2. Prosthodontics Flashcards
SDA and RPD
When does SDA occur
Indications for SDA
Contraindication for SDA (2)
Indications for RPD (2)
Contraindications for RPD (2)
Advantages of RPD (2)
Disadvantages of RPD (2)
Occurs where 3-5OUs are left
Sufficient occlusal contacts to provide enough occlusal table
Poor prognosis for remaining dentition, untreated/advanced periodontal disease
Missing teeth, no suitable bridge abutments
Functional SDA, mobiel teeth
Simple, restores function
Plaque retention, aesthetics
Definitions
Support
Retention
Indirect retention
Stability
Functions of major connectors
Functions of minor connectors (2)
Definition of saddle
Definition of flange
Resistance of denture to occlusal directed load
Resistance of denture to vertical displacement
Resistance of denture to rotational displacement
Resistance of denture to horizontal (lateral) displacement
Connect components on one side of the arch to the other
Connect rests, clasps and bracing arms to major connector. Transfer functional stresses to/from abutment teeth
Edentulous area
Replacement tissue extending from gingival margin to vestibular sulcus
Kennedy classifications and descriptions (4)
Craddock classifications and features (3)
Class I - bilateral free-end saddle
Class II - unilateral free-end saddle
Class III - posterior bounded saddle
Class IV - anterior bounded saddle, crossing the midline
Class I - tooth-borne support - tooth embedded in bone, provides wide load distribution. Transmits load via periodontal membrane (comfortable)
Class II - mucosa-borne support - large coverage
Class III - mixed tooth and mucosa-borne support - free-end saddles/large saddle areas - >3 teeth missing
Reasons to record occlusion (3)
Types of occlusion recording (2)
Types of articulators (3)
Methods (3) and advantage/disadvantage of recording occlusion
If no teeth are present, what has to be recorded (2)
Prescribing position of anteriors (4)
Load a health tooth can carry
To help denture design, to ensure loading forces are applied correctly, to ensure denture is stable and not dislodged in function
Comformist approach, re-organised approach
Plane line/hinge, average value, semi-adjustable
Wax wafer (easy, inaccurate), wax record block and wax (easy, mis-record), wax record block and recording paste (easy, material bounce)
OVD and FWS
Index teeth in occlusion, mark centreline, correct incisor plane, correct antero-posterior position
Its own load plus 1 1/2 similar teeth
Support
Functions of rests (5)
Benefit of large rests
Rest placement (2)
Disadvantage of rest seat tooth preparation
Provide support for the denture from vertical opposing forces (oppose movement of base towards tissue), prevent movement of RPD towards mucosa, assist in distribution of occlusal load, prevent over-eruption of unopposed tooth, involved in reciprocation and indirect retention
Can direct force down long axis of the tooth
Adjacent to bounded saddle, mesial of abutment tooth in free-end saddle
Loss of occlusal stop when denture not worn
Mucosa support
Minimum distance between ginigival margins and acrylic denture
Features of Every partial denture (4)
Disadvantage of combine denture
3mm
Mucosa-borne, restores arch with contact points between denture and abutment teeth, wire stop prevents most posterior tooth drifting distally, open design
Mucosa compresses more than tooth within the periodontal membrane
Retention
Methods of providing retention (4)
Components and action of mechanical retention
Action of muscular retention
Components (4) and action (2) of physical retention
Features of ideal direct retention (2)
Types of frictional resistance (2)
Clasps on molars should point in which direction for Kennedy class IV and why (2)
Mechanical, muscular, physical frictional
Clasps - engage undercuts
Action of surrounding musculature on shape of non-impression denture surface
Using existing forces of adhesion (surface forces of saliva on denture and mucosa), cohesion (forces within saliva), surface tension and atmospheric pressure
Close to base, as close as possible (adjacent) to saddle
Guide planes, altered path of insertion
Forward, so if there is any rotation, the clasps can act to resist this
Features of ideal guide planes (2)
Function of guide planes
Ideal pattern of retention and why
Function of reciprocation
Minimum clasp length required to engage 0.25mm undercut
Minumum distance between undercuts and gingival margins
How is indirect retention obtained
Function of indirect retention
Where do retainers providing direct retention lie
