Healing mechanism of tooth extraction wounds in rats. I. Initial cellular response to tooth extraction in rats studied with 3H-thymidine

Changes in periodontium after extraction of a periodontally-involved tooth in rats

Purpose

Recent interest has focused on intentional replantation to restore an original tooth. Some studies have shown successful results with intentional replantation for periodontally involved teeth. For long-term success of replantation, a healthy periodontal status of the recipient site is required so that delayed replantation is more suitable for periodontally involved teeth. To reveal the ideal timing for delayed replantation of periodontally involved teeth, the healing process of extraction sockets after extraction of periodontitis-induced teeth in rats was evaluated.

Methods

Twenty-eight rats were randomly divided into two groups: a control group (n=8) and test group (n=20). In the test group, periodontitis was induced by a ligature around the cervix of the mandibular first molar of all of the rats. Two weeks later, the mandibular first molars were extracted in all of the animals. The animals were sacrificed on days 0, 3, 7, and 10 after extraction and histological and immunohistochemical analysis was performed.

Results

In histological analysis of the test group, inflammatory cell infiltrate was found abundantly in the remaining periodontium 3 days after tooth extraction and decreased gradually at later time points. In immunohistochemical analysis of the test group, both interleukin-6 (IL-6) and, tumor necrosis factor-α (TNF-α) were numerous in the furcation area at each postextraction day. IL-6 was stained more heavily between 3 and 7 days after extraction; at day 10 after extraction, little staining was observed. TNF-α staining was more intense at 3 days after extraction and gradually weakened at later points in time.

Conclusions

Within the limits of this study, it takes at least 10 days to resolve periodontal inflammation in rat extraction sockets.

Bisphosphonate administration prior to tooth extraction delays initial healing of the extraction socket in rats

Bisphosphonates (BPs) are clinically used for the treatment of bone metabolic abnormalities because they are powerful inhibitors of bone resorption. Osteonecrosis of the jaw has been observed after tooth extraction in a considerable number of BP-treated cancer patients, but the reason for this is not known. We studied the effects of BP on extraction socket healing in rats that were pretreated with BP prior to tooth extraction. Male Wistar rats (approximately 5 weeks old) were divided into experimental (BP) and control groups. In both groups, maxillary right second molars were extracted under general anesthesia. BP group rats were injected with 50 microl (1.0 mg/kg) alendronate into the right buccal alveolar bone every 4 days for 14 days, starting 2 days before tooth extraction. Control group rats were injected with physiological saline instead of alendronate. Rats were euthanized 3, 7, 10 or 14 days after tooth extraction, and maxillary bones were collected. Bone morphometric analysis using microfocus X-ray CT images and calculation of bone-resorption parameters based on hematoxylin and eosin or TRAP-stained pathological sections of the molar region showed that new bone formation in the extraction socket was delayed in the BP group relative to the control group during the first 7 days after extraction. A subsequent increase in new bone formation showed that bone resorption in the BP rats was eventually inhibited. This delay in initial healing may explain the jaw osteonecrosis observed in some BP-treated cancer patients.

Proliferative Activity, Apoptosis, and Histogenesis in the Early Stages of Rat Tooth Extraction Wound Healing

We examined the proliferative activity, apoptosis, and histogenesis in the early stages of the rat healing socket from just after extraction until new bone formation occurs. Thirty 11-week-old male Wistar rats underwent bilateral maxillary first molar tooth extraction. Five craniomaxillary tissue specimens were dissected at the following time points: at 12 h, days 1, 3, 5, 7 and 10 after surgery. The immunohistochemical expression of both proliferating cell nuclear antigen (PCNA) and the Ki67 counterpart of rodent (MIB5) for proliferative activity and both the TUNEL reaction and the immunohistochemical expression of single-strand DNA for apoptosis were evaluated using 6-mum-thick serial paraffin sections, which were prepared in the coronal plane. The positive cell counts in the socket were converted into the cell numbers per mm(2) as either the proliferative index (PI) or the apoptotic index (AI). The PI and the AI showed maximum levels at 5 days and 12 h after extraction, respectively. The proliferative activity in the early stages of extraction wound healing is initially distributed in the remaining periodontium with load-induced apoptosis, next in the proliferative fibrous tissue, and then around the trabeculae of the new bone marking its peak.

Cyclosporin-induced gingival overgrowth at the newly formed edentulous ridge in rats: a morphological and histometric evaluation

BACKGROUND

Since cyclosporin A (CsA)-induced overgrowth seldom occurs at sites distant from teeth, the periodontal ligament has been considered significant. The aim of this study was to examine overgrowth occurrence at the edentulous ridge--the sites without the ligament--after CsA therapy in rats.

