wound healing after mucoperiosteal surgery in the cat

0099-2399/96/2210-0507503.00/0 JOURNAL OF ENDODONTICS Copyright © 1996 by The American Association of Endodontists

SCIENTIFIC ARTICLES

Printed in U.S.A. VOL. 22, NO. 10, OCTOBER 1996

Wound Healing after Mucoperiosteal Surgery in the Cat

Knut A. Selvig, DDS, PhD, and Mahmoud Torabinejad, DMD, MSD, PhD

The purpose of this study was to examine possible tissue-dependent differences in rate of healing after mucogingival flap surgery. After intrasulcular incision and a vertical-releasing incision distal to the maxillary and mandibular cuspids, buccal, full- thickness mucogingival flaps were raised in four quadrants of 10 adult cats. The triangular flaps were left open for 30 min and then repositioned and sutured. Tissue reactions were studied histologi- cally after 1, 3, 7, 14, and 28 days of healing. Al- though new collagen occasionally was observed in the wound space in the free gingiva at 3 days, collagenous union between the cut dentogingival fibers and the flap seemed well established at 7 days. Flap reattachment to the denuded cortical bone was seen at 14 days in the region of the attached gingiva. In the region of the alveolar mucosa, however, residual coagulum and inflammatory reaction was present as late as at 28 days in several specimens. These observations indicate a marked difference in rate of healing among the different interfaces involved. These variations seem to be related to variations in size of the resulting wound space when a full-thickness mucoperiosteal flap is readapted over cervical root surfaces, alveolar bone crest, and denuded cortical bone, respectively.

When nonsurgical root canal therapy fails or is impractical, periradicular surgery is attempted to save teeth. This procedure includes incising and reflecting a mucoperiosteal flap, exposing root end(s) by removal of the overlying bone, root-end resection and cavity preparation, as well as placement of a root-end filling material. The normal architecture of tooth-supporting structures may change as a result of both the pathological process in periradicular tissues and the surgical procedure.

507

The wound healing process after periodontal flap surgery has been described in some detail in the periodontal literature, with particular emphasis on reattachment of gingival tissues to the exposed cervical root surface and the occurrence of bone resorption that may reduce the height of the alveolar crest (1-9).

The healing process after nonsurgical and surgical endodontic therapy has been less extensively studied. In the endodontic surgical procedure, the soft and hard tissues of the periodontium are subjected to incisional, dissectional, and excisional wounding. Harrison and Jurosky (10-12) have recently, in a series of studies in monkeys, examined the healing responses of the periodontal tissues to surgical wounding. Clot formation and migration of polymorphonuclear leukocytes and macrophages into the wound space occurred within 24 h. In the period from the first to the fourth day after a vertical or horizontal incision, the number of polymorphonuclear leukocytes in the wound space decreased and the concentration of macrophages increased. Within 2 days, a multi- layered epithelial seal was formed and within 4 days an epithelial barrier had been established. At 14 days, junctional and sulcular epithelia seemed normal and, at 28 days, all biological events in the wound-healing process were completed (10).

Healing responses of periodontal tissues seemed somewhat slower after the blunt dissectional wounding that results from the reflection of surgical flaps than in the incisional wound (11). Periosteal cells did not survive the flap reflection procedure. Col- lagen fibers of the periosteum appeared depotymerized, but remained attached to the cortical bone. It was hypothesized that this may have protected the bone surface against resorption and contributed to rapid reattachment of flapped tissues to cortical bone.

In a third study, Harrison and Jurosky (12) examined osseous wound-healing responses in experimental defects created in the cortical plate and subjacent trabecular bone. The coagulum that initially filled the defect was replaced by granulation tissue ema- nating from the endosteal tissues. Formation of new bone within the osseous defect proceeded from the deeper internal surfaces, and within 14 days new bone trabeculae filled most of the defect. At 28 days, more mature bone trabeculae were present and a cortical plate was being reformed.

The purpose of this study was to examine reattachment of mucoperiosteal flap tissues to the cervical root surfaces and the denuded surfaces of the alveolar process in the cat.

508 Selvig and Torabinejad

M A T E R I A L S AND M E T H O D S

Animals

Ten adult cats, weighing 6 to 8 lb, were used. The animals were housed individually and were fed with cat chow and water.

