Biomedical subjects

Christoph Bourauel

Publications and source records attributed to Christoph Bourauel.

13 recordsLinked to original sources

PubMed2005

Light-cured or chemically cured orthodontic adhesive resins? A selection based on the degree of cure, monomer leaching, and cytotoxicity.

PURPOSE: The purpose of this study was to estimate the degree of cure and monomer leaching of a light-cured and a chemically cured (no-mix) adhesive and to assess their biologic properties. MATERIAL: The degree of cure of adhesive specimens prepared with a procedure identical to the clinical bonding process was assessed by infrared spectroscopy. The adhesives were then immersed in normal saline solution for 2 months, and the residual monomer leached from the adhesives was quantitatively and qualitatively analyzed by liquid chromatography. The effect of the immersion media on human gingival fibroblasts' viability and proliferation was also evaluated with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and deoxyribonucleic acid (DNA) synthesis assays, respectively. The results were analyzed by analysis of variance and Tukey test (alpha = .05). RESULTS: No difference was found between the 2 adhesives with respect to their degree of cure and the amount of triethylene glycol dimethacrylate released; no diglycidyl dimethacrylate monomer was detected in the eluent. However, significant qualitative changes in the composition of the substances eluted from the 2 adhesives were observed. CONCLUSIONS: Whereas no cytotoxic effect was shown for either immersion media, a moderate reduction in the DNA synthesis was obtained by both adhesives, implying a minor cytostatic effect. Further research is required to assess the long-term biologic properties of adhesives, including potential estrogenic action.

Analysis of Variance↗

PubMed2005

Intraoral aging of orthodontic materials: the picture we miss and its clinical relevance.

The purpose of this editorial is to systematically analyze the variety and potency of various aging variables affecting the morphology, structure, and mechanical properties of polymeric and metallic orthodontic materials. The effects of aging on the longevity of the bond strength and mechanotherapy were analyzed: aging-induced plasticization of resin adhesives might lead to bond failure at forces of magnitude lower than those sustained at the initiation of treatment. Standard in vitro methodologies cannot show this effect, and thus laboratory bond strength protocols require modification to become clinically meaningful. Also, the force transferred from an activated archwire to a preadjusted bracket slot, as well as friction during free sliding, seems to be affected by the intraorally induced alteration of materials. Although the effect of intraoral environmental conditions on the superelastic properties of nickel-titanium (Ni-Ti) archwires and coil springs requires further research to establish the true spectrum of effects, it has been suggested that intraoral temperature variations might transiently affect their properties and that the fracture resistance of used Ni-Ti wires is reduced. Clinical implications are discussed for (1) in vivo-aged elastomeric ligatures and chains, which can be postulated to express much higher creep than their in vitro-aged counterparts; (2) the largely unknown effect of aging on the spring component of self-ligated brackets and the associated effect on ligation force; and (3) the intraorally induced alterations in the structural conformation of Invisalign appliances (Align Technology, Santa Clara, Calif). The objective of future research efforts in the field of orthodontic materials should include the development of clinically relevant methodologies. A clear definition of limitations of laboratory experimental configurations might be instrumental in confining the clinical impact of research findings to their actual extent.

Biofilms↗

PubMed2004

Titanium orthodontic brackets: structure, composition, hardness and ionic release.

OBJECTIVES: The aim of the present study was to investigate the composition, morphology, bulk structure and ionic release of two brands of titanium orthodontic brackets: Orthos2 (Ormco, USA) and Rematitan (Dentaurum, Germany). METHODS: Five specimens of each group were examined with computerized X-ray microtomography, to reveal the morphology and structure of brackets, whilst resin-embedded and metallographically polished specimens were subjected to SEM/EDS analysis and Vickers microhardness measurements. Brackets were also maintained in 0.9% saline for 2 months and the ionic release in the immersion medium was determined with Inductively Coupled Plasma Atomic Emission Spectroscopy. The results of the hardness and ionic release measurements were statistically analyzed with two-way ANOVA and Tukey's test (alpha = 0.05). RESULTS: Orthos2 brackets consisted of two parts, the base (commercially pure Ti grade II) and the wing (Ti-6Al-4V alloy), joined together by laser welding, producing large gaps along the base-wing interface. The base was of lower hardness (Hv = 145), than the wing (Hv = 392) and incorporated a standard foil base-mesh pad. Rematitan brackets consisted of commercially pure Ti grade IV, with a single-piece manufacturing pattern of virtually identical hardness (p > 0.05) at the base and wings, featuring a laser-etched base-mesh pad. The hardness of the Rematitan brackets was significantly lower than the hardness of the Orthos2 wings, but double the hardness of the Orthos2 base. Released Ti levels were below the threshold level (1 ng/ml) of analysis for both materials, whilst traces of Al (3 ppm) and V (2 ppm) were found in the immersion media for Ti-6Al-4V alloy. SIGNIFICANCE: The structural and hardness differences found may influence the torque transfer characteristics from activated archwires to the brackets and the crevice corrosion potential at the base-wing interface (Orthos2). The detection of Al and V in the immersion medium (Orthos2) may imply a different biological response from the two types of Ti brackets.

