TOOTH SIZE MEASUREMENTS AND BOLTON ANALYSIS FOR FAST-SET PLASTER MODELS VERSUS COMPUTER-BASED MODELS RENDERED FROM DUAL POUR ALGINATE IMPRESSIONS

Objective: The objective of this in vitro study is to compare measured values of pre-treatment tooth sizes and the Bolton overall and anterior analyses for fast-set plaster dental casts versus computer-based dental models made from a dual pour alginate impression.Materials and Methods: Maxillary and mandibular alginate impressions were made for a sample of thirty-six patients with permanent dentitions from first molar to first molar. Impressions were poured in fast-set orthodontic plaster within one hour and allowed to set for 8-10 minutes. Casts were removed from the impressions, cleaned of any observable plaster and re-examined for quality. Impressions were packaged and sent to OrthoCAD for generation of digital models. Measurements of mesiodistal tooth width were made using digital calipers or OrthoCAD proprietary software. Overall and anterior Bolton analyses were performed for all models. Measurements were repeated no less than two weeks later. Results were statistically analyzed for correlation coefficients and 2 x 2 MANOVA.Results: Correlations showed very high intrarater reliability for measurements made on both plaster and digital casts. Statistical significance was found for differences between plaster and digital casts in mesiodistal measurements of maxillary and mandibular anterior segments and total arch circumference, Bolton overall ratio and Bolton anterior ratio. Values of mean difference between plaster and digital casts for the anterior segment were 0.33 mm in the maxillary arch and 0.70 mm in the mandibular arch. Mean differences over the total arch were 0.68 mm in the maxillary arch and 1.35 mm in the mandibular arch. Value of mean difference between plaster and digital casts was 0.89% for the anterior Bolton ratio and 0.80% for the overall Bolton ratio.Conclusions: The results of this study show statistical differences for tooth size measurements between plaster casts made from the initial pour of alginate impressions and digital casts generated from the second pour. Statistical differences were also demonstrated for both the anterior Bolton ratio and total arch Bolton ratio, indicating differences between measurements were not the result of a uniform distortion occurring between the first and second pour. The small absolute value of mean differences may or may not have clinical significance. Individual practitioners should decide whether the absolute value for these small differences have clinical significance to their practice