Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 158-182). Also available on the Internet.

Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on September 25, 2009. Major professor: Scott Hazelwood, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Engineering with a specialization in Biomedical Engineering." "September 2009." Includes bibliographical references (p. 72-74). Also available on microfiche.

AIM & HYPOTHESIS: We hypothesized that the piezoelectric knife increases bone remodeling. The effect of a piezotome 2 prototype with different puissance and modulation settings on bone biology was compared under different bone resorption and/or bone formation conditions using an ex-vivo live bone organ culture MATERIALS & METHODS: We utilized an ex-vivo mouse calvarial bone culture system a n d piezocision surgical techniques with variable puissance and modulation settings under conditions of static versus dynamic, and formation versus resorption in order to decipher cellular, molecular, biological and genetic perturbations induced by piezocision surgery. In addition, we tested its impact on calvarial bone organ cultures in the presence of drugs such as bisphosphonate (zolendronic acid, ZOL) and insulin or its impact on bone healing with bone graft material such as Enamel matrix derivative (Emdogain). RESULTS: The impact of the piezoelectric knife extends beyond the immediate site of mineralized bone defect/damage. The impact is ~6 times greater than the apparent initial mineralized bone injury, 1.6 mm2, and extends to immediate surrounding local periosteal and endosteal cell layers, 11 mm2, leaving the mineralized bone layer intact. There were also major differences between the static and dynamic model systems in bone defect viii healing, resorption and new bone formation. There are also differences between the piezoelectric knife and bur in bone resorption and formation models and in both treated before or at the same time of the injury with bisphosphonate. In the calvarial defect repair model the defect closed much faster with the piezoelectric knife than with the bur. In a comparative study with controls versus piezotome or bur, and piezotome versus bur complete genomic analysis of changes revealed a large number of major differences in genomic expression levels. CONCLUSION: The extended effect of piezocision on the surrounding bone lining cells of the bone defect including de-vitalization of the proximal osteocytes within the intact mineralized bone matrix thet primes the bone to undergo rapid turnover. Piezocision incorporates high-frequency vibrational energy that can be transmitted a significant distance within the mineral phase and exploits the inherent bone cellular response mechanism(s) as defined by the global genearray analysis. / 2020-06-13T00:00:00Z

In vertebrates, PTH receptor 1 (PTH1R) plays a pivotal role in control of bone development and homeostasis; however, how it is regulated is poorly defined. Here we report that Kindlin-2 binds to and modulates PTH1R to regulate bone mass and PTH actions. Deleting Kindlin-2 expression using the 10-kb mouse Dmp1-Cre severely impairs the anabolic effects of intermittent PTH on bone in adult mice with or without ovariectomy. Of particular interest, Kindlin-2 and Pth1r double heterozygous mice (Dmp1- Cre; Kindlin-2 f/+ ; Pth1r f/+ ), but not either singly heterozygous mice (Dmp1- Cre; Kindlin-2 f/+ or Dmp1-Cre; Pth1r f/+ ), display severe osteopenia and fail to increase bone mass in response to administration of intermittent PTH. Mechanistically, Kindlin-2 interacts with the C-terminal cytoplasmic region of PTH1R. When overexpressed, this region efficiently inhibits the endogenous PTH/PTH1R signaling in osteoblasts, which is reversed by introduction of a point mutation that abolishes the Kindlin-2 interaction. Furthermore, Kindlin-2 loss inhibits PTH-induced CREB phosphorylation and cAMP production in vitro and in bone. PTH upregulates, while estrogen deficiency downregulates, expression of Kindlin-2 in vitro and in bone. Collectively, we demonstrate that interplay between Kindlin-2 and PTH1R regulates bone mass by modulating PTH1R and provide a potential therapeutic target for metabolic bone diseases

Previous research has provided evidence in support of apoptotic osteocytes playing a role in the bone remodeling process. In this study, we examined the regional and quadrantal variations of apoptotic and viable osteocytes in cyclically loaded and unloaded samples. Left tibias of C57 Black 6 Taconic mice (C57Bl/6) were cyclically loaded for either 2 weeks or 5 weeks, with the right tibias being used as controls. After loading, tibias were resected, processed, and then stained using either a TUNEL stain, to show apoptotic osteocytes, or a 2.0% methyl green solution, to reveal viable cells. Cross-sectional images from each tibia were then captured and analyzed in each region (distal, midshaft and proximal) and quadrant (cranial, lateral, caudal, and medial) by counting the number of osteocytes, both apoptotic and viable, and subsequently calculating the percentages and densities of those osteocytes. Individual analysis of each sample group showed that the 5 week loaded bones, with the most statistically significant p-values, had the most regional variations within the samples, specifically showing decreased apoptotic and viable osteocytes in the lateral quadrants. Comparative analysis revealed a statistically significant higher percentage and density of apoptotic osteocytes in 5 week loaded samples compared to all other samples. This provides further quantitative evidence in support of apoptotic osteocytes playing a role in bone remodeling.

