The document outlines the evolution of the concept of normal occlusion through three distinct historical periods: fictional, hypothetical, and factual, leading to the current understanding of occlusal relationships. It details contributions from key figures in orthodontics, including definitions, classifications, and significant measurements used to assess occlusion. The document also discusses various concepts like Andrews' six keys to optimal occlusion and Roth's functional keys, emphasizing the importance of factors influencing tooth position and occlusal functionality.

1. CHANGING CONCEPT OF
NORMAL OCCLUSION

2. CONTENTS
• Introduction
• Fictional period
• Hypothetical period
• Factual period
• Andrews six keys to optimal occlusion
• Roth’s Functional keys to occlusion
• Factors & forces that determine tooth
position
• Compensating curves
• Compensating curves
• Centric occlusion
• Centric relation
• Eccentric occlusion
• Functional occlusion
• Mutually protected occlusion
• Non-functional occlusion
• Methods to record centric relation
• Conclusion
• References

3. INTRODUCTION
• The development of concept of occlusion can be traced through fiction and
hypothesis to fact.
• The fictional approach was a convenient arrangement of a series of observation and
thoughts more or less logically arranged.
• The hypothetical approach was based on provisional acceptance of certain logical
entities.
• Fact is a truth known by actual experience or observation.
• Both the fictional and hypothetical approach are necessary preludes to the
establishment of fact.

4. Fictional
period
Hypothetical
period
Factual
period
Prior to 1900 1900-1930 1930 to present

5. FICTIONAL PERIOD
•Pioneers like Fuller, Clark and Imrie talked of “Antagonism”, “Meeting” or
“Gliding” of teeth.
•The creation of normal standard, a basis on which to compare departures from
normal was lacking.
•But this served as a working hypothesis or subsequently became established fact
after definitive research
Asbell BM- A Brief History of Orthodontics; AJODO 1998

6. • Eugene Talbot published his book on “Irregularities of the teeth and their treatment”
in 1903.
• The Talbot concept of normal occlusion was that it was a historical event, passed
in the decline of the species and normality was possible only with atavism or
throwback to our primitive ancestors

7. HYPOTHETICAL PERIOD
Edward H. Angle
• Channelised orthodontic thinking on occlusion and brought the real concept out of
fiction.
• In 1907, Angle summarised his views as ‘occlusion shall be defined as the normal
relation of the occlusal inclined planes of the teeth when the jaws are closed.’
• Angle cites the example of a skull of Negro male from Broomell which he names ‘Old
Glory’.
Katz MI, Sinkford JC, Sanders CF Jr. The 100-year dilemma: what is a normal occlusion, and how is malocclusion
classified? Quintessence Int. 1990 May;21(5):407-14..

8. • In Old Glory, all the teeth are present and arranged in a graceful curve.
He emphasizes that all teeth are necessary for maintaining occlusion.
He compares Old Glory with the profile of Belvedre, a white male.

9. • Angle furnished his ‘key to occlusion’ and emphasizes the first permanent molars
especially the upper first permanent molar and considers them to be most constant in
taking normal position.
• From the hypothesis of constancy of first molar and the ‘line of occlusion’, Angle
developed the concept that all teeth should be present if normal occlusion is to be
achieved.

10. Mathew Cryer and Calvin Case
• Cryer pointed out that Angle showed the straight profile of Apollo Belvedre and
chose a skull of negro male ‘Old Glory’ to exemplify ideal occlusion. He
questioned how one could mix a prognathic denture with an orthognathic profile.
• Case accepted Angle’s hypothesis of constancy of first molar. He related the facial
profile to each type of occlusion.

11. • Case proposed the concept of apical base.
• He was aware of the role of nose and chin and their influence on profile.
• Case proposed the concept of normal and ideal occlusion.
•The idea that teeth should be present to obtain normal facial contour was losing
ground.
•In 1908 Bennett proposed that the condylar movement was primarily rotatory on
opening from occlusion to rest position and later on after passing this point became
translatory.

12. Van Loon
• In 1915 Van Loon published criticism of Angle's classification.
• He oriented casts of teeth into plaster facial masks so that the true relationship of
the teeth to the soft tissue of the face could be evaluated.

13. Dewey
• Considered first molar as an organ of mastication, and they are very necessary in
producing normal occlusion
• But did not consider it as a basis of classification, as they are as liable as any other teeth
to assume an abnormal position under certain conditions.
• Dewey recommended that classification be based on the anteroposterior relation of
the arches as a whole rather than only the first molars.

