In vitro assessment of the mechanical properties of latex and non-latex orthodontic elastics

Orthodontic biomechanics with intermaxillary elastics

INTRODUCTION

Intermaxillary elastics are orthodontic resources widely used in various malocclusions. Their main advantages are low cost, easy insertion and removal by patients, and application versatility. As main disadvantages, we can highlight the need for cooperation from patients and the side effects normally present in treatments with this resource. Knowledge of the biomechanics involved in the use of intermaxillary elastics is essential to take full advantage of the desired effects and avoid unwanted effects in their use.

OBJECTIVE

Therefore, the objective of this article is to describe the anchorage preparation, connection methods, time and force of use, and side effects involved in the use of intermaxillary elastics for the treatment of anteroposterior, vertical and transverse problems. For that, clinical cases and biomechanics schemes will be presented, in which all these details will be described.

Mechanical Characterization and Structural Analysis of Latex-Containing and Latex-Free Intermaxillary Orthodontic Elastics

Class II malocclusion is one of the most common dental anomalies and the use of intermaxillary elastomers is the standard method in its treatment. However, orthodontic elastics cannot exert continuous force over a period of time due to force degradation. Our goal was to mechanically characterize the different types of elastomers during static and cyclic loads, based on uniform methodology and examine the morphological changes after loading. Ten types of latex-containing and four latex-free intermaxillary elastics were examined from six different manufacturers. To determine the mechanical characteristics of the elastomers, tensile tests, cyclical tensile fatigue tests and 24 h relaxation tests were performed, and the elastics were also subjected to scanning electron microscopy (SEM) and Raman spectroscopy. Regardless of the manufacturer, the latex-containing elastomers did not show significant differences in the percentage of elongation at break during the tensile test. Only one type of latex-containing elastomer did not tear during the 24 h cyclical fatigue test. Fatigue was confirmed by electron microscopy images, and the pulling force reduced significantly. During the force relaxation test, only one latex-free ligature was torn; the force degradation was between 7.8% and 20.3% for latex ligatures and between 29.6% and 40.1% for latex-free elastomers. The results showed that dynamic loading was more damaging to ligatures than static loading, latex-containing elastomers were more resistant than latex-free elastics, and which observation could have clinical consequences or a potential effect on patient outcome.

Effects of different storage temperatures on the properties of nonlatex orthodontic modules

Objective

To evaluate and compare the effect of variation in storage temperatures and duration on a tensile load at failure of elastomeric modules.

Methods

In total, 140 modules were used in the study, 20 of which were tested on day 0 as received from a company using a Universal testing machine for baseline estimation of tensile load at failure. The rest 120 modules were divided into 6 groups. Groups I, II, and III modules were stored at low (T1 = 1-5°C), moderate (T2 = 20-25°C) and high (T3 = 35-40°C) temperatures, respectively, for 6 months. Groups IV, V and VI modules were stored at temperatures T1, T2 and T3 for 1 year, respectively, and were tested for tensile load at failure.

Results

The tensile load at failure for the control group was 21.588 ± 1.082 N and for 6-month interval at temperatures T1, T2 and T3 was 18.818 N ± 1.121 N, 17.841 N ± 1.334 N and 17.149 N ± 1.074 N, respectively, and for 1 year, it was 17.205 N ± 1.043 N, 16.836 N ± 0.487 N and 14.788 N ± 0.781 N, respectively. The tensile load at failure decreased significantly from 6 months to 1 year among each temperature group.

Conclusions

Maximum force degradation was seen in modules at high temperature followed by medium temperature and low temperature at both 6 months and 1 year intervals, and tensile load at failure decreased significantly from 6 months to 1 year storage duration. These results conclude that the temperature and duration at which the samples were exposed during storage produce a significant change in the forces exerted by the modules.

