normal occlusion orthodontics

1. Normal Occlusion
Dr. Ayush Jain
Junior Resident – 1
Orthodontics and Dentofacial Orthopaedics
Department of Dentistry

2. CONTENTS
 Introduction
 Definition and Terminologies
 Concept of Occlusion
• Fictional
• Hypothetical
• Factual
 Factors and force determining tooth position
 Line of occlusion
 Plane of occlusion
 Andrews six keys to optimal occlusion
 Occlusal contact during mandibular movement
 Attrition occlusion
 Criteria for good occlusion
 Conclusion

3. INTRODUCTION
 The alignment and occlusion of the dentition are extremely important in
masticatory function.
 The basic activities of chewing, swallowing, and speaking depend
greatly not only on the position of teeth in the dental arches but also on
the relationship of opposing teeth as they are brought into occlusion.
 The goal of modern orthodontics according to Profitt is “the creation of
best possible occlusal relationship within the framework of acceptable
facial aesthetics and stability of result”.

4.  Occlusion is a Latin word-
 Clusion - closing
 Occ – up
 In simpler terms it is the act of closure or
being closed.
 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.

5.  The most comprehensive definition of occlusion was given by Jablonski
1982-
It is the relationship between all components of the masticatory system
in normal function, parafunction and dysfunction including the morphology
and functional features of the contacting surface of the opposing teeth and
restoration.
Occlusion – The relationship of maxillary and mandibular teeth when they are
in functional contact during activity of the mandible. -- G.P.T.

6. Terminologies used in occlusion
 Normal Occlusion : – Normal occlusion implies a situation commonly found in
the absence of disease. It should include not only a range of anatomically
acceptable values but also physiological adaptability. – It is always a range never
a point.
 Ideal Occlusion : – The concept of ideal or optimal occlusion refers both to an
aesthetic and physiologic ideal. It includes functional harmony, stability of
masticatory system & Neuromuscular harmony.
 Physiologic occlusion : – The occlusion that shows no signs of occlusion related
pathosis. It may not be an ideal occlusion but it is devoid of any pathological
manifestations in the surrounding tissues

7. Terminologies used in occlusion
 Traumatic occlusion : – An occlusion judged to be causative factors in the
formation of traumatic lesions of disturbances in the orofacial complex.
 Therapeutic occlusion : – It is a treated occlusion employed to counteract
structural interrelationship related to traumatic occlusion.

8.  Retruded axis position: – Position the condyle adopts during the
terminal hinge movement of opening or closing.
It is Synonymous with:- centric relation, terminal hinge relation and
hinge axis position.
 Most retruded position (Academy of Dental prosthetics, 1956)
 Most supero-posterior position in glenoid fossa (Academy of
Dental prosthetics, 1987)
 Anterior-superior position of condyle (GPT-9, 2017)

9.  Retruded contact position(RCP) : - occlusal position when the
first tooth contact occurs on mandibular path of closure with the
condyles in retruded axis position.
 Working side: – The side that the mandible moves towards in a
lateral excursion.
 Non-Working side: – The side that the mandible moves away
from during a lateral excursion.

10. Development of concept of occlusion
 Historically, much of the early development of dentistry was
inductive, reasoning from particular to the general. The idea of
development of occlusion can be traced through fiction and
hypothesis to fact.
 Three period’s:
 Fictional period- prior to 1900
 Hypothetical period- 1900 to 1930
 Factual period-1930 to present

11. Fictional period ( Prior to 1900)
 In fictional period, pioneers like Fuller, Clark and Imrie talked of
“antagonism”, “meeting” or “gliding” of teeth.
 Others relied on anatomic descriptions of morphology of the teeth as
individual units.
 But the creation of a normal standard, a typical relationship, a basis on
which to compare departures from the normal, was lacking.
 Kingsley 1880, The standard of normality of the dental arch is a curved
line expanding as it approaches the ends, and all teeth standing on that
line.
 This later became a working hypothesis and subsequently became
established fact after definitive research.

12.  Eugene Talbot’ Text: “Irregularities of the teeth and their treatment” in 1903.
 Attributes facial deformities to maternal impressions and delineates in great detail the adolescent
neuroses of nasal and facial bones, developmental neurosis of eye, the maxillary bone, the palate,
tooth position and so forth
 The Talbot Concept of normal occlusion: “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 ”

13.  In 1907, description of the occlusal
relationship of the teeth was made by
E.H. Angle.
 He defined occlusion as the normal
relation of the occlusal inclined planes
of the teeth when the jaws are closed.
 In ‘Old Glory’ all the teeth are present
and arranged in a graceful curve.
Hypothetical Period
(1900 to 1930)

14.  Angle’s postulate “Key of occlusion” that
the upper first molars were the key to
occlusion and considers them to be most
constant in taking normal position.
 This formed the basis of Angle’s
classification of malocclusion.
 Angle referred to the “line of occlusion” as
the line of greatest normal occlusal contact
 Angle developed the philosophy that all
teeth should be present if normal occlusion
is to be achieved, only then normal facial
features were possible.

15. Matthew Cryer and Calvin Case
 They opposed Angle
 How he could mix a prognathic
denture and orthodontic profile?
 How bimaxillary protrusion is
considered normal and individual
variation was not recognized?
 Case accepts Angle’s hypothesis of
constancy of first molar
 But rejected the fiction that “Normal
occlusion and normal facial lines are
inseparable.”
 He related the facile profile to each
type of malocclusion.

