Clinical Continued »
form of a slide that has both a vertical and horizontal compo- nent occurring in all three planes. According to Ash and Ramfjord, the horizontal ‘long centric’ from CRO to CO should be incorporated into a restoration with a post-restor- ative 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 dimen- sion 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 posi- tioned in retruded axis position (centric relation), any movement out of this position should disocclude the poste- rior segment, thus nullifying any horizontal cusp-fossae area contact. This belief, combined with
the immediate anterior disoc- clusion, forms the basis of a mutually protected occlusion and limits tooth wear. The PMS occlusal scheme, however, encourages multiple occlusal contacts during lateral move- ments (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 intercus- pation 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
Fig 16 Final view
“Though gnathology will produce stable long-term results, some patients may require more freedom in their occlusion”
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 everyday occlusal practice.
Case study Patient A was referred to me for a full mouth reconstruction and aesthetic improvements to her smile (Figures ı-2). Initial impressions, facebow and jaw registration were taken for mounted study models (Figure 3). The study models showed the degree of over-eruption of her anterior segments and disturbances to the occlusal plane.
Initial diagnostic waxing
(Figures 4 and 5), proto- types and prep guides were completed using a lower curve of Spee of a 4” radius (anatom- ical 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 disclu- sion style of occlusal scheme as recommended in the gnatho- logical approach. During the course of the
initial preparation and proto- types 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
ABOUT THE AUTHOR
A highly respected
specialist Pros- thodontist, Dr Paul Tipton has published many scientific articles in the dental press and is an expert lecturer
He is a past-president of the British Academy of Implant Dentistry (
www.baid.org.uk) and the current president of the British Academy of Restorative Dentistry (
www.bard.uk.com)
in his field with Tipton Training Academies in Dublin, Manchester and London.
He received specialist status
He takes referrals for complex restorative, aesthetic and implant patients in Manchester and London (
www.drpaultipton.co.uk). For more information call 07757 878 900
Scottish Dental magazine 57
in prosthodontics in 1999 from the GDC.
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 guid- ance. 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 move- ments. This was achieved by using a fully adjustable articulator to complete the restorations (Figures 6 and 7).
Conclusions The definitive anterior crowns were made of veneered zirconia (Figure 8). The poste- riors 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 9-ıı) as in the new intercuspal position there were no anterior contacts (Figure ı2) due to loss of the palatal ramps. The final aesthetic result can be seen in Figures ı3 to ı6. 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 recog- nition that other occlusal concepts, such as PMS and bilateral balance, may have a part to play in treatment of some patients.
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