Effect of Ridge-lap Surface Treatments on the Bond of Resin Teeth to Denture Base

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Purpose: To test in vitro the shear bond strength of resin teeth to an acrylic resin denture base given different ridge-lap surface treatments. Materials and Methods: Ninety rectangular dies were made with wax and traditionally invested in metallic or plastic flasks. The stone molds were covered with silicone, in which were included an acrylic molar with a wax stick fixed on the ridge lap surface. After deflasking, the wax sticks were removed, the teeth were cleaned with detergent, the ridge lap surface was submitted to different treatments (unmodified, bur-cut grooves, aluminum oxide particle sandblasting, monomer swelling, and primer swelling), and the teeth were replaced in the silicone molds. Metallic flasks were placed in a thermopolymerizing unit to polymerize heat-curing denture-base polymer, and plastic flasks were placed in a domestic microwave oven at 900 W to polymerize microwaveable denture base polymer. After deflasking, the specimens were submitted to the shear bond test in an Instron machine at a cross-speed of 1 mm/min. Results were submitted to ANOVA and Tukey's test (5%). Results: Shear bond strength values were influenced by the ridge-lap surface treatments only in the microwaved polymer. Sandblasting + monomer swelling and sandblasting + primer swelling interactions yielded lower strengths for microwaved polymer. Only the unmodified surfaces presented a significant difference when the resins were compared, where the microwaved polymer showed a higher value. Conclusion: Different tooth ridge-lap surface treatments promoted different strengths of the tooth/resin bond.133287293Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Effect of a new tension system, used in acrylic resin flasking, on the dimensional stability of denture bases

Statement of problem. The pressure of final closure may be released when the flask is removed from the mechanical or pneumatic press and placed in the spring clamp. This release in pressure may result in dimensional changes that distort the denture base. Purpose. The purpose of this study was to investigate differences between the dimensional stability of standardized simulated denture bases processed by traditional moist heat-polymerization and those processed by use of a new tension system. Material and methods. A metal master die was fabricated to simulate an edentulous maxillary arch without irregularities in the alveolar ridge walls. A silicone mold of this metallic die was prepared, and 40 stone casts were formed from the mold with type III dental stone. The casts were randomly assigned to 4 test groups (A-D) of 10 specimens each. A uniform denture base pattern was made on each stone cast with a 1.5-mm thickness of base-plate wax, measured with a caliper. The patterns were invested for traditional hot water processing. A polymethyl methacrylate dough was prepared and packed for processing. The flasks in groups A and B were closed with the traditional pressure technique and placed in spring clamps after final closure. The flasks in groups C and D were pressed between the metallic plates of the new tension system after the final closure. The group A and C flasks were immediately immersed in the water processing unit at room temperature (25degrees - 2degreesC). The unit was programmed to raise the temperature to 74degreesC over 1 hour, and then maintained the temperature at 74degreesC for 8 hours. The group B and D flasks were bench stored at room temperature (25degrees +/- 2degreesC) for 6 hours and were then subjected to the same moist heat polymerization conditions as groups A and C. All processed dentures were bench cooled for 3 hours. After recovery from the flasks, the base-cast sets were transversally sectioned into 3 parts (corresponding to 3 zones): (1) distal of the canines, (2) mesial of the first molars, and (3) mesial of the posterior palate). These areas had been previously established and standardized by use of a pattern denture in the sawing device to determine the sections in each base-cast set. Base-cast gaps were measured at 5 predetermined points on each section with an optical micrometer that had a tolerance of 0.001 mm. Collected data were analyzed with analysis of variance and Tukey's test. Results. Denture bases processed with the new tension system exhibited significantly better base adaptation than those processed with traditional acrylic resin packing. Immediately after polymerization (Groups A and C), mean dimensional change values were 0.213 +/- 0.055 mm for the traditional packing technique and 0.173 +/- 0.050 mm for new tension system. After delayed polymerization (Groups B and D), the values were 0.216 +/- 0.074 mm for the traditional packing technique and 0.164 +/- 0.032 mm for new tension system. With both techniques, dimensional changes in the posterior palatal zone were greater (conventional 0.86 +/- 0.038 mm; new system = 0.214 +/- 0.024 mm) than those elsewhere on the base-cast set. Conclusion. Within the limitations of this study, the new tension packing system was associated with decreased dimensional changes in the simulated maxillary denture bases processed with heat-polymerization.88328528

Influence of Different Soft Liners on Stress Distribution in Peri-Implant Bone Tissue During Healing Period. A 3D Finite Element Analysis

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The aim of this study was to evaluate the stress distribution in the bone adjacent to submerged implants during masticatory function in conventional complete dentures with different soft liners through finite element analysis. Three-dimensional models of a severely resorbed mandible with 2 and 4 submerged implants in the anterior region were created and divided into the following situations: (1) conventional complete dentures (control group); and conventional complete dentures with different soft liner materials, (2) Coe-Comfort, (3) Soft liner, and (4) Molteno Hard. The models were exported to mechanical simulation software and 2 simulations were done with the load in the inferior right canine (35 N) and the inferior right first molar (50 N). The data were qualitatively evaluated using the maximum principal stress and microstrain values given by the software. The use of soft liners provides decreased levels of stress and microstrains in pen-implant bone when the load was applied to canine teeth. Considering all of the values obtained in this study, the use of softer materials is the most suitable for use during the period of osseointegration.395575581Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Effect of Chemical and Microwave Disinfection on the Surface Microhardness of Acrylic Resin Denture Teeth

