Endosseous Implants and Immediate Provisionalization in the Aesthetic Zone: Computer-Guided Surgery

For the partially edentulous patient, a fixed partial denture with the use of abutments on the natural teeth was, at one time, the only alternative for a fixed restoration. With the introduction of dental implants, however, multiple single-unit restorations are now possible. They can provide a treatment option that preserves bone and does not compromise healthy teeth. The predictability and success of implant treatment has been well-documented for both completely edentulous and partially edentulous patients.1-5 With the increase in patients’ aesthetic awareness, the introduction of new and improved restorative materials, and procedures that offer superior aesthetic outcomes, including all-ceramic restorations first introduced in 1967 by McLean,6 these goals are a certainty. More recently, ceramic implant abutments were introduced, which can also aid in achieving excellent aesthetics.
Osseointegration of dental implants is the most important requirement for implant-supported restorations. Several factors affect the osseointegration process. These include, but are not limited to, bone quality, surgical technique, and patient habits. Incorrect implant localization and angulations are the primary cause of nonaxial loading during function, contributing to the loss of osseointegration.7 The objective of this therapy is a functional and aesthetic restoration, which can only be achieved by the optimal placement of endosseous implants. 
Clinicians concur that there is a need to use surgical guides for the correct placement of endosseous implants and to avoid aesthetic, functional, and phonetic complications.8,9 An ample variety of designs and techniques exist for the fabrication of surgical guides, ranging from simple ones (made from thermoplastic, vacuum-formed guides)to more complex ones (made from CT scans and CAD/CAM technology).
The use of 2-dimensional radiography (including panoramic, periapical, and bite-wing radiographs) may not allow the dentist to assess bone form and density adequately at the recipient site. As a result, the dentist typically must fabricate a surgical guide using a mounted cast and these radiographs. Several techniques for fabricating a surgical guide have been proposed, including the use of acrylic resin, vacuum-formed guides, among others.8,10,12 Depending on the complexity of the case, different surgical guides can be chosen. The use of CT scans combined with CAD/CAM technology for the fabrication of surgical guides not only provides a guide for the exact positioning of the implant, but also allows us to fabricate implant components such as abutments as well as temporary or definitive restorations prior to surgery.
Computer-designed and generated implant abutments have also changed the restorative protocols for implant dentistry. The Procera design software, which offers computer-aided design (3-D CAD), provides the opportunity to develop implant abutments from zirconia. Through this portion of the software, the user can custom-design abutments and fixed restorations using all-ceramic materials that potentially offer greater aesthetic results than the classic ceramo-metal restoration. Customized abutments from several materials may be fabricated with the 3-D CAD technique in the following manner:
A screw with a graduated pin for determining abutment height is placed into the implant replica embedded in the master cast. This is done to visualize and align the computer image with the master cast. The design software enables the alteration of the body of the abutment. Its angle, height, width, and taper can be modified. The gingival margin height and width, as well as the emergence angle, can also be modified. The completed abutment design is represented on the screen and transmitted electronically to the production facility, where it is then milled. The implant abutment is delivered within 4 days of sending in the order.13,14
The software enables the practitioner to fabricate individualized implant components with the desired height, width, and contour. These components are biocompatible and successfully mimic the appearance of natural teeth.15-18
This article describes the rationale in using the computer-guided implant surgery technique for the placement of 2 endosseous implants on a partially edentulous patient utilizing zirconia abutments as well as the use of temporary restorations prior to the implant surgery.

CASE REPORT

Figure 1. Initial view of the edentulous area.
A 42-year-old white female reported to the University of Michigan Department of Prosthodontics with a chief complaint of discomfort in the maxillary arch associated with the absence of the left central and left lateral incisors (Figure 1). In addition, she expressed displeasure with both the aesthetics and comfort of the provisional partial denture currently in use.
The patient was presented with 3 treatment options: a removable partial denture to replace the edentulous area; a 4-unit all-ceramic fixed partial denture; or the placement of 2 endosseous implants to replace the 2 missing maxillary incisors, as well as all-ceramic restorations. The patient decided upon the last option. It was also the patient’s desire to have immediate provisionalization done for aesthetic reasons. A complete medical examination and review of her medical history was performed. There were no medical findings that would contraindicate dental care, including elective surgery.

