Sample selection

This descriptive observational retrospective study was compliant with the guidelines of Strengthening the Reporting of Observational Studies in Epidemiology [22]. The study protocol received ethical approval from the Institute of Research and Management, Universiti Teknologi MARA (600-TNCPI (5/1/6). Data were collected at the Diagnostic Imaging Unit of Universiti Teknologi MARA between December 2020 and May 2021. The collected scans belonged to 151 female patients and 60 male patients between the age of 18 and 74 years (mean, 46 years). It was reported that there were no statistically significant differences between the measurements on the right and left sides [19]. The G*Power calculator was utilized for sample size calculation, and the sample size was estimated to be 192 teeth, using a Cohen effect size of 0.5, and 10% (n=19) was added to compensate for the estimated dropouts. To ensure a relatively low margin of error, a minimum of 64 teeth were planned to be included in each group for mandibular central incisors, lateral incisors, and canines. Therefore, CBCT images with 211 anterior mandibular teeth were collected for both sides, along with information on the sex, tooth types, and age of the patients.

The inclusion criteria for the clinical data were as follows: a) Asian race (Malay, Chinese, or Indian ethnicity) and 18–75 years of age; b) the presence of all mandibular anterior teeth, including the left and right sides (central incisor, lateral incisor, and canine); The exclusion criteria were images with a) evidence of dental trauma or root fracture; b) CBCT with distorted images or metal artifacts; c) radiographic images with fillings, restorations, or evidence of any apical lesions, bone loss, or resorption; and d) a history of periodontal and orthodontic treatment.