PRS03 - Lecture 10 - Denture Design Flashcards
What are the different kennedy classes?
Kennedy Class I - Bilateral free-end saddles
Kennedy Class II - Unilateral free-end saddle
Kennedy Class III - Unilateral bounded saddle
Kennedy class IV - Anterior bounded saddle (no mods possible)
Identify the classification of the picture below:
Kennedy Class I Modication I
Identify the classification of the picture below:
Kennedy Class II Modification I
Identify the classification of the picture below:
Kennedy Class III Modification I
What are the 3 support classifications?
Class I - Tooth Supported
Class II - Tissue supported
Class III - Tooth and tissue supported
What are the functions of rest seats? (2)
Vertical support
Direct functional forces to the long axis of the tooth
What are the 2 types of rest seats?
Occlusal
Cingulum
What are major connectors? (3)
Rigid connector that crosses palatally or lingually
Unites and stabilises parts of the prothesis on either side of the arch
By rigid x-arch construction
What are the 4 types of maxillary major connectors?
Strap
Horseshoe
Plate
Ring
What are the 4 types of mandibular major connectors?
Lingual bar - pear shaped in cross section
Lingual plate
Buccal bar - labial/buccal sulcus (used when you have lingual undercuts or lingual tori)
Dental bar
When should you use a lingual bar (over a plate)? (4)
2mm = from gingival margin -> top of bar
2mm = bottom of bar -> lingual sulcus
4mm = depth of bar
8mm = minimum space required from gingival margin -> depth of lingual sulcus
When would you use a buccal bar?
Lingual tori
What are minor connectors? (1)
Strong rigid part of the denture that connects other units to major connector
Give an example of a minor connector
Proximal plate - contacts the guide planes enabling the denture to follow the path of insertion
What is the function of retainers?
Components that help prevent displacement when under occlusal or masticatory load
What is retention? (1)
Resistance to vertically displacing forces
Where is direct and indirect retention obtained from? (2:5)
Direct retention (2)
Clasps (predominantly)
Tissue undercuts
Indirect retention (5)
Continous clasp (kennedy bar) - prevents forward rotation
Cummer arm (on canines) - prevents forward rotation
Occlusal rest
Major connector
Denture flange
What is indirect retention? (2)
Extention of the denture base that prevents displacement of the RPD through rotation
Considered for all cases but particularly for kennedy class I and 2 arches
How would you determine where indirect retention will come from? (3)
Pass a line through tips of most anterior and posterior clasps on opposing sides of the arch
Bisect the line (90o) on opposite side of the arch to the free end saddle
Saddles cannot be displaced by forward rotation due to diagonal opposing contact with natural tooth
What is denture base retention? (2)
Strong, rigid support for attachment of acrylic resin portion that carries artificial teeth
Retention is entirely mechanical
What is denture base material? (2)
Part of the denture that rest on oral mucosa (where there are missing teeth)
Functions to: (3)
Support artificial teeth in desired position
Unite metal base with artificial teeth
Restores contour where natural tissues are lost
What are the 3 components of a clasp?
Retentive
Support
Bracing
What are the different types of clasps? (3:3)
Occlusal approaching clasps
C (or semi-encircling)
Ring (or fully-encircling)
Recurve arm
GIngival approaching clasps
I bar
T (roach)
1/2 T (one armed T roach)
What determines clasp you would use? (4)
Survey lines (4)
High (very deep undercut) -> requires high flexibility class type
Medium -> occlusal + gingival approaching clasps
Low (little or no usable undercut) -> cant use gingival approaching clasps because it would be too close to soft tissues. You can either:
Add composite to create undercut
Create dimple preparation
Diagonal -> suitable for either type of clasp
Describe the arm of an occlusal approaching clasp (2)
Terminal 1/3 of clasp arm engages with the undercut area (retentive)
Remaining 2/3 of clasp arm lies on or above the survey line (non-retentive)
Describe the arm of a gingival approaching clasp (2)
Whole arm of clasp is beneath the survery line
Terminal tip is the only part that is in contact with tooth
What is the function of the bracing component of the clasp? (4)
(green)
1) When the denture is placed under load -> retentive portion of clasp flexes
2) This will exert pressure on tooth -> possible movement of teeth
3) The bracing component counters this movement - action is known as reciprocation
4) This effect can also be provided by the non-retentive part of the clasp
What materials are used for clasps? (4)
Gold - cast or wrought
Cobalt-chrome - cast or wrought (wiptam)
Stainless steel (SS) - wrought
Acetyl resin (dental D)
What are the properties of acetyl resin (dental D) clasps? (5)
Flexible
Aesthetic (tooth coloured)
Brittle
Need to be thick in cross-section
Expensive
How does the cross-section of occlusal and gingival approaching clasps differ?
Occlusal approaching - D-shape (flat surface against tooth) -> ↑ Rigid
Gingival approaching - O-shape (only tip in contact with tooth) -> ↑ Flexible
Compare the flexibility (modulus of elasticity) of the different clasp materials (6)
(highest to lowest)
Wrought gold
Wrought S.S
Wrought Co-Cr
Cast gold
Cast Co-Cr
What undercut gauge should be used for the different clasp materials (4)
Wrought gold -> 0.75mm
Wrought S.S -> 0.5mm
Wrought Co-Cr -> 0.5mm
Cast Co-Cr -> 0.25mm (occlusal approaching) + 0.5mm (gingival approaching)
Why should you use a 0.25mm undercut gauge for occlusally approaching Co-Cr clasps that have mesial and distal occlusal rests? (2)
Addition of distal rest ↓ flexibility of clasp by 50%
Retentive arm becomes stiffer
