Light Continuous Forces Research Articles

Stress Appraisal with Simulation of en masse Absolute Intrusion of Maxillary Anteriors deploying Strategic Mini-implant Locations: A Finite Element Analysis

One of the major challenges of fixed clinical orthodontics is the correction of deep overbite. Mini screw implants are ideally suited for absolute intrusion because they make it possible to apply light continuous forces of known magnitudes without producing any reciprocal reactionary effect on posterior teeth. The purpose of this FEM study was to evaluate and compare the stresses generated in maxillary anterior region during absolute en masse intrusion of six maxillary teeth using mini-implants at strategic locations. Materials and methods: Finite element model was generated using FEM software ANSYS and, on the same model, two different analyses were carried out for two groups with different points of force application as Group I consisted of two bilateral implants for en masse intrusion of maxillary anteriors and Group II consisted of a single mid implant. Results: Soft and hard bones showed significantly high stress distribution in Group I as compared to Group II. The total tooth deformation was found to be more with single point of force application which produced oblique force vectors. Conclusion: Stresses on the teeth are higher and distributed more evenly, when the point of force application is bilateral rather than a single source. Bilateral implants generate less stresses which are evenly distributed with minimum detrimental effect on the teeth during absolute intrusion.

Study of Stress Distribution in Maxillary Anterior Region during True Intrusion of Maxillary Incisors using Finite Element Methodology

ABSTRACT Introduction One of the major challenges of fixed clinical orthodontics is the correction of deep overbite. Miniscrew implants are ideally suited for absolute intrusion because they make it possible to apply light continuous forces of known magnitudes without producing any reciprocal reactionary effect on posterior teeth. The purpose of this finite element method (FEM) study was to evaluate and compare the stresses generated in maxillary anterior region during absolute en masse intrusion of six maxillary teeth using mini-implants at strategic locations. Materials and methods Finite element model was generated using FEM software and on the same model finite element analysis was carried out to study the stress distribution in maxillary anterior region during true incisor intrusion. Results Soft bone and hard bone showed significantly high stress distribution in maxillary anterior region. Conclusion Stresses on the teeth, soft bone and hard bone, were concentrated more on and near the central incisors as compared to lateral incisors. This was probably because the point of force application was between the central incisors and away from the lateral incisors. How to cite this article Padmawar SS, Belludi A, Bhardwaj A, Vadvadgi V, Saini R. Study of Stress Distribution in Maxillary Anterior Region during True Intrusion of Maxillary Incisors using Finite Element Methodology. Int J Experiment Dent Sci 2012;1(2):89-92.

Understanding the Shape-Memory Alloys Used in Orthodontics

Nickel-titanium (NiTi) shape-memory alloys (SMAs) have been used in the manufacture of orthodontic wires due to their shape memory properties, super-elasticity, high ductility, and resistance to corrosion. SMAs have greater strength and lower modulus of elasticity when compared with stainless steel alloys. The pseudoelastic behavior of NiTi wires means that on unloading they return to their original shape by delivering light continuous forces over a wider range of deformation which is claimed to allow dental displacements. The aim of this paper is to discuss the physical, metallurgical, and mechanical properties of NiTi used in Orthodontics in order to analyze the shape memory properties, super-elasticity, and thermomechanical characteristics of SMA.

Nickel-Titanium (NiTi) Arch Wires: The Clinical Significance of Super Elasticity

The introduction of nickel-titanium (NiTi) wires has revolutionized the field of orthodontics by delivering light continuous forces over a wider range of displacements than the traditional stainless-steel wires. Over the years improvements in NiTi wire manufacturing and composition have been introduced; however, the claimed wire capabilities are not always easy to verify in the clinical setting. We aim at presenting an overview of the use and applications of NiTi alloys in orthodontics. The implications of the metallurgical and mechanical properties and intraoral aging of the wires in their clinical application is discussed. Finally, time variants of orthodontic therapy duration with the use of NiTi and alternative arch wires are presented, and the clinical implication of superelasticity is analyzed.