The study presented attempts to prove the concept that mechanical changes in the structure of a bone can be predicted for a specific exercise by a subject specific model created from CT data, MRI data, EMG data, and a physiologic FE model. Previous work generated a subject specific FE model of a femur via CT and MRI data as well as created a set of subject specific biomechanical muscle forces that are required to perform a single leg extension exercise. The FE model and muscle forces were implemented into a single leg extension FE code (ABAQUS) along with a specialized bone remodeling UMAT. The UMAT updated the mechanical properties of the femur via a damage-repair bone remodeling algorithm. The single leg extension FE code was verified by applying walking loads to the femur and allowing the system to equilibrate. The results were used to apply the appropriate walking loads to the final FE simulation for the single leg extension exercise. The final FE simulation included applying the single leg extension loads over a one year period and plotting the change in porosity at various regions of the femoral neck. Although only two regions were found to generate valid results, the data seemed counterintuitive to Wolff’s Law which states that bone adaptation is promoted when the material is stressed. The model was successful in creating a subject specific model that is capable of predicting changes in the mechanical properties of bone. However, in order to generate valid FE model results, further understanding of the bone remodeling process and application via a FE model is required.

Indiana University-Purdue University Indianapolis (IUPUI) / Previous research indicates that overall, bone turnover decreases with age. The effects of aging on the remodeling of the mandibular condyle have not been studied. As part of the temporomandibular joint, the mandibular condyle (MC) is exposed to a unique pattern of loading. As such, data obtained from studies of other bones may not be applicable to accurately explain the behavior of trabecular bone of the mandibular condyle and its relationship to aging. Recent research has led to the finding that cortical bone turnover in the mandible is much higher than that seen in tibia, and that both sites decline with age. The purpose of this study was to histomorphometrically quantify the effects of aging on the bone remodeling of the canine MC, and to determine whether site-specific differences due to age occur in the dynamic and static parameters between MC and tibial condyle (TC). Fluorochrome labels were used to mark sites of bone formation in ten old and five young dogs. Specimens were obtained from one MC and one TC for each dog and were prepared for analysis of static and dynamic histomorphometric indices. Mineral apposition and bone formation were totally absent in the old group, as shown by the lack of fluorochrome labels. In the young group, they were significantly higher in the MC than in the TC (p < 0.01). Aging resulted in a significant increase of volume density of the subchondral bone (p < 0.05). Trabecular bone volume was not significantly affected by age in the samples studied. The results indicate that bone remodeling is markedly higher in MC than in the TC in young dogs. With aging, it declines to zero in both sites. Whether the loss of remodeling activity in these elderly animals indicates that they are fully adapted to their mechanical environment or that they have lost the intrinsic ability to remodel, remains to be determined.

Indiana University-Purdue University Indianapolis (IUPUI) / Fluoride has been used in the treatment of osteoporosis because of its apparent ability to directly initiate bone formation. However, fluoride's therapeutic efficacy is controversial. Clinical trials in the range of 50 to 75 mg/day demonstrated severe side effects and a lack of consistent therapeutic benefits. Animal studies have not fully proven a positive effect of fluoride on bone strength. The objective of this study was to determine the histomorphometric changes in the cortical bone of rabbits caused by high doses of fluoride. The hypothesis was that high-dose fluoride intake enhances bone modeling and inhibits bone remodeling. Twenty-four young adult (four months old) female, Dutch Belted rabbits were randomly divided in two groups. The control group received no fluoride in their drinking water, while the experimental group received 100-ppm fluoride. Both groups received approximately 12-ppm fluoride in their food. A pair of tetracycline labels was given two weeks apart before initiation of the experiment. Fluoride treatment was given for six months. A terminal pair of calcein green labels was given before the animals were euthanized. Histomorphometric measurements were made using stereological point-hit and linear-intercept methods. The histomorphometric findings were correlated with fluoride serum and bone levels and also with strength tests. The study demonstrated that fluoride increases bone modeling by increasing periosteal bone apposition and endosteal bone resorption. The net effect of fluoride was an enlargement of the cortical bone and bone marrow and, therefore, the total tissue cross-section. However, the observed increase in bone mass produced by fluoride did not have a positive effect on the mechanical properties of bone. Fluoride did not produce a change in the primary histomorphometric parameters of osteoid surface (OS/BS%) or mineralizing surface (MS/BS%). Fluoride treatment produced an increase in the cortical periosteal modified mineral apposition rate (CPMAR). The remaining dynamic indices (i.e. endosteal MAR, remodeling MAR, cortical endosteal BFR and total BFR, activation frequency and formation period) were not affected by fluoride. The study failed to show an inhibitory effect of fluoride on bone remodeling.

