The dimensions of preformed nickel-titanium archwires measured at the bracket positions corresponding to the central incisor, canine, and first molar

Introduction

Variation in the thickness of commercially available preformed rectangular archwires at the bracket positions has not been thoroughly studied. Therefore, this study measured the edgewise (height) and flatwise (width) dimensions of preformed rectangular nickel-titanium (NiTi) archwires at bracket positions corresponding to the central incisor, canine, and first molar and compared them among bracket positions.

Methods

Sixty types of preformed rectangular NiTi mandibular archwires indicated as 0.019 × 0.025-in were obtained from 14 manufacturers. The height and width dimensions of archwires were measured at 4 points (3 bracket positions corresponding to the central incisor, canine, and first molar, and 1 terminal end) of each side of each archwire using a micrometer and compared with the indicated dimensions using 1-sample t tests. Furthermore, the measured dimensions were compared among the 3 bracket positions using a 1-way analysis of variance and Bonferroni post-hoc test.

Results

The measured dimensions were significantly smaller than the indicated dimensions for all points except the central incisor point for height and significantly smaller than the indicated dimensions for all points for width. Comparisons among points showed that for height, the central incisor point was significantly larger than the first molar and terminal points. However, no significant differences were found for width at any point.

Conclusions

The measured dimensions of preformed NiTi archwires at the bracket positions were generally smaller than the indicated dimensions, with variations observed not only among products but also among manufacturers.

Highlights

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The dimensions of preformed nickel-titanium archwires were measured at 3 bracket positions.
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The measured dimensions tended to be smaller than the indicated dimensions.
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The measured dimensions varied among the points, and the central incisor was the largest.

After the development of the straight-wire appliance, preformed archwires have been used to facilitate archwire bending. When preformed archwires are ligated to the brackets, the teeth move according to the in-out, tip, and torque prescriptions built into the brackets. Therefore, the size of the archwire plays a crucial role in precisely controlling a tooth’s 3-dimensional position.

Discrepancies between the indicated and actual edgewise (height) and flatwise (width) dimensions of a bracket slot and the archwire can directly impact the play among them, potentially compromising the reliability and predictability of tooth movement in preadjusted brackets. Therefore, ensuring a close match between indicated and actual dimensions is essential.

Several previous studies have observed that the height of the bracket slots is greater than the dimensions indicated on each product. For example, in a recent study by Park et al an optical microscope was used to measure the heights of slots of 800 pieces of 4 types of metal injection molding brackets, and it was found that the heights of slots for all types of evaluated brackets were 2.6%-10.4% larger than the indicated dimensions.

In contrast, archwire dimension measurements have varied among previous studies, with some manufacturers producing larger dimensions and others smaller dimensions. For example, Tepedino et al cut 60 stainless-steel preformed rectangular archwires (0.019 × 0.025-in and 0.021 × 0.025-in) obtained from 3 manufacturers into 4-cm sections from the ends and precisely measured the height and width dimensions. The dimensions of these sections were measured using scanning electron microscopy and image processing software. Overall, they found most archwires to be 0.4%-1.4% undersized, but oversized archwires produced by 1 of the 3 manufacturers were also observed.

In most previous studies ^, ^, investigating this issue, the straightest parts of each archwire, which are the terminal ends of the archwire, were measured to prevent the possible effects of abnormal deformation of the cross-sectional shape because of bending during the manufacturing process. However, more anterior curved segments of preformed archwires should be investigated because these segments are where orthodontists place the archwire into the brackets.

The present study investigated differences in the dimensions measured at the bracket positions of preformed rectangular nickel-titanium (NiTi) archwires and the indicated dimensions. Furthermore, the present study compared the dimensions measured at the bracket positions corresponding to the central incisor, canine, and first molar among all points.

Two null hypotheses were considered: (1) there is no difference between the measured dimensions and the indicated dimension and (2) there is no difference between the dimensions measured at the bracket positions corresponding to the central incisor, canine, and first molar.

Material and methods

In this study, 0.019 × 0.025-in preformed archwires were measured; as such, archwires are commonly used in the later stage of the leveling and aligning phase with 0.022-in slot brackets.

