The effect of burnishing on the mercury vapor emission of amalgam.
Explore the source record for details and available documents.
Chemical Phenomena↗
Biomedical subjects
D B Boyer
Publications and source records attributed to D B Boyer.
Remineralization of dentin in vitro.
The remineralization of completely demineralized bovine dentin was studied in vitro by monitoring the velocities of fall of small particles through calcifying solutions. The density of a particle of dentin may be found from its velocity of fall through a fluid using Stokes' law. The minimum concentration product of calcium and acid phosphate ions of the solution in which remineralization would take place was 3.6 (mM)2 in the presence of 22 mM bicarbonate, pH 7.35, and ionic strength 0.1. This just above the solubility product of brushite (CaHPO4-2H2O). Incubation of decalcified dentin in a phosphoprotein removed from dentin during demineralization, or in phosvitin, had no effect on remineralization. The rates of remineralization and of the fraction remineralized were inversely proportional to particle size. This inverse correlation may be due to deposition of mineral in a surface layer of constant depth irrespective of particle size. The fraction of a particle remineralized was greatly increased by the use of highly supersaturated calcifying solutions or by the incorporation of fluoride into the solutions. The empirical reaction order of remineralization for both calcium and phosphate ions was found to be unity, which is, within the error limits, equal to the order of growth of seed crystals of hydroxyapatite in calcifying solutions of the same composition.
Animals↗
Microstructure of amalgam surfaces.
The polished amalgam surface was smoother than the burnished and the carved surfaces. The burnished surface was smoother than the carved surface. The granular structures on the burnished amalgam surface were found to be of tin-mercury alloy. Polishing appears to be the best finishing technique for amalgam restorations, and there is no substitute for it.
Dental Amalgam↗
Routine circumcision of the newborn: reasonable precaution or unnecessary risk?
Explore the source record for details and available documents.
Circumcision, Male↗
Aerobic exercise, maternal self-esteem, and physical discomforts during pregnancy.
Explore the source record for details and available documents.
Adult↗
Midwifery in Northern Belize.
During several volunteer experiences in the Corozal District in Northern Belize, the authors worked with and interviewed traditional midwives, midwife educators, administrators, and professional midwives, who practice in public health clinics, rural health outposts, and a government hospital. One interview with a traditional midwife from a rural Mayan village, garnered interesting information about her 63-year practice, which is compared with the practice of professional midwives. Issues important to midwifery and health care in Belize are discussed. The interviews and the authors' own experiences reveal changing birthing practices, as well as the continued importance of midwives in the care of childbearing women in Northern Belize.
Belize↗
Radiopacity of compomers, flowable and conventional resin composites for posterior restorations.
The objective of this study was to densitometrically determine the relative radiopacity (aluminum [Al]-equivalent values) of dentin, enamel, and 20 resin composite materials currently used for posterior restorations. Specimens 5 mm in diameter and 2 mm thick were fabricated from 20 materials (n = 7) for a total of 140 specimens. Human molars were longitudinally sectioned 2.0 mm thick to include both enamel and dentin. The optical densities of enamel, dentin, restorative materials, lead, and aluminum step wedge were obtained from radiographic images, using a transmission photodensitometer. The Al equivalent (mm) for each material was calculated from the linear regression equation of the log of normalized optical density and Al mm thickness obtained from the step wedge. A linear regression of the logarithm of normalized optical density and Al mm thickness was plotted (r2 = 0.9953), and the relative radiopacities, expressed as equivalent thickness of Al, were ranked ordinally. All materials tested, with the exception of an unfilled resin adhesive, complied with ISO Standard 4049, being at least as radiopaque as a 2.0 mm thickness of 99.6% pure Al. Four of six flowable composites had radiopacity values that fell between that of dentin and enamel, while two materials were more radiopaque than enamel. The three compomers tested had radiopacities greater than enamel. In addition, all traditional light- and chemical-cure resin composite materials tested were more radiopaque than enamel. All materials tested, with the exception of one adhesive resin, were at least as radiopaque as dentin and complied with ISO Standard 4049. Clinicians should be able to distinguish these restorative materials radiographically from recurrent decay, voids, gaps, or other defects that lead to clinical failure. Utilization of materials ranked more radiopaque than enamel would enable clinicians to distinguish the restorative material from tooth structure.
Absorptiometry, Photon↗
Effect of liners on cusp deflection and gap formation in composite restorations.