14. Friel
• In 1927 --published his stages of occlusion from 3 years of age to old age.
• Demonstrated --numerous changes in the primary dentition, which Angle did not
address, but also the variability of first molar position in a normal occlusion as it
undergoes its metamorphosis from the transitional mixed dentition to the worn teeth
of old age
• Friel--thus illustrated the difficulty of trying to force Angle's static ideal on a
changing mechanism.

16. Lischer and Paul Simon
• They broadened the concept of occlusion by relating the teeth to the rest of the face and
cranium.
• They related teeth in occlusal contact to cranial and facial planes.
• Though the concept of orbital plane as basis for determining antero-posterior position of
dentition did not stand up, it introduced the idea of facial ramification of malocclusion
outside the dental area.

17. Atkinson
• Defended Angle’s hypothesis of--a relationship between the maxillary first molar and the
cranium.
• But he showed that these relationships change with age and among different racial types.

18. Milo Hellman
• Hellman showed the racial variation in so called normal occlusion through
anthropological studies.
• Hellman and others studied the prognathism of the human dentition in relation to a
cranial base

19. FACTUAL PERIOD
• In 1930 Holly Broadbent and Hans Planer introduced an accurate technique of
roentgenographic cephalometry.
• Dividing line b/w static and dynamic occlusion.
• With the advanced study techniques, the factual period become functional period.
• By then, 3 components of occlusion are set up:
1. Interdigitation of teeth
2. Status of controlling musculature
3. TMJ integrity

20. • The goal of modern orthodontics according to Proffit is “the creation of best
possible occlusal relationship within the framework of acceptable facial aesthetics
and stability of result”.
• The position of the teeth within the jaws and the mode of occlusion are determined
by developmental processes that interact on the teeth and their associated
structures during the period of formation, growth and post natal modification.

21. ANDREWS SIX KEYS TO OPTIMAL OCCLUSION
1. MOLAR RELATION
2. CROWN ANGULATION
3. CROWN INCLINATION
4. ABSENCE OF ROTATIONS
5. TIGHT CONTACTS
6. OCCLUSAL PLANE

22. 1. Molar relation
• Distal surface of the distobuccal cusp of the upper first permanent molar occluded
with the mesial surface of the mesiobuccal cusp of the lower second molar
2. Crown angulation
• The gingival portion of the long axis of each crown --distal to the
incisal portion
Andrews-Straight-Wire, The Concept and Appliance, 1989

23. • Anterior crown inclination:
Maxillary incisors- +ve inclination Mandibular
incisors- Slight -ve inclination
3. Crown inclination
• Labiolingual or buccolingual inclination of the long axis of the crown.
• Posterior (Upper & lower) crown inclination:
Progressively more –ve from canines through 2nd molars

24. 4. Absence of rotations
5. Tight contacts
6. Occlusal plane
• Depth of curve of spee-- from flat to slightly concave

25. ROTH’S FUNCTIONAL KEYS TO OCCLUSION
• Centric occlusion should coincide with centric relation
• In protrusion, the incisors should disocclude the posterior teeth
• In lateral excursions of the mandible, the canine should guide the working side while
all the other teeth on that side and the opposite are disoccluded
• When the teeth are in centric occlusion, there should be even bilateral contacts in the
buccal segments.
Roth RH (1981). Functional occlusion for the orthodontist. J Cli Orthod, 15: 32-51

26. • Graber stressed that modern concepts of normal occlusion require three main areas :
1. Occlusal position (or) tooth contact position
- Masticatory habits, tooth inclination and malposition, shape of teeth, premature
contact, faulty restoration, tooth loss, the condition of periodontium affect the
occlusal positions
2. Postural resting position
3. TMJ
Graber

27. • A fourth element could be added:
anteroposterior development of the maxilla and mandible
• Each of these elements must be healthy, individually and in combination, for
optimal function and comfort.

28. FACTORS & FORCES THAT DETERMINE TOOTH
POSITION
• The alignment of the dentition in the dental arches occur as a result of complex
multidirectional forces acting on the teeth during and after eruption.
• Equilibrium position of opposing forces that are given by lips and cheeks from
outer side and tongue from inner side determine the (stable) position of the teeth .
• Hence the labiolingual and buccolingual forces are equal. This is called “neutral
position.”
Okeson, J. P. (2019). Management of temporomandibular disorders and occlusion

29. • Proximal and occlusal contacts are important in maintaining tooth alignment and
arch integrity.
• Mastication causing buccolingual and vertical movement of teeth results in wear of
proximal contacts.
• Mesial drifting force helps to keep teeth in contact.

