Computer guided implant treatment allows implants and associated restorations to be precisely placed during the same procedure directly through the gingiva with reduced postoperative complications and surgical time. When bone height is adequate but very narrow, the virtual guided sleeve is often placed too deeply into the ridge crest interfering with the seating of the surgical template. This case report of a patient exhibiting very narrow residual ridges due to severe resorption describes a new computer guided procedure using a single surgical template maintaining bone height and immediate restoration without a mucoperiosteal flap. The success of this technique is the result of innovative modifications in the software as well as instrumentation. Modifications include planning a different implant length virtually to raise the position of guide sleeves, alteration of drilling sequences, modifications of the start drill, incorporation of osteotomes, and use of an alternative implant seating mount. The combination of these methods allows for deeper site preparation and implant seating beyond the default settings, without any crestal bone reduction. These modifications not only make the guided concept possible for the entire preparation and seating procedures, but also allow for the slight removal of bone that would interfere with the implant seating through the surgical template without a mucoperiosteal flap. This new approach to computer guided surgery maintains prosthetic precision in the fabrication of a provisional restoration prior to implantation with minimal delivery adjustments using prefabricated conical abutments when placing implants at differing levels into the high narrow ridge.
Computer-guided minimally invasive implant treatment promises to revolutionize the way we practice implant dentistry. This new technology allows implants and associated restorations to be precisely placed at the same procedure directly through the gingiva in an hour or less. Because there is no incision, there is minimal postoperative discomfort or swelling and no sutures.
The typical dental implant approach that was introduced in the early 1980s requires 2 surgeries1 and the use of a removable bridge or denture for a half year or more. In 1990,2 it was first shown that implants could be placed and restored in a single visit, but this procedure, known as immediate loading, takes a full day of coordinated surgical, restorative, and laboratory interaction to perform. Advancements in computerized tomography (CT) scans,3 coupled with computer-assisted treatment planning,4 allowed the possibility to virtually plan the placement of implants in 3-dimensional (3D) orientation relative to the bone, soft tissue, and final planned prosthesis. In 2002, the concept of computer-guided techniques combined with immediate loading was clinically introduced in Leuven, Belgium.5 These early treatments were limited to the edentulous maxilla and required a full-thickness mucoperiosteal flap. Later, the procedure was refined to include flapless implant placement through virtual planning by producing a stereolithographic surgical template incorporating precision titanium drilling sleeves.6 By retrofitting specialized implant components into the stereolithographic surgical template, an implant-level model could be produced and a definitive prosthesis could be fabricated for immediate placement at implant insertion.
Besides the obvious advantages of being a less invasive procedure for implant placement, producing minimal postoperative discomfort or swelling, and allowing immediate fixed restoration delivery in one relatively short appointment, the treatment offers some not so obvious advantages in precision and patient safety.
However, there are limitations in the application of this new technology. Adequate bone and soft tissue are required to place the implant in the ideal position in relation to the planned restoration and to stabilize the surgical template. Preprosthetic surgery, such as grafting, alveoplasty, or soft-tissue modification, may be required with its associated healing and management. Further, because of the fixed distance from the occlusal portion of the titanium sleeves in the surgical template to the platform of the implant (9 mm), the seating of the surgical template can be obstructed when the residual ridge is too high in an area or when it is too narrow and requires reduction.
Two techniques have been described, both of which require opening a flap and significantly reducing bone before implant site preparation. One of these uses 2 sequential templates and allows the presurgical fabrication of a provisional prosthesis.7 The other uses only one template but does not allow for the presurgical fabrication of a temporary prosthesis (personal communication, Dr Richard Sullivan, Yorba Linda, Calif, November, 2008).
This case report of a complete bimaxillary edentulous patient exhibiting generalized severe lateral maxillary bone resorption with a very narrow high residual ridge and bilateral sinus pneumatization (class III Siebert)8 (Figure 1a, b, and c) demonstrates the preoperative status for a patient who will be treated with a flapless computer-guided procedure for implant placement using a single surgical template, maintenance of bone height, and delivery of preoperatively fabricated immediate fixed restoration. It should be noted that the standard guided planning and surgical protocol was used for 6 of the 8 implants. For placement of the 2 remaining implants, a new technique was introduced for use with the minimal ridge dimension that did not require reduction. The new technique, which is a modification of the standard protocol and instrumentation, is the subject of this article.
A 54-year-old woman presented to the Harvard School of Dental Medicine, Post-doctoral clinic, with a chief complaint of severe gagging from her maxillary complete prosthesis and an unstable mandibular removable prosthesis
The patient had a history of hepatitis C in remission, hypothyroidism, and hypercholesterolemia that were well controlled with medication. A history of cigarette smoking was reported (1 pack/day for the past 20 years). Complete smoking cessation therapy was unsuccessful but it did result in a reduction to 10 cigarettes/day.