Surgical Procedures

Each cat was anesthetized by an intramuscular injection of 40 mg/kg body weight ketamine hydrochloride (Fort Dodge Labora- tories, Inc., Fort Dodge, IA) and 1 mg/kg xylazine (Miles, Inc., Shawnee Mission, KS). Local anesthesia and hemostasis were obtained by infiltration of 0.5 ml of 2% lidocaine with 1:50,000 epinephrine in the vestibular mucosa at each surgical site. A standardized full-thickness triangular flap with a single vertical incision distal of the cuspid and an intrasulcular incision extending to the distal of the second premolar were raised buccally over the fight and left maxillary and mandibular alveolar processes. After incision and reflection, each flap was retracted for 30 min by placing a wet piece of gauze pad between the reflected flap and the cortical bone surface. The flaps were then reapproximated, sutured by three interrupted, plain gut sutures, and compressed for 2 to 3 min using saline-soaked gauze pads. The animals were placed on soft diet until killed.

Histological Procedures

Block biopsies, including a jaw segment with teeth and gingival tissues, were obtained after healing periods of 1 day, 3 days, 1 wk, 2 wk, and 4 wk. Two animals were killed/each observation period. After administering anesthesia, each animal was perfused with 10% buffered formalin. A total of 40 specimens, 8 for each observation period, were harvested. Three of the specimens were damaged during gross trimming and were discarded. One-half of the specimens were fixed in 10% formalin for 1 wk, decalcified in 5% formic acid, embedded in paraffin, and sectioned serially in a longitudinal, buccolingual plane. Alternating sections were stained with hematoxylin and eosin and with Sirius Red for collagen. Re- maining specimens were demineralized in EDTA, postfixed in os- mium tetroxide, embedded in epoxy resin, and step serially sectioned with glass knives. These sections were stained with 0.1% toluidine blue at pH 11. Unoperated areas near the surgical sites were fixed, embedded and sectioned as described, and were used as controls.

Histometrics

From each specimen, sections representing a location buccal to one of the roots, as indicated by the presence of the pulp chamber and root canal, were selected for analysis. Histological examina- tion and histometric analysis included measurements of wound dimensions and the distance, if any, between the wound space and the subjacent hard tissues (i.e. the amount of soft tissue attached to the root surface or alveolar process after incision). Also, tissue reactions were assessed using the parameters herein.

EPITHELIAL HEALING

This category consisted of epithelial cell migration, formation of epithelial seal, and formation of epithelial barrier.

Journal of Endodontics

ORGANIZATION OF BLOOD CLOT

This category consisted of the presence of erythrocytes, polymorphonuclear leukocytes, macrophages, fibroblasts, and collagen fibers in the wound space, as well as the width of wound space. These parameters were registered separately at the level of the free gingiva (supracrestally), the attached gingiva, and the oral mucosa. At later stages of healing, the exact width of the original wound space could not be ascertained, and the designation + was used to indicate that the location of the wound space was detectable because of differences in cellular density and composition, as well as fiber orientation or ## to indicate that healing seemed completed.

CONNECTIVE TISSUE HEALING

This category consisted of the presence of extravascular erythrocytes, polymorphonuclear leukocytes, and macrophages in tissues adjacent to the wound space.

HARD TISSUE RESORPTION AND REPAIR

This category consisted of the presence of resorption and repair on the root surface, presence of bone resorption and repair at the crest and on the cortical surface of the alveolar process, and evidence of necrosis.

Three step serial sections from each specimen block were eval- uated. Tissue events were graded following the criteria suggested by Harrison and Jurosky (10): 0 = event absent, + = present (detectable), + + = very evident, and ## = event completed. Where differences among sections existed within a specimen, the more advanced healing grade was assigned. When intersample variations occurred, the range was tabulated. In view of the extent of variation among specimens, a more detailed histometric analysis was not considered appropriate. Eight specimens were excluded from histometric analysis for technical reasons.

For linear measurements, the mean of three sections/specimen was first calculated. Tabulated values represent the mean of all specimen means/observation period.

RESULTS

Generally, the experimental specimens showed that the surgical incision had severed the dentogingival fibers at a distance of 0.2 to 0.5 mm from the root surface. In no instance had the cementum surface been completely denuded. Despite efforts to remove all soft tissue from the bone surface, variable amounts often remained attached to the cortical surface near the bone crest. In the region of the alveolar mucosa, the bone surface generally appeared to have been completely denuded during flap elevation.

