The nature of the side-shift in lateral mandibular movement and its implications in clinical practice

Abstract

S everal authors have reported that in excursive mandibular movement there is a lateral translation of the rotating condyle.‘-3 The name of Bennett” is closely associated with this phenomenon, although it represented only a small part of his article. This bodily shift that occurs in lateral movements had been previously noted5-” and has come to be described as the side-shift. The side-shift of the mandible must have an effect on the paths of movement of any of its constituent parts, in particular those traced by the cusp tips. Consequently, in the restoration of an occlusion, the nature of the side-shift has been considered a highly significant factor.9-‘2 This was particularly so when the concepts of an immediate side-shift (ISS) emerged. The ISS has been described as a direct lateral translation of the entire mandible before any rotational movement has taken place13 in contrast to a progressive side-shift (PSS).9 An investigation of ISS is intimately bound to considerations of the centric relation position (CRP), which has to be the starting point of any such movement. In the attempted recording of CRP, it appears possible to capture a “sagged” position of the condyle.14 ” Dawson” showed that when chin-point guidance is used in attempts to “jiggle” or manipulate the mandible into its most retruded position, the condyles may not be in their most superior position. A sagged condyle position could also be recorded when unguided retrusive movements are encouraged by placing the tip of the tongue far back into the palate. In this position the medial pole of the condyle may have lost its intimate contact with the medial wall of the glenoid fossa, and an ISS would then be possible. In other words, the sagged condyle becomes a so-called floating condyle (Fig. 1). Starting from the correct CRP with the medial pole braced against the medial wall of the fossa by the