The Effect of Extrinsic Factors on the Mechanical Behavior and Structure of Elastic Dental Ligatures and Chains

Force provided by elastomers used in orthodontics can be affected by several factors present in the oral cavity. The aim of our study was to investigate the role of mouthwashes, toothbrushing, and smoking in the force decay of such elastomers. Tensile strength, changes in the force continuously exerted, and force decay of elastic chains (Ortho Organizer and Masel Short Power Chain) and elastic ligatures (Dentaurum and Masel) by two separate manufacturers were measured. Measurements were initially made on untreated elastics, followed by exposure to different environmental factors including cigarette smoke, toothbrushing (mechanical plaque control), and two different mouthwashes (chemical plaque control). Changes on the surface of the elastics were studied with scanning electron microscopy (SEM). Untreated Masel elastic ligature showed lower tensile strength than Dentaurum elastic ligature (2339 cN vs. 3660 cN), while significantly higher tensile strength was measured for Ortho Organizer elastic chains than Masel chains (2639 cN vs. 1324 cN). The decrease in the elastic force of Masel ligature was greater in response to all external factors compared to Dentaurum. Although brushing with toothpaste and toothbrush impacted the force of both Masel and Ortho organizer ligatures negatively, force degradation was more apparent in the case of the Ortho organizer. Surface changes were more visible when applying Curasept mouthrinse, however force decay was higher in the Corsodyl group. Mechanical and chemical plaque control can influence the tensile strength and force decay of orthodontic elastomers, which should be considered by selecting the elastomers or determining their changing interval for the practice.

Do we know how much force we apply with latex intermaxillary elastics?

Objectives:

The aim of our study was to evaluate the variation of the forces provided by different branded elastics and to compare the force diminution that occurs after 24-h of use in wet environment.

Materials and Methods:

Elastics from four different manufacturer (American Orthodontics [AO], USA; Dentaurum [DENT], Germany; Ormco, USA; RMO, USA) with 3/16-inch (4.8 mm) lumen diameter, and two different force degrees (medium/heavy) were included in the study with a total of eight groups of elastics. First force measurements were performed with 50 elastics of each group at various stretching distances; lumen diameter ×2 (9.52 mm), ×3 (14.28 mm), the average canine-first molar length (22.3 mm), and the canine-second molar length (38.7 mm) under room temperature and dry air conditions. In addition, ten the elastics from each group were stretched at 22.3 mm distance in a custom-made plate and kept in 37°C distilled water. Twenty-four hours later, the force measurements were repeated.

Results:

Regardless of the brand and type (medium-heavy), all the tested elastics showed variations in matter of generated forces at different stretching distances. The variation amount increased as the length of elongation increased. The lowest standard deviation values were observed for both medium and heavy DENT elastic groups. When stretched to 3 times of their lumen size, the medium and heavy elastics both produced either lower or higher forces compared to the levels of force indicated by the manufacturers. The closest mean force to the force level stated by the manufacturer was provided with medium AO (3.6 g difference) elastics and heavy RMO counterparts (7.9 g difference). A significant 20–23% reduction of force was observed in all brands, both in medium and heavy elastics after passing 24-h in aqueous environment. No significant difference was observed in matter of force degradation between groups for both medium and heavy elastics (P < 0.05).

Conclusion:

The forces exerted by intermaxillary elastics were not found to be standard and the force stated on the package is not always provided precisely. A significant force loss around 20% was observed with all the elastics after 24-h of use in wet environment at 37°C.

Dynamic force decay evaluation of latex and non-latex orthodontic elastics

PURPOSE

To evaluate the force decay over time of latex and non-latex orthodontic elastics subjected to either static or dynamic stretching under simulated intraoral conditions.

MATERIALS AND METHODS

Four types of elastics (1/4-inch 4.5 ounces and 1/4-inch 6.5 ounces, each latex and non-latex) were subjected to either static stretching to 3 times internal diameter (ID) or dynamic stretching from 3 to 4.5 times ID in artificial saliva at 37 °C for 24 h. Forces generated by the elastics were measured at 0, 1, 2, 4, 8, 12, and 24 h. Differences among elastic types, time points, and between stretching regimens were tested for statistical significance (P < 0.05).

RESULTS

Both stretching regimens caused rapid force decay in all elastic types, which was significantly higher in the non-latex elastics than in the latex elastics. In contrast, there were no differences between elastic types made of the same material. With both stretching regimens, the force decay was significant only after the first hour for the latex elastics, whereas it remained significant up to 24 h for the non-latex elastics. All elastic types generated significantly lower forces after dynamic stretching than after static stretching with 70.2, 68.8, and 66.1% of the initial force remaining after 4, 8, and 24 h for latex elastics and 48.0, 40.8, and 29.5% for non-latex elastics.

CONCLUSION

Latex elastics retained significantly more force over time than their non-latex equivalents. Because of the higher force decay in a dynamic environment, it is important that non-latex elastics be changed more frequently.

