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After studying this chapter, the student will be able to do the following:
1. List the indications and contraindications for dental implants.
2. Describe the materials used for dental implants.
3. Recall the types and uses of dental implants.
4. Describe osseointegration.
5. Discuss the dental hygienist’s role in the maintenance of dental implants.
atrophic edentulous mandible
tooth form implants
I. Medical versus Dental Implants
The typical medical implant is a device that is placed entirely inside the body. The typical dental implant exists both inside and outside the body. A dental implant projects through the oral mucosa and, thus, is not completely surrounded by tissues, as with most medical implants (e.g., silicone breast, artificial hip, knee, and lens implants). An implant existing both inside and outside the body is susceptible to infection. The interface of the surface of the implant and the surrounding tissues is a potential entry site for bacteria and other microorganisms.
II. Indications and Contraindications for Dental Implants
1. Restoring an Edentulous Atrophic Mandible
Originally, dental implants were used predominantly for prosthodontic patients for whom no other treatment options were satisfactory. The most common prosthodontic problem has been making dentures for a patient with little or no mandibular ridge. When the teeth are lost, the alveolar bone (bone that supports the teeth) is no longer stimulated and will resorb. As the alveolar bone reduces in size or atrophies, the ridge available to support a denture shrinks. This is called an atrophic edentulous mandible. Dental implants have greatly improved the treatment of this condition, as shown in Figure 12.1. With the development and success of osseointegrated implants, dental implants are now used as an alternative or adjunct to other conventional prosthodontic treatments.
FIGURE 12.1. A mandibular fixed prosthesis supported by implants. Shown are A. a panorex of an implant-supported fixed prosthesis as well as B. photographs of the atrophic mandible with five implants, C. the prosthesis, and D. the implant-supported prosthesis in place. (Courtesy of Dr. Paul A. Schnitman, Wellesley Hills, MA, and Noble Biocare, Yorba Linda, CA.)
2. Restoring a Single Missing Tooth
For patients with a single missing tooth, a crown supported by a single endosseous implant is becoming a popular treatment option, as shown in Figure 12.2. The conventional option of a three-unit bridge requires that the two abutment teeth be prepared for crowns, as discussed in Chapter 1 and shown in Figure 1.5. Using an implant and a crown to replace a missing tooth may save previously unrestored (no fillings) abutment teeth from crown preparations. Often, the cost of one implant and a crown is comparable to the cost of a three-unit bridge. The specific cost will depend on the implant chosen, the placement procedures, and the final restoration.
FIGURE 12.2. An endosseous single-tooth implant restored with a crown. Shown are A. a radiograph of the implant, abutment, and abutment screw as well as B. clinical photographs of the implant, C. esthetic abutment and cylinder, and D. the crown supported by the implant. (See color images.) (Courtesy of Dr. Roger A. Lawton, Olympia, WA, and Noble Biocare, Yorba Linda, CA.)
Patients with systemic diseases that affect connective tissues may not be good candidates for dental implants. The most common of these diseases is diabetes. Smoking is the other major, common contraindication. Another factor to consider is the patient’s ability to maintain the implants. Effective plaque control, regular dental prophylaxis, and recall examination are critical to the long-term success of implants. It is also important for the patient to have realistic expectations about the resulting prosthesis. Considering the large amount of time, effort, and expense involved, some patients may expect more than can be delivered. With patients having expectations that cannot be met, it is best they avoid any extensive expensive dental treatment.
III. Materials Used for Dental Implants
It is important to realize that although the implant material is a significant factor, how the material is placed and used is more critical to the success of dental implants.
Titanium was briefly discussed in Chapter 10. Titanium and titanium alloys are very common implant materials in dentistry and medicine. Unfortunately, titanium is very difficult to cast; it is commonly manufactured for implants by machining into preformed shapes. The major advantage of titanium is that it will osseointegrate with bone if handled properly. Osseointegration is a kind of biologic bonding of bone to a material. Titanium is used for endosseous and most other types of implants. Numerous early researchers had worked with titanium implants but had limited success. Dr. P.I. Brånemark (an orthopedic surgeon) concurrently developed surgical procedures and implant materials; the results were the first reliable dental implants.
