Early osteocyte response to bone resorption stimuli

Over the last decade, increasing attention has been focused on the role of the osteocyte in bone remodeling, in view of its demonstrated ability to respond to mechanical and electric stimuli applied to bone. A previous "in vivo" study performed at our laboratory demonstrated that the application of orthodontic forces results in osteocytic lacunae enlargement. To our knowledge there are no data on cell and lacunae response to an inflammatory stimulus in the literature. The aim of this work was to determine whether osteocyte response to an inflammatory stimulus is comparable to that observed under mechanical stress and whether the ensuing cellular changes involve changes in the shape of the osteocyte and/or its lacunae. Three groups of ten male Wistar rats each, 200 to 250 g body weight, were used. Group I served as control. A cotton thread cervical ligature was placed around the first upper molars of animals in Group II, and those in Group III were fitted with an orthodontic appliance designed to exert a force toward palatine. All the animals were killed 24 hours after applying the stimuli. The histomorphometric determinations were measured on the interradicular crest between the two distal roots of the first upper molars. Osteocyte and lacunar volumes were measured and lacunar shape was analyzed. Group II exhibited a dense inflammatory infiltrate and slight resorption of the crest. Group III showed slight resorption of the vestibular wall. The lacunar volume increased in both experimental groups as compared to controls. The cell volume to lacunar volume decreased. These results suggest that osteocytes respond to inflammatory as well as to mechanical stimuli of bone resorption, enlarging lacunae without changes in cell volume.     

The fate of vital and devitalized bone grafts in the healing of interradicular lesions

The fate of vital and devitalized grafts of mature concellous bone from the jaws were studied in interradicular lesions in monkeys. 98 bifurcation defects were produced in premolars and molars and maintained by periodontal dressing inserted for four weeks. Ten to 15 weeks later fresh cancellous bone was transplanted into 32 defects. Other cancellous bone grafts were divitalized by boiling and transplanted into 34 bifurcations. The remaining 32 defects received no grafts. The animals were sacrificed to yield observation periods from 0 to 90 days. After decalcification of the specimens and embedding in paraffin, serial sections were cut at 8 microns and stained. The fate of viable and dead transplants were similar during the healing of the interradicular lesions. Except for a few osteocytes which seemed to survive transplantation in the fresh cancellous bone, the osteocyte lacunae were devoid of cells in both types of transplants after 1 week. The deepest located bone grafts became incorporated in new bone developed from the interradicular septum. The more superficially located grafts were rejected or were surrounded by a cementum-like substans. The influence of the grafts on bone regeneration was small and based solely on their osteoconductive effect.     

Influence of submandibulectomy on alveolar bone loss in rats

BACKGROUND: The incidence of dry mouth and its public health impact are increasing as the result of a progressively larger, medicated older population and because chronic diseases, like periodontitis, are prevalent pathologies among elderly patients. Periodontitis and continuous remodeling and rebuilding alveolar processes greatly affect the margin of the alveolar bone, and there is evidence indicating the role of submandibular glands in the regulation of immune/inflammatory reactions. The purpose of this study was to assess the effect of submandibular-sublingual complex ablation (Sx) on alveolar bone loss in rats submitted or not to ligature-induced experimental periodontal disease (EP). METHODS: Wistar male rats were submitted to Sx or sham operations (day 0). Two weeks later, unilateral EP was induced on the right mandibular first molars for 7 days with the contralateral side serving as control. Bone loss at the level of the dental pieces was estimated by bone histomorphometry on mesio-distally oriented sections of the molars and by the determination on lingual and vestibular mandibular surfaces of the distances from the cemento-enamel junction to the alveolar crest. RESULTS: Sx and EP significantly increased lingual and vestibular alveolar bone loss. Molars with EP exhibited greater lingual loss in Sx animals compared to those with the sham operation. EP induced similar interradicular bone loss in sham and Sx rats. CONCLUSION: Sx has a deleterious effect on the periodontal tissues, particularly marginal alveolar bone, indicating the importance of the submandibular/sublingual glands in maintaining healthy periodontal conditions.     

