Microstructural and mechanical characterization of contemporary lingual orthodontic brackets

SUMMARYOBJECTIVES: To investigate the composition and the microstructural and mechanical characterization of three different types of lingual brackets. MATERIALS AND METHODS: Incognito™ (3M Unitek), In-Ovation L (DENTSPLY GAC) and STb™ (Light Lingual System, ORMCO) lingual brackets were studied under the scanning electron microscope employing backscattered electron imaging and their elemental composition was analysed by energy-dispersive X-ray microanalysis. Additionally, Vickers hardness was assessed using a universal hardness-testing machine, and the indentation modulus was measured according to instrumented indentation test. Two-way analysis of variance was conducted employing bracket type and location (base and wing) as discriminating variable. Significant differences among groups were allocated by post hoc Student-Newman-Keuls multiple comparison analysis at 95% level of significance. RESULTS: Three different phases were identified for Incognito and In-Ovation L bracket based on mean atomic number contrast. On the contrary, STb did not show mean atomic contrast areas and thus it is recognized as a single phase. Incognito is a one-piece bracket with the same structure in wing and base regions. Incognito consists mainly of noble metals while In-Ovation L and STb show similar formulations of ferrous alloys in wing and base regions. No significant differences were found between ferrous brackets in hardness and modulus values, but there were significant differences between wing and base regions. Incognito illustrated intermediate values with significant differences from base and wing values of ferrous brackets. CONCLUSIONS/IMPLICATIONS: Significant differences exist in microstructure, elemental composition, and mechanical properties among the brackets tested; these might have a series of clinical implications during mechanotherap

Residual stress analysis of fixed retainer wires after in vitro loading: can mastication-induced stresses produce an unfavorable effect?

The aim of the present study was to compare four different types of fixed canine-to-canine retainer regarding the maximum and residual force system generated on a canine during the intrusive in vitro loading of the rest of the anterior teeth. Retainers constructed from Ortho-FlexTech gold chain 0.038×0.016-inch (rectangular, 0.96×0.40 mm²), Tru-Chrome® 7-strand twisted 0.027-inch (round, 0.68 mm diameter) steel wire, and Wildcat 0.0175-inch (round, 0.44 mm) and 0.0215-inch (round, 0.55 mm) 3-strand Twistflex steel wire bonded on the anterior teeth of an acrylic resin model, installed in the Orthodontic Measurement and Simulation System. The force system on the canine was recorded during the loading of the anterior teeth as well as the residual force system at the same tooth after the unloading. During maximum loading, the gold chain exerted the lowest and the 0.0215-inch archwire the highest force and moment magnitude. Residual forces and moments were exerted on the canine after the unloading in all retainer types, i.e., the evaluated fixed retainers were not passive after in vitro vertical loading. The lowest magnitude was measured in gold chain retainers and the highest in cases of the high formable/low yield strength 0.027-inch archwire. This fact may explain the unexpected movements of teeth bonded on fixed retainers detected long-term in vivo

A comparative assessment of forces and moments generated by lingual and conventional brackets

The aim of this study was to assess the effect of bracket type on the labiopalatal forces and moments generated in the sagittal plane. Incognito™ lingual brackets (3M Unitek), STb™ lingual brackets (Light Lingual System; ORMCO), and conventional 0.018 inch slot brackets (Gemini; 3M Unitek) were bonded on three identical maxillary acrylic resin models, with a palatally displaced right lateral incisor. The transfer trays for the indirect bonding of the lingual brackets were constructed in certified laboratories. Each model was mounted on the orthodontic measurement and simulation system and ten 0.013 inch CuNiTi wires were used for each bracket type. The wire was ligated with elastomerics and each measurement was repeated once after re-ligation. The labiopalatal forces and the moments in the sagittal plane were recorded on the right lateral incisor. One-way analysis of variance and post hoc Scheffe pairwise comparisons were used to assess the effect on bracket type on the generated forces and moments. The magnitude of forces ranged from 1.62, 1.27, and 1.81 N for the STb, conventional, and Incognito brackets, respectively; the corresponding moments were 2.01, 1.45, and 2.19 N mm, respectively. Bracket type was a significant predictor of the generated forces (P < 0.001) and moments (P < 0.001). The produced forces were different among all three bracket types, whereas the generated moments differed between conventional and lingual brackets but not between lingual bracket

