Three-unit fixed prostheses versus implant-supported single crowns
Gordon J. Christensen, DDS, MSD, PhD
In the past, there were only a few alternatives for the replacement of one missing tooth, the best of which was a cemented three-unit fixed partial denture (FPD). Historically, the three-unit FPD has been the most used and most successful therapy for single-tooth replacement. However, the proven success of dental implants during the last decade has made the decision regarding how to replace one missing tooth confusing for both dentists and patients. Sometimes the best treatment is an FPD; sometimes it is an implant-supported crown. There are numerous factors to consider when deciding whether to place a dental implant that will replace the one missing tooth, or whether to prepare the two teeth adjacent to the missing tooth and place an FPD. Which is the best choice?
In this column, I will list and discuss several factors that relate to the decision concerning the replacement of a missing tooth with either a three-unit FPD or an implant and a crown, and I will express my own observations on the potential for success of the two treatment alternatives. I hope the information will assist practitioners in educating patients as they make this often difficult decision.
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PATIENTS’ INTEREST
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There is no question that patients are interested in replacing their missing teeth with root-form dental implants. They often express the opinion that they do not want to "cut down" their healthy teeth to support the "bridge" and the missing tooth replacement. I have encountered many patients who will not consider an FPD, and they demand an implant supporting a single crown. However, most patients do not have the education and background to determine when to place an implant and when to replace the tooth with a fixed bridge. In my opinion, all patients with a missing tooth should be provided with adequate information to make a legitimate judgment about the two major restorative alternatives and the potential negative effects of leaving the missing tooth unrestored.
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COST OF SINGLE-TOOTH REPLACEMENT
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Patients view both treatment alternatives as expensive. I suggest that the dentist assist them in accepting the cost by informing them about the significant integrated laboratory and clinical costs, as well as the expense of materials and implants.
In a comparison of the clinical fees, I found that the fee for a three-unit FPD is less than that for an implant and crown, if the teeth adjacent to the missing tooth space are sound and do not require restorations. If the teeth on both sides of the missing tooth space are defective and need crowns, most dentists, logically, suggest an FPD to replace the missing tooth instead of one implant because of the lower overall cost for the patient.
The table
presents current available fee data from the American Dental Association (ADA)1 regarding implant-supported crown treatment costs, shown according to the 2007–2008 edition of Current Dental Terminology.2
If the teeth to be used as abutments for the fixed pros-thesis are not in need of crowns, a three-unit FPD without an implant is less expensive than placing an implant, an abutment and a crown. The table
shows the fees as reported by the ADA.1
If the decision is made to place a single implant, an abutment and a crown on the implant in the missing tooth area, as well as to restore the two defective teeth adjacent to the implant-supported crown with single crowns, the fee is significantly higher than those for either of the two alternatives described previously (Table).
A comparison of the three potential treatment alternatives shows that a three-unit FPD costs $2,614; the implant, abutment and crown are about 1.3 times that cost ($3,289); and the implant, abutment and crown with the two single crowns on adjacent teeth are about 1.9 times the cost of the three-unit FPD ($5,035).
Cost is a factor in making this important decision, and when dentists counsel patients regarding the most appropriate therapy, they should incorporate fees as part of the decision-making process.
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TIME INVOLVEMENT
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Time involvement is a major factor in some clinical situations surrounding the replacement of a single tooth. If the practitioner decides that because of bone quality or quantity, the implant must integrate into the bone before loading can occur, the range of time allowed for implant integration usually is four to six months. The time to make the crown adds another two weeks for a cumulative treatment time of 4
to 6 months for some implant-supported crowns. If the implant is loaded immediately after placement, the time for treatment includes only the time needed to make the crown, which usually is about two weeks for most practitioners.
The treatment time for a three-unit FPD without an implant usually is only two weeks. Some patients want to have the replacement accomplished as quickly as possible, and that often makes them favor having an FPD instead of undergoing implant therapy.
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EXPECTED SERVICE LONGEVITY
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Most patients are interested in how long a restoration is expected to serve. Estimates for service longevity vary widely, and it is difficult to compare the two techniques in this respect. Many studies have reported estimates for crown and FPD longevity.3–10 The reports range from a few years of service to as high as 84 percent survival of the FPDs at 20 years,10 with recurrent caries being the most reported reason for failure.
Data on the survival of single-tooth implant-supported crowns are more difficult to locate. Survival of the implant itself usually is reported at approximately 95 percent across many years.11–16
However, most studies do not report the survival of the crowns on the implants. One would assume that the individual crowns would have a restoration service potential similar to the porcelain-fused-to-metal abutment crowns in the studies cited earlier, but caries obviously would not be a failure factor with the implants. On the basis of my observations across several decades of placing crowns on both natural teeth and implants, I suggest that single crowns placed over implants should last at least 20 years from a functional standpoint. However, their esthetic longevity may be some years shorter owing to tissue shrinkage, which causes an unacceptable esthetic appearance and loss of superficial color fired onto the crowns.
