Mitteilung des Präsidenten der DGKFO

Use of a laser fluorescence device for the in vitro activity assessment of incipient caries lesions Abstract Purpose To evaluate the progression of demineralization during orthodontic treatment, the assessment of lesion activity is important in addition to the detection of lesion extent. This study aimed to evaluate the ability of laser fluorescence measurements to differentiate between active and inactive initial lesions in vitro. Methods In all, 63 extracted, permanent human teeth were available for the study. On each occlusal investigation site, surface extent and activity of caries lesions were classified visually using ICDAS/ICCMS (International Caries Detection and Assessment System/International Caries Classification and Management System) criteria, following laser fluorescence measurements. Teeth were hemisected and assessed for lesion depth. Methyl red dye was applied to validate lesion activity on the sections. A Mann–Whitney U-test was performed to evaluate differences between laser fluorescence measurements for active and inactive lesions. For visual and laser fluorescence findings, diagnostic accuracy (Az, sensitivity and specificity) were calculated. Results A total of 19 sound surfaces and 44 surfaces with ICDAS codes 1/2 were classified visually. The differences in laser fluorescence measurements between active and inactive lesions were not significant for the initial lesions (p > 0.05). Sensitivity/specificity for lesion depth was 90.5/92.3% (Az = 0.894), respectively, for visual assessment and 69.1/76.9% (Az = 0.745), respectively, for laser fluorescence. Sensitivity/specificity for activity assessment was 68.6/85.0% (Az = 0.768) for the visual method. For laser fluorescence measurements, no diagnostic accuracy values could be calculated for caries activity assessment. Conclusion The visual detection and activity assessment of initial lesions was more suitable than the laser fluorescence method. Based on the results of this in vitro study, use of laser fluorescence cannot be recommended for distinguishing between active and inactive initial caries lesions on occlusal surfaces.

Effect of in vitro aging by water immersion and thermocycling on the mechanical properties of PETG aligner material Abstract Purpose The mechanical properties of orthodontic aligners made from thermoplastic polymers decrease over time in the intraoral milieu. However, there is a lack of information on this topic in the literature. Thus, the elastic properties of polyethylene terephthalate glycol (PETG) aligner films were investigated in vitro under extreme temperature changes simulated by thermocycling, environmental temperature and water absorption. Materials and methods A total of 60 specimens made from PETG aligner films (CA Clear Aligner, Scheu Dental, Iserlohn, Germany) were divided into three groups (immersed in distilled water, subjected to accelerated ageing by thermocycling, control). These groups were again divided and tensile testing was performed for all groups at 22 and at 37 °C. Young’s modulus (E), 0.2% offset yield strength (Rp02) and ultimate tensile strength (UTS) were evaluated. Water absorption was determined using an analytical scale. Results All treated specimens showed water absorption, whereby specimens that were thermocycled absorbed 48% more water than the immersed ones. Young’s modulus and UTS were significantly lower for all three groups at 37 °C compared to the corresponding groups tested at 22 °C. Thermocycled and immersed groups showed a significantly lower Young’s modulus compared to the control group tested at the same temperature. The mean Rp02 was statistically different when comparing the control group tested at 22 °C to the one tested at 37 °C. Conclusions The results of this study add to the understanding of the clinically well-known degradation of orthodontic aligners during wear time. Extreme alternating temperatures along with warming up to intraoral temperature and water absorption can reduce the material’s Young’s modulus and may therefore promote a decrease of resulting orthodontic forces.

