Biomedical subjects

Christof Holberg

Publications and source records attributed to Christof Holberg.

7 recordsLinked to original sources

PubMed2006

Inter-individual variability of the facial morphology during conscious smiling.

INTRODUCTION: Since many simulation and animation procedures for mimicry are based on averaged values and do not take into account an individual's situation, the goal of this study was to investigate the intra- and inter-individual variability of conscious smiling. MATERIALS AND METHODS: Twenty-three surface points were marked on the faces of 31 adult test individuals. Six photographs of each subject's face were then taken under standardized conditions, one with a neutral facial expression and five while the individual was asked to smile (conscious smile "on command"). After digital superposition of the individual images (neutral and smiling) the displacements were measured for every measurement point on each individual. All data underwent statistical evaluation after normalization in the vertical and horizontal directions. Evaluation of intra- and inter-individual variability was carried out by analyzing the corresponding coefficients of variation and the formation of confidence intervals (confidence level 95%). RESULTS: The repeated measurements upon conscious smiling showed a moderate intra-individual variability with coefficients of variation under 10%. In contrast, the inter-individual variability of the measured values was relatively high. Here variation coefficients were measured of between 28% and 60% depending on the localization of the measuring point. The displacements' absolute magnitude was greatest in the lower facial third. The two corners of the mouth, the upper lip in the philtrum area, the cheeks and the side wings of the nose revealed the highest displacements. CONCLUSION: Due to the high inter-individual variability, an analysis based on averaged values or a simulation of the conscious smile must be viewed with a certain amount of criticism.

Adult↗

PubMed2006

Stresses at the cranial base induced by rapid maxillary expansion.

OBJECTIVE: An analysis of the distribution of stresses at the juvenile and adult cranial base after implementation of a rapid palatal suture expansion was the goal of this study. Of particular interest were stresses occurring near the cranial foramina containing vulnerable structures. MATERIALS AND METHODS: The stresses were simulated and analyzed using a finite elements model of the human cranial base. The model consisted of several skull bones (sphenoid, frontal bone, occipital bone, and the two temporal bones) with a total of 41,556 finite elements. To illustrate the differences between reactions in the juvenile and the adult, the differing bone elasticity was depicted as variations in the modulus of elasticity. RESULTS: At the juvenile cranial base only moderate stresses occurred during rapid palatal suture expansion, apparently precluding the likelihood of any serious complications in the area of the foramina. The situation in the adult, however, was different. Because of the reduced elasticity of the bony structures, considerable stress already occurred on light bending of the pterygoid process, especially in the area of the round foramen, the oval foramen, and the superior orbital fissure, all of which might lead to microfractures with injury of nervous and vascular structures. CONCLUSIONS: The lower the bone elasticity on carrying out a rapid palatal suture expansion, the more important safety measures are for protecting the cranial base. For this reason the pterygomaxillary connection should be severed on both sides in adults when carrying out a surgically assisted palatal suture expansion.

Adolescent↗

PubMed2006

Accuracy of facial plaster casts.

OBJECTIVE: The aim of this study was to evaluate the accuracy of facial plaster casts and their suitability for 3-D mapping. MATERIALS AND METHODS: All measurements were carried out on 15 adult probands (seven female and eight male; age range 19-31 years, mean 24.7 years). A plaster cast of the facial surface was prepared for all probands using alginate impressions. The plaster casts and the probands faces were digitized using a three-dimensional laser-scanner operating with structured light. The resulting point clouds were matched in a virtual environment to analyze the deviations between the cast and the facial surfaces, both qualitatively and quantitatively. RESULTS: The average deviations depended on the facial area and lay between 0.95 and 3.55 mm. Marked differences between the plaster cast and the facial surface were found, particularly in the area of the lips, at the roof of the nose, at the cheeks, and in the entire lower facial area. CONCLUSIONS: The regionally exacerbated soft tissue deformations that occur during impression of the facial surface lead to inaccuracies in the resulting plaster cast that forbids any use for morphometric analysis. Documentation of pathological findings in cleft lip and palate using facial plaster casts does appear to be justifiable.

Adult↗

PubMed2005

Three-dimensional soft tissue prediction using finite elements. Part I: Implementation of a new procedure.

