Frictional Forces Produced by Three Different Ligation Methods in Two Different Types of Brackets in 0.016 Nickel-Titanium Wire: An in vitro Study.

INTRODUCTION: The aim of this in vitro study was to compare the frictional forces produced by three types of ligatures (conventional elastic ligatures, unconventional elastic ligatures, and tooth-colored ligature wire) on ceramic bracket and stainless steel brackets with 0.016 nickeltitanium (NiTi) archwire in the dry state.
MATERIALS AND METHODS: Twenty each stainless steel brackets and ceramic brackets (0.022 slot central incisor brackets) were mounted on the acrylic block. This assembly was mounted on the Instron machine with the crossheads moving upward at a speed of 10 mm/min in the upper jaw of the Instron machine, one acrylic block with hook and a straight length of 0.016 NiTi wire was attached to it. This wire was ligated to brackets with three different ligation methods. In each test, the brackets were moved a distance of 4 mm, 8 mm, and 12 mm across the central space, and the load cell readings were recorded on the digital display. The difference between the readings is noted.
RESULTS: Stainless steel brackets with 0.016 NiTi archwire ligated with conventional, unconventional, and tooth-colored ligation with the movement of 4 mm, 8 mm, and 12 mm shows that the tooth-colored ligation indicating least frictional force decay. Comparison of frictional forces (in newtons) between ceramic brackets and stainless steel brackets using 0.016 NiTi wire for a movement of 12 mm shows that stainless steel bracket with tooth-colored ligation produced least frictional force compared with ceramic bracket.
CONCLUSION: Based on this study results, we can conclude that stainless steel brackets produce less frictional force compared to ceramic brackets. Similarly, tooth-colored ligatures can be preferred to reduce friction during leveling stage. Copyright:

INTRODUCTION

Friction is the resistance to motion when an object moves tangentially against another. In orthodontics, friction plays an important role both in the alignment stage and during retraction and improves treatment mechanics.

There are many factors that influence the frictional resistance such as bracket and archwire materials' surface conditions of archwire and bracket slot, wire dimension, torque at the wire bracket interface, type, and force of ligation. Least friction will reduce the treatment time.

Most investigations studying the effect of ligation on friction have concluded that elastomeric modules significantly increase resistance to sliding compared with stainless steel ligatures, especially when the latter are tied loosely. Several studies have demonstrated a significant decrease in friction using stainless steel brackets with a reduction in the time necessary for single tooth movement. Unconventional elastomeric ligature (UEL), once applied on conventional brackets, this ligature is completely passive.

The aim of the present in vitro study was to compare the frictional forces produced by three types of elastomeric ligatures (UEL and CEL and tooth-colored ligature wire) on ceramic bracket and stainless-steel bracket used with 0.016 nickeltitanium (NiTi) wire in the dry state.

Aims and objectives

The aims and objectives of this study were to evaluate the friction generated between archwire and bracket during sliding mechanics:

To evaluate the kinetic frictional force produced between stainless steel brackets 0.022 slot MBT prescription with 0.016 NiTi wires and ligated with conventional elastic ligatures, unconventional elastic ligatures, and tooth-colored ligature wire, independently

To evaluate the kinetic frictional force produced between ceramic bracket (0.022 slot MBT prescription) with 0.016 NiTi wires are ligated with conventional elastic ligatures, unconventional elastic ligatures, and tooth-colored ligature wire independently.

MATERIALS AND METHODS

A special acrylic block to record the resistance to movement of 0.016 NiTi wires through test brackets was constructed similar to one specified by Sayeh Ehsani 2009.[1]

Archwire dimension was chosen as 0.016 because it is the common wire used during leveling and alignment stage with 0.022-inch slot system brackets.[2]

Materials

Wires

Straight length of 0.016-inch NiTi

(RABBIT FORCE NiTi WIRES) each 8 cm long

Brackets (MBT PRESCRIPTION)

Stainless steel brackets – Upper central incisors

(0.022 Slot, Ormco Company)

Ceramic rackets– Upper Central Incisors (0.022 Slot, Invu (Libral Company).

Ligatures

Conventional Mini Modules (1.3 Mm, Leone)

UELs (LEONE COMPANY)

Tooth-colored ligature (Teflon ligature) (LEONE COMPANY).

Samples

Twenty ceramic upper right central incisor brackets

Twenty stainless steel upper right central incisor brackets

A total of 40 samples was taken and divided into two groups and for each group, five readings were taken. Each bracket was tested only once, and each time bracket, archwire, and ligature wire have been changed and replaced with new one so as to eliminate the influence of wear.

Group (a); Stainless steel brackets with 0.016 NiTi wire ligated with conventional modules.

Group (b); Stainless steel brackets with 0.016 NiTi wire ligated with unconventional modules.

Group (c); Stainless steel brackets with 0.016 NiTi wire ligated with tooth-colored ligatures.

Group (d); Ceramic brackets with 0.016 NiTi wire ligated with conventional modules.

Group (e); Ceramic bracket with 0.016 NiTi wire ligated with unconventional modules.

Group (f); Ceramic bracket with 0.016 NiTi wire ligated with tooth-colored ligatures.

Methodology

The test was done under dry conditions. The measurement of the friction between bracket and archwire was done with an INSTRON 3382 [Figure 1].

Figure 1

INSTRON 3382

Universal testing machine

It consisted of a simulated fixed appliance with the archwire in vertical position with Acrylic block in the center was constructed with two types of (stainless steel and ceramic) brackets.

Each bracket was bonded on the center of the three different acrylic blocks, respectively. Care was taken to keep the brackets along a straight line to prevent the generation of unwanted friction.

