Three-dimensional analysis of the interchangeability of a semiadjustable articulator system in service over time.

STATEMENT OF PROBLEM: Some contemporary articulator systems claim to be highly precise in their interchangeability, with tolerances below 10 µm in vertical error; however, the claims have not been independently verified. PURPOSE: The purpose of this study was to investigate the interchangeability of calibrated semiadjustable articulators in service over time. MATERIAL AND METHODS: A calibrated mounting articulator served as the master articulator, while the test groups were used articulators with a minimum of 1-year use by predoctoral dental students (n=10); used articulators with a minimum of 1-year use by prosthodontic residents (n=10); and new articulators (n=10). One set of mounted maxillary and mandibular master models was positioned in the master and test articulators. High-precision reference markers on the master models were used to determine interarch 3D distance distortions (dRR, dRC, and dRL), interocclusal 3D distance distortion (dRM), interocclusal 2D distance distortions (dxM, dyM, and dzM), and interocclusal angular distortion (dθM) relative to the master articulator. All measurements were conducted three times using a coordinate measuring machine and then averaged to derive the final data set. RESULTS: For interarch 3D distance distortion, the mean dRR ranged from 4.6 ±21.6 µm for new articulators to 56.3 ±47.6 µm for articulators used by prosthodontic residents; mean dRC ranged from 65 ±48.6 µm for new articulators to 119.0 ±58.8 µm for articulators used by prosthodontic residents; and mean dRL ranged from 12.7 ±39.7 µm for articulators used by prosthodontic residents to 62.8 ±75.2 µm for new articulators. For interocclusal 3D distance distortion, the mean dRM ranged from 21.5 ±49.8 µm for new articulators to 68.6 ±64.9 µm for articulators used by predoctoral dental students. For the 2D distance distortions, the mean dxM ranged from -17.9 ±43.4 µm for articulators used by predoctoral dental students to -61.9 ±48.3 µm for articulators used by prosthodontic residents; mean dyM ranged from 18.1 ±59.4 µm for new articulators to 69.3 ±115.1 µm for articulators used by prosthodontic residents; and mean dzM ranged from 29.5 ±20.2 µm for new articulators to 70.1 ±37.8 µm for articulators used by prosthodontic residents. Mean dθM ranged from -0.018 ±0.289 degree for new articulators to 0.141 ±0.267 degree for articulators used by prosthodontic residents. One-way ANOVA by articulator type revealed statistically significant differences among the test groups for dRR (P=.007) and dzM (P=.011) only, where articulators used by prosthodontic residents fared significantly poorer than the other test groups. CONCLUSIONS: The new and used articulators tested did not fulfill the manufacturer's claim of accuracy of up to 10 µm in the vertical dimension. Up to 1 year of time in service, none of the investigated test groups fulfilled the criterion for articulator interchangeability, even if the more lenient threshold of 166 µm were accepted.