Deformation of nickel-titanium closed coil springs: an in vitro study

A total of 130 springs were divided into 13 subgroups, according to their features and manufacturers (Morelli, Orthometric, Ormco and GAC) and activated from 100% to 1000% of the effective length of the nickel-titanium portion present at the spring, at 37 °C. Deactivation data were plotted and deformation was found graphically. The values were compared by analysis of variance and Tukey's post-hoc test.

Results:

Springs manufactured by Morelli had the same amount of deformation when they were activated up to 700% of Y activation; springs by Orthometric had the same amount of deformation up to 600-700% of Y; springs by Ormco had the same amount of deformation up to 700-800% of Y; and finally, the majority of springs by GAC had similar deformation up to 800%-1000% of activation. All springs tested could be activated up to 700% without rupture.

Conclusions:

Most subgroups were similarly deformed up to 700% of activation, without rupture of springs. Subgroups 4B, 4C, 4D and 4E showed the same amount of deformation up to 1000% of activation without any rupture at all.

Keywords:
NiTi; Deformation; Biomechanics.

Authorship

Camilla Ivini Viana Vieira

MSc,Universidade Estadual Paulista (UNESP), Department of Pediatric Dentistry, School of Dentistry, Araraquara, São Paulo, Brazil.Universidade Estadual PaulistaBrazilAraraquara, São Paulo, BrazilMSc,Universidade Estadual Paulista (UNESP), Department of Pediatric Dentistry, School of Dentistry, Araraquara, São Paulo, Brazil.

José Maurício dos Santos Nunes Reis

Assistant Professor, Universidade Estadual Paulista (UNESP), Department of Dental Material, School of Dentistry, Araraquara, São Paulo, Brazil.Universidade Estadual PaulistaBrazilAraraquara, São Paulo, BrazilAssistant Professor, Universidade Estadual Paulista (UNESP), Department of Dental Material, School of Dentistry, Araraquara, São Paulo, Brazil.

Luiz Geraldo Vaz

Full Professor, Universidade Estadual Paulista (UNESP), Department of Dental Material, School of Dentistry, Araraquara, São Paulo, Brazil.Universidade Estadual PaulistaBrazilAraraquara, São Paulo, BrazilFull Professor, Universidade Estadual Paulista (UNESP), Department of Dental Material, School of Dentistry, Araraquara, São Paulo, Brazil.

Lídia Parsekian Martins

Assistant Professor, Universidade Estadual Paulista (UNESP), Department of Pediatric Dentistry, School of Dentistry, Araraquara, São Paulo, Brazil.Universidade Estadual PaulistaBrazilAraraquara, São Paulo, BrazilAssistant Professor, Universidade Estadual Paulista (UNESP), Department of Pediatric Dentistry, School of Dentistry, Araraquara, São Paulo, Brazil.

Renato Parsekian Martins

Private practice and part-time Faculty, Universidade Estadual Paulista (UNESP), Department of Pediatric Dentistry, School of Dentistry, Araraquara, São Paulo, Brazil.Universidade Estadual PaulistaBrazilAraraquara, São Paulo, BrazilPrivate practice and part-time Faculty, Universidade Estadual Paulista (UNESP), Department of Pediatric Dentistry, School of Dentistry, Araraquara, São Paulo, Brazil.

Contact address: Renato Parsekian Martins E-mail: dr_renatopmartins@hotmail.com

Author contributions Conception or design of the study: JMSNR, LGV, LPM. Data acquisition, analysis or interpretation: CIVV, JMSNR, LGV. Writing the article: CIVV, RPM. Critical revision of the article: LGV, LPM. Final approval of the article: JMSNR, LPM, RPM. Obtained funding: CIVV, LPM. Overall responsibility: RPM.

" The authors report no commercial, proprietary or financial interest in the products or companies described in this article.

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables

Figures (7)
Tables (5)

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Figure 1
Nickel-titanium closed coil spring, the X dimension corresponds to the total length of the spring and the Y dimension corresponds to the length of the nickel-titanium portion.

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Figure 2
Nickel-titanium closed coil spring, before activation (B) and after 900% of activation (A). After heating it above a certain temperature (Af), the martensitic deformation will resume due to the shape memory effect.