16.  Case proposed the concept of apical base and divided dentofacial area
into four zones of movement.
 He was aware of the role of nose and chin button and their influence on
profile.
 Case advised the term Protrude and Retrude in reference to the relative
position of the teeth.

17.  Case proposed the concept of normal and ideal occlusion. According
to him Normal is always a range in physiology and anatomy.
 Van Loon, the Dutch physician served as a bridge between Calvin
case and Paul Simon.
 He used plaster cast of the face and teeth in anthropologic manner
which Simon developed further.
 First suggestion of a functional analysis or dynamic approach to
occlusion came with some experiments by Bennett in 1908.
 He proposed that the condylar movement was primarily rotatory on
opening from occlusion to rest position and later on after passing this
point became translatory.

18. B.E. Lischer and Paul Simon
 They broaden the concept of occlusion
by relating teeth in occlusal contact to
cranial and facial planes outside the
denture proper.
 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
consequences of malocclusion outside
the dental area.

19.  Simon wrote “ We must grasp and employ anthropologic
methods”.
 Simon 1926 : Orthodontic methods of investigation must
then approach those of craniofacial and cephalometry

20. Milo Hellman
 Showed the racial variation in
normal occlusion through
anthropological studies.
 He gives a recognition of
interdependence of the teeth and
the supporting craniofacial
structures

21. FACTUAL PERIOD
 1930 as the dividing line between the hypothetical and factual
periods, between static and dynamic concepts, between
ambiguous and more precise terminology.
 B. Holly Broadbent and Hans Planer in 1930 introduced
roentgenographic cephalometry which enabled to follow
longitudinally the oro-facial developmental pattern and the
intricacies of tooth formation, eruption and adjustment.
 With the introduction of this improved method of study, the
factual period was to become the functional period.
 Planer laid emphasis on efficiency of masticating mechanism.
He explained physiological rest position and vertical
dimension

22.  A third element of occlusion, the TMJ has been receiving
more attention. There is an intimate relationship between the
interdigitation of the teeth, the status of controlling,
musculature and the integrity of the TMJ.
 Panaromic Radiography techniques now available with their
greater ability to portray condylar-articular eminence fossa
relations more accurately.
 Wide agreement exist as the concept of occlusion as a
dynamic process.

23. Dynamic Occlusion
 Occlusion is a dynamic entity show variation according to racial, ethnic
, age and sex. Most girls by the age of 12 achieve relatively stable
occlusion whereas boys achieve that a bit later due to continuing
growth pattern.

24.  Three components of occlusion can be summed up as:
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- The status of the controlling musculature is
important in all three dimension
3. TMJ

25. Factors and Forces that Determine Tooth
Position
 The alignment of the dentition in the
dental arches occurs as a result of
complex multidirectional forces
 They are directed to forces which are in
equilibrium.
 Labial to the teeth are the lips and cheeks,
which provide relatively light but constant
lingually directed forces.
 On the opposite side is the tongue, which
provides labially and buccally directed
forces to the lingual surface of the teeth.
 Both the forces are light but constant and
these are the types of forces that over time
can move teeth within the dental arches

27.  Weinstein et al. in the paper entitled “ On an Equilibrium Theory
of Tooth Position” attempted to put the equilibrium theory a
sounder scientific base.
 Edward Angle believed that the environment of the dentition
was a major cause of malocclusion, and that it was possible to
produce a stable ideal occlusion without extraction of teeth
because environment could be modified by orthodontic
treatment.

28.  Proffit in this paper published in 1978 have stated:
 There are two factors present
1. Primary Factor-
Intrinsic forces from tongue and lips
Extrinsic forces : Habits , orthodontic appliance
Forces from dental occlusion
Forces from Periodontal membrane
 2. Secondary Factors
Influences on postural Relationships in the Stomatognathic System
Secondary Factors relation to eruption forces

29. The major primary factors in
the dental equilibrium appears
to be resting pressure of
tongue and lips, and forces
created with in the
periodontal ligament ,
analogous to force of eruption

31.  Proximal contact between adjacent teeth helps maintain the teeth in
normal alignment.
 Due to continuous movements during mastication of teeth overtime
results in wear of the proximal areas, it causes the mesial drifting.
 This helps maintain contact between adjacent teeth and thus stabilizes
the arch.

32. OCCLUSAL CONTACTS
 Prevents the extrusion or over
eruption of teeth
 Maintaining the arch stability.
 If a tooth is lost, not only will the
distal tooth likely to move
mesially but the unopposed tooth
also will likely to erupt.

