Dynamic fatigue resistance of implant-abutment junction in an internally notched morse-taper oral implant: influence of abutment design

PURPOSE: To compare dynamic fatigue resistance of one- and two-piece abutments connected to internally notched morse-taper oral implants. MATERIAL AND METHODS: Sixteen synOcta ITI implants were tightened into two metal models. SynOcta abutments for cement-retained restorations and solid abutments were divided into two equal groups and were torque-tightened into the implants. Each implant received a cement-retained crown. Cyclic dynamic axial and lateral peak loads of 75+/-5 N were applied on the implants for a duty of 500,000 cycles at 0.5 Hz, and at an angle of 20 degrees. Prior to the experiments and at each 100,000 cycles of loading, periotest values (PTVs) were measured. Removal torque values (RTVs) of the abutments were also measured with a custom-made torque device at the termination of the experiment. RESULTS: All abutments and implants were clinically immobile and without any signs of mechanical failure. The final PTVs for both abutments were similar and the difference between groups was insignificant (P>0.05). The RTVs of solid abutments were significantly higher than synOcta abutments (P<0.05). CONCLUSION: Predictable long-term clinical results can be achieved with solid abutments and synOcta abutments for cement-retained restorations. Solid abutments possess higher removal torque resistance than synOcta abutments when connected to synOcta ITI implants.     

Biologic Width around one- and two-piece titanium implants

Gingival esthetics around natural teeth is based upon a constant vertical dimension of healthy periodontal soft tissues, the Biologic Width. When placing endosseous implants, however, several factors influence periimplant soft and crestal hard tissue reactions, which are not well understood as of today. Therefore, the purpose of this study was to histometrically examine periimplant soft tissue dimensions dependent on varying locations of a rough/smooth implant border in one-piece implants or a microgap (interface) in two-piece implants in relation to the crest of the bone, with two-piece implants being placed according to either a submerged or a nonsubmerged technique. Thus, 59 implants were placed in edentulous mandibular areas of five foxhounds in a side-by-side comparison. At the time of sacrifice, six months after implant placement, the Biologic Width dimension for one-piece implants, with the rough/smooth border located at the bone crest level, was significantly smaller (P<0.05) compared to two-piece implants with a microgap (interface) located at or below the crest of the bone. In addition, for one-piece implants, the tip of the gingival margin (GM) was located significantly more coronally (P<0.005) compared to two-piece implants. These findings, as evaluated by nondecalcified histology under unloaded conditions in the canine mandible, suggest that the gingival margin (GM) is located more coronally and Biologic Width (BW) dimensions are more similar to natural teeth around one-piece nonsubmerged implants compared to either two-piece nonsubmerged or two-piece submerged implants.     

Stability of prototype two-piece zirconia and titanium implants after artificial aging: an in vitro pilot study

Background: Zirconia oral implants are a new topic in implant dentistry. So far, no data are available on the biomechanical behavior of two‐piece zirconia implants. Therefore, the purpose of this pilot investigation was to test in vitro the fracture strength of two‐piece cylindrical zirconia implants after aging in a chewing simulator. Materials and Methods: This laboratory in vitro investigation comprised three different treatment groups. Each group consisted of 16 specimens. In group 1, two‐piece zirconia implants were restored with zirconia crowns (zirconia copings veneered with Triceram®; Esprident, Ispringen, Germany), and in group 2 zirconia implants received Empress® 2 single crowns (Ivoclar Vivadent AG, Schaan, Liechtenstein). The implants, including the abutments, in the two zirconia groups were identical. In group 3, similar titanium implants were reconstructed with porcelain‐fused‐to‐metal crowns. Eight samples of each group were submitted to artificial aging with a long‐term load test in the artificial mouth (chewing simulator). Subsequently, all not artificially aged samples and all artificially aged samples that survived the long‐term loading of each group were submitted to a fracture strength test in a universal testing machine. For the pairwise comparisons in the different test groups with or without artificial loading and between the different groups at a given artificial loading condition, the Wilcoxon rank‐sum test for independent samples was used. The significance level was set at 5%. Results: One sample of group 1 (veneer fracture), none of group 2, and six samples of group 3 (implant abutment screw fractures) failed while exposed to the artificial mouth. The values for the fracture strength after artificial loading with 1.2 million cycles for group 1 were between 45 and 377 N (mean: 275.7 N), in group 2 between 240 and 314 N (mean: 280.7 N), and in the titanium group between 45 and 582 N (mean: 165.7 N). The fracture strength results without artificial load for group 1 amounted to between 270 and 393 N (mean: 325.1 N), for group 2 between 235 and 321 N (mean: 281.8 N), and between 474 and 765 N (mean: 595.2 N) for the titanium group. The failure mode during the fracture testing in the zirconia implant groups was a fracture of the implant head and a bending/fracture of the abutment screw in the titanium group. Conclusions: Within the limits of this pilot investigation, the biomechanical stability of all tested prototype implant groups seems to be – compared with the possibly exerted occlusal forces – borderline for clinical use. A high number of failures occurred already during the artificial loading in the titanium group at the abutment screw level. The zirconia implant groups showed irreparable implant head fractures at relatively low fracture loads. Therefore, the clinical use of the presented prototype implants has to be questioned.     

