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Biomedical subjects

W Harzer

Publications and source records attributed to W Harzer.

At least 37 records · Page 2Linked to original sources
PubMed1999

Biomechanical analysis of arch-guided molar distalization when employing superelastic NiTi coil springs.

Two typical treatment situations (distalization of a last molar, distalization of a molar with the guiding arch fixed on the most distal abutment tooth) were simulated experimentally using the Orthodontic Measurement and Simulation System (OMSS). For this purpose an upper first molar was guided along steel arches with differing cross sections (0.016" x 0.022"/0.41 mm x 0.56 mm; 0.017" x 0.025"/0.43 mm x 0.64 mm) using a nickel-titanium (NiTi) compression spring. The 6 NiTi springs investigated differed in their design and in the type of force delivery. The force application that was eccentric with respect to the center of resistance caused a conflict situation between the tube and the guiding arch through rotations of the molar. Although the force level of the springs was almost constant, the orthodontically effective forces measured fluctuated due to frictional losses. With progressing distalization the mean frictional forces increased, reaching values between 50 and 80% of the applied force of the compression springs. Simultaneously fluctuations in the frictional losses increased. Lower frictional losses were determined with a 0.016" x 0.022", than with a 0.017" x 0.025" guiding arch. Fixing the arch on the 3rd molar resulted in higher frictional losses compared to the distalization of a last molar. There were intensive interactions of the compression springs with the guiding arch and the tube. This resulted in extreme frictional losses even in the initial phase of the movement and in a complete stop to the distalizing movement in extreme cases. After removal of the convertible, the freedom of the molar movement could be regulated by the tension of the ligature wire. The friction varied accordingly. The distalization rate was not influenced by the force delivered by the compression spring. Small forces are biologically more favorable and thus should be preferred.

Analysis of Variance↗
PubMed1999

Laboratory analysis of superelastic NiTi compression springs.

The force/compression characteristics of 32 commercially available nickel titanium (NiTi) compression springs from seven distributors were investigated in vitro in order to support the orthodontist in deciding to select an appropriate spring for a given treatment. The geometrical properties of the coil springs, i.e., inner spring diameter, winding diameter and winding configuration, differed significantly, as well as the alloy composition and the thermo-mechanical treatment of the springs. All springs were mounted on a guiding rod made of an orthodontic steel wire (dimension: 0.016" x 0.022"), were compressed to a maximum extent and then relieved. Force/compression characteristics were measured at ambient temperatures of 27 degrees C, 37 degrees C and 47 degrees C. Three specimens were taken from each individual compression spring of a certain manufacturer and batch to check for constant material behaviour. A possible influence of sterilization on the mechanical properties of the compression springs was studied by autoclaving one spring of each manufacturer five times (6 minutes at 134 degrees C) and subsequently performing a force/deflection measurement. The NiTi compression springs were classified into three groups and covered a broad range of orthodontic forces between 0.5 N and 3.5 N. The width of the superelastic plateaus of the different NiTi coil springs reached from 0% to 66% of relative compression. An increase in the application temperature from 27 degrees C to 47 degrees C caused a rise in the height and a shortening of the width of the superelastic plateau. The resultant change in plateau force was as high as 0.4 N to 0.9 N, depending on the spring type investigated, the width of the plateaus was shortened by 4.0% to 15% of relative compression. All compression springs investigated displayed constant material behaviour within a certain batch. However, differences from one batch to another had a high level of significance. Forces on the plateau varied from one batch to the other by about +/-18%. An influence of sterilization on the force/compression behaviour could not be proved. Consequently, springs made of superelastic NiTi alloys cover a broad field of application with predefined and nearly constant force levels.

Analysis of Variance↗
PubMed1998

[Biomechanical analysis of arch-guided molar distalization with super-elastic nickel-titanium springs].