33. Tooth Alignment
 Intra-arch alignment
Intra-arch tooth alignment refers to the relationship of the teeth
to each other within the dental arch.
 Line of Occlusion
 Plane of Occlusion
 Occlusal Table

34. Line of Occlusion
A detailed consideration of Line of Occlusion, Robert M Ricketts, The Angle Orthod,1978, 48(4),274-281
 Angle (1906) – the line of greatest normal
occlusal contact.
 Angle (1907) - the line with which in form and
position, according to type, the teeth must be in
harmony if in normal occlusion
 There could be one line of occlusion and it must
be same as the architectural line upon which the
dental apparatus was constructed.
 Lower arch, base upon which upper arch is
moulded

35.  Action of inclined plane double mortar pestle
system
 The teeth work towards harmony and the arches
function together to promote, secure and stabilize the
occlusion rather than to force teeth out of normal
position.
Tripodisation.
 Tripodization- deflections is minimized and occlusion
function is not traumatic to the supporting apparatus.
 Logical deduction of Angle’s concept “ If there is one
true line of occlusion, it must pass through the contacts
of the individual arch. It must be common meeting
place for unison and synchronization.”

36. Variation in form and function
 Any aspect of orthodontics involves the problem of variation in the form of parts and variation
in function.
 Angle included eight variation-
1. Position
2. Interincisal relation
3. Size of teeth
4. Pattern of teeth
5. Length of cusp
6. Width of arch
7. Arch form
8. Curve of spee

37. Line of occlusion, Location and position
 Studies of the true buccal plane
representing the bucco-occlusal contact
the line is roughly associated with the Xi point
(the centroid of ramus) which approximates the
functional movement, centre of mandible as
well as entrance of the mandibular nerve into
mandible

38. Line of occlusion, Arch form
 Brader: first one to relate mathematical
relations with the theory of a trifocal ellipse,
particularly useful for upper arch.
 Schulhof: biparameter catenary curve for the
lower arch as a basis for estimating
individual arch form based on anterior tooth
size and arch width at molars.

39. Line of occlusion, Congruity factor

40. Plane of occlusion
 The plane of occlusion is the plane that would be
established if a line were drawn through all the buccal cusp
tips and incisal edges of the mandibular teeth then
broadened into a plane to include the lingual cusp tips and
continuing across the arch to include the opposite side
buccal and lingual cups tips.

41. Why plane of occlusion is curved and not flat?
Most jaw movements are complex, with the centers of rotation
constantly shifting, a flat occlusal plane will not permit
simultaneous functional contact in more than one area of the dental
arch.
Therefore the occlusal planes of the dental arches are curved in
a manner that permits maximum utilization of tooth contacts during
function. The curvature of the occlusal plane is primarily a result of
the fact that the teeth are positioned in the arches at varying degrees
of inclination

42. MESIODISTALAXIAL INCLINATION
 If from the lateral view an imaginary
line is drawn through the buccal cusp
tips of the posterior teeth (molars and
premolars), a curved line following
the plane of occlusion will be
established called as curve of spee

43. Curve of Spee
 Convex for the maxillary arch and
 Concave for the mandibular arch.
 These convex and concave lines match
perfectly when the dental arches are
placed into occlusion. This curvature of
the dental arches and is therefore
referred to as the curve of Spee.

45.  The development of the curve of Spee is that mandibular
permanent teeth erupt before their maxillary antagonists
 This differential timing could permit unopposed mandibular
permanent first molar and incisor eruption beyond the established
mandibular occlusal plane. The result of event would be
deepening in the curve.

46. 1. The occlusal plane in the deciduous dentition is relatively flat.
2. The largest increase in the maximum depth of the curve of
Spee occurs during, and results specifically from, the differential
eruption of the mandibular permanent first molars and incisors
relative to the deciduous second molars.
3. The curve of Spee maintains this depth until the mandibular
permanent second molars erupt, when it again deepens.
4. During the adolescent dentition stage, the curve decreases
slightly and then remains relatively stable
into early adulthood.
5. There are no significant differences in maximum depth of the
curve of Spee between either the right and left sides of the
mandibular arch or the sexes.

48.  Popular rule of thumb for estimating the resulting loss of arch circumference is that 1 mm
of arch circumference is needed for each millimeter of curve of Spee depth present.
 Baldridge and Garcia found the ratio to be more accurately expressed by the formulas
Y = 0.488 X - 0.51 and Y = 0.657 X + 1.34, respectively, where Y is the arch length differential
in millimeters and X is the sum of right and left side maximum depths of the curve of Spee in
millimeters.
 Measurements were taken at each cusp tip from the distobuccal cusp tip of the second
molar proceeding around the arch, recording each successive cusp tip coordinates of the
first molars, premolars, and canines. The center point of each incisal edge was recorded fo
each of the incisors.
 The mathematical relationship of the above recorded coordinates to a flat plane
determined by the incisal edges anteriorly and the distobuccal cusp tips of the second
molars posteriorly was derived by using the XYZ coordinates to calculate the total arch
circumference

49. C T represents the total arch circumference in three dimensional
space
The planar projection of the total arch circumference
is calculated using a similar method except the
depth coordinate z, i.e., depth of Spee, is excluded.

50. A graph of the findings obtained in this
study, as well as those of earlier investigators,
illustrates that the arch circumference loss related
to leveling the curve of Spee is not as an important
factor in causing incisor flaring as previously
thought.
The regression equation
derived from these data is Y = 0.2462 X - 0.1723,
where Y is the arch circumference differential in
millimeters and X the sum of the right and left side
maximum depths of the curve of Spee in millimeters.

