Tutorial 10 - properties and materials Flashcards
What properties of alginate make it the material of choice in many prosthodontic situations?
Advantages:
* accurate- good fine detail
* can be used when undercuts-can be withdrawn from mouth without distortion and accurately reproduces shape of undercut
* easy to use/good viscosity/low adhesive qualities
* comfortable for patient -non- toxic/non- irritant, taste and smell acceptable
* cheap, good shelf life, quick with easy working/setting time
* compatible with stone/plaster
*
Disadvantages:
* cannot be corrected
* tears easily
* distortion due to syneresis or imbibition – needs to be cast immediately
* mixing important – temp water, water/powder mix, complete mixing affect composition of material and qualities
* can only be poured once i.e. cannot be recast
What are the advantages and disadvantages of the silicone impression materials compared to alginate?
Advantages
Different viscosities available - ultra light, light, medium, heavy and putty
* accurate – with used of different viscosities
* good tear resistance
* dimensionally stable - can be cast some time after not immediately
* non toxic/irritant, pleasant taste/smell
* can be recast
* good shelf life
* good working/setting time and automix available
Disadvanatges:
cost vs alginate
* possible to lock into deep undercuts- although no common
* must use latex-free gloves (sulphur contamination impedes setting)
* hydrophobic – surfactants added to make more hydrophilic but then can suffer from imbibitio
What 3 main materials can be used to construct a partial denture?
3 main materials:
1. Acrylic
2. Cobalt Chromium (CoCr)
3. Thermoplastic – flexible nylon
Others framework materials include:
1. Type IV gold alloy – very expensive/outdated
2. titanium- light –weight and biocompatible but expensive and complicated casting
3. stainless steel- can be very thin and light, fracture resistant, corrosion resistant and good thermal conductivity
4. aluminium- accurate
Ideal Requirements of a denture base material?
*Biocompatible
*Adequate physical and mechanical properties
*high flexural and impact strength
*long fatigue life
*high abrasion resistance
*high thermal conductivity
*low density
*low solubility and absorption of oral fluids
*dimensionally stable
*ease of repair,ease of fabrication
*Cleansable
*good adhesion to denture teeth
*aesthetics.
What are some advantages and disadvantages of acrylic denture bases?
Polymethylmethacrylate PMMA Can be heat cured or self cured. Self cured has 80% strength of heat cured and more residual monomer.
Advantages
* cheap
* good for long span edentulous areas
* easy to reline – for transitional cases
* easy to add teeth to if teeth of poor prognosis in arch
* biocompatible
* Mainly mucosa support but clasps can be added for extra retention in stainless steel or gold
Disadvantages
* less hygienic as covers gingival margins
* porosity ( gaseous and contraction)
* low tensile strength and modulus of elasticity so prone to fracture
* low co-efficient of thermal conductivity – so patient cannot feel temperature of food and drinks as well
* allergy due to leaching of monomer of benzoic acid
* high co-efficient of thermal expansion but balanced by water absorption to some extent.
* thicker denture base
* difficult to seat into undercuts
* need for adhesives if retention poor
CO-CR detnure bases advantages and disadvantages?
Advantages:
*Hygienic as can be designed away from teeth
*Tooth support as well as mucosal support to spread load
*Retention from clasps
*Thinner and lighter framework
*Better proprioception/taste due to exposed mucosa
*Good thermal conduction and therefore appreciation of temperature of food/drinks
*Biocompatible
*High corrosion/tarnish resistance
*High surface lustre so plaque resistant
*High yield strength, cantilever bending strength, transverse strength, fatigue strength, impact strength, modulus of elasticity, ductility, resilience, toughness, hardness and sag resistance.
Disadvantages:
*cost
*aesthetics- clasps visible
*difficult to reline
*difficult to repair
*difficult to add to – denture framework must reach tooth to be added. soldering tags can be very expensive
*clasps can break
*tooth preparation for occlusal rests may be required
*increased lab and chairside time
Advantages and disadvantages of thermoplastic denture bases?
Advantages:
*Aesthetics- allows tissue tone to be seen through the material so clasps seem to ‘disappear’
*very thin and flexible
*good for transitional cases eg prior to implants
*can be combined with cocr base
*biocompatible – good for patients with allergy to acrylic resin
*patients with compromised neurological function
*unilateral bounded denture
*clinically unbreakable ?!