Intraoral Distraction of Segmental Osteotomies and Miniscrews in Management of Alveolar Cleft

Management of a wide alveolar cleft and alveolar bone graft failure is among the most difficult tasks for both surgeon and orthodontist. This article aims to introduce the techniques of intraoral distraction of segmental osteotomy for solving a wide alveolar cleft, and orthodontic management with miniscrews for solving alveolar bone graft failure; and also to evaluate the feasibility and clinical results of moving teeth into alveolar clefts. Interdental distraction osteogenesis was performed to minimize the alveolar cleft before alveolar bone grafting in 21 patients whose alveolar cleft was wider than a maxillary canine. All clefts were successfully approximated, and the 4- to 5-year results were shown to be stable. In addition, orthodontic protraction of the buccal teeth by using miniscrews as a temporary anchorage device was performed in 13 cases to minimize and/or eliminate the residual bony bridge or alveolar cleft after the previous failure of an alveolar bone graft. The buccal teeth were protracted with intermittent light continuous force. The results revealed that the residual bony bridges or alveolar clefts were minimized and that the space of the cleft was completely closed. The periodontal apparatus of the teeth that were moved into the residual bony bridge or alveolar cleft remained similar before and after the treatment. The orthodontic tooth movement into a residual alveolar cleft is clinically feasible in certain circumstances. However, the long-term status of the periodontal apparatus of the teeth that were moved into the alveolar cleft should be monitored.

Rate of tooth movement under heavy and light continuous orthodontic forces

Introduction The aim of this study was to measure the rate and the amount of orthodontically induced tooth movement under heavy (300 g) and light (50 g) continuous forces with superelastic nickel-titanium closing coils over a defined time (12 weeks). Methods Fourteen patients who required maxillary canine retraction into first premolar extraction sites as part of their orthodontic treatment completed this study. In a split-mouth design, precalibrated nickel-titanium closing coil springs delivering a force of 300 g or 50 g were used to distalize the canines after an alignment and stabilization period. Intraoral and maxillary cast measurements were made at the beginning of canine retraction (T0) and every 28 days for 84 days (T1, T2, T3) to assess total space closure, canine retraction rate, canine retraction and molar anchorage loss, and canine rotation. Results Statistical analysis showed that the amount of initial tooth movement (T0-T1) was not related to force magnitude; however, during the T1-T2 and T2-T3 periods, increased amounts and higher rates of tooth movement were found with heavy forces. These significantly increased the rate and the amount of canine retraction, but the adverse effects of loss of canine rotation control and anchorage were concomitantly increased. Light forces provided a greater percentage of canine retraction than heavy forces, with less strain on anchorage. Conclusions Initial tooth movement would benefit from light forces. Heavier forces tend to increase the rate and the amount of canine retraction but lose their advantage because of unwanted clinical side effects.

Editor's Summary and Q&A: Rate of tooth movement under heavy and light continuous orthodontic forces

The aim of this study was to measure the rate and the amount of orthodontically induced tooth movement under heavy (300 g) and light (50 g) continuous forces with superelastic nickel-titanium closing coils over a defined time (12 weeks).Fourteen patients who required maxillary canine retraction into first premolar extraction sites as part of their orthodontic treatment completed this study. In a split-mouth design, precalibrated nickel-titanium closing coil springs delivering a force of 300 g or 50 g were used to distalize the canines after an alignment and stabilization period. Intraoral and maxillary cast measurements were made at the beginning of canine retraction (T0) and every 28 days for 84 days (T1, T2, T3) to assess total space closure, canine retraction rate, canine retraction and molar anchorage loss, and canine rotation.Statistical analysis showed that the amount of initial tooth movement (T0-T1) was not related to force magnitude; however, during the T1-T2 and T2-T3 periods, increased amounts and higher rates of tooth movement were found with heavy forces. These significantly increased the rate and the amount of canine retraction, but the adverse effects of loss of canine rotation control and anchorage were concomitantly increased. Light forces provided a greater percentage of canine retraction than heavy forces, with less strain on anchorage.Initial tooth movement would benefit from light forces. Heavier forces tend to increase the rate and the amount of canine retraction but lose their advantage because of unwanted clinical side effects.

