All Partial denture Q's Flashcards
what 2 approaches can be used to establish occlusion
conformist
re-organised
at what stage does the occlusion need to be established by
between masters and jaw reg
what materials can be used to establish occlusion. How effective? (3)
- wax wafer - easy but innaccurate/deform easily
- Wax record block & wax
Easy and quick. Can see if natural teeth meet. Can mis-record due to wax causing jaw to deviate on closing . Can’t separate once recorded - Wax record block and bite recording paste. Easy
Can separate once recorded
Can see if natural teeth meet
Some bounce due to material
what should happen if there are no index teeth
OVD and FWS should be measured
how should an impression be taken for a partially dentate patient with bilateral free end saddles
use impression compound for the free end saddles, then place an appropriate adhesive then take alginate on top (alginate wash imp)
instructions for technician if casts CAN’T be hand articulated
Please pour up primary impression in dental stone and construct study model.
Construct special tray with spacer (1-2 sheets of wax depends on master impression material) with handles/ finger rests etc.
Please return models with special tray
Please construct primary record block for a preliminary jaw registration (base can be wax, shellac or light cure acrylic)
instructions for technician if casts CAN be hand articulated
Please pour up primary impression in dental stone and construct study model.
Construct special tray with spacer (1-2 sheets of wax depends on master impression material) with handles/ finger rests etc.
Please return models with special tray
what should be completed prior to master impression stage
Survey to decide the path of insertion
Survey to decide undercuts etc
Do you need to modify teeth to produce rest seats, guide plains and undercuts (Dr Cross lecture)
Draw the design on the laboratory work card
how can a special tray be modified
try in mouth,
if too far extended - trim
if too little extension - add greenstick
what instructions are given to a technician following master impressions
- what should be completed prior taking a master impression
Please pour up impression and construct model
cobalt chrome needs improved stone
Please construct wax record block
Specify base
Have they got your design?
Did you remember to prepare occlusal rests/guide planes before taking impression?
what are the aims of a jaw registration
buccal/labial contours of wax record block
lip support
Incisal plane
Posterior plane
Occlusal vertical dimension
Intermaxillary relationship to articulate casts
Tooth shade and mould
what does it mean if a trial/registration drops/ is easily displaced
overextended
too much lip support
name some important reference points to use during a jaw registration
Dento-facial midline Inter-pupillary line Ala-tragus line Curvature of lower lip Smile line Gingival margins of existing anterior teeth
what instructions are given to a technician following a jaw resistration to tooth trial
Please articulate casts to registration provided
Please set up teeth for wax trial or please construct metal framework or Metal wax Trial
Depends on the complexity of the denture/ occlusion/ tooth position
what instructions are given to a technician following a jaw registration to CoCr/tooth trial
please construct a CoCr framework and wax up for tooth trial
what instructions are given to a technician following a tooth trial
please proces in acrylic resin
what instructions should a patient be given following denture delivery
What instructions will you give? Insertion / removal Coping with new dentures Pain Denture cleansing Speech Eating Refer to clinic patient information leaflet
what changes can the patient expect with new dentures
speech affected - practice
eating - strange but practice
pain - pressure
when to clean a denture
after eating, before bed and in morning
never worn at night
how to wash a denture
over a sink full of water
using a soft toothbrush and non perfumed soap - washing up liquid
how should a denture be soaked
using tablet once daily
eg Milton
no more than 10 minutes (bleach denture)
soak overnight in plain water
name some aspects of pre-prosthetic surgery
Pre-prosthetic Surgery: Remove retained roots / unerupted teeth Remove pathology Improve contours of edentulous areas –by reducing bony prominences andhyperplastic soft tissue Eliminate prominent fraenal attachments
what aspects of tooth prep can be carried out (4)
Tooth preparation: Provide rest seats Establish guide surfaces Modify unfavourable survey lines Create retentive areas
purpose of a rest seat
Rest seat preparation:
Produce favourable tooth surface forsupport
Prevent interferencewith occlusion
Reduce prominence of the rest
how are rest seats made on anterior teeth
Rest seats on anterior teeth Maxillary teeth – a well-developedcingulum allows prep to stay within enamel. Use a cylindrical diamond stone with a rounded tip.
what rest seat should be used on a mandibular anterior
Mandibular teeth – Lingual surface too vertical and cingulum too poorly developed to avoid penetrating enamel. Incisal rest seats used.
how should rest seats be used on a posterior tooth
Reduce marginal ridge
Rests should be saucer-shaped to allow some horizontal movement and dissipation of occlusal forces
Rest seat should be deep enough to allow a rest of at least 1mm thick
If no space occlusally for a clasp to extend buccally from an occlusal rest, the preparation must be extended as a channel on to the buccal surface
what is a guide plane
Guide planes are two or more parallelaxial surfaces on abutment teeth, which limit the path of insertion of a denture. They may occur naturally, but more often need to be prepared.
- prepped by allowing tooth surfaces to become parallel with one another
what can guide planes provide
Increased stability
Reciprocation
Prevention of clasp deformation
Improved appearance
guidelines for guide plane prep
Guide surface should extend vertically 3mm but be kept as far from the gingival margin as possible
Not more that 0.5mm enamel should be removed
Describe the kennedy classification
what does it describe
Class I – Bilateral free-end
Class II – Unilateral free-end
Class III – Unilateral bounded
Class IV – Anterior bounded (crossing the midline)
describes anatomical classification that describes the number and distribution of edentulous areas present. It does not describe the type of support required.
define support
term used to describe the RESISTANCE of a denture to OCCLUSALLY DIRECTED LOAD
define the craddock classifications
I. = Tooth – Teeth provide a HARD tissue resistance to occlusal loading II. = Mucosa – A LARGE coverage provides resistance to occlusal loading III. = Tooth & Mucosa – A combination of HARD tissue and LARGE coverage when there are reduced number of teeth and large edentulous saddles.
how does tooth support work
Transmits load via the periodontal membrane.
