Online stuff Flashcards
What part of denture provides support
support: resistance of occlusally directed loads
- ->occlusal rests (stop mucosal damage)
what is bracing/ how is it provided
mechanical function, prevents lateral shifting of partial denture
supplied by bracing arm and rigid 2/3 of retentive clasp above survey line
what part of denture provides retention
clasp tips
what part of clasp enters undercut and why
terminal 1/3
stop damage to tooth/peri tissues
3 functions of surveying
poi
unwanted undercuts- block out
wanted undercuts- clasping teeth, mucosa for retention
when surveying, what to use as guide plane
a. mandibular with posterior saddles
b. maxillary with anterior saddles
a. mandibular: lingual surface (to accomodate lingual bar/plate) –> p
b. maxillary: labial contour –> posterior border lower
3 principles of clasping
-Active arm (retentive) will engage undercut for direct retention.
Reciprocal arm (bracing/lateral resisiting) prevents active arm displacing/traumatising tooth.
Occlusal rest distributes occlusal load through the teeth.
4 things clasp flexibility/effectiveness is dependent on
- material
- cross-sectional shape
- clasp length
- taper/angle of approaching arm
- position of retainer in relation to displacing force
undercut depths for each clasp material
0.25mm cobalt chrome
0.5mm ss, cast gold
0.75 wrought gold
(alphabetical order nearly)
CENTRIC JAW RELATION
a. define
b. alternative names
c. when its important
a. The relation of the mandible to the maxilla with the mandible in its most retruded position.
b. Retruded Jaw Relation, (RJR) and Retruded Contact Position (RCP).
c. position needed for bite registration
CENTRIC OCCLUSION
a. define
b. alternative names
A. maximal contact between opposing teeth
b. intercuspal occlusion, maximum intercuspation
4 things to do at jaw registration stage
- The centric jaw relation
- Lip support and other muscular support
- Mould and shade of teeth
- The occlusal rim surfaces to conform to the patient’s existing occlusion and dentition
main purpose of jaw registration stage
relationship between arches –> can articulate master casts
define freeway space
The space between the maxillary and mandibular occlusal surfaces when then mandible is in the rest position
define embrasure
The space between two adjacent teeth which opens out from their contact point
2 things used to record bite registration
- impression material paste
- modelling wax
what does fox’s occlusal plane do
aid in carving the maxillary rim until it is parallel to the line joining the inferior border of the ala of the nose to the midpoint of the tragus of the ear (alar tragal line)
when survery, function of tipping cast
a. laterally
b. antero-posteriorly
a. laterally: undercuts of a suitable depth may be generated on posterior teeth for clasping
b. antero-posteriorly: anterior (labial) undercut areas can be minimised or moved out of the denture bearing area (aesthetics)
what is path of displacement at 90 degrees to
horizontal occlusal plane
3 things that influence POI of a denture
-Retention
Guide surfaces
Aesthetics
minimum length of direct retainer and why
1cm (2/3 of this is retentive, 1/3 active in undercut)
what are face bows used to record
pt’s hinge axis of condyle
types of face bow
simple (Denatus/ denar)
Kinematic face-bow, also known as: adjustable, hinge axis locating and hinge-bow
function of
a. pantograph
b. face bow
a. pantograph: record protrusive and lateral border movements of the condyles
b. face bow: hinge axis of condyles
how to decide location of axis of rotiation of condyle
line canthus of eye –> tragus
what is the frankfort plane
line between inferior margin of orbit to superior margin of EAM
arcon/non-arcon articulators and which is better
arcon: condylar sphere in lower member (static difference between condyles and mandibular teeth in all directions –> more accurate
non-arcon: condylar sphere in upper member
Which articulator would you consider if there are sufficient teeth and the intercuspal position was stable for constructing dentures? why
average value
simple hinge not good enough, no need to overcomplicate with semi/fully adjustable
which articulator to use to create full path of border movements
fully adjustable
define balanced occlusion
Simultaneous contacts of the occluding surfaces of the teeth in various jaw positions.
Static
define balanced articulation
Simultaneous contacts of the occluding surfaces of the teeth during function.
