Early tissue reactions after circulatory and skeletal damage to the mandible of the rat

Dental pulp infarction in female rats following inhalation exposure to 2-butoxyethanol

Female Fischer 344 (F344)/N rats (10 per exposure group) were exposed to 2-butoxyethanol (BE) vapors (0, 31, 62.5, 125, 250, or 500 ppm 6 h/d, 5 d/wk, for 13 weeks) to characterize its prechronic toxicity. Dental lesions consisting of bilateral multifocal dental pulp thrombosis, pulp infarction, and odontoblast infarction were noted in the maxillary incisors of 3 of 4 rats from the 500-ppm group that were sacrificed when moribund during the first week of exposure. In addition, 1 rat from the 500-ppm group that was sacrificed on day 32 had similar unilateral incisor lesions but with additional findings consistent with a unilateral maxillary incisor fracture. In contrast, rats sacrificed after 13 weeks of exposure lacked dental lesions. In conclusion, BE has the potential to cause pulp thrombosis and odontoblast infarction in female rats. The apparent variability in response to BE noted in moribund sacrificed vs terminally sacrificed rats was attributed to development of tolerance to BE-induced hemolysis and subsequent incisor regeneration.

Effects of Le Fort I osteotomy on human gingival and pulpal circulation

The maxillary blood flow during the first 24 h following Le Fort I osteotomy was evaluated by laser Doppler flowmetry. Pulpal blood flow was recorded from two maxillary incisors and gingival blood flow was assessed from a site slightly apical to the interdental papilla of the maxillary central incisors of 12 patients receiving Le Fort I osteotomy, nine control patients receiving mandibular osteotomy, and 10 nonsurgical control subjects without orthodontic appliances. Measurements were made before surgery and at time intervals between 0-8, 8-16, and 16-24 h after surgery. The nonsurgical controls were tested at similar intervals. Gingival and pulpal blood-flow measurements did not change over time in the nonsurgical control group. Presurgical blood-flow values did not differ between the two surgical groups. Following surgery, mean gingival (but not pulpal) blood flow was significantly lower for patients treated with Le Fort I osteotomy than for patients treated with mandibular osteotomy. Follow-up examinations revealed that one patient receiving Le Fort I osteotomy experienced loss of gingiva and bone around both central incisors. This patient had one of the largest reductions in gingival blood flow.

Healing of mandibular body osteotomies after plate and intramedullary pin fixation

Osteotomies were created in the left body of the mandible of nine dogs and immediately stabilized with either a six hole dynamic compression bone plate or an intramedullary pin. Cortical bone healing and vascular supply were evaluated at weeks 2, 5, and 10 by microradiography, microangiography, and correlated histology of selected mandibular slices. Perforating arterioles from the buccal mucosa maintained vascular supply to rostral mandibular segments. The mandibular body rostral to the osteotomy site and caudal to the canine tooth suffered an interruption of vascular supply that was replaced by a temporary extraosseous supply during healing of the osteotomy. Intramedullary pin placement resulted in destruction of rostral teeth. There was an inflammatory response around the rostral portion of all intramedullary pins. Osteotomy sites involving tooth roots resulted in no disruption of the normal vascular or neural structures of the tooth pulp.

Microangiographic and histologic evaluation of revascularization and healing after genioplasty by osteotomy of the inferior border of the mandible

Correlated microangiographic and histologic studies in adult rhesus monkeys indicate that a pedicled genioplasty involving osteotomy of the inferior mandibular border maintains circulation and osseous viability of the repositioned genial segment. Circulation to the dental pulps was also not discernibly affected when accomplished a minimum of 8 mm below the root apices.

Quantitation of blood flow in the rat mandible after vertical osteotomy

Vertical osteotomies were performed in the mandibles of rats and combined with elevations of the buccal or bilateral mucoperiosteal pedicles. Isotope fractionation and particle distribution were used to measure blood flow in the distal and proximal segments of the mandible, the masseter muscle and the submandibular gland. Average decrease in blood flow ranged from 9-39% in the distal segment and from 8-24% in the proximal segment. Decrease in blood flow was most pronounced when bilateral mucoperiosteal pedicles were performed. Blood flow in the masseter muscle increased by 16-26% after osteotomy with mucoperiosteal elevations.

