title: Correlation between polymerization shrinkage stress and C-factor depends upon cavity compliance.
abstract: OBJECTIVE
  The literature reports inconsistent results regarding using configuration factor (C-factor) as an indicator to reflect the generation of polymerization shrinkage stress (PS) from dental restorative composites due to the constraint of cavity configuration. The current study aimed at unraveling the complex effects of C-factor on PS based on analytical and experimental approaches together, such that the reported inconsistency can be explained and a significance of C-factor in clinic can be comprehensively provided.
  
  
  METHODS
  Analytical models based on linear elasticity were established to predict PS measured in instruments (testing systems) with different compliances, and complex effects of C-factor on PS were derived. The analyses were validated by experiments using a cantilever beam-based instrument and systematic variation of instrumental compliance.
  
  
  RESULTS
  For a general trend, PS decreased with increasing C-factor when measured by instruments with high compliance. However, this trend gradually diminished and eventually reversed (PS became increased with increasing C-factor) by decreasing the system compliance.
  
  
  CONCLUSIONS
  Our study indicates that the correlation between PS and C-factor are highly dependent on the compliance of testing instrument for PS measurement. This suggests that the current concept on the role of C-factor in the stress development and transmission to tooth structures, higher C-factor produces higher PS due to reduced flow capacity of more confined materials, can be misleading. Thus, the compliance of the prepared tooth (cavity) structure should also be considered in the effect of C-factor on PS.
authors.affiliation: Biosystems and Biomaterials Division, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, United States.
authors.forename: Zhengzhi
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Biosystems and Biomaterials Division, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, United States. Electronic address: martin.chiang@nist.gov.
authors.forename: Martin Y M
authors.initials: MY
authors.lastname: Chiang
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003737:Dental Cavity Preparation; D003764:Dental Materials / Q000737:chemistry; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000379:methods; D003799:Dental Stress Analysis / Q000295:instrumentation*; D055119:Elastic Modulus; D008422:Materials Testing; D058105:Polymerization; D013499:Surface Properties
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C000590993:TPH Spectra
keywords: C-factor; Compliance of constraint; Dental restorative materials; Photopolymerization; Polymerization shrinkage stress