Oversized Osteotomy

Root Forms

The best way to manage problems is to practice avoidance. Most systems, including Nobel Biocare, Biomet-3i, Zimmer, Straumann, Neoss, and Camlog, offer implants of several diameters. If, during placement of a 3.5-mm diameter implant, the dental surgeon discovers that the endosteal threads have been stripped, a larger diameter implant is placed (if the ridge is 6 to 7 mm wide) that successfully retaps and grasps the internal environment of the osteotomy. Nobel Biocare offers a 4.3-mm implant as a replacement if the surgeon strips the bone while seating the standard 3.5-mm size. The Biomet-3i series is available in 3.25 and 4 mm and in larger diameters. An additional advantage of these implants is that they get wider toward the coronal end. The Camlog series 3.8-mm diameter implant has a threaded 4.3-mm backup size. However, a press-fit 3.8-mm implant also is available, and it can be used as a substitute for the stripped threaded implant site (Fig. 28-1).

FIGURE 28-1. Larger diameter implants are important for oversized osteotomies. If an implant does not fit snugly, one with a larger diameter should be used. A, Steri-Oss implant: a press-fit implant was substituted for a stripped threaded implant. B, Integral implant: same design but a larger diameter implant.

Zimmer makes a 3.25-mm, small-diameter (SD) Spline implant, as well as one with a standard 4-mm diameter; both are press-fit implants coated with hydroxyapatite (HA). The larger size is used when frictional grip cannot be obtained with the SD implant.

A helpful hint when Nobel Biocare or Biomet-3i implants are placed in maxillae and in soft mandibles: The countersink and bone-tapping or threading instruments should not be used; rather, because maxillary bone usually is very compliant, the implants should be allowed to tap themselves into position. These systems are technique sensitive. The last two steps (i.e., bone tapping and implant seating) are performed with an ultra-low-speed handpiece or by hand. The threads are fine and closely approximated to one another. An electrical or piezosurgical motor diminishes the tactile sensitivity of even the most skilled surgeon.

If the bone lacks sufficient density to stop the rotation by frictional braking, continuing rotation of the bone tap or the implant itself may strip the internal bony threads. Therefore, the tapping and seating operations are performed with discrimination and care, and a mark on the rotary instrument is used to dictate the exact moment to reverse the motor’s direction.

A safer approach is to stop the motor at a point four or five rotations from final seating and complete the procedure with the handheld ratchet wrench (Fig. 28-2). The wrench is held near its working end to neutralize the great leverage of its long handle. This leverage, if not governed carefully, may be responsible for stripping the internal bony threads. The preliminary efforts at placement are made by attempting to turn the implant with the wheel only (Fig. 28-3). If after all these precautions, the implant does not come to a final and firm stop, it should be removed, and the next-larger diameter implant should be inserted, placed without the formality of bone-tapping or threading devices. Practice and experience help flatten the learning curve.

FIGURE 28-2. If resistance is too great to permit threading with the wheel wrench, the ratchet wrench is used. The greatest control is obtained by holding the wrench near its center and supporting it with the other, countertorquing hand. As leverage increases, tactility diminishes.

FIGURE 28-3. Threaded implant systems supply the clinician with wheel wrenches, which are used in less dense bone for discriminate rotation.

If the osteotomy becomes oversized during insertion of a press-fit or threaded implant from a system without an available larger diameter, the implant should be removed, and some 250-to 500-μm tricalcium phosphate (TCP), particulate HA graft material should be placed against the internal walls of the osteotomy. The implant should be moistened with blood or saline and rolled in the particulate slurry until a thin layer of the slurry clings to it. The implant then is reinserted to achieve a frictional fit. Coverage of the osteotomy site with a guided tissue regenerative membrane (GTRM) can improve the chances of successful osseointegration. A maximum space of 0.5 mm is allowable for this technique (Fig. 28-4).

FIGURE 28-4. Retention of press-fit implants coated with hydroxyapatite (HA) can be improved by moistening them in blood and rolling them in 40- to 60-mesh HA. The adherent particles help wedge the implant firmly into its host site.

