CHAPTER 9 Root Form Implant Surgery: Generic
Before undertaking the placement of any type of root form implant, the practitioner should read this section in its entirety. It lists the introductory techniques of insertion for all types of root forms. In addition, recommendations are found in the tables of Chapter 4 for the selection of a wide variety of implant designs. The techniques for placement of the specific proprietary designs are presented in chapters 10 and 11.
This chapter first presents the generic, step-by-step technique for insertion of root form implants. The illustrations and explanatory notes demonstrate the procedure in a sequence that starts with gingival incision and ends at a point that satisfies the introductory requirements for all systems. The final osteotomies and techniques for specific implant insertions are described in the following sections. If the instructions in this chapter are followed, a “generic” root form implant can be inserted and uncovered. That is, these steps are identical for most root form systems.
After acquiring an understanding of each maneuver, the reader should refer to Chapter 4. Its charts describe most of today’s implant varieties, their general grouping, material and design characteristics, surface finishes, methods of primary retention (during the integration period), and basic restorative options. Several systems offer implants with diameters of 3, 3.25, and 3.3 mm (small diameter). Especially in the maxillae, such implants often may be inserted after a 3-mm diameter drill is used without the formality of tapping, enlarging, or countersinking.
The diameters of drills should be increased in increments of 0.5 mm only (Brookdale Generic System). Bone density is a determining factor, as are internal irrigation, drill speed, torque, and bur sharpness. The smaller each graduation of bur size, the less heat and trauma are generated to the host site and the more accurate the osteotomy.
Not all systems supply all drill sizes. Different manufacturers supply a variety of sizes that may be selected to complete an entire generic set. For example, Nobel Biocare does not manufacture burs or a console that supplies internal irrigation; Calcitek recommends a round starter bur (the rosette); and Brasseler supplies graduated-diameter, internally irrigated spade drills.
Unless a computed tomography (CT) scan is available, the actual bone dimensions are known only at the time of flap reflection, and they dictate where the implants can be placed and what sizes should be chosen. However, the surgeon will find it significantly beneficial to use a surgical guide or template, so that the ideal locations for all implants are presented clearly where bone dimensions can accommodate them.
In all endosteal implant procedures, the dental surgeon must take care not to impair vital structures. The use of infiltration anesthesia in the mandible helps guide drilling depths when the mandibular canal is approached, because the patient will report lip tingling. Slow drilling keeps intraosseous temperatures at safe levels. Saline irrigants can be chilled preoperatively to aid temperature control.
Pressure should not be used when osteotomies are prepared; rather the drills should be allowed to find their own way. In systems that require bone tapping, use of a ratchet wrench by hand is preferable. Avoid this step completely if the bone is compliant enough to allow the implant to tap itself to place (e.g., Nobel Biocare, Biomet-3i, Zimmer). This level of pliability is found most frequently in the maxillae.
In the planning stages, a surgical template should be prepared for implant placement (see Chapter 4 and this chapter). However, the surgeon should keep in mind that sometimes, even the most careful planning does not yield satisfactory results because the bony ridge is not found directly below the soft tissues. The surgeon must be versatile enough to alter the positions and angles of the implants at the time of surgery.
Particularly in the maxillae, but also in less dense mandibles, some of the preparatory steps may be eliminated (i.e., tapping, or threading, the bone and use of the final sizing drill and the countersink drill). In this less dense bone, the implant can seat itself and thread and countersink the host site bone.
As surgeons gain more experience, they will find that the same template may be used for radiographic diagnosis (Chapter 4), for surgical placement, and even for uncovering the implants. Fabrication of the surgical template is a necessary step in the planning and placement of implants. Its design is based on the anatomic, prosthetic, and esthetic considerations. If (as discussed in Chapter 4) a diagnostic, 5-mm, ball-imbedded Omnivac template is available and each ball has been processed at a potential implant site, simply removing the balls allows the device to be used as an implant site locator. However, a template can be fabricated to be used specifically for intraoperative guidance.
A surgical template also can be fabricated with computer-aided design and manufacturing (CAD/CAM) using computed and cone beam volumetric tomography (CT/CBVT) virtual implant planning (i.e., Nobelguide from Nobel Biocare, and Sicat’s Siroguide from GalaxisImplant). The latter requires some proficiency in computer-guided surgery, and the related fabrication costs are much higher than the traditional Omnivac template.
Three types of templates can be made using either the Omnivac or CAD/CAM process: a template for single tooth replacement or edentulous spans between natural teeth; a free-end saddle template for edentulous areas; and a template for completely edentulous sites.
The process of single tooth replacement begins with marking a cast at the ideal location for the implant. A denture tooth then is fixed in place with sticky wax. Next, an Omnivac shell is created using 0.02-inch clear material. After the material has cooled, the plastic is trimmed to include at least two teeth on either side of the operative area. In the edentulous area, the parts of the appliance that extend buccally and lingually beyond the points of flap retraction (approximately 6 mm) should be shortened. The denture tooth is removed, and the occlusal and lingual surfaces of the denture teeth area are snipped away with a fine shears. The device should be cold sterilized and placed into position over the bone after flap retraction. It is stabilized by the teeth on either side of the host site, and it serves as an efficient surgical guide (Fig. 9-1).
