Periodontal disease and the complete dental prophylaxis (Proceedings)

August 1, 2011

Article

Periodontal disease begins as an infiltrate subjacent to the epithelium of the gingival margin and rapidly extends throughout the marginal gingiva to affect the connective tissue underlying both the oral and the sulcular epithelium. In addition, there are pathologic alterations of both the sulcular and the oral epithelium of the marginal gingiva.

Pathogenesis of periodontal disease

There is a significant correlation between deposit amounts and pocket depths and between deposits and hyperplastic tissues with the additional factor of infection by periodontal pathogens. The size of hyperplastic tissue mass and pocket depth increases concurrently as the disease becomes more severe.

Bone loss begins at the bifurcation of the second premolars and around the first premolars. As the disease progresses, the third and fourth premolars and then the first molars become involved. Bone resorption appears sooner and more severely in the bifurcation regions than interproximally. The first and second premolars are the teeth most frequently lost from periodontitis usually exhibiting bilateral symmetry in the disease process. The predilection for bone loss at the bifurcation of totally normal teeth is located at the base of the gingival sulcus and is readily accessible.

The clinical features and pathogenesis of periodontitis is characterized by conversion of the normal gingiva to acutely inflamed, highly vascular, collagen poor granulation tissue. The disease begins as an acute vasculitis upon which a lymphoid cell response becomes superimposed. However, at an early stage, proliferation of the tissues of the gingival margin and the soft tissue wall of the gingival sulcus occurs and enlargement becomes apparent. With the passage of time, this structure, which presents clinically as a rolled margin, enlarges and, in cross section, presents a mushroom-like appearance with a cauliflower-like surface. The structure is comprised of collagen poor, highly vascular granulation tissue with a dense infiltrate of lymphoid cells and a variable population of PMNs - vasculitis persists.

With time, this structure becomes smaller although in general there is a clear line of demarcation between the normal and the disease tissue. Enlargement continues until no normal gingiva remains. During this process, extensive bone resorption occurs. The soft tissues behave in one of two ways, either the hyperplastic granulation tissue remains located near the cemento-enamel junction and a deep periodontal pocket forms comparable to the situation usually seen around human teeth, or alternatively, the soft tissue retreats along the root surface as the bone resorbs. In cases of the latter type, the disease may progress to the point of tooth exfoliation without significant pocket formation.

Gingival anatomy

The total periodontium consists of the connecting and supporting tissues of the teeth. These are the gingiva, periodontal ligament, cementum, and alveolar bone.

The attached gingiva is the part of the oral mucosa that covers the alveolar processes of the jaw and surrounds the necks of the teeth. The gingival sulcus is the shallow crevice or space around the tooth bounded by the surface of the tooth on one side and the epithelium lining the free margin of the gingiva on the other.

The attached gingiva is the most important oral mucosal tissue. It is the first line of defense against periodontal disease, protecting the subjacent bone and supporting tissues. Without an adequate zone of gingiva to maintain support to the tooth and protect the alveolar bone, the crestal and alveolar bone will be lost to disease. The width of the attached gingiva is a very important clinical parameter. It is defined as the distance between the mucogingival junction and the projection on the external surface of the bottom of the gingival sulcus or the periodontal pocket. It is firm, resilient, and tightly bound to the underlying periosteum of alveolar bone.

The facial aspect of the attached gingiva extends to the relatively loose and movable alveolar mucosa from which it is demarcated by the mucogingival junction.

The mucogingival junction remains stationary throughout adult life, changes in the width of the attached gingiva are due to modifications in the position of the coronal end.

The gingival sulcus is the shallow V-shaped space or groove between the tooth and gingiva that encircles the newly erupted tooth, only the junctional epithelium persists. The sulcus consists of the shallow space that is coronal to the attachment of the junctional epithelium and is bounded by the tooth on one side and the sulcular epithelium on the other. The coronal extent of the gingival sulcus is the gingival margin.

Periodontal disease progresses from the marginal gingiva to the gingival sulcus with subsequent reduction and loss of the epithelial attachment. Without the epithelial attachment the underlying alveolar bone and periodontal ligament are destroyed. The loss of supporting bone results in loosening and eventual loss of the tooth.

