title: Investigation of polymerisation shrinkage strain, associated cuspal movement and microleakage of MOD cavities restored incrementally with resin-based composite using an LED light curing unit.
abstract: OBJECTIVE
  To investigate the polymerisation shrinkage strain, associated cuspal movement, degree of conversion (DC) and cervical gingival microleakage of mesio-occlusal-distal (MOD) cavities restored with four resin-based composite (RBC) filling materials placed incrementally using a light emitting diode (LED) light curing unit (LCU).
  
  
  METHODS
  Standardised extensive MOD cavity preparations on extracted teeth were performed on 40 sound upper premolar teeth. Restoration of the teeth involved the placement of RBCs in eight increments with the appropriate bonding system before irradiation using an LED LCU. Buccal and palatal cusp deflections at each stage of polymerisation were recorded using a twin channel deflection measuring gauge. Following restoration, the teeth were thermocycled, immersed in a 0.2% basic fuchsin dye for 24 h, sagittally sectioned and examined for cervical microleakage. The DC was determined using a Fourier transform infra-red (FT-IR) spectrometer.
  
  
  RESULTS
  No significantly difference (P=0.677) in cuspal movement was recorded for Z100 (13.1+/-3.2 microm) compared with Filtek Z250 (8.4+/-3.5 microm), P60 (7.3+/-3.8 microm) and Admira (6.7+/-2.7 microm). The LED LCU deflections were compared with a halogen LCU used in a conventional (Fleming GJP, Hall D, Shorthall ACC, Burke FJT. Cuspal movement and microleakage in premolar teeth restored with posterior filling materials of varying reported volumetric shrinkage values. Journal of Dentistry, 2005;33:139-146) and soft-start mode (Fleming GJP, Cara RR, Palin WM, Burke FJT. Cuspal movement and microleakage in premolar teeth restored with posterior filling materials cured using 'soft-start' polymerization. Dental Materials, 2006, , in press) and a significant reduction in cuspal movement was identified for curing type and material type (P<0.001 and P=0.002, respectively). No significant differences were noted between the four RBC materials investigated when the DC or microleakage scores were examined for the LED LCU.
  
  
  CONCLUSIONS
  It would appear that irradiation of RBCs using the LED LCU offered a significant reduction in associated cuspal movement in large MOD cavities. However, the microleakage scores following polymerisation were significantly increased with dye penetration into the pulp chamber from the axial wall evident in teeth restored with the LED LCU.
authors.affiliation: Materials Science Unit, Division of Oral Biosciences, Dublin Dental School & Hospital, Trinity College Dublin, Dublin 2, Ireland. garry.fleming@dental.tcd.ie
authors.forename: G J P
authors.initials: GJ
authors.lastname: Fleming
authors.forename: S
authors.initials: S
authors.lastname: Khan
authors.forename: O
authors.initials: O
authors.lastname: Afzal
authors.forename: W M
authors.initials: WM
authors.lastname: Palin
authors.forename: F J T
authors.initials: FJ
authors.lastname: Burke
mesh_terms: D001641:Bicuspid; D004396:Coloring Agents; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D001840:Dental Bonding; D003737:Dental Cavity Preparation / Q000145:classification; D003763:Dental Leakage / Q000145:classification*; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D003793:Dental Restoration, Permanent / Q000145:classification* / Q000379:methods; D004867:Equipment Design; D006801:Humans; D008027:Light; D008029:Lighting / Q000295:instrumentation*; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D011108:Polymers / Q000737:chemistry; D012394:Rosaniline Dyes; D012822:Silicon Dioxide / Q000737:chemistry / Q000528:radiation effects; D012833:Siloxanes / Q000737:chemistry / Q000528:radiation effects; D017550:Spectroscopy, Fourier Transform Infrared; D013314:Stress, Mechanical; D013499:Surface Properties; D019228:Tooth Crown / Q000473:pathology*; D015040:Zirconium / Q000737:chemistry / Q000528:radiation effects
chemical_list: D004396:Coloring Agents; D003188:Composite Resins; D003764:Dental Materials; C444701:Filtek Z250; D008689:Methacrylates; C443708:P60 Condensible Resin Composite; D011108:Polymers; D012394:Rosaniline Dyes; D012833:Siloxanes; C083568:Z100 composite resin; C479084:admira; C025485:basic fuchsin; D012822:Silicon Dioxide; D015040:Zirconium