Coronas

Journal of Oral Rehabilitation 2009 36; 451–461

Coronal tooth structure in root-treated teeth prepared for complete and partial coverage restorations
F. MURPHY, A. MCDONALD, A. PETRIE, G. PALMER & D. SETCHELL
Institute, Eastman Dental Hospital, 256 Gray’s Inn Road, London WC1X 8LD, UK UCL Eastman Dental

SUMMARY This in vivo study assessed the remaining coronal tooth structure in teethprepared for complete and partial coverage restorations using 3Dscanning and a Tooth Restorability Index (TRI). The cuspal coverage preparation designs selected by 10 postgraduate dentists and 10 general dental practitioners were recorded in a questionnaire. Eighteen patients had molar root treatment completed at the Eastman Dental Hospital and were prescribed a coronal-radicular amalgam core andcast restoration. Each tooth was prepared in vivo by one operator for a cast restoration. Two clinical impressions were made to produce two dies: one of remaining coronal tooth structure before crown preparation and a second die of coronal tooth structure in vivo after crown preparation. For teeth prepared for partial coverage in vivo (n = 13), a third die was prepared in vitro representing remainingtooth structure after complete coverage preparation. The

three dies were of tooth structure prior to core placement. All dies (n = 31) were scanned using a laser profilometer and the volume of remaining tooth structure calculated. Four observers scored 31 dies using the TRI. The percentage loss of coronal tooth volume following a complete instead of a partial coverage preparation varied from3Æ29% to 45Æ23% and the mean TRI fell from 10Æ7 to 7Æ5 units. There was a strong correlation between mean TRI and scanned volume of tooth structure (P = 0Æ013). Over 50% of the dentists altered their initial choice of restoration design from complete to partial coverage. Complete coverage preparations removed more tooth structure than partial coverage. KEYWORDS: coronal, tooth structure, root-treatedteeth, complete and partial coverage preparations, tooth restorability index Accepted for publication 8 March 2009

Introduction
Although not evidence-based, it is generally agreed that the amount of residual tooth structure is important to longevity of a tooth and its restoration (1). Root-treated teeth frequently have a limited amount of remaining tooth structure. It is recommended thatroot-treated posterior teeth should be provided with cuspal coverage restorations (2), although it is acknowledged that preparation of an already compromised tooth for this type of restoration will further reduce the remaining

Submitted in partial fulfilment of the degree of Master of Dental Science in Conservative Dentistry, UCL Eastman Dental Institute, University College London.

toothstructure. Recommendations have been made with regard to an acceptable minimum height of remaining coronal tooth structure (3–7), root dentine thickness (8) and length of ferrules (9–11). However, the recommendations of these studies are based on in vitro research, which is limited with respect to simulating the elasticity of the periodontal ligament, bone and tooth structure and the reproduction of theclinical environment including functional forces. A partial coverage design of restoration is likely to be more conservative of tooth structure than a complete veneer restoration. Very few studies have been published addressing the advantages and disadvantages of partial coverage restorations, other than examining the

ª 2009 The Authors. Journal compilation ª 2009 Blackwell Publishing Ltddoi: 10.1111/j.1365-2842.2009.01952.x

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F . M U R P H Y et al.
difference in resistance and retention form of various preparation designs (12, 13). Two studies compared the differences in the amount of tooth structure removal using various preparation designs on anterior Typodont resin teeth (14) and extracted human teeth (15). The extent to which tooth structure is preserved by using a...