August, 2010

The Evaluation and Comparison of Force Degradation of Latex and Non-Latex Intraoral Elastics in a Simulated Oral Environment An In-Vitro Study

Dr Shashanka.P.Kumar ^a ,Dr Dinesh M.R.^b, Dr Amarnath B.C.^c, Dr Dharma^d, Dr Prashanth C.S.^e,  Dr Akshai Shetty K.R^f.

a — Senior Lecturer, V.S.Dental College & Hospital.

b – Professor & Head, R.V.Dental College & Hospital.

c –  Professor & Guide, R.V.Dental College & Hospital.

d –  Professor, R.V.Dental College & Hospital.

e– Professor, R.V.Dental College & Hospital.

f—Asso Professor, R.V.Dental College & Hospital.

Abstract

Latex rubber bands are routinely used to deliver orthodontic force in orthodontics. As the incidence of allergic reaction to latex is rising, the use of non-latex alternatives are increasing. So this study was intended to evaluate and compare the force degradation of latex and non-latex intraoral elastics, to know the change in schedule of the elastic wear, check the force values claimed by the manufacturer and to know any differences in force exerted by the elastics from the different batches of the same manufacturer.

The initial force delivered by randomly selected latex and non-latex elastics were recorded for extensions of 225%, 300% and 450% using an Instron universal testing machine. Then the elastics were engaged on to a special jig having posts at a distance of 14.8mm, 19.0mm and 28.4mm in order to extend the diameter of the elastics by 225%, 300% and 450% respectively and incubated at 37°C in artificial saliva for 24 and 48 hours of time. The amount of force exerted at these time intervals were measured and the results were tabulated and compared. Mean and standard deviations were calculated for each group. The data was analyzed using ANOVA.

The non-latex elastics showed less force decay when compared to a latex variant. Force degradation was high during the first 24 hours. No significant difference in force exerted was observed between elastics of different batches from the same manufacturer.

These results show that non-latex elastics are a viable alternative to the latex elastics and that the elastics should be changed on a daily basis.

Key words : Force degradation; Latex ; Non-latex; Instron ; Artificial Saliva.

I would like to thank Dr .Madhav Murthy (3M UNITEK) for helping me in conducting the study in 3M INNOVATION centre at Bangalore.

Introduction

The usage of elastics in the field of orthodontics can be probably traced to the year 1846 when E. Baker used a thin sheet of Indian rubber for retraction¹. With the advent of elastics, a new tool was born in the orthodontist’s armamentarium. As of now orthodontists and elastics have become inseparable in the present era.

Latex rubber bands are routinely used to deliver orthodontic force. However, because of the increasing incidence of allergic reactions to latex, the use of non-latex elastics is increasing².To apply an ideal orthodontic force an elastomer needs to maintain appropriate force, however conventional elastomers exhibit a high degree of irreversible force decay and are affected by environmental factors such as alkalinity of saliva, temperature changes and prestretching.

In addition, saliva and bacteria can infiltrate the weak molecular structures on latex rubber surfaces resulting in discoloration and expansion. For this reason, new materials with greater physical stability, biocompatibility and without allergens are needed. ^{3, 4, 5, 6}

Reactions to latex materials have become more prevalent and better  recognized (since 1988 adoption of universal precautions).⁷ Most  documented allergic reactions to latex products have identified the residual  rubber protein as the antigen⁸.

The prevalence of the latex sensitization is from 2.9% to 4.7 % in hospital workers. In addition 4% to 8% of the general population were reported to be  positive to the natural rubber allergy by serologic testing with latex immunoglobulin E antibodies. Because latex allergy is prevalent among occupationally exposed groups and patients, the need for non-latex alternative is increasing ⁹.

Reactions to latex carry a wide range of risk with them including dermatologic reactions, respiratory reactions, systemic reactions and in extreme cases even the anaphylactic shock.^{10, 11, 12,13,14,15}

Clinician using orthodontic elastics should know the forces applied to teeth at a given extension and how this force declines over a period of time.

Thus in any comparison between latex and non-latex elastics, the nearly instantaneous elastic force at a given extension and force relaxation over a  period of time needs to be independently assessed.

Since the use of non-latex elastics is increasing, this study was done to evaluate and compare the force degradation of latex and non-latex orthodontic elastics for different time intervals and different percentages of stretching. Thereby, to know and compare any change in schedule of wearing latex and non-latex elastics.

objectives of the study

1)     To evaluate and compare the rate of force degradation in latex and non-latex intraoral elastics from two different companies at regular intervals of time and   different percentages of elongation.