Plaque

The ultimate and total remission, prevention, or control of all periodontal prophylaxis, disease and surgery is directly controlled by the elimination of plaque. An absolutely plaque free condition is unavailable but all prevention measures succeed with plaque control as does the remission of periodontal disease and the advancement of a proper periodontal surgical end result. Without plaque control all measures and methods will eventually fail.

Microbial plaque is a structured, resilient, yellow-grayish substance that adheres tenaciously to teeth. It is comprised of bacteria in a matrix of salivary glycoproteins and extracellular polysaccharides like glucans (e.g., dextrans, mutans) and fructans (e.g, levan). This matrix makes it impossible to rinse plaque away with water; it must be removed mechanically by means of hand instruments, the toothbrush or other oral hygiene aids. Supragingival plaque and subgingival plaque are two distinct morphological and microbiological entities. Supragingival plaque is seen above the free gingival margin and subgingival plaque occurs below the free gingival margin.

The relationship of plaque is quite clear that "marginal" plaque and subgingival plaque are directly responsible for the initiation and progression of periodontal diseases. It is probable that Supragingival plaque strongly influences the growth, accumulation, and pathogenic potential of subgingival plaque, especially in the early stages of gingivitis and periodontitis. Once the disease has progressed and periodontal pocket formation has taken place, the influence of Supragingival plaque on all but the most coronally located subgingival plaque is minimal.

In the subgingival region it is possible to differentiate between adherent and nonadherent plaque. A dense plaque layer of varying thickness adheres to the tooth (root) surface. The composition of this adherent layer resembles the Supragingival plaque associated with gingivitis: some gram-positive cocci but primarily filaments and Actinomyces species. The adherent plaque can become mineralized to form subgingival calculus.

Calculus

Calculus is calcified plaque. By itself it is not pathogenic, but due to its rough surface it is an ideal substrate for retention of pathogenic microorganisms. Mouth breathing leads to dehydration of the oral cavity, rendering the plaque tougher and stickier. The protective function of saliva is reduced.

Dental prophylaxis

Before dental prophylaxis is undertaken a thorough oral examination of the entire mouth for other problems must be undertaken at this time. Other maladies are noted and prophylactic procedures are begun.

Prophylaxis begins with the gross removal of calculus with either a hand or mechanical instrumentation. Ultrasonic cleaning devices are of three types

1. Those whose functional tips work in a linear pattern

2. Those whose functional tips work in an elliptical pattern

3. The new devices whose functional tips work in a circular 360-degree pattern.

The 360-degree pattern has proven superior to the linear and elliptical patterns. Bacterial ultrasonic debridement of supragingival and subgingival plaque and calculus can be effectively accomplished with the 360-degree functional tip pattern combined with an advanced irrigation systems. Near total debridement of plaque and calculus can be effectively removed without the need for hand instrumentation.

The use of a rotosonic bur (Roto-Pro) placed in a high-speed dental handpiece to remove plaque and calculus has gained some acceptance by a few veterinarians. They are used supragingivally and subgingivally. This method of calculus and plaque removal results in crown and root scarification that is highly plaque retentive. Often tooth damage cannot be removed with dental polishing procedures.

Dental polishing

The majority of veterinary hospitals do not polish teeth after removal of plaque and calculus. Tooth surface irregularities are created to a greater or lesser degree with all methods of plaque and calculus removal. As stated above, these irregularities serve to trap and retain plaque at a much more rapid rate than polished teeth. Polishing is very simple matter. It entails the use of a rubber polishing cup and dental pumice in a slow speed dental handpiece.

The slow speed handpiece can either air or electrically driven. A complete rubber cup and pumice polishing must include the coronal aspect and the subgingival root surfaces of the teeth. Care must be exercised when using the rubber cup on the tooth surface not to create undo heat. Excessive heat can produce pulpal necrosis. This is controlled by having an adequate amount of pumice between the prophy cup and the tooth surface at all times.

Irrigation

The gingival sulcus must then be irrigated after polishing has been accomplished. Current have shown that there is an immediate reorganization of the bacterial component in the gingival sulcus post prophylactically. The pooled bacteria must be flushed from the gingival sulcus as a final prophylactic procedure. The flushing or irrigating device can be either a blunt 18-gauge needle and a 40cc syringe or a Water Pick type device. All solutions are effective for mechanical flushing. They include a fine water stream, saline, a mixture of 50% hydrogen peroxide and water, or a Chlorhexidine solution. Due to its powerful antibacterial effect, Chlorhexidine is the irrigation medicament of choice.

