C.A. Hoppert

The Production of Dental Caries in Rats Fed an Adequate Diet

Inasmuch as the subject of dental caries has recently been thoroughly reviewed by Bunting (1) and Hanke (2), it seems unnecessary to present another review at this time. Perhaps it is sufficient to state that at present the prevailing opinions about the cause of caries involve deficiencies of one or more dietary factors. The bacteriological origin has for the moment been relegated to the background. It is the purpose of this paper to describe some simple experiments indicating that caries may be produced on diets that are apparently entirely adequate with respect to the various factors deemed essential for normal dental development and maintenance. These experiments seem to show, therefore, that the caries-producing process is independent of the internal structure of the tooth, and probably involves acid fermentation as the responsible factor. In 1929 there was begun a series of experiments with rats in which were fed diets similar to those used by Mellanby (3) in the production of hypoplastic teeth in puppies. The basal oatmeal-diet was modified by supplementing it with various dried vegetables, to see what effect these might have on the structure of the bones and teeth. A group receiving the stock ration (yellow corn 60, whole-milk powder 30, linseed meal 6, alfalfa meal 3, sodium chloride 1) was included as a normal control. At the end of the experimental period of sixteen weeks the rats were killed, and the bones and teeth examined. Con-

Hereditary limitations of the infectious and transmissible nature of experimental dental caries

Abstract We have confirmed that dental caries is an infectious and transmissible disease in albino rats. However, the transmission of this disease was significantly demonstrated only with rats which were genetically susceptible. Rats bred for susceptibility to caries showed an increase in caries activity after depressing the penicillin-sensitive flora and reinoculating with faeces. Rats bred for resistance to caries did not show a significant increase in caries activity after depressing the penicillin-sensitive flora and reinoculating with faeces. This confirms the view that the genotype of a rat is one factor in determining its resistance to dental caries. Faeces from either caries-susceptible or caries-resistant rats induced caries to the same extent in susceptible rats. This indicates that caries-resistant rats were naturally exposed to a caries-active flora, but failed to develop this disease extensively.

Microbiologic Differences in the Oral Cavities of the Hunt-Hoppert Caries-Resistant and Caries-Susceptible Rats

H UNT and Hoppertl-6 have shown heredity to be a factor in the development of dental caries in rats. By consistent inbreeding and selection, they have produced two strains of rats, a susceptible strain which develops caries within approximately 70 days of age, and a resistant strain which, on the average, develops caries between 400 and 500 days. Studies on the oral microflora of these rats were made by Jay,7 who recovered lactobacilli more frequently and in greater numbers in the susceptible than in the resistant rats, even in very young animals. The purpose of this study was to investigate, further, differences in the oral microflora of these rats.

Morphology of Molar Teeth and Occlusion in Young Rats

Knowledge of the gross anatomy and occlusion pattern of molar teeth in rats is necessary to relate experiments on dental caries in rats to research on causes of caries in man. The gross anatomy of the crowns in rat molars is described, and a hypothetical account of occlusion is advanced.

A Comparison of Salivary Protease Activity in the Hunt-Hoppert Caries-Resistant and Caries-Susceptible Rats

From the Departments of Microbiology and Public Health, Zoology, and Chemistry, Michigan State University, East Lansing, Mich. HUNT and Hoppertl-6 developed 2 strains of rats, one caries-susceptible and the other caries-resistant. The susceptible animals show dental caries at approximately 70 days of age and the resistant ones at about 585 days. Rosen, Benarde, Hunt, and Hoppert7 investigating possible differences in the oral microflora of the 2 strains found that lactobacilli and Streptococcus salivarius were recovered more frequently from caries-susceptible than from caries-resistant rats. Rosen, Benarde, Fabian, Hunt and Hoppert5 found that the saliva of susceptible animals had a lower relative viscosity than that of resistant animals. Subsequently, this investigation was extended to the study of enzymes occuring in the saliva of these strains. A preliminary study showed that the widest difference occurred with protease. Sreebny, Meyer, and Bachman9 found that submaxillary gland extracts of Hunt-Hoppert caries-susceptible male rats had approximately 5 times as much protease activity as resistant males. The object of this study was to determine whether these differences in protease activity also existed in the saliva of these animals. Both male and female animals were included in this study in order to determine the possible influence of sex on the protease activity of the saliva.