2)     To evaluate and compare any significant inter batch variations in force degradation of the samples provided by the manufacturers.

3)     To evaluate and compare the force values claimed by the manufacturers.

4)     To know the change in wearing schedule of latex and non-latex elastics as influenced by their force degradation.

METHODOLOGY

This study intends to evaluate the initial force and the trend of force decay of latex and non-latex elastics.  The characteristic decay of elastics were studied in an artificially simulated oral environment.  All tested elastics were received in sealed plastic bags from the manufacturer.

Elastics:

Latex and non-latex elastics from two different manufacturers, American orthodontics and Dentarum were used in this study. Elastics of medium weight and internal diameter of 1/4^th of an inch were selected.

Stainless Steel Jigs:

Three stainless steel jigs with ten sets of predetermined inter post distance of 14.8mm, 19.0 mm and 28.4 mm were fabricated to simulate 225%,300% and 450% of stretching respectively.

Testing Apparatus:

An Instron universal testing machine (model No.4467) with 10 Kg load cell and cross head speed of 25mm per minute was used to measure the force in grams exerted by the elastics.

Artificial Saliva:

The concentration of the inorganic ions used in preparation was as follows⁴¹:

Sl. No	Inorganic Constituents	Concentration mg / ltr
1	Ammonium Chloride	233 mg / ltr
2	Calcium chloride dehydrate	210 mg / ltr
3	Magnesium chloride hexahydrate	43 mg / ltr
4	Potassium chloride	1162 mg / ltr
5	Potassium dihydrogen orthophosphate	354 mg / ltr
6	Potassium thiocyanate	222 mg / ltr
7	Sodium citrate	13 mg / ltr
8	Sodium hydrogen carbonate	535 mg / ltr
9	Disodium hydrogen orthophosphate	375 mg / ltr
10	Distilled water	1000 ml
11	pH	6.8

Petridish:

A container to hold the stainless steel jig immersed in artificial saliva for incubation.

Mounts:

Hooks to engage the elastics on to the fixed and moving arms of the Instron machine.

Incubator: (GE electronics)

This was used in this study to regulate the temperature at 37⁰ C to simulate oral environment.

Plastics Bags:

Air sealed plastic bags to prevent moisture contamination during storage.

RESULTS

This study was conducted on one hundred and eighty samples. The test samples were divided into groups and subgroups as follows to facilitate the test procedure.

Group I — Latex American orthodontics

Group I samples were again sub divided into group Ia, Ib, Ic, Id and Ie each comprising of three elastics from different batches of the same manufacturer.

Group II — Latex Dentarum

Group II samples were again sub divided into group IIa ,IIb, IIc, IId and IIe each comprising of three elastics from different batches of the same manufacturer.

Group III — Non-latex American orthodontics

Group III samples were again sub divided into group IIIa, IIIb, IIIc, IIId and IIIe each comprising of three elastics from different batches of the same manufacturer.

Group IV —Non-latex Dentarum

Group IV samples were again sub divided into group IVa, IVb, IVc, IVd and IVe each comprising of three elastics from different batches of the same manufacturer.

The force values for one hundred and eighty elastics at various time intervals i.e. initial, 24 hours and after 48hours and different percentage of stretching i.e. 225%, 300% and 450% were calculated and tabulated (table III).

Group I samples at 225% of stretching showed mean value of 120.07+/-0.33 grams of force initially. After incubating for 24 hours and 48 hours at 37⁰ C in artificial saliva they showed mean values of 85.00+/- 1 gram and 75.67+/- 1.15 grams respectively.

Force degradation of 29.20% was observed between initial and 24 hours of   stretching and an additional 7.77% of force decay was observed after next 24 hours of incubation.  The results are shown in table I and table II and graphical representations are  made in graph I and graph Ia .

Group I samples at 300% of stretching showed mean value of 131.84+/-0.59 grams of force initially. After incubating for 24 hours and 48 hours at 37⁰ C in artificial saliva they showed mean values of 90.00+/- 1 gram and 81.67+/- 1.53 grams respectively.

Force degradation of 31.74% was observed between initial and 24 hours of stretching and an additional 6.31% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representations are  made in graph II and graph IIa.

Group I samples at 450% of stretching showed mean value of 177.73+/-1.56 grams of force initially. After incubating for 24 hours and 48 hours at 37⁰ C in artificial saliva they showed mean values of 111.00+/-1 grams and 88.33+/- 1.53 grams respectively.

