不同形态(牙合)面固位螺钉对种植牙单冠稳定性的影响

目的:种植义齿成功率较高,但仍存在一些问题.较常见的是单冠修复体固位螺钉的松动,其原因很多,本实验就不同形态固位螺钉对修复体稳定性的影响进行临床和实验分析.方法:一、对6年内BLB种植系统两种不同形态牙合面固位螺钉(锥形和平头直角)固位的单颗磨牙及双尖牙的稳定性进行对比分析.二、采用三维有限元的分析方法,对以上两种不同形态牙合面固住螺钉进行实验,计算其在相同扭力(20Ncm)下所获得的预负荷F1,拧紧力矩Ta,防松力矩Tb及其分布,并在上述扭力下,给修复体施加垂直向150N、300N、与垂线成20度角的150N牙合力,观察F1、Ta、Th的分布与变化.结果:一、临床中锥形螺钉与直角螺钉在稳定性上有显著性差异.分组比较中前磨牙组直角螺钉更稳定;直角螺钉组前磨牙更稳定.戴牙时间越长松动概率越高.性别与年龄对稳定性的影响没有显著性差异.二、三维有限元分析中,直角螺钉能够获得更大的预负荷F1.直角螺钉拧紧力矩Ta及防松力矩Tb在螺纹处分布较多,而锥形螺钉主要分布在螺钉头处.在受到150N垂直载荷及与垂线成20度角加载时,预负荷F1、力矩Ta、Th均下降,其中直角螺钉保留的预负荷较高,锥形螺钉总力矩值降低大于直角螺钉.当受到较大牙合力300N时两种螺钉损失的顸负荷及力矩都很大,直角螺钉剩余量较大.结论:临床结果与实验结果统一,1、直角牙合面固位螺钉的稳定性优于锥形螺钉.2、双尖牙的稳定性优于磨牙.3、戴牙时间越长越容易造成修复体松动.4、性别与年龄对螺钉的稳定性没有明显影响.5、修复体载荷过大会降低修复体的稳定性.     

螺钉形态和牙位对单冠种植牙稳定性影响的临床分析

目的分析面螺钉固位的种植义齿单冠修复体螺钉松动的原因。方法对237人262颗磨牙及双尖牙的单牙种植体进行单冠面螺钉固位修复,其中牙冠的面固位螺钉有两种不同形态,记录牙冠稳定性的临床资料,并从螺钉形态、牙位的角度进行统计分析。结果锥形螺钉与直角螺钉在修复体稳定性上有统计学差异。分组比较时,前磨牙组中两种螺钉有统计学差异,直角螺钉更稳定;直角螺钉组中前磨牙组更稳定。结论直角型面固位螺钉的稳定性优于锥形螺钉,双尖牙的稳定性优于磨牙。     

螺钉固位与粘固固位种植义齿单冠循环疲劳性能的比较

目的比较动态负荷下螺钉固位与粘固固位种植单冠修复体的固位与机械力学特性。方法将粘固固位和螺钉固位单冠修复体标本固定在227kg的压力感受器上,通过计算机控制,在15kg循环负荷下进行疲劳实验。比较实验前、后单冠修复体的松动度,观察2组标本经受疲劳实验后的失败模式。结果螺钉固位组与粘固固位组单冠平均初始动度值分别为3.62±1.00、3.61±1.31,差异无显著性。螺钉固位组与粘固固位组单冠平均负荷次数分别为(2.16±1.28)M（百万次）、(2.60±2.28)M,差异无显著性。两组的机械失败方式不同。结论粘固固位和螺钉固位均能为修复体提供足够的固位力。两种固位方式因界面连接不同,导致机械失败的方式也不同。     

