When possible, anesthesia for the posterior mandible (see Chapter 4) should be administered only by infiltration. This allows the lower lip to remain unanesthetized, which grants the surgeon the built-in protection of having the patient possibly respond as the neurovascular bundle is approached (Fig. 12-2).

FIGURE 12-2. A conventional, single-stage mandibular blade implant. Bone, connective tissue, or both anchor the infrastructure in place by growing through the interstices. The shoulder is placed at least 2 mm below the ridge crest. Such titanium implants may be adjusted by bending for abutment parallelism.

The incision is made by placing a BP No. 15 blade against bone and, using the fine linea alba at the ridge crest as a guide, drawing the scalpel firmly forward. Care must be taken not to deviate from this critical narrow avascular zone. Novel crestal incisions of any design (e.g., S-type or visor type) that deviate from the crest should not be used, because areas of gingivae included within them may become necrotic. When the incision must be extended distally beyond the fixed gingiva in the posterior mandible and into the retromolar pad, the surgeon must keep in mind the location of the pterygomandibular space and its contents. To avoid injuring these tissues, the surgeon should palpate the anterior border of the ramus and direct the incision over this structure, which often is found about 5 mm laterally.

The incision should be sharp and clean so that it need not be retraced. Retracing the incision creates strips of periosteum that interfere with the gingival and superficial osseous vascular supply (Fig. 12-3).

FIGURE 12-3. Incisions for blades are made in the linea alba at the crest of the ridge.

The incision needs no buccal or lingual relief posteriorly; however, at the anterior end, it should be extended buccally and lingually around the most distal tooth in position. These two extensions offer sufficient relief to allow adequate exposure of the host bone. Reflection of the flaps is initiated anteriorly at the mesial papilla of the most distal tooth and completed by moving the elevator posteriorly (Fig. 12-4). This exposes the ridge to the base of the vestibules buccally and lingually.

FIGURE 12-4. Flaps should be reflected with a sharp periosteal elevator to expose enough bony structure to permit entry of the bur for the osteotomy.

The periosteal elevator should be sharp so that it incises the periosteal fibers rather than tearing them. If these fibers are resistant to the elevator, the full-thickness flap may be lifted with a mouse-tooth (Adson) forceps, and the periosteal fibers can be cut with a No. 12 blade (see Chapter 8).

The ideal location for the osteotomy is at the crest of the ridge. If the ridge is knife edged, it must be flattened (Fig. 12-5). This can be done by placing retractors (beaver tails, blunt rakes, or periosteal elevators) and using a pear-shaped diamond (SFX-30/L) in the high-speed handpiece or Impactair. A minimum width of 3 mm must be achieved.

FIGURE 12-5. Retraction must be sufficient to allow evaluation of the ridge morphology; however, excessive exposure should be avoided. This knife-edged ridge requires flattening with a diamond bur or rongeur forceps.

The operative then site should be inspected, using the following steps.

1. The mental neurovascular bundle is located. It should not be exposed or dissected unless its integrity is threatened by the procedure.

2. The external oblique and mylohyoid ridges, as well as the configuration of the cortical plates inferior to them, are evaluated. Extreme undercuts or exaggerated concavities, such as the submandibular and canine fossae, require redirection or relocation of the osteotomy.

3. The width of the ridge is recorded, not only at the crest but also at all points apically that correspond with the planned depth of the implant. If the ridge is less than 4 mm wide at the deepest part of the planned implant site, the operative plan must be carried out with great care. Perforations of the bone must be detected and treated with grafting materials (see chapters 7 and 8).

4. The nature and quality of the cortex must be established. Its color, consistency, and morphology should be noted, because these elements offer evidence of good local health (i.e., ivory color, free porosities, and properly shaped with minimal irregularities or defects).

5. The condition of the newly reflected mucoperiosteal flaps is assessed. Tears, loss of tissue, and ischemic appearance are recorded. If the flaps are considered irreparable, the surgery should be cancelled or delayed. Chapter 7 explains how to make primary closures when the supply of tissue is absent or the flaps fall short of approximating each other.

Osteotomy

The surgeon is well advised to use a preoperatively prepared surgical template (see Chapter 4 for fabrication details). Once the ridge height, morphology, and width are considered acceptable, the osteotomy site is selected. A No. 1 round bur is placed in the high-speed handpiece, and after the anteroposterior length has been established by measuring the chosen implant, bur holes are made at the anterior and posterior ends of the planned groove.

A saline-cooled, No. 1 round bur is used to make a series of bur holes just through the cortex between the anterior and posterior witness marks, along the crest of the ridge (Fig. 12-6). When this is finished, the alignment and location of the holes are assessed. If they are straight and properly located, they can be connected with a 700XXL fissure bur (Fig. 12-7). Light brushing motions and copious amounts of coolant are important. The shank of the bur is scored at the point that signifies the proper osteotomy depth. Using a firm but light grasp, the surgeon deepens the host site to the score line on the bur. The osteotomy must be deep enough to allow the shoulder to be buried beneath the bone margins to a depth of 2 mm. Any deep irregularities are flattened by brushing the bur gently through the bone groove. The osteotomy is tested with the periodontal probe to assess its depth and smoothness and to check for any cortical plate perforations (Fig. 12-8).