Removable Prosthetics Flashcards
What are the indications for rebasing a successful complete denture? (5)
- the patient reports that it has been worn successfully but a deterioration in retention has been noticed since it was first made
- the oral tissues are healthy
- there is no significant loss of occlusal vertical dimension or gross tooth wear
- the occlusal relationships remain satisfactory
- the polished surface shapes are successful
What is retching?
Involuntary contraction of the muscles of the soft palate or pharynx
What can you use to secure a denture firmly? (4)
- locator abutments
- ball abutments
- gold bar
- CAD CAM titanium bar
What are the powder constituents of acrylic? (3)
- polymer- PMMA beads
- initiator- benzoyl peroxide
- pigments- salts of cd/fe or organic dyes
What are the liquid constituents of acrylic? (4)
- monomer- MMA
- cross linking agents- ethyleneglycodimethacrylate
- inhibitor- hydroquinone
- activator- only self cure N,N dimethyl- p- toluidine
How do you process acrylic using a water bath/electrical oven? (3)
- cycle 65*C to decompose benzoyl peroxide
- do not exceed 100.3*C (BP of monomer)
- e.g 7 hours at 70C and then 100C for 3 hours
What are the disadvantages of acrylic? (4)
- low impact resistance
- poor resistance to fracture fatigue
- poor impact strength
- water absorption and candida growth
What are the constituents of a cobalt chromium alloy? (5)
- cobalt 35-65%
- chromium 25-35%
- molybdenum <4%
- nickel 0-30%
- traces of Be, Si, C
What are the affects of carbon? (3)
- hardness
- strength
- ductility
What are the advantages of CoCr? (4)
- stronger
- thinner
- low corrosion
- high biocompatibility but nickel allergies
What are the disadvantages of CoCr? (3)
- difficult to polish
- clasp fractures- work hardening
- in laboratory high casting temperature
What is steel?
An alloy of iron and <2% carbon
What are the additions of stainless steel? (2)
- addition of 18% chromium improves corrosion resistance
- addition of 8% nickel improves corrosion resistance and strength
What is the processing of stainless steel? (3)
- work hardening
- can be soldered or welded
- cannot heat treat
How are acrylic denture teeth produced?
In reusable moulds by dough moulding or injection moulding
What is a tissue conditioner?
Temporarily applied to permit a more equal distribution of load and assumption of more normal mucosal distribution. Helps to get an ill fitting denture to more closely fit the ridge
What is a soft (resilient lining)?
Applied as a shock absorber to avoid pain from movement of the denture upon nerves, chronic ulceration, flabby ridges. Useful occasionally when large undercuts can flex in and out
What temperature do tissue conditioners and soft linings work at? (2)
- soft at mouth temperature
- glass transition temperature at < or =37*C
What are the types of materials of tissue conditioners/soft linings? (3)
- acrylic polymers with solvent
- acrylic polymers or co polymers with an inert ester to act as a plasticiser
- silicones
What are the requirements of tissue conditioners? (4)
- non irritant
- non toxic
- when set tissue conditioners should be soft but not capable of undergoing substantial permanent deformation
- many are visco elastic
What are the problems with soft linings? (4)
- in time food can become embedded within soft liner
- plasticisers of the acrylic lost with time > hardening and dimensional changes
- silicones susceptible to candida
- sometimes difficult to achieve bond between silicone and PMMA denture base
What are the types of precision attachments? (2)
- ball on post and diaphragm
- tubelock
When is a two part denture useful?
When gross tissue loss and different paths of insertion
What is the design of a two part denture? (2)
- split pins on cobalt chrome denture
- acrylic slots into pins on different path of insertion
What kind of denture would you use for bruxists? (4)
- metal backing to teeth
- cobalt chromium reduces fracture
- use of cross linked teeth as better wear resistance
- acrylic post dam increases retention
What is digital dentistrys application to prosthodontics?(4)
- digital dentures
- implants
- CAD CAM crowns and bridges
- digital smile design
What are the advantages of digital dentures? (4)
- improved aesthetics
- digital record so can produce another
- no need for articulators
- time saving in laboratory
What are the disadvantages of digital dentures? (4)
- cost very expensive
- bond of teeth to base (potential weakness)
- software updates and system becomes obsolete
- clinical techniques (learning curve)
How can digital technology be used with implants? (3)
- planned surgery with CBCT
- guided surgery
- milled titanium frameworks
What is the NICE definition of frailty?
A state of increased vulnerability to poor resolution of homeostasis after a stressor event
What is the legislation protecting a vulnerable adult?