不同边缘设计的聚合瓷高嵌体修复后牙体组织的有限元应力分析

目的建立不同边缘设计的下颌第一恒磨牙高嵌体修复后的三维有限元模型,分析修复体和牙体组织的应力变化。方法通过口腔科专用的锥形束CT扫描离体下颌第一恒磨牙,建立牙齿的三维图像,利用Solidwoks2010软件和有限元分析软件Ansys12.0建模并进行受力分析;得到等效（Von Mises）应力云图。根据应力云图,分析90°肩台、135°肩台、内线角圆钝的直角肩台三种不同边缘设计的聚合瓷高嵌体修复后修复体和牙体组织的应力分布情况。结果①三种肩台设计聚合瓷高嵌体修复后,无论是垂直向还是斜向加载,等效应力主要集中在加载部位和牙根侧壁,牙颈部应力均明显减轻。②无论是施加150N还是300N载荷,垂直加载时,90°肩台和135°肩台设计时,在牙合面窝洞轴髓线角处均有应力集中区,而内线角圆钝的直角肩台设计在此处应力分布均匀;斜向加载时,牙合面洞型侧壁等效应力峰值比较均是：90°肩台设计〉135°肩台设计〉内线角圆钝的直角肩台设计。结论①采用三种边缘设计的复合树脂高嵌体修复时,都明显减轻了牙颈部的应力分布。②在覆盖牙尖的树脂高嵌体修复时,边缘设计最好采用内线角圆钝的直角肩台设计。     

前牙单端全瓷粘接桥的三维有限元分析研究

目的 采用三维有限元分析法分析七组不同设计的前牙全瓷单端粘接桥的修复体及其支持组织的应力分布。方法 通过CBCT扫描成人上颌,模拟21牙缺失,根据11基牙舌侧翼板的不同设计,建立七组（A-G组）粘接桥的三维有限元模型,在七组桥体上进行垂直与斜向45°加载,利用MSC.Nastran2012软件进行修复体及其支持组织的应力分析。结果 修复体应力主要集中在连接体处,在垂直载荷时VonMises应力值E组最大,粘接面积相似时,VonMises应力值随翼板近远中长度减小而降低,A组最大主应力最高;斜向载荷时B组应力值最大,G组最小;11基牙在斜向载荷时G组应力值最高;邻面粘接剂在两种载荷下G组应力值均最大。结论 在垂直和斜向载荷下,修复体连接体处为应力集中区域;舌侧全覆盖翼板粘接桥整体应力分布较合理;随着粘接面积减小,前伸接触时修复体和邻面粘接剂所受应力增加,易出现修复体折断和脱粘接;正中咬合时,无舌侧翼板的粘接桥所受应力最小,但修复体脱粘接风险最高。     

边缘形式对大面积缺损第一磨牙髓腔固位冠应力分布的影响

目的:探讨下颌大面积缺损第一磨牙经根管治疗后,采用髓腔固位冠修复,其边缘设计形式对牙体组织及修复体力学的影响。方法:建立右侧下颌第一磨牙的三维有限元模型,磨牙存在牙冠大面积缺损,根管治疗后采用髓腔固位冠修复,设计2种边缘预备形式,即90°边缘和对接边缘,对模型进行加载,观察各部分的最大主应力(εMax)。结果:2种修复方式下,牙体和修复体的应力集中区域有所不同。其中牙釉质和修复体的应力受边缘设计因素的影响较大。在垂直载荷下,釉质的εMax峰值在对接边缘组较90°边缘组下降了42.88%,应力集中分别位于边缘的釉牙本质界处和边缘的釉质表面。在垂直载荷下,全瓷修复体的εMax峰值在对接边缘组较90°边缘组下降了45.55%,应力集中分别位于边缘近髓腔区域和边缘近牙体表面。在舌颊向载荷下,全瓷修复体的εMax峰值在对接边缘组较90°边缘组下降了12.58%,应力集中分别位于髓腔底部和边缘近牙体表面。结论:在髓腔固位冠的设计中,对接边缘的设计形式更有利于保护牙釉质和改善修复体的应力,从生物力学角度对修复体的稳定性起到积极的作用。     

