To Compare the Accuracy of 0.022 Inch Slot of Stainless Steel and Ceramic Orthodontic Brackets Marketed by Different Manufacturers.

AIM OF THE STUDY: The aim of the present study was to analyze the accuracy of 0.022 inch slot of stainless steel and ceramic orthodontic brackets marketed by different manufacturers.
MATERIALS AND METHODS: An in vitro study was done on upper left central incisor bracket of MBT 0.022 slot of American orthodontics (AO), 3M Unitek, Ormco with each 20 of stainless steel and ceramic brackets divided into six groups, and the total sample was 120. The brackets were scanned with stereo microscope of Magnus Company and Image Pro plus analysis software was used to evaluate the mesial face and base, distal face and base.
RESULTS: Comparison in between the groups of stainless steel showed that 3M Unitek brackets showed higher slot widths as compared to AO and Ormco which was statistically significant (P < 0.05). Comparison in between the groups of ceramic brackets of AO brackets showed higher slot widths as compared to Ormco and 3M Unitek ceramic brackets which was statistically significant (P < 0.05).
CONCLUSION: By this study, there was a difference between stated values and measured values of brackets displaying inaccuracies in dimension. A clear impreciseness about the appliance could be needed during the finishing and detailing stage to avoid loss of torque control due to slot oversize and the divergence of slot walls. Copyright:

INTRODUCTION

The definition of bracket as an orthodontic attachment secured to a tooth for the purpose of engaging the arch wire by Raymond C Thurow. The transferred force from active components such as arch wire, springs, and elastomeric chains to the teeth is done by brackets which are passive components.

The placing of archwires in a preadjusted bracket is designed to produce three-dimensional tooth moving forces. These forces are created as a result of the intimate fit of wire into the bracket slot, and any “play” or “slop” between these components will result in incomplete transmission of the bracket prescription to the tooth and its supporting tissues.[1] Standardization is an essential tool required for technological progress.[1] The on-going appliance evolution resulted in two orthodontic bracket slot sizes that a clinician may choose to use when correcting a patient's malocclusion today. These two dimensions, 0.018 inch (0.4572 mm) and 0.022 inch, are separated by four thousandth of an inch, a somewhat unusual description in a metric modern world, where the scientific community measures in millimeters and micrometers.

Using of undersized wires and oversized bracket may negatively affect the final three-dimensional position of the tooth.

Kusy and Whitley[2] suggested that there should be an exact description of slot geometry and standardization in SI units. The binding angle is an important factor, as if contact angle between archwires and bracket increases resistance to sliding mechanics can occur. For this the bracket slot dimension and the archwires dimensions should be precise.

The size difference in slot and the irregularities from the manufacturing process of brackets causes improper engagement of archwires leading to loss of torque control.

The purpose of the present study was to measure and check the accuracy of 0.022 inch slot brackets in stainless steel brackets and ceramic brackets of different manufacturers, both at the top and base of the slot and to evaluate the extent of variation between the reported and actual slot width.

MATERIALS AND METHODS

Twenty stainless steel and ceramic left upper central incisor brackets of MBT 0.022 inch slot from each of three different manufacturing companies (American orthodontics [AO], 3M Unitek and Ormco) were selected randomly for the evaluation of slot dimensions. The sample consists of 120 brackets in total and divided into six groups 20 in each group.

Method of study design

Each bracket was positioned on the surface of a white cardboard with 2 cm × 2 cm by means of modeling clay for its stability and marked with a number from 1 to 20 to provide a clear view of the slot walls from the side of the bracket when viewed under the stereomicroscope. The bracket manufacturing company to which it belongs to American orthodontics (AO) as shown in Figure 1, 3M Unitek as shown in Figure 2 and Ormco which were marked on the cardboard for easy identification from 1 to 20 for stainless steel and ceramic brackets

Figure 1

American orthodontics Stainless steel numbered from 1 to 20

Figure 2

3M Unitek Stainless steel numbered from 1 to 20

The brackets were viewed under a stereomicroscope of Magnus Company at × 40. Each bracket was scanned and captured individually in the stereomicroscope on both the mesial and distal sides to produce digital images of slot size. The images were exported to the computer and calibrated with Image Pro Plus analysis software.

