Chapter 3 Surgery of the Edentulous and Partially Edentulous Maxilla
Treatment planning usually is initiated at the restorative dentist’s office. It involves establishing the patient’s goals regarding what the patient wants at the completion of implant therapy. Once these goals have been established, the surgeon is consulted, and an assessment of bone availability is performed.
A panoramic radiograph and physical examination often are sufficient to determine whether satisfactory bone bulk is present for the placement of implants into the maxilla. The panoramic radiograph allows an estimate of the amount of vertical bone available in the premolar and molar regions. A good-quality panoramic radiograph can confirm the presence of adequate anterior maxillary bone for the placement of implants at least 10 mm long. Occasionally, a reformatted computed tomography (CT) scan or complex motion tomogram is obtained to confirm the presence of bone before implant placement. If cross-sectional radiography is planned, a radiopaque stent significantly increases the amount of information gathered. The radiopaque material, typically 20% to 30% barium sulfate combined with a clear acrylic, causes the teeth in the patient’s prosthesis to become radiopaque in the cross-sectional image. This image provides information concerning the relationship of the bone to the desired teeth.
The amount of bone in the anterior and posterior maxillae should be determined. The anterior maxilla consists of the area anterior to the lateral walls of the nose or the anterior border of the sinus. The posterior maxilla consists of the regions of the second premolars and molars. The following four conditions are considered:
A prosthetic plan is completed, with the aid of the restorative dentist, after the amount of bone has been determined. Parel’s classification of the edentulous maxilla is useful for conceptualizing the prosthetic plan (Box 3-1).
|Class I||Only maxillary teeth are missing, but patient has retained alveolar bone almost to its original level.|
|Class II||Teeth and some alveolar bone have been lost.|
|Class III||Teeth and most alveolar bone have been lost to the basal level.|
For the Class I maxilla, a fixed, implant-borne restoration can be fabricated, because the patient has adequate alveolar bone to support the soft tissues and is missing only the teeth. Usually greater than 10 mm of bone height is present in both the anterior maxilla and the posterior maxilla. For a fixed crown and bridge restoration, implants need to be placed within the confines of the teeth of the planned restoration. In addition, implant placement should avoid excessive angulation to ensure that the implants can draw as a single unit. Placement should avoid the embrasure regions to promote an esthetic outcome and oral hygiene. Finally, the implants should be placed 3 mm apical to the gingival margin of the planned restoration to allow the restorative dentist to develop a natural emergence of the crowns from the gingiva. A well-made, detailed surgical template is essential for a fixed crown and bridge restoration. The template should have full palatal coverage with anatomic retention at the hamular notches (posterior maxilla), enabling the stent to be placed in a repeatable, stable, and accurate position that allows the surgeon to follow its prescription when placed into the mouth.
If the patient with a Class I edentulous maxilla desires a tissue-borne overdenture on four implants because of financial constraints, the overdenture bar must avoid an excessive space-occupying design, because the patient is missing only teeth and not alveolar bone.
The Class II maxilla rarely can be managed esthetically with a fixed crown and bridge prosthesis, because this class requires the labial flange of the maxillary prosthesis to support the nasolabial soft tissues. A useful technique for determining the need for acrylic to support the soft tissues is to duplicate the patient’s maxillary dentures and remove the labial flange, leaving only the teeth. The resultant soft tissue profile with the modified duplicated maxillary denture can help the implant team and the patient decide on the treatment plan. In addition, a deficiency of alveolar bone necessitates the placement of implants more apical than is ideal, resulting in excessively long teeth, teeth with pink acrylic, a removable lip “plumper,” or a type of hybrid prosthesis with space between the prosthesis and implants.
A fixed crown and bridge prosthesis, a fixed-removable (e.g., spark erosion or milled) prosthesis, or a type of removable overdenture prosthesis may be prescribed. The fixed implant-borne and fixed-removable prostheses require at least six (preferably eight) endosseous implants to support a maxillary implant-borne prosthesis adequately. Zygomatic implants are the exception (see later discussion). These traditional fixed or fixed-removable prostheses require posterior maxillary vertical bone height for implants placed in the first molar region. The removable tissue-borne prosthesis requires four implants placed into the anterior maxilla to support a bar, which has retentive vertical stress-breaking attachments. All the edentulous maxillary prostheses usually are fabricated with cross-arch stabilization of the left and right implants.
