Robert D. Mundell

Osseous guided tissue regeneration using a collagen barrier membrane.

The formation of mature, fibrous tissue in surgical osteotomy sites during the healing process can produce clinically undesirable results such as nonunion or encapsulation of alloplastic implants. The techniques of guided tissue regeneration have been used to ameliorate this problem by presenting a barrier to the invasion of fibrous tissue elements into the wound-site clot. The most frequently used barrier material, polytetrafluoroethylene is effective, but suffers the disadvantage of requiring surgical removal after clot organization is completed. A biocompatible, resorbable membrane that will effectively control the type of tissue that can invade and organize a clot would be advantageous, because it would not require surgical removal. In the present study, the efficacy of a collagen membrane to effect guided tissue regeneration in a rabbit zygomatic arch osteotomy model was tested. Complete, bilateral narrow (1 mm) or wide (5 mm) vertical osteotomies were created in eight adult New Zealand white male rabbits. On one side, the wound site was surrounded by a collagen barrier membrane prior to closure, while the other side was left uncovered (control side). Four animals were killed at 2 and 4 weeks postoperatively for gross radiologic and histologic examination of the wound site. The wide osteotomy sites without a barrier membrane showed invasion by fibroblasts resulting in fibrous nonunion, while the contralateral sides with the barrier membrane showed no fibrous tissue ingrowth and bony union by 4 weeks postoperatively. Although narrow wound sites without the barrier membrane showed fibrous tissue formation, the perimeter of the defects showed some new bone deposited at the periosteal surface, bridging the osteotomy site and producing osseous union.(ABSTRACT TRUNCATED AT 250 WORDS)

A pilot study of the clinical problem of regionally anesthetizing the pulp of an acutely inflamed mandibular molar

The diplomates of the American Association of Endodontists were surveyed regarding difficulties in regionally anesthetizing acutely painful mandibular molar teeth. Frequently patients developed evidence of adequate regional block anesthesia but experienced pain when the dentist attempted access. A pilot projection was undertaken to determine if a scientific basis existed for this problem. With the animal under general anesthesia, the mandibular nerve of a cat was isolated and then regionally blocked. A stimulating electrode was implanted in a cuspid tooth and a receiving electrode in the cortex of the brain. When a state of inflammation was created in the tooth in the presence of a regional block, there was an increasing cortical response to this stimulation. It was concluded that the pilot project offered a realistic technique for the study of this clinical entity.

The effects of guided tissue regeneration and fixation technique on osseous wound healing in rabbit zygomatic arch osteotomies.

The development of fibrous nonunions after craniofacial surgery is thought to result from an interaction of biomechanical stress and the differential migration of various tissue types into the wound site during healing. The present study is designed to test this hypothesis through the manipulation of guided tissue regeneration and osteotomy fixation techniques in an experimental rabbit model. Bilateral, critical size (5 mm), vertical osteotomies (n = 32) were produced in the zygomatic arches of eight adult rabbits. The mobile bony segments were fixed rigidly or nonrigidly using bone microplates and screws or osteosynthetic wires. The defects were then covered with a resorbable collagen membrane or left uncovered. The rabbits were followed for 4 weeks with serial dorsoventral cephalographs and the zygomatic arches harvested for histological analysis. Cephalometric results revealed significantly (p < 0.001) increased bone growth in the margins of the defects covered with the collagen membrane; however, no significant (p > 0.05) differences were noted between fixation techniques. Histological analysis revealed that defects fixed rigidly and covered by the membrane showed the most rapid and organized osseous wound healing, followed by the defects that were fixed nonrigidly and membrane covered. The defects not covered by the collagen membrane showed invasion by fibroblasts resulting in fibrous nonunions. These results demonstrate the efficacy of guided tissue regeneration with a resorbable collagen membrane in preventing fibrous tissue ingrowth in large bony defects. The addition of rigid fixation at a potentially mobile site appeared to enhance bony trabecular organization but not the osteogenic rate in this rabbit model.

Studies on experimental malocclusion in rabbits. 1. Method of induction of malocclusion and its effects on the temporomandibular joint

Abstract A method for the induction of lateral malocclusion in rabbits has been described. The effects of lateral malocclusion on the temporomandibular joint of the rabbit are reported. It was found that animals with a mild degree of malocclusion did not show noticeable changes in the temporomandibular joint, even after an experimental period of 20 weeks. Animals with moderate to severe treatment showed marked changes. The changes were different in character, depending upon the length of time the treatment had been in force at the time of the animals death. Prominent changes included osteoclasia and chondroclasia, principally in the condyle. Extension of the duration of lateral malocclusion permitted completion of adaptive changes in the temporomandibular joint and formation of new condylar bone and cartilage.

