Immunohistochemical comparison of lateral bone augmentation using a synthetic TiO2 block or a xenogeneic graft in chronic alveolar defects.

OBJECTIVES: To evaluate osteogenic markers and alveolar ridge profile changes in guided bone regeneration (GBR) of chronic noncontained bone defects using a nonresorbable TiO2 block. MATERIALS AND METHODS: Three buccal bone defects were created in each hemimandible of eight beagle dogs and allowed to heal for 8 weeks before GBR. Treatment was assigned by block randomization: TiO2 block: TiO2 -scaffold and a collagen membrane, DBBM particulates: Deproteinized bovine bone mineral (DBBM) and a collagen membrane, Empty control: Only collagen membrane. Bone regeneration was assessed on two different healing timepoints: early (4 weeks) and late healing (12 weeks) using several immunohistochemistry markers including alpha-smooth muscle actin (α-SMA), osteopontin, osteocalcin, tartrate-resistant acid phosphatase, and collagen type I. Histomorphometry was performed on Movat Pentachrome-stained and Von Kossa/Van Gieson-stained sections. Stereolithographic (STL) models were used to compare alveolar profile changes. RESULTS: The percentage of α-SMA and osteopontin increased in TiO2 group after 12 weeks of healing at the bone-scaffold interface, while collagen type I increased in the empty control group. In the defect area, α-SMA decreased in the empty control group, while collagen type I increased in the DBBM group. All groups maintained alveolar profile from 4 to 12 weeks, but TiO2 group demonstrated the widest soft tissue contour profile. CONCLUSIONS: The present findings suggested contact osteogenesis when GBR is performed with a TiO2 block or DBBM particulates. The increase in osteopontin indicated a potential for bone formation beyond 12 weeks. The alveolar profile data indicated a sustained lateral increase in lateral bone augmentation using a TiO2 block and a collagen membrane, as compared with DBBM and a collagen membrane or a collagen membrane alone.

DXA reference values of the humanoid sheep model in preclinical studies.

BACKGROUND: Merino land sheep are a popular pre-clinical large animal model in research on systemic skeletal diseases such as osteoporosis. Interpretation of studies is difficult because many reference parameters are missing or not established. This study aims to determine the reference parameters of the skeletal system (peak bone mass = PBM, T-Score). A defined standard allows an easier comparison of the study data of the animal model with human studies (T-Score). MATERIALS AND METHODS: A total of 116 Dual Energy X-ray Absorptiometry DXA measurements were performed on 74 untreated sheep. The average age of the animals was 57 months. The BMD, BMC, and fat content of the sheep were determined by the relevant human region of interest (ROI). From this, the PBM and from this the T-score for each of the animals were calculated. RESULTS: Using 682 DXA measurements BMD and BMC were determined to provide an indication to PBM. For BMD a significant correlation to the age of the animals was observed (p = 0.043). A significant correlation was also seen for BMC (B) (p ≤ 0.001). In the age-dependent analysis, a widespread of values above the linear regression line was measured for both BMD and BMC between the 50th and 90th months of life. From an age of about 90 months, a wider spread of values below the linear regression line was found, although the average values continued to rise. DISCUSSION: The evaluation of the 116 DXA measurements allowed the determination of the PBM for merino land sheep. With the help of the PBM, a T-score was calculated for each animal. The statistical analysis shows significant differences in BMD values between the different animal groups in each of the four ROIs investigated. Individual control or sham groups per study are therefore not sufficient. To improve comparability, an independent reference group should be established. CONCLUSION: An independent reference group for PBM and a T-score was established from four to six-year-old animals. The bone density increases with the age of the animals. Around the fourth year of life, a first peak could be observed. Also, after the seventh year of life, a further peak with the beginning plateau phase was observed. When compiling a group of animals for an osteoporosis model, animals from the age of seven years should, therefore, be used.

Osteocytes Influence on Bone Matrix Integrity Affects Biomechanical Competence at Bone-Implant Interface of Bioactive-Coated Titanium Implants in Rat Tibiae.

Osseointegration is a prerequisite for the long-term success of implants. Titanium implants are preferred for their biocompatibility and mechanical properties. Nonetheless, the need for early and immediate loading requires enhancing these properties by adding bioactive coatings. In this preclinical study, extracellular matrix properties and cellular balance at the implant/bone interface was examined. Polyelectrolyte multilayers of chitosan and gelatin or with chitosan and Hyaluronic acid fabricated on titanium alloy using a layer-by-layer self-assembly process were compared with native titanium alloy. The study aimed to histologically evaluate bone parameters that correlate to the biomechanical anchorage enhancement resulted from bioactive coatings of titanium implants in a rat animal model. Superior collagen fiber arrangements and an increased number of active osteocytes reflected a significant improvement of bone matrix quality at the bone interface of the chitosan/gelatin-coated titan implants over chitosan/hyaluronic acid-coated and native implants. Furthermore, the numbers and localization of osteoblasts and osteoclasts in the reparative and remodeling phases suggested a better cellular balance in the chitosan/Gel-coated group over the other two groups. Investigating the micro-mechanical properties of bone tissue at the interface can elucidate detailed discrepancies between different promising bioactive coatings of titanium alloys to maximize their benefit in future medical applications.