For patients who smoke or drink alcohol heavily or who have uncontrolled diabetes or other systemic diseases that prevent bone grafting, the surgeon’s only option for placing implants is to use the available bone. After a discussion with the restorative dentist, the amount and location of available bone can be determined.
For the patient with adequate anterior vertical bone height and a treatment plan for anterior implants to provide overdenture support, four implants can be placed. Placement of at least four implants is recommended for an implant-supported overdenture in the maxilla, because fewer than four maxillary implants will not predictably resist the forces placed on them (Figure 3-1, A-B, and DVD Figure 3-1, A-F). Two implants are contraindicated to retain a maxillary overdenture.
• FIGURE 3-1 A, Panoramic radiograph showing the placement of four implants to retain a maxillary prosthesis. Often, sufficient bone is present in the anterior maxilla to allow placement of four implants without bone grafting.
• FIGURE 3-1 B, Bar fabricated with ASC52 attachments on its distal aspect. The bar cross-arch stabilizes the maxillary implants and aids mechanical distribution of masticatory forces in this 56-year-old man.
(Prosthetics by Dr. Larry McMillen.)
Preoperative radiographs and a physical examination can reveal the height and thickness of the alveolar ridge. Four implants in the anterior maxilla, often combined with vertical stress-broken attachments placed at the distal aspects, are used to support a rigid bar. The anterior maxillary implants should be placed within the confines of the borders of the planned prosthesis and not labial to the borders of the teeth. The implants should be placed to avoid impingement of the teeth in the overdenture and to allow space for fabrication of the bar. Careful attention to the position of the incisal edges of the lower teeth provides important information and prevents conflicts of space between the lower teeth and the palatal portion of the overdenture and the underlying bar.
At surgery, the surgeon should understand the prosthetic plan and recognize the ideal locations of the implants. Often these implants can be placed slightly palatal to the crest to engage more of the palatal bone, providing a thicker width of labial bone (Figure 3-2, A-E). A local anesthetic is infiltrated into the labial and palatal regions of the anterior maxilla. Incisions for implants placed into the anterior maxilla usually are placed over or slightly palatal to the crest. Vestibular incisions are avoided in the anterior maxilla, because they can shorten the vestibule and increase the patient’s postoperative discomfort.
• FIGURE 3-2 B, Incision is made slightly palatal to the crest. After subperiosteal reflection, the implants are placed. The slightly palatal location of the implants is shown with maintenance of a thick labial plate, which preserves the labial bone and prevents implant dehiscence.
(Prothetics by Dr. Troy Patterson.)
The incision is made along the crest, moving labially around the incisive papilla to avoid transecting its contents, and carried to bone through the periosteum. A full-thickness mucoperiosteal flap is raised, with care taken to prevent trauma to the flap. If necessary, vertical release incisions can be made distal to the planned implant locations to help raise the flap superiorly and thus expose the facial aspect of the maxillary bone. An anterior midline release is not used; it would increase postoperative morbidity because of the disturbance in the anterior lip musculature.
A full-thickness palatal reflection is then accomplished. The contents of the incisive canal are preserved and not incised. The palatal reflection should allow visualization of the slope of the vertical palatal bone to ensure that the surgeon can visualize the insertion of the implants without violating either the labial or the palatal cortical bone, thereby keeping the implant body within bone. The visualization also allows determination of the probable need for osteotomes, either round or flat, to widen the ridge during implant placement.
After the labial and palatal tissues have been reflected, the surgeon should have a good view of the crestal bone thickness and the contours of the palatal and facial cortical bone. The dissection often must be extended superiorly to identify the piriform rim, especially for the more atrophic maxilla. The thickness of bone is confirmed, and the surgical stent is placed. The areas of planned implant placement are examined.
