Bone Structure Changes in Iliac Crest Grafts Combined with Implants

Background: Remodeling of onlay grafts combined with implants to the mandible results in predictable changes in the graft's radiographic density. We studied the relationship between changes in radiographic density and trabecular structure during the first year after onlay grafting with simultaneous implant placement to the mandible. Purpose: The aim of this study was to evaluate changes in bone structure after onlay grafting. Materials and Methods: Standardized extraoral radiographs were taken regularly of 16 mandibular sides. Bone structure was measured using the Carl Zeiss Vision KS 400 3.0 imaging system. The parameters studied were trabecular area and perimeter, cavity area and perimeter, end points, branching points, skeleton length, branch angle and direction, and texture. Results: No differences were found between measurements ventrally versus dorsally of the implant, nor close to versus away from the implant. Early cortical changes suggest partial resorption and formation of a more complex structure. In the fourth quarter after surgery, progressive resorption is seen in the graft's upper cortex. In the graft's upper spongiosa, most parameters indicate bone formation during the first postoperative year. Loading‐induced structure changes could not yet be found. Conclusion: The technique can be used to study changes in the architecture of bone grafts. Changes found in the graft's architecture are in accordance with changes in bone density.     

Radiographic Features of Mandibular Trabecular Bone Structure in Hypodontia

Purpose: Radiographic parameters of mandibular trabecular bone structure between 67 subjects having hypodontia and those without were studied on digital panoramic radiographs. Materials and Methods: Three regions of interest (ROI) were defined: the ascending ramus, apical of the mandibular molar and mesial of the first mandibular molar. The effects of the presence of hypodontia and the ROI on the mandibular trabecular bone structure were tested for statistical significance by means of multivariate analysis. Results: Radiographic parameters of trabecular bone architecture were found to differ between various regions of the mandible (p = 0.000), but not between the group of hypodontia subjects and their controls (p = 0.23). There was no interaction effect between the ROIs and the two groups (p = 0.79). For people having hypodontia, some directional parameters of trabecular bone have a reverse correlation with the number of missing teeth. The fractal dimension and the number and perimeter of white segments in the binarized image correlate positively with the number of congenitally missing teeth. Conclusions: A limited number of parameters of radiographic mandibular trabecular bone structure correlate with the number of missing teeth. However, a markable difference in radiographic parameters of mandibular trabecular bone structure between hypodontia and non‐hypodontia subjects could not be demonstrated.     

Influence of experimental hemi-occlusion on mandibular morphology and internal structure in growing rabbit

We induced experimental hemi-occlusion in growing rabbits to investigate the effect of masticatory laterality on the morphology and internal structure of the mandible. Three-dimensional morphometric data from micro-CT were used to compare changes in mandibular morphology and internal structure. Rabbits in the experimental group were placed under general anesthesia and their left maxillary and mandibular molars cut as far as the cervical area using a rabbit molar cutter. Thereafter, the teeth were cut once every 2 weeks. Rabbits were kept until they were 17 weeks old. For morphometric analysis of the mandible, we measured mandibular body length, mandibular length, mandibular ramus height and gonial angle. To analyze cancellous bone structure, we measured total volume, cancellous bone volume, cancellous bone volume density, trabecular thickness, trabecular number, trabecular separation, and trabecular spacing. Mandibular ramus height and gonial angle were significantly greater on the occlusal side in the experimental group than on the non-occlusal side. Cancellous bone volume density, trabecular thickness and trabecular number were significantly greater on the occlusal side in the experimental group than on the non-occlusal side, whereas trabecular separation and trabecular spacing were significantly lower on the occlusal side. The results indicate that differences in mechanical stimuli during the growth phase resulting from masticatory dysfunction or parafunction affect the morphology and internal structure of the mandible.     

