Setting teeth Flashcards
What is the aim of setting teeth
The 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.
If these aims can be accomplished it will greatly improve patient self-confidence and protect their ‘denture privacy’
Is there any difference between setting teeth for cobolt chrome or a PMMA base?
no
n.b. Although 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)
What different materials can artificial teeth take?
acrylic
porcelain
what is the most popular material for artificial teeth for RPDs
Polymethyl methacrylate acrylic (PMMA) resin
Properties of plastic/acrylic teeth
- Chemical bond with the denture base
- Natural appearance and feel-silent in function
- Tough
- Soft-low abrasion resistance
- Easily trimmed and polished/customised
- Cold flow under pressure
- Insoluble in mouth fluids-some dimensional change
Properties of porcelain teeth
- Mechanical attachment with the denture base. (silane coupling agent)
- Natural appearance-possible noise in function
- Brittle
- Friable -grinding removes surface glaze
- Hard-high resistance to abrasion
- Inert in mouth fluids-no dimensional change
- High heat distortion-no permanent deformation under forces of mastication
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
An example of software to help you choose teeth moulds and shade guides?
enigma
What things do you have to do when setting teeth
- choosing the material of artificial teeth
- choose an appropriate tooth mould (size)
- customise artificial teeth/ adjustments (shade)
- set teeth considering aesthetics and function
What information do we need from the tooth mould chart?
- shape of tooth (square, ovoid, tapered)
- length of anterior teeth
- height of central incisor
- width of central incisor
- function and design
How do acrylic teeth bond to the denture base
chemically
How do porcelain teeth bond to the denture base
mechanically
via a metal retention pin incorporated within the tooth on anterior teeth
via a hollowed area that will fill with the denture base on posterior teeth
what is setting teeth often dictated by
the arrangement and position of the remaining natural teeth
teeth cannot be set without considering blocking out for the insertion of the denture (?)
What is a common reason for compromise when setting teeth
tooth loss may also involve tooth drifting and change in available space to set the artificial teeth
What are the 3 types of tooth shape?
tapered
ovoid
square
how can we accomodate for the fact that partical dentures frequently require customising
choosing a larger mould
why should you not adjust the tooth mould from the incisal tip/cervical margin
can affect the shade
where should you adjust the tooth mould from
the ridge lap
How can debonding occur
during the preparation of artificial teeth when setting the teeth for trial
The more the ridge lap is reduced the less bonding area is available.
The ‘softer’ bonding area if reduced in area can affect the bond with the ‘enamel’ layer having a harder surface.
how does the ridge lap differ in material from the rest of the artificial tooth
Artificial teeth comprise of at least two layers of material; the ridge lap is made up of a more heavily cross-linked acrylic, specifically to bond with the denture base.
How do you prevent tooth de-bonding for heat cured dentures (adhesive failure)
Grind teeth with DIAMOND cutters to produce a rougher abraded surface (micro-abrasion)
No wax or grease on the tooth surface – use detergent when boiling out (removing the wax from the flask)
Ensure no residue of mould seal on the tooth surface.
How do you prevent tooth de-bonding for self cured dentures (cohesive failure)
Grind teeth with DIAMOND cutters to produce a rougher abraded surface (micro-abrasion)
No wax or grease on the tooth surface – use detergent when boiling out (removing the wax from the flask)
Ensure no residue of mould seal on the tooth surface.
Add a drop of monomer to the tooth surface and allow to soak into the tooth before addition the self cure PMMA
When removing tooth surface, what views should we look at the teeth with
- frontal
- sagittal
- occlusal
what can we use to ensure teeth are placed correctly in the arch
survey lines
why is it not advisable to have large areas blocked out
creates ‘dead spaces’ resulting in food impaction
How can we check occlusion
- the 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 tooth guidance using the canines or groups of teeth e.g. premolars
What happens after teeth have been customised?
they can be attached to the trial base plate with modelling wax
What is a trial denture
The denture base for the trial denture stage (and occlusal rim stage) is a temporary base that will be discarded at the processing stage of denture production.
What is a trial denture made of
Rigid base with wax saddle
Light-cured acrylic or shellac
A trial to establish tooth position/finishing lines may be used for cobalt chromium then teeth are positioned onto the Co Cr base once constructed for trial.
How do you provide symmetry to the appearance
Set the teeth to the long axis of the corresponding tooth.
Contact points should also correspond to the natural dentition
Why do posterior teeth sometimes not conform to the classical arrangement of teeth?
The 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.
Where should the final adjustment of tooth length happen?
at chairside
