Direct Retention Flashcards
What is retention?
Resistance to displacement of the denture from the denture bearing tissues in a vertical direction
What is stability of a denture?
Ability of denture to resist functional displacement in any direction so the denture remains in steady constant position
Name 5 methods for direct retention
- Mechanical retention
- Guide planes
- Muscular control
- Physical forces of adhesion
- Precision attachments
Describe how indirect retention may be achieved
Change axis of rotational displacement to make clasps operate as intended
What is a clasp?
A resilient metal projection from the denture base which grips natural tooth and retains denture in its functional position
Where are clasps usually placed?
Teeth adjacent to saddles if they have suitable undercuts
Describe 5 general considerations when designing clasp retention
- Gingival health
- Presence and position of undercuts
- PoI and aesthetics
- Occlusion
- Do not complicate by using too many
Name 2 types of clasp design
- Occlusally approaching
2. Gingivally approaching
What is the difference between occlusally and gingivally approaching clasps?
Occlusally approaching clasps enter the undercut from the occlusal surface whereas gingivally approaching enter the undercut from gingival surface
Discuss occlusally approaching clasps
- Consist of one or two arms which encircle tooth
- Retentive arm approaches survey line form occlusal surface
- Terminal 1/3 of the clasp is below survey line
- One arm clasp referred to as circumferential if encircles tooth
- Provide retention plus bracing and support
Discuss gingivally approaching clasps
- Not in contact with the tooth surface along their whole length
- Arm approaches survey line from gingival margin
- Provide retention only (not bracing or support)
Name 3 types of GACs
- “I” bar
- “T” bar
- Reverse “L” bar
Name 4 considerations to take into account when designing clasps
- Flexibility of clasps
- Clasp materials
- Position of undercut
- Depth of undercut
What does the position of an undercut determine in terms of clasp design?
Effectiveness of clasp
What does the depth of an undercut determine in terms of clasp design?
Determines where the clasp tip is placed
Name 4 considerations with regards to the flexibility of clasp
- Material (MoE)
- Length of clasp
- Diameter
- Cross sectional form of clasp
Name 5 common clasp materials
- Wrought gold
- Wrought stainless steel
- Wrought nickel-chrome
- Wrought nickel-titanium
- Cast cobalt-chrome
Name a non-alloy which may be used as a clasp material
Nylon
What is the depth a cast cobalt-chromium clasp is used at?
0.25mm
Describe the differences between using cast CoCr and wrought stainless steel as clasp materials
- CoCr has high MoE so must be longer, thinner and taper
- CoCr must be at undercut 0.25mm and length 15mm
- Stainless steel can be shorter and placed at 0.75mm
Describe how uppercuts on upper and lowers differ and its effect on clasp placement
- Lower molars have better undercut on lingual surface so circumferential OAC goes to mesiolingual U/C
- Upper molars have better undercut on buccal surface so circumferential OAC goes to mesiobuccal U/C
Explain when are GACs often employed
High survey line as not enough room above survey line for first 2/3 of clasp to be above survey line
Name 4 ways to attach a clasp to a denture base
- Integral part of cast framework
- Embedded in acrylic resin
- Soldered to denture base
- Welded to denture base
In terms of bracing, caries, gingival health, aesthetics and tolerance, describe where OACs or GACs are better
Bracing - OACs Caries - OACs Gingival Health - OACs Aesthetics - GACs Tolerance - OACs
Name 3 things which must be stated on a clasp prescription
- Select which tooth and undercut
- Decide if OAC or GAC
- Decide whether material is cast or wrought