51.  coefficient is 0.918.
The arch circumference loss related
to leveling the curve of Spee is not as an important
factor in causing incisor flaring as previously
thought.
For example, with a severe curve of Spee
whose total depth is 9 mm, the total arch circumference
loss is 2.04 mm
[Y= 0.2462 (9) - 0.1723 = 2.04 mm].
This is 52.6% of the closest
value suggested by any earlier investigator. If in this
severe curve of Spee, the 2.04 mm arch circumference
is added to the arch distance anterior to the
Canines, the incisal edges of the central
incisors are advanced 0.78 mm, which corresponds
to tipping a typical mandibular incisor 3.2°.
This is less incisor tipping than is frequently seen after
arch leveling with continuous arch wires containing
reverse curves of Spee.

52. Thus the curve of Spee
may in fact be leveled without excessive flaring of
the incisors by using appropriate biomechanics to
achieve predetermined treatment objectives.

53. Significance :
 The curve of spee results in alignment of each tooth for
maximum resistance to the functional loading, the long
axis of each lower tooth is aligned nearly parallel to its
individual arc of closure around the condylar axis.
 This progression positions the cusp tips on a curve that is
directly related to the condylar axis by a progressive
series of tangents.

54.  Andrews in describing the 6 characteristics of normal
occlusion, found that the curve of Spee in subjects with
good occlusion ranged from flat to mild, noting that the
best static intercuspation occurred when the occlusal plane
was relatively flat. He proposed that flattening the
occlusal plane should be a treatment goal in orthodontics.

55. BUCCOLINGUAL AXIAL INCLINATION
 If a line is drawn through the buccal and lingual
cusp tips of both the right and the left posterior
teeth, a curved plane of occlusion will be
observed, referred to as curve of wilson

56. Curve of Wilson
 The curvature is convex in the maxillary arch
 concave in the mandibular arch.
 If the arches are brought into occlusion, the
tooth curvatures will match perfectly. This
curvature in the occlusal plane observed from
the frontal view is called the curve of Wilson.

57. Significance
 Resistance to loading:
 The axial inclination of
posterior teeth is nearly
parallel with the strong
inward pull of the internal
pterygoid muscle

58. Bonwill’s triangle
 Observers sought to develop some
standardized formulas that would
describe intra arch relationships.
 Bonwill, one of the first to describe the
dental arches, noted that an equilateral
triangle existed between the centers of
the condyles and the mesial contact
areas of the mandibular central incisors.
He depicted this as having 4-inch sides.

59. Curve of Monson
 In 1932 Monson utilized
Bonwill’s triangle and
proposed a theory that a
sphere existed with a radius
of 4 inches whose center was
an equal distance from the
occlusal surfaces of the
posterior teeth and from the
centers of the condyles.

60. Inter arch Tooth Alignment
 Inter arch tooth alignment refers to the relationship of the teeth in one arch to those in the other. When the
two arches come in to contact, as in mandibular closure, the occlusal relationship of the teeth is established
 The length and width of maxillary arch is higher when compared to mandibular arch
 A line that begins at the distal surface of the third molar, extends mesially through all of the proximal
contact areas around the entire arch, and ends at the distal surface of the opposite third molar represents the
arch length.
 Both arches:-same length (maxillary arch, 128 mm; mandibular arch, 126 mm).
 The arch width is the distance across the arch. The width of the mandibular arch is slightly less than that of
the maxillary arch; thus when the arches occlude, each maxillary tooth is more facially positioned than the
occluding mandibular tooth.

61.  The maxillary lingual cusps occlude along the central fossa areas
of the mandibular teeth. This occlusal relationship protects the
surrounding soft tissue.
 The buccal cusps of the maxillary teeth prevent the buccal
mucosa of the cheek and lips from falling between the occlusal
surfaces of the teeth during function.
 Likewise the lingual cusps of the mandibular teeth help keep the
tongue from getting between the maxillary and mandibular teeth.
 Occasionally, because of discrepancies in skeletal arch size or
eruption patterns, the teeth occlude in such a manner that the
maxillary buccal cusps contact in the central fossa area of the
mandibular teeth. This relationship is referred to as a cross bite.

63. CENTRIC CUSP-
The buccal cusps of the mandibular posterior teeth and the lingual cusps of the maxillary posterior teeth
occlude with the opposing central fossa areas.
These cusps are called the supporting cusps,or centric cusps, primarily responsible for maintaining the
distance between the maxilla and mandible. This distance supports the vertical facial height and is called
the vertical dimension of occlusion.
The centric cusps are broad and rounded.
When viewed from the occlusal, their tips are located approximately one-third the distance into the total
buccolingual width of the tooth

64. NON-CENTRIC CUSP-
 The buccal cusps of the maxillary posterior teeth and the lingual cusps of the mandibular
posterior teeth are called the guiding or noncentric cusps.
 These are relatively sharp, with definite tips that are located approximately one-sixth the
distance the total buccolingual width of the tooth

65.  Occlusal table is considered the inner aspect of
the tooth, since it falls between the cusp tips.
 Occlusal area outside the cusp tips is called the
outer aspect.
 The inner and outer aspects of the tooth are made
up of inclines that extend from the cusp tips to
either the central fossa areas or the height of the
contour on the lingual or labial surfaces of the
teeth called inner and outer inclines.