Indiana University-Purdue University Indianapolis (IUPUI) / The bisphosphonate etidronate, a drug commonly used to treat osteolytic bone disorders, produces a long lasting inhibition of bone resorption. Since continual bone remodeling appears crucial for the long-term success of endosseous implants, the effects of this drug on the bone surrounding implants were investigated. The specific objective was to quantify the static and dynamic histomorphometric properties of bone surrounding implants placed in 12 beagle dogs treated with this drug. The dogs were divided into three groups (4 dogs/group) based on the bisphosphonate treatment dose: 0, 0.5 and 5.0 mg/kg/day. Since remodeling is different at distinct sites around implants, we analyzed bone at different distances (<1, 1-2 and 2-3 mm from the implant) and in different regions (periosteal and endosteal calluses and intracortical bone). Factorial ANOVA with repeated measures was used to compare site and regional differences in the dose groups. Results show that etidronate treatment produced a decrease in remodeling activity in the treated groups. The high dose group had impaired bone formation and a complete inhibition of remodeling. Low dose produced the same trend, but was not statistically different from controls. The significant differences (p < 0.05) were shown by the high dose group compared to controls for Mineralizing Surface (MS/BS), Activation Frequency (AcF), Mineral Apposition Rate (MAR), Bone Formation Rate (BFR), Formation Period (FP), Mineralization Lag Time (MLT), Adjusted Apposition Rate (AjAr) and Bone Volume (BV/TV), while Osteoid Volume (OV/TV) and Osteoid Thickness (OTh) were higher (p < 0.05) in the high dose group. Since it has been suggested that a remodeling rate of 500 percent per year is achieved in the first millimeter around an implant in successful osseointegration, the area within the first millimeter, as expected, was more affected by all the parameters than further away. These results agree with earlier studies in which areas of high remodeling were shown to be more affected by bisphosphonate therapy than areas of low remodeling. The area closest to the implant showed significantly greater BV/TV, Void Volume (VV/TV), Osetoid Volume over Bone volume (OV/BV), Osteoid Surface (OS/BS), MS/BS, BFR, FP, AcF and MLT while OV/TV was significantly increased in the area most distant from the implant. It was found that etidronate interfered with normal bone mineralization, since there was a decrease in MLT and an accumulation of osteoid. If remodeling is high around implants so as to repair or prevent microdamage, then etidronate could impair this from happening, thereby resulting in eventual implant failure. Though these high doses are not ordinarily used for the clinical treatment of osteoporosis, a low dose might still be harmful if given long-term. These data confirm our hypothesis that etidronate affects bone resorption and mineralization around an implant, when given at the high dose. Two hypotheses were rejected, since in this study, the effect of etidronate was not dose-dependent. This study was supported by NIH 2PO1AG05793, Merck and CO., and Procter and Gamble Pharmaceuticals.