30. CENTRIC CUSPS
• Buccal cusps of the mandibular posterior teeth and lingual cusp of the maxillary
posterior are the centric or supporting cusps
• These cusp plays major role in mastication and to maintain vertical dimension
between maxilla and mandible

31. NON-CENTRIC CUSPS
• The buccal cusp of maxillary posterior teeth and lingual cusp of the mandibular
posterior teeth are also called as shearing or guiding cusps.
• These are responsible for-
Shearing of food.
Minimizing tissue impingement.
Maintain bolus of food on occlusal table for mastication gives stability to mandible
in full occlusion.
Guide the mandible during mastication by neuromuscular feedback

32. CURVE OF SPEE
• The curve of spee given by F. Graf Von Spee in Germany in 1890
• It refers to the antero-posterior curvature of the incisal edges of mandibular
incisors , buccal cusps of bicuspid and molar continuing as an arch through the
condyle.
• If the curve is extended, it would form a circle of about 4 inch diameter. This
curvature is within the sagittal plane only.
Marshall SD-Development of the curve of spee; AJODO,2008
COMPENSATING CURVES

33. MEASUREMENT OF CURVE OF SPEE
• The maximum depth of the curve of Spee was measured as the maximum of the
perpendicular distances between the buccal cusp tips of the mandibular teeth and a
measurement plane described by the central incisors and the distal cusp tip of the
most posterior tooth in the mandibular arch.

34. • On average, the curve of Spee initially develops as a result of mandibular permanent first
molar and incisor eruption.
• The curve of Spee maintains this depth until the mandibular permanent second molars erupt
above the occlusal plane, when it again deepens.
• During the adolescent dentition stage, the curve depth decreases slightly and then remains
relatively stable into early adulthood.

35. CURVE OF WILSON
• It is a curve that contacts the buccal and lingual cusps tips of the mandibular
posterior teeth.
• It helps in two ways:-
Teeth --aligned parallel to the direction of medial pterygoid --optimum resistance
to masticatory forces.
The elevated buccal cusps prevent food from going past the occlusal table.

36. CURVE OF MONSON
• Monson (1920)
• Connected the curve of spee and curve of Wilson to all cusps and incisal edges,
which forms a sphere of a 4 inch radius, mandibular arch adopted itself to the
curved segment of a sphere.

37. Occlusion
Centric
Eccentric
Functional
Lateral
Canine
guided
Group
function
Protrusive
Non-
functional

38. CENTRIC OCCLUSION
• According to Peter Dawson(1974) : Centric occlusion refers to the relationship of the
mandible to the maxilla when the teeth are in maximum occlusal contact, irrespective
of the position or alignment of the condyle-disk assemblies. This is also referred as
acquired position of the mandible or maximum intercuspal position( MIP)
Peter E. Dawson. Evaluation, Diagnosis, and Treatment of Occlusal Problems, 2nd ed.. Mosby

39. CENTRIC RELATION
• Centric relation --- “the maxillomandibular relationship in which condyles
articulates with the thinnest avascular portion of their respective discs with the
complex in the anterosuperior position against the slope of articular eminence. This
position is independent of tooth contact.”
Rinchuse, D. J., & Kandasamy, S. (2006). Centric relation. The Journal of the American Dental Association, 137(4), 494–501.

40. The Importance of centric relation in orthodontics:
• In orthodontics, diagnosis and treatment planning should be performed by the
evaluation of a malocclusion with the mandible in centric relation (CR), i.e. the
natural musculoskeletal position of the condyle in the fossa, in order to obtain the
true maxillary - mandibular skeletal and dental relations in the three planes of
space.

41. • If this is overlooked an incorrect diagnosis and treatment plan of the actual
malocclusion, along with its unfavourable consequences may result.
• During every appointment a patient has to be monitored in CR so that the
mechanotherapy is guided to accomplish the final ideal static and functional occlusion
with the mandible in position.
• If this is disregarded, several prematurity that may later cause traumatic occlusion or
craniomandibular disorders may result.

