different brands but if we must, we should select those that are more stable under different illuminations

Long-term microwaving of denture base materials: effects on dimensional, color and translucency stability.

INTRODUCTION: While the combined effect of microwave irradiation with cleansing solutions on denture base materials has been investigated, the effects of only using microwave irradiation and, more importantly, in a long-term basis, was not studied yet. OBJECTIVE: The purpose of this study was to evaluate the effect of a long-term repeated microwaving on the dimensional, color and translucency stability of acrylic and polyamide denture base materials. MATERIAL AND METHODS: Thirty two specimens (32 mm x 10 mm x 2.5 mm) from polyamide (Valplast) and PMMA (Vertex Rapid Simplified) denture base materials were made. Eight specimens from each material were immersed in distilled water (control) and 8 were subjected to microwave exposure at 450 W for 3 minutes for a period simulating 224 days of daily disinfection. Linear dimension, color change (ΔE*) and translucency parameter (TP) were measured at baseline and after certain intervals up to 224 cycles of immersion, using a digital calliper and a portable colorimeter. The results were analysed using two-way repeated measures ANOVA to estimate possible differences among predetermined cycles and material type. Regression analysis was also performed to estimate the trend of changes with time. Statistical evaluations performed at a significance level of 5%. RESULTS: Data analysis showed significant changes in length at baseline with an increasing number of cycles (p<0.05) and a significant interaction of cycle-material (p<0.001). The ΔΕ* parameter was significantly higher with a higher number of cycles (p<0.001), but it did not vary between materials (p>0.05). TP decreased similarly in both materials following microwave action but in a significantly higher level for Valplast (p<0.001). CONCLUSIONS: The results indicated that long-term repeated microwaving affects linear dimensional, color and translucency changes of both materials. Differences between PMMA and polyamide material were noted only in dimension and translucency changes.

Mandibular implant-retained overdenture relining procedure with an attachment system: A step-by-step demonstration of the technique.

BACKGROUND AND OVERVIEW: Because of continuous alveolar bone resorption, implant-retained overdentures need to be relined. The purpose of this study was to describe a method for relining an implant-retained overdenture. CASE DESCRIPTION: The authors present a step-by-step technique. A 65-year-old patient sought care for trauma and pain in the oral mucosa underneath his mandibular implant-retained overdenture. The overdenture had been fabricated 4 years previously. In addition, the patient mentioned the denture's lack of stability during function. On the basis of the patient's dental history, and clinical and radiographic examination results, the authors found alveolar bone resorption. CONCLUSIONS AND PRACTICAL IMPLICATIONS: In this case report, the authors describe the technique, analyze the procedure of implant-retained overdenture relining with a Locator attachment system (Locator abutment, H3, SP MB SZL03 for internal hex implants; MIS Seven), and describe how to restore the contact of the denture base with the denture-bearing tissues. The goal of this technique for the general dentist is to eliminate patients' tissue trauma and pain and increase the stability and support of the prosthesis.

Long-term microwaving of denture base materials: effects on dimensional, color and translucency stability

Abstract While the combined effect of microwave irradiation with cleansing solutions on denture base materials has been investigated, the effects of only using microwave irradiation and, more importantly, in a long-term basis, was not studied yet. Objective The purpose of this study was to evaluate the effect of a long-term repeated microwaving on the dimensional, color and translucency stability of acrylic and polyamide denture base materials. Material and Methods Thirty two specimens (32 mm x 10 mm x 2.5 mm) from polyamide (Valplast) and PMMA (Vertex Rapid Simplified) denture base materials were made. Eight specimens from each material were immersed in distilled water (control) and 8 were subjected to microwave exposure at 450 W for 3 minutes for a period simulating 224 days of daily disinfection. Linear dimension, color change (ΔE*) and translucency parameter (TP) were measured at baseline and after certain intervals up to 224 cycles of immersion, using a digital calliper and a portable colorimeter. The results were analysed using two-way repeated measures ANOVA to estimate possible differences among predetermined cycles and material type. Regression analysis was also performed to estimate the trend of changes with time. Statistical evaluations performed at a significance level of 5%. Results Data analysis showed significant changes in length at baseline with an increasing number of cycles (p<0.05) and a significant interaction of cycle-material (p<0.001). The ΔΕ* parameter was significantly higher with a higher number of cycles (p<0.001), but it did not vary between materials (p>0.05). TP decreased similarly in both materials following microwave action but in a significantly higher level for Valplast (p<0.001). Conclusions The results indicated that long-term repeated microwaving affects linear dimensional, color and translucency changes of both materials. Differences between PMMA and polyamide material were noted only in dimension and translucency changes.

