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ePaper created 2016-11-11, 09:18:10 | version 1.38.0
2016 Pakistan Edition DENTAL TRIBUNE 7 CLINICAL PRACTICE May suggested that uniform tooth contact and resultant wear on several teeth in lateral occlusion was a positive and inevitable outcome. As a modification of canine guidance, the Pankey Mann Schuyler philosophy in complete full mouth reconstruction was to have simultaneous contacts of the canine and posterior teeth in the laterotrusive (working) excursion, known as group function, and only anterior teeth contact in the protrusive excursive movement. Schuyler further suggested that incisal guidance without freedom of movement from a centric related occlusion (CRO) to a more anterior tooth intercuspation (CO) will ‘lock- in’ the posterior occlusion (long centric). The incisal guidance, along with ‘long centric’, is determined by the distance from transverse horizontal axis-centric relation and the normal freedom of movement in the envelope of function. This method requires that the incisal guidance be established and the mandibular posterior buccal cusps be placed to a height measured along the occlusal plane as dictated by the curve of Monson. The maxillary posterior teeth are developed after the completion of the mandibular restorations as dictated by a wax functionally generated path record. The definitive restorations are equilibrated into a centric relation position with mandibular buccal cusps onto a flattened fossae-marginal ridge contact with ‘freedom in centric’ anterior guidance and group function in laterotrusive (working) excursion. Deflective contacts Though 90% of natural dentitions have a deflective occlusal contact or an occlusal ‘prematurity’ between centric related occlusion (CRO) and centric occlusion (CO), it is usually in the form of a slide that has both a vertical and horizontal component occurring in all three planes. According to Ash and Ramfjord, the horizontal ‘long centric’, from centric related occlusion to centric occlusion, should be incorporated into a restoration by means of a post restorative occlusal adjustment. Dawson illustrates the ‘freedom in centric’ concept within the lingual concavity of the maxillary anterior teeth. He redefines long centric as ‘freedom to close the mandible either into centric relation or slightly anterior to it without varying the vertical dimension at the anterior teeth’. Additionally, long centric accommodated changes in head position and postural closure (Mohl position). Gnathology versus PMS Gnathologists believe that once the condyles are positioned in retruded axis position (centric relation), any movement out of this position should disocclude the posterior segment, thus nullifying any horizontal cusp- fossae area contact. This belief, combined with the immediate anterior disocclusion, forms the basis of a mutually protected occlusion and limits tooth wear. The PMS occlusal scheme, however, encourages multiple occlusal contacts during lateral movements (group function or wide centre) and during protrusive movements (long centric). This may have the effect of increasing tooth wear. It is, therefore, logical that the PMS occlusal scheme recommends that occlusal wear is physiological, not pathological as suggested by gnathologists. The task of adjusting maximum intercuspation contacts in two different positions on an articulator may result in a lack of precision in both positions. However, the masticatory system has the ability to adapt to various influences and though, in the author’s opinion, the concept of gnathology will produce stable long-term results, some patients may require more freedom in their occlusion and the PMS concepts are not to be dismissed in these patients. Indeed, some PMS concepts such as waxing-up the curve of Spee and Monson prior to occlusal rehabilitation are incorporated into every day occlusal practice. Case study Patient A was referred to me for a full mouth reconstruction and aesthetic improvements to her smile (Figures 1-3). Initial impressions, facebow and jaw registration were taken for mounted study models (Figure 4). The study models showed the degree of over-eruption of her anterior segments and disturbances to the occlusal plane (Figures 5-8). Initial diagnostic waxing (Figures 9-12), prototypes (Figures 13 and 14) and prep guides (Figures 15 and 16) were completed using a lower curve of Spee of a 4” radius (anatomical average as recommended by the PMS techniques). Initial prototypes were placed with large palatal ramps on the upper anterior teeth to allow anterior tooth contacts and thus an immediate disclusion style of occlusal scheme as recommended in the gnathological approach. During the course of the initial preparation and prototypes and after a period of stabilisation, the patient was struggling to come to terms with the palatal ramps from a speech and comfort point of view. The decision was made to change the occlusal scheme to a PMS ‘freedom in centric’ style approach where initial guidance in both left and right lateral excursions came from posterior teeth until such time as the canines contacted and then took over as canine guidance. In protrusion, a similar long centric was established on posterior teeth so that in protrusive movements the initial guidance was from the posterior teeth until such time as the incisors touched and then took over the further smooth protrusive movements. This was achieved by using a fully adjustable articulator to complete the restorations (Figures 17 and 18). Conclusions The definitive anterior crowns were made of Procera all ceramic (Nobel Biocare) (Figures 19-21). The posteriors were constructed of traditional porcelain fused to metal with large flat areas on the palatal cusps for the establishment of both ‘long and wide centric’ (Figures 22- 24) as in the new intercuspal position there were no anterior contacts (Figure 25) due to loss of the palatal ramps. The final aesthetic result can be seen in Figures 26 to 29. Occlusion and the various occlusal concepts have caused – and continue to cause – debate. Whilst the author has been trained throughout his career in the concepts of gnathology, there is the recognition that other occlusal concepts, such as PMS and bilateral balance, may have a part to play in treatment of some patients. During the rest of this series, the principles of gnathology will be used in the treatment of the partial or full mouth reconstruction. Acknowledgements For the writing of this article on advanced restorative techniques, the author would like to thank the following people for their help: Dr Ibrahim Hussain, BDS, M.Med.Sci.Implantology – implant surgeon Dr Andrew Watson, BDS, MSc, specialist in endodontics Mr Bradley Moore – dental technician, ADS Laboratory, Harrogate. DT UK Fig 28: Lower anteriors final view Fig 29: Full face final view Fig 27: Upper anteriors final view Fig 17: Upper right restoration on fully adjustable articulator Fig 18: Upper left restoration on fully adjustable articulator Fig 19: Anterior crowns front view Fig 20: Anterior crowns right hand view Fig 21: Anterior crowns left hand view Fig 22: Upper arch occlusal view Fig 23: Upper right quadrant with palatal ramps Fig 24: Upper left quadrant with palatal ramps Fig 25: Intercuspal position with no anterior contacts Fig 26: Upper anteriors