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Biomedical subjects

M Augthun

Publications and source records attributed to M Augthun.

At least 19 recordsLinked to original sources
PubMed2001

Application of laser measuring, numerical simulation and rapid prototyping to titanium dental castings.

OBJECTIVES: This paper describes a method of making titanium dental crowns by means of integrating laser measuring, numerical simulation and rapid prototype (RP) manufacture of wax patterns for the investment casting process. METHODS: Four real tooth crowns (FDI No. 24, 25, 26, 27) were measured by means of 3D laser scanning. The laser digitized geometry of the crowns was processed and converted into standard CAD models in STL format, which is used by RP systems and numerical simulation software. Commercial software (MAGMASOFT) was used to simulate the casting process and optimize the runner and gating system (sprue) design. RP crowns were 'printed' directly on a ModelMaker II 3D Plotting System. A silicone negative mold (soft tool) was made from the RP crowns, then more than hundreds wax crowns were duplicated. The duplicated crowns were joined to the optimized runner and gating system. By using the investment casting process 20-25 replicas of each crown were made on a centrifugal casting machine. All castings were examined for porosity by X-ray radiographs. RESULTS: By using the integrated scanning, simulation, RP pattern and casting procedure, cast crowns, free of porosity, with excellent functional contour and a smooth surface finish, were obtained from the first casting trial. SIGNIFICANCE: The coupling of laser digitizing and RP indicates a potential to replace the traditional 'impression taking and waxing' procedure in dental laboratory, with the quality of the cast titanium prostheses also being improved by using the numerically optimized runner and gating system design.

Calcium Sulfate↗
PubMed2001

Numerical simulation of the casting process of titanium tooth crowns and bridges.

The objectives of this paper were to simulate the casting process of titanium tooth crowns and bridges; to predict and control porosity defect. A casting simulation software, MAGMASOFT, was used. The geometry of the crowns with fine details of the occlusal surface were digitized by means of laser measuring technique, then converted and read in the simulation software. Both mold filling and solidification were simulated, the shrinkage porosity was predicted by a "feeding criterion", and the gas pore sensitivity was studied based on the mold filling and solidification simulations. Two types of dental prostheses (a single-crown casting and a three-unit-bridge) with various sprue designs were numerically "poured", and only one optimal design for each prosthesis was recommended for real casting trial. With the numerically optimized design, real titanium dental prostheses (five replicas for each) were made on a centrifugal casting machine. All the castings endured radiographic examination, and no porosity was detected in the cast prostheses. It indicates that the numerical simulation is an efficient tool for dental casting design and porosity control.

Journal Article↗
PubMed1999

Numerical study of porosity in titanium dental castings.

A commercial software package, MAGMASOFT (MAGMA Giessereitechnologie GmbH, Aachen, Germany), was used to study shrinkage and gas porosity in titanium dental castings. A geometrical model for two simplified tooth crowns connected by a connector bar was created. Both mold filling and solidification of this casting model were numerically simulated. Shrinkage porosity was quantitatively predicted by means of a built-in feeding criterion. The risk of gas pore formation was investigated using the numerical filling and solidification results. The results of the numerical simulations were compared with experiments, which were carried out on a centrifugal casting machine with an investment block mold. The block mold was made of SiO2 based slurry with a 1 mm thick Zr2 face coat to reduce metal-mold reactions. Both melting and casting were carried out under protective argon (40 kPa). The finished castings were sectioned and the shrinkage porosity determined. The experimentally determined shrinkage porosity coincided with the predicted numerical simulation results. No apparent gas porosity was found in these model castings. Several running and gating systems for the above model casting were numerically simulated. An optimized running and gating system design was then experimentally cast, which resulted in porosity-free castings.

Journal Article↗
PubMed1999

Numerical simulation of porosity-free titanium dental castings.

The objective of this research was to analyse, predict and control the porosity in titanium dental castings by the use of numerical simulation. A commercial software package (MAGMASOFT) was used. In the first part of the study, a model casting (two simplified tooth crowns connected by a connector bar) was simulated to analyse shrinkage porosity. Secondly, gas pores were numerically examined by means of a ball specimen with a "snake" sprue. The numerical simulation results were compared with the experimental casting results, which were made on a centrifugal casting machine. The predicted shrinkage levels coincided well with the experimentally determined levels. Based on the above numerical analyses, an optimised running and gating system design for the crown model was proposed. The numerical filling and solidification results of the ball specimen showed that this simulation model could be helpful for the explanation of the experimentally indicated gas pores. It was concluded that shrinkage porosity in titanium dental casting was predictable, and it could be minimised by improving the running and gating system design. Entrapped gas pores can be explained from the simulation results of the mould filling and solidification.

Chemical Phenomena↗
PubMed1998

Anterior disk displacement of the temporomandibular joint. Significance of clinical signs and symptoms in the diagnosis.