Torque efficiency of a customized lingual appliance Abstract Purpose Torque control in lingual orthodontics is key to obtain optimal esthetic results. The aim of this in vitro experimental study was to verify the efficiency of the ligature–archwire–slot system in torque control using a customized lingual appliance. Methods An idealized cast with eight extracted human teeth was created and a set of customized lingual brackets was obtained. Tests were performed with the following wires: 0.016″ × 0.022″ nickel-titanium (NiTi), 0.016″ × 0.024″ stainless steel (SS), 0.017″ × 0.025″ βIII titanium (βIIITi), 0.0182″ × 0.0182″ βIIITi, 0.018″ × 0.025″ SS, 0.018″ × 0.025″ NiTi, 0.018″ × 0.025″ βIIITi, and three types of ligatures were tested using a universal testing machine to calculate the efficiency in torque control. A blind statistical analysis was performed. Results Based on post hoc multiple comparisons, differences were found for two of the three ligatures when using the 0.016″ × 0.022″ NiTi wires (p < 0.001 for both ligatures). When considering all ligatures, 0.018″ × 0.025″ SS and 0.018″ × 0.025″ βIIITi were significantly different from all other wires (p < 0.001 in all cases). With a moment of 5 Nmm, the 0.016″ × 0.022″ NiTi wire developed median angles of 26.7, 29.8, and 38.7° with the three ligatures, respectively, while the 0.018″ × 0.025″ SS developed median angles of 12.9, 10.7, and 12.7°, respectively. Conclusions The ligature type and geometry did not affect the efficiency of torque control, except for the 0.016″ × 0.022″ NiTi wire. The wires generating the greatest moments were the 0.018″ × 0.025″ SS and 0.018″ × 0.025″ βIIITi.

Molecular biology of periodontal ligament fibroblasts and orthodontic tooth movement Abstract Purpose The circadian clock plays an important role in many physiological states and pathologies. The significance of its core genes in bone formation and tooth development has already been demonstrated. However, regulation of these genes and their influence on periodontal and bone remodeling in periodontal ligament (PDL) fibroblasts remains to be elucidated. Our hypothesis was that the circadian clock influences markers for periodontal and bone remodeling and therefore orthodontic tooth movement itself. Materials and methods Human PDL fibroblasts were cultured and synchronized in circadian rhythms with the help of a dexamethasone shock. Cells were harvested at 4 h intervals. Reverse transcription and quantitative RT PCR (real time polymerase chain reaction) were performed to assess the mRNA levels of the clock genes ARNTL, CLOCK1, PER1, and PER2. Subsequently, mRNA expression of important marker genes for periodontal and bone remodeling, OPG, RANKL, OCN, OPN, RUNX2, COL1A1, IL1β, KI67, and POSTN, were examined at time points of ARNTL amplitude expression. Results Gene expression of core clock genes varied over 48 h in accordance with the circadian rhythm. Functional markers, except KI67, showed significant differences at time points of maximum fluctuation especially of ARNTL. Conclusions PDL fibroblasts express circadian clock genes. Our results suggest that genes associated with bone and periodontal remodeling are influenced by the circadian rhythm. Further research will have to refine the understanding of this influence for orthodontic treatment.

Effect of different attachment geometries on the mechanical load exerted by PET‑G aligners during derotation of mandibular canines Abstract Aim Derotation of rounded teeth has proved difficult for aligners to achieve. In this study, we investigated the effect of aligner attachment geometry on the three-dimensional (3D) force and moment (F/M) values exerted during derotation of a mandibular canine. Materials and methods The experiment setup comprised an acrylic mandibular arch model with a separated right canine (tooth 43) mounted on a hexapod via a 3D F/M sensor. Polyethylene terephthalate glycol (PET‑G) aligners with thicknesses of 0.5, 0.625, and 0.75 mm were tested in combination with quarter-sphere, vertical-ellipsoid, and pyramidal attachments bonded to tooth 43. The experimentally measured movement consisted of mesio- and distorotation of tooth 43 in 1° steps up to ±15° in each direction. Results Compared with no attachment, vertical-ellipsoid and quarter-sphere attachments increased the rotational moment by a median factor of 1.5–12.3. Moment increases for pyramidal attachments were significantly smaller (Mann–Whitney U‑test, p < 0.05). Quarter-sphere attachments inhibited the intrusive forces up to 6.07° distorotation, whereas the intrusion prevention range for most aligner attachment combinations was significantly smaller (2.95° for vertical-ellipsoid and 2.88° for pyramidal attachments; Mann–Whitney U‑test, p < 0.05). None of the attachment geometries could completely prevent intrusive forces during mesiorotation. Conclusion The quarter-sphere geometry had the best overall mechanical properties because it induced relatively high rotational moment increases and counteracted unwanted intrusive forces most effectively of all three geometries. The determined maximum attachment dislodgement and intrusion prevention angles of approximately 6° provide a guide to determining setup increments for mandibular canine derotation.