Home care

Home care is daily maintenance to control the formation of plaque and diet control for oral and general health. Companies specializing in veterinary dental products have provided the veterinarian and the consumer with literature that details home care products and procedures.

Proper brushing techniques must be shown to the client. Clients can teach or train their animals to stand for daily tooth brushing. They should be taught how to retract the cheek, place the toothbrush in the mucobuccal fold, brush the lateral surfaces of the teeth. A circular motion debriding the gingiva, gingival sulcus, and the crowns of teeth should be stressed.

The client should not attempt to remove the calcareous deposits themselves with dental scalers or hand instruments available through pet stores. They can create a tremendous amount of damage not only to the periodontium but the tooth surface as well. The end result is a mouth shy dog that will not stand for future routine home care procedures. Prophylaxis is best left in the hands of the veterinarian and his staff.

Periodontal surgery

Periodontal surgery involves a special discipline of dentistry that requires extensive flap management techniques. Surgical treatment modalities are directly related to the degree of bone loss, pocket formation, pocket location and the amount of remaining attached gingiva.

Fact sheet of bacterial plaque from healthy to acute periodontitis

Bacterial plaque contents and types of bacteria vary with individuals: There is a possibility of 200 to 400 different types of bacteria that can be found in the mouth: Bacteria that yield periodontal disease in each individual will vary: When and how much plaque is needed to produce periodontitis is unknown:

A normal healthy mouth has 750 million bacteria per cc of saliva: Bacteria initiate plaque growth by means of their ability to adhere to the tooth surface (pellicle): The supragingival plaque depends upon the interaction of the bacteria surface with the salivary glycoproteins of the pellicle. Strep sanguis and gram-positive rods are the major bacteria, which initiate Supragingival plaque.

After large amounts of plaque develop the type of bacteria shift to filamentous and gram-negative organisms, included are: Streptomyces, Strep sanguis, Staph epidermidis, Rothia dentocariosa, Actinomyces viscosus, Actino naeslundii: There appears to be no marked difference in bacteria composition between the supra and subgingival microflora associated with healthy states. Supragingival plaque control in periodontal healthy states appears to be sufficient to control formation of diseased associated plaque and thereby prevent periodontal disease.

The initial development of gingivitis is a consequence of bacteria associated with an increase of Supragingival plaque formation. Gram-positive filaments and rods mainly actinomyces are the major influenced bacteria producing gingivitis. Gram-negative forms of bacteria follow Actinomyces in later stages of gingivitis. Gram-negative forms of bacteria follow Actinomyces in later stages of gingivitis, these are: Spirochetes, Bacteroides, Fusobacterium, Vibrio and other motile forms.

Gingivitis uncontrolled leads to bone loss and periodontitis; chronic forms of periodontitis show subgingival plaque to contain active Israeli, Actino, Neslundii, Actinomyces viscosus, with various concentrations of Bacteroides melaninogenias, Fusobacterium, Capnocytophaga, Campylobacter and Selenomonas: acute forms of periodontitis microbiota is characterized by gram-negative microorganisms including, Bacteroides gingivalis, Bacteroides melaninogenicus, Wolinella recta, Hemophilus, Capnocytophaga and Selenomonas sputigena. Gram-negative organisms produce this rapid distortion because of their elaboration endotoxins and their ability to invade the adjacent gingival tissue.

Common microorganisms isolated from the healthy and the diseased periodontium

Health

• Streptococcus

• Actinomyces

• Capnocytophaga

• Veillonella

Gingivitis

• Actinomyces

• Bacteroides

• Fusobacterium

• Peptostreptococcus (+ Health)

• Propionibacterium

• Streptococcus

• Veillonella

• Treponema

Periodontitis

• Eubacterium

• Eikenella

• Wolinella (+ Gingivitis)

• Black-pigmented Bacteroides

• Selenomonas

Initial preparation for therapy and surgical periodontics

The term "initial therapy" is used to describe the various procedures used. This is therapy aimed at the etiology of the disease process, while the surgical treatment methods primarily serve to correct morphologic alterations and to provide access to the root surfaces. Six to eight weeks post initial therapy is required to allow for regeneration of tissue. The extent of the periodontal involvement can't be seen. Often after therapy, diagnoses are grossly changed.

