Force Decay Behavior of Orthodontic Elastomeric Chains in Simulated Oral Conditions

Abstract

Background Elastomeric chains are widely used for incisor retraction and space closure. However, the force they exert diminishes over time, and this makes it difficult to determine the actual force transmitted to the dentition. The force decay may also be affected by exposure to saliva, foods, beverages, and prophylactic agents. Objective To assess the force degradation of four commercially available orthodontic elastomeric chains (AlastiK, 3M; Generation II Power Chain, Ormco; Elastic Chain, Morelli; and Plastic Chain, American Orthodontics) over 28 days in simulated oral conditions using tooth movement and a prophylactic fluoride rinse regimen. Method A total of 80 chain samples, with 20 samples of each chain type having four loops each, were stretched to 25 mm on custom-fabricated acrylic resin jigs with provision for a space closure mechanism. The samples were divided equally into two groups: a control group, in which ten samples of each chain type were maintained in artificial saliva at 37°C, and a test group, in which ten samples of each chain type were maintained in artificial saliva at 37°C and additionally subjected to simulated tooth movement with jig closure of 0.25 mm/week and a twice-daily regimen of prophylactic fluoride rinse. Force decay was measured using a digital force gauge at the time of engagement on the jigs, at one hour, four hours, and at one, seven, 14, 21, and 28 days. Percentage force decay was calculated, and the results were subjected to one-way analysis of variance (ANOVA), post-hoc Tukey, post-hoc Bonferroni, and 't' test. Results Maximum force degradation was observed at one day for all four chain materials in both groups, followed by a steady force loss over 28 days, the difference being significant for all materials at various time intervals (p<0.05). No significant difference was observed between any material at any given time in the control group (p>0.05); however, significant differences were observed in the test group. Under simulated oral conditions, force decay was maximum for the Plastic Chain, American Orthodontics (67.9 ± 6.24%), and minimum for the Generation II Power Chain, Ormco (51.9 ± 9.78%) at the end of the test period. Conclusion Plastic Chain, American Orthodontics, and AlastiK, 3M chain, exhibited higher force decay when compared to Generation II Power Chain, Ormco, and Elastic Chain, Morelli. Simulated oral conditions significantly affected the force decay of elastomeric chains, and it may be desirable to change elastomeric chains at 14 days for optimum retraction force.

Keywords: elastomeric chains; fluoride mouthrinse; force decay; force degradation; synthetic elastics.

Figure 1. Fabrication of individual acrylic resin jig halves.

A: stainless-steel mold; B: condensation silicone impression; C: acrylic resin jig half

Figure 2. Custom acrylic jig with standard expansion screw and stainless-steel pins 25 mm apart.

Figure 3. Control and test group acrylic resin jigs with elastomeric chains engaged on stainless-steel pins.

Group A­­_C: Control samples of AlastiK (3M); Group A_T: Test samples of AlastiK (3M); Group O­­_C: Control samples of Generation II Power Chain (Ormco); Group O_T: Test samples of Generation II Power Chain (Ormco); Group M­­_C: Control samples of Elastic Chain (Morelli); Group M_T: Test samples of Elastic Chain (Morelli); Group AO­­_C: Control samples of Plastic Chain (American Orthodontics); Group AO_T: Test samples of Plastic Chain (American Orthodontics)

Figure 4. Force measurement with digital force gauge.