Ralph R. Steinman

Relationship of Fluid Transport Through the Dentin to the Incidence of Dental Caries

The rate of fluid movement in the teeth of 28-day-old rats is inversely related to the incidence of dental caries after 13 weeks of the same diets. The early hypomineralization found in the dentin at 28 days is a result of altered metabolism imposed by a reduced rate of fluid transport in the rats fed a cariogenic diet.

Pharmacologic Control of Dentinal Fluid Movement and Dental Caries in Rats

Parasympathetic stimulants were found to encourage the movement of fluid through the dentin from the pulp to the dentinoenamel junction. Regular treatment with a parasympathetic stimulant in rats that had all their major salivary glands removed significantly reduced the incidence of dental caries. Treatment with bradykinin in rats on a noncariogenic diet encouraged the movement of fluid into the tooth. When given regularly for 15 weeks, bradykinin caused significant dental caries.

The Effect of Desalivation Upon Pulpal Function and Dental Caries in Rats

The role of pulp and saliva in caries susceptibility and resistance was evaluated using a combination of endodontic treatment and desalivation. Evidence was presented that the pulp plays a major role in caries susceptibility. It is suggested that pulpal function is modified by hormonal factor(s) originating from salivary glands. In the rat, saliva appears to play a minor role in resistance to caries.

The effect of dietary factors on intradentinal dye penetration in the rat

Fluorescent dye injected systemically into rats penetrated the dentinal tubules of molar teeth in a dynamic fashion. The presence of dye was established using histological and fluorescence microscopy techniques. The rate of intradentinal dye penetration was dependent on dietary factors: it was high in rats chronically fed Purina rat chow and low in rats fed a cariogenic, high-sucrose diet. In addition, parotidectomized rats showed low levels of intradentinal dye penetration, even though they were maintained on Purina chow. One and 2 ml of plasma from Purina-fed rats were effective in stimulating the dye penetration in intact and parotidectomized rats, whereas 2 and 4 ml of plasma from rats fed a high-sucrose diet were ineffective when infused in either intact or parotidectomized animals. The results suggest that rats fed Purina chow have a significantly higher titre of a circulating, dye penetration stimulating factor than animals fed a high sucrose diet. This circulating factor could be the equivalent of the parotid hormone isolated from porcine tissue. It is suggested that dietary factors may affect secretion of a parotid hormone and thereby regulate the rate of dentinal fluid movement. There is therefore the prospect of a functional relationship between diet, the regulation of dentinal fluid flow by an endocrine system and dental health.

Effect of Infusing Selected Chemical Compounds on Dentinal Fluid Movement in the Rat

Intra-arterial infusion of carbamyl phosphate or of carbamyl-DL-aspartic acid into rats on a cariogenic diet greatly stimulated the movement of fluid through the odontoblastic processes. The infusion of sodium cyanate also stimulated fluid movement. Guanidine HCl and L-asparagine were active at higher concentrations. Purifying the urea on a mixed-bed ion exchange resin virtually removed its stimulatory effect on dentinal fluid movement. The action of urea is apparently attributable to contamination with sodium cyanate.

Comparison of Caries Incidence in Exercised and Immobilized Rats

In a previous study (R. R. Steinman, M. G. Hardinge, and R. W. Woods, J. D. Res., 37:865, 1958), utilizing over 300 rats through three generations on eight different combinations of human foods, a direct correlation was found between the nutritional status of the rats and their incidence of caries. As the animals showed a deterioration from generation to generation, the teeth showed a corresponding deterioration. The purpose of the present study was to determine the possible effect of a physical deterioration brought about by other than nutritional means upon the incidence of incipient carious lesions in the albino rat. Twenty-eight Osborn-Mendel rats from four litters were weaned at 21 days of age and placed on the following cariogenic diet: casein, 24; sucrose, 65; salts U.S.P. XIV, 4; corn oil, 5; dehydrated liver, 4; vitamin mix, 2; choline, 0.2 parts. These 28 animals were divided into two equal groups of littermates. One group of animals was placed in a large cage which allowed space to run. Food and water were given ad libitum. For 4 hours a day these rats were placed in a rotating cage which caused them to walk rapidly for 16 minutes and rest for 8 minutes. They had water available during this time. The other group of 14 rats was restricted by placing them within wire cages which allowed no freedom of movement, and food and water were available at all times. All animals were sacrificed at 29 days of age and the jaws frozen immediately. The jaws were sectioned in the deep freeze by the method dveloped in this laboratory (R. R. Steinman, C. G. Hewes, and R. W. Woods, J. D. Res., 38:592, 1959). Incipient lesions were visualized in the dentin by using ninhydrin and X-ray, interproximal and occlusal. The results concerning the effect of physical restraint upon the incidence of incipient carious lesions are shown in the table.