Force degradation of 38.11% was observed between initial and 24 hours of stretching and an additional 12.19% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representations are made in graph III and graph IIIa.

Group II samples at 225% of stretching showed mean value of 128.85+/- 2.43 grams of force initially. After incubating for 24 hours and 48 hours at   37⁰ C in artificial saliva they showed mean values of 92.00+/-1 grams and 82.67+/- 2.52 grams respectively. Force degradation of 28.59% was observed between initial and 24 hours of stretching and an additional 7.25% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representations are made in graph I and graph Ia.

Group II samples at 300% of stretching showed mean value of 139.97+/- 0.41 grams of force initially. After incubating for 24 hours and 48 hours at  37⁰ C in artificial saliva they showed mean values of 97.00+/-1 grams and  88.67+/- 2.00 grams respectively. Force degradation of 30.69% was observed between initial and 24 hours of stretching and an additional 6.44% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representations are made in graph II and graph IIa.

Group II samples at 450% of stretching showed mean value of 183.90+/-4.21 grams of force initially. After incubating for 24 hours and 48 hours at 37⁰ C in artificial saliva they showed mean values of 119.33+/-0.58 grams and 96.00+/- 1.52 grams respectively. Force degradation of 35.11% was observed between initial and 24 hours of stretching and an additional 12.68% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representation are made in graph III and graph IIIa.

Group III samples at 225% of stretching showed mean of 98.87+/-0.91 grams of force initially. After incubating for 24 hours and  48 hours at 37⁰ C in artificial saliva they showed mean values of  75.67+/-1.15 grams and 71.33+/- 1.53 grams respectively. Force degradation of 23.47% was observed between initial and 24 hours of stretching and an additional 4.38% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representations are  made in graph I and graph Ia.

Group III samples at 300% of stretching showed mean value of 111.59+/-2.41 grams of force initially. After incubating for 24 hours and 48 hours at 37⁰ C in artificial saliva they showed mean values of 82.67+/-1.53 grams and 76.33+/- 1.63 grams respectively. Force degradation of  28.47% was observed between initial and 24 hours of stretching and an additional 5.82% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representations are made in graph II and graph IIa.

Group III samples at 450% of stretching showed mean value of 144.69+/-1.02 grams of force initially. After incubating for 24 hours and  48 hours at 37⁰ C in artificial saliva they showed 103.00+/-1.00 grams and 88.33+/- 1.53 grams respectively. Force degradation of 28.81% was observed between initial and 24 hours of stretching and an additional 10.14% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representations are made in graph III and graph IIIa .

Group IV samples at 225% of stretching showed mean value of 124.78+/-1.66 grams of force initially. After incubating for 24 hours and 48 hours at 37⁰ C in artificial saliva they showed mean values of 94.00+/-1 grams and 91.00+/- 1.00 grams respectively. Force degradation of 24.67% was observed between initial and 24 hours of stretching and an additional 2.40% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representations are made in graph I and graph Ia.

Group IV samples at 300% of stretching showed mean value of 148.21+/-1.42 grams of force initially. After incubating for 24 hours and 48 hours at 37⁰ C in artificial saliva they showed 109.00+/-1 grams and 101.67+/- 2.08 grams respectively. Force degradation of 26.46% was observed between initial and 24 hours of stretching and an additional 4.94% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representations are made in graph II and graph IIa.

Group IV samples at 450% of stretching showed mean value of 198.84+/-3.72 grams of force initially. After incubating for 24 hours and 48 hours at 37⁰ C in artificial saliva they showed mean values of 142.00+/-2.00 grams and 125.33+/- 2.52 grams respectively. Force degradation of 28.59% was observed between initial and 24 hours of stretching and an additional 8.38% of force decay was observed after next 24 hours. The results are shown in table I and table II and graphical representations are shown in graph III and graph IIIa.

Latex elastics at 225% of stretching showed a mean force of 124.46+/- 5.05 grams initially and 88.50+/- 3.94 and 76.67+/- 6.80 grams of force after incubation for 24 hours and 48 hours respectively. Non-latex elastics at 225% of stretching showed a mean force of 111.83+/- 14.25 grams initially and 84.83+/- 10.09 and 78.33 +/- 7.79 grams of force after incubation for 24 hours and 48 hours respectively. The percentage of difference between latex and non-latex variants after 24 hours of incubation was 4.75% and 6.42% in
the next 24 hours of incubation. The percentage of change between latex elastics at 24 hours and 48 hours of incubation is 7.09% and the difference in percentage between non-latex elastics at 24 and 48 hours of incubation is 5.82 % respectively for 225% of stretching.  Results are shown in table IV.

