Biomedical subjects

D B Boyer

Publications and source records attributed to D B Boyer.

At least 37 records · Page 2Linked to original sources

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↗

PubMed1992

Evaluation of new methods for composite repair.

This study evaluated the effectiveness of air abrasion (sandblasting), hydrofluoric acid (HF) etching, and acidulated phosphate fluoride (APF) for composite repair. Five different composites (three hybrids, one small-particle, and one microfill) were used to test the effects of different compositions and particle sizes. A phosphonate resin bonding agent was used for all repair procedures. In general, air abrasion provided the strongest repairs, approximately 60% of cohesive strength. The effect of HF varied with different composites, either improving or reducing the repair strength. APF gave the lowest interfacial bond strengths for all composites except the microfill.

Acid Etching, Dental↗

PubMed1992

Effect of matrix systems and polymerization techniques on microleakage of Class II resin composite restorations.

This study investigated the effect of different sized light curing tips (2 mm and 11 mm) with curing techniques associated with different matrix systems (Mylar with reflective wedge and metal with wooden wedge) on microleakage of a posterior resin composite material (P-50) placed using a bonding agent (Scotchbond 2). Eighty Class II mesial and distal slot preparations (40 with enamel gingival margins and 40 with dentin gingival margins) were randomly divided into four equal groups: 1) metal matrix, large tip; 2) Mylar matrix, light emitting wedge, large tip; 3) Mylar matrix, light emitting wedge, small tip; 4) metal matrix, small tip. Three-way ANOVA indicated no statistical differences among groups using small and large curing tips. The results showed significantly more leakage (alpha = 0.05) in the dentin gingival cavosurface margin groups than the enamel cavosurface margin groups. The results also showed significantly greater leakage in the polymerization procedures associated with the metal matrix groups (alpha = 0.05) compared to polymerization procedures associated with the Mylar matrix groups.

Analysis of Variance↗

PubMed1991

Bond strength and failure analysis of light-cured denture resins bonded to denture teeth.

This study examined the tensile bond strength and failure sites of one heat-cured (Microlon) and two visible light-cured (Triad and Extoral) denture resins to two types of denture teeth. The resins were processed into cylinders against denture teeth milled to the same size. Half of the specimens were thermocycled. After tensile testing, statistical analysis (p 0.05) showed that the strongest bond was achieved with the heat-cured resin Microlon, whereas Triad resin displayed the stronger bond between the two light-cured resins. Scanning electron microscopic analysis showed that the nature and location of the fracture sites was different among the three resins tested.

Acrylic Resins↗

PubMed1991

Hardening of dual-cured cements under composite resin inlays.

This study was conducted to determine the extent of hardening of three dual-cured cements under composite resin inlays and to determine the effectiveness of a light-reflecting wedge in promoting curing of the cements in the proximal margin. The exposure times needed to optimally harden the cements were determined by directly exposing the cements to the curing light. Composite resin inlays were bonded in an extracted molar with Dual cement, Dicor light-activated cement, and Duo cement. Cure-Thru reflective wedges were placed in the gingival embrasure of half of the specimens. None of the cements hardened completely by 24 hours when we used an exposure time that met or exceeded that recommended by the manufacturers. The chemical-cure component did not completely cure the cements when light was attenuated by the tooth and restoration. The light-transmitting wedge had little effect on hardening of the cements.

Analysis of Variance↗

PubMed1991

Photo-activation of resin cements through porcelain veneers.

The purpose of this study was to determine the effects of porcelain opacity, chemical catalyst, and exposure time on polymerization of light-activated resin-composite cements. Samples of microfill and hybrid composites, with and without catalyst (i.e., dual-cure and visible-light-activated), were polymerized by exposure to visible light through porcelain discs of different opacities. Microhardness testing (KHN) was used to compare degree of cure for each material at various exposure times. Porcelain opacity did not significantly affect hardness. However, the results indicated that a chemical catalyst and prolonged curing times might be essential for clinical success.

