Korean J Orthod.  2015 Jul;45(4):198-208. 10.4041/kjod.2015.45.4.198.

Effect of activation and preactivation on the mechanical behavior and neutral position of stainless steel and beta-titanium T-loops

• de Castro
• Moreira R
• Braga AC
• Ferreira A
• Pollmann M

• KMID: 2400578
• DOI: http://doi.org/10.4041/kjod.2015.45.4.198

Abstract

OBJECTIVE
To quantify, for each activation, the effect of preactivations of differing distribution and intensity on the neutral position of T-loops (7-mm height), specifically the horizontal force, moment to force (M/F) ratio, and load to deflection ratio.
METHODS
A total 100 loops measuring 0.017 x 0.025 inches in cross-section were divided into two groups (n = 50 each) according to composition, either stainless steel or beta-titanium. The two groups were further divided into five subgroups, 10 loops each, corresponding to the five preactivations tested: preactivations with occlusal distribution (0degrees, 20degrees, and 40degrees), gingival distribution (20degrees), and occlusal-gingival distribution (40degrees). The loops were subjected to a total activation of 6-mm with 0.5-mm iterations. Statistical analysis was performed using comprised ANOVA and Bonferoni multiple comparison tests, with a significance level of 5%.
RESULTS
The location and intensity of preactivation influenced the force intensity. For the M/F ratio, the highest value achieved without preactivation was lower than the height of the loop. Without preactivation, the M/F ratio increased with activation, while the opposite effect was observed with preactivation. The increase in the M/F ratio was greater when the preactivation distribution was partially or fully gingival.
CONCLUSIONS
Depending on the preactivation distribution, displacement of uprights is higher or lower than the activation, which is a factor to consider in clinical practice.

Keyword

Neutral position; Preactivation; T-loop

MeSH Terms

Analysis of Variance
Stainless Steel*
Stainless Steel

Figure

• 

  Figure 1 A, Schematic representation of the T-loop and respective dimensions (mm). The front end of the loop is indicated by alpha (α), while beta (β) indicates the rear end of the loop. B, Test board: The OrthoMeasure Moment/Force/digital comparator (Orthomeasurments®; Division of Young Research & Development, Avon, CT, USA) was used to quantify the horizontal forces.

• 

  Figure 2 Schematic representation of the T-loop activation for each group. A, Numerical identification of the four bend locations; B, schematic representation of the T-loop with 20° preactivation (10° insertion in bends 1 and 2); C, 40° preactivation (20° insertion in bends 1 and 2); D, 20°° preactivation (10° insertion in bends 3 and 4) ; E, 40°° preactivation (10° insertion in bends 1, 2, 3, and 4).

• 

  Figure 3 Photograph of the inserted loop.

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  Figure 4 Mean force values and 95% confidence intervals (CI) for activation and preactivation in each material (beta-titanium [TMA] and stainless steel [SS]).

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  Figure 5 Mean moment to force (M/F) ratio values and 95% confidence intervals (CI) according to activation and preactivation in each material (beta-titanium [TMA] and stainless steel [SS]).

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  Figure 6 Mean load to deflection (L/D) ratio values and 95% CI by activation according to preactivation values for each material (beta-titanium [TMA] and stainless steel [SS]).

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  Figure 7 Schematic representation of the T-loop generated by the LOOP computer program (dHAL Orthodontic Software®, Athens, Greece). A, 20° activation/Apply Moment (neutral position); B, 40° activation/Apply Moment (neutral position); C, 20°° activation/Apply Moment (neutral position); D, 40°° activation/Apply Moment (neutral position).

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