An intra-oral hydraulic system for controlled loading of dental implants

This study reports a method for controlling loads on an in vivo dental implant and its application for the investigation of early loading versus delayed loading of dental implants. The method was developed for the purpose of studying an ongoing hypothesis that amounts to bone loss around dental implants are related to mechanical-mediated adaptation of the alveolar bone. Using a customized intra-oral hydraulic system, the daily loading over a dental implant has been completed and recorded for six Sinclair swine. Each pig had a 5-month duration implant loading. During the experiments (loading), no analgesic treatment was supplied. The mean of the in vivo daily loadings was confirmed through an in vitro bench test after each animal was euthanized. Variations of the averaged loading input among the six animals were smaller than 10%. Preliminary data produced by the model suggests that cervical bone loss is less for early loading than for delayed loading. The current system is expected to provide a useful load control model for the study of alveolar bone adaptation around dental implants in relation to various loadings.     

Mechanical behavior of bovine nasal cartilage under static and dynamic loading

Abnormal mechanical loading may trigger cartilage degeneration associated with osteoarthritis. Tissue response to load has been the subject of several in vitro studies. However, simple stimuli were often applied, not fully mimicking the complex in vivo conditions. Therefore, a rolling/plowing explant test system (RPETS) was developed to replicate the combined in vivo loading patterns. In this work we investigated the mechanical behavior of bovine nasal septum (BNS) cartilage, selected as tissue approximation for experiments with RPETS, under static and dynamic loading. Biphasic material properties were determined and compared with those of other cartilaginous tissues. Furthermore, dynamic loading in plowing modality was performed to determine dynamic response and experimental results were compared with analytical models and Finite Elements (FE) computations. Results showed that BNS cartilage can be modeled as a biphasic material with Young's modulus E=2.03±0.7 MPa, aggregate modulus H_A=2.35±0.7 MPa, Poisson's ratio ν=0.24±0.07, and constant hydraulic permeability k₀=3.0±1.3×10⁻¹⁵ m⁴ (N s)⁻¹. Furthermore, dynamic analysis showed that plowing induces macroscopic reactions in the tissue, proportionally to the applied loading force. The comparison among analytical, FE analysis and experimental results showed that predicted tangential forces and sample deformation lay in the range of variation of experimental results for one specific experimental condition. In conclusion, mechanical properties of BNS cartilage under both static and dynamic compression were assessed, showing that this tissue behave as a biphasic material and has a viscoelastic response to dynamic forces.     

Development and design of a novel loading device for the investigation of bone adaptation around immediately loaded dental implants using the reindeer antler as implant bed

The assessment of the behavior of immediately loaded dental implants using biomechanical methods is of particular importance. The primary goal of this investigation is to optimize the function of the implants to serve for immediate loading. Animal experiments on reindeer antlers as a novel animal model will serve for investigation of the bone remodeling processes in the implant bed. The main interest is directed towards the time and loading-dependant behavior of the antler tissue around the implants. The aim and scope of this work was to design an autonomous loading device that has the ability to load an inserted implant in the antler with predefined occlusal forces for predetermined time protocols. The mechanical part of the device can be attached to the antler and is capable of cyclically loading the implant with forces of up to 100 N. For the calibration and testing of the loading device a biomechanical measuring system has been used. The calibration curve shows a logarithmic relationship between force and motor current and is used to control the force on the implant. A first test on a cast reindeer antler was performed successfully.     

Stress transfer properties of different commercial dental implants: a finite element study

Dental implantology has high success rates, and a suitable estimation of how stresses are transferred to the surrounding bone sheds insight into the correct design of implant features. In this study, we estimate stress transfer properties of four commercial implants (GMI, Lifecore, Intri and Avinent) that differ significantly in macroscopic geometry. Detailed three-dimensional finite element models were adopted to analyse the behaviour of the bone-implant system depending on the geometry of the implant (two different diameters) and the bone-implant interface condition. Occlusal static forces were applied and their effects on the bone, implant and bone-implant interface were evaluated. Large diameters avoided overload-induced bone resorption. Higher stresses were obtained with a debonded bone-implant interface. Relative micromotions at the bone-implant interface were within the limits required to achieve a good osseointegration. We anticipate that the methodology proposed may be a useful tool for a quantitative and qualitative comparison between different commercial dental implants.     

