Software-supported periodontal diagnostics with three-dimensional cone-beam computed tomography compared to conventional two-dimensional panoramic imaging and clinical diagnostics (a prospective study).

AIM: Aim of this study comprised the software-supported evaluation of measurement accuracy between cone-beam computed tomography (CBCT) and panoramic radiographs in the assessment of the periodontal bone level in patients with periodontitis and comparison with clinical periodontal parameters. MATERIAL AND METHODS: Twenty patients with severe periodontitis (stage III-IV) were evaluated clinically and radiographically (panoramic and CBCT). Diagnostic interpretation comprised three blinded investigators with different levels of experience. Specific software-basing measurement procedure evaluated radiological distances for the mesial, central, and distal bone levels on the oral and vestibular sides of the teeth investigated and furcation upper and lower boundary. Jaw localization, anatomical region-of-interest, the number of roots and experience of the observers were evaluated. All measurements were carried out twice by the same observers within a 6-week interval. RESULTS: Slightly higher measurement deviations (SD) in the range of 0.47 (0.40) mm were found for CBCT evaluation compared to panoramic imaging. Pearson correlation analysis showed statistically strong positive correlation for the mesial and distal aspects, moderate positive correlation was found for the investigated furcations between both radiographic modalities. Compared to the clinical reference, the mean total error of measurement (SD) was larger for panoramic imaging (0.66 (0.48) mm) than CBCT (0.27 (0.08) mm) for all three observers. CONCLUSIONS: Software-supported CBCT analysis delivers better diagnostic information about the bony periodontal conditions of the patient compared to two-dimensional radiographs. However, it remains unclear if these additional information lead to better periodontal outcomes.

Characterization of MOSFET dosimeters for low-dose measurements in maxillofacial anthropomorphic phantoms.

The aims of this study were to characterize reinforced metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters to assess the measurement uncertainty, single exposure low-dose limit with acceptable accuracy, and the number of exposures required to attain the corresponding limit of the thermoluminescent dosimeters (TLD). The second aim was to characterize MOSFET dosimeter sensitivities for two dental photon energy ranges, dose dependency, dose rate dependency, and accumulated dose dependency. A further aim was to compare the performance of MOSFETs with those of TLDs in an anthropomorphic phantom head using a dentomaxillofacial CBCT device. The uncertainty was assessed by exposing 20 MOSFETs and a Barracuda MPD reference dosimeter. The MOSFET dosimeter sensitivities were evaluated for two photon energy ranges (50-90 kVp) using a constant dose and polymethylmethacrylate backscatter material. MOSFET and TLD comparative point-dose measurements were performed on an anthropomorphic phantom that was exposed with a clinical CBCT protocol. The MOSFET single exposure low dose limit (25% uncertainty, k = 2) was 1.69 mGy. An averaging of eight MOSFET exposures was required to attain the corresponding TLD (0.3 mGy) low-dose limit. The sensitivity was 3.09 ± 0.13 mV/mGy independently of the photon energy used. The MOSFET dosimeters did not present dose or dose rate sensitivity but, however, presented a 1% decrease of sensitivity per 1000 mV for accumulated threshold voltages between 8300 mV and 17500 mV. The point doses in an anthropomorphic phantom ranged for MOSFETs between 0.24 mGy and 2.29 mGy and for TLDs between 0.25 and 2.09 mGy, respectively. The mean difference was -8%. The MOSFET dosimeters presented statistically insignificant energy dependency. By averaging multiple exposures, the MOSFET dosimeters can achieve a TLD-comparable low-dose limit and constitute a feasible method for diagnostic dosimetry using anthropomorphic phantoms. However, for single in vivo measurements (<1.7 mGy) the sensitivity is too low.

Impact of malpositioning on panoramic radiography in implant dentistry.

