Finite element analysis of archwire parameters and activation forces on the M/F ratio of vertical, L- and T-loops.

BACKGROUND: The ability of a loop to generate a certain moment/force ratio (M/F ratio) can achieve the desired tooth movement in orthodontics. The present study aimed to investigate the effects of elastic modulus, cross-sectional dimensions, loop configuration geometry dimensions, and activation force on the generated M/F ratio of vertical, L- and T-loops. METHODS: A total of 120 three-dimensional loop models were constructed with the Solidworks 2017 software and used for simulating loop activation with the Abaqus 6.14 software. Six vertical loop variations, 9 L-loop variations, and 9 T-loop variations were evaluated. In each group, only one parameter was variable [loop height, ring radius, leg length, leg step distance, legs distance, upper length, different archwire materials (elastic modulus), cross-sectional dimension, and activation force]. RESULTS: The simulation results of the displacement and von Mises stress of each loop were investigated. The maximum displacement in the height direction was recorded to calculate the M/F ratio. The quantitative change trends in the generated M/F ratio of the loops with respect to various variables were established. CONCLUSIONS: Increasing the loop height can increase the M/F ratio of the loop. This increasing trend is, especially, much more significant in T-loops compared with vertical loops and L-loops. In vertical loops, increasing the ring radius is much more effective than increasing the loop height to increase the M/F ratio of the loop. Compared with SS, TMA archwire loops can generate a higher M/F ratio due to its lower elastic modulus. Loops with a small cross-sectional area and high activation force can generate a high M/F ratio. The introduction of a leg step to loops does not increase the M/F ratio of loops.

Force System with Vertical V-Bends: A 3D In Vitro Assessment of Elastic and Rigid Rectangular Archwires.

A proper understanding of the force system created by various orthodontic appliances can make treatment of patients efficient and predictable. Reducing the complicated multi-bracket appliances to a simple two-bracket system for the purpose of force system evaluation will be the first step in this direction. However, much of the orthodontic biomechanics in this regard is confined to 2D experimental studies, computer modeling/analysis or theoretical extrapolation of existing models. The objective of this protocol is to design, construct and validate an in vitro 3D model capable of measuring the forces and moments generated by an archwire with a V-bend placed between two brackets. Additional objectives are to compare the force system generated by different types of archwires among themselves and to previous models. For this purpose, a 2 x 4 appliance representing a molar and an incisor has been simulated. An orthodontic wire tester (OWT) is constructed consisting of two multi-axis force transducers or load cells (nanosensors) to which the orthodontic brackets are attached. The load cells are capable of measuring the force system in all the three planes of space. Two types of archwires, stainless-steel and beta-titanium of three different sizes (0.016 x 0.022 inch, 0.017 x 0.025 inch and 0.019 x 0.025 inch), are tested. Each wire receives a single vertical V-bend systematically placed at a specific position with a predefined angle. Similar V-bends are replicated on different archwires at 11 different locations between the molar and incisor attachments. This is the first time an attempt has been made in vitro to simulate an orthodontic appliance utilizing V-bends on different archwires.

Clinical Efficacy of a Mouth-Exercising Device Adjunct to Local Ointment Intra-Lesional Injections and Surgical Treatment for Oral Submucous Fibrosis: a Randomized Controlled Trial.

BACKGROUND: Oral physiotherapy or mouth exercise is considered to be an adjunct but mandatory treatment modality for oral submucous fibrosis (OSMF). This study planned to evaluate the clinical efficacy of a newly designed mouth exercising device (MED) in OSMF patients receiving local ointment, intra-lesional drugs and surgical treatment. MATERIALS AND METHODS: A total of 231 OSMF patients were selected and treated with basic regime including topical corticosteroids, oral antioxidants and the icecream-stick exercise regime and allotted randomly to two equal groups A and B. Group-A patients were additionally given MED. Subgroups A1 and B1 patients with an inter-incisal distance (IID) 20-35mm were not given any additional therapy; subgroup A2 and B2 patients (IID 20-35mm) were treated additionally with intra-lesional injections. Subgroups A3 and B3 with IID<20mm were managed surgically. IID was measured at baseline and at 6 months recall. The change in IID measurements was calculated and statistically analyzed using 2-way ANOVA and Tukeys multiple post hoc analysis. RESULTS: Average improvement in IID after six months of recall visits was observed to be 8.4 mm in subgroup-A1 (n-53) compared to 5.5 mm in B1(n-50) (p<0.01). The IID improvement in subgroup-A2 was found to be 9.3mm (n-46) compared to 5.1 mm in B2 (n-48) (p<0.01). In the surgery group, mouth opening improvement was observed to be 9.6 mm in subgroup A3 (n-18) compared to 4.8 mm for B3 (n-16) (p<0.01). CONCLUSIONS: Use of the MED appears to be effective for increasing oral opening in OMSF patients in conjunction with local, injection and/or surgical treatment.

