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Dental Tribune Middle East & Africa Edition No.2, 2016

Dental Tribune Middle East & Africa Edition | 2/2016 20 restorative Advanced Restorative Techniques and the Full / Partial Mouth Reconstruction - Part 2 Occlusal Concepts ByProf.PaulTipton,UK Most 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 den- tal materials, such as titanium and zirconia, has had a major influence on aesthetic dentistry and implan- tology during this time period. As a result, the profession may have an over-reliance on new materials rath- er 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 East- manDentalHospitalin1987. 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 require- mentsandsomenewerconceptswill be discussed in greater detail whilst dealing with the overall topic of full mouth reconstruction. This article discusses the topic of occlusion and occlusalconcepts. Gnathology Stallard first coined the term gna- thology in 1924, defining it as the sci- encethatrelatestotheanatomy,his- tology, physiology and pathology of the masticatory system. McCollum formed the Gnathological Society in 1926 and is credited with the discov- ery of the first positive method of lo- cating the transverse horizontal axis and transferring the recording to an articulatorusingafacebow. Stuart became associated with the Gnathological Society early and published the classic ‘Research Re- port’ with McCollum in 1955. Their observationsledtothedevelopment of the principles of mandibular movements, transverse horizontal axis, maxillomandibular relation- ships, and an arcon-style articula- tor that was designed to accept the transfer of these occlusal records. The goal was to truly capture max- illomandibular relationships that accurately reproduced border jaw movements and which would then allow the technician to produce the most stable, functional and aes- thetic 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, func- tionandaesthetics. Fundamentalsofgnathology The fundamentals of gnathology in- clude the concepts of retruded axis position (centric relation), anterior guidance, occlusal vertical dimen- sion, the intercuspal design, and the relationship of the determinants of mandibular movements recorded using complex instrumentation to the occlusion in fixed prosthodon- tics. This has evolved into the five principles of occlusion I embrace today: 1.RCP=ICParoundRAP 2.Mutuallyprotectedocclusion 3.Anteriorguidance 4.Nonon-workingsideinterferences 5.Posteriorstability. The early gnathologists studied the recorded tracings made dur- ing mandibular movements. When the mandible travels forward along the sagittal plane it is considered a protrusive excursion or protrusion. Therefore, retrusion is the move- ment toward the posterior; and it is the most retruded physiologic rela- tion of the mandible to the maxilla toandfromwhichtheindividualcan make lateral movements that ini- tially 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-di- mensional position, resulting in its description as the rearmost, upper- most, and mid- most (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 posi- tion. Whilst there canbediscussions between groups astotheexactdef- inition of RAP, it is generally accept- ed as a muscular relaxed,reproduc- ible and braced position that is an area not a pin- point and can only be achieved with relaxed mus- culature. Placing the condyles with the correctpositionandhavingimmedi- ate disclusion (canine guidance and incisor guidance) upon movement awayfromthatposition,withnover- ticalorhorizontaldeflectivecontacts is fundamental to gnathology. Tooth wear is considered pathological in gnathology and one of its funda- mental concepts is trying to advance adentitionwithminimalwear. Alternativeocclusalconcepts: PankeyMannSchuyler 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 differ- ent 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) in- stead of inter-cuspal position (ICP). Beyron, following his observations on Australian Aborgines, suggested that uniform tooth contact and resultant wear on several teeth in lateral occlusion was a positive and inevitable outcome. As a modifica- tion of canine guidance, the Pankey Mann Schuyler philosophy in com- plete 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 protru- siveexcursivemovement. 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- Figure2:ICP Figure3:Upperarchpre-op Figure1:Fullfacepre-opview Figure4:Facebowrecording in’ the posterior occlusion (long cen- tric). The incisal guidance, along with ‘long centric’, is determined by the distance from transverse horizontal axis-centric relation and the nor- mal 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 oc- clusal plane as dictated by the curve of Monson. The maxillary poste- rior teeth are developed after the completion of the mandibular res- torations as dictated by a wax func- tionally generated path record. The definitiverestorationsareequilibrat- ed into a centric relation position with mandibular buccal cusps onto Figure5:Uppercast front view Figure9:Diagnosticwaxingfront view Figure6:Uppercast right-handview Figure10:Diagnosticwaxingright-handview Figure7:Uppercast left-handview Figure11:Diagnosticwaxingleft-handview Figure8:Lowerstudycast Figure12:Lowerwax-up ÿPage24 In the second part of the series on advanced restorative techniques, Prof. Paul Tipton focuses on occlusal concepts

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