Topography of the outer mandibular symphyseal region with reference to the autogenous bone graft

The mandibular symphysis is preferred as a donor site for the relatively small grafts needed for the autogeneous bone graft procedure. This study was undertaken to determine the morphology and composition of the cortical and trabecular bone in the mandibular symphyseal region using 35 mandible specimens from Koreans. The topographical patterns through the thickness of the cortical plate and the width of the trabecular bone were observed. In this study, the labial cortical plate of the mandible became thicker from the superior to the inferior aspects (P < 0.05). However, the trabecular bone width exhibited a different distribution pattern compared to the thickness of the labial cortical plate. This observation concerning the cortical and trabecular bones assists in determination of the depth of osteotomy. The results provide useful information on the mandibular symphysis graft prior to dental implant placement. These results will enable the volume of the cortical plate in the mandibular symphyseal region and its proper size, depth, and location to be predicted when removing a graft block.     

Augmentation of the mandible with GTR and onlay cortical bone grafting. An experimental study in the rat

The aim of the present study was to evaluate the effect of augmenting the mandible with onlay mandibular bone grafts that were covered with e-PTFE membranes according to the principle of guided tissue regeneration (GTR). The experiment was carried out in 30 rats. The inferior border of the mandible and parts of the mandibular body were exposed on both sides. On one side, an autogenous bone graft that was harvested from the angle of the mandible was placed on the inferior border of the mandible and was fixed with a titanium microimplant. Subsequently, the graft was covered with an e-PTFE membrane. The contralateral side, serving as control, was treated the same way except for the placement of the membrane. Groups of six animals were sacrificed 15, 30, 60, 120 and 180 days following surgery, and specimens that were prepared from the experimental and control sites were analyzed histologically. The bone graft underneath the membrane initially presented superficial resorption but, subsequently, the space that was created by the membrane gradually became filled with bone. After 180 days, the area underneath the membrane was completely filled with bone and it was impossible to distinguish between the bone graft and the newly formed bone. Generally, the bone grafts at the control sides were characterized by a gradual resorption during the entire experimental period. At 180 days after transplantation, only a few grafts at the control sites had retained their height, and there was frequently a lack of continuity between the bone graft and the underlying mandibular bone. It can be concluded that onlay mandibular bone grafts combined with GTR may improve the predictability of mandibular augmentation, in comparison to bone grafting alone.     

Dental imaging of trabecular bone structure for systemic disorder screening: A systematic review

The purpose of this systematic review was to evaluate the potential use of dental imaging assessment of trabecular bone structure in the maxillomandibular complex as an adjuvant screening tool to identify systemic disorders. Five electronic databases and grey literature were searched. Studies were included if they investigated subjects with altered trabecular bone determined by dental radiographs. The QUADAS‐2 assessed the risk of bias (RoB) among the studies, while the GRADE determined the strength of evidence. A total of 14 studies that included 1,466 individuals were considered eligible for the qualitative analysis. All studies presented an overall low RoB and low concern regarding applicability. Systemic disorders such as osteoporosis, osteogenesis imperfecta, diabetes, and primary hyperparathyroidism, with their respective control groups, were analyzed among the included studies. Osteoporosis was the condition presenting the most significant results, and 72% of the studies detected changes in the maxillomandibular trabecular bone structure. Studies exploring diabetic edentulous patients found less dense trabecular bone pattern (p < 0.05). In summary, periapical and panoramic radiographs, computed tomography, and cone beam computed tomography imaging could be considered useful for the assessment of the mandibular trabecular bone structure of patients affected by osteoporosis and patients with diabetes.     

Micro X-ray computed tomography analysis for the evaluation of asymmetrical condylar growth in the rat