Static and Cyclic Load-Deflection Characteristics of NiTi Orthodontic Archwires Using Modified Bending Tests

Near-equiatomic nickel-titanium (nitinol) has the ability to return to a former shape when subjected to an appropriate thermomechanical procedure. One of the most successful applications of nitinol is orthodontic archwire. One of the suitable characteristics of these wires is superelasticity, a phenomenon that allows better-tolerated loading conditions during clinical therapy. Superelastic nitinol wires deliver clinically desired light continuous force enabling effective tooth movement with minimal damage for periodontal tissues. In this research, a special three-point bending fixture was invented and designed to determine the superelastic property in simulated clinical conditions, where the wire samples were held in the fixture similar to an oral cavity. In this experimental study, the load-deflection characteristics of superelastic NiTi commercial wires were studied through three-point bending test. The superelastic behavior was investigated by focusing on bending time, temperature, and number of cycles which affects the energy dissipating capacity. Experimental results show that the NiTi archwires are well suited for cyclic load-unload dental applications. Results show reduction in superelastic property for used archwires after long-time static bending.

Strains in periodontal ligament and alveolar bone associated with orthodontic tooth movement analyzed by finite element

Orthodontic tooth movement (OTM) is achieved by applying an orthodontic force system to the brackets. The (re)modeling processes of the alveolar support structures are triggered by alterations in the stress/strain distribution in the periodontium. According to the classical OTM theories, symmetric zones of compression and tension are present in the periodontium, but these do not consider the complex mechanical properties of the PDL, the alveolar structures' morphology, and the magnitude of the force applied. Human jaws segments obtained from autopsy were microCT-scanned and sample-specific finite element (FE) models were generated. The material behavior of the PDL was considered to be nonlinear and non-symmetric and the alveolar bone was modeled according to its actual morphology. A series of FE-analyzes investigated the influence of the moment-to-force ratio, force magnitude, and chewing forces on the stress/strain in the alveolar support structures and OTM. Stress/strain findings were dependent on alveolar bone's morphology. Because of the nonlinear behavior of the PDL, distinct areas of tension, and compression could not be detected. Secondary load transfer mechanisms were activated and the stress/strain distribution in the periodontium was concealed by occlusal forces. We could not confirm the classical ideas of distinct and symmetrical compressive and tensile areas in the periodontium in relation to different OTM scenarios. Light continuous orthodontics forces will be perceived as intermittent by the periodontium. Because roots and alveolar bone morphology are patient-specific, FE-analysis of orthodontic loading regime should not be based on general models.

In vitro evaluation of force-expansion characteristics in a newly designed orthodontic expansion screw compared to conventional screws

Expansion screws like Hyrax, Haas and other types, produce heavy interrupted forces which are unfavorable for dental movement and could be harmful to the tooth and periodontium. The other disadvantage of these screws is the need for patient cooperation for their regular activation. The purpose of this study was to design a screw and compare its force- expansion curve with other types. A new screw was designed and fabricated in the same dimension, with conventional types, with the ability of 8 mm expansion (Free wire length: 12 mm, initial compression: 4.5 mm, spring wire diameter: 0.4 mm, spring diameter: 3 mm, number of the coils: n0 ine, material: s0 tainless steel). In this in vitro study, the new screw was placed in an acrylic orthodontic appliance, and after mounting on a stone cast, the force-expansion curve was evaluated by a compression test machine and compared to other screws. Force-expansion curve of designed screw had a flatter inclination compared to other screws. Generally it produced a light continuous force (two to 3.5 pounds) for every 4 mm of expansion. In comparison with heavy and interrupted forces of other screws, the newly designed screw created light and continuous forces.