Unoperated

Gingival tissues exhibited only slight evidence of an inflammatory reaction that was confined to the marginal region despite the presence of dental calculus and plaque in several specimens. The marginal periodontal ligament (PDL), crestal bone, and vestibular tissues in unoperated areas were free of pathosis. Loss of periodontal attachment was not observed.

Vol. 22, No. 10, October 1996

FIG 1. (A) Normal gingiva in the premolar region in the cat. Note the sharp contour of the gingival margin. (B) Adjacent section stained for collagen illustrating the dense fibrous structure of gingiva, mucosa, and periosteum. Arrow indicates bottom of the extremely shallow sulcus. B, alveolar bone; C, cementum; D, dentin; E, enamel space; JE, junctional epithelium; OE, oral epithelium. Staining: (A) hematoxylin and eosin; (B) Sirius Red. Original magnifications x30.

The gingival margin had a sharply pointed profile in buccolingual section (Fig. 1). There was a very shallow sulcus and, corre- spondingly, a minimal extent of sulcular epithelium. The dento- epithelial junction consisted mainly of junctional epithelium that showed an absence of rete pegs. Inflammatory cell infiltrates in the gingival connective tissue were generally limited to the region immediately subjacent to the sulcular epithelium.

The free and attached gingiva, as well as the cervical part of the PDL, exhibited a dense and well-orientated fiber structure. Indi- vidual dentogingival fibers, which could be traced for a consider- able distance from their insertion in the cementum surface, blended into the connective tissue of the free gingiva or the periosteum at the bone crest. These fibers had a diameter of 5 to 10 /xm at the cementum surface, but tapered to a thickness of 2 to 5 /xm within the gingival soft tissue.

The cortical bone generally had a smooth surface contour; however, large communications between endosteal spaces and periosteum were occasionally encountered. Density and size of Sharpey's fibers and soft tissue fibers attached to the vestibular aspect of the alveolar process were less readily assessed than those of the cementum, because of the orientation of the periosteal fibers that was mainly parallel to the bone surface.

1 Day

At the earliest observation period, some specimens showed artifactual separation of the flap from the underlying bone and connective tissue surface, indicating that the coherence of the

Surgical Wound Healing 509

FiG 2. (A) Wound healing 1 day after crestal incision and reflection and repositioning of a mucogingival flap, (B) Adjacent section stained for collagen shows more clearly the 150- to 300-/~m-wide wound space (W) that separates the repositioned flap (F) from the root-retained fibers and the cortical surface of the alveolar process. B, bone; E, enamel space. Staining: (A) hematoxylin and eosin; (B) Sirius Red. Original magnifications x30.

fibrin clot was insufficient to withstand the trauma during retrieval of the specimens. The gingival margin exhibited a variable profile dependent on whether the incision was located crestally or more intrasulcularly. The wound space was sharply outlined by the cut ends of dentogingival collagen fibers. Width of the wound space in the free gingiva varied widely among specimens, from 10/xm to --300 /xm (Fig. 2), with a mean value of 190/xm (Table 1).

The wound space contained a blood clot, mainly composed of fibrin mesh and erythrocytes and a distinct lining of fibrin along the wound margins. Leukocytes showed higher density in peripheral areas than in the center of the clot, and were also present in adjacent connective tissue walls, indicating active migration. The cellular reactions appeared considerably more intense along the inside of the flap than in the root-attached connective tissue (Fig. 3). One specimen showed extensive macrophage invasion at this early time point. Results of the histometric assessment of cellular reactions in the wound space at the levels of the free gingiva, attached gingiva, and oral mucosa are reported in Table 2.

The wound space over cortical bone also varied in width between specimens (Table 1). A fine layer of periosteal tissue, up to 40 /xm in thickness, was often present on the bone in the area corresponding to attached gingiva, both at 1 day and at later times, whereas complete denudation had been achieved underneath the vestibular mucosa (Fig. 4, Table 3). The vertical extension of denuded vestibular bone surface was somewhat greater in the mandibular specimens than in the maxilla, wherein the base of the zygomatic arch appeared to have limited the vertical dimension of the experimental wounding. Osteocytes within the cortical bone appeared unaffected by the experimental procedure.

