Effect of pH on in vitro biocompatibility of orthodontic miniscrew implants

Orthodontic temporary anchorage devices (TADs) are successfully used as compliance-independent anchorage devices in orthodontics to prevent many of the shortcomings of traditional anchorage methods [1]. Removable miniscrews are available in a range of body lengths and diameter, and are mainly made of pure titanium, titanium alloy, and stainless steel (SS) [2]. Literature in this regard has reported a great number of clinical studies suggesting that TADs may provide stable anchorage during the orthodontic treatment without requiring patient cooperation[3].

In an oral environment, miniscrews are exposed to a number of potentially damaging physical and chemical agents. Such conditions may contribute to corrosion of the metal components of any intraoral appliance, and an increasing number of studies have demonstrated that the oral cavity, owing to its peculiar physical, chemical, enzymatic, and microbial characteristics, may play a significant role in the biodegradation of metallic biomaterials [4,5]. Food intake and microbial flora can induce a decrease in the physiologic pH of saliva (5.3 to 7.8) [6,7]. Although buffering action is an important function of saliva (mainly through bicarbonate, phosphate, urea) [7], these transient variations may affect corrosion resistance of metal devices [8]. Many studies have investigated the role of pH in metal ion release from orthodontic alloys. The majority of them, in different experimental conditions, report ion release increase on decrease of the pH [9-15].