OriginalJ. Showa Univ. Dent. Soc. 15: 51-58, 1995

Optical Fibers as Orthodontic Archwires : Optiflex

Mohamad Faysal TALASS

Department of Orthodontics, Showa University School of Dentistry 2-1-1 Kitasenzoku, Ohta-ku, Tokyo, 145 Japan

(Chief Prof Yoshinobu Shibasaki)

Abstract: The purpose of this article is to introduce Optiflex(TM), the first non-metal arch-wire in orthodontics. This clear archwire is comprised of three layers: a silicone dioxide core, a silicon resin middle layer and a stain-resistant nylon outer layer. It is available in two sizes: 0.017" and 0.021". Optiflex was compared to three other flexible archwires (Niti, Respond and Nitinol) by means of tensile, bending and time-dependent effects tests. The results showed that :1. The tensile strength of Optiflex was significantly lower than that of metal archwires.2. The force delivered by Optiflex was much lighter and more constant than those delivered by other archwires.3. The force of Optiflex was less than half the force delivered by at "Respond" archwire of similar size.4. Time-dependent effects of Optiflex were almost identical to those of nickel-titanium.

These mechanical advantages, along with its esthetic properties and stain resistance, make Optiflex a unique addition to orthodontic archwires currently available. The new archwire is highly effective in the alignment of crowding in most orthodontic cases, particularly adults with special esthetic considerations.Key words: optical fibers, archwire, esthetics, Optiflex

The demand for esthetic orthodontic appliances

has increased in the late 1980's. As a result, different types of esthetic brackets have become

popular in spite of their various shortcomings.However, the archwire remains quite visible.Some orthodontic alloys with enhanced mechan-ical properties were developed in the late 1970's

and 1980's1-11). They have substantially improved the design of the orthodontic appliances, reduced the force magnitude and shortened the treatment

time. Their esthetic appearance, however, did not meet the growing expectation of an ever

demanding public.This article introduces a new orthodontic arch-

wi re which combines esthetics with unique mechani-cal properties. To our knowledge, Optiflexml)

(Ormco Corporation) is the first non-metal arch-wire used in orthodontics. It is made of a modified

clear optical fiber (Fig. 1). The idea of using optical fibers in orthodontics has been cultivated

through several years of research and development.A US patent has been granted for this concept in 1989 (US patent No. 4869666: An orthodontic

archwire).An industrial optical fiber is usually composed

of a silicon-dioxide (glass) core surrounded by

one or more layers of organic materials which enhance its optical and mechanical properties.

Since the glass core is the most important element in an optical fiber, the following properties of

glass should be remembered when using modified optical fibers as orthodontic archwires :

1. Under applied stress, metals stretch plasti-

cally beyond their elastic limit and fail when the ultimate strength is reached. Conversely, glass

has no significant plastic deformation. It extends elastically up to its breaking strength (Fig. 2).

2. As long as the ultimate strength (fracture

point) is not reached, glass is a 'flexible' material,Present address: Talass Orthodontic Center, P.O.

Box 13016 Dubai UAE

2 昭 和歯学 会雑誌 第15巻 第2号

Stress-Strain Curve

METALSGLASS

contrary to the common belief.The clinical case shown (Fig.3) demonstrates the flexibility of an Optiflex archwire with a glass core.

3. In general, maximum tensile strength of metals is usually much higher than that of glass.However, tensile properties of glass can be altered by making it into a fiber.The maximum tensile strength of industrial glass fibers is about 60 to 70 percent that of metals.The effect of geometry on tensile strength is illustrated (Fig.4).

Structure: Optiflex is a clear orthodontic arch-wire made of a modified optical fiber.It is available in two sizes: 0.017-inch for the 0.018" slot and 0.021-inch for the 0.022" slot.Optiflex is comprised of three layers (Fig.5):

1. A 99.9 % pure silicon dioxide core that

provides the force for moving teeth.2. A silicon resin middle layer that protects

the core from moisture contamination.It is an important layer since water contamination reduces the strength of the silicon dioxide bonds in the

glass core and accelerates silica decay under stress.3. A stain-resistant nylon outer layer that

prevents external damage of the fiber.

