Tooth mobility restriction by multistranded and CAD/CAM retainers-an in vitro study.

OBJECTIVES: Orthodontic retainers should restrict physiological tooth mobility as little as possible. While this has been investigated for multistranded retainers, there is a lack of data for novel CAD/CAM retainers. To address this, the present study compared the restriction of physiological tooth mobility in multistranded retainers and different CAD/CAM retainers. MATERIAL/METHODS: One group of multistranded (n = 8) and five groups of CAD/CAM retainers (nickel-titanium (NiTi), titanium grade 5 (Ti5), polyetheretherketone (PEEK), zirconia (ZrO2), and cobalt-chromium (CoCr); each n = 8) bonded from canine to canine were investigated for their influence on vertical and horizontal tooth mobility using an in vitro model of a lower arch in a universal testing machine. Load-deflection curves were determined and statistically analysed. RESULTS: All retainers restricted tooth mobility to varying extents. The retainers had less of an influence on vertical tooth mobility, with less of a difference between retainers (14%-38% restriction). In contrast, significant (P ≤ 0.05) differences were observed between retainers in the restriction of horizontal tooth mobility. ZrO2 retainers had the greatest impact, restricting horizontal tooth mobility by 82% (68 ± 20 µm/100N), followed by CoCr (75%, 94 ± 26 µm/100N) and PEEK (73%, 103 ± 28 µm/100N) CAD/CAM retainers, which had comparable effects on horizontal tooth mobility. Ti5 (54%, 175 ± 66 µm/100N) and NiTi (34%, 248 ± 119 µm/100N) CAD/CAM retainers had less of an influence on horizontal tooth mobility, and were comparable to multistranded retainers (44%, 211 ± 77 µm/100N). LIMITATIONS: This is an in vitro study, so clinical studies are needed to draw clinical conclusions. CONCLUSIONS: Multistranded and CAD/CAM retainers have different effects on tooth mobility in vitro. These effects should be further explored in future in vivo studies.

A new CAD/CAM tooth mobility simulating model for dental in vitro investigations.

OBJECTIVES: To validate a new tooth mobility simulating in vitro model for biomechanical tests of dental appliances and restorations. MATERIAL AND METHODS: Load-deflection curves for teeth in CAD/CAM models (n = 10/group, 6 teeth/model) of the anterior segment of a lower jaw with either low tooth mobility (LM) or high tooth mobility (HM) were recorded with a universal testing device and a Periotest device. All teeth were tested before and after different ageing protocols. Finally, vertical load capacity (Fmax) was tested in all teeth. RESULTS: At F = 100 N load, vertical/horizontal tooth deflections before ageing were 80 ± 10 µm/400 ± 40 µm for LM models and 130 ± 20 µm/610 ± 100 µm for HM models. Periotest values were 1.6 ± 1.4 for LM models and 5.5 ± 1.5 for HM models. These values were within the range of physiological tooth mobility. No visible damage occurred during ageing and simulated ageing had no significant effect on tooth mobility. Fmax values were 494 ± 67 N (LM) and 388 ± 95 N (HM). CONCLUSION: The model is practical, easy to manufacture and can reliably simulate tooth mobility. The model was also validated for long-term testing, so is suitable for investigating various dental appliances and restorations such as retainers, brackets, dental bridges or trauma splints. CLINICAL RELEVANCE: Using this in-vitro model for high standardised investigations of various dental appliances and restorations can protect patients from unnecessary burdens in trials and practice.

Influence of Individual Bracket Base Design on the Shear Bond Strength of In-Office 3D Printed Brackets-An In Vitro Study.

