Periodontal wound healing in the absence of periodontal ligament cells

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.     

Connective tissue attachment formation following exclusion of gingival connective tissue and epithelium during healing

The present investigation was designed to evaluate the potential for reformation of connective tissue attachment on exposed and planed root surfaces by preventing the dentogingival epithelium and the gingival connective tissue from interfering with healing following periodontal surgery. Following the elevation of soft tissue flaps, the buccal and proximal alveolar bone of 24 teeth (48 roots) was removed to mid-root level in 6 monkeys and the exposed root surfaces were carefully planed in order to remove the root cementum. Before the flaps were repositioned and sutured, a membrane (Millipore® filter) was placed over the denuded part of the root surfaces of 16 teeth (test teeth) in order to prevent the epithelium and the gingival connective tissue from interfering with healing. The membrane was adjusted to cover the tooth surfaces from midcrown level to approximately l mm apical to the bone crest. No membranes were placed around the remaining 8 teeth (control teeth) before flap repositioning. The animals were sacrificed 6 months after surgery. The jaws were removed and histological sections of test and control teeth including their buccal periodontal tissues were produced. Nine of the test teeth had to be excluded from examination due to technical failures in the surgical procedure or tissue preparation. New cementum with inserting collagen fibers was observed on all remaining 14 test roots. The length of this newly formed fibrous attachment corresponded to approximately 50% of the distance from the apical extension of root planing to the cemento-enamel junction. In the majority of the control teeth no new attachment had formed but a “long” junctional epithelium was lining the root surfaces to the apical extension of root planing. In 3 control roots a small amount of new cementum with inserting collagen fibers was found in the most apical area of root planing. The results showed that the reformation of a connective tissue attachment was considerably favored by the placement of membranes which prevented the dentogingival epithelium and the gingival connective tissue from interfering with healing.     

New attachment formation on teeth with a reduced but healthy periodontal ligament

The present investigation was undertaken to examine whether a new connective tissue attachment will form on previously periodontitis-involved roots when reduced but healthy periodontal ligament tissue persists following periodontal treatment and the epithelium is prevented from migrating into the wound. In each of 4 monkeys, periodontal tissue breakdown was induced around one maxillary and one mandibular second premolar or first molar by placing orthodontic elastics around the teeth. The elastics were kept in situ until about 50% of the supporting tissues had been lost. 3 months following removal of the elastics, the crowns of the teeth were resected. The pocket epithelium and subjacent granulation tissue were excised and the cementum of the periodontitis-involved part of the roots was removed using a diamond bur. The roots were covered with a mucosal flap. The animals were sacrificed after 3 months of healing. The jaws were removed and histological sections of the experimental roots including their surrounding periodontal tissues were produced. The microscopic analysis disclosed that in all roots, new cementum with inserting collagen fibers had formed in the apical portion of the previously exposed root surfaces. It was always in continuity with the original cementum layer apical to the instrumental part of the root and was thickest in its apical portion, becoming gradually thinner in the coronal direction. In the roots, which for the entire length of the study remained covered by the oral mucosa, the extension in the coronal direction of this newly formed fibrous attachment amounted to an average of 1.0 mm with a range from 0.1 mm to 2.6 mm. These findings were interpreted to mean that new attachment is formed by coronal migration of cells originating from the periodontal ligament.     

New attachment following surgical treatment of human periodontal disease

Abstract The present experiment was undertaken to test the hypothesis that new connective tissue attachment may form on a previously periodontitis involved root surface provided cells originating from the periodontal ligament are enabled to repopulate the root surface during healing. A mandibular incisor with advanced periodontal disease of long standing (the distance between the cemento-enamel junction and the alveolar bone crest was 9 mm) was subjected to periodontal surgery using a technique which during healing prevented the dentogingival epithelium and the gingival connective tissue from reaching contact with the curetted root surface. Preference was hereby given to the periodontal ligament cells to repopulate the previously diseased root surface. After 3 months of healing a block biopsy containing the incisor and surrounding tissue was sampled. The histological analysis revealed that new cementum with inserting principal fibers had formed on the previously diseased root surface. This new attachment extended in coronal direction to a level 5 mm coronal to the alveolar bone crest. This finding suggests that new attachment can be achieved by cells originating from the periodontal ligament and demonstrates that the concept that the periodontitis affected root surface is a major preventive factor for new attachment is invalid.     

