Is there a change in the mandibular cortical shape index in panoramic radiographs over time? A longitudinal retrospective study

BACKGROUND: A longitudinal study design was conducted to assess the mandibular cortical shape index (CI) in panoramic radiographs retrospectively. An association between age and a deterioration of different radiological parameters on panoramic radiographs was stated in cross-sectional studies. As longitudinal studies are rare, this one is designed to assess radiological changes over time. MATERIALS AND METHODS: In this longitudinal study, The archive of the dentomaxillofacial radiology department was searched for panoramic radiographs of patients who have two radiographs with a time lapse of at least 15 years between both. The radiographs were then examined and the CI was categorized into three categories: normal, mild, and severely eroded. The following factors were examined to determine if they had an effect on possible changes of the CI using the Chi-square test: The time period between both radiographs, the gender and the age of the subjects when both radiographs were made also compared using the Kolmogorov–Smirnov test. RESULTS: Ninety radiographs met the inclusion criteria. The mean age, when the 1(st) radiograph and the 2(nd) radiograph were made, was 48.7 and 66.9 years, respectively. A deterioration of the CI over time was observed and only 31.1% of the radiographs remained in the same CI category while 57.8% dropped down by one category and 11.1% dropped down by two. The change of CI was significant (P < 0.001 using the McNemar's test). CONCLUSION: In this longitudinally designed study, a deterioration of the CI over time when assessing the nonstandardized panoramic radiographs could be confirmed. This study shows that 68.9% of the patients had CI deterioration of at least one category over the average time of 17.96 years. This is the first study to quantify the CI deterioration over time to our knowledge.