A free-end saddle template is made in the same way as the single tooth design, with minor changes. Four or more teeth anterior to the edentulous area are included in the Omnivac, and the shell margin is extended posteriorly past the anticipated distal extent of the incision line. In this way, the device is stabilized by a large number of anterior teeth and by its position on the soft tissues posteriorly, which are not to be elevated (e.g., tuberosity retromolar pad) even after flap reflection.
For completely edentulous sites, a new denture is fabricated at least to the wax try-in stage. If an existing removable denture is being converted or an original full denture is to be used, it is relined with a chairside material, such as Viscogel. Next, the denture is flasked using Kentosil in a denture duplicator with petroleum jelly as a lubricant. The denture is removed, and clear acrylic resin is poured into its place. The flask is closed, and the acrylic resin is allowed to polymerize. When it is removed from the elastomer, it is a duplicate of the original denture in clear acrylic. The borders are trimmed and polished.
In the areas to be implanted, the lingual and occlusal aspects of the teeth are cut away with a bur in the form of a U-shaped trough; the incisal and facial surfaces are left intact. The fenestrated area denotes the sites where the implants are to be placed to satisfy the reconstructive and aesthetic needs of the case. Individual holes can be made, although this may prove too restrictive. The clear labial surfaces allow direct viewing during the preparation for osteotomies (Fig. 9-2). This not only ensures proper angulations, but also shows that the transepithelial abutments (TEAs) emerge from optimal areas, such as the cingula of incisors and the occlusal surfaces of molars.
FIGURE 9-2. The occlusal surface and lingual flange of the processed acrylic resin surgical template are opened, and the proposed implant sites are exposed. The labial tooth surfaces remain as guides to the surgeon.
An infiltration technique is used to anesthetize the patient. A crestal incision then is made directly to bone, with adequate relief at either end, and the mucoperiosteum is reflected, exposing the bony operative site (Fig. 9-3, A and B). At this point, the bone is assessed. If the ridge is too narrow (i.e., knife edged), the surgeon must determine whether it can be flattened to an acceptable width and still have sufficient depth to accommodate an implant. If so, side-cutting rongeur forceps are used, and then a small, round vulcanite bur or a fissure type with irrigation (Fig. 9-3, C). Final smoothing is done with a bone file (Fig. 9-3, D). If the narrow ridge cannot be corrected but is deep enough, the surgeon should consider ridge augmentation (see Chapter 8) or placement of a blade implant (see Chapter 12).
FIGURE 9-3. A, Incisions are made at the crest of the ridge. Relieving incisions may be required. B, Reflection of the mucoperiosteal flaps permits good visibility of the ridge crest. C, Rongeur forceps or a bur may be used to flatten (and widen) a knife-edged ridge. D, The final osteoplasty is performed with a bone file. E, Calipers are used to verify the ridge width.
After the ridge has been prepared and measurements indicate that the width is adequate (i.e., at least 5.25 mm) (Fig. 9-3, E), the osteotomies are made. As an alternative, ridge-widening procedures may be undertaken (see Chapter 8). (The surgeon must keep in mind that implants must be spaced one full width apart.) A colored sleeve is placed on the shaft of each drill at the level of the planned depth of each osteotomy (yellow Disposaboots currently are used) (Fig. 9-4). The drill tip pierces the rounded end, and the sleeve is slid up the shaft to mark the proper length.
The sterilized, clear acrylic, Omnivac surgical template is placed in the patient’s mouth. The flanges are trimmed so that they will nestle comfortably beneath the reflected flaps of tissue; in this position, the flanges keep the flaps reflected. The template is stabilized with the host bone that appears directly beneath the U-shaped window. The starter bur (No. 2 round) is set in the center of each proposed implant site and rotated only into the cortex. Copious coolant is used, even though most starter burs are not equipped for internal irrigation. For each planned implant, a similar starter hole is made and then deepened just through the cortex (Fig. 9-5, A).
FIGURE 9-5. A, The surgical template is put in position. It both retracts the flaps and guides the placement of the starter osteotomy, just through the cortex. B, The second step is made with the 1.6-mm pilot drill, at the proper angulation and site, for distances of up to 11 mm. C, An intraoperative radiograph is taken to confirm the length and location of the pilot drill. D, Intraoperative radiographs are always used when nerves are near the host sites. A simple technique, which maintains sterility and keeps the patient’s hand out of the field, involves a gas-sterilized Styrofoam film holder, which is held in position by paralleling pins or burs that pierce its soft block (arrow). E, The resulting film shows safe progress during the operation, as well as accuracy of distances, parallelism, and positioning. The first 1.6-mm diameter drill, if satisfactory, facilitates a simple, flawless operation. F, Pins are placed in each osteotomy to preserve continuing parallelism of adjacent bone cuts.