After clinical and radiographic examination (if necessary) has been accomplished a thorough and complete prophylaxis is done before a treatment plan can be formulated. One cannot make a treatment plan with surgical intervention for a mouth in an acute inflammatory stage, full of debris and exudate.

Initial therapy (plaque control, debridement, root planing, curettage) is considered to be the most important phase of complete periodontal treatment. In the truest sense it is "casual therapy", since it is etiologic factors that are eliminated. Periodontal surgery is targeted mainly toward correction or elimination of the consequences of the disease process.

In cases of gingivitis (i.e., Grade one, two and the first part of three) initial therapy is usually the only treatment necessary. An exception is fibrous gingiva, which may persist even after inflammation is eliminated.

After initial preparation the dog or cat is sent home and placed on a strict home care routine and reevaluated after regeneration of mature tissue has occurred.

Surgical periodontics

NOTE: There can be bone loss in dogs and cats without pocket formation. The gingiva follows the loss of bone but maintains the anatomical relationship commonly seen in the premolar area of dogs. Surgical intervention is not indicated here. There is marginal modality to eliminate this condition. This condition requires constant home care and veterinary maintenance; often prophylaxis at two to three month intervals.

When pocket formation exceeds the ability to eliminate the sulcular pathogens on a daily basis to prevent progression of the pocket depth surgical intervention is indicated.

In planning a surgical procedure the attached gingiva must be kept in mind. After surgical correction of the pocket a minimum of 1.5 to 2mm of attached gingiva must remain to maintain the underlying alveolar bone.

Indications and methods of periodontal surgery

The choice of a periodontal surgical technique depends on the type and severity of the periodontal disease as well as the pathomorphologic situation at the site to be operated.

Odontoplasty

This is very controversial procedure that should be confined to the removal of dental anomalies such as, irregular enamel projections that are rarely seen on the palatal aspects of upper teeth or ill-fitting margins of crown restorations.

The most commonly taught method of odontoplasty involves the removal of the cervical line enlargement of enamel existing coronal to the cemento-enamel-junction,(CEJ) to eliminate the pocket formed by the crown of the tooth below and the gingiva above the molar teeth that traps plaque. This unnecessary scarification of tooth surface not only creates extreme sensitivity but takes away the natural tooth anatomy that deflects food away from the gingiva during mastication.

Accumulated plaque above or below the crown of any tooth it is removed simply by brushing these surfaces on a routine basis as opposed to tooth mutilation. If tooth structure is removed, it is very important to treat these teeth with topical fluoride to make them less sensitive after the enamel reduction and polishing. Odontoplasty is rarely indicated and should not be abused! If in doubt omit the procedure.

Periodontal surgical procedures may be categorized as:

1. Gingivectomy

2. Flap procedures with conservative flap reflection

3. Flap procedure with flaps reflected completely, permitting various possibilities for flap repositioning

4. Mucogingival surgery

The indication for gingivectomy is limited to cases of pronounced gingival enlargement, shallow suprabony pockets, and localized "minor tissue removal", in combination with flap surgery. It is contraindicated for treatment of infrabony pockets and osseous thickening when attached gingiva is narrow or absent.

Flap procedures with conservative flap reflections are the most universally applicable periodontal surgical modality. It is particularly indicated for treatment of mild to moderate periodontitis.

The fully reflected mucoperiosteal flap is indicated in severe periodontitis with irregular bone loss. In such cases, osteoplasty (alveolar ridge recontouring) may also be performed.

Gingivectomy

Gingivectomy is the removal of gingival pockets by the excision of gingiva. It is also used to recontour the gingival tissue to its proper anatomical form. This procedure is referred to as Gingivoplasty. Gingivectomy or Gingivoplasty can be used in combination with other surgical procedures such as flap operations.

Indications for gingivectomy are, 1) gingival hyperplasia, and 2) shallow suprabony gingival pockets that do not extend beyond the muco-gingival line, while retaining an adequate zone of attached gingiva.

Contraindications include, absence of attached gingiva, horizontal or vertical bone loss below the mucogingival junction or line.

Gingivectomy can be performed with an electrosurgical unit if an abundance of attached gingiva is present. Electrosurgery is best suited for use in cases of gingival hyperplasia where an abundance of gingiva is present and the added benefit of cautery is needed. Most cases of gingivectomy should be performed with sharp dissection.

