Biomedical subjects

C Bourauel

Publications and source records attributed to C Bourauel.

At least 19 recordsLinked to original sources

PubMed2006

Experimental-numerical analysis of minipig's multi-rooted teeth.

The paper pertains to the analysis of the biomechanical behaviour of the periodontal ligament (PDL) by using a combined experimental and numerical approach. Experimental analysis provides information about a two-rooted pig premolar tooth in its socket with regard to morphological configuration and deformational response. The numerical analysis developed for the present investigation adopts a specific anisotropic hyperelastic formulation, accounting for tissue structural arrangement. The parameters to be adopted for the PDL constitutive model are evaluated with reference to data deducted from experimental in vitro tests on different specimens taken from literature. According to morphometric data relieved, solid models are provided as basis for the development of numerical models that adopt the constitutive formulation proposed. A reciprocal validation of experimental and numerical data allows for the evaluation of reliability of results obtained. The work is intended as preliminary investigation to study the correlation between mechanical status of PDL and induction to cellular activity in orthodontic treatments.

Animals↗

PubMed2005

Numerical simulation of the biomechanical behaviour of multi-rooted teeth.

The elastic properties of the periodontal ligament (PDL) in eight multi-rooted teeth were examined in a combined experimental and numerical study in six minipigs. The initial tooth movement of the mandibular primary molars surrounded by the periodontium was registered three-dimensionally (3D) in an optomechanical measuring system. The dissections were then embedded in resin and cut in transverse sections. Based on these sections, 3D finite element (FE) models were constructed and numerically loaded with the same force systems as used in the experiment. The material behaviour of the PDL registered in the experiment was non-linear and could be approximated with a bilinear parameter set consisting of two Young's moduli, E1 and E2, and one ultimate strain, epsilon12, separating both elastic regimes. When a deficient congruence existed between the experimental and numerical force/deflection curves the material parameters were varied to obtain a satisfactory congruence. The material behaviour determined for these specimens delivered mean values of E1 = 0.05 MPa, E2 = 0.18 MPa and epsilon12 = 6.4 per cent for the elastic behaviour of the multi-rooted minipig teeth. There was no significant difference in the material parameters determined for specimens with two, four or six roots. The results were in close agreement with the material parameters of the PDL, determined in previous investigations of single-rooted human and pig teeth.

Animals↗

PubMed2005

3D reconstruction of dental specimens from 2D histological images and microCT-scans.

Direct comparison of experimental and theoretical results in biomechanical studies requires a careful reconstruction of specimen surfaces to achieve a satisfactory congruence for validation. In this paper a semi-automatic approach is described to reconstruct triangular boundary representations from images originating from, either histological sections or microCT-, CT- or MRI-data, respectively. In a user-guided first step, planar 2D contours were extracted for every material of interest, using image segmentation techniques. In a second step, standard 2D triangulation algorithms were used to derive high quality mesh representations of the underlying surfaces. This was accomplished by converting the 2D meshes into 3D meshes by a novel lifting procedure. The meshes can be imported as is into finite element programme packages such as Marc/Mentat or COSMOS/M. Accuracy and feasibility of the algorithm is demonstrated by reconstructing several specimens as examples and comparing simulated results with available measurements performed on the original objects.

Algorithms↗

PubMed2005

Early responses of periodontal ligament cells to mechanical stimulus in vivo.

Previous studies have indicated that human periodontal ligament cells undergo osteoblastic differentiation via the ERK pathway under mechanical stress in vitro. This study aimed to verify this principle in vivo. The right upper first molars of 25 anesthetized rats were loaded with constant forces of 0.1 N for up to 8 hrs. The untreated contralateral side served as a control. Paraffin-embedded sections were analyzed by immunohistochemistry for proliferating cell nuclear antigen (PCNA), runt-related transcription factor 2 (Runx2/Cbfa1), and phosphorylated extracellular signal-regulated kinases 1/2 (pERK1/2). In selected areas under tension, the proportions of Runx2-positive and pERK1/2-positive cells increased within 8 hrs of loading, whereas these proportions in selected areas under pressure were significantly lower than those in control teeth. Moreover, there were no significant changes in the number of PCNA-positive cells. Thus, mechanical stimulus up-regulates Runx2, and this regulation may be achieved via the ERK pathway.