66. There is a small area of the noncentric cusps that can
have functional significance.
This area is located on the inner incline of the non centric
cusps near the central fossa of the tooth and either
contacts with or is close to a small portion of the outer
aspect of the opposing centric cusp.
The small area of the centric cusp(about 1 mm) is the
only area in which an outer aspect has any functional
significance. This area has therefore been called the
functional outer aspect. There is a small functional outer
aspect on each centric cusp that can function against the
inner incline of the non centric cusp.

67. Buccolingual Occlusal Contact
Relationship
Bucco-occlusal (B-O) line
If an imaginary line is extended through all the buccal cusp tips
of the mandibular posterior teeth, the bucco-occlusal (B-O) line
is established
Linguo-occlusal (L-O)line
If an imaginary line is extended through the lingual
cusps of the maxillary posterior teeth, the linguo-occlusal (L-O)
line is observed.
Central fossa (C-F) line
If a third imaginary line is extended through the central
developmental grooves of the maxillary and mandibular posterior
teeth, the central fossa (C-F) line is established. In the normal
well-aligned arch, this line is continuous and reveals the arch
form

68. To visualize the buccolingual relationships
of the posterior teeth in occlusion, one must
simply match up the appropriate
imaginary lines.
The B-O line of the mandibular teeth
occludes with the C-F line of the maxillary
teeth.
The L-O line of the maxillary teeth occludes
with the C-F line of the mandibular teeth.

69. Mesiodistal Occlusal Contact
Relationship
Cusps typically contact in one of two areas:
 Central fossa areas Marginal ridge and embrasure areas

70. Cusp-fossa Occlusion
 In this type of occlusion, the stamp cusp of one tooth occludes in a single fossa of a
single opponent. The upper stamp cusps fit into all the fossae of the lower teeth while
the lower stamp cusps fit into all the upper fossae except the distal ones of bicuspids.
 This kind of arrangement where contacts occur between single opposing teeth is called
a cusp-fossa occlusion

71. Advantages of cusp-fossa relation
o Forces are directed along the long axis of tooth.
o There is greater stability to entire arch of teeth and less of a
tendency toward tooth movement.
o There is less chance of food impactions between embrasure.
o In normal inter-arch tooth relationship each tooth occludes with
two opposing teeth.

72. Cusp-embrasure Occlusion
 Another type of occlusion between the upper and lower teeth is called the cusp-
embrasure or tooth to two teeth occlusion.
 In this type of arrangement each tooth occludes with two opposing teeth.

73. Classification of mal-occlusion
Common Occlusal Relationships of the Posterior Teeth
Common Occlusal relationships of the Anterior teeth

74. Common Occlusal Relationships of
the Posterior Teeth
The variation in molar relationship was first described by Angle in
1899.
He considered the maxillary first permanent molar as a fixed
anatomical point in the jaws and the key to occlusion.
Angle’s classified malocclusion into three broad categories
Class I, II, or III molar relationship

75. The Angle Class I molar relationship is the most common
found in the natural dentition. It is characterized by:
1. The mesiobuccal cusp of the mandibular first molar occludes in
the embrasure area between the maxillary second premolar and
first molar.
2. The mesiobuccal cusp of the maxillary first molar is aligned
directly over the buccal groove of the mandibular first molar.
3. The mesiolingual cusp of the maxillary first molar is situated in
the central fossa area of the mandibular first molar.
Angle’s Classification of molar relationship: Class I

77. Angle’s Classification of molar relationship: Class II
 In some patients the maxillary arch is large or advanced
anteriorly or the mandibular arch is small or positioned
posteriorly.
 Mandibular first molar being positioned distal to the class I
molar relationship
 Characteristics:
1. The mesiobuccal cusp of the mandibular 1st molar occludes
in the C-F area of the maxillary 1st molar.
2. The mesiobuccal cusp of the mandibular 1st molar is
aligned with the buccal groove of the maxillary 1st molar.
3. The distolingual cusp of the maxillary 1st molar occludes in
the C-F area of the mandibular 1st molar.

79. Angle’s Classification of molar relationship: Class III
 The class III characteristics are as follows:
 The distobuccal cusp of the mandibular first molar
is situated in the embrasure between the maxillary
second premolar and first molar.
 The mesiobuccal cusp of the maxillary first molar
is situated over the embrasure between the
mandibular first and second molar.
 The mesiolingual cusp of the maxillary first molar
is situated in the mesial pit of the mandibular
second molar.
 Each occlusal contact pair is situated just mesial to
the contact pair in a class I relationship, about the
width of a premolar.

81. OCCLUSAL RELATIONSHIPS OF THE
ANTERIOR TEETH
 The normal relationship will find the incisal edges of the mandibular
incisors contacting the lingual surfaces of the maxillary incisors.
 These contacts commonly occur in the lingual fossae of the maxillary
incisors approximately 4 mm gingival to the incisal edges.
 Labial aspect, 3 to 5 mm of the mandibular anterior teeth is hidden by
the maxillary anterior teeth.
 crowns of the mandibular anteriors are approximately 9 mm in
length, a little more than half the crown is still visible fromthe
labial view.

82.  The labial inclination of the maxillary anterior
teeth and the manner in which the mandibular
teeth occlude with them do not favor resistance to
heavy occlusal forces.
 If, during mandibular closure, heavy forces occur
on the anterior teeth, the tendency is to displace
the maxillary teeth labially.
 Therefore, in a normal occlusion, contacts on the
anterior teeth in the intercuspal position are much
lighter than on the posterior teeth.
 The anterior tooth contacts that provide guidance
of the mandible are called the anterior guidance.