Gingivectomy procedure

1. Pocket depth is outlined with the use of a periodontal probe on all surfaces of the tooth. The pocket depth is marked with the end of the periodontal probe by punching a hole into the gingiva at the pocket depth creating a bleeding point. This procedure is carried out on all areas requiring gingivectomy.

2. The measured punch marks are connected by sharp dissection using a #15 blade. The blade is placed at an obtuse angle to the long axis of the tooth, producing a beveled incision that post surgically will result in a fine "feathered" gingival margin.

3. The excised gingival is removed with curettes and gingival scalers.

4. A light dental prophylaxis, consisting primarily of rubber cup and prophy paste procedure, should be performed immediately after surgery and again no later than one to two weeks post surgically of extensive gingivectomy surgery.

Flap procedures

This is the most commonly performed periodontal surgery procedure. A reflection of gingival tissue to gain access to the deeper periodontal structures is employed. A full thickness or partial thickness flap is used to gain access to the subgingival structures. The entire soft tissue complex (gingiva, mucosa, periosteum) is separated reflected from the root and alveolar bony surfaces when a full thickness is employed.

Flap procedures are indicated when there is an active pocket that does not respond to initial treatment of curettage, root planing, and home care. These pockets can be located beyond the mucogingival line, with bone loss, and marginal deformity. Flap procedures are contraindicated when gingiva enlargement or hyperplasia is better treated with gingivectomy.

Flap procedures have the advantages of direct vision and access to the pocket or defect for proper scaling and root planing. The pocket epithelium can be eliminated with an internal bevel incision. The flap may be replaced to its original position or repositioned to the residual height of bone. Little or no attached gingiva is actually lost.

Procedure

An internal beveled incision is made severing the sulcular epithelial attachment. This is done with an #11 or #15 blade. The incision line should follow the gingival contour. The gingival flap is reflected following the same gingival scalloped line with a small periosteal elevator. Fine curettes are used to remove remnants of pocket epithelium and granulation tissue. Systematic root planing is performed with repeated irrigation. Root planing is the most important part of both the modified Widman procedures and all other periodontal surgical procedures. Corrections of osseous defects (see osteoplasty below) are performed if needed at this time.

The labial and palatal flaps are closed over the interdental areas without tension using uninterrupted sutures. The flaps are adapted to the underlying bone and the necks of the teeth, using absorbable suture of choice. New "papillae" were created by the scalloped form of the initial incision.

Osteoplasty

Visual access provided by the fully reflected flap can provide access to areas where bone recontouring is necessary. Osteoplasty is used to reshape lost bony architecture or to reverse bony architecture (reverse of normal anatomical contours.

Flap procedure is contraindicated where uniform horizontal bone loss is present throughout the arch.

Osteoplasty can best be performed with the use of slow speed round burs. Sterile saline must be used for cooling during this destructive procedure, as heat is generated even at low speeds.

Bulbous bony margins should be eliminated, especially on the facial surface between the teeth, by narrowing the buccal and lingual cortical plates. This allows subsequent replacement of the soft tissue flaps to conform to the reshaped bone, establishing proper gingival anatomy, with regeneration of physiological morphology of the gingival margin.

Prophylaxis should be performed ten days post surgically. The exposed crown and root surfaces are thoroughly polished using a soft rubber cup and mild prophy paste or dentifrice. It is important to remember that the wound healing processes (regeneration, formation of the junctional epithelium) are not yet complete, and that the prophy paste and rubber cup should not be forced into the sulcular area.

Mucogingival surgery

Mucogingival surgery is performed when there is a need to widen the band of attached gingiva or to cover a denuded root surface. This includes gingival extension without free gingival graft, gingival extension with free gingival graft, and replacement of lost attached gingiva by lateral sliding flap procedures.

The indications for free gingival grafts are cases of gingival recession on single teeth or small groups of teeth beyond the mucogingival line.

Procedure free gingival graft

1. A horizontal incision along the mucogingival line is planned. The rostral and caudal extents of the incision curve apically toward the vestibule into areas where sufficient attached gingiva is present.

