[Dimensional accuracy and stability of the complete denture impression tray]

When recording final impressions for complete dentures, the dimensional stability of the tray material is of significance for the final result. The aim of this study was to measure the dimensional changes in different tray materials prior to and after border moulding. Self-curing acrylic, thermoplastic acrylic and shellac were measured at fixed intervals with the aid of a measuring microscope. The trays were constructed on metal master models with respectively nine reference points for the upper tray and eight points for the lower tray. Self-curing acrylic produces the most contraction as a function of time, followed by thermoplastic acrylic. Shellac exhibits the least contraction c.q. dimensional change. Thermoplastic acrylic material proved to be the most stable after border moulding. Shellac was totally unreliable due to the major changes following border moulding.