The typical characteristics of orthodontic devices and their effectiveness during tooth movement are of major importance for the success of orthodontic treatment and the stability of the result. To investigate this situation, two typical tooth movements were simulated experimentally using an Orthodontic Measurement and Simulation System (OMSS). These were Distalisation of an upper last molar and Distalisation of a molar including fixation of the guiding arch to a distal supporting last molar. The movements were simulated by employing various different NiTi coil compression springs and two standard steel guiding arches with the dimensions 0.016" x 0.022" and 0.017" x 0.025". The six NiTi springs differed significantly in shape and force characteristics. The eccentric application of the orthodontic force system relative to the centre of resistance brings about a tilting of the tube and arch via molar rotation. Although the forces developed by the springs are relatively constant, frictional losses result in variations in the effective orthodontic forces. With progressive distalisation, the average frictional losses varied between 50% and 80% of the spring-generated force, and frictional variations increased. Lower frictional losses were seen with a 0.016" x 0.022" guiding arch as compared with one measuring 0.017" x 0.025". In comparison with distalisation of a last molar, fixation of the arch to a third molar was associated with higher frictional losses. The interaction of the springs with the tube-guiding arch system could be so powerful that frictional losses were detected already during the initial phase of movement, and in extreme cases led to cessation of distalisation. The rate of distalisation was not affected by the forces generated by the springs. For physiological reasons, therefore, springs developing smaller forces should be used preferentially.

Biomechanical Phenomena↗
PubMed1997

Premolar child-to-parent grafting within the framework of orthodontic serial extraction.

While allografting of human teeth holds all the risks and problems of immunological reactions or host-versus-graft reactions encountered in any organ transplantation, root resorption and thus the loss of the grafted tooth may be delayed by several decades if the transfer is between close relatives and minimum histocompatibility is 50%. In 2 cases premolars with incomplete root growth, which had to be extracted because of considerable crowding, were transplanted from child to mother and child to father, respectively. The grafts healed without complications and after a retention time of several weeks the teeth were attached. Three years after transplantation the teeth show only minor signs of root resorption and are fully functional.

Adult↗
PubMed1997

Comparative study of excitation patterns in the masseter muscle before and after orthognathic surgery.

This study was designed to inquire into changes occurring in the electromyographic activity throughout the masseter muscle after orthognathic surgical treatment of various bite anomalies. A total of 32 adult patients showing distinct class II (n = 15) or class III malocclusions (n = 17) were entered into the investigation. All patients had monopolar surface electromyograms of the masseter muscle taken prior to presurgical orthodontic treatment and after removal of their orthodontic appliances after surgery. Twenty eugnathic adult patients served as controls. Unlike bipolar lead readings, simultaneous sampling from 16 electrodes permits the registration of the overall excitation pattern in the entire muscle. Recordings were taken during clenching, chewing and protrusion of the lower jaw against a defined force. Comparison with preoperative EMGs proved postsurgical distribution of excitation in class 11 patients to approximate the excitation pattern of eugnathic patients. By contrast, correction in class III malocclusions produced a shift in excitation maxima in the sense of a cranial advance. Harmonization, as evident in class II patients, did not occur. The postoperative discords in masseter excitation patterns, as observed after correction of class III anomalies, are indicative of the risk of relapse and the prolonged phase of retention associated with these conditions.

Adult↗
PubMed1996

Indications for compensatory extractions in orthodontic space closure in the frontal segments.

This follow-up study presents patients who underwent orthodontic space closure in the maxilla after traumatic loss of frontal teeth or aplasia of a lateral incisor. Comparison covers findings obtained from casts and cephalograms in 24 patients with or without compensatory extraction. The findings indicate that acceptable results regarding axial tooth positioning and profile can be obtained without compensatory extraction. Prerequisites are distal occlusion of the first molars by one premolar width and continuous monitoring for regular overbite and uncrowded lower incisors. If orthodontic space closure can be achieved only by compensatory extraction, the indication for this space closure procedure calls for even more critical judgement.

Bicuspid↗
PubMed1996

Facial structure and functional findings in patients with progressive muscular dystrophy (Duchenne).

