Bj. Love et al., CONTROLLING ADHESION OF ORTHODONTIC ADHESIVES THROUGH ADJUSTMENT OF THE INTERPHASE MECHANICAL-PROPERTIES, The Journal of adhesion, 45(1-4), 1994, pp. 149-159
Adhesives for ceramic orthodontic brackets are so strong that instance
s of enamel fracture and bracket fracture have occurred during removal
. Our approach to minimize the potential enamel damage was to modify t
he mechanical properties of the adhesive, a BIS GMA-silica composite,
by use of diethyl phthalate which is a common plasticizer. The plastic
izer, used in amounts up to 20% of the adhesive weight, significantly
decreases the adhesive modulus and tensile strength. One objective of
this research is to evaluate plasticizer stability in the adhesive via
functional testing in a simulated oral environment. A second objectiv
e was to simulate, by use of finite element analysis, clinical loading
conditions during orthodontic treatment and removal. The finite eleme
nt analysis determined the changes in computed stresses due to plastic
ization. After 25 days in an artificial saliva solution held at 60 deg
rees C, the bracket removal torque was lower for the 10% plasticized a
dhesive group than that for the non-plasticized group. The 3-D linear
elastic finite element analysis found that plasticization should not l
ead to premature failure when typical treatment loadings were applied.
The torsional loading conditions simulating bracket removal reported
peak stresses in excess of the plasticized adhesive tensile strength i
n the corner regions. Thus, modelling of the adhesive as a layer with
distinct mechanical properties appears reasonable.