Most of the tooth structure that is observable when looking into the mouth is dental enamel. It is a coating about 1/16 inch (1 to 1.5 mm) thick that covers the internal portion of the tooth, the dentin (FIG. 16.1). Enamel is the hardest substance in the body, and it protects the tooth from injury. Enamel is not present on the tooth root (the portion of the tooth that is in the bone). The portion of the tooth that protrudes into the mouth is called the clinical crown.

FIG. 16.1 This tooth has been cut in half. Note the thin layer of enamel on the outside of the top of the tooth. This enamel is removed when a crown (cap) is made for the tooth.

When a large portion of the enamel covering the clinical crown has been destroyed by dental caries (decay), has had fillings, is broken or worn, or is defective in other ways, the enamel layer must be replaced with an artificial crown (cap). Artificial crowns (caps) fit onto prepared (trimmed) teeth like a stocking cap fits on your head. Crowns (caps) are cemented into place, replacing the enamel and some of the dentin (FIG. 16.2).

FIG. 16.2 A, Worn, decayed, and discolored teeth. B, Teeth restored with crowns (caps), bite open. C, Bite closed into chewing position.

If a single tooth or a few teeth are missing, the enamel may be removed from teeth adjacent to the space, and a fixed prosthesis (fixed bridge) may be cemented into place to fill the space created by the tooth removal (FIG. 16.3).

FIG. 16.3 A, Two missing upper lateral incisors. B, Fixed prostheses (bridges), attached to the canines (eye teeth) and replacing the lateral incisors, are undetectable.

Crowns (caps) and fixed prostheses range from simple to highly complex, depending on the situation. They may be metal alone, metal with tooth-colored porcelain fired over it, or, in some situations, porcelain, ceramic, or plastic alone. Most dentists delegate the construction of crowns (caps) and fixed prostheses to dental laboratory technicians, while the preparation (trimming) of the teeth and seating of the crowns (caps) or prostheses are accomplished by the dentist and the clinical staff.

Costs for crowns (caps) and fixed prostheses are higher than most other oral treatment because of the clinical skills necessary, the expense for significant laboratory time, the cost of metals, and long-term follow-up.

Most general dentists accomplish simple to moderately complex fixed prostheses. However, complex clinical situations are often referred to prosthodontists, who have had more education and/or experience in this area.

This chapter discusses clinical conditions that you will recognize and lists types of treatment that your general dentist or prosthodontist can provide.

WHAT YOU SEE OR FEEL

Conditions, Signs, or Symptoms Related to Fixed Prosthodontics

1. One Missing Tooth

(FIG. 16.4). If one tooth is missing in the front of the mouth, the situation is unsightly, and most persons prefer to have the space filled with an artificial tooth as soon as possible. A missing tooth in the back portion of the mouth, in a location where it is not observable, may or may not require replacement because of appearance. However, most teeth that are removed, regardless of where they were located in the mouth, can cause significant movement of surrounding teeth and collapse of the occlusion (bite) (FIG. 16.5). If your missing tooth has caused an unsightly space in your smile, you may want to replace it soon; but if one of your back teeth was removed, you should discuss the potential collapse of the bite with your dentist before choosing from your alternatives. Usually, you have the following treatment alternatives:

A. Fixed prosthesis (traditional bridge involving at least one tooth on each side of space as abutment teeth) (149)

B. Fixed prosthesis (Maryland bridge) (less prepared [less trimmed] teeth on each side of the space, with conservative bridge holding a false tooth and usually leaving the front portion of the abutment [supporting] teeth intact) (152)

C. Cantilever fixed prosthesis (traditional bridge involving one or more teeth on one side of space, only as abutments) (151)

D. Removable partial denture (all plastic) (162)

E. Removable partial denture (traditional metal and plastic) (162)

F. Removable partial denture, precision or semi-precision (plastic and metal fitted to crowns [caps]) (162)

G. Implant(s) with crown(s) (caps) or prosthesis fixed on top to replace teeth (72)

H. Implant(s) with removable partial denture placed on top of them (70)

FIG. 16.4 A missing front tooth is unacceptable in appearance to most people.

FIG. 16.5 Don’t wait too long! This person waited a few years before attempting to replace the tooth, and the result (collapse) is evident.

