Deformation and retentive force following in vitro cyclic fatigue of cobalt-chrome and aryl ketone polymer (AKP) clasps

ObjectiveTo compare the retention force of individual clasps made from cobalt chromium (CoCr) or new aryl ketone polymer (AKP) material, Ultaire™ AKP, following prolonged fatigue testing along ideal and non-ideal paths of removal and to assess 3D deformation of the active and passive clasp tips.MethodsCoCr and AKP clasps were manufactured in their standard, respective processes, digitally scanned prior to testing, then cycled 15,000 times over an e.max analogue crown in artificial saliva. Retentive load was measured in situ, as a function of cycles. Clasps were rescanned to assess deformation and along with their antagonists subjected to SEM to assess localised wear.ResultsDistortion of the CoCr clasps was consistently larger than Ultaire™ AKP clasps, irrespective of removal path. CoCr clasps had significantly higher retentive forces than AKP clasps, for both removal paths. Ultaire™ AKP clasps showed a lower but relatively constant retentive force. The non-ideal path of removal affected retentive forces for both clasp materials. SEM showed localised removal of glaze for e.max crowns used with CoCr clasps.SignificanceUltaire™ AKP clasps showed significantly less permanent deformation and lower retentive force than CoCr clasps. Unlike CoCr, the Ultaire™ AKP clasps did not work harden, nor had as large a reduction in retentive force and accompanying permanent deformation; the retentive force for the Ultaire™ AKP clasps was consistent over 15,000 cycles of fatigue mimicking prolonged clinical use. The AKP material was more robust; showing minimal deformation even in non-ideal paths of removal, as many patients would routinely use.     

两种方法修复牙列缺损的临床研究

目的：比较两种方法用于修复后牙游离缺失伴残根残冠的修复效果。方法：选择38例后牙游离缺失伴残根残冠的患者,按随机数字表法将其分为两组,分别采用冠外栓道式精密附着体义齿（n=17）和卡环固位活动义齿修复（n=21）,5年后对修复效果进行评价。结果：冠外栓道式精密附着体义齿组出现1例崩瓷,无冠桩松动脱落、根折、桩折、牙周炎和根尖周炎,无活动部分破损,成功率为94．1％;卡环固位活动义齿组出现8例失败,成功率为61．9％,两组成功率比较差异有统计学意义（P〈0．05）。结论：对于后牙游离缺失伴残根残冠的牙列缺损病例,选用冠外栓道式精密附着体义齿修复的临床效果较好,值得临床推广使用。     

铸造牙间卡用于可摘局部义齿修复

目的:改善铸造可摘局部义齿固位体的美观性,减轻颊侧固位体的异物感。方法:在两基牙间的颊、龈外展隙内设置牙间卡(发夹卡)。结果:固位体金属外露少、隐蔽性好,美观明显改善,同时,体积小,无异物感。对34例不同牙缺失患者的使用,经1~2年观察,修复体固位良好,基牙未见松动和移位。结论:铸造牙间卡在美观、制作和异物感等方面明显优于常规铸造冠外固位体。     

乙酰胆碱、蛙皮素和P物质对人食管下括约肌张力调节的细胞内信号转导机制

目的 观察蛋白激酶C(PKC)和钙调蛋白信号转导通路在乙酰胆碱、蛙皮素和P物质对人食管下括约肌钩状纤维和套索纤维张力调节中的作用.方法 应用PKC信号通路特异性阻断剂H7和钙调蛋白信号通路特异性阻断剂CGS9343B,以食管和胃底环形肌作对照,测定抑制套索纤维和钩状纤维肌细胞收缩的情况.结果 乙酰胆碱与蛙皮素和P物质引起的收缩,应用H7(5±1)%、(5±2)%、(6±2)%和无钙培养(4±1)%、(6±1)%、(3±1)%的方法,可以有效阻断钩状纤维的收缩(22±1)%、(23±1)%、(24±1)%;以CGS9343B(3±1)%、(4±2)%、(6±1)%和4mmol/L锶离子处理(5±2)%、(3±1)%、(6±2)%可以有效阻断套索纤维(23±2)%、(24±2)%、(26±1)%的收缩.结论 人食管下括约肌的套索纤维细胞依赖钙调蛋白信号通路和内源性钙离子释放产生最大收缩效应.钩状纤维细胞依赖PKC信号通路和外源性钙离子流入产生最大收缩效应.     

Fitness and retentive force of cobalt-chromium alloy clasps fabricated with repeated laser sintering and milling

Purpose

With computer-aided design and computer-aided manufacturing (CAD/CAM), the study was conducted to create a removable partial denture (RPD) framework using repeated laser sintering rather than milling and casting techniques. This study experimentally evaluated the CAM clasp and compared it to a conventional cast clasp.

3种钴铬钼合金美观卡环用于前磨牙的固位力分析

目的:研究3种不同设计的钴铬钼合金卡环在前磨牙的固位力变化,为临床选择适合美观要求的卡环提供依据.方法:采用EZ20万能测力仪,测定钴铬钼合金的传统三臂卡、改良RPI卡环和变异Y形卡环在上颌第二前磨牙的0.25、0.50、0.75 mm 3个倒凹深度上的固位力.采用SPSS22.0软件包对数据进行统计学分析.结果:在0.25和0.50 mm倒凹深度时,卡环固位力大小排序为传统三臂卡＞变异Y形卡环＞改良RPI卡.在0.75 mm倒凹深度,循环开始时卡环固位力大小排序与前2组相似,但在衰减后改变为变异Y形卡环＞传统三臂卡＞改良RPI卡.结论:对位于美学区域的前磨牙区,进入0.75 mm倒凹深度的变异Y形卡环即可提供足够的固位力,又位于美观固位区并靠近龈缘,临床设计义齿时可优先考虑.     

