Hinge Axis

Question 1

How do we define hinge axis today?

Answer 1

Transverse Horizontal Axis: An imaginary line around which the mandible may rotate. (GPT-6)
This rotation averages about 12o or 18-25mm of incisal opening according to Rahn, and occurs
during centric relation.

Question 2

How do we define centric relation:

Answer 2

centric relation \sĕn΄trĭk rĭ-la΄shun: acronym is CR; a maxillomandibular relationship, independent of tooth contact, in which the condyles articulate in the anterior-superior position against the posterior slopes of the articular eminences; in this position, the mandible is restricted to a purely rotary movement; from this unstrained, physiologic, maxillomandibular relationship, the patient can make vertical, lateral orprotrusive movements; it is a clinically useful, repeatable reference position

Question 3

What are four theories of location of hinge axis?

Answer 3

1. Absolute location
   Pt hinge axis must = articulator hinge axis
2. Arbitrary location
   no value in hinge axis, this group fails to realize that if articulator does not = pt hinge axis… the path of closure will not be the same.
3. Hinge axis does not exist or be replicated
   - cant accurately locate or simluate one axis thus arbitrary is just as good.
4. Split Axis theory
   - two axis of rotation, one in each condyle and they parallel eachother.

Question 4

Is the path of closure the same as the arc of closure? (No)

Answer 4

Is the path of closure the same as the arc of closure? (No)

The path results from closing rotation and a gliding path.

Question 5

How accurate are individuals in locating a true hinge axis?

Answer 5

• Kurth and Feinstein said within 2 mm when restricting opening to ¾ inch at the incisal pin.
• Borgh and Posselt said within 1.5 mm when a 10 degree arc was used and within 1.0 mm when a
  15 degree arc was used.
• Lauritzen and Wolford were able to achieve an accuracy of 0.2 mm when using a 10 degree arc of
  movement.

Question 6

Does the mandible flex and why do we care?

Answer 6

Yes it does. This response is a function of the mechanical properties of the bone as well as the type,
magnitude, direction, and point of application of the force.
The later pteygoid muscle is most frequently cited as inducing mandibular flexure.

Question 7

• ## What are the clinical implications of the mandible flexing?

Answer 7

• What are the clinical implications of the mandible flexing?
• Producing an inaccurate cast if flexure occurs during impressions
• Mandibular flexure may influence stress on abutment teeth
• Adduction of the mandible may effect the ultimate stability of a lower denture

Question 8

• Mandibular flexure may influence stress on abutment teeth

- Adduction of the mandible may effect the ultimate stability of a lower denture

Answer 8

What width changes were seen in various mandibular positions and manipulations in the Gates and
Nichols article?
Opening 0-0.3 mm decreased value in arch width
Protrusion 0.1-0.5 mm decreased value in arch width
Horizontal retruding force 0.11 mm increased value in arch width
Therefore the amount of mandibular arch width change during impression making can be minimized
by preventing any protrusive movement and /or opening beyond 20 mm.

Question 9

Accuracy of an Ear Piece Face-bowTo record variations between the kinematic axis and earpiece determined axis and measure
the magnitude and direction between the two points on selected subjects.

Answer 9

The earpiece facebow related the maxilla to the hinge axis with the 5mm acceptable range 50%
of the time.

Question 10

Hinge Axis

“Many hinge axes exist”

Answer 10

Page. Many hinge axes exist

Gates and Nichols. The width of the mandible changes due to intrinsic and extrinsic forces.
Simpson. Use a point 10mm from the superior border of the tragus on Camper’s line for an arbitrary
http://nnd40

Question 11

Hinge Axis.

Arc may result from compound movements

Answer 11

Preston. Arc may result from compound movements

Question 12

Hinge axis

There is only one position of hinge axis

Answer 12

Granger. There is only one position of the hinge axis.
Aull. Only one hinge axis.
Beard and Clayton. One hinge axis

Question 13

Hinge axis “The study of natural motion does not show a hinge axis”

Answer 13

Shanahan. Study of natural motion does not show a hinge axis

Question 14

Hinge Axis 95% of patients true axis is within 5mm of the arbitrary hinge Axis (13 mm anterior to
the tragus on the tragus- canthus line.

Answer 14

Schallhorn. 95% of patients true axis is within 5mm of the arbitrary hinge Axis (13 mm anterior to
the tragus on the tragus- canthus line.

Question 15

Hinge Axis 33% of a patients true hinge axes are within 5 mm of the patients true axis.
Walker. 20% were within 5mm

Answer 15

Lauritzen and Bodner. 33% of a patients true hinge axes are within 5 mm of the patients true axis.
Walker. 20% were within 5mm