In vitro assessment of bone-implant interface using an acoustic emission transmission test

The aim of this in vitro study was to determine the feasibility of monitoring the primary stability of dental implants using a simple transmission test with acoustic emission. Forty screw-shaped titanium dental implants were installed in the middle of 10 fresh bovine ribs obtained from different animals. The implants were divided into two size groups, 8.5 mm x 3.5 mm and 13 mm x 4.5 mm, and were inserted in either tight- or loose-fitting conditions. For each implant, pulses of acoustic energy were injected at the centre of a customised gold abutment 3 mm in height using a standard pencil lead break source (Hsu-Nielsen source). A total of 30 acoustic emission recordings were made for each implant in which the transmitted energy was measured on the surface of the bone using an acoustic sensor mounted at the middle of the rib. The transmitted acoustic energy for the implants under tight-fitting conditions was significantly higher than for the loose-fitting for both sizes of implant. The acoustic emission energy values for the 13 mm implants were also higher than for the 8.5 mm implants. The results indicate that implants with good primary stability (tight-fitting) had higher acoustic emission energy than implants where primary stability was poor (loose-fitting). The longer and wider implants produced higher acoustic emission energy than shorter and narrower implants. Together, the findings suggest that a simple transmission test, properly calibrated, should be able to assess the quality of the contact between the implant and the bone in the clinical situation.     

Design and fabrication of custom-made dental implants

Dental implant has been attracting more and more attention due to their advantages of reliability and comfort. It is estimated that 10% of people will need dental implants in their life time. Especially, companies offer a system for customer to choice. But, no one research on custom-made dental implants. Traditional implants have their limitation and they are not better fit due to the difference of patient??s oral condition. The advantages of custom implant are accuracy fit and esthetic emergence profile. So, custom-made implant is desirable. Another key problem of custom-made dental implant is manufacturing. Dental implant is difficult to machine due to its complex features and its material (titanium). With the ever increasing demand for tight tolerance and increased complexity and accuracy, traditional machine tools have become ineffective for machining them. So, we design and built a PC-based CNC Turn-Mill-Hob professional machining center for machining our custom-made dental implants accurately and efficiently. This paper introduces our method: firstly, the custom-made dental implant in various oral conditions is designed by using our implant database. And then, FEA results indicate the stress distribution and magnitude of implant-bone interface for dentist referring. Finally, samples are automatic machined by our machining center.     

Histological evaluation on bone regeneration of dental implant placement sites grafted with a self-setting alpha-tricalcium phosphate cement

This study aimed to evaluate the histological characteristics of the new bone formed at dental implant placement sites concomitantly grafted with a self-setting tricalcium phosphate cement (BIOPEX-R). Standardized defects were created adjacent to the implants in maxillae of 4-week-old male Wistar rats, and were concomitantly filled with BIOPEX-R. Osteogenesis was examined in two sites of extreme clinical relevance: (1) the BIOPEX-R-grafted surface corresponding to the previous alveolar ridge (alveolar ridge area), and (2) the interface between the grafting material and implants (interface area). At the alveolar ridge area, many tartrate-resistant acid phosphatase (TRAPase)-reactive osteoclasts had accumulated on the BIOPEX-R surface and were shown to migrate toward the implant. After that, alkaline phosphatase (ALPase)-positive osteoblasts deposited new bone matrix, demonstrating their coupling with osteoclasts. On the other hand, the interface area showed several osteoclasts initially invading the narrow gap between the implant and graft material. Again, ALPase-positive osteoblasts were shown to couple with osteoclasts, having deposited new bone matrix after bone resorption. Transmission electron microscopic observations revealed direct contact between the implant and the new bone at the interface area, although few thin cells could still be identified. At both the alveolar ridge and the interface areas, newly formed bone resembled compact bone histologically. Also, concentrations of Ca, P, and Mg were much alike with those of the preexistent cortical bone. In summary, when dental implant placement and grafting with BIOPEX-R are done concomitantly, the result is a new bone that resembles compact bone, an ideal achievement in reconstructive procedures for dental implantology.     