(1) Background: Novel high-performance polymers for medical 3D printing enable in-office manufacturing of fully customized brackets. Previous studies have investigated clinically relevant parameters such as manufacturing precision, torque transmission, and fracture stability. The aim of this study is to evaluate different design options of the bracket base concerning the adhesive bond between the bracket and tooth, measured as the shear bond strength (SBS) and maximum force (Fmax) according to DIN 13990. (2) Methods: Three different designs for printed bracket bases were compared with a conventional metal bracket (C). The following configurations were chosen for the base design: Matching of the base to the anatomy of the tooth surface, size of the cross-sectional area corresponding to the control group (C), and a micro- (A) and macro- (B) retentive design of the base surface. In addition, a group with a micro-retentive base (D) matched to the tooth surface and an increased size was studied. The groups were analyzed for SBS, Fmax, and adhesive remnant index (ARI). The Kruskal-Wallis test with a post hoc test (Dunn-Bonferroni) and Mann-Whitney U test were used for statistical analysis (significance level: p < 0.05). (3) Results: The values for SBS and Fmax were highest in C (SBS: 12.0 ± 3.8 MPa; Fmax: 115.7 ± 36.6 N). For the printed brackets, there were significant differences between A and B (A: SBS 8.8 ± 2.3 MPa, Fmax 84.7 ± 21.8 N; B: SBS 12.0 ± 2.1 MPa, Fmax 106.5 ± 20.7 N). Fmax was significantly different for A and D (D: Fmax 118.5 ± 22.8 N). The ARI score was highest for A and lowest for C. (4) Conclusions: This study shows that conventional brackets form a more stable bond with the tooth than the 3D-printed brackets. However, for successful clinical use, the shear bond strength of the printed brackets can be increased with a macro-retentive design and/or enlargement of the base.

Comparison of six different CAD/CAM retainers vs. the stainless steel twistflex retainer: an in vitro investigation of survival rate and stability.

PURPOSE: To compare failure rates and maximum load capacity (Fmax) of six different computer-aided design/computer-aided manufacturing (CAD/CAM) retainers with those of the hand-bent five-stranded stainless steel twistflex retainer. MATERIALS AND METHODS: Six groups (n = 8 per group) of commercially available CAD/CAM retainers (cobalt-chromium [CoCr], titanium grade 5 [Ti5], nickel-titanium [NiTi], zirconia [ZrO2], polyetheretherketone [PEEK], and gold) and twistflex retainers were tested for long-term sufficiency and for Fmax using a self-developed in vitro model. All retainer models underwent a simulated ageing process of about 15 years (1,200,000 chewing cycles with a force magnitude of 65 N at 45° followed by storage in water at 37 °C for 30 days). If retainers did not debond or break during ageing, their Fmax was determined in a universal testing machine. Data were statistically analysed using Kruskal-Wallis and Mann-Whitney U­tests. RESULTS: Twistflex retainers did not fail (0/8) during ageing and had the highest Fmax (445 N ± 51 N). Ti5 retainers were the only CAD/CAM retainers that also did not fail (0/8) and had similar Fmax values (374 N ± 62 N). All other CAD/CAM retainers had higher failure rates during ageing and significantly lower Fmax values (p < 0.01; ZrO2: 1/8, 168 N ± 52 N; gold: 3/8, 130 N ± 52 N; NiTi: 5/8, 162 N ± 132 N; CoCr: 6/8, 122 N ± 100 N; PEEK: 8/8, 65 ± 0 N). Failure was due to breakage in the NiTi retainers and debonding in all other retainers. CONCLUSION: Twistflex retainers remain the gold standard regarding biomechanical properties and long-term sufficiency. Of the CAD/CAM retainers tested, Ti5 retainers seem to be the most suitable alternative. In contrast, all other CAD/CAM retainers investigated in this study showed high failure rates and had significantly lower Fmax values.

Concept for the Treatment of Class III Anomalies with a Skeletally Anchored Appliance Fabricated in the CAD/CAM Process-The MIRA Appliance.

