Search PubMed⌕ Search

Biomedical subjects

W Harzer

Publications and source records attributed to W Harzer.

At least 19 recordsLinked to original sources
PubMed2005

[Computed tomographic examination of muscle volume, cross-section and density in patients with dysgnathia].

PURPOSE: The individual jaw position is determined by the masticatory muscle among other factors. Before surgical treatment of malocclusions, thorough evaluation of the muscles is required to estimate the relapse risk. MATERIALS AND METHODS: By means of computer tomography, lateral radiographs of the skull and denture models, the relationships between morphological parameters of the masticatory muscles and the jaw bone were analyzed. Furthermore, possible causes for the extent of the malocclusion are described. RESULTS: A patient group with deep overbite was found to have significantly higher muscle densities (measured in Hounsfield units [HU]) in the medial pterygoideus muscle (59.89 +/- 3.91 HU to 48.94 +/- 4.14 HU, p < 0.01), masseter muscle, and genioglossus muscle (p < 0.05) in comparison to open bite patients. Significant differences of the muscle cross-section were measured in the masseter muscle between patients with retroclined maxillary incisors and with an open bite (5.4 +/- 0.7 cm (2) to 3.8 +/- 0.4 cm (2), p < 0.05). CONCLUSION: The results show a correlation between different jaw positions and masticatory muscles. They also suggest that the function of each muscle may be different. Additional examinations of the muscle structures are required for verification of the influence of the masticatory muscles on facial morphology.

Bone Density↗
PubMed2005

An evaluation of resonance frequency analysis for the determination of the primary stability of orthodontic palatal implants. A study in human cadavers.

BACKGROUND: The primary stability of short orthodontic implants is important for anchorage. METHODS: For this study 14 cadaveric human heads were used. The stability of orthodontic implants (Straumann) with lengths of 4 and 6 mm and different localization (palatal suture or paramedially) were evaluated. The implants with length of 6 mm were only placed in the suture and primary stability was non-invasively determined with the resonance frequency (Osstell). The invasive method for the analysis of the morphometric parameters of the implant/bone contact was carried out by means of histological and radiological examinations. RESULTS: The 6 mm implants have significant better primary stability in the palatal suture as 4 mm implants paramedially (P<0.05). No differences were found between 6 and 4 mm implants in the palatal suture and between 4 mm implants in palatal suture to paramedially. The histological and radiological results demonstrate the ability to measure the implant stability by investigation of the bone offer and density around the implant. Bone structure, especially the pore size in the trabecular bone and the precision of placement may influence the stability. CONCLUSION: This study shows that the short implant gives sufficient bone fixation, independently of placement. The quality of implantation and bone structure are more important than the length of the orthodontic implant.

Bone Density↗
PubMed2005

Stress, burnout and health in the clinical period of dental education.

The study examined the extent of stress, burnout and health problems experienced by fourth and fifth year dental students from the three universities of Dresden, Freiburg and Bern. The objectives of the study were to: (i) identify frequent sources of stress and to report the prevalence rates of burnout and health problems in dental students, (ii) determine the rate of students suffering from severe burnout symptoms and (iii) identify stress factors related to the burnout symptoms of emotional exhaustion and depersonalization. A total of 161 dental students from Dresden, Freiburg and Bern participated in the study. They completed the Psychosocial Stress Inventory, the Maslach Burnout Inventory and the Health Survey Questionnaire. Frequent sources of stress were limitation of leisure time, examination anxiety and the transition stress that was related to the adaptation to the demands of the clinical phase of dental education. Few differences existed between the students of the fourth and the fifth study year. Study-related stress was lowest in Bern and considerably higher in Dresden. Differences of mean levels of burnout symptoms were found only for the burnout dimension of emotional exhaustion. Students from Dresden and Freiburg were more emotionally exhausted than students from Bern, students from Dresden also reported more health problems than students from Bern or Freiburg. Ten per cent of the dental students suffered from severe emotional exhaustion, 17% complained about a severe lack of accomplishment and 28% reported severe depersonalization symptoms. Forty-four per cent of the variance of emotional exhaustion was explained by study-related factors such as lack of leisure time, examination anxiety and transition stress. The only predictor of depersonalization was a lack of social integration, accounting for 3% of the variance. A lack of social integration may be an indicator of low social competence which may cause difficulties in dealing with patients adequately and therefore result in depersonalization. The results indicate a need to identify the group of students who may have insufficient social skills for dealing adequately with the patients, and to train them accordingly.

Adult↗
PubMed2005

X-ray microanalysis of elements in the masticatory muscle after paresis of the right masseter.