Torque expression of 0.018 and 0.022 inch conventional brackets

The aim of this study was to assess the effect of the moments generated with low- and high-torque brackets. Four different bracket prescription-slot combinations of the same bracket type (Mini Diamond® Twin) were evaluated: high-torque 0.018 and 0.022 inch and low-torque 0.018 and 0.022 inch. These brackets were bonded on identical maxillary acrylic resin models with levelled and aligned teeth and each model was mounted on the orthodontic measurement and simulation system (OMSS). Ten specimens of 0.017×0.025 inch and ten 0.019×0.025 inch stainless steel archwires (ORMCO) were evaluated in the low- and high-torque 0.018 inch and 0.022 inch brackets, respectively. The wires were ligated with elastomerics into the brackets and each measurement was repeated once after religation. Two-way analysis of variance and t-test were conducted to compare the generated moments between wires at low- and high-torque brackets separately. The maximum moment generated by the 0.017×0.025 inch stainless steel archwire in the 0.018 inch brackets at +15 degrees ranged from 14.33 and 12.95 Nmm for the high- and low-torque brackets, respectively. The measured torque in the 0.022 inch brackets with the 0.019×0.025 inch stainless steel archwire was 9.32 and 6.48 Nmm, respectively. The recorded differences of maximum moments between the high- and low-torque series were statistically significant. High-torque brackets produced higher moments compared with low-torque brackets. Additionally, in both high- and low-torque configurations, the thicker 0.019×0.025 inch steel archwire in the 0.022 inch slot system generated lower moments in comparison with the 0.017×0.025 inch steel archwire in the 0.018 inch slot syste

A comparative assessment of torque generated by lingual and conventional brackets

The aim of this study was to assess the effect of bracket type on the labiopalatal moments generated by lingual and conventional brackets. Incognito™ lingual brackets (3M Unitek), STb™ lingual brackets (Light Lingual System; ORMCO), In-Ovation L lingual brackets (DENTSPLY GAC), and conventional 0.018 inch slot brackets (Gemini; 3M Unitek) were bonded on identical maxillary acrylic resin models with levelled and aligned teeth. Each model was mounted on the orthodontic measurement and simulation system and 10 0.0175 × 0.0175 TMA wires were used for each bracket type. The wire was ligated with elastomerics into the Incognito, STb, and conventional brackets and each measurement was repeated once after religation. A 15 degrees buccal root torque (+15 degrees) and then a 15 degrees palatal root torque (−15 degrees) were gradually applied to the right central incisor bracket. After each activation, the bracket returned to its initial position and the moments in the sagittal plane were recorded during these rotations of the bracket. One-way analysis of variance with post hoc multiple comparisons (Tukey test at 0.05 error rate) was conducted to assess the effect on bracket type on the generated moments. The magnitude of maximum moment at +15 degrees ranged 8.8, 8.2, 7.1, and 5.8 Nmm for the Incognito, STb, conventional Gemini, and the In-Ovation L brackets, respectively; similar values were recorded at −15 degrees: 8.6, 8.1, 7.0, and 5.7 Nmm, respectively. The recorded differences of maximum moments were statistically significant, except between the Incognito and STb brackets. Additionally, the torque angles were evaluated at which the crown torque fell well below the minimum levels of 5.0 Nmm, as well as the moment/torque ratio at the last part of the activation/deactivation curve, between 10 and 15 degrees. The lowest torque expression was observed at the self-ligating lingual brackets, followed by the conventional brackets. The Incognito and STb lingual brackets generated the highest moment

Salivary levels of cariogenic bacterial species during orthodontic treatment with thermoplastic aligners or fixed appliances: a prospective cohort study.

