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Biomedical subjects

Stefan Hassfeld

Publications and source records attributed to Stefan Hassfeld.

At least 19 recordsLinked to original sources
PubMed2006

Precision of landmark positioning on digitized models from patients with cleft lip and palate.

OBJECTIVE: To quantify the precision of landmark positioning on digitized casts of patients with unilateral cleft lip and palate. PATIENTS: Forty plaster models of newborns up to 8 months of age were selected from the archive of the Department of Orthodontics of the University of Heidelberg. MATERIAL AND METHOD: The plaster-cast models were digitized with a Micromeasure 70 three-dimensional laser scanner (Micromeasure, Bischoffen, Germany). The laser scanner used in this study operates with a precision of 0.15 mm on the x- and y-axes and 0.06 mm on the z-axis. In the intraobserver study, a single observer placed anatomical landmarks in four rounds, with at least 4 weeks between each round. In the interobserver study, four different observers each placed the same landmarks once. For the two different studies, an ideal location for each landmark was calculated by averaging the landmark positions of the four rounds or observers. The distance between each of the four landmark positions and the ideal landmark was measured. RESULTS: A 95% confidence interval for the landmark positioning error was calculated. For the intraobserver investigation, this error was 0.34 to 1.30 mm, and for the interobserver investigation it was 0.7 to 2.00 mm. CONCLUSION: Because both investigations displayed comparable error intervals, it was concluded that different observers could perform landmark positioning for the same studies.

Cleft Lip↗
PubMed2005

Physiological shift of facial skin and its influence on the change in precision of computer-assisted surgery.

Methods of recording landmarks on the facial skin without the use of markers have become increasingly accepted in image-guided surgery. However, position or muscular activity may change the skin's geometry and generate a lack of agreement between the facial contours recorded before and those recorded during the operation. In the present study, we measured this physiological shift of facial skin and evaluated its influence on the accuracy of stereotactic recording. We made laser-scans of the skin of 20 conscious patients while they were sitting and lying, both at rest and when smiling. The laser-scans were referenced to the corresponding computed tomographic dataset, and the accuracy of the recording was calculated. Gravitational or muscular shifts of the skin reduced the mean (S.D.) accuracy of recording to 1.7 (0.3)mm. The loss of accuracy was significantly correlated with the dynamic and gravitational wrinkling of the facial skin and with the body mass index of each patient.

Adolescent↗
PubMed2005

Infiltrating basal cell carcinoma of the neck 34 years after irradiation of an haemangioma in early childhood. A case-report.

A case of a 34-year-old Caucasian male is presented with a basal cell carcinoma deeply infiltrating the structures of the neck, including skeletal muscles and reaching the parotid gland. Radical surgical removal under meticulous histological control was performed. 18 months postoperatively, the patient is still free of recurrence. Thirty years ago the patient had undergone radiotherapy for an infantile haemangioma of the skin of the neck. The effects of this treatment when given in childhood in the aetiology of a basal cell carcinoma are discussed.

Adult↗
PubMed2005

Relationship between the risk of mandibular angle fractures and the status of incompletely erupted mandibular third molars.

BACKGROUND: Several studies have shown the increased risk of mandibular angle fractures associated with incompletely erupted mandibular third molars. But only a few reports analysed in detail the relationship of the status of eruption of this tooth and this type of fracture. OBJECTIVES: The purpose of this study was to clarify the influence of the eruption status of incompletely erupted mandibular third molars on the incidence of mandibular angle fractures. METHODS: Four hundred and thirty-six mandibular halves in 218 patients with mandibular fractures, aged between 15 and 40 years old, were analysed using panoramic radiographs. RESULTS: The incidence of angle fractures in the mandibular halves with incompletely erupted mandibular third molars was 30.8% and this was statistically significantly higher than that in another group (p<0.0001). Deeply located mandibular third molars clearly showed a higher incidence of this fracture when compared with the adjacent second molar (p<0.0001). CONCLUSION: The results of this investigation showed that incompletely erupted mandibular third molars close to the inferior border of the mandible have a high risk of angle fractures.

Adolescent↗
PubMed2005

Artefacts in magnetic resonance imaging caused by dental material.