Numerical simulation of bone remodelling around dental implants

Crestal bone loss can result in the failure of dental implants and can be caused, by among other factors, the development of non-physiological mechanical conditions. Bone remodelling (BR) is the physiological process through which bone adapts itself to the mechanical environment. A previously published mathematical model of BR is used in this work to study the homogenized structural evolution of peri-implant bone. This model is used to study the influence of the diameter and length of a dental implant of pure titanium on its long-term stability. The temporal evolution of porosity and microstructural damage of the peri-implant bone are the variables analysed in this study. The results show that damage and porosity increase as the implant length decreases and, more pronouncedly, as its diameter decreases. The increase in damage and porosity levels is localized, as many other studies confirm, at the implant neck due to the stress concentration that is created in that area. The main conclusion of this study is that in implants with a diameter equal to or greater than 3 mm the damage is under control and there is no mechanical failure of the peri-implant bone in the long term.     

Design of a stability-detecting device for dental implants

Resonance frequency (RF) analysis technology was used to design a dental implant stability detector. The device uses a miniature-sized electromagnetic triggering rod to elicit vibration in a dental implant. Vibrational signals were recorded via an acoustic receiver. To assess the in vivo performance of the test apparatus, animal models were used. Implants were placed in the left tibia of 12 rabbits using a conventional surgical procedure. Standard 3.2 mm x 8 mm implants were placed in each test tibia with pre-tapping cavities of 3.2 mm and 3.7 mm diameters to simulate either a 'well-fitting' or a 'loosely fitting' situation. The RF values of the test implants were detected by the newly developed device which was directly mounted on the healing abutments of the implants. The results showed that the RF values of the implants under well-fitting conditions significantly increased (p < 0.01) 3 weeks after surgery and reached a plateau at around 6-7 weeks. Meanwhile implants with higher initial RF values had shorter healing times and higher final RF values at the plateau. Based on these findings, it was concluded that the idea of using the current designed device for detecting the degree of bone healing during the osseointegration process seems feasible.     

Relative influence of surface topography and surface chemistry on cell response to bone implant materials. Part 2: biological aspects

A current medical challenge is the replacement of tissue which can be thought of in terms of bone tissue engineering approaches. The key problem in bone tissue engineering lies in associating bone stem cells with material supports or scaffolds that can be implanted in a patient. Beside bone tissue engineering approaches, these types of materials are used daily in orthopaedics and dental practice as permanent or transitory implants such as ceramic bone filling materials or metallic prostheses. Consequently, it is essential to better understand how bone cells interact with materials. For several years, the current authors and others have developed in vitro studies in order to elucidate the mechanisms underlying the response of human bone cells to implant surfaces. This paper reviews the current state of knowledge and proposes future directions for research in this domain.     

Finite element stress and strain analysis of the bone surrounding a dental implant: effect of variations in bone modulus.

The long-term clinical performance of a dental implant is dependent upon the preservation of good quality bone surrounding the implant and a sound interface between the bone and the biomaterial. Good quality bone is itself dependent upon the appropriate level of bone remodelling necessary to maintain the bone density and the avoidance of bone microfracture and failure. Both processes are governed by the stress and strain distribution in the bone. In this study, a dental implant which had the same geometry as the Branemark system, but with a bioactive surface coating added to produce a direct bond to the bone, was analysed. A finite element stress and strain analysis has been carried out for a range of bone density distributions under axial and lateral loading. The predictions indicated that there was no evidence of strain shielding around the neck of the implant. With lateral loading, high values of von Mises stresses (18 M Pa) were predicted around the neck of the implant. A reduction in the elastic modulus of the bone around the neck of the implant by a factor of 16 only produced a twofold reduction in the peak stress. This resulted in stress levels capable of inducing fatigue failure in this much weaker bone. This analysis has demonstrated that it is extremely important to have good quality dense bone around the neck of the implant to withstand the predicted peak stresses of between 9 and 18 M Pa. Failure to achieve this after implantation and subsequent healing may result in local fatigue failure and resorption at the neck upon resumption of physiological loading.     