OBJECTIVES: The widely used panoramic radiography as a special kind of tomography underlies intrinsic procedural restrictions such as poor definition, inconsistent magnification, geometric distortion and spatial depositioning of objects situated outside the focal trough. This results in a non-anatomic display of the radiographed anatomic structures. Individual mandibular angle and width of the jaws, adjustment of the focal trough, jaw incongruence as well as patient positioning increase the inconsistency in display of the radiographed objects. This study precisely evaluated the quantitative impact of object malpositioning on the display in panoramic radiography. MATERIALS AND METHODS: A special dental implant model was highly accurate three dimensionally malpositioned and panoramic radiographs were taken. Automated image analysis was performed to exclude subjective assessment error. RESULTS: Precise and retraceable object deposition of up to 5 mm or 5° resulted in relevant deposition of objects and significant changes in object size and inter-object distances in the panoramic image. Unidirectional malpositioning lead to multiple errors in display. CONCLUSIONS: The extent of malpositioning-related display errors additionally to the known physicotechnical insufficiencies of the panoramic radiography demonstrates its limitations in precisely interpreting spatial relationships. CLINICAL RELEVANCE: Measurements within the panoramic radiography must not claim reliability. For a single object securely positioned in the focal trough and perpendicular to the central X-ray beam, measurements may be trustworthy on clinical scale. Once sterical relationships to other structures are evaluated, reliability must be questioned.

Quantification of human growth hormone in serum with a labeled protein as an internal standard: essential considerations.

To manage and inform diagnostic or therapeutic decisions, measurement results which are accurate, specific, and comparable between laboratories are required. Two challenges associated with this are the definition of the measurand and the commutability of the reference standard used. Once the measurand is defined, the next step in improving standardization is developing traceable quantification methods for proteins in biological fluids. A novel reference method for the quantification of recombinant human growth hormone (rhGH) in serum has been developed using multistep sample cleanup at the protein level, tryptic digestion, and isotope dilution mass spectrometry (IDMS). Critical considerations for using isotopically labeled rhGH as the internal standard are described. A bulk serum sample was prepared at the clinically relevant level of 10 ng/g and quantified using the method described to give results traceable to the International System of Units (SI) with a total measurement uncertainty of <20%. Results compared favorably with an orthogonal traceable method using total tryptic digestion, peptide separation, and isotope dilution mass spectrometry.

Comparison between observer-based and AI-based reading of CBCT datasets: An interrater-reliability study.

Objective: To assess the performance of human observers and convolutional neural networks (CNNs) in detecting periodontal lesions in cone beam computed tomography (CBCT), a total of 38 datasets were examined. Three human readers and a CNN-based solution were employed to evaluate the presence of periodontal pathologies in these datasets. Materials and Methods: Datasets were acquired with a Veraview X800 L P (JMorita Mfg. Corp., Kyoto, Japan). Three general dentists, previously calibrated by a general principal investigator, read the datasets in 3D MPR mode using Horos(LGPL license at Horosproject.org and sponsored by Nimble Co LLC d/b/a Purview in Annapolis, MD, USA) as a DICOM reader. All pathological changes including vertical bone loss, furcation involvement, and periradicular osteolysis were detected. Furthermore, the same datasets were analyzed automatically by Diagnocat (Diagnocat LLC, Prague, Czech Republic), a deep CNN. Finally, the performance of the dentists and the CNN were compared and evaluated. Results: The CNN's performance was significantly lower compared to the human readers in the search for different types of lesions. The human observers achieved good to very good interobserver agreement, except for the evaluation of the vertical lesions, which resulted in a moderate agreement. Conclusion: The CNN used in this study was found to be ineffective in identifying periodontal lesions and was not adequately trained to offer significant assistance in the automated evaluation of periodontal lesions in CBCT datasets.

Digital method for quantification of circumferential periodontal bone level using cone beam CT.