Animals↗

PubMed2004

[Design and testing of a novel measuring system for use in dental biomechanics--principles and examples of measurements with the hexapod measuring system].

A novel measuring set-up based on a hexapod system for use in dental biomechanics is described. It was specially developed to measure force/deflection characteristics of different dental materials and devices. The functionability and suitability of the system for use in experimental biomechanics were investigated in two different studies. In a first study the micro mobility of prosthetic telescopic crowns prior to and after simulated wear was determined to investigate the influence of wear processes on the stability of the anchorage elements and thus of prostheses. This study investigated the ability of the setup to load a specimen with high forces or torques of up to 100 Newton. The second study looked at the force/deflection characteristics of orthodontic anchorage pins used in orthodontics to additionally stabilize the anchorage unit, for example during molar movement. In this study specimens were loaded with small forces of less than 10 Newton, as are typically used in orthodontics. Using the setup, the deflection behaviour of these devices under high and low loading was measured at a resolution of approximately one micrometer or one angular second.

Biomechanical Phenomena↗

PubMed2003

Three-dimensional analysis of endosseous palatal implants and bones after vertical, horizontal, and diagonal force application.

The effects of bite and orthodontic forces exerted on endosseous palatal implants are not completely understood. This applies especially to the biomechanical properties inherent in the different implant geometries and resulting bone remodelling reactions on the one hand, and to the influence on the direction and magnitude of the applied forces on the other. The results of this study should help in the selection of implants for clinical use. Three types of endosseous implants (all 9 mm in length and 3.3 mm in diameter, made of titanium) were used for this investigation. Type 1 was a simple, cylinder-shaped implant; type 2 a cylinder-shaped implant with a superperiosteal step; and type 3 a cylinder-shaped implant, subperiosteally threaded, with a superperiosteal step. The load on the implant was investigated under three conditions of bite and orthodontic forces from 0.01 to 100 N (vertically, horizontally, and diagonally). The study results were calculated by means of a finite element (FE) method. Vertical loading caused bone deformation of more than 600 microeps at the simple implant. The largest deformations at this load were found in the trabecular bone with all three implant geometries. However, trabecular bone deformation was reduced by a superperiosteal step. Horizontal loading of the implants shifted the deformation from the trabecular to the cortical bone. Furthermore, a large deformation was measured at the transition from cortical to trabecular bone. The smallest deformations (less than 300 microeps) were found for implants with a superperiosteal step and diagonal loading (type 2). The use of threads provided no improvement in loading capacity. All implant types investigated showed good biomechanical properties. However, endosseous implants with a superperiosteal step had the best biomechanical properties under low loads. Thus, the trend should be to optimize the design of implants by producing small implants with additional anchorage on the bone surface.

Biomechanical Phenomena↗

PubMed2003

Experimental and numerical determination of initial tooth mobility and material properties of the periodontal ligament in rat molar specimens.

The mechanical parameters of the periodontal ligament (PDL) in rat specimens were investigated in a combined experimental and numerical approach. Tooth mobility of the rat mandibular first molar was measured in vitro using a high precision experimental set-up. Finite element models (FEM) were developed, based on histological sections of the measured specimens, to simulate tooth mobility numerically under the same force systems as used in the experiment. Force/deflection curves from the measurements showed a significant non-linear behaviour of elastic stiffness of the PDL. A bilinear material parameter set was assumed to simulate tooth deflections. The numerical force/deflection curves were fitted to the experimental curves by repeatedly calculating theoretical tooth deflections and varying the parameters describing the non-linearity. Mean values of E1 = 0.15 MPa, E2 = 0.60 MPa and an ultimate strain of epsilon12 = 6.3 per cent were derived for the elastic behaviour of the rat PDL. Comparing fresh specimens and those frozen in a 0.9 per cent saline solution, differences between the measurements were significant. Using the agent, Periston, for freezing significantly reduced the deviation. The results indicated that strains in the PDL with a maximum of 14 per cent at the furcation were 10(4) times higher than strains in the bone, while the variability of stress values in both PDL and bone was not significant.