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Figure 3
Space closure after extraction of first premolars where a nickel titanium spring was attached to a hook from the first molar to a hook distal to the canine (23 mm distance), remaining active even after space closure (minus 7 mm of pre-molar space).

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Figure 4
A) Load/deflection graph for the springs of the subgroup 1A activated at 900% of Y (20.7 mm of activation or 29.3 mm if the size of the spring is accounted). The blue box corresponds to the distance between the hook of the first molar and a hook distal to the upper canine (minus size of the spring), as in Figure 3 (23 mm minus X). Note that to take full advantage of the springs' SE properties, an increase of approximately 3 mm in the eyelets (not in nickel titanium portion) would be required in order to maintain the force in the SE plateau. That would shift the blue box to the left the same 3 mm. B) Same situation on the subgroup 1B, however, full SE capability would not be achieved in last 2 mm or so of space closure, since the force would start to decrease due to lack of stress.

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Figure 5
A 15- mm long nickel-titanium spring (nickel-titanium portion with 9.8 mm), activated 9.8mm. A spam of activation from the hook of a first molar to the canine, from 23 mm to 16 mm (similar to Figure 3), is shown by the blue arrow. In this case, due to the springs length, that activation would account 8 mm, deactivating to 1 mm after space closure. Note that no superelasticity will not exist in this spring at this activation.

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Figure 6
A 7 -mm long nickel-titanium spring (2.3 mm of nickel-titanium portion) activated approximately 16 mm, which would result in an activation of 23 mm. It can be observed that due to the shape of the load-deflection graph, the pseudo-plateau area, or the near-to-constant force, of the spring would not be used during a 7 mm space closure.

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Figure 7
A 9- mm long nickel-titanium spring (3.9 mm of nickel-titanium portion) activated 23.4 mm, or 600% the length of its SE material. A spam of activation from 14 mm to 7 mm is shown by the blue arrow. Note that a pseudo-plateau can be used in this situation only if the spring is overactivated 10 mm beyond its affixation. The amount of overactivation will depend on the spring's total length, the length of nickel-titanium portion, and the interbracket distance.

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Table 1
Commercial brands and groups division.

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Table 2
Average deformation in millimeters (SD in parenthesis) and in percentage values of the total length of group 1 springs.

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Table 3
Average deformation in millimeters (SD in parenthesis) and in percentage values of group 2 springs.

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Table 4
Average deformation in millimeters (SD in parenthesis) and in percentage values of the total length of group 3 springs.

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Table 5
Average deformation in millimeters (SD in parenthesis) and in percentage values of the total length of group 4 springs.

Figure 1 Nickel-titanium closed coil spring, the X dimension corresponds to the total length of the spring and the Y dimension corresponds to the length of the nickel-titanium portion.

Figure 2 Nickel-titanium closed coil spring, before activation (B) and after 900% of activation (A). After heating it above a certain temperature (Af), the martensitic deformation will resume due to the shape memory effect.

Figure 3 Space closure after extraction of first premolars where a nickel titanium spring was attached to a hook from the first molar to a hook distal to the canine (23 mm distance), remaining active even after space closure (minus 7 mm of pre-molar space).

Figure 4 A) Load/deflection graph for the springs of the subgroup 1A activated at 900% of Y (20.7 mm of activation or 29.3 mm if the size of the spring is accounted). The blue box corresponds to the distance between the hook of the first molar and a hook distal to the upper canine (minus size of the spring), as in Figure 3 (23 mm minus X). Note that to take full advantage of the springs' SE properties, an increase of approximately 3 mm in the eyelets (not in nickel titanium portion) would be required in order to maintain the force in the SE plateau. That would shift the blue box to the left the same 3 mm. B) Same situation on the subgroup 1B, however, full SE capability would not be achieved in last 2 mm or so of space closure, since the force would start to decrease due to lack of stress.

Figure 5 A 15- mm long nickel-titanium spring (nickel-titanium portion with 9.8 mm), activated 9.8mm. A spam of activation from the hook of a first molar to the canine, from 23 mm to 16 mm (similar to Figure 3), is shown by the blue arrow. In this case, due to the springs length, that activation would account 8 mm, deactivating to 1 mm after space closure. Note that no superelasticity will not exist in this spring at this activation.

