MECHANCIAL PROPERTIES OF ELASTIC THREAD FORCE SYSTEMS IN CANINE EXPOSURES AND APPLICATION OF FORCE

Abstract

Objectives: To investigate differences in the modulus of elasticity, tensile strength, and load at breakage for elastic thread alone and elastic thread with gold chain in combination used in force application of palatally impacted and exposed maxillary canines. Methods: Two groups with n=6 in each were tested. A circular portion of elastic thread was cut, tied and measured to the nearest hundredth of a millimeter and recorded. Five links of a gold chain were cut and an elastic thread was tied to the fifth link opposite the bondable eyelet. The length of the elastic thread and the total apparatus was measured to the hundredth of a millimeter and recorded. An Instron with a ramp speed of 100 mm/min was used for all testing. Results: The addition of the gold chain, as compared to the elastic thread alone, increased the modulus from 8.8 MPa (SD 3.7) to 17.0 MPa (SD 5.03), (p< 0.04) and significantly decreased the maximum tensile stress at breakage from 92.1N (SD 5.0) to 84.1N (SD 1.6), (p<0.004) and the tensile stress at maximum load from 107.8 N (SD 6.7) to 93.8N (SD 4.8), (p<0.002). The stress-strain curve for both groups demonstrated an initial linear behavior followed by non-linear behavior, partially obeying Hooke’s Law, due to the inherent nature of the elastic thread. The addition of the gold chain introduced a rigid element by reducing the of length of the elastic thread by one-half, altering the properties of the assembly. Conclusions: The modulus of elasticity (stiffness) increases and the toughness and resiliency decreases when a gold chain is added to the assembly and compared to elastic thread alone. This could indicate that in the gold chain group, more initial force/strain is delivered to the tooth and there is less stress relaxation over time due to the decrease in the amount of elastic thread. Therefore, the elastic thread alone delivers a more constant and continuous force to the tooth. The use of elastic thread alone may provide a biomechanically more efficient approach to orthodontic movement of impacted and open exposed teeth.