Pain intensity during the first 7 days following the application of light and heavy continuous forces

The purpose of the present study was to determine whether a force of 20 cN can be biologically active for tooth movement and to examine the pain intensity during the application of light (20 cN) or heavy (200 cN) continuous forces for 7 days. In the first experiment, a force of 20 cN was applied to eight canines in five volunteers. The mean tooth movement during 10 weeks was 2.4 mm. In the second experiment, two forces of 20 or 200 cN were applied to maxillary premolars in 12 male subjects (aged 24-31 years) to measure pain intensity for 7 days. Spontaneous and biting pain were recorded every 2-4 hours on a 100 mm visual analogue scale (VAS). Wilcoxon signed-rank test was used for statistical analysis. Comparing the VAS score at force initiation with the other time points, there was no significant difference in spontaneous pain for either group, or in biting pain for the light-force group. However, biting pain in the heavy-force group during the time period from 6 to 156 hours was significantly (P < 0.05) greater than that at force initiation. Comparing the VAS scores between the light- and heavy-force group, VAS scores for biting pain in the heavy-force group during the time period from 8 to 100 hours was significantly (P < 0.05) greater than that in the light-force group. A force of 20 cN can move teeth, but pain intensity while biting may be greater approximately 8 hours to 5 days following the application of heavy continuous force compared with light force.

Morphological changes in the rat periodontal ligament and its vascularity after experimental tooth movement using superelastic forces

The aim of this study was to statistically assess the morphological changes of the rat periodontal ligament (PDL) and its vascularity in relation to varied magnitudes of superelastic force in experimental tooth movement using nickel-titanium (NiTi) alloy wire. Forces of 0.8, 1.6, 4, 8, and 18 g were applied to the upper first molars of five groups of 10-week-old male Wistar rats (300-320 g) for 1, 7, 14, 21, and 28 days. A control group with no orthodontic appliance application was assessed in accordance with the five experimental periods. The specimens were observed under light microscopy, processed by computer imaging, and analysed statistically with Tukey's HSD non-parametric test. One day after the start of the experiment, a few blood vessels could be seen in the compressed PDL with forces of 0.8 and 1.6 g. The cross-sectional areas of blood vessels (CAV) and periodontal ligament (CAPL) in the experimental groups where a force of over 4 g was applied were significantly smaller than those where 0.8 and 1.6 g forces were used, and in the control group. On day 7, large CAV were seen in the 1.6, 4, and 8 g groups. On day 28, the 8 and 18 g groups showed significantly larger CAPL than the 0.8, 4 g, or control groups. The findings suggest that a light continuous force, under 1.6 g, maintains the vascular structure during experimental tooth movement. In contrast, a heavy continuous force over 4 g causes the vascular structure to be absent in the early stages of tooth movement, but a dynamic regeneration of the PDL with vascularity and expansion follows.

Cytokines in crevicular fluid and orthodontic tooth movement

This review aimed to evaluate studies on cytokines in the gingival crevicular fluid (GCF) during orthodontic treatment, summarizing the regulation patterns of the most commonly studied cytokines and exploring their clinical implications. To achieve this, a number of key databases were searched using MESH terms and free text terms. An additional search was made by reference tracking. The procedures suggested by the QUOROM statement were followed. Data from the included studies were extracted into orthodontic mechanics, GCF sampling/handling methods, and cytokine measurements. From the 85 relevant studies identified, 23 studies could be included. Common drawbacks consisted mainly of inadequacies in the study design (e.g. short duration and small number of study subjects). The most consistent result was a peak of cytokine levels at 24 h. Associations existed between prostaglandin E(2) (PGE(2)) and interleukin-1beta (IL-1beta) and pain, velocity of tooth movement, and treatment mechanics. Interleukin-1beta and PGE(2) showed different patterns of up-regulation, with IL-1beta being more responsive to mechanical stress and PGE(2) more responsive to synergistic regulation of IL-1beta and mechanical force. The results might be taken to support, at the cellular level, the use of light continuous forces for orthodontic treatment.

