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Context Although in recent times more research has been done on interactions of metallic dental objects in magnetic resonance imaging (MRI), radiologists are often uncertain whether the objects should be removed or can be retained prior to an impending examination. On the one hand, they want to avoid unnecessary material removal which is associated with costs and potential damage of the dental object. On the other hand, they fear material-induced susceptibility artefacts will impair the diagnostic workup so that examinations will have to be repeated. The lack of information complicates adequate decision making for radiologists. Aim The aim of this survey was to evaluate the information that is currently available to radiologists regarding orthodontic appliances of the head and neck region in the MRI and determine how to handle these situations in a radiologist's every day routine. Therefore, this study can reveal the need for further research. Materials and methods The questionnaire was published in the 9/2017 issue of the journal Der Radiologe and sent as an electronic version by the BDR (Professional Association of German Radiologists) to their approximately 1800 members. In addition, the radiological institutes of 55 German university and maximum care clinics were contacted. Results In all, 74 evaluable responses were received within a period of 16 weeks, representing a response rate of 3.7%. Altogether, the participants rate the risks of a detachment or heating of orthodontic appliances as too high. The interviewed radiologists categorize the available data as insufficient and they almost unanimously (97.3%) demand a declaration requirement for the manufacturers. There is a clear need for further education (78.3%). Intraoral measurement of the magnetic permeability is considered as a useful tool to determine possible interactions with the MRI by 40.5%.

Es wurde die Gegenfeldfestigkeit hoch koerzitiver Dentalmagnete in der 1,5- und 3‑T-Magnetresonantomographie (MRT) untersucht und gepruft, ob dadurch geschadigte Magnete durch Remagnetisieren in den alten Zustand versetzbar sind. Es wurden in einer justierbaren Halterung je 20 SmCo-Magnete in sechs simulierten Positionen der zahnarztlichen Prothetik/Epithetik exponiert: P : im Unterkiefer, parallel zum Hauptfeld B0, A: im Oberkiefer, antiparallel zu B0, Ad: antiparallel mit um 45° rekliniertem Kopf, Av: antiparallel um 45° inkliniert, G: Glabella, 90° zu B0, M: Mastoid, 90° zu B0. Im Ausenfeld vor dem Portal wurden die parallele (Pex), antiparallele (Aex), Glabella (Gex) und Mastoid (Mex) -Positionen erneut gepruft. Nach jeder Exposition wurden die Magnete remagnetisiert. Als Aquivalent der Magnetkraft wurde die relative Anderung der Flussdichte bestimmt. Bei 1,5 T kam es nur in den abgewinkelten Positionen Ad und Av und in der Ausenposition Aex zu klinisch relevanten Verlusten der Flussdichte zwischen 7 % und 10 %. Das starke Gegenfeld von 3 T erzeugte bei den antiparallelen Positionen A und Aex mit 72 % und 33 % sehr hohe Verluste. In den antiparallel inklinierten und reklinierten Positionen Ad und Av wurden die Magnete durch den Verlust von 96 % ihrer ursprunglichen Flussdichte nahezu entmagnetisiert. Unabhangig von ihrer Schadigung liesen sich alle Magnete anschliesend wieder vollstandig aufmagnetisieren. Sofern die induzierten Artefakte diagnostisch irrelevant sind, konnen hoher koerzitive SmCo-Magnete bei 1,5 T in situ bleiben. Im antiparallel wirkenden 3‑T-Hauptfeld kann ihre Haftkraft komplett verloren gehen. Dann sollten sie vom Hersteller remagnetisiert werden. Die In- oder Reklination des Kopfes verstarkt den Einfluss des Hauptfeldes.