两种摩擦系数对种植体基台的固位螺钉松动影响的有限元分析

目的:通过三维有限元法,研究种植义齿在扭矩一定的情况下,摩擦系数改变对固位螺钉松动的影响.方法:本研究应用Ansysis 9.0软件,计算结果由三维数字化图像和图表两种形式来说明:三维数字化图像反映每种模型在各种工况下的应力分布总特征和趋势;图表说明摩擦系数为0.26和0.12种植体基台所受三种外力不同的情况(螺杆等效应力最大值应力、最大值部位、位移最大值).结果:在垂直加载35N力情况下,摩擦系数为0.26,螺钉上的最大等效应力为19.076MPa,摩擦系数为0.12,螺钉上的最大等效应力为21.404MPa;在水平加载10N力的情况下,摩擦系数为0.26,螺钉上的最大等效应力为19.118MPa,摩擦系数为0.12,螺钉上的最大等效应力为21.474MPa;在倾斜45°加载70N的情况下,摩擦系数为0.26,螺钉上的最大等效应力为44.336MPa,摩擦系数为0.12,螺钉上的最大等效应力为45.214MPa,螺钉上的应力分布规律大致相同,均在螺钉的第一个螺纹附近.结论:种植体基台施加的垂直35N、水平10N、倾斜45°70N不同外力,对固位螺钉应力及剩余位移的影响也不同,它们之间呈线形相关.固位螺钉柄与螺丝头交界变化的部位,为螺丝的危险界面.     

反复松紧过程对种植体与基桩结合稳定性的影响

目的探讨在调整TiAdap基桩时,反复松紧过程对种植体和基桩的结合稳定性是否有影响。方法15个Branemark种植体(5RP,5NP,5WP)分别与5个TiAdapRP,5个TiAdaptNP、5个TiAdaptWP组成3组,3组分别用32N.cm、20N.cm、45N.cm扭力将种植体和基桩拧紧,然后再用扭力控制仪将两者松开,记录扭力的数据,重复5次。结果方差分析显示5次拧紧-松开过程记录的扭力第1组无显著性差异(P=0.5319);而第2、3组存在显著性差异(P=0.0084,0.0049),差别主要存在于第1次拧紧-松开过程和后4次松紧之间,后4次松紧过程之间无显著性差异。结论表明反复松紧过程对种植体和基桩结合稳定性的影响主要在第1次松紧过程。     

根上附着体桩柱形态设计对牙本质应力分布的影响

附着体桩柱形态的设计不仅影响到桩柱固位,而且影响牙本质应力分布。本研究用三维有限元法分析临床常见的６种桩柱形态设计对牙本质应力分布的影响。结果表明：锥形桩柱设计对牙本质有楔的作用,其应力值明显高于平行桩柱,为平行桩的１．１倍;螺纹桩柱设计,牙本质最大应力值是非螺纹桩柱的１．０６倍。然而,桩柱形态设计对牙本质应力分布的影响明显小于载荷作用方向对牙本质应力分布的影响。４５度斜向载荷作用下,相同设计的桩柱其牙本质最大应力值是垂直载荷作用下牙本质最大应力值的２．１倍。因此,临床修复设计中,减小侧方咬合力是预防牙本质折裂的主要手段。     

不同设计的Ⅱ类洞型对修复体应力的影响

目的　评价不同Ⅱ类复合洞型对银汞合金和复合树脂修复体产生应力的影响。方法在下颌第一磨牙设计 5种近中邻面Ⅱ类复合洞型 ,分别用银汞合金和复合树脂充填 ,采用三维有限元法对充填体承受垂直和侧向力后所产生的应力分别进行计算分析。结果　 5种Ⅱ类洞型受到 1 0 0N垂直、侧向作用力后 ,在传统和改良洞型中 ,除银汞合金产生的压应力和受侧向力时的切应力传统洞型比改良洞型小外 ,其余的应力值均是传统洞型比改良洞型大。在有固位沟狭孔、无固位沟狭孔和碟型 3种洞型中 ,复合树脂修复体产生的各种应力均明显小于银汞合金者 ;2种狭孔和碟型洞型产生的应力值均比传统和改良洞型小者。结论　银汞合金充填洞型设计为有固位沟狭孔洞型较好 ;复合树脂修复时洞型设计为无固位沟狭孔型较好     