基于CBCT的下颌第一磨牙区即刻种植相关的影像学研究

目的利用CBCT研究下颌第一磨牙区即刻种植适宜的植入位点、植入角度与植入深度,为术前数字化设计和临床操作提供参考依据。方法选取100例符合纳入标准的患者CBCT影像学资料,测量下颌第一磨牙区的牙槽骨厚度、颊侧及舌侧骨板厚度、牙根间隔宽度,同时测量下颌第一磨牙与下颌神经管及舌侧骨倒凹的关系,并进行统计学分析。结果由近中至远中,下颌第一磨牙的牙槽骨厚度及颊侧骨板厚度逐渐增大,舌侧骨板厚度逐渐减小;由牙槽嵴顶至根尖,牙根间隔宽度逐渐增大,最大为(5.00±1.42)mm;近中根、远中根、远舌根、牙根间隔顶至下颌神经管的距离分别为(7.47±2.38)mm、(7.19±2.49)mm、(9.59±1.94)mm、(15.90±2.39)mm;由近中至远中,下颌神经管颊侧及舌侧骨板最大厚度分别为(6.54±1.25)mm、(2.53±0.84)mm;下颌舌侧骨倒凹角度为(149.67±8.30)°,倒凹深度为(1.51±0.43)mm。结论在下颌第一磨牙区即刻种植前可通过CBCT规划合适的种植路径,注意避开下颌神经管和舌侧骨倒凹。若根尖至下颌神经管的安全距离足够,可从牙根间隔处植入,若安全距离不足,植入位点可偏近中舌侧,植入角度可适当舌倾。     

Compensatory bone formation in young and old rats during tooth movement

The aim of this study was to investigate compensatory lingual alveolar bone formation during tooth movement in young and old rats, using the vital bone marker tetracycline. Wistar male rats were separated into the following groups: 13-week-old rats without appliances (13C: control, n = 5), 60-week-old rats without appliances (60C: control, n = 5), 13-week-old rats with appliances (13E: experimental, n = 10), and 60-week-old rats with appliances (60E: experimental, n = 10). The upper first molars of the 13E and 60E groups were moved lingually using fixed appliances. On the third day of tooth movement, tetracycline (TC) was intra-peritoneally injected in all animals including the controls. On the 21st day of tooth movement, the animals were killed and unfixed, and undecalcified, 5-microm frozen frontal sections of the rat first molar areas in both control and experimental groups were examined under light and fluorescent microscopes. In the 13C group without tooth movement, tetracycline labelling lines were obvious in the alveolar crest, apical areas, and interradicular septum, indicating vertical alveolar bone growth. However, in the 60C control group, tetracycline labelling was almost undetectable throughout the alveolar bone. Although the lingual alveolar crest was resorbed from the periodontal side after lingual tooth movement, the sharp, bright labelling lines were still present from the crest to the lingual periosteal alveolar bone in the 13E group. In the 60E group the lines appeared in the lingual periosteal alveolar bone containing the crest, indicating considerable new bone formation. The results indicate that compensatory bone formation occurs in the alveolar crest area and, consequently, alveolar bone height is maintained, even in aged rats.     

应用血管铸型法探讨犬牙周膜微血管网的缓冲作用

目的：通过研究牙周膜和周围牙槽骨微循环的构筑,探讨犬的牙周膜微血管网的缓冲作用。方法：成年健康杂种犬4条,应用血管铸型法,沿犬下颌骨的下牙槽动脉灌注合成树脂Mercox,在10%盐酸中脱钙,在20%氢氧化钾溶液中溶解软组织,标本干燥后喷金,在扫描电镜下观察。结果：来源于牙周膜血管的静脉,通过Volkmann管汇入根间隔牙槽骨的静脉,与汇入颊（舌）侧牙槽骨静脉相比,血管数目多且管径粗大;在根间隔的静脉呈扩张的窦样管状,根间隔的骨髓腔与颊（舌）侧骨髓腔相比,容积大并且数量多。结论：犬牙周膜微循环中,来源于牙周膜的静脉血主要汇流入根间隔静脉网;根间隔中的窦样管状静脉具有贮存血液的作用,与牙周膜的缓冲作用有关。     