Figure 6 A 7 -mm long nickel-titanium spring (2.3 mm of nickel-titanium portion) activated approximately 16 mm, which would result in an activation of 23 mm. It can be observed that due to the shape of the load-deflection graph, the pseudo-plateau area, or the near-to-constant force, of the spring would not be used during a 7 mm space closure.

Figure 7 A 9- mm long nickel-titanium spring (3.9 mm of nickel-titanium portion) activated 23.4 mm, or 600% the length of its SE material. A spam of activation from 14 mm to 7 mm is shown by the blue arrow. Note that a pseudo-plateau can be used in this situation only if the spring is overactivated 10 mm beyond its affixation. The amount of overactivation will depend on the spring's total length, the length of nickel-titanium portion, and the interbracket distance.

Table 1 Commercial brands and groups division.

Commercial brand	Specification	Length (mm)*	X (mm)	Y (mm)	Force plateau (gf)*	Subgroup	n
Group 1 (Morelli Ortodontia, Brazil)		7	8.6	2.3	250	1A	10
Group 1 (Morelli Ortodontia, Brazil)		9	10.3	3.9	250	1B	10
Group 2 (Orthometric, Brazil)		7	6.8	2.1	175	2A	10
Group 2 (Orthometric, Brazil)		9	8.9	4.1	250	2B	10
Group 3 (Ormco, USA)	Light	9	8.85	3.25	80	3A	10
Group 3 (Ormco, USA)	Heavy	9	9	3.1	150	3B	10
Group 4 (GAC, USA)	Sentalloy 25g	10	8.5	3.2	25	4A	10
	Sentalloy 50g	10	8.5	3.2	50	4B	10
	Sentalloy 100g	10	8.5	3.2	100	4C	10
	Sentalloy 150g	10	8.5	3.2	150	4D	10
	Sentalloy 200g	10	8.5	3.2	200	4E	10
	Sentalloy 250g	10	8.5	3.2	250	4F	10
	Sentalloy 300g	10	8.5	3.2	300	4G	10

* information supplied by manufacturer.

Table 2 Average deformation in millimeters (SD in parenthesis) and in percentage values of the total length of group 1 springs.

Activation	Subgroup 1A Deformation			Subgroup 1B Deformation
Activation	n	%	mm	n	%	mm
400%	10	2.6%	0.06 (0.05)^A	10	1.3%	0.05 (0.07)^A
500%	10	3.9%	0.09 (0.05)^A	10	3.1%	0.12 (0.08)^A
600%	10	3.9%	0.09 (0.11)^A	10	5.6%	0.22 (0.18)^A
700%	10	9.1%	0.21 (0.09)^AB	10	7.7%	0.30 (0.33)^A
800%	10	17.4%	0.40 (0.18)^B	10	16.4%	0.64 (0.50)^AB
900%	10	29.6%	0.68 (0.26)^C	10	36.4%	1.42 (0.68)^BC
1000%	10	35.2%	0.81 (0.36)^C	9	55.9%	2.18 (1.28)^C
p		< 0.001			< 0.001

Table 3 Average deformation in millimeters (SD in parenthesis) and in percentage values of group 2 springs.

Activation (%)	Subgroup 2A Deformation			Subgroup 2B Deformation
Activation (%)	n	%	mm	n	%	mm
400%	10	10.0%	0.21 (0.18)^A	10	6.6%	0.27 (0.18)^A
500%	10	13.8%	0.29 (0.24)^A	10	14.4%	0.59 (0.26)^A
600%	10	15.7%	0.33 (0.28)^A	10	22.4%	0.92 (0.37)^AB
700%	10	36.2%	0.76 (0.38)^AB	10	36.8%	1.51 (0.84)^BC
800%	9	66.2%	1.39 (0.68)^BC	5	44.1%	1.81 (0.63)^C
900%	7	96.7%	2.03 (0.84)^C	1	81.2%	3.33
1000%	4	102.4%	2.15 (1.74)^C	0	-	-
p		< 0.001			< 0.001

Table 4 Average deformation in millimeters (SD in parenthesis) and in percentage values of the total length of group 3 springs.