Dynamic
4 advantages of balanced articulation
-Minimise trauma to supporting structures
Preserve remaining structures and reduce lateral forces to residual ridges
Enhance denture stability
Restore masticatory efficiency to a reasonable level
how to achieve balanced articulation with partial dentures
creating balancing contacts and working contacts between the upper and lower posterior artificial teeth
types of balanced occlusion
Anatomic occlusion
Lingualised occlusion
what governs articulation of artificial teeth and points 5
Hanau’s Quint: 3 incl Condylar inclination Incisal guidance Occlusal plane inclination Compensating curve Cuspal inclination
which 3 of these can be adjusted by the dentist
Incisal Guidance – part of the articulator
Cuspal Inclination – on the occlusal surfaces of the artificial teeth
Compensating Curve – created during setting of the teeth
what is ideal incisal guidance
prob with partial dentures
minimal to stop tipping
partial dentures- minimal control due to natural overjet/overbite
what is the compensating curve
posterior teeth aligned with curve of spee
curve of mandibular incisal/occlusal surfaces
what is curve of wilson
curve between buccal and lingual cusps of mandibular posterior teeth
what is the BULL rule
if there are occlusal anomolies in finished dentures –> only the Buccal Upper and Lingual Lower cusps must be ground until balances is achieved
3 options of williams classification
tapering
square
ovoid
when is palatal vault used 2
They can act as a guide in determining arch form
They can act as an aid in determining tooth alignment
what does willis gauge measure 2
resting face height (when in rest position)
occluding face height (when in centric occlusion)
value of freeway space
2-3mm
how much incisor shows beneath resting lip line
2mm
ala tragal line
a. alternative name
b. what it is parallel to
a. camper’s line
b. occlusal plane
define curve of spee
An arc of a circle 65 mm to 70 mm radius that touches the tips of all the mandibular teeth when the skull is viewed laterally (ie on L or R side; when continued it touches the anterior surface of the condyles.
define curve of monson
lateral curve of the occlusion of natural teeth in which each cusp and incisal edge touches or conforms to a segment of the surface of a sphere 4 inches (102 mm) in radius with its centre in the region of the glabella
6 principles of every design
- restoration of contact points completes arch (see next q)
- denture base large as poss in mucosa-supported
- gingivally free (wide embrasures) for OH, 3mm
- flanges for antero-posterior stability
- stops on distal molar to prevent drifting
- free occlusion (minimise occlusal forces)
4 reasons to restore contact points
- aids retention
- protects gingiva
- limits tooth movement
- reduces stagnation areas
every principles: 3 ways to gain retention
friciton
adhesion
cohesion
how to note tooth for immediate replacement on denture design
mark with X on diagram
write ‘for immediate replacement’
define indirect retention
retention obtained by the extension of a
partial denture base to provide the fulcrum of
a class II lever
anterior and perpendicular to axis of rotation
define direct retention
component of denture that resists withdrawal along path of insertion
4 factors influencing POI
- retention
- guide surfaces
- aesthetics
- dead space interferences
3 types of rest and where they are
molar/premolar: occlusal rests
max canines: cingulum rests
mandibular canines: incisal rests
2 essential features of a rest
- rigid
- does not interfere with occlusion
3 ways to gain retention
- mechanical (clasps)
- physical (saliva)
- muscular
4 design criteria for effective clasp
- flexible clasp arm
- reciprocation
- encirclement
- passivity
when is indirect retention needed
free-ended saddles (class I or II)
define reciprocation
to balance horizontal forces from retention
when denture being taken in/out
define major connector and minor connector
major connector: links saddle areas
minor connector: links rests, clasps etc to major connector
5 major connectors of maxilla
ring horseshoe palatal coverage palatal strap palatal bar
what max major connectors can be used with
a. anterior teeth need replacing
b. torus
a. ring, palatal coverage, horseshoe
b. horseshoe or ring
what type of denture is tooth and mucosa supported
free end dentures
other teeth provide tooth support, posterior saddles mucosa supported
3 outcomes of not surverying
loose/tight denture
loss of pt confidence
wasted surgery time
2 types of surveyor and which we use
Nesser: black bit at top