Changes in mineral content, mineral deposition and vascular supply of the mandible after osteotomy

Circulatory and skeletal damage in the form of a vertical osteotomy of the mandible, proximal to the entry of the inferior alveolar artery and mandibular perforantes, alone or in combination with unilateral or bilateral mucoperiosteal reflections were undertaken on young growing rats. Changes in mineral content and mineral deposition in the hard tissues of the mandibles were studied using microradiography and by labelling with tetracycline and lead acetate. Microangiography was performed to evaluate changes in the vascular supply. Resorption of the compact bone was seen in the central part of the compact bone, in the lower border of the mandible and in the incisal part of the alveolar bone. There was resorption of the cementum and dentin in the molar teeth. Remodelling processes were seen in the compact bone starting from vascular channels and on the surface of the bone trabeculae, ten days after osteotomy. Microangiography revealed that there is a collateral vascular system existing across the midline via the symphysis region, via submucosal tissue, via the mucoperiosteal pedicle to the inferior border of the mandible and via the network of small vessels in the periodontal membrane. It was concluded that the circulation to the peripheral parts of the mandible could in part be kept up by a retrograde flow in the collateral systems when the main circulation had ceased.

Effects of dextrans, heparin and hyperbaric oxygen on mandibular tissue damage after osteotomy in an experimental system

The effect of heparin, dextran 40, dextran 70 and hyperbaric oxygen (HBO) therapy to reduce tissue damage after mandibular osteotomy was tested in an experimental system. Tissue damage was recorded morphologically and blood flow and vascular bed was determined by isotope techniques. Subcutaneously administered heparin reduced morphologically determined tissue damage in the incisor odontoblastoma, pulp and ameloblastoma. Furthermore, central and peripheral bone damage was prevented by heparin. Dextrans had no preventive effect on tissue damage. HBO treatment reduced tissue damage in a similar manner to heparin but also induced reparative events as osteodentin formation in pulps and chondroid reactions in bone. Effects on blood flow and vascular bed provided a basis for a possible role for HBO and heparin treatment in tissue damage after osteotomy.

Experimental mandibular fracture: effect on bone circulation and metabolism after treatment with anticoagulants

An experimental model was designed for the study of mandibular fracture healing in Sprague-Dawley rats. Healing and remodellation were studied by routine histology and the vascular supply of the mandible by micro-angiography. The blood supply to the body of the mandible was similar to that seen in long bones. The arterial vascular system appeared to be intimately involved with the formation of bone. The vessel configuration varied in relation to the progress of healing. The effect of heparin, dextran 40 and dextran 70 therapy to increase blood flow in the fracture region was tested. Dextrans had no effect on fracture healing whereas heparin induced an increased chondroid reaction in the callus. Serum alkaline phosphatase was measured as a marker for hard-tissue formation. The enzyme activity was reduced after fracture with a minimum activity three days after fracture.

Experimental mandibular fracture: studies on bone repair and remodellation

An experimental mandibular fracture model was developed in Sprague-Dawley rats. Healing and remodellation were studied using routine histology, microradiography and incorporation of tetracycline and lead acetate. Bone healing after fracture started by outgrowth of bone trabeculae from the periosteum and from marrow spaces in the mandibular corpus and coronoid process. Stabile fracture healing was seen after 14-16 days, which correlated to the time when bone trabeculae were seen to cross the fracture diastasis morphologically. Formation of reparative bone was produced by direct formation of bone trabeculae but also via formation of a chondroid tissue which was later resorbed and replaced by bone.

Studies on protracted tissue reactions and repair after circulatory and skeletal damage to the rat mandible

The effect of circulatory and skeletal damage to the distal part of the mandible was studied on young growing rats after interruption of the inferior alveolar artery. The central part of the mandible including the incisor was most vulnerable to circulatory trauma. Maximal damage was seen when the inferior alveolar artery was interrupted combined with bilateral reflection of the mandibular periosteum. The damage produced then was a necrosis of the incisor pulp, odontoblasts and enamel organ and extensive resorption of the centrally-located compact bone. When both sides of the mucoperiosteum remained intact, damage to the main vessels of the mandible did not produce total necrosis of the incisor pulp. Reparative events with production of a fibrous connective tissue of the pulp and osteodentin production were seen. After resorption of sequestered bone was finished, this was replaced by a cell-rich type of bone which also replaced the alveola of those animals which had had their incisors excised. Hypercementosis was seen in the molars after 1 year. No respiratory activity in the incisor pulps was seen after the circulatory damage.