3 Days

At 3 days postsurgery, the incisional wound was bridged by an epithelial layer 2 to 3 cells in thickness (Fig. 5), although some specimens exhibited a patent wound surface and necrosis of junctional epithelium (Fig. 6). The coagulum exhibited a variable

510 Selvig and Torabinejad Journal of Endodontics

TABLE 1. Wound healing after reflection and repositioning of a triangular flap

Days Postsurgery

Attached Gingiva Oral Mucosa Free Gingiva

1 3 7 14 28 1 3 7 14 28 1 3 7 14 28

Mean 190 200 + 80 ## 110 80 40 +/## ## 70 40 +/## 200 +/## ±SD 110 120 130 90 70 50 110 50 90 Range

Minimum 10 10 0 10 10 30 0 20 0 0 0 Maximum 300 310 300 300 150 80 220 150 200 380 500

n 8 5 6 6 6 8 5 6 6 6 6 5 6 7 6

Width of wound space (,u.m) in the region of the free gingiva, at tached gingiva, and oral mucosa by postoperat ive period. + - location of w o u n d space detectable, but measurements not possible because of advanced healing; ## - heal ing completed; n - no. of specimens.

FIG 3. (A) Flap tissue and (B) root-retained tissue 1 day postsurgery. There is reduced density of fibroblasts, but minimal inflammatory cell reaction in the root-retained tissue. By contrast, the coagulum attached to the inside of the flap shows marked invasion of polymorphonuclear granulocytes. B, alveolar bone. Hematoxylin and eosin; original magnification ×200.

extent of organization, apparently depending on the width of the wound space. There was a distinct cellular infiltration both in the coagulum and in the wound margins, although a reduced cellularity of the root-attached wound margin was apparent in some specimens. Sections stained with Sirius Red showed indications of collagen within the clot; however, it could not be completely excluded that this represented pre-existing fibers. There was less

advanced organization of the blood clot on the bone surface than in the gingival area and, apparently, limited clot adhesion to bone. Although necrosis of osteocytes subjacent to denuded bone was observed in one specimen, this was not a prominent finding.

1 Wk

At 1 wk, epithelialization of the wound surface appeared complete, although the repaired junctional epithelium varied in thickness and in contour of its basal layer. A fine network of new collagen, as well as distinct fibrous structures, was identified in the wound space. The wound space, however, remained readily identifiable by lower fiber density and more irregular fiber orientation than in adjacent tissue (Fig. 7).

A cell-rich granulation tissue or incompletely organized coagulum was present on the bone surface. Other specimens exhibited more advanced healing also against bone, similar to that seen in the free gingiva.

Although bone resorption was generally absent at 1 and 3 days, most of the 1-wk specimens showed superficial resorption lacunae cresta]ly as well as on the vestibular cortex (Table 3). Undermining resorptive activity was also noted in the crestal area. These processes were of limited extent, and osseous repair was observed in all of these specimens, if not at all resorption sites. One specimen exhibited deep, cervical root resorption extending half-way to the pulp. The defect was filled with epithelialized tissue. This was interpreted as a pre-existing defect and not a consequence of the experimental surgical procedure. Osteocyte necrosis was observed in one specimen. One specimen exhibited new bone and fiber attachment on the outer bone surface near the crest.

TABLE 2. Wound healing after reflection and repositioning of a triangular flap

Days Postsurgery

Free Gingiva Attached Gingiva Oral Mucosa

1 3 7 14 28 1 3 7 14 28 1 3 7 14 28

Erythrocytes + + + + ## ## ## + + + + ## ## ## + + + + + + + + + +/## PMNs + + + + +/## +/## ## + + + + ## ## ## + + + + + +/## Macrophages + + + + / + + + +/## ## + + + +/## ## + +/## + + + + + +/## Fibroblasts 0 0/+ + + ++/## ## 0/+ + + + ## ## 0 0 ++ /## +/## ++/## Collagen fibers 0 0 + + + +/## ## 0 0 + + + + ## 0 0 + + +/## + +/## Fibrous connective 0 0 0 + +/## ## 0 0 + +/## + +/## ## 0 0 + + +/## + +/##

tissue

Cellular events in the wound space. 0 - absent; + - evident; + + - very evident; ## - event completed; PMNs - po lymorphonuc lear leukocytes.