This study measured deformation of cusps and gap formation associated with MOD resin composite restorations in maxillary premolars with and without the use of low elastic modulus liners. Low elastic modulus liners may reduce the deformation by absorbing polymerization shrinkage stress. Forty maxillary premolars were mounted in stone and slot MOD cavities were prepared. Teeth were randomized into four groups. In Group A, cavities were etched, Single Bond was applied and the cavities were restored with Z-100 composite. In Group B, the same was done except that a layer of flowable composite (Revolution) was place and cured after the bonding agent. In Group C, the same steps were followed as Group A but a layer of glass ionomer (Vitrebond) was placed and cured before the bonding agent. In Group D, a thin layer of composite was placed (after the bonding agent) as a base and cured and the cavities were filled. The distance between indexed cusp tips was measured before the restorations were finished and five minutes and 24 hours after the restorations were completed. The samples were then sectioned mesiodistally and epoxy resin replicas were made and prepared for SEM evaluation of gap formation. The mean contraction of the cusps in microm at 5 minutes and 24 hours, respectively, for each group was A) 47 and 30, B) 35 and 21, C) 23 and 8 and D) 40 and 28. Groups A and D resulted in the highest deformation, B was intermediate and C was the lowest. There was no statistically significant difference in gap formation between the groups.
Analysis of Variance↗
Serum indirect bilirubin levels and meconium passage in early fed normal newborns.
The purpose of this study was to investigate the effect of early feeding of the normal newborn with formula and sterile water on: time of initial meconium passage, serum indirect bilirubin levels at 48 hours of life (HOL), observed jaundice at 48 HOL, and percentage of weight change at 48 HOL. Thirty normal, term newborns were sequentially assigned to one of three treatment groups: a control group given the routine hospital feeding of up to 30 ml of sterile water at 4 HOL and up to 30 ml of formula at 8 HOL; a water-fed group given up to 30 ml of sterile water at each feeding at 1, 2, and 3 HOL; and a third group fed formula at the same times and in the same amounts as the water-fed group. The time of initial meconium passage was significantly earlier in both groups of early fed infants than in the control group, F = 4.202, p = .026. The difference between the water-fed and the formula-fed groups was not statistically significant, but the mean time of passage was earlier in formula-fed infants. Serum indirect bilirubin levels at 48 HOL did not differ significantly, F = 0.412, p = .666, although the mean for the formula-fed group was lower. The correlation between the time of initial meconium passage and serum indirect bilirubin levels at 48 HOL was r = .3271, p = .083. Nine infants in the control group were jaundiced, compared to six in the water-fed group and six in the formula-fed group, a difference that was statistically significant, chi 2 = 6.79, p = .034.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗
Acid-etched, resin bonded cast metal prostheses: a retrospective study of 5- to 15-year-old restorations.
Eighty-five resin bonded prostheses were evaluated in a retrospective study over a 15-year period. All had been in function for at least 4.5 years. Multifactorial variables were studied to ascertain their effect on debonding and the health of the oral tissues. The results showed: (1) the caries rate of the retainer teeth was 6%, (2) the mean gingival indices for the prostheses were significantly higher (P > .0001) than those of the remaining dentition, (3) 61% of the restorations had not debonded (if failure resulting from trauma was not included, the incidence of debonding dropped to 19%), and (4) all patients liked their prostheses.
Analysis of Variance↗
Effects of secondary curing on indirect posterior composite resins.
This study was designed to compare strength, elastic modulus (stiffness), and hardness for five composite resin materials that are used for laboratory-fabricated posterior composite restorations. Ten specimens of each material were processed according to the manufacturer's instructions. Statistical analysis indicated that there were significant differences in mechanical properties among the materials tested. In addition, materials that are incrementally light cured prior to secondary processing were tested for changes in mechanical properties following secondary processing. It was determined that secondary processing provided improvement in flexural strength (11%) when compared to samples that were only light cured.
Acrylic Resins↗
Enhancement of resin bonding to heat-cured composite resin.
The purpose of this study was to evaluate the effectiveness of various surface treatments used to enhance the bond strength of resin cements to two different laboratory-processed composite resins. Seventy specimens of a microfilled composite resin (Concept) and 70 specimens of a micro-hybrid composite resin (Herculite XRV) were fabricated in metal wells and subjected to heat (250 degrees F) and pressure (85 psi) curing. An additional 70 specimens of each material were fabricated in the shape of disks and also subjected to the same heat/pressure curing. All composite resins were subjected to one of seven treatment regimens. The like-treated specimens were then bonded together using dual-curing resin cement and a uniform seating force (106 gm). After 7 days, bonded specimens were thermocycled 1000 times at 5 and 55 degrees C, and debond shear strengths were determined on a Universal Testing Machine. The use of microabrasion (50 microns aluminum oxide at 60 psi) and ceramic layer deposition (30 microns aluminum oxide with a ceramic additive at 75 psi) consistently improved the shear bond strength of the resin cements to both composite resins. The other treatment combinations provided varying effects. In conclusion, microabrasion or ceramic layer deposition are preferred methods to enhance the bond of resin cements to composite resins.
Acid Etching, Dental↗