Predicting time-dependent remodeling of bone around immediately loaded dental implants with different designs

The purpose of this study was to predict time-dependent biomechanics of bone around cylindrical screw dental implants with different macrogeometric designs under simulated immediate loading condition. The remodeling of bone around a parallel-sided and a tapered dental implant of same length was studied under 100 N oblique load by implementing the Stanford theory into three-dimensional finite element models. The results of the analyses were examined in five time intervals consisting loading immediately after implant placement, and after 1, 2, 3 and 4 weeks following implantation. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x-(implant lateral direction with a projection of the oblique force) and y-(implant longitudinal direction) axes of the implant were evaluated. The highest value of the maximum and minimum principal stresses around both implants increased in cortical bone and decreased in trabecular bone. The maximum and minimum principal stresses in cortical bone were higher around the tapered cylindrical implant, but stresses in the trabecular bone were higher around the parallel-sided cylindrical implant. Strain energy density around both implants increased in cortical bone, slightly decreased in trabecular bone, and higher values were obtained for the parallel-sided cylindrical implant. Displacement values slightly decreased in time in x-axis, and an initial decrease followed by a slight increase was observed in the y-axis. Bone responded differently in remodeling for the two implant designs under immediate loading, where the cortical bone carried the highest load. Application of oblique loading resulted in increase of stiffness in the peri-implant bone.     

Biomechanical simulation of various surface roughnesses and geometric designs on an immediately loaded dental implant

Experiment with rapid prototyping technique and validation finite element model was performed to evaluate the biomechanical behavior of an immediately loaded mandibular implant. Also, 18 finite element models of six implant designs and three surface roughnesses with anisotropic bone material properties were analyzed to compare the bone stresses and the sliding at the bone-implant interface under a vertical or lateral force of 130 N. The results show that bone stress (strain) of an immediately loaded implant is heavily dependent on the implant design and surface roughness. Improving the initial interfacial interlocking using a threaded implant has a higher priority than using cylindrical or step designs with a rough surface for an immediately loaded implant.     

Influence of abutment design on the success of immediately loaded dental implants: experimental and numerical studies

The aim of the present study was to investigate experimentally and numerically the influence of a fine threaded- against a roughened-cervical region of immediately loaded dental implants in combination with straight and 20°-angled abutments on the implant primary stability. A total of 30 implants were inserted in bovine rib-segments, 14 cervically roughened implants and 16 implants with fine cervical threads. Each implant system received two abutments, straight and 20°-angled. Implant displacements and rotations were measured using a biomechanical measurement system. Subsequently, eight samples were selected for geometrical reconstruction and numerical investigation of stress and strain distributions in the bone by means of the finite element method. Experimentally, both implant systems showed similar behaviour with the straight abutments concerning displacements and rotations. However, fine threaded implants showed much less displacement and rotation against roughened implants when angled abutments were considered. Numerically, stresses were within 35-45 MPa in the cortical bone for both implant systems. The strains showed highest values within the spongious bone with the roughened implants connected to angled abutments. The results indicate that implants with fine cervical threads could be recommended in particular with angled abutments. The outcomes of this study are currently confirmed by long-term clinical investigations.     

The evaluation of the interface between bone and a bioceramic dental implant

Methods for evaluating the interface between bone and an experimental dental implant have been analyzed. The material studied was a titanium implant coated with a mixture of alumina and titanium dioxide by means of a plasma-jet system with the dog as the animal model. The evaluations were made on two levels: (1) in vivo, by analyzing radiographs of the peri-implant zone with a video display computer (2) in vitro, after explantation, by analyzing vertical and horizontal sections of the sample with an optical and a scanning electron microscope, and by a video display computer analysis of the microradiographs of these sections.     

Topographic scale-range synergy at the functional bone/implant interface

We sought to explore the biological mechanisms by which endosseous implant surface topography contributes to bone anchorage. To address this experimentally, we implanted five groups of custom-made commercially pure titanium implants of varying surface topographical complexity in rat femora for 9 days; subjected them to mechanical testing; and then examined the interfacial bone matrix by electron microscopy. The five implant surfaces were prepared by combinations of dual acid etching and grit blasting the titanium substrates and, in some cases, modifying the created surfaces with the deposition of nanocrystals of calcium phosphate, which resulted in 10 samples per group. In parallel, we cultured rat bone marrow cells on surrogate implants constructed from polymer resin coated with the same calcium phosphate nanocrystals, and monitored the deposition of bone sialoprotein by transmission electron immunohisto-micrography. We found that implant samples modified with sub-micron scale crystals were bone-bonding, as described by the interdigitation of a mineralized cement line matrix with the underlying implant surface. The in vitro assay showed that bone sialoprotein could be deposited in the interstices between, and undercuts below, the nanocrystals. In addition, when mineralized, the cement line matrix globules occupied micron-sized pits in the implant surfaces, and in part obliterated them, creating an additional form of anchorage. Our results also showed that collagen, elaborated by the osteogenic cells, wrapped around the coarse-micron features, and became mineralized in the normal course of bone formation. This provided a mechanism by which coarse-micron implant features contributed to a functional interface, which we have previously described, that is capable of resisting the mechanical loading that increases as peri-implant bone matures. Thus, our findings provide mechanistic explanations for the biologically-relevant criteria that can be employed to assess the importance of implant surface topography at different scale-ranges.     

