Orthodontics

1. DEPARTMENT OF ORTHODONTICS AND DENTOFACIAL
ORTHOPAEDICS.
JOURNAL CLUB PRESENTATION.
Force Degradation of Orthodontic latex elastics analyzed in Vivo
and in Vitro
Liu Yang, Chenxing Lv, Fan Yan and Jianying Feng
Presented by: Guided by:
Dr. Deeksha Bhanotia Dr. Mridula Trehan.
M.D.S. Second year. Professor & Head
NIMS Dental College and Hospital Department of Orthodontics
and Dentofacial Orthopaedics
1

2. Contents:
1. Introduction.
2. Objectives of Study.
3. Materials and Method.
4. Statistical Analysis.
5. Results.
6. Discussion.
7. Conclusion.
2

3. Introduction:
Intraoral latex elastics are used to help orthodontic
mechanics in the delivery of force to the teeth.
Generally an auxiliary method, latex elastics are
characterized by:
high flexibility,
relatively enduring force
low cost.
Patients can easily change the elastics by
themselves and maintain good oral hygiene.
3

4. Latex elastic materials are made of natural
macromolecule compounds.
One of the inherent disadvantages of elastics is that
force levels decrease over time.
To achieve optimum orthodontic tooth movement,
this force decay must remain within acceptable
limits.
4

5. Although elastic bands are used extensively,
their mechanical properties are not well-defined.
Particularly, these properties are influenced
by factors related to the material, such as
loss of elasticity
amount of force decay and
composition of the elastics
Also influenced by environmental
factors, such as: the composition of saliva,
intraoral pH,
temperature variations,
food texture, pigments.
5

6. Objective of the Study:
The objective of this study was to evaluate
the characteristics of force degradation of latex
elastics of 10 kinds of elastics over 48 hours,
both in vivo and in vitro.
6

7. Materials and Method
 Materials:
Latex elastics from 1 company (3M Unitek, St
Paul, Minn) were used.
Fifty samples in each of 10 sizes were tested.
All the latex elastics were within their expiration
dates and stored in sealed plastic packages in an
appropriate environment.
7

8.  The force value of the 3.5-ounce elastics was
regarded as 100 g of force and that of the 2-ounce
elastics was regarded as 60 g of force.
 Force extension was measured in a ZHIQU testing
machine.
8

9.  Tensile readings were recorded in gram force with
a duration of 10 seconds for each elastic.
 Two hooks were coupled to the machine, one at
the upper connection point and the other at the
bottom, aiming to the insertion of the elastics for
their extension.
9

10.  The length of the setting force (100 or 60 g of
force) was measured by electronic digital display
(accuracy of 0.01 mm; Vernier, Germany
Masterproof Company, Shanghai, China).
 The average length of each group was the distance
of extension.
10

11. Methods:
 The following inclusion and exclusion criteria were
applied, and 10 volunteers were chosen:
students of the School of Stomatology, Zhejiang
Chinese Medical University with
good physical and mental health,
regular life, no history of orthodontic treatment,
no bruxism, no dentition defect,
no moderate or severe periodontal disease
no dentition crowding.
11

12.  A silicon rubber impression was collected for each volunteer,
and maxillary and mandibular gypsum models were
produced.
 Personalized thermoplastic retainers for both jaws were
made on a vacuum pressure film machine (China Guang
ming Medical Device Company, Suzhou, China).
12

13.  The distance of extension to produce initial force
values of 60g and 100 g of force was represented
by 2 buttons .
 Light solidification glue was used to fix the buttons
on each quadrant of the clear retainers.
 Each volunteer was told to place the latex elastics
on the buttons
13

14. Ten types of the latex elastics were used for the in
vivo experiment.
Timing started once volunteers began to wear the
clear retainers.
Each volunteer was required to test 5 elastics of
the same types and wear the elastics for 48 hours
(except during meals) without changing them.
The volunteers were told to avoid eating food
except the basic 3 meals every day to prevent
breakage of the elastic bands.
14

15. Force measurements were made at 10 intervals: 0, 1,
3, 6, 9, 12, 18, 24, 36, and 48 hours.
To ensure the consistency of the tests, all
measurements were performed by 1 person (LY).
15

16. With a pair of tweezers, each elastic was carefully
transferred from the volunteer to the testing
machine in the sequence of time intervals.
At a specific distance, the force value of the elastic
showed on the test machine decreased rapidly at
the initial stage, then tended to decline at a slower
and more stable rate.
16

17.  The constant value in the test machine within 10
seconds was regarded as the force value of the
elastic, and each elastic was read 3 times for an
average value.
 The latex elastics of 1/4-inch (2 ounce) and 1/4-
inch (3.5 ounce) are frequently used in clinical
treatment, thus they were chosen as the control
groups for the in vitro experiment.
17

