14: Mandibular Subperiosteal Implant Surgery

CHAPTER 14 Mandibular Subperiosteal Implant Surgery

COMPLETELY EDENTULOUS DESIGNS

Preventing injury to mental or dehiscent mandibular nerves is important. The implant design should be selected with care in advance (Fig. 14-2), and if any question of dehiscence arises, a tripodal infrastructure (discussed later in the chapter) should be planned.

The more complex impressions are made in several parts. The surgeon, therefore, should have the materials and equipment on hand to make an index so that the segments of the impression can be assembled accurately. Tissue thickness measurements are obtained so that the laboratory can construct a casting with abutments that have accurate cervical height.

The laboratory also must receive a good surgical centric recording that relates the bony mandible to the cranial base, or the implant abutments may be placed in incorrect and unusable positions. Complete mandibular implants should not be made in opposition to natural maxillary dentition.

Procedure

Before beginning surgery, the surgeon should examine the intact mucosa that covers the mandible. The sublingual adnexa are palpated (i.e., sublingual glands, mylohyoid and genioglossus muscles, plicae sublinguales, Wharton’s ducts). These adnexa usually lie above the ridge crest. The vestibules often are ill defined, and a mucosal linea alba is seen at the ridge crest (Fig. 14-3).

Bilateral mandibular block anesthesia is used. Local infiltrations in the form of long buccal blocks and infiltrations deeply into the anterior area also should be used. These infiltrations create profound anesthesia, so that aggressively made flaps can be reflected fully for properly designed implants. The limit for the average adult is eight ampules of 2% lidocaine for the first hour. Subsequent injections are administered only after the solutions given at the outset have been absorbed.

After administering the anesthetic but before making an incision, the surgeon uses a sharpened periodontal millimeter probe to measure the thickness of the mucoperiosteum at the four to six potential permucosal sites (points of implant after emergence) on the linea alba. These measurements are recorded on a chart.

Incision

A Bard-Parker (BP) No. 15 blade is used to trace the linea alba, a fine white scar on the crest of the ridge that results from the trauma of past extractions and denture wearing. The incision starts at one retromolar pad and proceeds around the arch to the contralateral side (Fig. 14-4). If the radiograph shows that the mental foramina are at or near the crest of the ridge, the incisions are curved slightly lingually to avoid injuring the emerging neurovascular bundles. In addition, a vertical relieving incision is made just lateral to the labial frenulum. Incisions are made directly to bone so that they need not be retraced.

Reflection

A sharp periosteal elevator is used to reflect the mucoperiosteum. Full-thickness flaps are elevated carefully. If the flaps resist reflection, a BP No. 12 blade is used, hugging the bone, to cut scar adhesions. The following structures must be exposed and visualized:

After vital anatomic structures have been exposed, the two lingual flaps are sutured to each other with 2-0 black silk sutures, which are brought across the dorsum of the tongue. If the tongue slips from beneath these shoestring ties, its lateral border is included on either side in the suturing process. These sutures are tied tightly so that the tongue, floor of the mouth, and lingual flaps are bundled compactly together in the midline and the mandible is well exposed for impression making (Fig. 14-5). The exposed bone is protected with saline-moistened sponges; this creates hemostasis and prevents dehydration of the tissues.

Impression Making

3. Impression material (Surgident’s Neoplex regular) is mixed thoroughly, the tray is loaded with the material, and the implant is seated per rehearsal (Fig. 14-7). It is held firmly in position for 8 minutes. A valuable handling characteristic of this material is that it need not be used until after it passes through its sticky or stringy stages. A puttylike consistency is proper for manipulation.

If the impression is accurate and has a smooth texture, it is set aside while copious saline is used to irrigate and thoroughly debride the host site. If the tray is unsatisfactory, making a new impression best solves the problem; the surgeon should not try to correct the faulty impression. A panoramic radiograph should be taken postoperatively to detect fragments of residual impression material, which are radiopaque. These fragments can be removed during second-stage surgery.

Closure

2. The buccal flap is grasped at the right posterior end of the incision with a Gerald forceps. Closure is performed using 3-0 black silk suture on a FS 2 or C-13 cutting needle (Fig. 14-10) in a continuous box-lock suture (see Chapter 6). The routine postoperative regimen is used (see Appendix G). The patient’s original mandibular denture may be adapted for use as a transitional appliance after it is lined with a tissue conditioner, such as Coe-Comfort or Viscogel.

Implant Design

5. To establish cervical lengths and the height of the bar over the mucosa, 3 mm are added to the tissue thickness measurements. Sufficient space is allowed for cleaning, placement of retention clips or devices, and some implant settling and soft tissue hypertrophy (Fig. 14-12). The laboratory should be instructed to articulate the models and wax and cast an implant of surgical Vitallium in accordance with the outlined design. Bar configurations to accommodate internal clips, Hader clips, O-rings, or other retentive devices must be requested at the time of casting (see Chapter 26). Individual abutments, rather than a bar, may be used if the patient’s prosthetic requirements are best suited by this approach. In such cases, a sturdier infrastructure must be designed to substitute for the rigidity offered by the Brookdale bar.

The patient is recalled for second-stage surgery after 36 hours or in 4 to 6 weeks. Any period between these times results in poor healing.

Jan 5, 2015 | Posted by in Implantology | Comments Off on 14: Mandibular Subperiosteal Implant Surgery
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