Oral Prosthodontic Rehabilitation
Thomas J. Balshi, DDS, PhD, FACP
PROSTHETIC TREATMENT FOR LOST TEETH
There are five types of prosthetic approaches to replacing missing teeth (Table 1).
Temporary Removable Partial Dentures (Provisional Restoration)
Traditionally the simplest form of tooth replacement has been the use of removable dental appliances (fig. 1). Easily fabricated, light weight, temporary removable appliances provide the partially edentulous patient with immediate esthetic replacement. This form of treatment gives the athlete psychological and often physical comfort, but limited functional ability.
Long-Term Removable Partial Dentures
When the hard and soft tissues have healed after traumatic tooth loss, a stronger removable prosthesis can be constructed using chrome cobalt castings to fasten the prosthesis to the remaining dentition. This is an inferior alternative form of treatment to "permanent" tooth replacement.
Another indication for the use of removable partial dentures is replacement of multiple missing teeth. When five or six consecutive teeth are avulsed, the adjacent abutment teeth are widely spaced. In this condition, the use of a traditional fixed partial denture may be contraindicated. For example, the loss of all the maxillary anterior teeth (six teeth) would require the use of multiple posterior teeth for the construction of a fixed prosthesis. This prosthetic design would place the remaining abutment teeth under severe strain because of the forces applied to the anterior cantilevered pontic (tooth replacement) section. A removable partial denture may put less stress on these abutment teeth. Likewise it is not uncommon when large numbers of teeth are traumatically lost that portions of the alveolar ridge are also lost. When this occurs, the removable partial denture also provides an esthetic replacement for the missing residual ridge tissue.
Fixed Partial Dentures (Traditional Crown and Bridge)
With technologic advances, non-removable prosthodontics for the replacement of missing teeth is preferred over removable appliances. Using crowns and fixed bridges (Fig. 2) to replace avulsed maxillary anterior teeth can generally be considered after a preparatory treatment program.
A thorough diagnosis is required when considering a fixed prosthesis of this nature. A traumatic impact to the mouth, creating the loss of some teeth, may also have an impact on the remaining teeth. Teeth and bone adjacent to a trauma site may sustain fractures. Complete radiographic examination is necessary to determine the condition of the potential abutment teeth, their nerves, and surrounding bone. Testing these teeth for mobility will effect the number required as support for a non-removable prosthesis.
|Figure 5 A
An implant supported prosthesis can replace not only missing teeth but missing alveolar bone and mucosal tissue (gum tissue) when these structures have been traumatically lost.
(Courtesy of Nobel Biocare, Yorba Linda CA)
|Figure 5 B (Below)
When only tooth is lost and overlying mucosa retained, an implant supported prosthesis can be constructed simply to replace the missing tooth structure. (Courtesy of Nobel Biocare, Yorba Linda CA)
|Figure 6 After the appropriate healing time the fixture is re-exposed and the titanium abutment securely fastened after aligning the interlocking hex between the cylinder and the top of the implants. (Courtesy of Nobel Biocare, Yorba Linda CA)|
|Figure 8 Proper depth for different fixtures is indicated on the screw taps as well as various measuring instruments used during stage I surgery. (Courtesy of Nobel Biocare, Yorba Linda CA)|
|Figure 7 Fixture installation. Sequential drilling to prepare the osteotomy site is performed with single use disposable carbon steel drills and taps. Top row: Mucoperiosteal flap, round pilot drill perforates cortical plate, 2 mm diameter twist drill establishes implant depth, guidepin confirms long axis angulation, measuring instrument used to determine exact length of the implant, 3mm diameter pilot drill starts the final preparation, 3mm twist drill completes the depth of preparation. Bottom row: 3mm diameter guidepin confirms angulation, counter sink prepares the crestal bone, the final measurement determined, titanium tap establishes threads in the areas of dense bone, implant placed at 15 to 20 RPM, final hand tightening of implant in bone, removal of carrying device and placement of cover screw prior to mucosal closure. (Courtesy of Nobel Biocare, Yorba Linda CA)|
Prosthetic Treatment for Lost Teeth
-Temporary removable partial dentures (provisional restoration)
Diagnostic pulp testing for nerve vitality in the proposed abutment teeth is also important after traumatic injury. If the supporting abutment teeth for a fixed prosthesis are traumatically injured or sustain partial fractures, root canal therapy for the abutment teeth and the use of a post and core restoration will be a necessary part of the prosthetic treatment.
Following trauma, the soft tissue morphology changes as the edema diminishes. Therefore, an interim restoration is recommended before the construction of a final fixed prosthesis. This healing time serves well to permit the patient time to accommodate to both the concept of a fixed prosthesis, as well as the physical change in the mouth. The complete reduction of edema in the healing edentulous ridge is necessary to establish a physiologic relationship between fixed replacement teeth and the remaining vital tissues. This period also provides the patient an opportunity to learn new oral hygiene methods required to maintain a healthy mucosal response to the prosthesis.
The advantage of a traditional fixed partial denture is the stability of the restoration and its esthetic value. The greatest disadvantage of this prosthesis is the biologic insult to the abutment teeth. Removal of enamel and dentin frequently leads to insult of the pulp requiring subsequent endodontic (root canal) treatment. In addition, the margins of the crowns, when placed subgingivally (below the gum lines) can lead to periodontal insult and subsequent gingival irritation and alveolar bone loss.
Resin-bonded Fixed Partial Denture (Maryland Bridge)
Advancement in enamel bonding during the past 3 decades permits the replacement of small numbers of teeth with resin bonded retainers. These fixed bridges can be used as an interim form of tooth replacement, and in some rare cases, as a long-term form of prosthetic treatment.
Resin bonded retainers rely on the ability to isolate healthy, clean enamel on the adjacent abutment teeth and produce a mechano-chemical bond between the metallic wings of the prosthesis and the abutment tooth enamel (Fig. 3).
Careful patient selection is essential for the effective use of a resin bonded fixed partial denture. Adequate occlusal (bite) clearance for the lingual retentive wings must be determined in advance. The strength and longevity of this prosthesis is only as strong as the resin bond between the enamel and the base metal alloy of the restoration. When the design relies totally on the bond strength, these bridges become loose and often fall out within 5 years.
Resin bonded bridges are generally constructed with base metal alloys usually containing nickel. Patients with known allergies to the contents of the base metal alloys should not be considered as candidates for this treatment. Increased allergies to metals containing nickel and beryllium have been reported particularly in females. Patients who brux or clench are not good candidates for resin bonded bridges and should be treated with more strongly retained prostheses. next page
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