Fundamentals of Fixed Prosthodontics. James C. Kessler
implants have developed into a reliable treatment modality that can be depended upon to provide long-term replacement of a single missing tooth as well as multiple missing teeth. By no means, though, should the fixed partial denture be regarded as a thing of the past. Not all patients or situations are suitable for implants, just as not all patients or situations are suitable for fixed partial dentures. Judicious treatment planning is still of critical importance.
The implant is ideally suited for the replacement of a single tooth if the teeth that would have served as abutments are untouched by caries or previous restorations. On the other hand, if those teeth need extensive restorations, the patient can be saved expense and additional treatment if the restorations also serve as retainers for a fixed partial denture. Long-span prostheses that will place greater demands on the skills of the dentist, on the resistance of the retainers, and on the abutments and their periodontal support can be avoided by using implant-supported fixed partial dentures instead of tooth-supported fixed partial dentures.
The maximum number of posterior teeth that can be safely replaced with a fixed partial denture is usually two. In rare circumstances, three can be replaced, but that should be attempted only under ideal conditions. An edentulous space created by the loss of four adjacent teeth, other than four incisors, is best restored with implant-supported crowns or a removable partial denture. If more than one edentulous space exists in the same arch, even though each could be individually restored with a fixed partial denture or implants, finances may dictate the use of a removable partial denture. This is especially true when the spaces are bilateral and each involves two or more teeth.
Third molars are not shown in any of the examples in this chapter, and no situation is shown in which a third molar would be a prospective abutment. Rarely can third molars be used as abutments because they have been removed from the mouths of so many patients. Even when they are present, they frequently display incomplete eruption; short, fused roots; and/or a marked mesial inclination in the absence of a second molar.
A third molar should be considered as a potential abutment only if it is upright and completely erupted, with little or no mesial inclination and with long, distinctly separate roots. It also must have a healthy cuff of attached, keratinized gingiva that completely surrounds the tooth. The unattached mucosal tissue that frequently surrounds the distal 30% to 60% of third molars will become inflamed adjacent to even a well-fitting crown margin, and the abutment is likely to fail periodontally.
The following examples are given as a reference that applies under ideal conditions, listing the abutment teeth that normally would be used. Retainer designs should be based on adequate retention, esthetics, and conservation of tooth structure. Clinical situations vary widely, and less conservative designs are required when caries, decalcification, or morphologic traits (such as short clinical crowns) dictate. The configurations in the following scenarios assume that the prospective abutments are still in their original positions. If the abutments have drifted, the situation could become less, and on occasion more, demanding, depending on the current position of the tooth. Fewer or additional abutments may become necessary if there has been drifting or bone loss. The ratios shown for root surface areas are intended as a general guideline, based on average tooth dimensions1,2 and root surface areas.3 An abutment-pontic root ratio of 1.0 or greater is considered to be favorable.4
Conventional partial coverage retainers could be used for many of the prostheses described. However, the reluctance of many patients to accept any display of metal and the lack of dentist familiarity with these preparations require that this design be used only on selected posterior abutments. Likewise, while resin-bonded fixed partial dentures (ie, Maryland bridges) can provide a suitable replacement for single missing teeth, experience with this type of retainer has shown that it demands a well-defined, albeit a very conservative preparation. They are not the “quick and dirty” restorations that some people thought when they first appeared on the scene in the 1980s. They may be used as an intermediate retainer on young patients with teeth that are not fully formed or fully erupted or whose bone is not developmentally stable.
A fixed partial denture can be classified as either simple or complex, depending on the number of teeth to be replaced and the position of the edentulous space in the arch. The classic simple fixed partial denture is one that replaces a single tooth. Dental implants have expanded the treatment possibilities for the replacement of missing teeth markedly. Two scenarios are presented for each missing tooth, describing the use of a conventional tooth-borne fixed partial denture and an implant-supported crown. There are some situations in which a fixed partial denture cannot be placed with a reasonable expectation of success.
In the scenarios that appear on the following pages, the fixed partial denture solution is followed by the implant solution. In the illustrations, implant restorations are indicated by a shaded tooth with a circle in the center; tooth-borne fixed partial denture retainers are represented by a shaded tooth with contours; and fixed partial denture pontics are shown as a shaded outline of the tooth with no morphology.
Simple Fixed Partial Dentures (One Tooth)
Complex Fixed Partial Dentures (One Tooth)
Simple Fixed Partial Dentures (Two Teeth)
Complex Fixed Partial Dentures (Two Teeth)
Complex Fixed Partial Dentures (More Than Two Teeth)
Complex Fixed Partial Dentures (Pier Abutment)
References
1. Shillingburg HT Jr, Kaplan MJ, Grace CS. Tooth dimensions—A comparative study. J South Calif Dent Assoc 1972;40:830–839.
2. Shillingburg HT, Kessler JC, Wilson EL. Root dimensions and dowel size. CDA J 1982;10:43–49.
3. Jepsen A. Root surface measurement and a method for x-ray determination of root surface area. Acta Odontol Scand 1963;21:35–46.
4. Ante IH. The fundamental principles of abutments. Mich State Dent Soc Bull 1926;8:14–23.
Simple Fixed Partial Dentures (One Tooth)
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Missing: Maxillary central incisor Abutments: Central incisor and lateral incisor Considerations: Abutment discoloration or rotation, improper width of edentulous space, or proximal caries will require metal-ceramic restorations (MCRs). In that eventuality, the crowns can double as retainers, and the space can be restored with a fixed partial denture. Retainers: MCR crowns. Resin-bonded retainers might be used if the patient is very young and if the abutments are healthy teeth that have never been restored. Pontic: Modified ridge lap MCR Abutment-pontic root ratio: 1.9 |
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Missing: Maxillary central |