Effect of water storage on the shear strength and fatigue limit of the reline resin bond to denture base resins.

PURPOSE: This study evaluated the effect of water storage (WS) on the shear bond strength (SBS) and shear bond fatigue limit (SBFL) between denture base and reline resins. In addition, a possible correlation between SBS and SBFL was evaluated. MATERIALS AND METHODS: Two denture base (Lucitone 550-L and Acron MC-AC) and two reline resins (Ufi Gel Hard- UGH and Tokuso Rebase Fast-TR) were selected. Cylinders (20 x 20 mm) of each denture base resin were processed, and the reline resins were packed on the bonding surfaces using a split mold (3.5 x 5.0 mm). Specimens of each denture base-reline resin combination were subjected to shear forces (0.5 mm/min) until fracture. A staircase approach was used to determine the SBFL. Specimens were submitted to either 10,000 cycles (5.0 Hz) or until fracture. For both SBS and SBFL, specimens were tested after relining (control) and after 30 days of WS. Data (MPa) were analyzed with 2-way ANOVA and Tukey's tests (α = 0.05). To test for a possible correlation between the SBS and SBFL, a linear regression analysis was performed. RESULTS: WS significantly increased (p < 0.05) the SBS of AC-TR and AC-UGH and the SBFL of AC-TR, AC-UGH and LUGH. After WS, UGH produced higher (p < 0.05) SBS than TR, regardless of the denture base resin used. Regardless of the experimental groups and the denture base resins used, UGH produced higher (p < 0.05) SBFL than TR specimens. A strong positive linear correlation (r(2) = 0.949) was observed between the SBS and SBFL. CONCLUSION: Overall, UGH promoted the highest SBS and SBFL. WS increased the SBS and SBFL of the AC relined specimens. A positive correlation was observed between the two variables.

Superficial distribution and identification of antifungal/antimicrobial agents on a modified tissue conditioner by SEM-EDS microanalysis: a preliminary study.

PURPOSE: This study evaluated the incorporation pattern of antifungal/antimicrobial agents added to a tissue conditioner by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis. MATERIALS AND METHODS: The nystatin dosages incorporated into the tissue conditioner (Softone, Bosworth Co., Skokie, IL) powder were 500,000 U (G1) and 1,000,000 U (G2). The addition of miconazole was at 125 mg (G3) and 250 mg (G4), and ketoconazole was at 100 mg (G5) and 200 mg (G6). Chlorhexidine diacetate was blended at levels of 5% (G7) and 10% (G8) w/w of the total amount (6.35 g) of the tissue conditioner. The drug powder concentrations were blended with the tissue conditioner powder at different concentrations before the addition of the tissue conditioner liquid (5 mL) to the mixture. One group (G0) without any drug incorporation was used as control. Specimens (n = 5) (36 x 7 x 6 mm(3)) were plasticized at room temperature for 10 minutes and carbon sputter coated. All specimens were submitted to SEM-EDS analysis. RESULTS: Nystatin and miconazole specimens exhibited particles with irregular shapes and sizes uniformly distributed. Ketoconazole specimens showed small spherical particles with a slight distribution throughout the matrix. Chlorhexidine specimens exhibited irregular particles up to approximately 50 mum in size randomly dispersed within the matrix. CONCLUSIONS: Within the limitations of this in vitro study, the modified tissue conditioner showed differences in the particle distribution and size of the antifungal/antimicrobial agent added to the plasticized matrix. Further studies would discriminate the most important particle features that may influence the drug leaching from the plasticized matrix.

Effect of a post-polymerization treatments on the flexural strength and Vickers hardness of reline and acrylic denture base resins

