Effect of physical consistency of food on the biomechanical behaviour of the mandible in the growing rat

This study investigated the effect of a soft diet, given to growing rats, on the biomechanical behaviour of the mandible. Female rats, 30 d of age, received an ordinary diet in the form of pellets (i.e. hard‐diet group), and another group of female rats received the same diet, but ground and mixed with water, forming a paste (i.e. soft‐diet group). The experiment lasted 8 wk. Body‐weight and body‐length gains were not affected by the consistency of the diet. No significant differences were found between groups concerning the length, height, and area of the right hemimandible. Mechanical properties of the right hemimandibles were determined using a three‐point bending test, in which bones were stressed on a perpendicular line immediately posterior to the posterior face of the third molar. Structural properties (load at yielding, load at fracture, structural stiffness, and elastic energy absorption) and geometric properties of the fracture section (cross‐sectional area, cortical area, and moment of inertia) were significantly lower in hemimandibles of rats of the soft‐diet group than in those of rats of the hard‐diet group. Material properties of the mandibular bone tissue (elastic modulus and maximal elastic stress), which were estimated through appropriate equations, did not differ between groups. It was concluded that the reduced physical consistency of the diet, possibly associated with a reduced masticatory load, diminished the skeletal load‐bearing capacity of the mandible in growing rats. This observed reduction in the bone structural behaviour was attributed to changes occurring at the level of bone mass and its geometrical properties because intrinsic properties of the bone material tissue were unaffected.     

Effect of masticatory function on the internal bone structure in the mandible of the growing rat

The influence of changes in the masticatory function on bone mass, bone density and cortical thickness was analyzed in different functional units of the mandible of the growing rat. Young male albino rats were fed either a hard diet or a soft diet for 4 wk. Undecalcified coronal sections were selected from five mandibular regions and microradiographic images of the specimens alongside an aluminium stepwedge were obtained. Bone mass and density were measured at selected sites with a computer-aided image analysis system. Cortical thickness was measured on diagrams. The reduced masticatory function in the soft diet group produced different adaptive responses in the tested regions of the mandible. Some regions showed reduced cortical thickness (underneath the incisor and lateral to the first molar and some locations of the ramus), a few showed reduced bone density (medial to the first molar and in the ramus), and only one showed both (in the ramus). Reduced bone mass was associated mostly with thinner cortical bone rather than lower cortical bone density. Changes in cortical thickness and changes in bone density may be two different mechanisms for adjusting local mechanical properties in the mandible of the rat. Masticatory muscle function is a determinant for the amount and density of cortical and trabecular bone and may possibly influence results of orthodontic tooth movement and its possible relapse.     

The effects of mandibular retractive force on the growing rat mandible

The purpose of this study was to investigate the three-dimensional effects of a mandibular retractive force on the growing rat mandible and mandibular growth after the force was removed. Eighty 4-week-old male Wistar rats served as experimental animals and 100 4-week-old male Wistar rats served as the control group. The experimental rats were divided into four groups. Thirty grams of retractive force was applied to each mandible for 4 weeks. Each group was then killed after 4-, 8-, 10-, 12-, or 16-week periods. At the time of death, tibia, skull, and mandible were removed, measurements of those bone specimens were taken, and histologic examinations were performed. Compared with the control group, the experimental group demonstrated no significant differences in body weight nor in the length of measurements of the tibia, skull, and proximal end of the tibia. The mandibles of the experimental group demonstrated shorter anteroposterior length, higher coronoid processes, and a thicker corpus in the retromolar region and condylar neck. The condylar cartilages of the experimental group showed moderate adaptation in the histologic sections. However, mandibles of the experimental animals did not show any catch-up growth behavior after removal of the force. It was concluded that the mandibular retractive force could produce overall growth retardation and transformation of growing rat mandibles, but the force had no effect on the growth behavior after the appliance was removed.     

Effects of ovariectomy on turnover of alveolar bone in the healed extraction socket in rat edentulous mandible

Objective

The number of patients with postmenopausal osteoporosis receiving dental implants because of edentulism is increasing. Since osseointegration around implants requires formation and maintenance of new bone, knowledge of how ovariectomy (OVX) affects turnover of mandibular and maxillary bone is required. In the present study, we investigated the effects of OVX on turnover of alveolar bone in the healed extraction socket of the rat left mandibular incisor.

Methods

The molars and the incisor on left side in 6-month-old Sprague–Dawley female rats (n = 38) were extracted and left to heal for 4 months. Animals were then ovariectomized and killed at the time of OVX (baseline) (n = 4), 6 weeks (n = 10), 6 months (n = 12) and 9 months (n = 12) post-OVX. Changes in bone mass and bone turnover were assessed using static and dynamic histomorphometric parameters.

