RESUMEN
PURPOSE: This study evaluated the wear area of human enamel opposing 2 conventional and 2 low-fusing dental porcelains, as well as abrasive wear, attrition, surface hardness, and fracture toughness for the 4 porcelain substrates. MATERIALS AND METHODS: Two low-fusing and 2 conventional metal-ceramic porcelains were used to form 15-mm-diameter disks (n = 10), which were fired according to manufacturer's recommendations. Enamel cusps (n = 40) were formed from extracted third molars. All ceramic and enamel specimens were finished to a 1000-grit silicon carbide surface. The Oregon Health Sciences University (Portland, OR) oral wear simulator was used to deliver a 20-N load from the cusps to the ceramic substrates through a food-like slurry. The sliding action of the cusps over an 8-mm linear path produced abrasive wear. A static 70-N load was applied at the end of the path to create attrition. This sequence was repeated at 1.0 Hz for 50,000 cycles. Ceramic wear was measured with a profilometer (+/-2 micrometers), and enamel wear was evaluated using optical scanning methods. After wear testing, the hardness and fracture toughness of the ceramic surfaces were determined, and scanning electron photomicrographs were made using representative ceramic and enamel specimens from each group. Enamel wear areas, abrasion and attrition depths, hardness, and fracture toughness values were subjected to analysis of variance and Tukey-Kramer post hoc tests to determine significant differences. RESULTS: Enamel wear was not significantly different for low-fusing and conventional porcelains (p =.29). The wear of conventional and low-fusing ceramic substrates was also not significantly different (p =.79). However, depth of porcelain wear caused by attrition was in general significantly greater than abrasive wear (p =.0004). Although no significant differences were found in the measured porcelain hardness values (p =.08), 1 conventional porcelain exhibited fracture toughness significantly greater than 1 low-fusing porcelain (p <.01). CONCLUSIONS: No differences in wear patterns were noted among low-fusing compared with conventional metal-ceramic porcelains, but static loading resulted in significantly greater attrition compared with the observed sliding abrasive wear. J Prosthodont 2001;10:8-15.
Asunto(s)
Cerámica/química , Esmalte Dental/patología , Porcelana Dental/química , Alisadura de la Restauración Dental , Restauración Dental Permanente , Abrasión de los Dientes/patología , Atrición Dental/patología , Análisis de Varianza , Materiales Biocompatibles/química , Fuerza de la Mordida , Compuestos Inorgánicos de Carbono/química , Resinas Compuestas/química , Pulido Dental , Dureza , Humanos , Procesamiento de Imagen Asistido por Computador , Compuestos de Litio/química , Microscopía Electrónica de Rastreo , Compuestos de Silicona/química , Estadística como Asunto , Estrés Mecánico , Propiedades de Superficie , Abrasión de los Dientes/clasificación , Atrición Dental/clasificaciónRESUMEN
PURPOSE: This study compared denture base resin shear bond strengths to silicoated Au-Pd, Au-Pd-Ag, Au-Ag-Pd-Cu, high-Pd, and Ni-Cr-Be alloys used to fabricate frameworks for hybrid implant prostheses. Microleakage between alloy and resin was also compared among groups after specimen fracture. MATERIALS AND METHODS: Twelve cylindrical specimens were cast for each alloy. Each specimen was made from a ring-shaped pattern (diameter [d] = 12 mm and height = 4 mm) and machined to achieve uniform hollow centers (d = 6.5 mm). Castings were abraded with 250-micron aluminum oxide and ultrasonically cleaned in distilled water before silicoating. Denture base resin was processed to the internal surfaces of the silicoated specimens. All specimens were thermocycled (1,000 cycles) between 4 degrees C and 50 degrees C, and placed in basic fuchsin dye for a week. A punch (d = 3.8 mm) driven at a cross-head speed of 0.5 mm/min was used to push out the resin specimens. The force required to cause failure was converted to the nominal shear bond strength for each specimen, and mean shear bond strengths for the 5 groups of specimens (N = 12) were compared using one-way analysis of variance and the Tukey-Kramer HSD multiple range test (alpha = 0.05). Six of the 12 debonded resin samples for each alloy were selected at random and evaluated for dye penetration. Using an 80-square grid, the percentage of dye penetration was evaluated with an optical microscope (x25) to determine the percentage of grid area penetrated by the dye. One-way analysis of variance was used to compare the degree of microleakage among groups. RESULTS: The mean resin-alloy shear bond strengths for the Au-Pd (9.6 +/- 3.7 MPa) and Au-Ag-Pd-Cu (9.2 +/- 1.5 MPa) alloys were significantly greater than mean resin-alloy shear bond strength for the Au-Pd-Ag alloy (5.6 +/- 1.9 MPa). No other significant differences in resin-alloy shear bond strengths were noted among the alloy groups. No significant differences were noted for dye penetration into the resin specimens bonded to any of the 5 alloys. The mean grid area penetrated by the dye was 25% when results for the alloys were pooled. CONCLUSIONS: Alloy type influences the shear bond strength of a denture base resin to silicoated alloys, but no difference in bond strength was found between Au-Pd, Au-Ag-Pd-Cu, high-Pd, and Ni-Cr-Be alloys. In addition, under the conditions of this study, all groups showed a similar degree of microleakage, which penetrated approximately 25% of the bonded specimen surface area.
