Fused filament fabrication (FFF): influence of layer height on forces and moments delivered by aligners-an in vitro study.

OBJECTIVES: To investigate the effect of layer height of FFF-printed models on aligner force transmission to a second maxillary premolar during buccal torquing, distalization, extrusion, and rotation using differing foil thicknesses. MATERIALS AND METHODS: Utilizing OnyxCeph3™ Lab (Image Instruments GmbH, Chemnitz, Germany, Release Version 3.2.185), the following movements were programmed for the second premolar: buccal torque (0.1-0.5 mm), distalization (0.1-0.4 mm), extrusion (0.1-0.4 mm), rotation (0.1-0.5 mm), and staging 0.1 mm. Via FFF, 91 maxillary models were printed for each staging at different layer heights (100 µm, 150 µm, 200 µm, 250 µm, 300 µm). Hence, 182 aligners, made of polyethylene terephthalate glycol (PET-G) with two thicknesses (0.5 mm and 0.75 mm), were prepared. The test setup comprised an acrylic maxillary model with the second premolar separated and mounted on a sensor, measuring initial forces and moments exerted by the aligners. A generalized linear model for the gamma distribution was applied, evaluating the significance of the factors layer height, type of movement, aligner thickness, and staging on aligner force transmission. RESULTS: Foil thickness and staging were found to have a significant influence on forces delivered by aligners, whereas no significance was determined for layer height and type of movement. Nevertheless, at a layer height of 150 µm, the most appropriate force transmission was observed. CONCLUSIONS: Printing aligner models at particularly low layer heights leads to uneconomically high print time without perceptible better force delivery properties, whereas higher layer heights provoke higher unpredictability of forces due to scattering. A z-resolution of 150 µm appears ideal for in-office aligner production combining advantages of economic print time and optimal force transmission.

Design, numerical simulation, and in vitro examination of a CAD/CAM-fabricated active orthodontic treatment element.

AIM: Orthodontic treatments with custom-made active elements may lead to more efficient treatment with fewer side effects. The objective of the present in vitro study was to determine whether individually constructed, mathematically simulated, and 3D-printed power chains could generate adequate forces for orthodontic tooth movement. MATERIALS AND METHODS: An individual measurement device was developed using a high-precision load cell, amplifier, and microcontroller for signal processing. Elastic chains were designed and subsequently printed from two different thermoplastic polyurethane (TPU) filaments and a thermoplastic elastomer (TPE) filament. With the CAD data, a finite element analysis (FEA) was performed to calculate the reactive forces to be expected at different activation levels. The measured force development of the test objects was compared with the results from the FEA. RESULTS: The results showed a high precision of the measurement device, with an intraclass correlation coefficient (ICC) of 0.999 and a Dahlberg error of 0.05 N. The measured forces ranged from 196 to 681 g. There was a significant correlation between the measured and calculated forces (R 0.91 to 0.98). DISCUSSION: In the present study, the fully digital workflow of producing an individualized active orthodontic treatment element, which developed almost exactly the force values calculated in the FEA, was shown. Future clinical use seems promising, in combination with fully individualized and digitally planned treatment approaches. This offers the possibility to integrate these insights from exemplary applications into patient-specific digital planning in orthodontics. The combination of CBCT root reconstruction, intraoral scans with customized brackets, and wires is the perfect starting point to add mechanical and numerical simulations. This would be the next step from shape-driven planning to force-driven planning. The goal is to reduce treatment time and negative side effects, eg, root resorption. CONCLUSION: The present in vitro study is the first to show the possible individualized construction and 3D printing of elastic chains exhibiting reproducible, predefined forces.

Standard and limit values for the symmetry of articulation parameters in the temporomandibular joint area - evaluations of the associated project of the SHIP study.

