CHAPTER 10 Root Form Implant Surgery: Proprietary I
The generic steps leading to the definitive procedures described in this section can be found in Chapter 9. Not all the systems described in this chapter begin after the use of the 3-mm spade drill. For example, for small-diameter implants, the sequence must stop at the 2.5- or 2.7-mm drill. If the surgeon uses the 3-mm spade drill for these systems, the host sites will be too wide. Therefore, the dental surgeon must read each section carefully before beginning.
Although this chapter may not mention all the implant sizes available, Table 4-2 lists dimensions for each type and style. For the practitioner who does not want to use the generic system, as described in Chapter 9, to begin the osteotomy for the chosen implant system, the illustrations begin their instructive patterns with the full spectrum of drills, starting with the smallest diameter offered by the specific manufacturer.
Although most implant systems are quite similar, they are packaged differently. For example, Noble Biocare is available in a scored glass tube that snaps in half on finger pressure. Biomet-3i comes in a blister pack that includes the surgical cover screw. Some of the designs are manufactured as self-tapping implants in wide and small diameters. Various coatings (e.g., hydroxyapatite [HA], titanium oxide [TiO2], and titanium plasma spray [TPS]) also are available for some implants. The directions for placement are similar for each system (e.g., Osteotite, NobelActive, Advent), but the instruments have different names. In the directions that follow, Nobel Biocare’s Brånemark instrument names are used. These implants are available in diameters ranging from 3.25 to 6 mm and in varying lengths (5.5 to 18 mm) for most applications, even up to a 52.5-mm length, which is used as an extraoral implant to be inserted into the Zygoma. Insertion techniques vary slightly according to the size of the implant.
FIGURE 10-2. A, Nobel Biocare implant. B, According to the manufacturer’s recommended procedure, the surgeon begins by using the guide drill to half its diameter to penetrate the cortical plate at the proposed implant site. C, The 2-mm twist drill is used to the final implant depth. D, The counterbore is used to enlarge the coronal portion of the osteotomy in preparation for the 3.5-mm twist drill (E). F, Countersink drill. G, Depth gauge. H, Screw tap. I, The implant is inserted attached to the handpiece connector. J, The open-ended wrench stabilizes the handpiece connector while the fixation screw is removed from the implant. K, Cover screw inserter. L, Placement of the cover screw with the small hexagon screwdriver. M, The Nobel Biocare implant is seated so that its cover screw is flush with the crest of bone.
The uncovering procedure is described in Chapter 9. The appropriate healing collar or cuff or an abutment is placed, depending on the thickness of the tissue and its esthetic needs. Healing cuffs should protrude approximately 2 mm above the free gingival margin. Special abutments are used that are similar in contour and diameter to the anticipated restoration. These abutments are kept in position until the tissues have matured sufficiently to allow the impression procedures. Generally, this takes 2 weeks.
TiUnite is Brånemark’s patented, enhanced titanium oxide (TiO2) layer. As are other TiO2 surfaces, it is osteoconductive, and its texture and porosity are ideal for bone apposition and for creating an enhanced environment for bone formation. The enlarged surface area and structure, which absorb blood proteins and aid in bone growth, are very similar to human cancellous bone.
The Mk III implant is a universal, self-tapping implant that can be used for all conditions in which sufficient bone volume is available for an implant. (Refer to Chapters 2, 4, and 7 for bone volume criteria for root form implants.) Mk III implants are available in three diameters: narrow platform (NP), 3.3 mm; regular platform (RP), 3.75 and 4 mm; and wide platform (WP), 5 mm. Seven lengths are available: 7, 8.5, 10, 11.5, 13, 15, and 18 mm. The line also includes a 5.5-mm long implant (i.e., the NobelSpeedy Shorty), which has been approved for immediate function. The osteotomy sequence and protocol for this implant are similar to those for the NobelSpeedy Groovy implant.
The Mk III 3.3-mm NP implant is used when interproximal space is limited or minimal alveolar bone width is available to accommodate an RP implant. Narrow-diameter implants have less mechanical strength; therefore the surgeon must carefully evaluate the expected loads and the support the planned restoration will require to function.
WP implants are used when the potential functional loads of the restoration and the available anatomy justify the use of a wider implant. Although the mechanical strength of implants has been improved considerably, bone quality and quantity remain patient-dependent variables. Both the amount and quality of bone can be limiting factors when the higher occlusal loads found in the posterior regions of the jaws are factors in the treatment.
The Mk IV implant is a tapered implant intended for use in soft bone. The tapered design and double threads achieve and enhance initial implant stability in soft trabecular bone. The RP implants have a 4-mm diameter, and the WP implants have a 5-mm diameter. As with the Mk III implants, seven lengths are available (7, 8.5, 10, 11.5, 13, 15, and 18 mm). All drills and components are marked so that the implantologist can prepare the implant site to the correct depth and create a secure, predictable implant position. Twist drill preparation is deeper than the final position of an implant apex. Depending on the diameter of the twist drill, the apical part of the drill deepens the site about 1 mm.
(Courtesy Nobel Biocare, Yorba Linda, Calif.)
Fig. 10-4 presents the osteotomy sequence for a narrow-platform implant.
A 4-mm diameter RP implant can be used in soft bone or when initial stability cannot be achieved with a 3.75-mm diameter RP implant. In very dense bone, a Mk III Screw Tap may also be required. Drills of different diameters can be used, depending on the bone quality and implant diameter.
The Mk IV implant is recommended for use in predominantly soft bone (classes III and IV). The surgeon must pay particular attention to bone quality. Optimum results depend on selection of the appropriate drill diameter after the bone quality at each site has been evaluated. In principle, the osteotomy sequences are the same as for placement of a Mk III implant (Fig. 10-7).
Insertion with the hand wrench above 50 Ncm of torque is not recommended. Instead, the implant should be backed out and the site should be pretapped at low speed with the Mk IV Screw Tap, accompanied by copious irrigation. The implant then can be reinserted into the pretapped site.
The Mk IV implant is not recommended for use when predominantly dense cortical bone is present. In some patients, 2 to 3 mm of dense cortical bone is found in the posterior mandible, with loose trabecular bone underneath. Even if the rest of the bone in the area is soft, seating the Mk IV implant may be difficult because the implant cannot compress the thick layer of cortical bone. In such cases, the Mk IV Screw Tap can be used through the cortical layer (Fig. 10-8).
The Zygoma implant is used in patients with severe alveolar atrophy in the posterior maxilla when augmentation procedures are not possible because of financial or medical considerations. These extremely long endosseous implants can be secured into the zygomatic processes. When inserted there, along with two to four strategically placed, standard implants in the anterior maxilla, a bar-overdenture (two Zygoma implants + two anterior implants) or a fixed-detachable or fixed prosthesis (two Zygoma implants + four anterior implants) can be fabricated and put into function.
Consequently, Zygoma implants should be rigidly connected to stable conventional fixtures in the anterior maxilla. Based on clinical experience and biomechanical theoretical calculations, a full arch restoration in the maxilla with two Zygoma implants (one on each side) should be assisted by at least two stable, standard Brånemark implants in the anterior maxilla, or even better, by four standard implants (Fig. 10-10).
(Courtesy Nobel Biocare, Yorba Linda, Calif.)
Bending moment forces are known to be the most unfavorable type, because they have the potential to jeopardize the long-term stability of an implant-supported restoration. To reduce bending moments, the distribution of forces should be optimized by:
Zygoma implants are available in the TiUnite line and with a machined titanium surface. The surgeon must have experience in maxillofacial surgical techniques to perform the implantation procedure. (A d/>