OBJECTIVES: The objective of this study is to develop a new approach for radiographically measuring circumferential periodontal bone level using cone beam CT (CBCT) data. Accuracy and precision were assessed using direct probe measurements on a human skull as a reference. MATERIALS AND METHODS: Digital quantification of circumferential periodontal bone levels was conducted considering bone level measurements, infrabony crater, and furcation detection. For this purpose, a human bony cadaver skull with a restoration free dentition was used, showing periodontal bony defects of teeth 15-17,25-27,35-37,45-47 (FDI classification). Image datasets were acquired using a Promax 3D CBCT device (Planmeca Oy, Helsinki, Finland) at 80 kV and 8 mA, 160 µm voxel size. Circumferential radiographic measurements between cemento-enamel junction and the alveolar crest for the mesial, central, and distal bone levels on the oral and vestibular sides of the examined teeth were carried out based on a prototype of specifically developed software. The measurements were performed by an expert panel of three independent, calibrated, and blinded observers. Manual probe measurements of the periodontal bone loss served as reference standard. RESULTS: The adopted software allowed the quantification of periodontal bone loss at all examined teeth. Overall deviation between radiographic and manual measurements of the observers ranged between 0.36 and 0.69 mm; hereby, 83 % of all results were <0.5 mm. Comparing overall accuracy between the ten turns of radiological measurements, accuracy for all observers ranged from 0.29 to 0.46 mm. The present study design showed a 100 % detection of furcation involvement for radiographic evaluation. CONCLUSIONS: The adoption of a special measurement procedure in terms of a 3D coordinate system, which is placed through and perpendicular to the long axis of the tooth, allows consistent measurement positions of the mesial, central, and distal bone levels both for the oral and vestibular sides of the alveolar crest. In this way, reliable and reproducible quantification of circumferential periodontal bone loss using CBCT data with standardized resolution of 160 µm can be performed in all three dimensions. CLINICAL RELEVANCE: This new approach of radiographically assessing circumferential periodontal bone level using CBCT data shows a first promising attempt of accurate detection of periodontal bony defects. Yet, possible negative impact of further clinical parameters in terms of artifact occurrence will have to be furthermore carefully investigated.

Qualitative and quantitative evaluation of bony structures based on DICOM dataset.

PURPOSE: The aim of this study was to investigate bone mass using different cone-beam computed tomographies (CBCTs) combined with image analysis and to determine whether bone quantity or quality was detected. MATERIALS AND METHODS: Different measurements recorded on mandible bones of pigs in the retromolar region were evaluated on ProMax 3D (Planmeca Oy, Finland) and the ILUMA™CT (IMTEC™ Imaging, Ardmore, OK) to calculate a calibration curve. The spatial relationships of pig mandible halves relative to adjacent defined anatomical structures were assessed by means of 3D visualization software. In addition to the screenshot, their bone quality was evaluated in accordance with the Lenkholm and Zarb classification. RESULTS: The CBCT calibration curves based on the measurements taken from the ProMax and ILUMA CT showed linear correlation. Huge Hounsfield units intervals were found between the 2 CBCTs and there was no correlation with the computed tomography. Exact information on the micromorphology of the bone cylinders was not available. A subjective correlation according to Lenkholm and Zarb showed overlapping in all groups. CONCLUSIONS: CBCT is a good choice for analyzing bone mass. However, it does not provide any information on bone quality. To obtain information on the microarchitecture of the spongiosa, it is necessary to use a computed tomography with finite element analysis.

Comparison of manual and dose reduction modes of a MORITA R100 CBCT.

OBJECTIVE:: To compare effective dose differences when acquiring (1) dose reduction mode and (2) manual mode in a MORITA R100 CBCT. METHODS:: 24 exposure protocols with different technique factors were performed in both the dose reduction mode and the manual mode in a Veraviewepocs 3D R100 cone beam CT device. 48 TLD were placed in a RANDO head phantom at 24 different sites. Effective doses were calculated according to the formalism published in the 103rd ICRP report. RESULTS:: Effective doses for the dose reduction mode protocols ranged from 14 to 156 µSv [mean = 57 µSv, standard deviation (SD) = 37 µSv], whereas effective doses for the manual mode protocols ranged from 22 to 267 µSv (mean = 94 µSv, SD = 65 µSv). Thus, across all protocols, the dose reduction mode leads to a drop of the effective dose by 38 % (SD = 6 %). CONCLUSIONS:: The estimated effective doses are significantly lower if dose reduction protocols are acquired.

