One of the most difficult issues facing the modern restorative dentist is when and how to restore an Endodontically treated tooth. Endodontic fees (like all dental fees) continue to increase annually. Patients who have had a posterior tooth Endodontically treated frequently are unable to afford immediate full cuspal coverage because their annual insurance benefit maximums have been reached. This problem is not unique to Manitoba but it is more frequently seen here because of the high numbers of patients that are insured and the decision of many dentists to accept assignment of benefits.
Once these benefits run out, the patient and clinician are faced with a choice:
1. The patient immediately pays directly out of pocket for the entire restoration. - Rarely acceptable to the patient
2. The patient retains the temporary restoration as is until the next calendar year. - Frequently chosen by patients but risky.
3. The tooth is restored in the most inexpensive manner possible (Band/IRM, amalgam or composite build-up (with or without post retention)). The problem with this approach is that the patient sometimes considers the core buildup as "functional" and "permanent". The patient's acute symptoms are gone and often they have little motivation to have the final crown placed, especially if the cost is only partially borne by their insurance benefits. By default this then becomes the "definitive restoration".
The question remains: How important is this decision and how does it affect the long-term prognosis of this tooth? Some studies have suggested that a well-constructed coronal restoration has a greater effect on endodontic success than the quality of the endodontic obturation. (Cheung GS Endodontic Failures- Changing the Approach. Int Dent J 1996; 46:131-8) and (Ray HA and Trope M Periapical status of endodontically treated teeth in relation to the technical quality of the root filling and the coronal restoration. Int Endod J 1995; 28:12-8.)
During my discussions with General Practitioners, I was surprised to learn of their opinions regarding the restorative recommendations of their Endodontists. While Endodontists are perceived as excellent in managing emergencies and endodontic problems, the consensus was that their restorative knowledge was limited to dental school teaching or their experiences as a generalist and was out of date. Furthermore, many clinicians believe that the endodontists' overall perceptions may be skewed, since the endodontist sees an inordinate amount of symptomatic cases for retreatment and rarely sees the referral's asymptomatic successes. The Endodontist's recommendation of full cuspal coverage of treated posterior teeth was thought by some dentists to be excessive and some believed it infringed upon the referral's right to decide on the restoration of the tooth as they saw fit.
I began to research the topic of restoration of endodontically treated teeth and the effect on long term prognosis, in order examine whether there was evidence to support the concept that crowning these teeth was necessary for long term success. Anecdotal evidence seemed to support the idea that lack of proper cuspal protection was detrimental to the long-term prognosis of the tooth. However, such beliefs must be recognized as empirical because valid research has not been performed to substantiate this claim. The studies that have been performed appear to have so many variables (endodontic technique, post placement or not, restorative material used, age of patient, time of placement, number of proximal surfaces at access, etc.) that in most cases the research cannot be reliably compared. No proper studies of longevity have ever been performed specifically examining gold, ceramic or resin onlays or cusp covered complex amalgam restorations in Endodontically treated teeth. The increase in popularity of bonded restorations also has contributed to the perception by some clinicians that crown placement is "not necessary" for long-term retention of posterior teeth.
I recently was made aware of an excellent published study that examined this exact problem in detail: Relationship between crown placement and the survival of Endodontically Treated Teeth - Aquilino S. and Caplan D. J of Pros Dent 2002; 87:256-63. The paper first examined previous studies and then attempted to create a complex statistical model that could explain the reasons for tooth loss in endodontically treated teeth. Over 1000 teeth were chosen randomly at a University clinic. Teeth that did not receive a "definitive" restoration were excluded from the study. (This is important because these unrestored teeth have been shown to have exceedingly high failure rates and could have unfairly influenced the data.) After very stringent criteria were applied, 208 teeth in 156 patients were used in the study. 33 incisors, 25 canines, 72 premolars 43 first molars and 30 second molars. 50% were originally carious. 95 teeth had been restored with a post a pore (cast or preformed) and 108 with amalgam, resin, and glass ionomer without a post. 129 of the 203 teeth had a crown placed while 74 were restored with amalgam or resin composite. 20% of teeth required extraction during the follow up period, 14 with crowns and 28 with direct restorations.
Different test models were used to try to isolate individual factors that influenced survival of the tooth.The results of the study showed:
1. Endodontically treated teeth that were crowned after obturation had significantly better survival than RCT teeth without crowns.
2. The number of proximal contacts at time of endodontic access was significantly associated with survival. Teeth with 2 proximal contacts at access had better survival estimates that teeth with 1 or 0 proximal contacts.