Allows the supported denture base to feel like the natural dentition.
Is more comfortable for the patient.
Protects the soft tissue from trauma.
Is likely to stay in close contact with its supporting structures over a period of time.
how does mucosal support work
Must cover as large an area as possible.
Reduction of the occlusal table
Allows the denture base to move slightly.
Possible damage to adjacent gingival margins
name examples or rests and their adv/dis
- incisal rests - lower anteriors, poor aesthetics, interfere with occlusion, NEVER on wear facets.
- cingulum rests - prep required unless prominent cingulum, canines/ incisors, good aesthetic, less rotational forces
how does an RPI work
name its components
The rest mesially acts as an axis of rotation. As the proximal plate and I bar rotates downwards and mesially around the axis of rotation during occlusal load. The I bar and proximal plate disengage from the tooth/undercuts, thus avoiding potentially traumatic torque. -Rest (occlusal) Mesial of the tooth Rounded on the impression surface Proximal plate (Adjacent to saddle) guide surface of 2-3mm undercut to permit movement I-bar clasp (Gingivally approaching) Greatest prominence of the tooth contour
cobalt chrome denture adv/dis
- saddles/denture teeth attached to denture base
- stronger in thin section, less bulky, high flexural strength
- high abrasion resistance
- tooth support using occlusal rests as part of framework
- minimise gingival margin coverage, favourable design features
- radiopaque
- limited scope to make adjustments
- difficult to repair
- high thermal conductivity
acrylic denture adv/dis
- saddles/teeth part of base
- need adequate thickness of material, not vulnerable to #
- vulnerable to abrasion
- thermal insulator
- not usually radiopaque
- simple procedure to add on
- easy to replace components
purpose of a rest
where should they be placed to maximise function
support denture against apically directed load
Rests are often placed on the OCCLUSAL surface of a tooth since this will direct occlusal forces down the long axis (root) of the abutment teeth.
The default position to place a rest for a BOUNDED saddle is IMMEDIATELY adjacent to the saddle. Additional rests may be incorporated. The default position may have to be changed depending on the opposing dentition.
where should rests be placed on a tooth adjacent to a free end saddle
eg mesial of tooth adjacent to saddle
how is mucosal support achieved
Mucosal support is dependent upon as large an area possible of mucosa being covered.
However since soft tissue is compressible it is inadvisable to the base with 3mm of the gingival margins are this will place pressure at the tooth and tissue gingival attachment
define retention
RESISTANCE of a denture to LIFTING AWAY from the tissues (VERTICAL DISLODGING FORCEs).
how can retention be achieved
-mechanical - clasps
-muscular forces - control
-physical forces
adhesion - force of saliva on mucosa/denture
cohesion - forces within saliva
define direct retention
define indirect retention
- resistance to vertical displacement of denture
- resistance to rotational displacement of denture
name 2 types of clasp and examples of each
occlusally approaching clasp - single arm/circumferential/ring clasp
gingivally approaching clasp - i bar clasp
how is indirect retention achieved
The retention obtained by the extension of a partial denture base to provide the fulcrum of a class II lever. [The retainer(s) providing direct retention lie between the fulcrum and that part of the denture which is subject to the displacing force].
why would a plate be used in a denture
- width
- design preference
- negative aspects
plate is thinner in cross section but can still retain rigidity.
mucosal supported designs
covers gingival margins - OH concern
why would a bar be used in a denture
- measurements required
8mm - 3mm from gingival margin, 4mm for bar, 1mm above raised functional depth of FoM.
needs to be thick in cross section - 2mm
what is a minor connector
guidance
components that stem from the major connector eg rests
- be rigid
- finish above the survey line
- cross gingival margin at right angles
- cover as little gingival tissue as poss
example of maxillary CoCr shape connectors
palatal plate, mid palatal plate, anterior plate, horseshoe plate/bar, anterior/posterior bar (ring)
examples of maxillary acrylic connectors
anterior, mid palatal, full coverage, horseshoe, posterior palatal, spoon, modified spoon, every
examples of mandibular CoCr connectors
lingual bar, dental bar, lingual plate, sublingual bar, lingual bar with dental bar (continuous), labial bar
how to cope with a flabby ridge
both mucocompressive and mucostatic impression needed
take normal impression with medium body PVS, cut impression from flabby ridge area. Place light body PVS here and retake impression.
For master imps, cut window out of special tray, take mucostatic imp then use lightbody PVS - minimal pressure and displacement
ideal properties of a denture base material
-lightweight (low density)
-dimensionably stable
-not sensitive to pH of mouth (not sensitive to oral fluids)
-abrasion resistance
-thermal conduction
high YM
-high softening temperature
non toxic/irritant
colour/trnaslucency
stages of acrylic polymenrisation
- activation of initiator (free radicals) - heat to 72 degrees, self cure
- initiation - benzoyl peroxide
- propagation - growth of polymer chain
- termination
acrylic powder constituents
- benzoyl peroxide - initiator
- Pmma particles
- pigments
- plasticiser - quick dissolving of monomer
- co-polymer - improve mech props
acrylic liquid constituents
- methacrylate monomer
- inhibitor - hydroquinone (prolong shelf life)
- co-polymer - improve mech props
how to restore a excessive FWS in worn dentures
- occlusal pivots/restore occlusal surface with autopolymerising acrylic resin
- replica technique
