Electrical stimulation may be used in an attempt to condition the masticatory muscles prior to recording CR, together with electromyographic instrumentation to determine lack of muscle splinting. These tend to be patients who appear to have lost occlusal vertical dimension (OVD), either with excessive wear or tooth loss, and where an increase in OVD, and therefore an occlusal reorganisation, is planned. When using a fluid material, a stable anterior stop is imperative for the mandibular incisors to rest against (Fig 8-17a,b). Optical bite registration is based on optical impressions of â¦ As with an ICP record, obtaining accuracy to within a few micrometres is necessary if you are to make the most of the technology you are using. Excessive tooth wear is often compensated for by dentoalveolar extrusion. Again, trim for proper seating on casts. Wax rims are, however, supported only by soft tissues, so when patients bite onto a wax rim the baseplate is displaced into the soft tissues. Hence, anterior teeth are better positioned than posterior teeth to accept the non-axial forces associated with excursive loading of the mandible. They should be so shaped that they represent the lost teeth and supporting structures. It is not difficult, but it only comes with practice. Simply squeezing the casts together with, for example, an elastic band is not the answer, as the material will deform under pressure, resulting in unpredictable occlusal changes. The reasons may include: distorted casts â undetected impression distortion can result in normal looking casts, blebs and faults on the occlusal surfaces, a limited number and arrangement of teeth, malocclusions, such as open bites (Fig 8-10) or cusp-to-cusp occlusion. The answer to this is no, not for routine examinations. The dentist should give some advice to reach this position. A rigid acrylic stent provides greater reliability than wax rims. Rather than linking opposing copings together, the upper copings are made with a rounded occlusal excrescence, which is coated in petroleum jelly. For this purpose, it is helpful to use a Lucia jig at the selected vertical dimension, as described below. give a positive response me, the e-book will agreed appearance you Fig 8-6b There were also non-working-side interferences (again marked in red) on the upper right first and second molars. In addition, the occlusal plane and fullness of the lips are established, and other orientation marks for the artificial teeth are traced. The important thing to remember about this type of material is that it needs to be trimmed, whether it is being used as a sectional or full-arch registration (Fig 8-11a,b). This ensures that the restored tooth will be correctly aligned and interdigitating with the opposing teeth on normal closing of the jaws. In such circumstance it is better to use a low-viscosity material, such as a silicone registration mousse, or a traditional zinc-oxide eugenol registration paste carried on a gauze frame. More unusual causes of deflective contacts and interferences include jaw fracture and tooth movements occurring during pregnancy (Fig 8-1). The extent of the examination will vary from patient to patient. In order to determine the variation of individual terminal hinge axis positions in the sagittal plane, 118 stomatognathicly healthy patients were subjected to three occlusal registration methods. An irregular, broken or dog-legged appearance suggests an interference, either on the tooth itself or on a tooth distant to it (Fig 8-6a,b). The occlusal registration is an important diagnostic source of information for dentists and orthodontists. It is always worth knowing if the patient is a bruxist, as this will help in both the diagnosis of problems of excessive occlusal loading (see Chapter 3) and the prescription of suitably robust restorations. If the styli marks from all three registrations correspond, you can be confident about the registration. All of them locate to three reference points on a patient. Parafunction is often episodic, and so the detection of faceting and vertical microfractures does not mean that bruxism is active at that time. Alternatively, syringe the mousse onto the occlusal surfaces of the lower arch and manipulate the patient into CR. Images obtained using the 3 methods were analyzed using ImageJ software. Nevertheless, some patients are difficult to manipulate. Look out for an anterior thrust associated with a deflective RCPâICP slide. The key to success with a Lucia jig is to ensure that the occluding portion lies flat against no more than two incisors. Murray, M.C. One solution is to construct an acrylic stent or bar; this acts as a rigid vehicle to carry registration material, thereby avoiding the less reliable wax occlusal rims. The Whip Mix facebow uses the nasal bridge (nasion), while the third reference point for the Denar is a fixed distance, marked on the cheek with a pen, above the incisal edge of the right lateral incisor (Fig 8-19). The influence of experimental interfering occlusal contacts on the postural activity of the anterior temporal and masseter muscles in young adults. The DVD shows a number of tips, including: drying the teeth and smearing material on the occlusal surfaces prior to seating the tray to avoid occlusal air blows (Fig 8-8), pulling unset material over the heel of the tray with a mouth mirror to help keep the impression in the tray on removal from the mouth, trimming the impression to allow inspection and reduce distortions prior to pouring up (Fig 8-9). Without trimming, and sometimes even with trimming, the mounting will often feel springy when the registration is sandwiched between the casts. If you do not use adhesive with a perforated tray or you give insufficient time for the adhesive solvent to evaporate, the risk of this distortion is greatly increased. Nevertheless, in a small minority of patients, the muscle splinting consistently returns the teeth to ICP and the mandible remains extremely difficult to manipulate. Occlusal registration: science or art? (Courtesy of Dentsply International.). Furthermore, restorations may, on occasion, be made on casts mounted in CR. Where one is used, it should be as minimal as is required to locate the casts accurately. Figures 8-25 to 8-31 illustrate various considerations for jaw relation registration. The characteristics and performance of materials used in occlusal records as well as the accuracy and reliability of available methods for identifying these contacts have been extensively investigated. Problems with hand-held casts occur when they cannot be easily and reliably located in a stable intercuspal relationship. The simplest and most frequently used technique involves bimanual manipulation to locate the patientâs condyles in CR (Fig 8-15) and then taking a hard wax record, as shown in detail on the DVD. Sometimes, as shown in the DVD (animation I) and discussed in more detail in Chapter 3, posterior contacts can act as pivots or fulcrums.
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