The Influence of Thermocycling on the Flexural Strength of a Polyamide Denture Base Material.

OBJECTIVE: The aim of the present study was to evaluate the influence of thermocycling on the flexural strength of a polyamide base denture material. MATERIALS AND METHODS: A polyamide denture base material (Valplast) was tested, whereas a PMMA material (Vertex) was used as a control. Thirty specimens of each material were fabricated for flexural strength testing according to ISO 1567. They were prepared and stored in water at 37°C for 48 hours. The specimens of each material were divided into three equal groups (n=10). Flexural strength testing was performed immediately after water storage and after thermocycling (5°C / 55°C, 2 c/min) for 3000 and 5000 cycles. A three point flexural test was performed on a universal testing machine at a crosshead speed of 5 mm/min. The final flexural strength was calculated using the formula: FS = 3 PL/2 bd2. A two-way ANOVA with post-hoc analysis using Tukey's procedure was applied at .05 level of statistical significance. RESULTS: A statistically significant reduction in flexural strength was recorded after thermocycling at 3000 cycles for PMMA and at 5000 cycles for both materials. The flexural strength of PMMA was significantly higher compared to polyamide for all the conditions tested (p<0.05). CONCLUSION: Thermocycling had a significant adverse effect on the flexural strength of polyamide and PMMA denture base materials.

Effects of cleansing methods on 3-D surface roughness, gloss and color of a polyamide denture base material.

OBJECTIVE: The purpose of this study was to determine the effects of two denture cleansing methods on 3-D surface roughness, gloss and color of denture base materials. MATERIALS AND METHODS: Thirty disks from nylon (Valplast) and 30 from heat-polymerized acrylic denture base material (Paladon 65) were made and 10 of each material were immersed in water (control), Val-Clean (peroxide cleanser) and Corega Extradent (peroxide cleanser) plus microwaving for a period simulating 30 days of daily cleansing. 3-D surface roughness, gloss and color parameters were measured before and after cleansing using an interferometric profilometer, a gloss meter and a colorimeter. The results were statistically analysed by regression, paired-t, Mann-Whitney and Kruskal-Wallis tests at α = 0.05 level of significance. RESULTS: The results showed significant differences at baseline in L* and b* parameters between materials (p < 0.01), with a significantly lower gloss (p < 0.05) and higher roughness (p < 0.05) for Valplast. After cleansing, Δϵ* was significantly greater in Valplast than Paladon 65 (p < 0.05). Gloss of both materials decreased significantly within the Corega Extradent plus microwave solution (p < 0.05), while roughness increased significantly only for Paladon 65 (p < 0.05). CONCLUSIONS: Valplast was found to have a significantly lower gloss and a higher roughness than Paladon 65 before cleansing. After cleansing, ΔE* increased more in Valplast than in Paladon 65, gloss of both materials decreased and roughness only of Paladon 65 increased within the Corega extradent plus microwaving method.

A Survey of Removable Partial Denture (RPD) Retentive Elements in Relation to the Type of Edentulism and Abutment Teeth Found in Commercial Laboratories, Athens, Greece.

OBJECTIVE: The aim of this survey was to record removable partial denture (RPD) retentive elements and abutment teeth in partially edentulous patients, identified in commercial laboratories in Athens, Greece. MATERIAL AND METHODS: 628 master casts with the corresponding cast metal frameworks used in the construction of RPDs were evaluated. Casts were photographed to identify the number and position of existing teeth, the partial edentulism class and the retentive elements. Prevalence tables and the x(2) test were used for the statistical analysis of the collected data (α=.05). RESULTS: There were 276 maxillary (43.9%) and 352 (56.1%) mandibular casts. Maxillary edentulism entailed almost a total absence of right third molars in 96.7% and left third molars 96.0% of casts, with lower rates for the first and second molars. Edentulism in the posterior mandible presented a similar pattern. The most profound findings concerning retentive elements were: 91.9% of the retainers used were clasps and the remaining 8.1% were attachments. Of the clasps used, 48.9% were of the Roach Τ type, a finding more common in Kennedy Class I as compared to other Kennedy Classes (p<0.01). The circumferential clasps accounted for 19.3% of the total clasps used, and it was less frequently presented (8.8%) in Kennedy I Classes (p<0.01). CONCLUSIONS: Roach clasps were used in the majority of cases whereas RPI clasps and attachments were rarely used.

