Australasian Dentist Issue 92

CATEGORY 70 AUSTRALASIAN DENTIST Introduction Temporomandibular disorders (TMDs) were classified by Dworkin and LeResche into three major groups: 1. muscle diagnoses, 2. disc displacements and 3. arthralgia, arthritis, and arthrosis (Dworkin and LeResche 1992). A systematic review by Manfredini questioned whether the use and effectiveness of occlusal splints or oral appliances was justified for the treatment of TMDs (Manfredini et al. 2017). A study by Lundh et al. followed the progress of the ‘natural course’ of internal derangement without clinical intervention compared to occlusal splint therapy. Flat occlusal splints without balancing contacts were compared to ‘no treatment’ in the management of 51 patients with TMJ disc displacement without reduction. After 12 months, 40% of patients treated with flat splints (without balancing side contacts) were worse off and 36% of the ‘no treatment’ group improved (Lundh et al. 1992). In 2001, Darveniza bio-designed occlusal schemes bymodifying classic tooth anatomy to restorative anatomical shapes required to create ‘full occlusal protection’ and discussed the term ‘hinge occlusion’. An ideal ‘hinge occlusion occurs when reproducible hinging of the TMJs correlates with bilateral simultaneous contact (without incline contacts posteriorly) of the teeth in centric relation’ (Darveniza 2001). The author uses the termhinge occlusion or hinge bite to describe the existing occlusal scheme when a patient makes first contact at the end of the hinging arc of closure in centric relation. Fully protective occlusal splint The author believes that splint design affects clinical outcome and, until now, occlusal splint designs have not fully addressed the length of excursive paths and the relationship to overjet and disclusion. Conservative management of TMDs for the author usually starts with ‘Full Counselling’ and a ‘Fully Protective Occlusal Splint’ and then ‘Formal Occlusal Splint Therapy’. A ‘Fully Protective Occlusal Splint’ can be defined as a bio-designed occlusal splint offering full occlusal protection at hinge occlusion and over the longest possible length of excursive movements not affecting lip comfort. To bio-design a raise that allows the longest possible protective lateral and protrusive path without affecting lip comfort usually ends a few millimetres short of border movement. Bio-designing starts with a personalised protective occlusal scheme in the splint to cater for the patient’s individual TMD and unprotected occlusal scheme. Formal occlusal splint therapy After fitting the splint and full counselling, ‘formal occlusal splint therapy’ follows. It involves a timed sequence between a minimum of four splint adjustments over a minimum three-month period along with on-going counselling. Splint adjustments involve equilibrating the changed centric stops in hinge occlusion and refining the excursive movements. Splint adjustments restore the splint to full occlusal protection thereby discouraging parafunction and encouraging relaxation of painful, spasmed, and shortened cranio-mandibular muscles. Relaxation and diminution of pain, in these cranio- mandibular muscles allows mandibular re- positioning, and concomitantly displaced TMJ discs to ideally re-align to their original position over time. Dramatic changes to the number and position of the centric stops on the splint occurs usually in the early splint adjustment appointments. In the later adjustments reproducibility of the number and position of the centric stops usually occurs and this mostly coincides with a diminution of TMD signs and symptoms. This protocol has been refined since designing the ‘Fully Protective Occlusal Splint’ four decades ago in 1981 and presenting it at the University of Queensland continuing education clinical course in 1984. This splint has now been colloquially called the ‘Darvo splint’. Relevant occlusal splint design The cornerstone of occlusal splint design was the Michigan splint when introduced to the profession in 1966 by Ramfjord and Ash. In the Ramfjord and Ash 1966, 1971 and 1983 editions, the design of the full arch maxillary splint was largely qualitative and included descriptive photographs, line diagrams and texts. These described: 1. a thin splint (1-2mm thick in molar region) (Ramfjord and Ash 1994), 2. an anterior biteplane which should be slanted perpendicular to the mandibular incisors for only centric contact and 3. 1-2 mm from centric should be a slight ‘cuspid raise’ to avoid balancing contacts (Ramfjord and Ash 1966). In 1994, Ramfjord and Ash reflected on the Michigan splint design: 1. protrusive guidance was imparted by cuspid raises and not beyond that point to prevent protrusive and balancing interferences and 2. they concluded that ‘occlusal splints are much more effective without incisal guidance’ although ‘some incisal contact may occur in the late stage of protrusion’ (Ramfjord and Ash 1994). Many dentists are unaware that the original Michigan splint has no incisal protrusive raise but rather an anterior flat biteplane designed only for lower incisor centric stops and instead utilises very small canine raises for protrusive and lateral paths. This results in short excursive paths and potentially damaging protrusive and lateral crossover with a retrusive mandibular vector emanating from the distal side of the canine raise. In this author’s experience, these extreme crossovers have been associated with some unresolved TMDs. These thin splints often develop holes and prematurely fracture resulting in poor compliance. These design shortcomings in this author’s opinion have LINICAL Part 1: Preliminary investigation of 200 TMD patients using ‘Fully Protective Occlusal Splints’ with ‘Formal Occlusal Splint Therapy’ By Dr Michael Darveniza MDSc PhD (Qld) FRACDS, Prosthodontist: Lismore, New South Wales.