Asunto(s)
Aleaciones Dentales/química , Recubrimiento Dental Adhesivo , Revestimiento para Colado Dental/química , Bases para Dentadura , Metilmetacrilato/química , Abrasión Dental por Aire , Óxido de Aluminio/química , Análisis de Varianza , Aleaciones de Cromo/química , Cobre/química , Aleaciones de Oro/química , Humanos , Ensayo de Materiales , Paladio/química , Colorantes de Rosanilina , Silanos/química , Plata/química , Estadística como Asunto , Estrés Mecánico , Propiedades de Superficie , TermodinámicaRESUMEN
Complete-arch implant prostheses continue to exhibit horizontal and vertical misfit between frameworks and abutments. It has been suggested that these gaps may be eliminated and that restoration-induced stresses may be reduced by luting frameworks to screw-retained abutments intraorally. This study measured and compared the strains generated by clinically acceptable, conventional frameworks were made from a single master cast representing a bone simulant model of an edentulous mandible with five Nobel Biocare implants and 4-mm abutments. Two strain gauges were also embedded in the bone simulant model to measure strains at two locations. Resin-luted frameworks were made by securing abutments to the clinical model with five gold slot screws tightened to 10 Ncm. Strain-indicator readings were recorded at a standardized time following the initial fastening of each prosthesis (n = 3). Mean principal strains were determined and compared using a one-way repeated measures analysis of variance. A statistically significant difference was found in the principal strains between the conventional cast and the resin-luted frameworks. Overall, there was a decrease in the magnitude of strain for the resin-luted frameworks. Intraoral luting of frameworks may decrease the strains produced in the bone around implants.
Asunto(s)
Pilares Dentales , Arco Dental/fisiología , Revestimiento para Colado Dental , Implantes Dentales , Diseño de Prótesis Dental , Prótesis Dental de Soporte Implantado , Cementos de Resina , Análisis de Varianza , Bisfenol A Glicidil Metacrilato/química , Cementación , Revestimiento para Colado Dental/química , Cementos Dentales/química , Aleaciones de Oro , Humanos , Arcada Edéntula/fisiopatología , Mandíbula/fisiología , Modelos Anatómicos , Cementos de Resina/química , Estrés MecánicoRESUMEN
PURPOSE: To measure and compare the strains transferred by screw-fastening one-piece full-arch prostheses as cast and after sectioning and soldering. MATERIALS AND METHODS: Photoelastic resin was applied directly to five 3.75 x 13-mm Brånemark implants, situated 7 mm apart, in a silicone mold of an edentulous mandible. Four strain gauge rosettes were also incorporated in the resin to allow strain measurements at four locations. Three frameworks were made from a single master cast produced from an impression of the five-implant model with 4-mm abutments. These frameworks were sequentially secured to the master model with five gold slot screws tightened to 10 N cm. Strain indicator readings were recorded at a standardized time following the initial fastening of each prosthesis. The test was repeated three times. Each of the three castings were subsequently sectioned and soldered in two locations, mesial to the two terminal fixtures. After soldering, the three superstructures were returned to the master model for measurement of postsolder strains three times each. A one-way repeated-measures ANOVA was performed to determine differences between mean principal strains between the as-cast and postsoldered groups. RESULTS: A statistically significant difference was found in the principal strains between the as-cast and soldered frameworks. Overall, there was a decrease in the magnitude of strain for the soldered frameworks. CONCLUSIONS: Sectioning and soldering improved the as-cast accuracy as far as the amount of strain transferred to the bone simulant.
