Fixed Complete Denture Using Implants and Computer-Guided Technology

The success of implant therapy begins with meticulous treatment planning and properly performed implant placement. Prosthetic complications may occur with misaligned placement of implants, especially when multiple implants are involved.1

INTRODUCTION

There are numerous prosthetic options to restore the completely edentulous patient. One of these options involves the use of dental implants and a fixed complete denture; including a titanium framework that is fabricated through a computer-assisted milling (CAM) process. On this framework individual preparations may be designed to accommodate aesthetic restorations, using all-ceramic restorative materials.2,3 These fixed complete dentures can also be fabricated adding heat-cured acrylic resin and acrylic resin teeth to the framework instead of individual preparations and all-ceramic restorations. Most of these implant retained restorations require cantilever sections that are attached to multiple units.4
It is important to understand that the same complications that occur with fixed partial dentures on natural dentition may also occur with implant-retained or -supported restorations. When using cantilevers in combination with dental implants, the stress is biomechanically transferred to the framework, implants, and ultimately to the bone.5,6 In the literature, several different techniques can be found that reduce the load on the cantilever area, directly reducing the load received by the bone.7 These techniques include, but are not limited to, the use of acrylic resin on the occlusal surfaces to absorb forces, relief of occlusal contacts on the cantilever area, and avoiding the use of porcelain or gold.8
Implant placement has become a primary option in clinical dentistry and many clinicians believe that it is the standard of care. It requires proper diagnosis and case selection. Patients could present with unpredictable osseous anatomy at the proposed implant location, often making it difficult for the dentist to determine if there is sufficient bone in which to place an implant. The utilization of 2-dimensional (2-D) radiography (including periapical, bite-wing, and panoramic radiographs), may not allow the dentist to adequately assess the form and density of bone at the recipient site.

Surgical Guides
For the placement of the dental implant, the dentist typically fabricates a surgical guide using a mounted cast and these 2-D radiographs. Several techniques for fabricating a surgical guide have been proposed, including the use of acrylic resin, vacuum formed guides, among others.1-6 The use of these surgical guides aides in the correct placement of implants. The intent is to assure proper implant placement so prosthodontic complications can be kept to a minimum.

Computer-Guided Technology
Recently, implant surgery has incorporated computer-guided technology that enables the dentist to fully evaluate the osseous morphology with 3-dimensional (3-D) views, and more accurately plan for the placement of implants. This method provides improved accuracy as a result of better diagnosis and a more accurate surgical guide.9-13 This approach is becoming the standard of care for predictable implant positioning.14-17 Specifically, a computed tomography (CT) scan is taken with a radiographic guide that mimics the position of the desired teeth. With the addition of the computer software, a simulation of the implant surgery prior to performing the actual surgery on the patient is possible. This computer software reformats the CT scan and enables 3-D simulations of the bone, its density, amount, and its relationship to the radiographic guide.
The software also enables us to thoroughly evaluate a patient’s anatomy that can then be used to design a blueprint of the anticipated surgical and prosthetic treatment plan. At this point, once the most appropriate position for the implants is identified one can place on the software the desired number, size, position and angulations of the dental implants. Subsequent to this step, the data is sent via an Internet connection to a milling center (Procera [Nobel Biocare]) and a stereolithography cast is fabricated there with the preplanned implant sites. From this cast, a surgical template is fabricated to guide the surgeon as to the precise position of each dental implant.18-21 Examples of software include Nobel­Guide (Nobel Biocare), SurgiGuide (CSI Materialise) and Virtual Implant Placement Software (Implant Logic Systems).

Early Loading
According to the original Bränemark protocol,22,23 the time period for the osseointegration of an implant in preparation for loading was between 3 and 6 months. Changes in implant design and surface characteristics have led to the concept of early loading of implants, decreasing the unloaded time to less than 2 to 4 weeks24,25 and even immediately loading the im­plants. The success of immediately loaded of implants has been well documented.24-30 Patient selection is critical31,32 host factors, implant design, and occlusal loads may all impact osseointegration of the implants, and the success of the procedures.24

Choices in Treatment Modalities
There are many suggested treatment modalities to achieve optimal prosthetic design including: retrofitting an existing denture by converting it into a provisional restoration and utilizing acrylic resin or acrylic resin metal-reinforced frameworks. Another treatment modality is composed of a laboratory-processed provisional utilizing a precast framework and a processed complete denture that is coupled intraorally after implant placement.33 The creation of a provisional prosthesis after a surgical procedure can be difficult and most of all time-consuming.33
This article will discuss a technique utilizing a computer-assisted surgical design, a surgical template, a flapless surgical procedure, and a prefabricated fixed complete denture for immediately loading dental implants.

