Papers by Panagiotis Christou
Journal of Materials Processing Technology, 2015
The properties of parts manufactured by Laser Sintering (LS) are, amongst others, influenced by t... more The properties of parts manufactured by Laser Sintering (LS) are, amongst others, influenced by the packing and flow efficiencies of the powders being processed. In particular, this study investigated the influence of the bulk and flow characteristics of two thermoplastic elastomers, present in three different particle size distributions (PSD), on the resulting part properties. The powder characteristics examined, were the packing and bulk density as well as the flow efficiency of the powder samples. The resulting part properties were evaluated in terms of their mechanical properties (tensile), surface quality and density. The results helped to validate the basic input from previous studies interconnecting the powder behaviour with the properties of sintered part's. The majority of the components with increased tensile properties were manufactured with powder fractions that showed enhanced bulk density and enriched flowability. The part's surface quality demonstrated a high dependence on the packing and the surface roughness of the raw powder bulk. A strong connection between the packing density of the powder bulk and the porosity of the sintered parts has been revealed for the observed polymers. In contrast to previous studies which have rarely taken into account the characteristics of the un-sintered powder and correlated them to the properties of components fabricated by LS, this work provided a novel approach describing the interconnection between the powder behaviour and the part properties.
AUTHORS/INSTITUTIONS: M. Schimmel, F. Müller, Division of Gerodontology and Removable Prosthodont... more AUTHORS/INSTITUTIONS: M. Schimmel, F. Müller, Division of Gerodontology and Removable Prosthodontics, University of Geneva, Geneva, SWITZERLAND; M. Schimmel, Division of Gerodontology, University of Bern, Bern, SWITZERLAND; P. Christou, Private Practice of Orthodontics, Geneva, SWITZERLAND; H. Miyazaki, Department of Oral Health Science, Niigata University, Niigata, JAPAN; D. Halazonetis, Department of Orthodontics, National and Kapodistrian University of Athens, Athens, GREECE; F.R. Herrmann, F. Müller, Department of Internal Medicine, Rehabilitation and Geriatrics, University Hospitals of Geneva, Geneva, SWITZERLAND; Group Author Abstracts: ABSTRACT BODY: Objectives: Chewing efficiency may be evaluated using cohesive specimen, especially in elderly or dysphagic patients. The aim of this study was to evaluate three two-coloured chewing gums for a colour-mixing ability test and to validate a new purpose built software (ViewGum©). Methods: Dentate participants (dentate-group) and ede...
Journal of Dentistry, 2015
Keywords:
2010 IEEE Global Telecommunications Conference GLOBECOM 2010, 2010
As Wireless Sensor Networks (WSNs) expand their reach, their applications require lower energy co... more As Wireless Sensor Networks (WSNs) expand their reach, their applications require lower energy consumption than those provided by current offerings. In this paper, a novel platform is introduced, which employs a reconfigurable device (CPLD) in order to enhance the processing power of typical sensor nodes and, more importantly, reduce the overall energy consumption in common tasks such as routing and security. Our real-world measurements, demonstrate that the proposed system can reduce the energy consumption of the Cost Estimation algorithm of the widely used XMesh routing protocol by 71.5%. Higher energy conservations (more than 90%) can be achieved at Blowfish Encryption, when this is implemented on our new platform.
2009 16th International Conference on Systems, Signals and Image Processing, 2009
Abstract A crucial factor in numerous Wireless Sensor Networks (WSNs) is the security they provid... more Abstract A crucial factor in numerous Wireless Sensor Networks (WSNs) is the security they provide. A promising approach for providing high-levels of security at a low energy cost is the low-power reconfigurable Complex Programmable Logic Devices (CPLDs). This ...
Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology, 2002
Journal of Oral Rehabilitation, 2007
The aim of this study was to investigate different assessment methods of a two-colour chewing gum... more The aim of this study was to investigate different assessment methods of a two-colour chewing gum test for masticatory efficiency to determine its validity for research and clinical purposes. Twenty adult volunteers, eleven women and nine men (mean age of 27.5 years), participated in this study. All participants perceived their masticatory efficiency as normal. The task was to chew five samples of a two-colour chewing gum for 5, 10, 20, 30 and 50 cycles respectively. Maximum bite force was measured. All samples were assessed twice by two independent operators both, as 'bolus' and after flattening to 1 mm thick 'wafers'. The latter were scanned and the unmixed pixels counted using Adobe Photoshop Elements to calculate the ratio of unmixed colour to the total surface. Digital image processing confirmed a significant correlation between colour mixing and chewing duration (P < 0.001). Subjective assessment proved less accurate with fair to substantial intra-examiner agreement for 'bolus' (0.20 < kappa < 0.63) and substantial to almost perfect agreement for 'wafer' (0.60 < kappa < 0.88). Inter-examiner agreement was consistently moderate or substantial only for specimen chewed 20 cycles or longer. No significant correlation was found between the colour mixture and the maximum bite force. Digital image processing of the two-colour chewing gum test specimen provides reliable quantitative data for chewing efficiency. Visual assessments were less reliable but might still be useful in screening for chewing deficiencies in a clinical setting. In this context, the test should be performed with a flattened specimen chewed, probably for 20 cycles.