Short-term clinical results of Nobel Direct implants: a retrospective multicentre analysis

PURPOSE: The present retrospective clinical study was undertaken to evaluate the survival rate and marginal bone conditions around Nobel Direct one-piece implants. The purpose was also to compare the results with when these implants are used for immediate/early loading with implants allowed to heal before loading. MATERIAL AND METHODS: Forty-three consecutive patients previously treated with 117 Nobel Direct implants at four different centres were evaluated. The implants had been used in both jaws for treatment after loss of single and multiple teeth. Immediate/early loading (within 2 weeks) with a provisional crown/bridge was applied to 95 implants, while 22 implants healed unloaded for 6 weeks to 6 months before loading. Calculations of marginal bone loss were performed in radiographs taken at placement and after an average of 10.2 months (range 1-18 months) of loading. RESULTS: Six (5.1%) of the 117 implants were removed during the follow up. All failed implants belonged to the immediate/early loading group giving a failure rate of 6.3% for this group and 0% for two-stage implants. The failure rate was higher for flapless (7.9%) than for flap surgery (0%). The marginal bone loss was -2.4 mm (SD 1.5) for all implants, while 37.6% showed more than 3 mm of loss during the follow up. Bone loss increased with time of follow up. Implants subjected to immediate/early loading showed more bone loss than two-stage implants: -2.6 mm (SD 1.5) vs. -1.6 mm (SD 1.1). Moreover, 41.3% of immediately loaded and 22.7% of two-stage implants presented with more than 3 mm of bone loss. CONCLUSIONS: This short-term retrospective analysis showed a poor clinical outcome of Nobel Direct implants. Extensive marginal bone loss (>3 mm) was found around more than 1/3 of the implants evaluated. Less resorption and no failures were experienced when implants were allowed to heal from 6 weeks to 6 months before occlusal loading. Within the limitations of the present study design, data indicate that immediate loading, the use of this implant for multi-unit constructions and flapless surgery are risk factors for failure of Nobel Direct implants.     

Comparative finite element analysis of mandibular posterior single zirconia and titanium implants: a 3-dimensional finite element analysis

PURPOSEZirconia has exceptional biocompatibility and good mechanical properties in clinical situations. However, finite element analysis (FEA) studies on the biomechanical stability of two-piece zirconia implant systems are limited. Therefore, the aim of this study was to compare the biomechanical properties of the two-piece zirconia and titanium implants using FEA.MATERIALS AND METHODSTwo groups of finite element (FE) models, the zirconia (Zircon) and titanium (Titan) models, were generated for the exam. Oblique (175 N) and vertical (175 N) loads were applied to the FE model generated for FEA simulation, and the stress levels and distributions were investigated.RESULTSIn oblique loading, von Mises stress values were the highest in the abutment of the Zircon model. The von Mises stress values of the Titan model for the abutment screw and implant fixture were slightly higher than those of the Zircon model. Minimum principal stress in the cortical bone was higher in the Titan model than Zircon model under oblique and vertical loading. Under both vertical and oblique loads, stress concentrations in the implant components and bone occurred in the same area. Because the material itself has high stiffness and elastic modulus, the Zircon model exhibited a higher von Mises stress value in the abutments than the Titan model, but at a level lower than the fracture strength of the material.CONCLUSIONOwing to the good esthetics and stress controllability of the Zircon model, it can be considered for clinical use.     

