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Biomedical subjects

R R Miethke

Publications and source records attributed to R R Miethke.

At least 37 records · Page 2Linked to original sources
PubMed1993

[A FEM study for the biomechanical comparison of labial and palatal force application on the upper incisors. Finite element method].

The present study was designed to compare the biomechanical response of upper incisors to labial and lingual force applications. A three-dimensional finite element model was developed to analyze tooth displacement and stress distribution in the periodontal ligament. Lingually and apically directed forces of 1 N were applied at one point on the labial and at three points on the lingual surface of the crown. Tooth displacement and stress distribution resulting from lingual force applications were compared with those from the labial side. The following results were obtained: 1. Lingual horizontal forces produced similar patterns of tooth displacement and stress distribution, irrespective of the point of application (labial--lingual). 2. Apically directed vertical forces applied at the lingual points produced more uniform tooth displacements and stress distributions, although the force applied on the lingual side close to the CEJ, which happened to be most distant from the tooth's long axis, generated a pattern of movement somewhat different from the remaining two lingual force applications. The present results suggest the crucial role of the positional relation between the long axis of the tooth, respectively the center of resistance, and the point of force application. It can be deduced that lingual force application may produce more optimal tooth movement in terms of intrusion and subsequent stress distributions in the periodontal ligament.

Biomechanical Phenomena↗
PubMed1993

[An in-vitro study on improving the bonding strength of steel bands with the use of glass ionomer cements].

An in-vitro investigation was carried out with the aim of improving bond strength at the glass-ionomer cement/stainless steel interface, thus reducing loosening rates. In bovine incisors it had previously been shown that the week point is the glass-ionomer cement/stainless steel, rather than the enamel/glass-ionomer cement interface. In a simple, standardized experimental set-up permitting reproducible measurements, the semi-flexible and irregularly shaped orthodontic bands were replaced by solid stainless steel cylinders made of the same alloy, and both shear and tensile bond strength were measured. Using this set-up, five different types of surface preparation were compared in terms of their bond strength. The highest bond strength was found to be associated with a steel surface sandblasted with coarse aluminium oxide. In further experiments, the devices provided by the manufacturer for dosing powder and liquid were found to be quite inaccurate. This is particularly unfortunate, since the bonding properties of the glass-ionomer cement investigated proved to vary significantly with small variations in the powder:liquid ratio. To reduce the rate of loosening of orthodontic bands, the cement should be mixed at refrigerator temperature, using capsules filled by the manufacturer with the optimal dosages, and then used with bands previously sandblasted with coarse aluminium oxide powder.

Animals↗
PubMed1993

[The integration of a computer learning program for x-ray cephalometric analysis into student training].

A computer program was written for teaching undergraduate students definitions and localizations of reference points on cephalometric X-rays. The efficacy of the program as a teaching method was tested by comparing two junior/sophomore groups. While one group attended a conventional lecture for an hour, the other worked with the computer program for the same length of time. Prior to and immediately after instruction by the two methods each group marked reference points on various cephalometric tracings, which were then compared for accuracy. The result was that the students who worked with the computer marked significantly more reference points correctly than their counterparts who attended the lecture. 80% of the students belonging to the group which used the computer judged the program to be a positive educational experience. Such computer training proved to be an efficient tool for teaching students simple facts which require memorization and, equally important, the use of such educational aids. At the same time frees the instructors to dedicate more of their time to teaching more complicated and complex subject matters. A further benefit of the training program described in this article is that it can also be used to train chairside orthodontic assistants in private orthodontic practices.

Cephalometry↗
PubMed1992

[The tensile strength of bracket adhesives depending on the adhesive layer thickness--an in-vitro study].

The purpose of this study was to determine the influence of the thickness of the adhesive layer between bracket base and enamel surface on tensile bond strength. Stainless steel brackets with retentive net bases were bonded to bovine incisors with adhesive layers varying in thickness from a minimum of 0.0 mm to a maximum of 0.8 mm. Eight different orthodontic adhesives were investigated; in order to simulate the procedure of indirect bonding, combinations of two different adhesives were also tested. It was found that the highly filled composites provided greatest bond strength. Increasing the thickness of the adhesive layer had no significant influence on tensile bond strength. In the case of light-cured composites, maximum tensile bond strength was achieved at a thickness of the adhesive layer of 0.2 mm. This is probably due to better penetration of light at this thickness. In the case of chemically curing no-mix adhesives, it was impossible to produce effective adhesive layers thicker than 0.2 mm, presumably because curing at the primer paste interface becomes a problem at greater thickness. The influence of cement thickness on tensile bond strength was basically identical whether brackets were bonded with one or two adhesives. Thus, an additional adhesive-adhesive interface has no influence on bond strength. If adhesive layer thickness of more than 0.2 mm are required, a chemically cured, highly filled paste-paste system should be used.

