咀嚼负荷对幼兔髁突软骨细胞BrdU标记影响的研究

目的 探讨咀嚼负荷对幼兔髁突软骨发育及软骨细胞中BrdU标记的影响。方法 出生10 d龄的32只幼兔,随机分为喂食固体硬饲料组和喂食粉末软饲料组。连续2周每天每只腹腔注射BrdU （50 mg/kg）,在2、4、6、8周时每组处死4只幼兔,HE观察组织形态学变化测量软硬组髁突厚度变化,免疫组化检测BrdU表达。结果 髁突软骨前部厚度硬食组明显高于软食组,在中部无明显差异,髁突软骨后部厚度软食组高于硬食组。BrdU免疫组化染色显示,发育期髁突软骨各层及软骨下骨骨髓腔内均有BrdU阳性标记,前部的增殖层表达最显著。第2周,硬食组在前、中、后3个部位的BrdU阳性率都高于软食组;第6周,软食组的中、后部位的阳性率高于硬食组;第8周,软硬组均检测不到阳性细胞。结论 软食组在低咀嚼力刺激下,幼兔髁突软骨细胞增殖启动较慢。适当的咀嚼压力能促进髁突软骨细胞的增殖,同时幼兔发育期的髁突生长还受到基因等内环境因素影响。     

不同咀嚼负荷对幼兔髁突软骨内印度豪猪蛋白-人甲状旁腺激素相关蛋白通路表达的影响

目的 分析不同咀嚼负荷作用下,幼兔髁突软骨内印度豪猪蛋白（Ihh）-人甲状旁腺激素相关蛋白（PThrP）通路表达的差异性,探讨咀嚼应力负荷对髁突软骨Ihh-PThrP信号通路的影响。方法 选取10 d龄幼兔48只,随机分为硬食组和软食组,分别喂以同种颗粒状（硬食）和粉状（软食）,于饲养的第2、4、6、8周处死。采用苏木精-伊红（HE）染色、免疫组织化学、免疫印迹、实时定量荧光聚合酶链反应检测Ihh和PThrP mRNA和蛋白的动态变化。结果 HE染色显示硬食组髁突软骨厚度高于软食组的厚度;第2、4、6、8周,Ihh蛋白、PThrP蛋白和mRNA表达量在两组中呈递减趋势;软食组中Ihh和PThrP蛋白以及mRNA表达量显著低于硬食组。结论 较低的咀嚼负荷会造成髁突软骨生长因子Ihh和PThrP分泌减少,Ihh-PThrP通路表达迟缓,软骨发育受阻碍;适当的咀嚼负荷对髁突的正常发育有至关重要的作用。     

咀嚼力降低对发育期大鼠髁突发育的组织学影响

目的：探讨咀嚼力降低对断乳后大鼠下颌骨髁突尺寸和髁突软骨厚度的影响。方法：16只刚断乳的雄性大鼠随机分为两组。一组喂以标准的硬食,另一组以粉末状软食喂养。4w后,取每只大鼠的一侧髁突进行长度和宽度的测量,另一侧髁突进行组织学观察。结果：软食组大鼠的髁突长度、宽度和软骨层厚度均明显小于硬食组。结论：咀嚼力降低会导致下颌骨髁突生长减慢和髁突软骨厚度的变化。     

咀嚼力降低对发育期大鼠髁突软骨中细胞增殖和凋亡的影响

目的：研究咀嚼力降低对发育期大鼠下颌髁突软骨细胞增殖和细胞凋亡活性的影响。方法：40只18d雄性大鼠随机分为两组。一组喂以标准的硬食,另一组以粉末状软食喂养。于大鼠4周、5周、6周、7周龄时取其髁突软骨,分别采用免疫组织化学染色和TUNEL染色,观察髁突软骨中增殖细胞核抗原阳性细胞数和凋亡细胞数。结果：在4～7周,PCNA阳性细胞数在软、硬食组都逐步上升。但在各相同时间点,软、硬食组的PCNA阳性细胞数不存在统计学差异。在4～7周,硬食组大鼠髁突软骨中凋亡细胞数基本保持一致,而软食组凋亡细胞数随时间推移而降低,但在4周、5周、6周时,软食组的凋亡细胞数均明显多于同期硬食组（P〈0.05）。结论：咀嚼力降低对发育期大鼠髁突软骨中的细胞增殖活性影响不大,但却使细胞凋亡的数量增加,提示咀嚼力降低可能加速了髁突软骨中细胞的分化、成熟、凋亡,进而影响髁突的正常发育。     