Elastics Selector Gauge as Orthodontics Device Applied to Inter-Maxillary Traction during Malocclusion Correction

Elastics are the simplest device that can be used during a class correction in orthodontics, and despite the simplicity of a latex band, they are very effective and powerful. The resultant inter-maxillary force affects not only the teeth, but even the mandibular position, and consequently the temporomandibular joints (TMJ). The purpose of our work is to simplify the use of elastics, and to reduce the amount of inventory for orthodontists, because there is a lot of merceology available on the market, and different ways of using the elastics. The use of elastics in clinical practice is based on the force extension values, which are given by the manufacturer for the different sizes of the elastics, generally when they are stretched to three times their lumen size. Various configurations allow for the correction of different malocclusions. We propose a new classification and a new device, the elastic selector gauge, in order to allow clinicians to quickly and easily choose the right elastic in all conditions.

Force decay evaluation of latex and non-latex orthodontic intraoral elastics: in vivo study

Objective:

This clinical study was conducted in order to evaluate force decay over time of latex and non-latex orthodontic intraoral elastics.

Methods:

Patients (n = 15) were evaluated using latex and non-latex elastics in the periods of : 0, 1, 3, 12 and 24 hours. The rubber bands were transferred to the testing machine (EMIC DL-500 MF), and force values were recorded after stretching the elastic to a length of 25mm. Paired t test was applied and analysis of variance (ANOVA) was used to evaluate the variation of force generated. LSD (Fisher’s least significant difference) post-hoc test was thus employed.

Results:

As regards the initial forces (zero time), the values of force for non-latex elastic were slightly higher than for the latex elastic. In the subsequent times, the forces generated by the latex elastic showed higher values. Regarding the material degradation, at the end of 24 hours the highest percentage was observed for non-latex elastic.

Conclusions:

The latex elastics had a more stable behavior during the studied period, compared with non-latex.

The effect of toothpastes with bleaching agents on the force decay of elastomeric orthodontic chains

Objective:

The aim of this study was to evaluate the effect of agents available in whitening toothpastes (Crest^® and Sensodyne^®) in vitro on the force decay of elastomeric chains used in orthodontics.

Materials and Methods:

A total of 300 specimens of elastomeric chains were divided into five groups (n = 60) and were evaluated. These groups included (1) the regular Crest® toothpaste and distilled water solution, (2) whitening Crest^® toothpaste and distilled water solution, (3) regular Sensodyne^® toothpaste and distilled water solution, (4) whitening Sensodyne^® toothpaste and distilled water solution, and (5) distilled water as a control group. The samples' force was measured using Instron at intervals of 0, 1, 7, 14, 21, and 28 days. Data were analyzed by SPSS software.

Results:

At the initial time point, the difference in the force values of elastomeric chain between any of the groups was not significant (P > 0.05). On the 1^st day, there was a significant difference (P < 0.05) between all groups except the groups of whitening Crest^®, regular, and whitening Sensodyne^® (P > 0.05). On days 7, 14, and 28, the rate of decline for all groups was statistically significant (P < 0.05).

Conclusions:

According to the results obtained in the present study, it seems that toothpastes without whitening agents have less effect on force decay of elastomeric chain over time.

A comparison of orthodontic elastic forces: Focus on reduced inventory

OBJECTIVES

To compare orthodontic elastics with different force extension characteristics, thereby aiming to reduce the orthodontist's inventory for elastics.

MATERIALS AND METHODS

Thirty nonextraction class I models were used to determine extension distances. Light, medium, and heavy forced Latex elastics of size 1/4 and 3/16 (from three manufacturers) were used. Thirty elastics from each pack were selected, for a total sample size of 540 elastics. Elastic force was measured at three extensions: three times the lumen (A), first molar to opposing canine (B), and second molar to opposing canine distance (C). Force values were compared with the analysis of variance followed by the post hoc Scheffe test.

RESULTS

Mean distance for extensions B and C were 22.3 and 38.7 mm, respectively. There was a continuous but significant increase in the force of 1/4 elastics when stretched from A to extension C. A significant increase in the force level of 3/16 elastics was only noted when stretched from A to B. Overall, 1/4 elastics had a wider range of force coverage in the extensions used, compared to 3/16 elastics.

CONCLUSIONS

The use of 1/4 elastics is sufficient to cover the range of forces in orthodontic treatment.

Influence of temperature and humidity on the long-term storage of latex and non-latex orthodontic elastics

OBJECTIVES

The objective of this study was to evaluate the influence of long-term storage on latex and non-latex orthodontic elastics.