The patient elected to have fixed implant supported fixed prostheses in both maxillary and mandibular arches using computer-guided implant placement with immediate fixed provisional restorations (NobelGuide, Nobel Biocare, Yorba Linda, Calif). The patient was informed that she was at higher risk of implant failure because of her smoking, but she was willing to accept the risk.
Treatment proceeded with extraction of the remaining mandibular teeth and placement of an immediate denture opposing the patient's existing maxillary denture. After 4 months of healing, new maxillary and mandibular dentures were fabricated to establish appropriate function and esthetics. These same dentures also functioned as radiographic guides to transfer precise tooth position and tissue contours to the virtual computer-planning process (NobelGuide). Gutta percha markers were placed in each denture according to protocol.
The patient was next scanned with the dentures using the CBCT (i-CAT, Imaging Sciences, Hatfield, Pa). Four scans were made. First, each jaw was scanned separately with its denture held in place with its own radiographic index to ensure complete seating. This was followed by scanning of each denture separately in the same orientation as they were positioned while they were scanned in the patient's mouth. The DICOM (Digital Imaging and Communication in Medicine) data files were converted in the planning software, and both jaws were evaluated for implant-supported fixed prostheses. A 3D plan for the mandible was developed that included an implant-supported fixed prosthesis on 5 implants. The initial plan was to place implants and prostheses in each arch at the same operative procedure. However, it became apparent that the limited available bone in the maxilla (Figure 1b) presented complexities that would have made it difficult to treat both arches together. Accordingly, the maxilla was treated in a separate procedure.
Maxillary planning was undertaken to produce a surgical template for the placement of 8 implants and an immediate loaded provisional restoration. However, in 2 areas of very thin ridge width (Cawood class IV), the implants needed to be placed apically to this thin ridge crest to gain adequate bone width for implant placement. This introduced a problem in that the guided software system includes the use of guided sleeves, which are ultimately produced in the surgical template. These sleeves not only maintain axial orientation but also maintain depth of drilling and aid in seating the implant. Accordingly, the occlusal surface of the guided sleeves is located at a fixed distance from the platform of the implant placed within the software (9 mm).
This had the effect of positioning the virtual guided sleeve too deeply into the ridge crest and beyond the soft tissue. This would make it so that the surgical template, if produced, could not be seated properly in the patient's mouth (Figure 2).
Therefore, in order to position the planned implants to the seating depth desired, it was necessary to bypass the default setting between the implant platform and the position of the affected guided sleeves. This bypass included the following strategies:
Increasing the planned virtual implant length to allow for coronal repositioning of the guided sleeve depth
Changing the drilling sequence, beginning with a 1.5-mm diameter twist drill that was not part of the site preparation protocol
Modifying the first drill normally used—the Start Drill—to allow deeper depth of insertion beyond a depth limiting stop
Using osteotomes in a guided fashion for further site preparation beyond the initial 1.5-mm diameter
Using an alternative implant seating mount to allow further depth of implant placement than the conventional guided instrumentation
Increasing planned virtual implant length
The ideal position of the implant was planned, and the arrow shows that the virtual guided sleeve interfered with the ridge crest (Figure 3a). The planned implant length was increased from 7 to 10 mm (Figure 3b). When the implant length is changed, the software automatically positions the implant 3 mm more apically while maintaining the same implant platform position and thus increasing the length at the apical section of the implant. Another feature of the software was then used that allows the implant seating depth to be changed, apically or coronally, in 0.5-mm increments while maintaining the precise axial orientation that had been established. When used in this manner, the new virtual 10-mm implant was moved 3 mm coronally, which had the effect of moving the guided sleeve 3 mm coronally also, so that it was now clear of the bone and soft tissue, which would allow for full seating of the surgical template without interference from the guided sleeves (Figure 3c). This meant that if the drilling were to proceed from the newly positioned guided sleeve for a 10-mm implant, the apical extent of the site preparation would be appropriate for the desired 7-mm implant.
This bypass solved the problem of how to proceed with guided drilling to the appropriate apical depth while still producing and seating the surgical template without any soft tissue or bone interference.
For the first 6 implants anterior and posterior to these compromised sites, the standard drilling sequence was used and the implants were placed (Figure 4). After this, the operative procedure for the final 2 implants was modified as follows and the implants were placed (Figure 5).
