Changes of bone mineral density and biomechanical properties of the femur after ipsilateral tibia fracture and fixation in rats / 医用生物力学

Objective To investigate the changes of bone mineral density (BMD) and biomechanical properties of the femur after ipsilateral tibia fracture in rats, and its relationship with the tibia fracture union. Methods Forty 3-month-old female SD rats were divided into 2 groups randomly and evenly: the surgery group and the control group. The surgery group received middle shaft fracture and fixation surgery on the right tibia. BMD of the right femur was measured both before the surgery and at 2nd, 4th, 6th, 8th, 10th, 12th week after the surgery, respectively. Ten rats in the surgery group and ten rats in the control group were executed at 6th and 12th week after the surgery, respectively, to test the biomechanical properties of their right tibia and femur. Results The radiological union rate and mechanical union rate of the tibia were 50% and 70%, respectively, at 6th week after the surgery, and those at 12th week after the surgery were both 100%. At 2nd, 4th, 6th, 8th week after the surgery, BMD of the right femur in the surgery group was significantly lower than that in the control group (P<0.05). Compared with the control group, there was no statistical difference in BMD of the right femur at 10th, 12th week after the surgery. Biomechanical properties of the right tibia and femur at 6th week after the surgery showed obviously worse than those at 12th week after the surgery (P<0.05). Analysis showed that the fracture union was highly related with mechanical properties of the tibia (P<0.01), which was also highly related with BMD and mechanical properties of the femur (P<0.001). Conclusions In the early stage of tibia fracture, disuse osteoporosis might occur due to the decrease of BMD and worse mechanical properties in the ipsilateral femur, but as the tibia fracture united, BMD and biomechanical properties of the femur became normal again.

The acceleration of titanium implant osseointegration by low intensity pulsed ultrasound: an experimental study in rats / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To establish an animal model of titanium implant and to investigate the effects of low intensity pulsed ultrasound (LIPUS) on the implant osseointegration.</p><p><b>METHODS</b>Twenty-four female Sprague Dawley (SD) rats were used. Titanium implants were inserted into tibia metaphysis bilaterally in each SD rat. Since the second day following implant surgery, LIPUS stimulation were carried out around the implant on the right side for 20 minutes per day, and implants on the left side remain untouched as self-control. Eight rats were sacrificed and tibiae specimens were harvested on the end of the 4th, 8th, and 12th week respectively. X-ray picture, micro-CT analysis and histological sections were performed to evaluate the effects of LIPUS on the implant osseointegration.</p><p><b>RESULTS</b>Osseointegration at the interface between the implant and bone tissue was observed bilaterally. In the micro-CT histomorphometry analysis, the percentage of osseointegration (%OI) of experiment side were (45.708 ± 3.316)%, (46.231 ± 1.954)%, and (46.807 ± 1.451)% on the end of the 4th, 8th, and 12th week. Meanwhile, the %OI of control side were (43.021 ± 3.558)%, (44.272 ± 3.023)%, and (44.894 ± 4.215)% respectively. The %OI on the 4th weekend, bone volume ratio (BV/TV) on the 4th and 8th weekend, trabecular thickness (Tb. Th) and degree of anisotropy (DA) on the 8th and 12th weekend of the experiment side tibia were significantly greater than those on the control side (P < 0.05). The histological examination showed that the thickness of new bone around the implant and the bone-implant contact area was obviously greater in the LIPUS treated side compared to the control side.</p><p><b>CONCLUSIONS</b>The LIPUS therapy may accelerate the bone healing and osseointegration at the interface between titanium implant and bone, and promote remodeling of bone trabecula on the early stage.</p>

Fracture resistance and failure modes of endodontically treated human teeth restored with four different post-core systems / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To compare the fracture resistance and failure modes of endodontically treated human upper premolars restored with different post-core systems.</p><p><b>METHODS</b>32 extracted human upper premolars were endodontically treated and crowns were sectioned at 2 mm above the labial cement enamel junction (CEJ). The teeth were randomly and equally divided into 4 groups: Group A, teeth restored with cast metal post and metal crown; group B, Tenax Fiber White fiber post and metal crown; group C, EverStick fiber post 1.5 mm in diameter and metal crown; group D, EverStick fiber post 1.5 mm in diameter and add another 1.2 mm diameter EverStick fiber post and metal crown. All the teeth were embedded in acrylic resin blocks, and were subjected to a compressive load at 1 mm/min crosshead speed which delivered at a 45 degrees to the long axis until the first sign of failure was noted. The fracture load and the mode of fracture were recorded.</p><p><b>RESULTS</b>Fracture resistances of the four groups of restored teeth were not significantly different (P>0.05). However, fracture modes in fiber post groups were nearer to CEJ than cast metal post group.</p><p><b>CONCLUSION</b>Fracture resistance of endodontically treated teeth restored with EverStick fiber post is enhanced that it can meet the clinical need, although the flexural resistance of EverStick fiber post itself is the weakest. Fracture modes of all fiber post groups are more favorable than cast metal post group.</p>