Heilungsverhalten und Knochenregeneration von maxillären Osteotomien im experimentellen Kaninchenmodell

Einführung: Die Entstehung fibröser Ankylosen anstelle knöcherner Heilung nach orthognather Chirurgie wird Interaktionen von biomechanischen Stressfaktoren und der im Vergleich zu Osteoblasten differenzierteren und schnelleren Migration von Fibroblasten in den Wundbereich zugeschrieben. Ziel dieser Studie war die Überprüfung dieser Hypothese im experimentellen Kaninchenmodell unter Anwendung von gesteuerter Knochenregeneration (GTR) und Osteosynthesen. Material und Methode: In den Oberkiefern von 12 erwachsenen New-Zealand-White-Kaninchen wurden als Osteotomien (n = 24) beidseitig Critical-size-Defekte (4 mm) gesetzt. Die Oberkiefersegmente wurden im Vergleich zur kontralateralen Seite mit Mikroplattenosteosynthesen und -schrauben oder Drahtosteosynthesen stabilisiert. Zusätzlich wurden die Defekte entweder mit einer resorbierbaren Kollagenmembran abgedeckt oder nicht. Postoperativ, nach 2 und nach 4 Wochen wurden Fernröntgen im posterior-anterioren und seitlichen Strahlengang durchgeführt. Anschließend wurden die Oberkiefer für histologische Analysen gewonnen. Ergebnisse: Mit radiologischen und histomorphometrischen Analysen wurde nachgewiesen, dass von Membranen abgedeckte Defekte in stabil fixierten Osteotomien schnellere und früher organisierte neue Knochenformation zeigten. Diese mit Membranen abgedeckten Defekte in stabil fixierten Osteotomien enthielten im Vergleich zu nicht mit Membranen abgedeckten Defekten in stabil fixierten Osteotomien 40% mehr neuen Knochen. Defekte ohne Membranabdeckung in instabil fixierten Osteotomien zeigten Fibroblastenproliferation und fibröse Ankylosierungen. Schlussfolgerung: Die Ergebnisse dieser Studie am experimentellen Kaninchenmodell belegen, dass Interaktionen zwischen verminderter Fibroblastenproliferation durch gesteuerte Knochenregeneration und Osteotomiesegmentstabilisierung mittels Osteosynthesen postoperativ fibröse Ankylosen hintanhalten und neue Knochenregeneration und Heilung der Osteotomien fördern. Purpose: The development of fibrous nonunions following orthognathic surgery is thought to result from an interaction of biomechanical stress and the differential and more rapid migration of fibroblasts compared to osteoblasts into the wound site during healing. The present study was designed to test this hypothesis through the manipulation of guided tissue regeneration and osteotomy fixation techniques in an experimental rabbit model. Materials and methods: Bilateral critical size (4 mm) defects ¶(n = 24) were produced in the maxillae of 12 adult New Zealand White rabbits. The maxillary segments were rigidly or nonrigidly fixed using bone microplates and screws or osteosynthetic wires. The defects were then covered with a resorbable collagen membrane or left uncovered. The rabbits were followed for 4 weeks with serial dorsoventral and lateral oblique cephalographs and the maxillae were then harvested for histological analysis. Results: Radiographic and histomorphometric analysis revealed that rigidly fixed defects, covered with membrane, showed the most rapid and organized new bone formation. The rigidly fixed defects with membrane averaged approximately 40% more new bone in the osteotomy site than the rigidly fixed defects with no membrane. Nonrigidly fixed defects with no membrane also showed an ingrowth of fibroblasts and fibrous nonunions. Conclusion: These results suggest that an interaction between the decreased fibrous tissue ingrowth through guided tissue regeneration and osteotomy segment stability from rigid fixation prevented postoperative fibrous nonunions and facilitated new bone regeneration and osteotomy site healing in this rabbit model.PURPOSE The development of fibrous nonunions following orthognathic surgery is thought to result from an interaction of biomechanical stress and the differential and more rapid migration of fibroblasts compared to osteoblasts into the wound site during healing. The present study was designed to test this hypothesis through the manipulation of guided tissue regeneration and osteotomy fixation techniques in an experimental rabbit model. MATERIALS AND METHODS Bilateral critical size (4 mm) defects (n = 24) were produced in the maxillae of 12 adult New Zealand White rabbits. The maxillary segments were rigidly or nonrigidly fixed using bone microplates and screws or osteosynthetic wires. The defects were then covered with a resorbable collagen membrane or left uncovered. The rabbits were followed for 4 weeks with serial dorsoventral and lateral oblique cephalographs and the maxillae were then harvested for histological analysis. RESULTS Radiographic and histomorphometric analysis revealed that rigidly fixed defects, covered with membrane, showed the most rapid and organized new bone formation. The rigidly fixed defects with membrane averaged approximately 40% more new bone in the osteotomy site than the rigidly fixed defects with no membrane. Nonrigidly fixed defects with no membrane also showed an ingrowth of fibroblasts and fibrous nonunions. CONCLUSION These results suggest that an interaction between the decreased fibrous tissue ingrowth through guided tissue regeneration and osteotomy segment stability from rigid fixation prevented postoperative fibrous nonunions and facilitated new bone regeneration and osteotomy site healing in this rabbit model.

Healing of osseous maxillary sinus defects using guided tissue regeneration: An experimental study in rabbits

The healing capabilities of the maxillary sinus in rabbits with and without a collagen barrier membrane after bilateral critical size defects were investigated at 4 wk after surgery. One maxillary sinus had a collagen membrane barrier positioned over the surgical site, whereas the other maxillary sinus surgical site served as a control. A histological evaluation showed that the experimental (barrier) defect had more complete osseous healing when compared with the control (nonbarrier) maxillary sinus defect. From the analysis of the Students t test for paired samples and the Wilcoxonpaired signed-ranks test, the healing capabilites of the maxillary sinus with the collagen barrier membrane could be considered statistically significant. It seems that the placement of the collagen barrier membrane after maxillary sinus exposure could have a beneficial effect.