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FIG 4. Fine layer of periosteum (P) remains on bone corresponding to the level of the attached gingiva. The width of the wound space over bone is 100 to 150/~m (between arrows). The space between the flap and the subjacent tissues developed during specimen process- ing and is artifactual. One day postsurgery. Sirius Red; original magnification x 15.

Surgical Wound Healing

FIG 5. Epithelial barrier (arrows) established across the wound space at 3 days postsurgery. Also note massive leukocyte invasion in the fibrin clot (FC), as well as in subepithelial connective tissue. Root- retained fibrous tissue (right) shows low cellularity. Epoxy-embedded specimen, stained with toluidine blue. Original magnification x150.

2 and 4 Wk

At 2 wk, healing of gingival connective tissue and junctional epithelium appeared essentially complete, and little further change could be detected between 2 and 4 wk. The gingival margin in all specimens had a rounded profile, as compared with the more knife-edge profile of the gingival margin on the unoperated, lin- gual aspect. The vertical height of the free gingiva varied between specimens from 900 to 2,000/xm. The original wound space was identifiable at 2 wk primarily by higher cell density and change in fiber density and orientation near the bone crest (Fig. 8). Location of the incision was frequently demarcated by a deep epithelial projection. In two specimens, the basal surface of the repaired

TABLE 3. Bone tissue reactions after reflection and repositioning of a triangular flap

Days Postsurgery

1 3 7 14 28

Osteocyte necrosis 0 1 1 1 0 Crestal resorption 0 0 3 2 6 Crestal repair 0 0 2 1 6 Cortical resorption 1 0 6 2 4 Cortical repair 0 0 4 1 4 Cortical-retained periosteum 3 5 5 3 *

No. of specimens 8 5 6 6 6

No. of specimens showing presence of event. * Not identifiable because of the advanced stage of healing•

junctional epithelium exhibited deep projections, apparently at the site of the healed incisional wound. At 4 wk, gingival fiber structure appeared indistinguishable from that on the unoperated, lin- gual aspect of the same teeth (Fig. 9).

Although fiber repair was very complete at the bone crest, areas of persisting coagulum and inflammatory reactions were present adjacent to the bone surface in mucosal areas in 5 of 6 specimens at 2 wk and in 2 of 6 specimens as late as 4 wk postsurgery (Figs. 10 and 11). Most specimens showed repair of superficial resorption defects in the root surface and on both the periosteal and PDL aspects of the bony crest at 4 wk.

DISCUSSION

This study examined healing after experimental full-thickness flap surgery in the cat. Although no collagen fibers seemed to bridge the incisional wound 3 days postsurgery, a gradual maturation of the granulation tissue could be followed over the 1- to 4-wk observation period. In general terms, the time sequence of wound maturation seemed to follow that described in earlier studies of wound healing in human, monkey, and dog gingiva (1-I 1), as well as in other tissues (13, 14). At 4 wk, density and orientation of connective tissue fibers in the free and attached gingiva appeared completely restored. The gingival margin had, however, not resumed a knife-edge profile at this time.

Epithelial healing is known to occur rapidly in incisional wounds in the oral cavity (4, 10, 11). The results confirmed that this, in particular, is the case in the gingival region. In the present

512 Selvig and Torabinejad Journal of Endodontics

FIG 6. (A) Wound healing 3 days postsurgery. The wound space (large arrows) and adjacent tissue show high cellularity. There is a large clot (small arrows) peripheral to the alveolar process. (B) Detail from adjacent section illustrates absence of junctional epithelium, intense inflammatory cell infiltration, and low cellularity in root-retained connective tissue (*). Stained with hematoxylin and eosin. Original magnifications: (A) ×40; (B) ×150.

FIG 7. (A) At 1 wk postsurgery the location of the wound space (W) is identifiable by high cellularity. (B) Adjacent section stained for collagen illustrates that the collagen content within the wound space is relatively low. Staining: (A) hematoxylin and eosin; (B) Sirius Red. Original magnifications ×25.