2. The assistant pulls on the lip to create tension in the vestibular mucosa. A #15 blade is used to make the horizontal incision 1mm deep along the mucogingival line, without encroaching upon the periosteum. The extent of the incision corresponds to the plan. Hemorrhage as a result of the terminal anesthetic with vasoconstrictor is slight.

3. Mucosal connective tissue and muscle fibers are sharply dissected away from the periosteum. This procedure is simplified by applying tension to the lip. The cutting edge of the scalpel is maintained at an oblique angle to the periosteum. The recipient bed should consist of periosteum freed of all submucosal tissues so that the graft will be firmly attached in the bed when healing is complete. The recipient site, also known as the extension wound should be wider at its apical extent than the planned graft. The free margin of the vestibular mucosa can be affixed to the periosteum apically using absorbable sutures, however this is not mandatory.

4. Sterilized aluminum foil is used to make a pattern the precisely fits into the recipient bed. The apical edge of the pattern should be 2mm short of the apical border of the bed. The foil is placed at the preselected donor site of abundant attached gingiva as seen at the upper and lower canine area, 2-3mm removed from the gingival margin. A scalpel is used to incise around the pattern to a depth of 1mm.

5. The graft is completely freed from the underlying tissue approximately 1mm thick with use of a #15 blade.

6. Hemorrhage of the donor site is generally slight, but if it is persistent, pressure applied over a gauze square will stop it. In the extremely rare instance of excessive hemorrhage, the severed vessel may have to be ligated with absorbable suture.

7. A tissue adhesive such as cyanoacrylate may be applied directly to cover the donor site. After the removal, the graft is placed on a sterile glass or wooden slab next to the foil pattern. The graft is thinned appropriately and trimmed to correspond exactly to the pattern.

8. The finished graft should be held in place on the periosteum for two to three minutes using a moist gauze square under finger pressure. This prevents formation of thick blood clots beneath the graft which would tend to lift the graft from the bed. The graft is sutured with 5/0 absorbable suture.

9. One month postoperatively the graft is usually healed, sufficiently exhibiting the pale color of healthy keratinized attached gingival. Due to shrinkage the graft is about 20% smaller than when placed, but may be expected to remain this size for years without additional change.

Sliding flap

The purpose of this procedure is to cover root surfaces denuded by a gingival defect or periodontal disease, replace lost attached gingiva, or widen the zone of attached gingiva.

Procedure:

1. A rectangular incision, resecting the periodontal pockets or gingival around the exposed tooth extending to the periosteum, including a border of 2 to 3mm of bone rostral and caudal to the root to provide a connective tissue base to which the flap can attach is accomplished. The rectangle should extend apically into the alveolar mucosa to provide space for the zone of attached gingiva. Remove the resected soft tissue without disturbing the narrow zone of periosteum around the root. Scale and root plane all root surfaces.

2. The periodontium of the donor site should be healthy, with a satisfactory width of attached gingiva. Inflammation should be eliminated before the flap operation is undertaken. A full thickness or partial thickness flap may be used; the latter is preferable, for it offers the advantages of more rapid healing in the donor site.

3. With a #15 blade, make a vertical incision from the gingival margin to outline a flap adjacent of the recipient site. Incise to the periosteum of the bone and extend the incision into the oral mucosa to the level of the base of the recipient site. The flap should be sufficiently wider that the recipient site to cover the root and provide a broad margin for attachment to the connective tissue border around the root. The interdental papilla at the caudal end of the flap or a major potion of it should be included to secure the flap in the interproximal space between the donor and recipient teeth.

a. Make a vertical incision along the gingival margin and interdental papilla. Insert a blade into the incision and directing the blade apically. Separate a flap consisting of epithelium and a thin layer of connective tissue leaving the periosteum on the bone. Hold the edge of the flap with tissue forceps and continue the dissection to the desired depth in the oral vestibule. Tailor the margin of the flap to conform to the recipient site and thin if bulbous gingival is present.

4. It sometimes becomes necessary to make a releasing incision to avoid tension on the base of the flap. Tension impairs the circulation when the flap is moved. To do this, make an oblique incision into the alveolar mucosa at the caudal corner of the flap pointing in the direction of the donor site.

5. Slide the flap laterally onto the adjacent root. Make sure it lies firmly and flat without excess on the base. Fix the flap to the adjacent gingiva and alveolar mucosa with interrupted sutures. An absorbable suture may be made around the involved tooth to prevent the flap from slipping apically.