Effects of Abutment Screw Coating on Implant Preload

Purpose: The aim of the present study was to investigate the effects of tungsten carbide carbon (WC/CTa) screw surface coating on abutment screw preload in three implant connection systems in comparison to noncoated titanium alloy (Ta) screws. Materials and Methods: Preload of WC/CTa abutment screws was compared to noncoated Ta screws in three implant connection systems. The differences in preloads were measured in tightening rotational angle, compression force, initial screw removal torque, and postload screw removal torque after 1 million cyclic loads. Preload loss percent was calculated to determine the efficacy of maintaining the preload of two abutment screw types in relation to implant connection systems. Results: WC/CTa screws provided 10° higher tightening rotational angle than Ta screws in all three connection systems. This difference was statistically significant (p < 0.05). External‐hex butt joint implant connections had a higher compression force than the two internal conical implant connections. WC/CTa screws provided a statistically significantly higher compression force than Ta screws in all three implant connections (p < 0.05). Ta screws required statistically higher removal torque than WC/CTa screws in all three implant connections (p < 0.05); however, Ta screws needed statistically lower postload removal torque than WC/CTa screws in all three implant connections (p < 0.05). Ta screws had a statistically higher preload loss percent than WC/CTa screws in all three implant connections (p < 0.05), indicating that WC/CTa screws were superior in maintaining the preload than Ta screws. Conclusions: Within the limits of present study, the following conclusions were made: (1) WC/CTa screws provided higher preload than noncoated Ta screws in all three implant connection systems. (2) The initial removal torque for Ta screws required higher force than WC/CTa screws, whereas postload removal torque for Ta screws was lower than WC/CTa screws. Calculated Ta screw preload loss percent was higher than for WC/CTa screws, suggesting that WC/CTa screws were more effective in maintaining the preload than Ta screws. (3) Internal conical connections were more effective in maintaining the screw preload in cyclic loads than external‐hex butt joint connections.     

Influence of occlusal forces on stress distribution in preloaded dental implant screws

STATEMENT OF PROBLEM: Abutment and prosthetic loosening of single and multiple screw-retained, implant-supported fixed partial dentures is a concern. PURPOSE: The purpose of this study was to investigate stress distribution of preloaded dental implant screws in 3 implant-to-abutment joint systems under simulated occlusal forces. MATERIAL AND METHODS: Three abutment-to-implant joint systems were simulated by using the 3-dimensional finite element analysis method: (1) Branemark external hexagonal screw-retained abutment, (2) ITI 8-degree Morse tapered cemented abutment, and (3) ITI 8-degree Morse tapered plus internal octagonal screw-retained abutment. A thermal load and contact analysis method were used to simulate the preload resulting from the manufacturers' recommended torques in implant screw joint assemblies. The simulated preloaded implants were then loaded with 3 simulated static occlusal loads (10 N; horizontal, 35 N; vertical, 70 N; oblique) on the crown position onto the implant complex. RESULTS: Numeric and graphical results demonstrated that the stresses increased in both the abutment and prosthetic screws in the finite element models after simulated horizontal loading. However, when vertical and oblique static loads were applied, stresses decreased in the external hexagonal and internal octagonal plus 8-degree Morse tapered abutment and prosthetic screws with the exception of the prosthetic screw of ITI abutment after 70-N oblique loading. Stresses increased in the ITI 8-degree Morse tapered cemented abutment after both vertical and oblique loads. CONCLUSION: Although an increase or decrease was demonstrated for the maximum calculated stress values in preloaded screws after occlusal loads, these maximum stress values were well below the yield stress of both abutment and prosthetic screws of 2 implant systems tested. The results imply that the 3 implant-to-abutment joint systems tested may not fail under the simulated occlusal forces.     

