CHAPTER 20 Preliminary Prosthodontics: Fabricating a Template
Whatever the ultimate design of the prosthetic, if the jaw to be treated is fully edentulous, the patient should be supplied with a preliminary complete denture. Occlusal corrections to the opposing jaw also must be made. This may involve balancing the natural dentition, adding crowns or onlays, or completely habilitating the faulty opposing dentition. If this is not a practical solution, processed acrylic occlusal onlays should be used as an interim solution. The goal of the restoration should be an ideal occlusal relationship for the implant-supported jaw.
When the denture is inserted, a corrected occlusal plane should appose it. This may involve increasing the vertical dimension and correcting centric occlusion. The trial period that follows is an essential interval of study that should ensure that the patient has become accustomed to and comfortable with the changes. If the patient complains of unrelenting facial or temporomandibular joint (TMJ) pain or aching, premature occlusal contact during chewing, or problems with deglutition that are not ameliorated by time, accommodations are made by increasing the interocclusal dimensions and shortening the teeth.
At this point, the treatment plan is finalized. Choices of a device and other elements are made on the basis of available bone and its quality; the patient’s capabilities, aspirations, and finances; and the dental surgeon’s skills and prejudices. The resulting prosthesis may be an overdenture totally supported by the tissue and retained by an O-ring or ball attachments. It may use two implants, three or more implants (with a fixed cemented or fixed-detachable mesostructure bar, which may be partly or fully implant supported), or five or more implants (buttressing an anatomic fixed bridge or a bar-borne hybrid fixed prosthesis) (Fig. 20-1). Whatever arrangement is chosen, the completed support mechanism (abutments, attachments, bars) must fit within the confines of the newly completed denture. If this cannot be done, the envisioned final appliance will be too large, which will create possibly insoluble esthetic and functional problems.
FIGURE 20-1. A panoramic radiograph showing a mixed tooth- and implant-supported, fixed, cementable, porcelain fused to metal prosthesis in the maxilla and an implant-supported, fixed-detachable hybrid mandibular prosthesis.
The denture, therefore, plays a significant role in the processes of planning, management, and fabrication of the complex restorative device. If the patient already wears a denture that satisfies the required tooth and flange positions, it can be replicated for use in creating the appliance. However, if the existing prosthesis is unacceptable, a new one that presents correct functional and esthetic characteristics must be made.
An acceptable denture is made by following the classic steps of prosthesis fabrication. Impressions are made using stock trays and modeling compound or alginate. A counterimpression of the opposing arch also should be made. The surgeon should make a record base on the cast of the edentulous arch, followed by a facebow recording, which is used to mount the maxillary cast. The record base is corrected to the proper vertical dimension and centric relationship, the denture teeth are selected and set, and the trial denture is fitted. Centric and vertical records are confirmed, and the patient must approve the esthetics. This trial denture does not require processing; however, in most cases it should be processed, because it has value as an interim prosthesis.
FIGURE 20-2. A radiographic template is tried in the mouth to check fit and comfort. By disoccluding the template in the anterior, 3 mm of cold-cure acrylic can be added to allow the jaw to be in a resting position. Petroleum jelly is placed on the opposing dentition to ensure that the cold-cure acrylic adheres only to the template. The radiographic markers in this template are composed of amalgam and acrylic in a 1:3 ratio.
FIGURE 20-3. A, The Lang denture duplicator. The patient’s dentures (or an acceptable wax try-in) are required to fabricate a duplicate denture. B, First, the denture is seated in alginate in one half of the denture duplicator. The alginate is allowed to set. Then, alginate is placed in the other half of the duplicator, which is fully closed. C, After the alginate has set, the two halves are separated (because alginate does not stick to set alginate, the two halves can be separated easily). An accurate reproduction of the internal surface of the denture is revealed. D, The denture is removed from the set alginate. The reproduced tissue and external surfaces are clearly identified. E, Clear, cold-cure acrylic is overfilled into the concave reproduction of the external side of the denture. F, The duplicator is fully closed and locked into position. Escaping excess acrylic ensures that no voids are present in the template.
FIGURE 20-5. A, The clear acrylic duplicate denture after removal from the duplicator. Excess flash is always present. B, Excess flash and rough spots are trimmed with an acrylic bur. C, The finished template should be free of sharp edges and have smooth flanges.
FIGURE 20-6. A, The template is tried in the mouth to ensure comfort and proper occlusion. Final adjustments often are required at this step. B, A temporary fixed prosthesis may be duplicated in a Lang duplicator to form a surgical template and CT scan template.