Two points were marked at face of the bracket on its superior end and the inferior end. Similarly, two points were selected at base on its superior end and the inferior end. By doing so the software automatically produces an option to select the accurate point from which the slot dimensions at the face and base were calculated.

The images with the dimensions on the stainless steel and ceramic brackets at mesial and distal sides at face and base were captured and stored.

The dimensions of brackets from face to base were evaluated on both mesial and distal sides. Comparisons were made between stainless steel and ceramic brackets of AO, Ormco and 3M Unitek. A comparison was also made to calculate the difference between the stainless steel and ceramic brackets at mesial slot face and base, the distal slot face and base within AO, Ormco and 3M Unitek brackets. The comparisons were also made in between three different groups (AO, Ormco and 3M Unitek) at mesial and distal face and base.

The values obtained were compared to the dimensions published by each manufacturer. The values were also compared with the standard value.

RESULTS

One-way analysis of variance (ANOVA) was used to compare the mean slot width on the mesial face, mesial base and distal base of stainless steel brackets of different brands with a standard value. Results showed that all the brands showed that slot width showed higher values as compared to the standard values.

Post hoc test showed that all the brands showed a higher mesial face, mesial base and distal base slot width value of stainless steel brackets as compared to standard value. The differences were also found to be statistically significant (P < 0.05). Comparison in between groups showed that 3M Unitek brackets showed higher slot widths as compared to Ormco and AO which was statistically significant (P < 0.05) which is shown in Graph 1.

Graph 1

Multiple comparisons for stainless steel bracket at mesial face and base, distal face and base

One-way ANOVA was used to compare the mean slot width on the mesial face of stainless steel brackets of different brands with a standard value. Results showed that all the brands showed that slot width on the face of mesial side showed higher values as compared to the standard values as shown in the Table 1.

Table 1

Comparison of mean slot width on the mesial face of stainless steel brackets of different brands

	n	Mean±SD	95% CI for mean		P	Post hoc
			Lower bound	Upper bound
1. Standard	20	0.558800	0.558800	0.558800	<0.001 (Significant)	1<2-4
2. American orthodontics	20	0.561850±0.0022542	0.560795	0.562905		2>1
3. Ormco	20	0.561400±0.0022572	0.560344	0.562456		1<3<4
4. 3M Unitek	20	0.563150±0.00163	0.562387	0.563913		4>1, 3

SD: Standard deviation, CI: Confidence interval

One-way ANOVA was used to compare the mean slotwidth on the distal base of ceramic brackets of different brands with a standard value. Results showed that all the brands showed that slot width showed higher values as compared to thestandard values as given in Table 2.

Table 2

Comparison of mean slot width on the distal base of ceramic brackets of different brands

	n	Mean±SD	95% CI for mean		P	Post hoc
			Lower bound	Upper bound
1. Standard	20	0.558800	0.558800	0.558800	<0.001 (Significant)	1<2
2.American orthodontics	20	0.561500±0.0019601	0.560583	0.562417		2>1, 3, 4
3.Ormco	20	0.559350±0.0023458	0.558252	0.560448		3<2
4. 3M Unitek	20	0.559650±0.0021095	0.558663	0.560637		4<2

SD: Standard deviation, CI: Confidence interval

Post hoc test showed that all the brands showed a higher mesial face slot width value of Stainless steel brackets as compared to standard value. The differences were also found to be statistically significant (P < 0.05).Comparison in between groups showed that 3M Unitek brackets showed higher slot widths as compared to AO and Ormco which was statistically significant (P < 0.05) as shown in the Table 3.

