Steven Armstrong DDS, PhD
Root canal treated teeth restored with crowns have 18% higher survival rate than without crown coverage.
Limited search finds lower levels of evidence to suggest that crowns may improve survival rate of endodontically treated teeth.
Does the placement of a crown improve the survival rate of a root canal treated (RCT) teeth?
Two researchers searched 1 electronic database from 1960 to 2006 using keywords “restorations”, ”crown”, “endodontic” and “success.” They also manually searched the literature to identify randomized controlled clinical trials and observational studies that evaluated the restoration of RCT teeth with either a crown or a direct restorative material. Only English-language studies that reported "results of all patients, restorations on anterior and/or posterior RCT teeth for at least 2 years and have sufficient data to generate life table analyses" were included. Ten studies out of 1,609 initial references met these inclusion criteria. A formal procedure to measure "good scientific practice" of these ten included studies was completed by 2 calibrated researchers.
The 10-year survival fractions for RCT teeth restored with crowns and direct restorative materials were 81% (±12%) and 63% (±15%), respectively. The quality assessment of studies involved in this analysis shows that the quality of the clinical studies is far from ideal.
Root canal treated teeth covered with crowns have 18% higher survival rate than without crown coverage. The studies that provided evidence for this conclusion were of poor quality.
Source of Funding:
Importance and Context:
Which RCT tooth needs a crown? To adequately answer this question requires more information than currently is available. When planning treatment for a RCT tooth, one common approach is to place crowns on posterior teeth and to crown anterior teeth when there is extensive loss of tooth structure. A full coverage crown, if not indicated, will remove extensive tooth structure, waste health care dollars and limit future treatment options. However, not placing a crown when it is indicated may lead to premature loss of the tooth. In the United States, nearly 1 out of every 5 restorations is a crown (Beazoglou et al. 2007). This comes with a greater cost as compared to large amalgams (Kolker et al., 2006). This paper addresses a vital clinical treatment planning decision that should be based on the best available evidence. This will help ensure that the optimal restorative option is selected and health care dollars are wisely spent.
Strengths and Weaknesses of the Systematic Review:
This systematic review fulfilled many of the AMSTAR criteria for methodological quality. However, the search was limited to 1 electronic database, English-language only and did not consider all publication types. The authors performed a quality assessment of the included studies and tested the appropriateness of combining the data at the two-year interval. The following weaknesses were identified: 1) individual study characteristics and results were not reported, which limited their ability to interpret the results while eliminating the possibility of determining relative benefit/risk ratios; 2) the same data set (Aquilino and Caplan, 2002; Caplan et al., 2002) was used twice when the authors calculated the cumulative failure rate, contrary to the researchers’ warning (Caplan et al., 2002); 3) different study types were not separately evaluated, i.e. randomized controlled clinical trial (a total of 1) and observational studies (a total of 9); 4) it is unclear how many studies comprised the 10-year survival fraction; and 5) the authors made no attempt to separately analyze irreversible failures from reversible/repairable ”failures.”. These weaknesses may have artificially widened the difference between survival rates.
Strengths and Weaknesses of the Evidence:
Only 1 (Manocci et al, 2002) of the 10 identified studies was a randomized controlled clinical trial, and thus capable of identifying the restoration-type as the causative agent for any observed difference in survival rates. Limited to premolars, this randomized controlled clinical trial found no significant difference in survival rates between crowns and a resin-based composite core with a carbon fiber post. The included studies substantially vary in their definitions of failure and in the type of materials used. Also, the number of studies is insufficient to compare the types of material. As a result of these weaknesses, the evidence for improved survival of RCT teeth with the placement of a crown should be interpreted cautiously. In addition, the authors failed to adequately account for other factors, like the amount of remaining tooth structure that might influence tooth survival. No randomized controlled clinical trial exists that compares RCT teeth restored with crowns to direct restorations placed to cover weakened cusps.
Implications for Dental Practice:
Low levels of evidence suggest that crowns improve survival rate of RCT teeth. An 18% higher failure rate at 10 years was determined for RCT teeth without crowns compared to with crowns; however, the reported cumulative survival rate difference at 10 years for the reasons stated above may be indicative but not conclusive. The decision to crown a tooth should consider each patient’s circumstances, as well as those factors that have been reported as predictive of RCT success, i.e. tooth type, presence of caries at time of endodontic access, amount of remaining tooth structure at time of endodontic access, patient age, plaque levels, number of missing teeth, and a history of facial trauma (Aquilino and Caplan, 2002; Caplan and Weintraub, 1997). References: (1) Aquilino SA and Caplan DJ. Relationship between crown placement and survival of endodontically treated teeth. Journal of Prosthetic Dentistry 2002;87:256-263. (2) Beazoglou T, Eklund S, Heffley D, Meiers J, Brown LJ, Bailit H. Economic Impact of Regulating the Use of Amalgam Restorations. Public Health Reports 2007;122:657-663. (3) Caplan DJ, Kolker J, Rivera EM, Walton RE. Relationship between number of proximal contacts and survival of root canal treated teeth. International Endodontic Journal 2002;35:193-199. (4) Caplan DJ, Weintraub JA. Factors related to loss of root canal filled teeth. Journal of Public Health Dentistry 1997;57:31–9. (5) Kolker JL, Damiano PC, Flach SD, Bentler SE, Armstrong SR, Caplan DJ, Kuthy RA, Warren JJ, Jones MP, Dawson DV. The Cost-Effectiveness of Large Amalgam and Crown Restorations over a 10 Year Period. J Pub Health 2006;66(1):57-63. (6) Manocci F, Bertelli F, Sherriff M, Watson TF, Ford TRP. Three-year clinical comparison of survival of endodontically treated teeth restored with either full cast coverage or with direct composite restoration. Journal of Prosthetic Dentistry 2002;88:297-301.