The articulation parameters, especially the horizontal condylar inclination angle (HCI), the Bennett angle (BA), and the immediate side shift (ISS) were determined in 259 subjects (100 males; 159 females) of the associated project with reference to the population-representative baseline study (Study of Health in Pomerania, SHIP 0). The evaluations were based on a clinical functional status and electronic motion recording with the ultrasonic measuring system Jaw Motion Analyser (JMA, Zebris, Isny, Germany). The reference plane, to which all measured values were represented and the HCI calculated, was the hinge axis infraorbital plane (HA-IOP). The HCI was determined after an excursive movement with a length of 4 mm to the HA-IOP in the sagittal view and the BA after a mediotrusive excursion movement of 6 mm in the horizontal view to the midsagittal plane. For the standard and limit values, the average value in addition to the standard deviation and the 10th and 90th percentile value (10th percentile value, 90th percentile value) were determined: HCI right 52.1 ± 10.14 degrees (39.4 degrees, 64.0 degrees), HCI left 53.1 ± 9.67 degrees (42.3 degrees, 67.0 degrees), BA right 15.2 ± 7.53 degrees (6.7 degrees, 25.0 degrees), BA left 14.2 ± 7.84 degrees (5.4 degrees, 24.1 degrees). The HCI was approximately 2 to 3 degrees larger in females (males: right 50.5 ± 9.47 degrees, left 51.9 ± 8.99 degrees; females: right 53.1 ± 10.42 degrees, left 53.8 ± 10.03 degrees). Likewise, the BA in the age group ≥ 40 years (males: right 14.4 ± 6.62 degrees, left 13.1 ± 7.14 degrees; females: right 17.0 ± 9.02 degrees, left 16.9 ± 8.72 degrees). The latter proved to be statistically significant in the t test for independent samples, assuming variance equivalence on the right, with P = 0.009, and with rejection of the variant equivalence on the left, with P = 0.002. The right and left HCI and BA joint values showed highly significant linear dependence at P < 0.001, but rather low, however, for the HCI with r2 = 0.175 for the HCI and r2 = 0.228 for the BA. In 46% of cases, the right and left HCI values differed up to 5 degrees only; a further 20.9% were in an interval difference of between 5 and 10 degrees. The following results were shown for the differences in the BA: 56.4% of the cases were between 0 and 5 degrees, and 26.2% were in the interval ranges of 5 to 10 degrees. ISS occurred in 18.1% of cases on the right side of the joint, and in 27.8% of cases on the left side. On both sides of the joint it was significantly more frequent in the age group ≥ 40 years with assumed variance equality than in the age group < 40 years (P = 0.002 right, P = 0.003 left). The groups relating to the Helkimo index (HI) did not differ significantly in all function-specific parameters. If it is assumed that there is no significant influence on the occlusion if the HCI values differ by 7 to 8 degrees from the average value, only approximately one third of all cases (35.1%) were characterized by a purely average value setting in the articulator. In 41.7% of cases, one joint value was situated outside the average value range; in 23.2% of the cases both values were outside the average value range. Without a measurement of the condylar path inclination, however, it is impossible to decide to what extent the HCI deviates from the average value, and which joint side is larger or smaller than the other and to what extent. These results suggest that in extensive and complex cases, the articulator should be adjusted according to individual, function-specific joint values.

Fully digital workflow for presurgical orthodontic plate in cleft lip and palate patients.

OBJECTIVE: In most cases, according to our treatment concept, a presurgical orthodontic treatment (POT) is performed on patients with cleft lip and palate (CLP). The aim of this case report is to demonstrate a completely digital workflow for the production of a palate plate. MATERIALS AND METHODS: For the assessment of the maxillary arch, a digital impression of the jaw was made on two patients with an intraoral scanner (Cerec Omnicam Ortho). After reconstruction of a virtual model from the scan data, appropriate areas of the jaw could be blocked out and a plate constructed. This was printed with a DLP three-dimensional (3D) printer (SHERA EcoPrint D30) with class IIa biocompatible material. After minor surface finishing, the plates could be incorporated in the patients' mouths. RESULTS: The scans could be performed in a short time without affecting the very young patients. All clinically relevant areas for the production and digital measurement of the models could be recorded. The plates showed an extremely good fit, and there were no differences in wear compared with a conventionally manufactured plate. CONCLUSION: For the first time, a risk-free digital impression of the edentulous jaw in CLP babies with a subsequently completely digitally constructed and 3D-printed palatal plate could be shown.

Orthodontic treatment and biological limits: a retrospective clinical trial.