This study evaluated the effect of water-bath and microwave post-polymerization treatments on the flexural strength and Vickers hardness of four autopolymerizing reline resins (Duraliner II-D, Kooliner-K, Tokuso Rebase Fast-TR and Ufi Gel Hard C-UGH) and one heat-polymerized acrylic resin (Lucitone 550-L), processed using two polymerization cycles (short cycle - 90 minutes at 73ºC and 100ºC for 30 minutes; and long cycle - 9 hours at 71ºC). For each material, thirty specimens (64 x 10 x 3.3 mm) were made and divided into 3 groups (n=10). Specimens were tested after: processing (control group); water-bath at 55ºC for 10 minutes (reline materials) or 60 minutes (L); and microwave irradiation. Flexural strength tests were performed at a crosshead speed of 5 mm/min using a three-point bending device with a span of 50 mm. The flexural strengths values were calculated in MPa. One fragment of each specimen was submitted to Vickers hardness test. Data were analyzed by 2-way ANOVA followed by Tukey's HSD test (alpha=0.05). L microwaved specimens (short cycle) exhibited significantly higher flexural strength means than its respective control group (p<0.05). Water-bath promoted a significant increase (p<0.05) in flexural strength of K and L (long cycle). The hardness of the tested materials was not influenced by the post-polymerization treatments. Post-polymerization treatments could be used to improve the flexural strength of some materials tested.

Dynamic mechanical properties of hard, direct denture reline resins.

STATEMENT OF PROBLEM: Dynamic mechanical properties of hard, direct reline resins are important factors in the clinical success of dentures. However, little information is available on the nature of these properties. PURPOSE: This study evaluated the dynamic mechanical properties of a variety of hard, direct reline resins: (1) visible light-polymerized, powder-liquid type, (2) visible light-polymerized, paste-type, (3) autopolymerized, powder-liquid type, as classified by component composition and mode of polymerization activation, namely, type of delivery system, and (4) heat-polymerized denture base materials. MATERIAL AND METHODS: The dynamic mechanical analysis (DMA) of 8 commercial hard denture reline materials (HDR) (2 visible light-polymerized, powder-liquid type, 4 visible light-polymerized, paste-type, and 2 autopolymerized, powder-liquid type), and 2 heat-polymerized denture base materials was obtained at a frequency of 1 Hz at 37 degrees C. Five specimens of each material, 40.0 x 7.0 x 2.0 mm, were made to measure the elastic (storage) (E') and inelastic (loss) (E'') moduli, and loss tangent (tan delta). These parameters were compared with MANOVA and Student-Newman-Keuls test (alpha =.05). RESULTS: The E' values of 3 visible light-polymerized, paste-type reline resins were significantly higher than those of the other 5 reline resins. However, the E' values of all reline resins were significantly lower than those of the 2 heat-polymerized denture base resins. Except for 1 autopolymerized reliner, all reline materials had significantly lower E'' than the heat-polymerized denture base resins. The tan delta values of all but 1 visible light- and autopolymerized reliners were significantly higher than those of the heat-polymerized denture base materials. CONCLUSIONS: Three visible light-polymerized, paste-type reline resins showed greater stiffness than the visible light- or autopolymerized, powder-liquid type reline resins. However, all of the hard, direct reline resins, including the 3 paste-type materials, exhibited greater flexibility compared to the heat-polymerized denture base resins.

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.

Factors affecting the strength of denture repairs.

Fracture of dentures is a common clinical finding in daily prosthodontic practice, resulting in great inconvenience to both patient and dentist. A satisfactory repair should be cost-effective, simple to perform, and quick; it should also match the original color and not cause distortion to the existing denture. Different repair materials, surface designs, and mechanical and chemical surface treatments have been recommended in order to obtain stronger repairs. This article reviews some of the available literature with regard to the most important factors that may influence the strength of denture repairs.

Effect of a post-polymerization treatments on the flexural strength and Vickers hardness of reline and acrylic denture base resins.

This study evaluated the effect of water-bath and microwave post-polymerization treatments on the flexural strength and Vickers hardness of four autopolymerizing reline resins (Duraliner II-D, Kooliner-K, Tokuso Rebase Fast-TR and Ufi Gel Hard C-UGH) and one heat-polymerized acrylic resin (Lucitone 550-L), processed using two polymerization cycles (short cycle - 90 minutes at 73 degrees C and 100 degrees C for 30 minutes; and long cycle - 9 hours at 71 degrees C). For each material, thirty specimens (64 x 10 x 3.3 mm) were made and divided into 3 groups (n=10). Specimens were tested after: processing (control group); water-bath at 55 degrees C for 10 minutes (reline materials) or 60 minutes (L); and microwave irradiation. Flexural strength tests were performed at a crosshead speed of 5 mm/min using a three-point bending device with a span of 50 mm. The flexural strengths values were calculated in MPa. One fragment of each specimen was submitted to Vickers hardness test. Data were analyzed by 2-way ANOVA followed by Tukey's HSD test (alpha=0.05). L microwaved specimens (short cycle) exhibited significantly higher flexural strength means than its respective control group (p<0.05). Water-bath promoted a significant increase (p<0.05) in flexural strength of K and L (long cycle). The hardness of the tested materials was not influenced by the post-polymerization treatments. Post-polymerization treatments could be used to improve the flexural strength of some materials tested.

