The effect of repeated stretching on the force decay and compliance of vulcanized cis-polyisoprene orthodontic elastics

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.

Analysis of Class II Intermaxillary Elastics Applied Forces: An in-vitro Study

Objectives

The aims of this study were: (1) to assess the average inter-arch distances characterizing Class II malocclusions, (2) to analyze the applied forces at those distances by different elastics, and (3) to compare measured forces with those declared by manufacturers, both in dry and wet environments.

Materials and Methods

Settings and sample population: Class II models of 167 adult subjects (96 women and 71 men, age: 28 ± 3 years) referred to the Orthodontic Department of the University of Turin, Turin, Italy, between January 2018 and January 2020, were collected. Distances between facial axes (FA) points of upper canines and lower first molars (A), upper first premolar and lower first molar (B), upper second premolar and lower first molar (C), upper canine and lower first premolar (D), and upper canine and lower second premolar (E), were measured using 3Shape Ortho® Viewer program. Different elastics' diameters and forces were tested at those distances. The MTS Insight® Electromechanical Testing System was used to measure the tensile forces of elastics. The applied forces were measured in dry (T0) and wet conditions, after 1 (T1), 6 (T2), and 12 h (T3).

Results

Average distances were calculated: A = 24.64 mm (SD 2.10), B = 16.3 mm (SD 1.94), C = 9.78 mm (SD 1.77), D = 9.8 mm (SD 1.88), and E = 15.99 mm (SD 2.06). Significant differences (p < 0.05) were highlighted between the measured force and the force declared by manufacturers, and all elastics had a significant force decay (p < 0.05).

Conclusion

The results showed that 3/16" 4.5 oz are the most reliable elastics in terms of applied force with respect to the declared one and in terms of force degradation.

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.

Comparison of the Force Released by Intermaxillary Elastics Used for Different Time Periods

Objective

The objective of the present study was to compare the strength degradation of the force of intermaxillary elastic used for different periods.

Methods

The sample included intermaxillary elastics used for 20 adult patients with bilateral Class II or III malocclusion in orthodontic treatment with fixed appliances, with a mean age of 27.25 years. Latex orthodontic elastics with 3/16 inch of diameter were used, with an average stretching of three times its diameter. The elastics were used in the same patient bilaterally for different periods, with each pair of elastics used for 1, 12, 24, and 48h. Thus, the sample consisted of 200 elastics, with 40 being used in each period (one pair used by each patient) and 40 new elastics without use tested as control. Elastics were tested using a universal testing machine, stretched with a velocity of 30 mm/min, and the force was evaluated in stretches of 15, 20, 25, and 30 mm. The degradation force was compared in the four different times of use and control by one-way ANOVA (analysis of variance) and Tukey tests.

Results

There were significant differences among the groups in all evaluated stretches (15, 20, 25, and 30 mm). The control elastics presented higher average forces numerically and statistically significant for all tested times, except for the elastic used for 1h. The elastics used for 1, 12, and 24h had similar forces among them, with a significant difference to the elastics used for 48h.

Conclusion

It is recommended to change the intermaxillary elastics after 24 h of use.

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.

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.

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.

Influence of different beverages on the force degradation of intermaxillary elastics: an in vitro study

OBJECTIVE

The aim of this study was to evaluate in vitro the effects of frequently ingested beverages on force degradation of intermaxillary elastics.

MATERIAL AND METHODS

One hundred and eighty 1/4-inch intermaxillary elastics (TP Orthodontics) were immersed into six different beverages: (1) Coca-Cola®; (2) Beer; (3) Orange juice; (4) Red wine; (5) Coffee and (6) artificial saliva (control). The period of immersion was 15 min for the first and second cycles and 30 min for the third to fifth cycles. Tensile forces were read in a tensile testing machine before and after the five immersion cycles. One-way repeated measures ANOVA was used to identify significant differences.

RESULTS

Force degradation was seen in all evaluated groups and at all observation periods (p<0.05). A greater degree of degradation was present at the initial periods, decreasing gradually over time. However, no statistically significant differences were seen among groups at the same periods, showing that different groups behaved similarly.

CONCLUSION

The chemical nature of the evaluated beverages was not able to influence the degree of force degradation at all observation periods.

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.

Perceived vs measured forces of interarch elastics

INTRODUCTION

Orthodontists depend on perceptions derived from education and clinical experience to judge the optimal forces in patient treatment. The purpose of this study was to survey practicing orthodontists to determine the interarch latex elastic forces they prescribe in different malocclusion scenarios.

