1. The importance of occlusion in oral function and dysfunction A. De Laat Copenhagen 2007

2. Introduction  Aim of dentistry and orthodontics in particular : maintenance and restoration of masticatory function  Other goals : speech, esthetics, ….  ? Preventive action concerning development of dysfunction (and pain)

3. Outline  Dental occlusion and normal jaw function : - mastication, forces - swallowing (and speech) - mastication and development of occlusion  (Mal)occlusion and Temporomandibular Disorders - etiological role ? - management of TMD - other orofacial pains

4. Mastication Lundeen, Gibbs, 1972-1985

5. Influence of food

6. Influence of tooth morphology

7. Influence of age

8. Influence of jaw relationship P. Proeschel (1988, 2006)  Different chewing patterns :

9. Soft food – Tough food

10. Angle Class

11. Cross bite

12. Reversed sequencing

13. Conclusion  Differences between groups with different (mal)occlusions or tooth morphology DO exist….. But are they important …?

14. Bite force M. Bakke (2006)  “Objective measure” of one parameter  Relatively simple measurement

15. Maximum Bite Force  Unilateral molars : 300-600 N  Premolars : 70 %  Front teeth : 40 %  Bilateral molars : 140 % - 200 % (PVDF)  Maximum (Eskimo’s) : 1750 N (Waugh 1937) Hagberg 1987, Bakke et al 1989, Ferrario et al 2004, Tortopidis et al 1998

16. Maximum bite force  Depends on number of teeth  Gender difference  Importance of motivation and cooperation Rugh and Solberg 1972

17. Maximum bite force  Influence of pain : arthritis or TMD results in decrease of 40 % (Wenneberg et al 1995, Stohler 1999)  Correlated to PPT (Hansdottir and Bakke 2004)

18. Maximum bite force  Influence of age (constant from 20-50 y, decreases later, Bakke et al 1990 )  Decreases with increasing facial height, gonial angle,… ( Ingerval & Helkimo 1978, Throckmorton et al 1980, Proffitt et al 1983, Braun et al 1995 )  No influence of tooth decay or loss of periodontal support ( Miyaura et al 1999, Morita et al 2003 )

19. Maximum bite force  Dentures......and implant-support helps… (Bakke et al 2002, Van Kampen et al 2002)

20. Malocclusion and bite force  Negative influence of : - overjet on incisal MBF (Ahlberg et al 2003) - unilateral cross-bite (Sonnesen et al 2001) - open bite (Bakke & Michler 1991)

21. Conclusions  Occlusal contact area seems most correlated, more than malocclusion  But…does it matter,since - only 10-20 % of variation explained (while e.g. thickness of masseter explains 55 %...) - normal chewing forces are only 15-30 % of MBF….

22. Masticatory ability and performance P.H. Buschang  Anatomical (occlusal contact area, malocclusion …); physiological (muscle strength, training, gender,…) and psychological components interplay in mastication, and deficiencies in one part can be compensated for by others  “Masticatory performance” is an objective measure, directly linked to food breakdown, nutrition, digestion

23. Masticatory performance  Particle size distribution of (test-)food, chewed a standard number of cycles  Methodology : fractional sieving  Typical food (peanuts, carrot, bread,…) Optosil, or specially developed test-foods

24. Masticatory performance is influenced by :  Number of teeth/occluding units (but subjects with missing teeth do not chew longer…)( Helkimo et al 1978, Yurkstas et al 1965, Henrikson et al 1998 )  Patients with dentures increase the number of chewing strokes and wait longer to swallow (? Corrected for age )  Mixed dentition : increase in early, decrease in late phase

25. MP and malocclusion  Less potent effect than mutilated dentition  In cross-sectional studie, MP of Class III patients is up to 60 % lower ( English et al 2002, Lundberg et al 1974, Zhou and Fu 1995 ). MP of Class II is 30 to 40 % lower ( Henrikson et al 1998 ) but Median Particle Size (MPS) was not significantly different ( Toro et al 2006 )

26. MP and malocclusion  After a predetermined number of chewing cycles (20,30,40), the Median Particle Size is larger in subjects with ICON (index for complexity, outcome,need) 43  but no differences in particle distribution or masticatory frequency ( Ngom 2007 )

27. MP and digestion  Animal experiments clearly indicate relation between food particle size and digestion ( Gyimesi et al 1972 )  In man, also incompletely chewed food is digested. In elder persons, MP has been linked to GI-problems : 49 % of patients without posterior teeth have gastritis vs 6 % when no teeth are missing ( Mumma 1970 )

28. Mastication and developing occlusion  Over the centuries, malocclusion seems to have increased 10-fold and modern life- style and nutrition have been suggested as cause ( Corrucini 1984, Varrela 1990,1992 ), even more than genetics ( Townsend et al 1998 )  Nutrition influences elevator muscle development and muscle function influences transverse and vertical facial dimensions ( Kiliaridis 2006 )

29. CONCLUSIONS  Malocclusion influences the chewing cycle  Number of occlusal contacts and units influences the maximum bite force  Class II and III patients have a lower masticatory performance but….  Probably not of clinical significance in non- compromised patients