Dental Tribune United Kingdom Edition

May 21-27, 201224 Clinical United Kingdom Edition T he term neuromus- cular occlusion has become associated with certain limited methodolo- gies that are used to obtain a muscle-compatible occlusal relationship. In reality, there are several different approaches that can be used to determine a “neuromuscular” maxillo-mandibular relation- ship, even with a fully edentu- lous case. Within each method, however, the common basis for all muscle-oriented approach- es involves first determin- ing the resting length of the masticatory muscles. Historically, opening the bite has been considered hazardous and/or foolhardy by many dentists and with good reason. Arbitrary open- ing of the bite, especially when accomplished strictly on an articulator, can result in a difficult, uncomfortable and unappreciative patient. Some dentists have recommended against ever opening a bite, perhaps after an especially troublesome experience with a patient. In spite of the risks, there are some advantages associat- ed with opening an over-closed bite. The identification can be traced back at least 70 years to an ENT physician, Dr J B Costen.1-3 Dr Costen discov- ered, perhaps quite by acci- dent after referring many of his symptomatic, edentulous patients to a local dentist for new dentures, that many re- turned with their head and ear pain symptoms greatly relieved. His publications were positively received at the time and, in fact, what we refer to today as temporo- mandibular disorders (TMDs) were originally referred to as “Costen’s Syndrome.” While we know today that many TMD patients are not over- closed, over-closed patients do often exhibit some of the signs and symptoms commonly associated with TMD. Thus, although over-closure in and of itself is not pathognomonic of TMD, it should be consid- ered as a risk factor. The use of the patient’s own muscles to determine the ver- tical dimension of occlusion was already being explored in the 1940s by people like or- thodontist John R Thompson.4 Sears5 introduced the concept of the “Pivot Appliance” in the 1950s, which was designed to open the bite enough to allow the patient’s muscles to reposition the mandible. Fol- lowing their lead, others6-28 have subsequently evolved the current array of neuromus- cular registration methods presently in use. At the same time, several studies29-32 have demonstrated that a muscle- determined position, although similar, is not identical to centric relation. Common signs and symp- toms of over-closure When asked, over-closed patients often report symptoms such as frequent headaches, dull pain of the elevator mus- cles and pain or stiffness in their neck muscles. Ear stuffi- ness, tinnitus and/or vertigo are also commonly reported. A more subtle symptom, less often reported, is frequent gastrointestinal distress in various forms that has no clear, identifiable cause. This may also be ac- companied by a report of difficulty in chewing and/or swallowing. An over-closed patient will usually report several, but not all, of the following symptoms: 1. Frequent headaches with no identifiable cause 2. Ear stuffiness with no indi- cation of ear pathology 3. Difficulty in chewing tough foods 4. Difficulty or discomfort in swallowing 5. Frequent gastrointestinal distress 6. Vertigo 7. Tinnitus 8. Persistent dull pain in mas- ticatory elevator muscles 9. Neck pain or stiffness 10. Possible increased wear of incisor teeth Under examination, a number of signs indicating over-closure may appear. These include: 1. A measured freeway space greater than 3mm 2. EMG or visual identifica- tion of a tongue-thrust swallow 3. The appearance of less than fully erupted molars 4. A deep curve of Spee 5. One or more posterior edentulous spaces 6. Lingually tipped mandibu- lar molars 7. EMG identification of el- evator muscle hyperactivity at rest of more than 2.0 micro- volts average (or 2.2 micro- volts RMS) 8. Worn and shortened teeth (there is no scientific evidence that human teeth “grow out” in response to wear in the way that elephant’s teeth do) 9. Horizontal skin creasing and saliva weeping at the cor- ners of the mouth 10. A so-called “Shimbashi” measurement (in centric occlu- sion) of less than 16mm from the cemento-enamel junction of the maxillary central inci- sor to the cemento-enamel junction of its opposing man- dibular tooth 11. Long-term chronic in- ternal derangement of the TM Joint(s) However, patients rarely seek dental treatment for any of these objective signs. In- stead, they are more likely to seek rehabilitative treatment for headache, jaw-ache, ear- ache, difficulty in chewing/ swallowing or for purely aes- thetic reasons. In other cases, they are unaware of their condition, apparently due to their excel- lent adaptability. In the over- closed patient the “reason” for treatment, either cosmetic or functional, is often depend- ent more on his/her individual adaptability than on the den- tal conditions present. While some signs simply indicate the “progress of the destruction” that a pathological maxillo- mandibular relationship fos- ters, other signs may indicate a successful adaptation. 1. Freeway space > 3mm (if pain level is low, it is an adap- tation, otherwise it is not) 2. Tongue thrust swallow (if full arch tongue thrust, usually a successful compensation) 3. The appearance of less than fully erupted molars (tongue inhibition of natural eruption) 4. A deep curve of Spee (of- ten associated with one or more missing molars or a deep anterior overbite with retro- clined upper incisors) 5. One or more posterior edentulous spaces (leads to deep curve of Spee) 6. Lingually tipped posterior teeth (tongue thrust during swallow, restricted maxillary arch) 7. Hyperactivity of elevator muscles at “rest.” (an adapta- tion, successful if no elevator muscle pain) 8. Worn/short teeth, ab- fractions (ground off) (not a successful adaptation) 9. Skin creasing at corners of mouth (may appear as aesthetic problem only, not an adaptation) 10. Saliva weeping at corners of mouth (an aesthetic and functional problem, not an adaptation) 11. CEJ (cemento-enam- el junction) to CEJ in C.O. < 16mm. (less than the normal adaptive range) 12. Internal derangement(s) of the TMJ (if no degenera- tion, may be a successful adaptation) Maxillo-mandibular bite relationships Centric Occlusion (CO = habitual) The maxillo-mandibular position of maximum intercus- pation is most often the dental treatment position, primarily by default. This is of neces- sity whenever single tooth preparations or small restora- tions are involved, since they must fit within the patient’s existing occlusal scheme. Dr Derek Mahony presents the first article of this two-part series Re-establishing a physiologic vertical dimension for an over-closed patient Fig 1 BioJVA* testing for normal TM joints