MATERIALS AND METHODS

The sample consisted of 300 orthodontic elastics, 150 latex and 150 non-latex (American Orthodontics^® *(AO) and Morelli^®) of medium force and a standard size of 3/16'' divided into 20 groups, 10 for each manufacturer, with 15 specimens each. The groups (G1*-G10* and G1-G10) were made up based on the manufacturer, storage temperature (ambient and refrigerated), material, and ambient humidity (exposed and non-exposed). The elastics were stretched and their forces measured in five progressive increases of 100% of their inner diameter, starting at a level of 200% stretching, by the MESDAN LAB 3000^® (MESDAN, Italy) testing machine. The tests were carried out at two different times: immediately in as-received state and again after 1 year. Data were analysed using SPSS 16.0 software, the Student's t-test, one-way analysis of variance (ANOVA) and the Tukey's post-test.

RESULTS

There was a statistically significant difference between the average forces exerted by the latex elastics compared to the non-latex elastics for all distention levels evaluated, except for 300%; however, the different storage conditions of temperature and humidity did not interfere in the mechanical properties.

CONCLUSION

Both the latex and non-latex elastics may be stored under any of the conditions tested in the present study, since there were no changes in the potential of the force exerted by the elastics in relation to their percentage stretch over a 1-year period.

Force degradation of orthodontic latex elastics: An in-vivo study

INTRODUCTION

Our objectives were to assess the force degradation of orthodontic latex elastics over 48 hours in vivo and to study the relationship between the amount of mouth opening and the degree of force decay.

METHODS

Fifty-two orthodontic patients wearing fixed appliances using Class II elastics were asked to wear premeasured-force 3/16-in heavy and medium intermaxillary elastics. The force amounts were measured and compared at different time intervals.

RESULTS

Fifty percent of the force was lost after 3.9 hours for the medium elastics and after 4.9 hours for the heavy elastics. A continuous significant force drop in all elastics was seen at all time intervals (P <0.05, P <0.001). There was greater force loss in the heavy elastics compared with the medium elastics in vivo at all time intervals (P <0.001); the rates of force loss, however, were similar.

CONCLUSIONS

Fifty percent of force degradation occurred in the first 4 to 5 hours. Because of breakage and for oral hygiene purposes, orthodontic elastics should be changed daily; otherwise, elastics can be used for 48 hours. Force decay of the elastics was correlated to the lateral distance between the maxillary canine and the mandibular first molar in occlusion.

Synergic effect of salivary pH baselines and low pH intakes on the force relaxation of orthodontic latex elastics

Background:

Latex elastics are still in common use due to their low cost and high flexibility to improve sagittal discrepancies or interdigitation of teeth. Mechanical properties of elastics are influenced by several environmental factors such as pH changes. This study evaluated similar latex elastics to define the influence of synergic effect of intermittent low pH and various baselines pH of saliva.

Materials and Methods:

Four groups of latex elastics (3-M Unitek, 3/16 inch) were tested (n = 15 in each group). Two groups of elastics were immersed in two tanks of artificial saliva with different pH levels of 7 and 5, and two groups were immersed in two tanks of artificial saliva with intermittent drop of pH to 4. The force was measured when the elastics were stretched to 25 mm. These measurements were taken in 0, 4, 8, 12, 24, 36, and 48 h for each group. Repeated measures analysis of variance (RMANOVA) and post-hoc Tukey's test were used to assess the findings. The level of significance was 0.05%.

Results:

The interaction between pH and time analyzed with RMANOVA showed no significant differences (P > 0.05) except in 36 h (P = 0.014). The Tukey's analysis showed that each comparison between any two groups did not indicate significant differences (P > 0.05) except between Groups 1 and 3 and between Groups 2 and 3 (P < 0.05).

Conclusion:

No significant correlation was seen between fluctuation of pH and force degradation in latex elastic band except in 36 h.

Latex and nonlatex orthodontic elastics: In vitro and in vivo evaluations of tissue compatibility and surface structure

Objective: 

To test the null hypothesis that there is no difference between latex and nonlatex orthodontic elastics with respect to tissue compatibility and surface structure.

