Biomedical subjects

D B Boyer

Publications and source records attributed to D B Boyer.

At least 19 recordsLinked to original sources

PubMed2003

Dynamic viscoelastic behavior of resin cements measured by torsional resonance.

OBJECTIVE: The purpose of the study was to measure the viscoelastic properties of four dental resin composite cements using a dynamic mechanical analysis technique. METHODS: Dynamic torsional loading was conducted in the frequency range from 1 to 80 Hz. Cement specimens were tested after storage in 37 degrees C water for 24 h. One group was thermal cycled prior to testing. Measurements were taken at 21, 37, and 50 degrees C. Storage modulus, loss tangent and other viscoelastic parameters were determined from the amplitude/frequency curves. RESULTS: Storage moduli of the cements ranged from 2.9 to 4.1 GPa at 37 degrees C. Loss tangents ranged from 0.054 to 0.084. Storage moduli decreased in a regular way with increasing temperature, whereas, loss tangents increased. Thermal cycling caused small decreases in storage moduli. SIGNIFICANCE: Resin cements with higher filler loading were found to have higher storage moduli and lower loss tangents. Since these properties have been associated with better clinical performance in the areas of retention and prevention of fracture of porcelain and resin restorations, the more highly filled cements may be recommended. Temperature variations influenced viscoelastic behavior of the cements. However, within the temperature range studied no sharp drop in modulus was seen, so the materials should function satisfactorily in the oral cavity.

Analysis of Variance↗

PubMed2001

Mode of failure in the dentin-adhesive resin-resin composite bonded joint as determined by strength-based (muTBS) and fracture-based (CNSB) mechanical testing.

OBJECTIVE: To determine the failure mode between dentin-adhesive resin-resin composite bonded joint produced with a chevron-notch short-bar (CNSB) and microtensile test methods. METHODS: Forty teeth were randomly selected for microtensile and forty for CNSB specimen fabrication and stored in 0.5% chloramine T at 37 degrees C until respective static load to failure testing at 30 and 180days. Failure modes were categorized by SEM and tested with Fisher's exact test. Within respective mechanical testing methods the probability of failure curve distributions being significantly different were analyzed by the Wald chi-square statistic. RESULTS: The characteristic fracture toughness at 30- and 180-day storage was 0.82 and 0.87MPam(1/2), while the Weibull Modulus (m) for the failure distributions, was 4.60 and 4.56, respectively. No significant difference was demonstrated in the failure distributions between these groups (p=0.45). The characteristic tensile strength (muTBS(o)) at 30- and 180-day storage was 52.53 and 14.71MPa with an m of 3.04 and 1.56, respectively. Failure distributions for muTBS groups were significantly different (p<0.001). K(IvM) failure modes, regardless of storage time, were within the adhesive joint with 30-day debonds primarily through the top region of the hybrid layer (THL) and after 180-days involving the bottom of the hybrid layer (BHL). The 30-day muTBS group demonstrated a propensity to debond in dentin or resin composite substrates but after 180-days storage debonds again involved the BHL. SIGNIFICANCE: The weak links in the dentin-adhesive resin-resin composite bonded joint may be the interphase regions between the THL and the adhesive resin and the BHL and dentin.

Adhesiveness↗

PubMed2001

The influence of water storage and C-factor on the dentin-resin composite microtensile bond strength and debond pathway utilizing a filled and unfilled adhesive resin.

OBJECTIVE: To test the elastic wall concept utilizing adhesive resins of varying stiffness in a low- and high-C-factor cavity design after short- and long-term water storage. METHODS: A flat and box-shaped cavity was restored on occlusal dentin with a resin composite using a filled and unfilled adhesive resin from which microtensile specimens with a 0.5mm(2) cross-sectional area were formed. After storage for 30- and 150-days the microtensile bond strength (muTBS) was determined in a Zwick materials testing machine and the subsequent debond pathway was examined under scanning electron microscopy. Fisher's exact test was used to determine differences in joint and substrate failure modes and a Weibull regression model with gamma frailties was used to test for differences between failure distributions. Tests for three-way and two-way interactions were also completed for storage time, C-factor and adhesive. All tests were at 95% confidence levels. RESULTS: The characteristic strength (TBS degrees ) for the Optibond FL adhesive applied on a flat cavity was 47.57 and 20.90MPa and a box-shaped cavity was 49.26 and 17.49MPa for short- and long-term storage, respectively, while the corresponding TBS degrees for the unfilled Optibond adhesive on the flat cavity design was 36.93 and 32.68MPa and in a box-shaped cavity was 32.84 and 15.46MPa. Combining all groups according to storage time revealed a three-fold increase in the debond pathway including the bottom of the hybrid layer. SIGNIFICANCE: Evidence suggests that the durability of the bonded joint is threatened by hydrolysis and the most susceptible region is the bottom half of the hybrid layer and in low C-factor cavity designs a more flexible adhesive resin liner was more durable.

