A comparison of torque expression between stainless steel,titanium molybdenum alloy,and copper nickel titanium wires in metallic self-ligating brackets

Objective:The force moment providing rotation of the tooth around the x-axis (buccal-lingual) is referred to as torque expression in orthodontic literature. Many factors affect torque expression, including the wire material characteristics. This investigation aims to provide an experimental study into and comparison of the torque expression between wire types.Materials and Methods:With a worm-gear–driven torquing apparatus, wire was torqued while a bracket mounted on a six-axis load cell was engaged. Three 0.019 × 0.0195 inch wire (stainless steel, titanium molybdenum alloy [TMA], copper nickel titanium [CuNiTi]), and three 0.022 inch slot bracket combinations (Damon 3MX, In-Ovation-R, SPEED) were compared.Results:At low twist angles (<12 degrees), the differences in torque expression between wires were not statistically significant. At twist angles over 24 degrees, stainless steel wire yielded 1.5 to 2 times the torque expression of TMA and 2.5 to 3 times that of nickel titanium (NiTi). At high angles of torsion (over 40 degrees) with a stiff wire material, loss of linear torque expression sometimes occurred.Conclusions:Stainless steel has the largest torque expression, followed by TMA and then NiTi.     

自锁托槽与传统托槽早期远中移动尖牙速度的对比研究

目的 比较拔牙治疗初期,Damon自锁托槽与普通MBT直丝弓托槽(3M Unitek金属托槽)远中移动尖牙的速度.方法 选取上颌唇侧尖牙低位阻生的青少年正畸患者36例,均采用拔除双侧上颌第一前磨牙的治疗方案,随机将患者分为A、B、C3组,在双侧上颌尖牙处随机粘接Damon自锁托槽(分别标记为AD,BD,CD组)或者MBT直丝弓托槽(分别标记为AM,BM,CM组):A组不加任何辅助加力装置,B组配合使用Ⅱ类牵引辅助尖牙远中移动,C组使用Laceback辅助尖牙远中移动,治疗开始后4周和8周分别测量尖牙远中移动的距离,并进行统计学分析.结果 4周后,B组中粘接自锁托槽的尖牙远中移动的距离明显大于粘接MBT托槽者(P＜0.01);8周后,A组及B组中粘接自锁托槽的尖牙远中移动的距离明显大于粘接MBT直丝弓托槽尖牙者(P＜0.05).组间比较显示:4周后,B组中粘接自锁托槽的尖牙远中移动的距离明显大于A组以及C组(P＜0.005);8周后,B组中粘接自锁托槽的尖牙远中移动的距离明显大于A组(与AD、AM相比P＜0.005)以及C组(与CD相比P＜0.05,与CM相比P＜0.005).结论 在拔除上颌第一前磨牙矫治唇侧低位尖牙阻生的病例中,使用自锁托槽矫治能够显著加快尖牙远中移动的速度,尤其配合早期Ⅱ类牵引时更明显.     

Evaluation of dental composite shrinkage and leakage in extracted teeth using X-ray microcomputed tomography

ObjectiveUse X-ray microcomputed tomography (μCT), to test the hypothesis that composite shrinkage and sites of potential leakage in human teeth are non-uniformly distributed and depend on cavity geometry and C-factor.MethodsTwo holes of equal volume but different dimensions were drilled into the exposed dentin of extracted human molars. The cavities were filled with composite and teeth were scanned, before and after curing, using μCT. Three-dimensional (3D) reconstructions of the data were prepared and analyzed using image analysis software.Results3D reconstructions showed that cavity geometry did not affect the polymerization shrinkage. The shrinkage for all restorations was 2.66 ± 0.59%, and cavity dimensions did not affect the volume lost, either in quantity or location on the sample. Potential leakage sites were identified by gap formations and found to be non-uniformly distributed along the tooth–composite interface. Leakage in regions calculated by μCT was confirmed by visualization of sectioned samples with confocal laser scanning microscopy.SignificanceμCT evaluation will add tremendous value as part of a suite of tests to characterize various properties of dental materials. The non-uniform distribution of potential leakage sites about the cavities that was determined by μCT emphasizes the inadequacy of traditional methods of determining leakage, which are capable of analyzing only limited areas. Additionally, μCT evaluation can produce quantitative analyses of shrinkage and leakage, compared to the conventional methods, which are qualitative or semi-quantitative. Finally, experimentally determined shrinkage and leakage of composite in extracted teeth agrees with the results of similar experiments in model cavities, confirming the validity of those models.     

Release of cobalt from cobalt chromium alloy constructions in the oral cavity of man

Abstract – The release of cobalt from a cobalt chromium alloy construction with a major palatal connector (palatal strap) in the maxilla was determined for 10 test subjects. The concentration of cobalt in unstimulated whoie saliva and tongue scrapings was estimated 21, 14 and 7 di respectively before and 1,2, 3, 10, 20 and 30 d after insertion of the cobalt chromium alloy construction. The method used to quantify the cobalt content was nameless atomic absorption spectrophotometry (AAS). The results showed that the median cobalt concentration in saliva and tongue scrapings increased after the insertion of the cobalt chromium alloy construction, with the highest values occurring in the first 2 d after insertion. The tongoe scrapings, in general, showed higher cobalt median values than saliva did at all times of estimation. The sampling method described in the present study seems to be useful in long-term investigations in man, where numerous sample collections in the oral cavity are required in order to determine metal content. The risk of negative biologic effects on the human organism caused by the cobalt released from die alloy is discussed.