Enlargement of periosteocytic lacunae associated to mechanical forces

Demineralization of bone has been linked to the action of osteocytes via the process of osteocytic osteolysis. The aim of this study was to assess the influence of mechanical forces produced during orthodontic movements on the osteocytic lacunae. Orthodontic movements were achieved employing a device constructed "ad hoc" for rats that exerts a force of approximately 70 gr. The experimental animals and the corresponding controls were killed 48 and 96 hours after the onset of the experiment. Histologic sections oriented along the bucco-palatine axis were employed to measure the area of osteocytic lacunae to infer information on volume in keeping with standard stereological concepts. Regions alongside resorption areas of cortical bone and resting areas of palatine bone were evaluated. Osteocytic lacunae associated to erosive surfaces were rounded and rose markedly in area after the application of the orthodontic force (58.4 +/- 6 mm2). Elongated lacunae were present in relation to resting areas (24.8 +/- 2 mm2). The present study shows an association between the increase in size of osteocytic lacunae and the resorption fronts induced by the application of orthodontic forces. This finding would suggest that the osteocyte would participate in the resorption process of bone submitted to pressure.     

Effect of topical administration of monosodium olpadronate on experimental periodontitis in rats

BACKGROUND: Periodontitis is characterized by gingival inflammation, periodontal pocket formation, and bacterial plaque that lead to alveolar bone destruction. Research studies have recently begun to evaluate the effect of antiresorptive agents using experimental models of periodontitis. Bisphosphonates are the most frequently tested antiresorptive agents; their main effect is inhibition of bone resorption. The aim of this study was to perform a histomorphometric evaluation of the preventive effect of monosodium olpadronate (OPD), an aminobisphosphonate, on experimental periodontitis (EP). METHODS: Twenty male Wistar rats were used in this experiment. The animals were assigned to one of two groups: group I: EP; and group II: EP plus topical administration of OPD (EP + OPD). The contralateral side in both groups served as untreated controls (CI and CII), respectively. Mesio-distally oriented sections of each lower first molar were obtained for histomorphometric evaluation. RESULTS: The treated group (EP + OPD) exhibited marked inhibition of bone loss; interradicular bone volume was significantly greater than that observed in the EP group. The height of the periodontal ligament in the interradicular alveolar bone, which served as an indirect measure of bone loss, was found to be significantly increased in the EP group as compared to the EP + OPD group. Osteoclasts in the OPD treated group were detached from the bone surface, were round in shape, and exhibited a loss of polarity and lack of ruffled borders. CONCLUSIONS: The dose used herein was found to inhibit bone loss and to cause marked morphologic changes in osteoclasts. The drug effectively prevented bone loss caused by periodontitis.     

Alveolar bone response in an experimental model of renal failure and periodontal disease: a histomorphometric and histochemical study

BACKGROUND: Chronic destructive periodontal disease is characterized by gingival inflammation, periodontal pocket formation, and bacterial plaque that lead to alveolar bone destruction. Polymorphonuclear neutrophil leukocytes (PMNs) are the first line of defense against infection caused by dental plaque bacteria. Renal patients present functional abnormalities of PMN, including impaired chemotaxis, phagocytosis, and intracellular killing of bacteria. In view of the above, the aim of this work was to evaluate the effect of renal failure on bone damaged by periodontal disease using histomorphometric and histochemical parameters. METHODS: Twenty male Wistar rats weighing 250 g were assigned to one of the following four groups: 1) control (no treatment); 2) renal failure (RF); 3) periodontal disease (PD); and 4) renal failure plus periodontal disease (RF+PD). All the animals were sacrificed 31 days after the onset of the experiment. Mesio-distally oriented sections of the first lower molar were obtained for histomorphometric and histochemical evaluation. RESULTS: Total erosion, active erosion, and total number of tartrate-resistant acid phosphatase-positive (TRAP+) osteoclasts were found to be increased in the RF+PD group compared with the PD group. CONCLUSION: Our results demonstrate increased bone resorption in animals with untreated renal failure and periodontal disease, and thus indicate that the release of different factors by inflammatory cells is magnified, accelerating the progression of the disease in this animal model.     