Alloys↗

PubMed2004

Torque capacity of metal and polycarbonate brackets with and without a metal slot.

The aim of the present study was to investigate slot deformation and the equivalent torque capacity of polycarbonate brackets with and without a metal slot in comparison with those of a metal bracket. For this purpose, the expansion characteristics and, in a further investigation, the labial crown torque of an upper central incisor, were measured in a simulated intra-oral clinical situation, using the orthodontic measuring and simulation system (OMSS). Three types of bracket with a 0.018 inch slot were tested: polycarbonate Brillant without a metal slot, Elegance with a metal slot and the metal bracket, Mini-Mono. For testing purposes the brackets were torqued with 0.016 x 0.022 inch (0.41 x 0.56 mm) and 0.018 x 0.022 inch (0.46 x 0.56 mm) ideal stainless steel archwires. In the activating experiments, significantly higher torque losses and lower torquing moments were registered with both rectangular archwires with the polycarbonate brackets than with the metal bracket. In the simulation tests, significantly higher torquing moments were registered with the metal bracket than with the polycarbonate brackets. The values for the Elegance bracket were between those of the Mini-Mono and Brillant brackets. The OMSS model approximates the clinical situation, with the torque loss being notably higher than in the in vitro activating experiments. This is due to the adjacent teeth giving the archwire additional play. In addition, the torquing process may twist the archwire, resulting in subsidiary forces. On the basis of the present results, all three brackets can be recommended for torquing. However, in view of the high torque losses, the torques programmed in the straightwire technique must be seen as questionable. Data should be provided by the manufacturer on the bending to be expected in polycarbonate brackets, which has to be offset by additional torque, or the bracket torque should be omitted from the technical specifications.

Dental Alloys↗

PubMed2004

Correlation of stress and strain profiles and the distribution of osteoclastic cells induced by orthodontic loading in rat.

The aim of this study was to investigate whether stress or strain within the periodontal ligament (PDL), or rather in the bone, plays a role in initiating biological responses in orthodontic tooth movement. The upper first molars of 11 Wistar rats were moved mesially with a closed nickel titanium alloy coil spring for 3-12 d and three rats served as controls. After preparation of the maxillae for paraffin histology, tartrate-resistant acid phosphatase (TRAP) activity was evaluated to detect osteoclasts and their mononuclear precursors in four regions around the mesial root. Based on histological sections, finite element models were developed. The stress/strain distributions associated with the orthodontic loading were determined in the alveolar bone and in the PDL and compared with the osteoclast distributions. In the PDL, the normal stresses and strains were compressive (negative) in regions where the number of osteoclasts was highest, whereas the positive normal tensile stresses and strains were coincident with regions with small numbers of osteoclasts. The results indicate a direct correlation of the calculated stress/strain values in the PDL with the distributions of osteoclasts in the alveolar bone and PDL. Thus, these seem to be the dominant mechanical factor of tissue reaction to orthodontic force application, whereas the mechanical loading of the bone does not seem to play a role in orthodontic bone remodeling.

Acid Phosphatase↗

PubMed2003

Effect of soluble receptors to interleukin-1 and tumor necrosis factor alpha on experimentally induced root resorption in rats.

OBJECTIVE: In this study, the role of the inflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) in the course of mechanically induced root resorption was investigated. METHODS: Mechanical induction of root resorption was performed on the upper left first molars in 18 male Wistar rats according to the method of Nakane and Kameyama. Starting on day minus 1, six animals received daily intraperitoneal injections of 2 ml of 1 micro g/ml soluble receptors to IL-1 (sIL-1RII) and another six animals were administered the same dose of soluble receptors to TNFalpha (sTNFalpha-RI). Six animals served as a control. On d 7 the left maxillae were prepared for histological and morphometric analysis of the extent of the root resorption that had developed. RESULTS: The qualitative and quantitative results demonstrated that in both receptor groups the amount of root resorption was significantly reduced. Especially following systemic application of sTNFalpha-RI, root resorption was nearly completely prevented. CONCLUSIONS: Our results indicate that IL-1 and more particularly TNFalpha are important for the induction and the further process of mechanically induced root resorption in the rat.

Acid Phosphatase↗

PubMed2003

Patterns of maxillary alveolar arch growth changes of infants with unilateral cleft lip and palate: preliminary findings.