CASE REPORT

Figure 1. Preliminary frontal view.

A 69-year-old man presented with a fixed complete denture in the maxilla, and a poor fitting removable partial denture retained by the left canine in the mandible (Figure 1). The patient had been using the removable partial denture (RPD) for more than 5 years with both mandibular canines, but had the right canine extracted 2 months prior to his visit. The pa­tient’s chief complaint was his inability to use his lower RPD. After performing a comprehensive dental and medical examination as well as a review of his medical history, there were no findings that would contraindicate dental care—including elective surgery and implant surgery.
Several treatment options were offered to the patient, including the following: extraction of the left mandibular canine and the fabrication of a conventional complete denture; extraction of the left mandibular canine placement of 2 endosseous implants in precise position and the fabrication of an over-denture; and extraction of the left mandibular canine, placement of 5 endosseous implants and the fabrication of a fixed complete denture, among others. The patient chose the third option.
The first step was to extract the left lateral mandibular canine. The patient was given the option to have a immediate complete denture after the extraction. The patient declined this possibility.

Figure 2. Record base and occlusal rim.

Figure 3. Trial denture tooth set-up.

A record base was fabricated (Coe Tray [GC America]) and an occlusal rim made using Base Plate Wax (Kerr) (Figure 2); the correct occlusal vertical dimension and tooth position was determined. Teeth were added to determine and confirm tooth position for aesthetics,34 phonetics,35 and the occlusal vertical dimension (OVD) (Figure 3).36 Radiopaque markers were placed into the record base of the trial denture; 2.0 mm holes into the buccal and lingual surfaces distributed along the trial denture record base. The holes were filled with gutta-percha (Mynol gutta-percha [Block Drug Corp]) to function as the radiopaque markers. An interocclusal record was made with a polyvinylsiloxane (Regisil 2x [DEN­TSPLY Caulk]) at the patient’s appropriate centric relation and OVD.
At this point, the patient was referred for a CT scan using a double scan technique.37 The first CT scan was made with the trial denture in place in the mouth, the second CT scan was made of only the trial denture without the patient. Both scans (consisting of up to 200 individual projections) are necessary to form the eventual 3-D images of the bone and prosthesis. Next, the data from the CT scan was introduced into the planning software (NobelGuide). This software allowed the evaluation of the osseous tissue and other im­portant anatomical structures in relation to the position of the denture teeth present in the trial denture.38

Figure 4. Mandible on computer software.

Figure 5. Implants positioned in the desired position.
Figure 6. Implants positioned in the desired position with trial denture in position and the friction horizontal pins.

Figure 7. Surgical guide.

The software lets us coordinate the radiographic views from the CT scan and the surgical plan for the implant surgery. (Note: the NobelGuide software is sophisticated, requiring several days of training to operate. As a result, only the highlights of the planning process will be described here.) Taking into considerations anatomical structures and the position of the teeth, 5 endosseous implants were planned in the mandible. In addition, the plan required 4 friction-anchored pins to stabilize the surgical guide during the implant surgery procedure (Figures 4 to 6). The implants were planed anterior to the mental foramen all regular platform external hexagon (Nobel Speedy Groovy [Nobel Biocare]) were 4.0 mm x 13 mm in length; the most distal implant on the left side of the mandible was the exception at 10 mm in length.
The data was then transferred to a milling center (Procera) to fabricate the stereo-lithography surgical guide39 with the preplanned osteotomy sites of the dental implants (Figure 7). Once the surgical guide was returned from the production facility, a guided cylinder (Nobel Biocare) was placed on the metal sleeves of the guides. It was then attached on one side by the guided screw (Nobel Biocare) (Figure 8), and on the other side by the implant replica (Nobel Biocare) (Figure 9). A pink-colored (VPS) soft-tissue moulage (Ivoclar Vivadent) was placed on the internal surface of the surgical guide, stopping past the junction of the guided cylinder and the implant replica. After this, the area was poured using type V gypsum material (Die-Keen [Heraeus Kulzer]) (Figure 10).

Figure 8. Surgical guide with friction horizontal pins and guided screws.

Figure 9. Surgical guide with friction horizontal pins and implant replicas.

Figure 10. Final cast with soft tissue and implant replicas in the adequate position.

Figure 11. Trial denture jig for tooth positioning and fabrication of the titanium bar.