BACKGROUND AND AIM: The prediction of soft tissue esthetics is important for achieving an optimal esthetic outcome in orthodontic treatment planning. Applicable procedures have so far been restricted to two-dimensional profile predictions that have not proven to be very reliable. The goal of this investigation was therefore to develop a novel finite element-based procedure that allows a three-dimensional, easily visualized, quantitative analysis and prediction of soft tissue behavior for the clinician. The procedure to be developed should be easy to handle and not entail any additional radiation exposure for the patient. MATERIAL AND METHODS: Using a three-dimensional scanner, the facial surfaces of 20 probands were digitalized and individual FEM models were generated. RESULTS: After reduction of data redundancy via several conversion steps, a patient-specific simulation model was prepared consisting of 20,000 to 40,000 individual elements to which specific physical properties could be assigned. The average time required for generating a virtual model was 50 minutes. Problems occurring during model generation were rare (mainly shadowing phenomena and movement artifacts). CONCLUSION: The procedure outlined herein makes the reliable generation of patient-specific simulation models possible for facial soft tissue prediction in orthodontics.

Adult↗

PubMed2005

Three-dimensional soft tissue prediction using finite elements. Part II: Clinical application.

BACKGROUND AND AIM: The goal of this study was to analyze the validity and prediction accuracy of a newly-developed procedure for three-dimensional soft tissue prediction based on Finite Element Method, and to compare the results with prediction produced using an existing two-dimensional prediction program (Dentofacial Planner Plus). PATIENTS AND METHODS: In twelve patients who underwent combined surgical-orthodontic treatment, profile prediction was generated using both procedures preoperatively and then compared at predefined measurement points with the patient's actual postoperative soft tissue status. RESULTS: The deviations observed depended on the facial region, whereby the prediction errors for both procedures were much greater in the lower facial third than in the midfacial third. Calculating in all the measurement points, the mean horizontal prediction error was 0.32 mm for the Finite Element Method and 0.75 mm for the Dentofacial Planner Plus. Overall, we were able to demonstrate the new procedure's superior validity and quality of visualization. In addition to profile prediction, the procedure allows a differentiated three-dimensional assessment of esthetically important regions such as the cheeks, nasolabial folds and the nasal wings. Additional X-radiation is not necessary in this risk-free and stress-free procedure. CONCLUSION: Three-dimensional soft tissue prediction employing finite element modeling is a useful aid for implementing esthetically-optimized treatment planning.

Adult↗

PubMed2005

Effects of rapid maxillary expansion on the cranial base--an FEM-analysis.

BACKGROUND AND AIM: Rapid maxillary expansion not only has local effects on the midpalatal suture and the maxillary region, but also on deep anatomical structures of the viscero- and neurocranium. This study's aim was to analyze the distribution pattern of stresses on the juvenile and adult sphenoid by the finite element method (FEM) induced by rapid maxillary expansion. Of special interest were stresses and deformations around the sphenoidal foramina with their vulnerable neural and vascular structures. MATERIAL AND METHOD: A finite element model of the sphenoid consisting of 19,383 single elements was used for the analysis. RESULTS: The virtual experiments showed that rapid maxillary expansion leads to moderate stresses and deformations in the juvenile sphenoid, so serious complications are unlikely in this region. The situation is different in adulthood because of decreasing elasticity of the skeletal structures. Due to lateral bending of the pterygoid processes, marked stress develops in the round and oval foramen regions and those of the superior orbital fissure, where fractures causing neural and vascular injury can occur. CONCLUSION: The surgical separation of the maxilla from the sphenoid is an important means of preventing complications in the region of the cranial base in adults.

Computer Simulation↗

PubMed2005

Cone-beam computed tomography in orthodontics: benefits and limitations.

INTRODUCTION: In order to obtain an overlay-free assessment of dental structures for resorption and ankylosis diagnostics, conebeam computed tomography (CBCT) is being employed more and more often in orthodontics alongside dental CT. OBJECTIVE: The aim of this study was to investigate the quality and accuracy of CBCT in the imaging of dental structures and to compare it with the imaging quality produced by dental CT. Moreover, we intended to assess the specific advantages and disadvantages of CBCT in clinical use. MATERIALS AND METHODS: The image quality of CBCT and dental CT was examined for a total of 417 teeth and their surrounding structures. 208 teeth were diagnostically recorded using volume tomography and 209 with dental CT. The axial images were assessed for metal and movement artifacts and whether there was an imprecise depiction of the enamel-dentin and pulp interface. The definition and reproductive quality of all teeth were evaluated when imaging the periodontal ligament space in the cervical, middle and apical root thirds. RESULTS: In contrast to dental CT, metal artifacts were barely apparent in the CBCT and when so, only very feebly, whereas we only observed disruptions in image quality from movement artifacts with CBCT. Image quality of the dental and surrounding bony structures was far better with dental CT on the whole than it was with CBCT. During imaging by CBCT, the periodontal ligament space either could not be, or if so, then only poorly assessed for 86% of the teeth, while this figure was only 20% for dental CT. Furthermore, the enamel-dentin interface and pulp cavity's edges were on the whole much more sharply defined in the dental CT. CONCLUSION: Dental CT still represents the gold-standard for inspecting the dental roots and their surrounding bone.

Artifacts↗