Pivot appliances - is there a distractive effect on the temporomandibular joint?

The purpose of this study was to investigate the distractive effect of posterior occlusal pivots on the temporomandibular joint. The study comprised 23 healthy subjects. None of them had a third molar and none of them had a missing tooth or showed tooth mobility. All subjects clenched (i) on 1 mm tin foil positioned between the teeth 17/47 and 27/37; (ii) on a stiff bite registration material of 1 mm thickness that prevented protrusion because of its bold occlusal relief. During clenching on the tin foil and on the protrusion preventing bite registration material, respectively, the vertical and horizontal condylar position was measured using a 6 d.f. ultrasonic motion analyser. Clenching with maximal force on the tin foil lead to a noticeable anterior downward directed movement of the condyle. Clenching on the protrusion preventing pivot, however, caused a statistically significant upward condylar movement of about 0.3 mm. These results indicate that occlusal pivots have no distractive effect on the temporomandibular joint but can lead to unwanted joint compression, if they are designed in a way that is preventing protrusion.