Comparative evaluation of torque prescription of commercially available 018Roth and 022MBT PEA brands in maxillary anterior teeth

Abstract

Background

Torque is an important component of preadjusted edgewise prescriptions to achieve ideal/optimum tooth position and more so in aesthetics sensitive maxillary anterior teeth. Thus, the need to audit available commercial brands of 018Roth and 022MBT was felt and in vitro analysis of eight brands namely 3M Unitek, Dentaurum, d-tech, IMD Medical, Libral Leone, Modern Orthodontics, Ormco and Ortho Organizer, was carried out.

Methods

The method involved perfect superimposition of two standardized images: one delineating facial axis of the tooth with stainless steel straight wire and other with full dimension arch wire engagement in bracket. The two images were superimposed and opacity of one of the images altered using Adobe Photoshop software to reveal the position of two wires. The angle obtained between two wires gave a direct read-out of torque expression. The comparison was statistically done with one-way ANOVA and Tukey's HSD test.

Results

In 018Roth group, IMD Medical did not show any significant difference from the standard while comparison independent of standard showed that IMD, Modern Orthodontics and Ormco were not significantly different from each other. In 022MBT group, IMD Medical, d-tech, 3M Unitek and Modern Orthodontics did not have statistically significant difference from and independent of standard.

Conclusion

Significant variations from the standard values of both 018 Roth and 022 MBT exist in the market products and thus selection of product must be based on proper guidance in addition to clinical acumen/experience. Also the methodology provides easy to use, inexpensive set-up in the clinical settings.

Introduction

The lower third of the face and maxillary anterior teeth are vital for social communication and aesthetics. One of the main aims and patient requirement of orthodontic treatment is to reposition maxillary anterior teeth to achieve optimum aesthetics. The difficulties in obtaining satisfactory treatment results with the standard edgewise technique resulted in the development of brackets with in-built prescription in the 1960s.

Several attempts at building treatment into the appliance were made in the first half of the 20th century^{1, 2, 3, 4} but the first real effort to present a structured assessment was made by Andrews.⁵ His description of the ‘Six Keys to Normal Occlusion’ and development of the first fully programmed appliance system ushered a new era in the history of Orthodontics.

Andrew's straight wire appliance was modified by Roth^{6, 7} and later by McLaughlin (MBT)^{8, 9} to overcome the short comings of original straight wire appliance. These two appliance systems named after their inventors; Roth and MBT pre-adjusted appliance (PEA) system, are the mainstay of orthodontic mechano-therapy.

Most orthodontic treatment is undertaken with less than full-sized archwires and consequently, some lack of control exists. If this is coupled with inaccuracies in the manufacture of these brackets the undesirable results such as undue torque loss in the maxillary anterior segment can be profound.¹⁰

Today the market is flooded with numerous brands manufacturing/marketing Roth and MBT PEA available in varied costs. But, very few studies^{11, 12, 13, 14, 15} have tried to study the efficacy of these different brands in delivering the prescribed scientific specifications; torque in question in present study, with no direct study in clinically relevant set-up.

The aim of the present study was to evaluate the efficacy of eight different brands of Roth 018 and MBT 022 PEA systems in delivering the prescribed torque in maxillary anterior teeth under standard experimental set-up with the primary objective of inter-brand comparative evaluation of torque expression and comparison of each brand in each group with the standard prescription of Roth 018 and MBT 022 PEA systems respectively. The commonly used brands in the Indian market were selected to have an overview of their efficacy. The cost of these examined brands varied by a factor of 1.5–5.

