Long-term effects of storage and thermal cycling on the marginal adaptation of provisional resin crowns: a pilot study.
BACKGROUND
Provisional resin crowns may be used for an extended period while complex treatments are completed. The crowns function intraorally; therefore, moisture absorption and thermal cycling may affect the physical properties of acrylic resin, causing a change in marginal gap size.


OBJECTIVE
The purpose of this pilot study was to examine the effect of long-term water absorption and thermal cycling on marginal gap size of polymethyl methacrylate copolymer and bis-acrylic composite resin crowns.


METHODS
Specimens (n = 10) were fabricated from 2 acrylic resins: a polymethyl methacrylate (Alike) and a bis-acrylic composite resin (Provitec). Specimens were first fabricated on a metal master die. Custom die stems were fabricated for each specimen from a low-fusing alloy (Cerroblend) to eliminate the factor of polymerization shrinkage. Specimens were then fitted to assure a standardized, pre-experimental marginal gap range of < or = 25 microm. Specimens were stored in a humidor at 37 degrees C and 97% relative humidity for 1 year and subsequently thermal cycled (5 degrees C to 60 degrees C, 6-second dwell time, for 8000 cycles). Measurements in micrometers of the marginal gap were recorded using a microscope equipped with a digital video camera and image analysis software before and after treatment. A 2-way analysis of variance with a split design was performed for factors of materials and treatment (alpha = .05).


RESULTS
For the factor of material, there was no significant difference; however, there was a significant difference between treatments, with a significantly greater increase in marginal gap size after thermal cycling (P < .002).


CONCLUSIONS
Provisional crowns made from either a bis-acrylic resin composite or a polymethyl methacrylate copolymer demonstrated loss of marginal adaptation during a simulated long-term period of service.
Ehrenberg
David
D
Department of Restorative Dentistry, New Jersey Dental School, Newark, 07103, USA. ehrenbda@umdnj.edu
Weiner
Gabriel I
GI
Weiner
Saul
S
D000180:Acrylic Resins / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003442:Crowns; D017267:Dental Prosthesis Design; D003794:Dental Restoration, Temporary; D006801:Humans; D006813:Humidity; D007091:Image Processing, Computer-Assisted; D008137:Longitudinal Studies; D008422:Materials Testing; D008853:Microscopy; D010865:Pilot Projects; D019904:Polymethyl Methacrylate / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature; D014741:Video Recording
D000180:Acrylic Resins; D003188:Composite Resins; D019904:Polymethyl Methacrylate