Setting teeth for RPD Flashcards
aim when for setting teeth for RPD
aim when setting artificial teeth for partial dentures is to have the teeth set in a position that will complement the existing teeth,
- thus restoring the arch, aesthetics and function.
impact on patient if aim of setting teeth achieved
will greatly improve patient self-confidence and protect their ‘denture privacy’
point to remember when setting teeth for CoCr base
for cobalt chromium bases the scheme for mechanical retention for the PMMA to metal base must be considered. (post or mesh depending on available space)
CoCr is setting directly over free end saddles – can impact
- May need to reduce the acrylic teeth to accommodate
how can artificial teeth be selected to look natural?
Not set to perfect, slightly irregular, shade and tone varies to hide false teeth
2 types of artificial teeth material
acrylic and procelain
most popular artificial teeth material
acrylic
what are tooth cards used for
to choose shade of acrylic artificial teeth
properties of plastic acrylic teeth
Chemical bond with the denture base
- Only processed 50% and then rest when finalising so better bond
Natural appearance
Silent in function
tough
- 5 year durance
Soft-low abrasion resistance
Easily trimmed and polished/customised
Cold flow under pressure
Insoluble in mouth fluids-some dimensional change
bonding of acrylic teeth
teeth bond chemically with the PMMA denture based – this is an important
consideration but attention must be paid to the removal of the tooth bond layer (cross-lining).
what do acrylic teeth look like
natural
advantage of acrylic teeth being easily trimmed
can be customised
are acrylic teeth hard wearing?
only best quality
properties of porcelain teeth
Mechanical attachment with the denture base. (silane coupling agent)
- No chemical bond at all
Anterior teeth – metal pin on back, mechanical retention
Posterior – hollow area
Natural Appearance
Make noise when bite potentially
Brittle
Friable
- grinding removes surface glaze
Hard-high resistance to abrasion
- Wear down opposing dentition
Inert in mouth fluids-no dimensional change
High heat distortion
- no permanent deformation under forces of mastication
how are anterior porcelain teeth attached?
mechanically attached, by metal pins in anterior teeth
how are posterior porcelain teeth attached
mechanically attached, by holes (diatorics) manufactured into posterior teeth.
can porcelain teeth be easily customised?
no - cannot trim the ridge lap area or polished surface which therefore normally precludes their use.
is porcelain hard wearing
yes - very
in some cases would not be recommended for occlusion opposing natural teeth because of this hardness.
properties of modified acrylic/composite/polymers
Chemical bond with the denture base.
Partial bonding - recommended mechanical and / or bonding agent (4-meta)
Higher abrasion resistance
what are mould charts used for
to select mould or shape of tooth
how to choose mould/shape of tooth from mould chart
copy what the patient already has
technician may override choice if they see a problem with your chosen mould
where should shade selection be carried out
in clinic
under natural light - hard to match under unnatural light
advantage and disadvantage of better designed acyclic teeth
more expensive
but more natural looking – see mamelons through incisor tip
3 common tooth shapes
square
ovoid
tapered
4 bits of information from the tooth/mould chart
square, ovoid and tapered are most commonly used shapes
length of anterior teeth - two dimensional
- length of canine to canine
- length of central incisor
width of central incisor
what must be considered when selecting tooth mould
angulation guidance of cusps
high cusps – impact on contact, unstable denture during function
higher cuspal angle – can be better for mastication for molars
what often dictates where teeth are set when making a partial denture
the arrangement and position of remaining natural teeth
firstly, re-establish midline (central incisor) and compromise around that
why understanding the material that is used to make RPDs is important
impact clinical decision
- communicate well with other team members
- good knowledge can ensure you are comfortable with treatment plan
why may you need to compromise when setting teeth
available space
(e.g. accomodate central and lateral in smaller space than naturally be)
since tooth loss may also involve tooth drifting and a change in available space to set the artificial teeth.
