A Study of Mineral Density Surrounding Resorption Sites in Teeth

A n investigation of mineral density surrounding lacunar resorption sites in cases of both internal and external root resorption, was carried out on 37 human primary and permanent teeth. In addition, equivalent areas of the roots of 14 normal appearing teeth were studied for comparison. Thirty-two of the teeth were analyzed using microradiographic and microhardness techniques and the remainder were studied microscopically after histologic preparation. The teeth used for microradiographic analysis were embedded in plastic, bisected and half of each tooth was sectioned at 70-100 p. Microadiographs were taken at 9.5 kv and exposed to 30 milliamperes for 25 to 40 minutes. The other halves of the teeth were used for microhardness tests using a Tukon Microhardness Tester. One series of microhardness measurements was made 10 to 40 p from sites of active resorption in root dentin and a second series was made 250 to 500 p from these sites. The hardness measurements of the first series were found to be significantly lower than those of the second in cases of both external and internal resorption. Hardness values of the surface of normal appearing roots were also less than areas 250 to 500 p deeper in the dentin. Microradiographs did not reveal any definite zone of subsurface demineralization although some resorption sites were bordered by irregular areas of decreased radiodensity which may be due to superimposition of several resorption sites within the thickness of the tooth section. Histologic observations did not reveal a definite subsurface demineralization gradient. The lacunar resorption front was found to be a multilocular and completely interconnected system. The cause of tooth resorption other than that related to the process of eruption and shedding of teeth, has interested numerous investigators for many years. The condition of irregular cavities within teeth resulting in "pink spots" was noted as early as 1890 by Miller, in 1894 by Gaskill and in 1920 by Mummery. There have been numerous studies of the characteristics of this pathologic process as well as a number of investigations concerned with its etiology. To gain information concerning the prevalence of root resorption Massler and Malone ('54) examined the radiographs of permanent teeth of 708 persons and found 86.4% of the teeth examined or an average of 16 teeth in each person undergoing resorption to some extent. Thoma ('35) pointed out that tooth resorption may originate either on the internal or the external surfaces of the root. Considering the latter type, Henry and Weinmann ('51) found approximately 77% of external root resorption occurring in the apical third of the tooth, 20% in the middle third and only 4% in the gingival third. It was located most often on the mesial and the buccal surfaces of the roots. They concluded resorption occurs more readily on those root surfaces facing physiologic movement, the areas where trauma was the greatest. They also found, as did Warner et al. ('47) that repair of roots with cementum or dentin-like substance occurred in a high percentage of the cases. Stafne and Slocumb ('44) found the central incisor the most frequently involved tooth. In consideration of causes, most investigators believed trauma was an important factor. This may be caused by occlusal interferences, (Orban, '28) orthodontic appliances, (Ketcham, '29; Hemley, '41; Oppenheim, '42) or chemical agents used in restoring teeth (Via, '55; Cabrini et al., '57; Rabinowitch, '57). Also the prolonged effects of inflammation is believed an important predisposing factor to this disease. Again Cahn ('32) and Scopp ('56) believe that idiopathic resorp tion may be due to an increase of pulpal blood supply which aids in the resorption AM. J. ANAT., 120: 55-70. 55 56 J. K. AVERY, R. A. MEYERS AND L. E. HALE of calcium salts. Others believe systemic factors, perhaps hormonal, such as hyperthyroidism as suggested by Becks ('33) and by Henry and Weinmann ('51) or hyperparathyroidism which according to Young ('63) may predispose this process in experimental animals. There are many causes of resorption of both the internal and external surfaces of the root however, which cannot be explained by any of the above mentioned causes. Recently modern scientific methods have been used in an attempt to gain further insight into the etiology of this process. Burstone ('53) found the ground substance of dentin adjacent to the area of internal resorption to contain more than normal amounts of glycoprotein material. He theorized this increase may be due in part to proteolytic activity of pulpal bacteria superimposed on the primary processes of resorption. Sognnaes ('59) utilizing microradiographic techniques found no evidence of a demineralization gradient in tooth resorption. In 1961, utilizing electron microscopy, he found a half micron alteration of the dentin surrounding a Howship's lacunae. There has been much work done on bone resorption and several investigations are pertinent to this discussion. Greulich ('61 ) utilizing high resolution, ultrasoft microradiography studied the distribution of organic mass at the sites of bone resorption. He observed a band or rind approximately 1-1.5 in width at the point of junction of the osteoclast. Goldhaber and Barrnett ('60) demonstrated succinic dehydrogenase in osteoclasts and Burstone ('60) found dehydrogenase, acid phosphatase and leucine aminopeptidase in osteoclasts. Balough ('63) found osteoclasts to contain DPNH diaphorase, TPNH diaphorase, lactic and succinic dehydrogenase. Fullmer ('64) also noted osteoclasts contain high amounts of the latter. Ultrastructural studies by Hancox and Boothroyd ('63) revealed mineral crystals in the vacuoles of the osteoclasts and the resulting exposed collagen was noted to be enclosed in the folds of the cells' ruffled border. It was suggested that an initial mineral loss is followed by digestion of the fibrous matrix. In an attempt to gain furher information of the characteristics of the mineral density of the calcified tissue surrounding lacunar resorption sites in dentin, the present study was planned and has employed microradiographic, microhardness and histologic techniques. MATERIALS AND METHODS