FIG 8. (.4) Almost complete repair at 2 wk postsurgery. The wound space is barely identifiable. A large coagulum remains in the mucosa peripheral to the alveolar process (arrow), (B) Adjacent section stained for collagen illustrates low fiber density in the wound supracrestal space (between arrows). Also note absence of bone resorption in this specimen. B, bone; JE, junctional epithelium. Staining: (A) hematoxylin and eosin; (B) Sirius Red. Original magnifications: ~) ×15; (B) ×60.

study, sulcular and junctional epithelium at 1 wk appeared completely repaired, but of immature architecture as judged by variations in thickness and irregular basal contour. Somewhat more rapid healing, including an epitheIial seal on day 1 and collagen synthesis on day 2, has been reported after endodontic flap surgery in monkeys (10, 11). Apparently great care was exercised in those studies to minimize the surgical trauma and to ensure close ap-

proximation of the flapped tissues. However, healing was more variable associated with greater gaping of the wound (11). The present study also left the impression that the rate of healing is closely related to the width of the wound space, although the role of this factor is difficult to evaluate in a cross-sectional study.

Similarly, rapid repair of the incisional lesion in the supracrestal connective tissue seemed to have occurred in all instances. The

Vol. 22, No. 10, October 1996 Surgical Wound Healing 513

FIG 9. (A) Longitudinal section through mandibular first premolar illustrating operated periodontium buccally (left) and unoperated periodontium lingually (right). Tissue structure is indistinguishable from normal at 4 wk postsurgery. The gingival margin, however, has a rounded contour. (B) Detail from adjacent section stained for collagen illustrates regenerated supracrestal fibers. Staining: (A) hematoxylin and eosin; (B) Sirius Red. Original magnifications: (..4) x20; (B) x60.

importance of preserving root-attached connective tissue fibers when an intrasulcular incision is made has been emphasized by several investigators (5, 7, 10). The present study showed pro- nounced cellular reactions on the inside of the flap. The root- attached tissue, by contrast, showed reduced cellularity in some instances. Apparently the nutritional supply to this area had been jeopardized by the crestal incision. This observation is in accord with the finding that, when an excisional wound such as a gingi- vectomy is made along the gingival margin, repair of the marginal gingiva occurs through ingrowth from the mucosal wound margins with very little contribution from the orifice of the PDL (15).

The findings also showed that the rate of healing may vary among closely adjacent locations in the oral soft tissues. The mucoperiosteal flaps had apparently been repositioned exactly to their original position during surgery and were held in place by sutures, resulting in an uneventful healing response in supracrestal

FIG 10. Completed supracrestal repair at 2 wk. Insignificant bone resorption seems to have been limited to the cortical surface (arrows). A large coagulum remains peripheral to the alveolar process (lower left-hand corner). Hematoxylin and eosin; original magnification x50.

soft tissues. At the flap/bone interface (i.e. in the regions of the attached gingiva and the oral mucosa), however, the rate of healing appeared less rapid and varied considerably, as evidenced by residual aggregates of fibrin clot in these regions as late as 4 wk postsurgery. The slowest healing rate was seen over the bone in the alveolar mucosal region. Harrison and Jurosky (11) also noted that healing of mucoperiosteal and osseous tissues after blunt dissection is slower than that of the incisional wound. Others have reported new bone formation 1 wk after flap surgery, unfortunately without specifying the location of osteoblastic activity or whether or not the bone had been completely denuded (9). Hiatt et al. (4) observed bone repair after 2 wk and noted that all new bone formation began at the crest of the alveolar bone.

The slower reparative reaction along the buccal surface of the alveolar process is, presumably, a consequence of the inert nature of this cortical surface. The compact nature of the cortical bone, and consequently the limited nutritional supply to the granulation tissue from this surface, as well as the sparseness of fibers attach- ing the periosteum to the bone that made it very easy to elevate the mucoperiosteal flaps, may account for a poor wound bed for formation and attachment of new collagen fibers. Thus, the poten- tial for adequate response to injury may be less than in the supracrestal region. Recent observations on gingival microvasculature and its regeneration after excisional surgery also indicate that the cortical surfaces of the alveolar process contain few vascular channels and that these contribute little, if at all, to revasculariza- tion of adjacent granulation tissue (15).

514 Selvig and Torabinejad

FIG 11. Evidence of extensive resorpt ion of marginal bone. A large coagu lum persists in the mucosa lateral to the alveolar process (*). 4 wk specimen. Hematoxy l in and eosin; original magni f icat ion ×30.