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DIFFICULTY OF THE TREATMENT
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As a prosthodontist who has placed many single-tooth replacement implants and the subsequent abutments and crowns, I can state that the procedure is relatively easy to accomplish for healthy patients who have adequate bone. Similarly, average three-unit FPDs are relatively easy to accomplish. I judge that the two techniques are similar in complexity, except that many dentists whose orientation is restorative care do not place implants, and so they must delegate that aspect of the procedure to a dentist competent in surgery.
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DISCOMFORT FOR THE PATIENT
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When observing the many clinical procedures of individual dentists and typical patients requiring the replacement of one tooth, I have noted that either technique can be almost painless—or painful, if the dentist uses more intensive procedures. Most patients tell me that for a day or two after crown preparation procedures, the soft tissue around the tooth preparations is irritated. Similarly, most of my patients who receive single implants inform me that there is mild discomfort and awareness of the surgical area for the first few days, but the pain disappears after that time. In my experience, most patients receiving a single implant do not feel it is necessary to take the analgesics prescribed on an as-needed basis. Regarding discomfort or anxiety on the patient’s part, the implant and the subsequent abutment and crown may seem more painful than the three-unit FPD because of the stigma associated with the word "surgery," which frightens some patients.
I suggest that single crowns placed over implants should last at least 20 years from a functional standpoint. However, their esthetic longevity may be some years shorter owing to tissue shrinkage.
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ORAL HYGIENE
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My experience with many patients receiving either of these treatments leads me to conclude that the two treatments, if accomplished well, do not differ in permitting the patient to accomplish adequate oral hygiene. However, pontics on FPDs often are made in so-called "ridge lap" forms, which commonly are observed coming from laboratories and, unfortunately, are accepted by some practitioners. Such ridge-lap anatomy is difficult to clean on an FPD. Properly fabricated crowns for implants are no more difficult to clean than are natural teeth.
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ESTHETIC RESULT
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This subject could fill an entire book. Either procedure has limitations relative to the eventual esthetic result. Either procedure can be excellent or poor esthetically, depending on the bone and soft tissue present, the clinician’s skill and the laboratory technician’s skill. Each of the procedures may have esthetic limitations related to the presence of anatomical anomalies, tooth malalignment, soft-tissue irregularities or lack of adequate underlying bone. Often, surgical procedures are necessary to correct the defects before treatment begins for either an FPD or a single crown over an implant. It is my opinion that in a typical clinical situation, either technique can produce adequate-to-excellent esthetic results, but that occasionally prerestorative oral surgical or periodontal treatment is necessary to achieve optimum esthetic results for either therapy.
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OTHER FACTORS
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The following factors also can influence the decision to select one therapy over another:
- – smoking, which usually is considered to be negative relative to placement of implants;
- – poor oral hygiene history, which may indicate that implant placement could be better than repair and retention of questionable teeth;
- – physical activities, such as potentially traumatic athletic activity, which may require restorations that resist breakage;
- – retained, mobile, periodontally treated teeth that may be better restored with conventional FPDs than with implants;
- – bruxism and clenching that usually indicate the need for high-strength restorations.
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SUMMARY
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Historically, three-unit FPDs have served patients well in replacing a single missing tooth. However, the three-unit FPD procedure is invasive if teeth adjacent to the space are not in need of restorations. The technique of implant placement and restoration of the missing tooth with an implant-supported crown is replacing the three-unit FPD procedure. Research appears to indicate that the single-implant procedure and implant-supported crown have greater longevity than does the FPD restoration on natural teeth. It appears that the state of the art is, whenever possible, placing a single implant-supported crown to replace a single missing tooth.
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FOOTNOTES
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Dr. Christensen is the director, Practical Clinical Courses, and co-founder and senior consultant, CR Foundation, Provo, Utah. He also is the dean, Scottsdale Center for Dentistry, Ariz. Address reprint requests to Dr. Christensen at CR Foundation, 3707 N. Canyon Road, Suite 3D, Provo, Utah 84604.
The views expressed are those of the author and do not necessarily reflect the opinions or official policies of the American Dental Association.
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REFERENCES
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- American Dental Association, Survey Center. 2007 Survey of dental fees. Chicago: American Dental Association; 2007:25–6.
- American Dental Association. CDT 2007–2008 Current Dental Terminology. Chicago: American Dental Association; 2007.
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PATIENTS' INTEREST
COST OF SINGLE-TOOTH REPLACEMENT