BACKGROUND Fixed orthodontic appliances might be associated with intraoral adverse effects on enamel, due to plaque accumulation and their colonization by oral microbes. At the same time, the demand for esthetic alternatives to orthodontic treatment, like thermoplastic aligners, is growing. However, thermoplastic aligners may behave differently intraorally than fixed appliances in terms of bacterial colonization and biofilm formation. Therefore, the aim of this prospective cohort study was to assess the salivary prevalence of the cariogenic bacteria Streptococcus mutans, Lactobacillus acidophilus, and Streptococcus sanguinis among adolescents treated orthodontically with thermoplastic aligners or fixed appliances. METHODS Thirty adolescent patients (17 girls/13 boys; mean age 13.8 years old) were assigned to treatment with either (i) self-ligating fixed appliances with nickel-titanium archwires or (ii) aligners constructed from clear transparent polyethylenterephthalat-glycol copolyester (PET-G) thermoplastic sheets. Whole stimulated saliva was collected from each patient at three time points: at baseline (before bonding and initiation of orthodontic therapy or before insertion of the thermoplastic aligners), after 2 weeks, and after 1 month. A simplified plaque index, a simplified gingival index, and the decayed, missing, and filled teeth (DMFT) index were assessed from the clinical examination of the patients. Microbiological analysis of salivary bacteria was performed by quantitative polymerase chain reaction, followed by descriptive and inferential statistics at the 5% level. RESULTS Although patients treated with aligners had significantly lower plaque and gingivitis scores throughout treatment compared to patients treated with fixed appliances, no significant difference could be found between the S. mutans counts of the two groups at any time through treatment (P > 0.05). On the other hand, patients treated with aligners had significantly lower salivary S. sanguinis counts at all time points than patients treated with fixed appliances (P < 0.05). Finally, almost no L. acidophilus were identified in the collected saliva samples in either of the treated samples. CONCLUSIONS Within the limitations of this study, there were no differences in the salivary counts of S. mutans or L. acidophilus among adolescent patients treated for 1 month with thermoplastic aligners or self-ligating appliances. On the other hand, patients treated with aligners had lower salivary levels of S. sanguinis compared to those treated with self-ligating appliances

Adverse reactions to orthodontic materials

Adverse effects can arise from the clinical use of orthodontic materials, due to the release of constituent substances (ions from alloys and monomers, degradation by-products, and additives from polymers). Moreover, intraoral aging affects the biologic properties of materials. The aim of this review is to present the currently identified major adverse effects of the metallic and polymeric components found in orthodontic appliances and materials. Corrosion in metallic orthodontic attachments releases metal ions, mainly iron, chromium, and nickel. The latter has received the greatest attention because of its reported potential for an allergic response. The formation of an oxide layer may inhibit the outward movement of ions, thereby acting as an obstacle for release. Titanium alloys have superior corrosion resistance than stainless steel. The efficiency of polymerisation is considered an essential property for all polymers. A poor polymer network is susceptible to the release of biologically reactive substances, such as bisphenol-A (BPA), which is capable of inducing hormone-related effects. The close proximity of a light-curing tip to the adhesive, pumice prophylaxis after bonding, indirect irradiation and mouth rinsing during the first hour after bonding may decrease BPA release. The adverse effects of some orthodontic materials should be considered during material selection and throughout orthodontic treatment, in order to minimise possible undesirable implications

A comparative assessment of the forces and moments generated during orthodontic incisor intrusion with three different biomechanical systems