Citric acid conditioning of roots affects guided tissue regeneration in experimental periodontal wounds

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.     

Histologic evaluation of an allogeneic mineralized bone matrix in the treatment of periodontal osseous defects

The aim of this study was to evaluate the potential of an allogeneic bone matrix to regenerate new bone, cementum, and periodontal ligament around a previously diseased root surface. Four patients with severe chronic periodontitis and teeth with hopeless periodontal or restorative prognoses participated in this study. One tooth with a severe intraosseous defect was selected per patient. At baseline, measurements of probing depth, gingival recession, and clinical attachment level were obtained. Following flap reflection, a root notch was placed at the apical extent of the calculus; the root was debrided, and the allogeneic bone graft material was placed into the defect. After a minimum of 6 months of healing, the teeth were removed en bloc and prepared for histologic examination. Two of four teeth demonstrated regeneration of new bone, cementum, and periodontal ligament. One tooth healed by new connective tissue attachment, and another by junctional epthelium.     

Healing following implantation of periodontitis affected roots into bone tissue

The aim of the present experiment was to study whether new connective tissue attachment can occur to root surfaces which have been exposed to the oral environment and subsequently implanted into bone tissue. Twelve teeth in three beagle dogs were subjected to progressive periodontal breakdown to half the root length by placing cotton floss ligatures around the neck of the teeth. Following crown resection and root hemisection, the teeth were root filled and the roots thoroughly scaled and planed. Each root was extracted and implanted into bone cavities prepared in edentolous areas of the jaws in such a way that epithelial migration into the wound and bacterial infection were prevented during healing. Root implantation and sacrifice of the animals were scheduled to allow for observation periods of 1, 2 and 3 months. The results demonstrated that new connective tissue attachment did not occur to root surfaces which had been exposed to the oral environment, but healing was characterized by repair phenomena, i.e. mainly root resorption and ankylosis. In those areas of the roots where periodontal ligament tissue was preserved following tooth extraction, a functionally oriented attachment apparatus was reformed. The results indicate that in addition to apical migration of junctional epithelium and regrowth of subgingival plaque, the type of cells which repopulate the wound area may jeopardize new connective tissue attachment.     

Evaluation of human recession defects treated with coronally advanced flaps and either enamel matrix derivative or connective tissue. Part 2: Histological evaluation

BACKGROUND: A number of surgical procedures are effective in covering denuded root surfaces. The first paper in this series evaluated the subepithelial connective tissue graft and the coronally advanced flap with enamel matrix derivative (EMD). That paper revealed no significant difference in the percent of root coverage between the two treatments (P = 0.82). There is limited human histological evidence of the type of attachment achieved with these types of procedures. This paper presents a human case report detailing the histological nature of the attachment of these two treatments to the root surfaces previously exposed by recession. METHODS: One patient presented with two hopeless teeth that were randomized to receive either a subepithelial connective tissue graft or a coronally advanced flap plus EMD. The surgery was accomplished in accordance to the protocol previously described. The teeth and a small collar of tissue were removed at 6 months and underwent histological analysis. RESULTS: Histological evaluation of the subepithelial connective tissue graft revealed a connective tissue attachment between the tooth and graft, and no histological evidence of cementum, bone, or periodontal ligament (PDL) and, therefore, regeneration. In addition, there appeared to be some resorption of the dentin adjacent to the graft. Histological evaluation of the coronally advanced flap with EMD revealed new cementum, organizing PDL fibers and islands of condensing bone at a constant distance from the root surface. CONCLUSIONS: The subepithelial connective tissue graft in this study was found to have adhered to the root surface primarily by a connective tissue attachment with some evidence of root resorption. The coronally advanced flap with EMD was found histologically to have all the tissues necessary for regeneration: new cementum, organizing PDL fibers, and islands of condensing bone. These histologic sections strongly suggest that enamel matrix derivative works in a biomimetic fashion by mimicking the natural process of tooth development.     