The ligatures of the central brackets were first tightened and unwound by three turns to permit free sliding along the archwire. The end of the ligature was then tucked under the archwire. The acrylic blocks with this assembly were mounted on the Instron machine with the crossheads moving upward at a speed of 10 mm/min in the upper jaw of the Instron machine one acrylic block with hook and a straight length of 0.016 NiTi wire was attached to it.

In each test, the brackets were moved a distance of 4 mm, 8 mm, and 12 mm across the central space, and the load cell readings were recorded on the digital display.

Statistical analysis

Descriptive statistics including mean standard deviation was estimated from the sample for each study group. Mean values were compared by students t-test/one-way ANOVA appropriately. Multiple range tests by TURKEYS-HSD (honesty significant difference) procedure were employed to identify the significant groups at 1% level picture.

RESULTS

Stainless steel brackets with 0.016 NiTi archwire ligated with conventional.

Unconventional and tooth-colored ligation with the movement of 4 mm, 8 mm, and 12 mm shows that the tooth-colored ligation produced the least frictional force [Table 1].

Table 1

Comparison of frictional force (in Newtons) between Ni-Ti wire and ceramic bracket ligated by various methods for a movement of 12 mm

Type of ligation	n	Mean (Newtons)	SD	F	P*
Conventional ligation	20	0.64	0.07	2.12	0.21 (NS)
Unconventional ligation	20	0.72	0.05
Tooth colored ligation	20	0.76	0.10

*ANOVA. NS: Not significant, SD: Standard deviation

Comparison of frictional forces (in newton) between ceramic brackets and stainless-steel brackets using 0.016 NiTi wire for a movement of 12 mm shows that stainless steel brackets with tooth-colored ligation produced least frictional forces compared with ceramic brackets [Table 2].

Table 2

Comparison of frictional force (in Newtons) between Ni-Ti wire and Stainless-steel bracket ligated by various methods for a movement of 12 mm

Type of ligation	n	Mean (Newtons)	SD	F	P*
Conventional ligation	20	0.71 (a)	0.02	13.52	0.001 (HS)
Unconventional ligation	20	0.91 (a)	0.18
Tooth colored ligation	20	0.29 (b)	0.01

*ANOVA. HS: Highly significant, SD: Standard deviation

DISCUSSION

There are numerous factors that affect friction such as archwire and bracket ligation, biomechanics, and patient factors such as saliva.

Our study was aimed at comparing three different ligation methods and its effect on friction. Hence, all other parameters affecting friction were standardized. In the present study, an acrylic block was made for mounting the ceramic and stainless steel brackets which were fixed in the lower jaw of the Instron testing machine.

The central bracket was moved in the space for a distance of not <5 mm. A constant load of 100 g was placed in the central bracket to stimulate load acting at the center of the resistance. The upper jaw of the machine with acrylic block was moved up, and the readings were recorded.

The difference between load cell readings and load on the power arm thus represented the frictional force loss.

Method of ligation

Previous studies have shown that elastomers produce more friction than stainless steel ligatures. Dhopatkar and Rock (2003 to 2006)[3] by their studies stated that slick modules produce less friction than elastomeric modules.

In this study, stainless steel brackets with 0.016 NiTi wire for the movement of 4 mm produced higher frictional forces when conventional and unconventional ligation was used than compared with tooth-colored ligation. Edwards and Jones[4] proved figure eight ligation produces more friction than normal ligation.

The two main factors leading to greater frictional resistance in conventional ligation were the arch dimension creating more area of contact and second the force of conventional ligation.

Wires

Angolkar et al.[5] stated that stainless steel wires produce less friction compared to Niti and TMA wires, Vaughan and Duncanson[6] Ogata and Nanda (1997 to 1996)[7] proved rectangular wires produce more friction compared to round wires.

Farronato and Maijer[8] by their studies stated Teflon-coated archwires produced lower frictional levels than the correspondent uncoated archwires.

Coating with Teflon has excellent esthetic properties. Teflon coatings suppressed corrosion processes completely.

Brackets

Angolkar et al. 1990[5], Bednar et al. 1991[9], Downing et al. 1994[10], Karamouzos et al. 1997[11], Kusy and Whitley 2001[12], and Nishio et al. 2004[13] in their studies proved stainless steel brackets had lower forces of friction than polycrystalline or single-crystal ceramic brackets. For most of the comparisons of the ceramic brackets, single-crystal bracket tended to be lower in friction than polycrystalline brackets.

In this study with stainless steel brackets, tooth-colored ligation produced least friction followed by conventional ligation. Unconventional ligation produced maximum frictional force.

However, with ceramic brackets, conventional ligation produced least friction followed by unconventional ligation and tooth colored, but there was no significant difference between the last two.

When we compare stainless steel with ceramic brackets contradicting usual expectation conventional and unconventional ligation produced more friction with stainless steel brackets than ceramic brackets.

Clinical implications

Esthetics, duration of treatment, and time for each appointment are the three main criteria for the patients in the present-day clinical situations. Teflon-coated ligatures in combination with ceramic brackets are esthetically pleasing and reduce the overall treatment time by producing very less friction.

With any in vitro study, certain variables are not considered which can affect the clinical situations and these could affect orthodontic tooth movements such as masticatory forces, oral functions, different degrees of malocclusion, width and compressibility of periodontal ligament, tooth rotation, torque at the wire bracket interface, bracket/archwire angulations, temperature, and the effect of saliva. These limitations could have influenced the findings of the present in vitro study.

CONCLUSION

Based on this study results, we can conclude that stainless steel brackets produce less frictional force compared to ceramic brackets; similarly tooth-colored ligatures can be preferred to reduce friction during leveling stage.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.