Journal of Oral Rehabilitation, 2011
Facial weakness is frequently observed in patients with hemispheric stroke. Most reports refer to... more Facial weakness is frequently observed in patients with hemispheric stroke. Most reports refer to qualitative assessment. The aim was to quantify the upper and lower facial muscle function in patients with hemispheric stroke. Three different facial expressions (forced smile, posed smile and maximum eyebrow lift) and facial rest position were mapped using a 3D video system. Twenty-seven patients with hemispheric stroke (PG) and 22 controls (CG) were recruited. Facial asymmetry was expressed as absolute side differences between four corresponding distances. In PG, a longer distance was found from inner canthus to oral commissure (dist1) on the impaired side in all investigated poses (PG non-affected-affected side: range of all poses 1·18 ± 4·45 to 1·80 ± 2·37 mm; CG right-left side: range -0·69 ± 1·55 to -0·43 ± 1·39 mm, Mann-Whitney tests: 0·0002 < P < 0·0423). In addition, the ratio of the impaired to the non-affected side was different in PG for dist1 in rest and eyebrow lift (Wilcoxon tests: 0·0011 < P < 0·0288). CG showed asymmetries in rest and forced smile (Wilcoxon tests: P = 0·0392 and P = 0·0424). Furthermore, dist1 in PG showed higher variances than in CG (F-tests: 0·0001 < P < 0·0445) except for the relative dist1 at rest (F-test: P = 0·0533). The distance between inner eyebrow corner and inner canthus showed no side difference in both groups during eyebrow lift (n.s.); nevertheless, two patients showed distinct asymmetries. The employed 3D video system proved sensitive in assessing facial muscle function. The results confirm and quantify that the lower facial muscles are more affected by hemispheric stroke than the upper ones and show that the measured distances were more variable in post-stroke patients than in control subjects.
Journal of Oral Rehabilitation, 2010
The aim of the study was to investigate the thickness of the masseter muscles in stroke patients ... more The aim of the study was to investigate the thickness of the masseter muscles in stroke patients when compared to a control group (CG). Hospitalised stroke patients (18 men, 13 women; age 69.0 +/- 12.7 years) were compared to a CG (13 men, 11 women; age 68.8 +/- 10.8 years) composed to correspond to in age, gender and dental state. The thickness of the masseter muscle was recorded by means of a real-time ultrasound scanner on both sides, twice under contraction and twice in relaxed condition. In the stroke patients, the thickness of the masseter muscle of the affected side (aff) was smaller than the one of the non-affected side (non-aff) both, under contraction (aff 13.1 +/- 2.4 mm; non-aff 13.8 +/- 2.3 mm, P </= 0.004) and relaxation (aff 13.1 +/- 2.5 mm; non-aff 13.6 +/- 2.3 mm, P </= 0.05). No consistent side differences were found in the thickness of the masseter muscles in CG (contracted right: 14.1 +/- 3.2 mm, left: 14.2 +/- 3.1 mm and relaxed right: 14.0 +/- 3.2, left: 14.3 +/- 3.2 mm, n.s.). The results suggest an influence of stroke on the stomatognathic system; because in patients with hemispheric stroke, a side difference is established in their oral functions. This asymmetric stimulation of the masticatory muscles may have caused this difference in the masseter muscle bulk.
Journal of Oral Rehabilitation, 2013
Blending of chewing gums of different colours is used in the clinical setting, as a simple and re... more Blending of chewing gums of different colours is used in the clinical setting, as a simple and reliable means for the assessment of chewing efficiency. However, the available software is difficult to use in an everyday clinical setting, and there is no possibility of automated classification of the patient's chewing ability in a graph, to facilitate visualisation of the results and to evaluate potential chewing difficulties. The aims of this study were to test the validity of ViewGum - a novel image analysis software for the evaluation of boli derived from a two-colour mixing ability test - and to establish a baseline graph for the representation of the masticatory efficiency in a healthy population. Image analysis demonstrated significant hue variation decrease as the number of chewing cycles increased, indicating a higher degree of colour mixture. Standard deviation of hue (SDHue) was significantly different between all chewing cycles. Regression of the log-transformed values of the medians of SDHue on the number of chewing cycles showed a high statistically significant correlation (r² = 0.94, P < 0.01). ViewGum eliminates drawbacks of previous two-colour chewing gum test methods by the simplicity of its application. The newly developed ViewGum software provides speed, ease of use and immediate extraction of clinically useful conclusions to the already established method of chewing efficiency evaluation and is a valid adjunct for the evaluation of masticatory efficiency with two-colour chewing gum.