Table 3

Post hoc tests for stainless steel mesial face

Multiple comparisons Dependent variable: Stainless steel - Mesial face (Tukey HSD)
Group	Inter group comparisons	Mean difference	SE	P	95% CI
					Lower Bound	Upper Bound
					Standard	American orthodontics	−0.0030500*	0.0005665	0.000	−0.004538	−0.001562
	Ormco	−0.0026000*	0.0005665	0.000	−0.004088	−0.001112
	3M Unitek	−0.0043500*	0.0005665	0.000	−0.005838	−0.002862
American orthodontic	Standard	0.0030500*	0.0005665	0.000	0.001562	0.004538
	Ormco	0.0004500	0.0005665	0.857	−0.001038	0.001938
	3M Unitek	−0.0013000	0.0005665	0.108	−0.002788	0.000188
Ormco	Standard	0.0026000*	0.0005665	0.000	0.001112	0.004088
	American orthodontics	−0.0004500	0.0005665	0.857	−0.001938	0.001038
	3M Unitek	−0.0017500*	0.0005665	0.015	−0.003238	−0.000262
3M Unitek	Standard	0.0043500*	0.0005665	0.000	0.002862	0.005838
	American orthodontics	0.0013000	0.0005665	0.108	−0.000188	0.002788
	Ormco	0.0017500*	0.0005665	0.015	0.000262	0.003238

*The mean difference is significant at the 0.05 level. HSD: Honestly significant difference, CI: Confidence interval, SE: Standard error

Post hoc test showed that all the brands showed a higher mesial face and base, distal face, and base slot width value of ceramic brackets as compared to standard value. The differences were also found to be statistically significant (P < 0.05). Comparison in between groups showed that AO brackets showed higher slot widths as compared to Ormco brackets which was statistically significant (P < 0.05) as given in Table 4 and Graph 2.

Table 4

Post hoc tests for ceramic distal base

Multiple comparisons Dependent variable: Ceramic - Distal base (Tukey HSD)
Group	Inter group comparisons	Mean difference	SE	P	95% CI
					Lower bound	Upper bound
					Standard	American orthodontics	−0.0027000*	0.0005873	0.000	−0.004243	−0.001157
	Ormco	−0.0005500	0.0005873	0.785	−0.002093	0.000993
	3M Unitek	−0.0008500	0.0005873	0.474	−0.002393	0.000693
American orthodontics	Standard	0.0027000*	0.0005873	0.000	0.001157	0.004243
	Ormco	0.0021500*	0.0005873	0.003	0.000607	0.003693
	3M Unitek	0.0018500*	0.0005873	0.012	0.000307	0.003393
Ormco	Standard	0.0005500	0.0005873	0.785	−0.000993	0.002093
	American orthodontics	−0.0021500*	0.0005873	0.003	−0.003693	−0.000607
	3M Unitek	−0.0003000	0.0005873	0.956	−0.001843	0.001243
3M Unitek	Standard	0.0008500	0.0005873	0.474	−0.000693	0.002393
	American orthodontics	−0.0018500*	0.0005873	0.012	−0.003393	−0.000307
	Ormco	0.0003000	0.0005873	0.956	−0.001243	0.001843

*The mean difference is significant at the 0.05 level. HSD: Honestly significant difference, CI: Confidence interval, SE: Standard error

Graph 2

Multiple comparisons for ceramic bracket at mesial face and base, distal face and base

DISCUSSION

According to Major et al.,[5] the speed brackets were marginally less in size near the base, i.e., 0.556 mm (0.0222 inches) with marked rounding and broad fillets when the base joins wall and minimal. The bracket company GAC In-Ovation measurement was 0.564 mm at the base resembling a trapezoidal shape. Among the manufacturing tolerance by a bracket Damon Q's base was found to be 0.572 mm (0.0225 inches) with maximum values. Of all the three tested bracket companies Damon Q's base was recorded to be 0.572 mm (0.0225 inches) which were right angled corners with rounded internal lines.

Brown et al.[8] has examined ten bracket series from different manufacturers of 0.022 inch and 0.018 inch, for which the Opal ovex of 0.018 inch slot had average closest to the nominal stated value. For 0.022 inch slots, the closest average sizes were AO mini masters was 0.0001 inch undersized. GAC innovation has smallest standard deviation; a company bracket has largest standard deviation.