Authors– Nakano H, Watahiki J, Kubota M, Maki K, Shibasaki Y, Hatcher D, Miller AJ Objectives – To investigate the influence of forced lateral bite on mandibular growth, micro X‐ray computed tomography (CT) was used for the purpose evaluating condylar cartilage and cancellous bone formation in 10 male Wister rats (3 weeks of age). Settings and sample population – The rats were divided into two groups – experimental and control. In experimental group, an inclined crown was cemented onto the maxillary incisors to produce 2.5 mm shift toward the left side during mastication. Right–left differences in whole mandibular length, mandibular height, condylar size, trabecular structure of the condylar head and three‐dimensional (3‐D) finite element analysis were assessed using 3‐D images reconstructed from micro X‐ray CT scans when the mice had reached 21 weeks. Measurements and Results – Asymmetrical growth was found in the experimental group, in which the left condylar head became thicker and shorter than the right condylar head during development. When comparing the left and right condyles of the experimental animals, histomorphometric analysis from micro X‐ray CT showed that the bone volume (BV) of the cancellous bone, the surface area of the cancellous bone (BS), the BS/BV ratio, the BV fraction (BV/TV), and the trabecular thickness and trabecular number were less for the right condyle than for the left condyle. Conclusions – These findings suggested that artificial changes in the mastication do influence the growth of condylar head, condylar bone trabecular structure, and mineralization.     

Trabecular structure and composition analysis of human autogenous bone donor sites using micro-computed tomography

ObjectivesTo evaluate the bone microstructure of autogenous graft bone in elderly people (mean age, 66 years), we compared the bone volume/total volume and bone mineral density of four donor sites that are commonly harvested for maxillofacial surgery and dental implant treatments, using X-ray micro-computed tomography.MethodsEighteen Japanese cadavers were included in this study. Overall, 66 harvested bones (mandibular symphysis, mandibular ramus, ilium, and tibia) were studied. Micro-computed tomography scans of four sites were performed to analyze the trabecular structures, bone mineral density, and bone volume/total volume in these bones.ResultsThe mandibular symphysis bones showed the highest bone volume/total volume and bone mineral density at the four sites. There was a significant difference in the bone volume/total volume between the mandibular symphysis and tibia groups. There was also a significant difference in bone mineral density between the mandibular symphysis group and the ilium and tibia groups. In the three-dimensional observations, the structures of the mandibular trabecular were plate-type. The structures of the tibial bone were mixtures of plate- and rod-types. In the ilium, most trabecula were rod-shaped.ConclusionsMandibular symphysis and ramus had a higher bone volume/total volume and bone mineral density of the four sites and did not show regressive changes in our findings. Mandibular bone is the most suitable source of autogenous graft bone material because of its superior bone quality and quantity.     

基于micro-CT的下颌牙龈癌颌骨侵犯的影像学评估及分析

目的： 对下颌牙龈癌颌骨侵犯进行影像学评估及分析,为进一步优化手术方案及术后治疗提供影像学依据。方法： 选择60例下颌牙龈癌手术患者,分析术前曲面体层片、平扫和增强CT,并对其中符合条件的30例手术标本进行micro-CT三维重建,分析骨密度、骨小梁厚度、骨小梁分离度等相关参数。采用SPSS 22.0软件包对数据进行统计学分析。结果： 常规影像学检查,曲面体层片、平扫及增强CT均有不足,micro-CT三维重建可以准确区分骨松质及骨皮质,评估下颌骨侵犯的范围及程度,相应的数据参数分析癌边缘及癌中心与正常下颌骨组织的皮质骨骨密度显著降低（P<0.05）,骨小梁厚度显著变薄（P<0.05）,松质骨骨密度显著降低（P<0.05）。癌中心与正常下颌骨组织骨小梁分离度增加（P<0.05）。结论： 目前对于下颌牙龈癌的手术方案还存在争议,进一步提高CT检查精度,可能会为制定下颌牙龈癌手术方案提供更精确的指导。     

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.     

Quantitative and morphological studies of the trabecular bones in the condyloid processes of the Japanese mandibles; changes due to aging

The structure of bone changes with advancing age. In order to observe changes in the trabecular bone structure of the mandibular condyloid process and their relationship to age, the mandibular condyloid process and third lumbar vertebra were extracted from cadavers from several age groups, and changes in trabecular bone structure due to age were compared. Comparison of the trabecular bones of the lumbar vertebra and condyloid processes from single cadavers by age revealed a clear reduction in trabecular bone density and width in the lumbar vertebra accompanying advancing age. In the condyloid process in contrast no major changes were observed; it appears that the effects of aging are slight.     