Materials and Methods

Optiflex was compared to three commonly used orthodontic archwires Niti, Respond (Ormco Corporation, CA, USA) and Nitinol (3M Unitek Corporation, CA, USA) by means of tensile, bending and time-dependent effects tests.All results were the mean of ten testings performed on individual samples.Each point represented the average of ten separate recordings, where the results were inconclusive, the test was repeated.The tests were as follows:

1. Tensile test: A conventional tensile test was performed using an Instron tensile testing machine.Flat jaws combined with two pieces of 600 mesh sand paper were used to hold the arch-wires for testing.Gauge length was 200 mm, cross head speed was 200 mm/min and maximum load was 50 kg.Fractures were accepted only if they took place at least 5.0 mm away from the

jaws.2. Cantilever beam bending test: Cantilever

beam testing was performed using a 1.0 in lb.Tinius Olsen machine (Tinius Olsen Testing Machine Co.Inc., Willow Grove, PA, USA).Each specimen was held in a vice at one end and the load was applied to the free end.The archwires were bent 90 degree at a constant speed and the bending moment was recorded at 5 degrees inter-vals.The load was then removed manually and the moment was recorded at 10 degrees intervals.

3. Three-point bending test: Bend testing was also performed using a fixture with a span of 14.0 mm.The supports were dowel pins of 3.0 mm in diameter which were the same as the load im-

porting edge at the middle of the specimen.An Instron tensile testing machine was used in con-

junction with the bending fixture for this test.Cross head speed was 5.0 mm/min and maximum load was 1.0 kg.The load was applied to the middle of the specimen and traveled at the constant speed of 5.0 mm/min for 4.0 mm and then removed with the same speed.Loading and unloading data were collected and stress/deflection values were calculated for all archwires.

4. Time-dependent effects: Time-dependent ef-fects were tested after Burstone et al.H) The four archwires were engaged in brackets placed inter-

proximally 3.0 mm apart with a 6.5 mm occluso-gingival discrepancy between the center bracket

Fig. 1 Optiflex archwire.

Fig. 2 Schematic presentation of stress-strain

curves for metals and glass.

EL: elastic limit, US: ultimate strength.

平 成7年6月 53

a

c

b

d

Maximum Tensile Strength

Steel Glass 61ass

Fiber

and the adjacent ones for periods of 1 min, 1 h

and 3 days. Time-dependent permanent deforma-tions in the archwires were evaluated in this test.

Results

The results of the tests were as follows: 1. Tensile test: The average tensile strength

of Optiflex, Respond, Niti and Nitinol archwires are shown (Fig. 6). As expected, Optiflex tensile strength was significantly lower than those of

other wires. Nitinol, Respond and Niti had 5.1 times, 4.5 times, and 3.5 times the tensile strength

of Optiflex, respectively. 2. Cantilever beam bending test: The results

of the cantilever beam bending test of 0.017" Optiflex, 0.017" Respond, 0.016" Niti and 0.016" Nitinol archwires are shown (Fig. 7). The stiff-ness of Optiflex was significantly lower than those of other archwires. At maximum deflection (90 degrees), the bending moment of Nitinol reached 12.25 Nm. Niti and Respond showed somewhat similar values at 6.75 and 5.5 Nm. respectively, while Optiflex showed a significantly lower value of 1.6 Nm. In addition to its low magnitude, the moment/deflection curve of Optiflex was unique as the loading and unloading segments of the curve were almost identical between 35 and

Fig. 3 Clinical flexibility of an Optiflex archwire with a glass core.

3-a: pretreatment, 3-b: initial placement of archwire, 3-c: pre-surgical alignment ofteeth,

3-d: post treatment.

Fig. 4 Conceptual maximum tensile strength of

steel, glass and glass fibers.

Fig. 5 Structure of Optiflex.

A: Silicone dioxide core.

B: Silicone resin middle layer.

C: Stain resistant nylon outer layer.