The potential coronal migration of periodontal ligament tissue following experimental regeneration

The aim of the present study was to determine if the periodontal ligament cells can migrate onto curretted root surfaces following an experimental regeneration procedure. Buccal mucoperiosteal flaps were elevated in all three premolar regions in 5 mongrel dogs. The buccal bone was reduced to approximately 7 mm from its original level on 30 roots. Before the elevated flaps were replaced and sutured, Gore-Tex filters were adjusted to cover exposed root surfaces. No membranes were placed over 10 root surfaces, which served as controls. After 7 weeks of healing, the animals were sacrificed and all the roots were examined for histological evaluation of contralateral experimental and control teeth. With polychrome staining, the new periodontal ligament fibers of the curetted root surfaces were dyed methyl blue and the adjacent gingival collagen fibers were dyed red. On the experimental surface, coronal migration of periodontal ligament cells and connective tissue attachment were identified over long distances of curetted root surface. Periodontal ligament spaces were more prevalent in experimental sites than in control root surfaces. The results of the experiment suggest that the periodontal ligament cells actually migrated onto the curetted root surfaces when a periodontal space was created by physical barriers.     

Connective tissue regeneration to periodontally diseased teeth

The possibility of obtaining new connective tissue attachment to periodontally diseased root surfaces following replaced flap procedure was studied in seven single-rooted teeth from six patients with advanced chronic periodontilis. Mucoperiosteal flaps were raised and supraosseous soft tissues curetted from the lesion. In order to establish a landmark for histological observations located within the periodontal pocket, a notch was made into the root just apical to existing subgingival calculus. A similarly placed notch was used in a previous report (Cole et al. 1980). Following thorough root planing, the flap was replaced and sutured. Four months later block biopsies were removed. The results demonstrated that none of the specimens showed soft connective tissue adhering to the tooth or evidence of new cementum coronal to the notch. A thin junctional epithelium had proliferated to the level of, or beyond the notch. Therefore, among these seven specimens, unequivocal proof of new attachment to diseased root surfaces following conventional full thickness flap procedures was not demonstrated. This is in contrast to the previous report (Cole et al. 1980) wherein new attachment was obtained in all of 10 specimens treated by full thickness flap surgery supplemented with citric acid conditioning of the root surface.     

Healing following surgical treatment and root demineralization in monkeys with periodontal disease

Abstract The aim of the present investigation was to study the potential for new attachment to root surfaces which 1) had become devoid of attachment either by mechanical removal or in conjunction with experimental periodontal tissue breakdown and 2) subsequently had been conditioned with citric acid. Three adult monkeys (Macaca cynomolgus) were used. Periodontal pockets were produced during a 2–6-month period around the maxillary central incisors and first and second premolars and around the mandibular central incisors by the placement of orthodontic elastics. Surgical treatment of the pockets was carried out with the use of a flap procedure. During surgery, the roots of the premolars on the right side of the jaws were first scaled and planed and subsequently treated with citric acid. Citric acid conditioning was not performed on the premolars of the left side. In the front tooth regions the surgical treatment included citric acid conditioning of the mandibular central incisors in two animals and of the maxillary central incisors in one animal. Surgical procedures were also carried out around the mandibular second premolars and first molars which had not been exposed to periodontal tissue breakdown. Folio wing flap elevation, the buccal bone plate was mechanically removed within an area corresponding to that of bone loss produced by the experimental periodontitis model in the maxillary premolars. The cementum layer of the surgically denuded portion of the roots was removed by root planing. In all treated teeth, a notch was prepared in the buccal root surfaces at the level of the alveolar bone crest. Six months following treatment the animals were sacrificed and histologic sections prepared. Linear measurements were made along the root surface from the apical border of the prepared notch to the apical termination of the junctional epithelium and to the crest of the alveolar bone. The results demonstrated that cementum formation and new connective tissue attachment did not occur on root surfaces previously exposed to periodontal pockets and subsequently subjected to scaling and root planing or on root surfaces surgically deprived of their supporting bone and previously “non-exposed” cementum layer. Cementum formation and new connective tissue attachment also failed to occur following citric acid conditioning of root dentin surfaces. In all sections representing all three treatment groups, the attachment between the gingiva and the root was established by epithelium.     