Unlike previous studies, ^, ^, which measured preformed archwire dimensions using the terminal end, this study measured the dimensions of the archwires at bracket positions corresponding to the central incisor, canine, and first molar.

In this study, a template was fabricated to determine the bracket positions corresponding to the central incisor, canine, and first molar of the dental arch on the basis of the bracket slot (BS) points at the bottom of the bracket slots ( Fig 1 ). The mean canine depth (4.84 ± 0.70 mm) and mean first-molar depth (26.66 ± 1.57 mm) of normal occlusion were used on the basis of previous studies.

First, a reference horizontal line was drawn on graph paper (x-axis). A line was drawn perpendicular to the horizontal line (y-axis), and the intersection of the lines was used as the origin point. The points indicating the mean canine depth and mean first-molar depth of a normal occlusion from the origin point were plotted on the y-axis, and a line was drawn orthogonally to the y-axis. In addition, based on previous studies, ^, ^, the terminal point was also measured. To determine the terminal point of the preformed archwire, a point 50 mm from the origin point was plotted on the y-axis, and a line was drawn orthogonally to the y-axis as well.

In total, 60 types of 0.019 × 0.025-in preformed rectangular NiTi alloy mandibular archwires from 14 different manufacturers available in Japan as of April 2022 were selected. A list of the preformed archwires used is shown in Table I .

Table I

The 60 types of preformed archwires from 14 manufacturers

No.	Product name	Manufacturer
1	Ortho Form II	3M Unitek Orthodontic Products, Monrovia, Calif
2	Ortho Form III
3	Smooth Arch Form	Acme Monaco, New Britain, Conn
4	Natural Arch Form I	American Orthodontics, Sheboygan, Wis
5	Natural Arch Form II
6	Natural Arch Form III
7	TANZO Low Force Natural Arch Form I
8	TANZO Low Force Natural Arch Form III
9	TANZO Mid Force Natural Arch Form I
10	TANZO Mid Force Natural Arch Form III
11	VLP Arch
12	M-flex	Daeseung Medical, Seoul, South Korea
13	Proform	Dynaflex, St Ann, Mo
14	Euro smile	Forestadent, Pforzheim, Germany
15	McLaughlin Bennett 5.0 Ovoid Form
16	McLaughlin Bennett 5.0 Square Form
17	McLaughlin Bennett 5.0 Tapered Form
18	Straight Arch Form
19	Bioform I	G & H Wire, Franklin, Ind
20	Bioform II
21	Bioform III
22	Bioform IV
23	Bioform V
24	Europa Form I
25	Europa Form II
26	Europa Form II (Damon)
27	Trueform I
28	Trueform II
29	Euroform	Lancer Orthodontics, Vista, Calif
30	Trueform
31	Broad Arch Form Large 27°C CuNiTi	Ormco, Glendora, Calif
32	Broad Arch Form Large 35°C CuNiTi
33	Broad Arch Form Large 40°C CuNiTi
34	Broad Arch Form Large NT
35	Broad Arch Form Small 27°C CuNiTi
36	Broad Arch Form Small 35°C CuNiTi
37	Broad Arch Form Small 40°C CuNiTi
38	Broad Arch Form Small NT
39	Orthos Arch Form Large 35°C CuNiTi
40	Orthos Arch Form Large 40°C CuNiTi
41	Orthos Arch Form Large NT
42	Orthos Arch Form Small 35°C CuNiTi
43	Orthos Arch Form Small 40°C CuNiTi
44	Orthos Arch Form Small NT
45	Tru-Arch Large 27°C CuNiTi
46	Tru-Arch Large 35°C CuNiTi
47	Tru-Arch Medium NT
48	Tru-Arch Small 27°C CuNiTi
49	Tru-arch Small 35°C CuNiTi
50	Tru-Arch Small NT
51	ProForm	Ortho Organizers, Carlsbad, Calif
52	Natural arch	Rocky Mountain Orthodontics, Denver, Colo
53	S Arch Form	Shofu, Kyoto, Japan
54	Accu Form	Tomy International, Tokyo, Japan
55	Bio-Arch I	TP Orthodontics, La Porte, Ind
56	Bio-Arch II
57	Bio-Arch III
58	Bio-Arch V
59	Straight Arch Form
60	Straight Arch II Form