title: Effect of temperature and humidity on post-gel shrinkage, cusp deformation, bond strength and shrinkage stress - Construction of a chamber to simulate the oral environment.
abstract: OBJECTIVE
  Evaluate the effect of environment on post-gel shrinkage (Shr), cuspal strains (CS), microtensile bond strength (μTBS), elastic modulus (E) and shrinkage stress in molars with large class II restorations.
  
  
  METHODS
  Sixty human molars received standardized Class II mesio-oclusal-distal cavity preparations. Restorations were made with two composites (CHA, Charisma Diamond, Heraus Kulzer and IPS Empress Direct, Ivoclar-Vivadent) using three environment conditions (22°C/50% humidity, 37°C/50% humidity and 37°C/90% humidity) simulated in custom developed chamber. Shr was measured using the strain gauge technique (n=10). CS was measured using strain gauges. Half of the teeth (n=5) were used to assess the elastic modulus (E) and Knoop hardness (KHN) at different depths using microhardness indentation. The other half (n=5) was used to measure the μTBS. The composites and environment conditions were simulated in a two-dimensional finite element analysis of a tooth restoration. Polymerization shrinkage was modeled using Shr data. The Shr, CS, μTBS, KHN and E data were statistically analyzed using two-way ANOVA and Tukey test (significance level: 0.05).
  
  
  RESULTS
  Both composites had similar Shr, CS, μTBS and shrinkage stress. CHA had higher elastic modulus than IPS. Increasing temperature and humidity significantly increased Shr, CS and shrinkage stress. μTBS were similar for groups with lower humidity, irrespective of temperature, and higher with higher humidity. E and KHN were constant through the depth for CHA. E and KHN values were affected by environment only for IPS, mainly deeper in the cavity. Shrinkage stress at dentin/composite interface had high inverse correlation with μTBS. Shrinkage stress in enamel had high correlation with CS.
  
  
  CONCLUSIONS
  Increasing temperature and humidity caused higher post-gel shrinkage and cusp deformation with higher shrinkage stresses in the tooth structure and tooth/restoration interface for both composites tested. The chamber developed for simulating the oral environment conditions will improve the realism of in vitro studies. Clinical significance Simulating oral temperature and humidity is important to better determine the biomechanical behavior of composite resin restoration. Avoiding high humidity during restorative procedures using rubber dam isolation may reduce cuspal deformation and shrinkage stress and improve the bonding strength of posterior composite restorations.
authors.affiliation: Federal University of Uberlandia, Uberlandia, MG, Brazil.
authors.forename: Aline Aredes
authors.initials: AA
authors.lastname: Bicalho
authors.affiliation: Federal University of Uberlandia, Uberlandia, MG, Brazil.
authors.forename: Silas Júnior Boaventura
authors.initials: SJ
authors.lastname: de Souza
authors.affiliation: Federal University of Uberlandia, Uberlandia, MG, Brazil.
authors.forename: Camila Maria Peres
authors.initials: CM
authors.lastname: de Rosatto
authors.affiliation: University of Tennessee Health Science Center, Memphis, TN, USA.
authors.forename: Daranee
authors.initials: D
authors.lastname: Tantbirojn
authors.affiliation: University of Tennessee Health Science Center, Memphis, TN, USA.
authors.forename: Antheunis
authors.initials: A
authors.lastname: Versluis
authors.affiliation: Federal University of Uberlandia, Uberlandia, MG, Brazil. Electronic address: carlosjsoares@umuarama.ufu.br.
authors.forename: Carlos José
authors.initials: CJ
authors.lastname: Soares
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding; D003737:Dental Cavity Preparation / Q000379:methods*; D018772:Dental Marginal Adaptation; D003776:Dental Porcelain / Q000737:chemistry*; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D020342:Finite Element Analysis; D006244:Hardness; D006801:Humans; D006813:Humidity; D066298:In Vitro Techniques; D008422:Materials Testing; D008963:Molar; D058105:Polymerization; D013696:Temperature; D013718:Tensile Strength
chemical_list: D000538:Aluminum Silicates; C084111:Charisma composite resin; D003188:Composite Resins; C075815:IPS-Empress ceramic; D003776:Dental Porcelain
keywords: Cusp deformation; Dental composites; Finite element analysis; Humidity; Shrinkage; Strain gauge; Temperature