The biomechanical analysis of relative position between implant and alveolar bone: finite element method

Background: The purpose of this study is to analyze biomechanical interactions in the alveolar bone surrounding implants with smaller‐diameter abutments by changing position of the fixture–abutment interface, loading direction, and thickness of cortical bone using the finite element method. Methods: Twenty different finite element models including four types of cortical bone thickness (0.5, 1, 1.5, and 2 mm) and five implant positions relative to bone crest (subcrestal 1, implant shoulder 1 mm below bone crest; subcrestal 0.5, implant shoulder 0.5 mm below bone crest; at crestal implant shoulder even with bone crest; supracrestal 0.5, implant shoulder 0.5 mm above bone crest; and supracrestal 1, implant shoulder 1 mm above bone crest) were analyzed. All models were simulated under two different loading angles (0 and 45 degrees) relative to the long axis of the implant, respectively. The three factors of implant position, loading type, and thickness of cortical bone were computed for all models. Results: The results revealed that loading type and implant position were the main factors affecting the stress distribution in bone. The stress values of implants in the supracrestal 1 position were higher than all other implant positions. Additionally, compared with models under axial load, the stress values of models under off‐axis load increased significantly. Conclusions: Both loading type and implant position were crucial for stress distribution in bone. The supracrestal 1 implant position may not be ideal to avoid overloading the alveolar bone surrounding implants.     

牙齿移动对根尖及根周硬组织的影响

目的为了观察和分析牙齿在移动过程中对牙根长度及根周硬组织的影响。方法本研究选择25名采用方丝弓矫治技术进行正畸治疗的患者,以150～180克的力推尖牙远中移动。使用德国西门子产的X线牙片机拍摄尖牙牙片,用芬兰产的Digora(DXR-40)数字化牙科扫描仪及其软件进行测量,比较尖牙移动前后的牙根长度,牙槽骨高度及牙槽骨密度。结果被矫治的尖牙在加力一个月后根尖平均吸收1.59mm,牙槽骨高度平均丧失2.59mm,牙槽骨密度平均下降14.88国际单位。结论正畸治疗过程中的矫治力可能对牙根长度产生影响,而且也可能影响牙槽骨的高度和密度。     

Peri-implant bone tissue strains in cases of dehiscence: a finite element study

When patients with a narrow alveolar bone ridge are treated with oral implants, a dehiscence can occur. The lack of bony support at the buccal or lingual side of the implant may present an unfavourable situation from a biomechanical point of view. The hypothesis as to whether the presence of dehiscence leads to an increased risk of marginal bone overload was tested by means of the finite element method. Three different situations for a cylindrical oral implant, which was placed in a mandible, were modelled: i) no dehiscence, ii) a dehiscence at the buccal side and iii) dehiscences at the buccal and lingual sides. It was found that the presence of buccal and/or lingual dehiscences led to a marked increase in marginal bone strains at the mesial and distal sides of the implant, thus increasing the risk of bone tissue overload at these locations. Marginal bone strains at the buccal and/or lingual sides, however, did not increase.     

上颌后牙区垂直骨量不足应对策略的生物力学评价

近年来,种植技术在上颌后牙区的应用逐渐增多,与传统修复方式比,种植修复具有美观,舒适,不损害天然牙等优点.由于骨质疏松和上颌窦的存在,上颌后牙区常常骨量不足,进而导致种植体植入后种植体周围骨应力过载,因此上颌后牙区的种植治疗面临着极大的挑战.医生解决骨量不足的技术有很多,但在种植方法选择上常常依赖于临床经验,却忽视了不...     

The influence of bone mechanical properties and implant fixation upon bone loading around oral implants

Finite element models were created to study the stress and strain distribution around a solitary BAnemark implant. The influence of a number of clinically relevant parameters was examined: bone‐implant interface (fixed bond versus frictionless free contact), bone elastic properties, unicortical versus bicortical implant fixation and the presence of a lamina dura. Bone loading patterns in the vicinity of the implant seem to be very sensitive to these parameters. Hence they should be integrated correctly in numerical models of in vivo behaviour of oral implants. This necessitates the creation of patient‐dependent finite element models.     

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.     

The influence of bone mechanical properties and implant fixation upon bone loading around oral implants.

Finite element models were created to study the stress and strain distribution around a solitary BAnemark implant. The influence of a number of clinically relevant parameters was examined: bone-implant interface (fixed bond versus frictionless free contact), bone elastic properties, unicortical versus bicortical implant fixation and the presence of a lamina dura. Bone loading patterns in the vicinity of the implant seem to be very sensitive to these parameters. Hence they should be integrated correctly in numerical models of in vivo behaviour of oral implants. This necessitates the creation of patient-dependent finite element models.     