Material and methods

Thirty maxillary anterior teeth (N = 30) with normal anatomy comprising five of each tooth type i.e. right and left, PEA systems of 3M Unitek, Dentaurum, D-tech, IMD Medical, Libral Orthodontics (Leone), Modern Orthodontics, Ormco and Ortho Organizer of Roth 0.018 (torque 12°, 8°, −2°) and 0.022″ MBT (torque 17°, 10°, −7°), 0.018″ × 0.025″, 0.022″ × 0.028″, 0.016″ × 0.022″ stainless steel (SS) wires, light cure adhesive (Enlight from Ormco), uniform sized plastic containers, digital read-out vernier calliper, stationary items, orthodontic armamentarium, digital camera, standard set-up for image acquisition and a computer with Adobe Photoshop software.

Thirty selected teeth were marked on the labial side horizontally (denoting the height of the bracket for Roth and MBT) and vertically (along the facial axis of the crown of the tooth) with the red and black permanent marker respectively. The intersection of these two markings formed the location for placement of the bracket. Each tooth was partially embedded in the Plaster of Paris (POP) block in plastic containers. The tooth was placed in such a way that it resembled as close as possible to the tooth emerging from the maxillary alveolus with root embedded in the POP and crown exposed out (Fig. 1). Each tooth was marked with the label for identification on the top and lateral surface of block, e.g. for right upper central incisor as RUCI 1, RUCI 2, RUCI 3, RUCI 4 and RUCI 5.

Fig. 1.

Tooth marked labially in two planes and lateral view of POP block for image acquisition.

The 0.016″ × 0.022″ SS straight length arch-wire was cut into 30 parts of 2–3 in. each and one segment was fixed on each tooth at the marked location carefully with light cure composite ensuring that wire is tangent to the point of intersection of horizontal and vertical guidelines, to resemble parallelism with the facial axis (Fig. 2). Fig. 3 shows the standardization procedure; platform for placing camera and plaster blocks at the fixed distance with anti-rotation mechanism for plaster blocks to ensure uniform placement of each block throughout the experiment and full dimension bent wires with digital read-out of dimensions. Then each tooth block with 016″ × 0.022″ straight SS wire placed along its facial axis, as shown in Fig. 2, was placed at the marked location and imaged with the camera. No alterations were done in the image and these 30 images were stored as the base folder. After this, these wires were removed and any attached composite on tooth surface was gently removed and the diminished markings on the tooth surface were re-done.

Fig. 2.

0.016 × 0.022 straight wire delineating facial axis of the sample.

Fig. 3.

Standardized platform for image acquisition and full dimension wires with digital read-out of values.

A 2″ length of 0.018″ × 0.025″ and 0.022″ × 0.028″ wire, as shown in Fig. 3, was bent at right angle (L-shaped) using Tweed ribbon arch plier ensuring 90° bend with no introduction of torque. This was followed by the testing procedure.

The brackets of each brand were placed at the marked location on the tooth with light cure composite (Fig. 4). The L-shaped wires of 0.018″ × 0.025″ and 0.022″ × 0.028″ were engaged in the respective brackets firmly using 0.010″ SS ligature. One bracket brand in each category was tested at a time. The images were obtained for each brand of Roth and MBT, and stored in the respective folders in the computer without any alteration. This led to formation of 16 folders, 08 each for 018 Roth and 022 MBT.

Fig. 4.

Sample image of brackets bonded on pre-marked location on tooth.

The images from each brand folder were superimposed on the corresponding images of the base folder using Adobe Photoshop image software. Since the images were standardized, perfect superimposition was achieved. Thereafter, opacity of one of the superimposed image was changed using the software. This revealed the position of the two wires i.e. one placed along the facial axis and the other engaged in the bracket slot. Fig. 5 vividly describes the experimental procedure of image acquisition and their processing.

Fig. 5.

Vivid description of image acquisition, superimposition and software modulation.

The print-out of these images was taken and the angle formed by these two wires was measured manually using Camel protractor to an accuracy of 0.5°. This angle provided the read-out of the torque expression of particular bracket brand (Fig. 6). The data collected was compiled and subjected to further statistical evaluation.

Fig. 6.

Angle between two wires and its direct read-out as torque expression.

