Biomedical subjects

D B Boyer

Publications and source records attributed to D B Boyer.

At least 19 recordsLinked to original sources

PubMed1998

Microtensile bond strength testing and failure analysis of two dentin adhesives.

OBJECTIVES: This investigation was conducted to determine the tensile bond strength of two dental adhesive using a recently introduced "microtensile" bond strength testing design and to verify the failure mode for each test specimen with scanning electron microscopy (SEM). METHODS: Extracted human molars were mounted in stone and the enamel was removed the occlusal surface perpendicular to the long axis of the tooth. A composite resin crown was formed on this flat dentin surface utilizing each dental adhesive system according to manufacturer's instructions. Twenty-four hours later the bonded test specimens were sectioned perpendicular to the adhesive joint, producing six to seven thin slabs per tooth. These dentin/adhesive/composite resin slabs were sectioned free from the stone block and mounted into custom Plexiglas fixtures for trimming and subsequent tensile bond strength testing at 7 d post-bonding. The bond strength of the two adhesives was statistically compared with the t test. The broken specimens were examined with SEM to determine the fracture location or failure mode. Failures for each adhesive system were categorized as either interfacial (joint or mixed) or substrate (dentin and composite) and evaluated by Fisher's exact test. RESULTS: The tensile bond strength and failure modes of All-Bond 2 (Bisco) and Optibond FL (Kerr) were not significantly different. Sixty per cent (12/20) of fractures involving All Bond 2 occurred at the interface, with seven being entirely maintained within the joint, whereas Optibond FL had 35% (7/20) involving some portion of the interface, two totally within the joint. Cohesive fractures of either dentin or composite accounted for 55% of the total failure modes (21/40). The remaining dentin thickness did not affect the measured tensile bond strength. SIGNIFICANCE: This versatile new method permits multiple measurements from a single tooth or small surface areas within a restoration but careful interpretation of the failure mode is required to prevent inappropriate conclusions about the utility of the test.

Crowns↗

PubMed1998

Effect of hybrid layer on fracture toughness of adhesively bonded dentin-resin composite joint.

OBJECTIVES: Micromechanical retention from the hybrid layer is generally believed to be the mechanism of adhesion of current generation dentin bonding agents. The purpose of this investigation is to evaluate the interfacial fracture toughness of a commercial dentin bonding agent with and without this hybrid layer. METHODS: Ten extracted molars (AB2) were flattened on the occlusal surface, All-Bond 2 Universal Adhesive System (Bisco) was applied according to manufacturer's directions and a resin composite (Prodigy, Kerr) crown was formed. Another group of ten molars (AB2Cl) was handled identically with the exception of a 1 min gentle scrubbing application of 5.25% sodium hypochlorite after acid etching to remove the acid-exposed collagen. Plane-strain chevron-notch short bar fracture toughness specimens were fabricated from all 20 composite crowns and tested according to ASTM E1304-89. Each group was tested to failure in tensile mode at 0.1 mm min-1 and the maximum load at failure was used to determine plane-strain fracture toughness (KQvM). Weibull parameters were calculated and fracture probability distributions were tested for significant difference at the 95% confidence level. Scanning electron microscopy was employed on broken specimens (18/20) to describe the failure mode. RESULTS: Weibull distributions were not significantly different with characteristic plane-strain fracture toughness from maximum load (KQvM0) of 0.97 MPa m1/2 and 0.81 MPa m1/2 and a Weibull modulus of 4.7 and 3.9, respectively, for AB2 and AB2Cl. All AB2 samples failed within the adhesive joint, while the AB2Cl crack propagated from the interphase of adhesive resin and dentin to 1-2 microns into dentin. SIGNIFICANCE: Under the conditions of this study, the presence of collagen did not contribute to a significantly stronger bonded joint. Interfacial fracture toughness evaluation of the dentin-resin composite bimaterial interface shows promise for future investigations.

Collagen↗

PubMed1998

Viscoelasticity and aging of dental composites.