3. Teeth with dental caries at the time of access had significantly poorer 5 and 10-year survival rates.
4. Second molars had significantly poorer survival rates than all other teeth combined. They failed 5 times more frequently than other teeth.
5. When other factors were eliminated, statistical analysis showed that Endodontically treated teeth without crowns were lost 4 times more frequently than teeth crowned after obturation.
Several factors must be acknowledged when viewing the results:
1. Tooth numbers were limited by the need for very stringent controls regarding completeness of documentation, knowledge of prior restorative procedures performed before crown placement and statistical parameters of the study.
2. The study recognized that poor survival of second molars could have been influenced by many factors other than the placement of a crown. These included: Occlusal stresses, difficult canal endodontic anatomy, access and restricted visibility.
3. Crown placement eliminated the effect of foundation type on RCT tooth survival. The placement of a crown therefore appears to be more important than the type of foundation (core) for the survival of Endodontically treated teeth.
4. Many other factors limited interpretation of the results of the study. These include: the effect of socioeconomic factors on treatment received (in a dental school clinic), periodontal disease, the number of adjacent missing teeth etc.
5. Because of the limitations of the study, a direct cause-and-effect relationship could not be established. The authors say that a Randomized Controlled Clinical Trial is necessary, something that is difficult to perform with complex multidisciplinary treatment. This is probably why such studies have not been previously been published. They suggested that properly conducted studies may also be able to answer questions as to the "cost effectiveness" of providing crowns for these teeth.
Conclusions of the Study:
1. Endodontically treated teeth without crowns were lost at a 6.0 times greater rate than teeth with crowns when tooth type and the presence of caries at access were controlled.
2. Second molars and teeth with caries at the time of access also were lost at a greater rate.
3. Though treatment recommendations should be made on an individual basis, the association between crowns and the survival of RCT teeth should be recognized during treatment planning if long-term tooth survival is the goal.
How does this translate to actual practice procedures?
Endodontic treatment in posterior teeth can be difficult and expensive. But, when performed properly, it has a very high rate of success. This level of confidence can only be achieved when the restoring dentist and the Endodontist work together to provide the optimal post- endodontic/restorative treatment for the patient. The patient and referring dentist must understand that proper, timely restoration of the tooth is just as much of an emergency as treatment of a symptomatic pulp. It is contrary to the patient's best interest to ask that Endodontic treatment be performed immediately for a toothache, yet have patients wait months to have the same posterior tooth properly restored. (Note: Exceptions are when we are waiting for radiographic evidence of healing or for symptoms to resolve. In that case it is important to ensure adequate coronal seal.) Protracted attempts to temporize the tooth with Cavit or IRM for more than a few weeks risks loss of coronal seal, fracture and overall failure.
Endodontists have an interest (both ethical and financial) in ensuring the best chance for long-term survival of the case. Why? Because treatment failures are expensive…for the endodontist! Some endodontists (myself included) have a policy of not charging patients for conventional retreatment if they have performed the initial treatment within a certain period of time. (In many cases insurers will not pay a 2nd time, a factor that further influences this decision.) If subsequent surgery is required, it is often done at a significant discount as a courtesy to the patient. That is how confident we are in our treatment… when the tooth is properly restored. Lack of proper restoration introduces a variable that we Endodontists cannot control, a variable that risks losing this level of confidence in our treatment.
Informed Consent and Strategies to enhance long-term survival of endodontically treated teeth
The concept of informed consent now demands that we tell patients certain things prior to referral for endo treatment:
1. Failing to restore posterior teeth with full crowns risks much higher risk of long-term failure of the tooth and loss of their initial endodontic investment.
2. Core restorations or multisurface amalgam/composites placed in endodontically treated posterior teeth are NOT a permanent solution. They are associated with 6-x greater risk of loss of the tooth, especially second molars and teeth with fewer intact proximal surfaces at time of access.
3. Waiting for a new calendar year with an access temp (in order to use insurance benefits for restoration), risks loss of the tooth through fracture or endo failure.
4. In the event that the patient elects not to place a definitive restoration immediately after the endodontics, it is the responsibility of the referring dentist to know this before the case is referred. Although this is not ideal, the referral can minimize the risk by making arrangements for immediate post-op long-term temporization (6 months) via stainless steel band, copper band, temp crown or other more "protective" temporary restoration.
Preservation of the patient's initial Endodontic investment demands that we restore the tooth for the long term. When finances dictate that optimal restorative treatment cannot be performed, patients and their referring dentists must understand the increased risk to the endodontic treatment and overall long-term success of the case. The literature is in general agreement that the best long-term results are achieved when posterior teeth are crowned immediately after endodontic treatment.