In a previous article I talked about tips for consistent models. While good models are of critical importance so is putting them in an articulator that sufficiently replicates the functional movements of your patient. When we think about the different types of articulators in use today there are significant differences among them. There are two common general categories: Semi-adjustable (such as the Sam 3) and small non-adjustable (such as a Foster Articulator) or as one of my instructors Herbert T. Shillingberg used to call them, snake killers.
His assertion, at least at the time, was that these small non-adjustable articulators are really only good for a snake to slither across an open articulator and then slam it shut, thereby killing the snake. While I love calling them snake killers too, the simple fact is despite their design flaws, sometimes they work. The flaws with these articulators stem from their size. Given their small size there is no way to arrange the models to accurately replicate the patients functional movements.
If we simply look at where these instruments place the joint, simple physics dictate the resultant axis of motion in both closure and lateral movements and is grossly inaccurate as depicted by green in the illustrations above. While I bet every dentist has used this type of articulator at one time or another, they have the high potential to introduce significant error that may affect your restorative case. Additionally if used for planning, the error they introduce may influence the decisions you make in planning. While you might be able to use it for some restorative cases, I would never recommend they be used for diagnostic planning.
The other frequently used class of articulators is semi-adjustable such as the Sam 3. They are not 100 percent accurate but for most patients the error they introduce is not significant enough to affect your decision-making during planning or negatively impact the fabrication of your patient's restorations. What makes semi-adjustable articulators much more accurate is their size and that they simulate the average patient's joint and function with a reasonable level of accuracy as depicted by red in the above illustrations. The important thing to realize here is that all semi-adjustable articulators are based on averages so if your patient is extremely small or large and outside of these averages, the accuracy is negatively impacted.
John R. Carson, DDS, PC, Spear Visiting Faculty. [ www.johnrcarsondds.com ]