Towards the limit of quantifying low-amplitude strains on bone and in coagulum around immediately loaded oral implants in extraction sockets

The purpose of this study was to quantify strains in coagulum around immediately loaded oral implants in extraction sockets at the ex vivo level. Bilateral maxillary premolar teeth of two fresh human cadavers were extracted and psi 4.1 x 12 mm Straumann TE implants were placed in the sockets of first and second premolars by utilizing mesio-distal and palatal anchorage, respectively. Installation torque value (ITV) of each implant was measured by a custom-made torque wrench and resonance frequency analyses (RFAs) were undertaken to determine intraosseous stability. Upon abutment connection, a gold coping allowing the placement of a miniature load cell to contact the underlying solid abutment was fabricated. A linear strain gauge was connected to the coping at a distance for strain measurements in coagulum around the implant neck in the extraction socket. Linear strain gauges were also bonded on the labial marginal bone of each extraction socket. Strain measurements were performed at a sample rate of 10 kHz simultaneously monitored from a computer connected to data acquisition system and under a maximum load of 100 N on each implant with or without human coagulum in the extraction socket. Low-amplitude strains were measured around immediate implants. The increase in load increased strains on labial marginal cortical bone around implants (P < 0.05). Bone strains were higher on the implant loaded, when coagulum was present in the bone defects (P < 0.05). Strains within coagulum around mesiodistally anchored implants were higher than palatally anchored implants (P < 0.05). The type of implant on anchorage and presence of coagulum has an impact mechanotransduction to buccal marginal bone around immediate implants.     

Histologic and histomorphometric evaluation of early and immediately loaded implants in the dog mandible

New bone formation around US III OSSTEM implants after early and immediate loading was evaluated in this study. Three premolars and the first and second molars were first removed from the left mandible of five dogs. At 3 weeks after extraction of the teeth in the left mandible, the corresponding teeth in the right mandibles were removed. After 12 weeks of bone healing, five implants were placed in the left mandible. At 3 weeks after placement of implants in the left mandible, another five were placed in the right mandible. At the time of placing implants in the right mandible, four implants on each side were restored using a fixed provisional restoration. The anterior-most implant was not loaded and was used as controls. Periotest measurements performed immediately after implantation and after 16 weeks loading indicated implant stability for all groups tested. At 16 weeks after loading, the rate of peri-implant bone formation for the early loaded, immediately loaded (IL), and control implants were observed to be 75.00, 73.37, and 62.04%, respectively. It was thus concluded that early stability was achieved in early and IL implants using fixed provisional restoration, thereby resulting in the high rate of peri-implant bone formation.     

Histomorphometric evaluation of immediately loaded SSII implants of different surface treatments in a dog model

This study compared splint (experimental) and nonsplint (control) methods for immediately loaded implants and examined the bone-implant contact rate for smooth, oxidized, and resorbable blast medium (RBM) surfaces. The first through fourth mandibular premolars were extracted from six young adult dogs. Twelve weeks after extraction, implantation was performed at the extraction sites. The SSII OSSTEM implant had one of three surface treatments: smooth, oxidized, or RBM. Sixteen weeks after implantation, the dogs were euthanized; the hemimandibles were obtained and processed histologically to obtain nondecalcified sections. Longitudinal sections were made for each implant and analyzed using light microscopy. Independent of the splinting method, a significantly higher bone-implant contact was observed for implants with oxidized and RBM surfaces when compared with implants with smooth surfaces. Irrespective of the splinting method, immediately loaded implants with oxidized and RBM surfaces may result in higher bone-implant integration when compared with implants with smooth surfaces.     