咀嚼力降低对大鼠髁突软骨中Bax和Bcl-2 mRNA表达的影响

目的：探讨咀嚼力降低对发育期大鼠下颌髁突软骨中凋亡相关蛋白Bax和Bcl-2 mRNA表达水平的影响.方法：40只18 d雄性大鼠随机分为2组.一组喂以标准的硬食,另一组以粉末状软食喂养.于大鼠4周、5周、6周、7周龄时取其髁突软骨以RT-PCR方法检测其中Bax和Bcl-2mRNA的表达水平.结果：正常硬食组大鼠髁突软骨中Bax mRNA和Bcl-2 mRNA的表达均随时间延长而降低.软食对Bcl-2mRNA表达的影响不大,但却使Bax mRNA表达上调.软食组Bax mRNA与Bcl-2 mRNA的比值在6周和7周时明显高于硬食组p＜0.05）.结论：咀嚼力降低使发育期大鼠髁突软骨Bax mRNA表达水平和Bax mRNA/Bcl-2 mRNA的比值上升,但对Bcl-2 mRNA影响不大.     

骨保护素对去卵巢小鼠髁状突骨和软骨的影响

目的观察外源性骨保护素(osteoprotegerin,OPG)对去卵巢小鼠髁状突骨及软骨的影响。方法4月龄雌性未孕小鼠30只,其中20只行双侧卵巢摘除术,10只行假手术(A组)。4周后将双侧卵巢摘除20只随机分为B、C两组各10只,B组予安慰剂,C组皮下注射OPG 10 mg/kg,每周2次。治疗2个月后,测定各组动物髁状突的骨小梁面积、数量,软骨层的厚度及软骨层内部各层细胞的数量等。结果B组髁状突的骨小梁面积、数量较A组明显降低。C组髁状突的骨小梁面积、数量较A、B组明显增加,软骨层厚度增加、软骨层内部肥大细胞层较A、B组明显增厚。结论小鼠去卵巢后可成功建立髁状突骨质疏松模型;OPG对去卵巢小鼠髁状突有抑制骨吸收作用,并可能促进软骨细胞增殖,促使软骨细胞向成骨过渡。     

不对称性颌间牵引对成年SD大鼠颞下颌关节软骨下骨组织形态的影响

目的 通过观察不对称牵引引起的成年SD大鼠髁突软骨下骨组织形态学变化,了解关节外不对称机械应力对髁突软骨下骨的影响.方法 选用10周龄雄性SD大鼠220只（随机分为轻力组104只、重力组104只、对照组12只）,实验组动物使用关节外固定加力装置,分别施加0.39、1.18 N,加力28 d拆除加力装置.在3、7、14、28、31、35、42、56 d取得标本,对髁突软骨的形态、骨小梁密度进行观察分析并进行统计学处理.结果 正常髁突软骨下骨骨小梁连续,与髁突表面垂直以顺应髁突的力学环境,在负荷加载后出现骨小梁形态和排列变化,密度发生相应波动.结论 髁突软骨下骨在外力刺激下,出现排列和骨小梁密度的变化以适应变化的机械应力环境.     

兔下颌骨髁突软骨年龄相关性改变的组织学研究

目的 探讨不同年龄段兔下颌骨髁突软骨的生理特征变化。方法 选取1、4、12和32周龄健康雌性新西兰大白兔各3只,脱钙处理后进行5 μm 连续切片,苏木精-伊红染色。分别对关节盘所覆盖的髁突表面纤维软骨区域软骨各层厚度进行测量分析。采用SPSS19.0软件包对数据进行统计学处理。结果 髁突软骨全层（P=0.008）、成熟层（P=0.008）和肥大层（P=0.007）在1周和4周组间厚度显著下降,在4~32周内厚度变化不明显。连续各组之间纤维层和增殖层厚度无显著改变;32周组纤维层厚度显著高于1周组（P=0.024）。结论 兔髁突软骨全层、成熟层和肥大层在1~4周内明显变薄,成骨活性大于成软骨活性,为下颌骨生长发育的重要阶段;在4~32周内各层厚度改变不明显,成骨和成软骨活性相对平衡。成年期髁突适应和耐受关节腔微环境变化的能力可能较强。     