Connective tissue reattachment as related to presence or absence of alveolar bone

The present study was designed to examine if alveolar bone, located adjacent to a root surface deprived of its periodontal ligament and cementum layer, can stimulate the reformation of a connective tissue attachment. The maxillary and mandibular incisors in 3 monkeys were extracted. Immediately after tooth extraction, the buccal root surfaces of the incisors from the left side of the jaws were planed by means of curettes to a level corresponding to half the root length. All teeth were then reimplanted into their original sockets. However, before tooth reimplantation, the buccal alveolar bone plate was removed in 2 of the monkeys to a level corresponding to half the depth of the sockets. The animals were sacrificed 6 months after the reimplantation procedure. The jaws were removed and histological sections of the experimental teeth and adjacent periodontal tissues were produced. The sections were analyzed in the microscope and subjected to histometric measurements. The results demonstrated that, irrespective of the presence or absence of alveolar bone, a fibrous reattachment failed to form on that part of the reimplanted teeth which had been deprived of their periodontal ligament. This indicates that alveolar bone located adjacent to a root surface may have limited influence on the biological conditions which determine whether periodontal healing results in connective tissue reattachment or new attachment.     

Human histologic evaluation of bioactive ceramic in the treatment of periodontal osseous defects

This study examined the healing of intrabony defects around 5 teeth treated with bioactive glass ceramic (PerioGlas). Healing was evaluated by clinical measurements, radiographic observation, and histologic analysis. The protocol included a presurgical phase of scaling and root planing therapy, with measurements obtained immediately prior to the surgical procedures and after 6 months of healing. Following therapy there was a mean of 2.7 mm of probing depth reduction, 2.2 mm of clinical attachment gain, and 0.5 mm of recession. The histologic analysis revealed healing by a long junctional epithelium with minimal new connective tissue attachment to the teeth, except in one case where the intrabony region demonstrated new cementum formation and new connective tissue attachment. Graft particles were found to be biocompatible, as evidenced by being embedded in a stroma of dense connective tissue with minimal inflammatory infiltrate. There was minimal new bone formation limited to the most apical borders of the defects. No signs of periodontal regeneration as defined by new cementum, periodontal ligament, and bone formation on a previously diseased root surface were observed. Although the clinical results are encouraging and radiographs evidenced radiopacities within the defects, histologic analysis revealed that as a periodontal grafting material, bioactive glass ceramic has only limited regenerative properties.     