Purpose The purpose of this study was to evaluate the effect of simulated disinfections (2% glutaraldehyde, 1% sodium hypochlorite, and microwave energy) on the surface hardness of Trilux, Biocler, Biotone, New Ace, and Magister commercial artificial teeth. Materials and Methods Specimens (n = 10) were made with the teeth included individually in circular blocks of acrylic resin, leaving the labial surface exposed. Cycles of simulated chemical disinfection were accomplished with the specimens immersed in the solutions at room temperature for 10 minutes, followed by tap water washing for 30 seconds and storage in distilled water at room temperature for 7 days until the next disinfection. Simulated disinfection by microwave energy was carried out in a domestic oven with 1300 W at a potency of 50% for 3 minutes with the specimens individually immersed in 150 ml of distilled water. Control (no disinfection) and the experimental groups (first and third disinfection cycles) were submitted to Knoop hardness measurements with indentations at the center of the labial tooth surface. Data were submitted to repeated measure two-way ANOVA and Tukey's test ( = 0.05). Results Biocler, Magister, and Trilux showed lower surface microhardness when submitted to microwave. Lower microhardness for Biotone was promoted by hypochlorite, while no significant difference was shown for New Ace. The third disinfection cycle significantly decreased the tooth surface hardness only for microwave. Conclusions Different disinfection methods promoted different effects on the microhardness of different types of artificial teeth. Surface microhardness of the teeth was less affected by the simulated chemical disinfections when compared to microwaved specimens.22429830

Flapless Single-Tooth Immediate Implant Placement

Purpose: This 15-year prospective study evaluated the success rate and preservation of the gingival margin of single implants placed in a flapless procedure loaded immediately after extraction or after a healing period. Materials and Methods: Immediate flapless implant placement was performed in patients who fulfilled specified inclusion criteria. Implants were either immediately restored with a provisional crown or left unloaded (received healing abutment only). Impant success and gingival margin levels were evaluated after implant placement and after 1 to 15 years. Results: A total of 305 healthy nonsmoking subjects (90 men, 215 women) were treated with 430 immediate implants during a 15-year period (December 1994 to December 2009) and monitored for 1 to 15 years. Two hundred seventy-five implants received an immediate provisional crown, and 155 received a healing abutment. The implant survival rate was 93.03% (+/- 3.74%). The immediate provisional helped to maintain the original gingival margin, although the implant survival rate was higher for implants that were not immediately restored (96.78%) than for the implants that were immediately restored with a provisional (90.9%). Conclusions: This 15-year prospective study showed a favorable implant success rate related to the flapless immediate implant placement protocol with healing abutment placement or an immediate provisional crown to replace a single missing tooth.28378378

Influence of different metal flask systems on tooth displacement in complete upper dentures

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Objective: To verify the occurrence of tooth displacement in dentures processed by moist hot-polymerisation using traditional and experimental metal flask systems. Materials and methods: Waxed complete dentures were randomly assigned to three groups (n = 10), including traditional (TF) and experimental flasks (DF and HHF). Metal pins were placed at the incisal edge of maxillary central incisors (I), buccal cusp of first premolars (P) and mesiobuccal cusp of second molars (M). Transversal (I-I, P-P and M-M) and anteroposterior (LI-LM and RI-RM) distances were measured before and after denture processing using an optical microscope. The dentures were processed by hot water curing cycle (9 h/ 74 degrees C). Collected data were analysed by ANOVA, Paired Student's t-test and Holm-Sidak method (p < 0.05). Results: All measured distances demonstrated contraction after polymerisation, except for LI-LM in TF and RI-RM in DF and HHF. Statistically significant differences were found between the distances P-P for DF and HHF, and M-M for all groups. Comparison among flask systems revealed statistically significant difference in the P-P distance for the TF and HHF. Conclusion: Different flask systems did not cause variation in tooth displacement during denture processing, with the exception of P-P distances for the TF and HHF. There is no evidence that different metal flask systems would promote tooth displacement of clinical significance.2913035Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Dimensional accuracy of upper complete denture bases: the effect of metallic flask closure methods

To verify the dimensional accuracy of upper complete denture bases under the effect of different methods of metallic flask closure. Wax record bases were assigned to six groups: 1-2: traditional clamp; 3-4: RS system; and 5-6: flask with screws. Flasks were immediately polymerised or bench stored for 6 h prior to polymerisation. Resin base-cast sets were sectioned at regions corresponding to the canines, first molars and posterior palatal zone. Gap discrepancies were measured at five points: right and left ridge crests, palatal midline, and right and left marginal limits of the flanges. An optical micrometer was used for measurement purposes. Data were submitted to anova, and the means compared by Tukey's test (alpha = 0.05). Results revealed significant differences in the flask closure technique, polymerisation time, section, and their interactions. Discrepancy values for the RS system and flask with screws were significantly lower than those related to the traditional clamp, regardless of whether resin polymerisation was immediate or delayed for 6 h. Flask closure methods should be considered when the denture base stability and comfort of the patient are being assessed during clinical use of the dentures.2615864Sao Paulo State Foundation [03/12278-1]Sao Paulo State Foundation [03/12278-1