A common problem in computer tomography (CT) based imaging of the oral cavity is artefacts caused by dental restorations. The aim of this study was to investigate whether magnetic resonance imaging (MRI) of the oral cavity would be less affected than CT by artefacts caused by typical dental restorative alloys. In order to assess the extent of artefact generation, corresponding MRI scans of the same anatomic region with and without dental metal restorations were matched using a stereotactic frame. MRI imaging of the oral and maxillofacial region could be performed without reduction of the image quality by metallic dental restorations made from titanium, gold or amalgam. Dental restorations made from titanium, gold or amalgam did not reduce the image quality of the MRI sequence used in imaging of the oral and maxillofacial region for dental implant planning. In this respect MRI is superior to CT in implant planning.

Animals↗
PubMed2005

The outcome of various cements in combination with titanium reconstruction plates after segmental resection of the mandible.

We report on 82 patients who had segmental resection of the mandible and immediate reconstruction with titanium plates, which were supplemented by polymethylmethacrylate cement (n=32), glass ionomer cement (n=27), silicone (n=9), or nothing (n=14). The mean (S.D.) follow-up time was 92 (26) months. Six months after operation, 27 (46%) of the plates with polymethylmethacrylate cement or glass ionomer cement were removed. During the same time period, four (28%) of the plates were removed in the group with no additional material and two (22%) in the group that had silicone. There was a significant difference in survival time of the metal between the group with silicone and the group with glass ionomer cement (p=0.014, log rank). Although silicone performed slightly better than the reconstruction plate on its own, we doubt whether any cement is necessary.

Aluminum Silicates↗
PubMed2005

Copy number gains on 22q13 in adenoid cystic carcinoma of the salivary gland revealed by comparative genomic hybridization and tissue microarray analysis.

Adenoid cystic carcinoma (ACC) of the salivary gland is a neoplasm characterized by slow but inevitable local progression and terminal hematogenous metastasis. To detect novel imbalanced chromosomal regions associated with tumorigenesis, we used chromosomal comparative genomic hybridization to screen 27 ACC. The most common aberration was copy number gain of 22q13 (nine cases) followed by gains of 16p (seven cases) and 17q (four cases) and copy number losses on 6q (six cases). To further delineate the prevalence of 22q13 copy number gains in ACC, fluorescence in situ hybridization was performed for five bacterial/phage artificial chromosome (BAC/PAC) probes from the 22q13 consensus region with 57 ACC on a tissue microarray. The overall prevalence of copy number gains on 22q13 was 30% of the tumors in the fluorescence in situ hybridization analysis, irrespective of histologic differentiation (cribriform/tubular vs. solid) or tumor event (primary vs. recurrent). We therefore assume that copy number gain of 22q13 is a novel frequent finding in ACC that may be involved in the initial pathogenesis of this neoplasm by proto-oncogene activation.

Adult↗
PubMed2005

Accuracy of image-guided implantology.

OBJECTIVES: The accuracy of two commercially available systems for image-guided dental implant insertion based on infrared tracking cameras was compared with manual implantation. MATERIAL AND METHODS: Phantoms of partially edentulous mandibles were used. In a master phantom, pilot boreholes for dental implants were placed. These boreholes were reproduced in slave phantoms using either of the two image-guided systems and manual implantation. The resulting positions were determined using a coordinate measurement machine and compared with the master model. RESULTS: In comparison with manual implantation, the difference of borehole positions to the master phantom was significantly lower using either of the systems for image-guided implant insertion. CONCLUSION: Image-guided insertion of dental implants is significantly more accurate than manual insertion. However, the accuracy that can be achieved with manual implantation is sufficient for most clinical situations.

Cephalometry↗
PubMed2005

Intraoperative augmented reality: the surgeons view.

Augmented Reality (AR) is a promising tool for intraoperative visualization. Two different AR systems, one projector based, one based on see-through glasses were used on patients. The task was the transfer of preoperative planning into the intraoperative reality, or the visualization of space occupying lesions, respectively. The intraoperative application of both systems is discussed from the surgeons point of view.

General Surgery↗
PubMed2005

Accuracy of assessing infrabony defects using a special digital filter for periodontal bone loss.

PURPOSE: To assess the accuracy of linear measurements of bone loss within infrabony defects on digitized radiographs after digital filtering particularly designed to image periodontal bone loss. METHODS: Before surgery, 50 standardized radiographs of 50 infrabony defects were obtained. Intrasurgically the distances from the cementoenamel-junction (CEJ) to the alveolar crest (AC), from the CEJ to the bottom of the bony defect (BD), and the depth of the infrabony component (INFRA) were assessed. All radiographs were digitized and the distances CEJ-AC, CEJ-BD, and INFRA were measured on digitized but unchanged radiographs and after use of the filter. RESULTS: There was a small overestimation of CEJ-AC (0.35-0.68 mm) and underestimation of CEJ-BD (0.84-1.12 mm) and INFRA (0.66-0.76 mm). Accuracy of measurement of the distance CEJ-AC was influenced by vertical angulation difference (P= 0.047) and the intrasurgical CEJ-AC (P= 0.003). Accuracy of CEJ-BD was influenced by intrasurgically assessed bone loss (P= 0.012). Accuracy of INFRA was influenced by individual patient, intrasurgically assessed INFRA (P< 0.001), and filter (P= 0.018).