Animals↗
PubMed1992

Histologic investigation of the human pulp after thermodebonding of metal and ceramic brackets.

Twenty-five human permanent teeth scheduled for extraction for orthodontic reasons were used to study the effect of thermodebonding on the pulp tissue. One week before brackets were removed the teeth were bonded with either metal or ceramic brackets, with two alternative adhesives. For debonding, three different techniques were used: (1) debonding of ceramic brackets warmed up indirectly by resistance heating of a metallic bow applied to the bracket slot, (2) debonding of metal brackets warmed up directly by inductive heating of the bracket itself, and (3) debonding of ceramic brackets warmed up indirectly by inductive heating of metallic plier tips, applied to the mesial and distal bracket surfaces. Teeth with metal brackets removed without heat by squeezing the wings together served as a control group. The teeth were extracted 24 hours after debonding and subjected to a light microscopic study after histologic preparation and staining. In addition, the location of adhesive remnants was evaluated. While the thermodebonding of metal brackets worked properly and without any obvious pulp damage, there were problems related to the thermodebonding of ceramic brackets: (1) if more than one heating cycle was necessary, several teeth showed localized damage of the pulp with slight infiltration of inflammatory cells, (2) bracket fractures occurred frequently, and enamel damage could be shown, and (3) often with Transbond (Unitek/3M, Monrovia, Calif.) as the adhesive, more than one heating cycle was necessary for bracket removal, and thus patients complained about pain.

Adolescent↗
PubMed1991

[The effect of physiological tooth mobility on the friction between the bracket and the arch].

This study compared frictional forces which occurred in vivo and in vitro. A testing device was used which allowed reproduction of friction measurements carried out on upper central incisors of volunteers under laboratory conditions with the bracket fixed immovable. By this means changes of friction due to physiological tooth mobility and occlusal load of the bonded teeth could be investigated. While the friction measured in vitro with immovable brackets and in vivo without occlusal load did not differ significantly, additional tooth movement by occlusal load resulted in significant reduction of friction magnitude. It should be kept in mind that the mobility of those teeth investigated was absolutely normal, while it is usually increased during orthodontic treatment. Due to this effect and influences resulting from chewing various kinds of food, it can be estimated that the frictional forces occurring with orthodontic treatment are even smaller in comparison to in vitro experiments with immovable brackets.

Biophysical Phenomena↗
PubMed1991

[Usefulness of the sum angle according to Björk (Jarabak)].

The term sumangle (SA) according to Björk has been attributed in the literature to Jarabak. The term was not used by Björk in his original works. Because of the demonstrated relations the sumangle can be deducted from the simplified calculation SA = X + 360 degrees, whereby X is the angle between the reference lines NS-ML. Beside from this fact also the high unreliability of defining the necessary reference points makes the sumangle a questionable measurement of vertical skeletal development. Therefore other trigonometric parameters as for instance the Y-axis are preferable.

Cephalometry↗
PubMed1991

[Protraction--it's use and abuse].