Alveolar Process↗

PubMed2003

[Simulation of bone strain by orthodontic implants using the finite element method].

Load direction of applied forces, implant geometry and other biomechanical parameters lead to varying reactions in the surrounding bone structure. Three types of endosseous implant measuring 9 mm in length and 3.3 mm in diameter with and without superperiosteal step, and a threaded surface were investigated with the aid of a finite element method using the COSMOS/M 2.5 program. The load on the implant was investigated under vertical, horizontal, and diagonal forces of between 0.01 N and 100 N. Vertical loading of simple implants caused bone deformation of more than 600 mu eps. The application of the superperiosteal step clearly reduced the deformation. The largest deformations under vertical loading were observed in the trabecular bone with all 3 implant geometries. On horizontal loading the deformation shifted from the trabecular to the cortical bone and was particularly marked at the transition between the two. The smallest deformations, less than 300 mu eps, were measured at implants with a superperiosteal step under diagonal loading. The thread did not improve loading capacity. Implants with a superperiosteal step are recommended since they contribute to more rapid healing and strengthening of the bone.

Bone and Bones↗

PubMed2003

[Numerical study of tension and strain distribution around rat molars].

A knowledge of the mechanical processes triggered in the bone and periodontal ligament (PDL) by orthodontic forces applied to a tooth is of decisive importance for an understanding of the subsequent remodelling around the tooth. To investigate these mechanical relationships, three-dimensional finite element (FE) models of the first lower molar in the rat were established. On the basis of digitized serial histological sections, these FE models were generated semi-automatically. Using various simplified geometrical variations, an appropriate FE model for the analysis of the stress and strain distributions was established. The numerical analyses were carried out under a mesially directed force of 0.1 N. Stress distributions in the bone and PDL showed a similar pattern, while strains in the bone were lower than in the PDL by a factor of 10-5. The data confirm the assumption that strain patterns in the PDL may be the key stimulus of bone remodelling.

Animals↗

PubMed2002

Corrosion and permanent fracture resistance of coated and conventional orthodontic wires.

The corrosion processes are presumed to have negative consequences on biocompatibility, aesthetic appearance and the frictional behavior between the bracket and the guiding arch during orthodontic treatment. A group of new guiding arches are the coated orthodontic wires. The present in-vitro study investigated the corrosion behavior and permanent fracture resistance of eight coated wires of different dimensions. Five superelastic nickel titanium (NiTi) wires (Titanol Low Force River Finish Gold and Gold 2: Forestadent Corp.; Titanol Superelastic tooth colored: Forestadent Corp.; Bioforce Sentalloy longuard: GAC Corp.; NiTi Imagination: GAC Corp.), two beta-titanium-wires (TMA Low Friction longuard: Ormco Corp.; TMA Low Friction longuard Purple: Ormco Corp.) and one steel wire (Stainless Steel Imagination: GAC Corp.) were selected. For comparison reasons three uncoated arch wires (Rematitan Lite Dimple: Dentaurum Corp.; Titanol Low Force River Finish: Forestadent Corp.; Bioforce Sentalloy: GAC Corp.) were included in the investigation. Surface modifications were made of teflon, polyethylene and by ion implantation. The corrosion processes have been carried out by the use of a specialized electrochemical cell. In a second experimental series the wires were exposed to mechanical stresses. Finally, all wires were examined in a scanning electron microscope. The results indicated that teflon coating prevented the corrosion of the wires. As expected, the beta-titanium wires did not corrode either. The other wires showed rupture potentials between 187 mV and 602 mV (NHE). After mechanical stress testing the wires could be subdivided into three groups. In the first group no differences could be recognized, the second group showed changes in their crystallographic structure and in the last group the teflon coating was peeled off from the surface of the wires.