Results

Based on the Null hypothesis that there is no variation in the torque expression of different commercial brands of Roth 018 and MBT 022 PEA, the data obtained were statistically analyzed using one way ANOVA for multiple group simultaneous comparison and Tukey's HSD for group wise comparison. The examined commercial brands were compared with the standard prescription and independent of standard. Table 1, Table 2 gives the results for Roth 018 and MBT 022 respectively. p value of <0.05 was considered significant.

Table 1.

Roth 018 brands comparison with standard and independent of standard.

Roth 018 brands comparison with the standard
Brands	N	Mean	SD	Mean differencea	‘p’ value	95%CI of mean diff
Comparative value		22.00
3M Unitek	30	13.10	1.626	8.90	0.000	5.30	12.49
Dentaurum	30	13.80	1.217	8.20	0.000	4.60	11.79
D-tech	30	16.45	0.694	5.55	0.000	1.95	9.15
IMD	30	19.30	1.643	2.70	0.391	0.89	6.30
Libral Leone	30	16.05	1.849	5.95	0.000	2.35	9.55
Modern Orthodontics	30	17.50	3.240	4.50	0.004	0.90	8.10
Ormco	30	18.05	1.462	3.95	0.020	0.35	7.55
Ortho Organizer	30	13.45	1.022	8.55	0.000	4.95	12.15

Roth 018 inter-brand comparison independent of standard
Group	Subset for alpha = 0.05
	1	2	3
3M Unitek	13.100
Ortho Organizer	13.450
Dentaurum	13.800
Libral Leone	16.050	16.050
D-tech	16.450	16.450
Modern Orthodontics		17.500
Ormco		18.050
IMD		19.300	19.300
‘p’ value	0.061	0.076	0.225

Table 2.

MBT 022 brands comparison with standard and independent of standard.

MBT 022 brand comparison with the standard
Brands	N	Mean	SD	Mean differencea	‘p’ value	95%CI of mean diff
Comparative value		34.00
3M Unitek	30	30.60	2.929	3.40	0.943	3.04	9.84
Dentaurum	30	21.10	3.044	12.90	0.000	6.46	19.34
D-tech	30	31.35	2.702	2.65	0.998	3.79	9.09
IMD	30	33.40	4.303	0.60	1.000	5.84	7.04
Libral Leone	30	25.40	2.748	8.60	0.002	2.16	15.04
Modern Orthodontics	30	28.40	2.924	5.60	0.159	0.84	12.04
Ormco	30	24.20	3.493	9.80	0.000	3.36	16.24
Ortho Organizer	30	26.10	2.485	7.90	0.005	1.46	14.34

MBT 022 brands comparison independent of standard
Group	Subset for alpha = 0.05
	1	2	3	4
Dentaurum	21.100
Ormco	24.200	24.200
Libral Leone	25.400	25.400	25.400
Ortho Organizer	26.100	26.100	26.100
Modern Orthodontics		28.400	28.400	28.400
3M Unitek			30.600	30.600
D-tech			31.350	31.350
IMD				33.400
‘p’ value	0.190	0.395	0.064	0.098

Result for Roth 018 (Table 1)

IMD Medical did not show any significant difference with the average value of 19.30 against standard value of 22. Ormco, Modern Orthodontics, d-tech and Libral Leone were not significantly different from each other but had statistically significant variation from IMD Medical and standard while Dentaurum, Ortho organizer and 3M Unitek were weakest in all comparison. The descending order of efficient torque expression was as: IMD > Ormco, Modern Orthodontics > d-tech, Libral Leone > Dentaurum, Ortho organizer, 3M Unitek.

Result for MBT 022 (Table 2)

IMD, d-tech, 3M Unitek and Modern Orthodontics did not have statistically significant difference while Dentaurum, Libral Leone, Ormco and Ortho organizer showed statistically significant difference from the standardized prescription. Dentaurum showed statistically significant difference from all others scoring the lowest value in MBT 022 interbrand comparison independent of standard. The descending order of efficient torque expression was as: IMD, D-tech, 3M Unitek, Modern Orthodontics > Ortho organizer, Libral Leone > Ormco, Dentaurum.

