Direct and indirect retainers & Biomechanics

Question 1

definition of retention

Answer 1

resistance to forces that are putting prostheses away from tissue

aka dislodgement

Question 2

simple machine is composed of

Answer 2

fulcrum, effort, resistance

Question 3

3 types of levers and relation to rpd

Answer 3

Class I
-effort on one side, resistance on other side, ideal, ex. biting
Class II
-resistance same side as effort (longer effort), sticky food that can dislodge RPD, most relevant for retention
Class III
-resistance same side as effort (longer resistance), RPD is pressed down to tissue

Question 4

direct retainers are located on which side of fulcrum line

Answer 4

same side of fulcrum line where dislodgement occurs
-always the clasps

Question 5

indirect retainers are located on which side of fulcrum line

Answer 5

opposite side of fulcrum line where dislodgement occurs
-rests

Question 6

three fundamental planes of movement

Answer 6

sagittal plane
-rotate around medio-lateral axis
-denture base moving toward and away supporting ridge

horizontal plane
-rotate around vertical axis
-vertical axis near midline
-stability

frontal plane
-around antero-posterior axis
-fulcrum line extending through rest and along edentulous ridges on ONE SIDE OF ARCH

Question 7

type of force that can cause damage to tooth structure

Answer 7

non-axial loading

Question 8

greatest magnitude of rotation around is in this plane

Answer 8

sagittal plane, medio-lateral fulcrum line
-movement produced when biting
-greatest magnitude but not most damaging (force is mesio-apical, greatest vector in apical direction)

Question 9

movement of free-end is along this plane, what is it called

Answer 9

along horizontal plane (vertical axis), fishtailing

Question 10

movement along this plane is considered the most damaging, why

Answer 10

frontal plane (antero-posterior), because there is no adjacent tooth and there is thinner support on buccal and lingual

Question 11

mucosa only offers ___% of support provided by PDL, soft tissues are ____ times more displaceable than adjacent teeth, ____ displacement under 4 newtons of force

Answer 11

0.4%, 250 times, 500um

Question 12

compression of mucosa is unfavorable because ___ is inhibited and causes ___

Answer 12

blood flow, resorption-remodeling

Question 13

what is it called when one end of RPD is supported and other is not

Answer 13

support deficit (free end case)

Question 14

what happens when clasp moves while it is engaged on undercut

Answer 14

rotational movement (torquing, bottle opening effect)

Question 15

what is more important for retention and stability than number of clasps

Answer 15

spatial distribution (pagkakahiwahiwalay ng clasps)

Question 16

most stable clasp configuration

Answer 16

quadrilateral (clasp anterior and posterior to each edentulous space)

Question 17

second most ideal clasp configuration

Answer 17

tripodal (unilateral free end, one clasp placed adjacent to defining distal extension space)

Question 18

least stable configuration

Answer 18

bilateral (bilateral free end, no other choice, resistance aided by denture base and height of residual ridge)

Question 19

rationale for clasping both sides of arch

Answer 19

cross-arch stabilization, added stability by engaging teeth on contralateral side

Question 20

3 stress releasing clasp designs

Answer 20

RPI, RPA, RPH

Question 21

benefit of placing clasp posterior to fulcrum in RPI

Answer 21

it moves downward and forward (disengages)

Question 22

meaning of RPA

Answer 22

Rest-Proximal Plate-Aker’s clasp

Question 23

relief component of RPA

Answer 23

engages undercut on mesial, 2/3 of clasp is not engaged/has space

Question 24

why was RPI modified and i-bar moved from mesiodistal bulge to far zone

Answer 24

cleansability and stable reciprocation, further retention because clasp hits mesiodistal bulge when it tries to dislodge

Question 25

indication for RPH

Answer 25

cases where vestibular anatomy cannot support i-bar but want more esthetic design than RPA

Question 26

methods to reduce loading on mucosa

Answer 26

-full coverage denture base
-functional impression
-mesial rests
-stress-breaking major connector

Question 27

denture base is extended up to ____ for added stability and retention

Answer 27

buccal vestibule/lingual sulcus

Question 28

what is functional impression and when is it used

Answer 28

impression taken while mucosa is compressed, used for final impression

-mitigates support deficit and aids in lessening torquing

Question 29

placing a rest farther mesially from edentulous area results in more (vertical/perpendicular) biting forces which are resisted (worse/better)

Answer 29

vertical, better

Question 30

wheelbarrow principle in prostho

Answer 30

farther away rest from free-end, lesser load is placed on that abutment