The rate of reparative dentine formation in transplanted mouse molar teeth.

Similar rates of reparative dentine matrix formation were observed during the formation of cellular dentine, irregular and regular secondary dentine during repair of transplanted teeth. Primary dentinogenesis in molar teeth in situ occurred at a similar rate. These observations indicated that dentinogenesis is an identical process carried out at identical rates irrespective of the morphology of the end product or the stimulus for its formation.     

Differentiation of new odontoblasts and dentine bridge formation in rat molar teeth after tooth grinding

The cusp tips of the molar teeth of the right side of the jaws of 58 male Sprague-Dawley rats were ground producing an area of damage in the pulp horn which corresponded to the area below the cut dentinal tubules.

The rats were sacrificed at various time intervals after tooth grinding, the jaws with the teeth were fixed, decalcified and sectioned serially at 5 μ and stained with haematoxylin and eosin, Mallory's, Masson's and pa-S stains.

The sequence of pulpal reactions such as displacement of odontoblastic nuclei, inflammatory responses and healing were found to correspond well with previous reports. Spindle-shaped cells believed to be new odontoblasts appeared in increasing numbers after 24 hr. Formation of a dentine bridge began below the area of necrosis at 48 hr with the appearance of separate Mallory positive areas which later apparently fused with the dentine projecting from the side walls. The first complete dentine bridge was found at 4 days after tooth grinding. The bridges became thicker and more regular later. At 8 days well-defined tubules could be seen.

Sixteen rats were injected with tritiated thymidine (³H-TdR) at various time intervals after tooth grinding. At each time interval except one, two rats were sacrificed 1 hr after ³H-TdR injection. One rat at each time interval was allowed to live for 3 days after ³H-TdR injection. The jaws with the teeth were fixed, decalcified and sectioned serially at 5 μ. Autoradiographs were made from sections in the areas of pulpal damage and from sections of control teeth. The autoradiographs from the rats sacrificed 1 hour after ³H-TdR injection showed an increase in mitotic activity at 24 hr, 48 hr, and 4 days with the greatest increase at 48 hr. The rats injected with ³H-TdR at 24 and 48 hr after tooth grinding and sacrificed 3 days later, showed labelled cells among the new odontoblasts.

It is postulated that the new odontoblasts responsible for dentine bridge formation and new dentine were derived from undifferentiated pulpal cells. The remaining original odontoblasts did not proliferate in the ground teeth or in the control teeth. Labelled cells which did not migrate to the odontoblastic layer might have been newly differentiated fibroblasts or other new cells taking part in the repair of the pulpal tissue.     

An autoradiographic study of experimental odontogenic cyst formation in the mouse.

Proliferative populations of cells within the epithelial lining of developing experimental odontogenic cysts were identified by labeling with 3H-thymidine. Mouse molar teeth extracted from 10-day-old mice were transplanted subcutaneously and host animals were injected with 3H-thymidine 1 h prior to sacrifice. The cysts which developed around the crown of the transplanted teeth were prepared for autoradiographical examination. Labeling indices were high initially but decreased rapidly as the cysts enlarged. The pattern of labeling, however, bore no resemblance to the labeling of the reduced enamel epithelium from which the cysts developed. It was concluded that labeling activity reflects only the state of development and activity of the cyst and not the origin of the cyst.     

The histology and microbiology of acute occlusal dentine lesions in human permanent molar teeth.

Acute occlusal caries of molar teeth was investigated and on microscopic examination a pattern was seen in the bacterial invasion of the tissue. A primary wave of bacterial attack, found by bacteriological isolation techniques to consist of homofermentative lactobacilli, was demonstrated at the advancing periphery of the lesion. A secondary wave of mixed superinfection followed the primary invasion. The two zones of infection could be clearly identified because there was a bacteria-free interval between them and because there were histological characteristics exclusive to each.     

An autoradiographic study of experimental odontogenic cyst formation in the mouse

Proliferative populations of cells within the epithelial lining of developing experimental odontogenic cysts were identified by labeling with ³H-thymidine. Mouse molar teeth extracted from 10-day-old mice were transplanted subcutaneously and host animals were injected with 3H-thymidine 1 h prior to sacrifice. The cysts which developed around the crown of the transplanted teeth were prepared for autoradiographical examination. Labeling indices were high initially but decreased rapidly as the cysts enlarged. The pattern of labeling, however, bore no resemblance to the labeling of the reduced enamel epithelium from which the cysts developed. It was concluded that labeling activity reflects only the state of development and activity of the cyst and not the origin of the cyst.     

A morphometric analysis of the cross-sectional area of dentine occupied by dentinal tubules in human third molar teeth

The number and the mean percentage tubular cross-sectional area of dentinal tubules per square millimetre were calculated in specimens of coronal dentine of 13 intact human third molar teeth from patients 18 to 28 years of age. The dentine was fractured at various known distances from the dentino-enamel junction. Near the dentino-enamel junction the number of tubules per square millimetre was 22 000 and the mean tubular cross-sectional area was 3.6%. Midway between the pulpal wall and the dentino-enamel junction the number of tubules was 37000 mm^?2 and the mean tubular cross-sectional area was 6.2%. Close to the pulp the number of dentinai tubules was 48000 mm^?2 and the mean cross sectional area of tubules was 10.2 percent. The number of tubules per square millimetre more than doubled and the area occupied by tubules increased threefold from the dentine close to the dentine -enamel junction, to that close to the pulp. These differences in tubular patterns at different depths in dentine are clinically significant in dentine permeability, the treatment of traumatized teeth, and pain transmission in dentine.     