Adult support and protection (scotland) act 2007
What are the pathological changes relating to dentures? (3)
- acute or chronic reactions to microbial denture plaque
- a reaction to constituents of denture base materials
- mechanical denture injury
What is the bacteria in angular cheilitis? (3)
- candida albicans
- staph aureus
- beta haemolytic streps
What can denture irritation hyperplasia be treated with?
Tissue conditioner e.g coe comfort
What are the solutions to flabby ridges?
New denture covering whole denture bearing area with good peripheral seal and opposing arch denture giving posterior support
What are the allergic reactions in dentistry?
Nickel containing Co/Cr or PMMA especially self cure relines as higher monomer
What is the definition for a reline?
Adding new base material to the tissue surface of an existing denture in a quantity sufficient to fill the space which exists between the original denture contour and the altered tissue contour
What are the indications for a temporary reline? (3)
- tissue conditioning when grossly ill fitting dentures
- post immediate dentures
- after implant surgery
When is a soft reline useful?
If parafunctional habits, very atrophic ridges and in cancer/cleft patients
What are the disadvantages of soft relines? (3)
- plasticiser leaches
- deteriorates with time
- harbours microorganisms
What are the uses of permanent relines? (4)
- peripheral seal problems
- correction of errors following inadequate master impression
- immediate dentures
- prolongs lifespan of some older dentures
What are the common types of denture fractures? (5)
- midline
- tooth detaches from denture base
- loss of flange
- acrylic saddle detaches from co/cr baseplate
- clasp fracture
Why do dentures fracture? (4)
- impact
- acrylic in thin section
- work hardening of metal
- parafunctional habits
How do you do a simple repair?
If fractured pieces can be located together, disinfect and send to lab, cast poured, fractured area removed, new acrylic processed
How do you do a repair if a piece of denture is missing?
Impression taken with fractured denture in mouth, disinfected, cast poured and new acrylic processed into defect
How do you do a repair on an acrylic cobalt chrome denture?
May need to add retentive tags. Solder on tags and/or use 4-META or silicate co/cr to retain acrylic on co/cr
What are the materials for temporary repairs? (2)
- self cure acrylic
- cyanoacrylate glue
What are the types of additions? (3)
- immediate addition
- post immediate addition
- retention
What is a post immediate addition?
When a tooth is lost after denture construction and at a later date a tooth is added
What is retention addition?
When denture retention is inadequate a clasp is added to try to improve retention. Usually a wrought stainless steel clasp
What are the clinical issues with additions?
Additions usually require an impression of the arch with the denture to be added to in the mouth during an impression
What is bracing?
The resistance of a denture to displacement by functional forces
What are the clinical uses of permanent soft lining materials? (3)
- atrophic ridge and mucosa
- undercut ridges
- obturators
What is the advantage of acrylic soft lining materials?
Good bonding between denture base and lining material
What are the advantages of silicone based materials?
Maintains softness
What are the disadvantages of silicone based materials? (5)
- failure of acrylic/silicone bond
- rough surface which is difficult to modify
- susceptible to candida colonisation
- risk of denture fracture
- more complex laboratory technique required for soft lining materials
What are the components of temporary soft lining materials? (2)
Powder- polyethyl methacrylate
Liquid- ethanol, plasticiser
What are the clinical uses of temporary soft lining materials? (3)
- temporary relines
- tissue conditioner
- functional impressions
What are temporary relines used for? (3)
- used for dentures undergoing modification during the transitional phase after implant placement
- oncology patients
- used in ill fitting dentures to allow recovery of inflamed tissues in the denture bearing area
What materials do we use on the atrophic ridge? (2)
- soft lining materials
- molloplast B
How do we reduce trauma to the atrophic ridge? (2)
- reduce the number of posterior teeth on the denture
- over denture abutments
What methods ensure a good base fit? (2)
- valves
- precision attachments
How do you do the neutral zone technique for tooth position? (4)
- record the jaw relationships in the normal way
- construct a stable mandibular base in acrylic and build occlusal stops to the correct vertical dimension
- patient carries out functional movements such as speech and swallowing to record the shape of the neutral zone
- the technician will make buccal and lingual indices around the neutral zone impression. This will identify the area where the teeth can be placed
What are the indications for implants? (3)
- atrophic ridge and poor ability to control prosthesis
- reconstructive phase after surgery e.g oncology
- loss of bone following trauma e.g. RTA
What are the local risk factors for implants? (4)
- insufficient depth or width of bone
- bone disease e.g osteoporosis
- bisphosphonates
- pts have received radiography for oral malignancy
What are the complications around bar retained prosthesis?
Soft tissue hyperplasia
Describe how you would test for the following features of a complete denture:
- retention,
- stability,
- support,
- adaptation
- extension
- tug on incisor teeth,
- move side to side,
- apply pressure,
- rock denture in different axes,
- border mould
What is the interfacial surface tension?