The clear acrylic denture fulfills its first critical function in presurgical CT scanning. Chapter 4 describes in detail the techniques for embedding a radiopaque medium into premeasured grooves; this process is essential for verifying the locations and dimensions of host sites intraoperatively (see Fig. 20-2). Adding a 3-mm occlusal run to the appliance stabilizes the jaw and provides comfort in the resting position.
After the appliance had been used for CT scanning, it can be used as a surgical template. However, an additional alteration is required. The occlusal incisal edge and lingual acrylic of all potential implant host sites must be cut away (Fig. 20-7). This allows surgical access to the bone while the template occupies its anatomic position. The radiopaque markers allow the surgeon to transfer image findings and dimensions directly to the bony host sites (see Chapter 4).
Suturing completes the first stage of implant surgery. The original denture now continues its essential role as a stent and wound protector while providing the patient with cosmetic and functional benefits. It requires alteration and relining to satisfy this purpose.
After the healing collars or abutments have been attached, the original denture again can be adapted to serve. After the soft lining has been stripped out, it is altered to fit over the permucosal protrusions or transepithelial abutments (TEAs), where it can function through completion of the reconstruction. As an alternative, it can be trimmed back to its dentoalveolar components by grinding away the palate and flanges and then used with cement or even abutment fixation screws as a transitional prosthesis. The significance and versatility of this appliance and its clones cannot be overemphasized.
Surgical templates are necessary to position implants accurately and predictably. Two different designs of surgical templates are recommended for partially edentulous areas. The first style replicates the provisional denture restoration and is made on the corrected replicated cast. The second style uses an Omnivac template but relies on adjacent teeth and soft tissues for support and positioning. If more than two implants are planned, the surgical template that replicates the provisional prosthesis, rather than the Omnivac template, should be used (Fig. 20-8).
FIGURE 20-8. An example of a template for a partially edentulous patient. In this case, the template was fabricated from an acceptable acrylic partial denture in a manner described for complete templates. As an alternative to this procedure, a template can be fabricated based on a suitable wax-up (see Chapter 4).
A surgical guide for placement of implants can be fabricated either on a cast or using a computer-aided design/computer-aided manufacturing (CAD/CAM) system. The guide is made from the diagnostic wax-ups (model-based method) or from computerized planning of implant placement (computer-based method).
The first steps are the physical and radiologic examinations of the patient (see chapters 3 and 4). The implantologist then decides which planning method to use (model based or computer based). The fabrication company (e.g., SciCat [Sirona], Procera [Nobel Biocare], Navigator system [Biomet-3i]) provides the necessary components to create a customized surgical template. Based on the design of the surgical template, they also supply the implants and the surgical and laboratory instruments required to facilitate the operation.
The surgical treatment in the computer-guided approach is based on minimally invasive, guided keyhole surgery. For the patient, this means considerably less pain and swelling than with conventional treatment. This approach also reduces the number of appointments and chair time for the patient. In addition, the patient can return to work and/or social life immediately after treatment, because this method is based on the concept of immediate function. For many practitioners and patients, this means a significant cost savings.
The combination of immediate function and a temporary or final prosthesis that is ready at surgery (e.g., Teeth-in-an-Hour [Nobel Biocare], Diem [Biomet-3i]) radically shortens treatment. By planning the treatment and transforming the data into a surgical template, the surgeon achieves a higher level of safety and predictability. Three-dimensional surgical planning programs have exceptional predictability and produce optimum implant placement. Planning allows for preproduction of either the final or a temporary prosthesis at implant level, or a combination of choice of abutments. Each system provides a total solution that supports the surgeon from the planning stage to completed oral rehabilitation. The software (i.e., Procera or Galaxis) makes the process simple and convenient. Also, because the implantologist knows what instruments and components are needed beforehand, inventory requirements are minimal, and the process is orderly.
If the patient has only a few teeth in the opposing jaw and does not wear a partial prosthesis, the surgeon must make sure to fill the area where the teeth are missing with occlusion index material to make contact with the alveolar ridge. This ensures a horizontal, well-balanced bite registration. The radiographic guide is used to simulate the teeth, soft tissue surface, and edentulous space during the CT scan.
The existing denture (if applicable), if it covers the buccal, lingual, and occlusal aspects and extends over the buccal and lingual soft tissues to the vestibular extension, presents an ideal setup of teeth in terms of occlusion, position, occlusal height, and lip support.
To fabricate a radiographic guide, the surgeon must use acrylic or a material with a similar density. If the jaw is fully edentulous, the existing optimized prosthesis or, if necessary, a new prosthesis should be used. For single and partial cases, the laboratory should be instructed to fabricate an acrylic radiographic guide.
(Courtesy Nobel Biocare, Yorba Linda, Calif.)