Greater understanding and acceptance of the new concept “bone quality”, which was proposed by the National Institutes of Health and is based on bone cells and collagen fibers, are required. The novel protein Semaphorin3A (Sema3A) is associated with osteoprotection by regulating bone cells. The aims of this study were to investigate the effects of mechanical loads on Sema3A production and bone quality based on bone cells and collagen fibers around implants in rat maxillae. Grade IV-titanium threaded implants were placed at 4 weeks post-extraction in maxillary first molars. Implants received mechanical loads (10 N, 3 Hz for 1800 cycles, 2 days/week) for 5 weeks from 3 weeks post-implant placement to minimize the effects of wound healing processes by implant placement. Bone structures, bone mineral density (BMD), Sema3A production and bone quality based on bone cells and collagen fibers were analyzed using microcomputed tomography, histomorphometry, immunohistomorphometry, polarized light microscopy and birefringence measurement system inside of the first and second thread (designated as thread A and B, respectively), as mechanical stresses are concentrated and differently distributed on the first two threads from the implant neck. Mechanical load significantly increased BMD, but not bone volume around implants. Inside thread B, but not thread A, mechanical load significantly accelerated Sema3A production with increased number of osteoblasts and osteocytes, and enhanced production of both type I and III collagen. Moreover, mechanical load also significantly induced preferential alignment of collagen fibers in the lower flank of thread B. These data demonstrate that mechanical load has different effects on Sema3A production and bone quality based on bone cells and collagen fibers between the inside threads of A and B. Mechanical load-induced Sema3A production may be differentially regulated by the type of bone structure or distinct stress distribution, resulting in control of bone quality around implants in jaw bones.

Objectives: Intermittent injection of parathyroid hormone (PTH) is used to treat osteoporosis. The concept of bone quality was updated 20 years ago; however, these updates have not been adopted in implant dentistry. This study aimed to investigate the effects of intermittent administration of PTH on bone quality around implants in rat tibiae. Methods: Grade IV-titanium-threaded implants that were 3.5 mm long and 2.0 mm wide were placed in a randomly selected side of the proximal tibiae of 12-week-old female Wistar rats. Three weeks after implant placement, the rats were randomly divided into PTH-administration and saline-injection groups (PTH and VC, respectively; n ¼ 7 per group). Micro-computed tomographical, histomorphometric, and immunohistochemical analyses were performed to evaluate bone quality and quantity surrounding the implants. Results: PTH significantly increased bone volume and bone mineral density in bones not associated with the implants as compared to these values in the VC group. PTH significantly increased bone area and the amount of collagen within the total inside areas of all implant threads compared to that observed in VC. Moreover, PTH significantly increased the number of osteoblasts, osteocytes, and osteoclasts in the total inside and/or outside areas of all implant threads and altered the ratio of type I and III collagen to total collagen fibers. Conclusions: Within the limitations of this study, intermittent administration of PTH improved both bone quantity and bone quality based on the types and numbers of bone cells and the types of collagen fibers surrounding implants placed into rat tibiae.

Objectives: This study aimed to investigate the effects of early loads on bone quality and quantity around implants and to compare the effects of early loads on bone quality and quantity with the effects of conventional loads. Materials and Methods:Grade IV-titanium implants with buttress threads were placed in rat maxillary bone 4 weeks after extraction of first molars. A controlled mechanical load (10 N, 3 Hz, 1800 cycles, 2 days/week) was started via the implants 1 and 3 weeks after implant placement for 2 weeks (early and conventional loads, respectively). Bone quality, defined as distribution of bone cells, types and orientation of collagen fibers, and production of semaphorin3A, its receptor neuropilin-1, and sclerostin, were quantitatively evaluated. Results:Early loads substantially and positively affected bone quality by changing the preferential alignment of collagen fibers with increased production of type I and III collagens, semaphorin3A, and neuropilin-1, increased osteoblast numbers, decreased production of sclerostin, and decreased osteoclast numbers both inside and outside the implant threads, when compared with non-loaded conditions. Conventional loads changed bone quality around implants slightly. Interestingly, early loads had significantly stronger effects on bone quality and quantity based on the evaluation parameters than conventional loads.Conclusions: This is the first report to provide scientific evidence for load initiation time based on both bone quality and quantity around implants. These new findings show that implants with buttress threads transmitted early loads optimally to bone tissue by improving bone quality and quantity inside and outside the implant threads.

Osteocytes play important roles in controlling bone quality as well as preferential alignment of biological apatite c-axis/collagen fibers. However, the relationship between osteocytes and mechanical stress remains unclear due to the difficulty of three-dimensional (3D) culture of osteocytes in vitro. The aim of this study was to investigate the effect of cyclic mechanical stretch on 3D-cultured osteocyte-like cells. Osteocyte-like cells were established using rat calvarial osteoblasts cultured in a 3D culture system. Cyclic mechanical stretch (8% amplitude at a rate of 2 cycles min−1) was applied for 24, 48 and 96 consecutive hours. Morphology, cell number and preferential cell alignment were evaluated. Apoptosis- and autophagy-related gene expression levels were measured using quantitative PCR. 3D-cultured osteoblasts became osteocyte-like cells that expressed osteocyte-specific genes such as Dmp1, Cx43, Sost, Fgf23 and RANKL, with morphological changes similar to osteocytes. Cell number was significantly decreased in a time-dependent manner under non-loaded conditions, whereas cyclic mechanical stretch significantly prevented decreased cell numbers with increased expression of anti-apoptosis-related genes. Moreover, cyclic mechanical stretch significantly decreased cell size and ellipticity with increased expression of autophagy-related genes, LC3b and atg7. Interestingly, preferential cell alignment did not occur, irrespective of mechanical stretch. These findings suggest that an anti-apoptotic effect contributes to network development of osteocyte-like cells under loaded condition. Spherical change of osteocyte-like cells induced by mechanical stretch may be associated with autophagy upregulation. Preferential alignment of osteocytes induced by mechanical load in vivo may be partially predetermined before osteoblasts differentiate into osteocytes and embed into bone matrix.

The aim of this study was to clarify whether marginal grooves on dental implants affect osseointegration, bone structure, and the alignment of collagen fibers to determine bone quality under loaded conditions. Anodized Ti-6Al-4V alloy dental implants, with and without marginal grooves (test and control implants, respectively), were used (3.7 × 8.0 mm). Fourth premolars and first molars of 6 beagle mandibles were extracted. Two control and test implants were placed in randomly selected healed sites at 12 weeks after tooth extraction. Screw-retained single crowns for first molars were fabricated. Euthanasia was performed at 8 weeks after the application of occlusal forces. Implant marginal bone level, bone to implant contact (BIC), bone structure around dental implants, and the alignment of collagen fibers determining bone quality were analyzed. The marginal bone level in test implants was significantly higher than that in control implants. Occlusal forces significantly increased BIC in test implants ( P = .007), whereas BIC did not change in control implants, irrespective of occlusal forces ( P = .303). Moreover, occlusal forces significantly increased BIC in test implants compared with control implants ( P = .032). Additionally, occlusal forces preferentially aligned collagen fibers in test implants, but not control implants. Hence, marginal grooves on dental implants have positive effects on increased osseointegration and adapted bone quality based on the preferential alignment of collagen fibers around dental implants under loaded conditions.