Blade and Plate Form Implants

The following suggestions are suitable for one-piece and submergible blades. If the osteotomy is larger than the blade infrastructure, a second Omni or Ultronics blade (these are supplied in “blank” form) should be trimmed longer or deeper to create a frictional fit in the bone slot (if anatomic structures permit). With all non-HA-coated blades, both custom and catalog, primary retention is achieved by bending the infrastructure into a gently curved S pattern. This provides a primary frictional fit by locking the blade into position while the process of osteogenesis takes place. Two titanium-tipped, cone socket pliers are used to bend the blades; very gentle but firm pressure is applied so that the bends are gradual rather than acute (Fig. 28-5).

FIGURE 28-5. A, B, Blade osteotomies, if too wide, may require corrective maneuvers. Titanium-tipped, cone socket pliers can be used to bend gentle irregularities into the infrastructure, providing instant retention.

If the interfacial void is more than 0.5 mm, the use of particulate graft material mixed with demineralized freeze-dried bone (DFDB) is strongly recommended as an osteoinductive grout.

Perforations of Cortical Plates: Root Form, Plate Form, and Blade Implants

When osteotomies are performed for the seating of endosteal implants, whether laminar, grooved, slotted, or cylindric, a perforation is possible, even if the host site is capacious. The perforation, which can be medial, lateral, or apical, can occur because of misdirection of a drill or because of an unexpected anatomic irregularity (e.g., the submandibular fossa beneath the mylohyoid ridge) (Fig. 28-6).

FIGURE 28-6. A constant awareness of anatomic characteristics prevents perforation of the cortical plate, which occurs with no signal to the dental surgeon. After osteotomies are completed and before implants are placed, soundings must be made with a blunt probe.

If the ridge width is inadequate when expansion techniques are started, fracture can occur, with displacement or even loss of the cortical segment. If periosteum is attached to the endangered cortical plate, replacing it after implant insertion and suturing presents a good prognosis for healing. If the fragment becomes detached, it can be wedged back into position, but the prognosis is guarded. If the implant’s diameter prevents replacement, the bone segment should be particulated, and with DFDB used as an expander, it should be applied to the external surface of the defect. The patient’s blood serves as a fibrinous grouting medium. Closure is performed after a resorbable membrane is placed over the entire graft complex.

Plate fracture often is difficult or impossible to avoid. It should be left untreated if no displacement occurs. However, the dental surgeon should always test for perforations. After each osteotomy is completed (for all implant types, including endodontic implants), its integrity is tested with a long, thin, blunt probe (e.g., the Kerr Dycal instrument or a 40-mm No. 50 endodontic reamer). If the tip falls through an inaccessible fault or perforation, it would be wise to cover the area with a membrane (see Chapter 8 ), tease a Colla-Plug over it, or gently tap some synthetic or autogenous bone at the base of the defect. The soft tissues are then closed, bone healing occurs for 6 months, and reoperation is performed. If the mandibular canal is involved, a Colla-Plug is placed gently into the base of the defect to avoid forcing graft particles into the neurovascular bundle. If the perforation is in a visible and operable location (e.g., the labial cortex), the implant is allowed to remain in position, and its exposed portion is covered with particulate bone (preferably autogenous), which can be harvested from the tuberosity. The repair is completed by covering the graft with laminar bone (Lambone), and primary closure is performed.

If an unintentional perforation occurs during preparation of an osteotomy beneath the antral floor, but the tip of the drill does not penetrate or injure the sinus membrane, the implant is placed and allowed to extend beyond the cortex for up to 2 mm, thereby “tenting” the sinus lining. If the implant progresses to integration, it remains in successful equilibrium with its environment. If it fails to integrate, the extension into the cavity space (which offered no additional bony retention) poses the threat of formation of an oroantral fistula (Fig. 28-7). An unintentional perforation is managed in a predictable and acceptable manner, as recommended by the Summers technique (see Chapter 8).