54 昭和歯学会i雑誌 第15巻 第2号

WIRE TYPE

ANGLE OF DEFLECTION ()

90 degrees of deflection, a phenomenon not seen in other archwires.

The results of an identical cantilever test of 0.021" Optiflex, 0.021" Respond, 0.020" Niti and 0.020" Nitinol archwires are shown (Fig.8).Here again the bending moments of Nitinol , Niti and Respond were significantly higher than that

of Optiflex, which showed a maximum bending

moment of 2.1 Nm.3. Three-point bending test: The results of

the three-point bending test of 0.017" Optiflex, 0.017" Respond, 0.016" Niti and 0.016" Nitinol archwires are shown (Fig.9).The results dem-

onstrated the same pattern previously shown

Fig. 6 Tensile strength of Nitinol, Niti, Respond and Optiflex (MPa) .

Fig. 7 Cantilever beam bending tests of 0.017" Optiflex , 0.017" Respond, 0.016" Niti and 0.016" Nitinol (Bending moments in Nm).

平 成7年 6月 55

Fig. 8 CantileverbeambendingtestsofO.021z/OptiHex,0.021"Respond,0.020"NitiandO.020"

Nitinol(BendingmomentsinNm).

Fig. 9 Three-point bending tests of 0.017" Optiflex, 0.017" Respond, 0.016" Niti and 0.016" Nitinol (Bending stress in MPa).

56 昭和歯学会雑誌 第15巻 第2号

(Fig. 7), taking into account the difference in beam constriction. The actual data of the Optiflex tests are presented (Table 1).

The results of an identical three-point bending test of 0.021" Optiflex, 0.021" Respond, 0.020" Niti and 0.020" Nitinol are shown (Fig. 10). The curves were similar to those shown (Fig. 9), taking into account the change in the diameter of the archwires. The actual data of the Optiflex tests are presented (Table 2).

4. Time dependent effects: As shown (Fig. 11), Optiflex and Niti archwires exhibited excellent time-dependent effects, with insignificant defor-mations after periods of 1 min, 1 h and 3 days.

Nitinol showed a noticeable deformation after 1 h and 3 days. Respond, however, showed the

greatest amount of permanent deformation which was noticed immediately following ligation.

Fig. 10 Three-point bending tests of 0.021" Optiflex 0.021" Respond, 0 .020" Niti and 0.020" Nitinol (Bending stress in MPa).

Table 1 Three-point bending test data of 0.017" Optiflex (14.0 mm span-4.0 mm. travel-Free ends).

Table 2 Three-point bending test data of 0.021" Optiflex (14.0 mm span-4.0 mm travel-Free ends).

平 成7年 6月 57

TIME - DEPENDENT EFFECTS

Discussion and Clinical Considerations

1. Optiflex properties: The new archwire ex-hibited excellent mechanical properties. Apparent tensile strength of Optiflex was much lower than those of other archwires (Glass vs. Metals).However, it seems that the clinical effect of the low tensile strength is not greatly significant in orthodontic treatment. On the other hand, bend-ing tests showed that the forces applied with Optiflex is much lighter and more constant than those delivered by other acrhwires. Therefore it is less likely to cause initial patient discomfort or

root resorption. Clinicians accustomed to use

heavier forces may consider the light force of Optiflex inadequate to move teeth. However,

clinical reports12,13) have shown that Optiflex can move teeth effectively using light continuous force which is less than half the force applied with a

Respond wire of a similar size. The relative

flexural modulus of Optiflex, Respond, Niti and Nitinol can be demonstrated (Fig. 12). Optiflex

also showed excellent time dependent effects which were similar to those of nickel-titanium. Because

glass has no significant plastic deformation, Opti-flex usually retains its flexibility to the point of fracture. This phenomenon provides Optiflex

Fig. 11 Time dependent effects of 0.017" Optiflex, 0.016" Niti, 0.016" Nitinol and 0.017"

Respond after 1 min, 1 h and 3 days.

Fig. 12 Relative flexural modulus of Nitinol, Niti, Respond and Optiflex.