人工唾液和乳酸对钛合金卡环疲劳强度影响的研究

目的:探讨人工唾液和乳酸对钛合金卡环疲劳强度的影响.方法:用成品卡环蜡型制作钛合金卡环15个,分为3组,分别在空气中、人工唾液和乳酸溶液中进行测试,初始载荷强度和疲劳失效前的载荷循环次数被自动记录.疲劳裂纹进行扫描电镜分析.结果:钛合金卡环在不同测试条件下的初始载荷强度无差异(P＞0.05).在空气中的循环次数最高,在乳酸溶液中的循环次数最低.SPSS软件分析表明3组之间的疲劳强度有显著性差异(P＜0.01).结论:结果表明人工唾液和乳酸溶液均使钛合金卡环的疲劳强度下降.     

弯制卡环与铸造卡环对龈下微生物的影响

目的了解卡环戴入前后基牙龈下微生物变化,考察弯制卡环与铸造卡环对龈下微生物影响的差异.方法检查戴牙前、戴牙后1周、1月和3月,弯制卡环和铸造卡环所在基牙龈下可培养细菌总量及革兰氏阴性菌构成比的变化.结果与戴牙前相比,戴牙后1周、1月和3月龈下可培养细菌总量及革兰氏阴性菌构成比均明显增加,差异有统计学意义(P＜0.05),戴牙后1月,弯制卡环与铸造卡环所在基牙龈下革兰氏阴性菌构成比有统计学差异(P＜0.05).结论在本文观察期(3个月)内,卡环的戴入造成龈下微生物中革兰氏阴性菌构成比显著增加,弯制卡环与铸造卡环对龈下微生物中革兰氏阴性菌构成比的影响没有显著差异.     

Internal porosities,retentive force,and survival of cobalt–chromium alloy clasps fabricated by selective laser-sintering

PurposeThe purpose of this study was to evaluate internal porosities, retentive force values and survival of cobalt–chromium (Co–Cr) alloy clasps fabricated by direct metal laser-sintering (DMLS) and compare them to conventionally cast clasps.MethodsEmbrasure clasps were digitally designed fitting teeth 35 and 36 on identical metal models (N = 32). Sixteen clasps were fabricated using DMLS (group DMLS) and another sixteen clasps were additively manufactured from wax and then cast from a Co–Cr alloy (group CAST). Internal porosities were examined using micro-focus X-ray (micro-CT) and analyzed applying Kolmogorov–Smirnov test, Mann–Whitney test, and T test (significance level: p < 0.050). A universal testing machine was used to determine the retentive force values at baseline and after 1095, 5475, 10,950 and 65,000 cycles of simulated aging. Data were analyzed employing Kolmogorov–Smirnov test, one-way ANOVA, and Scheffé’s post-hoc test (significance level: p < 0.050). Survival was estimated for 65,000 cycles of artificial aging using Kaplan–Meier analysis.ResultsMicro-CT analysis revealed a higher prevalence (p < 0.001), but a more homogeneous size and a significantly smaller mean (p = 0.009) and total volume (p < 0.001) of internal porosities for group DMLS. The groups showed mean initial retentive force values of 13.57 N (CAST) and 15.74 N (DMLS), which significantly declined over aging for group CAST (p = 0.003), but not for group DMLS (p = 0.107). Survival was considerably higher for group DMLS (93.8%) than for group CAST (43.8%) after 65,000 cycles of aging.ConclusionsClasps made by laser-sintering could be an alternative to conventional cast clasps for the fabrication of removable partial denture frameworks.     

The effect of thermo-mechanical fatigue on the retentive force and dimensional changes in polyetheretherketone clasps with different thickness and undercut

PURPOSEEsthetic expectations have increased the use of polyetheretherketone (PEEK) clasps as alternatives to Cr-Co in removable partial dentures (RPDs). The objective of this study was to evaluate the retentive force and dimensional change of clasps with different thickness and undercut made from PEEK by the thermo-mechanical fatigue.MATERIALS AND METHODSPEEK clasps (N = 48) with thicknesses of 1 or 1.50 mm and 48 premolar monolithic zirconia crowns with undercuts of 0.25 mm or 0.50 mm were fabricated. Samples are divided into four groups (C1-C4) and were subjected to 7200 thermal aging cycles (at 5 - 55℃). The changes in the retentive force and dimensions of the clasps were measured by micro-stress testing and micro-CT devices from five measurement points (M1 - M5). One-way ANOVA, paired t-test, two-way repeated ANOVA, and post-hoc tests were used to analyze the data (P < .05).RESULTSThe retentive forces of C1, C2, C3, and C4 groups in initial and final test were found to be 4.389-3.388 N, 4.67 - 3.396 N, 5.161 - 4.096 N, 5.459 - 4.141 N, respectively. The effects of retentive force of all PEEK clasps groups were significant decreased. Thermo-mechanical cycles caused significant dimensional changes at points with M2, M4, and M5, and abraded the clasp corners and increased the distance between the ends of the clasp, resulting in reduced retentive forces (P^* = .016, P^* = .042, P < .001, respectively).CONCLUSIONThermo-mechanical aging decreases the retentive forces in PEEK clasps. Increasing the thickness and undercut amount of clasps decreases the amount of dimensional change. The values measured after aging are within the clinically acceptable limits.