OBJECTIVE: Because of significant differences in pathomorphology at birth, it may be that a better treatment outcome prognosis exists for patients with incomplete versus complete cleft forms. Can reaction patterns be extracted from changes in maxillary dimensions of different cleft forms within the first year of life to support this hypothesis? SUBJECTS: Chronologically consecutive casts of the maxilla (1 week and 3, 6, and 12 months of life) of 15 patients with complete unilateral cleft lip and palate (cUCLP) and 13 patients with incomplete unilateral cleft lip and palate (iUCLP). All patients were treated with passive palatal plates. Cheiloplasty was performed at 6 months of age. No primary osteoplastic surgery was carried out. INTERVENTIONS: Following digitizing with a three-dimensional laser scanner, all cast surfaces were computer reconstructed, aligned, and superimposed. Distances between the surfaces were determined and expressed graphically. Computer-aided determination of defined maxillary dimensions was performed. The volumes of segmented surfaces were determined and compared. RESULTS: Within the first year of life, decreased sagittal but increased transverse alveolar growth for patients with iUCLP was found. The increase in alveolar crest length in patients with iUCLP was 50% less within the first year of life than in patients with cUCLP. In the same patients, the volumes of the molar segments were, on average, larger at each registration stage and the increase in these volumes larger within the first year of life. CONCLUSION: Conclusions regarding the direction and extent of growth cannot be drawn from the visible level of severity of the malformation.

Alveolar Process↗

PubMed2002

The frictional behavior of coated guiding archwires.

BACKGROUND: The vast range of orthodontic wires made of different alloys makes it increasingly difficult for orthodontists to judge them. Coated orthodontic wires form a group of innovative guiding archwires. MATERIAL AND METHODS: In the present in vitro study the frictional behavior of eight coated wires of different dimensions was investigated in archwire-guided canine retraction in the upper jaw. For this purpose five superelastic nickel titanium alloy wires (Titanol Low Force River Finish Gold and Gold 2: Forestadent, Pforzheim Germany; Titanol Superelastic tooth colored: Forestadent, Pforzheim Germany; BioForce Sentalloy Ionguard: GAC, Central Islip, NY, USA; NITI Imagination: GAC, Central Islip, NY, USA), two beta-titanium wires (TMA Low Friction Ionguard: Ormco, Glendora, CA, USA; TMA Low Friction Ionguard Purple: Ormco, Glendora, CA, USA), and one steel wire (Stainless steel Imagination: GAC, Central Islip, NY, USA) were selected. The coatings were made of Teflon or polyethylene, and by ion implantation. Three uncoated archwires (Rematitan Lite Dimple: Dentaurum, Pforzheim, German; Titanol Low Force River Finish: Forestadent, Pforzheim, Germany; BioForce Sentalloy: GAC, Central Islip, NY, USA) were used for comparison purposes. The force losses due to friction were measured using the Orthodontic Measurement and Simulation System (OMSS). RESULTS: The results indicated that all coatings can reduce frictional losses compared with an uncoated reference wire by the same manufacturer. Measured frictional losses ranged from 48.3-6.1%, with the Teflon coatings reducing the frictional losses to less than 10% in some cases. CONCLUSION: An unequivocal correlation between the surface roughness and frictional forces of the wires could not be verified by scanning electron microscopy.

Biomechanical Phenomena↗

PubMed2002

Torque capacity of metal and plastic brackets with reference to materials, application, technology and biomechanics.

AIM: The aim of the present study was to investigate slot deformation and the equivalent torque capacity of plastic brackets in comparison with those of a metal bracket in vitro and to simulate them under clinical conditions. MATERIAL AND METHOD: For this purpose the expansion characteristics of the brackets and their resistance to extraoral mechanical loading were compared in in-vitro activating experiments. In a further investigation, the labial crown torque of an upper central incisor was measured in a simulated intraoral clinical situation, using the Orthodontic Measuring and Simulation System (OMSS). Four types of bracket manufactured by Forstadent, Pforzheim, Germany, were tested: the plastic brackets Aesthetik-Line and Brillant, the latter from a previous series (Brillant-old) and from a modified series (Brillant-new), and the metal bracket MINI-MONO. For testing purposes the brackets were torqued with 0.016" x 0.022" (0.41 x 0.56 mm) and 0.018" x 0.022" (0.46 x 0.56 mm) ideal steel archwires (Remanium, Dentaurum, Ispringen, Germany). RESULTS: In the activating experiments, significantly higher torque losses and lower torquing moments were registered with both rectangular archwires with the plastic brackets than with the metal bracket. In the simulation tests, significantly higher torquing moments were registered with the metal bracket than with the plastic brackets. The OMSS model approximates the clinical situation, with the torque loss being notably higher than in the in-vitro activating experiments. This is due to the adjacent teeth giving the archwire additional play. In addition, the torquing process of the rectangular wire may deform the archwire, resulting in subsidiary forces. CONCLUSION: On the basis of the present results, the Brillant and Aesthetik-Line plastic brackets and the MINI-MONO metal bracket can be recommended for torquing. In view of the high torque losses, however, the torques programmed in the straight wire technique must be seen as questionable. It would be helpful to the practitioner if data were provided by the manufacturer on the flexing to be expected in plastic brackets, which has to be offset by additional torque or the possible renunciation of bracket torque.

