Little consistency has been manifest among investigators in choosing an appropriate experimental model for maxillofacial bone research. In an effort to develop a protocol for the experimental analysis of maxillofacial nonunions, previous studies using calvarial and mandibular defects as models were reviewed. The creation of nonunions in animals within the calvaria and mandible was size dependent. Defects of a size that will not heal during the lifetime of the animal may be termed critical size defects (CSDs). A rationale was postulated for testing bone repair materials (BRMs) using CSDs in a hierarchy of animal models. This rationale suggests that testing should be initiated in the calvaria of the rat and rabbit, followed by testing in the mandibles of dogs and monkeys. While calvarial CSDs have been established in the rat, rabbit, and dog, further research is necessary to determine the CSD in the calvaria of the monkey, as well as the mandibles of dogs and monkeys.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a154625.pdf

The critical size defect as an experimental model for craniomandibulofacial nonunions.

Two hundred fifty-seven patients with oral leukoplakia were studied and followed for an average period of 7.2 years. All lesions were more than one cm in size and had been present and observed for a minimum of 6 months. Of the initial biopsies, 235 revealed a benign hyperkeratosis and 22 others contained some degree of epithelial dysplasia. Seventy-three percent of the patients used tobacco, with cigarette usage being the predominant form. Forty-five patients (17.5%) subsequently developed squamous carcinomas in the hyperkeratotic epithelial site in an average time of 8.1 years. Eight of these malignant transformations came from patients who originally had epithelial dysplasia. High risks for malignant transformation also included non-smoking patients, the clinical presence of erythroplasia (erythroleukoplakia), and a clinical verrucous-papillary hyperkeratotic pattern. Duration of the leukoplakia progressively increased the total number of malignant transformations, with the largest rate occurring in the second year. This study confirms that oral leukoplakia is a precancerous lesion and that certain characteristics indicate greater risks and warrant consideration of more aggressive management.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1097-0142%2819840201%2953%3A3%3C563%3A%3AAID-CNCR2820530332%3E3.0.CO%3B2-F

Oral leukoplakia and malignant transformation. A follow-up study of 257 patients.

In this study, standard and prototype reinforced e-PTFE membranes were used to evaluate the pattern of bone regeneration in membrane-protected defects in the mandibles of four dogs. Following a healing period of 2 and 4 months, control sites without membranes exhibited incomplete osseous healing with a persisting defect. Test sites with membranes demonstrated significantly better bone healing, although bone regeneration was not yet completed at 4 months. The histologic evaluation showed that bone regeneration, once activated, progresses in a programmed sequence through a series of maturation steps, which closely resemble the pattern of bone development and growth.

Healing pattern of bone regeneration in membrane-protected defects: a histologic study in the canine mandible.

Incidence rates of oral cancer and natural history of oral precancerous lesions in a 10-year follow-up study of Indian villagers.

Guided bone regeneration (GBR) is commonly used in combination with the installment of titanium implants. The application of a membrane to exclude non-osteogenic tissues from interfering with bone regeneration is a key principle of GBR. Membrane materials possess a number of properties which are amenable to modification. A large number of membranes have been introduced for experimental and clinical verification. This prompts the need for an update on membrane properties and the biological outcomes, as well as a critical assessment of the biological mechanisms governing bone regeneration in defects covered by membranes. The relevant literature for this narrative review was assessed after a MEDLINE/PubMed database search. Experimental data suggest that different modifications of the physicochemical and mechanical properties of membranes may promote bone regeneration. Nevertheless, the precise role of membrane porosities for the barrier function of GBR membranes still awaits elucidation. Novel experimental findings also suggest an active role of the membrane compartment per se in promoting the regenerative processes in the underlying defect during GBR, instead of being purely a passive barrier. The optimization of membrane materials by systematically addressing both the barrier and the bioactive properties is an important strategy in this field of research.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/eos.12364

Guided bone regeneration: materials and biological mechanisms revisited.

Surgical procedures for the rapid and complete restoration of facial bones were investigated in a three-year study. Mandible restorations obtained with a combination marrow and bone graft, contained in filter-lined metallic implants, point to a superior method for restoring large avulsive defects sustained in high-velocity missile warfare. Further adaptation of this procedure offers improved approaches to the treatment of other problem defects encountered in oral surgery. Filter-lined metallic implants of bone and marrow were tested in facial wounds experimentally produced to simulate battle casualties. The surgical technic developed by this research is believed to be far superior to bone grafting methods previously used and has many potential applications to clinical dentistry.

Restoration of osseous defects in maxillofacial casualties

Hyperbaric oxygen was used in the treatment of intractable osteomyelitis of the mandible. Dentists are frequently called on to manage postoperative bone infections. In spite of comprehensive antibiotic therapy, the occurrence of osteomyelitis after tooth extraction is not infrequent. The dentist is then faced with management of an intractable infection of the bone that seems to resist all conventional therapy. Hyperbaric oxygenation from the study reported here appears to offer a new type of treatment for these resistant cases of osteomyelitis.

Hyperbaric Oxygen Treatment of Mandibular Osteomyelitis: Report of Three Cases

Implants and Transplants: Review of Recent Research in this Area of Oral Surgery

This is a preliminary report regarding a technique combining a subperiosteal metal implant and a marrow-bone graft The purpose of this procedure is to restore the mandibular bone, which covers and protects the exposed mandibular canal and nerve, and to augment this graft procedure by a metal implant The metal implant acts as a tray or crib to hold the bone graft in position and to protect it during initial healing period Following this period, the implant will then receive the major part of the occlusal forces and will transmit them directly to the bone rather than against the mucosa The implant posts are made so they can be removed to allow for the initial healing of the bone graft without communication with the oral cavity Small screws are placed in position for about four weeks during healing to prevent bone from closing the screw holes The postoperative course was uneventful, and results from the standpoint of function and comfort (Fig 19) are excellent There is no evidence of pressure paresthesia which was previously present when the patient used a soft tissue-borne mandibular denture The marrow-bone graft is remodeling excellently, and in many areas, bone completely covers the metal implant Clinical evaluations in three other patients as well as research on animals are currently being successfully conducted to investigate all aspects of this combination procedure After 14 months, the initial clinical use of the technique has been most encouraging

Philip J. Boyne

Papers

Restoration of osseous defects in maxillofacial casualties

Hyperbaric Oxygen Treatment of Mandibular Osteomyelitis: Report of Three Cases

Implants and Transplants: Review of Recent Research in this Area of Oral Surgery

Combined use of subperiosteal implant and bone-marrow graft in deficient edentulous mandibles: A preliminary report

The effect of calcified bone matrix on the osteogenic potential of hematopoietic marrow