Micro-computed tomography evaluation of the glenoid fossa and mandibular condyle bone after bilateral vertical ramus mandibular distraction in a canine model

The aim of this study was to quantify bone microarchitecture within the glenoid fossa and mandibular condyle following mandibular distraction osteogenesis. Eight 6- to 9-month-old male beagle dogs underwent bilateral vertical mandibular distraction with semiburied distractors (12 days of distraction at 1 mm per day). One unoperated animal served as control. After distraction the animals were divided into two groups (N = 4) and killed after 1 or 2 months of consolidation. Three-dimensional trabecular architecture was analyzed by micro-computed tomography (microCT). At both sites the overall trends were similar. In the glenoid fossa, there was decreased bone volume, trabecular number, and connectivity density and increased trabecular separation at 1 month and decreased trabecular thickness and increased structure model index compared with the control (P < 0.05). In the mandibular condyle, there was decreased bone volume, trabecular number, and connectivity density at both 1 and 2 months, with decreased trabecular thickness and increased structure model index at 2 months only compared with the control (P < 0.05). The bone became less dense and more rodlike. These bone changes are similar to those seen by the effects of aging or impaired normal function. Thus, in the short term, changes occur in the bone microstructure of the glenoid fossa and mandibular condyle after vertical mandibular ramus distraction in the canine model.     

Micro-computed tomography evaluation of the glenoid fossa and mandibular condyle bone after bilateral vertical ramus mandibular distraction in a canine model

The aim of this study was to quantify bone microarchitecture within the glenoid fossa and mandibular condyle following mandibular distraction osteogenesis. Eight 6- to 9-month-old male beagle dogs underwent bilateral vertical mandibular distraction with semiburied distractors (12 days of distraction at 1 mm per day). One unoperated animal served as control. After distraction the animals were divided into two groups (N = 4) and killed after 1 or 2 months of consolidation. Three-dimensional trabecular architecture was analyzed by micro-computed tomography (muCT). At both sites the overall trends were similar. In the glenoid fossa, there was decreased bone volume, trabecular number, and connectivity density and increased trabecular separation at 1 month and decreased trabecular thickness and increased structure model index compared with the control (P < 0.05). In the mandibular condyle, there was decreased bone volume, trabecular number, and connectivity density at both 1 and 2 months, with decreased trabecular thickness and increased structure model index at 2 months only compared with the control (P < 0.05). The bone became less dense and more rodlike. These bone changes are similar to those seen by the effects of aging or impaired normal function. Thus, in the short term, changes occur in the bone microstructure of the glenoid fossa and mandibular condyle after vertical mandibular ramus distraction in the canine model.     

Sex and age differences in bone morphology of mandibles

abstract — Histomorphometric analysis of mandibular specimens has been performed in order to demonstrate possible sex and age differences in percent bone mass and bone activity in the mandible. The material consisted of 32 autopsy specimens from the right premolar region of the mandibular body in subjects with sudden unexpected death and without known bone disease. The subjects were divided in a young group (20–43 years of age) and an old group (60–90 years of age); each group consisted of eight females and eight males. Microradiograms of buccolingual ground sections of 100 μm were used. Quantitation of (1) percent bone area of cortical and trabecular bone and (2) total bone surface/bone area and resorption surfaces/total bone surface in trabecular bone, were done by electronic point-counting. The analysis did not reveal any significant sex or age differences in the trabecular bone with respect to percent bone mass, trabecular coarseness and bone activity. In the buccal and lingual cortices a significant age difference was demonstrated, but there was no sex difference in percent bone mass. Cortical porosity in mandibles clearly increases with increasing age, but seems to be independent of sex.     

