Dentistry and Practices [ISSN: 2581-4990]

A 16 Year Retrospective Study of Survivability of Crowns placed in a Canadian Dental School Environment

Author(s): P Ricard, M Barczak, A Nowakowski, I Pesun and Kim A

Statement of problem: Single unit fixed dental restorations are placed on teeth which are heavily restored exhibiting some coronal breakdown either from, caries or trauma, endodontically treated posterior teeth requiring restoration due to tooth structure loss, or an esthetic requirement. With a gravitation to preserving the natural dentition for as long as possible, long-term clinical studies are required to assess the success of full coverage restorations, survivability, and reasons for failure. 
Purpose: The purpose of this study was to determine the survivability, and reasons for failure, of crown restorations fabricated and placed a Canadian dental school undergraduate clinic, The University of Manitoba, Rady Faculty of Health Sciences, Dr. Gerald Niznick College of Dentistry, in Winnipeg, Manitoba, Canada. 
Materials and Methods: Patient records including digital and paper charts were examined by searching AxiUm, the University of Manitoba‚Äôs dental management software. Ethics approval was obtained from the University of Manitoba Research Ethics Board (H2016:295) (HS20000). All crowns placed between January 1, 2002 and May 30, 2018 was reviewed. Time to failure was recorded and categorized as short-term (within sixty months), or long-term (sixty to 192 months). Reason for crown failure was collected. Kaplan-Meier statistics with an associated P value comparing each fixed restoration were used to derive survival curves using Origin Lab Pro statistical software. 
Results: Between June 1, 2002 and May 30, 2018, 2302 metal ceramic crowns, 2354 full metal crowns, 187 porcelain/ceramic crowns, 14 partial veneer crowns, and 50 CAD/CAM lithium disilicate (LiS2-) crowns were placed in patients attending the University of Manitoba Dr. Gerald Niznick College of Dentistry undergraduate student dental clinic. Over the course of 192 months, 191 metal ceramic crowns (8.3%), 177 full gold crowns (7.5%), 12 porcelain/ceramic crowns (6.4%), 4 partial veneer crowns (36.4%), and 4 CAD/CAM LiSi2 crowns (8.0%) failed over the course of 16 years. 
Short term failures (five years or less) consisted of 93 full metal crowns (4.0%), 108 metal ceramic crowns (4.7%), 9 porcelain crowns (4.8%), 2 partial veneer crowns (14.3%), and 4 CAD/CAM LiSi2 crowns (8.0%). 
Of failures occurring in the first sixty months, full metal crowns and CAD/CAM LiSi2 failures primarily consisted of a need for endodontic treatment due to a loss of tooth vitality (39.8% and 50% respectively). For metal ceramic crowns and all-ceramic crowns, failure was primarily due to the fracture of the ceramic material making up the crown (46.3% and 77.8% respectively). 
After 192 months of service, the survivability of full metal crowns was 92.5%, metal ceramic crowns 91.7%, all ceramic/porcelain crowns 93.6%, partial veneer crowns 63.6%, and CAD/CAM LiS2- crowns 92.0%. 
Overall, the main reasons for failure beyond 60 months up to 192 months for full metal and metal ceramic crowns was recurrent caries, at 61.9% and 42.2% respectively. 
Conclusions: Within the parameters of this study, full metal, metal ceramic, all ceramic, CAD/CAM LiSi2, and partial veneer crowns had good survival rates (92.5%, 91.7%, 93.6%, and 92.0% respectively). 
More than half of all crown failures occurred within the first 60 months (55.7%). The most common reason for failure over the entire 192 month span of the study was recurrent decay, followed by crown restoration material failure. 
Clinical Implications: Dental practitioners have many options for restoring the teeth, however the consideration for esthetics versus functionality and strength for large restorations can prove challenging. 
The dental professional must ensure that the appropriate and best option for the patient is chosen to improve the longevity of the tooth and crown, while preventing further deterioration to remaining tooth structure. 
This can also dictate the type of material available to use as a restorative option, as the amount of remaining tooth structure is critical to the restorative process.

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