The presence of a residual fibrin clot over the bone in the alveolar mucosal region as late as 4 wk postsurgery, however, cannot be explained by lack of blood supply but is, more likely, because of a larger size of the initial coagulum in this region.

This study allowed observation of collagen fiber repair in the wound space. Although very little if any stainable collagen was present at 3 days, a fibrous union was well established in the marginal gingiva at 7 days. Because the tensile strength of a surgical wound appears directly related to the collagen content of the granulation tissue that shows a rapid increase beginning ap- proximately the fourth day after wounding (14, 16, 17), it seems unreasonable to remove sutures before 4 days. It should be kept in mind, however, that the rapid establishment of an epithelial barrier and fibrous repair in the incisional part of the wound does not guarantee that the entire surgical flap has become reattached to its bony base.

Bone resorption did not seem to be a major reaction and was, in accord with earlier observations (11), of limited extent and not significantly affecting the crestal height. The short duration of bone exposure and the absence of gingival inflammation before surgery may have contributed to the limited extent of resorption and osteocytic cell death in this study. Loss of alveolar height, which may later be restored, has been frequently reported after both split thickness and full-thickness flap surgery, as reviewed by Wood et al. (6). Obviously, differences between studies may be related to species differences, extent and design of surgical procedure (including extent of bone denudation), as well as other procedural differences.

Journal of Endodontics

Superficial root resorption was observed at 7 and 14 days and resorption defects undergoing repair at 4 wk. The limited extent of root resorption observed was obviously related to the incision technique that in all cases left a layer of root-attached soft tissue protecting the root surface. Earlier investigators have emphasized the importance of preserving a thin layer of epithelium and connective tissue attached to the root surface to prevent apical epithelial downgrowth (5, 10). In this connection it was interesting to note that the inflammatory reaction to the surgical wounding was less intense within this tissue than within the flap tissue. Thus, the root surface was protected from direct contact with the inside of the flap by a relatively inert fibrous layer.

Idiopathic cervical root resorption was a common finding in an earlier study that included animals of varying age and periodontal disease status (18). Its occurrence has been postulated to be related to occlusal trauma, as well as to spontaneous periodontal disease. In the present study, which included animals with a healthy periodontium, only one instance of deep, spontaneous resorption was encountered. Thus, this type of resorption was less frequent than previously reported.

It should be kept in mind that studies of periodontal wound healing have been conducted in a variety of animal species, including humans. Species differences in microanatomy, oral micro- biota, rate of wound healing, and other factors may, thus, represent a confounding factor in interpretation of tissue reactions and in comparing results o f different studies.

In conclusion, this study showed that the rate of healing after mucoperiosteal flap procedures is most rapid in areas where the wound bed consists of soft connective tissue, such as in the region of the free gingiva and in areas of intact periosteal fibers. Reat- tachment of flap tissues to a denuded bone surface seems considerably delayed, compared with healing of the gingival soft tissue incisional wound. The slowest rate of tissue repair occurs in the alveolar mucosal region.

This study was supported in part by a grant from the Norwegian Research Council.

Technical assistance by Rita Greiner-Simonsen is gratefully acknowledged.

Dr. Selvig is a professor in the department of Dental Research, School of Dentistry, University of Bergen, Bergen, Norway; and also in the Advanced Education Program in Periodontics, School of Dentistry, Loma Linda Univer- sity, Loma Linda, CA. Dr. Torabinejad is a professor of endodontics and director of graduate endodontics, School of Dentistry, Loma Linda University, Loma Linda, CA.

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A Word for the Wise

For those aggrieved by litigation, the correct citation to one of the hoariest and better known aspersions on the legal professions is Henry VI Pt. 2 Act IV Scene 2 line 72: "The first thing we do, let's kill all the lawyers." It is spoken by Dick the Butcher to Jack Cade, while planning Cade's Rebellion of 1450. Cade's reply (alluding to the wax seals used in legal documents of the time) was, "Nay, that I mean to d o . . . for I did but seal once to a thing, and I was never my own man since." This may well reflect Shakespeare's own view, for he was often embroiled in litigation.

H. Lancaster

wound healing after mucoperiosteal surgery in the cat

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