Evaluation of design parameters of osseointegrated dental implants using finite element analysis

Finite element analyses were performed for various shapes of dental implant to study effects on stress distribution generated in the surrounding jaw bone and to determine an optimal thread shape for even stress distribution. It was found that the square thread shape filleted with a small radius was more effective on stress distribution than other dental implants used in the analyses. Additional analyses were performed on the implant with the thread shape obtained from previous analyses for varying other design parameters, such as the width of thread end and height of thread for various load directions, to determine the optimal dimensions of the implant. Stress distribution was more effective in the case when the width of thread end and the height of thread were 0.5p and 0.46p, respectively, where p is the screw pitch. Then, using the optimal implant thread dimensions determined previously, stress analyses were performed with various screw pitches and implant lengths, to investigate effects on stress distribution and to find the way to reduce the maximum effective stress generated in the jaw bone. Results show that the maximum effective stress decreased not only as screw pitch decreased gradually but also as implant length increased.     

Biomechanical aspects of marginal bone resorption around osseointegrated implants: considerations based on a three-dimensional finite element analysis

OBJECTIVES: Although bone loss around implants is reported as a complication when it progresses uncontrolled, resorption does not always lead to implant loss, but may be the result of biomechanical adaptation to stress. To verify this hypothesis, a three-dimensional finite element analysis was performed and the influence of marginal bone resorption amount and shape on stress in the bone and implant was investigated. MATERIAL AND METHODS: A total of nine bone models with an implant were created: a non-resorption (Base) model and eight variations, in which three different resorption depths were combined with pure vertical or conical (vertical-horizontal) resorption. Axial and buccolingual forces were applied independently to the occlusal node at the center of the superstructure. RESULTS: Regardless of load direction, bone stresses were higher in the pure vertical resorption (A) models than in the Base model, and increased with resorption depth. However, cortical bone stress was much lower in the conical resorption models than in both the Base and A models of the same resorption depth. An opposite tendency was observed in the cancellous bone under buccolingual load. Under buccolingual load, highest stress in the implant increased linearly with the resorption depth for all the models and its location approached the void existing below the abutment screw. CONCLUSIONS: The results of this analysis suggest that a certain amount of conical resorption may be the result of biomechanical adaptation of bone to stress. However, as bone resorption progresses, the increasing stresses in the cancellous bone and implant under lateral load may result in implant failure.     

Survival of NobelDirect implants: an analysis of 550 consecutively placed implants at 18 different clinical centers

Background: A recently introduced implant, the NobelDirect (Nobel Biocare AB, Göteborg, Sweden), has previously been documented with substantial bone resorption in a large number of operated cases. PurposeL The aim of this study was to evaluate the failure rate of NobelDirect implants in a retrospective multicenter survey. Materials and Methods: A total of 550 NobelDirect implants consecutively placed in over 269 patients at 18 centers were evaluated with regard to failure rate after an average follow‐up of about 1 year. Results: The overall failure percentage was 10.9% (59 failures). The 58 implants not loaded directly showed only one failure (1.7%) versus 58 failures (11.8%) of those implants that were loaded directly. A chemical x‐ray photoelectron spectroscopy analysis of an implant from the original batch showed up to 3.5% silicon at parts of the implants. A retrieval analysis of one implant removed at 2 years after placement demonstrated bone resorption down to the level of the fifth thread. Conclusions: It is concluded that the NobelDirect implant, if placed with a punch procedure, ground down in situ, and loaded directly, shows an unusually high failure rate at 1 year.     

