Occlusion in Orthodontics

Question 1

Types of Occlusion

Answer 1

Occlusion can be:
–> Static occlusion
Horizontal relations of the mandible to the maxilla.
Vertical relations ·of the mandible to the maxilla.
–> Functional occlusion
Protrusive relations
Lateral relations

Question 2

Significance of Centric relation

Answer 2

It is a reproducible position of the mandible relative to the maxilla, irrespective of the guidance that the occlusal surfaces of the teeth may provide. The centric occlusion is usually forward from the centric relation position by 1-2 mm

Question 3

Roth’s Key of occlusion

Answer 3

Key 1: Coincidence of intercuspal position and retruded contact position.
Key 2: Maximum and stable cusp-to-fossa contacts throughout buccal segments.
Key 3: Disclusion of the posterior teeth in mandibular protrusion by even contacts on the incisors.
Key 4: Lateral movements of the mandible are guided by working side canines, with disocclusion of all other teeth on both working and non-working sides

Question 4

Signs and symptoms of occlusal interference or premature contacts

Answer 4

Occlusal wear
Excessive tooth mobility
Temporomandibular joint sounds
Limitation of opening movements
Myofascial pain
Contracture of mandibular musculature making manipulation difficult or impossible
Some sort of tongue thrust swallow

Question 5

Bennet angle/Progressive side shift

Answer 5

The angle obtained after the non-working side condyle has moved anteriorly and medially relative to the sagittal plane.

Question 6

Bennet shift
Bennet movement
Immediate side shift
Mandibular side shift

Answer 6

The bodily lateral movement of the mandible towards the working side during lateral excursions.

Question 7

Condylar angle /
Condylar path

Answer 7

The angle given by ‘ the downward· and forward slope of the glenoid fossa.

Question 8

Jaw closing and opening muscles

Answer 8

Jaw closing muscles
>Masseter
>Medial pterygoid
>Temporalis

Jaw opening muscles
>Lateral pterygoid
>Anterior digastric muscle

Question 9

Prevalence of occlusion classes (Saudi Arabia)

Answer 9

Class I: 66.51% (Out of this only 3-4% of individuals have ideal class I occlusion)
Class II: 17.70%
Class III: 15.79%

Question 10

The differences between the retruded contact position and the intercuspal position

Answer 10

0.5-1.5 mm with Angle class I occlusion

Question 11

According to Angle, the key to normal occlusion in adults is the anteroposterior relationship. It’s based on which teeth?

Answer 11

First molars and canines

Question 12

In a normal occlusion Curve of Spee should be …. mm

Answer 12

1 - 1.5 mm
Ideally, there should not be any curve of Spee in the ideal occlusion, but in most of the dentition, some amount of curve of Spee is present. Some amount of curve of Spee, i.e., up to 1-1.5 mm if present is considered normal.
In orthodontics, goal is to keep the curve of Spee flat, so that during the retention period of the orthodontic treatment, some amount of relapse will take
place and a minor degree of curve will develop.

Question 13

In classifying the occlusion in a patient with permanent molar loss, the most important additional observation to reinforce initial evaluation is

Answer 13

Canine relation

Question 14

In postural rest the midlines are coinciding and well centered. The mandible slides lateral from the rest position into a crossbite in occlusion. This is caused by tooth guidance and is called as:
A- Latero occlusion
B- Pseudo Crossbite
C- Latergnathy
D- Both A and B

Answer 14

D- Both A and B

Question 15

In a patient, cross bite in which the midline shift is present in occlusion and postural rest position, this condition is called as

Answer 15

Laterognathy

Question 16

Dental arch form is ultimately determined by
A- Facial type
B- Angle classification
C- Facial growth pattern
D- Balance between facial and Intra oral muscle

Answer 16

D- Balance between facial and Intra oral muscle

Question 17

Proper occlusion is maintained by
A- Proximal contacts
B- Cusp fossa relationship
C- Muscle pressure
D- All of the above

Answer 17

D- All of the above

Question 18

In an ideal occlusion, centric occlusion
Should coincide with:
A- Centric relation
B- Should vary
C- Is not important
D- None of the above

Answer 18

A- Centric relation

Question 19

In a patient, the distobuccal cusp of the upper first molar coincides with the mesiobuccal groove of lower first molar. The dental classification for this patient is:

Answer 19

Class - II

Question 20

Functional pseudo-overbite is cause by supraeruption of which teeth?