By measuring five upper left central 0.022-inch self-ligating brackets of six different bracket series in Bhalla et al.[4] study, the brackets taken from four different manufacturers found the dimensions of bracket to be between 5% and 15% larger than the mentioned values. They reported the brackets to be and that slot walls diverged from the base to the top of all the brackets. It was noted that brackets from the same manufacturer may vary in size as well.

When comparing Kusy and Whitley[23] study which was done with 24 unique bracket series from eight different companies of three different brackets unspecified. Three different slot sizes of 0.018, 0.0185, and 0.022 inches from four various materials. The final data showed that 15% of the brackets were smaller than actual and slot sizes exceeded the nominal value by as much as 16% and 8%. A clear understanding about the consequences faced due to inaccurate dimensions of the bracket may lead to incorrect finishing. In the present study AO SS bracket showed the mean value of 0.561850 mm ± (0.0022542) at the mesial face, 0.561850 mm ± (0.0019808) at distal face, mesial base 0.560800 mm ± (0.0020926), at the distal base 0.560800 mm ±0.0022384.

Whereas AO ceramic brackets on mesial face shows a mean value of 0.562400 mm ± 0.0021861 mm, mesial base showed a mean value of 0.561350 mm ± 0.0020844 mm, distal base showed 0.561500 mm ± 0.0019601 mm.

Pai et al.[6] found that the 3M Unitek and Ormco brackets of both 0.022 inch and 0.018 inch slot of Roth prescription showed wider at the face than at the base indicating walls divergent from base of the bracket. The slot size for Ortho Organizer 0.018 inch and 0.022 inch slot brackets was close to the standard values.

In contrary the present study Ormco stainless steel brackets at mesial face showed mean value of 0.561400 mm ± (0.0022572), distal face showed an increased value of shows a mean value of 0.561900 mm ± (0.0022455), mesial base showed 0.560450 mm ± (0.0025348), distal base showed an increased value of a mean value of 0.560600 mm ± (0.0025423) distal face showed 0.562450 mm ± (0.0019861).

Likely Ormco ceramic brackets at mesial face showed a mean value of 0.560700 mm ± (0.0020800), distal face shows a mean value of 0.560950 mm ± (0.0022589), mesial base 0.559100 mm ± (0.0021001), distal base shows a mean value of 0.559350 mm ± (0.0023458).

Tangri et al.[7] have found that there was a significant difference in the slot size between the mesial and distal aspects of MBT 0.022 inch slot Equilibrium brackets, Sapphire brackets and Leone brackets except 3M Unitek brackets and Ortho organizer brackets. He concluded that the results of this study indicated that orthodontic bracket slots were different than stated by the manufacturers.

In the present study 3M Unitek stainless steel 0.022 inch brackets showed increase in slot size at mesial and distal face and base. 3M Unitek SS brackets at mesial face of 3M Unitek shows a mean value of 0.563150 mm ± (0.0016311), mesial base of 0.562400 mm ± (0.0016983), distal face of 3M Unitek shows a mean value of 0.563450 mm ± (0.0012344), distal base of 3M Unitek shows a mean value of 0.562350 mm ± (being 0.0013485).

3M Unitek ceramic brackets mesial face shows a mean value of 0.561150 mm ± (0.0022775), distal face shows mean value of 0.561550 mm ± (0.0023050), mesial base shows a mean value of 0.559250 mm ± (0.0019160), distal base shows a mean value of 0.559650 mm ± (0.0021095).

CONCLUSION

In summary, the results of this study indicate that orthodontic bracket slots were all larger than stated by the manufacturers.

The overall slot widths for SS brackets at mesial base and face and distal base and face were greater for 3M Unitek

The overall slot widths for Ceramic brackets at mesial base and face and distal base and face were greater for AO

This research considers the evident lack of standardization of these accessories during manufacturing process, which may be clinically associated with undesirable changes in tooth positioning and movement.

Therefore, it is suggested to conduct studies that investigate this lack of standardization of torque and angulations as specified by the manufacturers for straight-wire brackets with different prescriptions.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.