Changing the drilling sequence
After the standard Start Drill, a 2-mm twist drill is normally used to prepare the osteotomy to the apical extent of the implant length desired. In this situation, for the 2 compromised sites requiring implant depth of placement beyond the default design of the system, a 1.5-mm diameter anchor pin drill was used to guide the standard Start Drill. The rationale for this substitution was to guide the countersink function of the Start Drill further apically than the stop would allow. Simply removing this start drill stop to allow deeper insertion with subsequent less guiding by the guiding sleeve (discussed later) would compromise the ability of the Start Drill to maintain its orientation as it was inserted further beyond the guided sleeve. To help direct and maintain the proper orientation, it was found that the Start Drill has an apical extension tip that is 1.5 mm in diameter. Therefore, making the initial penetration to depth using a 1.5-mm drill instead of a 2-mm drill allowed a second point of guidance for the tip of the modified Start Drill as less guidance was available from the guided sleeve. This was important in maintaining proper orientation as the modified Start Drill was inserted to within 1 mm of the apical extent of the guided sleeve. This second point of guidance from the 1.5-mm diameter channel enabled the depth of penetration necessary for the 7-mm implant collar using a surgical template design for a 10-mm implant, even though the modified Start Drill was reaching the limits of guidance offered by the guided sleeve (Figure 6a).
Because no drill guide is available for the guide sleeve in the 1.5-mm diameter, it was necessary to fabricate one. To accomplish this, an anchor pin sleeve with an outside diameter of 3 mm and inside diameter of 1.5 mm was luted to the inside of a 3-mm drill guide (Figure 6b). After recontouring the shank, this allowed a 1.5-mm twist drill to be passively inserted through this modified drill guide to the implant depth required.
Modifying the Start Drill
The manufacturer's protocol first uses a Start Drill, which has two functions: the first is to work as a soft-tissue punch and the second is to act as a countersink to provide the additional diameter of preparation required for seating the implant platform. The Start Drill has a depth-limiting flange that functions as a stop at the guided sleeve to control seating depth to the default setting for the implant platform. After the use of the Start Drill in its tissue punch and countersink functions, the site is typically drilled to depth with a 2-mm diameter drill followed by a larger drill as appropriate for bone density and implant diameter.
The objective of this guided procedure was to place the implants in a closed manner. Even though the drilling could be accomplished to full depth with this software bypass, the standard start drill would limit deeper seating of a shorter implant in this prepared site because the countersink aspect of the preparation would not be deep enough; it would be 3 mm short of the depth necessary for full seating of a 7-mm implant in the site because of buccal residual bone interference.
To allow a closed approach and achieve deeper seating, the guided Start Drill was modified by removing its depth-limiting stop (Figure 7). Maintaining axial orientation once the Start Drill reached the full extent of the guided sleeve was achieved guiding the tip of the start drill along the channel created by using the 1.5-mm anchor pin drill (discussed earlier).
Using osteotomes to expand the site diameter
Because of advanced resorption in these 2 sites, it was desired to prepare the sites as much as possible through the surgical template with osteotomes11 to expand the bone rather than allow drills to remove it. As previously stated, the 1.5-mm diameter, rather than the 2-mm diameter, was used initially to full depth. This was followed with 2-mm, 2.8-mm, and 3.0-mm diameter osteotomes through their associated drill guides placed into the template (Figure 8).
Substitution of an alternative implant delivery mount
This system functions not only for guidance of axial orientation but also for depth of drilling and implant insertion. Because the surgical template was designed for a 10-mm implant, with the intent to insert a 7-mm implant 3 mm more apically (Figure 9), a 12-mm implant mount was used from the first-generation Branemark single tooth instrumentation kit (DIA 140 Branemark fixture mount complete long shaft, Nobel Biocare, Yorba Linda, Calif).
Before removal of the surgical template, a guided tissue punch was used through the template. This was followed by use of a bone mill on each implant to ensure full seating of the planned abutments. Because of the depth of implant placement in the 2 compromised sites, we could not use the guided abutments that are typically used as part of this system to facilitate immediate loading. The guided abutments compensate for slight discrepancies in placement depth, but because they could not be used, standard nonguided multiunit abutments were used to bring the restorative platform to within 1 mm of the soft tissue (Figure 10a). The provisional restoration was prefabricated with 1 temporary cylinder and denture flanges to aid in initial seating and orientation. Then intraoral luting of the remaining 7 temporary abutment cylinders to the prefabricated provisional restoration was accomplished, after which the flanges were removed (Figure 10b). Seating of the prefabricated provisional restoration was confirmed by postoperative X ray (Figure 11).
This article describes a new modified technique of guided surgery that allows flapless implant placement with use of a single surgical template and maintenance of bone height. This approach allowed for deeper site preparation and implant seating beyond the default settings of the manufacturing process and instrumentation. With this method, the entire implant preparation and seating procedure could be done guided and the excess bone that would interfere with implant seating could be removed through the template. By mathematical calculation, a shorter implant and a longer abutment were substituted for a longer implant and a shorter abutment in the virtual planning process. This had the effect of maintaining prosthetic precision for the fabrication of a provisional restoration before implant placement with minimal delivery modifications. However, if the plan had been followed according to protocol for 2 implants in the bicuspid regions bilaterally, the sleeve would have interfered with the crest of bone.
To overcome this, several modifications were made in the standard guided protocol so that the procedure could be accomplished in a closed fashion without the reduction of alveolar bone and while allowing for immediate placement of a fixed implant supported prosthesis.