Journal Article↗

PubMed2002

[Comparison of mechanical properties of orthodontic nickel-titanium wires].

Two packages each, containing 10 wires per package, of different batches of 25 different types of orthodontic archwires made of super-elastic nickel-titanium alloys measuring 0.41 x 0.56 mm2, were investigated. The wires were characterized by obtaining the following measurements at an ambient temperature of 37 degrees: a three-point bending test with the supporting points spaced 10 mm apart, and determination of the torque/bending angle curves using a pure bending test. The force/deflection curves provided the parameters characterizing the super-elastic unloading plateau: average force, slope and endpoint. From the torque/bending angle curves, the parameters average torque, plateau endpoint and the elasticity parameters were determined. Average force (0.8-4.5 N), endpoint (0.2-0.9 mm) and the slope of the unloading plateau (0.2-2.1 N/mm) of the three-point bending test clearly differed for individual wires. Significant differences were also seen for average torque (1.5-11.5 Nmm), unloading plateau endpoint (2.7-20.0 degrees) and elasticity parameters epsilon 4, E4, E5 and E6 in the pure bending test. Individual batches showed only minor differences. The results permit the conclusion to be drawn that super-elasticity is applicable to only a small portion of the wires examined. Although other wires showed super-elastic behaviour, the unloading plateaus has a force level of up to 6 N, and cannot be recommended for orthodontic application. The super-elastic plateau is often of use only for deflections greater than 1.5 mm. The use of super-elastic archwires made of nickel-titanium alloys makes sense only when the elastic properties of the respective wires are known. This makes the provision by the manufacturer of relevant data on the elastic properties of wires a necessity.

Biomechanical Phenomena↗

PubMed2001

Differences between two transpalatal arch systems upon first-, second-, and third-order bending activation.

Transpalatal arches are used in passive mode to improve anchor-age and in activated mode to achieve single tooth movement or movement of segments of teeth in first-, second- and third-order. Clinically it seems that the commonly used palatal arches of the Goshgarian type (here in the MIA system) as well as the precision TMA lingual arches of the Burstone system are not equally suitable for all kinds of activations. Using the Orthodontic Measurement and Simulation System (OMSS) the force systems and the efficacy of activated arches of both systems were examined in an experimental study with respect to different malpositions. The following first-, second- and third-order activations were chosen: symmetrical expansion and compression up to 4 mm, symmetrical distal rotation up to 15 degrees, unilateral distal tipping of 15 degrees and symmetrical buccal root torque up to 10 degrees. Attachments of the MIA system (MIA Rotation Lingual Sheaths, 0.072" x 0.036") and of the Burstone system (precision lingual hinge cap, 0.032" x 0.032", unused and a pair after a 4-week introral application period) were measured. Lingual arches made of 0.036" round stainless steel wire (MIA) and 0.032" x 0.032" TMA (Burstone system) were prepared with a height of 18 mm and a width of 30 mm. First-order activation bends (expansion and compression) of the MIA palatal arches caused forces up to 4.4 N compared to 1.8 N of the TMA arches, due to the lower load/deflection rate of the latter. The malpositions were corrected effectively by both systems. Due to the higher stiffness the moments delivered by the MIA palatal arches (39 Nmm) were higher in distal rotation compared to those of the TMA arches (14 Nmm) and the correction was more effective. In second-order activations (tipping) the MIA system delivered no or only small moments because of the curved shape of the attachments. A correction of only 30% was achieved compared to 80% with the Burstone system. In third-order activations, in contrast, the Burstone attachments caused considerable loss of torque. This was obviously due to the strong deformation of the slot by the intraoral loading. If it were possible to improve the dimensional stability of the hinge cap, all corrections carried out with the Burstone TMA system would involve distinctly smaller forces and moments than the MIA system but would still ensure good effectiveness.