Materials and Methods: 

Latex and nonlatex elastics were implanted in the subcutaneous connective tissue of 45 Wistar rats. In the control groups, no material was implanted (sham). After 24 hours, 3, 7, 14, and 21 days, the animals were euthanized; tissue samples were processed and analyzed by descriptive and semi-quantitative microscopic analysis and quantification of plasma extravasation. The surface structure of elastics was evaluated by scanning electron microscopy (SEM). The results were analyzed by analysis of variance (ANOVA), Tukey test and Kruskal-Wallis test at 5% significance level.

Results: 

Peri-implant plasma extravasation was significantly higher (P &lt; .05) in the animals that received latex elastics compared with those with nonlatex elastics and those that were control animals. The microscopic analysis revealed a more intense inflammatory infiltrate in the initial periods without statistically significant difference (P &gt; .05) between the experimental and control groups. The SEM analysis revealed that the latex elastics presented microspheres and porosities, while the nonlatex elastics exhibited crystals on their surface and absence of porosities.

Conclusion: 

The null hypothesis was rejected since the latex elastics were more irritating to the connective tissue than the nonlatex elastics in the initial periods and presented a more porous surface.

Natural rubber latex allergy: implications for the orthodontist

Natural rubber latex (NRL) allergy can have potentially serious consequences, and reports of orthodontic patients reacting to NRL have increased significantly over recent years. It is therefore important for the orthodontist to know how to manage patients with an NRL allergy and how to deal with possible reactions to NRL. Safe and effective practice depends on recognizing patients who are at risk of NRL allergy, and an awareness of materials and equipment that contain NRL and the availability of suitable NRL-free alternatives.

Superficial morphology and mechanical properties of in vivo aged orthodontic ligatures

INTRODUCTION

The degradation of elastic ligatures in the oral environment results in the need of periodic replacement to maintain the optimal force during the orthodontic treatment. The purpose of this study was to perform a clinical prospective randomized study of the degradation of orthodontic elastomeric ligatures in the oral environment by scanning electron microscopy (SEM) and tensile strength test.

METHODS

Two hundred elastic ligatures were randomly selected and placed around the brackets of 5 volunteers and removed in groups of 10, at different times (1, 2, 3, and 4 weeks). The control group was performed by another fifty ligatures which were not submitted to the oral degradation. The analyses were done by scanning electron microscopy (SEM) and strength mechanical test.

RESULTS

The tensile strength test results showed reduction in the ultimate strength values after four weeks ageing in the oral environment and no statistical difference in the yield strength values (p < 0.05). The orthodontic elastomeric ligatures surface was significantly degraded in the oral cavity after four weeks. The elastomeric degradation began in the first week when the increase in the roughness could be detected just in some areas. Afterwards, the surface became gradually rougher and, after 4 weeks, it was totally rough with some crack areas.

CONCLUSIONS

The elastic ligatures aged in the oral environment showed higher superficial degradation and lower loss of mechanical properties after the maximum experimental period.

THE EFFECT OF CYCLIC STRETCHING SPEED ON THE FORCE DEGRADATION OF ORTHODONTIC ELASTIC BANDS

This study evaluated the effect of the cyclic stretching speed on the force degradation of orthodontic elastics. Forty-five natural rubber bands (3M Unitek™) were stretched at different speeds in three groups: (1) static stretching test, (2) cyclic stretching test at a speed of 80 mm/min, and (3) cyclic stretching at a speed of 160 mm/min. A material tester and customized strain gauge were used to measure the residual force of the elastics in 37°C artificial saliva at different times. One-way repeated-measure analysis of variance followed by Scheffe's post-hoc comparison and t-test were used for statistical analysis. In Group 1, the force of the elastics degraded with time, with two separate phases being observed — distinctive degradation after 15 min and stabilization after 120 min. The cyclic stretching in Group 2 produced a significant deviation in the residual force and the initial force from the first minute, and stabilization after 300 min. After 1,440 min, 60% of the bands had snapped. Under accelerated stretching, no areas of relative stability were observed between the start of stretching to the start of breaking. After 1,440 high-speed stretches, 87% of the elastics in Group 3 snapped. These results indicate that the stretching speed affects the stability of the residual force of elastics. Cyclic stretching at high speed immediately induces a rapid degradation of the elastic's force and increases its probability of breakage.

The influence of pH levels on mechanical and biological properties of nonlatex and latex elastics

OBJECTIVE

To evaluate the influence of pH levels on interarch elastics with regard to force decay and cytotoxicity.