Gerodontology, 2011
Objective: The aim of this study was to test the hypothesis that impairment of orofacial function... more Objective: The aim of this study was to test the hypothesis that impairment of orofacial function following stroke affects the patients' oral health-related quality of life (OHRQoL). Material and methods: From the University Hospitals of Geneva, 31 stroke patients (18 men, 13 women, mean age 69.0 ± 12.7 years) with unilateral facial and limb palsy were recruited (patient group, PG). In the study, the Oral Health Impact Profile (OHIP)-EDENT was utilised to assess OHRQoL. Further examinations comprised a test of masticatory efficiency and lip force, stroke severity National Institute of Health Stroke Scale and dental state. The control group (CG) consisted of 24 subjects with similar age, gender and dental state. Results: The PG mean OHIP-EDENT sum score was 18.8 ± 15.5 and proved higher than one of the CG, indicating a lower OHRQoL in the PG (p < 0.01). The score of the sub-domains 'functional limitation' and 'physical pain' were significantly higher in PG (p < 0.03 and p < 0.02, respectively). The masticatory efficiency was significantly lower in the PG (p < 0.0001) and was associated with the OHIP-EDENT sum score and its sub-domains, except for 'physical disability'. This effect was not present in the CG. Conclusion: The OHRQoL is significantly reduced in hospitalised stroke patients whereby functional impairment seems predominant when compared with psychological and psycho-social aspects.
American Journal of Orthodontics and Dentofacial Orthopedics, 2010
Introduction: The aim of this study was to investigate a new digital 3-dimensional infrared video... more Introduction: The aim of this study was to investigate a new digital 3-dimensional infrared video system to determine its accuracy, precision, and validity in measuring facial distances. Methods: Bench experiments were performed by measuring the vertical and diagonal distances of chessboard squares of known length to determine the system's accuracy and precision. To test the system's validity, 16 healthy volunteers participated in this study. Vertical and horizontal distances of the face were measured electronically at rest, and on posed and aggressive smiles. All measurements were repeated after 8 weeks. Direct measurements of the intercanthal distance were obtained twice with calipers. Results: A minor systematic error was found in the bench experiments, with the highest absolute error of 0.227 6 0.39 mm. The analysis with this video system showed good reproducibility of all measured distances when the mean of 2 frames was used to compare distances. Digital measurements of the intercanthal distances showed high agreement with the clinically obtained values. Conclusions: This digital video system can measure geometric distances in a 3-dimensional environment with high precision. Facial distances can be measured with good accuracy and precision, allowing applications in research and clinical practice. (Am J Orthod Dentofacial Orthop 2010;137:580.e1-580.e10)
American Journal of Orthodontics and Dentofacial Orthopedics, 2010
Advances in Medical Sciences, 2000
Examine the prevalence of carotid artery calcifications in standard dental panoramic radiographs ... more Examine the prevalence of carotid artery calcifications in standard dental panoramic radiographs (OPT), their association to gender, medical history and oral status. Assess the predictive value of a dental OPT in early diagnosis of carotid artery calcifications. Fourteen patients admitted to Geneva University Hospital for recent ischemic stroke and stenosis of the carotid artery confirmed by Duplex sonography. All OPTs were digitised and subsequently assessed independently by two operators. From 21 carotid artery calcifications detected with Doppler sonography 15 were visible on the corresponding OPT, most of them on the right side (n=11). No correlation was found between the side of calcification and cerebral lesion. Hypertension and periodontal disease were the most prevalent cardiovascular risk factors. Dentists who either detect carotid artery calcifications in OPTs or see patients with severe periodontitis should consider a prophylactic specialist examination.
Journal of Materials Processing Technology, 2015
ABSTRACT The properties of parts manufactured by laser sintering (LS) are, amongst others, influe... more ABSTRACT The properties of parts manufactured by laser sintering (LS) are, amongst others, influenced by the packing and flow efficiencies of the powders being processed. In particular, this study investigated the influence of the bulk and flow characteristics of two thermoplastic elastomers, present in three different particle size distributions (PSD), on the resulting part properties. The powder characteristics examined, were the packing and bulk density as well as the flow efficiency of the powder samples. The resulting part properties were evaluated in terms of their mechanical properties (tensile), surface quality and density. The results helped to validate the basic input from previous studies interconnecting the powder behaviour with the properties of sintered part&#39;s. The majority of the components with increased tensile properties were manufactured with powder fractions that showed enhanced bulk density and enriched flowability. The part&#39;s surface quality demonstrated a high dependence on the packing and the surface roughness of the raw powder bulk. A strong connection between the packing density of the powder bulk and the porosity of the sintered parts has been revealed for the observed polymers. In contrast to previous studies which have rarely taken into account the characteristics of the un-sintered powder and correlated them to the properties of components fabricated by LS, this work provided a novel approach describing the interconnection between the powder behaviour and the part properties.
Uploads
Papers by Panagiotis Christou