Periodontal Repair in Dogs: Effect of Wound Stabilization on
study evaluated a biodegradable polylactic acid matrix as a
Wikesjö and Rolf Nilvéus wound sta-
bilizing implant in reconstructive periodontal surgery. Supra-alveolar circumferential periodontal defects, 5 to 6 mm large, were surgically created around the mandibular premolars in 7 beagle dogs. The root surfaces in left and right jaw quadrants were treated with either heparin or saline. In this model, root surface treatment with heparin compromises periodontal repair and results in a long junctional epithelium and a reduced connective tissue repair to the root surface, whereas saline treatment results in almost complete connective tissue repair. Following heparin or saline treatment a polylactic acid implant was placed on 1 premolar in each quadrant. After 4 weeks of wound healing, the dogs were sacrificed and tissue blocks prepared for histometric analysis. Postoperatively, the implant became exposed and infected in 3 dogs and had to be removed. Therefore, the results reflect the 4 dogs in which healing progressed uneventfully. Connective tissue repair to the root surface in teeth treated with heparin averaged 82% of the defect height. Mean connective tissue repair in teeth treated with heparin and the implant was significantly greater and comprised approximately 99% of the defect height (P < 0.05). Teeth treated with saline either with or without the implant also healed with almost complete connective tissue repair. The results support the importance of wound stabilization in periodontal wound healing. Development of biodegradable implant systems aimed at stabilizing and supporting the healing wound seems a desirable direction for future research in regenerative periodontal procedures. J Periodontol 1990; 61:719-724. Key Words: Tooth résorption; root; dental implants; connective tissue; odontal diseases/therapy; polylactic acid; biogradation; wound healing.
Experimental studies in dogs have demonstrated that when mucoperiosteal flaps are elevated and sutured to cover most of the crown of teeth with extensive periodontal defects, connective tissue repair to the root surface is predictable.1"5 In contrast, when the flap margins are placed and sutured slightly above the cemento-enamel junction (CEJ), healing results in partial epithelialization of the wound.1-6 However, when the flap margins are "anchored" at this level by single interdental sutures luted to the crowns of the teeth, connective tissue repair is comparable to that observed following coronally elevated flaps.6 From these findings it appears that in addition to adequate primary wound coverage, some other measure must be satisfied to enhance connective tissue repair to the root surface. The coronally elevated flap as well as the crown "anchored" flap procedure may offer this additional measure by contributing increased stability to the healing wound. It is generally not feasible to position and secure the flaps School of
with sutures "anchored" to the teeth except in rare clinical situations.7 Other means of establishing wound stabilization, therefore, need to be explored. Various implant materials have been used in periodontal reconstructive surgery.8 The graft materials, whether autografts, allografts, or of alloplastic nature, are mostly granular and may be suitable for use in infrabony and furcation defects but not for wound stabilization in reconstructive surgery of supraalveolar periodontal defects. Polylactic acid is a biodegradable ester polymer developed by Kulkarni et al.9-10 It has been used in orthopedic surgery in various configurations; for example, spun into fibers11 or machined to screws and plates.12 Thin sheets of polylactic acid have been used in periodontal reconstructive surgery13-14 and porous cubes or granules used to enhance the healing of alveolar extraction sites.15'16 The porous material is arranged in a network of randomly sized and positioned interstices which communicate with each other and the outer boundaries of the material. The material is rigid and may be carved to almost any shape. These properties
J Periodontol December 1990
PERIODONTAL WOUND STABILIZATION
seem to be valuable in accomplishing adequate wound stabilization for supraalveolar periodontal defects. The purpose of this study was to histologically evaluate the porous polylactic acid implant material as a wound stabilizing measure in reconstructive surgery of supraalveolar periodontal defects in dogs.
MATERIALS AND METHODS Animals and
Seven young adult male beagle dogs were used. Bilateral circumferential horizontal periodontal defects were surgically created in the 2nd, 3rd, and 4th mandibular premolars (P2, P3, and P4) immediately followed by reconstructive surgery. The defects measured approximately 5 to 6 mm from the CEJ to the margin of the alveolar bone. The defects in P2 were slightly smaller than in P3 and P4. All surgical procedures and dog maintenance followed a standard laboratory protocol earlier described.17 This study was part of an institutionally approved protocol in periodontal wound healing in dogs. Wound
Root surface treatment followed a protocol earlier described.18 Briefly, the root surfaces were carefully instrumented to remove all cementum. They were then isolated with rubber dam and treated with either heparin1" or saline in alternate quadrants. Heparin or saline treatments were carried out as 5-minute continuous drop applications. Overflow of the heparin solution or saline was continuously aspirated. The root surfaces were then allowed to dry for 2 minutes assisted by a gentle stream of air. After removal of the rubber dam, porous blocks of polylactic acid,* carved to a profile similar to the removed alveolar bone, were loosely fitted to either P2 or P4 in heparin and saline treated quadrants (Figs. 1 and 2). The base of the implant material rested on the reduced alveolar bone while its coronal border reached just apical to the CEJ. Every second dog received the implant around the left and right P2 and every other around the left and right P4. Thus, 4 experimental conditions were created: 1) heparin treatment; 2) heparin treatment and polylactic acid implant; 3) saline treatment, and 4) saline treatment and polylactic acid implant. The flaps were sutured to cover the implant, leaving the flap margins 1 to 2 mm coronal to the cemento-enamel junction. Sutures were removed after 7 to 10 days. A broad spectrum antibiotic* was administered daily for 2 weeks following surgery. Daily plaque control was achieved by irrigation with a 2% Chlorhexidine solution.¡l The dogs were sacrificed 4 weeks after surgery.