Adhesiveness↗

PubMed2001

Effect of polyaramid fiber reinforcement on the strength of 3 denture base polymethyl methacrylate resins.

PURPOSE: The interactive effects of synthetic polyaramid reinforcement fibers on the transverse strength of intact and repaired heat-polymerized denture base acrylic resins were investigated. MATERIALS AND METHODS: Three polymethylmethacrylate (PMMA) polymers were tested: Acron MC (GC International Corp, Scottsdale, AZ), Lucitone 199 (Dentsply International Inc, York, PA), and Microlon (The Hygienic Corp, Akron, OH). With each polymer, there were 2 controls and 4 experimental groups (n = 9 per group). The treatment groups were intact heat-polymerized PMMA control, PMMA with unreinforced repair, PMMA with polyaramid reinforced repair, intact polyaramid reinforced heat-polymerized PMMA control, polyaramid reinforced PMMA with unreinforced repair, and polyaramid reinforced PMMA with polyaramid reinforced repair. The transverse fracture strengths of the samples were measured with a 3-point bending test on a Zwick Universal Testing Machine (Zwick of America, Inc, East Windsor, CT). RESULTS: The highest mean strength at fracture was recorded with intact polyaramid reinforced heat-polymerized PMMA controls for all resins. Analysis of variance showed significant differences in transverse strength (p < .05) by experimental group, by material, and by interaction of group and material. Tukey HSD (honestly significant difference) Multiple Comparisons Test (alpha = 0.05) showed that intact polyaramid reinforced heat-polymerized PMMA controls were significantly stronger than intact heat-polymerized PMMA controls and all the other treatment groups. Use of polyaramid reinforcement in repair of unreinforced PMMA or polyaramid reinforced PMMA did not result in significantly increased transverse strength. CONCLUSIONS: Polyaramid reinforcement significantly increased the transverse strength of intact heat-polymerized PMMA. Polyaramid fibers did not significantly increase strength to reinforce PMMA repairs.

Acrylic Resins↗

PubMed2000

Effect of stepped light intensity on polymerization force and conversion in a photoactivated composite.

PURPOSE: This study evaluated the effect of stepped light intensity on the polymerization shrinkage forces and degrees of conversion of a hybrid composite. MATERIALS AND METHODS: Composite specimens were bonded between two steel rods (5.00 mm diameter, 1.25 mm apart, configuration factor = 2) mounted in a universal testing machine using a constant displacement mode. Polymerization contraction force was recorded for 300 seconds under four light exposure conditions: group 1: 40 s x 800 mW/cm2; group 2: 10 s x 100 mW/cm2 + 30 s x 800 mW/cm2; group 3: 60 s x 800 mW/cm2; group 4: 10 s x 100 mW/cm2 + 50 s x 800 mW/cm2. Maximum curing force (N300 s) and maximum force rate of the four groups were compared using one-way analysis of variance (ANOVA) (alpha = 0.05) and the Tukey test. Degree of conversion in all groups was evaluated at two depths (top surface and 2 mm) using Fourier transform infrared spectroscopy (FTIR). RESULTS: Mean maximum shrinkage forces and standard deviations (SD) were: group 1, 177 N (SD = 23); group 2, 172 N (SD = 11); group 3, 213 N (SD = 15); group 4, 197 N (SD = 17). Mean maximum forces for stepped and standard groups with the same duration (1 and 2; 3 and 4) were not statistically different; means for groups 2 and 3 were statistically different. Maximum force rates were not significantly different (p = .1548). Force:time curves were S-shaped. Specimens exposed to stepped curing exhibited longer delays before force was recorded. Mode of curing was shown not to contribute to overall cure, but both duration of cure and the depth (top surface vs. 2.00 mm) were significant with an interaction effect.

Analysis of Variance↗

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↗