RELIABILITY AND VALIDITY OF A TRANSVERSE HORIZONTAL AXIS LOCATION INSTRUMENT

Previous studies have demonstrated a relatively accurate location of the transverse horizontal axis (THA) with several different instrument systems. This study statistically evaluated the reliability and validity of an instrument used to locate a known THA on a mannequin. Three experienced prosthodontists were the subjects. Each operator used 15 mm of interincisal are to locate the THA. The mandibular stylus was aligned by the investigator with the known horizontal axis. The vertical microdot flags were positioned so the stylus was over a known coordinate and were repositioned so the operator could attempt to locate the axis. The known coordinates were varied with each of four trials. Subjects No. 1 and 3 demonstrated the best coefficient of reliability, 0.25. The 95% confidence interval for linear deviation from the known was 0.44 ± 0.10 mm on the right side and 0.97 ± 0.10 mm on the left side. These confidence intervals did not include zero. A statistically better result was achieved on the right side compared with the left side (F1,3 = 131.24, p = 0.0014). The results of this study indicate that a random error factor of 0.3 to 1.2 mm can be expected when this instrument system is used clinically. © 1990.