FIGURE 28-7. Antral floor perforations should be avoided. A few millimeters of overextension are allowable, because the sinus membrane can be pushed upward and remain intact. Greater penetration requires instant removal of the implant and primary repair with a pedicle graft.

Air bubbles leaking from the osteotomy indicate perforation into the maxillary sinus (Fig. 28-8). In these cases, an acceptable remedy is deep repair with a Colla-Plug and graft material, followed by placement of a shorter implant. If this appears to be unsatisfactory, a primary closure is made with a buccal (undermined) pedicle graft (see Chapter 7), the flap is sutured over intact bone, and the sinus regimen in Appendix G is prescribed. If osseointegration takes place, no treatment is necessary. If osseointegration fails to occur and a connective tissue interface results, the possibility of maxillary sinusitis arises. The patient should be told about the implant’s proximity to the antral floor, and the symptoms of sinusitis should be described. If the symptoms occur at a later date, the implant’s status is assessed, and if it is failing, it is removed. The communication between the oral and antral cavities is repaired with either a buccal or palatal pedicle graft. These procedures, as well as nasal antrostomy, the Caldwell-Luc procedure, and antral lavage are described later in this chapter.

FIGURE 28-8. To prevent calamitous maxillary sinus complications, the surgeon should test the osteotomy by asking the patient to exhale gently through the nose while compressing the nares. Bubbling indicates an oroantral communication.

Significant bleeding characterizes perforation of the mandibular canal, which can be confirmed by a periapical radiograph with a probe or gutta percha point in place. The best cure for this is avoidance. The following are the four most successful ways to prevent mandibular canal perforation:

If the canal has been entered, as indicated by inordinate bleeding, the implant should not be placed (Fig. 28-9). Rather, the incision is closed, because the nerve may heal spontaneously. If signs of regeneration (i.e., tingling or formication) do not occur within several months, the patient should be referred to a specialist who performs mandibular neurorrhaphy procedures.

FIGURE 28-9. If operative perforations of the mandibular canal are not recognized before implant seating, grievous accidents may occur. Retrieval of this implant becomes an invasive procedure.

(The discussion of surgical anatomy in Chapter 4 details the possible locations of the mental foramina and the peculiarities of the route taken by their neurovascular bundles.) When implants are to be placed in the region of the mental foramen, this structure is exposed so that its position is localized clearly when the osteotomies are performed. Even with viewing, however, the dental surgeon must bear in mind that the bundle often courses forward, anterior to the foramen, for 4 to 6 mm before curving back to its exit (Fig. 28-10, A). In some cases, two or more mental canals are present (Fig. 28-10, B). If the canal is entered or the nerve is injured, the implant should not be placed. Rather, the wound should be closed in the hope that the dysesthesia will correct with time. If the symptoms persist unchanged for 6 weeks, microsurgical neurorrhaphy should be considered.

FIGURE 28-10. A, The location of the anterior mental loop can be very deceiving if the surgeon uses the clinical mental foramen as a guide. B, This panoramic view shows an inferior alveolar nerve that bifurcates before exiting at two separate mental foramina.

If the bone perforation occurs in an area without a vital structure (particularly in the vertical direction) and a decision is made to seat the implant, or if discovery of the overextension occurs postoperatively, the patient is treated with antibiotics. After conditions appear to have stabilized (i.e., amelioration of postoperative ecchymosis, trismus, and edema), the perforation is evaluated.

If the perforation is through the mandibular inferior border, the surgeon should determine whether the implant can be palpated through the submandibular skin and whether it is sharp. If it is, it may cause chronic injury to the overlying musculature. If degloving through the intraoral route cannot be performed, a small skin incision may be required so that the extended segment of the implant can be trimmed with cooled diamond drills until it becomes level with the inferior border of the mandible. If it is not trimmed, the patient should be informed about the condition and asked to await the first recurrent episode of pain or swelling before taking action (Fig. 28-11).