42. ECCENTRIC OCCLUSION
• Refers to contact of teeth that occurs during movement of mandible.
• Functional occlusion
• Non-functional occlusion

43. FUNCTIONAL OCCLUSION
• Functional occlusion is defined as an arrangement of teeth which will provide the
highest efficiency during all excursive movements of the mandible which are
necessary during function
Types:-
• Lateral
• Protrusive

44. LATERAL FUNCTIONAL OCCLUSION
• It includes tooth contacts that occur on canines and posterior teeth on the side
towards which the mandible moves.
• 2 types:
Canine guidance/ Canine protected occlusion
Group function

45. CANINE GUIDANCE
• During lateral excursion, the opposing upper and lower canines of the working side contact
thereby causing disclusion of all posterior teeth on the working and balancing sides.
• The theory of canine protected occlusion-- D' Amic , Naga and Shaw and is based on the
impression that the canine tooth is the guide to mandibular excursion.

46. CANINE GUIDANCE
• The establishment of canine guidance is aimed in the orthodontic completion due to several
factors:
• The strategic positioning of the canine in the arch, with compact bone --better tolerates the
occlusal forces than the medullary bone of the posterior teeth; activates less muscles when
the canine teeth are in contact than when posterior teeth contact each other.
• So, when canine- in contact-- dissipate the horizontal forces, while promoting the
disocclusion of the posterior teeth
Oltramari , Conti, Navarro, Almeida, Almeida Pedrin, Ferreira, Fernando. (2007). Importance of occlusion aspects in the
completion of orthodontic treatment. Brazilian dental journal. 18. 78-82.

47. GROUP FUNCTION
• During lateral movement, the buccal cusps of the posterior teeth on the working
side are in contact.
• There is no contact on the non-working side.
Clark JR, Evans RD. Functional occlusion: I. A review. J Orthod. 2001 Mar;28(1):76-81

48. PROTRUSIVE FUNCTIONAL OCCLUSION
• It includes the eccentric contacts that occur when the mandible moves forward.
• Ideally six mandibular anterior teeth contact along the lingual inclines of maxillary
anterior teeth while the posterior disocclude.
• These are called as a guiding inclines of the anterior teeth

49. • Disclusion of the posterior teeth must be immediate
• It occurs in 3 stages
• 1. Initial contact
• 2. Beginning of anterior discluding factor
• 3. End to end position

50. • For proper disclusion there must be proper overjet and overbite– so that there is
free mandibular movement
• If the patient presents an increased overjet (more than 3 mm), a longer period is
necessary for the anterior teeth to contact, which results in anterior guidance at the
expense of the posterior teeth

51. • During completion of the orthodontic treatment--important to establish an overjet and
overbite of 2 mm, --facilitates the achievement of the anterior guidance.
• Mandibular second molars --must be included in the orthodontic treatment to avoid
interferences during the protrusive movement.
Oltramari , Conti, Navarro, Almeida, Almeida Pedrin, Ferreira, Fernando. (2007). Importance of occlusion aspects in the
completion of orthodontic treatment. Brazilian dental journal. 18. 78-82.

52. • Cusp to fossa occlusion : Supporting cusp occluding into fossa. This produces an
interdigitation of the cusps and fossa of one tooth with the fossa of only one
opposing tooth. This is tooth-to-one-tooth relation
• Cusp to embrasure / Marginal ridge occlusion : Occlusion of one supporting cusps
into a fossa and the occlusion of another cusp of the same tooth into the embrasure
area of two opposing teeth. This is a tooth-to-two-teeth relation.

53. • An occlusal scheme in which the posterior teeth prevent excessive contact of
anterior teeth in maximum intercuspation and the anterior teeth disengage the
posterior teeth in all mandibular excursive movement
• Canine protected occlusion is a form of mutually protected articulation
MUTUALLY PROTECTED OCCLUSION

54. NON-FUNCTIONAL OCCLUSION
• They are tooth contacts that occur in the segment away from which the mandible
moves. For example if the mandible is moved to the left side, contact occur on
right side.

55. METHODS TO RECORD CENTRIC RELATION

56. • Phillip Ptaff was the first to describe his technique for bite recording, he called
it taking bite.
• In 1955 Shanahart described a technique he called swallowing or free closure.
Moreno JA, Romero LL, Camacho CG, Canseco Jiménez JF, Cuairán Ruidíaz V. Assessment of two techniques for the recording of
mandibular central relationship: gothic arch versus power centric relation. Revista Odontológica Mexicana. 2015;19(1):27-32.