Effect of tensile force on expression of PTHrP and thickness of hypertrophic zone in organ-cultured mouse spheno-occipital synchondroses

Objective Responses of spheno-occipital synchondroses to direct tensile stress have not been identified before. This study was, therefore designed to evaluate expression of PTHrP, and thickness of hypertrophic zone in spheno-occipital synchondroses in response to such stress, using mouse in vitro model. Methods Spheno-occipital synchondroses together with adjacent structures were excised from fifty-five 2-day-old mice that were randomly assigned to 6 control and 5 experimental groups for 5 experimental periods ( n = 5). In the experimental groups, tensile force of 0.2 g was applied across the synchondroses, using helical springs. In 5 control groups, the springs were made inactive. Both groups were then cultured for 6, 24, 48, 72 h and 7 days. Another control group was cultured without any springs for 7 days to compare with natural growth of the synchondroses from a group of five 9-day-old mice. Alcian blue-PAS staining was used to study growth of the synchondroses; immunohistochemical staining to identify PTHrP and type X collagen expression. The area of PTHrP expression and thickness of hypertrophic zone, demarcated by type X collagen expression, were measured. Results Quantitative analysis showed that PTHrP expression increased significantly at hour 24 of the force application in the experimental group ( p < 0.05), then reduced from hour 24 to 72 with a significant drop from hour 24 to 48 ( p < 0.01); and the thickness of hypertrophic zone significantly increased at hour 48 ( p < 0.01). Conclusions Our findings suggested that the growth of spheno-occipital synchondroses could be modified by tensile stress; and a light continuous force could enhance its growth, as evidenced by an increase in PTHrP expression and thickness of hypertrophic zone.

Self-Ligation and the Periodontally Compromised Patient: A Different Perspective

Orthodontic therapy is not contraindicated for patients with advanced periodontal destruction, provided that factors such as inflammation, plaque, subgingival calculus, and occlusal trauma are well controlled both before and during the orthodontic treatment. The application of extremely light continuous forces might have a better effect on the cell biology of tooth movements. By minimizing necrosis, and the subsequent hyalinization and indirect resorption, it might be possible to achieve continuous progress in tooth movement, avoiding the repeated interruptions occurring when the blood vessels are occluded, and reducing the great risk for further bone loss when treatment is rendered for individuals with decreased osseous support. A new generation of low friction, passive self-ligating brackets, in combination with newer wire and coil materials and longer activation spans, seems to be capable of exerting lower force levels providing more favorable periodontal reactions in patients with previous bone loss. A patient treated following these principles and using these newer technologies is presented.

Three-dimensional analysis of orthodontic tooth movement based on XYZ and finite helical axis systems

The purpose of this study was to demonstrate the advantage of the finite helical axis (FHA) system in the biomechanical analysis of orthodontic tooth movement by comparing it with the rectangular coordinate (XYZ) system. Ten patients (6 females and 4 males, mean age 23 years 7 months) were selected. Maxillary canine retraction using light continuous forces of two different magnitudes (0.5 and 1 N) was used to retract the right and left maxillary canines in subjects who required maximum posterior anchorage. The findings were compared based on midpalatal implants that provided a fixed reference for measurement. The significance of the difference between the results with the two different force magnitudes was determined using Wilcoxon's signed-rank test. With both the XYZ and the FHA system, no significant differences in the amount of distal movement of the canines over 2 months were found between the two force magnitudes. However, the results showed that the canine was likely to incline distally during tooth retraction with a force of 1 N compared with a force of 0.5 N (P < 0.05). With the FHA system, the result indicated that the canine was likely to incline palatally during tooth retraction with a force of 0.5 N compared with a force of 1 N (P < 0.05). In this study, the combination of these two different approaches for describing tooth movement clearly showed a difference between light continuous forces of 0.5 and 1 N.

Impacted tooth treatment with modified Nance appliance

Traction of impacted tooth often requires patient compliance to place elastics to surgically exposed impacted tooth. It can be very difficult and time-consuming. The aim of this article was to describe an impacted tooth tractor, Moon's appliance, which was modified from the Nance holding arch appliance. Moon's appliance eliminates patient compliance and generates a light continuous force. We achieved the desired treatment results for impacted tooth using this appliance. This new fixed appliance can be a reasonable alternative to conventional appliances.

