Supragingival Margin And Large Gingival Embrasure

Freedom From Dental Disease

Treating gum disease with homemade remedies

Get Instant Access

Data from jepsen A: Acta Odontol Scat id 21:35, 1963.

Data from jepsen A: Acta Odontol Scat id 21:35, 1963.

Shape Roots Abutment Fpd

Fig. 3-23. A, Because of the conical shape of most roots, the actual area of support (A) diminishes more than might be expected from the height of the bone (H). In addition, the center of rotation (R) moves apically and the lever arm (L) increases, magnifying the forces on the supportive structure. B, A fixed partial denture replacing a maxitlary first molar. The first premolar is an abutment providing additional stabilization for this FPD on abutment teeth with compromised bone support. (A redrawn from Roseustiel SF: ln Rayne J, editor: General dental treatment, London, 1983, Kluwer Publishing.)

Fig. 3-23. A, Because of the conical shape of most roots, the actual area of support (A) diminishes more than might be expected from the height of the bone (H). In addition, the center of rotation (R) moves apically and the lever arm (L) increases, magnifying the forces on the supportive structure. B, A fixed partial denture replacing a maxitlary first molar. The first premolar is an abutment providing additional stabilization for this FPD on abutment teeth with compromised bone support. (A redrawn from Roseustiel SF: ln Rayne J, editor: General dental treatment, London, 1983, Kluwer Publishing.)

Gingival EmbrasureOvercontoured Margins Restoration
Fig. 3-24. A, Supragingival margins and large gingival embrasures facilitate plaque control in a periodontally compromised patient. B, Poor prosthetic contours and margins have contributed to this failure.

teeth need very careful assessment where significant bone loss has occurred.

In general, successful fixed prostheses can be fabricated on teeth with severely reduced periodontal support, provided the periodontal tissues have been returned to excellent health, and long-term maintenance has been ensured 33 (Fig. 3-24). When extensive reconstruction is attempted without complete control over the health of the periodontal tissues, the results can be disastrous.

Healthy periodontal tissues are a prerequisite for all fixed restorations. If the abutment teeth have normal bone support, an occasional lapse in plaque removal by the patient is unlikely to affect the long-term prognosis. However, when teeth with severe bone loss resulting from periodontal disease are used as abutments, there is very little tolerance. It then becomes imperative that excellent plaque-removal technique be implemented and maintained at all times.

Span Length. Excessive flexing under occlusal loads may cause failure of a long-span fixed partial denture (Fig. 3-25). It can lead to fracture of a porcelain veneer, breakage of a connector, loosening of a retainer, or an unfavorable soft tissue response and thus render a prosthesis useless. All FPDs flex slightly when subjected to a load-the longer the span, the greater the flexing. The relationship be-

Deflection Dental Fixed Prosthesis

Fig. 3-25. Failure of a long-span fixed partial denture.

Failures Fixed Partial Denture

Fig. 3-26. The deflection of a fixed partial denture is proportional to the cube of the length of its span. A, A single pontic will deflect a small amount (D) when subjected to a certain force (F). B, Two pontics will deflect 23 times as much (8 d) to the same force. C, Three pontics will deflect 33 times as much (27 D).

Fig. 3-26. The deflection of a fixed partial denture is proportional to the cube of the length of its span. A, A single pontic will deflect a small amount (D) when subjected to a certain force (F). B, Two pontics will deflect 23 times as much (8 d) to the same force. C, Three pontics will deflect 33 times as much (27 D).

tween deflection and length of span is not simply linear but varies with the cube of the length of the span. Thus, other factors being equal, if a span of a single pontic is deflected a certain amount, a span of two similar pontics will move 8 times as much, and three will move 27 times as much31 (Fig. 3-26).

Replacing three posterior teeth with an FPD rarely has a favorable prognosis, especially in the mandibular arch. Under such circumstances it is usually better to recommend an implant-supported prosthesis or a removable partial denture.

When a long-span FPD is fabricated, pontics and connectors should be made as bulky as possible to ensure optimum rigidity without jeopardizing gingival health. In addition, the prosthesis should be made of a material that has high strength and rigidity (see Chapter 16).

Replacing Multiple Anterior Teeth. Special considerations in this situation include problems with appearance and the need to resist laterally directed tipping forces.

The four mandibular incisors can usually be replaced by a simple fixed partial denture with retainers on each canine. It is not usually necessary to include the first premolars. If a lone incisor remains, it should be removed because its retention will unnecessarily complicate the design and fabrication of the FPD and can jeopardize the long-term result. Mandibular incisors, because of their small size, generally make poor abutment teeth. It is particularly important not to have overcontoured restorations on these teeth because plaque control will be nearly impossible. Thus the clinician may have to make a choice between (1) compromised esthetics from too thin a ceramic veneer and (2) pulpal exposure during tooth preparation. A third alternative would be selective tooth removal.

The loss of several maxillary incisors presents a much greater problem in terms of restoring appearance and providing support. Because of the curvature of the arch, forces directed against a maxillary incisor pontic will tend to tip the abutment teeth. Unlike the mandibular incisors, the maxillary incisors are not positioned in a straight line (particularly in patients with narrow or pointed dental arches). Tipping forces must be resisted by means of two abutment teeth at each end of a long span anterior FPD. Thus, when replacing the four maxillary incisors, the clinician should generally use the canines and first premolars as abutment teeth.36

There may be considerable difficulty in achieving a good appearance when several maxillary incisors are being replaced with a fixed partial denture. Obtaining the best tooth contours and position for appearance and phonetics can be a challenge. A good attempt can be made with the diagnostic waxing procedure, evaluating any esthetic problems. As treatment progresses, a provisional restoration is provided (see Chapter 15). This may be used to test appearance and phonetics. It may also be readily shaped and modified to suit the patient, and the final restoration can be made as a copy of it, thereby avoiding any embarrassing misunderstandings when the finished fixed prosthesis is delivered.

If anterior bone loss has been severe, as can happen when teeth are lost due to trauma or periodontal disease, there may be a ridge defect (Fig. 3-27). In these patients, a removable partial denture should be considered, especially when the person has a high smile line, since a fixed partial denture generally replaces only the missing tooth structure, not the supporting tissues. Again, a provisional restoration may help the patient determine the most appropriate treatment. A surgical ridge augmentation procedure37 may also be an option, although the results can be unpredictable.

Was this article helpful?

0 0

Responses

  • judy
    What causes failure of long span fpd?
    8 years ago

Post a comment