58 昭和歯学会雑誌 第15巻 第2号

with a wide range of action which accomodates most dental malalignments.

Beyond its mechanical advantages, Optiflex exhibited unique esthetic properties unmatched by any other orthodontic wire to date including teflon-coated stainless steel or nickel-titanium. It is completely clear, stain resistant and does not lose its clear "look" even after several weeks in the oral environment.

2. Clinical considerations: In order to take full advantage of the superior properties of Opti-flex, clinicians must not subject the archwire to conditions which may undermine glass perfor-mance. When using Optiflex, clinicians must follow these guidelines :

1) Metal ligatures can fracture the glass core of the archwire. Therefore, Optiflex must be tied into the brackets only with elastomeric ligatures.

2) Sharp bends similar to those commonly

placed in metal archwires should be avoided since they can fracture the core of Optiflex.

3) Instruments with sharp edges (scalers, di-rectors, etc.) should not be used to force Optiflex into the bracket slot. Instead, a gentle force with the clinician's finger is more appropriate.

4) Sharp distal end cutters can be used to cut the end of the archwire distal to the molars. The clinician must make sure that the remaining little segment of Optiflex is not left in the patient's mouth.

5) Friction between elastomeric ligatures and the outer surface of the archwire (Nylon) elim-inates unwanted sliding of Optiflex to either side . Therefore, "cinch back" is not needed when using Optiflex.

6) Patients must be informed about the nature and structure of Optiflex. They must avoid a rough diet which can harm the archwire and delay treatment progress.

Summary and Conclusions

Optiflex is the first non-metal orthodontic arch wire which combines a highly esthetic appearance with unique mechanical properties. Due to its unique structure, Optiflex light continuous force

can be highly effective in moving teeth without

patient discomfort or root resorption. Optiflex is effective in the alignment of crowding in most

orthodontic cases, especially adult patients who

wish braces which are not be readily visible, for

reasons related to personal concerns or profes-sional considerations.

References

1) Andreasen GF, Hileman TB: An evaluation of 55-cobalt substituted wire for orthodontics. J Am Dent Assoc, 82: 1373-1375, 1971

2) Andreasen GF, Brady PR: A use hypothesis for 55 nitinol wire for orthodontics. Angle Orthod, 42: 172-177, 1972

3) Andreasen GF, Barrett RD: An evaluation of cobalt-substituted Nitinol wire in orthodontics. Am J Orthod, 63: 462-470, 1973

4) Civjan S, Huget EF, DeSlmon LB: Potential applications of certain nickel-titanium (Nitinol) alloys. J Dent Res, 54: 89-96, 1975

5) Andreasen GF, Morrow RE: Laboratory and clinical analyses of Nitinol wires. Am J Orthod, 73:142-151, 1978

6) Lopez I, Goldberg J, Burstone CJ: Bending char-acteristics of Nitinol wire. Am J Orthod, 75: 569-575, 1979

7) Goldberg AJ, Burstone CJ: An evaluation of beta-titanium alloys for use in orthodontic appli-ances. J Dent Res, 58: 593-600, 1979

8) Burstone CJ, Goldberg AJ: Beta-titanium: a new orthodontic alloy. Am J Orthod, 77: 121-132, 1980

9) Goldberg AJ, Burstone CJ: Status report on beta-titanium orthodontic wires. Council on Dental Materials, Instruments, and Equipment. J Am Dent Assoc, 105: 684-685, 1982

10) Burstone CJ, Qin B, Morton JY: Chinese NiTi wire—A new orthodontic alloy. Am J Orthod, 87: 445-452, 1985

11) Miura F, Mogi M, Ohura Y, Hamanaka H: The super-elastic property of Japanese NiTi alloy for use in orthodontics. Am J Orthod, 90: 1-10, 1986

12) Talass ME: Optiflex archwire treatment of a skeletal class III openbite. J Clin Orthod, 26: 245-259, 1992

13) Talass ME: Practice building with clear mechan-ics. Clinical Impressions, 1: 10-14, 1992

(Received February 3, 1995)