Often the crest of the maxilla is narrow and widens within a few millimeters of the crest. Specific sites may be wider than others, indicating a site that is more ideal for the implant when bone bulk is considered. However, before placing the implant in a site slightly different from that prescribed by the surgical stent, the surgeon should ensure that the prosthetic plan will not be adversely affected.
Because the maxillary crest usually has sharp edges and slopes, the first step is the creation of a depression in the ridge that allows accurate engagement of the drills. The implant sites are scored with either rongeur forceps or a round bur, creating a divot into the bone. The round bur is used to initiate the osteotomy site and to determine the specific location of the implant in the middle of the crest. Accurate placement of this round bur hole is important, because subsequent drills will start in this round hole; changing the position may be difficult once the drilling process has started. If the first drill needs adjustment in position (e.g., the hole is too far labial or palatal), the round bur is used to relocate the hole slightly palatal, labial, distal, or mesial, guided by the need to place the implants into adequate bone and in the correct location. The surgeon must always critically examine the implant sites; the implants must be placed accurately to ensure successful prosthetic treatment.
Subsequent graduating-sized drills initiate and expand the implant site until the final drills are used. If the ridge is excessively narrow, round or flat osteotomes can be used to expand it, or the ridge may require grafting before implant placement. Usually the ridge has sufficient width for placement of the implants. If the ridge width is deficient, the surgeon should consider whether osteotomes can be effective or whether onlay grafting is indicated. If the ridge width is 3 mm, osteotomes can be used to expand it in most cases. However, if the ridge is thin and does not expand as the bone is examined superiorly, the use of osteotomes or ridge splitting in a ridge less than 3 mm is not predictable. For these cases, onlay grafting is indicated and should be discussed with the patient. (See Chapter 4 for examples of onlay grafting of the anterior maxilla with symphyseal bone.)
Implants for overdentures typically are placed with their centers slightly palatal to the crest to avoid dehiscence and thin bone over the facial aspect of the implants. The incisive canal should be avoided as a site for implant placement. Implants should be placed to prevent dehiscence of the implant within the incisive canal. Specifically, implants for overdentures are placed in the canine and premolar locations, depending on the availability of bone. An implant can be placed in the lateral incisor position if necessary. However, implants placed in the central incisor locations complicate the prosthetic rehabilitation, because the presence of the abutments and bar near the midline may result in excessive palatal bulk in the denture; this outcome may be bothersome to the patient.
If a dehiscence of bone occurs in the midportion of the implant because of concavity of the ridge, particles of dense, nonresorbable hydroxylapatite (HA) are placed to obliterate the defect. Use of a membrane depends on the surgeon’s clinical judgment. In general, a membrane is not necessary for small dehiscences.
After the implants and the implant cover screws have been placed into the implant bodies, the incision is closed. Occasionally the periosteum must be released to allow tension-free closure. If no graft has been placed, the type of suture depends on the clinician’s preference. If a graft has been placed, nonresorbable sutures are indicated.
The patient’s current prosthesis should be left out of the mouth for 7 to 10 days after implant surgery. However, if the patient cannot accept this recommendation, the surgeon or restorative dentist should remove the labial flange to the gingival margin of the denture teeth and relieve the crest region. This extremely relieved maxillary prosthesis then can be glued in with denture adhesive on the palate without adhesive on the incision sites. Patients can wear the modified prosthesis for esthetic reasons, but they must consume a liquid, pureed diet for 2 weeks.
If the patient’s goal is to have a denture that accommodates a palateless prosthesis, enabling the patient to chew all textured foods without the prosthesis, a sufficient number of implants (depending on the tissues for support) is required to resist the forces of mastication. For these patients, six to eight implants for a fixed implant-supported or removable prosthesis is recommended, with an adequate number of implants located posteriorly to support the molars.
The edentulous patient with a Class I maxilla requires only the placement of implants to replace the missing teeth (Figure 3-3, A-G). In most patients with a Class I maxilla, who have lost their teeth with minimal bone loss, the labial bone has an irregular contour. These patients may benefit from augmentation of the labial bone to smooth the bone contour and enhance the final restoration, especially for those with high smile lines (Figure 3-4, A-I).