PRESURGICAL PROCEDURES

Figure 2. The preliminary cast.
Preliminary, irreversible hydrocolloid impressions (Jeltrate  [DENTSPLY International]) were taken of the patient’s maxillary and mandibular arches; these were poured using type III dental stone (Microstone [Whip Mix Corp]; Figure 2). Maxilloman-dibular relationship records, including a face-bow transfer, were taken using occlusal registration wax (Aluwax Dental Products) and baseplate wax (Truwax [Dentsply International]). The case was mounted using these records on a semiadjustable articulator (Hanau Wide-Vue [Water Pik]).
A new, interim, removable partial denture was fabricated with no metal clasps. This transitional prosthesis was fabricated to help assess the proposed tooth position and aesthetics.
A series of holes, 2.0 mm in diameter, were then drilled into the interim removable partial denture and filled with gutta-percha (Ultradent Products) to serve as radio-paque markers. At this point, the patient was referred for a CT scan using a double-scan technique.14 The first CT scan was made with the provisional removable partial denture in place in the mouth; the second CT scan was made of only the provisional removable partial denture without the patient. Both scans, consisting of up to 200 individual projections, were required to form the eventual 3-D images of the bone and prosthesis. Then the data from the CT scan was introduced into the Procera NobelGuide software (Nobel Biocare). The planning 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 interim partial denture.
The NobelGuide software is sophisticated and requires several days of training to learn how to operate. For this reason, only some of the most significant steps of the planning process will be described here.  This software enables us to coordinate the radiographic views from the CT scan and the surgical plan for the implant surgery.
Based upon the available bone and the position of the denture teeth, 2 implants were planned for placement into the anterior maxilla. External hexagon Bränemark implants (Nobel Biocare) were planned: a 4.0x13.0-mm in the position of the upper left central incisor, and a 3.3x13.0-mm implant in the area of the upper left lateral incisor.   In addition, the plan required 2 anchored pins to stabilize the surgical guide during the implant surgery procedure.
The surgical plan was sent via the Internet to the Procera milling center in Göteborg, Sweden, for the fabrication of the surgical guide that would accommodate the appropriate drill sizes for the implants.
Figure 3. The surgical guide, as received from the production facility.

When the surgical guide was received in the dental clinic (Figure 3), it was utilized in conjunction with the casts to fabricate a template that illustrates the position of the implants on the cast before the surgery. The possibility for fabrication of custom abutments, as well as provisional restorations prior to the surgery, is a consequence of the reliability found via the planning software and surgical guides. The surgical guide contains all the information necessary for the fabrication of the master cast including the position, size, and angulations of the implants. This makes it possible to accurately fabricate the abutments and the provisional fixed restorations.

Figure 4. The preliminary cast is sectioned in the area of the proposed implant placement. Figure 5. The surgical guide is shown fitting passively on the sectioned cast.
The edentulous area in the maxillary cast is sectioned where the implants are going to be placed (Figure 4). The surgical guide is placed onto the cast to ensure passive fit and adequate space for the components needed for planning the procedure (Figure 5).
The transfer components (guided pin and abutment) are placed through the metal sleeves of the surgical guide, creating an assembly with the implant replicas that dictate the exact position where the implants are going to be placed. The surgical guide with the assembly is placed onto the sectioned cast.
Figure 6. Guided pins and abutment have been placed into the surgical guide. Surgical guide placed onto the cast, and soft-tissue moulage (PVS) injected onto the internal surface of the surgical guide. Figure 7. The modified soft-tissue cast with correct positioning of the dental implants.
A polyvinyl siloxane (PVS) soft-tissue moulage (Gingitech [Ivoclar Vivadent]) was created by injecting the PVS material onto the internal surface of the surgical guide with an approximate thickness of 2 mm to aid in crown profile emergence and verify the fit of abutments on the implants (Figure 6). The remaining space of the cast was poured using a type V gypsum material (Die-Keen [Heraeus Kulzer]; Figure 7).
Two custom zirconia abutments were fabricated using the 3-D CAD technique previously described. The provisional restorations were fabricated using acrylic resin (Lang Dental Manufacturing) and adapted to the margins of the previously fabricated zirconia custom abutments.

