Evaluation of the Accuracy of Measurements Made on Images Taken From the Mouth for Dental Arches

Malocclusion

Validity, Reliability, Reproducibility, Intra-oral images, Plaster models, Digital images, Little's index of irregularity, Bolton's analysis, Tooth-size-arch-length-discrepancy

The general trend in the orthodontic practice is to become digital in many aspects. Since 1980s, digital photographs have been available and they play a principal role in the orthodontic practice for documentation and diagnosis purposes. Now photographs have an important role in teaching, scientific research and medical examination. Successful orthodontic treatment is based on a comprehensive diagnosis and treatment planning. A few of the fundamental factors in the diagnosis are the spacing condition, tooth size, arch form and dimensions, as well as the tooth-arch discrepancies. Intraoral photographs' major role is to enable orthodontists to document and analyze the occlusal relationships as well as the dental and soft-tissue features in order to arrive at a good diagnosis and an appropriate treatment plan. In 1975, Robert Little developed Little's irregularity index (LII). The index was proposed to assess teeth irregularity, crowding, relapse, and alignment of anterior teeth as it measured the linear displacements in the horizontal plane between contact points of anterior teeth, ignoring vertical displacement, from mesial surface of one canine to the contra-lateral one. The sum of the 5 liner measurements of displacements was the LII score. The higher the index value, the more severe irregularity of the teeth was. LII has been originally developed for mandibular incisors to study relapse; however, researchers have used it to assess upper and lower incisors irregularity Tooth-size-arch-length discrepancy (TSALD) is widely used on study models to assess the level of harmony between tooth size and the supporting basal bone. Bolton analysis is another important measurement used to identify disharmony between maxillary and mandibular tooth size which is considered an important factor to ensure the success of orthodontic treatment. With the application of the suggested formulas, the overall ratio should be 91.3% (±1.91) and the partial (anterior) ratio should be 77.2% (±1.65). The validity and reliability of performing the above mentioned analyses on images taken of the dental arches have not been evaluated yet in the literature. This is the aim of the current project.

Assessment of the LII scores, TSALD, Bolton analysis has been performed by the majority of previous studies using plaster models and calipers in a direct manner. Others have measured previous variables indirectly using 2-dimensional and 3-dimensional (3D) methods. 2D methods have included 2D scans of plaster models or 2D images of the occlusal views. The obtained images have been then analyzed either manually or on-screen using dedicated software. 3D methods have included digital models and have been used by several researchers. Although the wealth of knowledge 3D methods provide, they require the use of 3D imaging techniques with the resultant additional costs, time and labor. Many studies have used 2D digital images of poured plaster models to perform software-based measurements of tooth movement during active treatment but these studies have not reported the accuracy and reproducibility of their methods. Dental impressions have been required to obtain proper study models. This procedure is a time- and labor-consuming for the orthodontist and could be exhausting to the patient. When braces are fitted, impression taking becomes a difficult task and if several impressions are required in the context of a research project, this would impose additional burden to patients and researchers. Therefore, taking intra-oral images of dental arches instead of impressions seems to be a very convenient alternative. Validity and reliability of measurements made on photographs of study models have been evaluated in previous reports. However, it seems to be that there is only one paper in the literature with the aim of validating the use of intra-oral images of the dental arches for performing dental measurement. They found that the analysis of LII was valid. However, the practicability of their suggested method of imaging was questionable and their evaluation was only confined to the LII, which is not the only variable that is used in our ordinary plaster model analysis. Therefore, the primary aim of the current work were to evaluate the validity and reliability of measurements made directly on intraoral photographs compared to those made on poured plaster models in the assessment of the LII, TSALD, and Bolton ratios. As a secondary aim, the comparisons were also accomplished with those measurements made on photographs taken of the corresponding poured plaster models .

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