Biomechanical comparison of four different miniscrew types for skeletal anchorage in the mandibulo-maxillary area

This study compared four miniscrew types for skeletal anchorage (Aarhus, FAMI, Dual Top and Spider) regarding their biomechanical properties contributing to primary stability. Insertion torque measurements and pull-out tests in axial (0 degrees ) as well as in the 20 degrees and 40 degrees direction were performed. Stiffness of the screw-bone construct was calculated from the load-displacement curve. Conic FAMI and Dual Top screws had higher insertion torques. Insertion torques were raised by drill-free insertion of FAMI and Dual Top screws. Statistically significant differences were found between the 4 screw types in pull-out tests. The highly significant differences between the four screws for peak load in the axial (0 degrees ) and 20 degrees direction were not apparent in 40 degrees angular loads. For the conical screws, peak load values increased in angular compared with axial load. The Dual Top screw achieved the highest values for peak load and stiffness. 12 Dual Top and 1 Spider screw heads fractured in the pull-out tests. A conical drill-free screw design achieves higher primary stability compared with cylindrical self-tapping screws. This effect was more obvious in insertion torque estimations rather than in pull-out tests. The Dual Top screws, although biomechanically superior to other screw types, were most prone to fractures.     

Preloads Generated with Repeated Tightening in Three Types of Screws Used in Dental Implant Assemblies

PURPOSE: Abutment screw loosening, especially in the case of cemented single tooth restorations, is a cause of implant restoration failure. This study compared three screws (titanium alloy, gold alloy, and gold-coated) with similar geometry by recording the preload induced when torques of 10, 20, and 35 Ncm were used for fixation. MATERIALS AND METHODS: Two abutment types were used-prefabricated preparable abutments and cast-on abutments. A custom-designed rig was used to measure preload in the abutment-screw-implant assembly with a strain gauge. Ten screws of each type were sequentially tightened to 10, 20, and 35 Ncm on ten of the two abutment types. The same screws were then loosened and re-tightened. This procedure was repeated. Thus, each screw was tightened on three occasions to the three insertion torques. A linear regression model was used to analyze the effects on preload values of screw type and abutment type for each of the three insertion torques. RESULTS: The results indicated that the gold-coated screw generated the highest preloads for all insertion torques and for each tightening episode. Further analysis focused on the effects of screw type and abutment type for each episode of tightening and for each fixation torque. The gold-coated screw, fixed to the prefabricated abutment, displayed higher preloads for the first tightening at 10, 20, and 35 Ncm. Conversely, the same screw fixed to the cast-on abutment showed higher values for the second and third tightening for all fixation torques. All screws showed decay in preload with the number of times tightened. Given the higher preloads generated using the gold-coated screw with both abutment types, it is more likely that this type of screw will maintain a secure joint when tightened for the second and third time. CONCLUSION: All screw types displayed some decay in preload with repeated tightening, irrespective of abutment type and insertion torque. The gold-coated screw showed markedly higher preloads for all insertion torques and for all instances of tightening when compared with the uncoated screws.     

Implant-abutment screw joint preload of 7 hex-top abutment systems.

