Soft diet causes greater alveolar osteopenia in the mandible than in the maxilla
Introduction
In rat models of occlusal hypofunction, bone formation is significantly suppressed in the bucco-lingual direction, and the stiffness of the alveolar bone is reduced.1, 2 The results of various studies have indicated that a soft diet during the developmental period causes a delay in the growth of the muscles of mastication and in jaw bone development5, 6 as well as changes in the growth of the viscerocranium.7
There are some disparities in the mechanisms of bone metabolism between the upper and lower jaw bones, particularly in terms of the pattern of bone resorption after the loss of teeth. Alveolar osteopenia in the edentulous mandible results in a knife-edge shape of the residual ridge, which contrasts to the smoother surface of the edentulous maxilla.8 Differences in bone remodelling were observed between the maxilla and mandible in tooth extraction model in dogs.9 Densitometry evaluation showed higher alveolar bone mineral density in the mandible as compared with the maxilla that was due to the thick cortical bone.10 A finite element human model demonstrated that occlusal load induced greater displacement of the mandibular teeth than the maxillary teeth at the time of occlusal contact.11 While the differential responses between the two jaw bones in response to diet have been examined, the changes to the bony microstructure between the maxilla and mandible in response to a soft diet are not thoroughly understood. The purpose of this study was to compare the alveolar bone microstructure in the upper and lower jaws in response to a soft diet during growth using micro-CT analysis.
Section snippets
Experimental model
Three-week-old male Wistar rats were randomly divided into a control group (n = 6) and an experimental group (n = 6). Rats in the control group were fed a standard pellet diet, while the rats in the experimental group were fed a diet in gel form (DietGel 76A, ClearH2O, Portland, Maine, USA) for 9 weeks. Body weight was monitored daily. After the experimental period, all animals were anesthetized with an interperitoneal injection and killed by cervical dislocation. The maxilla and mandible of each
Body weight
The body weights of the rats were monitored throughout the experimental period, and no significant differences were found between the soft diet and control groups.
Micro-CT images of alveolar bone structure
The marrow spaces of the inter-radicular alveolar bone were increased in the experimental group as compared with that in the control animals. This tendency was more prominent in the mandible (Fig. 3) than in the maxilla (Fig. 2).
Quantitative evaluation of alveolar bone structure
In response to a soft diet, the values determined for the Vm were increased both in the maxillary and
Discussion
Mechanical stress acting on the bone plays a crucial role in the maintenance of bone homeostasis, and a prolonged lack of mechanical stimulation leads to disuse osteoporosis.12 The unloading of occlusal forces to the alveolar bone results in atrophic changes in alveolar bone and periodontal tissue.13, 14, 15
This study revealed a greater impact of soft diet feeding on the mandibular alveolar bone than the maxillary alveolar bone in the M1 region. Micro-CT analysis showed a tendency towards lower
Funding
This study was financially supported in part by Grants-in-Aid for Scientific Research (23593020 and 22792042) from the Japanese Ministry of Education, Culture, Sports, Science and Technology.
Conflict of interest
None declared.
Ethical approval
The experimental procedures described here were approved by the Institutional Animal Care and Use Committee (#0110199A) and performed in accordance with the Animal Care Standards of Tokyo Medical and Dental University.
Acknowledgment
We wish to thank Nobuhito Nango (Ratoc System Engineering, Tokyo, Japan) for technical support and providing valuable advice for our micro-CT analyses.
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