Resonance frequency analysis of overdenture retainer implants with immediate loading

doi: 10.1111/j.1741‐2358.2011.00488.x
Resonance frequency analysis of overdenture retainer implants with immediate loading Objective: To evaluate 16 patients of both sexes with lower overdenture and upper complete dentures, by analysing the resonance frequency of the initial and late stability of implants used to retain the overdenture under immediate loading. Background: Oral rehabilitation treatment with complete dentures using implants has been increasingly more common among the specialists in the oral rehabilitation area. This is an alternative for obtaining retention and stability in treatments involving conventional complete dentures, where two implants are enough to retain the overdenture satisfactorily. Materials and methods: The Osstell? Mentor device was used for the analysis in the initial period (primary stability), 3 and 15 months after the installation of the lower overdenture (secondary stability). The statistical analysis was performed with the repeated measures model (p < 0.01). Results: The implant stability quotients were observed to increase after 15 months of the rehabilitating treatment. Conclusion: The use of overdentures over two lower implants should become the treatment of choice for individuals who have a fully edentulous mandible.     

A comparative analysis based on different strength criteria for evaluation of risk factor for dental implants

A numerical analysis is developed to study the interaction phenomena between endousseus titanium dental implants and surrounding jawbone tissue. The interest is focused on the most appropriate evaluation of the stress state arising in the tissue because of the implant under physiological loading. The problem is considered with regard to linear elastic response of the one and to short time effect. Different configurations of bone-implant system are described, using axial-symmetrical and three-dimensional models, by means of finite and geometric element method. The investigation attains to the stress states induced in bone that lead to a limit condition near the effective failure surface. The parameter commonly adopted in literature, such as the Von Mises stress, represents an excessive simplification of problem formulation, leading to an incorrect evaluation of the real failure risk for the implant, due to the assumption of the isotropic and deviatoric nature of the adopted stress measure. More suitable criterion can be assumed, such as the Tsai-Wu criterion, to take into account the anisotropy that characterises the response of bone, as well as the influence of a hydrostatic stress state. The analysis developed offers a comparison of results by using different criteria, leading to an evaluation of reliability of the procedure to be followed and addressing also to an evaluation of a risk factor for the implant investigated.     

Movement behavior of teeth and dental implants in periotest measurement in occlusion--an in vitro study]

Early diagnosis of periodontal disease is essential for the planning of restorative, prosthetic and surgical treatment. The usual clinical methods are mostly subjective. Although the Periotest device has been specially developed for the diagnosis of periodontal disease, it can also be used to aid occlusal adjustment after insertion of inlays or artificial crowns. To investigate this application of the Periotest, a jaw model with idealized dental crowns incorporating motion and force sensors has been constructed. Motion and force are recorded during measurements with the Periotest. The maximum amplitudes in the apical (vertical) direction obtained with unpolished occlusal points increased with increasing occlusal load. With polished contact points, the maximum values in the apical direction revealed no dependence on occlusal load. The maximum amplitudes of movement and force in the oral (horizontal) direction decrease with increasing occlusal load both with polished and unpolished contact points. With the first, the teeth appear to slide one upon the other such that the overall distance between them remains unchanged, and no additional apical forces develop. In the case of rough contact points, additional forces develop, and falsify Periotest measurements.     

An investigation of lymphatic vessels in the feline dental pulp

The existence of lymphatic vessels in the dental pulp has been a matter of continuing controversy. We have now used light microscopy to examine semithin transverse sections of perfusion-fixed incisors and canines in cats. Lymphatics were found in all the teeth studied. In most teeth they were present in the coronal, middle, and apical regions of the pulp; but in a few they were lacking coronally and in the middle. Within individual teeth, lymphatics were found in the subodontoblastic zone or more centrally in the pulp; but none were found in the odontoblast layer or in the pulp horns. Vessels located by light microscopy were subsequently examined by transmission electron microscopy. Their ultrastructural features were typical of lymphatics and included irregular, attenuated endothelium with adjacent cells joined in different ways. Occasional gaps connected the extracellular spaces with their lumens, and abluminal endothelial projections appeared to form open end bulbs. There was very little basement membrane, but anchoring filaments were found near the abluminal surface of the endothelium and near collagen fibrils. The total cross-sectional area of lymphatic vessels was measured in semithin sections and, with pulp area, increased from the coronal region to the middle. However, both areas decreased from the middle to the apical region suggesting either that lymph flows faster as it reaches the foramens of the apical delta or that some vessels leave the tooth through lateral root canals. Using the methods of light and transmission electron microscopy, therefore, we have shown that pulp lymphatic vessels exist. Questions remain, however, about their distribution within teeth, variations between teeth, and routes of exit from teeth.     