1. “cp Ti,” or “commercially pure” titanium, is used for many types of medical and dental implants. As with other pure metals, cp Ti is not very strong, but it is strong enough for some dental implant uses.
2. “Ti-6 Al-4 V,” or titanium with 6% aluminum and 4% vanadium, is a common aerospace alloy that has been used for dental implants. It is much stronger and stiffer than cp Ti. Dental and medical versions of this alloy have more restrictive composition requirements compared with other industries.
B. Apatite-Coated Titanium
Another popular implant material is hydroxyapatite (HA) bonded to titanium metal. Apatites are a broad class of calcium phosphate materials. The hydroxyapatite of hard tissues, such as teeth and bone, is one example. Hydroxyapatite materials also osseointegrate. Titanium coated with HA is commonly used successfully for many different types of implants. HA-coated implants have had increased clinical success when compared to Ti in certain clinical situations.
C. Other Materials
Dental implants have been made from many other materials. The results were not good; therefore, the search continued until titanium was tried with the proper techniques. These materials included metals, ceramics, and polymers.
Gold, stainless steel, and cobalt–chromium alloys were used with little success.
Hydroxyapatite and other calcium phosphate materials are currently used as implant materials. Vitreous (glassy) carbon, pyrolytic carbon, and aluminum oxide (sapphire) have also been tried with little success.
A variety of polymers, including acrylic resin, have been used. Polymers have had little success as prosthodontic implants, but other uses have been developed. Gore-Tex is a polymer material that is implanted as a “barrier” to tissue growth in periodontics. Gore-Tex is expanded polytetrafluoroethylene, the same polymer as Teflon.
IV. Various Types of Dental Implants
A. Endosseous or Tooth Form Implants
Endosseous implants or tooth form implants are screwed or pressed into a hole that is cut into the mandible or maxilla. All the implants shown in the illustrations of this chapter are endosseous implants. They reside inside the bone, thus the name “endosseous.”
A variety of shapes are classified as endosseous implants. Some are cylinders, with threads on the surface like a bolt or a screw; others have straight sides. Still others, called blade implants, are shaped somewhat like a blade, with notches cut into it. Current use of implants is dominated by cylindrical endosseous shapes. Endosseous implants are used to support a single crown, multiple crowns, a bridge, or a denture.
B. Transosseous or Staple Implants—Optional
A transosseous implant was used to stabilize a mandibular denture. It consists of a plate and several bolts that transverse the mandible in the anterior region. The plate is placed on the underside of the mandible, and the bolts extend through the bone and gingiva into the oral cavity. The bolts have nuts screwed onto the intraoral side of the mandible to keep the implant in place. An extraoral incision under the chin is required to place a transosseous implant.
C. Subperiosteal Implants—Optional
Subperiosteal implants were also used to stabilize a mandibular denture. Subperiosteal implants are placed on the mandibular bone below the periosteum and involve two surgical procedures.
1. The first surgical procedure reflects or “flaps” (peels back) the mucosa and periosteum of the mandible, exposing the denture-bearing alveolar bone. An impression is made of this denture-bearing bone. The soft tissue is then sutured back over the bone.
2. Next, a cast is poured, and framework that supports the eventual denture is cast by a dental laboratory. The framework sits directly on the bone and has several posts that extend through the mucosa and support the denture. Chromium–cobalt is the most common alloy used to cast the framework. Chromium–cobalt is not as biocompatible as titanium; therefore, titanium is also used.
3. The second surgical procedure again reflects the soft tissues covering the alveolar bone, and the framework is put into place. The soft tissue is then put back into place and holds the framework in position. At times, surgical bone screws are used to stabilize the implant.
4. Clinical examples of subperiosteal implants can be found with a web search.