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Experimental animal and clinical studies have increased understanding of the biology of healing following periodontal regenerative therapy and factors that may influence the outcome. Formation of a new connective tissue attachment rather than a long junctional epithelium at the tooth-gingival flap interface is dependent upon the completion of a series of interactions among the root surface, plasma and tissue factors, and the connective tissue of the gingival flap. First, plasma proteins must adsorb to and remain in undisturbed contact with a generally noncompromised root surface. Next, adhesion of the established fibrin clot to the root surface must remain intact. Within days, a cellular and fibrous attachment will form; however, the tooth-gingival flap interface will still be vulnerable to wound-rupturing forces. Within two weeks the interface may have gained sufficient mechanical strength to offset such forces, at least in limited periodontal defects. Eventually, maturation of the fibrous attachment, including bone and cementum formation, will occur, particularly following adequate space provision by barrier membranes (guided tissue regeneration). A novel research focus involves how advances in molecular biology can translate to periodontal regenerative therapy. Bone morphogenetic proteins (BMPs) have been shown to support healing in a variety of skeletal sites. Recent research has demonstrated clinically significant alveolar bone and cementum regeneration with the use of a recombinant human BMP-2 implant. Such data suggest that growth-promoting substances, such as rhBMP-2, may significantly enhance periodontal regeneration and that use of such substances may radically recast current periodontal regenerative therapy.

Experimentation in animal models has created a basis for highly improved therapeutic procedures in reconstructive periodontal surgery. This symposium has discussed several animal models currently used; additional models have been described in recent literature. The presentations by Drs. Caton, Wikesjö, and Lynch illustrated the need for further discussion of some of the problems inherent in animal experimentation, including: standardization of periodontal defect configuration; adequate recording of preoperative attachment level; minimizing the effect of biological variability; use of surgically-created versus naturally-developed periodontal lesions; choice of observation period; and regenerative potential of the model chosen.

The effect of citric acid conditioning of the root surface in conjunction with gingival flap surgery including barrier membranes (expanded polytetrafluoroethylene) was clinically evaluated in 26 intrabony periodontal defects in 23 patients. Control treatment included gingival flap surgery with barrier membranes alone. Twelve defects were treated with the experimental and 14 with the control protocol. Healing was evaluated 12 months after surgery. Initial probing depths approximated 6.9 mm and defect depths measured during surgery exceeded 4 mm. The patients exhibited good oral hygiene over the study interval as substantiated by low plaque and bleeding scores. Acid conditioning of the root surface did not enhance periodontal healing in this study, similar amounts of defect resolution were observed following either treatment protocol. Probing depth reduction generally approximated 1.8 mm; gain of clinical attachment, 0.8 mm; and defect bone fill, 1.2 mm. Under the prevailing conditions, the barrier membrane procedure apparently gave a healing result beyond which further improvement could not be achieved by root surface conditioning.

Cemental tears have been described both in exposed and unexposed cementum. The phenomenon is believed to be elicited by overloading or acute trauma from occlusion. In this case report a patient, with a history of periodontal health, presented with an acute periodontal lesion on the distal aspect of a bridge abutment tooth. Periapical radiographs demonstrated an extensive vertical intrabony defect adjacent to the vital abutment tooth containing a radiopaque "foreign body." Histological examination of the surgically removed "foreign body" revealed a piece of dental cementum with some attached soft tissue. The lesion responded well to a surgical approach. Healing was uneventful and periodontal health was restored. This case illustrates that cemental tear should be considered as a differential diagnostic entity in isolated sites with rapid periodontal breakdown.

Wound healing in an incisional wound is a highly predictable process which has been studied extensively hour-by-hour and day-by-day. Healing in a periodontal defect following gingival flap surgery is, conceptually, a more complex process as one wound margin consists of calcified tissue, including the avascular and rigid root surface. Another complicating factor in this wound healing is the transgingival position of the tooth. Experimental studies, however, have indicated that healing at a dento-gingival interface under optimal conditions occurs at the same rate as in a skin wound. Generally, periodontal healing is characterized by maturation of gingival connective tissue, limited regeneration of alveolar bone and cementum, and the formation of a long junctional epithelium. Such observations have nurtured the hypothesis that the epithelium of the surgical flap needs to be prevented from early access to the root surface during the healing period to achieve connective tissue repair of the root surface-gingival flap interface. Recent experimental findings suggest, however, that connective tissue repair to the root surface following reconstructive periodontal surgery is a function of the establishment and maintenance of a root surface-adhering fibrin clot. Since fibrin adherence to the wound margins is a natural event, it is additionally suggested that apical migration of the gingival epithelium in periodontal surgical wounds may only follow interruption of the adherence of the fibrin clot to the root surface.

