Photoelastic comparison of stress induced by using stainless-steel versus nickel-titanium spreaders in vitro

By Joyce AP, Loushine RJ, West LA, Runyan DA, Cameron SM.

Date: 06/1999
Journal: JOE

Summary: 

Purpose: to demonstrate the location and distribution of stresses created upon lateral condensation in curved canals

and to compare the distribution of stress when using stainless-steel (SS) or nickel-titanium (NiTi) spreaders.

N= T20 simulated, tapered canals

Materials/Methods:

•20 standardized models simulating curved canals (32 degrees) were formed within photoelastic acrylic resin blocks.

•Size 35 gutta-percha cones were coated with sealer and inserted to the end of each canal.

•Size 30 finger spreaders made of either SS or NiTi were mounted in an Instron model universal testing machine.

•The spreaders were guided into the canal of each prepared model, and advanced until a 20 Newton (N) load was applied.

•Ektachrome slides were taken of each model: (a) with no force applied, to rule out any built-in stress in the model; and (b) with a 20 N force applied. •The fringe patterns for each spreader were compared.

Most highlighted Results: 

•The stainless-steel spreaders created three areas of concentrated stress. The nickel-titanium spreaders induced stress patterns spread out along the surface of the canals.

Clinical significance:

the distribution of stress using NiTi spreaders in teeth with curved canals may result in a decreased incidence of vertical root fracture.

weakness (limitation): clinically, the cushion effect provided by PDL may affect the pattern of stress distribution.