Aim Metal dental products lack precautionary statements regarding MR compatibility due to an exemption in the labelling obligation. Hence, it is difficult for radiologists to decide whether to remove fixed metal objects in patients prior to MRI. A solution could be the direct determination of the magnetic permeability (µr) as a decisive material-related predictor of artifact formation and other interactions. Thus, the applicability of an industrially used measurement device as a screening instrument and the relevance of the manufacturer’s application restrictions in vitro and in vivo were tested. Methods Precision and trueness were tested using self-made test objects with different dimensions and different permeability. To clarify whether the measurement results are affected by the remanence (BR) induced in the objects, 28 brackets of different materials were exposed to a weak and a strong external magnetic field and the magnetic flux density before and after these exposures was compared. The clinical test was performed on a volunteer with an orthodontic appliance experimentally composed of brackets with different levels of magnetic permeability (µr). Validity and intra- and interrater reliability were calculated using two rater groups consisting of four dentists and four medical-technical radiology assistants (MTRA), respectively. Results With coefficients of variation below 0.14%, precision was excellent regardless of object surface and size. Trueness was high on objects with µr ≤ 1.002, and decreased with increasing µr, for which size-dependent correction factors were calculated. Intra- and interrater reliability and validity were excellent and independent of professional intraoral manipulation experience. Conclusions The permeability measurement allows for a valid and reliable determination of the magnetizability of intraoral metal objects. When used as a screening tool to detect nonartifact-causing objects, no correction factor needs to be calculated. For the first time, it offers radiologists a decision support for the selective removal of only the highly permeable components of the multiband apparatus.

In a double-blind randomized controlled clinical trial, the impact of face-bow registration for remounting complete dentures (CDs) on oral health-related quality of life (OHRQoL) was evaluated. New CDs of 32 subjects were clinically remounted using intraoral pin registration. CDs were transferred into a semi-adjustable articulator corresponding to group #1: mean settings with Bonwill triangle and Balkwill angle, and group #2: arbitrary hinge axis with a face-bow registration. After occlusal adjustment, subjects were followed up after 3 (T1) and 84 (T2) days. The primary outcome was the change of OHRQoL by OHIP-G49, while as secondary outcome, mucosal alterations were evaluated over time. Mean values of OHIP-G49 total sum scores and OHIP-dimensions were calculated for baseline (T0) and days 3 (T1) and 84 (T2) after intervention. Based on bootstrapping methods (changes of total OHIP sum score) and the Wilcoxon test (changes of sum scores of OHIP dimensions), analyses of between-group differences were performed. Mean values (MV) of OHIP-G49 sum scores decreased in both groups from T0 (#1 48.56; #2 45.46) to T1 (#1 31.43 (p = 0.012); #2 43.20) and to T2 (#1 29.06; #2 29.40), which represents an improvement in OHRQoL. MV of OHIP-dimension sum scores decreased from T0 to T1 in both groups (#1 seven dimensions; #2 four dimensions); the decrease of sum scores was tested as not statistically significant (p > 0.05). From the patient’s perspective, mean-value-based remounting methods are of value. The use of a face-bow was not perceived as superior. From the patient’s perspective, remounting of CDs will be positively perceived, irrespective of the use of a face-bow.

Although in recent times more research has been done on interactions of metallic dental objects in magnetic resonance imaging (MRI), radiologists are often uncertain whether the objects should be removed or can be retained prior to an impending examination. On the one hand, they want to avoid unnecessary material removal which is associated with costs and potential damage of the dental object. On the other hand, they fear material-induced susceptibility artefacts will impair the diagnostic workup so that examinations will have to be repeated. The lack of information complicates adequate decision making for radiologists.The aim of this survey was to evaluate the information that is currently available to radiologists regarding orthodontic appliances of the head and neck region in the MRI and determine how to handle these situations in a radiologist's every day routine. Therefore, this study can reveal the need for further research.The questionnaire was published in the 9/2017 issue of the journal Der Radiologe and sent as an electronic version by the BDR (Professional Association of German Radiologists) to their approximately 1800 members. In addition, the radiological institutes of 55 German university and maximum care clinics were contacted.In all, 74 evaluable responses were received within a period of 16 weeks, representing a response rate of 3.7%. Altogether, the participants rate the risks of a detachment or heating of orthodontic appliances as too high. The interviewed radiologists categorize the available data as insufficient and they almost unanimously (97.3%) demand a declaration requirement for the manufacturers. There is a clear need for further education (78.3%). Intraoral measurement of the magnetic permeability is considered as a useful tool to determine possible interactions with the MRI by 40.5%.

The opposing field stability of highly coercive dental magnets in external magnetic fields of 1.5 and 3 T magnetic resonance imaging (MRI) was investigated. It was further assessed if remagnetizing can reverse the flux density in the magnets.Using an adjustable fixture, 20 SmCo magnets were exposed and 6 positions of prosthodontics and epithetics were simulated: P : in the lower jaw parallel to the main field BWith 1.5 T clinically relevant loss of flux density between 7% and 10% occurred only in the angled positions Ad and Av and the external position AHighly coercive SmCo magnets can remain in situ during a 1.5 T MRI scan unless the resulting artifacts are diagnostically relevant. Exposure to the 3 T main field in antiparallel position may result in a complete loss of the adhesive force. In this case the magnets should be remagnetized by the manufacturer. Inclination or reclination of the head reinforces the effect of the main field.