The investigation of 15 patients who have a progressive muscular dystrophy of the Duchenne type (PMD) shows the affection of various groups of muscles of the stomatognathic system, studied by means of electromyography and mechanical force measurements. We observed the following deviations in patients with PMD; transversal overdevelopment and sagittal shortening of the dental arch; reduction of overbite and overjet; sagittal underdevelopment of the cranial, maxillary and mandibular base; retrusion of incisors; concave profile; increase in bizygomatic width; and a difference in time between the attack on the musculi orbicularis oris and that on masticatory muscles. In our study, the activity of the jaw muscles diminished 2 years earlier compared with the perioral muscles. This, and also the enlargement of the hypotonic tongue, causes a transversal expansion of skull and dental arches. This expansion was strongly pronounced in the lower jaw; we invariably observed a posterior crossbite. In contrast to the transversal overdevelopment, we observed a sagittal underdevelopment of skeletal and dental parameters, as well as a retrusion of the incisors. The results of surface electromyography showed the affection of the masseter muscle in patients who had PMD. By means of the Fast-Fourier transformation, we observed a displacement of the median frequency as compared with the lower frequency range.

Adolescent↗
PubMed1995

[The dental and skeletal changes in early Class II treatment with a Klammt open activator].

In order to evaluate the initiation of treatment of Angle class II malocclusion at an early age, seventy-six patients, 34 girls aged on average 10.1 years and 42 boys, average age 11.3 years, were selected for the study. For the treatment we used the Klammt open activator. For evaluation purposes we used casts and cephalograms taken before and after treatment. The results showed distinctive differences between Angle class II/1 and II/2. The sagittal correction in class II/1 was a result of the reduction of the SNA angle, the mandibular protrusion, and the retrusion of the upper incisors. The face high index was normalized. No labial inclination of the lower incisors was registered. In the Angle class II/2 cases the SNA angle was unchanged. The sagittal correction was brought about exclusively through mandibular translation. The deep bite and the retrusion of the upper incisors weren't markedly improved. The lower incisors showed a labial tip. The incisor angle was unchanged. Our study showed that the ANB reduction on an annual basis is highest, when treatment is initiated at an age of 10 to 11 years for girls and 12 years for boys. On the growth curve this is a point in time below the accelerated growth phase of puberty.

Activator Appliances↗
PubMed1995

[The relationships between the EMG excitation pattern of the masseter muscle and the facial skeletal morphology].

The purpose of this study was to investigate the correlations between malocclusions and the electromyographic activity of the orofacial muscles as this activity reveals itself through multi-channel, simultaneous recording of surface potentials from the masseter muscle. Thirty adults with class II or class III malocclusion formed the study's patient base. Surgical correction of the anomaly was planned for all patients. Ten patients served as the control group. In addition to the standard diagnosis, EMG were recorded during various stress situations such as maximal intercuspidations, chewing, swallowing, and mandible protrusion. We obtained a so-called "myomap" by means of the simultaneous multi-channel recording of the surface potential of the right masseter. Comparison of the EMG revealed a higher activity from the masticatory muscles in the class II cases than in the class III cases. The analysis of the masseter excitation pattern brought to light interesting differences. A higher activity on the lower margin of mandible in the area of the superficial part of masseter was found in the class II cases, whereas contrary to this an increase in EMG activity was found above the deep part of masseter in class III cases. The differing distribution of excitation of the 2 parts of the muscle in class II and class III malocclusions confirms the correlation between muscle function and morphology.

Adolescent↗
PubMed1994

[The orthodontic classification of impacted canines with special reference to the age at treatment, the angulation and dynamic occlusion].

