comparison of the accuracy and reliability of measurements made on cbct and ios images with their made-on plaster models.

Conditions: Malocclusion

Summary: the orthodontist uses plaster models to collect information. this includes identification deviations, classification of malocclusion, formulation of treatment goals for specific patient. models are used to examine the morphology of individual teeth and also to visualize the placement of teeth in individual dental arches. study models it therefore appears to be one of the most important records for treatment planning. in usa, orthodontist can start practicing orthodontics which requires a lot of difficulty 300 new cases in a year and therefore may require an entire room to store plaster models. the minimum file retention period depends on the appropriate platform for the statute of limitations during which legal action for fault can be brought. in the usa, this time period varies from 5 to 15 years, varies from country to country. this platform can be started on the last day of treatment, or it can be postponed until the patient reaches adulthood. regardless of how it is viewed, long term storage is required. over ten years, if 300 new cases are initiated each year, that will represent 6,000 combinations of prototyping, pre-processing and post-processing. additional storage space may be required, maybe somewhere else, with financial implications. with the recent introduction of digital models and cbct images, the orthodontist now has an alternative to traditional plaster study models. digital technology makes it possible to analyze a computer using software capable of rotating, examining and measuring digital images of the model and dental arches from different points of view. the intraoral scanner is a hand-held device that creates digital impressions of the oral fossa and displays it in 3d on a computer screen after being processed by the scanning program for each device. by 1985 the first intraoral scanner was available for commercial use, and over time it had evolved to become smaller, faster, and more accurate. intraoral scanners provide easier treatment planning, better workflow, greater patient acceptance and shorter working time, but more studies are needed to investigate their accuracy and compare with traditional methods. the measurements of the tooth widths are one of the important elements in orthodontic diagnosis because of its role in calculating the partial and total bolton ratio, the ton relationship, and space analysis. therefore, the aim of this study will be to assess the accuracy and reliability of measuring teeth widths and bolton ratios based on three mains well -known methods (plaster models, cbct images and intraoral images) to ensure the safety of orthodontic diagnostic outputs.

several published studies analyzed teeth widths and bolton' ratios using cbct with plaster models, two-dimensional images, or three-dimensional images as the gold standard and applied to patients or skulls, but they did not use the sagittal axis orientation method for each tooth on the limit to determine its precise lateral mesial width, but the method of unified orientation was adopted in the transverse plane. the most important benefit of the cbct is that the measurements are made directly on the digital model, which eliminates the possibility of error that can occur with traditional methods (alginate blending, alginate hardening, casting) or some other digital methods (such as scanning plaster model). the special orientation method was adopted for each tooth separately so that the three axes of the software are perpendicular to the longitudinal axis of the tooth, and the maximum mesio-lateral width is determined on both the axial plane and the transverse plane, and the measurement is made on each of them, which is supposed to be identical in the case of correct orientation. this method is useful for determining the width of each tooth, regardless of its position within the dental arch or overlapping it with other teeth. the intraoral scan is the latest innovation in dentistry to generate three-dimensional models that can be studied, and many tests were conducted on it to determine its accuracy and reliability by determining teeth widths and the bolton ratios with the adoption of plaster models or two-dimensional images as a gold standard. looking at the published medical literature, and in an attempt to find a study similar to the current study, it was found that the comparisons regarding teeth widths measurements were among plaster models (as a gold standard) and cbct images or between plaster models (as a gold standard) and ios images, and no study was found that made a comparison triple among the previous three methods.

Eligibility criteria:
inclusion criteria: 1. age between 18 and 35 years. 2. full permanent dentition from right first molar to left first molar in both upper and lower arches. 3. participants should not be under orthodontic treatment. exclusion criteria: 1. tooth agenesis or extractions. 2. presence of large restorations that could change the mesiodistal diameters of the teeth. 3. teeth with anomalous shapes. 4. teeth with large carious lesions. 5. enamel defects that affect the morphology of crown. 6. severe crowding in the dentition (\< 6 mm). 7. missing or heavily restored teeth. 8. teeth with large carious lesions / enamel defects that affect the morphology of crown/

Keywords: plaster model cone beam computed tomography. intraoral scanner teeth widths bolton' ratios. cbct ios