BACKGROUND: The fundamental part of every successful orthodontic treatment is the detailed treatment planning including a precise determination of the virtual treatment objective (VTO) while considering the biological and anatomical limits. The aim of this study is to investigate and to compare the feasibility of the established reference values before and after orthodontic treatment and to determine the usefulness of this parameters as guidance for the sagittal anterior, sagittal posterior and transverse biological boundaries. MATERIALS AND METHODS: Thirty-two patients aged 9 to 18 years (12 male and 20 female) with all permanent teeth present were randomly selected for orthodontic treatment with fixed multibracket appliance regardless of the potential malocclusion. The parameters 6-PTV, 1-NB [mm] and the WALA ridge were set for the identification of the transverse, sagittal anterior and sagittal posterior tooth position. The measurements were carried out at the beginning (T0) and at the end (T1) of the orthodontic treatment. They were set in relation with their individual threshold values (G). After the results of the measurements were conducted using the software OnyxCeph3TM (version 3.2.185 (505), Image Instruments GmbH, Chemnitz, DE), they were statistically calculated in the software RStudio (2022.12.0 Build 353 © 2009-2022 Posit Software PBC). RESULTS: Among the 32 patients, the mean pre- and post-treatment changes measured through the three parameters in relation to the individual reference values were statistically significant (p < 0.01). The mean values for 6-PTV, 1-NB and the WALA ridge amounted 15.37 mm, 2.56 mm and 4.23 mm at the beginning of the treatment, while after the treatment the measured values amounted 20.31 mm, 2.4 mm and 5.55 mm. These measurements combined with the statistical analysis of the changes of WALA ridge (T0, T1) confirmed that the teeth have been successfully uprighted and aligned. Furthermore, the maxillary first molars have been moved slightly mesially, as proven by the changes in 6-PTV, without certainty as to whether bodily movement or mesial tipping took place. Additionally, the lower incisors have been protruded, slightly exceeding the individual threshold values. CONCLUSION: The parameters investigated provide a suitable assessment tool for recording the limits of the sagittal posterior, the sagittal anterior and the transverse dimension.

Influence of dental occlusion on oculomotory function-A pilot study.

The aim of this study was to examine the interaction between the oculomotory system and the stomatognathic system based on morphofunctional relationships between the corresponding cranial nerves, their core areas and the reticular formation as a "link" by means of optometric examinations. Test subjects (N = 100) were prospectively recruited and divided into two groups: a young-age (N = 53, age 6-16 years) and old-age group (N = 47, 23-78 years). We determined the horizontal range of convergence and divergence as well as the near convergence point. These optometrically measured parameters were recorded in both groups in the resting position, at maximal mouth opening and with bite-blocking via tin foils (0.5 mm and 1 mm), which were inserted occlusally of the first lower left molar. All oculomotory parameters were significantly altered by bite manipulation and maximal mouth opening. These effects could be observed regardless of age and gender and thus suggest an interaction between eye movement and the orofacial complex. Subjects with asthenopic symptoms showed no different reactions compared to healthy subjects. For a final statement on the correlation between the oculomotory and stomatognathic system, further investigations are necessary. An interdisciplinary cooperation between the different subject areas is recommended for further studies.

Investment casting with FFF (fused filament fabrication)-printed appliances: the intermediate step.

OBJECTIVE: Some modifications of orthodontic appliances such as the rapid maxillary expansion (RME) device with a Hyrax screw or Herbst are fabricated using traditional investment casting (lost-wax casting). This is precise but very labor-intensive. New technologies enable us today to use direct selective laser sintering (SLS) to produce freeform metallic structures. These machines are very expensive and only available in specialized laboratories. The aim of this investigation was to combine fused filament fabrication (FFF) 3D printing with wax-based filaments to produce orthodontic appliances via investment casting. METHOD AND MATERIALS: For demonstration purposes, a lingual arch, a palatal arch, and an RME appliance were digitally designed based on an intraoral scan. The *.stl files were sliced and printed with a dual-nozzle FFF printer. The object was printed with a wax-based filament especially suited for investment casting, and support structures were printed with water-soluble polyvinyl-alcohol (PVA) filament. The printed objects were cast in metal and finished. RESULTS: All appliances were successfully cast and polished. They were provisionally placed intraorally. The fit was clinically very good and comparable to traditionally crafted appliances. The printing and handling of the parts made of these special filaments is challenging. CONCLUSION: With this experiment, the successful production of investment casting using FFF printing was shown for the first time.

Modular 3D printable orthodontic measuring apparatus for force and torque measurements of thermoplastic/removable appliances.

The magnitude of forces and moments applied on teeth during orthodontic treatment is crucial to achieve the desired tooth movement. The aim of this study is to introduce a modular 3D printable orthodontic measurement apparatus (M3DOMA), which can be used for measurements of forces and moments acting on teeth during treatment with aligners. The measurement device was characterized regarding signal to noise ratio (SNR) of the sensors, repeatability of measurements, influence of thermoforming, as well as reliability. Forces and moments were evaluated for an activation range of 0.1-0.4 mm, comparing them among different activation patterns with two aligner thicknesses. The sensors exhibited a SNR from 13-33 dB. Repeatability with repeated measurements showed standard deviations ≤0.015 N and 0.769 Nmm. The influence of thermoforming represented by standard deviation of forces ranges from 0.019-0.147 N. The device showed a range of intra class correlation (ICC) for repeated measurements for all sensors from 0.932 to 0.999. Hence the reliability of the device has been proven to be excellent.

