PubMed · 7980978
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P Thomas. 1994-11-05. Second molar extraction.. https://doi.org/10.1038/sj.bdj.4808603
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The purpose of this study is to investigate whether the extraction of four premolars as a requirement of orthodontic therapy is a factor in the creation of tooth size discrepancies, and to determine whether any tooth extraction combinations create more severe discrepancies. The study is carried out on the pretreatment dental casts of 50 patients with malocclusions. The dental casts were selected according to the main criteria. No tooth-size discrepancy between the mandibular and maxillary dental arches should exist before treatment. Pretreatment mesiodistal dimensions of mandibular and maxillary teeth were measured, recorded on a computer program, and subjected to Bolton's analysis. Hypothetical tooth extractions were performed on each patient by the following combinations: all first premolars, all second premolars, upper first and lower second premolars, and upper second and lower first premolars. The resultant measurements were again subjected to Bolton's analysis to see whether a tooth-size discrepancy had been created. The results were evaluated statistically by the use of paired samples t test. The difference between the pretreatment and postextraction Bolton values was found statistically significant for the first premolar extraction and insignificant for the others. The removal of the four first premolars created the most severe tooth-size discrepancy, whereas the extraction of all four second premolars created fewer discrepancies and the smallest range in the size of discrepancies. The results of this study indicate a new point of view to the question of which teeth to extract when evaluated for tooth size aspect only.
The aim of this study was to determine the in vitro diagnostic performance for approximal caries and occlusal dentine caries diagnosis of the Digora system for digital radiography in relation to the exposure time. Radiographs were made of 220 extracted human posterior teeth and cuspids at exposure time levels of 3%, 6%, 10%, 20%, and 78% of the exposure time needed for E-speed film (image sets I, II, III, IV, and V, respectively). The image sets were put in random order (III, I, IV, II, V) and assessed independently by 3 observers using a 5-point confidence scale. True caries status was determined histologically after sectioning of the teeth. Evaluated parameters were: interexaminer kappa, sensitivity, specificity, Dz3/4 (the distance of one operating point to the diagonal in the ROC domain) and area under the ROC curve. The Spearman correlation coefficients between the parameters and both exposure time and order of viewing of the sets were calculated. For approximal surfaces, the ranges of mean parameter values were: sensitivity 26-33%, specificity 93-95%, Dz3/4 0.63-0.84, area 0.61-0.69. For occlusal surfaces, the ranges were: sensitivity 52-60%, specificity 91-95%, Dz3/4 1.03-1.34, area 0.79-0.87. Out of 24 pairwise comparisons between sets V and I, 5 were significant. Out of 24 comparisons between set V and II, only 2 were significant. It was concluded that diagnostic performance is unlikely to be impaired for an exposure time as short as 6% of E-speed film exposure. When reducing the exposure time to 3% of E-speed film exposure, caries diagnosis may be impaired.