Error variance and sensitivity associated with three different Periotron® instruments

Calibration curves for three different Periotron® instruments, two model HAR‐6000 and one HAR‐600, were determined using human serum. These curves revealed a quadratic relationship between the volume and Periotron® readout for all three models. The calibration curve data were subjected to an analysis of covariance to test the equality of the three slopes. These were found to be different (p < 0.00001) and pairwise comparisons of the slopes were done. The procedure showed that the differences, as measured by the different slopes of the three instruments, were statistically significant (p < 0.0001). Although there were only small differences in the response to volume ratios, and hence also in the slopes of the calibration curves of the two HAR‐6000 models, these were nevertheless significant (p ≤ 0.001). All three instruments showed good reproducibility as determined by error variances. The newer of the two HAR‐6000 models showed the best reproducibility while the other had values similar to those of the HAR‐600 instrument. It was concluded that the significantly differing response: volume ratios for the various Periotron® models necessitate the construction of calibration curves for these instruments before and during clinical studies. In addition, our data enable regular assessment of instrument reproducibility, which is an essential procedure in any long‐term project using them to measure periodontal status.