FIGURE 28-11. The inferior border of the mandible must be protected from penetration. Implants that occupy such positions may require removal and Colla-Plug and hard tissue replacement (HTR), or HA repairs may need to be performed. As an alternative, an overextended but otherwise satisfactory implant can be trimmed through a submandibular skin approach or by degloving.

If the perforation occurred through the nasal floor, a speculum with a source of good light is used to inspect the inferior nasal mucosa. If it has been penetrated and the implant can be seen, a method of trimming should be established. This is accomplished intranasally with a diamond drill (Atwood 473) or a pear-shaped bur in a water-cooled, straight handpiece or Impactair. The abraded nasal mucosa heals over the trimmed implant by secondary intention. Trimming also can be accomplished through an intraoral deep anterior vestibular incision. The pyriform aperture is exposed, and the nasal mucosa is elevated with a Freer elevator until the overextended implant can be seen. It is shortened with the same diamond drill. If the nasal mucosa has not been penetrated and the patient does not complain of nasal soreness, the site should be kept under observation until a symptom appears (Fig. 28-12).

FIGURE 28-12. The floor of the nose is another inviolate structure. If an implant pierces the nasal mucosa, it must be removed immediately or repaired by resection of the apex.

Fractured Buccal or Lingual Cortical Plates

Fracture of the buccal or lingual cortical plates can occur with any kind of endosteal implant, but they most frequently happen when the dental surgeon places blades or performs ridge expansion. With this type of fracture, the best choice is to discontinue the implant placement procedure. If the fractured plate appears to be attached to the mucoperiosteal flap, there is a good chance of reattachment and subsequent healing. If the implant achieves firm seating, the procedure might be salvaged with use of a GTRM and bone graft material, precise tailoring and placement of the membrane, and impeccable closure (see Chapter 8).

Inadequate Soft Tissue Flaps for Implant Coverage

After incision and flap reflection, the soft tissue flaps may be inadequate to cover implants, even if the tissues have been handled with great care. If the incision is not made directly on the crest of the ridge through the avascular, white line of scar tissue (i.e., the linea alba), the tissue between the incision and the linea alba may pull away. Novel or unique crestal incisions, such as S-shaped or vestibular visor designs, should not be used. Recent research has indicated that lingual and facial flap capillaries do not anastomose at the ridge crest. Noncrestal incisions, therefore, may result in a loss of vascularity to the tissues of the elevated flaps.

In addition, when implants are placed into a site immediately after tooth extraction or in ridge expansion maneuvers, a scarce amount of the tissue required for primary closure exists. If the implant, whether subperiosteal or endosteal, is bulky enough that the tissues from the facial and lingual sides cannot be brought together, the buccal or facial flap should be undermined. For this technique, a pair of sharp, curved scissors or a Bard-Parker (BP) No. 15 blade is used to elevate the mucosa from the underlying buccinator or orbicularis oris muscle (Fig. 28-13). The mucosal flap is released from its underlying muscle fibers, which allows it to be brought over the implant and ridge crest. Tension-free suturing can then be performed. Closure is done in a continuous horizontal mattress configuration. This technique is outlined in the discussions of suturing in Chapter 6 and of soft tissue management in Chapter 7. Of course, vestibular integrity is lost, and a subsequent vestibuloplasty may be required.

FIGURE 28-13. When implants need to be covered primarily and sufficient tissue is not available, the requisite flap can be obtained by undermining the mucosa from the adjacent buccal muscle surface. This flap can then be sutured without tension.

Broken Burs

Burs can break during the pilot osteotomy in preparation for the placement of any type of endosteal implant. This happens most often when the bur (usually a fissure type) binds in bone. Bur fracture can be prevented when binding occurs. Using the thumb and forefinger, the practitioner should grasp the handpiece beneath its head at the point of bur emission and press the fingers together. The bur is pinched between its head and the bone, forcing it vertically upward and out of the bone in a non-torque-influenced movement. Attempts should not be made to remove the bur by wiggling the handpiece shank; this maneuver is the major contributing cause of bur breakage.

