cosmetic dentistry - beauty & science

08 I I special topic _ minimally invasive cosmetic dentistry case finishing fundamentally focuses on six keys to occlusion (Fig. 3) described by Andrews,2 whereas in cosmetic dentistry, it is considered the last step of the clinical procedure and entails refining the micro-aesthetic components of the smile.Cosmeticdentistsspendtheirclinicaltime and effort rather on the aesthetics of the final result. This is because, aesthetic components are visible to both the clinician and patient, and the outcome can thus be appreciated immediately. However, the force components are invisible, and their negative effects are not easily appreci- ated clinically until the effects become chronic. Another reason that force finishing may be overlooked is that it requires special tools and clinical techniques to demonstrate and measure the force factors clinically. Therefore, force is the most neglected component in cosmetic den- tistry during case finishing. In cosmetic dentistry, forces are finished based on articulating paper mark interpretation and the patient’s proprioception feedback. It has been documented in the literature that ar- ticulating paper is a poor indicator of occlusal disharmony,3–5 and studies have shown that mark size varies with the same applied load, with differing thickness of paper, surface texture of tooth and restorations, and that mark inter- pretation is an operator-based subjective pro- cedure. Moreover, paper cannot measure the timing of occlusal forces.3–6 A proper case-finishing protocol must be based on both subjective and objective analysis. In order to measure the occlusal load and timing of occlusal forces, it is necessary to use proper tools, which can measure precisely and ob- jectively the necessary occlusal parameters re- quired in cosmetic case finishing. Computerised instrumentation to analyse occlusal forces was introduced by Tekscan Inc in 1984 as T-Scan I.7 Over the past 27 years, it has evolved to become a very precise diagnostic and treatment tool that is used to manage the force components in any conventional case-finishing approach to dentistry. Every clinical case is different, as it is related to the patient’s state of health, his or her func- tional requirements, and his or her aesthetic needs and desires. Function is directly related to the forces that a patient generates within his or her stomatognathic system. There are four different theories of occlusion. Each of these theories has their value, and treatments that are founded on each have been successful. These theories of occlusion differ in their considera- tion of the positioning of the jaw or temporo- mandibular joint during treatment, which are known as jaw-position theories (Fig. 4). Fig. 6_Force-finishing clinical facts. cosmeticdentistry 3_2012 1.Unilateral tooth contacts increase force in the opposite joint. 2.Bilateral even tooth contacts during ICP give more stability to the teeth,muscles and joints. 3.When the number of occluding teeth increases, the total percentage of forces to each tooth decreases. 4.The vertical forces created by tooth contacts are well accepted by the periodontal ligament, but horizontal forces cannot be effectively dissipated.39 These forces may create pathological bone responses or elicit neuromuscular reflex activity in an attempt to avoid or guard against theinclineplanecontacts.40 Hence,directingtheocclusalforcethroughthelongaxisofthetooth (axial loading) should be a goal of force finishing in the posterior teeth. Axial loading can be accomplished by cusp tip to flat surface contacts or by creating reciprocal incline contacts (also known as tripodisation). 5.The amount of the force that can be generated between teeth depends on the distance of the teethfromthetemporomandibularjoint,combinedwithappliedmuscularforcevectors(fulcrum principle).Greater force can be applied to the posterior teeth than to the anterior teeth.41–43 The posteriorteethfunction effectivelywhenacceptingthe axial forces(axialloading)appliedduring closureofthemouth.Theyaccepttheseforceswell,primarilyowingtotheirpositioninthearches because the force can be directed through the long axes and thus dissipated effectively.16 6.The anterior teeth are not positioned well in the arches to accept heavy axial force. They are normally positioned at a labial angle to the direction of closure,so loading them axially is nearly impossible.44 7.The anterior teeth,unlike the posterior teeth,are in proper position to accept horizontal forces of eccentric mandibular movements.43,45,46 8.The anterior teeth should immediately disclude the posterior teeth during excursive move- ments,13,14,16 resultinginfriction-freeexcursivemovementsthatlimitwearonteethandactivate low levels of excursive muscle function.47 9.Thecaninesarebestsuitedtoacceptingthehorizontalforcesthatoccurduringeccentricmove- ments.40,45,48 This is because: a) They have the longest and the largest roots and therefore the best crown/root ratio.44,49 b) They are surrounded by dense compact bone, which tolerates the forces better than the medullary bone found around the posterior teeth.50 c) Thecaninesarecentredonsensoryinputandtheresultanteffectonthemusclesofmastication. Apparently,fewer muscles are active when the canines contact during eccentric movements than when posterior teeth contact.51,52 d) Lower levels of muscular activity would decrease forces to the dental and joint structures, minimising pathosis.It is therefore suggested that during force finishing of left or right latero- trusive excursive movements, canine guidance is the preferred excursive control in order to best dissipate any damaging horizontal forces. When canine guidance cannot be achieved during case finishing, the most favourable alternative to canine guidance is group function. The most desirable group function consists of the canines, premolars and sometimes the mesiobuccal cusp of the first molar.Any laterotrusive contacts other than the mesial portion of the first molar are not desirable because of the increased amount of muscle force that can be created as the contact nears the fulcrum (temporomandibular joint).16 Fig. 6