Artefacts caused by orthodontic attachments limit the diagnostic value and lead to removal of these appliances before magnetic resonance imaging. Magnetic permeability can predict the artefact size. There is no standardised approach to determine the permeability of such attachments. The aim was to establish a reliable approach to determine artefact size caused by orthodontic attachments at 1.5 T MRI. Artefact radii of 21 attachments were determined applying two prevalent sequences of the head and neck region (turbo spin echo and gradient echo). The instrument Ferromaster (Stefan Mayer Instruments, Dinslaken) is approved for permeability measurements of objects with a minimum size (d = 20 mm, h = 5 mm). Eleven small test specimens of known permeability between 1.003 and 1.431 were produced. They are slightly larger than the orthodontic attachments. Their artefacts were measured and cross tabulated against the permeability. The resulting curve was used to compare the orthodontic attachments with the test bodies. Steel caused a wide range of artefact size of 10–74 mm subject to their permeability. Titanium, cobalt-chromium and ceramic materials produced artefact radii up to 20 mm. Measurement of artefacts of the test bodies revealed an interrelationship according to a root function. The artefact size of all brackets was below that root function. The permeability can be reliably assessed by conventional measurement devices and the artefact size can be predicted. The radiologist is able to decide whether or not the orthodontic attachments should be removed. This study clarifies whether an orthodontic appliance must be removed before taking an MRI.

Orthodontic appliances are often prophylactically removed prior to MRI examinations, although they are sometimes left in situ (out of ignorance). Either way, there is a risk of adverse consequences for the patient, as removing the appliance may incur avoidable costs and extensive dental treatment, whereas leaving them in can cause artifacts that can significantly impair the diagnostic quality of MRI. The aim of this study was to measure the size of experimental artifacts created by orthodontic devices and to develop criteria using sound material-science research for making MRI more compatible, thereby supporting radiologists and orthodontists in their efforts.Sixteen orthodontic small-device and wire specimens made of different steel and titanium or CoCr alloys were placed in a chambered water-filled phantom for MRI. Each was subjected to spin-echo and gradient-echo sequences at 1.5 and 3 Tesla.We observed that artifact formation depends on the material properties (specimen size, crystalline structure, manufacture-related processing) and on the specifications of the MRI system used (main field strength, sequence type). Our results varied considerably according to the steel grades. Artifact radii ranged from 14 mm (spin echo at 1.5 Tesla) to 51 mm (gradient echo at 3 Tesla). No artifacts occurred at 1.5 Tesla around the titanium and CoCr specimens; the same observation was made with one of the steel grades.Artifact size cannot be predicted merely from the designation "steel". Nor did the crystalline structure of the baseline material from which a steel device had been produced have major implications for artifact size. Relevant, however, was the magnetic permeability (or susceptibility) of the final products, which is not disclosed by the manufacturers, and it cannot be measured on fixed intraoral appliances. Furthermore, the present investigation reveals that some steel devices can remain in situ without triggering adverse consequences.

Purpose When using dental duo-magnet systems, a mini-magnet remains in the jaw after removal of the prosthesis. In some cases, implant-borne magnets may be removed, whereas tooth-borne magnets are irreversibly fixed on a natural tooth root. The goal of this paper is to identify the impacts of the duration and orientation of exposure on these magnets in a 1.5 or 3 Tesla MRI. Materials and methods For this study, 30 SmCo and 60 NdFeB magnets were used. During the first experiment, they were exposed with free orientation for 64 minutes. During the second experiment, the magnets were fixed in position and exposed at 1.5 and 3 Tesla while aligned in a parallel or antiparallel direction. Results While the duration of exposure in MRI is irrelevant, the orientation is not. The coercive field strength of these NdFeB and SmCo alloys is not sufficient to reliably withstand demagnetization in a 1.5 or 3 T MRI when aligned in an antiparallel direction. At 1.5 T neodymium magnets were reduced to approx. 34 % and samarium magnets to approx. 92 % of their initial values. At 3 T all magnets were reversed. Conclusion As a precaution, the worst-case scenario, i. e. an antiparallel orientation, should be assumed when using a duo-magnet system. If an MRI can be postponed, the general dentist should remove implant-borne magnets. If there is a vital indication, irreversible damage to the magnets is acceptable in consultation with the patient since the replacement costs are irrelevant given the underlying disease.