New insights in the reproducibility of visual and electronic tooth color assessment for dental practice.

BACKGROUND: The aim of the study was to compare a 2D and 3D color system concerning a variety of statistical and graphical methods to assess validity and reliability of color measurements, and provide guidance on when to use which system and how to interpret color distance measures, including ΔE and d(0M1). METHODS: The color of teeth 14 to 24 of 35 patients undergoing regular bleaching treatment was visually assessed and electronically measured with the spectrophotometer Shade Inspector™. Tooth color was recorded before bleaching treatment, after 14 days, and again after 6 months. VITAPAN® Classical (2D) and VITA-3D-Master® (3D) served as reference systems. RESULTS: Concerning repeated measurements, the 2D system was superior to the 3D system, both visually and electronically in terms of ΔE and d(OM1), for statistics of agreement and reliability. All four methods showed strong patterns in Bland-Altman plots. In the 3D system, hue was less reliable than lightness and chroma, which was more pronounced visually than electronically. The smallest detectable color difference varied among the four methods used, and was most favorable in the electronic 2D system. Comparing the methods, the agreement between the 2D and 3D system in terms of ΔE was not good. The reliability of the visual and electronic method was essentially the same in the 2D and 3D systems; this comparability is fair to good. CLINICAL RELEVANCE: The 3D system may confuse human raters and even electronic devices. The 2D system is the simple and best choice.

Reproducibility of electronic tooth colour measurements.

Clinical methods of investigation, such as tooth colour determination, should be simple, quick and reproducible. The determination of tooth colours usually relies upon manual comparison of a patient's tooth colour with a colour ring. After some days, however, measurement results frequently lack unequivocal reproducibility. This study aimed to examine an electronic method for reliable colour measurement. The colours of the teeth 14 to 24 were determined by three different examiners in 10 subjects using the colour measuring device Shade Inspector. In total, 12 measurements per tooth were taken. Two measurement time points were scheduled to be taken, namely at study onset (T(1)) and after 6 months (T(2)). At either time point, two measurement series per subject were taken by the different examiners at 2-week intervals. The inter-examiner and intra-examiner agreement of the measurement results was assessed. The concordance for lightness and colour intensity (saturation) was represented by the intra-class correlation coefficient. The categorical variable colour shade (hue) was assessed using the kappa statistic. The study results show that tooth colour can be measured independently of the examiner. Good agreement was found between the examiners.

Assessing the effect of multibracket appliance treatment on tooth color by using electronic measurement.

BACKGROUND: The purpose of this study was to investigate how tooth color is affected by multibracket appliance (MBA) treatment. METHODS: The color of teeth #14 to #24 of 15 patients with MBA was measured on body and gingival tooth segments using the spectrophotometer Shade Inspector™. Colors of both segments were recorded before start of MBA treatment (baseline T0), end of MBA treatment (T1; 2 years ±0.3), and 3 months after T1 (T2). A 2D color system and a 3D system served as reference systems. Multilevel models were used to analyze color change within segments and to compare the difference in color change between segments (treatment effect). RESULTS: 2D system. Changes within tooth segments from T0 to T2 were at worst 2.0 units (ΔE in the gingival segment), which is less than the threshold of 2.7 units for a clinically meaningful difference. Confidence intervals for the treatment effect indicated no clinically important differences in color change between body and gingival segments. 3D system. Changes within tooth segments from T0 to T2 were at worst 2.3 units (ΔE in the body segment), which is less than the threshold of 2.7 units for a clinically meaningful difference. Confidence intervals for the treatment effect indicated no clinically important differences in color change between body and gingival segments. Thus, MBA treatment did not lead to clinically relevant changes in tooth color. CONCLUSION: Within the limitation of this study the MBA treatment can be seen as a safe method with respect to tooth color.

Designing post-graduate Master's degree programs: the advanced training program in Dental Functional Analysis and Therapy as one example.

INTRODUCTION: The decision to consolidate European higher education was reached by the Bologna Conference. Based on the Anglo-American system, a two-cycle degree program (Bachelor and Master) has been introduced. Subjects culminating in a state examination, such as Medicine and Dentistry, were excluded from this reform. Since the state examination is already comparable in its caliber to a Master's degree in Medicine or Dentistry, only advanced Master's degree programs with post-graduate specializations come into consideration for these subjects. In the field of dentistry numerous post-graduate study programs are increasingly coming into existence. Many different models and approaches are being pursued. METHOD: Since the 2004-2005 winter semester, the University of Greifswald has offered the Master's degree program in Dental Functional Analysis and Therapy. Two and a half years in duration, this program is structured to allow program participation while working and targets licensed dentists who wish to attain certified skills for the future in state-of-the-art functional analysis and therapy. AIM: The design of this post-graduate program and the initial results of the evaluation by alumni are presented here. CONCLUSION: Our experiences show that the conceptual idea of an advanced Master's program has proved successful. The program covers a specialty which leads to increased confidence in handling challenging patient cases. The sharing of experiences among colleagues was evaluated as being especially important.