Another technique is to release the bur from the handpiece and facilitate trauma-free removal by rotating the bur counterclockwise with the fingers or Howe pliers.

When a bur breaks, it usually is deep in the osteotomy and possibly close to a vital structure (Fig. 28-14). Several technique-localizing radiographs should be taken, and then simple probing and suction should be tried. If these fail to dislodge the bur, the patient should be told of its presence, but only after completion of the procedure. The patient should be asked to sign a note acknowledging this information. If the patient is sedated, complete recovery must occur before the person is informed and the signature obtained. Aggressive attempts to remove broken burs or instruments destroy potential host sites and may be responsible for injuries to adjacent vital structures. Burs in noncritical areas can remain safely in place for years. Attempts to remove them should be made only if a local reaction is noted on an x-ray film at some later date.

FIGURE 28-14. Burs occasionally break in the bone. This most often occurs when the bur is allowed to bind, and the handpiece is wiggled in an effort to remove it. If the broken bur is not in a critical location, it is best left untouched.

Inoperative Instrumentation

Occasionally, handpieces bind, internal irrigators fail, and suction becomes clogged. The key to solving each problem is to anticipate it, take care of and check all equipment before surgery and, most important and despite the expense, have backup equipment, supplies, and implants on hand at all times.

Hemorrhage

Unusual bleeding may result from soft tissue dissection or intraosseous surgery. If a vessel is bleeding from within the soft tissues, it should be clamped with a fine hemostatic forceps and ligated or electrocoagulated. Often, however, simple tamponade solves such problems (Fig. 28-15). After approximately 5 to 10 minutes of pressure, most small vessels embolize. Firm pressure applied for 5 minutes or longer also usually stops hemorrhage within bone. If not, forcing bone wax into the bleeding site always offers satisfactory results (Fig. 28-16). Gelfoam, Surgicel, and Avitene (spun collagen) also are effective hemostatic agents. Placement of the implant itself into the final prepared hemorrhaging osteotomy often serves as an effective form of management.

FIGURE 28-15. Continued bleeding can be treated effectively by applying pressure with persistence and patience for at least 5 minutes.

FIGURE 28-16. A satisfactory technique for managing bone bleeding is to force bone wax into the osseous site. A, Sterile bone wax is available in individually wrapped packages. B, Small amounts can be used effectively by creating tamponade (i.e., the wax is burnished into the bleeding site with the tip of a periosteal elevator), because this creates tamponade.

If the hemorrhage originates deep in the soft tissues (e.g., the facial artery pulsating from within the buccal musculature), a 2-0 Vicryl suture (on a large half-round needle [40 to 65 mm]) is placed deeply posterior (proximal) to the bleeding site and tied in a figure-8 or circumferential configuration. The suture must encompass a mass of proximal tissue that contains the bleeding vessel within its loop. When the knot is tightened, the surrounding drawn-in soft tissues obtund the bleeding artery.

Life-threatening airway occlusion from hemorrhage or iatrogenic emphysema can occur. All cases involving such a complication require careful intraoperative and postoperative observation. If any question of a compromised airway arises, endotracheal intubation or tracheostomy should be considered. To minimize edema from surgical trauma, the patient should be kept posturally erect and given dexamethasone (e.g., 20 mg, administered intramuscularly [IM] or intravenously [IV], for a 154-pound [70-kg] adult).

Poor Angulation or Position of an Implant

Blade and Plate Form Implants

Poor angulation or positioning of an implant is rarely a problem if the implant is a one-piece device, because blades are made of flexible, resilient, and compliant metals, and their abutments may be bent into positions of parallelism (Fig. 28-17). Titanium-tipped, cone socket pliers are used to bend the implant so that foreign metals are not deposited on the surfaces of the blade. Submergible blades are treated with friction-fit abutment inserts in the same way when they are inserted. However, the adjustment is made before the implant is seated so that if the abutment fractures and cannot be retrieved from its socket, a new blade can be selected. After the neck is bent to achieve parallelism, the abutment is removed and kept until the second stage, when it can be inserted into the infrastructure socket. Because it has the proper angulation, it can serve as a usable, parallel abutment.

