Orthodontic Materials Flashcards
Why are fixed orthodontic appliances used?
Correction of moderate skeletal discrepancies
Correct Intrusion/extrusion
Overbite reduction
Closure of spaces
What are the advantages of self-cured acrylic resins compared to heat cured?
- Cheaper to produce
- Less technician time
Why is hydroquinone in the liquid component of acyric resisns?
Acts as an inhibitor for MMA monomer in liquid
What material is used to pour casts for orthodontic appliance construction?
Orthodontic stone
During the heat cure phase of powder/liquid base plate acrylic resin it is put in a water bath. Fow how long and at what temperature?
10hrs to cure in a water bath 7hrs at 70C and 3hrs at 100C
Compare orthodontic stone to dental stone
Not as strong as dental stone
Facilitates model trimming
Longer working time
Addition of whiteners (improve appearance of study model)
What are elastic ligatures
Small rubber bands stretched around wings of the bracket slot.
These can be tied in specific ways to direct teeth in particular directions
What are the disadvantages of heat cured acrlic resins?
- Production cost
- Technician time increased
What material can be used to hold bent wires in place during base plate construction?
Sticky wax
What are the advantages of heat cured acrylics compared to self cured?
- More robust (stronger)
- Less porous
- More resistant to abrasion
- Contains less monomer
What form is PMMA when it is in the powder? How does it react with the MMA monomer in the liquid?
Found as PMMA polymer beads
These beads dissolve in the monomer
Comment on how acrylic is applied to a cast model during base plate constuction
The acrylic (orthodonticresin) is applied
incrementally on the gypsum model to build up the acrylic resin base until the desired thickness is reached
What type of reaction takes place when the acrylic resin mix is heat cured?
Free radical addition polymerisation reaction
What is the primary function of the base plate?
To incorporate all the components together as a functional unit
What is N,N-dimethyl-p-toluidine?
Activator found in liquid for self-cured acrylic resins
Compare syntehtic rubber to natural rubber
Synthetic rubber (PU) has greater resistance to heat, cold and can withstand stresses, pressures and abrasion when compared with natural rubber
What is an ideal thickness for a base plate?
1.5mm to 2mm
What are the active components of a fixed orthodontic appliance?
- Separators (metal or elastic)
- Archwires
- Elastics
- Springs
Why is benzoyl peroxide added to the powder component of a heat cured acrylic resin?
Acts as the initiator to heat cured reaction
Explain why excess resin is easily removed if a gel is used rather than a powder/liquid sytem when making a base plate?
Since the gel form (UDMA) only cures when a light source (visible light) is directed on to it
What are the passive components of a fixed orthodontic appliance?
- Brackets
- Bands
- Lock pins
- Ligature wires
What are synthetic elastics made from?
Polyurethane rubber (PU)
What are some disadvantages of latex elastics?
Oxygen atoms in air can attach to carbon atoms making them brittle and lose elasticity
Contact with oils and sunlight harms them
Patients may be allergic
Removable appliances generally consist of what two components?
Consists of wires and acrylic base plate
What are the disadvantages of self cured acrlic resins?
- More prone to water uptake
- Residual monomer may cause hypersensitivity
What is latex elastics?
Natural rubber from trees (isoprene)
What are the disadvanteges of Synthetic rubber (PU)?
- They tend to distort permanently with time in the mouth and lose elasticity
- Chemical degradation with water (long-term)
What type of acrylics can be used in a base plate?
What form do they come in and how do they cure?
PMMA
* Powder and liquid
* Heat cured / Room temp cured
UDMA
* Gel
* Light cured
UDMA - Urethane dimethacrylate
What are some disadvantages of removable appliances?
- Patients can leave them out for long periods of time
- They affect speech
- A technician’s input is required to make the appliances
- They are inefficient for multiple tooth movements
- Lower removable appliances are more difficult to tolerate
What are connected elastic ligatures and what is their function?
Ligatures that come in variety of strengths which are used to close spaces between teeth or move specific groups of teeth together as the same time.