Krupp: all silver. we use this
3 rules of clasps(esp retentive arms)
- use with occlusal rests –> maintain the retaining arm in the desired vertical position
- use RECIPROCATION to stop tooth movement when active arm is working (ie resisting displacement away from tissues)
- does not compromise OH
what does indirect retention prevent
rotation
3 ways to prevent lateral denture displacement
- bracing arms of clasps
- flanges
- connectors on inclined surfaces (eg lingual plate)
what does the RPI system apply to
mandibular bi-lateral free end saddles dentures
at what point do you design denture
after primary impression, using primary casts
4 factors influencing dimensional stability of imp materials
- continuation of reaction beyond setting time
- internal stress mouth-room temp
- possible shrinkage due to loss of volatile bi-products
- slow elastic memory
3 variables that affect how an impression material is manipulated
- ideal characteristics of long work time and short set time
- working time determined by room temp
- setting time determined by mouth temp
what does stability refer to
resistance to functional forces
impression accuracy depends on 3
- adequate adhesion/retention with tray
- fluidity on insertion
- sufficient elasticity and tear resistance
which synthetic elastomer is used as monophase
medium-bodied
which material can cause blistering/irritation if splashed on to skin
condensation cured silicone
least hydrophobic elastomer
which can be made less hydrophobic, how
polyether
addition-cured silicone (ADDED surface active agen
2 uses of zinc oxide-eugenol as impression material
- close-fitting special trays for secondary impressions
- complete dentures
describe alginate 3
mucostatic low viscosity viscoelastic (use snap removal) subject to dimensional change (esp if left to dry out) susceptible to syneresis/ imbibition
use of compound impression material
foundation for a wash impression
types of compound impression material
high and low fusing
a. what impression material must be cast immediately 4
b. what impression material must be left before casting and why
a.compound CAST COMPOUND
Condensation cured silicone
polyether
alginate (or kept in damp environment
b. addition-cured silicone. release of hydrogen during setting may cause surface pitting
least viscoelastic elastomer
polyether
type of acrylic used for
a. denture base
b. repairs and additions
c. special trays
a. denture base: class 1 type 1
b. repairs and additions: class 2 type 1
c. special trays: type 4
what acrylic types have similar components
type 1 class 1 (heat processed) type 2 class 1 (auto polymerising)
5 components of acrylic powder PPPIS
polymer pigments plasticiser initiator synthetic fibres
role of each of the following in acrylic powder:
a. dibutyl phthalate
b. salts of calcium/iron/organic dyes
c. peroxide
d. polymethylmethacrylate beads
e. nylon/acrylic
a. dibutyl phthalate: plasticiser
b. salts of calcium/iron/organic dyes: pigments
c. peroxide: initiator
d. polymethylmethacrylate beads: polymer
e. nylon/acrylic:synthetic fibres
example and % of peroxide used
benzoyl peroxide 0.5%
4 components of acrylic liquid
monomer
cross-linking agent
initiator
activator (only in auto-polymerising resins, type 2)
role of each of the following in acrylic liquid:
a. N’N-dimethyl p toluidine
b. methylmethacrylate
c. ethyleneglycol dimethacrylate
d. hydroquinone
a. N’N-dimethyl p toluidine: activator (only in auto-polymerising resins, type 2)
b. methylmethacrylate: monomer
c. ethyleneglycol dimethacrylate : cross-linking agent
d. hydroquinone: initiator
how much of these in acrylic liq
a. ethyleneglycol dimethacrylate
b. hydroquinone
a. ethyleneglycol dimethacrylate : 10%
b. hydroquinone: trace
what is acrylic
a. monomer
b. polymer
a. monomer: methylmethacrylate
b. polymer: polymethylmethacrylate (beads)
appearance of acrylic polymer before opacifiers/pigments/fibres
clear, glass like
boiling point of monomer, why is this important
100.3 C
above this it will boil (turn to gas) in denture –> GASEOUS POROSITY
vapour pressure of monomer at room temp
high
what happens during polymerisation
monomer –> polymer
methylmethacrylate –> polymethylmethacrylate
4 uses of type 1 class 1 acrylic
- denture bases (full and partial)
- splints
- artificial teeth
- relines
ratio of powder: liq acrylic and why
2.5:1 powder:liquid
reduce volumetric shrinkage to 5-6%
what happens to acrylic during polymerisation if there is
a. too much powder
b. too much liquid
a. too much powder: dry, unworkable, does not flow during bench pressing, plus GRANULAR POROSITY