Thin layer of fluid present between two parallel planes of rigid material. Ability of fluid to wet the rigid material
What is interfacial viscous tension?
The force holding two parallel planes together that is due to the viscosity of the interposed liquid
What is the management for an irregular occlusal plane on natural teeth? (5)
- no adjustments
- minimal localised occlusal grinding
- radical occlusal adjustment
- extraction of teeth
- overlay appliances
How do you make replica blocks in the construction of a replica denture? (3)
- 1st impressions
- melt shellac over the impression as a base
- wax poured into sprue holes with shellac inside
What is the material for the second impression in the replica technique?
Wash impression using a light bodied material e.g aquasil, rapid liner
How do you assess labial fullness?
Assessed side on, should be 90*C angle between base of nose and lip
Nasal philtrum and upper lip
How do you assess the incisal level?
1-2mm below upper lip at rest
What kind of putty do you use in the replica technique?
Condensation cured silicone putty
Name 5 biometric guides to tooth position
- incisive papilla (5mm posterior to incisal edges),
- overbite,
- overjet,
- smile line,
- buccal corridor
What tool can be used to check if the horizontal plane is even?
Fox’s bite plane
What are the advantages of immediate dentures? (4)
What are the advantages of immediate dentures? (4)
What are some contraindications to immediate replacement dentures?
- financial,
- physical coping,
- sedation or GA Xs,
- surgical extractions
What are the advantages of over dentures? (3)
- can be used to support denture
- preserve alveolar bone
- retain proprioception
What are the advantages of immediate dentures? (2)
- maintenance of vertical and horizontal jaw relationships
- covering of x socket may protect blood clot and promote early healing
What are the contraindications to immediate replacement dentures? (4)
- financial
- physical coping
- sedation or GA Xs
- surgical extractions
What are the functions of flanges? (4)
- retention
- healing
- undercuts
- aesthetics
When are open face flanges considered? (3)
- bulky upper anterior alveolar ridge
- undercuts too deep to be utilised for retention
- flange would give too much support to upper lip
What are the disadvantages of open flange IRDs? (3)
- resorption of ridge leads to gap
- difficult aesthetic transition to flange
- reduced retention
Where are stops placed in lower and upper trays?
lower: incisal region and retromolar pads,
upper: incisive papilla and along post dam area
What is the spacing and material, and technique for spaced special tray impressions?
3mm spacing,
low/medium viscosity alginate,
placement of stops,
mucostatic technique
What is the spacing and material, and technique for close-fitting special tray impressions?
1mm spacing,
thin layer of wash impression
What impression technique must you avoid for a flabby ridge?
avoid mucocompression - use 2 stage technique (or single stage with low viscosity material and perforated tray)
How can you fix a broken denture where the 2 pieces fit together closely?
Cold cure acrylic resin
Name 2 materials that can be used for soft linings and the pros and cons of them
Ester (mma + plasticizer): good bond to denture but short clinical life,
Silicone: better performance but poorer bond to pmma
name 2 methods on implant denture retention and a problem associated with each
Retentive anchors: poor OH
Bar-retained prosthesis: soft tissue hyperplasia
What is the depth of undercut for:
a) cobalt chrome
b) stainless steel
c) gold
a) 0.25mm
b) 0.5mm
c) 0.75mm
For a lingual bar:
a) how much should it clear gingival margins by?
b) width
c) minimum depth of lingual sulcus
d) height
a) 3mm
b) 3.5mm
c) 7mm
d) 4mm
For a sub lingual bar:
a) width
b) minimum depth of lingual sulcus
c) height
a) 4mm
b) 5mm
c) 2mm
What are the advantages of using cobalt chromium as a saddle? (4)
- strong
- less bulky
- more hygienic if designed well
- high abrasion resistance
What are major connectors? (4)
- unites partial denture saddles
- provides bracing
- provides indirect retention
- acts as a splint
What does the force required to displace a clasp vary with? (4)
- depth of undercut engaged
- length/cross section
- flexibility of arm
- angle of approach
What is the definition of support?
Resistance to vertical load directed through denture to underlying mucosa
What are the problems with casts? (3)
- air bubbles
- distorted impressions
- heel interfaces
How do you reduce the load of a free end saddle? (4)
- decrease the size of the occlusal table
- use narrow teeth
- use fewer teeth
- reduce cusp interference on lateral loading
When does the cast usually need tilted?
For a bilateral free end saddle
What bacteria are in denture debris? (4)
- s aureus
- e coli
- k pneumoniae
- alpha streps
What are the disadvantages of alkaline peroxides as a denture cleaner? (2)
- does not effectively deal with calculus or darker stain
- not for soft linings