OBJECTIVE: Intermaxillary elastics, anchored skeletally, represent a promising concept for treatment in adolescent patients with skeletal Class III anomalies. A challenge in existing concepts is the survival rate of the miniscrews in the mandible or the invasiveness of the bone anchors. A novel concept, the mandibular interradicular anchor (MIRA) appliance, for improving skeletal anchorage in the mandible, will be presented and discussed. CLINICAL CASE: In a ten-year-old female patient with a moderate skeletal Class III, the novel MIRA concept, combined with maxillary protraction, was applied. This involved the use of a CAD/CAM-fabricated indirect skeletal anchorage appliance in the mandible, with interradicularly placed miniscrews distal to each canine (MIRA appliance), and a hybrid hyrax in the maxilla with paramedian placed miniscrews. The modified alt-RAMEC protocol involved an intermittent weekly activation for five weeks. Class III elastics were worn for a period of seven months. This was followed by alignment with a multi-bracket appliance. DISCUSSION: The cephalometric analysis before and after therapy shows an improvement of the Wits value (+3.8 mm), SNA (+5°), and ANB (+3°). Dentally, a transversal postdevelopment in the maxilla (+4 mm) and a labial tip of the maxillary (+3.4°) and mandibular anterior teeth (+4.7°) with gap formation is observed. CONCLUSION: The MIRA appliance represents a less invasive and esthetic alternative to the existing concepts, especially with two miniscrews in the mandible per side. In addition, MIRA can be selected for complex orthodontic tasks, such as molar uprighting and mesialization.

Precision of slot widths and torque transmission of in-office 3D printed brackets : An in vitro study.

PURPOSE: To investigate a novel in-office three-dimensionally (3D) printed polymer bracket regarding slot precision and torque transmission. METHODS: Based on a 0.022″ bracket system, stereolithography was used to manufacture brackets (N = 30) from a high-performance polymer that met Medical Device Regulation (MDR) IIa requirements. Conventional metal and ceramic brackets were used for comparison. Slot precision was determined using calibrated plug gages. Torque transmission was measured after artificial aging. Palatal and vestibular crown torques were measured from 0 to 20° using titanium-molybdenum (T) and stainless steel (S) wires (0.019â€³â€¯× 0.025″) in a biomechanical experimental setup. The Kruskal-Wallis test with post hoc test (Dunn-Bonferroni) was used for statistical analyses (significance level p < 0.05). RESULTS: The slot sizes of all three bracket groups were within the tolerance range according to DIN 13996 (ceramic [C]: 0.581 ± 0.003 mm; metal [M]: 0.6 ± 0.005 mm; polymer [P]: 0.581 ± 0.010 mm). The maximum torque values of all bracket-arch combinations were above the clinically relevant range of 5-20 Nmm (PS: 30 ± 8.6 Nmm; PT: 27.8 ± 14.2 Nmm; CS: 24 ± 5.6 Nmm; CT: 19.9 ± 3.8 Nmm; MS: 21.4 ± 6.7 Nmm; MT: 16.7 ± 4.6 Nmm). CONCLUSIONS: The novel, in-office manufactured polymer bracket showed comparable results to established bracket materials regarding slot precision and torque transmission. Given its high individualization possibilities as well as enabling an entire in-house supply chain, the novel polymer brackets bear high potential of future usage for orthodontic appliances.

Diagnostic compatibility of various fixed orthodontic retainers for head/neck MRI and dental MRI.

OBJECTIVES: To evaluate the diagnostic MRI compatibility of different fixed orthodontic retainers using a high-resolution 3D-sequence optimized for artifact reduction. MATERIALS AND METHODS: Maxillary and mandibular retainers made of five different materials were scanned in vitro and in vivo at 3 T MRI using an MSVAT-SPACE sequence. In vitro, artifact volumes were determined for all maxillary and mandibular retainers (AVmax; AVmand). In vivo, two independent observers quantified the extent of artifacts based on the visibility of 124 dental and non-dental landmarks using a five-point rating scale (1 = excellent, 2 = good, 3 = acceptable, 4 = poor, 5 = not visible). RESULTS: Rectangular-steel retainers caused the largest artifacts (AVmax/AVmand: 18,060/15,879 mm3) and considerable diagnostic impairment in vivo (mean landmark visibility score ± SD inside/outside the retainer areas: 4.8 ± 0.8/2.9 ± 1.6). Smaller, but diagnostically relevant artifacts were observed for twistflex steel retainers (437/6317 mm3, 3.1 ± 1.7/1.3 ± 0.7). All retainers made of precious-alloy materials produced only very small artifact volumes (titanium grade 1: 70/46 mm3, titanium grade 5: 47/35 mm3, gold: 23/21 mm3) without any impact on image quality in vivo (each retainer: visibility scores of 1.0 ± 0.0 for all landmarks inside and outside the retainer areas). CONCLUSIONS: In contrast to steel retainers, titanium and gold retainers are fully compatible for both head/neck and dental MRI when using MSVAT-SPACE. CLINICAL RELEVANCE: This study demonstrates that titanium and gold retainers do not impair the diagnostic quality of head/neck and dental MRI when applying an appropriate artifact-reduction technique. Steel retainers, however, are not suitable for dental MRI and can severely impair image quality in head/neck MRI of the oral cavity.