A need exists for well-defined animal models to objectively evaluate surgical principles and a possible role for biochemical wound conditioning and biomaterials in promoting periodontal regeneration. To test an existing model for its usefulness in quantitative evaluation of periodontal wound healing, large supraalveolar periodontal defects were surgically created around the mandibular premolars (P2, P3, P4) in left or right jaw quadrants in 5 beagle dogs. The defects were exposed to the oral environment for 6 months and were then subjected to reconstructive flap surgery (chronic defects). Healing in these defects was compared to healing following reconstructive surgery in similar contralateral defects which had not been exposed to plaque and calculus (acute defects). The animals were sacrificed after a 4-week healing period and tissue blocks including teeth and surrounding structures were processed for histometric analysis. Mean defect height (+/- s.d.) for chronic and acute defects amounted to 4.6 +/- 0.3 and 4.4 +/- 0.4 mm, respectively. Mean connective tissue repair to the root surface in chronic defects amounted to 62% (range 49% to 74%) of the defect height. Mean connective tissue repair in the acute defects exceeded 94% of the defect height in 4 of the dogs, but amounted to only 48% in 1 dog. Regeneration of alveolar bone and cementum was limited under both experimental conditions. Root resorption was frequently encountered, whereas ankylosis was seen in only few teeth. This study indicates that healing may vary not only as a result of controlled experimental variables, but also due to differences in biological response between dogs or to fortuitous traumatic factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Fourteen intrabony periodontal defects and six furcation defects (Class II) were treated by a flap procedure which included the use of a polytetrafluoroethylene membrane to allow guided tissue regeneration. After 4 to 6 weeks of healing, the membranes were retrieved and examined by scanning electron microscopy for the presence of adherent cells and other tissue elements. The cervical open pore-structured collar of the membrane, which in most cases had become partially exposed to the oral cavity, had a deposit of bacterial plaque. Bacterial Bacterial colonies and a scatter of single cells in some instances extended into the mid-third of the membrane. Fibroblast-like cells and, in some specimens, blood vessels and fibrous structures were seen in the mid-third and deep parts of the membrane. Generally, however, the occlusive portion of the membrane was characterized by a sparseness of adherent tissue elements. There did not seem to be a systematic difference in the nature and distribution of the adherent structures on the inner and outer surfaces of the membrane. The findings suggest that, in addition to preventing flap tissues from contacting the root surface, an important function of the membrane is to protect the integrity of the underlying blood clot by diverting mechanical stress acting on the flap during early stages of healing.

Root surfaces, exposed by periodontal disease, were studied after treatment with sodium hypochlorite. Observations of the anorganic specimens demonstrated that substantial changes occur in root surfaces incident to periodontal disease. A mineralized surface coating was seen in all areas of the involved root surface, although local regions occurred where the coating was apparently unmineralized. These findings generally confirmed the results of a previous study where the same specimens were studied without hypochlorite treatment. It is concluded that the coating is probably identical to the dental cuticle, and stems from adsorption of components of the gingival inflammatory exudate to the root surface. The coating may also be the carrier matrix for exogenous cytotoxic substances, previously thought to be located in the cementum. The findings may have implications for the way of treating periodontitis-involved root surfaces.

Root surfaces of extracted human teeth with advanced periodontal disease were studied by the apically migrated junctional epithelium, the topography characteristic of uninvolved cementum was frequently masked by a surface coating. The thickness of the coating increased in a coronal direction where it often blended with calculus. The observations indicate that this surface coating may originate from the inflammatory exudate and corresponds to the dental cuticle. The findings also indicate that the coating may be mineralized and may contain exogenous substances. These observations illustrate a need for further study and reexamination of the rationale for removal of tooth substance during scaling and root planing.

This study was designed to test the effect of tetracycline on healing subsequent to periodontal surgery. Aqueous solutions of tetracyclines are highly acidic and may therefore represent a suitable substitute for citric acid. Furthermore, tetracyclines react with dental hard tissues to from long-lasting antimicrobial compounds, and they have a retarding effect on pellicle and plaque formation and an antienzymatic effect. The alveolar bone around mandibular premolars was surgically reduced up to 6 mm from the cementoenamel junction in two beagles. The denuded root surfaces were exposed to the oral environment during 3 months without plaque control. Regenerative surgery was then carried out, using root surface conditioning with 1% tetracycline and coronally repositioned flaps. Six months later, histologic evaluation showed connective tissue attachment extending to the cementoenamel junction in most of the specimens. Superficial root resorption was prevalent in the cervical region, below which a collar of replacement resorption partly surrounded the roots in a characteristic manner. Morphometric analysis showed that attachment gain was similar to that obtained with citric acid in a preceding series of seven dogs. These preliminary results indicate that connective tissue attachment gain after topical use of tetracycline is similar to that obtained with citric acid. In addition, the antibacterial capacity and biological effects of tetracycline warrant further study of its possible clinical use in periodontal reconstructive surgery.