Adult↗
PubMed2004

Frameless image guidance improves accuracy in three-dimensional interstitial brachytherapy needle placement.

PURPOSE: The aim of this work was to adapt a computer-assisted real-time three-dimensional (3D) navigation system for interstitial brachytherapy procedures. METHODS AND MATERIALS: The 3-D navigation system Surgical Planning and Orientation Computer System (SPOCS; Aesculap, Tuttlingen, Germany) was adapted for use in interstitial brachytherapy. A special needle holder with mounted infrared-emitting diodes (IRED) for 3D navigation-based needle implantation was developed. Measurements were made on a series of different phantoms to study the feasibility and the overall accuracy and precision of the navigation system with regard to single-needle application and volume implants (multiple-needle implantations). In all, 250 single implants and 20 volume implants were performed. Accuracy was measured as the target registration error (TRE) between the preoperatively defined and the achieved target position. RESULTS: Analyses of the 250 different targets showed a mean TRE for single-needle applications of 1.1 mm (SD +/- 0.4 mm), 0.9 mm (SD +/- 0.3 mm), and 0.7 mm (SD +/- 0.3 mm) in the x, y, and z direction, respectively. The maximal deviation was 2.3 mm. The corresponding TRE in the x, y, and z direction for volume implants was 1.6 mm (SD +/- 0.4 mm), 1.9 mm (SD +/- 0.6 mm), and 1.0 mm (SD +/- 0.4 mm), respectively. The maximum deviation was 2.9 mm. CONCLUSIONS: The adaptation of a commercially available surgical planning and navigation system to interstitial brachytherapy is feasible. It enables virtual planning and improved accuracy in 3D interstitial needle implantation.

Brachytherapy↗
PubMed2004

Piezosurgery: an ultrasound device for cutting bone and its use and limitations in maxillofacial surgery.

Piezosurgery uses modulated ultrasonic vibration to allow controlled cutting of bony structures. Delicate bony structures can be cut easily and with great precision, without destruction of soft tissue. We have found this device useful when exact cutting of thin bones is essential. However, it is of only limited use in cutting thick bones and in regions with limited access.

Bone and Bones↗
PubMed2004

Advanced surface-recording techniques for computer-assisted oral and maxillofacial surgery.

Markerless recording of patients based on natural anatomical surfaces makes planning of computer-assisted surgery much easier, as it is not necessary to place and measure markers. Recording of the surgical site with a laser scan takes the place of conventional marker-based recording. We have used auricles as well as the maxilla and mandible as reproducible surfaces. The geometric congruence of the laser scanned surface with the corresponding surface in the computed tomographs data-set and the applied intraoperative accuracy after recording with a laser scanner have been evaluated, and the system was successful in the maxilla (mean precision: 0.8mm, standard deviation: 0.3mm). In the mandible, the tongue and mobile floor of the mouth led to geometric incongruence and inadequate laser scanning. An exact recording using auricles was possible only as long as the auricles had not been temporarily deformed by the head support during CT imaging.

Ear, External↗
PubMed2004

Influence of marginal and segmental mandibular resection on the survival rate in patients with squamous cell carcinoma of the inferior parts of the oral cavity.

AIM: The aim of this retrospective study was to investigate whether radical (segmental resection) or conservative (marginal) resection of mandibular bone influenced patients, survival. PATIENTS AND METHODS: A series of 136 patients selected for partial mandibular resection for the treatment of squamous cell carcinomas of the lower oral cavity was evaluated retrospectively. Fifty-four patients underwent marginal and 82 cases segmental resection of the mandible. The mean follow-up periods were 91.1+/-30.1 months and 91.5+/-26.2 months, respectively. Data was extracted from the patient records and transferred into a database for statistical evaluation. Results Mean survival was 63.0+/-35.3 months for marginal and 53.1+/-32.3 months for segmental resection. The overall survival rate was analysed according to Kaplan-Meier and the test of significance (Log Rank) which yielded no statistically significant difference in the survival rate between both groups (p=0.1119). Numbers of recurrences, second primaries, metastases and/or postoperative complications were similar in both groups, i.e. no statistically significant differences were observed (ANOVA, Post-hoc Scheffé test). Conclusion In cases with an indication for bone resection, marginal resection may achieve satisfactory control and is as effective as segmental resection.