-Lock, 10 units/ml, Elkins Sinn Inc., Cherry Hill, NJ (diluted to 1 unit/ml in saline). *Drilac Cube, Osmed, Costa Mesa, CA (6% polylactic acid, 94% air). 5Combiotic, Pfizer Inc., New York, NY. :iHibitane, ICI Ltd., Macclesfield, Great Britain.
Figure 1. The polylactic acid implant material before (A) and after (B) preparation for the implant site. The body of the material is carved to a U-shape (B:a) to fit one interproximal and the buccal and lingual aspect of the defect. Separate blocks are carved to fit the furcation (B:b) and to close the U-shaped block in the remaining interproximal aspect of the defect (B:c).
Histological Procedures Block biopsies including experimental teeth and surrounding soft and hard tissues were obtained at sacrifice. The blocks were decalcified, trimmed, dehydrated, and embedded in paraffin. Serial sections, 7 µ thick, were cut in a bucco-lingual plane throughout each tooth. Every 14th section, approximately 100 µ apart, was stained with Masson's trichrome and an adjacent section with hematoxylin and eosin. Judged by the size of the root canal and the pulp chamber, the most centrally located section was identified for both the mesial and the distal root. This section and the 2 adjacent step serial sections on each side were used for analysis. Measurements were performed at 30X magnification using a microscope linked to a computer aided manual data collection system." The following linear measurements were taken for the buccal and lingual surfaces of each root of the teeth: Defect height: the distance between the apical extension of the root planing and the cemento-enamel junction. Junctional epithelium: the distance from the apical to
'Videoplan, Carl Zeiss Inc., Kontron, Eching bei München, West Germany.
Volume 61 Number 12
Analysis Surface, tooth, Data
and dog means for each of the measurecalculated using the 5 selected step serial sections. Differences for treatments between dog means were analyzed using Student's f-test for paired observations. Differences for treatments between dog means relative to connective tissue repair were also analyzed using the nonparametric Quade test.19 Additionally, the frequency of teeth presenting with root résorption and ankylosis was calculated. Presence of these features in 1 or more sections from each tooth resulted in a positive score. ments were
RESULTS Clinical Observations
Healing proceeded uneventfully in 4 of the 7 dogs. The gingival margin receded to slightly coronal to the CEJ in saline treated teeth with or without the adjunctive biodegradable implant. Similarly, in heparin-treated teeth with the polylactic acid implant, the gingival margin maintained a position coronal to the CEJ. In contrast, in teeth receiving heparin treatment alone the gingival recession progressed apical to the CEJ. In 3 dogs the implant became exposed and the surgical sites infected. The implant had to be removed and the wounds debrided. Thus, the histological observations were limited to the 4 dogs in which healing proceeded uneventfully. Histological Observations Figure 2. The mandibular premolar teeth (P2, P3, and P4) after surgical reduction of the bone and root preparation (A); after fitting of the polylactic acid implant material (B); following wound closure and suturing (C). the coronal extension of the junctional epithelium along the root surface. Connective tissue repair: the distance between the apical extension of the root planing and the apical termination of the junctional epithelium. Cementum formation: the distance between the apical extension of the root planing and the coronal extension of a continuous layer of cementum or a cementum-like deposit on the root surface. Bone formation : the distance between the apical extension of the root planing and the coronal extension of newly formed alveolar bone along the root surface. Root résorption: the combined linear heights of distinct résorption lacunae along the root surface. Ankylosis: the combined linear heights of ankylotic union of newly formed alveolar bone and the root surface. Implant height: the distance between the apical extension of the root planing and the coronal extension of the polylactic acid implant.
Healing features of heparin and saline treated teeth in this study were similar to those earlier reported for these treatments. 17·1 Briefly, heparin-treated defects healed partially with a long junctional epithelium and partially with connective tissue repair. Saline-treated teeth showed almost complete connective tissue repair to the root surface. Regeneration of cementum and alveolar bone was limited and similar for the 2 treatments. Root résorption was observed in all teeth and was often prominent immediately apical to the junctional epithelium. Few teeth exhibited ankylosis. The polylactic acid implant was present in the sections from all implant sites (Fig. 3). The most coronal part of the implant had been resorbed and replaced by connective tissue. The implant often exhibited infiltration of multinucleated giant cells. This cellular activity did not seem to affect the adjacent root surface. However, regeneration of
bone and cementum from the base of the wound seemed inhibited in these teeth. Histometric Observations Mean defect height for the 4 treatments was similar and ranged between 5.0 ± 0.2 and 5.6 ±1.3 mm (Table 1). Mean connective tissue repair to the root surface comprised 98.5% of the defect height, or more, for saline treatment and for saline or heparin treatment in conjunction with the
polylactic acid implant.
PERIODONTAL WOUND STABILIZATION
J Periodontol December 1990
heparin treatment was significantly smaller and averaged 81.6% of the defect height (P