Latex elastics at 300% of stretching showed a mean force of 135.90+/- 4.47 grams initially and 93.50+/- 3.94 and 84.83+/- 3.82 grams of force after incubation for 24 hours and 48 hours respectively. Non-latex elastics at 300% of stretching showed a mean force of 129.90+/- 20.12 grams initially and 95.83+/- 14.46 and 89.00 +/- 14.87 grams of force after incubation for 24 hours and 48 hours respectively. The percentage of difference between latex and non-latex variants after 24 hours of incubation was 4.96% and 6.10% in the next 24 hours of incubation. The percentage of change between latex elastics from 24 hours and 48 hours of incubation is 6.39% and the difference in percentage between non-latex elastics from 24 hours and 48 hours of incubation is   5.25 % respectively for 300% of stretching. Results are shown in table IV.

Latex elastics at 450% of stretching showed a mean force of 180.81+/- 4.42 grams initially and 115.17+/- 4.62 and 92.16+/- 4.76 grams of force after incubation for 24 hours and 48 hours respectively. Non-latex elastics at 450% of stretching showed a mean force of 171.77+/- 29.76 grams initially and 122.50+/- 21.41 and 105.83 +/- 21.44 grams of force after incubation for 24 hours and 48 hours respectively. The percentage of difference between latex and non-latex variants after 24 hours of incubation was 7.62% and 10.63% in the next 24 hours of incubation.

The percentage of change between latex elastics from 24 hours and 48 hours of incubation is 12.72% and the difference in percentage between non-latex elastics from 24 hours and 48 hours of incubation is   9.71 % respectively for 450% of stretching. Results are shown in table IV.
This study was conducted on one hundred and eighty elastics.   The elastic samples were divided into four groups to facilitate the test procedure.

Group I consisted total of forty five latex elastics (American orthodontics)

They were again sub divided into three sets of groups Ia , Ib, Ic, Id and  Ie, each sub group comprising of three elastics were randomly selected from different batches , totaling to fifteen elastics.

These three sets with each set comprising of fifteen elastics were subjected to 225%, 300% and 450% of stretching at various time intervals-i.e. initial, 24 hours and after 48 hours of incubation at 37°C in artificial saliva. The forces were recorded and tabulated.

Group II consisted total of forty five latex elastics (Dentarum)

They were again sub divided into three sets of groups IIa, IIb, IIc, IId and IIe, each comprising of three elastics randomly selected from different batches, totaling to fifteen elastics.

These three sets with each set comprising of fifteen elastics were subjected to 225%, 300% and 450% of stretching at various time intervals-i.e. initial, 24 hours and after 48 hours of incubation at 37°C in artificial saliva. The forces were recorded and tabulated.

Group III consisted total of forty five non-latex elastics (American orthodontics)

They were again sub divided into three sets of groups IIIa, IIIb, IIIc, IIId and IIIe each comprising of three elastics randomly selected from different batches, totaling to fifteen elastics.

These three sets were subjected to 225%, 300% and 450% of stretching at various time intervals-i.e. initial, 24 hours and after 48 hours of incubation at 37°C in artificial saliva. The forces were recorded and tabulated.

Group IV consisted total of forty five non-latex elastics (Dentarum)

They were again sub divided into three sets of groups IVa, IVb, IVc, IVd and IVe each comprising of three elastics randomly selected from different batches, totaling to fifteen elastics.

These three sets were subjected to 225%, 300% and 450% of stretching at various time intervals-i.e. initial, 24 hours and after 48 hours of incubation at 37°C in artificial saliva. The forces were recorded and tabulated.

The initial forces of elastics were calculated using Instron universal testing machine. The amount of force exerted for 225%, 300% and 450% of stretching were noted.

The same elastics were engaged on to the post of the stainless steel jig which expanded the internal diameter of the elastics by 225%, 300% and 450%.  The stainless steel jigs were immersed in artificial saliva completely and incubated at 37⁰ C for 24 hours, to simulate oral environment.

After 24 hours of incubation these elastics were taken on to the Instron machine and the amount of force degradation was calculated and tabulated for 225%, 300% and 450% of elongation.

Later the same procedure was repeated after 24 hours totaling to 48 hours of   incubation with the same elastics and the force degradation was calculated and tabulated in grams by similar method.