Immunohistochemical study of bone sialoprotein and osteopontin in healthy and diseased root surfaces

BACKGROUND: Periodontal disease is marked by inflammation and damage to tooth-supporting tissues. In particular, damage occurs to factors present in cementum that are thought to have the ability to influence the regeneration of surrounding tissues. Bone sialoprotein and osteopontin are major non-collagenous proteins in mineralized connective tissues associated with precementoblast chemo-attraction, adhesion to the root surface, and cell differentiation. The purpose of this investigation was to determine whether the expression and distribution of bone sialoprotein and osteopontin on root surfaces affected by periodontitis are altered compared to healthy, non-diseased root surfaces. METHODS: Thirty healthy and 30 periodontitis-affected teeth were collected. Following fixation and demineralization, specimens were embedded in paraffin, sectioned, and exposed to antibodies against bone sialoprotein and osteopontin. Stained sections were assessed using light microscopy. RESULTS: Bone sialoprotein was not detected in the exposed cementum (absence of overlying periodontal ligament) of diseased teeth. In most areas where the periodontal ligament was intact, bone sialoprotein was detected for healthy and diseased teeth. For teeth reactive for bone sialoprotein, the matrix of the cementum just below the periodontal ligament was moderately stained. A similar immunoreactivity pattern for osteopontin was observed. CONCLUSIONS: The absence of bone sialoprotein and osteopontin staining along exposed cementum surfaces may be due to structural and compositional changes in matrix components associated with periodontal disease. This may influence the ability for regeneration and new connective tissue attachment onto previously diseased root surfaces.     

Connective tissue regeneration to periodontally diseased roots, planed and conditioned with citric acid and implanted into the oral mucosa

This investigation used autogenous submucosal implants of root sections to study the connective tissue healing to periodontally diseased roots which had previously been planed and demineralized with citric acid. Eighteen implants were performed, with each being removed 2 to 24 weeks after implantation. The results showed new connective tissue attachment to the old cementum and to the dentin. After 18 weeks, in all specimens new cementum had formed on the dentin, with collagen fibers attached to it. No deposition of new cementum on the old cementum was noted. The formation of new cementum on roots placed in an environment without periodontal ligament cells might be ascribed to the inductive principle of demineralized dentin. The results suggest that a diseased root which has been planed and conditioned with citric acid is likely to form a new connective tissue attachment, even if it is placed in an environment without periodontal ligament cells. They also suggest that the factor inhibiting potential new connective tissue attachment is the condition of the root surface, rather than the lack of an adjacent progenitor cell population.     

Effect of citric acid conditioning on fibroblast cell density in periodontal wounds

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.     

Periodontal attachment responses to surgical injury in the cat. Removal of buccal bone with and without placement of foreign body at ligament periphery

Recently, PDL progenitor cells were claimed essential for the establishment of new connective tissue attachment to root surface. To further test new periodontal attachment after surgical injury, portions of the buccal alveolar plate were removed from the canines of 4 cats. Removal of bone was carried out with or without removal of the underlying PDL, and in half of the experimental sites, dental amalgam was placed at ligament periphery. Tissue blocks were prepared for routine histologic evaluation (H & E) and specific collagen stains (Mallory Trichrome and Mallory PATH). Exfoliation of amalgam was noted in 6 experimental sites during the healing period. At all sites, plaque accumulation and marginal gingivitis were observed before sacrifice. Histologic observation demonstrated limited new connective tissue attachment to root surfaces at PDL periphery where bone, PDL and cementum had been removed. Where PDL was retained, connective tissue attachment was present which appeared to be the result of fiber interdigitation between root-inserted fiber ends and gingival wound edge fibers. "Blockage" of PDL cell migration by amalgam could not be well controlled. However, the placement of amalgam seems to have interfered with new connective tissue attachment and/or cementogenesis. In 5 specimens, root resorption had progressed into dentin. At these sites, collagen tufts appeared to arise from dentin. These tufts were in intimate contact with zones of dense inflammatory cellular infiltrate and connective tissue elements. We suggest that this observation may be a further tissue response to injury, namely: root resorption with the unmasking of dentinal collagen, which may finally lead to fiber interdigitation.     