Discussion

Andrews⁵ did an extensive study to derive first true straight wire appliance (SWA) which was a significant development over the conventional edgewise appliance as it aimed at achieving level slot line-up without wire bending. Andrews demonstrated that the third key i.e. labio-lingual inclination of teeth to the occlusal plane had significant implication on the space requirement in the dental arch. Insufficient torque in the upper labial segment might lead to unclosed space distal to the canines or where if all the spaces were closed the buccal segment relationship might not be Class I. This clearly signifies the importance of torque in the maxillary anterior segment.^{5, 10}

Dr. Roth after using Andrews appliance for 17 years made certain modifications in the appliance to make it more user friendly. Roth chose Andrews minimum extraction series brackets and produced the Roth prescription with torque values for maxillary anterior teeth as 12°, 8° and −2°, for all clinical situations.^{6, 7}

Similarly, based on their clinical experience of 18 years with SWA, McLaughlin, Bennet & Trevisi (MBT) introduced another prescription for sliding mechanics in 0.022″ slot with 0.019″ × 0.025″ working archwire.^{8, 9} The MBT prescription for torque in maxillary anterior segment was 17°, 10° and −7°.

These two appliances i.e. Roth and MBT have become the mainstay of conventional orthodontic therapy. Each of these modifications in the original SWA had their positives over the Andrews appliance to make it more result oriented in the shortest possible time with minimum inventory. Thus, the products in the market should be able to match-up to these prescribed standards to meet the expected end result.

This research project was aimed at comparative evaluation of torque prescription of eight commercially available products in the Roth 0.018 and MBT 0.022 category. The choice of MBT 0.022 and Roth 0.018 was based on the fact that MBT was introduced for sliding arch mechanics in 0.022″ slot with 0.019″ × 0.025″ working wire while Roth is used more often in segmental arch mechanics.

According to Andrews,¹⁶ Creekmore et al.¹⁷ the most important reason for inability to achieve ideal result with the SWA was due to inaccurate bracket positioning. To overcome this inaccuracy in this experiment all the brackets of each brand were placed at the pre-determined and marked location on the tooth under in vitro conditions,^{6, 8, 9} thus eliminating the possibility of inaccuracy in the result that can stem-up because of this.

Miethke et al.¹⁸ stressed on the need of custom made brackets and full-sized archwire use for maximum torque expression. Since this project involved the testing of torque expression of commercially available different products, full-sized archwire was used to differentiate between under or over torqued prescription.

Loenen et al.,¹⁹ Vigorito et al.,²⁰ and Mestriner et al.²¹ tried to ascertain the influence of vertical displacement of bracket on the torque expression and showed wide variations can be present. They concluded that placement of a bracket on a tooth at varying heights, within a clinically acceptable range, resulted in considerable differences in the amount of torque expressed. On an average, 1-mm vertical shift of the brackets from occlusal to cervical affected the torque values, by approximately 2° in central and lateral incisors, 3° in canines and 8° in premolars and molars.²⁰

But in the present experimental study the brackets were placed at the pre-determined, precisely marked locations,^{6, 8, 9} so the possibility of inadvertent placements, as it can happen in the oral cavity, was minimal. Still 0.5 mm vertical displacement error was taken into consideration which could have resulted from the mild angular variation of the bracket positioning gauze and remained indistinguishable from the marked position on the tooth surface. This was taken into consideration during analysis of the results.