A (3H)-thymidine autoradiographic study of cell proliferative activity of injured parodontal tissues of 5-week-old mice

Evaluation of the cell proliferative changes which occur in response to trauma in young mice was investigated autoradiographically. Forty-four 5 week-old female mice of the short-lived Brookhaven National Laboratory (BNL) strain were gingivectomized surgically, removing the papilla mesial to the maxillary first molar. One hour prior to death, each animal received 1.0 μCi of tritiated thymidine per g of body weight by subcutaneous injection. Following death, the maxillae were removed, and the appropriate tissues were prepared for histologic and autoradiographic studies. Labelling indices were determined of various parodontal tissue cell compartments. The results were compared with previously published control values and rat data. Response of the mouse parodontal tissues to injury was, by and large, similar to that of the rat, with the exception that the proliferative activity of mouse tissues was significantly lower and occurred sooner following injury. The differences do not appear to be biologically significant in young animals. On the basis of the present findings, it was concluded that the size of the normal proliferative activity cannot be taken as (1) an index of the rate of repair, (2) an indication of the required length of repair, or (3) a measure of the proliferative capacity of the tissue. Normal labelling indices reflect only the level of cell turnover occurring in a given cell compartment, at a given anatomical site, in response to current physiological demands of the organism.     

The role of host tissue in repair of transplanted mouse molar teeth: a reappraisal of induction of odontoblasts during tooth development and repair.

After autoclaving to inactivate donor tissue, teeth were transplanted subcutaneously. Disrupted donor tissue was removed by phagocytic cells and host tissue grew into the empty pulp chamber of the graft. The host tissue failed to differentiate or form reparative dentine. This suggests that donor pulp cells carry out repair of transplanted teeth and are able to differentiate and function normally in the absence of the factors normally thought to induce their differentiation. It is suggested that during tooth development the enamel organ induces widespread potentiality in the dental papilla to differentiate into odontoblasts but papilla cells only transform into odontoblasts as they are needed. The epithelial root sheath may act only as a limiting membrane during root formation.     

An autoradiographic study of the sensory innervation of teeth. I. Dentin.

Autoradiography of axoplasmically transported proteins revealed that the coronal dentin of rat molar teeth receives sensory innervation from the trigeminal ganglion. The labeled processes appear to run in dentinal tubules and sometimes reach the peripheral dentinal region near the enamel.     

Glycoproteins in the dentine of human deciduous teeth.

Dentine from permanent and deciduous human teeth was demineralized with EDTA. The EDTA extracts were fractionated by gradient elution from DEAE-cellulose which revealed a peak in the extract of deciduous dentine which was absent from that of permanent dentine. Subsequent fractionation by gel-filtration and ion-exchange chromatography resulted in the isolation of two, apparently homogeneous, glycoproteins. The major component differed considerably from known glycoproteins of mineralized tissues, while a minor component was closely akin to certain dentine phosphoproteins in amino acid composition.     

A light and electron microscopic study of the early stages of root surface formation in molar teeth in the rat

The forming root surfaces of first molar teeth of twelve-day old rats were examined by light and transmission electron microscopy. A thin layer of the outermost dentinal matrix, approx. 1.0–1.5 μm wide, did not mineralize initially. The layer was lined externally by epithelial cells containing organelles suggestive of secretory activity. Electron-dense granular material resembling that produced by ameloblasts was observed in the epithelial intercellular spaces and in the unmineralized layer. The so-called initial layer of acellular cementum in the rats is therefore not cementum but a dentinal matrix to which epithelial secretory products are added.     

In-vivo incorporation of [3H]-proline into rabbit dental pulp collagen.

Collagen metabolism of rabbit dental pulp was studied by following the incorporation of [³H]-proline into pulp collagen. The specific activity of hydroxyproline was studied in various collagen fractions in rabbit incisor and molar teeth of different ages. The specific activity of the collagen fractions was consistently higher in incisor than in molar pulps at all ages, except for the pepsin-resistant fraction. In the molar at most ages, the pepsin-resistant fraction had a specific activity equal to, or greater than, that in the fractions solubilized by either acid or pepsin. The results demonstrate the high metabolic activity of dental pulp, and rapid incorporation of new collagen into the insoluble fibre network.     

A randomized study of sodium hypochlorite versus formocresol pulpotomy in primary molar teeth

International Journal of Paediatric Dentistry 2013; 23: 145–152 Background. Alternatives to vital pulpotomy treatment in primary teeth are being sought because of the high formaldehyde content of traditional formocresol (FC) pulpotomy medicaments. Aim. The aim was to compare the clinical and radiographic success of vital pulpotomy treatment in primary molars using 3% sodium hypochlorite (NaOCl) versus a 1 : 5 dilution of Buckley’s FC. Design. Pulpotomies were performed in primary molars of healthy children between 3 and 10 years old. Sixty‐five primary teeth were randomized into two groups that were evaluated for treatment outcomes. Following treatment, the pulp chamber was filled with zinc oxide eugenol (ZnOE) and restored with a stainless steel crown cemented with glass ionomer cement. Clinical and radiographic outcomes were recorded at 6 and 12 months. Results. The control (FC) and experimental (NaOCl) groups demonstrated 100% clinical success at 6 and 12 months. The NaOCl group had 86% (19/22) radiographic success at 6 months and 80% (12/15) at 12 months. The FC group had 84% (21/25) radiographic success at 6 months and 90% (9/10) at 12 months. No significant differences were found in the radiographic outcomes between the two groups at 6 and 12 months (Fisher’s exact test; P = 0.574 and P = 0.468, respectively). Conclusion. NaOCl demonstrated clinical and radiographic success comparable to FC.