不同粘接剂对后牙分裂桩冠修复应力分布影响的有限元分析

目的 建立下颌第一磨牙残根分裂桩冠修复的三维有限元模型,分析不同粘接剂粘接时残根应力分布特点,从而得到在不同情况下与分裂桩冠修复相匹配的最佳粘接剂。方法 选取健康的下颌第一磨牙离体牙,沿釉牙骨质界将冠部去除,对处理后的残根进行CT扫描。将CT影像导入逆向工程软件,重建下颌后牙残根的三维有限元模型;制作与残根相匹配的纯钛分裂桩冠修复体,同样进行CT扫描,在MIMICS中重建出修复体的模型,并进行装配,对比分析不同粘接系统在垂直载荷及侧向载荷下对根管内部及残根断面应力的分布特点。结果 建立了下颌第一磨牙残根的三维有限元模型及分裂桩冠有限元模型,并进行匹配安装。随着粘接剂弹性模量的增加,根管内的最大应力也在增加,磷酸锌的弹性模量最大,根管内承受的应力最大;Superbond C&B的弹性模量最小,根管内承受的应力最小,且侧向载荷的应力要远大于垂直载荷。在垂直载荷下,对于不同粘接剂,施加在残根断面的载荷比较平均。在侧向载荷下最大应力要远大于垂直工况。使用磷酸锌粘接剂时残根断面的应力最小,使用SuperbondC&B时残根断面应力最大。结论 在分裂桩冠修复后牙残根时,不同的粘接剂对牙体组织的应力保护作用有很大区别。当根管口处牙体组织较为薄弱时,为避免其发生劈裂,建议采用弹性模量较大的粘接剂,如磷酸锌;当根管口处牙体组织抗力形较好而牙根较细或根管壁薄弱时,建议采用弹性模量较小的粘接剂,如Superbond C&B。     

Effect of dental implant cross-sectional design on cortical bone structure using finite element analysis

Purpose: This finite element analysis investigation evaluated the effect of different implant cross‐sectional designs on bone stress levels under different loading patterns. Materials and Methods: Finite element analysis program was used to construct four different three‐dimensional models describing 4 × 10‐mm implants in blocks of cortical and trabecular bone. A 5‐mm‐long abutment was modeled above each implant. The implant in model 1 was unthreaded, while in model 2 the implant was circularly threaded. The third implant in model 3 had the cross‐sectional shape as a 16‐sided star‐shaped design. The implant in model 4 was constructed unthreaded, with a diameter of 4.5 mm. Vertical and horizontal loads of 100 N each were applied on the top middle node of each implant assembly. All nodes at the bottom surface of the bone models were restrained. Results: By comparing models 1, 2, and 3, the lowest bone stress values under vertical and horizontal forces were observed around the unthreaded implant in model 1 (8.92 and 94.52 MPa, respectively). The highest stress value under vertical loading was shown around the threaded implant in model 2 (10.07 MPa), whereas the highest stress value under horizontal loading was observed around the star‐shaped implant in model 3 (108.40 MPa). Model 4, with a wider unthreaded design, had stress values under vertical and horizontal loading of 7.32 and 71.35 MPa, respectively. Conclusions: It was concluded that the unthreaded implant design produced the least bone stress. An increase in implant diameter could produce marked reduction in stress value in the bone around the neck of the implant.     

二单位式与四单位式种植牙周骨界面应力分布规律差异的三维有限元分析

为了探讨人工种植牙的数目、上部结构对种植牙周骨界面应力分布的影响，本实验应用三维有限元分析方法，对二单位和四单位式杆式覆盖种植义齿种植牙周骨界面的应力分布规律进行了探讨。结果表明：最大压应力、最大拉应力二单位式与四单位式均位于颈周密质骨，二单位式大于四单位式，两者有显著差异性，（Ｐ＜０．００１）。四单位式最大拉、压应力，远中种植牙要大于近中种植牙。最大位移运动二单位式小于四单位式，四单位式近中种植牙大于远中种植牙。二单位式与四单位式位、压应力主要集中于颈部，其它部位与颈部相比有非常显著的差异性，（Ｐ＜０．０００１）。结论：种植牙数目的增加，可以减小种植牙周颈部密质骨内的最大应力值。四单位式种植义齿颈周骨内应力要小于二单位式种植牙，从这点上看，四单位式种植义齿要优于二单位式种植义齿。多个种植牙种植时，杆的连接，改变了种植牙周骨内的应力分布规律，其应力主要由种植牙颈周密质骨来承担     

Biomechanical optimisation of the length ratio of the two endosseous portions in distraction implants: a three-dimensional finite element analysis