Asunto(s)
Diseño de Prótesis Dental , Prótesis Dental de Soporte Implantado , Soldadura Dental , Análisis del Estrés Dental , Proceso Alveolar/fisiología , Análisis de Varianza , Fuerza Compresiva , Técnica de Colado Dental , Retención de Prótesis Dentales/instrumentación , Ensayo de Materiales , Modelos Dentales , Ajuste de Prótesis , Estrés Mecánico , Resistencia a la TracciónRESUMEN
PURPOSE: To measure and compare strains transferred to a bone simulant by screw-fastening implant overdenture bars with various levels of fit or misfit. MATERIALS AND METHODS: Photoelastic resin was cast directly to two 3.75 X 13-mm Branemark fixtures (Nobelpharma USA Inc, Chicago, IL) situated 20 mm apart in a silicone mold of an edentulous mandible. Two strain-gauge rosettes were also incorporated in the resin to allow precise determination of principal stresses at two locations. Four groups of three overdenture bars with 0-, 180-, 360-, and 500-micrometer vertical gaps were fabricated. These bars were sequentially secured to the abutments with gold slot screws tightened to 10 N-cm. Strain indicator readings were recorded at a standardized time following the initial fastening of each bar. The test was repeated three times for each overdenture bar. RESULTS: Mean principal stresses and strains at the location of the rosettes were determined. The magnitude of these stresses and strains increased significantly with each increase in gap size. Strains were several times larger mesial to the fixture than they were distal. CONCLUSIONS: Strains are transferred to the bone when misfitting prostheses were secured. Some of the strains mesial to the fixture appeared to be unfavorable for regions of lower bone density when the groups with designed gaps were secured. These data will be compared with those in ongoing animal studies regarding the cellular response to prosthesis misfit.
Asunto(s)
Diseño de Prótesis Dental/efectos adversos , Retención de Prótesis Dentales/instrumentación , Prótesis Dental de Soporte Implantado , Análisis del Estrés Dental , Prótesis de Recubrimiento , Proceso Alveolar/fisiología , Análisis de Varianza , Implantes Dentales , Elasticidad , Humanos , Mandíbula/fisiología , Ensayo de Materiales , Modelos Dentales , Ajuste de Prótesis , Estadísticas no Paramétricas , Estrés MecánicoRESUMEN
PURPOSE: A three-dimensional mathematical model of the maxilla was developed that was used to analyze the stresses and strains produced by an abutment system capable of three abutment angulations. MATERIALS AND METHODS: Computed tomography was used to derive the geometry and density values used for the maxillary model. A 3.8 x 10-mm cylindrical implant was embedded in the right central incisor position at a 35 degrees angle to the horizontal plane and parallel to the angulation of the bone site. All geometric and elastic properties for the fixture and the surrounding bone were included in the model. A simulated occlusal load of 178 N was applied along the long axis of 0 degrees, 15 degrees, and 20 degrees abutments. The mathematical models were solved by the Cray Y/MP Ohio Supercomputer (Cray, Eagan, MN) using the ABAQUS software program (Hibbitt, Karlsson, and Sorenson, Providence, RI). RESULTS: Numerical and graphic results were generated for the maximum (tensile) and minimum (compressive) stresses and strains. Principal stresses occurred predominantly in the cortical bone layers, whereas strains occurred mostly in the cancellous bone. CONCLUSIONS: In general, there was an increase in the magnitude of stress and strain as the abutment angulation increased. Reported stresses and strains for all three angles were within or slightly above the physiological zone derived from animal studies. A need to investigate the response of human bone to stress and strain was indicated.
Asunto(s)
Pilares Dentales , Implantes Dentales , Análisis del Estrés Dental , Proceso Alveolar/fisiología , Animales , Simulación por Computador , Diente Canino , Implantación Dental Endoósea , Diseño de Prótesis Dental , Humanos , Incisivo , Maxilar , Modelos Biológicos , Análisis Numérico Asistido por Computador , Estrés MecánicoRESUMEN
PURPOSE: This study determined the effect of various bone models on the stresses and strains generated under occlusal loading of a dental implant. MATERIALS AND METHODS: A two-dimensional finite-element model was created for stress analysis. The geometric and elastic properties of a 3.8 x 10-mm Steri-Oss implant embedded in a segment of premaxilla were modeled. Computed tomography scanning of a dried maxilla half was used to determine representative geometry and density of this region. Material properties for bone were varied to simulate the following: all-cancellous bone, cancellous bone with a thin (1.5-mm) crestal isotropic cortical layer, cancellous bone with a thick (3-mm) crestal isotropic cortical layer, and cancellous bone with a thick (3-mm) layer of transversely isotropic (orthotropic) cortical bone. RESULTS: Low stresses and high strains surrounded the fixture apex for the all-cancellous bone model. When a layer of cortical bone was added, higher crestal stresses and lower apical strains were observed. The thicker layer of isotropic cortical bone produced stresses at least 50% less than the thinner layer. The assumption of transverse isotropy (orthotropy) increased stresses and strains by approximately 25% compared with isotropic bone. CONCLUSIONS: Crestal cortical layer thickness and bone isotropy have a substantial impact on resultant stresses and strains. Clinical assessment of these parameters is recommended.
