CHANGES IN GNATHOSONIC AND TOOTH CONTACT CHARACTERISTICS INDUCED BY EXPERIMENTAL OCCLUSAL INTERFERENCES CREATED USING A FULL-CAST DOUBLE CROWN

Occlusal sounds, contact timings and time moments were measured and an alysed on 10 subjects onto whom an occlusal interference was created e xperimentally. A full-cast double crown was unilaterally set on the up per first molar of each subject, then gradually elevated for 0.06, 0.1 0, 0.20 and 0.30 mm by inserting a pre-calibrated metal folio. Occlusa l sound was measured with an analyser designed for the purpose. Timing s and time moments were analysed with a T-scan system. All measurement s were performed at least 10 times per subject. The results showed tha t prolonged occlusal sound duration, changes in acoustic signal wavefo rm and increased shift of the centre of effort were observed concomita ntly with crown elevation. Differences in these values at 0.06 mm;as c ompared with those at baseline were not statistically significant. Thi s could be explained through a physiological compensation by the perio dontal ligament. The differences with baseline were statistically sign ificant from 0.10 mm ongoing. The distribution of occlusal conacts was determined by the use of a newly developed parameter. Referred to as 'Tap Score', the parameter consists of converting contact timings occu ring in seven ranges into least-square-based weighted scores. Analysis of the tap score disclosed evident imbalance between the crowned and the non-crowned side starting from 0.10 mm elevation, whereby a forwar d shift of the major contact point was observed on the non-crowned sid e. Our study demonstrated that evident changes in gnathosonic and T-sc an parameters are likely to occur at a crown elevation within a 0.06-0 .10 mm range. Not only did the results show the analytical capacity of the combined use of occlusal sound analyser and T-scan, but also they confirmed that a method using simple chairside devices, e.g. T-scan a nd Dental Sound Checker, could be helpful in bringing further understa nding and information on occlusal interference.