MATERIALS AND METHODS

One nonlatex (NLAO) group and one latex (LAO) group were tested (n  =  10). Elastics were stretched to 25 mm and were held for 1, 6, 12, and 24 hours in artificial saliva solutions with pH levels of 5.0, 6.0, and 7.5. Force magnitudes were measured at 25 mm of activation. The cytotoxicity assay was performed using cell cultures (L929 mouse fibroblast cell line), which were subjected to the cell viability test with neutral red ("dye-uptake"). Force decay and cytotoxicity were assessed using analysis of variance, the Sidak method, and a Tukey's test.

RESULTS

The interactions between group, pH, and time showed no statistically significant differences (P  =  .29). When pH per time (P  =  .032) and group per time (P  =  .0009) were considered, these interactions showed statistically significant differences (P < .05). The pH did not interfere directly in the degradation results of the tested elastics. The cytotoxicity test showed that group LAO presented lower cell viability when compared with group NLAO over the course of the entire experiment. There was a gradual reduction in cell viability from 1 hour to 24 hours. A significant difference (P < .05) was found between the interactions group pH and the control group of cells, except between group NLAO at the time point of 1 hour at different pH values and at the time points of 6 and 12 hours with pH 5 (P > .05).

CONCLUSIONS

No significant correlation between pH, force decay, and cytotoxicity was observed.

Force relaxation characteristics of medium force orthodontic latex elastics: a pilot study

To evaluate force extension relaxation of different brands and diameters of latex elastics subjected to static tensile testing under an apparatus designed to simulate oral environments, sample sizes of 5 elastics from American Orthodontics (AO), Tp, and Morelli Orthodontics (Mo) of equivalent medium force, (3/16, 1/4, and 5/16 inch size) were tested. The forces were read after 1-, 3-, 6-, 12- and 24-hour periods in Emic testing machine with 30 mm/min cross-head speed and load cell of 20 N. Two-way ANOVA and Bonferroni tests were used to identify statistical significance. There were statistically differences among different manufacturers at all observation intervals (P < 0.0001). The relationships among loads at 24-hour time period were as follows: Morelli>AO>Tp for 3/16, 1/4, and 5/16 elastics. The force decay pattern showed a notable drop-off of forces until 3 hours, a slight increase in some groups from 3-6 hours and a more homogeneous force pattern over 6-24 hours.

Force extension relaxation of medium force orthodontic latex elastics

OBJECTIVE

To evaluate the force extension relaxation of different manufacturers and diameters of latex elastics subjected to static tensile testing under dry and wet conditions.

MATERIALS AND METHODS

Sample sizes of 15 elastics from American Orthodontics (AO) (Sheboygan, Wis), TP (La Porte, Ind), and Morelli Orthodontics (Sorocaba SP, Brazil) were used. Equivalent medium force products were tested--3/16, 1/4, and 5/16 inch lumen size from each manufacturer--making a total of 1080 specimens. An apparatus was designed to simulate oral environments during elastics stretching. Forces were read after 1, 3, 6, 12, and 24 hour periods using the Emic Testing Machine (Emic Co., Sao Paulo, Brazil) with 30 mm/min cross-head speed and load cell of 20 N (Emic Co). Kruskal-Wallis and Dunn's tests were used to identify statistical significance.

RESULTS

Statistical differences between AO and the other brands were noted for all testing times. Significant variation in mechanical properties was observed in latex elastics from Morelli. Relationships among loads at the 0 hour time period were as follows: Morelli>AO>TP for 3/16 elastics (P = .0016), 1/4 elastics (P = .0016), and 5/16 elastics (P = .0087).

CONCLUSION

Significant differences in force extension relaxation were noted for elastics from these manufacturers. Force relaxation over the 24 hour time period was AO>Morelli>TP for 3/16 elastics, AO>TP>Morelli for 1/4 elastics, and TP>AO>Morelli for 5/16 elastics. The force decay pattern showed a notable drop-off of forces during 0 to 3 hours, a slight increase in force values from 3 to 6 hours, and a progressive force reduction over 6 to 24 hours.

The effect of pH levels on nonlatex vs latex interarch elastics

OBJECTIVE

To evaluate the force decay characteristics of nonlatex vs latex interarch elastics within the normal range of salivary pH levels.

MATERIALS AND METHODS

Two nonlatex groups and one latex quasi-control group were tested. Elastics were stretched to 15 mm and were held for 10 seconds (baseline), 4 hours, 8 hours, and 12 hours in artificial saliva solutions with pH levels of 5.0, 6.0, and 7.5. Force magnitudes were measured at 25 mm of activation. Each specimen was used once. Measurements were assessed using three-way analysis of variance (ANOVA).