Asunto(s)
Implantes Dentales , Análisis del Estrés Dental/métodos , Maxilar/anatomía & histología , Maxilar/fisiología , Proceso Alveolar/anatomía & histología , Proceso Alveolar/fisiología , Fenómenos Biomecánicos , Densidad Ósea , Elasticidad , Humanos , Presión , Resistencia a la TracciónRESUMEN
This study was conducted to determine the effect of abutment angulation on the stress field near a specific dental implant. Photoelastic resin was cast directly to five 3.8 x 10-mm Steri-Oss implants in 50 x 70 x 13-mm molds. One additional model was fabricated with a strain gauge rosette embedded in the resin to allow precise determination of normal stresses. Zero-degree, 15-degree, and 20-degree abutments were assembled on each of the six implants, subjected to 178 N load, and viewed with a circular polariscope. Observed fringe patterns were photographed for all six models, and strain indicator readings were recorded for the strain gauge model. Numerical data from the strain gauges produced results that agreed with the visual interpretation of the isochromatic fringes. Strain gauge data were also used to calculate the principal stresses and strains. Although a statistically significant increase in stress and strain was found for each increase in abutment angulation, all three abutments produced principal strains that appear to be within the physiologic zone for bone. All values for stress and strain were determined at the location of the rosette, approximately 4 mm from the implant. Higher stresses and strains exist in regions closer to the fixture.
Asunto(s)
Pilares Dentales , Implantes Dentales , Análisis del Estrés Dental/métodos , Análisis de Varianza , Birrefringencia , Diseño de Prótesis Dental , Elasticidad , HumanosRESUMEN
PURPOSE: This investigation compared the stress production characteristics of five abutment angulations for a specific implant system. MATERIALS AND METHODS: Photoelastic resin was cast directly to a 3.75 x 10-mm Branemark fixture (Nobelpharma USA, Inc, Chicago, IL) in a 50 x 70 x 13-mm mold. A strain gauge rosette was also incorporated in the resin to allow precise determination of normal stresses at a specific point. Each 4-mm abutment (15 degrees, 25 degrees, and 35 degrees from Implant Innovations (West Palm Beach, FL) and 0 degree and 30 degrees from Nobelpharma) was assembled on the fixture, subjected to 178N load, and viewed with a circular polariscope. Observed fringes were photographed and strain indicator readings were recorded. RESULTS: Mean observed fringe order and mean principle stress and strain at the location of the rosette were determined. CONCLUSION: At the location of the rosette, all five of the abutments produced principal strains (compressive and tensile) within the physiological zone for bone. The rosette was located approximately 4 mm away from the fixture. Higher stresses and strains can be expected in regions closer to the implant.
Asunto(s)
Pilares Dentales , Implantes Dentales , Diseño de Prótesis Dental , Análisis del Estrés Dental , Análisis de Varianza , Elasticidad , HumanosRESUMEN
The three-dimensional finite element stress analysis method was used to determine the pattern and concentration of stresses within the Screw-Vent endosseous implant and its supporting tissues. For this commercially pure titanium implant, maximum stresses were located within the implant collar immediately below the bony crest. These stresses were at least 18 times less than the endurance limit of commercially pure titanium (259.90 MPa). Maximum stresses (19.57 MPa) in the bone were lingual to the superior portion of the collar. Previous longitudinal radiographic studies of a similar implant have revealed bone loss mesial and distal to the implant. For the Screw-Vent, mesial and distal stresses (maximum 0.38 MPa) were much lower than those buccal and lingual to the implant. The clinical significance of the stress transfer to the bone buccal and lingual to the implant has yet to be determined.