The data was analysed statistically using ANOVA and results were tabulated and graphical representations were made.

PHOTOGRAPH NO I:

PHOTOGRAPH NO II:

PHOTOGRAPH NO III:

Discussion

The successful manipulation, redirection and application of forces are the hallmarks of a precise orthodontic mechanotherapy. “Force” ironically is the medicament that the practitoners of the art and science of orthodontics have directed, since time immemorial, to wage a battle against aberrant balances of the teeth and the jaws.

The use of orthodontic elastics has been recorded since the 18th Century. The elastics are successful over other tools used to deliver orthodontic force because of their ability to exert continuous force, convenience of use, cost-effectiveness and their compatibility in the oral environment are a few of the many factors favoring elastics.

The resiliency of elastic products has been exploited to form force delivery systems in orthodontics. However, as with all objects living and non-living, elastics do succumb to the laws of nature. Their force levels decrease with respect to the initial forces exerted. This property is known as the force decay.

Maintaining optimum force is the key to successful orthodontic therapy, so the force decay should be minimal and within acceptable limits. To apply an ideal orthodontic force, an elastomer needs to maintain the appropriate force. However, conventional elastomers exhibit a higher degree of irreversible force decay and are affected by oral environmental factors.

Hence, it was decided to evaluate  and compare the amount of force degradation  in latex and non-latex elastics in a simulated oral environment.

Since the incidence of latex allergy is rising, the need for a non-latex alternative is increasing. The use of non-latex orthodontic elastics is required in patients with known latex sensitivity and will likely become more common if the incidence of latex sensitivity continues to rise 2. Hence, it is imperative to evaluate and compare the mechanical properties of these non-allergenic new materials.

Although there have been a number of studies concerning dental elastomers and the degradation of strength with time, varying results have been reported. This inconsistency is the result of many different kinds of materials and experimental methods, making it difficult to compare the different products.

In this experiment, products of the same size were used and their physical properties were examined with standardized environments.

In this study a total of one hundred and eighty elastics were used. It had both latex and non-latex varieties of elastics of the same size from two different manufacturers.

The percentage of elastic expansion was done in order to simulate maximum (450%), moderate (300%) and minimum (225%) opening of the mouth and also 300% of stretching to compare the forces as claimed by the manufacturers.

Experiments carried out in dry and simulated oral environments of 100% humid conditions reported no significant differences for the different conditions6. Greater force decay was observed in wet conditions than in dry conditions for the same temperature. So the present study was done in a simulated oral environment, using artificial saliva and incubated at 370 Celsius. 22, 32, 42

Studies on biophysical properties of orthodontic rubber elastics concluded that the storage of elastic ligatures done using paper envelopes resulted in a loss of tension. Investigators advised storing the elastics in desiccator type of plastic containers.  Hence, the elastics were procured from the manufacturers in sealed plastic bags, with recent manufacturing dates and storage was done using airtight plastic bags during the study43.

Intermaxillary elastics are used mainly over a length of 20 to 40 mm, producing forces of 60 to 300 grams. Previous studies have shown that during the course of a day, due to opening and closing of the mouth, about one third of the elasticity of the elastics was lost and for this reason, elastics should be changed daily44.

In this study a significant amount of force loss was observed at 225% of stretching after first 24 hours. Force decay of 29.20% in group I, 28.59% in group II, 23.47% in group III and 24.67% in group IV was observed after a 24 hour incubation as shown in table II and graph I. The force loss in group III (non-latex, American orthodontics) showed less force degradation of 23.47% during the initial 24 hour period of testing. Whereas group I (latex, American orthodontics) showed the highest, force degradation of 29.20% at 225% of stretching after the first 24 hour period of incubation.

After 48 hours of incubation there was not much difference observed when compared to the initial 24 hours. The difference of 7.77 % in group I 7.25% in group II, 4.38% in group III and 2.40% in group IV was observed at the same percentage of stretching.
Group IV, (Non-latex, Dentarum) showed the least amount of force degradation, (2.4%) among all the other groups, as shown in table II and graph Ia.

At 300% of stretching there was a significant amount of force loss after 24 hours of incubation time. Force degradation up to 31.74% in group I, 30.69% in group II, 28.47% in group III and 26.46% in group IV was recorded after 24 hours of incubation as shown in table II and graph IIa . The force loss in group IV ( non-latex, Dentarum) showed less force degradation of 26.46%  during initial 24 hour period of testing .where as group I ( latex, American orthodontics) showed the highest  force degradation of 31.74%  at 300% of stretching during the first 24 hour period.