生长期山羊囊内骨折复位术中保留髁突软骨的重要性及组织学研究

目的：通过组织学观察,探讨髁突囊内骨折内固定术中保留和切除髁突软骨对髁突生长发育的影响。方法：6个月龄山羊12只,随机分为实验组（n=8）和对照组（n=4）。实验组双侧髁突造成囊内骨折并同期行手术复位固定．一侧保留髁突软骨,另一侧切除髁突软骨。术后3个月、6个月处死动物,切取髁突标本行石蜡切片和硬组织切片观察骨折愈合和髁突生长情况。结果：实验组髁突骨折愈合良好,钛板被新生骨组织覆盖;HE染色显示．保留髁突软骨组,髁突软骨结构清晰,与正常对照髁突相同,软骨成骨活跃,髁突生长发育正常;切除髁突软骨组,髁突软骨层消失,表面为成熟的骨细胞覆盖,直接与关节盘的纤维组织相连,新生骨组织少见：硬组织切片显示,钛板与骨组织直接结合．未见组织渗出和排异反应。结论：手术复位髁突囊内骨折时保留髁突软骨,不会影响髁突的生长发育;损伤髁突软骨．会造成髁突与关节盘黏连．引起髁突生长发育障碍。     

肾上腺素受体信号在磨牙异常咬合致大鼠髁突软骨下骨丢失中的作用

目的:探索肾上腺素受体信号在磨牙异常咬合致大鼠髁突软骨下骨丢失中的作用。方法:采用正畸分牙法建立磨牙异常咬合大鼠模型(实验组)及对照组,对照及实验组大鼠分别接受腹膜注射生理盐水(溶剂注射组)或β受体阻滞剂普萘洛尔(普萘洛尔注射组)。用Micro-CT检测各组大鼠髁突软骨下骨密度及骨小梁结构学参数变化,用酶联免疫吸附法测定各组软骨下骨去甲肾上腺素浓度,用实时定量聚合酶链反应及免疫组化检测各组软骨下骨肾上腺素受体表达。结果:4、8周实验组软骨下骨密度、骨体积分数及骨小梁厚度均较其对照组降低,但其骨小梁间隙及去甲肾上腺素含量则较对照组增高(P<0.05);实验组大鼠髁突软骨下骨中Adrb2基因及蛋白的表达较其对照组增高(P<0.05),但Adrb1及Adrb3基因的表达在两组间无显著差异(P>0.05);普萘洛尔注射可显著逆转实验组大鼠髁突软骨下骨丢失,其软骨下骨小梁密度、骨体积分数、骨小梁厚度及间隙等参数均较溶剂注射实验组显著改善(P<0.05)。结论:异常的咬合力可通过激活β2肾上腺素受体信号促进髁突软骨下骨骨丢失。     

Effect of low masticatory function on condylar growth: a morphometric study in the rat.

The aim of this study was to estimate the influence of functional alterations on the size of the mandibular condyle and to elucidate in detail, by means of histomorphometric analysis, the effect of changing the consistency of the diet on different portions of the condylar cartilage in growing rats. Forty growing rats were randomly divided into 2 groups. One group received the normal hard diet for rats; the other group received a standardized soft diet. The experimental period was 28 days. Ten animals from each group were used for gross morphometric analysis; the other 10 animals were used for histologic analysis of the condyle. The morphometric analysis of the condylar cartilage was based on the 25th, 50th, and 75th percentiles of the mediolateral sections of the condyles. The sections were divided into 3 parts: the anterior, intermediate, and posterior part; 4 measurements were performed in each. Significant differences were found in the condylar length and width between the groups, the soft diet group having a smaller condyle. The histomorphometric analysis of cartilage thickness showed significant differences between the 2 groups, being thinner in the anterior part and thicker in the posterior part of the condyle in the soft diet group. These routine histologic findings cannot explain the gross morphologic differences in the condylar size between the groups; this means that increased condylar cartilage thickness is not necessarily evidence of increased condylar growth. The results from this study indicate that a low masticatory function leads to decreased growth of the condyle and changes in the thickness of the cartilage. This may be the effect of an alteration in the stress distribution in the temporomandibular joint area, because of the absence of large masticatory forces.     

Effects of age on the ability of the rat temporomandibular joint to respond to changing functional demands