Effects of ovariectomy on trabecular structures of rat alveolar bone

An association between postmenopausal osteoporosis and tooth loss has been proposed. However, histomorphometrical changes in alveolar bone following estrogen deficiency are rarely reported with data on microtrabecular structural changes. To clarify the relationship between estrogen deficiency and tooth loss, we histomorphometrically analyzed the trabecular structural changes of mandibular alveolar bone in ovariectomized rats. Twenty-four adult female Fischer rats were used. Eight rats were sacrificed on day 0 (baseline). The remaining 16 rats were divided into two groups. One group was ovariectomized bilaterally (OVX) and the other group was subjected to sham surgery (Sham). After administration of tetracycline and calcein, the animals were sacrificed 60 days after surgery. Bone histomorphometry, node-strut analysis and measurement of thickness of alveolar bone proper were performed on the interradicular septum of the first molar on the sagittal surface. The trabecular bone volume and trabecular number of the OVX group were significantly lower than those of the baseline and Sham groups. All of the bone resorptive and formative parameters of the OVX group were significantly higher (about one-and-a-half times) than those of the Sham group. Several osteoclasts were seen lining the irregular, eroded surface facing the bone marrow in the OVX group. Furthermore, the OVX group tended to have low microtrabecular stiffness and showed significantly thinner distal alveolar bone proper than in the baseline and Sham groups. In summary, estrogen deficiency caused osteoporotic changes and thin alveolar bone proper in the interradicular septum of rat first molar. This phenomenon might accelerate destruction of alveolar bone and tooth loss, especially in elderly women affected by periodontal disease.     

A histomorphometric study of alveolar bone modeling and remodeling under experimental anaemia and polycythaemia in rats

Alveolar bone is the least stable of the periodontal tissues, because it is subjected to continuous modeling and remodeling. OBJECTIVE: To perform a histological and histomorphometric evaluation of bone modeling and remodeling of periodontal alveolar bone under experimental anaemia and polycythaemia. METHODS: Thirty Wistar rats were divided into three groups: control (C), animals were i.p. injected with 0.5 mL of saline solution; anaemia (A), animals were injected with 6 mg/100 b.w. of phenylhydrazine every 48 h; polycythaemia (P), animals were transfused with 2.5 mL/100 b.w. of 80% suspension of homologous erythrocytes. All the animals were sacrificed 14 days after the onset of the experiment. The mandibles were resected, fixed in formalin, radiographed, processed and embedded in paraffin. Bucco-lingually oriented sections were obtained at the level of the mesial root of the first lower molar, and stained with hematoxylin-eosin. Histological and histomorphometric studies were performed on the buccal and lingual plates of periodontal alveolar bone. RESULTS: Histological and histomorphometric studies showed a statistically significant decrease in bone formation both in buccal and lingual plates in group A (anaemia) as compared to group C (control). An increase in active bone formation was found in the lingual plate in group P (polycythaemia) as compared to group C (control). CONCLUSION: The results obtained using this experimental model evidenced alterations in bone modeling and remodeling under conditions of anaemia and polycythaemia and/or associated factors.     

The pattern of alveolar bone activity during development and eruption of the molar in the rat

The pattern of alveolar bone activity around the developing and erupting mandibular first molar of the rat was studied by autoradiography. The rats were hilled at 1 day and 1, 2, 3 and 4 weeks after birth. One hour prior to sacrifice, they were injected with ³H-proline intraperitoneally. At one day after birth, the alveolar bone surfaces surrounding the tooth germ were unlabeled. At one week, the surface of the alveolar bone mesial to the developing tooth crown revealed heavy labeling, whereas the remaining surfaces surrounding the crown were unlabeled. The interdental septum between the first and second molars appeared at this stage. lts mesial surface was unlabeled troughout the four stages. Formation of the interradicular septum was ohserved at two weehs, and the future crestal area displayed very intense labeling. At three weeks, the crestal, mesial and distal surfaces of the interradicular septum showed heavy labeling. However, the apical one-third of the mesial surface of the septum was unlabeled at four weeks. The surfaces of the fundic bone just beneath the primitive pulp chamber and beneath the open ends of the roots were unlabeled throughout the entire period. At three and four weeks, the interdental and interradicular crests exhibited very heavy labeling, more intense than that at the crest of the alveolar bone mesial to the first molar.     