O reparo ósseo de alvéolos após exodontia dos molares superiores em um modelo animal em ratos Wistar (Rattus norvegicus, albinus) de osteonecrose dos maxilares associada ao uso de bisfosfonatos foi avaliado através de analise microscópica e molecular. Foram utilizados 48 ratos (Rattus norvegicus, albinus, Wistar) machos, com 12 semanas de vida e peso aproximado de 300 gramas, que foram dividos em 4 grupos. Cada grupo era composto por 12 animais, sendo 2 grupos experimentais AZ e AZ-Cirúrgico (AZ-C), que foram submetidos a administração de ácido zoledrônico, 0,6 mg/kg a cada 28 dias com um total de 5 doses e 2 grupos controles CO e CO-Cirúrgico (CO-C) com administração de cloreto de sódio 0,9% no mesmo volume e frequencia do ácido zoledrônico. Todas as soluções foram administradas por via intraperitoneal. O grupo AZ-C e o grupo CO-C foram submetidos a exodontia do primeiro, segundo e terceiro molares superiores 45 dias após a primeira aplicação das soluções. Todos os animais foram eutanasiados após 150 dias do início do experimento (105 dias após as exodontias). As maxilas dos animais foram avaliadas macroscopicamente para presença de lesões espontâneas e com uma sonda clinica número 5 as regiões das exodontias dos molares foram avaliadas para presença ou ausência de solução continua do epitélio. Após feita a avaliação macroscópica as regiões das exodontias dos molares superior esquerdo e do lado contralateral de cada animal foram submetidas a análises qualitativa e quantitativa para presença de sequestros ósseos, restos radiculares, área de osteonecrose, área de espaço trabecular, área de reação periosteal, através de estudos por microscopia óptica pela coloração Hematoxilina e Eosina. Análise quantitativa da expressão do RNAm de proteínas envolvidas no processo de reparo ósseo RANK, RANKL, OPG e VEGF, pelo método de reação em cadeia da polimerase em tempo real (RealTimePCR) também foi realizada. A avaliação macroscópica mostrou que 91,66% dos animais do grupo AZ-C e 41,66% do grupo CO-C apresentaram solução de continuidade do epitélio, sendo estatisticamente significante maior no grupo em terapia com ácido zoledrônico pelo este exato de Fischer (p<0,05). Todos animais do grupo AZ-C e nenhum do grupo CO-C apresentaram sequestros ósseos e todos os animais apresentaram presença de restos radiculares na análise microscópica. A área de osteonecrose foi maior nos animais do grupo AZ-C do que no grupo CO-C (p<0,005), não havendo diferença estatística entre as áreas de espaço trabecular, reação periosteal e osso total. Na análise molecular de RANK, RANKL, OPG e VEGF não houve diferença estatisticamente significante entre os grupos CO, AZ, COC e AZ-C, mesmo quando comparadas áreas de exodontia com áreas com dentes. Estes resultados levam a conclusão que o modelo animal utilizado no presente estudo é um modelo seguro, que o ácido zoledrônico interferiu no reparo ósseo dos alvéolos, causando um atraso na remodelação óssea da região e uma maior incidência de osteonecrose e sequestros ósseos. O ácido zoledrônico não afetou a expressão de RANK, RANKL, OPG e VEGF 105 dias após as exodontias. / The alveolar bone repair following extraction of maxillary molars in an animal model of bisphosphonate related osteonecrosis of the jaws in Wistar rats (Rattus norvegicus, Albinus) was assessed through microscopic and molecular analysis. A total of 48 rats (Rattus norvegicus, Albinus, Wistar rats) with 12 weeks old and weighing approximately 300 grams were used, they were divided into 4 groups. Each group consisted of 12 animals, with 2 experimental groups AZ and AZ-Cirúrgico (AZ-C), who underwent the administration of zoledronic acid, 0.6 mg / kg every 28 days with a total of 5 doses. And 2 control groups CO and CO-Cirúrgico (CO-C) with administration of sodium chloride at 0.9% in the same volume and frequency of zoledronic acid. All solutions were administered intraperitoneally. The group AZ-C and CO-C underwent to extraction of the first, second and third molars 45 days after the first application of the solutions. All animals were sacrificed after 150 days from the beginning of the experiment (105 days after extractions). The maxilla of the animals were assessed macroscopically for the presence of spontaneous lesions, and with a clinical probe number five the regions of the molar extractions were evaluated for the presence or absence of loss of continuity of the oral epithelium. After macroscopic evaluation, the upper left molar and contralateral side of the extraction regions of each animal were submitted to qualitative and quantitative analyzes for the presence of bone sequestrum, root fragments, osteonecrosis area, trabecular space area, area of periosteal reaction, through optical microscopic studies by hematoxylin and eosin staining. And quantitative analysis of mRNA expression of proteins involved in bone repair (RANK, RANKL, OPG and VEGF), by the method of RealTimePCR were carried out. Macroscopic evaluation showed that 91.66% of the AZ -C group and 41.66% of the CO-C group presented a loss of continuity of the epithelium, which was statistically significant higher in the zoledronic acid group according to the Fisher test (p<0.05). All animals in group AZ-C and none in CO-C group showed bone sequestrum and all animals in both groups had root fragments in microscopic analysis. The area of osteonecrosis was higher in the animals of AZ-C group than in CO-C (p<0.005), with no statistical difference between the areas of trabecular space, periosteal reaction and total bone. In the molecular analysis of RANK, RANKL, OPG e VEGF there was no statistically significant difference between the CO, AZ, CO-C e AZ-C groups, even when extraction regions were compared to non extractions areas. These results lead to the conclusion that the animal model described used in this study is a reliable model and zoledronic acid interferes with alveolar bone repair causing a delay in bone emodeling and a higher incidence of osteonecrosis and bone sequestrum. Zoledronic acid did not affect the expression of RANK, RANKL, OPG and VEGF 105 days after dental extractions.