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Effects of Decreased Occlusal Loading during Growth on the Mandibular Bone Characteristics.

Hichijo N, Tanaka E, Kawai N, van Ruijven LJ, Langenbach GE - PLoS ONE (2015)

Bottom Line: In the soft-diet group, mineralization below the molars was significantly increased (p<0.05) compared to the hard diet group.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthodontics and Dentofacial Orthopedics, Tokushima University Graduate School of Oral Sciences, Tokushima, Japan.

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus

Lateral view of a reconstructed right hemimandible showing the volumes of interest.C: Condyle; Selection is defined by the line connecting the two notches superior and inferior of this area. M: Attachment site of the superficial masseter muscle; the border line connects the notches ventrocaudal and craniodorsal to the mandibular angle. D: Alveolar cortical bone; the selection is defined by two lines drawn perpendicular to the lower border of the mandible, mesial and distal of the second molar.
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pone.0129290.g001: Lateral view of a reconstructed right hemimandible showing the volumes of interest.C: Condyle; Selection is defined by the line connecting the two notches superior and inferior of this area. M: Attachment site of the superficial masseter muscle; the border line connects the notches ventrocaudal and craniodorsal to the mandibular angle. D: Alveolar cortical bone; the selection is defined by two lines drawn perpendicular to the lower border of the mandible, mesial and distal of the second molar.

Mentions: For a detailed study of the bone characteristics, we used a micro-CT (μCT 40, Scanco Medical AG, Brüttisellen, Switzerland). During scanning all mandibles were similarly oriented and submerged in water to avoid dehydration. Scanning was performed at 10 μm spatial resolution and 45 kV peak voltage (effective energy: 24 keV). An integration time of 1200 ms was applied to substantially reduce noise and optimally discriminate between bone and background. An aluminum filter in the micro-CT and a correction algorithm reduced the effects of beam hardening [21]. A threshold of 642.8 mg hydroxyapatite/cm3 was used to distinguish bone from background. From the X-ray attenuation map, which contains the computed linear attenuation coefficients of each volume element (voxel) of the scan, mineralization of each voxel of the 3D reconstruction of the mandible was determined. From the 3D reconstructions the outer two voxel layers were peeled off to avoid the partial volume effects. For each mandible a distribution map of the cortical mineralization was obtained by projecting the mineral densities of all voxels in a 0.288-mm thick layer below the removed voxels on the surface of the mandible. A more detailed description of the method can be found in de Jong et al. [22]. Visual comparison showed possible local differences in surface mineralization degrees. Upon visual examination, various VOIs were determined selecting only the cortical bone at the attachment site of the masseter, the condylar head and below the second molar (Fig 1). For these VOIs, the cortical bone parameters (including bone volume, BV/TV and mineralization degree) were calculated taking into account the abovementioned threshold value. As mineralization was evaluated by including only "bone" voxels, the material density was calculated. Selection at the attachment site of the masseter and condyle is defined by the line connecting the two specific notches. For evaluation of alveolar cortical bone, the part of the second molar is picked up because of getting correct data from all mandibles.


Effects of Decreased Occlusal Loading during Growth on the Mandibular Bone Characteristics.

Hichijo N, Tanaka E, Kawai N, van Ruijven LJ, Langenbach GE - PLoS ONE (2015)

Lateral view of a reconstructed right hemimandible showing the volumes of interest.C: Condyle; Selection is defined by the line connecting the two notches superior and inferior of this area. M: Attachment site of the superficial masseter muscle; the border line connects the notches ventrocaudal and craniodorsal to the mandibular angle. D: Alveolar cortical bone; the selection is defined by two lines drawn perpendicular to the lower border of the mandible, mesial and distal of the second molar.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4465670&req=5

pone.0129290.g001: Lateral view of a reconstructed right hemimandible showing the volumes of interest.C: Condyle; Selection is defined by the line connecting the two notches superior and inferior of this area. M: Attachment site of the superficial masseter muscle; the border line connects the notches ventrocaudal and craniodorsal to the mandibular angle. D: Alveolar cortical bone; the selection is defined by two lines drawn perpendicular to the lower border of the mandible, mesial and distal of the second molar.
Mentions: For a detailed study of the bone characteristics, we used a micro-CT (μCT 40, Scanco Medical AG, Brüttisellen, Switzerland). During scanning all mandibles were similarly oriented and submerged in water to avoid dehydration. Scanning was performed at 10 μm spatial resolution and 45 kV peak voltage (effective energy: 24 keV). An integration time of 1200 ms was applied to substantially reduce noise and optimally discriminate between bone and background. An aluminum filter in the micro-CT and a correction algorithm reduced the effects of beam hardening [21]. A threshold of 642.8 mg hydroxyapatite/cm3 was used to distinguish bone from background. From the X-ray attenuation map, which contains the computed linear attenuation coefficients of each volume element (voxel) of the scan, mineralization of each voxel of the 3D reconstruction of the mandible was determined. From the 3D reconstructions the outer two voxel layers were peeled off to avoid the partial volume effects. For each mandible a distribution map of the cortical mineralization was obtained by projecting the mineral densities of all voxels in a 0.288-mm thick layer below the removed voxels on the surface of the mandible. A more detailed description of the method can be found in de Jong et al. [22]. Visual comparison showed possible local differences in surface mineralization degrees. Upon visual examination, various VOIs were determined selecting only the cortical bone at the attachment site of the masseter, the condylar head and below the second molar (Fig 1). For these VOIs, the cortical bone parameters (including bone volume, BV/TV and mineralization degree) were calculated taking into account the abovementioned threshold value. As mineralization was evaluated by including only "bone" voxels, the material density was calculated. Selection at the attachment site of the masseter and condyle is defined by the line connecting the two specific notches. For evaluation of alveolar cortical bone, the part of the second molar is picked up because of getting correct data from all mandibles.

Bottom Line: In the soft-diet group, mineralization below the molars was significantly increased (p<0.05) compared to the hard diet group.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthodontics and Dentofacial Orthopedics, Tokushima University Graduate School of Oral Sciences, Tokushima, Japan.

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus