Search PubMed⌕ Search

Biomedical subjects

D Drescher

Publications and source records attributed to D Drescher.

At least 19 recordsLinked to original sources
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↗
PubMed1999

Simulation of orthodontic tooth movements. A comparison of numerical models.

Orthodontic tooth movements are based on the ability of bone to react to mechanical stresses with the apposition and resorption of alveolar bone. Currently, the underlying biophysical, biochemical, and cellular processes are the subject of numerous studies. At present, however, an analytical description of orthodontic tooth movements including all components of the processes involved seems to be impossible. It was the aim of the present study to develop a mechanics-based phenomenological model capable of describing the alveolar bone remodeling. Thus, 2 different models were developed. The first is based on the assumption that deformations of the periodontal ligament (PDL) are the key stimulus to starting orthodontic tooth movement. The second supposes that deformations of the alveolar bone are the basis of orthodontic bone remodeling. Both models were integrated into a finite element package calculating stresses, strains and deformations of tooth and tooth supporting structures and from this simulating the movement of the tooth and its alveolus through the bone. Clinically induced canine retractions in 5 patients as well as force systems were exactly measured and the tooth movements were simulated using both models. The results show that the first model allows reliable simulation of orthodontic tooth movements, whereas the second is to be rejected.

Alveolar Process↗
PubMed1999

The influence of bracket design on frictional losses in the bracket/arch wire system.

In arch guided tooth movement, the essential role played by bracket configuration with respect to sliding friction has been recognized by the manufacturers, a fact which has had an increasing impact on the design and marketing of new bracket models in recent years. The aim of the present in-vitro study was to investigate the influence of different bracket designs on sliding mechanics. Five differently shaped stainless steel brackets (Discovery: Dentaurum, Damon SL: A-Company, Synergy: Rocky Mountain Orthodontics, Viazis bracket and Omni Arch appliance: GAC) were compared in the 0.022"-slot system. The Orthodontic Measurement and Simulation System (OMSS) was used to quantify the difference between applied force (NiTi coil spring, 1.0 N) and orthodontically effective force and to determine leveling losses occurring during the sliding process in arch guided tooth movement. Simulated canine retraction was performed using continuous arch wires with the dimensions 0.019" x 0.025" (Standard Steel, Unitek) and 0.020" x 0.020" (Ideal Gold, GAC). Comparison of the brackets revealed friction-induced losses ranging from 20 to 70%, with clear-cut advantages resulting from the newly developed bracket types. However, an increased tendency towards leveling losses in terms of distal rotation (maximum 15 degrees) or buccal root torque (maximum 20 degrees) was recorded, especially with those brackets giving the arch wire increased mobility due to their shaping or lack of ligature wire.

Cuspid↗
PubMed1999

X-ray diagnosis of impacted upper canines in panoramic radiographs and computed tomographs.

Ten orthodontists were asked to diagnose the number of impacted upper canines and the number of resorbed lateral and/or central incisor roots in 30 panoramic radiographs (P1) from 30 patients. In order to objectify these diagnoses, transversal CT images of all 30 patients were examined in addition. Addition of the recordings in the 30 patients revealed that the 10 orthodontists had diagnosed 350 impacted/displaced canines. On comparison of the P1 and CT results, the latter revealed that, in fact, 390 canines were impacted or displaced, not just 350. Addition of the recordings further showed that, based on P1, the investigators had diagnosed 73 resorptions in the 1,200 incisors examined. However, the CT showed 160 resorptions; this corresponds to a sensitivity value of 45.6%. The CT showed 1,040 incisors with no resorptions, whereas the investigators diagnosed only 925 teeth as not resorbed in the P1. The specificity was thus 88.9%. These results show that, due to their low reliability, panoramic radiographs are not an appropriate means of diagnosing resorptions in front teeth in connection with impacted canines.

Adolescent↗
PubMed1999

Corrosion and biocompatibility of orthodontic wires.

With the increasing number of orthodontic treatments using devices containing nickel and the growing prevalence of nickel allergy in the average population, biocompatibility studies of these devices have become a topic of major interest. The corrosion behavior of orthodontic wires is a decisive factor determining their biocompatibility. Therefore four nickel-titanium guiding arches, a titanium-molybdenum and a stainless steel wire were analyzed for corrosion behavior under realistic conditions. Pure potentiostatic, pure mechanical and combined potentiostatic and mechanical stresses were applied to the specimens. Subsequently, the surfaces of the wires were investigated employing atomic force microscopy (AFM) and nickel loss was measured with an atomic absorption spectrophotometer. The results yield information about the relative corrosion tendency of the wires under in vitro conditions. The wires examined can be classified into two groups, one with a high and a second group with a low tendency towards corrosion, that is American Orthodontics Memory wire as well as GAC Neo Sentalloy and Ormco Ni-Ti as well as Unitek Nitinol respectively. Although corrosion behavior under clinical conditions can not be directly derived from these results, analyses of wires after clinical usage indicate that changes of wire surfaces might show the same characteristics under in vitro conditions.

Journal Article↗
PubMed1998

Frictional forces when rectangular guiding arches with varying edge bevel are employed.

In orthodontic treatment employing arch guided tooth movement, rectangular wires are usually used to achieve three-dimensional controlled tooth movement. In the intention to optimize sliding mechanics and to improve the comfort of patients, edge beveled rectangular orthodontic wires are offered by different manufacturers. The objective of the study presented was to investigate the influence of differing but defined wire roundings on sliding mechanics of canine retraction. Employing the 0.018" slot system, 0.016" x 0.022" standard steel wires (Remaloy and Remanium, Dentaurum Comp.) were tested. Force loss due to friction during canine retraction was determined using the Orthodontic Measurement and Simulation System (OMSS). In the arch guided distalization of canines, the average loss of force caused by friction was determined to be approximately 50%. Comparing wires with different edge bevel, the rounded wire in contrast to the wire with sharpest edge configuration results in a reduction of friction. Even a moderate wire rounding of the 0.016" x 0.022" steel wire results in about 10% reduction in frictional losses. However, dynamic analysis of tooth movement with the OMSS shows that there is no further improvement of sliding mechanics using wires with edge bevel exceeding the standard rounding of rectangular wires. In contrast, a strong edge bevel may result in a considerable loss of leveling.

Cuspid↗
PubMed1998

Assessment of the space for the lower wisdom teeth. Panoramic radiography in comparison with computed tomography.

From 13 patients a computed tomograph (CT-scan) and a panoramic radiograph (Orthophos, program 1, P1) were examined with respect to the spatial conditions of the lower wisdom teeth. In the panoramic radiograph the available space for the third molars of the lower jaw was determined by calculating the ratio (Q) of 2 distances: the mesiodistal crown diameter and the retromolar space. In the axial CT 3 different positions of the third molar were distinguished: third molar located anterior to the ramus mandibulae = sufficient space, partially within the ramus = restricted space, totally within the ramus = deficient space. These positions were compared with the findings in the panoramic radiograph, firstly in relation to the ramus and secondly in relation to a line (L) perpendicular to the occlusal plane at the intersection of the anterior border of the ramus and the crista temporalis. Furthermore, the mesial rotation of the third molar was measured and the relation of the bony structures surrounding the teeth were described. Comparison of the CT results with the quotients of the P1 showed that, for those wisdom teeth molars with an available space above 50% to under 100%, any of the 3 CT gradings was found. Assessing the projection of the ramus over the third molar as seen in the P1, 60% of the P1- and CT-results corresponded. The relation between the line L and the third molar showed coincidence in 76% of all cases. These results and the mesial rotation of the wisdom teeth as well as their different relation to the bony environment are possibly important factors concerning their eruption prognosis. The three-dimensional CT-scan gives new possibilities for further investigations of third-molar problems.

Adolescent↗
PubMed1998

In vitro analysis of the initial tooth mobility in a novel optomechanical set-up.

An optomechanical set-up was developed to accurately measure displacement/force curves of the initial tooth mobility in vitro. The system presented is capable of recording all six components of a tooth movement resulting from an applied orthodontic force system, and consists of a laser diode-based optical part and a six degree of freedom mechanical part. Three laser diodes were mounted in orthogonal arrangement on the tooth of a specimen and their light (lambda = 670 nm) was focused on the surfaces of three position sensing detectors. The laser beams thus defined a cartesian rigid body coordinate system and the movements of the tooth could directly be derived from the movements of the laser spots on the surfaces of the optical detectors. The force system was applied and simultaneously measured via a three-dimensional force-torque transducer mounted on a six-axis positioning table. Measuring accuracy of the tooth displacements was in the range of 9.0 microns and 0.022 deg for translations and rotations, respectively. Resolution and accuracy of the mechanical system was approx. 0.02 N for the measurement of forces and 0.5 Nmm for torques. Displacement/force diagrams of the specimen of a swine's mandible are presented, showing the relationships between applied force system and tooth displacement of the lower first premolar. The accuracy reached proved to be sufficient for the verification of numerical (Finite Element) models of the initial tooth mobility.

Alveolar Process↗
PubMed1998

Surface roughness of orthodontic wires via atomic force microscopy, laser specular reflectance, and profilometry.

The surface roughness of orthodontic archwires is an essential factor that determines the effectiveness of arch-guided tooth movement. Using the non-destructive techniques of atomic force microscopy (AFM) and of laser specular reflectance, the surface roughness of 11 nickel-titanium orthodontic wires, a stainless steel and a beta-titanium wire was measured. The results were compared with those obtained using surface profilometry. The smoothest wire, stainless steel, had an optical roughness of 0.10 micron, compared with 0.09 micron from AFM and 0.06 from profilometry. The surface roughness for the beta-titanium wire measured by all three methods was approximately 0.21 micron, while that of the NiTi wires ranged from 0.10 to 1.30 microns. As the surface roughness not only affects the effectiveness of sliding mechanics, but also the corrosion behaviour and the aesthetics of orthodontic components, the manufacturers of orthodontic wires should make an effort to improve the surface quality of their products.

Corrosion↗
PubMed1997

Superelastic nickel titanium alloy retraction springs--an experimental investigation of force systems.

The purpose of the present investigation was to study the mechanical characteristics of canine retraction springs made of superelastic nickel titanium (NiTi) alloys. A modified Burstone T-loop was used to construct an experimental canine retraction spring 10 mm in height and 10 mm in length. Twenty-five NiTi T-segments were hand made from the superelastic orthodontic alloys Ormco NiTi and Soar Sentalloy (dimensions 0.016 x 0.022"). The T-segments were equipped with arms made of rectangular standard steel wire (0.017 x 0.025"). The following geometrical and mechanical parameters of the retraction springs were analysed: radius and bending angles of the T-segments, distalizing force and M/F ratio during activation and the force/deflection rate of the springs. The error in the geometric parameters was in the range of 5-10 per cent, irrespective of the alloy used to produce the T-segments. On the other hand, the force systems of the springs were strongly influenced by the alloy and the batch under investigation. There were differences in the distalizing force of up to 100 per cent, i.e. at the beginning of the unloading plateau the distalizing force varied from 0.4 to 2.5 N. The force/deflection rate varied between a value of 0.06 and 0.15 N/mm, whereas the moment/force ratio reached values of 6.5-7.0 mm. Within a single batch, a reproducibility of these mechanical properties of approximately 5 per cent could be obtained. These results confirm that each orthodontic device made of superelastic NiTi alloys has to be calibrated individually. The manufacturers should pay more attention to keeping the material properties of their NiTi alloys constant.

Calibration↗
PubMed1996

Analysis of forces and moments in arch guided molar protraction using Class I and Class II elastics. An in-vitro study.

The use of class I and II elastics in arch guided tooth movement of the lower molars belongs to the proven clinical methods to achieve space closure even though risks are present. The vertical force component of class II elastics tends to interact with the sagittal force and thus the vertical force may change the desired sagittal force and movement direction. The objective of the study presented here was to investigate friction behavior and the movement dynamics of the arch guided protraction of the lower first molar being acted on by differing class I and class II elastic band geometries. The influence of class I and class II elastics at different force levels (1 N and 2 N) were studied. The pattern of the force line varied in the area of angulation from 0 degree to 40 degrees relative to the arch plane. The orthodontic measurement and simulation system (OMSS) was employed to determine force loss due to friction and to analyze side effects. In the arch guided mesialization of the lower first molar, the vertical component of class II elastics induces a minor force loss in comparison with class I elastics. This holds, however, only for the lower 1 N force level. When employing class II bands at a greater force level and with increased angulation, relatively greater force loss and increased side effects, such as extrusion and mesial tipping of the first molar, occur.

Biomechanical Phenomena↗
PubMed1995

[The effect of molar position on the distalization behavior of indirect headgear].

The asymmetric indirect headgear is a frequently used method to achieve an unilateral distalization of a molar. Cases have been observed, however, in which the distalization does not proceed in the way or to the degree predicated by the geometry of the outer bow. Among other factors, this discrepancy can be attributed to the geometry of the inner bow. This study demonstrates quantitatively and qualitatively the influence unilateral mesial movement and/or molar rotation exerts on the force system of the indirect headgear. The study makes evident that a neutralization of the molar's sagittal asymmetrical position by means of adjusting the length of the inner bow cannot be omitted. The study recommends the use of special headgear tubes extended in an oro-vestibular direction to eliminate the asymmetrical dynamics which arise in cause of the mesial rotation of a molar.

Biomechanical Phenomena↗
PubMed1995

[Incisor roots in the mandibular symphysis in the computed tomogram and in the lateral teleradiogram].

On the basis of lateral cephalograms and computer tomograms (CT) the position of the incisor roots and the bone structure surrounding them were studied. Nine patients each had an axial CT of the mandibular symphysis area and, in addition, 6 of these patients had lateral cephalograms. In order to compare both images, we defined a classification scheme as follows: Class 1 = the incisor roots are projected into the midst of the oral corticalis of the symphysis; class 2 = the roots are in contact with the oral corticalis; class 3 = the incisor roots are at a distance to the oral corticalis. The results from the 2 types of visualization were then compared. When looking at the bone structures surrounding the incisor roots, the lateral cephalograms failed to yield an exact differentiation. Such details can be best examined in the axial CT layers, because in the lateral cephalogram the 4 incisor roots are over projected to 1 root. The space for movement of the incisors is narrow. The root of each and every patient showed a different position in oro-buccal direction. This fact must be taken into consideration in clinical practice, especially when employing fixed appliances with 3-dimensional root control.

Evaluation Studies as Topic↗
PubMed1995

[The mobility of the anterior teeth after the direct bonding of lingual retainers. A comparison of in-vitro and in-vivo measurements].

Lingual retainers are today widely used in the long-term stabilization of incisors. In that they are left in place for a period of years, the question arises to what extent lingual retainers allow sufficient physiological movement. To answer this question first an in-vitro study of the inflexibility of various retainers under horizontal and vertical load was carried out. Next the retainer which limited physiological movement to the least degree was studied in-vivo. Both dynamic and static mobility measurements of the lower jaw front teeth were carried out on 5 patients before and after bonding the retainers. A self developed measuring instrument was used to make the static measurements and a periotest device was employed in the dynamic measurements. The in-vitro tests indicated that, with the exception of the retainer made of multistranded 0.0155" wire or glass fiber, a significant reduction in tooth mobility can be expected with all the retainers. However, the static in-vivo measurement carried out with the 0.0155" wire resulted in a distinct reduction in tooth movement. The dynamic measurements using the periotest device confirmed this finding. With regard to clinical practice within the framework of long-term retention, highly flexible retainers appear to be the most suitable and are to be recommended.

Cuspid↗