Introduction

The skeletal system plays a pivotal role in children's growth, development, and overall health. Bones provide structural support, protect vital organs, facilitate movement, and serve as a reservoir for minerals essential for numerous physiological processes. Understanding the intricacies of bone health in a healthy paediatric population is of utmost importance, as it lays the foundation for lifelong musculoskeletal well-being. Bone mineral density, is one of the most important factors to measure bone quality, as it is a reliable and non-invasive method. There are various available techniques that have been used to assess and/or quantify bone density. Radiographic imaging, such as dual-energy X-ray absorptiometry (DXA), remains the gold standard for evaluating bone mineral density. Another frequently used technique is panoramic radiography. Many valid indicators have been developed and used to analyze bone quality and quantity in panoramic radiographs, two of which are the Mandibular cortical index (MCI) and Mandibular Cortical Width Index (MCW). These two indices were created during the past several decades to evaluate the mandibular bone mass's quality and quantity and detect resorption in panoramic radiography.

Aim

The primary aim of the study is to systematically record and evaluate qualitatively and quantitatively the cortical bone of healthy children aged 6-18 years. Secondary objectives are:​

1. To evaluate the distribution of bone density in different gender and age groups.
2. To evaluate cortical bone quality in different gender and age groups.
3. To investigate the possibility that bone density is affected by factors that generally alter occlusion and indirectly masticatory forces such as the presence of extensive carious lesions, missing teeth, extensive resin composite restorations, and Stainless-Steel Crowns.

The ultimate goal of the study is to create reference tables of the thickness of the cortical bone in a healthy Greek population of children and adolescents.

Material and Methods

It was a double-blinded retrospective cohort study evaluating mandibular cortical bone of healthy children and adolescents through dental panoramic radiographs taken in the context of the patient’s dental needs. The dental records of all patients from the Department of Paediatric Dentistry and the Department of Orthodontics (Dental School, National and Kapodistrian University of Athens) treated between 2012 and 2021 were searched for patients, aged 6-18 years of age, with a dental panoramic radiograph available. The period selected ensured that all radiographs are comparable as they have been performed with the same radiographic machine and the possible magnification is the same.

Panoramic radiographs of 660 children aged 6-18 were divided into different groups according to age and gender. The inclusion criteria were panoramic radiographs of good quality of patients with updated medical and dental records. Exclusion criteria were panoramic radiographs of poor quality of patients with diseases/ conditions/ treatments affecting the bone e.g. eating disorders, prematurity, early puberty, musculoskeletal disorders, etc. and of patients undergoing/ undergone orthodontic treatment.

Quantitative assessment was performed by measuring the cortical bone width bilaterally using the Mandibular cortical width (MCW) Index (according to PaulssonBjörnsson et al. 2015) and qualitative assessment using mandibular cortical index (MCI) (according to Klemetti et al 1994). MCI is a qualitative index that evaluates the morphology of the threshold of the cortical bone with the trabecular bone distally to the mental foramen at both sides of the mandible. It is categorized according to a three-point scale C1, C2, C3. MCW is a quantitative index that evaluates the thickness of the cortical bone in both sides of the mandible. In each side a line was drawn along the lower border of the mandible, followed by four perpendicular lines to the tangent at the following points:​

1. Antegonion
2. the mesial cementoenamel junction of the first molar perpendicular to the mandibular base
3. the most superior cusp tip of the second premolar perpendicular to the mandibular base
4. the most superior cusp tip of the first premolar perpendicular to the mandibular base

The thickness of the cortical bone was measured using the software Image J (Image J 1.50c4 for Windows XP). As the software measures length in pixels (1024x1024 pixels;​ 8-bit;​ 1 MB), all measurements were converted into mm using a calculated coefficient factor. The examiners were calibrated prior to the initiation of the study for both qualitative and quantitative evaluation.

Results

The mean age of the patients was 11.7 years (SD:​ 3.37 years). Regarding the stage of dentition, for 30.6% of the patients it was early mixed, 23.3% late mixed and 46.1% permanent.

A statistically significant correlation was observed between bone morphology and gender, with girls having more frequent even and sharp endosteal margin of the cortex(C1) compared to boys and boys having more frequent endosteal margin which shows semilunar defects(C2). When bone was evaluated on both the right and left side as in total, a statistically significant correlation was observed with age groups. In particular, the endosteal margin of the cortex was even and sharp on both sides frequently in patients aged 8 to 11 years old compared to other ages. On the other hand, the endosteal margin showed semilunar defects (lacunar resorption) and/or seems to form endosteal cortical residues on one or both sides were more frequent in patients 14+ years old.

In addition, a statistically significant positive relationship was found between all points assessing bone thickness and age (years), meaning that as age increases, bone thickness also increases. Our study also showed statistical differences in terms of the correlation between cortical bone thickness and type of dentition, namely between mixed dentition and permanent dentition. We found that in mixed dentition C1 predominates and in permanent dentition decreases and increases C2.

Νο correlation was found between bone morphology according MCI Index or bone thickness and the presence of carious lesions, missing teeth, resin composite restorations, and stainless-steel crowns. Furthermore, we created reference tables of bone morphology and the thickness of the cortical bone in a healthy Greek population of children and adolescents.

Conclusions

Within the limitations of this study, it can be concluded that:​

• A statistically significant difference was found between gender and bone morphology according to MCI Index. The endosteal margin of the cortex is even and sharp more frequent in girls compared to boys and shows seminular defects more frequent in boys than girls.
• The developmental stage of dentition was statistically significant correlated with the cortical bone thickness, i.e. cortical bone thickness was significantly higher in permanent dentition compared to early or late mixed dentition.
• There is no correlation between cortical bone thickness or bone morphology and factors such as the existence of extensive caries, composites, stainless steel crowns and missing teeth.
• More broad and well-designed studies are required to support the correlations between age/gender and bone morphology or thickness.
• The results of this study can be an important guide for the clinical dentist, who may check the cortical bone thickness in a panoramic radiograph and refer the patient for further examination. Early detection and adequate treatment of low BMD is essential especially when osteoporosis prevention should occur on time or when orthodontic treatment will occur (bone density affects tooth movement).