Analysis of Variance↗
PubMed2004

Markerless laser registration in image-guided oral and maxillofacial surgery.

PURPOSE: The use of registration markers in computer-assisted surgery is combined with high logistic costs and efforts. Markerless patient registration using laser scan surface registration techniques is a new challenging method. The present study was performed to evaluate the clinical accuracy in finding defined target points within the surgical site after markerless patient registration in image-guided oral and maxillofacial surgery. PATIENTS AND METHODS: Twenty consecutive patients with different cranial diseases were scheduled for computer-assisted surgery. Data set alignment between the surgical site and the computed tomography (CT) data set was performed by markerless laser scan surface registration of the patient's face. Intraoral rigidly attached registration markers were used as target points, which had to be detected by an infrared pointer. The Surgical Segment Navigator SSN++ has been used for all procedures. SSN++ is an investigative product based on the SSN system that had previously been developed by the presenting authors with the support of Carl Zeiss (Oberkochen, Germany). SSN++ is connected to a Polaris infrared camera (Northern Digital, Waterloo, Ontario, Canada) and to a Minolta VI 900 3D digitizer (Tokyo, Japan) for high-resolution laser scanning. RESULTS: Minimal differences in shape between the laser scan surface and the surface generated from the CT data set could be detected. Nevertheless, high-resolution laser scan of the skin surface allows for a precise patient registration (mean deviation 1.1 mm, maximum deviation 1.8 mm). CONCLUSIONS: Radiation load, logistic costs, and efforts arising from the planning of computer-assisted surgery of the head can be reduced because native (markerless) CT data sets can be used for laser scan-based surface registration.

Data Display↗
PubMed2004

Radiographic parameters for prognosis of periodontal healing of infrabony defects: two different definitions of defect depth.

BACKGROUND: The aim of the present study was to evaluate defect width and two different definitions of defect depth as prognostic factors of periodontal healing in infrabony defects treated by regenerative therapy 6 and 24 months after surgery. METHODS: In 32 patients with moderate to advanced periodontitis, 50 infrabony defects were treated by the guided tissue regeneration (GTR) technique using non-resorbable or bioabsorbable barriers. Clinical parameters were assessed, and 50 triplets of standardized radiographs were taken before surgery and 6 and 24 months after surgery. Using a computer-assisted analysis, the distances cemento-enamel junction (CEJ) to alveolar crest (AC), CEJ to bony defect (BD), horizontal projection of the most coronal extension of the bony wall to the root surface to BD, width, and angle of the bony defects were measured. Depth of the bony defect was 1) calculated as CEJ-BD minus CEJ-AC (INFRA1) and 2) measured as horizontal projection of the most coronal extension of the bony wall to the root surface to BD (INFRA2). RESULTS: Whereas statistically significant vertical clinical attachment level gains (CAL-V: 3.36 +/- 1.59 mm/ 3.41 +/- 1.72 mm; P < 0.001) could be found both 6 and 24 months after surgery, bony fill (0.70 +/- 2.52 mm; P = 0.056/1.21 +/- 2.55 mm; P < 0.005) was significant 24 months post-surgically only. In a multilevel regression analysis, CAL-V gain was predicted by bioabsorbable membrane (P = 0.005), baseline probing depths (PD) (P < 0.001), and actual smoking (P < 0.05). Bony fill could be predicted by baseline depth of the infrabony component as determined by INFRA2 (P < 0.05), angulation of bony defect (P < 0.005), and gingival index at baseline (P < 0.001). In narrow (< 37 degrees) and deep (> or = 4 mm) infrabony defects, bony fill was more pronounced than in wide and shallow defects (P < 0.001). CONCLUSIONS: Improvement achieved by GTR in infrabony defects can be maintained up to 24 months after surgery. Narrow and deep infrabony defects respond radiographically and are to some extent clinically more favorable to GTR therapy than are wide and shallow defects. The infrabony component of bony defects, as determined by the distance from the most coronal extension of the lateral bony wall to BD (INFRA2), is a better predictor of bony fill than that determined by AC-BD (INFRA1).

Absorbable Implants↗