The analogous intraoral judgement of the abutment prep angle is almost impossible! At least avoid undercuts.

AIM: A total occlusal convergence angle φ of 6° is a typical crown preparation requirement. It was shown that it is hard to achieve clinically. The present study aimed to compare ability of students to judge different steepnesses including a -1° undercut of prepared canines and molars under clinical conditions with different analogue tools. MATERIALS AND METHODS: The complete dentures of a patient were duplicated without the teeth 16, 23, 33, 46. For each of these gaps, 6 crown stumps were milled with φ/2 = -1°, 3°, 6°, 9°, 12° and 15°, each of which was insertable using mini-magnets. 48 students each from the 1st, 6th and 9th semester estimated these angles intraorally with various aiding tools: In addition to basic dental instruments, a parallelometer mirror, an analogue clock dial with a 6° visualization and a scale of tooth stumps with φ/2 between -1° and 15°. RESULTS: The widely demanded 3° were hardly recognized, but assumed to be steeper or even undercut. In contrast, the -1° divergent stump walls were predominantly estimated as parallel-walled or slightly conical. With increasing taper, the stumps tended to be classified as steeper, i.e. "better". The additional tools did not result in a general improvement of the estimation performance. Students from higher semesters did not achieve better results. CONCLUSION: We question the objectivity of an exclusively visual assessment of crown stump taper. It appears, that dental training should at least focus on avoiding undercuts as minimal prerequisite for an accurate intraoral scanning procedure. Digital control of the preparation angle by an intraoral scan and immediate clinical implementation of these results could help to produce appropriate preparations.

[Metal objects of the head and neck region in magnetic resonance imaging : Survey among radiologists]. / Metallobjekte der Kopf-Hals-Region in der Magnetresonanztomographie : Umfrage unter Radiologen.

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%.

[Alteration of flux density of highly coercive SmCo magnets used in prosthodontics and epithetics in 1.5 T and 3 T MRI]. / Flussdichteänderungen prothetischer/epithetischer SmCo-Magnete mit hoher Koerzitivkraft im 1,5- und 3­T-MRT.

PURPOSE: 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. MATERIAL AND METHODS: 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 B0, A: in the upper jaw antiparallel to B0 in a straight position, Ad: antiparallel, reclined by 45°, Av: antiparallel, inclined by 45°, G: glabellar region 90° to B0 and M: mastoid region 90° to B0. The effects of exposure in the exterior field directly at the opening for the parallel (Pex), antiparallel (Aex), glabellar (Gex) and mastoid (Mex) positions were also investigated. After each exposure the magnets were remagnetized. The flux density was determined as an equivalent of the adhesive force. RESULTS: With 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 Aex. In the antiparallel positions A and Aex the strong external field of 3 T caused very high losses of 72% and 33%, respectively. In the inclined and reclined antiparallel positions Ad and Av the magnets lost 96% of their flux density and were almost fully demagnetized. All of the magnets could be fully remagnetized regardless of the degree of damage. CONCLUSION: Highly 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.

Influence of a face-bow on oral health-related quality of life after changing the vertical dimension in the articulator: a randomized controlled trial. Part II.

OBJECTIVES: 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. MATERIALS AND METHODS: 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. RESULTS: 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). CONCLUSIONS: From the patient's perspective, mean-value-based remounting methods are of value. The use of a face-bow was not perceived as superior. CLINICAL RELEVANCE: From the patient's perspective, remounting of CDs will be positively perceived, irrespective of the use of a face-bow.

Does a face-bow lead to better occlusion in complete dentures? A randomized controlled trial: part I.

OBJECTIVES: In a double-blinded randomized controlled clinical trial, the impact of face-bow registration for remounting complete dentures (CDs) on the occlusal parameters (part I) was evaluated. MATERIALS AND METHODS: New CDs of 32 patients were duplicated and mounted after intraoral pin registration according to mean settings (group 1) and (group 2) using a face-bow (arbitrary hinge axis). The vertical dimension was reduced to the first occlusal contact point, and a bite record was fabricated in the articulator. The number of contacts and the number of teeth in contact were evaluated by a computer program (laboratory result). After randomization, half of the CDs were adjusted according to protocol of group 1 and group 2 and delivered to the patients. After 3 days (T1) and 84 days (T2), clinical static contact points and teeth in contact were counted. Contact points and teeth in contact of both groups (laboratory results) and at different moments (clinical results) were analyzed statistically with the F test and bootstrapping. RESULTS: Laboratory: No. 2 (face-bow) showed more occlusal contact points than no. 1 (mean setting), p > 0.05. The number of teeth with at least one occlusal contact was significantly higher in no. 2 (p = 0.027). Clinic: The mean number of teeth with at least one clinical contact point was significantly higher in no. 1 (no. 1 = 7.13, no. 2 = 5.31; p = 0.042). Extent of the vertical shift poorly correlated with number of laboratory occlusal contact points (R 2 = 0.017). CONCLUSIONS: Considering the complex multistep study design, a limited number of participants, and referring to one specific arbitrary face-bow, the following conclusion could be drawn: no substantial difference by the use of the arbitrary face-bow compared to a mean setting could be determined, when changing the vertical dimension in the articulator within a remounting procedure of complete dentures. CLINICAL RELEVANCE: Further research is necessary to determine the effects of different arbitrary face-bows on the fabrication and adaptation of removable dentures.

Magnetic permeability as a predictor of the artefact size caused by orthodontic appliances at 1.5 T magnetic resonance imaging.

OBJECTIVES: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSIONS: 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. CLINICAL RELEVANCE: This study clarifies whether an orthodontic appliance must be removed before taking an MRI.

The intraoral permeability measurement as a screening for artifact formation by orthodontic products in MRI.

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.