Results

Bone turnover was increased by ovariectomy (OVX) as reflected by increased static parameters of bone formation and resorption. The changes in dynamic parameters were not statistically significant. Cancellous bone volume/total volume (%) in the post-OVX group decreased more than that in the control group.

Conclusions

Our results suggest that OVX increases the turnover of alveolar bone in the healed extraction socket of rat mandibular incisor, resulting in a decrease of cancellous bone volume with time.     

Variations in bone mass within the cortices of the mandible.

A study of intermandibular variations in bone mass in cortices between regions of the alveolar process and mandibular body and between buccal and lingual cortices in the same region has been carried out. The material consisted of 24 autopsy specimens of half mandibles from normal subjects. Microradiograms of ground sections from incisor, premolar, and molar regions were used. Quantitation of bone mass in percent within the cortices was done by an electronic point-counting system. The analysis indicates that bone mass may lie on nearly the same level all over in the entire lingual cortex. In buccal cortex, bone mass may vary from region to region, as a fall in bone mass from incisor to premolar to molar region in the buccal alveolar cortex, and a rise in bone mass from premolar to molar region in the mandibular body may occur. Bone mass in buccal incisor cortex of mandibular bodies shows great individual variations. Generally, bone mass may lie on a lower level in the buccal than in the lingual incisor and premolar cortec of the mandibular body while bone mass elsewhere lies on nearly the same level in the same part of the two cortices. Bone biopsies should be taken in either the premolar or the molar region of mandibular bodies.     

The effect of streptozotocin-induced experimental diabetes mellitus on calvarial defect healing and bone turnover in the rat

Tooth socket healing is delayed in diabetes mellitus due to impairment of the healing process. One reason for the poor healing may be an abnormal vascular response. The object of our experiments was to study the effect of diabetes mellitus on bone healing using a calvarial wound. Streptozotocin, injected intraperitoneally, was used to induce diabetes in rats. Both insulin-treated, streptozotocin-dosed animals and normal rats were used as controls. Bone formation was measured in the diabetic femur and tibia, and healing of bone defects by guided tissue regeneration was assessed. Cancellous bone volume and bone formation in the femur were greatly reduced in the diabetic model, indicating either a defect of mineralization or osteoid formation. The length, dry weight, ash weight and calcium content of the tibiae of diabetic rats were significantly less than those of the control groups. In a second experiment, a sterile wound was made in the calvaria of diabetic rats, and covered internally and externally with Gore-Tex membrane. Exuberant formation of a primitive bone was evident, with little evidence of osteoclastic resorption of the necrosed bone ends. This was despite the impaired bone formation observed in the long bones in the first experiment.     

Variations in bone mass within the cortices of the mandible

abstract – A study of intermandibular variations in bone mass in cortices between regions of the alveolar process and mandibular body and between buccal and lingual cortices in the same region has been carried out. The material consisted of 24 autopsy specimens of half mandibles from normal subjects. Microradiograms of ground sections from incisor, premolar, and molar regions were used. Quantitation of bone mass in percent within the cortices was done by an electronic point-counting system. The analysis indicates that bone mass may lie on nearly the same level all over in the entire lingual cortex. In buccal cortex, bone mass may vary from region to region, as a fall in bone mass from incisor to premolar to molar region in the buccal alveolar cortex, and a rise in bone mass from premolar to molar region in the mandibular body may occur. Bone mass in buccal incisor cortex of mandibular bodies shows great individual variations. Generally, bone mass may lie on a lower level in the buccal than in the lingual incisor and premolar cortex of the mandibular. body while bone mass elsewhere lies on nearly the same level in the same part of the two cortices. Bone biopsies should be taken in either the premolar or the molar region of mandibular bodies.     

The effect of dietary factors on intradentinal dye penetration in the rat.

Fluorescent dye injected systemically into rats penetrated the dentinal tubules of molar teeth in a dynamic fashion. The presence of dye was established using histological and fluorescence microscopy techniques. The rate of intradentinal dye penetration was dependent on dietary factors: it was high in rats chronically fed Purina rat chow and low in rats fed a cariogenic, high-sucrose diet. In addition, parotidectomized rats showed low levels of intradentinal dye penetration, even though they were maintained on Purina chow. One and 2 ml of plasma from Purina-fed rats were effective in stimulating the dye penetration in intact and parotidectomized rats, whereas 2 and 4 ml of plasma from rats fed a high-sucrose diet were ineffective when infused in either intact or parotidectomized animals. The results suggest that rats fed Purina chow have a significantly higher titre of a circulating, dye penetration stimulating factor than animals fed a high sucrose diet. This circulating factor could be the equivalent of the parotid hormone isolated from porcine tissue. It is suggested that dietary factors may affect secretion of a parotid hormone and thereby regulate the rate of dentinal fluid movement. There is therefore the prospect of a functional relationship between diet, the regulation of dentinal fluid flow by an endocrine system and dental health.     

