The effect of crown placement on tooth mobility

Objectives: When a crown is constructed for a tooth, the natural morphology of the occlusal surface cannot be reproduced exactly. The new occlusal surface introduces minor changes that cannot always be identified. These changes may be accommodated by the periodontal ligament and the occlusion may adjust naturally. The aim of this study is to measure the mobility of the tooth before and after crown cementation and identify any changes that might occur regarding tooth mobility. Methods: This study investigated 30 male and female fully dentate patients, aged between 23-60 years, already attending for routine restorative treatment but excluding orthodontic care, patients with partial or full dentures and pregnancy. Ethical approval was obtained and the selected patients attended a first examination before crown preparation. Undergraduate students carried out the treatment. For each restoration, tooth mobility was recorded using an electronic tapping device, the Periotest, which measures the movement of the tooth after four gentle taps are applied to it. Tooth mobility (PTV) is calculated from the time delay between successive taps of the instrument due to tooth stiffness in the socket. These measurements were repeated at the recall appointments immediately post-cementation of the crown, one month, six months and a year later. Pilot studies have shown the reproducibility of the Periotest measurements for teeth that are not under treatment. Results: Data analysis shows a mean PTV of 0.6+2.5 initially and -0.8+2.2 at 4 week recall for the control group (n=23). For the treatment group the PTV was -0.7+1.7 initially and 1.3+3.0 after crown cementation returning to 0.9+3.4 after 4 weeks (n=7). Results suggest a slight increase in tooth mobility after crown cementation. Conclusions: The Periotest is a valid technique for measuring changes in tooth mobility following crown cementation.