Effects of Decreased Loading on the Mandible

Background Bone mass and mineralization are largely influenced by loading. The purpose of this study was to evaluate the reaction of the entire mandibular bone in response to decreased load during growth. It is hypothesized that decreased muscular loading will lead to bone changes as seen during disuse, i.e. loss of bone mass. Methods and Findings Ten 21-day-old Wistar strain male rats were divided into two groups (each n=5) and fed on either a hard- or soft-diet for 11 weeks. Micro-computed tomography was used for the investigation of bone mineralization, bone volume, bone volume fraction (BV/TV) and morphological analysis. Mandibular mineralization patterns were very consistent, showing a lower degree of mineralization in the ramus than in the corpus. In the soft-diet group, mineralization below the molars was significantly increased (p<0.05) compared to the hard diet group. Also, bone volume and BV/TV of the condyle and the masseter attachment were decreased in the soft-diet group (p<0.05). Morphological analysis showed inhibited growth of the ramus in the soft-diet group (p<0.05). Conclusion Decreased loading by a soft diet causes significant changes in the mandible. However, these changes are very region-specific, probably depending on the alterations in the local loading regime. The results suggest that muscle activity during growth is very important for bone quality and morphology

Impact of Bone Volume Upon Condylar Activity in Patients With Unilateral Condylar Hyperplasia

Purpose: Unilateral condylar hyperplasia or hyperactivity (UCH) is a bone overgrowth disorder affecting the mandible. The purpose of this study was to determine the relations among age, condylar bone structure, condylar bone volume, and condylar bone activity on single-photon emission computed tomographic (SPECT) scans in patients with UCH. Materials and Methods: This study included 20 patients with a clinical presentation of progressive mandibular asymmetry and a positive bone SPECT scan. A bone SPECT-derived standardized uptake value (bSUV) for the condylar region was determined. All patients underwent condylectomy to arrest further progression of the disease. The resected condyles were scanned with a micro-computed tomographic scanner (18-μm resolution). Bone architectural parameters were calculated with routine morphometric software. Results: The mean bSUV of the condyle on the affected side was 15.32 (standard deviation [SD], 8.98) compared with 9.85 (SD, 4.40) on the nonaffected side (P =.0007). For trabecular bone structure, there was a nonsignificant correlation between the SUV of the affected condyle and the measured bone volume fraction (r = 0.13; P =.58) and trabecular thickness (r = 0.03; P =.90). Conclusion: No meaningful relation was found between condylar bone volume fraction and condylar activity on bone scan; therefore, the impact of bone volume fraction on the results of bone scans is limited. The measured condylar activity on SPECT scan seems to be primarily a reflection of the remodeling rate of bone

Graphs depicting the BV/TV.

<p>(A) Condyle, (B) Attachment of the masseter, (C) The part below the second tooth. **Significant difference between both groups (p<0.05).</p

Landmarks and measurement items for linear analysis (A) and angular analysis (B) by 3D reconstructions.

<p>Me: Menton (most inferior point of mandibular symphysis). Gn: Gnathion (most anterior point on bony contour of mandibular symphysis). Go: Gonion (most outward and everted point on angle formed by junction of ramus and body of mandible). Co: Condylion (most superoposterior point on mandibular condyle). Cp: Coronoid process (most superior point on coronoid process of mandible). Me-Co: Total length of the mandible (distance measured between menton and condylion). Me-Go: Base length of the mandible (distance measured between menton and gonion). CpH: Height of coronoid process (a perpendicular line from coronoid process to the line connected to gnathion and menton). CoH: Height of mandibular ramus (a perpendicular line from condylion to the line connected to gnathion and menton). CoGo/GnMe: Gonial angle (angle made from the line connected to condylion and gonion and the line connected to gnathion and menton). CoGn/GnMe: Ramus angle (angle made from condylion, gnathion and menton).</p

Graphs depicting the material mineralization of the cortex at the (A) Condyle, (B) Attachment of the masseter, (C) The part below the second tooth.

<p>**Significant difference between both groups (p<0.05).</p

Lateral (3-A) and medial (3-B) views of the cortical mineralization.

<p>Left column: bones of the hard-diet group, Right column: bones of the soft-diet group. The colours red, yellow, green, blue, and purple indicate mineralization ranges 718.4–863.0, 863.0–1007.7, 1007.7–1152.4, 1152.4–1297.0, and 1297.0–1441.7 mg HA/ccm, respectively.</p

A representative 3D reconstructions of the hard-diet group (A) and the soft-diet group (B).

<p>Scale bar = 5 mm. Note the much smaller size of the soft-diet mandible.</p

Graphs depicting the bone volume.

<p>(A) Condyle, (B) Attachment of the masseter, (C) The part below the second tooth. **Significant difference between both groups (p<0.05).</p

Comparison of mandibular measurements between the hard- and soft-diet groups.

<p>Comparison of mandibular measurements between the hard- and soft-diet groups.</p