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The Tipped Mandibular Molar as a Bridge Abutment: Part II

Nonrigid Connectors

In a previous article (The Tipped Mandibular Molar as a Bridge Abutment: Part 1), the author concluded that the majority of mild to moderate cases of tilted mandibular molars did not require orthodontic alignment. The treatment of a tilted molar that has not been uprighted orthodontically requires the clinician to consider several options: 1) correcting the tilt and providing a proper path of insertion utilizing an adequate preparation design and/or potential modification of the mesial aspect of the tilted third molar; or 2) addressing the tilt of the prepared tooth and the adjacent third molar in the laboratory phase. This discussion addresses the second option in which the tooth is prepared without giving special consideration to the tilt of the molars. This approach may ultimately result in two abutments that do not have a common path of insertion or a path of insertion that is interrupted by the mesial aspect of the tilted third molar.

Abutments Without a Common Path of Insertion

The preparation of a tilted molar along its long axis may result in a mesial tilt that lacks a common path of insertion with the second premolar. Under such circumstances, the fixed partial denture (FPD) may have to be fabricated in two pieces with a nonrigid connector (ie, a rigid attachment) (Figure).1

It is the author's opinion that such a treatment plan is inferior to traditional preparation designs that create a common path of insertion. The use of an attachment for a relatively simple case unnecessarily complicates the laboratory procedure and increases treatment expenses. If the tilted molar cannot be prepared in a manner that establishes a common path of insertion, a severe tilt may be present. This condition should be handled orthodontically due to the periodontal and occlusal considerations mentioned in the previous editorial. The only situation that may justify the utilization of an attachment is human error. If an unintentional undercut is observed following the fabrication of the master model, the patient can be recalled in order to remove the undercut and fabricate a new final impression. An alternate option is to eliminate the undercut on the master cast and complete the FPD. The preparation can subsequently be adjusted with the use of a reduction coping  (a metal coping with a vacancy at the area of the undercut) as a guide, which enables the previously fabricated FPD to be seated. The final alternative requires the fabrication of the FPD in two separate pieces that are connected with an attachment. The use of a reduction coping or an attachment are compromises, however, and not recommended as optimal treatment.

Addressing the Mesial Aspect of the Third Molar

The presence of a tilted third molar may also cause difficulties in obtaining a common path of insertion at the distal aspect of the FPD. Traditionally, clinicians have avoided the preparation of the distal aspect of the second molar and completed a reverse preparation design (a proximal half-crown). This type of FPD, however, is difficult to fabricate in the laboratory. It is the author's opinion that the correct treatment is to reduce the mesial aspect of the third molar until a path of insertion is achieved. The reduced aspect is subsequently polished and sealed with unfilled or filled composite resin. If the treatment is performed properly, the long-term results of the tooth reduction should not be of clinical concern.2 In orthodontics, air-rotor stripping - in which space is gained by reducing the proximal areas - is an acceptable treatment modality for mild to moderate crowding of the teeth.

Conclusion

The fabrication of a simple posterior three-unit FPD in two pieces connected with a nonrigid connector is not necessary in the majority of clinical situations. Proper preparation design is an effective method of achieving a common path of insertion. The mesial aspect of the tilted third molar should also be reduced in order to provide a path of insertion and a finish line rather than utilizing exotic preparation designs.

* Dean: Ostrow School of Dentistry, University of Southern California, Los Angeles, California.

References

  1. Shillingburg HT. Fundamentals of Fixed Prosthodontics. 3rd ed. Carol Stream, IL: Quintessence Publishing, 1997:99-100.
  2. Crain G, Sheridan JJ. Susceptibility to caries and periodontal disease after posterior air-rotor stripping. J Clin Orthodont 1990;24(2):84-85.
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