Longitudinal quantitative radiodensitometric study of treated and untreated lower molar furcation involvements

38 first or second lower molars from 16 patients showing furcation involvements of degrees 1 and 2 were treated after motivation and hygiene instruction, either by subgingival curettage, or by the modified Widman surgical procedure or by furcation plasty. The plaque index, the gingival index of inflammation and the depth of interproximal and interradicular pockets were recorded before and up to 1 year after the 3 therapeutical procedures. The above clinical indices were also followed for 2 years in 15 lower molars from 7 untreated patients. A quantitative radiographical analysis of the interradicular bone was performed in all patients, by using superposable identical radiographs and a computer-assisted photodensitometric technique. In the 3 groups of treated patients, the clinical scores were, in general, improved by the 3 therapeutic modalities. In the furcation areas, the plaque index was always higher on the lingual side, whereas the depth of "horizontal" pockets was always greater on the buccal side. Except for the lesions treated by furcation plasty, no change could be noticed clinically in the depths of vertical or horizontal penetration of a periodontal probe in the furcation areas. The quantitative radiographic analysis, however, clearly showed a loss in the first 2 mm of superficial bone during the 2 months following the 3 therapeutical procedures: this loss was followed by a statistically significant recovery and, for the group treated by curettage, even by a net gain during the 6 to 12 months following therapy. The radiographical density of the deeper layer of bone did not change in the group treated by curettage only. It showed a loss in the first 2 months following the 2 surgical procedures but a statistically significant recovery in the months thereafter. As for the group of untreated patients, at the examinations performed initially, 6 months, 1 and 2 years later, the number of plaque-free and non-bleeding sites in the furcation areas was lower on the lingual as compared to the buccal side, whereas the frequency distribution of furcation involvements was similar on both aspects. No significant changes were found in the various clinical parameters throughout the 2 years of the study. On the contrary, a significant loss of average density of the superficial layer of interradicular bone was already measured on the superposable radiographs 6 months after the initial examination and was found to increase thereafter. No changes of radiodensity could be measured for the deeper layer of bone.(ABSTRACT TRUNCATED AT 400 WORDS)     

比较非手术治疗对重度慢性牙周炎磨牙不同部位牙周病变的疗效

目的:根据磨牙中重度慢性牙周炎发生不同部位病变比较非手术治疗的疗效。方法:根据单个磨牙深牙周袋发生的部位(颊侧或舌/腭侧)将收集的上、下颌磨牙各分为两组(上颌I组、上颌II组、下颌I组、下颌II组),观察各组治疗前后牙周指标的变化,比较疗效差异。结果:4组病例治疗后6周各项牙周指标均较基线有明显改善,差异有显著性(P<0.01)。上颌两组间及下颌两组间比较,可见6周时上颌II组的PD、BI、CAL均高于上颌I组,差异有显著性(P<0.01);下颌II组的PD、BI、CAL高于下颌I组,差异有显著性(P<0.01)。结论:发生在磨牙的牙周炎症无论是上颌还是下颌,颊侧病变的预后均好于舌/腭侧,差异有显著性。     

Effect of restraint stress on the progression of experimental periodontitis in rats

BACKGROUND: A hypothesis of an increased risk for destructive periodontal diseases due to psychological stress has long been promoted. However, the research on stress and periodontal disease is still in its infancy. One of the reasons is thought to be that there is no suitable animal model for investigating the relationship. METHODS: One hundred male Wistar rats were included. A nylon ligature was placed around the second right maxillary molars. The animals were then divided into group S, exposed to a restraint stress for 12 hours/day for up to 10 days, and group N, controls. Ten animals were sacrificed on days 2, 4, 6, 8, and 10. Blood samples were taken, and the blood glucose level and the concentrations of adrenocorticotropic hormone, corticosterone, and adrenaline were measured as the markers of stress. The atrophies of the thymus and the spleen were measured. The furcation area of the second maxillary molars was examined histologically and histometrically. RESULTS: In group S, all values of stress markers were increased, and the thymus and the spleen were atrophied. Whereas group N showed only slight alveolar bone resorption, a marked alveolar bone resorption occurred in group S between days 8 and 10. An increase in beaded nerve terminals occurred around the vessels in the furcation area of group S. CONCLUSION: The results of the present study suggest that the restraint stress modulates the progression of periodontal inflammation and that this rat model is suitable for investigating the association between stress and periodontal disease.     

