Journal of Dental Research

An investigation by electron diffraction, transmission and scanning electron microscopy, and energy-dispersive X-ray analysis has shown that Ta additions to a 40-30-30 Co-Cr-Ni-base alloy strengthen by ordering and by formation of coherent α-Co₃Ta precipitate. However, increasing Ta content increases the proportion of the hexagonal phase and decreases ductility.

The addition of either 25 or 100 ppm fluoride to the drinking water of Wistar rats produced a banded appearance on the mandibular incisors but had no significant effect on the impeded or unimpeded eruption rates of the incisors.

Bactericidal activity of a phenolic and a quaternary ammonium compound was assessed in the presence and absence of protein when certain bacteria were adsorbed to porous and nonporous surfaces. Organisms were more resistant when adsorbed to porous surfaces. Protein contributed to increased survival of bacteria only when adsorbed to porous surfaces.

Carious lesions in the root surfaces of extracted human teeth were sampled qualitatively for the presence of bacterial forms. Streptococcus mutans was a predominant organism from this lesion. The filamentous organisms appeared typical of the genus Actinomyces. Bacterial strains from the advancing front of the lesions were aerobic gram-positive diphtheroids, with the key characteristics of the genus Arthrobacter.

Weanling female rats were given subcutaneous injections of contraceptive steroids (norethynodrel and mestranol), tetracycline supplements in drinking water, or both, for seven weeks. Norethynodrel-mestranol treatment caused a significant increase in dental caries activity; this increase was prevented by intermittent supplements of tetracycline in drinking water.

Improvements in the neutron activation technique for studying microleakage were achieved by selecting more suitable tracers and by using a more accurate method for evaluation of the activation data. Dysprosium was the most suitable tracer; it provided the least variation in the results and allowed the fastest activation and counting procedure.

Spiramycin concentrations were determined in plasma and parotid and sublingual fluids of unanesthetized dogs 1 to 6 and 24 hours after a single oral dose of the antibiotic. Plasma levels were highest 1 to 4 hours after dosage. Sustained sublingual secretion and peak parotid levels of spiramycin occurred at later collection times.

A method for reorientation of a monkey in a cephalostat was refined and the accuracy of the procedure was determined.

The object of these studies was to determine the effect of topically applied bacterial proteases on posteruptive maturation of rat molars, on remineralization of incipient lesions in rats, and on the caries-preventive effect of fluoride in rats as evidenced by changes in hypomineralized areas in molars. Our findings showed that the topically applied proteases had no effect on the foregoing phenomena.

Heat treatment caused an increase in ductility. Aging caused an increase in strength and hardness with a decrease in ductility. Overaging caused decreases in strength and ductility. Solution treating resulted in a single phase. The precipitation of coherent intermetallic compounds caused maximum strengthening with minimum loss of ductility.

Dental caries and periodontal disease experience varied considerably among four populations of Indian communities although environmental conditions seemed similar.

The prevalence of dental caries in 1,155 white and black preschool children was studied in the United States in 1969 and 1970. The results demonstrated that white children of the lower socioeconomic level had a significantly greater prevalence of dental caries than middle class white children, but a significantly lower prevalence than black children, most of whom represented the lower social class.

Supplementation of cariogenic diet 2700 with 25, 35, or 50% of cereal products had no influence on the gain in body weight or on the caries activity of caries-susceptible rats. Substitution of half of the sucrose in diet 2700 by other cereal products had no influence on the growth of rats, but resulted in small decreases in caries activity; one corn product was the most effective.

Penetration of commercial and dental waxes was studied. Measurements indicated that resistance of paraffin and dental inlay waxes to penetration was closely related to the temperature at which solid-solid transformations occurred. Annealed waxes were more resistant to penetration than unannealed waxes.

The fluoride sensitivity and the lethal concentration of LS cells were determined. The cells were adapted to grow in the presence of lethal concentrations of fluoride. The adaptation persisted after removal of fluoride. Any possible binding of the fluoride to medium components was excluded.

