Palatine Rugae Research Articles

Mechanoreceptors of the hard palate of the mongolian gerbil include special junctions between epithelia and meissner lamellar cells: A comparison with other rodents

As a part of our comparative morphological study of mechanoreceptors in rodent oral mucosae, the hard palate of the mongolian gerbil (a kind of sand rat) was investigated by light and electron microscopy. Subepithelial connective tissue papillae of palatine rugae contained a dense distribution of lamellated corpuscles that showed an ultrastructure similar to that of Meissner corpuscles of primates. The corpuscles in the palate of the mongolian gerbil, however, frequently formed compound large corpuscles with a palisade-like extension. Antemolar rugae predominated in containing such compound "Meissner" corpuscles. Superficial cytoplasmic lamellae of the corpuscles closely adhered to overlying epithelial cells without an intervening basal lamina. Although a small number of simple corpuscles was seen in the first antemolar rugae, no similar corpuscles were encountered in other parts of the palate. On the other hand, numerous Merkel cell-nerve endings were seen in epithelial pegs and sometimes in epithelial ridges of palatine rugae. Quinacrine labelling showed that intermolar rugae contained a rather dense distribution of Merkel cells in comparison with antemolar rugae. The present and previous data indicate that the pattern of palatine mechanoreceptors of the mongolian gerbil is analogous to that of the mouse, but not of the rat.

A comparative electron microscopic analysis of mechanoreceptors in the hard palate of the mouse ( Mus musculus; Rodentia) and the musk shrew ( Suncus murinus; insectivora)

These mechanoreceptors were studied with particular regard to their type and the distribution. In both species they were concentrated in the crests of transverse palatine rugae. In the mouse, Meissner corpuscles, glomerular corpuscles, and Merkel cell nerve endings were seen in every palatine ruga, though the first antemolar ruga also contained simple and atypical lamellated corpuscles. In contrast, the palatine rugae of the musk shrew contained only simple corpuscles and Merkel cell nerve endings. Meissner corpuscles in the mouse palate were frequently aggregated to form a palisade-like, huge corpuscle. Anterior intermolar rugae especially contained a larger number of such huge corpuscles. Simple corpuscles in the palate of the musk shrew were more densely distributed in the anterior than in the posterior rugae. In both species Merkel cell nerve endings were localized within epithelial downgrowths of the rugal crest. These downgrowths tended to increase in number anteroposteriorly.

Relationship of first primary palatine rugae to the maxillary canines in man.

Fifty dentate maxillary casts, obtained from thirty-four males and sixteen females, were mounted in the three-dimensional co-ordinate system of a contour meter. A transverse line of reference (x-axis) was drawn through the distal contact points of the maxillary canines, at a right angle to the y-axis which passed through the contact points of the maxillary central incisors. Relative to the canine-to-canine baseline, the locations of the lateral borders of the right and left first primary rugae were determined. The rugae were distributed on both the anterior and posterior sides of the baseline, and the anterior and posterior distances from the baseline were on the average about 1 mm. The age of the subjects, ranging from 12 to 52 years, appeared to be unrelated to the frequencies of anteriorly and posteriorly positioned rugae. Right and left first primary rugae, located on the anterior side of the baseline, showed a minute asymmetry in their topography. By contrast, there was topographical symmetry when the rugae were located on the posterior side of the baseline.

A longitudinal study of anteroposterior growth changes in the palatine rugae.

Palatine rugae have been used as internal dental cast reference points for quantification of tooth migration. Some, but not all, investigators have reported the medial rugal region to be stable or to show predictable change. The purpose of this study was to use the longitudinal data base of the Child Research Council of Denver to examine the anteroposterior stability of the medial rugal region. Dental casts of 20 females and 21 males with untreated normal Angle Class I occlusions were selected. Time intervals measured were: T1--primary teeth erupted, T2--earliest cast with permanent first molars erupted, T3--earliest cast with canines and pre-molars erupted, and T4--ages 16 to 22. Distinctive left and right anterior and posterior rugae which appeared on all four casts were identified, the medial ends marked, and the anteroposterior distances measured. The data were evaluated with the paired t test, repeated-measures ANOVA, and Tukey's multiple comparison procedure. From T1--T4, the medial rugal region increased 1.4 +/- 0.6 mm in females and 2.3 +/- 0.8 mm in males. Only two cases showed a trend toward stability. There were no significant differences by side. Significant increases in size occurred between T2 and T3 for females and males and between T3 and T4 for males. Analysis of these data indicates that the medial rugal region increases significantly in anteroposterior length, but not uniformly between the sexes across observation times. Such changes are characteristic of general craniofacial growth and suggest that the rugal region is responding to the differential growth of the underlying bone. Therefore, medial rugal landmarks appear not to be stable reference points for tooth migration research.

The teratogenic potential of cacodylic acid in the rat and mouse.

Cacodylic acid, an organic arsenical herbicide, was administered to time-pregnant albino CD rats and CD-1 mice on days 7-16 of gestation. The compound was given by gastric intubation as a solution in distilled water. Rats received 0, 7.5, 15, 30, 40, 50, or 60 mg/kg/day in 0.2 ml/day intubation volume; mice received 0, 200, 400, or 600 mg/kg/day in 0.1 ml/day. Following maternal sacrifice on day 18 (mice) and 21 (rats), fetuses were weighed and fixed for skeletal and visceral examinations. Fetal and maternal toxicity was observed in both species. In the mouse, maternal toxicity was evident at the lowest dose, while teratogenic response was confined to cleft palate at 400 and 600 mg/kg/day. The effective maternal toxic dose in the rat was 40 mg/kg/day. In this species, incidence of irregular palatine rugae, i.e., ridges that were discontinuous and/or not lying in apposition at the palatal raphe, was significantly (p less than 0.001) dose-related. The results suggest an "apparent no effect level" for this anomaly below 30 mg/kg/day.

The effects of tooth movement on the palatine rugae

A review of the structural and functional characteristics of the palatine rugae was presented, and a system of rugae classification was reviewed. Only slight morphologic alterations were seen in 127 rugae as a result of tooth movement, indicating that the rugae patterns were not appreciably altered. Quantitative evaluations of the rugae were not clinically useful. However, the general direction of the angles of the rugae are of benefit to a classification system.

Histochemical Studies of Alkaline Phosphatase on the Lingual Mucosa

A strong alkaline phosphatase reaction was found in all cell nuclei in the papillae of the connective tissue corresponding to each lingual papilla of mice. It was also established that the strong activity is first shown on the 19th embryonic day, when formation of the lingual papillae is completed and cornification of the superficial epithelium on the dorsal surface of the tongue begins. Subsequently this remains the same throughout life.On the other hand no alkaline phosphatase activity was demonstrated in the papillae of other parts such as the lip, the palatine rugae or the genital eminence. In contrast to this finding may be cited the fact that according to JOHNSON et al the papillae at the bottom of the follicle of the developing hair show a strong activity. With these points in mind it seems permissible to hypothesize that a strong alkaline phosphatase activity in the lingual papillae is associated with some structural peculiarity of these regions, such as strong cornification.As for the reactions of the lingual papillae in other species of mammals, the same picture was seen in dogs, rats and rabbits as in mice, but those in men, horses, cattle, cats, guinea pigs and hamsters were found to be negative.