RESULTS

The three-way interaction between group, pH, and time was not significant (P = .13); the group-by-pH interaction also was not significant (P = .70). However, pH-by-time (P = .0179) and group-by-time (P = .0001) interactions were significant. American Orthodontics nonlatex generated significantly higher loads than Auradonics nonlatex. American Orthodontics nonlatex produced significantly higher forces than American Orthodontics latex at 4, 8, and 12 hours, but not at 10 seconds. American Orthodontics latex was significantly stronger than Auradonics nonlatex at 10 seconds, but not at 4, 8, and 12 hours.

CONCLUSIONS

No clinically significant correlation between pH and force decay was observed.

Evaluation of force degradation characteristics of orthodontic latex elastics in vitro and in vivo

OBJECTIVE

To evaluate the characteristics of force degradation of latex elastics in clinical applications and in vitro studies.

MATERIALS AND METHODS

Samples of 3/16-inch latex elastics were investigated, and 12 students between the ages of 12 and 15 years were selected for the intermaxillary and intramaxillary tractions. The elastics in the control groups were set in artificial saliva and dry room conditions and were stretched 20 mm. The repeated-measure two-way analysis of variance and nonlinear regression analysis were used to identify statistical significance.

RESULTS

Overall, there were statistically significant differences between the different methods and observation intervals. At 24- and 48-hour time intervals, the force decreased during in vivo testing and in artificial saliva (P < .001), whereas there were no significant differences in dry room conditions (P > .05). In intermaxillary traction the percentage of initial force remaining after 48 hours was 61%. In intramaxillary traction and in artificial saliva the percentage of initial force remaining was 71%, and in room conditions 86% of initial force remained. Force degradation of latex elastics was different according to their environmental conditions. There was significantly more force degradation in intermaxillary traction than in intramaxillary traction. The dry room condition caused the least force loss.

CONCLUSIONS

There were some differences among groups in the different times to start wearing elastics in intermaxillary traction but no significant differences in intramaxillary traction.

Effect of disinfecting solutions on the mechanical properties of orthodontic elastomeric ligatures

OBJECTIVE

To assess the effect extended exposure to disinfectant solutions has on the tensile load at failure and glass transition temperature (T(g)) of orthodontic elastomeric ligatures.

MATERIALS AND METHODS

Elastomeric ligatures from three manufacturers: Rocky Mountain Orthodontics (RMO, Denver, Colo), American Orthodontics (AO, Sheboygan, Wis), and 3M Unitek (3M, Monrovia, Calif) were exposed to two disinfectant solutions, Vital Defense-D and Cidexplus, for up to 28 days. Unexposed ligatures were also tested. Tensile load at failure was determined by stretching the ligatures using a universal testing machine until they fractured. Glass transition temperature was determined using differential scanning calorimetry (DSC).

RESULTS

For tensile load at failure and glass transition temperature of the ligatures, significant differences were observed among the different manufacturers and exposure times. Type of disinfectant solution was a significant factor with T(g), but not with failure load. The 3M ligatures had the highest tensile load at failure and most positive T(g) followed by AO and RMO, respectively. Compared to unexposed ligatures, strength significantly decreased after one hour of disinfectant exposure. Glass transition temperature was also significantly affected with extended disinfectant exposure, but the different disinfectants changed T(g) in opposite directions.

CONCLUSION

Exposure of elastomeric ligatures to disinfectant solution for one hour or more decreases their strength.

In vitro neuronal cytotoxicity of latex and nonlatex orthodontic elastics

Although the toxicity of many dental materials has been thoroughly investigated, the toxicity of orthodontic elastic materials has not been extensively tested. We evaluated the neurotoxicity of 3 latex and 3 nonlatex orthodontic elastics in murine cerebral cortical cell cultures. Standard-sized pieces of each material from 3 manufacturers (American, Masel, and GAC) were placed on culture well inserts, allowing the material to be exposed to the culture bathing media without causing physical disruption of the cells. Cell death was quantified by assaying the release of the cytosolic enzyme lactate dehydrogenase. Exposure of cortical cultures to the nonlatex elastics did not cause significant neuronal death, but exposure to each of the latex elastics resulted in significant neuronal death. The neuronal death induced by each of the latex elastics was blocked by adding the metal chelator, EDTA (calcium disodium ethylenediaminetetraacetate). Because many latexes use zinc-containing compounds in the prevulcanization process, and the death induced had characteristics similar to zinc-induced neuronal death, it seems likely that the toxicity of latex elastics was mediated by zinc release. Because ingestion of zinc is not a health risk, the results suggest that, in spite of the finding that latex elastics have higher in vitro cytotoxicity than nonlatex elastics, the use of latex elastics in orthodontics is acceptable.