The calcium and phosphorus dissolved from enamel were determined in 0.5-hour fractions during flow of a weak acid solution through small chambers containing surfaces of tooth enamel. The results demonstrated reactions of Ca and P dissolution and concurrent reactions of CaF₂ formation at the surface of enamel minerals.

Tooth emergence in 376 black and white children between the ages of 4 and 33 months was studied in southeastern Michigan. The results indicate a trend in both groups for boys to show earlier tooth emergence in early stages and for girls to show earlier tooth emergence in later stages of deciduous tooth emergence.

Changes in body weight were induced by varying particle size of the same food fed to old male rats with impaired masticatory function. Ingestion of coarse particles for ten weeks produced continuous gradual weight losses. Feeding of pulverized food resulted in significant weight recovery.

Eight non-plaque-forming oral organisms were grown in paired mixed cultures with Streptococcus mutans in an in vitro plaque assay system. The amount of plaque that formed was compared with that formed by pure cultures of S mutans. Four organisms had no effect on the total amount of plaque that formed, three organisms caused decided inhibitions, and one organism greatly increased total plaque formation.

Adhesive tag like extensions into acid-etched tooth enamel can be directly observed in great detail by means of a modified scanning electron microscope technique. No taglike extensions of the adhesive were observed in tooth enamel that was not acid-etched before bonding of the adhesive.

Frequent eating of small amounts of sucrose for a period of three days resulted in the in vivo accumulation in plaque of about 1% dextran and about 3% levan.

Bone scanning with technetium-99m-labeled polyphosphate and a scintillation camera were used to follow the mineral metabolism associated with the reformation and eruption of previously extracted posterior rabbit teeth. Uptake of technetium-polyphosphate was significantly higher throughout the phase of active tooth eruption.

Chromosomes of the bone marrow cells of three Siamese kittens with cleft palate and one normal kitten were examined. The pedigrees of all the abnormal kittens were examined and common ancestry was demonstrated. No numerical or morphologic difference in the autosomes was found in the kittens with cleft palate or the normal kittens.

The antibacterial properties of a 0.50% stannous fluoride mouthwash and a 0.27% sodium fluoride mouthwash of equivalent fluoride ion concentration (0.12%) were examined using standard bacteriologic plate count procedures. The stannous fluoride solution produced a significant bacterial effect, but the bactericidal activity of the sodium fluoride solution was negligible.

A force-displacement transducer technique was used to evaluate the setting characteristics of six anterior restorative materials. This technique produces graphs of setting characteristics from which the working time and settling time of a material can be easily determined.

Application of the potentiostatic polarization technique to the metallographic etching of set dental amalgam is described. Etching studies of amalgam prepared from a lathe-cut, a spherical, and a silver-copper dispersed-phase amalgam alloy are reported. The γ₂ phase in set dental amalgam can be characterized by this electrochemical technique.

A triple fluorochrome labeling sequence was used to measure the osseous activity in the coronoid process after the removal of the temporal muscle. Statistically significant differences between the control and the experimental animals were found for hematoporphyrin, DCAF, DCTC, and total labeled bone.

A sensitive and quantitative assay to measure the early calcium loss from surface enamel exposed to organic acids and metabolic products of cariogenic bacteria was designed. It will be useful to show the effects of metabolic products from cariogenic organisms on the surface of enamel and the effectiveness of dental therapeutic agents before animal studies.

The pain-reducing and calming properties of nitrous oxide mixed with oxygen were evaluated with the use of placebo and standard control groups. Subjects under nitrous oxide had higher pain thresholds and a higher tolerance for shock than placebo and control subjects. They also reported themselves as more relaxed than did placebo and control subjects.

An electron probe microanalyzer was used to determine compositional variations of the Ca/P ratio in the core and sheath areas of individual rods in human enamel. The Ca/P ratio in the core is that of a calcium-deficient hydroxyapatite, whereas the ratio in the sheath is that of almost stoichiometric apatite. Treatment with HCl or EDTA alters the Ca/P ratio in the core and the sheath.