• FIGURE 3-3 A, Maxillary teeth of this 62-year-old man were removed 6 months before implant surgery. The teeth were removed secondary to caries. His workup indicates that the alveolus has been maintained and that adequate bone is present for a fixed, implant-borne maxillary prosthesis. At surgery, eight implants are placed, with a duplicate denture used as the surgical guide. The incision design avoids the anterior maxilla and incisive canals, and the parallelism of the preparations allows all the implants to draw as a unit.
• FIGURE 3-3 B, Labial bone in the right side is thin, with a portion of the implants exposed. For a fixed restoration, the locations for implant placement depend on the surgical planning; consequently, the implants cannot be placed too far toward the palatal side, necessitating these locations. The implants must be placed directly under the teeth. For a bar-retained prosthesis, additional space is required for the bar; therefore, the implants must be placed more palatally.
• FIGURE 3-3 D, At exposure of the implants, a crestal incision is made, and the flap is reflected. The inner thickness of the flap is thinned with a scalpel, limiting the pocket depth that surrounds the abutments to 3 mm. After 2 weeks, the gingiva around the abutments has healed and is ready for impressions.
• FIGURE 3-4 A, This 49-year-old man desires a fixed maxillary restoration. His presurgical analysis shows that he is missing 2 mm of vertical alveolar bone. His planned restoration can be achieved with implants and a full-arch, porcelain-fused-to-metal prosthesis. Irregularities are noted in the labial ridge contour, which will undergo augmentation during implant surgery. The preoperative panoramic radiograph shows excellent bone height.
• FIGURE 3-4 B, Preoperative workup includes a complete waxup of the planned prosthesis, which is tried in the mouth to confirm esthetics and obtain the patient’s approval before surgical placement of the implants. The waxup is converted into acrylic, and a surgical guide is fabricated. Because the second molars are present bilaterally, full-arch coverage is not required. The precise locations of the implants are prescribed by drilling holes through the surgical guide. These holes are 3 mm wide, which coincides with the intermediate drill of the chosen implant system.
• FIGURE 3-4 C, Intraoperative photograph showing the surgical guide in position; the implants are visible through the holes in the guide. The depth to which the implants are countersunk also is guided by the flange of the surgical guide, which accurately shows the position of the gingival margin of the planned restoration.
• FIGURE 3-4 E, Dense, particulate HA is placed over the irregularities in the ridge. A collagen membrane is placed over the HA to retain it in the desired location. As one side is grafted, the incision is closed with 4-0 silk sutures.
• FIGURE 3-4 F, After 5 months, the implants are exposed. A crestal incision is made to transpose keratinized gingiva (KG) to the labial aspect of the healing abutments. The smooth contour of the alveolus is demonstrated. After 3 weeks of healing, the patient is ready for transfer impressions.
(Prosthetics by Dr. Steven Locasio.)
Patients with a Class II maxilla, who have lost their teeth but have a moderate amount of bone, must have an esthetic evaluation. These patients may require the labial flange of a removable prosthesis to provide nasolabial support. They may have sufficient bone for the placement of implants, but without additional lip support, the result may be compromised (Figure 3-5, A-F). The patient’s denture can be duplicated in clear acrylic, and the flange can be completely removed. If the modified denture is placed into the mouth and the lip support is adequate, a fixed restoration can be used. However, the locations of the implants and the need for removable prosthetics to aid in the maintenance of effective oral hygiene also are important considerations.
• FIGURE 3-5 A, This 45-year-old woman requested a fixed restoration in the maxilla. The preoperative evaluation revealed loss of teeth, as well as loss of some alveolar bone height and horizontal bulk. Eight implants were placed from canine to molar, avoiding the anterior four incisor sites.
(Prosthetics by Dr. Larry McMillen.)
• FIGURE 3-6 A, Maxilla showing loss of a significant amount of maxillary horizontal alveolar bulk. For treatment, eight implants are placed in the remaining bone, and a spark erosion prosthesis is fabricated. This fixed-removable type of prosthesis locks onto the bar with small clips. The bar is precision fabricated to mate precisely with the inner metal substructure in the denture.