Objective vs subjective analyses of arch form and preformed archwire selection.

INTRODUCTION: Maintaining a patient's original arch form increases treatment stability. In this study, we assessed the agreement between subjective analyses of arch form and archwire selection by orthodontists and an objective method with Cast Analyzer Iranian X software (Khallaghane Mehr, Tehran, Iran). METHODS: Thirty-six casts with normal occlusion were scanned with a laser. The software generated the best-fit curve using a fourth-degree polynomial equation to the clinical bracket points on the casts; then it selected the best preformed nickel-titanium archwire based on the root mean square calculation either objectively or semiobjectively. Three orthodontists selected the best-fit curve and archwire subjectively using the casts. To assess intraexaminer reliability, the same orthodontists reevaluated 10 casts after 2 weeks. To assess interexaminer reliability, the 3 orthodontists performed the analyses with the software and on the casts. Agreements were evaluated with the intraclass correlation coefficient and Dahlberg's formula. RESULTS: The semiobjective method (visual selection of wire by orthodontists using the software) yielded the best results. The differences were clinically negligible between the objective (fully automated) and semiobjective methods (1.30 vs 1.36 mm). CONCLUSIONS: The objective method improved wire adaptation to the clinical bracket points. Agreement among orthodontists regarding wire selection will improve significantly when they are trained to use the software.

An in vivo study on the incidence and location of fracture in round orthodontic archwires.

OBJECTIVE: The main objective of this in vivo study was to determine the incidence and location of fracture in round nickel-titanium (NiTi) and round stainless steel orthodontic archwires, both commonly used in orthodontics. Secondarily, this study sought to determine if there is any correlation between archwire fracture and gender, diameter of the archwire, arch type (maxillary/mandibular) or bracket used. DESIGN: In vivo study. MATERIALS AND METHODS: One thousand orthodontic patients (1434 archwires) were evaluated during regular treatment visits to assess archwire fracture and location. The patient's gender, age, type of archwire (round NiTi and round stainless steel), diameter of the archwire, arch type, location of fracture (anterior or posterior) and period of service before fracture were recorded. STATISTICAL ANALYSIS: Chi-square statistical test was utilized to address the frequency and the correlation between the different variables. Level of statistical significance (α) was set at 0.05. RESULTS: Twenty-five archwire failures were reported (1.7%) of the total sample size. All fractured archwires were NiTi, and 76% of the fractures were located in the posterior region. No statistical significance was found between archwire fracture and gender, arch type (maxillary/mandibular), archwire diameter or bracket type. CONCLUSION: The frequency of archwire fracture during regular orthodontic visits is very low. The most common archwire fracture site is the posterior region. NiTi wires are the most commonly fractured archwire. No statistically significant correlation exists between archwire fracture and gender, arch type, bracket type or diameter of archwire.

Three-dimensional deformation comparison of self-ligating brackets.

INTRODUCTION: Archwire rotation is used in orthodontic treatment to alter the labiolingual orientation of a tooth. Measurement of the 3-dimensional (3D) motion of the orthodontic brackets requires a new configuration of the orthodontic torque simulator. METHODS: The orthodontic torque simulator was coupled with a stereo microscope and 2 cameras to allow for the 3D bracket motion to be determined during wire twisting. The stereo camera images were processed with a 3D digital image correlation technique to determine the 3D deformation of the orthodontic brackets. Three self-ligating brackets (Damon Q, Ormco, Orange, Calif; In-Ovation R, GAC, Bohemia, NY; and Speed, Strite Industries, Cambridge, Ontario, Canada) were compared by using the 3D digital image correlation method to demonstrate the difference in 3D motion of self-ligating brackets components. RESULTS: Contour plots of the 3 brackets demonstrate the 3D motion of the bracket tie-wings and the archwire retentive component. The 3D motion of the bracket tie-wings and archwire retentive component were quantified. The displacement values of the archwire retentive component measured with the 3D orthodontic torque simulator were found to be 2.0 and 3.5 times less for the In-Ovation and Damon Q brackets than the values in previous studies that examined the compliance of the archwire retentive component. CONCLUSIONS: The 3D digital image correlation method used to quantify bracket deformation showed the 3D motion of the bracket tie-wings and the motion of the archwire retentive component. The use of a 3D optical measurement system is useful to understand the motion of the archwire retentive component but is not necessary to quantify bracket tie-wing motion. This measurement technique can be used to evaluate brackets of varying designs.

Mechanical properties of Opus closing loops, L-loops, and T-loops investigated with finite element analysis.