Biomechanical Phenomena↗

PubMed2002

Determination of the elasticity parameters of the human periodontal ligament and the location of the center of resistance of single-rooted teeth a study of autopsy specimens and their conversion into finite element models.

MATERIAL AND METHODS: The aim of this study was to determine the elasticity parameters of the human periodontal ligament by measuring three-dimensionally the initial buccolingual tooth displacements of eight single-rooted teeth in human jaw specimens, using a noninvasive method. Subsequently the specimens were used to develop finite element models presenting the same individual geometry as the respective autopsy material. These models formed the basis for computerized movement simulations, whose characteristic was brought into line with the experimentally registered movements by adapting the elasticity parameters of the periodontal ligament. Using the individual elasticity parameters determined in this way, with which the displacement of the computer models could be realistically calculated, the centers of resistance of the examined teeth were determined by simulating the effects of different force systems. RESULTS: The nonlinear character of the initial tooth movement could be effectively simulated by using a bilinear parameter set for the elasticity of the periodontal ligament and by determining a critical expansion value for the transition from the validity range of the first Young's modulus to the second. The mean Young's modulus of the first phase of movement was 0.05 MPa, that of the second phase 0.28 MPa, and the critical expansion 7.5% (Poisson's ratio mu = 0.3). The centers of resistance of single-rooted teeth were found to be at approximately 42% of the alveolar height from the alveolar crest to the apex, irrespective of root length and direction of loading. CONCLUSION: The elasticity parameters were found to be on a similar scale to those determined in previous studies on multi-rooted pig teeth.

Biomechanical Phenomena↗

PubMed2002

Integrated magnetic and elastic force systems.

Magnetic force increases as the distance (d) of the force- generating elements (F approximately 1/d(2)) decreases, whereas elastic force decreases as the distance decreases (F approximately kd). These opposing characteristics suggest that combining both force systems will establish an integrated system with a long-range working ability. The objective of this study was to determine the vertical closure force (F(X)) and the transverse axis moment (M(Y)) of an integrated force system, ie, attracting magnets with elastics (vertical or Classes II and III). F(X) and M(Y) were examined on the orthodontic measurement and simulation system. It was found that the integrated force system had a positive closure force (+F(X)) that never declined to 0 and a long working range. Three regions characterized the force-deflection curve of F(X): the magnetic region (0-3 mm, for magnets with 3/16-in medium elastics), in which the decline in magnetic force was larger than the increase in elastic force (6.3-2.5 N); the constant region (3-7 mm), in which the decline in magnetic force equaled the increase in elastic force (2.5-2.9 N); and the elastic region (7-10 mm), in which there was only an increase in elastic force (2.9-3.5 N). The transverse axis moment (+M(Y)), which tends to close the bite, developed especially in magnets with a single vertical elastic. Clinically, inactivation of vertical elastics by closing the mouth can be overruled by the integrated force system because it exerts adequate force level at both short and long distances.

Computer Simulation↗

PubMed2002

Three-dimensional analysis of morphological changes in the maxilla of patients with cleft lip and palate.

OBJECTIVE: Three-dimensional (3-D) morphological changes in the maxilla of patients with cleft lip and palate (CLP) have been recorded, mainly using two-dimensional cast analyses. Although these seem to be insufficient, no standardized 3-D method has been developed until now. In this study, accuracy, precision, and validity of a newly developed 3-D digital computer-aided procedure to visualize and metrically analyze the growth of the edentulous maxilla of infants with CLP have been evaluated. PATIENTS: The method was applied to 10 infants with complete unilateral CLP. INTERVENTIONS: Consecutive casts of the maxilla (1 week and 3, 6, and 12 months) of each patient were optically measured with a 3-D laser scanner. Following digitizing, the casts were computer reconstructed, aligned, and superimposed using specialized computer software. The distances between the surfaces were measured. Additionally, the surfaces were segmented perpendicular to the alveolar crest, the reference points being C1, C1', C2, C2', and I. The volumes of the resulting segments were determined and compared with one another. RESULTS: The newly developed analysis enables a visualization of the extent and direction of morphological changes in the maxilla of infants with CLP. With this method it is possible to quantify these changes of the volume of defined alveolar segments. CONCLUSIONS: The 3-D analysis developed is an ideal tool for the examination of 3-D morphological changes in the edentulous maxilla of patients with CLP. The results will serve as the starting point for a longitudinal study on the efficacy of different methods, not only of presurgical infant orthopedics but also of surgical procedures.

Alveolar Process↗

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↗