21: Preliminary Prosthodontics: Fabricating a Template

CHAPTER 20 Preliminary Prosthodontics: Fabricating a Template

After the patient has agreed with the treatment plan, the implantologist must perform a series of carefully planned steps.

FULLY EDENTULOUS JAW

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 a satisfactory occlusal height and plane have been established, procedures for the fabrication of an opposing full denture for the operative jaw can be started.

Impression making and record taking follow classic techniques. The denture should not be completed until the patient has expressed approval of her or his appearance.

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.

When a satisfactory result has been achieved, the denture serves as an indispensable guide. It has been designed to govern implant emergence profiles and abutment locations and lengths.

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.

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.

Replication of the Trial Denture

The trial denture is replicated for use as a surgical template in the following manner.

8. The denture also acts as a computed tomography (CT) radiographic guide (Fig. 20-2). To serve this function, it must be replicated in clear acrylic (Fig. 20-3, A to C). This can easily be done by a staff member, using a Lang duplicating flash filled with alginate (Fig. 20-3, D to F). The final clear acrylic reproduction has many uses. To enforce the dimensional stability, it should be seated on its model, placed in a pressure pot filled with hot water at a minimum of 1500 F, and further cured for 30 minutes (Figs. 20-4 to 20-6).

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.

In the second stage of surgery, the clear replica is used to localize the buried implants, especially if it was marked with amalgam-filled bur locator holes in the first stage.

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).

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.

Before surgery, the surgeon can have a temporary or final prosthesis fabricated that can be attached in the same session as the implant installation.

MODEL-BASED PLANNING

Definitions

ARMAMENTARIUM

The conventional approach to implant surgery follows these steps:

The computer-guided approach shortens the interval between surgery and the final prosthesis:

The results are significantly reduced chair time and increased profitability

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.

NOTE

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.

If the prosthetic treatment plan is to place a temporary or final screw-retained or cemented prosthesis at the time of implant placement surgery, the steps of the process are as follows:

Jan 5, 2015 | Posted by in Implantology | Comments Off on 21: Preliminary Prosthodontics: Fabricating a Template
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