83.  When a person has an underdeveloped mandible (class II molar relationship), the
mandibular anterior teeth often contact at the gingival third of the lingual surfaces of the
maxillary teeth. This anterior relationship is termed a deep bite (deep overbite).
 If maxillary incisors increased labial inclination, it is considered to be a division 1.
 When maxillary incisorslingually inclined, the anterior relationship is termed a class II,
division 2.
 An extremely deep bite can result in contact with the gingival tissue palatal to the
maxillary incisors.

84.  The horizontal distance by
which the maxillary anteriors
overlap the mandibular
anteriors, known as the
horizontal overlap (called
overjet)
 The vertical overlap (called
overbite).

85. ANDREWS SIX KEY TO NORMAL
OCCLUSION
Andrews LF. The six keys to normal occlusion. Am J Orthod. 1972;62(3):296–309: Sep; PubMed PMID:4505873.
 Key I : Molar relationship
 Key II : Crown angulation
 Key III : Crown inclination
 Key IV : Absence of Rotation
 Key V : Tight Contact
 Key VI : Curve of Spee
 Key VII : Tooth size

86. Key 1-Molar Relationship
1. The distal surface of the distal marginal ridge of the upper first permanent molar
contacts and occludes with the mesial surface of the mesial marginal ridge of the lower
second molar.
2. The mesiobuccal cusp of the upper first permanent molar fall within the groove
between the mesial and middle cusps of the lower first permanent molar

87. 3. The mesio-palatal cusp of upper first molar seats in the central fossa of the lower first molar
4. The buccal cusp of maxillary premolar have a cusp-embrasure relationship with the mandibular
premolars.
5. The lingual cusp of maxillary premolars have a cusp-fossa relationship with the mandibular canine
and first premolars.

88. 6. Maxillary canine has a cusp-embrasure relationship with the
mandibular canine and first premolar.
7. The maxillary incisor overlap the mandibular incisor and
midline coincide

89. Key 2- Crown angulation
 Crown angulation refers to angulation (or mesiodistal tip) of the long axis of the
crown, not to angulation of the long axis of the entire tooth.
 The gingival portion of the long axis of each crown was distal to the incisal
portion, varying with the individual tooth type.
 The long axis of the molar crown is identified by the dominant vertical groove
on the buccal surface of the crown.
 “+ reading”, when the gingival portion of facial axis of clinical crown is distal to
the incisal portion.
 “- reading”, when the gingival portion of facial axis of clinical crown is mesial to
the incisal portion

91. Key 3- Crown inclination
 Crown inclination refers to labiolingual or buccolingual
inclination of the long axis of the crown, not to the inclination of
the long axis of the entire tooth.

92. A. Anterior Crown Inclination-
 In upper incisors- Positive (+) crown inclination
 In lower incisors- Negative (-) crown inclination
B. Posterior Crown Inclination— Upper
 A minus crown inclination existed in each crown from the upper canine
through the upper second premolar.
 A slightly more negative crown inclination existed in the upper first and
second permanent molars
C. Posterior Crown Inclination— Lower
 A progressively greater "minus" crown inclination existed from the lower
canines through the lower second molars

94. Tip and Torque
 As the anterior portion of an
upper rectangular arch wire is
lingually torqued, a
proportional amount of mesial
tip of the anterior crowns
occurs.
 The ratio is approximately
4:1. For every 4 degrees of
lingual crown torque, there is
1 degree of mesial
convergence of the gingival
portion of the central and
lateral crowns.

95. Rotations
 Teeth should be free of
undesirable rotations.
 The molar, if rotated, would
occupy more space than
normal, creating a situation
unreceptive to normal
occlusion.

96. Tight Contacts
 Contact points should be tight (no spaces).
 Without exception, the contact points on the non-orthodontic
normals were tight.
 (Serious tooth-size discrepancies should be corrected with jackets or
crowns, so the orthodontist will not have to close spaces at the
expense of good occlusion.)

97. Occlusal Plane ( Curve of Spee)
 Flat plane should be a
treatment goal as a form of
overtreatment.
 There is a natural tendency
for the curve of Spee to
deepen with time.

98.  If the lower anterior teeth can be held
until after growth has stopped and the
third molar threat has been eliminated
by eruption or extraction, then all
should remain stable below, assuming
that treatment has otherwise been
proper.
 Intercuspation of teeth is best when
the plane of occlusion is relatively flat
.
 There is a tendency for the plane of
occlusion to deepen after treatment.
 To treat the plane of occlusion until it
is somewhat flat or reverse to allow
for this tendency.

99. Tooth size
 Aids in analyzing the proportionality of the maxillary and mandibular teeth i.e the
upper and lower teeth should be in proportion
 The presence of disproportionate in either arch can disturb the harmony
 Mclaugin and Bennet added the seventh key and concluded that proper anterior and
posterior teeth fir not possible until seventh key is fulfilled.