Many studies have been conducted on the influence of tooth morphology on torque expression, effect of vertical shifts of brackets on same tooth surface or few other factors.^{16, 17, 19, 20, 22} But, few have tried to evaluate the torque prescription of these commercial products.^{11, 12, 13, 14}

Streva et al.¹¹ evaluated the metallic brackets of MBT 0.022 prescription from six commercial brands; namely 3M Unitek, Abizil, American Orthodontics, TP Orthodontics, Morelli and Ortho organizer, for maxillary and mandibular canines. The methodology adopted comprised measurement of angle between lines made from reference points located at the bracket base and slot of the bracket. The images of the brackets mounted on the acrylic plates were obtained using a microscope coupled to computer with a CCD camera and image acquisition board. The images obtained by microscope were analyzed and whenever it was not possible to visualize the images adequately, they were submitted to the software filters.

The authors found that Morelli represented significant torque variation in the maxillary canines while American Orthodontics and Ortho Organizer presented statistically significant variations in the mandibular canines.

The common products in two studies included 0.022 MBT 3M Unitek and Ortho Organizer. In both the studies the results are similar for 3M Unitek while for Ortho Organizer our results are intermediate. This variation in result can be attributed to the sample of present study spread over all upper anterior teeth in contrast to Streva et al., in which sample is confined to canines only.

Moreover, the methodology adopted by Streva et al.¹¹ involves image magnification to locate reference points and lines, which itself can introduce errors. As brought out by authors, at times images were not vivid enough thus needed editing and exact location of reference points can be misjudged by this method thus introducing error in the final read-out. Further, the method is capable of measuring the torque in the face only and the authors failed to mention whether the torque in the brackets was present in the face or base or both.

In present study, the position of bracket on a tooth is uniform across all the 8 products of one system thus giving exact actual difference in the torque expression across the spectrum. The read-out of result did not involve any magnification and the images acquired were not subjected to any modification. Thus, there were no associated problems such as poorly visualized images, inability to locate reference points or torque in face/base dilemma.

Moreover, this work took into consideration the entire upper anterior teeth brackets of right and left side giving more comprehensive evaluation of the product and thus qualifies better to comment on a product compared to Streva et al.

Kusy et al.¹² measured 24 brackets from eight manufacturers microscopically, to the nearest 0.0001″ and found that while three bracket slots were smaller than the stated sizes, 20 others exceeded the stated sizes. The largest 0.018″ slot actually measured 0.0209″—nearly 0.003″ oversized. The largest 0.022″ slot measured 0.0237″, or almost 0.002″ oversized. Although, we did not measure the slot size of the products in consideration it is likely that some may have oversized slots. None of the products in present study can be said to have undersized slots since full dimension archwire was accommodated into them.

Kusy et al.¹² study is not a direct comparison with present study but shows the considerable manufacturing errors in the bracket slots. It can be agreed upon that if the bracket slot is oversized even the full dimension archwire will not be able to express full prescription and if it is coupled with the flaws in prescription incorporation into the appliance, the adverse influence on expression will be further compounded. In clinical settings where undersized wires are used, oversized bracket slots are likely to have adverse impact on the expression of the prescription¹⁰ and gets compounded further when the prescription in the brackets itself is short of the recommended values.^{7, 9}

Cash et al.¹³ evaluated the slot size of orthodontic brackets of upper left central incisor from eleven commercially available conventional, aesthetic and self-ligating bracket systems in the 0.022″ dimension. The authors found that all the bracket slots were oversized. Out of 11 commercial products only 3 were within 5% of their slated dimensions and the others were oversized by 12–24%. The bracket slots were not only oversized but the geometry of bracket slots was also variable with convergent or divergent walls.

This method again was not a direct method of torque expression measurement but indirectly indicated that torque expression of these examined products cannot be optimal. Moreover, for torque expression it the orientation of bracket slot to the base or bracket base itself or combination which determines the torque in the bracket. To measure the slot size is not adequate for this purpose because even the conventional edgewise brackets with no built-in prescription can give results similar to PEA brackets in term of slot size measurement.

