Effect of Mandibular Displacement on Condylar Cartilage Remodelling In Sprague Dawley Rats: A Micro-Structural Analysis

Three dimensional (3D) imaging of cartilage has always been difficult due to the inherent intermediary density between soft tissue and hard tissue in X-rays images, particularly in Micro Computer Tomography (MicroCT). Recent advances in imaging techniques have allowed for the enhancement of cartilage visualization for MicroCT use. Aim: The objective of this study was to provide a new insight in understanding changes in condylar cartilage, determined qualitatively and quantitatively, with normal growth and after the placement of an appliance over a 4 week period. Materials and Methods: Seventy Sprague Dawley rats (five weeks old) were divided into either a control group or an experimental group in which bite ramps were placed on the lower incisors at Day 0. Animals were sacrificed at Days 0, 7, 21 and 28. Right hemisections were then taken and stained with gadolinium chloride for six days before being scanned via a MicroCT unit. Condylar cartilage was digitally extracted from the scans and volumetric measurements were carried out and assessed quantitatively. Three dimensional images of the condyles were also assessed qualitatively for morphological changes between appliances and over the experimental duration. An intra-individual method error study was also carried out. Results Conformational changes were noted in the shape of the condyle between appliance groups and over the treatment duration. Qualitative assessment of the condyles demonstrated a reduction in size over time in all groups with a change in shape of the condylar heads. Anterior displacement of the mandible resulted in significant remodeling and distinctive shape changes that differ from both control and posterior displacement groups. Quantitative analysis demonstrated differences between control and appliance groups in regards to Total volume of the whole condylar head, Total cartilage volume, Total volume of the posterior hemisection of the condylar head and Posterior cartilage volume. The Method error study demonstrated the high reproducibility of results with a coefficient of variation of 5-13%. Discussion This study demonstrated a new method for analysing changes in the condylar head following orthopaedic intervention. Assessment of these changes in the condylar head can now be depicted via a three dimensional, non-destructive method. Hence, growth changes of the condylar head can now be evaluated in its totality compared to traditional methods of assessing cartilage changes sectionally via histological slices. Therefore, this provides a new avenue for improving our understanding in the changes that occur in the condylar head with growth and after intervention. It may also promote further investigations into the effects of systemic drugs on normal growth and manipulation of this important site of growth

Effect of Mandibular Displacement on Condylar Cartilage Remodelling In Sprague Dawley Rats: A Micro-Structural Analysis

Three dimensional (3D) imaging of cartilage has always been difficult due to the inherent intermediary density between soft tissue and hard tissue in X-rays images, particularly in Micro Computer Tomography (MicroCT). Recent advances in imaging techniques have allowed for the enhancement of cartilage visualization for MicroCT use. Aim: The objective of this study was to provide a new insight in understanding changes in condylar cartilage, determined qualitatively and quantitatively, with normal growth and after the placement of an appliance over a 4 week period. Materials and Methods: Seventy Sprague Dawley rats (five weeks old) were divided into either a control group or an experimental group in which bite ramps were placed on the lower incisors at Day 0. Animals were sacrificed at Days 0, 7, 21 and 28. Right hemisections were then taken and stained with gadolinium chloride for six days before being scanned via a MicroCT unit. Condylar cartilage was digitally extracted from the scans and volumetric measurements were carried out and assessed quantitatively. Three dimensional images of the condyles were also assessed qualitatively for morphological changes between appliances and over the experimental duration. An intra-individual method error study was also carried out. Results Conformational changes were noted in the shape of the condyle between appliance groups and over the treatment duration. Qualitative assessment of the condyles demonstrated a reduction in size over time in all groups with a change in shape of the condylar heads. Anterior displacement of the mandible resulted in significant remodeling and distinctive shape changes that differ from both control and posterior displacement groups. Quantitative analysis demonstrated differences between control and appliance groups in regards to Total volume of the whole condylar head, Total cartilage volume, Total volume of the posterior hemisection of the condylar head and Posterior cartilage volume. The Method error study demonstrated the high reproducibility of results with a coefficient of variation of 5-13%. Discussion This study demonstrated a new method for analysing changes in the condylar head following orthopaedic intervention. Assessment of these changes in the condylar head can now be depicted via a three dimensional, non-destructive method. Hence, growth changes of the condylar head can now be evaluated in its totality compared to traditional methods of assessing cartilage changes sectionally via histological slices. Therefore, this provides a new avenue for improving our understanding in the changes that occur in the condylar head with growth and after intervention. It may also promote further investigations into the effects of systemic drugs on normal growth and manipulation of this important site of growth