Healing of periodontal connective tissues following surgical wounding and application of citric acid in dogs

Topical application of citric acid to a root surface which has been scaled and root planed results in exposure of collagen fibrils of the dentin matrix. The purpose of this study was to examine the healing of gingival connective tissue adjacent to a root planed and subsequently acid conditioned root surface and to determine whether the exposure of dentin or cementum matrix collagen would facilitate the reestablishment of an attachment between the healing connective tissue and the root surface. Full thickness flaps were raised and labial alveolar bone removed over maxillary incisor roots of seven Labrador retrievers. The exposed root surface was planed before etching with citric acid (pH 1) for 3 min. The flap was then repositioned at its original level. Block sections were obtained after 7, 14, 21 and 42 days and the interface between the root surface and the healing wound tissue studied by light and electron microscopy. Compared to conventional flap surgery in the same animals, application of citric acid to the instrumented root surface resulted in an improved rate of connective tissue healing as well as a rapid and consistent reestablishment of connective tissue attachment through extensive interdigitation of new and old collagen fibrils at the tooth-gingiva interface. Subsequent reinforcement of the established connective tissue attachment included recalcification of the acid-affected dentin and deposition of new cementum.     

Healing following reimplantation of teeth subjected to root planing and citric acid treatment

The aim of the present study was to examine the effect of citric acid treatment on periodontal healing around teeth which were extracted, root planed and then reimplanted. Maxillary incisors and mandibular incisors, premolars and molars of 5 monkeys were used. The teeth were divided into 3 experimental groups. In 1 group, the teeth were extracted and immediately reimplanted into their own sockets. In a 2nd group, the teeth were extracted, root planed to a level corresponding to 50-75% of the root length and then reimplanted. In the 3rd group, periodontal breakdown extending to 50-75% of the root length was first induced by placing orthodontic elastic ligatures around the teeth. They were then extracted and root planed and transplanted into the sockets of the contralateral, periodontally healthy teeth which had just been extracted. Half the number of the teeth of groups 2 and 3 were treated with citric acid before reimplantation or transplantation. The animals were sacrificed after 6 months of healing. The jaws were removed and histological specimens prepared for microscopic examination. With the exception of a limited coronal regrowth of new cementum in the apical part of the planed portion of a few roots, connective tissue attachment failed to reform on most root surfaces deprived of their periodontal ligament tissue. Healing was most frequently characterized by root resorption and ankylosis. These were the most predominant features of healing both on root surfaces which had been deprived of the ligament tissue by mechanical means or during a course of experimentally-induced periodontal disease, and occurred in citric acid as well as non-citric acid treated roots. The findings imply that the result of healing following tooth reimplantation or transplantation is determined by the type of cells that repopulate the wound area adjacent to the denuded root surface.     

Regeneration of surgically removed buccal alveolar bone in dogs

The aim of the present study was to examine if the establishment of a new fibrous attachment to the root surfaces is accompanied by regeneration of surgically romoved buccal alveolar bone.
The experiments were carried out in two dogs with healthy periodontal conditions. The marginal 5–7 mm of the buccal alveolar bone between the mesial and distal line angles of each root of one maxillary second and one mandibular third premolar in both dogs was removed after elevation of a muco-peristeal flap. During this procedure attempts were made to minimize the mechanica injury to the root cementum and the supraalveolar connective tissue attachment. A notch was prepared in the root surfaces at the level of teh surgically esablished bone crest. This notch served as a landmark for measurements to be made in histological sections. The flaps were repositioned and sutured with interrupted mattress sutures. During the entire experimental period, meticulous plaque control was maintained. In each dog. the contralateral teeth served as non-treated controls. The animals were sacrificed 8 months after sugery and sections of all test-and control areas prepared for light microscopic examination.
The results of the study demonstrated that in all experimental areas, new cementum formation and fibrous reattachment occurred in the supraalveolar area between the marginal bone crest and teh junctional epithlium. In only two out of eight test areas did the alveolar bone regenerate to or close ot the normal distance from the apical portion of the junctional epithelium whereas in the remaining six areas, a long supracrestal connective tissue attachment was present.