SURGICAL PROCEDURE

Figure 8. Occlusal view of the endosseous implants placed using the surgical guide. Figure 9. The zirconia abutments placed on the endosseous implants immediately after surgery and torqued at 35 Ncm.
Figure 10. Provisional restoration cemented after surgery.

The surgery, utilizing a flapless technique, was performed under local anesthetic. External hexagon Bränemark implants were placed: a 4.0x13.0-mm implant in the area of the maxillary left central incisor, and 3.3x13-mm in the position of the maxillary left lateral incisor. The surgical guide was placed in the patient’s mouth, and 2 stabilization pins (designed on the computer software to secure the surgical guide in place) were inserted after creating an opening with a 1.2-mm drill. The first osteotomy site was prepared for the central incisor using the appropriate drilling guides and twist drills. The implant was placed using the prefabricated implant guide. After insertion of the implant, a template abutment was placed (Nobel Biocare) connecting the implant to the surgical guide. This provided additional stability for the guide. The same procedure was performed for the implant located at the site of the lateral incisor. The second implant was placed using the same drilling sequence and guides. After the two implants were placed, the surgical guide was removed (Figure 8). The custom abutments were then torqued to 35 Ncm (Figure 9). After verification of the fit to the abutment margins and the emergence profile was checked, the temporary restoration was cemented in place with zinc oxide eugenol (TempBond [Kerr Corporation]). The occlusion was verified and adjusted to ensure that only contacts in centric occlusion occurred, with no contacts in lateral protrusive movements (Figure 10).

DISCUSSION

The selection of treatment modalities has always been a dilemma. In the past few years, with the increased use of dental implants, this dilemma has become of greater concern due to the increased variety of treatments, including the possibility of treating edentulous patients with single-unit restorations on implants. The longevity and success rate of restorations are primary concerns for the patient as well as for the clinician. In a study by Romeo,19 cumulative implant survival rates were calculated for im-plants supporting single-tooth prostheses at a failure rate of 4.4% after a period of 7 years. Studies on the longevity of fixed partial dentures have been conducted, and they all reflect a common finding, that the main reason for failure is caries.20,21 Longevity of these fixed partial dentures on natural teeth are determined by the time in service. According to De Backer, et al,22 the 20-year survival rates show failure percentages of 33.8%. From these studies and many others, including case reports,23 clinicians have been performing more and more treatments in the realm of implant dentistry. The clinician has many decisions to make involving issues such as timing, type of loading (immediate loading, delayed loading), type of restorations (screw retained, cement retained), and type of cementation (definitive, temporary). With this new treatment modality, clinicians have a greater and more complete variety of viable options that must be taken into consideration for the treatment of the partially and completely edentulous patients. 

Conclusion

The placement of endosseous implants in edentulous areas has proven to be an excellent alternative for replacing single or multiple teeth. With the help of software designed for computer-guided surgery, it is possible to achieve accurate implant positioning and to fabricate provisional restorations, including abutments, before the surgery. These procedures work together to enhance aesthetic and functional results as well as minimize a patient’s time in the dental chair.


References

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Dr. Abbo is a clinical lecturer, Biologic and Materials Science, Division of Prosthodontics, at the University of Michigan School of Dentistry. He can be reached at (734) 763-3326 or abbovan@umich.edu.

Ms. Miller is a fourth-year dental student at the University of Michigan. She can be reached at millersz@umich.edu.

 



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