This investigation examined the ability of the tissues of the temporomandibular joint (TMJ) to adapt to changing functional demands in young, growing rats compared with mature rats. Functional demands on the TMJ were varied by feeding diets with different physical consistencies. The first group was fed a soft diet for the experimental period. The second group was fed a hard diet, and the third group was initially fed the soft diet, then switched to the hard diet at the mid-point of the experimental period. Gross dimensions of the condyle, mandible, and maxilla were measured with calipers. Thickness of the articular, proliferative, transitional, and hypertrophic zones of the condylar cartilage, and the amount of bone in the subcondylar region and condylar neck were measured on histological sections. Gross dimensions of the condyle were significantly smaller in the soft-diet group compared with the hard- and soft/hard-diet groups in both growing and mature rats. The individual zones of the condylar cartilage were also significantly narrower in the soft-diet group in both growing and mature rats. However, the soft/hard-diet group of mature rats showed only a significant reduction in the thickness of the articular zone of the condylar cartilage compared with the hard-diet group. There were also narrower proliferative and transitional zones in the mature rats fed a soft/hard diet. In contrast, all of these zones showed full recovery in the young rats fed a soft/hard diet. The data presented here suggest that increasing age may diminish the capacity of the TMJ to adapt to altered function and consequently may play a significant role in the development of degenerative joint disease.     

Effects of the masticatory demand on the rat mandibular development

The influence of masticatory loading stimulus on mandibular development is not fully clear. In this paper, experimental alterations in the daily muscle use, caused by a changed diet consistency, were continuously monitored, while adaptations in bone and cartilage were examined. It is hypothesised that decreased muscular loading will result in a decrease in the growth factor expression and mandible growth. Fourteen 21‐day‐old Wistar strain male rats were randomly divided into two groups and fed on either a hard or soft diet for 14 weeks. An implanted radio‐telemetric device recorded continuously muscle activity of the superficial masseter muscle. Chondroblast proliferation in the condylar cartilage was identified by insulin‐like growth factor‐1 receptor (IGF‐1r) immunostaining. Furthermore, an X‐ray was taken for cephalometric analysis. In the soft‐diet group, the duty time of the superficial masseter muscle at higher activity levels was significantly lower than that in the hard‐diet group. This decrease in muscular loading of the jaw system was accompanied by: a significant reduction in (i) articular cartilage thickness, (ii) expression of IGF‐1r immunopositive cells and (iii) mandible ramus height. In conclusion, a decrease in masticatory demand during the growth period leads to insufficient mandibular development.     

Effect of decreased loading on the metabolic activity of the mandibular condylar cartilage in the rat

The aim of this study was to measure the effect of decreased temporomandibular loading on the proliferative activity and the level of matrix production of the condylar cartilage. The effect of reduced joint loading on the activity of stromelysin-1 (MMP-3), which has been associated with conditions of articular cartilage matrix breakdown, was also examined. Eighty 14-day-old female rats were assigned to two groups. Following weaning at 20 days, the experimental group was fed a soft diet and the incisors were shortened regularly to keep them out of occlusion. The controls were fed a hard diet. The activity of tritiated thymidine incorporation and the incorporation of radiolabelled sulphur were measured 2, 6, 12, 24 and 48 hours after initiation of the experiment. The radiolabelled sulphur intake was significantly lower in the condylar cartilage of the experimental group 6-24 hours after initiation of the experiment, and tritiated thymidine activity was lower after 12-24 hours, indicating lower proliferation and matrix production. The cartilage in the experimental group showed marked immunostaining against MMP-3 in all cartilage layers 9 days after initiation of the experiment. In the control group, the staining was clearly seen only in the superficial fibrous layer and in the erosion front. A marked reduction in proliferative activity and proteoglycan synthesis in mandibular condylar cartilage was found after a continuous soft diet and suppressed incisal mastication in the rat. The results show that sufficient loading is important for condylar cartilage growth, to maintain both ideal proliferation and matrix chondrocyte production.     

The effect of dietary consistency on bone mass and turnover in the growing rat mandible.

Hard and soft diets were fed to weanling rats for up to 8 weeks. Some animals were switched after 4 weeks to the opposite diet. A histomorphometric study of bone formation activity at the mandibular ramus, body, and condyle was made after in vivo fluorochrome labelling. Mineral apposition rates at the lateral and inferior periosteal surfaces of the ramus were lower in the soft diet than in the hard diet animals. The rate of bone formation at the lateral periosteal surface of the ramus was significantly lower in soft than in hard diet animals. The medial periosteal surface of the ramus sometimes changed to bone formation in the soft diet groups. Condylar cartilage zones were somewhat thinner in soft diet groups. In the mandibular body, differences due to dietary consistency were less marked than near the gonial angle. Adaptation of periosteal bone and condylar cartilage to a new dietary consistency occurred within 4 weeks of switching. These results suggest that lateral and inferior periosteal bone growth of the ramus and condylar elongation were slowed in rats consuming soft diets. Decreased functional force during rapid mandibular bone growth causes changes in shape. The changes are due to regional decreases in osteoblast function, realignment of bone formation surfaces in the ramus area, and slowed growth in the condylar cartilage.