Self-ligating brackets: present and future

Friction and resistance to sliding in orthodontics: a critical review

Despite the emphasis it now receives in the marketing of self-ligating brackets, friction is not the major component of resistance to sliding in clinical treatment. Laboratory studies show that binding of the wire against the corners of the bracket, which occurs soon after tooth movement begins, is much more important than previously thought, and that notching of the archwire, which temporarily stops movement, can occur. Clinical studies support the view that resistance to bodily tooth movement by sliding has little to do with friction and, instead, is largely a binding-and-release phenomenon that is about the same with conventional and self-ligating brackets. The limited clinical trial data available now do not support the contention that treatment time is reduced (presumably because of lower friction) with self-ligating brackets.

Frictional resistance in plastic preadjusted brackets ligated with low-friction and conventional elastomeric ligatures

OBJECTIVE

To compare frictional resistance of the plastic preadjusted brackets ligated with the low-friction ligatures with those of the conventional elastomeric ligatures.

DESIGN

In vitro study.

SETTING

Department of Orthodontics, Faculty of Dentistry, Kyushu University, Fukuoka, Japan.

MATERIALS AND METHODS

The testing model consisted of four 0.022-inch plastic preadjusted brackets for the first premolar, the canine, the lateral incisor, and the central incisor. A superelastic nickel-titanium 0.014-inch wire and a stainless steel 0.019 x 0.025-inch wire were used for this test. The brackets were either aligned or out of line by 0.5, 1.0, 1.5 and 2.0 mm for the 0.014-inch wire and aligned for the 0.019 x 0.025-inch wire. The frictional forces in plastic preadjusted brackets with low-friction ligatures and conventional elastomeric ligatures were measured at a pulling speed of 0.1 mm/second. Welch t-tests were used to compare the mean differences of each testing measurement between the low-friction and the conventional elastomeric ligatures.

RESULTS

In both use of the superelastic nickel-titanium 0.014-inch wire and the stainless steel 0.019 x 0.025-inch wire, the brackets with the low-friction ligatures showed significantly lower frictional forces than those of the conventional elastomeric ligatures in both aligned and all misaligned brackets (P < 0.0001).

CONCLUSION

The study found the significantly lower frictional forces for the low-friction ligatures than those of the conventional elastomeric ligatures.