why would a larger mould be chosen for a tooth
to allow customisation
what can customisation effect
the denture base and tooth bond
where should artificial teeth be trimmed from
remove from the ridge lap
- Trim from the back
Removal from the length of the tooth, i.e. the cervical margin or the incisal tip can affect the shade.
why shouldn’t tooth be trimmed from incisal edge
too thin, tooth becomes thick and square looking
how much tooth should be trimmed
small bit at a time till fits the mucosa
what effect does removing tooth have on the bond
The more reduced the less chemical bond with denture base – more veneer like
Easily broken off
Too much trimming can look unnatural
what is the ridge lap in artificial teeth made of
more heavily cross linked acrylic
why would a tooth need reduced/trimmed
to fit a pronounced ridge or if a CoCr base being used
the more the ridge lap is reduced….
‘softer’ bonding area if reduced in area can affect the bond with the ‘enamel’ layer having a harder surface.
how to prevent de-bonding in heat cured dentures
Trim teeth with diamond cutters
- Produce a rougher, abraded surface (micro-abrasion)
Use a post for retention when space is limited for PMMA
- Ensure no wax or grease on teeth surface
- Use detergent when boiling out
- Remove as creates a barrier – less sticky
No mould seal residue present when processing
how to prevent de-bonding in self-cured dentures
Try to avoid heavy contact on the denture teeth – cuspal interference
- Not fully processed – soft
Cold cure
- Not fully set – easy to adapt (used for CoCr)
No wax or grease
- Use detergent when boiling out (removing wax from the flask)
No mould seal
Add a drop of monomer onto tooth surface and allow to soak in before acrylic (self cure PMMA)
where to look when considering removing tooth surface
in 3 dimensions (occlusal, frontal and sagittal view)
accommodate the dental arch firstly
what can overlap do
disguise falseness
how should teeth sit in correspondence with arch
in line with arch
survey line determines the extension of the flange
what does the survey line determine
the extension of the flange
why is not advisable to have large areas blocked out
therefore creating ‘dead spaces’ and resulting food impaction.
- Don’t want acrylic to enter the undercut
how far should tooth protrude in sagittal view
not too far, should blend into surrounding teeth
be careful as neck of tooth can protrude when incisal tip isn’t
what will articulator show
lateral excursion
check guidance - important when setting teeth
what should be checked in relation to guidance
wear facets on the natural teeth should be checked.
The artificial teeth must conform to the existing tooth surface wear.
The natural tooth guidance is followed by the artificial teeth.
- Check if teeth are going to collide with lower incisors
- Glides over, no premature contact (can break off)
when is the denture base used
for the trail denture stage (and occlusal rim stage)
what is the denture base
trial, temporary base which is discarded at the processing stage of denture production
types of denture base
rigid base with wax saddle
light cured, acylic or shellac
CoCr trial uses
lines which teeth are positioned to once CoCr base constructed for trial
- trial done in wax to see if any problems arise before making CoCr
what cast is used for the trial
duplicate cast or master cast
- trial should have positive fit
- clasps can be incorporated if required
why is light cure material not the best idea for tooth trial
wax can stick
how to provide symmetry to the appearance
set teeth to long axis
slight angulation maybe to correspond so symmetry maintained (mirror image of arch)
contact points should also correspond to natural dentition
what compromise/improvisation may be necessary for setting posterior teeth
May not conform to the classical arrangement of teeth
- Depends on the available space
position and occlusion is dictated by the natural teeth.
The denture teeth should not be set in contradiction to this guide.
Teeth are set according to the edentulous saddle tooth space.
- It is acceptable for example that a premolar is set in a space previously occupied by a molar.
Needs to follow the natural tooth guidance
where should the final adjustment of tooth length be
at chair-side if the denture is not tooth supported - some movement might be expected
why is it an advantage for the dentist to set teeth at chair-side
less time, less visits
lab may leave incisal tip longer
- so dentist can match ideally chairside
how can the flange effect the position of the denture
fills space
nothing else may fit there