FIGURE 28-17. One-stage blade implant abutments may be malaligned. A, Malalignment can be corrected by using two titanium-tipped cone socket pliers to bend the cervix. B, Careful manipulation with controlled effort results in parallelism of the abutment to adjacent implants or teeth.

Some companies offer 15-, 25-, and even 30-degree angulated, threaded abutments. A number of trial seatings with different abutments must be done at the time of surgery until the proper angulation is achieved.

Straight, screw-in abutments present problems when attempts are made to correct angulation. After the abutment has been placed in the implant, gentle bending should be attempted, but only before implantation. If angulation cannot be improved by bending or by use of an angled abutment, correction may be possible after integration by making a casted, telescopic, cementable coping in proper alignment.

Root Form Implants

The guidelines for blades can be applied in making angulation corrections for most root forms that have been placed in anatomically unacceptable positions. If press-fit implants with external threading and without antirotational devices (e.g., Spline) are used with angled one-piece abutments, the abutment is inserted into the implant before it is seated. The implant is rotated to a position that makes the abutment parallel to the adjacent teeth and tapped into its osteotomy (Fig. 28-18). The abutment is unscrewed, replaced with a healing screw, and maintained until integration, when it is replaced into the specific implant from which it had been taken.

FIGURE 28-18. A, Submergible (two-stage) implants may be placed in a nonparallel posture, as shown by these two trial-seating devices. B, Angled abutments are available in 15-degree and 25-degree inclinations. C, Alignment is ensured if correctly angled abutments are used. The abutment must be placed in the implant before it is seated.

Another alternative that can be used after integration is to make a direct impression for casting an angled, frictional-fit abutment that would require cementation. Sometimes placement of implants in the most appropriate position in bone (midway between the facial and lingual cortices) causes their abutments to be located too far to the labial or lingual or to emerge from unstable mucosa. If soreness or inflammation results, this problem can be solved with free palatal tissue grafting (see Chapter 7). In addition, angled abutments are available that can be rotated on the implant’s cervical platform; when appropriately positioned in one of a half dozen fixed stops, it is fastened by its fixation screw into the implant’s internal threading receptacle (see Chapter 22).

As outlined in Chapter 4, the nature and dimensions of the patient’s residual bone determines where, at what angle, and the number of root form implants that provide the best prognoses. Because the angulation of the ridge does not always allow ideal implant trajectories, a problem may exist that classic prosthetic procedures cannot solve. The implants may be canted in eccentric directions that would result in the retaining screws emerging from the labial surfaces of the completed prostheses or at other unacceptable sites when fixed-detachable techniques are the choice of reconstruction.

A more frequently chosen approach to the difficulty of poor angulation is to ignore (within reason) the optimum intraosseous site for implant placement and to insert the implant at an angle that offers the optimum emergence posture. This, however, may result in perforation of one of the cortical plates (management of perforations was discussed earlier in the chapter).

Prevention (i.e., not placing implants if their angulation problem appears to be insoluble), selecting blades or root forms that allow the use of significantly angled abutments, abutments with adjustable necks, angular corrections made with bone-grafting materials, or using subperiosteal implants all are alternatives that help guide operative decisions. Even though accurately made surgical templates should prevent improper placement of implants, occasionally implants are placed too close to one another. The proper distance is a full implant width between each root form (i.e., 3.25 to 5.5 mm). In cases involving closer proximity or poor angulation, the implants should be allowed to remain buried and left unused as “sleepers” (Fig. 28-19).

FIGURE 28-19. Implants placed in awkward positions may be left in position to “sleep” and possibly be put into function in the future.

Injuries to the Mandibular Neurovascular Bundle

When an implant or instrument unintentionally penetrates the mandibular canal, the implant is removed, and the patient is informed of the possibility of dysesthesia. Dysesthesia is less common, however, when infiltration, rather than nerve block, anesthesia is used.

