Clinical techniques

Sir, I am writing to point out an error in the article Recording the Retruded Contact Position: a Review of Clinical Techniques in BDJ 2004, 196: 395–402. On page 398, discussing the Myo-monitor, the author states, 'Proponents of the Myo-monitor suggest that the 'jaw-closer' muscles act simultaneously, via reflex contraction, to produce a reproducible retruded mandibular position.' This is a grossly inaccurate statement. As the President of Myotronics-Noromed, Inc, I will hereafter correctly describe the function and objective of the Myo-monitor's use.

The Myo-monitor is a muscle stimulator which induces involuntary contraction of the muscles controlled by the facial (VII) and masticatory (V) cranial nerves. Through the relaxation of these muscles the Myo-monitor is used to achieve a rest position from which a 'neuromuscular occlusion position' is established. The article incorrectly asserts that the Myo-monitor produces a 'retruded mandibular position'. According to Cooper¹ 'Identification of the mandibular rest position is used as a reference point for the selection of a neuromuscularly based occlusal position. Physiologic ergonomic principles dictate that the muscles function best at resting length.' 'From the rest position, the TENS stimulation is increased slightly, causing the mandible to rise on a trajectory.' 'A therapeutic occlusal position is selected approximately 1mm above the rest position on the neuromuscularly stimulated trajectory.' When used as described, the Myo-monitor most commonly produces a, physiologically valid mandibular position, most certainly not in a retruded position as stated in the article by Wilson and Banerjee.

The authors of the paper respond: We thank Mr Adib and wish to respond to the comments regarding our 'grossly inaccurate statement.' In our summary of the Myo-monitor, we state that the Myo-monitor is a jaw muscle stimulator which is '..reputed to achieve muscle relaxation and produce a neuromuscular mandibular position'. This correlates with your explanation. Thereafter, increased transcutaneous electrical stimulation of the mandibular elevator muscles, via cranial nerves V and VII, will produce mandibular closure about an arbitrary condylar axis ² , or trajectory as you put it.

This is not the retruded axis in the purist sense, when related to the Glossary of Prosthodontic Terms ³ , but it does produce mandibular closure, and ultimately tooth contact, on a path posterior to that of the subject's Intercuspal Position (ICP) ² . This must mean that the mandibular position produced by the Myo-monitor is a retruded one relative to ICP, and thus our statement 'Proponents of the Myo-monitor suggest that the 'jaw-closer' muscles act simultaneously, via reflex contraction, to produce a reproducible retruded mandibular position' is entirely valid. Whether this retruded mandibular relationship is indeed reproducible was considered in our appraisal of the available literature.