In order to examine the diagnostic significance of typical clinical symptoms in temporomandibular joint (TMJ) disorders for diagnosis of anterior disk displacement, clinical findings were compared with the degree of disk displacement in 84 TMJs of 59 patients with TMJ disorders, who were examined clinically and by means of magnetic resonance imaging (MRI). The control group consisted of 31 subjects with no TMJ symptoms. No significant correlation between the degree of anterior disk displacement and palpation pain of the masticatory muscles or clicking/crepitus of the TMJ could be found. Joint clicking was observed in 65% of patients with TMJ symptoms in normal disk position (NDP). The percentage of joint clicking was almost the same in patients with anterior disk displacement with reposition (ADWR) (68%). There were significant correlations between active mouth opening and disk position as well as between a history of pain and disk position. Patients with NDP and ADWR had almost identical mouth opening values: 48 (+/- 5) mm and 46 (+/- 5) mm respectively. In contrast to these groups the mean values decreased significantly to 42 (+/- 6) mm in patients with anterior disk displacement without reposition (ADWOR). There were no significant correlations between occlusal findings (centric relation and habitual relation, early occlusal contacts, abrasion facets) and disk position when viewed either collectively or individually.

Adult↗
PubMed1998

Computer aided prediction and control of shrinkage porosity in titanium dental castings.

OBJECTIVES: The main objectives were to investigate the possibility and reliability of quantitative prediction and control of the concentrated shrinkage porosity (macroporosity) in titanium dental castings by means of a numerical simulation technique; and finally to optimize the filling and feeding system design for dental castings. METHODS: A commercial software, MAGMASOFT (Giessereitechnologie GmbH, Germany), was employed to simulate the mold filling and solidification process, and predict the shrinkage tendency in a sample dental casting, two simplified tooth crowns with a connector bar between them. The numerically predicted shrinkages were compared with the experimental results. The experiments were carried out on a centrifugal casting machine. The same geometric and processing parameters of the casting as in the simulations were strictly controlled. RESULTS: The computer predicted shrinkage porosity coincided with the performed experiments, demonstrating the reliability of the numerical model and the thermal physical data chosen for the calculations. Based on the above numerical model, several filling and feeding systems for the same casting were numerically simulated and compared. Finally an optimized design for this sample casting was proposed, and porosity-free castings were obtained. SIGNIFICANCE: It was expected that the numerical simulation technique could be further developed for dental laboratories to aid the real dental casting design.

Computer Simulation↗
PubMed1998

In vitro studies on the effect of cleaning methods on different implant surfaces.

The effect of specific cleaning procedures was examined on the surfaces of 3 implant types with different coatings and shapes (plasma sprayed [PS]; hydroxyapatite coated [HA] implants; and smooth titanium surface screws) using a scanning electron microscope. Each implant was treated for 60 seconds per instrument with one of 6 different hygiene measures: plastic curet, metal curet, diamond polishing device, ultrasonic scaler, air-powder-water spray with sodium hydrocarbonate solution, and chlorhexidine 0.1% solution rinse. The air-powder-abrasive system, chlorhexidine rinse, and curettage with a plastic instrument caused little or no surface damage in all but the hydroxyapatite-coated fixtures. Therefore, these 3 methods were tested to determine their cleaning efficacy in a second clinical study, which did not include the HA-coated fixture. Two implants were placed on the facial aspects of both upper molar regions using individual acrylic plates. Thus, 2 fixtures on each side were examined in each patient. The examination revealed that only the sodium hydrocarbonate spray yielded a clean fixture without damage to the implant surface. In a third stage, which imitated the clinical procedure of the second approach, the cell growth of mouse-fibroblasts on implant surfaces was examined after cleaning the surface with plastic scaler and the air-abrasive system, which represents the least damaging and most effective methods. In contrast to the implant surfaces treated with plastic scalers, mostly vital cells were found on implants sprayed with the air-abrasive system.

Air↗
PubMed1997

[Temporomandibular joint morphology and morphometric findings in relation to degree of disk displacement. Comparative magnetic resonance tomography studies].

In order to evaluate magnetic resonance imaging (MRI) changes in correlation with different degrees of internal derangement of the temporomandibular joint, we evaluated 117 joints of 59 symptomatic patients and 31 volunteers. Data analysis included morphologic and morphometric characteristics. Sixteen joints (19%) were considered normal, 40 demonstrated anterior displacement with reduction (47%) and 27 anterior displacement without reduction (32%). In three of the volunteers anterior displacement with reduction was noted. Advancing anterior position of the disk was associated with reduced ability to open the mouth, progressive deformity and shortening of the disk, thinning of the bilaminar zone, regressive and proliferative bony changes of the condyle, reduced translatory movement of the disk and condyle, thinning of joint space, cranial and dorsal displacement of the condyle and flattening of the slope of the tuberculum. In addition to alterations in condylar and disk morphology, MRI can demonstrate various additional measurable changes that correlate well with the degree of anterior disk displacement.

Adult↗
PubMed1996

[Disk displacement of the temporomandibular joint: correlation of magnetic resonance tomography and clinical findings].

