Quantifying enamel demineralization from teeth with orthodontic brackets--a comparison of two methods. Part 2: validity.

This is Part 2 of an in vitro study investigating two techniques for recording and quantifying demineralization surrounding orthodontic brackets. In Part 1 the repeatability of computerized image analysis from digitally converted photographic slides and quantitative light-induced fluorescence (QLF) was explored. In Part 2 of the investigation the validity of each technique was examined. Thirty halved human molars, shaped to look like incisors and with an orthodontic bracket bonded to the buccal surface were used. A small area of each of the four edges of the bracket was variously exposed to a demineralizing gel for 0, 3, 7, or 14 days. Images of the teeth were taken and analysed using the two techniques. Repeat images and analysis were carried out blind. The sensitivity, specificity, positive, and negative predictive values were calculated. A negative result confirmed that there was no demineralization present in the majority of cases. A positive result was less reliable particularly for the occlusal and gingival regions. The 7- and 14-day demineralization patterns were detected every time using the photographic technique. The discrimination of the 0- and 3-day patterns was less reliable. The results of this study were extrapolated to allow for the prevalence of the condition following orthodontic treatment, and the implications of this for a putative clinical trial are discussed, together with the advantages and disadvantages of each method. Either technique would be applicable to use in a clinical trial.