大鼠颌骨骨皮质切开术后骨小梁三维结构的改变

目的 探索骨皮质切开术后牙槽骨骨小梁的结构改变规律.方法 选取健康Wistar雄性大鼠10只,在其左侧上颌第一臼齿近远中牙槽骨施行骨皮质切开术,右侧不做处理作为对照.分别在手术前,和手术后7、14、21及42天使用活体Micro-CT进行扫描,获得大鼠上颌牙槽骨以及牙齿的影像学数据,并对其进行分析.结果 术后14天大鼠牙槽骨的骨密度显著降低(P＜0.05),而术后42天又显著升高至比术前更高的水平(P＜0.01).各项三维结构的指标均显示先疏松后致密的趋势.结论 大鼠颌骨骨皮质切开术后,骨质疏松发生在术后14天前,以后逐渐致密,到术后42天已达到比术前更致密的水平.     

Characteristics of the cancellous bone of edentulous mandibles

Trabecular bone volume and trabecular connectivity (trabecular bone pattern factor) of edentulous mandibles were examined using undecalcified bone sections from the region of the 1st premolar to investigate atrophyrelated changes in mandibular cancellous bone. The mean trabecular bone volume was 21.8% in female mandibles and 36.4% in male mandibles. The mean trabecular bone pattern factor was ‐0.22 mm⁻¹ for female mandibles and ‐2.29 mm⁻¹ for male mandibles. The difference between the sexes was statistically conspicuous for both parameters, but did not attain statistical significance. A notable fact was the extreme range of variation in both trabecular bone volume and trabecular connectedness. A difference of 65% between the highest and the lowest trabecular bone volumes measured in the present study (min, 7.6%; max, 73.6%, both male) reflects the possible variation in trabecular density of edentulous mandibles.     

应用自体下颌骨外板行颅面部贴附植骨的临床研究

目的探讨应用自体下颌骨外板行颅面部不同部位贴附植骨后的体积变化情况。方法选择6例采用自体下颌骨外板同时行下颌角及部分体部（角体部）、上颌前部的贴附植骨患者为研究对象,采集患者术后即刻、术后半年的CT数据,利用三维CT分体重建和数据配准分割技术,对配准后的下颌角体部及上颌前部2个植骨区域的术后即刻与术后半年的2组数据同时进行分割,分别独立出2个下颌骨外板贴附植骨区域,对移植骨体积的变化进行测量分析。结果下颌骨外板贴附移植于下颌角体部,术后半年体积缩小20.8％±7.2%,差值分析显示吸收的主要部位为靠近下颌骨下缘及后缘;移植于上颌前部者体积缩小11.2％±2.3%。2个部位移植骨体积吸收率有统计学差异（P<0.05）。结论下颌骨外板贴附移植于颅面部不同部位,骨吸收的程度不同,受区局部力学环境的差异可能是影响因素之一;对吸收率的量化可更好地指导临床应用。     

Mineralized bone loss in partially edentulous trabeculae of ovariectomized rabbit mandibles

OBJECTIVE: The purpose of this study was to evaluate trabeculae changes in partially edentulous bone in ovariectomized rabbits. BACKGROUND: Numerous clinical studies have suggested that the greater risk for oral bone loss in females may be correlated with osteoporosis after menopause. Knowledge of trabecular changes in partially edentulous bone in animals with loss of ovarian function may be beneficial in the diagnosis and treatment of partially edentulous patients of postmenopausal women. METHODS: Twelve adult female Japanese white rabbits were examined. The mandibular incisors were initially extracted to simulate the partially edentulous bone. Six animals were bilaterally ovariectomized and the other six sham-ovariectomized 12 weeks after tooth extraction. The partially edentulous parts of distal mandibular bodies were processed undecalcified 12 weeks after ovariectomized or sham-ovariectomized surgeries and examined by quantitative trabecular bone histomorphometry. RESULTS: In ovariectomized rabbits, there were significant increases in trabecular separation, osteoid volume, osteoid thickness, osteoid width, eroded surface, and mineral apposition rate, and a significant decrease in trabecular number. CONCLUSION: The results of sparser trabecular structure, more trabecular osteoid, and increased trabecular bone turnover demonstrate mineralized bone loss in partially edentulous trabeculae of ovariectomized rabbit mandibles and suggest that the same loss may occur in postmenopausal women.     