Activator Appliances↗

PubMed2001

Two- or three-dimensional cast analysis in patients with cleft lip and palate?

AIM: The aim of the present study was to evaluate different two- and three-dimensional cast analyses for the assessment of maxillary dimensions in patients with complete unilateral cleft lip and palate, using a set of representative cast series. PATIENTS AND METHOD: Consecutive casts were taken from ten patients at 1 week, and at 3, 6, and 12 months, respectively. First, cast surfaces were digitized two-dimensionally using a scanner. Subsequently, landmarks were identified on screen and the previously defined maxillary dimensions were determined automatically by computer. Additionally, three-dimensional measurements were carried out using a specialized coordinate measurement table. The differences between the respective measurements were analyzed for statistical significance. RESULTS: The present study shows that the precision of the cast analysis is influenced above all by the quality of the casts and less by the precision of the measuring system employed. Moreover, misinterpretation of the results can be attributed to using an inappropriate reference system or to considering mean values only. When assessing linear and angular measurements located in approximately the same plane, no significant amount of additional information could be obtained by including the third dimension. CONCLUSION: Thus, two-dimensional measurement procedures are appropriate in principle for quick, reliable cast analysis in patients with cleft lip and palate.

Cephalometry↗

PubMed2001

Bone loading pattern around implants in average and atrophic edentulous maxillae: a finite-element analysis.

Introduction: Oral implants placed in the maxilla, especially the posterior region, have a lower success rate than those placed in the mandible. Poor bone quantity and quality have been suggested as a reason for this differential success rate. Objective: The purpose of this study was, therefore, to evaluate stress and strain distributions around loaded implants in the normal and atrophic maxilla by finite-element (FE) analyses. Material: FE models of a solitary implant were generated to determine stresses and strains in the bone adjacent to the implant surface under loading conditions. Study design: Different bony situations and implant lengths were used in a FE model. Static loads were applied axially and the resulting stresses and strains calculated. Results: Bone quality and quantity play a major role in decreasing bone strains adjacent to the implant surface under loading. It was found that stresses were more homogeneously distributed when more spongy bone was present. Decreased bone height was found to have less pronounced effects on strain and stress alterations than poor bone quality. Atrophic bony dimensions in combination with poor bone quality were associated with surface strains exceeding physiological levels (>6000 microstrains). Conclusion: Our investigation indicates that supraphysiological bone strains adjacent to the implant surface should be expected under mechanical loading in the atrophic maxilla. Copyright 2001 European Association for Cranio-Maxillofacial Surgery.

Journal Article↗

PubMed2001

[Planning orthodontic surgery with the Hexapod system].

Treatment of maxillofacial dysgnathia using a combined surgical/orthodontic approach requires careful orthodontic and orthognathic diagnosis and treatment planning. In the present study, a system enabling on-line presentation of the necessary displacements of the jaw during surgery, while improving the accuracy of the planning, is described. Using the hexapod principle, it is possible to plan operations with six degrees of freedom and to measure the three-dimensional movements of jaws and jaw segments within the planning stage. Routinely prepared casts are employed for simulation of the operation. The displacements of the jaw are presented in a manner familiar to the orthodontic surgeon, namely in a surgical record. The accuracy achieved with the hexapod is superior to that achievable intra-operatively.

Computer Simulation↗

PubMed2000

Application of bone remodeling theories in the simulation of orthodontic tooth movements.