Disadvantages:
·Debonding of acrylic teeth – undercuts or diatorics are cut into the centre of each tooth so that the melted fluid polyamide will flow into the undercuts for mechanical retention s the acrylic teeth will not bond to the nylon.
·difficult to use if decreased vertical dimension due to space needed for mechanical retention of teeth
·Difficult to reline
·Difficult to add to successfully- can be added to temporarily
·difficult to polish/adjust – leading to surface roughness
·discolouration
·lower hardness
What are the advantages and disadvantages of recording occlusion during jaw registration with WAX
cheap
*easy to use/readily available
*pt acceptability good
Disadvantages:
*has to be very sift and even heating or will deflect mandible as sets /cools quickly and becomes too hard
*co-eff of thermal expansion- errors on cooling
What are the advantages and disadvantages of recording occlusion during jaw registration with zinc oxide eugenol
Advantages:
*cheap
*low viscisity
*good detail
Disadvantages:
*taste/smell/burning sensation with xerostomia patients
*allergy
*brittle so can break
*locks into undercuts-will fracture
*long setting time
*messy
How does the elastic modulus of the denture clasp materials compare and what is the significance of this?
Cobalt-chromium alloys (Co-Cr alloys): High elastic modulus (210–230 GPa), providing stiffness and strong retention for durable and rigid clasps.
Titanium and Titanium alloys: Moderate elastic modulus (100–120 GPa), offering flexibility and reduced stress on teeth, making them suitable for partial dentures.
Stainless steel: High elastic modulus (190–210 GPa), combining strength and corrosion resistance for rigid clasps in removable partial dentures.
Gold alloys: Low elastic modulus (80–100 GPa), providing flexibility and reduced risk of tooth damage, but with less retention force.
Thermoplastic resins: Very low elastic modulus (1–3 GPa), offering high flexibility and comfort, though with lower retention strength compared to metals.
Give some reasons why some impressions are unsuitable
· important landmarks are missed = incorrect tray size or not centred
· incomplete peripheral rolled border = cheeks in way or not
released from sides of tray prior to border moulding
· teeth are in contact with the tray = tray seated incorrectly, or the tray is too small
· tears, drags or voids = air blows? poor mixing or moving/“reseating” impression
· poor detail = choice of material
· separation of material from
tray = no adhesive or storing heals down rather than face down
· trapping of cheek or tongue in impression = poor border moulding
· tray showing through = too much pressure on seating or over extended borders
· feather edge on impression = under extended tray which will need greenstick addition
What are the landmarks that need to be covered by maxillary impressions?
Hamular Notch
Maxillary Tuberosity
Fovea
Sulci
Frenae
Incisive Papilla
Palatal Rugae
Palatal Raphe
Alveolar Ridge
Teeth
What are the landmarks that need to be covered by mandibular impressions?
Retromolar Pad
Pear Shaped Pad
Retromylohyoid Fossa
Alveolar Ridge
Sulci
Frenae
Teeth
What are the 3 most common placed which prevent seating for Co-Cr?
Under rests
Interproximal minor connector
Interproximal parts of lingual plate
3 common areas that prevent seating on acrylic dentures are…
Collets
· Undercut flanges
· Undercuts not blocked out between teeth
To ensure you have recreated the correct ICP, what can you do?
Use 2 teeth as a point of reference to ensure they meet in the same way before and after the denture is instead
· Use articulating paper - different colours can be used with and with out the denture and the 2 colours should coincide if the articulation is correct.
· check against your original bite registration on the articulator
What can be the effects of an incorrectly recorded ICP?
Instability of denture
· Pain/discomfort
· Problems with chewing
· TMJ pain
· Poor aesthetics if increase lower face height
· Incompetent lips
· Speech affected
List some common problema nd solutions for this appointment
Pain/ulceration in sulcus – flanges too long- adjust flange height
· Pain on edentulous ridge – occlusion in correct- use articulating paper to identify high spots and adjust
· Looseness- tighten clasps, check posterior border is extended adequately if large upper partial denture, check frenal relief, check flanges not encroaching on muscle function, check denture base closely adapted to tissues
· Difficulty biting – check occlusion and if you have achieved ICP
· Pain in abutment teeth- pressure from tight framework- use occlude/disclosing wax to identify areas and adjust
· Gagging- check post extension and adaptation to tissues
· Problems with speech- check tooth position
Cheek biting- check tooth placement and cusp shape