The effect of oral ipriflavone on the rat mandible during growth

Different types of ipriflavone (IF) have been reported to be effective when used as a remedy for bone loss due to osteoporosis. However, no information is available regarding the relationship between IF and jaw bone structure. The aim of this study was to examine the effect of IF on rat mandibles during the growth stage. Thirty-two 5-week-old Wistar male rats were divided into four groups. The control group was fed a standard diet, group A received a low calcium diet (calcium content 30 per cent of the standard diet) for 6 weeks, and the other two groups were fed a low calcium diet for 3 weeks and then a standard diet without IF (group B) or with IF (group C) for 3 weeks. In addition, distilled water was provided for all groups. The effects of IF on mandibular size and bone mineral content were investigated, using lateral cephalometric analysis and peripheral quantitative computed tomography (pQCT).For mandibular length, the control group showed a significantly higher value than groups A and B (P < 0.01, P < 0.05, respectively), while group C demonstrated a significantly higher value than group A (P < 0.01). In addition, the control group and group C showed significantly higher values for mandibular ramus height than group A (P < 0.01). However, bone mineral density in trabecular bone was significantly higher in the control group than in the other groups (P < 0.01) and bone mineral density in cortical bone was significantly higher in the control group than groups A, B and C (P < 0.01, P < 0.01, P < 0.05, respectively). Bone mineral density in both trabecular and cortical bone was significantly higher in group C than in groups A and B (P < 0.01, P < 0.05, respectively). These results indicate that complete recovery from calcium deficiency to the level of the control group may not be attainable, even though IF enhances calcium absorption to act on bone cells and promote bone construction. The importance of calcium intake in the early stages of development was confirmed. These findings also suggest an effect of IF on jaw bone structure.     

染料木素对去卵巢大鼠颌骨代谢的改善作用

目的 探讨染料木素对去势大鼠颌骨代谢及雌性生殖系统的作用。方法 切除成年雌性大鼠双侧卵巢，造成绝经后骨质疏松的动物模型。双能X线法检测颌骨、股骨骨密度，生化法检测血清碱性磷酸酶(alkaline phosphatase，ALP)、酸性磷酸酶(acid phosphatase，ACP)，放射免疫法检测骨代谢因子IL-1β、IL-6、转化生长因子α(tumor necrosis factor-α，TNF-α)、降钙素和骨钙素，探讨染料木素对去势大鼠颌骨代谢的作用；通过血清雌二醇含量和子宫重量的变化监测染料木素的雌激素样副作用。结果 去势大鼠骨密度显著减少；血清ALP、ACP和IL-1β、骨钙素显著高于非去势组。口服染料木素后，大鼠骨密度显著增加；血清ALP、ACP、骨钙素显著增高，其中ALP和骨钙素的增加显著优于雌激素组，IL-1β和TNF-α显著降低；大鼠子宫重量系数显著低于雌激素组。结论 染料木素能够通过抑制骨吸收和促进骨形成有效改善去势大鼠颌骨代谢，副作用弱于雌激素。染料木素在防治颌骨乃至全身骨质疏松方面具有开发前景。     

Effects of ovariectomy and/or dietary calcium deficiency on bone dynamics in the rat hard palate, mandible and proximal tibia

The effects of ovariectomy and/or dietary calcium deficiency on bone dynamics were examined by comparing the histomorphometric changes in these bones. Five groups of rats were studied, (1) unoperated basal controls; (2) sham-operated, fed on a normal-calcium diet; (3) ovariectomized, fed on a normal-calcium diet; (4) sham-operated, fed on a calcium-deficient diet; (5) ovariectomized, fed on a calcium-deficient diet. The basal controls were killed at 6 weeks of age, and the remaining groups were killed at 18 weeks of age. The hard palate, mandible and proximal tibia were processed undemineralized for quantitative bone histomorphometry. Bone volume, eroded surface, osteoid surface and bone-formation ratio were calculated. A significant age-related increase in bone volume and a significant decrease in bone formation were observed in the hard palate and mandible, whereas no significant age-related increase in bone volume could be found in the tibia. In the hard palate, ovariectomy neither inhibited age-related increases in bone volume nor affected bone dynamics, while both the combined ovariectomy and dietary calcium deficiency and dietary calcium deficiency alone led to bone loss and increased bone turnover. In contrast, in the mandible and proximal tibia, ovariectomy alone as well as dietary calcium deficiency led to bone loss and increased bone turnover. Ovariectomy, therefore, produced no significant changes in the hard palate, but affected bone dynamics in the mandible and tibia. However, dietary calcium deficiency induced bone loss and increased bone turnover in the hard palate, mandible and proximal tibia, independently of ovariectomy.     