Operator safety during the acquisition of intraoral images with a handheld and portable X-ray device.

OBJECTIVES: The present study aims at investigating different radiation protection issues and dose values while acquiring intraoral images with a handheld X-ray device. METHODS: An Aribex NOMAD Pro 2™, a RANDO® male head phantom, a consistency testing body, a PTW NOMEX® Multimeter, and a PTW Farmer® Ionization Chamber Type 30,010 were used to investigate: (1) dose area products; (2) the expansion of the control area (CA); (3) the scattering pattern and (4) the potential risk for operators of the X-ray device. RESULTS: Dose area products at different exposure times were distributed linearly with a high correlation factor (>0.9). At 4000 simulated exposures, the greatest extent of the CA was 42 cm (mean = 16.7 cm, SD = 10.8 cm). The highest occurrence of scattering radiation resulted between the RANDO® phantom and the X-ray device. No scattered radiation was measured at the dorsal part of the phantom or on the operator site of a virtual vertical plane through the focal spot of the X-ray. CONCLUSIONS: Through this study, we could demonstrate that the application of an Aribex NOMAD Pro 2 device for intraoral imaging does not increase the risk for the operator if the device is controlled according to the manufacturer's specifications. Furthermore, we were able to show that the CA was significantly smaller than specified by European and other international radiation protection standards.

Growth hormone isoform-differential mass spectrometry for doping control purposes.

Mass spectrometry (MS) allows for monitoring growth hormone (GH) isoform compositions at high specificity. It is demonstrated that this capability can be used to reliably detect alterations as elicited by (putative) doping with 22 kDa-GH. Sample treatment consists of enzymatic protein cleavage, followed by 2-step liquid chromatography clean-up, prior to analysis by MS. The protocol does not depend on antibodies for analyte extraction at any stage. Therefore, MS opens an opportunity for independent confirmation, if combined with the antibody-based isoform differential test presently used in practice. To check the fitness-for-purpose of this concept, GH-free serum was spiked with pure 22 kDa- and 20 kDa-GH covering a representative range of concentrations (0.5-9.4 µg/L), while the 22kDa fraction was within a range of  80%-85%, or at 100%, the latter simulating an administration of 22 kDa-GH. Mean deviation of 22 kDa-fractions found was within less than 3% for samples with total GH>= 1 µg/L . Beyond this, results by antibody-free isoform-differential MS, as described, were in line with those of the World Anti-Doping Agency-approved antibody-based test for 18 native sera and 3 positive controls. In this context, relating 22 kDa-GH to total-GH rather than 22 kDa+20 kDa was considered as an alternative strategy to earlier approaches. However, 20 kDa-GH as an additional measurand, next to 22 kDa- and total-GH, provides useful extra information, as it directly indicates the presence or absence of a non-22 kDa-GH form.

Influence of lead apron shielding on absorbed doses from cone-beam computed tomography.

The aim of the present work was to investigate absorbed and to calculate effective doses (EDs) in cone-beam computed tomography (CBCT). The study was conducted using examination protocols with and without lead apron shielding. A full-body male RANDO® phantom was loaded with 110 GR200A thermoluminescence dosemeter chips at 55 different sites and set up in two different CBCT systems (CS 9500®, ProMax® 3D). Two different protocols were performed: the phantom was set up (1) with and (2) without a lead apron. No statistically significant differences in organ and absorbed doses from regions outside the primary beam could be found when comparing results from exposures with and without lead apron shielding. Consequently, calculating the ED showed no significant differences between the examination protocols with and without lead apron shielding. For the ProMax® 3D with shielding, the ED was 149 µSv, and for the examination protocol without shielding 148 µSv (SD = 0.31 µSv). For the CS 9500®, the ED was 88 and 86 µSv (SD = 0.95 µSv), respectively, with and without lead apron shielding. The results revealed no statistically significant differences in the absorbed doses between examination with and without lead apron shielding, especially in organs outside the primary beam.