Further evidence for a hypothalamus-parotid gland endocrine axis in the rat

The existence of a hypothalamus-parotid gland endocrine axis that stimulates intradentinal dye penetration (IDDP) in rat teeth was suggested in earlier studies and IDDP-stimulating factors were isolated or purified from porcine parotid glands and hypothalamic tissues, respectively. In the present study, infusion of carbamyl-DL-aspartic acid (CAA) into rats was used to demonstrate the role of the endogenous hormones of the hypothalamus-parotid gland endocrine axis in stimulating IDDP, as observed by fluorescence microscopy of longitudinal sections of molar teeth. Intra-arterial infusion of CAA into intact rats stimulated IDDP in a dose-related fashion (between 49-390 nmol/100 g body weight); however, infusion of 390 nmol into parotidectomized rats was ineffective. Infusion of plasma from CAA-treated rats was equally effective in stimulating IDDP in intact and in parotidectomized animals. In contrast, plasma obtained from parotidectomized, CAA-treated rats stimulated IDDP in intact recipient animals but not in parotidectomized ones. Moreover, plasma from adult rats treated with CAA after an electrolytic lesion of the hypothalamus, and infused back into young intact rats, was ineffective in stimulating IDDP. These results indicate that: (1) CAA requires the functional integrity of the parotid gland to express its IDDP-stimulating activity, (2) a hormonal factor is secreted by the parotids in response to CAA stimulation and is directly responsible for IDDP stimulation, (3) release of the endocrine parotid IDDP-stimulating factor after infusion of CAA involves a second endocrine factor that appears to originate from the hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Selected Dietary Additives on the Incidence of Dental Caries in the Rat

Weanling rats fed a cariogenic diet supplemented with carbamyl phosphate, in combination with egg shell meal and trace elements, showed a striking reduction in the incidence of caries. The cariostatic efficacy of carbamyl phosphate is significant because it stimulates fluid movement within odontoblasts via the hypothalamic-parotid gland endocrine axis.

Stimulation of intradentinal dye penetration by feeding in the rat

Dentinal fluid movement, as measured by intradentinal dye penetration (IDDP), may be under the control of an endocrine system that includes the parotid glands. It was earlier demonstrated that parotid hormone stimulates IDDP when infused into rats, and in the pig the onset of feeding signals the release into the circulation of immunoreactive parotid hormone (iPH), the titre of which remains elevated for more than 1 h after feeding. As, for technical reasons, it is impossible to measure iPH and IDDP activity in the same animal, the hypothesis that feeding causes IDDP stimulation in the rat was now tested. Feeding rats for 15 min stimulated IDDP to a level significantly higher than when fasting (0.418 +/- 0.040 versus 0.106 +/- 0.022, p < 0.001). Within the experimental conditions, IDDP stimulation lasted longer than 15 min. Sialoadenectomy before the feeding experiment did not change the feeding-stimulated IDDP response unless the parotid glands were removed. In parotidectomized and totally sialoadenectomized rats fed for 15 min, the level of IDDP was not different from that of sham-operated fasting animals. It is postulated that, in addition to the existence of possible local regulatory factors in the pulp, dentinal permeation may be under a physiological control mechanism involving a parotid endocrine function. It is also suggested that a hormonally controlled mechanism of dentinal fluid movement may play a systemic, protective role against the bacterial acidogenic challenge to teeth.

A radioimmunoassay procedure for quantitating parotid hormone

Abstract The methodology and characterization of a double antibody radioimmunoassay (RIA) for quantitating parotid hormone (PH) in biological fluids are reported. A specific antiserum against PH was raised in rabbits using PH conjugated to human serum albumin. Its binding capacity and association constant were 22 μg/ml and Ka = 1.01 × 10 −12 M −1 , respectively. The sensitivity of the RIA was 1.5 pg PH when a sequential incubation schedule was used. This RIA makes possible the quantitation of PH in biological fluids and tissue extracts.