Muscle activity and function appear to be related to ionic concentrations in the muscle. We investigated whether muscle paresis induced by injection of Botulinum toxin A (Botox) in 16-week-old pigs over a 56-day period is associated with ionic changes in the affected muscles. Tissue samples were taken from the masseter, temporalis, medial pterygoid, and geniohyoid muscles by a standardized method and used for energy-dispersive x-ray microanalysis in an environmental scanning electron microscope. The largest increase in Na(+) was measured in the right and left sides of the masseter muscle in treated animals. Additionally, a significant elevation of Na(+) was measured in the anterior part of the temporalis muscle and in the pterygoid muscle (P < 0.05). In temporalis and pterygoid muscles, an increase in sulfur in both sides of treated pigs' heads was observed. Botox((R)) has an indirect impact on ion concentrations, resulting in changes in muscle functional capacity and adaptive compensation of paretic muscle function by other muscles.

Animals↗
PubMed2004

Extractions as a form of interception in the developing dentition: a randomized controlled trial.

OBJECTIVE: To determine if the extractions of lower primary canines are an effective procedure to relieve crowding of the labial segment. STUDY DESIGN: randomized controlled trial. Subject sample: 83 cases were collected in clinics in Italy, Germany and Wales. The groups were followed over a 2-year period. METHODS: Subjects were randomly allocated to a primary canine non-extraction or extraction group. Dental casts of the patients were collected at the start and at the recall period of the trial. The outcome measures recorded were lower incisor crowding, arch length, intermolar width, overbite, overjet, lower clinical crown heights and lower incisor inclinations. STATISTICS: The Mann-Whitney test was used to compare the differences between the extraction and non-extraction groups. RESULTS: In both groups, crowding reduced 1.27 mm in the non-extraction group and 6.03 mm in the extraction group. The difference between the 2 groups was 4.76 mm (P<0.05). The arch perimeter decreased more in the extraction group by 2.73 mm (P<0.05). As the incisor inclination stayed essentially the same, the loss in arch length was attributed to the molars moving forward. The net gain from extracting deciduous canines was 2.03 mm. CONCLUSIONS: There was a reduction in lower incisor crowding as a result of lower primary canine extraction. However, arch perimeter decreased more in the extraction group leaving less space for the eruption of the lower secondary canines.

Child↗
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

Regional alterations in fiber type distribution, capillary density, and blood flow after lower jaw sagittal advancement in pig masticatory muscles.

Muscular remodeling is known to be a prerequisite for permanent correction of mandibular-maxillary malocclusion. The objective of this study was to clarify if an increase in type I fiber number is accompanied by an increased capillary density and improved muscular blood flow. Juvenile pigs received build-ups on the molars, which induced a protrusion of 7.6 + 1.5 mm. After 4 weeks of treatment, chronic lower jaw protrusion induced a marked muscle blood flow increase in the anterior and medial regions of the superficial part of the masseter and in the medial pterygoid muscle (P < 0.05). Furthermore, an increase in capillary density and in the amount of type I fibers was found in all regions of masticatory muscles with an increased muscle blood flow (P < 0.05). Finally, the capillary-to-fiber ratio increased (P < 0.05). Muscle blood flow and capillary density showed a strong linear correlation (r = 0.89, P < 0.01). These changes suggest a complex muscle adaptation for long-term, fatigue-resistant activity during the early corrective period of mandibular-maxillary malocclusion treatment.

Animals↗
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↗
PubMed2001

Early treatment of angle Class II, division 2 in combination with functional therapy of TMJ fracture.

Children who have sustained condylar fractures are treated with functional appliances because surgical repositioning of the condyle is more resource-intensive without producing better results. In cases with additional malocclusions it is practicable to combine the functional therapy of the fracture with skeletal Class II therapy. A 10-year-old boy suffering from a left condylar fracture and showing Class II, Division 2 malocclusion was treated with a skeletal functional appliance in combination with a utility arch for uprighting of the incisors. A modified transpalatal bar was then used to retain the incisor position. The remodeling process of the mandibular condyle following its fracture with dislocation signifies a high adaptability of the affected tissues. This reaction can be used simultaneously for effective sagittal repositioning of the mandible in certain cases of Class II malocclusion.

Athletic Injuries↗
PubMed2001

Tensor analytical evaluation of the effects of a skeletonized activator in the treatment of Class II, Division 1 patients.

PATIENTS AND METHOD: The study covered 40 patients (21 boys and 19 girls) whose Class II, Division 1 malocclusion was being treated with a Klammt open activator. To illustrate growth changes, tensor analysis was used as a superimposition-free comparative technique. At the beginning of treatment for Class II correction, the boys had a mean age of 11.3 years and the girls a mean age of 10.1 years. Patients were evaluated on admission and on attaining normal occlusion. 58 boys and 63 girls participating in a growth study at Kings College School of Medicine and Dentistry, London, served as controls. RESULTS: Prior to treatment the participants suffering from Class II, Division 1 malocclusion exhibited distinct growth deficits in vertical direction. In the control group, the principal direction of mean growth was found to be anterior-inferior. Under the influence of the activator, growth was found to develop in the same direction as in the controls, so that anterior positioning of the lower jaw and an increase in lower facial height were attained.