1. Protraction devices can be used to close excess spaces by moving posterior teeth forward, to protract maxillas, to rotate arch segments in cleft palate patients and to remove hyper anterior contacts in patients with TMJ derangements. 2. There are three types of protraction headgears: Chin support with cranial straps (Hickham), chin support with a forehead pad (Face mask) and zygoma support with a headband (Suborbital). They all have specific advantages and disadvantages. 3. The force magnitude from a protraction gear varies according to the desired effect from between app. 400 grams/side to move the maxillary anterior teeth forward and 800 grams/side to encourage maxillary sutural expansion. 4. The centers of rotation of the jaws and the dentition are located apically to the attachment of the protraction device. Therefore not only the intended mesially oriented force is produced but also the undesired side effect of both jaws moving around their centers of rotation. To avoid these negative effects the protraction elastics should always leave the arch in the canine area. 5. Basically Class III cases are due to either a short maxilla and/or a long mandible with variations in the vertical. App. 60% of all Class III cases have a short maxilla indicating the need for protraction. About 50% of the total Class III patient population would need surgery to finish with an ideal occlusion. However, many types of compromise treatments can be acceptable. 6. A good occlusion can only be accomplished in the presence of normal function. In Class III patients special attention should be given to possible nasal obstruction as well as to tongue posture and function. ENT cooperation and tongue spikes are often necessary to resolve these problems. 7. Class III elastics tend to rotate the maxilla and mandible counterclockwise. The resulting change in molar relationship is only due to the rotation of the occlusal plane which is unstable. Also because of the extrusional side effect there is an increase in vertical dimension which usually is undesirable. 8. Intraorally the protraction device can either be attached to a bonded acrylic expansion appliance or to a cemented Hyrax depending on the developmental stage of the dentition. To avoid traumatic occlusion conditions a modified splint should be used with the protraction gear in adults. 9. In all growing Class III patients overcorrection of overjet and overbite is very important. This way not only possible relapse is prevented but also the change of a posteriorly displaced mandible is avoided which could be a later cause for TMJ derangement. 10. When deciding whether the deformity is in the maxilla or in the mandible--the individualized Jacobson templates are very helpful.

Adolescent↗
PubMed1991

[Acceptance of headgear in children and teenagers].

This survey may provide a starting point for the improvement of the acceptability of headgears for children and teenagers during orthodontic treatment by taking aesthetic and material factors into consideration when selecting these appliances. The extent to which these findings are allowed to influence the planning of future treatment must be decided on an individual base; it is to be expected that such considerations will contribute both to the success of therapeutic aims and a reduction of costs in orthodontics.

Adolescent↗
PubMed1990

[Indication and effectiveness of the J-hook headgear].

In this article the three most important types of J-hook headgears, the horizontalpull, the high-pull and the verticalpull are demonstrated. Indications of these headgearsamples are the (asymmetrical) retraction of teeth and groups of teeth, intrusion of anterior teeth including a very effective support of torque control, inhibition of horizontal and vertical growth of maxilla and mandible, compensation of side effects of Class I and Class III rubberbands, midline-corrections and retention following surgical correction of open bites. The headgear force can either be distributed directly on the teeth to be moved, on hooks which are soldered on the archwire, on chin caps or mandibular troughs resp. on functional appliances. The advantages of the J-hook headgear are an excellent control of anchorage, the variability (primarily of the vector of forces), but also a consistency after having established the assigned force vector, a consistency which also includes the amount of choosen force. Further advantageous is the simultaneous retraction of teeth in both arches as is the easy and safe handling of this headgear by patients and by the orthodontic team. In contrast to these outstanding advantages there are only very few disadvantages. These have mainly to be seen in a tendency of dental arch expansion and the rare occurrence of certain pressure induced problems in the soft tissues of the skull. In the first case a constriction of the archwire and even more a transpalatal arch will help to prevent this from happening. In the second case the best counter measure is the use of accessory soft pads.

Adolescent↗
PubMed1989

[Materials properties of zinc phosphate cements after delayed setting on refrigerated slabs].

Two of the zinc phosphate cements commonly used in orthodontics were mixed, with special attention being paid to the longest possible working time, and examined by scientific methods. The results showed that mixing should generally be carried out on frozen slabs (-18 degrees C to -24 degrees C) and for not longer than 5 min. If a maximum compressive strength is required, mixing should be done at refrigerator temperature (+4 degrees C to +8 degrees C) for no more than 1.5 min by accepting a shorter working time. Neither cement shows any notable physicochemical differences, as regards the material.

Chemical Phenomena↗
PubMed1988

Correlations between lower incisor crowding and lower incisor position and lateral craniofacial morphology.

Crowding of the lower incisors is a problem encountered frequently in orthodontic practice. Successful therapy may depend on the orthodontist's ability to evaluate factors contributing to the overall pattern. Two of these factors, vertical skeletal morphology and lower incisor position in the lateral cephalogram, were evaluated. Dental casts and cephalograms of 100 children with primary mandibular incisor crowding (that is, primary discrepancy between mesiodistal tooth width and available space of the dental alveolar process and apical base) were examined in this study. Results indicated the following: (1) all vertical skeletal and lower incisor position measurements closely duplicated published norms, (2) no correlation was found between lower incisor crowding and either skeletal morphology or lower incisor position, (3) a factor analysis did demonstrate, however, that other selected variables were interrelated, and (4) the cause of lower incisor crowding must be attributed to factors not examined in this study.

Cephalometry↗