b. too much liquid: 21% volumetric shrinkage
stages of material consistency in acrylic setting 5
sandy
- sticky
- snap (dough)
- rubber (leather)
- hard
what determines stages of material consistency in acrylic setting
condition of polymer beads as they dissolve in monomer –> inc viscosity
ideal consistencies of acrylic material 2
long working time
short dough time
what is used for trial closure of acrylic
thin polythene/acetate sheet
2 functions of trial closure of acrylic
- vertical dimension less likely to increase
- assess amount of resin needed to fill mould
2 reasons flask is held in spring clamp during curing process
FLOW:
- flow of dough in to mould
- flow of excess out (reduce shrinkage, minimise inc in vertical dimension)
describe injection moulding technique
resin in through sprue hole, excess out through vent hole
why is injection moulding technique used
polymerisation starts far from sprue (entrance) hole –> more resin can flow in as polymerisation shrinkage occurs
in acrylic polymerisation, what happens at 65 degrees
benzoyl peroxide (initiator) decomposes –> FREE RADICALS
typical curing cylcle and what happens at each stage
- several hours at 70 C: most polymerisation occurs (parts of denture reach 100C due to exotherm)
- 3 hours at 100 C: complete polymerisation
- allowed to cool
alternative curing cycle
- placed in cold water
- heated to 100C over 1 hour
- boiled for 1 hour
- allowed to cool slowly to room temp
do thin or thick parts of denture base polymerise first and why
thick- due to exothermic reaction occurring more in thicker parts
2 causes of internal stresses during polymerisation of acrylic
- high coefficient of thermal expansion
- volumetric shrinkage
what causes warpage
internal stresses released by WARM WATER
initial setting reaction of autopolymerising resins
activator (NN’-dimethyl-p-toluidine) + initiator (benzoyl peroxide) –> free radicals –> initiate polymerisation
how polymerisation occurs for
a. large polymer beads
b. small polymer beads
a. large polymer beads: monomer absorbs in to surface
b. small polymer beads dissolve in to monomer liq
2 disadvantages of type 2 class 1 compared to heat-processed acrylic
- short working time –> no trial closure
- higher residual monomer content–> inferior chemical/mechanical properties eg 90C Tg temp
how to use type 2 class 2 acrylic resin
pourable:
pour in to hydrocolloid mould
sets at room temp
2 advantages of 2 class 2 acrylic resin
- removed easily from hydrocolloid mould
- minimal trimming/finnishing
2 disadvantages of 2 class 2 acrylic resin
- distortion from mould flexing
- high residual monomer –> poor chemical/mechanical properties
contents of type 4 LIGHT ACTIVATED acrylic
- UDMA monomer
- sub-micron particles of silica
- polymethylmethacrylate beads (organic filler)
- light-sensitive initiators: camphorquinone
- light-sensitive activators: amines
- non-reactive barrier compound: carboxymethyl/cellulose
what provides free radicals in type 4 light-activated acrylic
- light-sensitive initiators: camphorquinone
- light-sensitive activators: amines
function of non-reactive barrier compound carboxymethyl/cellulose in type 4 light-activated acrylic
prevent inhibition of polymerisation by oxygen
describe structure of set type 4 light-cured acrylic
effect of this on mechanical/ chemical prop
type of COMPOSITE material: polymethylmethacrylate beads bound in matrix
poor chemical/ mechanical properties compared to heat-processed type 1 acrylic
term for surface cracks in acrylic and acrylic type theyre common in
crazing type 4 (light cured)
3 reasons for crazing
- porcelain teeth in acrylic resins (bc acrylic has 10xhigher thermal coefficient)
- when monomer contacts existing denture during repair
- repeated drying out (water absorption –> tensile stresses at surface
function of cross-linking agent
bond polymer chains so monomer does not touch denture during repair –> minimise crazing
should denture be kept dry or moist? why?
moist. stops water absorption, which would cause tensile stress (type 4 acrylic)
type of denture subject to whitening/bleaching
causes 2 and how
type 4 (light cured) caused by too hot water/ exposure to solvents (eg acetone in saliva) structural change in matrix phase --> mismatch in REFRACTIVE INDEX between matrix/bead polymers--> colour change
what type of acrylic absorbs water
equilibrium % and when
2 effects
type 4
2% after several days
-crazing
-slight dimensional change
what organisms freq colonise fit surface (hence cleaning and soaking of denture)
candida
% residual monomer limits for acrylic types.
