Elsevier

Journal of Dentistry

Volume 37, Issue 1, January 2009, Pages 12-24
Journal of Dentistry

Ten-year outcome of crowns placed within the General Dental Services in England and Wales

https://doi.org/10.1016/j.jdent.2008.03.017Get rights and content

Abstract

Aim

It is the aim of this paper to consider the factors associated with the need for re-intervention on a crown, and the times to re-intervention.

Methods

A data set was established consisting of patients, 18 years or older, whose birthdays were included within a set of a randomly selected dates, one of which was chosen in each possible year of birth and whose restoration records contained the placement of one or more indirect restorations on courses of treatment with last date on the claim form after 31st December 1990, and with date of acceptance after September 1990 and before January 2002. For each tooth treated with a crown, the subsequent history of intervention on that tooth was consulted, and the next date of intervention, if any could be found in the extended data set, was obtained. Thus, a data set was created of crowns which have been placed, with their dates of placement and their dates, if any, of re-intervention.

Results

Data for over 80,000 different adult patients were analysed, of whom 46% were male and 54% female. A total of 47,474 crown restoration occasions were obtained from the data over a period of 11 years.

Metal crowns were found to have the longest survival—68% at 10 years, and all-porcelain crowns the shortest—48% at 10 years. Factors which were found to influence outcome of crowns included type of crown, age of patient, patient payment exemption status, patient attendance pattern and placement of a root filling in the same course of treatment as a crown.

Conclusions

Full-coverage all-metal crowns have longer survival times before re-intervention than metal-ceramic crowns and all-ceramic crowns. Root fillings are associated with reduced survival time of the crowns examined in this study.

Introduction

While direct placement restorations comprise the largest volume of restorations placed within the National Health Service (NHS) General Dental Services (GDS) in England and Wales,1 there is, nevertheless, a substantial number of crowns placed in any given year within the GDS (Table 1, Table 2),1 with these amounting to a total spend of £117.5 million in the year ending March 2005.1 This study examined the recorded intervals between placing a crown and re-intervention on the same tooth, this being obtained from a large representative sample of patients treated in the GDS of England and Wales between 1991 and 2001, full details of which have already been published.2, 3 The data consist of items obtained from the payment claims submitted by GDS dentists to the Dental Practice Board (DPB) in Eastbourne, Sussex, UK, now known as the NHS Business Services Authority (Dental Services Division). Regulations pertaining to the materials utilized in the construction of the restorations changed during the duration of this study, but, notwithstanding the exact constituents of the metal in metal-containing restorations, three principal groups of crowns dominate the data, namely, all-metal crowns, metal-ceramic crowns and all-ceramic crowns.

The interval between successive interventions is a statistical proxy for the ‘life’ of a restoration, but it must be recognized that there are many other measures in use in the world of dental research.

The start of the life of a restoration is well defined as a point of time, when the restoration is actually placed on the tooth. This date is not explicitly recorded in the administrative records provided to the DPB. In this project, the date of restoration placement was taken to be the last date recorded in the payment claim in respect of the course of treatment. In most cases this is the date of completion, when the dentist discharged the patient at the end of the course of treatment. In this regard, it could be considered that the date of placement of a crown would be close to the date of completion of treatment, since crowns are generally not placed until the remainder of a patient's mouth has been rendered dentally fit. The end of the life of a restoration is conceptually more difficult, and it also strays into the issue of censoring, which was discussed in a previous article.2

In this paper, the definition of the end of the life of a crown was taken to be the date of acceptance for the next course of treatment in which the tooth received an intervention other than maintenance, such as is defined in the Regulations as “stoning and smoothing”.

Re-intervention on a previously restored tooth has been considered to be associated with the original restoration,4 but it is nevertheless possible that there is no causal connection—the re-intervention may have been required in response to a circumstance not related to the original restoration. However, it could be considered that this is less likely to be the case with crowns than with other restorations, given the fact that crowns generally cover most of the surface of the tooth.

Clinical performance of crowns has been assessed by a variety of methods, although, perhaps surprisingly, the literature on bridges is more voluminous than for individual crowns. In this respect, it is of relevance to note that Goodacre et al. could find only eight studies, from a total of 163 papers in their literature review on complications in fixed prosthodontics, that reported incidence data on crowns which were not bridge retainers.5

Van Nieuwenhuysen et al.6 evaluated the outcome of extensive restorations in posterior teeth in a prospective, longitudinal study, calculating a median survival time of 14.6 years for crowns using Kaplan-Meier statistical methodology, compared with 12.8 years for large amalgam restorations, and finding that restoration survival was influenced by extension of the restoration, age of patient, pulpal vitality and use of pins.

Goodacre et al. have recently reported the complications associated with fixed prosthodontics using a variety of searching methods.5 A total of 1476 single crowns were identified in 8 studies and a total of 157 (11%) were associated with some type of complication. The three most common complications were need for endodontic treatment (3%), porcelain veneer fracture (3%) and loss of retention (2%). However, there was found to be little standardization of the reporting of complications, although the data indicated “generally good” performance of single crowns.

Several studies have reported the performance of gold crowns. Leempoel et al. observed crowns and partial crowns for a period of up to 11 years, with the results, presented in 1985, indicating survival rates of 91% for partial gold crowns at 11 years and 97% for full gold crowns.7 Haas et al. assessed the performance of gold crowns, with the results indicating 91% success after 10 years.8 Cross sectional studies have estimated annual failure rates, with the results again indicating good performance of gold crowns.9

It is the purpose of this paper to examine the time to re-intervention of teeth with crowns which have been placed within the GDS Regulations and present a detailed analysis of the factors which may influence this. Another paper will assess the restorations which are placed when a re-intervention is considered necessary.

Section snippets

Methods

The patients included in this study were defined as those whose birthdays were included within a set of randomly selected dates, one of which was chosen in each year. The restoration records consisted of all those records containing indirectly placed restorations which related to courses of treatment with last date on the claim after 31st December 1990, and with date of acceptance after September 1990 and before January 2002, and which were scheduled for payment between January 1991 and March

Results

Characteristics of the Sample Population

  • Out of the 23,165 patients who had received at least one indirect restoration (Table 3), 21,809 had received at least one crown. Of these 21,809 patients, 9849 (45%) were male and 11,960 (55%) were female.

  • Between them they accounted for 33,555 claims for payment sent to the DPB which related to crowns. Each of these related to a course of treatment involving all the care and treatment necessary to secure and maintain the oral health of a patient.

  • The

Discussion

This paper has presented the times to intervention for the different types of crown which are placed within the framework of the GDS and examined the factors associated with survival time. It is not possible to calculate median survival times for crowns examined in the present study because 50% failure is not reached. However, comparison is nevertheless possible with directly placed restoration types which have been previously investigated.3 In this respect, it is of interest to note the

Conclusions

Metal crowns were found to have the longest survival—68% at 10 years, and all-porcelain crowns the shortest—at 48% at 10 years. Factors which were found to influence outcome of crowns included type of crown, age of patient, patient payment exemption status, patient attendance pattern and placement of a root filling in the same course of treatment as a crown.

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