A New Clinically Relevant T-Score Standard to Interpret Bone Status in a Sheep Model.

BACKGROUND Osteoporosis is diagnosed by bone loss using a radiological parameter called T-score. Preclinical studies use DXA to evaluate bone status were the T-score is referenced on bone mineral density (BMD) values of the same animals before treatment. Clinically, the reference BMD represents values of an independent group of healthy patients around 30 years old. The present study established a clinically similar T-score standard to diagnose osteoporosis in a sheep model. MATERIAL AND METHODS We used 31 female merino land sheep (average 5.5 years old) to study osteoporosis. The following groups were compared using DXA measurement: 1) control; 2) ovariectomized (OVX); 3) OVX combined with a deficient diet (OVXD); and 4) OVXD combined with methylprednisolone administration (OVXDS). Further, an independent group of 32 healthy sheep (4-6 years old) were measured as an independent baseline. BMD was measured at 0 months, 3 months, and 8 months after treatment. RESULTS The same significance pattern between the treated groups and either baseline groups was seen. However, using an independent baseline changed the "clinical" interpretation of the data from an osteoporotic bone status (T-score <-2.5) after 3 months of OXDS treatment into an osteopenic bone status (T-score <-1.5 to -2.4). CONCLUSIONS Using an independent baseline enhanced the statistical significance and showed the clinical relevance. Furthermore, an independent baseline is a reliable alternative to use of a new control group for future experiments and thus reduces the number of animals needed by eliminating the need for a control and corresponding to clinical practice.

Osteocyte Regulation of Receptor Activator of NF-κB Ligand/Osteoprotegerin in a Sheep Model of Osteoporosis.

Osteoporosis induction in a sheep model by steroid administration combined with ovariectomy recapitulates decreased bone formation and substandard matrix mineralization in patients. Recently, the role of osteocytes has been frequently addressed, with focus on their role in osteoclastogenesis. However, the quantification of receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) signaling in osteocytes was not studied in sheep. The current study reproduced the sheep model of osteoporosis to study the RANKL/OPG ratio correlation to the method of osteoporosis induction. We investigated the induction of osteoporosis after 8 months using 31 female merino land sheep divided into four groups: control, ovariectomy, ovariectomy with dietary limitation, and ovariectomy with dietary limitation and steroid injection. In accordance to previous reports, the present study showed trabecular thinning, higher numbers of apoptotic osteocytes, and imbalanced metabolism, leading to defective mineralization. The global RANKL/OPG ratio in the spine after 8 months of steroid and dietary treatment was not different from that of the control. Interestingly, assessment of the osteocyte-specific RANKL/OPG ratio showed that the steroid-induced osteoporosis in its late progressive phase stimulates RANKL expression in osteocytes. Sclerostin is suggested to induce RANKL expression in osteocytes. The findings of this study can contribute to further explain the success of sclerostin antibodies in treating osteoporotic patients despite increased osteocyte-expressed RANKL.

Postembedding Decalcification of Mineralized Tissue Sections Preserves the Integrity of Implanted Biomaterials and Minimizes Number of Experimental Animals.

Bone histology of decalcified or undecalcified samples depends on the investigation. However, in research each method provides different information to answer the scientific question. Decalcification is the first step after sample fixation and governs what analysis is later feasible on the sections. Besides, decalcification is favored for immunostaining and in situ hybridization. Otherwise, sample decalcification can be damaging to bone biomaterials implants that contains calcium or strontium. On the other hand, after decalcification mineralization cannot be assessed using histology or imaging mass spectrometry. The current study provides a solution to the hardship caused by material presence within the bone tissue. The protocol presents a possibility of gaining sequential and alternating decalcified and undecalcified sections from the same bone sample. In this manner, investigations using histology, protein signaling, in situ hybridization, and mass spectrometry on the same sample can better answer the intended research question. Indeed, decalcification of sections and grindings resulted in well-preserved sample and biomaterials integrity. Immunostaining was comparable to that of classically decalcified samples. The study offers a novel approach that incites correlative analysis on the same sample and reduces the number of processed samples whether clinical biopsies or experimental animals.