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

Svrha: Ovim se istraživanjem željelo istražiti retentivne elemente djelomičnih proteza (RPD) i zubne nosače kod djelomično bezubih pacijenata identifikacijom u komercijalnim atenskim zubnim laboratorijima. Materijali i metode: Procijenjeno je 628 sadrenih modela zajedno s lijevanim metalom koji se rabi za izradu djelomične skeletirane proteze. Modeli su fotografirani kako bi se mogao identificirati broj i smještaj postojećih zuba, zatim klase djelomične proteze i retentivni elementi. Za statističku analizu podataka korištene su tablice prevalencije i x2 testa (α=.05). Rezultati: Analizirano je 276 maksilarnih modela (43,9 %) i 352 mandibularna (56,1 %). Nedostatak maksilarnih zuba očitovao se u gotovo potpunom nedostatku desnoga (96,7%) i lijevog (96%) trećeg kutnjaka, a također je bilo premalo prvih i drugih kutnjaka. Gubitak zuba u stražnjim dijelovima mandibule pokazivao je sličan uzorak. Od uočenih retentivnih elemenata najčešće su bile kvačice ( 91,9 %), a zglobne veze (attachment) korištene su u 8,1 posto slučajeva. Od kvačica je 48,9 posto bilo Roachovih T-tipa, najčešće Kennedyjeve klase I, u usporedbi s ostalim klasama prema Kennedyju (p<0,01). Cirkumferentnih kvačica bilo 19,3 posto od ukupnog broja kvačica i najrjeđe (8,8 %) su bile iz Kennedyjeve klase I (p<0,01). Zaključak: Najčešće se koristimo Roachovim kvačicama, a RPI-kvačicama i zglobnim vezama (attachment) rijetko.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 x2 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

Removal of denture adhesives from PMMA and Polyamide denture base materials

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.&nbsp;Results:&nbsp;Roughness of Polyamide was higher than PMMA and Fittydent showed greater volumetric changes than the others. Significant differences (p&lt;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

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).&nbsp;Results:&nbsp;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&gt;0.05).&nbsp;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

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&lt;0.0001), illumination a* and b* coordinates (p&lt;0.0001), but none of them was affected by the hydration state of teeth (p&gt;0.05). Intra-brand color differences ranged between 0.21-0.78ΔΕ* units with significant differences among brands (p&lt;0.0001), among illumination lights (p&lt;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&lt;0.0001), illumination lights (p&lt;0.0001) and hydration states (p&lt;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

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&lt;0.05) and a significant interaction of cycle-material (p&lt;0.001). The ΔΕ* parameter was significantly higher with a higher number of cycles (p&lt;0.001), but it did not vary between materials (p&gt;0.05). TP decreased similarly in both materials following microwave action but in a significantly higher level for Valplast (p&lt;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 Effect of Repeated Microwaving Disinfection on the Dimensional Stability of Acrylic Dentures

Svrha: Željeli smo istražiti i procijeniti učinak ponovljenih mikrovalnih dezinfekcija na dimenzijsku stabilnost akrilatnih proteza. Materijali i metode: Testirane su tri grupe proteza napravljene od toplinski polimerizirajućeg akrilata. Prva skupina – kontrolna, čuvala se u hladnoj vodi. Druga skupina proteza svaki je dan bila podvrgnuta mikrovalnoj dezinfekciji u vodi (mokra dezinfekcija), a treća skupina proteza nije se uranjala u vodu (suha dezinfekcija). Mjerenja su obavljena na tri referentne točke i to u dva puta: nakon stvrdnjavanja akrilata i 24-satnog uranjanja, te poslije tjedan dana. Dobiveni podatci analizirani su jednosmjernom analizom varijabilnosti (ANOVA) i Scheffeovim testom višestrukih raspona. Rezultati: Rezultati su pokazali da mokra i suha mikrovalna dezinfekcija uzrokuju iste dimenzijske promjene (skvrčavanje). Proteze koje su bile podvrgnute mokroj dezinfekciji najviše su se skvrčile (p < 0,05). Zaključak: Mikrovalna dezinfekcija može prouzročiti dimenzijske promjene (skvrčavanje) na akrilatnim protezama. Mikrovalna suha dezinfekcija može biti svakodnevna jer ne uzrokuje klinički značajne dimenzijske promjene.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

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 (E$_{IT}$) and elastic index (η$_{ΙΤ}$). 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 E$_{ΙΤ}$ for QC, PB with A, for PA, VE with B and ME with E, and for η$_{IT}$ 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

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