The results in the present study were consistent in terms of results obtained by Cash et al.¹³ although there is no direct comparison. In this study only one of eight products i.e. IMD Medical in Roth 0.018″ and four of eight products i.e. IMD Medical, D-tech, Modern Orthodontics and 3M Unitek in MBT 0.022″ group were not significantly different from the standard.

Pai et al.¹⁴ evaluated slot size of 4 different available commercial straight wire brackets in 0.018″ and 0.022″ Roth prescription namely 3M Unitek, TP Orthodontics, Ormco and Ortho Organizer. The methodology seems similar to that adopted by Cash et al. The authors found that slot of 0.018 Ortho Organizer was very close to standard while all others were either oversized or undersized significantly. Similarly, the slot size differed at the top and base as recorded by Cash et al.¹³

The results in the present study are also consistent with this study except that Ortho Organizer fared poorly in our study and the torque expression was significantly different from the standard.

The present study took into consideration evaluation of torque on individual tooth at a time and not on combined teeth in an arch. The torque expression in an individual tooth may not be exactly translated in the actual clinical settings. But, the better the appliance and close to the prescribed standards the better will be the chances of translation in actual setting.

As stated by Kapur et al.,²³ various physical and mechanical factors affecting torque control are the bracket material, slot size and design, the degree of play between the bracket and the wire, ligation, inter-bracket distance and the manufacturing process. The present study did not evaluate various physical and mechanical factors, as outlined above, affecting torque control and thus need independent evaluation. Since the cost of these products varies by a factor of 4–5, the material quality may be of some significance in final outcome.

In this study, the individual tooth variation in torque expression was minimum for central incisor and maximum for lateral incisor. This was observed uniformly across various brands. No other study has evaluated lateral incisor brackets for their slot size or torque expression ability and thus comparison with other studies is not possible. The reasons that can be attributed to this are the variable size and shape of lateral incisors, inadequate torque in brackets or oversized slots. This variability in the lateral incisor brackets to adequately express the required torque may be one of the reasons of failure to achieve correct labio-lingual position of the palatally blocked lateral incisors despite engagement of full dimension wires.

Conclusion

An important observation in this study was that 0.018 Roth 3M Unitek appliance was marketed with torque values of 14°, 8°, 0°, inconsistent with standard Roth 018 prescription, for central incisor and canine. The results showed that canine torque values were within normal limits but the values for central incisor were too less when compared with their brand value of 14° and the values for lateral incisors were also significantly less. Thus, overall value for product comes out to be 22 (14 + 8 + 0) against which the derived value of the product was compared for statistical evaluation. Thus, 3M Unitek is an exception product in the 0.018 Roth PEA group whose selection should be critically examined besides the statistical result.

Though some of the results are not statistically different amongst few brands, the clinical implications may be profound. The clinician must choose the product taking into consideration the results of this study and his clinical acumen. Thus, the present study can be a good guide to select the optimal commercial product in the 0.018″ Roth and 0.022″ MBT group in terms of torque requirements.

Another greatest advantage of this study is that, the experimental set-up in the study is designed for use in day-to-day clinical setting. This set-up can be made at the miniscule cost with available infrastructure in the clinic, do not need extra/special storage and can be used indefinitely. Any new bracket brand launched/intended for use can be conveniently tested and its merit decided upon.

Thus, significant variations from the standard values of both 018 Roth and 022 MBT exist in the market products. The present study, in addition to operators’ clinical acumen is an excellent guide to select optimal commercial brand of 018 Roth and 022 MBT in terms of torque requirement for maxillary anterior teeth. The methodology provide easy to use, inexpensive set-up in any clinical setting, giving each orthodontist his personal test lab and ability to evaluate cost-benefit ratio. The work in this study has taken into consideration only individual bracket torque expression when ligated in the slot, the most important factor determining torque expression, at pre-determined location on tooth surface while other factors affecting torque expression like bracket material and manufacturing process were beyond the scope of this work.

Conflicts of interest

The authors have none to declare.