Influence of thermal and mechanical stresses on the strength of intact and relined denture bases.

STATEMENT OF PROBLEM: Denture bases may become increasingly weaker as a result of thermal stress and flexural cyclic loading. Information regarding this potential problem and its relationship to the denture base reline is limited. PURPOSE: This study evaluated the influence of thermal and mechanical stresses on the strength of intact and relined denture bases. MATERIAL AND METHODS: Twenty-eight microwave-polymerized (Acron MC) intact denture bases were prepared in the shape of a 3-mm-thick maxillary denture. Additionally, fifty-six 2-mm-thick denture bases were relined with 1 mm of autopolymerizing resin (Tokuyama Rebase Fast II or New Truliner) (n=28). Intact and relined specimens were divided into 4 groups (n=7) as follows: without stress (control); a mechanical stress at 0.8 Hz for 10,000 cycles; 5000 thermal cycles between 5 degrees C and 55 degrees C; or a combination thermo-mechanical stress. The specimens were vertically loaded in compression with a rounded rod at 5 mm/min until failure, using a universal testing machine. Data on maximum fracture load (N), deflection at fracture (%), and fracture energy (N.mm) were analyzed by 2-way analysis of variance and Student-Newman-Keuls tests (alpha=.05). RESULTS: The strength of the denture bases relined with New Truliner was not significantly affected by any of the experimental conditions, but comparing the control groups, New Truliner exhibited the lowest maximum fracture load values. The maximum fracture load of intact denture bases (P=.002) and those relined with Tokuyama Rebase Fast II (P=.01) showed a significant decrease after thermal stress. Additionally, cyclic loading significantly decreased the maximum fracture load (P<.001), deflection at fracture (P=.025), and fracture energy (P<.001) of intact denture bases and those relined with Tokuyama Rebase (P values of .002, .039, and .001, respectively). CONCLUSION: Thermal and mechanical stresses exert deleterious effects on the strength of intact and/or relined denture bases, which vary according to the relining material used.

Efeito do reembasamento, da ciclagem térmica, da ciclagem mecânica e da desinfecção por microondas sobre a força máxima de fratura, deformação, energia de ruptura e estabilidade dimensional de bases de prótese / Effect of relining, thermal stress, mechanical stress and microwave disinfection on the maximum fracture load, deflection, fracture energy and dimensional stability of denture bases

O estudo avaliou o efeito do reembasamento, da ciclagem mecânica, da ciclagem térmica e da desinfecção por microondas sobre a força máxima de fratura, a deformação, a energia de ruptura e a estabilidade dimensional de bases de prótese. O efeito das ciclagens mecânica e térmica foi avaliado utilizando 28 bases de prótese intactas com 3 mm de espessura e 56 bases de prótese com 2 mm de espessura. Estas bases foram obtidas a partir de um modelo padrão metálico do arco superior confeccionadas com a resina acrílica para microondas Acron MC (AC-MC), de acordo com as instruções do fabricante (500W por 3 minutos). Para verificar o efeito do reembasamento, as bases de prótese com 2 mm de espessura foram reembasadas com 1 mm de material reembasador (New Truliner - NTL ou Tokuyama Rebase Fast II - TRFII). Em seguida, as bases de prótese intactas ou reembasadas foram divididas aleatoriamente em 4 grupos (n=7) e o ensaio mecânico de resistência à compressão foi realizado após seguintes condições experimentais: sem tratamento (controle); 5.000 ciclos térmicos entre 5º e 55ºC; 10.000 ciclos mecânicos a um frequência de 0,8 Hz e uma força de 150N e; ciclagem térmica e posterior ciclagem mecânica. Todas as bases de prótese foram submetidas ao ensaio mecânico em uma máquina universal Instron 5565, utilizando-se uma velocidade de 5mm/min e uma célula de carga de 10 kN...