Activator Appliances↗
PubMed2001

Differential expression of myosin heavy-chain mRNA in muscles of mastication during functional advancement of the mandible in pigs.

Surgical and orthodontic treatment of retrognathia aims to improve orofacial function by adaptation and training of muscle capacity, which is connected with a change in muscle fibre-type proportions. The aim here was to analyse the proportion of myosin-heavy chain (MyHC) gene expression in type I (slow twitch/ST) and type IIb (fast twitch/FT) fibres during sagittal advancement of the mandible by reverse transcriptase-polymerase chain reaction (RT-PCR). The experiments were carried out on 10-week-old pigs (six test animals, six controls) over a 28-day period. Six pigs were fitted with acrylic bite blocks for sagittal advancement of the mandible. Tissue was taken from seven different regions of the masseter, temporal, medial pterygoid, and geniohyoid muscles. The 84 samples were used for histological fibre differentiation with ATPase staining and for isolation of total RNA. To measure the two MyHC isoforms, RT-PCR (in a single tube reaction with MyHC I, MyHC IIb, and GAPDH primers) was used. A significant increase was registered in the percentage of ST fibres and in mRNA from MyHC I in the anterior region of the masseter and in the posterior region of the temporal muscle of the treated animals. The proportion of ST fibres to FT fibres was increased by up to 12% after functional advancement of the mandible. The histological findings corresponded with the data for fibre mRNA generated by RT-PCR.

Acrylic Resins↗
PubMed2001

Sensitivity of titanium brackets to the corrosive influence of fluoride-containing toothpaste and tea.

Titanium brackets are used in orthodontic patients with an allergy to nickel and other specific substances. In recent studies, the corrosive properties of fluoride-containing toothpastes with different pH values were investigated. The present in vivo study tested how the surfaces of titanium brackets react to the corrosive influence of acidic fluoride-containing toothpaste during orthodontic treatment. Molar bands were placed on 18 orthodontic patients. In these same patients, titanium brackets were bonded on the left quadrants and stainless steel brackets on the right quadrants of the upper and lower arches. Fifteen patients used Gel Kam containing soluble tin fluoride (pH 3.2), whereas 3 used fluoride-free toothpaste. The brackets were removed for evaluation by light microscopy and scanning microscopy 5.5 to 7.0 months and 7.5 to 17 months after bonding. The quality and quantity of elements present were measured by scanning microscopy. Macroscopic evaluation showed the matte gray color of titanium brackets dominating over the silver gleam of the steel brackets. The plaque accumulation on titanium brackets is high because of the very rough surface. Pitting and crevices were observed in only 3 of the 165 brackets tested. The present in vivo investigation confirms the results of in vitro studies, but the changes are so minor that titanium brackets can safely be used for up to 18 months. Wing surfaces should be improved by modifying the manufacturing process.

Adult↗
PubMed2001

Oxidative state and histological changes in muscles of mastication after conditioning training.

Stress due to endurance training of striated muscles leads to adaptive changes in the distribution of muscle fiber types (i.e. ratio of type I and type II fibers). Moreover, severe training leads to tissue hypoxia and oxidative stress in muscles. In the current study, we examined the relationship between histological changes and oxidative state in muscles of mastication during the acute adaptation phase to a sustained muscle load. Six domestic pigs received build-ups on the molar teeth in order to induce a sustained load of the muscles of mastication for a duration of four weeks. Afterwards the masseter (M1, M2, M3), medial pterygoid (PM), temporal (TP1, TP2), and geniohyoid muscles (GH) were removed and the fiber type distribution was determined by enzyme histochemistry. Additionally, the tissue content of glutathione and lipid peroxidation (LPO) products were measured. The above treatment led to muscle fiber transformation of type II into type I (M1, M2, TP2, PM) and a decrease of the GSH content (M1, M2 and TP2). The changes in the GSH/GSSG ratio were in accordance with the changes in proportions of muscle fiber types, with the lowest GSH/GSSG ratios in the most stressed muscles of the treated animals. No significant changes in LPO products were found. The decrease of the GSH/GSSG ratio in the most stressed muscles indicates an increased intracellular oxidative stress, which may be caused by tissue hypoxia during the chronic phase of muscle adaptation.

Adaptation, Physiological↗
PubMed2001

Effects of 28-day mechanical and chewing stress on content of bound and diffusible ions in muscles of mastication.

