Metals and Metalloids Release from Orthodontic Elastomeric and Stainless Steel Ligatures: In Vitro Risk Assessment of Human Exposure

Abstract

Elastomeric ligatures are increasingly used as a part of esthetic orthodontic treatment, particularly in children. The aim of the present study was to experimentally test whether these appliances may contribute to exposure to toxic elements. In the present study, elastomeric ligatures (ELs) were incubated in artificial human saliva for 1 month (a typical period of their use) and the release of 21 metals (Ba, Cd, Co, Cr, Cu, Fe, Li, Mn, Mg, Mo, Ni, Pb, Rb, Tl, Ti, Sb, Sr, Sn, Zn, U, V) and 2 metalloids (As and Ge) was studied using inductively coupled plasma–mass spectrometry. For comparison, stainless steel ligatures (SLs) were incubated for 1, 3, and 6 months (since sometimes their use is prolonged) under similar conditions. The determined metal levels were compared to the corresponding safety limits for human exposure. During 1 month, the ELs released Cd, Co, Cr, Mn, Ni, and Sn at total mean ± SD level of 0.31 ± 0.09, 0.98 ± 0.30, 3.96 ± 1.31, 14.7 ± 8.5, 13.8 ± 4.8, and 49.5 ± 27.7 μg, respectively. Other elements were always below the detection limits. In case of SL, the release of Co, Cr, Fe, Ni, Mn, and Sn was observed, and the determined values increased over the studied period. After 6 months, their total mean ± SD levels amounted to 28.6 ± 0.2, 21.7 ± 0.2, 623.5 ± 3.0, 1152.7 ± 1.8, 5.5 ± 0.3, and 22.6 ± 0.2 μg, respectively. The released metal levels from both ligature types were always below safety limits. The release of Ni from SL during 6 months would constitute 5.0 and 11.5% of tolerable intake in adults and children, respectively. The results of this in vitro study highlight that the use of ligatures in orthodontic treatment can be considered safe in terms of metal exposure although elastic ligatures replaced on a monthly basis appear to be advantageous in comparison to the prolonged use of stainless steel appliances.

In Vitro Comparison to Evaluate Metal Ion Release: Nickel-Titanium vs. Titanium-Molybdenum Orthodontic Archwires

“…In stainless steel ligatures, nickel release varied with mean values of 2.3, 2.9, and 5.0 observed at the one, three, and six-month marks, respectively. It indicated a progressive increase in nickel release throughout the study [12].…”

“…Inadvertent exposure to the discharged ions may result from this. Both in vitro and in vivo studies were conducted on the metal ion release from fixed orthodontic equipment, such as brackets and archwires [11,12].…”

Toxicological Profile of Biological Environment of Two Elastodontic Devices

“…Orthodontic appliances are meant to stay in contact with the oral mucosa for a long time, and for this reason, biocompatibility studies are an important step in ensuring their safe use. Conventional orthodontic appliances are usually composed of metals and alloys that can exert toxic effects on the cells of the oral cavity [27]. In addition, mobile orthodontic appliances contain different metal ions that can exert toxic effects at the cellular level.…”

Bacterial biofilm accumulation on self-ligating vs. elastomeric metal brackets: A review study

“…Steel ligatures have the advantages of maintaining their strength and form while withstanding deterioration in the oral environment. They are also simpler to clean than elastomeric ligatures and offer less retention of bacterial plaque [32]. Steel ligatures have the disadvantage of requiring a lot of time and effort from the operator [32,33].…”