METHODS

After extracting all right maxillary molars, 16 Sprague-Dawley rats underwent a 2-week healing period. The animals were separated into CsA and control groups. CsA rats received 15 mg/kg of CsA by gastric feeding for 4 weeks, while the control group received only mineral oil. At the end of study, all animals were sacrificed and stone models were immediately obtained by rubber-based impressions. The edentulous ridge morphology, including the bucco-lingual width and the vertical height, was measured on the models. For histometry, 10 sections were selected from the edentulous ridge of each animal after undecalcified tissue preparation. The soft tissue areas of the edentulous ridge and the trabecular bone morphology of the dental alveolus were measured.

RESULTS

CsA therapy produced a significant increase of the ridge width and height, measured from the stone models, when compared to the control group. Under histometry, CsA resulted in a significant increase of the epithelium, connective tissue, and total soft tissue areas. The measured trabecular bone volume was affected by both examining factors: the drug therapy and the location of the dental alveolus. CsA therapy produced a significant loss of bone volume but a significant increase of the bone-specific surface area. Although the mean osteoid volume was similar between CsA and control groups, a significant decrease of the fractional formation surface in the CsA group was revealed.

CONCLUSIONS

An enlarged edentulous ridge and an altered dental alveolar bone morphology were observed in CsA-treated animals at the end of the study; therefore, we suggest that CsA may induce not only a soft tissue overgrowth but also an alveolar bone alteration at the edentulous ridge. The hypothesis that tooth or periodontal ligament is an essential component for the overgrowth development is questioned.

Current perspectives in residual ridge remodeling and its clinical implications: a review

PURPOSE

This article reviews the current understanding of the biology of tooth extraction wound healing and residual ridge remodeling.

METHODS

The review of the biology of tooth extraction wound healing involves a discussion of the different cells populating the tooth extraction wound, the matrix formation, and the control of the repair process in the short-term. Defects in socket matrix formation or cellular activity will lead to stalled healing. The review of residual ridge remodeling describes the long-term result of tooth extraction and formation of residual ridges, in which the quantity of bone tissue continuously decreases. This may suggest that any potential regulatory factors of residual ridge resorption should have an adverse effect either on the increased catabolic activity by osteoclasts or on the decreased anabolic activity by osteoblasts. Both short-term tooth extraction healing and long-term residual ridge remodeling processes are interdependent. Furthermore, any potential genetic and environmental regulatory factors can affect the quality and quantity of bone by altering the gene expression events taking place in bone cells.

RESULTS

The intent of this article was to review the current progresses of biologic research on residual ridge remodeling and to relate the changes at molecular, cellular, and tissue levels. The understanding of residual ridge remodeling may provide a sound scientific basis for improved restorative and therapeutic treatments of the edentulous population.

Animal model for evaluating the effect of systemic estrogen deficiency on residual ridge resorption

The rate of resorption of residual ridges after tooth extraction varies among subjects. Despite many human studies, the etiologic factors of severe forms of resorption of residual ridges are unknown and probably multifactorial. To facilitate investigations of resorption of residual ridges, it is preferable to use an animal model with a dentoalveolar component similar to that of human beings. This study developed a rapid, nonhuman primate model in which one could measure resorption of residual ridges at the most critical period, with the least amount of time, minimal operation, and the least interference with normal nutrition. Three female Macaca fascicularis monkeys, 7 to 9 years old, were selected for simple extraction of four maxillary incisors, four mandibular incisors, and two mandibular canines. Lateral cephalographs were taken at weeks 0, 1, 2 to 3, 5 to 6, 8 to 9, 11 to 12, and 26 to 28 after extraction with a newly constructed cephalostat that allowed easy reproducibility of animal placement in the prone position. Height and area measurements were made of maxillary and mandibular anterior residual ridges in the superimposed cephalographs. Sequential mean bone loss data produced bone loss curves similar to those observed in humans. One animal underwent ovariectomy. The plasma levels of both estrogen and progesterone decreased over 25 days and stayed below the detection limits thereafter. Tooth extraction was done 4 weeks after the ovariectomy and the bone resorption pattern was able to be observed longitudinally with the newly established monkey cephalostat. The results indicated that Macaca fascicularis need not be sacrificed when used in longitudinal studies of resorption of residual ridges in a relatively short period of experimental time. This model can provide an excellent opportunity to investigate a causal relationship between the rate of resorption of residual ridges and predisposing systemic factors such as estrogen deficiency.

