title: The use of shimstock to assess occlusal contacts: a laboratory study.
abstract: OBJECTIVE
  This laboratory study investigated the influence of varying occlusal forces, occlusal contacts, or small gaps (0 to 8 microns) on the force required to pull 8-micron shimstock from between a tooth and a restorative material specimen.
  
  
  METHODS
  An apparatus was developed and calibrated to (1) produce and measure very small gaps (0 to 20 microns) and apply variable occlusal forces between specimens, and (2) pull shimstock consistently from between the specimens and measure the removal force. An unworn maxillary molar cusp and polished amalgam were used as the opposing specimens. Combinations of occlusal forces from 0 to 400 g and gaps of 0 (contact), 2, 4, 6, and 8 microns were tested.
  
  
  RESULTS
  Shimstock removal forces increased linearly with increasing occlusal force with 0-, 2-, 4-, and 6-micron gap settings. With 0-, 2-, and 4-micron gaps, there was no significant difference in removal force. With a 6-micron gap, the forces rose but at a lower gradient. With the 8-micron gap, the mean force was low (less than 12 g).
  
  
  CONCLUSIONS
  The shimstock removal force increased with occlusal force and was highest with the smaller gaps. Using 8-micron shimstock, 0-, 2-, and 4-micron gaps cannot be differentiated, a gap of up to 6 microns may still be assessed as a holding contact because the shimstock is still gripped, and even an 8-micron gap may be recorded as a light contact since there is still friction on removal.
authors.affiliation: Guy's and St Thomas's Hospital Trust, Eastman Dental Institute of Oral Healthcare Sciences, University of London, United Kingdom. kenharper88@hotmail.com
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Harper
authors.forename: Derrick J
authors.initials: DJ
authors.lastname: Setchell
mesh_terms: D000704:Analysis of Variance; D001732:Bite Force; D003723:Dental Amalgam; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D007574:Jaw Relation Record / Q000295:instrumentation* / Q000379:methods; D018709:Statistics, Nonparametric
chemical_list: D003723:Dental Amalgam