Healing mechanism of tooth extraction wounds in rats. II. Histochemical observations on hydrolytic and oxidative enzymes in tooth extraction wounds in the rat

A histochemical investigation of the bone formation process by guided bone regeneration in rat jaws. Effect of PTFE membrane application periods on newly formed bone

BACKGROUND

Guided bone regeneration (GBR) has been widely utilized for the promotion of bone augmentation in bone loss areas. However, little information has been available regarding chronological changes in newly formed bone and alterations in the nature of newly formed bone after removal of a barrier membrane. The present study attempted to establish a GBR model for rat maxillae. We also examined the effects of membrane application periods on newly formed bone and its remodeling process after removal of the membrane in this experimental model.

METHODS

Thirty-five Wistar rats were divided into 2 groups: a membrane application group and a membrane removal group. The chronological changes of newly formed bone were evaluated histologically and statistically.

RESULTS

At 2 weeks after the GBR procedure, bony cavities had completely filled the newly formed bone in the experimental side. In the control side, corticalization on the surface of the newly formed bone proceeded with a decrease in the bone marrow cavity, whereas the bone marrow space had enlarged by 12 weeks post-surgery in the experimental side. In the membrane removal group, the osteoblasts appeared on newly formed bone at 1 week after membrane removal. Comparatively thick compact bone had formed on the surface of the newly formed bone at 4 weeks after membrane removal, and corticalization proceeded later.

CONCLUSIONS

The long-term application of a barrier membrane induces the enlargement of the bone marrow spaces. We suggest that PTFE membrane removal in adequate time promotes the corticalization and maturation of the newly formed bone by the GBR technique.

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.

A histological study on tissue responses to titanium implantation in rat maxilla: the process of epithelial regeneration and bone reaction

The present study aimed to establish a titanium implantation model using rat maxillae as well as demonstrate the chronological tissue responses to implantation. Pure titanium implants were inserted in the upper first molar extraction sites of Wistar rats 1 month after tooth extraction. The animals were sacrificed at 1 to 30 days postimplantation, and prepared tissue specimens were processed for light microscopy. The removal of implants from tissue blocks was done using 2 methods: mechanical removal or a cryofracture technique. In the early stages, peri-implant tissues showed severe damage to the oral epithelium and collagen bundles with significant inflammatory cell infiltration. The peri-implant epithelium grew apically along the implant by 10 days postimplantation, and regenerated to show a similar feature of junctional epithelium seen in normal rats at 15 days postimplantation, at which time no signs of inflammation were observed. The regenerated collagen bundles in the connective tissue were arranged circumferentially to the implants in the horizontal sections. New bone formation first appeared around the implants at 5 days postimplantation, covering the entire perimeter of implants by 30 days postimplantation. Scanning electron microscopic observations of the surface texture of the removed implants suggest the probability of an adhesive mechanism between the implants and the peri-implant epithelium and/or the alveolar bone. These findings indicate that this experimental model is useful for detailed analysis of peri-implant tissue because of its easy implantation procedure.

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.

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.