Feasibility and Accuracy of Digitizing Edentulous Maxillectomy Defects: A Comparative Study.

PURPOSE: The aim of this study was to evaluate the feasibility and accuracy of using an intraoral scanner to digitize edentulous maxillectomy defects. MATERIALS AND METHODS: A total of 20 maxillectomy models with two defect types were digitized using cone beam computed tomography. Conventional and digital impressions were made using silicone impression material and a laboratory optical scanner as well as a chairside intraoral scanner. The 3D datasets were analyzed using 3D evaluation software. RESULTS: Two-way analysis of variance revealed no interaction between defect types and impression methods, and the accuracy of the impression methods was significantly different (P = .0374). CONCLUSION: Digitizing edentulous maxillectomy defect models using a chairside intraoral scanner appears to be feasible and accurate.

Improved surgical procedure using intraoperative navigation for the implantation of the SPG microstimulator in patients with chronic cluster headache.

INTRODUCTION: The ATI SPG microstimulator is designed to be fixed on the posterior maxilla, with the integrated lead extending into the pterygopalatine fossa to electrically stimulate the sphenopalatine ganglion (SPG) as a treatment for cluster headache. Preoperative surgical planning to ensure the placement of the microstimulator in close proximity (within 5 mm) to the SPG is critical for treatment efficacy. The aim of this study was to improve the surgical procedure by navigating the initial dissection prior to implantation using a passive optical navigation system and to match the post-operative CBCT images with the preoperative treatment plan to verify the accuracy of the intraoperative placement of the microstimulator. METHODS: Custom methods and software were used that result in a 3D rotatable digitally reconstructed fluoroscopic image illustrating the patient-specific placement with the ATI SPG microstimulator. Those software tools were preoperatively integrated with the planning software of the navigation system to be used intraoperatively for navigated placement. Intraoperatively, the SPG microstimulator was implanted by completing the initial dissection with CT navigation, while the final position of the stimulator was verified by 3D CBCT. Those reconstructed images were then immediately matched with the preoperative CT scans with the digitally inserted SPG microstimulator. This method allowed for visual comparison of both CT scans and verified correct positioning of the SPG microstimulator. RESULTS: Twenty-four surgeries were performed using this new method of CT navigated assistance during SPG microstimulator implantation. Those results were compared to results of 21 patients previously implanted without the assistance of CT navigation. Using CT navigation during the initial dissection, an average distance reduction of 1.2 mm between the target point and electrode tip of the SPG microstimulator was achieved. Using the navigation software for navigated implantation and matching the preoperative planned scans with those performed post-operatively, the average distance was 2.17 mm with navigation, compared to 3.37 mm in the 28 surgeries without navigation. CONCLUSION: Results from this new procedure showed a significant reduction (p = 0.009) in the average distance from the SPG microstimulator to the desired target point. Therefore, a distinct improvement could be achieved in positioning of the SPG microstimulator through the use of intraoperative navigation during the initial dissection and by post-operative matching of pre- and post-operatively performed CBCT scans.

Correlation of age and ossification of the medial clavicular epiphysis using computed tomography.