The Effect of Repeated Microwaving Disinfection on the Dimensional Stability of Acrylic Dentures.

OBJECTIVE: The aim of this study was to evaluate the effect of repeated microwave disinfections on the dimensional stability of acrylic dentures. MATERIALS AND METHODS: Three groups of dentures made of a heat polymerized acrylic resin were tested. I: dentures kept in water (control group). II: dentures microwaved daily while being immersed into water (wet disinfection). III: dentures microwaved daily without being immersed into water (dry disinfection).Measurements were taken across three reference points, on two occasions: after curing and immersion in water for 24 hours, and one week later.Data obtained were analyzed using one-way analysis of variance (ANOVA) and Scheffe's multiple range test. RESULTS: The results showed that the microwave disinfection provokes dimensional changes of the same pattern (shrinkage). The dentures which underwent wet disinfection exhibited the greatest shrinkage (p<0.05). CONCLUSIONS: Disinfection using microwave energy may cause dimensional changes (shrinkage) of complete dentures.The microwave "dry disinfection" method can be safely applied in everyday practice since the dimensional changes which occurred seem to be of no clinical significance.

A survey of removable partial denture casts and major connector designs found in commercial laboratories, Athens, Greece.

PURPOSE: This survey was conducted to study the prevalence of partial edentulism, the type of removable partial denture (RPD) support, the type of major connectors, and the frequency of their use in relation to the partial edentulism classes encountered, concerning patients in Athens, Greece. MATERIALS AND METHODS: The material comprised 628 final casts for RPDs. Each cast was photographed in a way that would allow the number of existing teeth, the classification of partial edentulism, the RPD support, and the particular parts of the metal framework to be identified. Data collected were analyzed statistically using prevalence tables and the χ(2) test. RESULTS: Two hundred seventy six (43.9%) casts were for the maxilla and 352 (56.1%) for the mandible. The most frequently encountered group was Kennedy class I for both arches, while class IV was the classification least encountered (p < 0.001). Of all RPDs constructed, 96.8% had a metal framework (tooth-borne and tooth/tissue-borne), while 3.2% of the RPDs were frameless (tissue-borne, acrylic dentures). The U-shaped palatal connector (horseshoe) in the maxilla and the lingual bar in the mandible were the most frequently used for all partial edentulism classes, at 55.2% and 95%, respectively. CONCLUSIONS: Analysis of the casts revealed that the type of major connectors selected does not comply with the indications for their applications, considering the lack of dental history and clinical examination. This notes the need for further training dentists and dental technicians in aspects of RPD framework design.

Temperature rise during intraoral polymerization of self-cured hard denture base liners.

The aim of this in-vivo study was to evaluate the temperature rise during polymerization of five chairside self-cured hard denture base reliners. For the same patient, 30 identical baseplates, exposing a space on their tissue surface to accommodate the lining material, were made of a light-cured denture base material. A hole was drilled in the center of this area to enable the thermocouple wire of the temperature measuring device to have direct access to the palatal surface of the baseplate. Six baseplates were used for each of the five lining materials tested. Temperature recordings were made every 15 seconds. Data were analyzed using single factor analysis of variance (ANOVA) and the Scheffe's post-hoc analysis for multiple comparisons. The mean maximum temperature values ranged from 40.2 degrees C to 45.7 degrees C being statistically different among the materials (P<0.001). The maximum peak temperature was 53 degrees C and the lowest 39 degrees C. Also the difference between the time each material reached the peak of temperature was statistically significant (P<0.0001). A temperature range of 5.5 degrees C was demonstrated among materials, with the highest polymerization temperatures recorded for Flexacryl Hard and the lowest for Rebase and GC Reline hard. Ufi-gel hard showed the fastest polymerization cycle and was the first to reach the maximum temperature. The available chairside hard liners must be chosen with care considering the thermal effect on the oral mucosa and the discomfort of patient.