短碳纤维增强聚醚醚酮内接骨板应用于断骨修复过程的有限元模拟

聚醚醚酮(PEEK)作为内植入材料,具有优良的生物相容性、力学性能和透X光等特点。在国外,用该材料制成的商业化产品,包括椎间融合器、牙冠和心脏瓣膜等,已经得到FDA认可。该材料经过纤维等手段增强后,性能可以任意调整到和植入部位组织或骨力学性能匹配,能制作出所需要的植入件。它有望取代骨科金属材料,成为内植入件的主流材料。在先期完成短碳纤维增强PEEK复合材料内接骨板制备和性能测量的基础上,本文选用具有代表性的不同弹性模量的4种骨板(不锈钢骨板、Ti6A14V骨板、碳/羟磷灰石骨板、C/PEEK骨板),采用有限元软件建立正常骨-骨板-断骨三维有限元模型,对骨修复过程中的3个阶段(断骨修复程度1%、50%、75%)分别进行模拟。结果表明:4种内接骨板在断骨处都会产生应力遮挡的现象。随着骨板弹性模量的增大,紧贴骨板下断骨中应力遮挡率越大,有骨板处和其对面没有骨板处应力遮挡率相差变大,没有骨板处断骨最大应变越大,且该处断骨层出现变薄的现象;在螺钉上产生的最大应力也增大,应力集中更明显,骨板内应力集中也越明显,C/PEEK骨板能明显地降低应力屏蔽。     

The effect on the fatigue strength of bone cement of adding sodium fluoride

New bone cements that include several additives are currently being investigated and tested. One such additive is sodium fluoride (NaF), which promotes bone formation, facilitating implant integration and success. The influence of NaF on the fatigue performance of the cement as used in biomedical applications was tested in this paper. In fact fatigue failure of the cement mantle is a major factor limiting the longevity of a cemented implant. An experimental bone cement with added NaF (12 wt%) was investigated. The fatigue strength of the novel bone cement was evaluated in comparison with the cement without additives; fatigue tests were conducted according to current standards. The load levels were arranged based on a validated, statistically based optimization algorithm. The curve of stress against number of load cycles and the endurance limit were obtained and compared for both formulations. The results showed that the addition of NaF (12 wt%) to polymethylmethacrylate (PMMA) bone cement does not affect the fatigue resistance of the material. Sodium fluoride can safely be added to the bone cement without altering the fatigue performance of the PMMA bone cement.     

A novel closed-loop electromechanical stimulator to enhance osseointegration with immediate loading of dental implant restorations

The degree of osseomechanical integration of dental implants is acutely sensitive to their mechanical environment. Bone, both as a tissue and structure, adapts its mass and architecture in response to loading conditions. Therefore, application of predefined controlled loads may be considered as a treatment option to promote early maturation of bone/implant interface prior to or in conjunction with crown/prosthesis attachment. Although many studies have established that the magnitude, rate of the applied strain, and frequency have significant effects on the osteogenic response, the actual specific relationships between strain parameters and frequency have not yet been fully defined. The purpose of this study was to develop a stimulator to apply defined mechanical stimuli to individual dental implants in vivo immediately after implantation, exploring the hypothesis that immediate controlled loading could enhance implant integration. An electromechanical device was developed, based on load values obtained using a two-dimensional finite element analysis of the bone/implant interface generating 1000 to 4000 pe and operated at 30 and 3 Hz respectively. The device was then tested in a cadaveric pig mandible, and periosteal bone surface strains were recorded for potential future comparison with a three-dimensional finite element model to determine loading regimens to optimize interface strains and iterate the device for clinical use.     

Effect of different implant abutment surfaces on OBA‐09 epithelial cell adhesion

For the long‐term success of implants, it is necessary to achieve a direct contact between the implant and the subjacent bone. To avoid bacterial penetration that could adversely affect the initial wound healing as well as the long‐term behavior of the implants, an early tissue barrier must form that is able to protect the biological peri‐implant structures. Given the need of an effective tissue early barrier around dental implants, the present study evaluated, in vitro, the influence of physical and chemical characteristics of two implant abutment surfaces on gingival epithelial cells (OBA‐9) adhesion. To this end, titanium (Ti) and zirconia (ZrO₂) disk‐shaped specimens were used mimicking the abutment components surfaces, while bovine enamel (BE) and glass cover slips (GCS) disks served as positive and negative controls, respectively. Roughness and surface free energy (SFE) of all materials were evaluated previously to cellular adhesion step. In sequence, the effect of each material on cells morphology and viability was analyzed after 1 and 24 hr. The results showed that roughness and SFE had no effect on the cell viability data or on their interaction (p = .559), independent of a post‐contact analysis of 1 or 24 hr. However, cells attachment and spreading increased after 24 hr on Ti and ZrO₂ than BE, corresponding to the highest SFE values. SFE appears to be an important property interfering on the quality of the soft tissue surrounding dental implants. These data can be considered a trigger point for developing new material surfaces.     