In vivo assessment of artefacts in MRI images caused by conventional twistflex and various fixed orthodontic CAD/CAM retainers.

PURPOSE: To assess magnetic resonance imaging (MRI) artefacts caused by different computer-aided design/computer-aided manufacturing (CAD/CAM) retainers in comparison with conventional hand bent stainless steel twistflex retainers in vivo. MATERIALS AND METHODS: MRI scans (3 Tesla) were performed on a male volunteer with different CAD/CAM retainers (cobalt-chromium, CoCr; nickel-titanium, NiTi; grade 5 titanium, Ti5) and twistflex retainers inserted. A total of 126 landmarks inside and outside the retainer area (RA; from canine to canine) were evaluated by two blinded radiologists using an established five-point visibility scoring (1: excellent, 2: good, 3: moderate, 4: poor, 5: not visible). Friedman and two-tailed Wilcoxon tests were used for statistical analysis (significance level: p < 0.05). RESULTS: Twistflex retainers had the strongest impact on the visibility of all landmarks inside (4.0 ± 1.5) and outside the RA (1.7 ± 1.2). In contrast, artefacts caused by CAD/CAM retainers were limited to the dental area inside the RA (CoCr: 2.2 ± 1.2) or did not impair MRI-based diagnostics in a clinically relevant way (NiTi: 1.0 ± 0.1; Ti5: 1.4 ± 0.6). CONCLUSION: The present study on a single test person demonstrates that conventional stainless steel twistflex retainers can severely impair the diagnostic value in head/neck and dental MRI. By contrast, CoCr CAD/CAM retainers can cause artefacts which only slightly impair dental MRI but not head/neck MRI, whereas NiTi and Ti5 CAD/CAM might be fully compatible with both head/neck and dental MRI.

Orthodontic shear bond strength and ultimate load tests of CAD/CAM produced artificial teeth.

OBJECTIVES: To investigate whether artificial CAD/CAM processed (computer-aided design/manufacturing) teeth could be a feasible option for the production of dental in vitro models for biomechanical testing. MATERIAL AND METHODS: Disks (n = 10 per group) made from two different CAD/CAM-materials, one fiber-reinforced composite (FRC; Trinia, Bicon) and one polymethylmethacrylate-based resin (PMMA; Telio CAD, Ivoclar Vivadent), as well as bovine teeth (n = 10), were tested for their shear bond strength (SBS) and scored according to the adhesive remnant index (ARI). In addition, CAD/CAM-manufactured lower incisor teeth were tested for their ultimate load (Fu). RESULTS: With regard to SBS, both PMMA (17.4 ± 2.2 MPa) and FRC (18.0 ± 2.4 MPa) disks showed no significant difference (p = 0.968) compared to bovine disks (18.0 ± 5.4 MPa). However, the samples differed with regard to their failure mode (PMMA: ARI 4, delamination failure; FRC: ARI 0 and bovine: ARI 1.6, both adhesive failure). With regard to Fu, FRC-based teeth could withstand significantly higher loads (708 ± 126 N) than PMMA-based teeth (345 ± 109 N) (p < 0.01). CONCLUSION: Unlike PMMA-based teeth, teeth made from FRC showed sufficiently high fracture resistance and comparable SBS. Thus, FRC teeth could be a promising alternative for the production of dental in vitro models for orthodontic testing. CLINICAL RELEVANCE: CAD/CAM-processed teeth made from FRC enable the use of standardized geometry and constant material properties. Using FRC teeth in dental in vitro studies has therefore the potential to identify differences between various treatment options with rather small sample sizes, while remaining close to the clinical situation.