The specific contributions of force and velocity to muscle power in older adults

The purpose of this study is to examine the relative importance of the force-based and velocity-based measures of muscle performance to explain inter-individual differences in power production capability and functional task performance. Participants included seventy-nine men and women: middle-aged healthy adults (MH: 40-55years), older healthy adults (OH: 70-85years), and older adults with mobility limitations (OML: 70-85years). Muscle power at 180°/s, isometric maximal torque, and maximal contraction velocity at 40% 1RM were measured during unilateral leg extension. The Short Physical Performance Battery (SPPB) was used to differentiate between healthy and mobility limited older adults. Functional task performance was assessed using multiple chair rise and stair climb tests. Leg extensor force (torque), but not maximal contraction velocity, was significantly associated with muscle power in MH. Both torque and velocity were significantly associated with muscle power in OH. Maximal velocity, but not torque, was associated with power in OML. Maximal velocity demonstrated an association with multiple chair rise time and stair climb time in OML, but not MH or OH. It is concluded that movement velocity is an increasingly important determinant of maximal power output with advancing age. Furthermore, movement velocity is also a critical component of functional task performance with aging and may contribute to functional deficits. These findings help to explain why the rate-dependent variable power has emerged as a critical component of both assessment and rehabilitation of muscular performance and physical function in older adults.     

Displacement of Dental Implants in Trabecular Bone under a Static Lateral Load in Fresh Bovine Bone

Aim: The study aims to provide objective data for the displacement of titanium screw implants in trabecular bone specimens. One hundred Semados implants (Bego, Bremen, Germany) were inserted in bovine type IV bone specimens. All implants had a diameter of 3.75 mm; 50 implants had a length of 8.5 mm and 50 implants had a length of 15 mm. Insertion torque was determined at intervals of 10, 20, and 30 Ncm. Implants were loaded horizontally with 10, 20, and 30 N for 2 seconds. An indicator strip was attached to the implant abutment to allow direct observation of implant movement relative to the bone surface. Horizontal displacement was assessed with an accuracy of measurement of 10 µm. Seven implants got lost by visible loosening. Degree of displacement was subject to evaluation with all others. Those implants showed a mean displacement of 59 µm for 10 N (n = 100), 173 µm for 20 N (n = 99), and 211 µm for 30 N (n = 93). The mean displacement of 15‐mm implants (16, 37, 51 µm) was significantly lower compared with 8.5‐mm implants (103, 311, 396 µm) corresponding to 10, 20, and 30 N as lateral loads. Conclusions: Displacement of screw implants in trabecular bone can be detected and visualized using commercially available endoscopes with a high magnification. A lateral load of 20 N indicates a mean displacement of over 100 µm and therefore results in a critical displacement.     

Biomedical Ti–Mo Alloys with Surface Machined and Modified by Laser Beam: Biomechanical,Histological, and Histometric Analysis in Rabbits

Purpose: In vivo bone response was assessed by removal torque, hystological and histometrical analysis on a recently developed biomedical Ti‐15Mo alloy, after surface modification by laser beam irradiation, installed in the tibia of rabbits. Materials and Methods: A total of 32 wide cylindrical Ti‐15Mo dental implants were obtained (10 mm × 3.75 mm). The implants were divided into two groups: 1) control samples (Machined surface – MS) and 2) implants with their surface modified by Laser beam‐irradiation (Test samples – LS). Six implants of each surface were used for removal torque test and 10 of each surface for histological and histometrical analysis. The implants were placed in the tibial metaphyses of rabbits. Results: Average removal torque was 51.5 Ncm to MS and >90 Ncm to LS. Bone‐to‐implant‐contact percentage was significantly higher for LS implants both in the cortical and marrow regions. Conclusions: The present study demonstrated that laser treated Ti‐15Mo alloys are promising materials for biomedical application.     