Answer 20

Incisors

Question 21

X occlusion is commonly seen among:
A- Australian aborigines
B- South east asians
C- Oriental population
D- Eskimo

Answer 21

ANS: A
If the mandible is so much narrower than the maxilla In these regions that the distance from the lower first permanent molar of one side to that of the other side is small, relative to the corresponding distance in the upper dental arch. Thus, when the lower first permanent of one side occludes with the upper,
the lower molars of the opposite side do not reach far enough buccally to occlude with their antagonist. This is known as X occlusion

Question 22

In normal occlusion the teeth have
A- Marginal contact
B- Surface contact
C- Cusp-to-cusp contact
D- Edge-to-edge contact

Answer 22

B- Surface contact
This is also known as cusp-fossa contact. Advantages of cusp-fossa arrangement over cusp embrasure arrangement:
»>Forces are directed more towards the long axis of the teeth
»>The arrangement leads to greater stability of the arch, decreasing the tendency towards tooth movement
»>The chance of food impaction in the embrasures is less

Question 23

Andrew’s Six Keys of Normal Occlusion are:

Answer 23

> > > Molar relationship - the mesiobuccal cusp of the upper first molar occludes with the groove between the mesiobuccal and middle buccal cusp of lower first molar. The distobuccal cusp of the upper first molar contacts the mesiobuccal cusp of the lower second molars.

> > > Crown angulation-all tooth crowns are angulated mesially

> > > Crown inclination:
Incisors are inclined toward the buccal or labial surface
Upper posterior teeth are inclined lingually, similarly from the canine to the premolars. Upper molar crowns are inclined slightly more than the canines and premolars.
Lower posterior teeth are Inclined lingually, progressively more from canines to premolars.

> > > Rotations- absence of rotations

> > > Spaces-spaces are not present between the teeth

> > > Occlusal plane/curve of Spee-this plane is either flat or slightly curved.

Question 24

Canine-guided occlusion is seen during
A- Centric relation
B- Centric occlusion
C- Non-functional occlusion
D- Lateral mandibular movements

Answer 24

D- Lateral mandibular movements

Question 25

The teeth which are most often referred to as the key of normal occlusion:
A- First permanent molars
B- First permanent molars and second primary molars
C- Maxillary and mandibular second primary molars
D- Second permanent molars

Answer 25

A- First permanent molars

Question 26

Functional Occlusal Plane

Answer 26

It is described as the line connecting the molars in occlusion to the bisector of the overbite

Question 27

Anatomic Occlusal Plane

Answer 27

It is described as the line passing through the occlusal of the premolars and the molars

Question 28

An anatomic crossbite, as contrasted with a functional crossbite usually demonstrated:
A- Marked wear facet
B- Smooth closure to centric occlusion
C- Deviated closure to centric occlusion
Symmetrical individual dental arches

Answer 28

B- Smooth closure to centric occlusion

Question 29

Balanced occlusion

Answer 29

The bilateral, simultaneous, anterior, and posterior occlusal contact of teeth in centric and eccentric positions.

Question 30

Christensen’s phenomenon

Answer 30

Christensen Phenomena: A gap occurring in the natural dentition or between the opposing posterior flat occlusal rims when the mandible is protruded (posterior open bite). It can lead to instability in full dentures unless compensating curves are incorporated into the dentures

Question 31

Three dimensional classification of occlusion was given by:
A- Angle
B- Deway
C- Simon
D- Baume

Answer 31

ANS: C
Malocclusion can occur in all the three planes:
»> Anteroposterior (Orbital plane/simon plane)
Protrusion
Retrusion

> > > Transverse (Mid sagittal plane)
Contraction
Distraction

> > > Vertical
Attraction
Abstraction

Question 32

Dental Classification in patient with premature loss of primary molar, additional relation to be noted is

Answer 32

Canines

Question 33

In mixed dentition the habitual occlusal position should ideally:

A: Have a 2 mm difference between it and centric occlusion
B: Be same as the centric occlusal position
C: Depends on the facial pattern
D: Has 2 mm behind centric occlusion in Angle’s class II malocclusion

Answer 33

B: Be same as the centric occlusal position

Question 34

In normal occlusion, the maxillary canine occlude in embrasure between

Answer 34

Mandibular canine and first premolar

Question 35

Seventh key of normal occlusion is:

Answer 35

Tooth size and arch length