Must be close to base, parallel to each other and the path of insertion
Increase stability and reciprocation
3 points/triangular - desirable to provide stability
Prevents pressure from clasp acting on tooth
15mm
0.25mm
By distal extension of RPD base
To provide a fulcrum of a class II lever
Between the fulcrum and that part of the denture which is subject to displacing forces
RPI
Definition Where is it used Components (3) Reason for use Functions
RPI on canine features (2)
Types of retention in acrylic denture (2)
Stress relieving clasp system
Free-end saddles (distal extension RPDs)
Mesial rest, proximal guide plate, gingivally approaching I-bar clasp
To prevent stress on last abutment tooth
Reduces load on teeth in combined dentures
Quite challenging - ideally mesial incisor (aesthetically poor, so often cingulum) rest
Frictional (wire stop), muscular (forces associated with muscles action on non-impression surface of dentures)
Connectors
Features of plates (4)
Features of bars (3)
Space requirements for bars (4)
Features of a closed denture design (3)
Features of an open denture design (4)
Minimum distance between upper connector and gingival margins
Minimum distance between lower connector and gingival margins
Thinner (in cross-section), increased mucosal coverage (reduced natural sensation), cover gingival margins, only for maxillary arch. Preferred choice
Thicker (2mm lingual bar), less mucosal coverage, gingival margins kept clear
8mm - 4mm height of bar, 3mm from gingival margins, 1mm above raised functional depth of floor of mouth
More contact, increased retention but increased gingival irritation
No gingival coverage, increased clearance, reduced irritation but reduced retention
5mm
3mm
Aim of setting teeth (2)
Features of acrylic teeth (5)
Features of porcelain teeth (4)
To complement existing teeth, restore arch, aesthetics and function
Chemical bond with denture base, soft, low abrasion resistance, silent in function. Ridge lap
Mechanical attachment, brittle, hard, high abrasion resistance
Stages in restorative treatment plan (4)
Features of mouth preparation (6)
Components of tooth preparation (4)
Functions of rest seat preparation (2)
Immediate treatment, hygienic/prepatory phase, corrective/reconstructive phase, maintenance
Initial prosthetic treatment (repairs, additions), pre-prosthetic surgery (remove retained roots, non-erupted teeth), periodontal treatment (establishes periodontal health), orthodontic treatment (optimises space), conservation and endodontic treatment, tooth preparation
Rest seats, guide planes, survey lines, retentive areas
Provides favourable tooth surface for support, prevents occlusal interference
Rest seat guidelines
Upper anteriors
Lower anteriors
Posterior teeth
Rest seat in cingulum (enamel)
Composite cingulum rest seat
Anywhere on tooth, as long as there is no occlusal interference
Types of problems and causes (8)
Design errors and consequences (2)
Function of primary impressions
Function of master impressions
Error during jaw relationship recording
Looseness (over/underextension), pain (overextension, engaging soft tissue undercuts), appearance (clasps), speech (shape of polished surface), food trapping, fracture, loss of natural teeth/additions, combination
No support (painful), no retention (loose)
To accurately record clinically relevant landmarks without excessive tissue distortion
To record the entire functional denture-bearing area
Wrong occlusal record
Casting and finishing
Casting aim
What is the refractory model
One advantage and disadvantage (2)
Retention casting process
Clasp casting process
Function of sprue
Ideal cooling and why (2)
Definition of investing
Features of casting (3)
Process of finishing (4)
Method of checking occlusion
Process after checking occlusion (3)
To produce a complete base that can be used to mount teeth
PO4-bonded investment
Stronger than gypsum, but subject to surface wear
Wax pattern chosen and attached close to major connector and joined using wax
Wax pattern replaces relief wax
Conducts molten metal into mould
From exterior to centre of metal inflow slowly - this should prevent cooling shrinkage producing voids
Mould prepared around refractory cast using same investment as it
Indication melting and vacuum/pressure casting. Mould removed, cast cleaned using sandblasting cabinet with AlO
Lost wax technique - 2-part mould opened and cast evacuated from mould. Space left filled using PMMA. Investing - flashing, filling mould - packing
Split cast system
Occlusal refinement, finish, polish