Biomechanical aspects of oral implants. Consensus report of Working Group 1

The method used by the working group was an iterative process based upon a structured review of the relevant literature by a group of reporters. The review papers were circulated to the members of the group before the conference and formed the basis for subsequent discussions. Each paper was subject to detailed collective analysis and subsequently modified on the basis of the panel's discussions and referenced to additional relevant literature where appropriate. The group assessed the levels of evidence for the statements made in the supporting documentation and recognized that it was necessary to adopt a compromise between acceptance of the lowest level, resulting in the largest body of material, and the highest level, which, in some cases, produced little evidence. While this approach does not represent endorsement of lower evidence levels per se, it was designed to provide conclusions of clinical utility within the existing knowledge base. The consensus statements were prepared after a detailed consideration of the papers submitted to the workshop by the working group. The papers were scrutinized, amended and approved by the group. The basis of each paper is described in the section on 'search strategy' and defines the parameters within which the consensus statements were prepared.     

ITI implants in combination with bone grafts: design and biomechanical aspects

In this article we describe the implantation of ITI implants in combination with bone grafts. Two different cases were considered: the augmentation of an atrophic maxilla or mandible where the transplant was fixed by means of ITI implants and the implantation into free transplants fixed by means of the THORP reconstruction plate system. These indications require 2‐stage procedures with submerged implants and transplants during the healing period. For this new applications, standard ITI implants were combined with specially developed new transgingival units of high manufacturing precision. The new design resulted in a maximum tightening moment of 4.0 N.m versus 1.25 N.m achievable with a conventional 2‐mm screw. Dynamic testing showed that, for the range of tightening moments of 0.25 N.m up to 1.0 N.m, the loosening moment after 2,000,000 cycles remained approximately 10% above the tightening moment. For the clinical application a tightening moment of 0.35–0.5 N.rn is recommended. The special design and the high precision of the extension parts results in a tight adaptation between the primary implant and the extension parts, which may be important for microbiological reasons.     

The staggered installation of dental implants and its effect on bone stresses

Purpose: The aim of this study was to investigate the effect of offsetting the middle or peripheral implant on the compressive stress values in the crestal bone around the neck of the dental implant. Materials and Methods: Three finite element models describing three titanium implants installed in quadrilateral pieces of bone was executed. A 2‐mm nickel chromium superstructure representing a bridge was modeled over the implant abutments. In model 1, implants were installed along a straight line. Model 2 had the middle implant installed outside the line connecting the two peripheral implants buccally. Model 3 had the mesial implant installed out of alignment. Six 100‐N loads were modeled on top of the mesial and middle implants of the three models individually. Loads 1 and 2 were directed vertically on the mesial and middle implants, while loads 3 and 4 represented the horizontal loads in the buccal direction. Loads 5 and 6 were directed mesially on the mesial and central implants. Maximal compressive stress levels in the crestal bone of the three models were then investigated. Results: The results demonstrated that offset implant installation revealed slightly lower bone stresses under buccally or lingually directed horizontal forces. Slightly higher bone stresses under vertical loads were observed. Horizontal mesial or distal loads resulted in slightly higher bone stresses than those caused by buccal or lingual loading. Conclusions: The in‐line implant alignment clearly had the safest compressive stress outcome on the surrounding structure under vertical loads. Under buccolingual loads, implant alignment with peripheral offset would have, relatively, the safest compressive stress outcome on bone.     

All-on-Four与穿颧种植在不同皮质骨厚度中的生物力学研究

目的：利用有限元分析法,比较在不同皮质骨厚度下后牙区垂直骨量严重不足的上颌无牙颌中All-on-Four与穿颧植体这两种不同种植设计中种植体、皮质骨的应力值与钛支架的变形量的差异,为临床种植方案的设计提供参考依据。 方法：选取一无牙颌上颌骨锥形束CT数据并利用其建立4个不同皮质骨厚度的模型,模型中还包括了种植体、基台、钛支架,在双侧后牙区施加200N垂直压力,计算出种植体、皮质骨的应力值及钛支架的变形量并进行统计分析。 结果：随着皮质骨厚度的增加,All-on-Four组与穿颧植体组中种植体、皮质骨应力值及钛支架变形量逐渐减小,在All-on-Four组中,当皮质骨厚度由0.5mm增加到1.5mm时,各数据降低明显,当皮质骨厚度由1.5mm增加到2mm时各数据变化较小,并且,当皮质骨厚度为1.5mm时,等效应力和变形量均达到一个较低的水平。在穿颧植体组中,随着皮质骨厚度的变化总体变化趋势均较小,穿颧植体组的种植体、皮质骨应力值及钛支架变形量均小于All-on-Four组,且5号位点皮质骨、2号位点皮质骨及钛支架变形量之间的差异有统计学意义（P<0.05）。 结论：对于后牙区垂直骨量严重不足的上颌无牙颌,皮质骨厚度的增加有利于减小种植修复的应力分布和钛支架的变形;当皮质骨厚度较小时（<1.5mm）,穿颧植体的种植方案是更为合适的选择;当皮质骨厚度较厚时（≥1.5mm）,虽然穿颧植体组中的数据表现较All-on-Four组好,但All-on-Four组中各数据已明显降低,此时,也可以考虑选择All-on-Four进行修复。     