后路矫形手术对青少年特发性脊柱侧凸患者脊柱高度的影响

要】 目的：评估后路矫形手术对青少年特发性脊柱侧凸（adolescent idiopathic scoliosis,AIS）患者脊柱高度的矫正程度及其影响因素。方法：2010年1月~2011年6月接受后路矫形内固定术的AIS患者277例,单弯（single curve,SC）173例,双弯（double curve,DC）104例,站立位主弯Cobb角平均53.63°±15.38°（40°~140°）,仰卧位主弯Cobb角43.87°±15.01°（20°~124°）。脊柱高度（spinal height,SH）定义为仰卧位全脊柱正位X线片上T1椎体上终板中点至S1椎体上终板中点之间的垂直距离。测量术前、术后SH,ΔSH为手术矫正SH值。评估不同Cobb角侧凸患者的ΔSH,并采用偏相关分析评估脊柱侧凸术前Cobb角、Cobb角矫正值、Cobb角矫正率、术前SH及术后SH与ΔSH的相关性。结果：SC组仰卧位Cobb角术后矫正至15.69°±9.21°（4°~79°）,DC组仰卧位主弯Cobb角术后矫正至19.50°±13.07°（3°~95°）,矫正率分别为69.7%和65.5%。SC组和DC组术前SH分别为41.29±2.96cm和39.97±3.26cm,术后SH分别为43.77±2.71cm和42.86±3.04cm。SC组术前仰卧位Cobb角分别为≤30°、31°~40°、41°~50°、51°~60°、61°~70°、71°~80°、>80°时,ΔSH分别为1.97±0.79cm、2.14±0.63cm、2.52±0.65cm、2.77±0.51cm、3.92±0.61cm、4.33±0.22cm、4.85±0.22cm;而在DC组中,ΔSH分别为2.37±0.60cm、2.35±0.69cm、2.56±0.53cm、3.27±0.40cm、3.79±0.94cm、3.89±1.11cm、5.46±0.91cm。ΔSH与术前Cobb角[SC：r=0.702,P<0.001;DC（主弯+次发弯）：r=0.718,P<0.001]、Cobb角矫正值[SC：r=0.659,P<0.001;DC（主弯+次发弯）：r=0.698,P<0.001]和术后SH[SC：r=0.182,P=0.017;DC（主弯+次发弯）：r=0.213,P=0.033]呈显著相关性,但与Cobb角矫正率[SC：r=0.083,P>0.05;DC（主弯+次发弯）：r=0.039,P>0.05]和术前SH[SC：r=-0.082,P>0.05;DC（主弯+次发弯）：r=-0.047,P>0.05]无明显相关性。结论：后路矫形手术可显著改善AIS患者的SH,术前Cobb角和Cobb角矫正值是影响SH矫正程度的主要因素,术后SH是次要影响因素,而Cobb角矫正率则影响不大。     

Effects of predrilling on the osseointegration potential of mini-implants

Objectives:To determine a reliable method of drilling a pilot hole when using a self-tapping surface-treated mini-implant and to evaluate stability after placement.Materials and Methods:Implant sites were predrilled in 12 rabbits with two devices: a conventional motor-driven handpiece and a newly developed hand drill. Mini-implants were then inserted in a complete random block design. Samples were divided into 1-week and 6-week groups to investigate osseointegration capacity in relation to the two time intervals. Mechanical and histomorphometric assessments were performed.Results:Mechanical analysis revealed no difference in maximum removal torque or total removal energy between the motor-driven predrilling group and the hand-drilling group. No difference was found between the 1-week group and the 6-week group. Histomorphometric evaluation showed no difference in the bone-implant contact (BIC) ratio or the bone volume (BV) area. For the time interval, a statistically significant increase in BIC and BV area was found in the 6-week group when compared to the 1-week group.Conclusions:The osseointegration potential of the motor-driven predrilling method was not different from that of the manual predrilling method with the newly developed hand drill. Hand drilling may be an attractive predrilling method in preference to the conventional motor-driven pilot drilling.     

Influence of the implant abutment types and the dynamic loading on initial screw loosening

PURPOSE

This study examined the effects of the abutment types and dynamic loading on the stability of implant prostheses with three types of implant abutments prepared using different fabrication methods by measuring removal torque both before and after dynamic loading.

MATERIALS AND METHODS

Three groups of abutments were produced using different types of fabrication methods; stock abutment, gold cast abutment, and CAD/CAM custom abutment. A customized jig was fabricated to apply the load at 30° to the long axis. The implant fixtures were fixed to the jig, and connected to the abutments with a 30 Ncm tightening torque. A sine curved dynamic load was applied for 10⁵ cycles between 25 and 250 N at 14 Hz. Removal torque before loading and after loading were evaluated. The SPSS was used for statistical analysis of the results. A Kruskal-Wallis test was performed to compare screw loosening between the abutment systems. A Wilcoxon signed-rank test was performed to compare screw loosening between before and after loading in each group (α=0.05).

RESULTS

Removal torque value before loading and after loading was the highest in stock abutment, which was then followed by gold cast abutment and CAD/CAM custom abutment, but there were no significant differences.

CONCLUSION

The abutment types did not have a significant influence on short term screw loosening. On the other hand, after 10⁵ cycles dynamic loading, CAD/CAM custom abutment affected the initial screw loosening, but stock abutment and gold cast abutment did not.