Assessing Marginal Adaptation of Hall Technique Fitted Preformed Metal Crowns

The Hall Technique is a method for managing caries in primary molar teeth by sealing it under preformed metal crowns (PMCs). It differs from conventional PMC use as no tooth preparation takes place prior to cementing the crown, relying on the crown seat and restoration/cement/tooth seal to stop caries progressing. Although clinical observation can assess this “fit” for different tooth types, quantification of marginal adaptation might help develop crowns with contours more appropriate for the Hall Technique for teeth where poor fit is regularly encountered (e.g. maxillary first primary molars) Objectives: To develop and pilot a protocol for quantifying marginal adaptation of PMCs placed on extracted primary teeth using the Hall Technique. Methods: The ability to measure PMC marginal adaptation was tested (following standardised protocol for fitting PMCs in-vitro) using three methods; 1. Analysis of cement volume between the PMC and tooth 2. Measurement of differences in linear dimensions of the tooth and PMC, and 3. Quantification of visible cement area on magnified images, following removal of roots. These methods were piloted on 20 maxillary, and 20 mandibular first primary molars. Results: Methodological disadvantages of methods 1 and 2 made them less suitable for assessing marginal adaptation than method 3. Pilot work found statistically significant differences between maxillary and mandibular teeth with linear measurements (method 2) (p<0.05), and when the cement area between the crown margin and tooth margin was measured (p<0.001) but no difference using cement volume analysis. Conclusion: The measured differences in marginal adaptation reflected clinical observation, Quantification of cement area following removal of tooth roots was the most appropriate method for assessing marginal adaptation of Hall Technique fitted PMCs. In collaboration with commercial manufacturers such information may be of value in providing crowns with improved dimensions to suit the Hall Technique. Supported by Tattersall Scholarship funding