INTRODUCTION: The objective of this research was to investigate the mechanical properties at both sides of Opus closing loops by analyzing the effects of loop shape, loop position, coil position, and tipping of the vertical legs. METHODS: Opus loops were compared with L-loops (with and without a coil) and a T-loop by using finite element analysis. Both upright and tipped vertical loop legs (70°) were tested. Loop response to loop pulling was simulated at 5 loop positions for a 12-mm interbracket distance and 10-mm loop lengths and heights. Three-dimensional models of the closing loops were created by using beam elements with stainless steel properties. The L-loops and Opus loops were directed toward the anterior side. Loop properties (horizontal load/deflection, vertical force, and moment-to-force ratio) at both loop ends were recorded at activation forces of 100 and 200 g. RESULTS: Upright Opus loops and L-loops showed the highest moment-to-force ratios (8.5-9.3) on the canine bracket when the loop was centered. The Opus loops and L-loops with tipped vertical legs and the T-loop had slightly lower moment-to-force ratios (7.8-8.5), with the maximum values occurring when the loop was placed close to the canine bracket end. CONCLUSIONS: Upright L-loops showed the highest moment-to-force ratios on canine brackets, whereas backward tipping of the vertical legs shifted mechanical properties closer to those of a T-loop. Loop properties varied with loop configuration and position. Clinicians should understand the specific characteristics of each loop configuration to most effectively exploit them for the desired tooth movements.

The use of fixed appliances in the UK: a survey of specialist orthodontists.

OBJECTIVE: To investigate the use of fixed appliances in the UK. DESIGN: Prospective postal questionnaire. SETTING: UK. PARTICIPANTS: All members of the General Dental Council Specialist List in Orthodontics still in active practice and not in training posts. METHOD: A preemptive letter of explanation was sent inviting orthodontists to participate in the survey. The questionnaire was subsequently posted to 935 specialists. Data analysis investigated differences in clinical practice related to varying provider groups, level of operator experience and geographical region. RESULTS: The response rate achieved was 66.3%. A majority of orthodontists routinely used the 0.022 inch pre-adjusted edgewise system, standard size Siamese pattern stainless steel brackets, conventionally ligated and bonded using standard etch and light cured composite. Nickel titanium and stainless steel were the most popular archwire materials. Anchorage was supported routinely by palatal and lingual arches in up to 25% and by headgear in over a third of respondents. Newer innovations showed variable popularity. Self-etching primer was used routinely by one-third of respondents with 11% use of self-ligating brackets. Banding of first molars was preferred by over 60% of clinicians. Bone screw implants were used by only 0.2% of respondents. Clinicians with less than 10 years experience used more headgear, light curing, MBT prescription and molar bonding. Operators with over 20 years experience used more chemically cured bonding, Roth prescription, banded first molars, 0.018 inch slot size and Tip-Edge(TM), with less use of headgear. Fixed appliance use differed from that reported in the US with lower use in the UK of standard edgewise and Roth systems, aesthetic, miniaturised and 0.018 inch slot brackets and rapid maxillary expansion. CONCLUSION: Most UK orthodontic specialists routinely used the 0.022 inch pre-adjusted edgewise system with standard size Siamese steel brackets bonded using standard etch and light cured composite with conventional ligation. Variations were seen between different provider groups, types of treatment funding, levels of operator seniority and geographical regions. Differences were noted particularly in the use of bracket prescription and design, types of molar attachment and anchorage control.

A survey on orthodontic retention procedures in The Netherlands.

The objective of this study was to survey retention procedures used in orthodontic practices in The Netherlands. A questionnaire was sent to all 279 orthodontists working in The Netherlands. The questionnaire consisted of six parts, mainly containing multiple-choice questions. Information as to background data on the individual orthodontist, retention in general, frequency of different types of removable or bonded retainers that were used, retention protocol, and the type and size of the wire used for bonded retainers was assessed. All statistical analyses were performed using Statistical Package for Social Sciences version 12.0.1. Tests for the relationship between two items were based on the chi-square test. The overall response rate was 91 per cent. Most orthodontists placed a bonded retainer in the upper and lower arch, except when the upper arch was expanded during treatment or when extractions were performed in the upper arch, in which case they placed a removable retainer. Opinions varied with regard to how many hours the removable retainers should be worn and the duration of the retention phase. Contraindications for bonded retainers were given by 96 per cent of the orthodontists, with poor oral hygiene being the most commonly mentioned. As far as bonded retainers were concerned, 84 per cent of the orthodontists preferred permanent retention. Fifty-nine per cent of the orthodontists believed that a practice guideline for retention after orthodontic treatment needs to be developed, which was confirmed by the varied responses in this survey.

Variability of the dental surface: effects on orthodontic treatment.