Próteses adesivas sem metal. Uma revisão de literatura / Resin bonded bridge. A literature review

As próteses adesivas surgiram como uma alternativa protética, tendo em vista o seubaixo custo, ser uma técnica mais conservadora e facilidade laboratorial. Mais recentemente, emrazão da necessidade de soluções clínicas estéticas, novos materiais foram introduzidos no mercadoe utilizados na confecção de próteses adesivas sem metal. Os materiais utilizados são: resinascompostas reforçadas por fibras e sistemas cerâmicos de alta resistência. O objetivo deste trabalhofoi discutir, por meio de uma revisão de literatura, as formas de preparo, os tipos de materiais, asvantagens e desvantagens da utilização de próteses adesivas sem metal. Com base nas informaçõesda literatura, pôde-se concluir que as próteses adesivas sem metal são uma alternativa promissorana substituição de um elemento dental devido a sua superioridade estética, biocompatibilidade efacilidade de confecção, principalmente para compósitos reforçados por fibras. Além disso, suaresistência apresenta resultados satisfatórios in vitro. Entretanto, há poucas evidências científicascom relação a formas de preparo ideais para os retentores de ambos os materiais a serem utilizadosrotineiramente na clínica. Assim, acompanhamentos longitudinais deveriam ser realizados paraverificar o comportamento dessas próteses na cavidade bucal antes que possam ser indicadas comotratamento de rotina na prática clínica diária.

The resin bonded bridge sets up as prosthodontic alternative based on its costeffective,conservative techniques and easiness of laboratory manufacturing. Nowadays, theclinical practice has been requiring esthetic solutions and, consequently, new materials have beenintroduced and used in the metal free resin bonded bridge manufacture. The materials used arefibre-reinforced composite and high-strenght ceramic systems. The purpose of this study was todiscuss through a literature review the cavity design, types of materials used and the advantagesand disadvantages of the metal free resin bonded bridges. Based on the reviewed literature it couldbe concluded that the metal free resin bonded bridges are a promising solution for the replacementof a tooth because of their improved esthetics, biocompatibility and simple technique, specialyfor the fiber reinforced composite. Moreover, this kind of prosthesis presents satisfactory in vitrostrenght results. However, there is little scientific evidence about the adequated cavity and connectordesigns that offer support to use this prosthesis in clinical routine. Therefore, longitundinal studiesshould be performed in order to investigate the clinical behaviour of these prosthesis in the oralenvironment before their indication as a routine modality of treatment.

Flexural strength of autopolymerizing denture reline resins with microwave postpolymerization treatment.

STATEMENT OF PROBLEM: Microwave postpolymerization has been suggested as a method to improve the mechanical strength of repaired denture base materials. However, the effect of microwave heating on the flexural strength of the autopolymerizing denture reline resins has not been investigated. PURPOSE: This study analyzed the effect of microwave postpolymerization on the flexural strength of 4 autopolymerizing reline resins (Duraliner II, Kooliner, Ufi Gel Hard, and Tokuso Rebase Fast) and 1 heat-polymerized resin (Lucitone 550). MATERIAL AND METHODS: For each material, 80 specimens (64 x 10 x 3.3 mm) were polymerized according to the manufacturer's instructions and divided into 10 groups (n = 8). Control group specimens remained as processed. Before testing, the specimens were subjected to postpolymerization in a microwave oven using different power (500, 550, or 650 W) and time (3, 4, or 5 minutes) settings. Load measurements (newtons) were made at a crosshead speed of 5 mm/min using a 3-point bending device with a span of 50 mm. The flexural strength values were calculated in MPa. Data analyses included 3-way and 2-way analysis of variance and the Tukey Honestly Significant Difference test (alpha = .05). RESULTS: The flexural strengths of resins Duraliner II and Kooliner were significantly increased (P = .0015 and P = .0046, respectively) with the application of microwave irradiation using different time/power combinations. The materials Lucitone 550, Tokuso Rebase Fast, and Ufi Gel Hard demonstrated no significant strength improvement compared to the corresponding control. Only after microwave postpolymerization irradiation for 3 minutes at 550 W did Lucitone 550 show significantly higher flexural strength (P =.001) than Tokuso Rebase Fast and Ufi Gel Hard relining resins. CONCLUSION: Microwave postpolymerization irradiation can be an effective method for increasing the flexural strength of Duraliner II (at 650 W) and Kooliner (at 550 W and 650 W for 5 minutes).