Thermoplastic Appliances Research Articles

Effects of mechanical properties of thermoplastic materials on the initial force of thermoplastic appliances

To measure the forces delivered by thermoplastic appliances made from three materials and investigate effects of mechanical properties, material thickness, and amount of activation on orthodontic forces. Three thermoplastic materials, Duran (Scheu Dental), Erkodur (Erkodent Erich Kopp GmbH), and Hardcast (Scheu Dental), with two different thicknesses were selected. Values of elastic modulus and hardness were obtained from nanoindentation measurements at 28°C. A custom-fabricated system with a force sensor was employed to obtain measurements of in vitro force delivered by the thermoplastic appliances for 0.5-mm and 1.0-mm activation for bodily tooth movement. Experimental results were subjected to several statistical analyses. Hardcast had significantly lower elastic modulus and hardness than Duran and Erkodur, whose properties were not significantly different. Appliances fabricated from thicker material (0.75 mm or 0.8 mm) always produced significantly greater force than those fabricated from thinner material (0.4 mm or 0.5 mm). Appliances with 1.0-mm activation produced significantly lower force than those with 0.5-mm activation, except for 0.4-mm thick Hardcast appliances. A strong correlation was found between mechanical properties of the thermoplastic materials and force produced by the appliances. Orthodontic forces delivered by thermoplastic appliances depend on the material, thickness, and amount of activation. Mechanical properties of the polymers obtained by nanoindentation testing are predictive of force delivery by these appliances.

A New Treatment Method to Retract Anterior Teeth with the Double J Retractor System in Class III Malocclusions

The double J retractor (DJR) is a novel method to close extraction space with the aid of mini-implants. DJR is placed lingually on the incisors and has a lower profile compared with the conventional lingual bracket appliance. It consists of a newly designed lingual level arm retractor connected to the lingual of the 6 splinted anterior teeth. The anterior segment is retracted with a mini-anchor-screw as a temporary skeletal anchorage device without brackets and wires on the posterior teeth. Compared with conventional orthodontic procedures, such as leveling, space closure, and finishing, the procedures used with DJR are reduced to 2 steps: space closure and alignment/finishing. With DJR, the anterior teeth are retraced first without the leveling stages, and then the leveling and finishing procedures are performed together for individual tooth alignment and detailing with conventional fixed appliances or invisible clear thermoplastic appliances, such as Invisalign (STAR28 Dental Group, Invisalign Center, Seoul, Korea). With new and simple appliances, the anterior teeth can be retracted with proper torque control and shorten the treatment period. Patient satisfaction could be maximized by prompt anterior teeth and lip retraction at the beginning of treatment. In this article, the biomechanics in the use of DJR are discussed together with the application for treatment of Class III malocclusions.

Removable thermoplastic appliances as orthodontic retainers--a prospective study of different wear regimens

The aim of this prospective study was to evaluate and compare stability after 6 months of Essix retainer use. Patients' perceptions of wearing the retainer were also evaluated. A total of 69 patients, 53 girls and 16 boys [mean age 15.7 years, standard deviation (SD) 1.96], were included in the study and randomized into two groups with different wear regimens; full-time wear for 3 months and thereafter at night (group A) compared to full-time wear for 1 week and thereafter at night only (group B). Sixty patients completed the study and thus, group A comprised 30 maxillary retainers and 18 mandibular retainers and group B 30 maxillary and 18 mandibular retainers. Little's irregularity index (LII), overjet, and overbite were measured at debond (T(1)) and after 6 months (T(2)). Differences within and between groups were analysed with a Mann-Whitney test. At T(2), all patients completed a questionnaire in order to evaluate their experience of wearing an Essix retainer and how they complied with the given instructions. Differences in LII during T(1)-T(2) were 0.44 and 0.49 mm for group A and B, respectively, but with no significant difference between the groups. There were also no significant changes in overjet and overbite within or between the groups during T(1)-T(2). According to the responses to the questionnaire, the retainer was well tolerated by the patients. It was therefore concluded that the Essix retainer is sufficient for maintaining the results after orthodontic treatment and that night-time wear is adequate.