Type I and type II muscle fibres have different ion concentrations. Muscles adapt to chronic stress by changing of fibre types and remodelling of the myosin heavy chains in the muscle fibres. The present investigation on ionic change during muscular contraction was carried out on 10-week-old pigs (6 treated animals, 6 controls) over a 28-day period. Six pigs received acrylic build-ups to induce mechanical advancement of the lower jaw and chronic chewing stress. Muscle tissue was taken from the masseter (M1, M2, M3), temporal (TP1, TP2), medial pterygoid (PM) and geniohyoid (GH) muscles by a standardized method. Eighty-four muscle samples were used for histological fibre differentiation with mATPase. Energy-dispersive X-ray microanalysis of muscles was carried out in an environmental scanning electron microscope. Endurance stress in the stressed muscles was seen as an increase of type I fibres (P < 0.001). This histological change and ionic alterations were measured in the anterior region of the masseter (M1 and M2) and in the posterior region of the temporal muscle (TP2). Smaller changes were found in the medial pterygoid muscle. We measured in this muscles increases in potassium, sulphur, chloride (P < 0.05) and even larger increases in phosphate (up to 1.5 mmol/g to 2.3 mmol/g, P < 0.001) and sodium (3-fold, P < 0.001). The results reveal the effects of chronic stress on muscle fibres and ion concentration in the muscle. Chronic stress resulted in an increase of type I fibres and increased ion concentration in the same muscle region. These are considered to be indicators of more efficient contraction. The changes in ion concentration are an important factor in muscle contraction.

Animals↗
PubMed2001

Hard palate deformation in an animal model following quasi-static loading to stimulate that of orthodontic anchorage implants.

The aim of the present investigation was to identify adequate implant treatment for young patients. In an animal model palate deformation was investigated by acute quasi-static loading. Three series of tests (with newborn, young and adult pigs) were performed, each with two groups (one or two-point stress) and 5-7 animals per group. Discs with a diameter of 3 and 5 mm were placed in group 1 in the suture area, and in group 2 at both the right and left sides of the suture. Deformation was analysed by a computerized three-dimensional (3D) photo-imaging evaluation system. In young animals the one-point load at a significantly lower force level led to fractures in comparison with the two-point load (P < 0.001). Similar results were measured by an increase in the size of one disc from 3 to 5 mm (P < 0.001). In contrast, adult pigs showed stable results with both methods. In general, a larger disc diameter led to less instability. The one-point load seems to be suitable for adult animals, whereas a two-point load might be favourable during ossification. The advantage of the two-point load is the generation of a higher stress and therefore improved control of dental fixation. However, further tests are necessary to investigate the long-term effects.

Age Factors↗
PubMed2001

Undergraduate orthodontic & paediatric dentistry education in Europe--the DentEd project.

As a result of a European Union funded project (DentEd), a programme of visits to dental schools throughout Europe has been underway since 1998. This report describes the philosophy behind DentEd, gives a brief description of the features of a visitation, and covers the orthodontic and paediatric dentistry teaching as reported in 26 different dental schools in 16 different countries. It is based on a report submitted to DentEd from a small working group that looked at various aspects of educational provision within the two disciplines across Europe. The value of this information to teachers within the two disciplines and to the wider dental community is briefly discussed. The report recommends the adoption of an integrated course for orthodontics and paediatric dentistry. The main objectives are that the student should be able to understand orofacial and psychosocial growth and development of the child, recognize aberrant growth and development, and manage the behaviour of the child, their straightforward preventive, restorative and occlusal needs, and to make appropriate and timely referral.

Curriculum↗
PubMed2000

Axiographic evaluation of mandibular mobility in children with angle Class-II/2 malocclusion (deep overbite).

Correction of the occlusion in Angle Class-II/2 patients is often more complicated and tedious than in Class-II/1 cases. Reasons given are the more comprehensive remodeling and functional adaptation processes of the temporomandibular joints (TMJ) since the articular tuberculum is more strongly developed in deep overbite, and a deep bite leading to a locked occlusion is dominant due to the steeper condylar path. Both characteristics are, however, considered to be the consequence of pronounced incisor retrusion. The present study covered 28 untreated Class-II/2 patients aged 8 to 12 years in whom functional TMJ adaptation to the retroclined maxillary incisors was studied with the help of electronic, 3D axiographic registrations of mandibular movements. Comparison with eugnathic age peers revealed increased mobility in mandibular protrusion and a somewhat steeper condylar path, although the latter was less pronounced than in adult patients. The results corroborate the concept of functional TMJ adaptation to incisor inclination and speak for early uprighting of maxillary incisors.

Adaptation, Physiological↗