2. A Few Missing Teeth

(FIG. 16.6). A few missing teeth usually cause an unsightly appearance and some loss of function. Almost always, the removal of a few teeth causes a collapse of the occlusion (bite) over a period of months to years (FIG. 16.7). Often the loss of a few teeth has been caused by trauma or ongoing periodontal (gum) disease, in which case periodontal therapy must be accomplished before fixed prostheses are placed. When a few teeth have been missing for months to years, significant soft-tissue and bone shrinkage usually have occurred. All of the conditions described infiuence the desirability or acceptability of the following treatment alternatives:

A. Fixed prosthesis (traditional bridge involving at least one tooth on each side of space as abutment teeth) (149)

B. Fixed prosthesis (Maryland bridge) (less prepared [less trimmed] teeth on each side of the space, with conservative bridge holding a false tooth and usually leaving the front portion of the abutment teeth intact) (152)

C. Cantilever fixed prosthesis (traditional bridge involving one or more teeth on one side of space only as abutments) (151)

D. Removable partial denture (all plastic) (162)

E. Removable partial denture (traditional metal and plastic) (162)

F. Removable partial denture, precision or semi-precision (plastic and metal is fitted to crowns [caps]) (162)

G. Implant(s) with crown(s) (caps) or prosthesis fixed on top to replace teeth (72)

H. Implant(s) with removable partial denture placed on top of them (70)

FIG. 16.6 This person has a poor appearance and diminished self-esteem.

FIG. 16.7 Observe how the lower teeth have overerupted into the space on the upper jaw.

3. Many Missing Teeth

(FIG. 16.8). Almost always, many missing teeth cause an unsightly appearance, moderate loss of function, and eventual collapse of the occlusion (bite). Periodontal disease may have caused the loss of teeth and may need treatment before a fixed prosthesis is placed. Significant soft-tissue and bone shrinkage can be present also. All of the above conditions infiuence the acceptability of the following treatment alternatives:

A. Fixed prosthesis (traditional bridge involving at least one tooth on each side of space as abutment teeth) (149)

B. Fixed prosthesis (Maryland bridge) (less prepared [less trimmed] teeth on each side of the space, with conservative bridge holding a false tooth and usually leaving the front portion of the abutment teeth intact) (152)

C. Cantilever fixed prosthesis (traditional bridge involving one or more teeth on one side of space only as abutments) (151)

D. Removable partial denture (all plastic) (162)

E. Removable partial denture (traditional metal and plastic) (162)

F. Removable partial denture, precision or semi-precision (plastic and metal fitted to crowns [caps]) (162)

G. Implant(s) with crown(s) (caps) or prosthesis fixed on top to replace teeth (72)

H. Implant(s) with removable partial denture placed on top of them (70)

FIG. 16.8 Many missing teeth can be restored well with fixed prostheses.

4. Broken or Cracked Tooth (Teeth)

(FIG. 16.9). When a significant amount of tooth structure has broken off, a crown (cap) is usually the strongest and most esthetic in appearance for restoration of the tooth. However, several treatment alternatives are also possible:

A. Crown (cap) (146)

B. Tooth-colored restoration (filling) (173)

C. Metallic restoration (filling) (170)

D. Extraction (92)

E. Fixed (149) or removable prostheses (bridges) (162)

FIG. 16.9 A, This tooth is severely broken. B, A crown (cap) was placed on the remaining reconstructed tooth root.

5. Teeth With Large Dental Caries (Decayed Areas)

(FIG. 16.10). Significant destruction of tooth structure by dental caries is usually repaired best by placing a crown (cap), but more conservative measures may be possible also:

A. Crown (cap) (146)

B. Tooth-colored restoration (filling) (173)

C. Metallic restoration (filling) (170)

D. Extraction (92)

E. Fixed (49) or removable prostheses (bridges) (162)

FIG. 16.10 A, Dental decay has produced an unsightly appearance in the upper front teeth. B, The condition was corrected with six crowns (caps).

6. Teeth With Large Defective Fillings

(FIG. 16.11). Placement of large fillings in teeth usually requires removal of a significant portion of tooth structure, and replacement with new fillings is often not possible. Crowns (caps) are usually the strongest and most esthetically acceptable of the following alternatives:

A. Crown (cap) (146)

B. Tooth-colored restoration (filling) (173)

C. Metallic restoration (filling) (170)

D. Extraction (92)

E. Fixed (149) or removable prostheses (bridges) (162)

FIG. 16.11 A, When old fillings degenerate seriously, the best alternative often is crowns (caps). B, Four crowns (caps) were placed on the upper front teeth.

7. Crooked Teeth

(FIG. 16.12). Many times, slightly to moderately crooked teeth can be straightened and improved in appearance by placing restorations (fillings, bonding, veneers) or crowns (caps). The following treatment alternatives are possible:

A. Crown (cap) (146)

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