Effects of continuous and interrupted orthodontic force on interleukin-1β and prostaglandin E 2 production in gingival crevicular fluid

The purpose of this study was to evaluate the effects of a light continuous force and an interrupted force with weekly reactivation on interleukin-1β (IL-1β) and prostaglandin E 2 (PGE 2); possible interactions between these 2 potent mediators of the bone resorption process were assessed in vivo. Ten healthy young adults (mean age 20.6 years, 2 men, 8 women) with 4 premolars extracted were assessed. In each subject, 1 maxillary canine (E1) received continuous force with a nickel-titanium coil spring. The opposite canine (E2) received an interrupted force with a screw-attached retractor; the force was reactivated weekly by 2 turns of the screw. An antagonistic canine was used as a control. Gingival crevicular fluid was collected from the distal side of each tooth, 10 times in 3 weeks, and IL-1β and PGE 2 levels were measured. For E1, the IL-1β level showed a significant elevation at 24 hours and then decreased and maintained an insignificant but high mean concentration, compared with the control site. The PGE 2 level showed a significant elevation at 24 hours and then decreased. For E2, a significant elevation of IL-1β level was observed at 24 hours and a greater significant elevation at 24 hours after the first reactivation, compared with the control sites. The PGE 2 level increased significantly at 24 hours and remained high for 1 week. The synergistic up-regulation of PGE 2 by appliance reactivation and secreted IL-1β was not evident with either type of force after 1 week. Both experimental sites showed significant tooth movement compared with the control sites at 3 weeks; however, there was no significant difference between the 2 experimental sites. A well-controlled mechanical stress with timely reactivation can effectively upregulate IL-1β secretion, but there might be limitations in increasing the mediator levels, because of the feedback mechanisms in vivo. In addition, the analysis of crevicular fluid is a useful method for assessing cellular response to orthodontic force in vivo.

Oral environment temperature changes induced by cold/hot liquid intake

The use of NiTi shape memory alloys, introduced into orthodontics because of their ability to develop light continuous forces that prove more effective than heavy intermittent forces in the teeth movement, requires the mastering of the functional properties of NiTi wires. More specifically, the recovery force acting on the teeth is a sensitive function of temperature: knowledge of oral temperature modifications is therefore required to understand the stress state modification felt during orthodontic therapy. The temperature modifications induced by cold or hot drink intake in the oral cavity were investigated by using arch wires, fixed to removable Hawley retainers, similar to those currently used in orthodontic practice, by means of six temperature sensors placed in correspondence with specific teeth. Similarly, the temperature changes were detected on a metallic frame, fixed onto the palatal zone to a Hawley retainer, where a palatal expander was placed to correct unilateral or bilateral crossbites in deciduous or in early mixed dentition. The maximum temperature change was observed in the interincisor area: The temperature modification on other teeth depends on the modality of drink intake, with the highest temperature variations being detected in the palatal zone. Hence modifications in the stress state during orthodontic therapy with NiTi wires are to be expected. (Am J Orthod Dentofac Orthop 1997;112:58-63.)

The pattern and control of eruptive tooth movements

Assumptions about eruptive tooth movements based on experience with adolescents may not be applicable to all ages. The eruptive process can be subdivided into six phases—three prefunctional stages of individual tooth eruption (follicular growth, pre-emergent eruptive spurt, and postemergent eruptive spurt) and three postfunctional stages of the eruption of the entire dentition (juvenile occlusal equilibrium, circumpubertal occlusal eruptive spurt, and adult occlusal equilibrium). Differences in tooth-eruption rates in each of these phases result from variations in systemic and local factors. A series of working hypotheses which incorporate recent research into a theoretical explanation of the control of eruption during each stage is presented. Prior to emergence, the force of eruption may influence the rate of bone resorption and later of gingival remodeling, but the resorptive processes occur independently and are the rate-limiting factors in pre-emergent eruption. After emergence, intermittent occlusal loading disrupts the generative or adaptive mechanisms of the periodontal ligament so that eruption slows. The light continuous forces from resting tongue pressure also are significant influences on tooth eruption during periods of rapid facial growth. Cellular adaptation of the alveolar bone and gingiva plays an important role in the control of tooth eruption in the adult.