Analysis of Variance↗

PubMed1990

Composition of clinically aged amalgam restorations.

Twenty-five amalgam restorations ranging in age from two to 25 years were obtained from five subjects. An electron microprobe was used to analyze the specimens for bulk elemental composition and phase composition, and the volume fractions of phases were determined by point-counting on back-scattered electron micrographs. Twenty-one of the specimens were conventional, low-copper amalgams, and the remaining four were high-copper amalgams. The bulk elemental compositions showed little variation from newly prepared amalgams except for the presence of a small amount of chloride and other contaminants. The compositions of the phases were essentially the same as is found in new amalgams, except that there was considerable internal amalgamation of gamma particles. The distribution of phases in the clinically aged amalgams was quite different from that of new amalgams. The low-copper amalgams had decreased amounts of gamma, gamma-1, and gamma-2 phases and increased beta-1 and tin-chloride. The high-copper admixed amalgams had decreased gamma, increased beta-1, and enlarged reaction rings (gamma-1 and eta').

Copper↗

PubMed1990

Prediction of postpartum depression.

This article briefly reviews definitions, etiology, and cultural aspects of postpartum depression. Studies attempting to predict postpartum depression are examined, and a summary of risk factors is given. The importance of educating all pregnant women about postpartum depression is stressed, and sample patient education information is presented.

Cultural Characteristics↗

PubMed1989

Cast metal, resin-bonded prostheses: a 10-year retrospective study.

A sample of 99 resin-bonded prostheses placed over a 10-year period were examined by four clinicians using a standardized criteria sheet. Areas examined included hard tissues, periodontium, retainer and pontic design, retention, the effect of occlusion on framework design and retention rate, and bonding media. The data from 7- and 10-year retrospective studies were compared for meaningful trends. Results showed (1) caries on retainer teeth was 3%, (2) gingival index of the retainer teeth was less than the gingival index of the rest of the mouth (0.7 +/- 0.5 versus 0.9 +/- 0.6), (3) the respective mean probing depths of retainer teeth of 34 patients in the 7- and 10-year studies were 2.2 +/- 0.4 mm and 1.9 +/- 0.7 mm, (4) the debond rate of all the prostheses from all causes was 31%, (5) the debond rate comparing etched metal and perforated retainers from all causes was 32% and 31% [corrected], respectively, and (6) 83% liked the prosthesis; 17% were noncommittal. The authors concluded that the resin-bonded prosthesis may be considered a permanent restoration and a valuable asset in the clinician's armamentarium.

Adult↗

PubMed1989

Comparative bond strengths of light-cured, heat-cured, and autopolymerizing denture resins to denture teeth.

Standard and interpenetrating polymer network acrylic resin denture teeth were milled into cylinders 8 mm in diameter and processed against cylinders of the three different resins. The specimens were reduced by milling to a diameter of 6 mm in the region of the tooth-resin interface and thermocycled for 24 hours. Specimens were then subjected to tensile loading until fracture. Group means were compared by using the Duncan multiple range test at the 5% level of significance. The strongest bond occurred between the heat-cured resin and the standard acrylic resin teeth. Intermediate strength was achieved with the heat-cured resin to the IPN teeth and the autopolymerizing resin to both types of teeth. Lowest strength was measured with the light-cured resin to both types of teeth.

Acrylic Resins↗

PubMed1989

Effects of etching and rinsing times and salivary contamination on etched glass-ionomer cement bonded to resin composites.

