Ex vivo surface and mechanical properties of coated orthodontic archwires

Abstract

This study examined the mechanical and physical properties of retrieved coated nickel-titanium (NiTi) archwires compared with unused samples. Ultraesthetic 0.016 inch coated archwires (G&H(R) Wire Company) were investigated. Ten as-received wires were subjected to a three-point bending test using conventional and self-ligating bracket systems. Surface roughness of the coating was measured with a contact stylus profilometer. Optical and scanning electron microscopes were used to assess surface topography. Ten archwires were used in vivo for a period of between 4 and 6 weeks. Retrieved archwires were subjected to the same tests. The percentage of the remaining coating was calculated using digital photography. Coated archwires were used in vivo for a mean period of 33 days. Differences between the mean values of the as-received and retrieved archwires were determined using t-tests. In the three-point bending test, with conventional elastomeric ligation, retrieved wires produced a lower unloading force (P < 0.001). Both retrieved and as-received coated archwires produced zero values of unloading force when deflected for 4 mm. When tested using a self-ligating bracket system, retrieved and as-received coated archwires produced the same amount of force (P > 0.05). With surface profilometry, all measured roughness parameters (except R(sm)) had greater surface roughness for the retrieved coated archwires (P < 0.05). Under microscopy, retrieved coated archwires showed discolouration, ditching, and delamination. Only 75 per cent of the coating was present in retrieved coated archwires. Retrieved coated archwires produced lower unloading force values than as-received coated archwires with conventional ligation. Surface roughness of coated archwires increased after use. Coated archwires have a low aesthetic value, with 25 per cent of the coating lost within 33 days in vivo.

Deflection and Flexural Strength Effects on the Roughness of Aesthetic-Coated Orthodontic Wires

“…Under the microscope, the coated archwires discolored, delaminated and their surface roughness increased after use. It was concluded that coated archwires have a low esthetic value, with 25% of the coating being lost after 33 days (15). The variation between initial and post-deflection roughness of the Group ANT was not significant, as this group presented high initial roughness values.…”

“…The quantity of tooth movement during orthodontic treatment depends on the force on the two surfaces, as well as roughness and nature of the materials involved (14). Problems associated with the loss of coating during clinical use have been related in the literature, and for this reason, simulation of clinical use was performed by means of the deflection test, in order to observe these changes (15,16). In this study, 70 orthodontic Niti wires coated with PTFE, epoxy resin, gold/rhodium metals and a group without coating were evaluated.…”

“…During deflection, these porosities may function as locations of stress concentration, which lead to fracture of the esthetic coating. Other studies have shown that after use in vivo the roughness of wires with coatings increases (15). However, further clinical studies are necessary in order to know whether the duration of orthodontic treatment would be longer due to this increase in roughness, taking into consideration the biologic complexity involved in tooth movement.…”

Coating stability and surface characteristics of esthetic orthodontic coated archwires

“…5 Some authors have experienced difficulties with these coated archwires, claiming that the color tends to change with time 6 and that the coating splits during use in the mouth, exposing the underlying metal. [7][8][9] However, despite these problems, these wires continue to be marketed and used in clinical practice, mainly when an esthetic alternative for a rectangular cross-sectional archwire is necessary. The surface quality of archwires affects the area of surface contact and influences the esthetic result, the corrosion behavior, the plaque accumulation, and the biocompatibility.…”

“…The surface quality of archwires affects the area of surface contact and influences the esthetic result, the corrosion behavior, the plaque accumulation, and the biocompatibility. 7 Among the properties in the search for the ideal archwire, the surface topography plays an important role and can critically modify the efficiency of orthodontic components. 10,11 Further, increased surface roughness can increase the friction coefficient 12 and is an essential factor in determining the effectiveness of archwire-guided tooth movement.…”