This preliminary study examined the healing following an experimental procedure designed to facilitate coronal migration of progenitor cells from the periodontal ligament circumferentially on roots of premolar teeth in beagle dogs. Mucoperiosteal flaps were reflected on the buccal and lingual aspects of premolars in six beagle dogs with periodontal disease. Following root preparation, pieces of orthodontic wire were placed interproximally on the crowns to bridge the spaces between teeth. Biobrane, a synthetic membrane bonded to a knitted nylon fabric and coated with collagen, was placed as a physical barrier between the roots and the flaps to be replaced. The membrane extended as a single piece from the cementoenamel junction (CEJ) to overlap the crest of alveolar bone by 3 to 4 mm on both the buccal and lingual surfaces of the three premolars in each quadrant. The membrane was attached to the crowns at the CEJ with resin. The flaps were replaced and sutured. Postoperative care included plaque control and the membranes were removed after 5 weeks. The dogs were sacrificed to provide observation periods of 8 and 16 weeks after placement of membranes. Histologic examination revealed new connective tissue attachment in the apical part of the 8- and 16-week experimental specimens. Some experimental specimens showed new attachment up to 2.94 mm while others showed a long junctional epithelium (JE). Root resorption was also seen in some specimens. These preliminary findings suggest that placement of physical barriers between root surface and flaps may be beneficial in facilitating coronal migration of progenitor cells from the periodontal ligament.

The present study was designed to test the hypothesis that during regeneration of cementum, the progenitor cells from periodontal ligament must come in contact with root dentin in order to differentiate into cementoblasts. After reflecting mucoperiosteal flaps, fenestration wounds were made in the buccal cortical plates of mandibular canines in 6 beagle dogs. The exposed root surfaces were curretted to remove all cementum. The exposed root surface on one side was demineralized with citric acid while the contralateral wound had saline treatment. The exposed root surfaces were then dried and pieces of Nuclepore membrane (pore size 0.1 mu) were attached to part of the exposed root surface to prevent contact of progenitor cells with root dentin. The fenestration wounds were then covered with Millipore filter to facilitate the population of wounds by progenitor cells from the periodontal ligament. Histologic analysis was performed after 3 months of healing. In specimens where the Nuclepore membrane had remained attached to root dentin, no new cementum was seen over the membrane. At the borders of the wounds and in specimens where the Nuclepore membrane had detached from root dentin, new connective tissue attachment was consistently seen. Also, root resorption was very rarely observed in both the acid-treated and control specimens. The present findings suggest that contact with root dentin may be necessary for progenitor cell differentiation into formative cells like cementoblasts.

The effect of citric acid conditioning of roots on the formation of a new connective tissue attachment was evaluated in the presence of a selective cell population. Fenestration wounds of standard sizes were made on the buccal aspects of mandibular premolars in 6 beagle dogs. The exposed root surfaces were curetted thoroughly and conditioned with citric acid (experimental) or distilled water (controls) for 3 minutes. The wounds were covered with Millipore filters to facilitate population of curetted root surfaces by cells from the adjacent periodontal ligament. Histologic analysis was made after 3 months of healing. The extent of new connective tissue attachment varied in both the experimental and control specimens. The percentage of surgically denuded root surface showing new cementum with inserting fibers was significantly lower in the experimental group compared with the controls. Root resorption was seen in both experimental and control specimens but involved a significantly larger percentage of denuded root surface in the experimental specimens. Ankylosis occurred more frequently in the experimental group compared with the controls, while no difference was seen in the degree of bone regeneration. The results indicate that new connective tissue attachment can form on denuded root surfaces by a selective cell population. Citric acid conditioning of roots appears to either delay or complicate healing in the presence of a selective cell population.

This experiment was designed to study the ability of mucoperiosteal flap connective tissue to form new attachment on partially demineralized roots as well as nondemineralized roots in a wound-model where periodontal ligament (PDL) cells are absent, and ingrowth of bone granulation tissue is controlled. After reflecting mucoperiosteal flaps, bone was removed circumferentially around the distal root of mandibular second premolars and the mesial root of mandibular third premolars in five beagle dogs. The roots were completely denuded from the cementoenamel junction to the apex and curetted to remove PDL and cementum. Following root canal filling, the denuded roots on one side were conditioned with citric acid while the contralateral roots served as controls. To prevent bone-derived granulation tissue from contacting denuded roots, sheets of Nuclepore membrane were placed over the exposed bone margins and secured in place with steel ligatures. The flaps were coronally positioned and sutured. Histologic examination was made after three months of healing accompanied by regular plaque control. Both the experimental (acid conditioned) and control roots showed epithelium extending into the apical third of denuded roots and root resorption confined to the root apices. Some experimental specimens showed connective tissue adhesion in the apical third of roots without any new cementum or oriented fibers. Inflammatory cell infiltrate was seen extending to the apical third of denuded roots in both groups. In this model, the flap connective tissue cells failed to form new cementum and inserting fibers. Whether this was the result of inflammation and epithelial downgrowth or the inability of flap connective tissues to form new attachment could not be concluded from the study.

The present experiment was undertaken to study the repopulation of curetted root surfaces by fibroblast-like cells in experimental periodontal wounds. 6 beagle dogs were used. After reflecting mucoperiosteal flaps, fenestration wounds were made through the buccal cortical plate exposing roots of maxillary canines in 6 beagle dogs. Exposed root surfaces were curetted to remove cementum and periodontal ligament. On 1 side, the exposed root surface was conditioned with citric acid (pH 1) for 3 min while the contralateral root was treated with distilled water. Millipore filters were placed over the wounds to prevent flap connective tissues from contacting the exposed root surface. Histometric analysis was made 10 days after wounding. Fibroblast-like cells were seen migrating into the fenestration space and were primarily aligned along the root surface. Cell densities measured at the borders and central part of the wound showed significantly lower values (p less than 0.01 and p less than 0.05) in acid-conditioned wounds compared to controls. No significant difference in cell density was noted between the borders and central part of the wound in the acid-conditioned group. In the controls, the cell density at the borders was significantly greater than at the center, suggesting active cell migration from the borders. The present findings suggest that citric acid conditioning of root dentin may result in a low cell density during the early stages of healing in experimental periodontal wounds.