This study measured the screw joint preload of the implant-abutment interface for 7 common hex-top abutment systems. Increasingly, prosthetic designs are utilizing a direct prosthetic connection to the implant, placing the implant-abutment screw joint under direct functional loads and moments. Sufficiently high screw joint preloads are required to maintain screw joint integrity and confer clinical longevity to implant prosthetic components to prevent such complications as abutment screw loosening and screw fracture. Strain-gauged abutment load cells were calibrated to measure screw joint pre-load at the implant-abutment interface. Torque delivery by electronic torque controller was varied at low- and high-speed settings. At manufacturer's recommended torques, the overall mean preload measured was 181.6 +/- 60.0 N for the Nobel Biocare Standard abutment, 291.3 +/- 41.2 N for the Nobel Biocare EsthetiCone abutment, 456.5 +/- 44.0 N for the Nobel Biocare MirusCone abutment, 369.7 +/- 32.9 N for the 3i Titanium Abutment post, 643.4 +/- 143.1 N for the Nobel Biocare CeraOne abutment, 536.3 +/- 68.6 N for the Nobel Biocare "Gold Cylinder to Fixture" abutment, and 556.9 +/- 145.6 N for the Nobel Biocare TiAdapt abutment. Analysis of variance revealed significant differences between abutment systems (P < .001) and between torque driver speed settings (P < .001). Implant-abutment screw joint preload of external-hex implants is dependent on abutment design, screw diameter, material, tightening torque, and torque controller speed.     

Implant abutment screw rotations and preloads for four different screw materials and surfaces.

STATEMENT OF PROBLEM: Chronic implant screw loosening remains a problem in restorative practices. Some implant manufacturers have introduced abutment screws with treated surfaces in an effort to increase preload and reduce potential loosening. Purpose. This study evaluated the materials and surfaces of 4 commercially available abutment screws on preload generation. MATERIAL AND METHODS: Twenty of each of the following abutment screws-Gold-Tite (Gt), TorqTite (Tt), gold alloy (Ga), and titanium alloy (Ta)-were divided into 2 groups. Measurements were recorded for each abutment screw on a mounted 3.75 x 18 mm external hex implant with a titanium abutment. Rotational angle measurements were conducted on the 4 abutment screws at 20 and 32 Ncm. Removal torque values were recorded and used to indirectly generate preload values. Random implant block specimens were sectioned and qualitatively evaluated with an SEM. RESULTS: At 20 and 32 Ncm, the largest rotational angles were recorded for the Tt groups: 21.2 +/- 3.1 degrees and 38.1 +/- 8.7 degrees, respectively. The greatest preload values at 20 and 32 Ncm were calculated for the Gt groups: 596.8 +/- 101.2 N and 1015.3 +/- 191.2 N, respectively. SEM analysis of the 4 implant block specimens revealed mating thread contacts located in the middle portion of the superior surface of the abutment screw thread. The greatest number of mating thread contacts were seen in the Gt implant block specimen (14 of 20 possible thread contacts). CONCLUSION: The Gt and Tt abutment screws with enhanced surfaces that help reduce the coefficient of friction produced greater rotational angles and preload values than the conventional gold alloy and titanium alloy screws.     

PRELOAD AND TORQUE REMOVAL EVALUATION OF THREE DIFFERENT ABUTMENT SCREWS FOR SINGLE STANDING IMPLANT RESTORATIONS

Several authors still consider the mechanical problems of fracture and component loosening as the main causes of failure of implant-supported restorations. The purpose of this in vitro study was to compare the preload of three types of screw for transmucosal abutment attachment used in single implant-supported prosthesis through strain gauge and removal torque measurements. Three external hex fixtures were used, and each received a transmucosal abutment (Cera One®), which was fixed to the implant with its respective screw: Group A- gold screw, Group B- titanium screw and Group C- surface-treated titanium screw (Ti-Tite®). Ten screws of each type were attached applying a 30.07±0.28 Ncm torque force and maintained in position for 5 minutes. After this, the preload values were measured using strain gauges and a measurement cell. Gold screws presented higher preload values (131.72±8.98 N), followed by surface-treated titanium screws (97.78±4.68 N) and titanium screws (37.03±5.69 N). ANOVA (p<0.05) and Tukey''s test (p<0.05) were applied. Statistically significant differences were found among the groups for both preload and removal torque values. In conclusion, gold screws may be indicated to achieve superior longevity of the abutment-implant connection and, consequently, prosthetic restoration due to greater preload values yielded.     