Effects of aging on several dental composites were studied using a torsion creep apparatus. A constant torque was applied from 1 second to 3 hours, and recovery was observed from 10 seconds to 2 days, for specimens aged from 3 hours to 8 weeks following polymerization. Specimens aged for shorter times exhibited more creep and less complete recovery than specimens aged for longer times. Modulus and creep results were qualitatively consistent with a composite model for particulate inclusions.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1997

Effect of composite type, light intensity, configuration factor and laser polymerization on polymerization contraction forces.

PURPOSE: To investigate the effect of composite type, light intensity, configuration factor and laser polymerization on polymerization contraction force. MATERIALS AND METHODS: Glass rods (10 pairs/group) were etched with HF acid, silanated, unfilled resin applied and light cured for 20 s. Rods were held vertically in chucks on a Zwick machine. A cylindrical matrix was filled with Silar chemical cure, Silux Plus microfill or Z-100 hybrid composite and the crosshead of the UTM positioned at an inter-rod distance corresponding to a specific ratio of bound to unbound composite surface area (configuration factor or C). Exposure time with the Demetron 401 conventional visible light curing unit (D401) was 40 s/side (80 s total). Exposure times for the ILT Model D5500 air cooled laser (LAC) and Model 5500ABL water cooled laser (LWC) was 20 s/side (40 s total). Experimental groups, n = 10 with constant factors in parentheses, included: (1) Silar chemical-cured (C = 3); (2) Z-100 hybrid (C = 3, D401, 100% intensity); (3) Silux Plus microfill (C = 3, D401, 100% intensity); (4) D401 100% light intensity = 476 mW (Z-100, C = 3, D401); (5) D401 50% intensity = 238 mW (Z-100, C = 3, D401); (6) D401 25% intensity = 119 mW (Z-100, C = 3, D401); (7-9) C = 5, 3 & 1 respectively (Z-100, D401, 100% intensity); (10) D401 with 13 mm tip = 391 mW/cm2 (Z-100, C = 3; D401); (11) D401 with Turbo Tip = 811 mW/cm2 (Z-100, C = 3; D401); (12) LAC = 265 mW, 689 mW/cm2 (Z-100, C = 3); (13) LWC = 365 mW, 1100 mW/cm2 (Z-100, C = 3). One Way ANOVA and Duncan's Multiple Range Test (alpha = 0.05) were performed separately for each variable. RESULTS: Homogeneous subsets by variable were: composite type Group 1 (25N) < Group 3 (65.8N) < Group 2 (90.4N); intensity Group 6 (73.9N) = Group 5 (77.7N) < Group 4 (90.4N); C-Factor Group 7 (81.8N) < Group 8 (90.4N) < Group 9 (103.4N); light source Group 12 (77.4N) = Group 13 (79.1N) < Group 10 (90.4N) = Group 11.(89.4N). The chemical-cured composite had the lowest maximum polymerization contraction force, the microfill was intermediate and the hybrid composite had the highest recorded force. Increases in light intensity increased the maximum force on the force/time curve. Maximum forces were inversely related to C-factor (C5 < C3 < C1) and directly related to composite volume in a non-rigid system which allowed compliance. Maximum force was not significantly different with the two tips tested on the conventional curing light. Forces obtained with laser polymerization were similar for the two laser groups, which were both statistically lower than the conventional light tested.

Analysis of Variance↗

PubMed1997

Dentin desensitizing agents: SEM and X-ray microanalysis assessment.

PURPOSE: To evaluate the effect of four proprietary dentin desensitizing agents on dentin tubular occlusion, chemical composition changes on the dentin surface, and the effect of saliva and toothbrushing on these agents. MATERIALS AND METHODS: Fifty dentin discs, obtained from 50 freshly extracted human premolar and molar teeth were used in this study. These were divided into five groups of 10 discs each. Five discs from each group were treated with the desensitizing agents, viewed under the SEM and subjected to energy dispersive X-ray analysis. The other five discs were treated with the desensitizing agents, immersed in artificial saliva, subjected to simulated toothbrushing equivalent to 3 weeks of normal brushing and viewed under the SEM. The agents studied were Sensodyne Dentin Desensitizer, Therma-Trol Desensitizer Gel, Gluma Desensitizer and All-Bond DS. RESULTS: The Kruskal-Wallis test followed by the Wilcoxon signed-rank test showed that Sensodyne Dentin Desensitizer exhibited the greatest amount of tubular occlusion among the unbrushed samples, followed by Therma-Trol Desensitizer Gel, Gluma Desensitizer and All-Bond DS (P < 0.05) in that order. Toothbrushing increased tubular occlusion in all cases except the Sensodyne Dentin Desensitizer treated samples.