种植体材料钛与种植体上部结构合金间电偶的腐蚀性

背景：大多数和钛种植体接触的牙科金属修复部分,会引起电偶腐蚀的发生。偶对在种植体界面产生带正电的局部环境,这会直接影响组织状况,尤其是骨吸收。 目的：评价TA2型商业纯钛分别与金合金、钴铬合金、钛合金及镍铬合金在体外的电偶腐蚀行为。 方法：在人工唾液中体外模拟TA2型商业纯钛分别与金合金、钴铬合金、钛合金及镍铬合金接触时的回路, 测量其作用15 h的混合电位和电偶电流值并描绘电流时间曲线。 结果与结论：4组合金接触8 h后电流达到稳定,稳定后电偶电流值排列顺序为钛/金合金<钛/钴铬合金<钛/钛合金<钛/镍铬合金。提示钛/金合金组电偶腐蚀最小,金合金是最适合作为种植义齿上部结构的材料;钛/镍铬合金组电偶腐蚀最大,镍铬合金是最不适合作为种植义齿上部结构的材料。     

Nacre/bone interface changes in durable nacre endosseous implants in sheep

Raw nacre implants persist even after 9 months of implantation into bone tissue in sheep. However the nacre surface undergoes a limited biodegradation process. Smooth-surfaced nacre implants were seen to become microporous after implantation. The results of these long-term, in vivo studies show that the overall process involves bone-resorbing cells, relies on a two-phase mechanism and may correspond to a regulation process. The rate of surface change depends on the bone implantation site and the nacre/bone interaction. The in vivo biodegradability of nacre is a highly variable parameter. The size and shape of the implanted nacre and the cellular environment of the implant are key factors in determining the biodegradation kinetics of the nacre in a living system.     

High-voltage electron microscopy and conventional transmission electron microscopy of the interface zone between bone and endosteal dental implants.

The interface between mandibular bone and endosteal dental implants was examined with an in vivo dog model. Undecalcified mandibular implant samples were observed with both conventional transmission electron microscopy and high-voltage transmission electron microscopy (HVEM). Results demonstrated the variable nature of the interfacial support tissues. Mineralized bone was often found within 50 nm of the implant surface, separated from that surface only by an electron dense deposit. Osteocytes were observed close to the interface encased within lacunae extending numerous cellular processes through canaliculi. An osteoblast was also observed directly at the interface within a developing lacuna. Other interfacial areas exhibited a finely fibrillar and more electron lucent morphology. Furthermore, other areas were shown to be composed of wider zones of extracellular products containing collagen fibrils, ground substance, and calcified inclusions. Because bone is an actively growing and remodeling tissue, these different morphological zones around the entire area of the implants would appear to confirm the dynamic tissue response to endosteal dental implants. Further, HVEM stereology was shown to be an exciting research tool to investigate this tissue response.     

Shear strength of loaded porous-glassy-carbon/bone interface—an experimental study on rabbits

The aim of the study was to measure the shear strength of bone/porous-glassycarbon interface in rabbit. Glassy carbon pellets were implanted into drill holes made through the medial articular surface of the proximal tibia of 15 rabbits. Shear strengths grew statistically significantly from 1 to 6 weeks ana reached a maximum of 4.6 MN/m². Microscopical examination of the sheared surfaces revealed that at 1 and 2 weeks the shearing occurred through the tissue surrounding the implant, and at 3, 6 and 12 weeks through the porous coating of the implant. To diminish the fragility of the porous coating, its porosity should be adjusted to 40%. Results of shear strength studies on current implant materials are reviewed.     

The effect of direct electrical current stimulation on the bone/porous metallic implant interface

Cylindrical porous plugs (6.35 mm dia. 11 mm long, average pore size of 190 μ dia.) made of electrically conductive Co-Cr-Mo surgical alloy powders were implanted in the canine femur. An electrical stimulation device (mercury battery, 1.35 V, connected in series with a 150 kΩ resistor) was attached to all implants directly. The in vivo current was about 8 μA for the stimulated implants while no current was delivered for the control ones.

After predetermined implant periods, tensile test specimens were made to measure the interfacial strength between bone and implants. Some samples were used for histological observations.

The present results show that in vivo electrical stimulation substantially increased the strength of the union between porous implants and bone when compared to the controls up to 12 weeks. Histological observations show that the increased strength is mainly due to the increased new bone formation in the pores of implants.

It was also observed that the fractional callus volume in the intramedullary canal for the stimulated samples retained more than the controls after reaching maximum at 3 weeks.     

Mechanical basis for bone retention around dental implants

This study, analytically, through finite element analysis, predicts the minimization of crestal bone stress resulting from implant collar surface treatment. A tapered dental implant design with (LL) and without (control, C) laser microgrooving surface treatment are evaluated. The LL implant has the same tapered body design and thread surface treatment as the C implant, but has a 2-mm wide collar that has been laser micromachined with 8 and 12 microm grooves in the lower 1.5 mm to enhance tissue attachment. In vivo animal and human studies previously demonstrated decreased crestal bone loss with the LL implant. Axial and side loading with two different collar/bone interfaces (nonbonded and bonded, to simulate the C and LL surfaces, respectively) are considered. For 80 N side load, the maximum crestal bone distortional stress around C is 91.9 MPa, while the maximum crestal bone stress around LL, 22.6 MPa, is significantly lower. Finite element analysis suggests that stress overload may be responsible for the loss of crestal bone. Attaching bone to the collar with LL is predicted to diminish this effect, benefiting crestal bone retention.     