Activation (%)	Subgroup 3A Deformation			Subgroup 3C Deformation
Activation (%)	n	%	mm	n	%	mm
300%	10	3.7%	0.12 (0.08)^A	-	-	-
400%	10	6.5%	0.21 (0.10)^A	-	-	-
500%	10	9.5%	0.31 (0.16)^A	-	-	-
600%	10	17.5%	0.57 (0.23)^A	10	17.7%	0.55 (0.24)^A
700%	10	42.1%	1.37 (0.37)^A	10	31.6%	0.98 (0.39)^A
800%	10	107.1%	3.48 (1.58)^B	10	66.1%	2.05 (1.05)^A
900%	5	147.1%	4.78 (0.98)^B	10	120.0%	3.72 (1.81)^B
1000%	3	137.5%	4.47 (3.67)^B	6	154.5%	4.79 (1.38)^B
p		< 0.001			< 0.001

- Non SE.

Table 5 Average deformation in millimeters (SD in parenthesis) and in percentage values of the total length of group 4 springs.

Activation	Subgroup 4A Deformation			Subgroup 4B Deformation			Subgroup 4C Deformation			Subgroup 4D Deformation
Activation	n	%	mm	n	%	mm	n	%	mm	n	%	mm
300%	-	-	-	-	-	-	10	2.2%	0.07 (0.05)	-	-	-
400%	10	3.4%	0.11 (0.09)^A	10	2.2%	0.07 (0.05)	10	2.2%	0.07 (0.06)	10	3.4%	0.10 (0.07)
500%	10	2.5%	0.08 (0.05)^A	10	2.2%	0.07 (0.06)	10	2.5%	0.08 (0.05)	10	4.1%	0.13 (0.13)
600%	10	3.4%	0.10 (0.12)^A	10	2.2%	0.07 (0.06)	10	2.5%	0.08 (0.06)	10	4.1%	0.13 (0.13)
700%	10	2.8%	0.11 (0.08)^A	10	2.2%	0.07 (0.06)	10	2.5%	0.08 (0.06)	10	3.4%	0.10 (0.12)
800%	10	14.0%	0.45 (0.29)^A	10	1.6%	0.05 (0.05)	10	2.5%	0.08 (0.04)	10	3.4%	0.10 (0.12)
900%	10	59.7%	1.91 (1.02)^B	10	1.3%	0.04 (0.04)	10	1.3%	0.04* (0.07)	10	3.8%	0.12 (0.19)
1000%	10	44.1%	1.41 (0.96)^B	10	-0.6%	-0.02 (0.14)	10	1.3%	0.04* (0.25)	10	2.8%	0.09* (0.19)
p	< 0.001			0.076			0.965			0.981
Activation	Subgroup 4E Deformation			Subgroup 4F Deformation			Subgroup 4G Deformation
Activation	n	%	mm	n	%	mm	n	%	mm
300%	-	-	-	-	-	-	-	-	-
400%	-	-	-	10	4.1%	0.13 (0.05)^A	-	-	-
500%	10	1.6%	0.05 (0.04)	10	4.1%	0.13 (0.07)^A	10	3.4%	0.10 (0.09)^A
600%	10	0.6%	0.02 (0.03)	10	3.8%	0.12 (0.08)^A	10	3.4%	0.10 (0.08)^A
700%	10	0.9%	0.03 (0.03)	10	3.4%	0.11 (0.06)^A	10	1.6%	0.05 (0.05)^A
800%	10	-0.01	-0.02* (0.18)	10	0.9%	0.03* (0.07)^A	10	0.9%	0.03* (0.86)^A
900%	10	1.6%	0.05* (0.27)	10	12.5%	- 0.4 (0.23)^B	9	38.1%	1.22 (1.41)^B
1000%	10	1.6%	0.05* (0.38)	10	72.5%	2.32 (0.66)^C	7	89.7%	2.87 (1.11)^C
p	0.975			< 0.001			< 0.001

* Non significant values.
- Non SE.

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Deformation of nickel-titanium closed coil springs: an in vitro study

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[1] Contact address: Renato Parsekian Martins E-mail: dr_renatopmartins@hotmail.com