Chi-Square Distribution↗

PubMed1996

Effect of ultrasonic vibration on post removal in extracted human premolar teeth.

The purpose of this study was to determine the effectiveness of ultrasonic vibration in removing Paraposts from extracted teeth. Paraposts were cemented in mandibular premolars to a depth of 9 mm with zinc phosphate cement and the teeth placed in four groups. Group 1 received no vibration. Group 2 received vibration for 4 min, group 3 received vibration for 12 min, and group 4 received vibration for 16 min. Tensile forces were applied to the posts and mean dislodgment forces compared. The mean force (kg) required to dislodge the Parapost in group 1 was 24.92 +/- 1.64 SEM; in group 2, 25.01 +/- 1.80; in group 3, 24.08 +/- 2.29; and in group 4, 12.41 +/- 2.60. There was a significant difference between group 4 and groups 1 to 3 (p = 0.0003). Results of this study indicate that 16 min ultrasonic vibration is an effective method for removing Paraposts from human premolar teeth.

Analysis of Variance↗

PubMed1996

Effect of varying etching times on the bond strength of ceramic brackets.

Damage to the enamel surface when debonding orthodontic ceramic brackets has been a clinical concern. Ideally, bond failure at the bracket-adhesive interface should occur without damaging the enamel surface. The purpose of this study was to determine the shear bond strength and debonding failure modes of ceramic brackets with varying etching times. Sixty freshly extracted human premolars were pumiced and divided into six groups of 10 teeth. Each group was assigned an etching time interval of either 30, 20, 15, 10, 5, or 0 seconds with 37% phosphoric acid. Ceramic orthodontic brackets were bonded to each etched tooth by using the same orthodontic bonding system. The teeth were mounted in phenolic rings and stored in deionized water at 37 degrees C for 48 hours. A Zwick universal testing machine (Zwick GmbH and Co., Ulm, Germany) was used to determine shear bond strengths. The residual adhesive on the enamel surface was evaluated with the Adhesive Remnant Index. The results of the analysis of variance indicated that there were significant differences in bond strengths between the various etching times (p=0.0001). The Duncan multiple range test revealed that the 5-second and no etch group exhibited significantly lower bond strengths. The results of the Chi square test evaluating the residual adhesives on the enamel surface also revealed significant differences (p=0.0001). However, when the 5- and 0-second groups were dropped from the test, the Chi square test revealed no significant differences between the 30-, 20-, 15-, and 10-second groups (p=0.211). In conclusion, decreasing etching time between 30 and 10 seconds does not significantly affect either bond strength or the site of bond failure.

Acid Etching, Dental↗

PubMed1995

The use of debonding pliers in the removal of ceramic brackets: force levels and enamel cracks.

The purpose of this study was to determine the magnitude of the applied forces when using pliers as a debonding method for removing three types of ceramic brackets. The following variables were evaluated: debonding strengths, the Adhesive Remnant Index, and enamel damage with transillumination. All the brackets in this investigation was debonded with a direct bond remover plier. An Instron Model Universal testing machine was used to measure debonding strengths. From the results of this study, the following conclusions can be drawn: (1) The diamteral compression mean bond strengths for the three bracket types tested ranged from a low of 67.8 Kg/cm2 to a high of 102.9 Kg/cm2 and are in the clinically acceptable range for orthodontic force application. (2) There was no significant difference in the mean bond strengths of the three ceramic brackets tested. (3) The ARI scores were found to range between 2 and 4 indicating a cohesive type of bond failure. (4) Transillumination was used to evaluate minute enamel damage, and the results indicated that most of the teeth (82.02%) experienced no increase in enamel cracks after debonding. The teeth that showed an increase in the number of cracks after debonding had a significantly higher mean bond strength (113.0 Kg/cm2) than those with no increase in the number of cracks (72.9 Kg/cm2).