Measurement of temperature change during the implant site preparation to determine influence of tool characteristics

Implant site preparation procedure is the most important factor that affects early osseointegration performance of a dental implant. During the side preparation procedure increase in the bone temperature above critic limit causes irreversible osteonecrosis. This heat rise compromises implant area around implants thus ending with unsuccessful osseointegration outcomes.In this experimental study drill tip geometry, drill tip angle and drill sharpness affects on procedure temperature were investigated. Experiments were carried on fresh bovine bones and implant sites were prepared individually for each experimental set.     

Fabrication of stepped hole on zirconia bioceramics by ultrasonic machining

Zirconia (ZrO₂) is a highly biocompatible ceramic material providing fracture strength properties that allow application as dental implants in biomedical engineering. In this present research, experimental analysis has been made for generating stepped hole on zirconia bioceramics with desired quality using ultrasonic machining (USM) process. Four independent controllable input process parameters are abrasive grain diameter, power rating, concentration of abrasive slurry, and tool feed rate. Material removal rate (MRR), overcut of larger diameter (OLD) hole, and overcut of smaller diameter (OSD) hole of stepped hole are considered as the responses. Response surface methodology (RSM) is used for modeling the performance of USM process. Multiobjective optimization has been performed to maximize the MRR and minimize the OLD hole and OSD hole of stepped holes. All the responses are improved at the optimal parametric condition and verified by confirmation test. The present research opens up the application feasibility of USM process for stepped hole generation on bioceramics and its utilization in biomedical field.     

Investigating the effect of clamping force on the fatigue life of bolted plates using volumetric approach

In this paper, the effects of bolt clamping force on the fatigue life for bolted plates made from Al7075-T6 have been studied on the values of notch strength reduction factor obtained by volumetric approach. To attain stress distribution around the notch (hole) which is required for volumetric approach, nonlinear finite element simulations were carried out. To estimate the fatigue life, the available smooth S-N curve of Al7075-T6 and the notch strength reduction factor obtained from volumetric method were used. The estimated fatigue life was compared with the available experimental test results. The investigation shows that there is a good agreement between the life predicted by the volumetric approach and the experimental results for various specimens with different amount of clamping forces. Volumetric approach and experimental results showed that the fatigue life of bolted plates improves because of the compressive stresses created around the plate hole due to clamping force.     

The effect of polyethylene thickness in fixed- and mobile-bearing total knee replacements

In this paper fixed- and mobile-bearing implants were simulated using a multibody dynamic model and a finite element model to investigate the contact pressure distribution in the ultra high molecular weight polyethylene tibial bearing component. The thickness of polyethylene varied from 6.8 to 12.3 mm and the polyethylene was modelled as a non-linear material. It was found that the contact pressure on the polyethylene decreased in the fixed-bearing implant when the thickness of polyethylene increased from 6.8 to 8 and 9.6 mm, but there was little further decrease in pressure with the increase of polyethylene thickness from 9.6 to 11.0 and 12.3 mm. In the mobile-bearing implant, no increase in contact pressure on the superior surface was found with the increase in the thickness of the polyethylene; however, the contact pressures on the inferior contact surface of the thicker designs were higher than those in the 6.8 mm design. The numerical results obtained in this paper are in good agreement with published experimental test results. Moreover, the paper presents a detailed pressure distribution on the tibial bearing component during a full gait cycle.     

The signaling pathway in modulating bone metabolism after dental implant in diabetes

Diabetes Mellitus is a systematic disease with complications in multi-organs, including decreased implant osseointegration and a high failure rate of dental transplants. Accumulating evidence indicates that the signaling pathway directly impacts the process of bone metabolism and inflammatory response implicated with dental implants in diabetic patients. This review summarizes the recent advance in signaling pathways regulate osseointegration and inflammatory response in dental transplantation, aiming to identify the potential therapeutic target to reduce the dental transplant failure in diabetes patients, with emphasis on the surface characteristics of the implant, inflammatory signaling, AMPK, PPARγ, WNT, ROS, and adiponectin signaling.     