A numerical model that calculates bone apposition and resorption around a tooth root on the basis of bone remodeling theories was developed to simulate orthodontic tooth movements. The model was used to calculate different kinds of orthodontic tooth movements, that were then compared with the expected movements based on clinical experience. For simulation of the movements the root of a canine was modeled in an idealized way in the form of an elliptical paraboloid and was processed with a finite element program. The finite element model was loaded with defined force systems. Two model assumptions were used to calculate the bone remodeling process. The mechanical loads firstly in the periodontal ligament and secondly in the alveolar bone were taken to simulate the following tooth movements: 1. mesial tipping around the center of resistance (force system at the bracket: isolated torque MY = 5 Nmm), 2. rotation around the long axis of the tooth (MZ = 5 Nmm), 3. uncontrolled tipping around the root tip (FX = 1 N, MZ = 5 Nmm), 4. canine retraction (FX = 1 N, MY = -9.5 Nmm, MZ = 5 Nmm), 5. and 6. extrusion/intrusion (FZ = +/- 0.5 N, MX = +/- 2.5 Nmm). Comparison with clinical experience was performed by calculating the orthodontic tooth movements based on the assumption of a fixed position of the center of resistance. It could be demonstrated that the numerical model of orthodontic bone remodeling can be used to calculate orthodontic tooth movements. However, the results are strongly dependent on the model assumptions. The model simulating the bone remodeling on the basis of the loading of the periodontal ligament delivers results that are in very good accordance with the biomechanical assumptions of the position of the center of resistance. However, marked side effects occurred with the second model, especially in the simulations of uncontrolled tipping, translation and intrusion/extrusion. Clinically, these side effects cannot be observed.

Bone Remodeling↗

PubMed2000

Construction and testing of a computer-based intraoral laser scanner for determining tooth positions.

An optical set-up for intraoral data acquisition based on the principle of laser triangulation was developed. The system consists of a pig-tailed laser with line generating optics, a stepping motor driven positioning stage, a commercial CCD (charge coupled device) camera system with frame grabber interface, a control personal computer and a mirror system compensating for the fact that there is no possibility of watching an object directly in the mouth under a certain angle except from a facial position during intraoral scanning. Due to the size of the prototype measurements were still restricted to plaster casts. In order to evaluate its accuracy, the measurements were compared with those taken with a commercial laser scanner and a coordinate measurement table. The accuracy of the prototype scanner was determined to be DeltaXYZ=0.04 mm using gauge blocks of given dimensions and proved to range between the commercial laser scanner and the coordinate measurement table (i.e., it was slightly better than that of the commercial scanner). Applications in orthodontics were demonstrated by scanning plaster casts and measuring distances on reconstructed surfaces. The measured distances showed a maximum deviation of about +/-0.2 mm compared with the data of the coordinate measurement table, which served as a reference. In addition, reconstruction of three-dimensional tooth movements was performed on the scan data. The translational and rotational parameters gained from the superimposition of scanned point clouds and describing tooth movement were also in good accordance with the reference. The achieved accuracy proved to be sufficient for further development which should include a reduction in size and the use of more precise device components.

Dental Occlusion↗

PubMed2000

[Semi-automatic generation of finite element meshes fo dental preparations].

The mechanical properties and elastic behaviour of periodontal tissue are a decisive factor in understanding initial tooth mobility and bone remodelling processes in orthodontics. An experimental set-up was designed to precisely determine a tooth's elastic response to different loading conditions. Segments of pig's maxilla bearing separated molars were used, and their mechanical response to loading was recorded. Subsequently, finite element analysis (FEA) was performed on the basis of the experimental data. The combination of experimental and numerical methods was used to determine the material properties of the periodontal ligament (PDL). The geometries of the preparations were reconstructed and FE meshes generated semi-automatically with the aid of the special computer program, CAGOG (Computer Aided Generator for Orthodontic Geometries) to optimally match the experimental geometry. Nonlinear material parameters were determined for the PDL and verified by comparing experimental and numerical results obtained in other specimens with an error of about 10%. This good correlation indicates that the selected method of mesh generation is appropriate for creating realistic FE models that can be compared with experimental results.

Animals↗