title: Comparison of variation in the light curing cycle with a time gap and its effect on polymerization shrinkage, degree of conversion and microhardness of a nanohybrid composite.
abstract: BACKGROUND
  Giving a time gap and distance during curing can decrease the polymerization shrinkage.
  
  
  OBJECTIVE
  To evaluate the effect of time gap and distance between the curing tip and restoration on the polymerization shrinkage, degree of monomer conversion (DOC), and microhardness of a nanohybrid composite.
  
  
  METHODS
  A total of 50 standardized cylindrical specimens (Z350, 3M ESPE) were fabricated using a brass mould. The curing was done in contact with the sample surface for 20 seconds in the control group. In the four experimental groups, curing was initiated at 1-cm distance, followed by variation in the time gap and the curing cycle. The polymerization shrinkage, DOC, microhardness was calculated.
  
  
  METHODS
  One-way analysis of variance (ANOVA) and post hoc-Dunnett test were used to analyze the data.
  
  
  RESULTS
  Curing at 1-cm distance for 10 seconds with a gap of 10 seconds and finishing the curing cycle with 20 seconds at 0 cm proved to be an appropriate technique to reduce the polymerization shrinkage without significantly affecting the DOC and microhardness.
  
  
  CONCLUSIONS
  A simple innovative modification of varying the distance of curing and a time gap in the curing cycle can decrease the polymerization shrinkage without affecting the DOC and microhardness.
authors.affiliation: Department of Conservative Dentistry and Endodontics, Sree Balaji Dental College and Hospital, Bharath University, Narayanapuram, Pallikaranai, Chennai, Tamil Nadu, India.
authors.forename: Arunajatesan
authors.initials: A
authors.lastname: Subbiya
authors.affiliation: Department of Conservative Dentistry and Endodontics, Sree Balaji Dental College and Hospital, Bharath University, Narayanapuram, Pallikaranai, Chennai, Tamil Nadu, India.
authors.forename: Newbegin Selvakumar Gold
authors.initials: NS
authors.lastname: Pearlin Mary
authors.affiliation: Department of Conservative Dentistry and Endodontics, Sree Balaji Dental College and Hospital, Bharath University, Narayanapuram, Pallikaranai, Chennai, Tamil Nadu, India.
authors.forename: Malathi
authors.initials: M
authors.lastname: Suresh
authors.affiliation: Department of Conservative Dentistry and Endodontics, Sree Balaji Dental College and Hospital, Bharath University, Narayanapuram, Pallikaranai, Chennai, Tamil Nadu, India.
authors.forename: Paramasivam
authors.initials: P
authors.lastname: Vivekanandhan
authors.affiliation: Department of Conservative Dentistry and Endodontics, Sree Balaji Dental College and Hospital, Bharath University, Narayanapuram, Pallikaranai, Chennai, Tamil Nadu, India.
authors.forename: Malarvizhi
authors.initials: M
authors.lastname: Dhakshinamoorthy
authors.affiliation: Department of Conservative Dentistry and Endodontics, Sree Balaji Dental College and Hospital, Bharath University, Narayanapuram, Pallikaranai, Chennai, Tamil Nadu, India.
authors.forename: Vridhachalam Ganapathy
authors.initials: VG
authors.lastname: Sukumaran
keywords: Curing distance; polymerization shrinkage; time gap
references.citation: Quintessence Int. 2010 May;41(5):417-25
references.pmid: 20376378
references.citation: Dent Mater. 2001 Jul;17(4):359-66
references.pmid: 11356214
references.citation: Quintessence Int. 2008 Feb;39(2):e74-84
references.pmid: 18560645
references.citation: Med Oral Patol Oral Cir Bucal. 2006 Mar 01;11(2):E215-20
references.pmid: 16505805
references.citation: J Dent Res. 2010 Jun;89(6):549-60
references.pmid: 20299523
references.citation: J Dent Res. 1984 Aug;63(8):1093-5
references.pmid: 6235253
references.citation: Oper Dent. 2005 Jul-Aug;30(4):474-80
references.pmid: 16130868
references.citation: Dent Mater. 2010 Sep;26(9):908-14
references.pmid: 20557926
references.citation: J Dent Res. 2001 Jun;80(6):1570-3
references.pmid: 11499515
references.citation: J Contemp Dent Pract. 2006 Jul 01;7(3):12-21
references.pmid: 16820803
references.citation: J Esthet Restor Dent. 2003;15(2):93-103; discussion 104
references.pmid: 12762473
references.citation: Dent Mater. 2012 May;28(5):512-20
references.pmid: 22217607
references.citation: J Dent. 1992 Jun;20(3):183-8
references.pmid: 1624624
references.citation: J Biomed Opt. 2004 May-Jun;9(3):601-8
references.pmid: 15189099
references.citation: Dent Mater. 1993 Jan;9(1):11-4
references.pmid: 8299861
references.citation: Dent Mater. 1994 Sep;10 (5):290-7
references.pmid: 7498589
references.citation: J Dent Res. 2005 Jul;84(7):663-7
references.pmid: 15972598
references.citation: J Dent. 1997 Nov;25(6):435-40
references.pmid: 9604575
references.citation: Oper Dent. 2006 Jan-Feb;31(1):3-10
references.pmid: 16536187
references.citation: Eur J Dent. 2010 Oct;4(4):440-6
references.pmid: 20922164
references.citation: J Dent. 1991 Oct;19(5):312-6
references.pmid: 1839631
references.citation: Dent Mater. 2005 Jan;21(1):36-42
references.pmid: 15681000