Force degradation of orthodontic latex elastics analyzed in vivo and in vitro.

INTRODUCTION

The objective of this study was to evaluate the characteristics of force degradation of latex elastics of 10 kinds of elastics over 48 hours, both in vivo and in vitro.

METHODS

For the in vivo study, 10 different kinds of elastics were randomly chosen for investigation: 1/8-inch (2 oz); 1/8-inch (3.5 oz); 3/16-inch (2 oz); 3/16-inch (3.5 oz); 1/4-inch (2 oz); 1/4-inch (3.5 oz); 5/16-inch (2 oz); 5/16-inch (3.5 oz); 3/8-inch (2 oz); and 3/8-inch (3.5 oz). Ten volunteers (aged 22-24 years) were selected to wear personalized clear retainers, which were made to hold the elastics in the mouth and stretched to a specific length. Control samples of 1/4-inch (2 oz) and 1/4-inch (3.5 oz) latex elastics were stretched to the same length and held in dry air conditions (temperature = 25°C) and in artificial saliva (temperature = 37°C, pH = 6.7). Force value and percentage of force degradation were estimated 10 times over a 48-hour period in both the in vivo and in vitro groups. A 1-way ANOVA and t test were used to identify statistical significance (P <0.05).

RESULTS

The force degradation of the latex elastic in vivo is greater than in vitro. In the in vivo groups, during the first hour, the extension rate of all elastics decreased sharply about 13.16%-18.79%, then the rate of force degradation declined. The degradation of initial force was about 29.35%-39.94% after 48 hours. The extension range of 2.0-oz elastics reduced less than that of the 3.5-oz elastics in vivo. At the same time, with the same initial force, elastics with larger inner diameters decreased more slowly than the smaller elastics (P <0.05).

CONCLUSIONS

The force degradation of latex elastic in vivo is much greater than that in both air and artificial saliva. In vivo, the force value of the orthodontic latex elastics decreased sharply in the first hour. The larger the inner diameter and smaller the setting force value were, the slower the force decay.