Student evaluation of problem-based learning in a dental orthodontic curriculum--a pilot study.

OBJECTIVE: The present questionnaire survey investigated student reception of problem-based learning (PBL) in the orthodontic curriculum with regard to acceptance, sense of purpose and motivation, knowledge and understanding, as well as tutorial support. METHODS: Over a period of two terms, we compared two different didactic methods (PBL and short presentations) by randomizing the participants of a course on orthodontic diagnostics into two different groups, who inversed methods after the first term. RESULTS: The two student groups did not show any significant differences with regard to assessments or examination performance. Therefore, acceptance of the PBL concept seems to be mainly associated with the motivation of individuals to use this method. The higher the motivation, the more positive is the attitude towards the PBL concept. Students seem to work more constructively and efficiently with PBL if they can judge the concept meaningful for themselves. CONCLUSION: In consideration of the relevant literature and the present results, PBL can be principally integrated into the dental curriculum as a method of learning. However, student motivation is vital to learning success.

Integration of an Objective Structured Clinical Examination (OSCE) into the dental preliminary exams.

INTRODUCTION: In the pre-clinical phase of the study of dentistry at the University of Greifswald, the course "Early Patient Contact (EPC)" is conducted within the framework of Community Medicine/Dentistry. The course is based on three pillars: the patient visiting program, special problem-oriented seminars, and communication training for doctors. The essential goal consists of providing students with real patient contact right at the beginning of their study of dentistry, thus making the study of dentistry patient-based very early on. Students are trained in taking comprehensive anamneses and recording clinical findings. METHODS: Within the framework of the dental preliminary exams, the course is evaluated using an OSCE on a standardized patient. Furthermore, the added value of an additional training unit (conducting anamnesis and clinical examination) in preparation for the OSCE was evaluated. The exam results of a group without training (control group) were compared with those of a group with training (intervention group). RESULTS: The intervention group performed significantly better than the control on the following items: the total number of points achieved on the OSCE early patient contact, and in the most important points of the anamnesis and clinical examination. In addition, the intervention group tended to score higher in terms of the item "oral health status". CONCLUSION: The present study showed a positive effect of an additional training unit on students' performance in the OSCE. Taking the limitations of the study and the results of a literature review into account, we recommend conducting such training as preparation for the OSCE.

Experimental investigations into visual and electronic tooth color measurement.

OBJECTIVE: The present study aimed to examine the validity of the visual color assessment and an electronic tooth color measurement system by means of Shade Inspector™ in comparison with a gold standard. Additionally, reproducibility of electronic measurements was demonstrated by means of two reference systems. MATERIAL AND METHODS: Ceramic specimens of two thicknesses (h=1.6 mm, h=2.6 mm) were used. Three experienced dental technicians using the VITAPAN Classical(®) color scale carried out all visual tests. Validity of the visual assessment and the electronic measurements was confirmed separately for both thicknesses by means of lightness and hue of the VITAPAN Classical(®) color scale. Reproducibility of electronic measurements was confirmed by means of the VITAPAN Classical(®) and 3D-Master(®). The 3D-Master(®) data were calculated according to lightness, hue and chroma. Intraclass correlation coefficient (ICC) was used in assessing validity/reproducibility for lightness and chroma, Kappa statistics were used for hue. A level ≥0.75 was pre-established for ICC and ≥0.60 for the Kappa index. RESULTS OF VISUAL COLOR ASSESSMENT: Validity for lightness was good for both thicknesses; agreement rates for hue were inconsistent. ELECTRONIC MEASUREMENT: Validity for lightness was fair to good, hue values were below 0.60. Reproducibility of lightness was good to very good for both reference systems. Hue values (VITAPAN Classical(®)) for 1.6 mm test specimens were upside, for 2.6 mm below 0.60, Kappa values for 3D-Master(®) were ≥0.60 for all measurements, reproducibility of chroma was very good. CONCLUSION: Validity was better for visual than for electronic color assessment. Reproducibility of the electronic device by means of the Shade Inspector™ was given for the VITAPAN Classical(®) and 3D-Master(®) systems.