Periodontal disease in the domestic cat

One hundred and fifty teeth from 15 cats of an average age of 6.8 years were examined macroscopically, radiographically, and histologically. Clinical inspection revealed plaque and calculus deposits on the facial surfaces of maxillary and mandibular premolars and molars. Radiography showed horizontal and vertical loss of alveolar bone with irregular defects of the dental hard structures. Histologically, typical features of gingival and periodontal destruction were found and resorptive lacunae were seen at the cemento-enamel junctions. In comparison with experimentally induced periodontitis in other animals, periodontal disease involving external root resorption seemed to occur spontaneously in the cat.     

Rationale for the lingual approach to mandibular osseous surgery.

The definitive treatment of periodontitis for pocket elimination and the establishment of periodontal architecture that can be effectively maintained with daily personal oral hygiene techniques is sometimes an elusive goal. Performing osseous reduction, primarily from the lingual aspect of the posterior mandible, definitely helps in accomplishing such a goal. This paper should not be interpreted to mean that osseous correction of bony defects should be approached strictly from the lingual, since almost all cases require some buccal recontouring if a satisfactory soft and hard tissue architectural form is to be achieved. Clinical observation and experience have shown that the anatomical patterns, seen in relation to the mandible, have a powerful effect on normal periodontal architecture as well as the types and locations of bony defects encountered. Tooth to bone relationships deserve attention. The buccal housing of the alveolar bone is frequently thin in the premolar region and occasionally on the first molar, while the external oblique ridge causes thicknened bone over the second molar. The vestibular depth on the buccal of the molars is often quite shallow, meaning that only a very limited amount of osteoplasty-osteoectomy can be performed from the buccal. The lingual housing of the alveolar bone is normally thickened and shelf-like from the distal of the third molars to the mesial aspect of the premolar region. Because the posterior teeth are inclined lingually from the second premolar distally, the buccal marginal bone height is higher occlusally than the lingual bone margins, with the interproximal bone therefore sloping somewhat apically and lingually. Interdental craters are the most common defect seen with the onset of periodontitis. Such defects in the lower arch tend to occur beneath the contact areas of the teeth, which are much further to the lingual than in the maxilla. The highest percentage of interproximal craters are shallow and not amenable to grafting techniques in the hands of most clinicians. These shallow craters are prime candidates for osseous reduction techniques. With the progression of periodontitis, the interproximal defects frequently extend to include infrabony lingual defects. Although obtaining lingual access for osseous reduction techniques is often difficult, osteoectomy-osteoplasty techniques performed primarily from the buccal of the posterior mandible frequently result in compromise of the lingual and over treating the buccal in terms of osteoectomy procedures. The lingual embrasure spaces are usually wider than on the buccal, and with adequate reduction of the mylohyoid ridge, greater access for oral hygiene procedures is provided.     

An electron microscopic observation on cells found in bone resorption area incident to experimental tooth movement.

For the purpose of investigating many of the cells in the bone resorption area incident to experimental tooth movement and characterizing the role of these cells for the periodontal tissue resorption at the ultrastructural level, orthodontic force was applied to 24 male rats. Orthodontic elastics were inserted into the interproximal space of the upper first and second molars. The mesial side of the interradicular septum of the second molar was observed. The electron micrsocopic findings were as follows: 1. Cell cohorts were found in the undermining bone resorption area. They are mainly composed of fibroblasts, endothelial cells, undifferentiated cells, macrophages and several kinds of osteoclasts. 2. Four different kinds of osteoclasts could be recognized from the morphological features: a) small osteoclasts situated apart from the bone surface, b) large osteoclasts rich in rough ER, c) classic large osteoclasts and d) degenerating osteoclasts. 3. Two different types of undifferentiated cells were observed in these area. One was a spindle-shaped bright cell rich in rough ER and the other was a round-shaped dark cell with numerous mitochondria and free ribosomes. 4. Macrophages showing phagocytosis were also found in the bone resorption area.