Insufficient alveolar height is one of the most common problems in oral implantation, and it may preclude placement of an implant or compromise the final aesthetic outcome of the restoration. To solve this problem, distraction implants (DIs) have been introduced because they can fulfill the functions of bony augmentation and implantation simultaneously and facilitate the operation, minimise the trauma, and shorten the duration of treatment. However, the high risk of complications such as device fracture from uneven distribution of stress or transport bone resorption from insufficient blood supply, has impeded their clinical use. As the cortical transport portion of the DI is more important for bearing occlusal force than the apical support portion, and the length of the transport portion is normally the height of the transport bone segment, lengthening the transport portion may help to obtain a rational distribution of stress and increase the blood supply to the transport bone. For those cases in which alveolar height is limited, the dimension of the DI must be minimised to be applicable, so it is important to find an optimised balance between the lengths of the transport and support portions for a better performance. We have made a finite element analysis to optimise the length ratio of transport:support portions. The effects of the length ratios on the stress distribution in the jawbones were evaluated. A ratio of 8:2 showed the minimum stress and most resistance to displacement. These results provide a valuable reference for further improvement of designs of DI and help to promote its clinical application.     

平台转换种植体周围应力分布的三维有限元分析

目的:分析平台转换种植体周围的力学分布特点。方法:利用CATIA画图软件,建立种植体支持的上颌第一前磨牙三维模型,分析垂直向和斜向加载条件下平齐对接(PM)和平台转换(PS)种植体周围的应力分布差异;比较不同材料基台平台转换冠修复后种植体周围的应力分布差异。结果:①PS型种植体在垂直加载和斜向加载时种植体周围骨组织内最大von Mises应力值均较PM型小。②不同材料基台种植体周围应力分布云图相似,应力均集中在种植体颈部。结论:①PS种植体周围骨组织最大应力值较PM种植体小,但基台、中央螺丝、种植体的应力增大。②斜向加载较垂直向加载种植体周围应力值大大增加,特别是基台及种植体部位较为明显。③基台材料对种植体周围应力值无明显影响。     

Healing and osseointegration of submerged microtextured oral implants

The success of dental implants is primarily dependent upon the degree of osseointegration or bone-to-implant contact (BIC), possibly facilitated by a roughened implant surface. This study was performed to histologically evaluate the nature of osseointegration and bone healing of submerged microtextured implants in eight dogs. Three months following tooth extraction in the posterior mandibulae, three microtextured submerged implants were placed in each quadrant. Block biopsies were harvested at 4 and 16 weeks (four dogs each) following surgery, and histologic preparation was performed. Histomorphometric analysis demonstrated that % BIC value increased marginally from 40% at 4 weeks to 48% at 16 weeks, without a statistically significant difference. The first bone-to-implant contact (f-BIC) at 16 weeks was significantly lower than the 4-week f-BIC (0.81 mm vs. 0.56 mm). In conclusion, this study found minimal change in BIC over time (from 4 to 16 weeks) in unloaded microtextured implants, while the mean f-BIC value significantly increased during this same observation period.     

Selection of optimal dental implant diameter and length in type IV bone: a three-dimensional finite element analysis

This study aimed to create a 3D finite element model for continuous variation of implant diameter and length, thereby identifying their optimal range in type IV bone under biomechanical consideration. Implant diameter ranged from 3.0 to 5.0 mm, and implant length ranged from 6.0 to 14.0 mm. The results suggest that under axial load, the maximum Von Mises stresses in cortical and cancellous bones decrease by 50% and 27%, respectively; and under buccolingual load, by 52% and 60%, respectively. Under these two loads, the maximum displacements of implant-abutment complex decrease by 39% and 43%, respectively. These results indicate that in type IV bone, implant length is more crucial in reducing bone stress and enhancing the stability of implant-abutment complex than implant diameter. Biomechanically, implant diameter exceeding 4.0 mm and implant length exceeding 9.0 mm are the combination with optimal properties for a screwed implant in type IV bone.     

圆柱状、根端带缝及膨胀式种植体在骨质疏松状态时生物力学比较的三维有限元分析

目的:比较圆柱状、根端带缝与膨胀式种植体在骨质疏松条件时功能状态下的生物力学效果。方法:分别建立包含柱状、根端带缝和膨胀式种植体的骨质疏松颌骨骨块三维有限元模型。对种植体轴向和颊舌向分别施加100 N和30 N的力,评估皮质骨和松质骨的最大应力和种植体-基台复合体的最大位移。结果:与圆柱状种植体相比,根端带缝种植体使皮质骨在轴向和颊舌向加载下应力峰值分别增加了3.62%和7.49%,膨胀式种植体则使其降低了11.3%和9.60%;对于在松质骨,带缝种植体使其应力峰值分别增加了37.8%和65.0%,而膨胀式种植体使其增加了107%和89.2%;轴向加载时带缝种植体和膨胀式种植体的种植体-基台复合体的最大位移分别增加了1.12%和减少了0.60%,在颊舌向加载时,最大位移分别增加了6.37%和7.04%。结论:在骨质疏松状态下,皮质骨的应力对种植体外形变化更敏感;膨胀式种植体表现出比圆柱状种植体和带缝种植体更好的应力分布和更低的应力值。     