种植修复后牙周菌群在不同时期变化的定量研究

目的观察种植修复后牙周菌群在不同时期的变化,比较牙周病人群和健康人群种植术后菌群分布差异。方法选择牙种植患者28例,接受37颗种植修复（无牙周病史19颗,有牙周病史18颗）,采取前后对照设计。采用细菌分离鉴定及菌落形成单位计数的检测方法,以正常同名天然牙为基线对照,追踪观察愈合基台龈袖口、全冠修复后1周、负荷12个月后牙龈沟菌丛变化情况。结果种植体龈沟液内的细菌数量增加构成日趋复杂,在愈合基台期细菌数量最低,冠修复后1年,两组人群的菌群数量和构成差异有显著性（P〈0．05）,而健康人群成功种植体和天然牙有相似的菌群构成;但以往有牙周病史的患者,种植体植入区域内普遍有牙周病原体量的增加。结论随着时间的延长,具有牙周病史的患者的种植体周围炎的风险增加。     

Proteome analysis of human serum proteins adsorbed onto different titanium surfaces used in dental implants

Titanium dental implants are commonly used due to their biocompatibility and biochemical properties; blasted acid-etched Ti is used more frequently than smooth Ti surfaces. In this study, physico-chemical characterisation revealed important differences in roughness, chemical composition and hydrophilicity, but no differences were found in cellular in vitro studies (proliferation and mineralization). However, the deposition of proteins onto the implant surface might affect in vivo osseointegration. To test that hypothesis, protein layers formed on discs of both surface type after incubation with human serum were analysed. Using mass spectrometry (LC/MS/MS), 218 proteins were identified, 30 of which were associated with bone metabolism. Interestingly, Apo E, antithrombin and protein C adsorbed mostly onto blasted and acid-etched Ti, whereas the proteins of the complement system (C3) were found predominantly on smooth Ti surfaces. These results suggest that physico-chemical characteristics could be responsible for the differences observed in the adsorbed protein layer.     

Finite element analysis of different loading conditions for implant-supported overdentures supported by conventional or mini implants

The effect of implants’ number on overdenture stability and stress distribution in edentulous mandible, implants and overdenture was numerically investigated for implant-supported overdentures. Three models were constructed. Overdentures were connected to implants by means of ball head abutments and rubber ring. In model 1, the overdenture was retained by two conventional implants; in model 2, by four conventional implants; and in model 3, by five mini implants. The overdenture was subjected to a symmetrical load at an angle of 20 degrees to the overdenture at the canine regions and vertically at the first molars. Four different loading conditions with two total forces (120, 300 N) were considered for the numerical analysis. The overdenture displacement was about 2.2 times higher when five mini implants were used rather than four conventional implants. The lowest stress in bone bed was observed with four conventional implants. Stresses in bone were reduced by 61% in model 2 and by 6% in model 3 in comparison to model 1. The highest stress was observed with five mini implants. Stresses in implants were reduced by 76% in model 2 and 89% increased in model 3 compared to model 1. The highest implant displacement was observed with five mini implants. Implant displacements were reduced by 29% in model 2, and increased by 273% in model 3 compared to model 1. Conventional implants proved better stability for overdenture than mini implants. Regardless the type and number of implants, the stress within the bone and implants are below the critical limits.     

Observations on the effects of static and impact loading on the human femur

The amount of energy required to fracture the shaft of the femur was shown to vary with the rate of application of the load. One member of each of 32 pairs of femora was fractured with a gradually applied bending load. The mean energy required to cause failure of the specimens was 20·50 ft-lb. Impact tests in which the same loading geometry was employed, were performed on the remaining member of each pair of specimens. The impact loading velocity was 32 ft/sec. The mean energy absorbed to the point of failure by the impact loaded specimens was 31·33 ft-lb.