Initial Forces and Moments Delivered by Removable Thermoplastic Appliances during Rotation of an Upper Central Incisor

To determine the forces and moments delivered to a maxillary central incisor during rotation by three different thermoplastic appliances with identical thickness. Five identical appliances were manufactured from each of three materials (Ideal Clear 1.0 mm, Erkodur 1.0 mm, Biolon 1.0 mm). An upper central incisor fixed in a measuring device was rotated around its central axis in 0.5-degree steps to +/-2.5 degrees, +/-5 degrees, and +/-7.5 degrees (equivalent to an activation of +/-0.17 mm, +/-0.34 mm, and +/-0.51 mm of the incisor edge) in the clockwise and anticlockwise directions with the respective appliance fixed in place. For statistical analysis, the moments Tz (rotation) and forces Fz (intrusion) were tested. Means and standard deviations for Tz and median and 25% and 75% quantiles for Fz were calculated. An analysis of variance (ANOVA) was performed. The minimal moment was determined at a rotation of -0.17 mm (-7.3 Nmm, +/-0.8), and the maximal moment at a deflection of -0.51 mm (-71.8 Nmm. +/-2.5) was recorded. The minimal value for Fz was measured at an activation of -0.17 mm (0.0 N), and the highest intrusive forces were evaluated for a rotation of -0.51 mm (-5.8 N). The particular material sometimes had a significant (P < .05) influence on the forces delivered and the moments. During rotation with aligners, an intrusive force can also be observed. The direction of rotation, and the materials used all exert an influence on the force delivery properties of the appliance.

Editor's Summary and Q&A: Influence of thermoplastic appliance thickness on the magnitude of force delivered to a maxillary central incisor during tipping

Introduction The aim of the study was to quantify the forces delivered by thermoplastic appliances made of 2 materials with 2 thicknesses to a maxillary central incisor during tipping. Methods Two materials were tested, each in 2 thicknesses: Erkodur (Erkodent Erich Kopp GmbH, Pfalzgrafenweiler, Germany) 1.0 and 0.8 mm, and Biolon (Dreve Dentamid GmbH, Unna, Germany), 1.0 and 0.75 mm. For each material, 5 appliances were produced. To measure the forces applied, an isolated measuring tooth, part of a standardized resin model, was deflected in 0.05° steps from 0° to 0.42° in the vestibular and palatine directions, after placing the respective appliance on the model. For statistical analysis, the force components Fx/tipping and Fz/intrusion at a displacement of ± 0.151 mm from the incisor edge were selected. Means and standard deviations were calculated. The Wilcoxon 2-sample test for group pairings was used. Results The norms for the mean Fx forces ranged from 1.62 (SD, 0.41) to 5.35 N (SD, 0.63). The mean Fz forces were between 0.07 (SD, 0.13) and −2.47 N (SD, 0.34). The highest intrusive forces were measured during vestibular displacement of the measuring tooth. The forces delivered by the thick appliances were overall significantly higher (P <0.0001) than those of the thin materials. The forces delivered by the Biolon appliances were generally significantly higher (P <0.0001) than those for the Erkodur materials. Conclusions The forces applied were mostly too high when compared with those stated in the literature as ideal. In addition to thickness, the thermoforming process influences the magnitude of the force delivered by a thermoformed appliance. The aim of the study was to quantify the forces delivered by thermoplastic appliances made of 2 materials with 2 thicknesses to a maxillary central incisor during tipping. Two materials were tested, each in 2 thicknesses: Erkodur (Erkodent Erich Kopp GmbH, Pfalzgrafenweiler, Germany) 1.0 and 0.8 mm, and Biolon (Dreve Dentamid GmbH, Unna, Germany), 1.0 and 0.75 mm. For each material, 5 appliances were produced. To measure the forces applied, an isolated measuring tooth, part of a standardized resin model, was deflected in 0.05° steps from 0° to 0.42° in the vestibular and palatine directions, after placing the respective appliance on the model. For statistical analysis, the force components Fx/tipping and Fz/intrusion at a displacement of ± 0.151 mm from the incisor edge were selected. Means and standard deviations were calculated. The Wilcoxon 2-sample test for group pairings was used. The norms for the mean Fx forces ranged from 1.62 (SD, 0.41) to 5.35 N (SD, 0.63). The mean Fz forces were between 0.07 (SD, 0.13) and −2.47 N (SD, 0.34). The highest intrusive forces were measured during vestibular displacement of the measuring tooth. The forces delivered by the thick appliances were overall significantly higher (P <0.0001) than those of the thin materials. The forces delivered by the Biolon appliances were generally significantly higher (P <0.0001) than those for the Erkodur materials. The forces applied were mostly too high when compared with those stated in the literature as ideal. In addition to thickness, the thermoforming process influences the magnitude of the force delivered by a thermoformed appliance.