Mitteilungen der DGKFO

Dehiscence and fenestration in anterior teeth Abstract Background Previous studies have reported incidence rates of dehiscence (DEH) and fenestration (FEN) as high as 36.51 and 51.09%, respectively. Only a few studies comparing DEH and FEN before and after orthodontic treatment (OT) are available in the literature. Purpose The aim of this study was to evaluate the occurrence of DEH and FEN in anterior teeth, before and after OT, using cone-beam computed tomography (CBCT). In addition, findings may provide a clinical basis for avoiding DEH and FEN during therapeutic tooth alignment. Patients and methods CBCT images of 21 patients near the end of their peak growth and development were included. DEH and FEN in the anterior teeth and thicknesses of the alveolar bone at the palatal (TP) and labiolingual (LL) sides of each anterior tooth were measured before and after OT. Results After OT, the incidence rates of mandibular anterior labial DEH, maxillary anterior TP-bone defect, and mandibular anterior lingual bone defect were increased by 20, 19, and 30%, respectively. Assessment of CT images prior to treatment showed that the teeth developing bone defects were significantly different regarding the apical alveolar bone thicknesses compared to the teeth that did not develop bone defects after OT, i.e., the incidence of DEH and FEN after OT was lower if the thickness of the apex to labiolingual alveolar bone before OT was as follows: the apex to labial alveolar bone thickness of the maxillary central incisor and maxillary lateral incisor was >4 mm, the apex to palatal alveolar bone thickness of the maxillary lateral incisor was >3 mm; the apex to labiolingual alveolar bone thickness of the lower incisor was >5 mm. Conclusion The incidence of post-OT DEH at the maxillary anterior and mandibular anterior lingual surfaces were increased significantly compared to before treatment. In general, the smaller the apex to labiolingual alveolar bone thickness, the greater the likelihood of bone defects occurring after OT. Evaluation of the apical position of anterior teeth in alveolar bone can help minimize the occurrence of bone defects after OT.

Wachstumsändernde apparative Kieferorthopädie im Gebiss der ersten Dentition (Milchgebiss)

Regulation of the autophagy-marker Sequestosome 1 in periodontal cells and tissues by biomechanical loading Abstract Purpose Orthodontic treatment is based on the principle of force application to teeth and subsequently to the surrounding tissues and periodontal cells. Sequestosome 1 (SQSTM1) is a well-known marker for autophagy, which is an important cellular mechanism of adaptation to stress. The aim of this study was to analyze whether biomechanical loading conditions regulate SQSTM1 in periodontal cells and tissues, thereby providing further information on the role of autophagy in orthodontic tooth movement. Methods Periodontal ligament (PDL) fibroblasts were exposed to cyclic tensile strain of low magnitude (3%, CTSL), and the regulation of autophagy-associated targets was determined with an array-based approach. SQSTM1 was selected for further biomechanical loading experiments with dynamic and static tensile strain and assessed via real-time polymerase chain reaction (RT-PCR) and immunoblotting. Signaling pathways involved in SQSTM1 activation were analyzed by using specific inhibitors, including an autophagy inhibitor. Finally, SQSTM1 expression was analyzed in gingival biopsies and histological sections of rats in presence and absence of orthodontic forces. Results Multiple autophagy-associated targets were regulated by CTSL in PDL fibroblasts. All biomechanical loading conditions tested increased the SQSTM1 expression significantly. Stimulatory effects of CTSL on SQSTM1 expression were diminished by inhibition of the c‑Jun N‑terminal kinase (JNK) pathway and of autophagy. Increased SQSTM1 levels after CTSL were confirmed by immunoblotting. Orthodontic force application also led to significantly elevated SQTSM1 levels in the gingiva and PDL of treated animals as compared to control. Conclusions Our in vitro and in vivo findings provide evidence of a role of SQSTM1 and thereby autophagy in orthodontic tooth movement.