螺旋形种植体骨界面初始应力的三维有限元分析

目的：分析螺旋形种植体植入下颌骨后骨界面初始应力的分布。方法：用三维有限元的方法对不同弹性模量和不同直径种植体植入后骨界面的初始应力进行分析。结果：螺旋形种植体植入下颌骨后，骨界面的初始应力大小为23．2MPa。主要分布在种植体和骨密质接触的颈部。结论：初始应力的大小与种植体弹性模量无关；随着种植体直径的增加，初始应力逐渐增大。     

下颌后牙区不同骨质内种植体即刻负载的三维有限元分析

Objective To assess and compare the peri-implant stress distribution of three posterior implants under immediate loading with 4 different bone qualities using three dimensional (3D) finite element (FE) analysis. Methods A 3D finite element model representing three implants in a portion of mandible at the 654-| region was developed, and three implants received a crown each. Four types of bone qualities (B1,B2, B3 and B4) were designed for the model. Load of 100 N was applied on the occlusal surfaces of the crowns at a 45° angle to the vertical axis of the implants. Results Von Mises stresses in the peri-implant bone of4-| in bone quality from B1 to B4 were ( 13. 17 ± 9. 32), ( 12. 95 ± 9. 14), ( 15. 00 ± 9. 44 ), and(16.81 ±10.74) MPa, and those of 5-| were (15.51 ± 10.32), (14.73 ±8.96), (16.79 ±8.40), and(18. 34 ±8.45) MPa. Stress in bone quality B4 showed the highest value, followed by B3 bone, the loweststress were found in B1 and B2 bone. It was significantly different (P ＜0. 05). However, von Mises stresses in different quality of bone around 6-| [(42.45 ±25.71), (41.66 ±25.29), (42.70 ±23.24), (42.06 ±23.66) MPa] were close to each other, and were as twice or three times as those of 4-| and 5-| , irrespective of different bone qualities. Conclusions The stress distribution around implant under immediate loading was not only affected by different bone qualities, but also by the direction of loading, and the latter may have a greater impact when a severe load delivered.     

螺纹旋转角度和密度对种植体初期稳定性影响的三维有限元研究

目的利用三维有限元模型研究种植体螺纹的旋转角度和密度对种植体初期稳定性的影响。方法建立即刻负载的5种种植体三维有限元模型（0．8mm、1．6mm和2．4mm螺距单螺纹种植体以及双螺纹和三螺纹种植体），进行垂直和水平加载，分析5种种植体颈部和根部的相对位移。结果在3种不同螺距的单螺纹种植体中，垂直加载时0．8mm螺距单螺纹种植体颈部和根部的综合相对位移最小（分别为1．600μm和1．199μm），2．4mm螺距单螺纹种植体颈部和根部的综合相对位移最大（分别为2．451μm和2．019μm）；在螺纹密度相同、旋转角度不同的3种种植体中，0．8mm螺距单螺纹种植体颈部和根部的综合相对位移最小，三螺纹种植体颈部和根部的综合相对位移最大（分别为1．994μm和1．602μm）；在螺纹旋转角度相同、密度不同的种植体中，双螺纹种植体颈部和根部的综合相对位移（分别为1．913μm和1．495μm）均比1．6mm螺距单螺纹种植体（分别为2．412μm和1．799μm）小，三螺纹种植体颈部和根部的综合相对位移均比2．4mm螺距单螺纹种植体小。结论随着种植体螺纹螺距的增加，种植体对抗垂直载荷的能力减弱；随着种植体螺纹旋转角度的增加，种植体对抗垂直载荷的能力减弱；随着种植体螺纹密度增加，种植体对抗垂直载荷的能力增加。