Quantitative bone remodelling resulting from the use of porous dental implants

Histomorphometric analyses were used to quantitatively determine the patterns of bony ingrowth which resulted from the placement of porous-surfaced dental implants into the mandibles of Rhesus monkeys for up to 74 months utilizing a two-stage approach. Quantitative histopathologic evaluations were made using ground section microscopy. Implant stability resulting from bone remodelling and ingrowth occurred to varying degrees with all implants. Bone ingrowth occurred from medullary trabeculae and contact with the adjacent cortical plates. Quantitative histomorphometric analyses revealed that in only one case was the bone ingrowth into the available internal pores less than 45%. Minimal fibrous connective tissue ingrowth was observed in the implant crypts and was not thought to be due to micro-motion. The observed bone remodelling indicated a favorable prognosis for long-term implant performance.     

不同牙种植体系统对种植体周围骨组织吸收的影响

BACKGROUND: The peri-implant bone absorption is closely related to the repair effect. OBJECTIVE: To compare the effects of three kinds of dental implant systems on the peri-implant bone absorption. METHODS: 116 patients who underwent the dental implant systems were collected, including 46 cases with 3I implant system, 40 cases with ITI implant system and 30 cases with BLB implant system. The peri-implant bone absorption, sulcus bleeding index and periodontal probing depth of three groups were detected at 1, 3, 6, 9 and 12 months after implantation, respectively. RESULTS AND CONCLUSION: The peri-implant bone absorption of three groups within 1 year after implantation was in a rise, and the bone absorption of BLB group was significantly higher than that of ITI and 3I groups at 3 and 12 months after implantation (P < 0.05). Compared with the natural teeth, the gingival sulcus bleeding index of three groups were all increased at different time points after implantation; the gingival sulcus bleeding index of BLB group was significantly higher than that of natural teeth at 6 months after implantation (P < 0.05); the gingival sulcus bleeding index of three groups were significantly higher than that of natural teeth at 9 months after implantation (P < 0.05). The periodontal probing depth of three groups showed an ascending trend at 6 months after implantation; the periodontal probing depth of three groups was higher than that of natural teeth at different time points after implantation, which exhibited significant differences at 6 and 9 months after implantation (P < 0.05). In conclusion, three kinds of dental implant systems exhibit differet effects on the peri-implant bone absorption, but all achieve excellent clinical efficacies.     

Effect of cancellous bone on the functionally graded dental implant concept

In a previous work by the author [H.S. Hedia and M. Nemat-Alla, Design optimization of functionally graded dental implant, submitted to be published in the J. Bio-Medical Materials and Engineering], a functionally graded material dental implant was designed without cansellous bone in the model. In this investigation the effect of presence cancellous bone as a thin layer around the dental implant was investigated.It is well known that the main inorganic component of natural bone is hydroxyapatite (HAP) and that the main organic component is collagen (Col). Hydroxyapatite HAP implants are not bioabsorbable, and because induction of bone into and around the artificially made HAP is not always satisfactory, loosening or breakage of HAP implants may occur after implantation in the clinical application. The development of a new material which is bioabsorbable and which has osteoconductive activity is needed. Therefore, the aim of the current investigation is to design an implant, in the presence of cancellous bone as a thin layer around it, from functionally graded material. In this study, a novel biomaterial, collagen/hydroxyapatite (Col/HAP) as a functionally graded material (FGM), was developed using the finite element and optimization techniques which are available in the ANSYS package. These materials have a self-organized character similar to that of natural bone. The investigations have shown that the maximum stress in the cortical bone and cancellous bone for the Col/HAP functionally graded implant has been reduced by about 40% and 19% respectively compared to currently used titanium dental implants.     

Optimal design of thread height and width on an immediately loaded cylinder implant: A finite element analysis

In this study, we used a finite element method to evaluate the maximum Von Mises stresses in jaw bones of immediately loaded implant with different thread heights and widths, and the maximum displacements in implant-abutment complex. The implant thread height ranged from 0.20 to 0.60 mm, and the thread width ranged from 0.10 to 0.40 mm. Compared to those in standard designed implants, the maximum Von Mises stresses in cortical and cancellous bones with axially loaded implants decreased by 18.85% and 47.46%, respectively, and by 16.38% and 63.46%, respectively in buccolingually loaded implants. The maximum displacement of implant-abutment complex loaded axially and buccolingually decreased by 13.78% and 6.97%, respectively. These results indicated that thread height played more important roles in affecting bone stresses and implant-abutment complex stability than thread width. Immediately loaded cylinder implants with thread height exceeding 0.44 mm and width ranging from 0.19 to 0.23 mm caused the lowest stresses to the type B/2 bone.