The aim of this study was to comparatively evaluate the intrusive/extrusive forces and buccolingual torquing moments generated during anterior intrusion using different incisor intrusion mechanics. Five wire specimens were used for each of the following intrusive arches and for each jaw: blue Elgiloy non-heat treated utility arch 0.016 x 0.016-inch; TMA utility arch 0.017 x 0.025-inch; Burstone TMA intrusion arch 0.017 x 0.025-inch; and reverse curve of Spee NiTi 0.016 x 0.022-inch only for upper jaw. The wires were inserted on bracketed dental arches constructed on Frasaco models, segmented mesially to the canines. Simulated extrusion of the incisors from 0.0-3 mm was performed using the Orthodontic Measurement and Simulation System (OMSS), and forces and moments were recorded in the saggital plane at 0.1mm vertical displacement increments. All measurements were repeated five times for each specimen. The values recorded at 1.5mm for all wires were used for the statistical evaluations for the anterior regions and the values recorded at 3.0mm were used for the statistical evaluations for the posterior regions. The results were analyzed with analysis of variance (nested ANOVA, two-way ANOVA) with forces and moments serving as the dependent variables and wire type as the independent variable. Post-hoc multiple comparisons were performed using the Tukey test (0.05 error rate). The comparison of the two major intrusion techniques for the maxillary anterior teeth, segmented and bioprogressive, regarding the anterior regions (at 1.5mm of incisor displacement), revealed that the Burstone TMA 0.017 x 0.025-inch intrusion arch exerted the lowest force on the incisors (upper 0.99 N, lower 1.25 N), followed by the TMA utility 0.017 x 0.025-inch (upper 1.33 N, lower 1.54 N) and the blue Elgiloy 0.016 x 0.016-inch utility (upper 1.43 N, lower 1.71 N). The highest force was recorded for the reverse curve of Spee NiTi and exceeded the value of 9 N. The lowest buccolingual moments were recorded with the upper Burstone intrusion arch (2.47 Nmm), whereas the highest was registered for the lower utility arch constructed with a 0.017 x 0.025-inch TMA wire (7.79 Nmm). Regarding the posterior regions (at 3.0mm of incisor displacement), the 0.016 x 0.016-inch Blue Elgiloy utility arch exerted the highest posterior extrusive forces, 15% higher than the 0.017 x 0.025-inch TMA utility and 40% higher in comparison with the 0.017 x 0.025-inch TMA Burstone intrusion arch.The lowest posterior moment in the saggital plane was generated by the 0.017 x 0.025-inch TMA Burstone intrusion arch. The 0.016 x 0.016-inch Blue Elgiloy utility arch exerted 15% higher posterior moments and the 0.017 x 0.025-inch TMA utility 25% higher. Forces and moments were consistently larger for the mandible compared to the maxilla for the same intrusion technique.Σκοπός της παρούσας εργασίας αποτελεί η συγκριτική αξιολόγηση των δυνάμεων εμβύθισης/υπερέκφυσης καθώς και των ροπών που αναπτύσσονται στο οβελιαίο επίπεδο κατά την ορθοδοντική εμβύθιση τομέων με διαφορετικά εμβιομηχανικά συστήματα. Τα συστήματα αυτά αξιολογήθηκαν τόσο στην πρόσθια, όσο και στην οπίσθια περιοχή κάθε οδοντικού τόξου, με τη βοήθεια της συσκευής μέτρησης και προσομοίωσης της ορθοδοντικής μετακίνησης (Orthodontic Measurement and Simulation System – OMSS). Κατασκευάσθηκαν από 5 διαφορετικά συρμάτινα τόξα, ξεχωριστά για κάθε γνάθο, utility 0.016 x 0.016 Blue Elgiloy, utility 0.017 x 0.025 TMA, τόξο εμβύθισης κατά Burstone 0.017 x 0.025 TMA προσδεδεμένο άπω των πλάγιων τομέων και ουλικά του προσθίου τμηματικού τόξου. Επίσης αξιολογήθηκαν 5 τόξα Nitinol αντίστροφης καμπύλης Spee 0.016 x 0.022 στην άνω γνάθο. Τα σύρματα αυτά τοποθετήθηκαν ενεργοποιημένα σε ακρυλικά εκμαγεία Frasaco, στα οποία η πρόσθια τομική περιοχή ήταν αποκομμένη. Για την αξιολόγηση της πρόσθιας περιοχής, η συσκευή OMSS προγραμματίστηκε να κάνει υπερέκφυση τομέων 0-1.5χιλ., ενώ για την οπίσθια περιοχή η υπερέκφυση έγινε ως τα 3χιλ. Οι δυνάμεις/ροπές μετρώνταν κάθε 0.1χιλ. και κάθε τόξο μετρήθηκε στη συσκευή 5 φορές. Η στατιστική επεξεργασία των δεδομένων έγινε με τη μέθοδο ανάλυσης διακύμανσης (nested ANOVA, two-way ANOVA). Οι δυνάμεις και οι ροπές ήταν οι εξαρτημένες μεταβλητές ενώ το είδος του σύρματος και η γνάθος (άνω ή κάτω) οι ανεξάρτητες μεταβλητές. Έγιναν πολλαπλές συγκρίσεις post hoc χρησιμοποιώντας τη δοκιμασία Tukey (.05 error rate). Κατά την σύγκριση των δύο κυρίων τεχνικών εμβύθισης προσθίων δοντιών, φάνηκε ότι στην πρόσθια περιοχή και σε υπερέκφυση των τομέων 1.5χιλ., το utility μπλε Elgiloy 0.016 x 0.016 ασκούσε τις υψηλότερης εντάσεως δυνάμεις εμβύθισης (άνω 1.43 N, κάτω 1.71 N), και λίγο μικρότερες το utility TMA 0.017 x 0.025 (άνω 1.33 N, κάτω 1.54 N) ενώ το Burstone TMA 0.017 x 0.025 ασκούσε τις χαμηλότερες (άνω 0.99 N, κάτω 1.25 N). Εξαιρετικά υψηλής εντάσεως δύναμη ασκούσε το τόξο NiTi αντίστροφης καμπύλης (9.3N). Την χαμηλότερη ροπή στο οβελιαίο επίπεδο εμφάνιζε το άνω Burstone TMA 0.017 x 0.025 (2.47 Nmm), ενώ την υψηλότερη το κάτω utility 0.017 x 0.025 TMA (7.79 Nmm). Όσον αφορά στην οπίσθια περιοχή του φραγμού, στα 3χιλ. υπερέκφυσης των τομέων, οι υψηλότερης εντάσεως δυνάμεις υπερέκφυσης μετρήθηκαν στο utility μπλε Elgiloy 0.016 x 0.016, οι οποίες ήταν κατά 15% μεγαλύτερες, σε σύγκριση με αυτές του utility 0.017 x 0.025 TMA και 40% μεγαλύτερες σε σύγκριση με το Burstone 0.017 x 0.025 TMA. Την μικρότερη ροπή στο οβελιαίο επίπεδο εμφάνισε το Burstone 0.017 x 0.025 TMA. Το utility μπλε Elgiloy 0.016 x 0.016 ασκούσε κατά 15% υψηλότερες ροπές στην περιοχή αυτή και το utility 0.017 x 0.025 TMA 25% υψηλότερες. Η ένταση τόσο των δυνάμεων όσο και των ροπών κάθε συγκεκριμένης τεχνικής εμβύθισης ήταν πάντα αυξημένη στην κάτω γνάθο

