System Of Design Flashcards
What are the alternatives treatments to partial dentures?
No treatment
Conventional bridge
Resin-bonded (Maryland) bridge
Implants retained prostheses
What GDC standard is important when informing patient?
Montgomery consent - 2.2
Why do clinicians design the denture and not technicians?
We have seen the patient:
Patient story & expectations
Condition of teeth & periodontium/oral health
Assessment of current dentures (if any)
Assessment of occlusion
More complete understanding of alternatives
To give clear cost information (GDC Standard 2.4)
What are the key principles of partial denture design
Replace lost teeth & tissues, restoring function, speech, & aesthetics
Minimize damage to adjacent teeth, restorations & tissues
Designed with periodontal health in mind
What are the components of a CrCo partial denture?
Major Connector (lingual bar) – connects parts
Cingulum rest (Support & indirect retention)
Acrylic tooth restoring natural tooth
Pink acrylic restoring lost mucosa & bone
Occlusal rest (Support)
(Ring) clasp (Retention)
What do the rests aim to do?
Avoid denture sinking into tissue
What do clasps engage in?
The undercut of the tooth
What is a saddle?
An area of oral mucosa where teeth are being replaced
What is craddock class 4? (added later)
Implant borne
What is craddock class 5? (added later)
Implant and mucosa borne
What is the craddock claddification?
Classifies how the saddle is loaded
What is Kennedy classification?
Classifies by position of saddles
What is Kennedy class 3?
Single bounded saddle not crossing the midline
What is Kennedy class 4?
Single bounded saddle crossing the midline
What happens if there is more than 1 edentulous saddle present?
Modifications
Use the most posterior saddle to define the main Kennedy classification
What does modification 1 mean?
One other saddle present
What class cannot be the main class if there is a modification?
Class 4 as any modification will be posterior to the midline
What is PEEK?
Poly ether ether ketone
Alternative to CoCr
Thin and strong
Expensive
Used for allergies to metal
What is flexible denture material made off?
Nylon
Very bad (porous)
Why is gold not used?
Expensive
What does a major connector connect?
Connects all the components
What do minor connectors connect?
Rests, clasps and bracing arms
What are the common mandibular major connectors?
Acrylic plate
Lingual bar
Lingual plate
What are the common maxillary major connectors?
Acrylic plate
Mid palatial bar/ strap
Anterior palatial bar (horseshoe)
Ring
Why is a lingual bar good?
Not close to teeth therefore good for PD tissues
Why is a lingual plate good?
Prevents rocking
good for space <8mm
Splints pd anterior teeth
Why should the denture be surveyed? (I.e. surveyor or digital surveying)
Help us choose retentive elements (clasps)
Path of insertion (and removal) of denture
What is retention?
Resistance of the denture to vertical displacement (lifting away from the tissues)
What method is used for retention?
Clasps
What is indirect retention?
Resistance to rotational displacement around a fulcrum axis
*fulcrum axis = the line of rotation – it is an imaginary line between the most posterior rest seats on the end of each arch
What classes is indirect retention seen mostly?
Class 1 and 2
What components give indirect rentention?
Occlusal and incisal rests
Connectors
What is used to give support?
Occlusal rests
Cingular rests
Incisal rests
What must sometimes happen for rests to be inserted? And what happens if there is inadequate support?
Sometimes we must prepare rests seats with a drill as we have insufficient occlusal space for a rest
Inadequate support: denture sinks into the tissues and traumatizes them
What does a high arched palate provide?
Better horizontal resistance
What is reciprocation of dentures?
Reciprocal arm of clasp prevents movement of clasped tooth
What is given to the technician regarding the denture?
The design sheet which you have provided
What should the width of a mid palatial bar be between?
7-12mm
What are the steps of designing as denture?
Consider;
1. Saddle(s)
2. Support
3. Retention
4. Indirect retention
5. Bracing
6. Connectors
7. Review & simplify
What is support?
“The resistance of the denture to occlusally directed load”
Resist movement TOWARDS the soft tissues, (vertical downwards)
Craddock classifications
What type of saddle has a craddock class 3?
free end saddle
What type of saddle has a craddock class 1?
bounded
Where should support (rests) be placed in a RPD?
as close as possible to a bounded saddle
on the mesial side of the abutment in a free-end saddle
What will happen if the rest is placed distally?
the tooth will want to tilt distally
When preparing an anterior tooth clasp what can be used instead of cutting tooth?
add composite instead
Why are incisal rests less common now?
due to apperance
What are the methods of direct retention?
- Clasps
- Soft tissue undercuts
- Adhesion (maxillary plates)
- Friction
- Path of insertion
muscle control
Why should the extension of the saddle have the max surface area possible?
increasing the footprint of the saddle and spreading the load more widely
In what pattern should the clasps be placed to increase max retention?
triangular
What is the RPI system and why is it used?
Type of Clasp.
Allows the free saddle to rotate slightly without damaging the soft tissues or abutment tooth
What does bracing/reciprocation aim to do?
what are they both provided by?
bracing - resistance against horizontal displacing forces acting on the denture base provided by major connectors and flanges
reciprocation - counteracts the tipping forces created by the clasps during denture placement and removal. provided by reciprocal clasp arm and connectors
What plate materials can be used?
PMMA
CoCr
What are the saddle choices?
flanged (flange goes directly into sulcus)
gum-fitted/ open-face
What are the disadvantages to each saddle choice?
flanged
if taking out many teeth, the buccal plate may fracture
gum-fitted
no retention from sulcus
difficult to clean
any alveolar resorption leaves a space
In partial denture construction a pin dam improves…
improves adaptation to underlying tissues
What is the minimum length of a CoCr occlusally approaching clasp?
15mm
The RPI is a stress relieving clasp system that works by
eliminating axial rotation (torque) from the distal of the abutment tooth
What is the distance for a mandibular lingual bar indicated?
at least 8mm from the floor of the mouth to the gingival margin