why is this limited
2.2% (type 1,3,4,5)
4.5% type 2 (autopolymerising)
(manufacturers limit to 1%)
excess monomer causes irritation
function of these additions to modified acrylic materials:
a. elastomers/ acrylic-elastomer copolymer
b. carbon fibre inserts
c. atoms w higher atomic numbers than resin eg comonomers/ bromine
a. elastomers/ acrylic-elastomer copolymer: improve impact strength
b. carbon fibre inserts: improve fatigue strength (stiffen)
c. atoms w higher atomic numbers than resin eg comonomers/ bromine:radiopacity
when are alternative polymers used and 2 examples
when pt allergic to polymethylmethacrylate
- polycarbonates
- vinyl polymers
how to cure alternative polymers
a. vinyl polymers
b. polycarbonates
a. vinyl polymers: low softening temp –> careful handling
b. polycarbonates: high Tg 150C –> injection moulding
ideal tear strength pf impression materials and why
moderate
too high –> problems with diastemas
too low –> tears when removed from undercut
causes of internal stresses of impression compound 3
- poor thermal conductivity
- high coefficient of thermal expansion
- large temp drop softening temp-room temp
2 uses of gutta percha
- record canal depth in endo
- lubricant in impression compound
list mucostatic impression materials
alginate
list mucodisplasive impression materials
impression compount
zinc oxide-eugenol
alginate setting reaction
sodium alginate + calcium sulphate –> sodium sulphate + calcium alginate
types of
a. impression compound
b. zinc oxide-eugenol
c. agar
d. synthetic elastomer
ALWAYS 1= MOST VISCOUS/HIGH FUSING
a. impression compound: 1 higher fusing, 2 lower fusing
b. zinc oxide-eugenol: 1 hard 2 soft
c. agar: 1 high viscosity, 2 med 3 low viscosity
d. synthetic elastomer: 0putty, 1 heavy body 2 medium body (monophase) 3 light body
what impression materials are susceptible to imbibition/syneresis
both: alginate, agar
imbibition only: polyether,
which impression material releases alcohol by-product
condensation-cured silicone
what determines viscosity of condensation cured silicone
quantity of inert filler
which material has sulphonic acid catalyst system that pts are often allergic to
polyethers
use of polyether
monophase in stock of special tray
v rigid –> accurate orientation for dental implants, dummy attachments
which impression material has highest tear strength
polysulphides
bi-product of
a. addition cured silicone
b. condensation cured silicone
c. polyether
d. polysulphide
a. addition cured silicone: none (maybe hydrogen)
b. condensation cured silicone: alcohol
c. polyether: none
d. polysulphide: water
2 impression materials that taste bad
zinc oxide eugenol
polysulphide
with which impression material in impression wax often found
zinc oxide-eugenol paste
which impression should not be handled with latex gloves and why
addition cured silicones
poisons catalyst
angles of special tray handles
upper: 45 degrees, incisal edge/crest of ridge in midline
lower: 10 degrees, incisal edge/crest of ridge in midline
when/ where finger rest is on special trays
lower close-fitting special trays
over premolar region
function of butadiene styrene in acrylic
(rubber) reists crack/fracture
when adding teeth to a denture, is denture base or tooth adapted first?
denture base
2 causes of denture fracture
impact
fatigue
4 factors of denture design that can cause fatigue fracture
- non-flanged
- large anterior diastema (stress between central incisors)
- abnormally large frenae –> deep notches in flanges needed
- posterior upper denture teeth too far buccally –> flexing of palate in midline when teeth occlude
6 ways the oral anatomy of the pt can cause fatigure failure of dentures
- high vaulted palate
- tori
- heavy bite
- bruxists
- opposed by natural teeth
- v fibrous posterior tuberosities –> posterior teeth less supported over ridge –> flexing around midline
6 ways the packing of acrylic in to processing flask can cause fatigue failure
- voids by careless packing
- contamination by dust/plaster
- not shaking polymer –> fibres conc in one area
- porosity
- incomplete polymerisation
- over polishing
define
Syneresis:
imbibition:
Syneresis: expulsion of liquid from a gel
imbibition: displacement of one fluid by another
what impression material has platinum catalyst
addition cured silicones
direction of circumferential clasps
lower: inwards
upper: outwards
denture base material for tooth borne designs and why
skeletal
using cobalt chrome anyway for clasps
what is a cummer arm
vertical bar extended from baseplate to gain indirect retention
difference between nesser and krupp surveyors
nesser tables can be removed
stages of surveying
establishment of a path of insertion (POI) and provision of guide planes (using the analysing rod),
Marking the outline position and extent of undercut areas (using the carbon marker),
Utilisation of undercuts for retention (using the undercut gauges),
Elmination of unwanted undercuts (using the wax trimmer or chisel).
gypsum setting time. What a) increases b) decreases
a) increases: Borax, Potassium Citrate, Sodium Chloride > 20%, water
b) decreases: Gypsum
gypsum setting expansion. What a) increases b) decreases
a) increases: increased spatulation
b) decreases: Potassium Sulphate, Sodium Chloride, Borax
*NaCl in every category but >20% to INCREASE setting time
borax ↑ setting time, ↓ setting expansion
potassium sulphate DECREASES, potassium citrate INCREASES
explain hygroscopic expansion and when its used
Setting expansion increases in water. Because crystals can grow freely, not limited by surface tension of water as they would be in air
gypsum-bonded investments, which are used specifically with full gold castings and bridgework
most important influence on accuracy of wax
coefficient of thermal expansion
types of modelling wax
Type 1 soft – hard at room temperature – used for veneers, etc.;
Type 2 hard – for wax patterns in moderate temperature climates;
Type 3 extra hard – used in warmer climates.
Types 2 and 3 can soften if left in the mouth for a prolonged period (a few minutes)
when to use fox’s occlusal plane guide
2 measurements is includes
many posterior teeth missing on maxillary rim
interpupillary line, alar tragal line
