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ePaper created 2016-11-11, 09:18:10 | version 1.38.0
Editor - Online Haseeb Uddin CLINICAL PRACTICE 6 DENTAL TRIBUNE Pakistan Edition May 2016 ost advanced restorative dentistry techniques have changed little over the last 20-30 years, including that of the full mouth reconstruction. However, the impact of new dental materials, such as titanium and zirconia, has had a major influence on aesthetic dentistry and implantology during this time period. As a result, the profession may have an over-reliance on new materials rather than tried and tested techniques. Some fundamental techniques are just as relevant today as they were when I started my Master’s degree in conservative dentistry at the Eastman Dental Hospital in 1987. During the course of this series of articles on advanced restorative techniques, some old techniques will be revisited in light of today’s aesthetic and restorative requirements and some newer concepts will be discussed in greater detail whilst dealing with the overall topic of full mouth reconstruction. This article discusses the topic of occlusion and occlusal concepts. Gnathology Stallard first coined the term gnathology in 1924, defining it as the science that relates to the anatomy, histology, physiology and pathology of the masticatory system. McCollum formed the Gnathological Society in 1926 and is credited with the discovery of the first positive method of locating the transverse horizontal axis and transferring the recording to an articulator using a facebow. Stuart became associated with the Gnathological Society early and published the classic ‘Research Report’ with McCollum in 1955. Their observations led to the development of the principles of mandibular movements, transverse horizontal axis, maxillomandibular relationships, and an arcon-style articulator that was designed to accept the transfer of these occlusal records. The goal was to truly capture maxillomandibular relationships that accurately reproduced border jaw movements and which would then allow the technician to produce the most stable, functional and aesthetic occlusal form for indirect cast restorations. The registration of the horizontal and sagittal movements of patients was believed to allow the maximum cusp height-fossae depth with proper placement of ridges and grooves to enhance stability, function and aesthetics. Fundamentals of gnathology The fundamentals of gnathology include the concepts of retruded axis position (centric relation), anterior guidance, occlusal vertical dimension, the intercuspal design, and the relationship of the determinants of mandibular movements recorded using complex instrumentation to the occlusion in fixed prosthodontics. This has evolved into the five principles of occlusion I embrace today: 1. RCP = ICP around RAP 2. Mutually protected occlusion 3. Anterior guidance 4. No non-working side interferences 5. Posterior stability The early gnathologists studied the recorded tracings made during mandibular movements. When the mandible travels forward along the sagittal plane it is considered a protrusive excursion or protrusion. Therefore, retrusion is the movement toward the posterior; and it is the most retruded physiologic relation of the mandible to the maxilla to and from which the individual can make lateral movements that initially defined retruded axis position (RAP) or centric relation (CR) to the gnathologist. Further investigations led the gnathologists to believe that mandibular (condylar) movements are governed by the three axes of rotation. The concept of retruded axis position evolved into a three- dimensional position, resulting in its description as the rearmost, uppermost, and midmost (RUM) position of the condyles in the glenoid fossa. More recently, with the input of anatomists and physiologists, the concept has also included a bone braced position slightly anterior to the RUM position. Whilst there can be discussions between groups as to the exact definition of RAP, it is generally accepted as a muscular relaxed, reproducible and braced position that is an area not a pinpoint and can only be achieved with relaxed musculature. Placing the condyles with the correct position and having immediate disclusion (canine guidance and incisor guidance) upon movement away from that position, with no vertical or horizontal deflective contacts is fundamental to gnathology. Tooth wear is considered pathological in gnathology and one of its fundamental concepts is trying to advance a dentition with minimal wear. Alternative occlusal concepts: Pankey Mann Schuyler As gnathology was evolving, several competing occlusal concepts and permutations were theorised, such as the Pankey Mann Schuyler (PMS) theory of occlusion. The Pankey Mann Schuyler concepts evolved out of an initial study group headed by LD Pankey on the east coast of America. Nomenclature was different and included centre relation (CR) instead of retruded axis position (RAP); centre related occlusion (CRO) instead of retruded contact position (RCP) and centric occlusion (CO) instead of inter-cuspal position (ICP). Beyron, following his observations onAustralianAborgines, Advanced Restorative Techniques and the Full / Partial Mouth Reconstruction - Part 2 Occlusal Concepts By Prof. Paul Tipton, UK M Fig 1: Full face pre-op view Fig 2: ICP Fig 3: Upper arch pre-op Fig 4: Facebow recording Fig 5: Upper cast front view Fig 6: Upper cast right-hand view Fig 7: Upper cast left-hand view Fig 8: Lower study cast Fig 9: Diagnostic waxing front view Fig 10: Diagnostic waxing right-hand view Fig 11: Diagnostic waxing left-hand view Fig 12: Lower wax-up Fig 13: Prototypes types upper arch Fig 14: Prototypes lower arch Fig 15: Upper prep guide Fig 16: Lower prep guide