101.  The OGS (Objective Grading System) is assessed by scores given to eight occlusal traits.
 Arch alignment,
 marginal ridges,
 buccolingual inclination,
 occlusal relationship,
 occlusal contacts,
 overjet, and
 Interproximal contacts
 Six keys to normal occlusion
1. Changes for key 1 (interarch relationship) were not significant
2. Only the maxillary second molars showed a significant improvement of key 2 (clinical
crown angulation) between time points.
3. Key 3 (clinical crown inclination) showed significant deterioration for the maxillary
second molars from T1 to T2, with frequent buccal inclination observed at T2.

102.  The increase of second molar buccal torque may be related to third molar
development and eruption. Another possible explanation is a decrease in
buccinator muscle tonicity, with age
Self-correction of maxillary second molar distoangulation
with time suggests that correction of this feature in orthodontic
patients during the early permanent dentition might constitute an
overtreatment and should be avoided to decrease treatment time.

103.  Conclusions
1. Aging slightly deteriorates the quality of normal occlusion.
2. Maxillary second molar tipped buccally from 13 to 60 years of
age.
3. Levelling of marginal ridges improved with tooth wear.
4. Maxillary second molar showed a change of mesiodistal angulation
with mesial movement of the crown during the observation
time.
5. Subjects without tooth loss showed a more significant tooth alignment
worsening than subjects with tooth loss.
6. Most of the subjects with normal occlusion demonstrate satisfaction with
their smile aesthetics and occlusal comfort at the sixth decade of life

104. Occlusal Contacts During Mandibular
Movement
 The term eccentric has been used to describe any movement of the
mandible from the intercuspal position that results in tooth
contact.
 Three basic eccentric movements :
1. Protrusive
2. Laterotrusive
3. Retrusive

105. Protrusive mandibular movement
 When the mandible moves forward from the intercuspal
position.
 Any area of a tooth that contacts an opposing tooth during
protrusive movement is considered to be in protrusive
contact.
 In a normal occlusal relationship, the predominant protrusive
contacts occur on the anterior teeth, between the incisal and
labial edges of the mandibular incisors against the lingual
fossa areas and incisal edges of the maxillary incisors.
 These are considered the guiding inclines of the anterior
teeth.

106.  On the posterior teeth the protrusive
movement causes the mandibular-centric
cusps (buccal) to pass anteriorly across the
occlusal surfaces of the maxillary teeth.
 Posterior protrusive contacts occur
between the distal inclines of the maxillary
lingual cusps and the mesial inclines of the
opposing fossae and marginal ridges.
 Posterior protrusive contacts can also
occur between the mesial inclines of the
mandibular buccal cusps and the distal
inclines of the opposing fossae and
marginal edges.

107. Laterotrusive mandibular movement
 Right and left mandibular posterior teeth move across their opposing teeth in
different directions.
 Contacts can occur on two incline areas.
 Between the inner inclines of the maxillary buccal cusps and the outer inclines
of the mandibular buccal cusps;
 The other is between the outer inclines of the maxillary lingual cusps and the
inner inclines of the mandibular lingual cusps.
 Both these contacts are termed laterotrusive.
 Working contact : Since most function occurs on the side to which the
mandible is shifted.

108.  During a lateral mandibular movement, the right and left mandibular
posterior teeth move across their opposing teeth in different
directions.
 Mediotrusive (nonworking) contacts occur on the inner inclines of
the maxillary lingual cusps opposing the inner inclines of the
mandibular buccal cusps.

110. Retrusive mandibular movement
 Occurs when mandible moves posteriorly from the intercuspal position.
 A retrusive movement is restricted by the ligamentous structures. it is quite small (1 or 2
mm).
 During a retrusive movement, the mandibular buccal cusps move distally across the occlusal
surface of their opposing maxillary teeth.
 Areas of potential contact occur between the distal inclines of the mandibular buccal cusps
(centric) and the mesial inclines of the opposing fossae and marginal ridges.
 In the maxillary arch, retrusive contacts occur between the mesial inclines of the opposing
central fossae and marginal ridges.
 Retrusive contacts occur on the reverse inclines of the protrusive contacts, since the
movement is exactly opposite.

112. Attritional Occlusion
 It is an occlusion which is continually changing through out the life and are caused
mainly by the tooth migration and changing anatomy of teeth, due to the physiological
process of attrition.
 The concept of “Attritional Occlusion” was introduced by Dr P.R.Begg in 1954 after
intense studies of dentitions in Australian Aboriginal skulls.

113. Begg’s Hypothesis
 He saw the skulls of australian aboriginals, and noticed that their teeth
were worn flat.
 Attritional occlusion was mainly observed in stone age man and begg
used australian aboriginals as a model.
 The teeth of these skulls had extensive occlusal and inter proximal
wear. The crowding and malocclusion was almost absent in these
skulls.

114.  All these time he was following the “Non Extraction Technique” advocated by Dr. Angle.
 But he was not satisfied with the post treatment results he obtained.
 In 1954, Begg reasoned that the relatively low incidence of malocclusion in stone age man is due
to the reduction by more than half an inch in the total length of each of these dental arches.
 This was caused by tooth attrition so that the smaller crowns (in mesio distal diameter) could be
more easily accommodated into the jaws.
 So he advised extractions and proximal stripping in patients with excess tooth substance so as to
attain a correct occlusion.

115.  Adult Australian aboriginal dentition - described by Begg as anatomically correct
attritional occlusion, including the edge-to-edge bite of the incisor teeth.