METHODS

Thirty orthodontists were presented with 4 clinical scenarios on study models, including Class II and Class III malocclusions in edgewise and light wires. These orthodontists described the size and location of the elastics they would use. The forces produced by the prescribed elastics were measured and compared with actual dry forces measured on a testing machine.

RESULTS

The orthodontists' force recommendations were a mean of 277 ± 89 g and a median of 256 g (range, 132-464 g) for a Class II malocclusion with edgewise wires; a mean of 183 ± 59 g and a median of 177 g (range, 59-284 g) for a Class II malocclusion with light wires; a mean of 290 ± 83 g and a median of 305 g (range, 151-562 g) for a Class III malocclusion with edgewise wires; and a mean of 216 ± 66 g and a median of 209 g (range, 119-344 g) for a Class III malocclusion with light wires. The force levels for light wires were statistically significantly lower than for edgewise wires.

CONCLUSIONS

There were considerable variations in the forces selected for all cases. "Expert" recommendations fell within 1 SD of the mean of the orthodontists' recommendations except for the light-wire Class III scenario. Since latex elastic force decays significantly during a patient's use, elastics should be selected with initially higher forces than desired.

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.

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.

Viscoelastic properties of demineralized dentin matrix

OBJECTIVES

To evaluate the viscoelastic properties of demineralized dentin matrix. Stress-relaxation studies were done on matrices in tension and strain elongation or creep studies were done in both tension and compression.

METHODS

Mid-coronal dentin disks were prepared from extracted unerupted human third molars. Disks were 0.5 mm thick for stress-relaxation or tensile creep experiments and 0.2-0.3 mm thick for compressive creep studies. 'I' beam specimens were prepared from dentin disks and the middle region was demineralized in 0.5 M EDTA (pH 7) for 4 days. The specimens were held in miniature friction grips in water and pulled at 100 micro m s(-1) to strains of 5, 10, 15 or 20% and then held for 10 min to follow the decay of stress over time. Creep was determined on demineralized dentin immersed in water in tension and in compression. Compressive creep was measured using an LVDT contact probe with loads of 0.02-0.5 N. Strain data were converted to compliance-time curves (strain/stress) and expressed as total compliance (J(t)), instantaneous elastic compliance (J(o)), retarded elastic compliance (J(R)) and viscous response (t/eta) or creep.

RESULTS

The dentin matrix exhibits both stress-relaxation and creep behavior. Stress-relaxation and tensile creep were independent of strain but compressive creep rates were inversely related to compressive strain. Creep values were about 10% at low compressive strains, but fell progressively to 1% at high strains. Compliance-time curves fell with stress and came closer together. However, tensile creep was about 3% regardless of the strain.

SIGNIFICANCE

The dentin matrix exhibits viscoelastic properties, but is not linearly viscoelastic. The relatively high creep rates of the matrix under low compressive loads may cause viscous deformations in poorly infiltrated hybrid layers in resin-bonded teeth under function.

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.

Calibration of force extension and force degradation characteristics of orthodontic latex elastics

The force-extension characteristics of orthodontic elastics made of natural rubber latex by 4 manufacturers were subjected to static testing under dry and wet conditions. The elastics consisted of 3 sizes: 3/16, 1/4, and 5/16 inch lumen sizes, each with forces specified according to the standard extension index of three times the lumen diameter. Most of the elastics did not match the specified index using the dry tests, but this should not be a serious clinical concern as all elastics showed acceptable regularity of force-extension characteristics. There was notable force degradation of all elastics when subject to water immersion, approximating 30% during the hour, but with an average less than 7% further loss up to 3 days. There were significant differences in force extension and force degradation characteristics between different extensions and force magnitudes for the elastics of the different manufacturers. It is suggested that the clinician could use the table of force degradation values for different extensions to select an appropriate elastic.

Surgical glove failures in clinical practice settings

Health care personnel often pay little attention to the barrier effectiveness of the surgical gloves they use in clinical settings. They may assume that all surgical gloves provide adequate protection against the transfer of bloodborne pathogens, chemicals, or mutagenic substances. Perioperative staff members frequently are unaware that their surgical gloves have failed until they find blood on their hands after operative procedures are completed. In this first article of a three-part series, the authors review current surgical glove testing standards, define surgical glove failure, and describe the reasons that surgical glove failure occurs in clinical practice settings.