OBJECT: The aim of this study was the examination of relationship between the age and the ossification of medial epiphysis of the clavicle referred to CT examination. MATERIALS AND METHODS: Concerning the epiphyseal ossification of the clavicle CT's of 100 patients (50 male and 50 female) between 16 and 25 years (10 patients for each year) were analyzed by three viewers. RESULTS: In the legal relevant age segment (16-25a) we saw a turnover from stage 3 to stage 4 at the age of 21 years. The calculated empiric distribution function showed 95% of stage 4 over 21 years while 75% of the patients with stage 3 were under 21 years. A reconstruction kernel suitable for osseous structures should be used, images should be viewed or presented in a bone window. CONCLUSION: According to these results it can be concluded that a person with stage 4 is probably 21 years or older, while a stage 3 leads to an estimated age under 21 years. On the other hand, a confidence level of 99.67% is not reached. Therefore, CT of the medial epiphysis of the clavicle will only be suitable for age estimation around the age of 21 years, if this relevant statistic obstacle is defeated. Bearing this in mind, further studies are needed to evaluate slice thickness as the most critical parameter.

Obstacles in spatial evaluation of CBCT-reformatted panoramic imaging.

OBJECTIVES: Conventional panoramic radiography (cPR) underlines procedure-related limitations in the display of objects. CBCT is presumed to overcome these constraints. To virtualize a cPR view, reformatted panoramic images (rPIs) can be generated. This study evaluated the rPI with regard to its susceptibility to sterical object deposition in comparison with cPR. METHODS: A specially developed implant model with dental implants each of 4.0-mm diameter and 11.0-mm length was depositioned by shift, rotation and tilt of 5.00 mm (±0.01 mm) of horizontal shift and 5.0° (±0.167°), respectively, on a highly precise goniometer rotation table, and cPRs and rPIs were generated. Automated evaluation of the cPRs was carried out using a specially developed software. rPIs were processed and analyzed by a semi-automated image analysis. RESULTS: Object deposition lead to distortive effects in the rPI analogue to cPR, but they appear in display only. Objects illustrated in the rPI were dimensionally correct, but sterical relations are elusive. Results are obtained for the horizontal shift, declination and reclination, lateral tilt and rotation. CONCLUSIONS: Distortions within the rPI represent the illustration of the hyperbolic-shaped layer out of the three-dimensional data set. With this study, we demonstrated these procedure-related inherent but practically underestimated consequences. Effects of sterical object malpositioning must be compensated by the observer by adequate virtual adjustment of the processed layer. Accurate virtual adjustment leads to vertical dimensions. Sterical relations, e.g. angulation of two objects, are irretraceable unless precisely referenced.

Optimized 14 + 1 receive coil array and position system for 3D high-resolution MRI of dental and maxillomandibular structures.

OBJECTIVES: The purpose of this study was to design, build and test a multielement receive coil array and position system, which is optimized for three-dimensional (3D) high-resolution dental and maxillomandibular MRI with high patient comfort. METHODS: A 14 + 1 coil array and positioning system, allowing easy handling by the technologists, reproducible positioning of the patients and high patient comfort, was tested with three healthy volunteers using a 3.0-T MRI machine (Siemens Skyra; Siemens Medical Solutions, Erlangen, Germany). High-resolution 3D T1 weighted, water excitation T1 weighted and fat-saturated T2 weighted imaging sequences were scanned, and 3D image data were reformatted in different orientations and curvatures to aid diagnosis. RESULTS: The high number of receiving coils and the comfortable positioning of the coil array close to the patient's face provided a high signal-to-noise ratio and allowed high quality, high resolution, 3D image data to be acquired within reasonable scan times owing to the possibility of parallel image acquisition acceleration. Reformatting the isotropic 3D image data in different views is helpful for diagnosis, e.g. panoramic reconstruction. The visibility of soft tissues such as the mandibular canal, nutritive canals and periodontal ligaments was exquisite. CONCLUSIONS: The optimized MRI receive coil array and positioning system for dental and oral-maxillofacial imaging provides a valuable tool for detecting and diagnosing pathologies in dental and oral-maxillofacial structures while avoiding radiation dose. The high patient comfort, as achieved by our design, is very crucial, since image artefacts due to movement or failing to complete the examination jeopardize the diagnostic value of MRI examinations.