We investigated artefacts caused from orthodontic appliances at 1.5-T MRI of the head and neck region and whether the image quality can be improved utilizing the artefact-minimizing sequence WARP.In vitro tests were performed by phantom measurements of different orthodontic devices applying different types of MR sequences [echoplanar imaging (EPI), turbo spin echo (TSE) and TSE-WARP, gradient echo (GRE)]. Two independent readers determined after calibration the level of artefacts. Subsequently, the interobserver agreement was calculated. The measurement of artefacts was based on the American Society for Testing Materials Standard F 2119-07. For in vivo imaging, one test person was scanned with an inserted multibracket appliance. The level of artefacts for 27 target regions was evaluated.In vitro: ceramic brackets and ferromagnetic steel brackets produced artefact radii up to 1.12 and 7.40 cm, respectively. WARP reduced these artefacts by an average of 32.7%. The Bland-Altman-Plot indicated that maximum measurement differences of 3 mm have to be expected with two calibrated observers. In vivo: the EPI sequence for brain imaging was not analysable. The TSE sequence of the brain did not demonstrate artefacts except for the nasal cavity. Conversely, the TSE sequence of the cervical spine revealed severe artefacts in the midface region. The GRE sequence appeared to be more susceptible to artefacts than did the TSE sequence.In vitro measurements allow an estimation of the in vivo artefact size. Orthodontic appliances may often remain intraorally when performing MRI. WARP showed a more significant effect in vitro than in vivo.

Glass fiber-reinforced endodontic posts are considered to have favorable mechanical properties for the reconstruction of endodontically treated teeth. The aim of the present investigation was to evaluate the survival of two tapered and one parallel-sided glass fiber-reinforced endodontic post systems in teeth with different stages of hard tissue loss and to identify risk factors for restoration failure. One-hundred and forty-nine glass fiber-reinforced endodontic posts in 122 patients were followed-up for 5-56 months [mean +/- standard deviation (SD): 39 +/- 11 months]. Glass fiber-reinforced endodontic posts were adhesively luted and the core was built with a composite resin. Cox proportional hazards models were used to evaluate the association of clinical variables and failure rate. Higher failure rates were found for restorations of anterior teeth compared with posterior teeth [Hazard-Ratios (HR): 3.1; 95% confidence interval (CI): 1.3-7.4], for restorations in teeth with no proximal contacts compared with at least one proximal contact (HR: 3.0; 95% CI: 1.0-9.0), and for teeth restored with single crowns compared with fixed bridges (HR: 4.3; 95% CI: 1.1-16.2). Tooth type, type of final restoration and the presence of adjacent teeth were found to be significant predictors of failure rates in endodontically treated teeth restored with glass fiber-reinforced endodontic posts.

Summary Objectives The aim of this study is to provide prospective clinical data for the survival of postendodontic reconstructions of teeth with varying degrees of hard tissue loss using tapered or parallel-sided post shapes. Methods Eighty-three patients got 105 glass fibre reinforced posts of tapered (Luscent Anchors ™ , Dentatus, Sweden) and parallel-sided, serrated (FibreKor ® , Jeneric Pentron, USA) post shape. A dual curing hybrid composite Compolute ® (3M ESPE, Germany) was used as luting material, EBS ® -Multi (3M ESPE) as adhesive system and Clearfil ® Core (Kuraray, Japan) for core built-up. The restorations were followed for a minimum of 24 months. The statistical analysis was performed on a random sub-sample of one restoration per subject. The Fisher exact test was used to compare frequencies of failures after 12 and 24 month. A Kaplan–Meier-analysis was used to analyse time-to-failure in both groups. Differences of survival time between post types were tested with the log-rank test. Results 3.8% of the restorations failed after 12 month, 12.8% after 24 month, respectively. The main failure type observed was post fractures. All but one failed teeth could be restored. There was no difference in failure frequency between post types after 12 or 24 months. The log-rank test showed no differences in survival between the two types of post ( p =0.37). Conclusion Parallel-sided and tapered glass fibre posts result after 2 years of clinical service in an equal rate of survival.