Finite element analysis to determine implant preload

STATEMENT OF PROBLEM: The nature of the forces used to clamp implant components together, and how they are generated and sustained, is lacking in the literature. PURPOSE: This study examined the dynamic nature of developing the preload in an implant complex using finite element analysis. METHODS: The implant complex was modeled in accordance with the geometric designs for the Nobel Biocare implant systems. A thread helix design for the abutment screw and implant screw bore was modeled to create the geometric design for these units of the implant systems. Using the software programs HyperWorks and LS3D-Dyna, 2 3-dimensional finite element models of (1) a Branemark System 3.75 x 10-mm titanium Mark III implant, a CeraOne titanium abutment, a Unigrip gold alloy abutment screw, and (2) a Replace Select System 4.30 x 10-mm titanium implant, a Straight Esthetic titanium abutment, and a TorqTite titanium abutment screw were created. Modeling the threads to the machining specifications permitted simulation of screw tightening. The abutment screws were subjected to a tightening torque in increments of 1 Ncm from 0 to 64 Ncm using ABAQUS software. Using these models, the effect of the coefficient of friction on the development of preload amount in the implant complex during and after abutment screw tightening was determined. In the first experiment, the coefficient of friction was set to 0.20 between the titanium bearing surface of the abutments and the implant bearing surfaces, and 0.26 between the gold abutment screw and the titanium implant screw bore. In the second experiment, the coefficient of friction was varied; the titanium implant and titanium abutment bearing surfaces were set to a coefficient of friction of 0.20, whereas the Mark III gold and the Replace Select titanium abutment screws and their respective titanium screw bores in the implants were set to 0.12. The preload amount (N) was determined from the finite element analysis. RESULTS: The stress distribution pattern clearly demonstrated a transfer of preload force from the screw to the implant during tightening. A preload of 75% of the yield strength of the abutment screw was not established using the recommended tightening torques. CONCLUSION: Using finite element analysis, a torque of 32 Ncm applied to the abutment screws in the implant assemblies studied in the presence of a coefficient of friction of 0.26 resulted in a lower than optimum preload for the abutment screws. To reach the desired preload of 75% of the yield strength, using a torque of 32 Ncm applied to the abutment screws in the implant assemblies studied, the coefficient of friction between the implant components should be 0.12.     

Micromotion and dynamic fatigue properties of the dental implant-abutment interface

STATEMENT OF PROBLEM: Clinical loading may result in micromotion and metal fatigue in apparently stable implant screw joints. This micromotion may contribute to tissue inflammation and prosthesis failure. PURPOSE: This study investigated dental implant screw joint micromotion and dynamic fatigue as a function of varied preload torque applied to abutment screws when tested under simulated clinical loading. MATERIAL AND METHODS: Fifteen noble alloy single-tooth implant restorations, each containing a hexed UCLA-style gold cylinder, were randomly assigned to 3 preload groups (16, 32, and 48 N.cm). Each group consisted of 5 implants (each 3.75 x 15 mm) and 5 square gold alloy abutment screws. A mechanical testing machine applied a compressive cyclic sine wave load between 20 and 130 N at 6 Hz to a contact point on each implant crown. A liquid metal strain gauge recorded the micromotion of the screw joint interface after 100, 500, 1,000, 5,000, 10,000, 50,000, and 100,000 cycles. Baseline data at 0 N.cm were collected before the application of the specified preload torque. RESULTS: The 16 N.cm group exhibited greater micromotion (P<.001) than both the 32 and 48 N.cm groups at all cycle intervals (2-way ANOVA, Tukey HSD). Micromotion of the implant-abutment interface remained constant (P=.99) for each of the preload groups through 105 cycles. CONCLUSION: Under the loading parameters of this study, no measurable fatigue of the implant-abutment interface occurred. However, dental implant screw joints tightened to lower preload values exhibited significantly greater micromotion at the implant-abutment interface.