18.  Both sizes of latex elastics were stretched to
the setting force in retainers as before. Instead
of being worn in the volunteers' mouths, the
retainers were placed respectively in dry air
conditions (constant temperature of 25̊C) and
artificial saliva (constant temperature of 37̊C
and pH =6.7).
 Force measurements were made at the same
time intervals as the in vivo experiment.
18

19.  Statistical analysis:
Force degradation curve fitting was performed with the
relevant software (SPSS, version 22.0; IBM, Armonk,
NY).
The force degradation of each group was averaged, and
the results were analyzed with 1-way ANOVA of variance
and t test (P <0.05).
19

20. Results:
 Means and standard deviations of force value and force degradation
from the latex elastics at the measured time intervals in vitro and in
vivo are shown in Table:
20

21. The average degradations of the 1/4-inch (2 ounce and
3.5 ounce) elastic force after 48 hours were in vivo
(33.83% and 36.94%) >artificial saliva (24.60% and
26.89%) > dry air condition (16.44% and 16.21%).
21
Force degradation highest in elastomers used in vivo Experiment

22. Continuous significant drops in elastic force for
the latex elastics were seen at all time intervals
(P<0.05) except between the 0- and 1-hour interval
for the 1/4-inch (2 ounce and 3.5 ounce) elastics.
22

23.  For the in vivo groups, the degradation of the elastic force was the
greatest within the initial 0-1 hour, and the degradation rate of the
elastic force was 13.16%-18.79% after 1 hour. Then, the degradation
of force value decreased steadily. The force degradation rate of the
latex elastics after 48 hours was 29.35%-39.94%
23

24.  At the same time point, it was found that under the same
force value specifications (60 and 100 g of force), the
degradation rate of latex with large diameter was slower
than that of elastics with smaller diameters (3/8-inch<5/16-
inch < 1/4 –inch <3/16-inch < 1/8-inch) .
24

25.  Degradation of the elastic force with the same diameter and
different initial force values was also compared. At the same
time interval, the elastic degradation rates of 3.5-ounce
groups with the diameters of 1/8-inch, 3/16- inch, 1/4-inch,
5/16-inch, and 3/8-inch were 32.89%- 39.94%, which were
larger than the degradation rates of the 2-ounce groups
(29.35%-34.97%).
25
Larger Force Degradation
group

26. Discussion:
Several factors can affect the mechanical properties of
latex elastics, such as the material of different companies, the
influence of saliva, pH, diet, and the effects of jaw
movements on structural relaxation. Patients frequently
undergo various oral activities in the daytime that can be
regarded as a dynamic environment for the elastics.
Therefore, simple in vitro testing is unable to represent the
actual clinical application. To be closer to clinical treatment
and provide a much more reliable guideline for clinical use, in
vivo study should be chosen.
26

27. Natural rubber is an elastomer with a structure formed by a
3-dimensional reticulate structure by cross-links. The elastic
properties depend on irregular twisted arrangements of long
molecular chains linking together at certain points by
covalent bonds between different atoms. Physical and
chemical properties of latex cause orthodontic elastics to
undergo fatigue creep and force degradation, which results in
force decay that is obvious in the oral environment.For in
vitro, as the control groups, this study used latex elastics 1/4-
inch (2 ounce and 3.5 ounce), which are commonly used in
the clinic.
27

28. The force degradation of the in vitro group was approximately
14.5%-16.6% in dry air and 22.0%-24.7% in artificial saliva.
The results of force degradation rate of the orthodontic latex
elastic were approximately consistent with other in vitro
experiments. The force degradation rate was much greater in
vivo than in vitro. The situation in vivo caused a force loss of
about 32.9%-35.0% after 48 hours. The decrease rate was the
fastest in the first hour both in vivo and in vitro, then gradually
and slightly decreased.
28

29. CONCLUSIONS:
1. The force degradation of the latex elastic was greater
in vivo than in air or artificial saliva.
2. The larger the inner diameter and smaller the setting
force value were, the slower the force decayed.
3. After 12 hours, force degradation was slower in many
groups, which could explain that a range of forces became
more appropriate for most clinical applications.
29

30. 30
Related Articles:
A Comparison of the rate of space closure using a nickel-titanium spring and an
elastic module: A clinical study.
R.H.A.Samuels,S.J.Rudge,L.H.Mair
A study of the efficiency of space closure after premolar extraction was
undertaken, comparing a nickel-titanium closed coil spring and an elastic
retraction module by using sliding mechanics along an 0.019 x 0.025-inch
stainless steel arch wire in 0.022 • O.028-inch preadjusted stainless steel brackets.
The rate of space closure in 17 subjects was analyzed from study models and was
found to be significantly greater and more consistent with the nickel-titanium
closed coil springs than with the elastic modules, in both arches. There were no
clinically observable differences in the tooth positions between the respective
techniques. (AM J ORTHOD DENTOFAC OFITHOP 1993;103:464-7.)

31. 31