Dental caries in caries-susceptible and caries-resistant albino rats (Rattus norvegicus) in the absence of secretions of the parotid gland.

I T HAS been known for some time that desalivation in rats increases the incidence of dental caries. Ginn and Volker1 desalinated rats and observed that the onset of caries was hastened and that the severity of the process was increased. Kite, Shaw, and Sognnaes2 tube fed both normal and desalivated rats and observed that tooth decay was prevented in caries-susceptible rats when the direct effects of food in the oral cavity were eliminated. Cheyne3 4 removed various combinations of the major salivary glands of the rat. The greatest amount of caries followed the removal of the parotid and submaxillary glands. The extirpation of the parotid alone produced only slightly more dental caries than did the intact controls.

Hereditary Basis of Caries Resistance in Rats

Lines of rats susceptible and resistant to dental caries were produced through 25 and 19 generations of breeding, respectively. Differences in mean caries time between the two lines were found to be as great as more than 500 days in some late generations. Heritability estimates yielded values of 0.40 and 0.62.

A Comparison of Certain Properties from Specific Major Salivary Glands of Caries-resistant and Caries-susceptible Rats

It has been suggested that certain hereditary factors for caries resistance in rats were associated with saliva. 92Continued investigation showed that these factors were probably associated with the saliva secreted by the submaxillary and sublingual glands but not the parotid glands.3 The purpose of this investigation was to study certain physical and chemical properties of rat saliva from these specific major glands and attempt to relate these to caries etiology.

The Use of Pentamethylentetrazol to Decrease Mortality during Collection of Saliva from Rats

A method for the collection of large quantities of rat saliva has previously been reported (Bernarde, Fabian, Rosen, Hoppert, and Hunt, J. D. Res., 35:326, 1956). In this technic, salivary flow is induced by pilocarpine after anesthesia with pentobarbital sodium.* In recent experiments this method for collecting saliva resulted in 40 per cent mortality in Hunt-Hoppert caries-resistant rats and 10 per cent mortality in the Osborne-Mendel-susceptible (OMS) rats. The causes of death were believed to be an accumulation of fluid in the upper respiratory tract and depression of the medulla oblongata (especially the respiratory center) by pentobarbital. Atropine sulfate was used to antagonize the action of pilocarpine, in order to stop the secretion of fluids into the upper respiratory tract. The use of atropine did not reduce mortality when given at the termination of saliva collection. Saliva was not produced when atropine was given before pilocarpine. Promazine hydrochloride,+ a tranquilizer, was next tried as a preanesthetic, in order to reduce the dosage of pentobarbital. Various ratios of this preanesthetic and pentobarbital were used. Results with this method indicated that, although mortality was slightly lessened, the amount of saliva collected was reduced. Pentamethylentetrazol,t a stimulant of the central nervous and respiratory systems, was then employed to counteract the depressant effect of pentobarbital upon the respiratory system. A total of 60 Hunt-Hoppert caries-resistant rats of various ages was divided into two groups with the same number of littermates in each group. The first group was given an intraperitoneal injection of 30 mg/kg pentobarbital sodium. When they had become anesthesized, they were given 7.5 mg/kg pilocarpine hydrochloride subcutaneously and placed in the collection holder. The flow of saliva was directed into small graduated centrifuge tubes. Ten minutes after salivation began, a subcutaneous injection of 50 mg/kg pentamethylentetrazol was administered. The animals were removed from the collection holder 20 minutes after they started salivating. The second group of rats was given the same treatment, but pentamethylentetrazol was not administered. The animals were observed 24 hours later for survivors. The animals receiving pentamethylentetrazol immediately tended to exhibit a faster rate of respiration, and some moved their heads briefly. Only 10 per cent (3 rats) of the pentamethylentetrazoltreated animals died, whereas 50 per cent (15 rats) of the controls died (P < 0.01). Two of the three experimental rats which did not survive died within seconds after receiving this drug. These two animals appeared very weak and might have responded if pentamethylentetrazol had been given earlier. The use of pentamethylentetrazol slightly reduced the amount of saliva collected, but the yield was sufficient for experimental use (see table).

Formation of Cariogenic Impactions in Rats

Large particles of rice in a modified HWC ration produced cariogenic impactions in the second transverse fissures of the first mandibular molars and in the transverse fissures of the second mandibular molars of rats. These particles were captured in caries-susceptible rats by the longitudinal sulcus terminating in each fissure.