Adhesives↗

PubMed1995

Debonding orthodontic ceramic brackets by ultrasonic instrumentation.

Breakage of ceramic brackets because of brittleness may cause such problems as aspiration of fragments and injury by flying debris. Portions remaining on the tooth must be laboriously ground off with a handpiece. This study investigated a potential method of lowering the force required to remove ceramic brackets, i.e., use of an ultrasonic chisel. Ceramic brackets were bonded to extracted incisors and canines. The degree of cure of a light-activated cement was systematically varied with different exposure times to a curing light. The brackets were sheared from the teeth with a universal testing machine and a chisel tip on a Cavitron. The ultrasonic chisel markedly reduced the force required to debond the brackets; however, the time of application averaged 16.6 seconds. Reducing the degree of cure of the cement had only a slight effect on the time required and the forces generated. This method of debonding is not recommended without further development.

Ceramics↗

PubMed1994

Polymerization shrinkage of composite resins: comparison with tooth deformation.

Polymerization shrinkage of two posterior composite resin restorative materials was measured by dilatometry. The results were compared with a decrease in cavity width of MOD preparations in extracted premolars restored with the composite resins. A highly filled hybrid composite exhibited greater free shrinkage and cuspal deformation than a hybrid composite with a lower filler content. Deformation of the cusps was less than the unrestricted shrinkage of the composite resins. Hydrated teeth exhibited less deformation than dehydrated teeth because of polymerization shrinkage. Greater cuspal deformations were measured with the microscopic technique than with interferometry because of differences in experimental design.

Acrylic Resins↗

PubMed1994

Effect of polyethylene fiber reinforcement on the strength of denture base resins polymerized by microwave energy.

This study investigated the effect of addition of polyethylene fibers on the transverse strength, deflection, and elastic modulus of two denture base acrylic resins polymerized by microwave irradiation. Specimens of each resin, Lucitone 199 and Acron MC, were fabricated with 0.0%, 0.5%, 1.5%, and 3.0% fiber loading. Specimens were tested with use of a three-point flexure apparatus with an Instron universal testing machine after storage in water for 10 days at 37 degrees C. The results showed that polyethylene fibers significantly decreased the transverse strength of Acron MC resin and slightly increased the transverse strength of Lucitone 199 resin at a loading of 0.5% by weight. Fiber loading did not significantly affect the deflection and the elastic modulus of either material.

Acrylic Resins↗

PubMed1994

Debonding forces applied to ceramic brackets simulating clinical conditions.

Debonding ceramic brackets is an area of concern to clinicians. Reports of enamel fractures and cracks have raised questions about the safety of the procedures used to remove these attachments. The purpose of this study was to compare the differences between the actual forces generated during bracket removal in the clinical setting and the shear forces applied during laboratory testing. Adhesive Remnant Index (ARI) scores are presented as a percentage of the total number of teeth tested and are compared between the two types of debonding methods. The ARI scores quantitatively express where the bond failure occurs during bracket removal. The results indicate that there is a significant difference between the mean bond strengths of the shear (107.8 kg/cm2) and the modified diametral compression (67.8 kg/cm2) forces. Debonding ceramic brackets with pliers requires the application of 30% less force to the enamel surface than debonding with the shear forces as tested in the laboratory. There were no significant differences in the ARI scores of the two groups--i.e. where the bond failures occurred.

Acid Etching, Dental↗

PubMed1994

Effect of a silane coupling agent on composite repair strengths.