After 48 hours of incubation there was not much difference observed when compared to the initial 24 hours. The difference of 6.31 % in group I, 6.44% in group II, 5.82% in group III and 4.94% in group IV was observed at the same percentage of stretching. Least amount of force degradation of 4.94% was observed in group IV (Non-latex, Dentarum) as shown in table II and graph IIa.

At 450% of stretching, after first 24 hours of incubation, force decay up to 38.11% in group I, 35.11% in group II, 28.81% in group III and 28.59% in group IV was observed as shown in table II and graph IIIa. The force loss in group IV  (non-latex, Dentarum) showed the least amount of force degradation of 28.59%  after a 24 hour period of incubation whereas group I (Latex, American orthodontics) showed the highest force degradation of 38.11% at 450% of stretching after the first 24 hour period of incubation as shown in table II and graph IIIa .

After 48 hours of incubation, there was not much difference observed, when compared to the initial 24 hours of incubation. The difference of 12.19 % in group I, 12.68% in group II, 10.14% in group III and 8.38% in group IV was observed at the same percentage of stretching as shown in table II and graph IIIa. Group IV (Non-latex, Dentarum) showed the least force degradation of 8.38% and group II (Latex, Dentarum) showed the maximum amount of force decay as shown in table II and graph IIIa.

Studies show 50 to 75% of initial force decay after 24 hours and an additional 10% loss of force over three weeks of time. This is similar to my study where maximum force loss observed was 25% to 35% after 24 hours and additional 10% of force decay was observed after 48 hours  ( table II) 6,20,22,42

The amount of force decay in 450% of stretching was more when compared to     300 % and 225% of stretching (table II) 8, 22, 45, 46. This can be attributed to the fact that elastics, which were expanded more, had exposed more surface area in the artificial saliva and the degradation was greater. Additional factors such as temperature changes, alkalinity of saliva and bacteria can infiltrate the weak molecular structure on the rubber surface resulting in discoloration and expansion. The p<0.001 shows significant difference statistically (Table I).

The initial forces were  similar to the forces claimed by the manufacturers but they were below the product specification  levels  after  incubation for  24 hours  and 48 hours in all the groups for different  percentage of stretching  ( table I).

Since the force degradation is too high in the initial 24 hours and subsequently, minimal during the next 24 hours, it is recommended to continue the elastic wear after the first day as the force decay is not much significant .But, though the degradation is too high in the first 24 hours the schedule of change of elastic wear recommended should be on a daily basis at an interval of 24 hours to maintain the force values closer to the product specification prescribed by the manufacturer .The p< 0.001 shows significant difference statistically when force decay at 24 hours and 48 hours of stretching were compared.

Comparing latex and non-latex elastics, non-latex elastics showed less force degradation when compared to latex at all given percentages of stretching and time             (Table IV) .36

Since there has been a rapid increase in reports on latex allergies and some cases of life threatening anaphylaxis 10, it could be wise and safe on the part of the clinician to switch over to a non-latex alternative as they are quite efficient as latex in force application (Table I, II and Graph I, II and III)   and at the same time the force degradation is comparatively less.

All elastics when tested within their subgroups for interbatch variation (Table III) showed the p > 0.005 which is statistically insignificant. This means manufacturers claims in standardization of the elastics were quite precise within acceptable limits.

Although this study was undertaken in a stimulated oral environment and tested using a universal testing machine, its comparison to actual oral environment would be futile. This is because the actual oral environment is subjected to many more stimuli like dietary components, thermal variations and mechanical stresses. This study was done at constant static stretch of the elastics upto 225%, 300% and 450% whereas in actual

clinical situation intermaxillary elastics are subjected to a cyclic stretch during various mandibular movements.

Thus, the scope for similar studies carried out in vivo including the natural effects remains to be explored.

SUMMARY AND CONCLUSION

The following conclusions were drawn from the study

1)      The percentage of force decay is less for non-latex elastics at all percentages of stretching and time when compared to the latex variant.  Therefore, non-latex elastics will be a viable alternative to latex elastics.

2)    Elastics tend to degrade over a period of time and it was known that the amount of force exerted after 24 hours was not up to the optimal requirement. So, elastics needed to be changed daily, to prevent delays in treatment.

3)    The amount of force decay is more when the percentage of stretching is greater.

4)    No significant variations were observed among the elastics within subgroups.

5)    The amount of initial forces claimed by the manufacturer is within the acceptable limits.

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