Platelet‐rich fibrin and collagen membrane in the preservation of the alveolar bone: Feasibility of the elemental inorganic composition and scanning electron microscopy analysis

The success of dental implants is related to the amount, quality, and composition of the alveolar bone. The placement of platelet‐rich fibrin (PRF) clot associated with a resorbable collagen membrane (RCM) in a postextraction alveolus is a technique used for ridge preservation. This case report study analyzed the ultrastructural characteristics of cross‐sectioned alveolar bone that received PRF and RCM using scanning electron microscopy and the inorganic composition using “energy dispersive X‐ray spectrometry,” in order to explore the feasibility of this method to clinical studies. Three alveolar bone samples from two male patients (37 and 58 years old), obtained in the procedure of placing the dental implant, were analyzed. Two bone samples previously received PRF and RCM (M37 and M58), the third sample represented a physiological bone formation without treatment (M37‐control). The bone sample M37 showed irregularly shaped islets of calcified material intermingled with connective tissue. The other samples, from the 58‐year‐old patient with PRF and RCM (M58); and the other untreated bone sample from the same 37‐year‐old patient (M37‐control) showed similar ultrastructural morphology with trabecular conformation without islets agglomerations. The inorganic composition analysis showed higher concentrations of calcium and phosphorus in both samples treated with PRF and RCM in comparison to the untreated bone sample. The Ca/P ratio was higher in the M37 sample compared to the others samples. The results showed morphology and inorganic composition differences among the treatments used, suggesting that this method is feasible to analyze parameters of the alveolar bone tissue.     

An image-based methodology to establish correlations between porosity and cutting force in micromilling of porous titanium foams

Porous titanium foam is now a standard material for various dental and orthopedic applications due to its light weight, high strength, and full biocompatibility properties. In practical biomedical applications, outer surface geometry and porosity topology significantly influence the adherence between implant and neighboring bone. New microfabrication technologies, such as micromilling and laser micromachining opened new technological possibilities for shape generation of this class of products. Besides typical geometric alterations, these manufacturing techniques enable a better control of the surface roughness that in turn affects to a large extent the friction between implant and surrounding bone tissue. This paper proposes an image analysis approach for optical investigation of the porosity that is tailored to the specifics of micromilling process, with emphasis on cutting force monitoring. According to this method, the area of porous material removed during micromilling operation is estimated from optical images of the micromachined surface, and then the percentage of solid material cut is calculated for each tool revolution. The employment of the aforementioned methodology in micromilling of the porous titanium foams revealed reasonable statistical correlations between porosity and cutting forces, especially when they were characterized by low-frequency variations. The developed procedure unlocks new opportunities in optimization of the implant surface micro-geometry, to be characterized by an increased roughness with minimal porosity closures in an attempt to maximize implant fixation through an appropriate level of bone ingrowth.     

Influence of pH and corrosion inhibitors on the tribocorrosion of titanium in artificial saliva

Dental implants are used to replace teeth lost due to decay, trauma, or periodontal diseases. Dental implants are most of the times subjected to micro-movements at the implant/bone interface or implant/porcelain interface (due to the transmitted mastication loads) and chemical solicitations (oral environment). Such implant becomes part of a tribocorrosion system, which may undergo a complex degradation process that can lead to implant failure. In this work, the fretting-corrosion behaviour of titanium grade 2 in contact with artificial saliva was investigated under fretting test conditions. Citric acid was added to artificial saliva to investigate a pH variation on the tribocorrosion behaviour of the material. Additionally, three different inhibitors were added to investigate cathodic and anodic reactions on the electrochemical response. Also, the influence of inhibitors included in the formulation of tooth cleaning agents or medicines was investigated. Degradation mechanisms were investigated by electrochemical noise technique that provided information on the evolution of corrosion potential and corrosion current during fretting tests. Depassivation and repassivation phenomena occurring during the tests were detected and discussed. Considering the influence of corrosion inhibitors, it was observed that the degree of protection varies with the nature of the inhibitors.     

Design and manufacture of custom hip prostheses based on standard X-ray films

This paper describes a methodology for designing custom hip implants based on standard X-ray films for the cases when the patient’s bone are not suitable for a standard hip implant. Software was developed that includes X-ray scanning, femoral canal obtaining, implant designing, fit evaluation, and drawing a 2D map. Hip implants can then be manufactured using the CAM (Computer Aided Manufacturing) technique. The design procedures, rationales are explained. Verification of a custom hip implant is presented in results and discussion of this paper. It was concluded that the hip implant matched the femoral cavities very well. The result of verification indicates that the method of designing hip implants is practicable.