If a nerve has been injured or cut and is within the bony canal, it may heal with time. The chance for healing is less if the injury occurs to a neurovascular bundle in soft tissues, such as the mental branch.

If the dysesthesia has not diminished or changed in depth, nature, or character after 6 weeks, exploration and possible repair should be considered. Although specially skilled oral and maxillofacial surgeons most often perform these procedures, knowledge of this technique is important. If the mental or other soft tissue neurovascular bundle is totally or significantly torn or separated, it should be repaired immediately. The tissues are reflected carefully, already opened, to below the foramen level, exposing the entire nerve complex. The mental neurovascular bundle is moderately resistant to injury, and gentle reflection exposes it fully. The distal portion of the nerve complex is made available, if any of it should be in evidence in the soft tissues lying lateral to the mandible. This gentle, blunt dissection can be easily performed with a mosquito hemostat grasping a moistened, 2 × 2-inch sponge and using a pushing maneuver.

If the proximal bundle offers insufficient length from within the foramen, the periosteum adjacent and posterior to it is elevated to the mandibular inferior border. A small, half-curved, blunted chisel or suitable elevator is inserted into the distal portion of the mental foramen to protect the bundle. A saline-cooled, Impactair or straight air turbine handpiece with a No. 4L round surgical bur then is used to brush the bone from behind the elevator (Fig. 28-20, A). The goal is to extend the mental foramen into the mandibular canal by removing its posterior lateral bony wall. With patience, care, and experience, this can be done with consistency. After 180 degrees of the canal has been removed (Fig. 28-20, B), a nerve hook is slipped beneath the neurovascular bundle so that it can be gently teased from its crypt. Usually, the sheath must be wrested carefully from internal bony spicular attachments.

FIGURE 28-20. Repair of the mentomandibular nerve requires careful tissue management. A, An Impactair with a round bur is used to brush away the bone overlying the canal. B, After exteriorization of the canal, the neurovascular bundle becomes visible. C, The nerve sheath is separated from the bundle, the two cut ends are brought together in an end-to-end anastomosis, and the neurorrhaphy is made with 10-0 black silk ophthalmic sutures. Magnification is essential for this operation. D, A slit polyethylene sheath is placed around the repaired nerve to protect it and to act as a conduit for unobstructed healing. E, The repaired nerve is replaced into the canal. F, Closure of the overlying soft tissue completes the operation.

Once the portion of the nerve bundle that occupied the canal has been extricated, it is made contiguous with the mental branch. After the vascular elements are dissected free, a generous additional length is present to facilitate repair of the nerve that had been sectioned or compressed iatrogenically. If 1 cm of distal (tissue) bundle is available and another 2 cm of the proximal portion can be exposed, an end-to-end anastomosis is made with 10-0 Vicryl or Prolene. At least six sutures are required, and four-power magnification must be used to guide their placement. Enclosing the repaired segment in a polyethylene tube (made from a piece of slit IV catheter) offers additional stability and a mortise form to influence unobstructed healing (Fig. 28-20, C to E). The tube and its contents are tucked into the widened canal, and the wound is closed primarily (Fig. 28-20, F). Positive results may not be seen for 18 to 24 months.

If the length is deficient even after exposure of both ends, a sural nerve graft is arranged.

Elective exposure of the intact bundle is performed when a deeper zone of usable bone is required for placement of a long endosteal implant or a transosteal implant for the posterior mandible.

Loss of Anesthesia

Regional anesthesia occasionally dissipates during stage one if repeated impressions are required. If anesthesia begins to fade before the procedure is finished, reinforcing or reinstituting it becomes difficult because of the change in pH in the surgically exposed tissues. Attempts can be made to supplement anesthesia with additional doses, but the procedure may have to be terminated before its completion. The dental surgeon must keep in mind that no more than eight anesthetic cartridges of 2% lidocaine (or less than 300 mg) should be given to an average weight (154-pound [70 kg]) adult at any one time. Additional amounts can be given with time as the drug is hydrolyzed. Local anesthetics also work more effectively if preoperative analgesics and IV sedatives are used.