Evaluation of quality of reformatted images from two cone-beam computed tomographic systems.

PURPOSE: The aim of the study was to compare image quality of two different systems based on cone-beam computed tomography (CBCT). STUDY DESIGN: Primary and secondary reconstructions were performed from data sets of the Siremobil Iso-C(3D) (Siemens Medical Solutions, Erlangen, Germany) and the NewTom 9000 (NIM s.r.l., Verona, Italy) using a dried human skull. Using defined anatomical structures, image quality was analysed by 10 examiners using a ranking scale. RESULTS: Regarding image quality there was no statistically significant difference between the two systems compared. CONCLUSION: The preliminary results show, that imaging of the facial skeleton using the Siremobil Iso-C(3D) can be performed with a quality comparable to the NewTom 9000.

Evaluation of transversal slice imaging in the diagnosis of tooth displacement with special consideration of the upper canines.

AIM: The exact localization and analysis of displaced, retained or impacted teeth can rarely be achieved by common radiologic methods providing eccentric or occlusal images. The aim of this study was to evaluate transversal slice imaging (TSI) as a diagnostic alternative, keeping radiation exposure under consideration. MATERIAL AND METHODS: In a pilot study, we simulated seven different canine positions in a phantom head. Each tooth position was visualized by transversal slice imaging and compared by several observers independently and blinded to computer tomography (CT) serving as the gold standard. The clinical study included the retrospective analysis of TSI samples from 27 patients (mean age 13.7 yrs.) according to these criteria: 1. location of the canine crown and root, 2. recognition of the crown, 3. stage of root development, 4. root dilaceration, 5. periodontal ligament space, 6. ankylosis, 7. relationship to neighboring teeth, and 8. resorptions of neighboring teeth. The evaluations of canine position were compared to the results gained intraoperatively. RESULTS: In the transversal slice images taken from a phantom head, the observers' estimations of the canine position were identical in five cases (71.4%). At least four observers using TSI described identical tooth positions in 89% of patients. In 2.5%, no statement concerning tooth position was feasible. Crown recognition was possible in 75% of cases. Ankylosis, periodontal ligament space, root development, dilacerations and resorptions were not assessable in the majority of the cases. CONCLUSION: Transversal slice imaging can be recommended as a second plane projection in diagnosing tooth displacement, especially concerning oro-vestibular localization (effective radiation dose 0.003-0.012 mSv). However, as far as periodontal ligament space, resorptions and root morphology are concerned, this method has its limits.

Magnetic field interactions of orthodontic wires during magnetic resonance imaging (MRI) at 1.5 Tesla.

BACKGROUND: Orthodontic appliances pose a potential risk during magnetic resonance imaging (MRI) due to forces on metallic objects within the static magnetic field of MRI systems. The aim of the present investigation was to measure forces on orthodontic wires caused by the static magnetic field of a 1.5-Tesla MRI system, and to assess the safety hazards associated with these forces. MATERIALS AND METHODS: Thirty-two different orthodontic wires (21 arch wires, eight ligature wires and three retainer wires) were investigated in a 1.5-Tesla MRI system (Magnetom Symphony, Siemens Medical Solutions, Erlangen, Germany). The translational forces were measured using the deflection angle test (ASTM F2052-02); rotational forces were assessed on a 5-point qualitative scale. RESULTS AND CONCLUSION: All retainer wires and the steel arch wires (the Noninium arch wire being the exception) were subjected to considerable rotational and translational forces within the MRI system's magnetic field. Translational forces were from 9.1- to 27.6-times as high as gravitational forces on these objects. Steel ligature wires and arch wires made of cobalt chromium, titanium molybdenum, nickel-titanium, and brass alloys showed no or negligible forces within the magnetic field. The translational and rotational forces within the MRI magnetic field should pose no risk to carefully-ligated arch wires. Steel retainer wire bonds should be checked to ensure secure attachment prior to an MRI investigation.