57. • McCollum used the technique of chin point guidance.
• The mandible is retruded using thumb
• Dawson recommended the bilateral manipulation technique. This technique stressed
the importance of guiding the lower jaw in an upper direction, placing the operator's
fingers into the gonial angles while thumbs applied pressure to the chin in order to
facilitate condylar positioning in centric relation.
• Articulators

58. TRANSCUTANEOUS ELECTRICAL NERVE
STIMULATOR (TENS)
• To record an ideal mandibular-maxillary relation
• When adequately adjusted to pulse at higher output, this device
will create a mandibular movement on a neuromuscular
trajectory
• This is the best static interpretation of a functional occlusion
Savastano, F. (2015). Contemporary Dental Occlusion in Orthodontics. BAOJ
Dentistry, 1(1), 1-4.

59. CONCLUSION
• Defining and achieving a final dental occlusion for patients is the key factor which
forms the basis of our treatment plan.
• Normal occlusion is not a rigid or static relationship.
• Normal interdigitation in deciduous and mixed dentition is abnormal in permanent
dentition and vice versa.
• Successful orthodontic treatment involves many disciplines, not all of which are always
within our control.
• Achieving the final desired occlusion is the purpose of attending to the six keys to
normal occlusion.

60. REFERENCES
• Asbell MB. A brief history of orthodontics. American Journal of Orthodontics and
Dentofacial Orthopedics. 1990 Aug 1;98(2):176-83.
• Andrews: Straight-Wire, The Concept and Appliance, 1989
• Katz MI, Sinkford JC, Sanders CF Jr. The 100-year dilemma: what is a normal occlusion,
and how is malocclusion classified? Quintessence Int. 1990 May;21(5):407-14.
• Roth RH (1981). Functional occlusion for the orthodontist. J Cli Orthod, 15: 32-51
• Palaskar JN, Murali R, Bansal S. Centric relation definition: a historical and contemporary
prosthodontic perspective. The Journal of Indian Prosthodontic Society. 2013 Sep
1;13(3):149-54.
• Marshall SD, Caspersen M, Hardinger RR, Franciscus RG, Aquilino SA, Southard TE.
Development of the curve of Spee. American Journal of Orthodontics and Dentofacial
Orthopedics. 2008 Sep 1;134(3):344-52.

61. REFERENCES
• Howat, A. P., Capp, N. J., & Barrett, N. V. J. (1991). Color Atlas of Occlusion &
Malocclusion. Mosby
• Oltramari , Conti, Navarro, Almeida, Almeida Pedrin, Ferreira, Fernando. (2007).
Importance of occlusion aspects in the completion of orthodontic treatment.
Brazilian dental journal. 18. 78-82.
• Clark, J. R., & Evans, R. D. (2014). Functional occlusion: I. A review. Journal of
orthodontics.
• Okeson, J. P. (2019). Management of temporomandibular disorders and occlusion
• Dawson, P. E. (2007). Functional occlusion: from TMJ to smile design. Elsevier
Health Sciences.

62. REFERENCES
• Batra P, Duggal R, Parkash H. Functional Occlusion in Orthodontics. Journal of
Indian Orthodontic Society. 2005;39(2):80-90
• Hassan R, Rahimah AK. Occlusion, malocclusion and method of measurements-an
overview. Archives of orofacial sciences. 2007;2:3-9.
• Moreno JA, Romero LL, Camacho CG, Canseco Jiménez JF, Cuairán Ruidíaz V.
Assessment of two techniques for the recording of mandibular central relationship:
gothic arch versus power centric relation. Revista Odontológica Mexicana.
2015;19(1):27-32.
• Savastano, F. (2015). Contemporary Dental Occlusion in Orthodontics. BAOJ
Dentistry, 1(1), 1-4.

63. CLINICAL IMPLICATIONS
Normal versus ideal occlusion
Normal occlusion implies more than a range
of anatomically acceptable values.
 It also indicates physiological adaptability and the
absence of recognizable pathological
manifestations. 63

64. CLINICAL IMPLICATIONS
Ideal occlusion is a state in which no neuromuscular
adaptation is needed because no occlusal interferences are present
• The concept of an ideal occlusion refers both to an esthetic and physiological
ideal
• It is a hypothetical formula which does not and cannot exist in man
64

65. CLINICAL IMPLICATIONS
Occlusal adaptive mechanisms
65