Effects on tooth movement of force delivery from nickel-titanium archwires

The aim of this project was to determine the in vivo effects of tooth movement with nickel-titanium archwires on the periodontium during the early stages of orthodontic treatment. The extent of tooth movement, severity of gingival inflammation, pocket probing depth, gingival crevicular fluid (GCF) flow, and the amount of the chondroitin sulphate (CS) glycosaminoglycan (GAG) component of the GCF of one maxillary canine in each of 33 patients treated with a pre-adjusted appliance were measured before and at four stages during the first 22 weeks of treatment. The methods involved the use of a reflex metrograph to determine the type of tooth movement and electrophoresis to quantitate the CS in the GCF. It was found that GCF flow increased after 4 weeks of tooth movement whereas the increase in the amount of CS in the GCF, which is taken to be indicative of periodontal tissue turnover, occurred at the later stage of 10 weeks. Teeth which showed the greatest amount of tooth movement continued to express large amounts of CS in large volumes of GCF until 22 weeks, whilst the CS levels in those teeth moving to a smaller extent declined. These data suggest that nickel-titanium archwires may produce a super-elastic plateau effect in vivo on canine teeth, which are initially displaced from the arch such that large amounts of tooth movement occur in the first 22 weeks of treatment.