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

Abstract

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 1st radiograph
and the 2nd 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.
Key Words: Bone density, facial bones, mandible, osteoporosis, panoramic radiography