116. Two Factors in Correct Occlusion
1. Changing Anatomy of Teeth
• Occlusally
• Incisally
• Proximally.
2. Tooth Migration
• Horizontal (mesial migration).
• Vertical (continual eruption).

117. Anatomically Correct Occlusion
 It can develop only when there is sufficient attrition of the teeth for
them to assume correct occlusal relationship.
 Stone age man’s teeth have occlusal and proximal attrition, this is so
marked that the dentine is exposed but are not subjected to dental
caries.
 In civilized man, the occlusion is anatomically incorrect because his
food is too soft and concentrated to cause tooth attrition.
 The incisal, occlusal, proximal and axial relations of civilized man’s
teeth remain almost static throughout life.

118. Deciduous incisors erupt in overbite relation
(primitive man & civilized man)
Incisal and occlusal wear---hard, coarse and gritty food.
Initially – oblique, later- horizontal relation of incisors
Lower incisors tip labially while upper incisors get more
upright until an edge to edge relationship is obtained—
seen in both deciduous,& permanent dentition of stone
age man.

119. In civilized man
Persistence of the anterior overbite
Lower incisors locked in a functionally
and anatomically incorrect position
Lower incisors restrained from proclining
Crowding of teeth

120. Effects of attrition on the evolution of human teeth
 Deposition of secondary dentin
 Continual vertical tooth eruption
 Continual mesial migration of the teeth
 Shapes and forms of the crowns of the teeth
--greatest thickness of the enamel and dentin covering the pulp is on the
occlusal, incisal, mesial and distal surfaces.
--lingual, buccal and labial surfaces of the teeth relatively thin.
 Small mesio-distal diameters of tooth necks and roots
 Pulpal pain did not evolve due to secondary dentine deposition

121.  Many forms of malocclusion of teeth found in civilized man are
entirely due to absence of tooth wear.
 In all this we see how nature has provided for the balance between
tooth size and jaw size by maintaining the correct tooth and inter arch
relationships.
 On the contrary, these basic factors for the correct occlusion are not
present in civilized man.
 Therefore the harmonious sequence of events does not occur in
civilized man. Failure of continual dental arch reduction therefore
causes mis-placed teeth, ill formed dental arches and malocclusion.
 In stone age man’s attritional dentition, centric occlusion does not
exist.

122.  Centric occlusion is regarded in normal occlusion as the very hallmark of
anatomically correct occlusion and absence of proper centric occlusion is
regarded as abnormal.
 However as there are no high cusps but just flat worn surfaces of teeth
occluding in attritional occlusion, there is nothing to guide the teeth into
centric occlusal relation.
 Each time stone age man swallows, his teeth seems to occlude differently,
some times to one side of the central line and sometimes to the other side.
 The current practice of grinding the buccal cusps of upper molars and the
lingual cusps of lower molars when equilibrating the teeth needs
reconsideration in view of the fact that it is the lingual cusps of upper
molars and the buccal cusps of the lower molars that become worn to the
greatest extent in stone age man’s attritional occlusion

123. Ideal Occlusion criteria
T A Timm, Herremans, Ash Jr, , Am J Orthod, Occlusion and orthodontics,
1976;70(2):138-45.

125. Criteria for Good Occlusion
–Hamish Thompson
1. Two complete arches of teeth with secure contact points and
occlusal surface contours adequate for the functions
required.
2. Root shape and alignment adequate to resist occlusal forces.
3. Rest position stable with adequate lip seal.
4. An interocclusal distance of 2-4 mm between rest position
and intercuspal position.
5. Simultaneous and bilateral occlusion between all teeth of
maxillary and mandibular arches at intercuspal position. No
deflective contacts.

126. 6. Cusp-fossa and cusp-ridge occlusion having tripod contacts.
7. Return of each tooth to its original position on removal of occlusal
force.
8. Articulation between retruded and intercuspal positions free from any
interferences causing lateral deflexion.
9. Stable vertical and horizontal overlap.
10. Empty mouth articular movements free from deflective contacts.

127. Conclusion
 Occlusion, especially in orthodontics during growth, is a
process, a process of growing and shifting interactive systems.
Orthodontics can be considered as the navigation of those
systems
 The achievement of the ideal functional occlusion provided a
satisfactory stability after orthodontic treatment.
 Thus, the success of the orthodontic treatment depends on the
establishment of the static and dynamic criteria.
 This minimizes the orthodontic relapse and prevents the
appearance of occlusal pathologies

128. REFERENCES
1. Principles and practice in orthodontics, T.M.GRABER, , 3rd edition
2. Management of temporomandibular disorders and occlusion, JEFFERY P. OKESON.
3. Occlusion, H. THOMSON.
4. Wheeler's Dental Anatomy, Physiology and Occlusion, Stanley J Nelson10th edition.
5. Classification of Malocclusion, Edward H Angle, The dental cosmos, 1899, 41(18),
248-357.
6. Six keys to normal occlusion, Lawrence F. Andrews, Am J Orthod, 1972, 62(3), 296-
309.
7. A detailed consideration of Line of Occlusion, Robert M Ricketts, The Angle
Orthod,1978, 48(4),274-281
8. T A Timm, Herremans, Ash Jr, , Am J Orthod, Occlusion and orthodontics,
1976;70(2):138-45