Attention was drawn to the possible significance of these findings in the field of accident protection studies.     

HOMGL-comparing genelists across species and with different accession numbers

Homology Gene List (HOMGL) is a web-based tool for comparing gene lists with different accession numbers and identifiers and between different organisms. UniGene, LocusLink, HomoloGene and Ensembl databases are utilized to map between these lists and to retrieve upstream or transcribed sequences for genes in these lists. We illustrate the use of HOMGL with respect to microarray studies and promoter analysis. AVAILABILITY: http://homgl.biologie.hu-berlin.de/     

江苏省黑莓区域性栽培试验

以黑莓（Rubus spp.）的Hull和Chester2个品种为试材在江苏省开展了区域性栽培试验。分析认为,在江苏全省各地黑莓均可正常生长、开花和结果,即为适宜生长区。从高产优质的角度考虑,宁镇扬低山丘陵地带和以连云港为主的滨海丘陵地区是黑莓种植的最适宜地区,但要注意适时灌溉;徐淮黄泛平原地区和沂沭河丘陵平原地带是黑莓的适宜栽培区,不利因素是干旱;江淮湖洼平原、里下河地区和沿海平原地区是黑莓的次适宜栽培区,不利偏多,不提倡大力发展。试验结果显示,适宜的自然条件是黑莓优质和高产的重要因素,但针对不利条件采取各种不同的栽培措施也十分重要。通过栽植地点的优化选择和栽培管理措施的强化加以弥补和调整,克服不利因子,在江苏全省范围内获得黑莓优质高产是完全可能的。     

In vivo forces on dental implants: hard-wiring and telemetry methods

Methods are presented for measuring vertical force components on bridged titanium dental implants in dog mandibles. These methods have included custom-made strain-gauge transducers, plus hard-wiring and telemetric schemes for data collection. The essential components of the measurement system are described, and typical bite force data are illustrated.     

Neutral zone and range of motion in the spine are greater with stepwise loading than with a continuous loading protocol. An in vitro porcine investigation

Biomechanical testing of the spine has traditionally been performed to help understand the normal function of the spine as well as to evaluate the effects of injury and surgical procedures on spinal behaviour. The overall objective of this investigation was to compare traditional stepwise loading with the recently introduced continuous loading protocol, determining the effect of loading protocol on the mechanical behaviour of the spine. For all tests, a custom spine testing machine was used to apply pure moments of flexion extension, axial rotation, and lateral bending to a maximum of 2 Nm, using six porcine cervical spine specimens (C2-C4). Motions of C2 with respect to C4 were measured with an optoelectronic camera system. Motion parameters calculated were range of motion (ROM), neutral zone (NZ), and the ratio of NZ and ROM. The continuous loading protocol had smaller values for all motion parameters in each loading direction (p<0.05). ROM for the continuous test ranged between 88% and 93% of that of stepwise for the three loading directions. The continuous protocol NZ was 56-75% of that of the stepwise test. The findings of the study demonstrate that the two loading protocols provide differing spinal behaviours.     

The different correlations between obesity and osteoporosis after adjustment of static mechanical loading from weight and fat free mass

Objectives:To explore complex correlations between obesity (OB) and osteoporosis (OP) after adjustment of static mechanical loading from weight and fat free mass (FFM).Methods:A total of 3749 Chinese aged ≥65 years were selected from our ongoing cohort study. OB indices and bone mineral density (BMD) were measured for each subject. Linear regression analyses were performed to explore the correlations between OB indices and OP under three adjustment models (unadjusted, adjusted with weight and adjusted with FFM).Results:Under no adjustment, three general obesity indices (body mass index: BMI, fat mass: FM, and percentage FM: PFM) were positively associated with BMD at three skeletal sites (P<0.001) in the regression analyses. However, after the adjustment with weight, these associations were mostly significant but reverse i.e., negatively in direction. After adjustment with FFM, the three indices were still positively and significantly (P<0.001) associated with BMD but regression coefficients were smaller compared to the unadjusted associations. Similar associations were observed for central adiposity and lower limb adiposity indices.Conclusions:The combined relation of OB to OP due to the physiological factors secreted from adipose tissues and the static mechanical loading from FM is positive in direction.