This study investigated the effect of salivary contamination on glass-ionomer/resin-composite bond strength after establishment of an appropriate etching and rinsing time for the glass-ionomer cement. Three hundred and thirty samples of glass-ionomer cement (Ketac-Fil) were injected into cavities prepared in acrylic molds. Groups containing 15 samples each were etched for 0, 15, 30, or 60 sec, after which Scotchbond and either Silux or P-30 were applied and polymerized. The samples were stored under water for 24 hr at 37 degrees C and were then tested in shear. A 30-second etching time was found to be optimal when Silux and P-30 were considered together. In a similar manner, a 20-second optimal rinsing time was determined. Samples of glass-ionomer cement were then contaminated with saliva, dried, and bonded to composite resins and tested in shear as before. Significantly lower bond strengths resulted than with the uncontaminated controls. Efforts to clean contaminated samples by rinsing or re-etching failed to increase the bond strength obtained with the contaminated samples.

Acid Etching, Dental↗

PubMed1989

Microleakage of indirect composite inlays.

The purpose of this in vitro study was to evaluate the microleakage of indirect composite inlays and to compare leakage of inlays with directly placed composite restorations. Standardized MOD preparations were cut in 50 extracted human molars. One gingival margin was placed in enamel above the CEJ, and the other was placed in dentin below the CEJ. Two groups of teeth were directly filled with composites (P-30 and Heliomolar) after being etched, and dentin bonding agents were applied. Two groups of teeth were restored with composite inlays that were fabricated on stone dies. The inlays were made and luted with the same two composites. The last group of teeth was restored with Heliomolar inlays luted with Dual cement. The specimens were thermocycled 300 times between 5 and 50 degrees C. Microleakage was evaluated by use of the silver-nitrate staining technique. The depth of leakage was measured microscopically after the teeth were sectioned. Both direct restorations and inlays showed substantial leakage at gingival-dentin margins; however, there was only superficial leakage at enamel margins. P-30 inlays and Heliomolar inlays cemented with Dual leaked less than direct restorations at the gingival-dentin margins. There was no difference in leakage of enamel margins of inlays and direct restorations, except that direct Heliomolar restorations leaked more than the others. There was no difference in leakage between Heliomolar restorations luted with light-cured or dual-cured cement.

Composite Resins↗

PubMed1989

Curing light-activated composite cement through porcelain.

The purpose of the study was to determine the exposure times needed to harden a light-activated composite cement through various thicknesses of porcelain. A negative exponential model was developed with which the relative hardness of a composite could be predicted from the product of the exposure time and the square root of the light intensity at 470 nm. Hardness data obtained by varying the exposure time and porcelain thickness were found to fit this model. A relationship was derived to predict the required exposure time, t, of a composite under porcelain with a transmission coefficient, Tc, and a thickness, l:t = toTc-1/2, where to is the exposure time of the composite alone.

Composite Resins↗

PubMed1989

The contribution of dental amalgam to mercury in blood.

We determined the exposure to mercury from dental amalgam by comparison of blood levels of mercury before and after removal of all amalgams from ten subjects. Baseline concentrations of mercury in whole blood were measured weekly for four to 18 weeks (median = 6.6 weeks) prior to removal. All amalgams were removed in a single appointment. The subjects had an average of 14 surfaces of amalgam, seven of which were occlusal surfaces. Weekly blood sampling was continued for five to 18 weeks (median = 7.6 weeks) after the amalgams were removed. The mean baseline concentration of total mercury in whole blood of the ten subjects was 2.18 (SD = 0.90) ng Hg/mL before the amalgams were removed. The baseline mercury levels were related to the number of amalgam surfaces. The linear correlation coefficient was 0.724 with number of occlusal surfaces, and 0.433 with total number of surfaces. After removal of the amalgams, nine of the ten subjects exhibited a statistically significant decrease in blood mercury at the 95% level of confidence. The mean decrease in mercury was 1.13 (SD = 0.60) ng Hg/mL. The half-time for elimination of mercury from blood after amalgam removal was 30.2 (SD = 5.8) days. Removal of the amalgams provided an additional exposure of 1.46 (SD = 1.17) ng Hg/mL that was rapidly cleared from the blood with a half-time of 2.9 days. The daily intake of mercury from amalgam in the subjects was estimated to be at least 1.3 micrograms.

Adult↗