Mechanical properties of contemporary orthodontic adhesives used for lingual fixed retention

OBJECTIVE The aim of the present study was to test the mechanical properties of different adhesives used in orthodontics for fixed retainers and to investigate their possible interrelations. MATERIALS AND METHODS Specimens of six different adhesive resins were prepared: Transbond XT, Transbond LR and an experimental BPA-free orthodontic adhesive, as well as IPS Empress Direct (IPS-ED), ZNano and Accolade. The mechanical properties tested were Martens hardness (HM), indentation modulus (EIT), the ratio of elastic to total work, commonly known as elastic index (ηIT) and Vickers hardness (HV). These properties were determined using instrumented indentation testing according to ISO 14577-2002. The results of the aforementioned properties were statistically compared with one-way ANOVA-test and Student-Newman-Keuls multiple comparison test at a=0.05, while possible correlations among the properties tested were analyzed by Pearson correlation. RESULTS Significant differences were identified among all the materials tested for HM, with Transbond LR presenting the highest value. This resin presented the highest EIT too. Significant EIT differences were identified among the materials and only ZNano and IPS-ED showed no significant differences for this property. Transbond LR and ZNano showed higher HV values. ZNano demonstrated the highest elastic index. Pearson analysis showed a strong positive correlation between HM and EIT (0.970), HM and HV (0.837), and EIT and HV (0.695), while a weak negative correlation was found between EIT and elastic index (-0.505). CONCLUSIONS The materials tested demonstrated significant differences in their mechanical properties, and thus differences in their clinical performance are anticipated