Mechanical and biological comparison of latex and silicone rubber bands

Latex rubber bands are routinely used to supply orthodontic force. However, because the incidence of allergic reactions to latex is rising, the use of nonlatex alternatives is increasing, and assessing the mechanical properties of the replacement products is becoming more important. The purposes of this study were to compare the mechanical properties of latex and silicone orthodontic rubber bands through static testing under dry and wet conditions, and to compare their biologic (cytotoxic) properties. Three brands of latex and 1 brand of silicone rubber bands were tested. When extended to 300% of the lumen diameter, the silicone group had an initial force equal to 83% of the product specifications; this was the lowest of the 4 groups. All 4 brands showed notable amounts of force degradation at the 300% extension when subjected to saliva immersion; this approximated a 30% force decay over 2 days. The latex bands all followed a similar pattern of force degradation, whereas the silicone bands showed a greater increase in force decay as the extension length increased. The silicone bands were less cytotoxic than 2 of the 3 types of latex. Although the silicone bands showed the least discrepancy of force degradation between air and saliva conditions, the amount of the force decay was the greatest. Therefore, great improvements in the physical properties of the silicone band are required before they can be considered an acceptable replacement for latex.

An in vitro comparison of 4 brands of nonlatex orthodontic elastics

The purpose of this study was to compare 4 brands of nonlatex orthodontic elastics with respect to initial force produced and force decay over a 24-hour period. Sample sizes of 12 elastics from American Orthodontics (Sheboygan, Wis), Ortho Organizers (San Marcos, Calif), GAC International (Islandia, NY), and Masel (Bristol, Pa) were used. Equivalent or near-equivalent products were tested: the quarter-in (6.35 mm), 4 or 4.5 oz (113 or 128 g) elastics from each company. An apparatus that repeatedly cycled the elastics to simulate interarch usage with chewing was used to measure force decay over a 24-hour period. Results showed a wide range of initial forces between the brands at an extension of 3 times the marketed internal diameter. The elastics from American Orthodontics, Ortho Organizers, and Masel generated forces statistically below their marketed force levels at 3 times their marketed internal diameter extensions. GAC elastics generated significantly higher forces than marketed at 3 times internal diameter extension. All elastics generated forces below those marketed at 2 times internal diameter. Initial force production was significantly correlated with the measured cross-sectional area of the elastics (P <.01). The force decay patterns of all brands were very similar, but there were significant differences in their abilities to withstand testing. Grouped average percentages of initial force at 4, 8, and 24 hours were 68%, 61%, and 49%, respectively, for the elastics that did not break during testing.

Integrated magnetic and elastic force systems

Magnetic force increases as the distance (d) of the force- generating elements (F approximately 1/d(2)) decreases, whereas elastic force decreases as the distance decreases (F approximately kd). These opposing characteristics suggest that combining both force systems will establish an integrated system with a long-range working ability. The objective of this study was to determine the vertical closure force (F(X)) and the transverse axis moment (M(Y)) of an integrated force system, ie, attracting magnets with elastics (vertical or Classes II and III). F(X) and M(Y) were examined on the orthodontic measurement and simulation system. It was found that the integrated force system had a positive closure force (+F(X)) that never declined to 0 and a long working range. Three regions characterized the force-deflection curve of F(X): the magnetic region (0-3 mm, for magnets with 3/16-in medium elastics), in which the decline in magnetic force was larger than the increase in elastic force (6.3-2.5 N); the constant region (3-7 mm), in which the decline in magnetic force equaled the increase in elastic force (2.5-2.9 N); and the elastic region (7-10 mm), in which there was only an increase in elastic force (2.9-3.5 N). The transverse axis moment (+M(Y)), which tends to close the bite, developed especially in magnets with a single vertical elastic. Clinically, inactivation of vertical elastics by closing the mouth can be overruled by the integrated force system because it exerts adequate force level at both short and long distances.