Figure 12. Acrylic resin pattern for fabrication of the titanium bar.

Figure 13. Titanium bar with retention pins for the acrylic resin.

Figure 14. Completed fixed complete denture on master cast, before surgery.

Figure 15. Fixed complete denture with guided abutments in place.

After the master cast is fabricated, it was mounted to the opposing cast with the original interocclusal record on an articulator (Hanau [Water Pik Technologies]). Another interocclusal record was made between the surgical template and the opposing arch on the articulator to transfer the centric relation and OVD information; during the surgery it will serve to stabilize the surgical guide until the friction-fitted horizontal stabilizing pins (Nobel Biocare) are placed. The horizontal stabilization friction pins were placed through the surgical template in the preplanned horizontal direction into the osseous tissues after an osteotomy using a 1.2-mm drill (Nobel Biocare). With the capability to transfer the exact implant positions, the definitive prosthesis was fabricated on the cast made from the surgical guide (Figure 10). The initial trial denture dictated the position of the artificial teeth for aesthetics, phonetics, and occlusion (Figure 11). The prosthesis is fabricated with a milled titanium bar (Figure 12 to 14).40-42
Flapless surgery was performed under local anaesthetic.43,44 The surgical template was inserted and position­ed with the centric relation inter­occlusal record. While the patient was closed into the interocclusal record, the friction-fit horizontal pins are placed using a 1.2-mm twist drill. The pins were positioned securing the surgical template, and the patient was allowed to open. The first osteotomy site was prepared adjacent to the most distal implant site utilizing the appropriate drilling guides and twist drills sequences (Nobel Biocare). The preplanned length and diameter of the implant was placed using the implant guide. After insertion of the implant (Nobel Speedy Groovy), a template abutment (Nobel Biocare) was inserted that connected the surgical template to the placed implant thus providing additional stability to the surgical tem­plate. The next implant was inserted in the opposite side of the arch, also adjacent to the most distal implant. After the implant was placed, a second template abutment was inserted. The surgical template at this stage is retained by 4 horizontal friction stabilization pins and 2 template abutments, ensuring its stability and accurate position. The remaining implants were placed using the same drilling guides and twist drills sequence.
After all implants were placed, the horizontal pins and the template abutments were removed. The prefabricated definitive prosthesis was inserted. Adjustable abutments (Nobel Biocare) were used (Figure 15), which allowed for discrepancies in the Z-axis. The adjustable abutments consist of interlocking cylinder sleeves with 2 pieces that slide within one another. This slide in the Z-axis allows for minor discrepancies during the placement of the im­plants, thus allowing a passively fitting framework.

Figure 16. Placement of fixed complete denture right after surgery.

Figure 17. Maximum intercuspation, frontal view.

Figure 18. Maximum intercuspation, left lateral view.

Figure 19. Maximum intercuspation, right lateral view.

Once the prosthesis was inserted, the occlusion was evaluated and the retaining screws were torqued into place. The occlusion was adjusted to have simultaneous centric relation contact and a lingualized balanced occlusal scheme which had already been determined at the time the trial denture was fabricated (Figure 16 to 19). The patient was evaluated at one week, one month, and one year after the procedure. No adjustments were necessary.

DISCUSSION
The procedure described has a great number of benefits: shorter over all treatment times, shorter surgery times, and it is less invasive (swelling is diminished, less post-op discomfort, faster initial healing times) due to the flapless technique. An immediate definitive prosthesis is fabricated before the surgery was even performed, and its immediate use is achievable.
The disadvantages of this approach could be some problems that begin within the planning stages. Surgical complications can include planning (software stage) and placement of the implants too deeply into the osseous tissues making it difficult to seat the prosthesis due to osseous tissue interference with the abutments. It is critical to ensure that the osseous tissue is cleared around the placed implant, allowing the abutment to be completely seated. Patients with limited opening could pose a problem due to the inability to fit the surgical guide plus the drills (that have an increased length to compensate for the thickness of the surgical guide) into the mouth.

SUMMARY
An alternative approach to managing the completely edentulous patient with implants and a fixed complete denture has been described. A trial complete denture was fabricated, a CT scan with a double scan technique was used with specialized surgical planning software to preplan the surgery and produce an accurate stereolithography surgical guide providing all the necessary information to fabricate a cast with the desired position/angulations of the implants. This enabled the fabrication of a fixed complete denture prior to the surgical procedure with the insertion of the prosthesis immediately after the surgery was performed.


References

 

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