BIB与ITI种植系统周边骨质吸收对比的研究

目的：放射线片评估BLB种植系统(HA涂层非螺纹柱状种植体)和ITI种植系统(TPS涂层螺纹柱状种植体)负载初期及负载后48个月种植体边缘骨吸收的差别。方法：87例患者116颗种植体按负载时间分五组进行X片牙槽骨边缘高度测定。结果：BLB种植系统骨吸收呈缓慢上升趋势，而TIT系统相对平稳，负载初TIT种植体周骨吸收高于BLB种植体，负载后36～48个月BLB种植体高于TIT种植体，两组均有统计学差异。结论：BLB种植系统骨结合更早，TIT种植系统远期骨吸收更少，更有利于保证种植的远期效果。     

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 aspects of oral implants

Abstract: The method used by the working group was an iterative process based upon a structured review of the relevant literature by a group of rapporteurs. The review papers were circulated to the members of the group before the conference and formed the basis for subsequent discussions. Each paper was subject to detailed collective analysis and subsequently modified on the basis of the panel's discussions and referenced to additional relevant literature where appropriate. The group assessed the levels of evidence for the statements made in the supporting documentation and recognized that it was necessary to adopt a compromise between acceptance of the lowest level, resulting in the largest body of material, and the highest level, which, in some cases, produced little evidence. While this approach does not represent endorsement of lower evidence levels per se , it was designed to provide conclusions of clinical utility within the existing knowledge base. The consensus statements were prepared after a detailed consideration of the papers submitted to the workshop by the working group. The papers were scrutinized, amended and approved by the group. The basis of each paper is described in the section on 'search strategy' and defines the parameters within which the consensus statements were prepared.     

Biomechanical stress in bone surrounding an implant under simulated chewing

The concept of reducing nonaxial loading of dental implants has been widely regarded as the standard procedure. The aim of this study was to reveal the biomechanical stress distribution in supporting bone around an implant and a natural tooth under chewing function. Three-dimensional finite element models of the mandibular first molar and the titanium implant both with the mandible in the molar region were constructed. The directions of displacement constraints were determined according to the angles of the closing pathways of chopping type and grinding type chewing patterns. The tooth model showed smooth stress distribution in the supporting bone with low stress concentration around the neck of the tooth. The implant model showed stress concentration in the supporting bone around the neck of the implant, especially in the buccal area. The grinding type model of the implant showed higher tensile stress concentration than the chopping type model at the lingual neck of the implant. The results of this study suggested the importance of considering occlusion under chewing function for understanding the biomechanics of oral implants.     

Biomechanical evaluation of dental implants with different surfaces: Removal torque and resonance frequency analysis in rabbits

STATEMENT OF PROBLEM

Macroscopic and especially microscopic properties of implant surfaces play a major role in the osseous healing of dental implants. Dental implants with modified surfaces have shown stronger osseointegration than implants which are only turned (machined). Advanced surface modification techniques such as anodic oxidation and Ca-P application have been developed to achieve faster and stronger bonding between the host bone and the implant.

PURPOSE

The purpose of this study was to investigate the effect of surface treatment of titanium dental implant on implant stability after insertion using the rabbit tibia model.

MATERIAL AND METHODS

Three test groups were prepared: sandblasted, large-grit and acid-etched (SLA) implants, anodic oxidized implants, and anodized implants with Ca-P immersion. The turned implants served as control. Twenty rabbits received 80 implants in the tibia. Resonance frequencies were measured at the time of implant insertion, 2 weeks and 4 weeks of healing. Removal torque values (RTV) were measured 2 and 4 weeks after insertion.

RESULTS

The implant stability quotient (ISQ) values of implants for resonance frequency analysis (RFA) increased significantly (P < .05) during 2 weeks of healing period although there were no significant differences among the test and control groups (P > .05). The test and control implants also showed significantly higher ISQ values during 4 weeks of healing period (P < .05). No significant differences, however, were found among all the groups. All the groups showed no significant differences in ISQ values between 2 and 4 weeks after implant insertion (P > .05). The SLA, anodized and Ca-P immersed implants showed higher RTVs at 2 and 4 weeks of healing than the machined one (P < .05). However, there was no significant difference among the experimental groups.

CONCLUSION

The surface-modified implants appear to provide superior implant stability to the turned one. Under the limitation of this study, however, we suggest that neither anodic oxidation nor Ca-P immersion techniques have any advantage over the conventional SLA technique with respect to implant stability.