The literature regards the surgical-orthodontic treatment of ectopic canine as being the optimal therapy. This treatment, however, often takes a long time and disturbances in the functional occlusion often occur after treatment is ended. For this reason it was decided to evaluate the treatment's success taking into consideration age at time of treatment, angulation, and functional occlusion. The post-treatment examinations of 66 patients up to five years after treatment reveal above all a correlation between treatment success and age at the time treatment begins. In addition patients with class II/2 and tooth aplasia were identified as constituting a risk group. These malocclusions, therefore, are a sign that there is a risk of ectopic canines. The occlusion type in laterotrusion movement provides group guidance. Beginning treatment after age 25 years should be critically evaluated, because the treatment period is prolonged.

Adolescent↗
PubMed1992

[The long-term observation of alveolar bone blood flow during tooth movement with the aid of skeletal scintigraphy in an animal model].

We observed in eleven dogs the blood flow in the alveolar bone during the tooth movement with the bone scintigraphy for one year. Additional we used for histological evaluation polychrome sequence marking and for improving of therapy electrostimulation. There is a correlation between tooth movement and blood flow. Four to six weeks after beginning tooth movement and blood circulation are reduced although the applied force was continuous all the time. This is an advice for stress interruption during treatment. Electrostimulation improves the conditions for tissue regeneration because the lifetime of osteoblasts is prolonged.

Alkaline Phosphatase↗
PubMed1991

[Findings for validity of Dresden cephalometric (by Hasund)].

Cephalometric analysis is essential in order to evaluate treatment results. 202 patients were investigated for the validity of the norm values according to Hasund. In order to test the validity of the growth prediction methods of Björk and Petrovic 23 class II div. 1 and 21 class III patients were analysed before and after treatment and the treatment results achieved compared with the growth prediction values. The results of the norm value tests showed that the population in Saxonia is more retrognath than that in the northern region of Germany (Hasund norm group). The study also showed that the Björk growth prediction and the Petrovic growth categories were not specific enough and it is therefore suggested that separate growth prediction methods should be used in class II div. 1 and class III groups.

Adolescent↗
PubMed1991

[Teleroentgenographic findings in adults with overbite. Teleroentgenographic morphology in closed-bite patients].

Lateral skull radiographs were analyzed in twenty patients with retroclined incisors. Greatest deviations from the comparison values were found in the region of the lower face. The mandible shows a retrognathic and counter clockwise rotated position. The height of the anterior lower face height and the dentoalveolar height are reduced. The interincisor angle ist distinct increased. Etiological aspects and the therapeutical consequences of the findings are mentioned.

Adult↗
PubMed1991

[Computer-assisted teleradiographic image interpretation in orthodontics].

The utilization of a computer supported cephalometric system using the analysis introduced by Hasund is demonstrated. In comparison to the traditional measurement by hand the advantages of a computerized analysis are: Time reduction, minimization of evaluation errors, the use of individualized norm values and the advantages in recording.

Cephalometry↗
PubMed1990

[The dentition and jaw growth of 60 mono- and dizygotic twins between the ages of 10 and 18].

60 twins were investigated between the age of ten and 18 years to obtain information about inheritance of tooth-crown size and growth of alveolar bone. The results suggest genetically controlled interaction between tooth germs during their formation. The intrapair differences decrease between ten and 18 years for the alveolar bone diameters. This is an advise for stronger genetically influences in higher age and an etiological factor for relapse after orthodontic treatment.

Adolescent↗
PubMed1990

Limiting factors of functional adaptation to orthodontic space closure.

The closure of spaces, especially in the incisor region, has been criticized as causing functional alterations in the masticatory system. The study comprised 80 patients, 30 with space closure and 50 as a control. The results showed that closure of incisor spaces caused marked occlusal alterations, but apparently no damage to the temporo-mandibular joint nor to muscle action, provided that treatment was completed before the age of 12 years.

Anodontia↗
PubMed1989

[The open bite--morphology and therapeutic consequences].

With cephalometric measurements we investigated the morphology of the malocclusion "Open bite" from adults. The main of abnormality is the divergence of the jaw bases and the compensatory growth of alveolar bone in vertical direction. Under consideration of the best time for beginning of the treatment we give advice for the etiologically orientated therapy.

Adult↗