Short-term etidronate treatment prevents glucocorticoid-induced bone debility of the mandible in growing rats

Authors – Fujita Y, Konoo T, Maki K Objectives – To analyse the effects of short‐term treatment with etidronate on the glucocorticoid‐induced retardation of bone growth and deterioration of bone structure in the prepubertal rat mandible. Materials and Methods – Fifty 5‐week‐old male rats were divided into five groups. Etidronate or vehicle treatment (5 mg/kg/day, daily, subcutaneous injection) was initiated after glucocorticoid administration (30 mg/kg/day, on alternate days, orally) for 6 weeks and was continued for 3 weeks. Then, bone growth was measured using lateral cephalometric analysis. Peripheral quantitative computed tomography was used to determine bone density, bone cross‐sectional area and bone strength. Results – Glucocorticoid‐treated rats had significantly lower body weight, mandibular length, cortical bone density, bone strength and cross‐sectional area in trabecular and cortical bone, but had significantly higher trabecular bone density than untreated rats. No significant difference in mandibular height was observed between the glucocorticoid‐treated group and the untreated control group. Etidronate treatment improved the glucocorticoid‐induced decrease in bone strength and increased density in trabecular and cortical bone above the untreated control level, but had no significant effects on the reduction in mandibular length. Conclusion – These findings suggest that etidronate can potentially reverse the glucocorticoid‐induced deterioration of internal bone structure, but has no beneficial effects on the glucocorticoid‐induced retardation of bone growth in the growing rat mandible.     

下颌牵张成骨速度对大鼠下颌骨形态的影响

目的研究大鼠下颌牵张成骨过程中牵张速度对大鼠下颌骨形态的影响。方法对139只雄性SD 大鼠施以单侧乙状切迹至下颌骨下缘的纵向骨切开,放置口外牵张器。3天的潜伏期后随机分成17组,分别以0mm/天、0.2mm/天、0.4mm/天、0.6mm/天的牵张速度连续加力5天,并在术后第3、6、10、24、38天处死。拍摄双侧下颌骨8×10 inch诊断领片,利用NIH Image Software测量及分析下颌骨长度及牵张间隙面积的变化。结果①快速牵张组的下颌骨长度大于中、慢速组,但低于预期伸长量。②中、慢速组的下颌骨伸长量近乎一致。③牵张间隙的面积随牵张量的增加而增加。结论牵张速度对下颌骨形态有很大影响。快速骨牵张可能导致下颌骨预期长度的减少,而这一变化为该治疗的风险所在。     

The effect of electrical stimulation on bone formation around hydroxyapatite implants placed on the rabbit mandible.

Nonresorbable, nonporous, particulate hydroxyapatite (HA) was implanted on the mandible in rabbits and stimulated electrically, 4 hours per day, during the first postoperative week. Stimulated and control implant sites were recovered 8 weeks postoperatively and examined histologically. The HA migrated into the mandible in the electrically treated specimens, and was routinely found in intimate association with preexisting mandibular bone. In the controls, the HA remained superior to the mandibular surface. In further studies (without electrical stimulation) in which the implant site was recovered 26 weeks postoperatively, HA was observed in the mandible; some HA particles migrated completely through the mandible and were found in the adjacent soft tissue. It was concluded that, under the conditions studied, electrical stimulation does not promote bone growth into HA, but rather produces the opposite result--it promotes more rapid movement of HA particles into the mandibular bone. The HA particle migration into the mandible observed (longer postoperative times) in the absence of electrical stimulation suggests that migration is a general property of HA particles when placed over bone under muscle.     

Effects of dietary consistency on the mandible of rats at the growth stage: computed X-ray densitometric and cephalometric analysis

Thirty 3-week-old male Wistar rats were grouped into a hard diet control group, a kneaded-diet group, and a powdered-diet group. After 6 weeks of growth, all rats were killed under deep anesthesia. The effects of dietary physical consistency on the mandible were investigated with respect to morphology and bone mineral content using lateral cephalometric analysis and computed X-ray densitometry. Significant differences between the experimental and control groups were determined by measuring the means and standard deviation of the coordinates and differences between 15 points selected on the mandibles. Gonion (Go), which is a measurement of depth to the X-axis, was significantly less in the powdered-diet group, while the kneaded-diet group showed no significant differences. The most posterior point of the coronoid process (Cr) and the most posterior point of condylar process (Cd), which are measures of height to the Y-axis, were less in the kneaded-diet group than in the control group. In the powdered-diet group, Cr, Cd, Go and Infradentale were significantly less than in the control group. On the other hand, the bone mineral content was significantly lower in the coronoid process and angle of mandible in only the powdered-diet group.