Richard S. Manly

Density and Refractive Index Studies of Dental Hard Tissues I. Methods for Separation and Determination of Purity

A rapid, quantitative method for the separation of the enamel, dentin, and cementum of a single tooth to obtain samples of known purity will permit the following investigations: 1) Normal values and ranges of variation in the composition of enamel and dentin. 2) Changes in composition associated with caries (5), pyorrhea or disturbances in nutrition, metabolism or endocrine balance. 3) Proportion of enamel to dentin in normal, hyperand hypoplastic teeth and changes due to attrition, erosion or caries. Methods for obtaining pure dentin or enamel by heating or grinding are unsatisfactory because of the time required and the incomplete recovery. The method described by Brekhus and Armstrong (3), based on the use of heavy liquids with density intermediate between dentin and enamel, offers a distinct improvement over previous methods, but leaves a few things to be desired. For instance, it would be advantageou§ to have (a) a more rapid method, (b) a check on the purity of the enamel and dentin fractions, and (c) an avoidance of filtration. According to the literature, a centrifugal separation method would seem to be desirable, especially when working with fine powders. Bernal and Crowfoot (2) found centrifugation to give a more accurate

Density and Refractive Index Studies of Dental Hard Tissues II. Density Distribution Curves 1,2

There is considerable variation in the values recorded in the literature for the density of the dental hard tissues. Hoppe (6), Karlstrom (4) and Thewlis (12) find the enamel density to be between 2.9 and 3.0 grams per cc. On the other hand, Morichini (9) reports a figure of 2.65; Pickerill (11) finds values between 2.72 and 2.85; Thurlow and Bunzell (13) set a figure of 2.49 while Brekhus and Armstrong (3) state the density to be between 2.6 and 2.7. For dentin there are fewer values and less disagreement. Black (2), in a study of a large series of wet dentin specimens found values between 2.06 and 2.11. Krause (7), Thewlis (12) and Brekhus and Armstrong (3) report the following values, respectively, 2.08, 2.10 and 2.24. Cementum was assumed by Brekhus and Armstrong to have a density of less than 2.04, since its removal was described by the use of a liquid of that density. No other experimental values have been reported. The differences in the quoted densities may be partly, but not wholly, explained on the basis of a variation in the density of the tissue itself, either occurring naturally or brought about by the differences in

Hereditary Opalescent Dentin III. Histological, Chemical and Physical Studies'

Hereditary opalescent dentin has been described under a variety of names but is probably less rare than the literature indicates (1). Clinically it presents a picture of excessive destruction of the teeth, together with a more or less noticeable violet color of the enamel and light to dark brown staining of exposed dentin. This anomaly is inherited as a dominant characteristic in which a severe disturbance in dentinal development appears to be the cause of the friability and peculiar color of the teeth (2). It is easily and specifically diagnosed by (a) its inherited nature, (b) the radiographic demonstration of the typical reduction in size or absence of pulp cavities and (c) the severe tooth destruction observed clinically.

The Abrasion of Cementum and Dentin by Modern Dentifrices

The first thorough study of the relation between dentifrices and certain types of wasting of tooth tissue was reported in 1907 by W. D. Miller (1). He concluded that certain of the tooth pastes and tooth powders then in use were capable of producing wedge-shaped notches in the cervical region of anterior teeth, a conclusion based largely on the fact that he could duplicate the notches by brushing extracted teeth. Since some of the dentifrices he tested could readily grind away enamel, their ability to notch teeth was not surprising. Subsequently much attention has been given to this problem by manufacturers of dentifrices and of dentifrice abrasives, by the American Dental Association, and by investigators in dental schools, and the danger of abrasion of enamel by commercial tooth paste or powder today is presumably less than at the time of Millers work. Abrasion of dentin by dentifrice preparations has not excited as much general interest as the possible abrasion of enamel, but it has been the subject of several important researches. Not only Miller, but more recently Bunting and Rickert (2), Head (3), Carney (4), Wright and Fenske (5), and Kimball (6) all have demonstrated that when human dentin is rubbed with dentifrice abrasives a definite amount of the dentin is worn away. Van der Merwe (7), Ray and Chaden (8), and Smith (9) also found that other test substances with hardnesses similar to dentin were likewise subject to some wear by dentifrice abrasives. Grades of calcium carbonate and of calcium phosphate apparently incapable of damaging enamel have been found more than 10 times as abrasive toward cementum and dentin (5). The magnitude of the wear has not been shown, however, under

Changes in the Volume Per Cent of Moisture, Organic and Inorganic Material in Dental Caries

Early workers discovered that carious dentin is extensively decalcified (Miller, 1883; Mayr, 1883; and Cohn, 1889), but absolute changes in water, organic and inorganic content have never been measured. The principal difficulty has been the small size of samples obtainable; entire carious lesions weigh only a few milligrams. Suitable micromethods are now available for this investigation. Analyses of dry dentin, sound and carious, previouslyreportedfrom this laboratory (Manly, in press) indicated that certain carious zones of dentin have the same organic to inorganic ratio as sound dentin. Since the discoloration indicates that some change has occurred, this constant ratio could best be explained by assuming a simultaneous loss of organic and inorganic material in such a way that their ratio remained the same. To check this assumption and to measure changes in moisture, carious dentin samples were taken by a new method which permitted measurement of volume (Deakins and Manly, 1939). Whole lesions and certain zones within the lesion were selected and analyzed for moisture, organic, ash, and volume. The experimental values confirmed the hypothesis for one zone of the lesion in which there was a gain in moisture, and a loss of organic and inorganic material in amounts that were often proportionate. For a second zone, extensive loss of mineral with replacement by water was the predominant feature, while in a third zone, major losses in both organic and inorganic content occurred and were compensated by a moisture gain.

A Method for Microdetermination of Density in Calcified Tissues

To determine the density of micro-quantities of calcified tissues, a method has been devised for the direct volume measurement of blocks of the tissue cut out with a micro-jigsaw. This avoids contamination with organic liquids employed in the usual flotation micro-procedures. Subsequent handling and transfer of the blocks are easier than in the case of powdered samples. Since only 1 to 4 cu. mm. of material are necessary for a determination, various zones of calcified tissues of small animals may be investigated. Furthermore, a direct volume determination was obtained, a fact of greater importance in our investigation of carious dentin. This made possible a measurement of void volume, and the estimation of the absolute changes in ash, organic, and water contents which occur in various zones of human dentin.