Probably the best way to prevent loss of anesthesia is to use bupivacaine (Marcaine) or ropivacaine (Naropin) along with lidocaine at a ratio of 1:1; this combination makes anesthesia last three to four times longer. If anesthesia cannot be re-established, even with the addition of IV sedation, the procedure is halted, the wound margins are closed with sutures, and an attempt is made to complete the operation another day. At least 1 week must pass before the surgeon operates again. This interim allows a greater possibility of success, because a more accurate tray can be made on the model derived from the failed impression.

Inability to Make an Accurate Impression

If a satisfactory bone impression cannot be registered after three attempts, the surgeon should seek help; if that is unavailable, the wound should be closed.

Inability to Remove an Impression or Seat a Tray Either for Full Upper (Pterygohamular Design) or Full Lower (Lateral Rami Design) Subperiosteal Implants

Both pterygohamular and lateral rami designs present the possibility of undercuts that can discourage a path of seating or removal. Sectioning the tray into halves or even into three parts for the mandible may solve this problem, with each of the parts fitting its own area of bone accurately (Fig. 28-21). After the tray segments are placed in position and fitted closely, or even allowed to overlap, they are removed. A number of protruding copper tubes or similar retentive devices are processed with heat or luted to their exterior surfaces. Each segment is filled with impression material and reseated. After the impression material has set, an index is taken over the tubes, using additional tray material to engage them. These indices must be removable. After removal of the tray segments, the retention tubes serve as guides for accurate reassembly with the indices. Suturing the wound completes the procedures.

FIGURE 28-21. When undercuts prevent placement or removal of a one-piece tray during the two-stage subperiosteal operation, the tray can be split into two or more sections, each seated separately, indexed, removed, and collated on the laboratory bench.

Using this technique, the surgeon can make the most complex impressions in sections and place them together for accurate completion of the casting by the laboratory.

Antral Perforations

When the mucoperiosteum is reflected in preparation for a maxillary subperiosteal implant impression, some eggshell-thin maxillary cortical bone overlying the sinus may lift away attached to the flap. The intact antral membrane often is noted; it is bluish gray and expands with each expiration. If it is torn, the margins are brought together gently with a nontoothed forceps, and it is covered with a square of Colla-Cote (collagen sheet) or a resorbable membrane (e.g., Surgicel or Vicryl mesh) (Fig. 28-22). The bone fragment is allowed to remain attached to the periosteum.

FIGURE 28-22. Often during the tissue reflection phase of the maxillary or pterygohamular subperiosteal implant, the lateral sinus wall lifts away with the elevated mucoperiosteal flap. Before closure, a sinus elevation procedure is performed; if that is not appropriate, a sheet of Vicryl mesh or similar resorbable membrane is laid over the defect.

The implant impression is made in the usual manner, with the Colla-Cote replaced as required at each step. On completion, the flaps are brought together with the cortical bone still in place, and the bone is positioned anatomically and sutured. The bone reattaches over the antrum in its proper location. The final casting design must not include struts placed over the repaired area or over any of the eggshell-type cortex overlying the antrum. If this design characteristic cannot be avoided, a sinus floor elevation and graft procedure is indicated (see Chapter 8). These procedures are performed at the first stage or just before implant placement during stage two.

Inaccurate Adaptation of Full or Unilateral Subperiosteal Implants

If an implant fails to go into place, particularly in maxillae, it is tapped with a mallet and an orangewood stick. Often, the implant snuggles into place after tapping because of the compliance of the supporting bony structures. In either jaw, if the implant obviously has been seated to its fullest extent and a rocking movement occurs when it is tested for stability, the fulcrum should be sought and an attempt should be made to adjust it by eliminating a bony protrusion or by cutting away a strut (but only if that strut is a noncritical component of the casting) and the remnants are fixed to the jaws with titanium bone screws. If the rocking cannot be eliminated, a new impression is made. This procedure is simplified by fabricating a tray from the cast on which the discarded implant had been made.

If the implant does not move into/>