SEM chemistry characterization of NiTi orthodontic archwire

Nominally near-equiatomic NiTi shape memory alloys have been studied for applications in the biomedical industry. Orthodontic archwires that produce different levels of force in the same wire have been developed. Those forces are based on the superficial radicular area of the tooth therefore radicular reabsorption and patient pain are disminished. The manufacturer information cites that the archwire Bioforce Sentalloy shows three zones with different forces. Recent papers have shown that the properties may be radically altered by simple inclusion of chemistry elements.

Objective: This study aims to explore the relationship between mechanical behavior that manufacturer reports with chemical composition.

Method: Quantitative and qualitative scanning electron microscopy analyses (SEM, JEOL, JSM-59000LV) were used to measure in each one of the three segments that the manufacturer mentions, the exterior and transversal surface of five NiTi archwires with cross-section dimensions of 0.016×0.022 in. The results obtained were statistically analyzed by ANOVA.

Results: The ANOVA-test showed no significant difference between archwires. SEM exterior surface analysis showed the presence of Ni (55%) and Ti (45%) in all wire. SEM transversal surface analysis revealed Ni (54%), Ti (45%) and Cu (0.74%) on posterior zone (molar area); Ni (55%), Ti (44%) and Al (0.73%) on medium zone (premolar area) and Ni (54%), Ti (45%) and Al (0.50%) on anterior zone (incisive zone).

Conclusion:. We believe that presence of aluminum and copper could be providing different forces as the manufacturer declares. These elements can form intermetalic compounds in the arch. However, we should verify this behavior.