PURPOSE: To evaluate the use of a silane coupling agent (Silane Bond Enhancer) for repair of a glass-filled hybrid resin composite (Herculite XR). MATERIALS AND METHODS: Composite specimens (n = 20) were either air-abraded (AA) with an intraoral sandblaster (Microetcher), etched with 9.6% hydrofluoric acid (HF) (Porcelain Etch Gel), or treated with both methods (AA/HF). A silane coupling agent was applied to half of the specimens after these initial surface treatments. Composite repairs were completed by application of a phosphonate ester bonding agent (Bondlite) and resin composite (XRV Herculite). Transverse strengths of repaired specimens and intact (control) specimens were determined using an Instron. RESULTS: The mean bond strengths of repaired specimens ranged from 41% to 62% of the composite's cohesive strength. All repair strengths were significantly lower than the cohesive strength, but were not significantly different from each other. Silanation slightly improved the transverse strength of specimens repaired using the HF and AA/HF methods, but not those repaired using the AA procedure.

Acid Etching, Dental↗

PubMed1994

Fracture resistance of teeth with bonded amalgams.

Breaking strength of the cusps of molars with MOD amalgam and composite restorations was measured with an Instron. Bonding of the amalgam and composite restorations with adhesives increased the resistance of the cusps to fracture, however, the cusp strength was not returned to that of intact, unprepared teeth. The relative effectiveness of the bonding agents with amalgam was C&B Metabond > Amalgambond > Panavia EX. Reinforcement by amalgam bonding was similar to or less than reinforcement with the composite restorations depending on the adhesive used.

Analysis of Variance↗

PubMed1993

Cusp movement in premolars resulting from composite polymerization shrinkage.

This study examined the effect of cavity size, hydration conditions and type of composite on cusp movement following placement of MOD composite restorations in vitro. A microscope with a micrometer stage was used to measure deflection of cusps for 14 days after initiation of curing. The intercuspal width decreased for the first few minutes after the composites were placed, then increased toward the original dimensions. Teeth with small cavities contracted less than those with large cavities, and recovery was complete or nearly complete only in teeth with small cavities. Hydrated teeth and restorations recovered more rapidly and more completely than those that were dry. Differences in deflection of the cusps were observed with two different restorative materials.

Absorption↗

PubMed1993

Analysis of debond rates of resin-bonded prostheses.

Debonding rates of 164 resin-bonded prostheses (RBP) placed from 1974 to 1985 were examined at recall. The yearly debond rates were calculated, the cumulative probability of failure was determined for the debonded RBPs, and Weibull distribution parameters were determined. For perforated prostheses, there was a high initial debond rate, followed by slowly decreasing rates for about 5 years. Increasing rates after 5 years indicated the beginning of wear-out. The Weibull parameters for the wear-out period of the perforated prostheses were: characteristic life = 128 (SE = 2) months, modulus = 1.27 (0.06), and threshold parameter = 0. Data were available for etched frameworks for 6 years and showed decreasing debond rates during this time. The characteristic life of the etched bridges was 318 (84) months. The cumulative failure data were also modeled with a cubic polynomial distribution that resulted in a U-shaped hazard function.

Adolescent↗

PubMed1993

Interferometric measurements of cusp deformation of teeth restored with composites.

A Michelson interferometry apparatus was used for measurement of the displacement of the buccal cusps of premolars after restoration of MOD preparations with composites. The effects of composite type, cavity size, and hydration conditions were examined. Interferometry permitted real-time measurement of cusp movement as it occurred. Contraction occurred very rapidly, about 1/3 of the 60-minute amount within the two-minute period of exposure to the curing light. Cusp movement was smooth rather than interrupted, indicating lack of microfracturing at deformations of 11-46 microns. Contraction, 0.94% for Heliomolar and 1.2% for P-50, was similar to the linear polymerization shrinkage of the resins. Less cusp movement occurred in small cavities than in large cavities. Hydrated teeth had less cusp movement than dehydrated teeth.

Acid Etching, Dental↗

PubMed1993

Effects of dentin permeability and hydration on the bond strengths of dentin bonding systems.

This in vitro study evaluated the shear bond strengths of five adhesive systems bonded to dentin with and without simulated physiologic hydrostatic pressure. To simulate pulpal pressure, bonding procedures were done on extracted teeth connected to a hydration apparatus. Bond strengths were significantly less for each adhesive system under simulated physiologic conditions. Amalgambond had significantly higher bond strengths than Clearfil Photo Bond, Gluma, Scotchbond 2, or Tenure, either with or without simulated pulpal pressure.

Analysis of Variance↗