PURPOSE: To evaluate the value of magnetic resonance imaging (MRI) in symptomatic patients with different degrees of internal derangement. MATERIAL AND METHODS: We prospectively investigated 117 temporomandibular joints (TMJ) of 59 symptomatic patients and 31 asymptomatic volunteers and correlated this with clinical parameters. RESULTS: There was a positive correlation between the degree of internal derangement and deformity of the disc, maximal mouth opening, signal intensity of the posterior band, thickness of the bilaminar zone, proliferative bony changes, size of the condyle and reduced translation movement of the condyle, which in addition moved upward and backward. Patients most often complained of pain which was dependent on the degree of disc displacement and condylar changes. Clinical parameters were found to be inaccurate in predicting disc displacement. CONCLUSION: Patients with internal derangement of the temporomandibular joint may be asymptomatic. Patients history may give the only pointer to the disorder.

Adult↗
PubMed1995

[Findings in the panoramic tomogram in orthodontic patients with functional disorders].

In our study of 107 patients, for whom data derived from clinical functional analysis, axiography and, in part magnet resonance imaging, were present, we were able to show that in routine orthodontic diagnosis the use of panoramic X-ray in the normal course of a general examination of the mandibular joint can also provide important indications of the presence of cranio-mandibular disorders. The panoramic X-ray revealed that in patients with Angle class II and front deep and open bite there were significantly mor changes in the form of the condyles. A definite morphologic finding of a retracted fovea pterygoidea was found frequently in patients with anterior disk replacement with or without reduction. Lastly, the panoramic X-ray showed that a change in form of the condyles, with in some cases a serious arthrosis, occurs significantly most frequent in patients with anterior displacement without reduction.

Adolescent↗
PubMed1994

[The diagnosis and orthodontic relevance of anterior disk displacement without reduction. Clinical, axiographic and magnetic resonance tomographic studies].

Magnet resonance imaging was used to diagnose 24 temporomandibular joints of 18 patients as having anterior disk displacement without reduction. By comparing clinical functional analysis, axiography, and magnet resonance imaging it was demonstrated that a valid diagnosis could be made on the basis of magnet resonance imaging alone. Former joint clicking and limitation and a dental Angle Class II were diagnostic indications of a disk displacement without reduction. Because of often only slight clinical symptoms or their absence, there is always a danger that disk displacement without reduction will go undiagnosed. In relation to orthodontic therapy, such patients are at risk, because pain can arise during treatment.

Adolescent↗
PubMed1993

[Occlusal splint therapy in reciprocal TMJ clicking. A critical observation within a follow-up study].

During post-treatment examination the effect of splint therapy on 14 temporomandibular joints (TMJ) with anterior disk displacement were examined using clinical and instrumental findings and magnet resonance imaging (MRI) to judge the therapeutical success of the treatment from an orthodontic perspective. A stable reposition of the TMJ disk was achieved in four joints, which showed no relapse over a two-year period of observation. The success of the therapy was dependent on the extent of the tissue damage to the TMJ and also on patient compliance. The MRI yielded therapeutically valuable information, which is not revealed in the clinical-instrumental analysis, on the tissue structure of the disk and the ligaments. In certain cases the use of MRI is necessary to confirm the clinical diagnosis.

Adolescent↗
PubMed1991

[Studies on the cell and tissue tolerance of a polymeric bone replacement material].

BOP (Biocompatible Osteoconductive Polymer) shows no cytotoxicity in vitro. After six months of subcutaneous implantation in mice a weak cellular tissue reaction is seen histologically. The hard tissue reaction after six months of implantation in fractured tibia bone shows less connective tissue between the implant material BOP and bone.

Animals↗
PubMed1991

[Study of cell supportability of clinically used soft denture liners].

The application of six soft denture liners showed different effects on the growth of gingival fibroblasts. The morphological and autoradiographical analyses revealed a graduated cellular biocompatibility. The results provide information for further examinations in more detail concerning the clinical biocompatibility of these materials.

Biocompatible Materials↗
PubMed1990

[Studies on the allergenic potential of palladium alloys].

Epicutaneous tests with test solutions of the European standard series and palladium chloride (1%) were performed in 486 patients of the University Hospital for Dermatology in Aachen. 17.9% of the patients exhibited Ni, 8.6% Co, 7.4% Pd and 4.1% Cr allergy. In 18 of 36 patients with a positive patch test reaction a further epicutaneous and epimucosal testing with metallic plates of pure palladium and a palladium alloy was performed. In 34 cases a positive skin reaction to palladium chloride was combined with a positive skin reaction to nickel sulphate. Only in one case was it possible to demonstrate an allergic reaction to a palladium metallic plate, which was tested additionally in artificial saliva. The results show that a dental alloy envisaged for use should be tested in an epicutaneous test, if the patient shows a positive reaction to the metallic salt solution. In case of positive patch tests to nickel sulphate, dental palladium alloys should not be used as an alternative unless sensitivity to palladium has been tested.

Dental Alloys↗