Accuracy of dental surveyors

Maximum lateral forces as measured by strain gauges mounted on the analysing rod of a Nesor surveyor for four operators during surveying procedures ranged from 81 to 110 cN (mean 92.4 cN). Maximum lateral forces used when trimming blockout and inlay wax ranged from 159 to 184 cN (mean 169 cN) and 137 to 196 cN (mean 172 cN), respectively. Mean tilting errors produced in the vertical surveying arm by lateral loads of 98 and 196 cN (i.e. weights of 100 and 200 g) were determined to be 0.29 and 0.42 degrees for five Nesor surveyors and 0.21 and 0.36 degrees for five Krupps surveyors, respectively. All surveyors had been in constant use for at least 12 years. Play in the bearings of the horizontal arm due to loads of the same magnitude applied obliquely produced an additional mean error of approximately 0.5 degrees in the Krupps surveyors. Finally, discrepancies of up to approximately +/- 0.04 mm were found in 10 undercut gauges in each of the nominal sizes 0.25, 0.50 and 0.75 mm. It is concluded that surveyors and their accessories should be checked and serviced regularly, and possible sources of error pointed out to potential users.