Effects of a mechanical barrier on the integration of cortical onlay bone grafts placed simultaneously with endosseous implant

Background: Previous experimental studies on onlay bone graft integration have shown either advantages or disadvantages to the use of mechanical barriers. This indicates that the role played by the biologic properties of transplanted bone and membrane in graft revascularization and bone remodeling has not yet been established. The outcomes regarding osseointegration of titanium dental implants applied in such a condition are still contradictory. Purpose: The rabbit's radius model that is grafted onto the mandibular lower border and covered by membrane can reproduce a challenging experimental situation to preliminarily study the factors involved in osseointegration under deprived blood vessels source. Materials and Methods: Fourteen New Zealand White rabbits had a 2.5‐cm segment of the right radius osteoectomized and fixed onto the right mandibular lower border using titanium screws. Two screw‐shaped titanium implants (2.5 mm wide 2.5 mm long) were installed 7 mm apart in the mid length of the grafted bone. In experimental sites, the graft with the implants and graft‐host bone junction were covered by expanded polytetrafluoroethylene (e‐PTFE) membrane; control sites were left uncovered. Eight animals from the experimental group and six animals from the control group were sacrificed at 6 and 24 weeks after surgery. Ground sections obtained from en bloc tissues containing graft, implants, and recipient bone were subjected to histologic evaluation and histomorphometric analysis (area occupied by the graft and bone‐to‐implant contact). Results: The graft showed significantly more resorption after 24 weeks than at 6 weeks (p .05) irrespective of the treatment (with or without membrane), although the amount of new bone was greater at 24 weeks in sites where a membrane was covering the graft. Compared with 6 weeks postoperatively, the bone‐to‐implant contact was considerably improved at 24 weeks (p .05), and the membrane seemed beneficial for implant osseointegration when compared with unprotected sites (p .05). As a result of graft resorption, the amount of soft tissue was considerably expanded in sites beneath membrane, accompanied by a sustained process of trabecular bone deposition close to the barrier. Conclusions: Cortical onlay grafts covered by membrane demonstrated delayed remodeling, probably as a consequence of a hindered process of graft revascularization. Grafts covered by membrane might rely on previous host bone resorption both to become revascularized and to remodel. The findings that the membrane‐protected grafts were most resorbed at 24 weeks might be attributable to better implant osseointegration, because the fixtures were exposed to greater mechanical stimulation in these sites.     

Microcomputed tomographic analysis of human condyles in unilateral condylar hyperplasia: increased cortical porosity and trabecular bone volume fraction with reduced mineralisation

Unilateral condylar hyperplasia or hyperactivity is a disorder of growth that affects the mandible, and our aim was to visualise the 3-dimensional bony microstructure of resected mandibular condyles of affected patients. We prospectively studied 17 patients with a clinical presentation of progressive mandibular asymmetry and an abnormal single-photon emission computed tomographic (SPECT) scan. All patients were treated by condylectomy to arrest progression. The resected condyles were scanned with micro-CT (18 μm resolution). Rectangular volumes of interest were selected in 4 quadrants (lateromedial and superoinferior) of the trabecular bone of each condyle. Variables of bone architecture (volume fraction, trabecular number, thickness, and separation, degree of mineralisation, and degree of structural anisotrophy) were calculated with routine morphometric software. Eight of the 17 resected condyles showed clear destruction of the subchondral layer of cortical bone. There was a significant superoinferior gradient for all trabecular variables. Mean (SD) bone volume fraction (25.1 (6) %), trabecular number (1.69 (0.26) mm^-1), trabecular thickness (0.17 (0.03) mm), and degree of mineralisation (695.39 (39.83) mg HA/cm³) were higher in the superior region. Trabecular separation (0.6 (0.16) mm) and structural anisotropy (1.84 (0.28)) were higher in the inferior region. The micro-CT analysis showed increased cortical porosity in many of the condyles studied. It also showed a higher bone volume fraction, greater trabecular thickness and trabecular separation, greater trabecular number, and less mineralisation in the condyles of the 17 patients compared with the known architecture of unaffected mandibular condyles.