Extraction wound healing in desalivated rats

Wound licking has been shown to promote extraoral wound healing among animals. Although the oral mucosa is bathed in saliva. Little information about the role of saliva in oral wound healing is found. The present study evaluates the healing of extraction wounds in desalivated rats. Experimental rats underwent sialadenectomy of the submandibular and sublingual glands and ligation of the parotid ducts. Maxillary left first molars were extracted. Rats were killed at 0, 1, 3, 5, 7, 10, 14, and 21 days after surgery and maxillae were prepared for light microscopy examination. Generally, a delay in socket healing in the desalivated rats was found. No differences were observed in blood clot formation. Replacement of the clot by granulation tissue was relatively slow concomitant with a longer inflammatory process. Bone formation kinetics were slower among the experimental rats.

Resorption of residual ridges (RRR) in rats

The post-extraction resorption of residual ridges (RRR) is a major and largely unsolved health problem, probably of multifactorial etiology. In order for one to study the role of specific factors in the pathophysiology of RRR, the use of animal models is desirable. The purpose of this study was to establish a reliable animal model and a standardized assay system to measure RRR for future experiments. A new oblique cephalometric device was designed to take pairs of xeroradiographs on the right and left sides of the rat skull and mandible at a 45-degree angle to the horizontal plane. Preliminary studies confirmed the reproducibility of the technique. All molars were extracted with minimal trauma from the right maxilla and mandible in five male Sprague-Dawley rats (40 days old). Longitudinal cephalographic examinations were performed before and immediately after extraction and at two, four, eight, and 12 weeks after extraction. Alveolar bone resorption was measured on enlarged cephalographs (5.7 X) at a point mesial to the mandibular first molar. Sequential mean bone resorption was 0.8 +/- 0.2 mm (S.D.), 1.0 +/- 0.3, 1.3 +/- 0.3, and 1.5 +/- 0.4, respectively. Graphically, these findings produced bone loss curves similar to those observed in man. These results indicate that the rat model may be utilized in longitudinal studies of the resorption of the residual ridge.

Neuro-histological reactions following tooth extractions

The neuro-histological reactions after tooth extraction were investigated in the extraction alveolus, the mandibular nerve and the trigeminal ganglion. In the ganglion, nerve cell bodies showing signs of retrograde reaction (chromatolysis and nuclear displacement) were seen 12 h after extraction. Maximal number of reacting cells were registered in the first postoperative week. Three weeks after extraction the number of reacting cells were at a normal low level. In the mandibular nerve no signs of axon degeneration could be demonstrated. In the alveolus, initial traumatic axon degeneration was followed by regeneration 2 days after extraction. Within the first postoperative week the alveolus was filled with connective tissue, in which many long thin axons were seen. Cancellous bone then filled the alveolus; the axons were thereby gathered - concentrated - into fascicles in the central part, with a direction towards the limbus. However, this was only passed by very few axons. Four months after extraction signs of axon degeneration were seen, and 2 months later the myelin sheaths also displayed degenerative signs. Ten months after extraction a minor area of connective tissue with a content of few axons and vessels was found at the bottom of the former alveolus. The histological appearance was of a small traumatic neuroma.

Effect of irradiation-timing on the initial socket healing in rats

The effect of a single dose of 1500 R on early postextraction socket healing was studied in jaws of rats. A severe delay in healing was found in animals irradiated 2 weeks prior to extraction. Retardation of healing to a lesser degree was demonstrated in sockets irradiated immediately after exodontia.

A biochemical study of aminopeptidases in the palatal mucosa of the rat following tooth extractions

Aminopeptidase activities were studied biochemically from the supernatants of the homogenates prepared from the normal and post extraction palatal mucosa of the rat. The determinations were carried out at 0.5, 1, 2, 4, 8 and 16 hours and 1, 2, 3, 5 and 7 days following extraction using N-L-aminoacyl-2-naphthylamines of arginine, glycine, leucine, proline and valine as the substrates. In addition, in the second part of the study the hydrolysis of N-L-aminoacyl-2-naphthylamines of alanine, histidine, isoleucine, lysine, phenylalanine, serine, threonine, tyrosine and valine was tested at 1, 3 and 5 days following extraction. The effect of chloride ions (0.2 M NaCl) on the hydrolysis of arginine and lysine derivatives was also tested. The specific activities of aminopeptidases obtained from the extraction-wound side were compared to those of the control side at each time interval. Tooth extraction caused a considerable reduction in the specific activities of aminopeptidases in the surrounding palatal mucosa immediately after extraction (at 0.5 hr.). The specific activities in the wound tissue remained generally below the control levels for 24 hours and reached their maximum within 5 days following extractions. The highest relative increase was obtained with N-L-valyl-2-naphthylamine. Arginine aminopeptidase was activated by chloride ions on an average 20 per cent more in the wound tissue than the control. This effect can be considered suggestive of the activation of aminopeptidase B in the post extraction palatal mucosa.