Influence of thermoplastic appliance thickness on the magnitude of force delivered to a maxillary central incisor during tipping

The aim of the study was to quantify the forces delivered by thermoplastic appliances made of 2 materials with 2 thicknesses to a maxillary central incisor during tipping. Two materials were tested, each in 2 thicknesses: Erkodur (Erkodent Erich Kopp GmbH, Pfalzgrafenweiler, Germany) 1.0 and 0.8 mm, and Biolon (Dreve Dentamid GmbH, Unna, Germany), 1.0 and 0.75 mm. For each material, 5 appliances were produced. To measure the forces applied, an isolated measuring tooth, part of a standardized resin model, was deflected in 0.05 degrees steps from 0 degrees to 0.42 degrees in the vestibular and palatine directions, after placing the respective appliance on the model. For statistical analysis, the force components Fx/tipping and Fz/intrusion at a displacement of +/- 0.151 mm from the incisor edge were selected. Means and standard deviations were calculated. The Wilcoxon 2-sample test for group pairings was used. The norms for the mean Fx forces ranged from 1.62 (SD, 0.41) to 5.35 N (SD, 0.63). The mean Fz forces were between 0.07 (SD, 0.13) and -2.47 N (SD, 0.34). The highest intrusive forces were measured during vestibular displacement of the measuring tooth. The forces delivered by the thick appliances were overall significantly higher (P <0.0001) than those of the thin materials. The forces delivered by the Biolon appliances were generally significantly higher (P <0.0001) than those for the Erkodur materials. The forces applied were mostly too high when compared with those stated in the literature as ideal. In addition to thickness, the thermoforming process influences the magnitude of the force delivered by a thermoformed appliance.

Initial forces generated by three types of thermoplastic appliances on an upper central incisor during tipping

The force properties of thermoformed appliances have not been systematically investigated. Therefore, the aim of the present study was to quantify the forces delivered by thermoplastic appliances manufactured from three different materials, with the same thickness, on a central upper incisor, during tipping. Five identical appliances were manufactured from three different materials all with a thickness of 1.0 mm (Ideal Clear, Erkodur, and Biolon). For measuring the forces, an isolated measuring tooth, as part of a standardized resin model incorporated in a newly developed measuring device, was tipped in nine 2.7 arc minute (0.04629 degree) steps, from 0 to 0.416 degrees in the vestibular and palatal directions around a rotational axis through the virtual apex, after positioning an appliance on the model. For statistical analysis, the force components Fx/tipping and Fz/intrusion at a displacement of +/-0.151 mm from the incisor edge were determined. Means and standard deviations (SDs) were calculated. The Kruskal-Wallis test for overall effects and the Wilcoxon two-sample test for individual group pairings were used (P < 0.05 significance level). The mean Fx forces ranged from -2.82 N (SD 0.62) to 5.42 N (SD 0.56). The mean Fz forces were between -0.14 N (SD 0.52) and -2.3 N (SD 0.43). The highest intrusive forces were measured during vestibular displacement of the measuring tooth. The forces delivered by the Biolon appliance were found to be much greater (P < 0.01) than those of the other materials. The forces delivered by the materials investigated were mostly higher than those stated in the literature.