OBJECTIVES: The Author studied the variability of the vestibular surfaces of tooth usually involved in orthodontic treatment. MATERIALS AND METHODS: 200 model casts of Italian subject with complete permanent dentition have been analyzed studying the clinical crown dimension and the angulations of tangents drawn at 3 and 4 mm. RESULTS: The authors found differences in the vestibular surfaces curvature in the last teeth of each series, more accemptuated in the lower than in the upper arch. CONCLUSION: The conclusions of this study are related to the use of orthodontic straight wire appliances. The use of standard values with a complete torque, independently from the individuals, is based on the hypothesis of equal positioning on the tooth surface and related to the teeth axis. A variation in the torque of the upper central incisor for different kinds of straight wire appliance related to extreme variation of vestibular curvature is hypothesised.

Frictional evaluations of dental typodont models using four self-ligating designs and a conventional design.

Abstract: After a previous study using typodonts and three standardized archwire (AW) sizes, the frictional evaluations of four self-ligating brackets were directed toward the optimal AW-bracket system. Four participating manufacturers suggested three AWs, which were a representation of the three stages of orthodontic treatment, to be coupled with their respective self-ligating design. Four replicated typodont models were mounted with a self-ligating design, and a fifth model was mounted with a conventional design that served as a control. The first experiment evaluated the manufacturer-suggested AWs against the respective self-ligating design. Because no third-stage AWs could engage their respective designs, a second experiment was implemented to gain more detailed analyses of the designs. This experiment included any successful manufacturer-suggested AWs from the first experiment against the four self-ligating designs and the control design. All self-ligating designs performed with the efficiency and reproducibility associated with expectations. Specifically, self-ligation outperformed the conventional brackets when coupled with up to 0.020- x 0.020-inch wires. The clearance of the various AW sizes and alloys changed with malocclusion. Furthermore, the parameter that best correlated with drawing forces was the bending stiffness of the AW, which was directly associated with the nominal dimension of each wire. The best AW-bracket system can be selected, when taking into account the stiffness (elastic modulus and size of the AW) along with the amount of malocclusion present, once the treatment plan is determined.

Biomechanical investigation of the hybrid retraction spring.

We succeeded in developing a retraction spring that shows virtually constant retracting forces up to an activation of about 4.5 mm through the use of various non-linear materials. Compared to all other known retraction springs, an actual bodily retraction is possible over a large range for the first time. The clinical application requires no more than one reactivation. The anti-tipping moment is 10 Nmm and is to be considered constant over the entire activation range. This anti-tipping moment produces an extrusive force for the canine and an intrusive force for the molar. This side-effect can be avoided by bending a sweep into the steel portion or compensated by bending a step into the steel portion of this retraction spring. The anti-rotational moment is about 3 to 5 Nmm measured over the entire activation range. In contrast to many other springs, the favorable M/F ratio for the anti-tipping movement allows an actual bodily retraction of canines. Even when the retracting force is no longer active, the moment that moves the root of the canine distally is still acting, so that the spring can also be used for the root movement. The M/F ratio for the anti-rotational movement is between 3 and 5 mm and therefore allows retraction of the canine without causing major distortions. Customary brackets with a .018" or .022" horizontal slot can be used, as the spring is designed for a .018" x .018" vertical slot. Each spring can be used for both the left and the right canines. The steel portion allows second-order and, if desired, third-order bends to be made. The additionally necessary bends have already been described. The hybrid retraction spring can also be applied for en masse retraction of incisors if a cross-tube is used for the anterior area.

Torque transmission between square wire and bracket as a function of measurement, form and hardness parameters.

The aim of the study was to investigate the influence of cross section, edge geometry and structural hardness on torque transmission between square wire and bracket. For this purpose, 5 different brands of stainless steel square wire in 3 dimensions (0.016" x 0.016", 0.016" x 0.022" and 0.017" x 0.025") were inserted into edgewise brackets with a slot size of 0.018" and loaded with different torques (1 and 3 Ncm). The slot and wire geometries were analyzed by computer on ground specimens before and after loading. In addition, the Vickers hardness and micro-hardness of the unstressed and stressed metal surfaces were determined. While the slot size was very accurately maintained, the wire dimensions deviated downwards by an average of 10%. Torque transmission led to notching and bending-up phenomena on the bracket slot flanks. A torque loading of 3 Ncm increased the torque play of 0.016" x 0.022" wires by 3.6 degrees, and of 0.017" x 0.025" wires by 3.7 degrees. In the case of 0.016" x 0.016" wires, an effective torque transmission was no longer possible. The average Vickers hardness of the wires was 533 kp/mm2, and that of the brackets 145 kp/mm2. The micro-hardness in the deformation area of stressed internal slot walls increased with increasing load transmission from 204 to 338 kp/mm2. As a result of excessively small wire dimensions and plastic deformation of the brackets, a relatively large torque play occurs. Deformation and notching in the area of the internal slot walls are inconsistent with demands for recycling brackets. A standardization of bracket wire systems stating the actual torque play would be desirable.