Physical properties of root cementum: Part 10. Comparison of the effects of invisible removable thermoplastic appliances with light and heavy orthodontic forces on premolar cementum. A microcomputed-tomography study

Orthodontic treatment with clear sequential removable thermoplastic appliances (TAs) is gaining popularity as an alternative to treatment with fixed appliances. The amount of orthodontically induced inflammatory root resorption generated by such appliances has not been investigated. In this prospective randomized clinical trial, we used x-ray microtomography to quantify resorption generated by treatment with ClearSmile appliances (ClearSmile, Woollongong, Australia) and compared the effects with those of heavy and light conventional orthodontic forces and no force. The sample consisted of 54 maxillary first premolars in 27 patients who required bilateral extractions as part of their planned orthodontic treatment. The subjects were randomly assigned to 3 groups, each with 9 subjects. A split-mouth design was used, and forces were applied to the first premolars. In group 1, TAs were used to move teeth on 1 side in a buccal direction at a rate of 0.5 mm every 2 weeks (TA movement); the contralateral teeth were not moved and served at controls. In group 2, TA movement was used on 1 side. A buccal force of 225 g from a beta-titanium alloy cantilever spring (heavy force) was used on the contralateral side. In group 3, TA movement was used on 1 side. A buccal force of 25 g from a cantilever spring (light force) was used on the contralateral side. The treatment duration was 8 weeks (56 days +/- 1 day). The TAs were changed every 14 days, and each patient used 4 appliances. The springs were not reactivated. At the end of the study period, the teeth were extracted according to a strict protocol to prevent root damage. Resorption was measured with an x-ray microtomograph (1072, SkyScan, Aartselaar, Belgium). Software analysis determined quantity, location, and distribution of root resorption craters. The control teeth had the least amount of resorption. The light-force teeth had approximately 5 times more resorption than the control teeth (P <.001). The TA teeth had similar but slightly greater resorption than the light-force teeth, or approximately 6 times greater than the control teeth (P <.001). The heavy-force teeth had the most resporption, about 9 times greater than the controls (P <.001). Clear removable TAs have similar effects on root cementum as light (25 g) orthodontic forces with fixed appliances.

A Novel Pressure Film Approach for Determining the Force Imparted by Clear Removable Thermoplastic Appliances

The force imparted by removable thermoplastic appliances (RTA) onto teeth has not been investigated in the past. This investigation was designed to explore a novel methodology to measure the magnitude and identify the pattern of this force. Eight patients with moderate malocclusion were selected. In each patient, the palatally mal-positioned upper first premolar was corrected by wearing a series of four ClearSmile RTA over a duration of 8 weeks. When constructing RTA, the ClearSmile Company was advised that the amount of movement to be programmed into each appliance was 0.5 mm. The Pressurex film was used to measure the pressure generated by ClearSmile RTA against the palatal surface of the upper first premolar for buccal tipping movement. Three measurements were conducted respectively upon the issue and retrieval of each appliance (after 2 weeks of wear), resulting in 24 pressure measurements for each patient. Digital imaging and spectrophotometry analysis were employed to quantify the stain intensity mounted by the pressure on the films. The irrelevant forces were subtracted out to allow an assessment of the force purely acting to buccally repositioning the tooth. The results revealed that (1) the mean force magnitude over 2 weeks of RTA wear was 1.12 N (SE = 0.72 N); (2) the higher force magnitude of 5.12 N (SE = 0.80 N) seen at the issue of the appliance declined drastically to -2.67 N at the time of retrieval. These findings suggest that ClearSmile RTA exerts a high level of force against the tooth to be moved at the initial stage followed by a rapid force diminish.

Positive resist material requirements for VLSI device fabrication. Part I : David J. Elliott. Solid St. Technol., 116 (May 1982)

This chapter provides information about the chemical structure of the popular thermoplastic orthodontic aligners, analyzes their mechanical properties for the as-received condition and after intraoral or artificial aging, and discusses the impact of these alterations on the efficacy of orthodontic treatment. Invisalign aligners are constructed from a thermoplastic polyurethane. Other manufacturers make greater use of polyethylene terephthalate glycol. Orthodontic forces delivered by thermoplastic appliances depend on amount of activation, material, thickness, and thermoforming process. However, in each aligner, most tooth movement occurs within the first 24 h. A strong correlation exists between mechanical properties, mainly hardness and elastic modulus, of the thermoplastic materials and force produced by the appliances. Additionally, appliances with higher hardness are expected to demonstrate better wear resistance. Aging causes a decrease of the residual stress within all materials with time and a deterioration of their clinical properties. The impact of this deterioration in tooth movement is not always clear. These materials absorb water with time and expand hygroscopically. Aligners were found not to release traceable monomers or by-products after short-term in vitro aging. Moreover, they did not seem to induce cytotoxic and estrogenic effects.