Orthodontic Materials

Question 1

Why are fixed orthodontic appliances used?

Answer 1

Correction of moderate skeletal discrepancies
Correct Intrusion/extrusion
Overbite reduction
Closure of spaces

Question 2

What are the advantages of self-cured acrylic resins compared to heat cured?

Answer 2

• Cheaper to produce
• Less technician time

Question 3

Why is hydroquinone in the liquid component of acyric resisns?

Answer 3

Acts as an inhibitor for MMA monomer in liquid

Question 4

What material is used to pour casts for orthodontic appliance construction?

Answer 4

Orthodontic stone

Question 5

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?

Answer 5

10hrs to cure in a water bath 7hrs at 70C and 3hrs at 100C

Question 6

Compare orthodontic stone to dental stone

Answer 6

Not as strong as dental stone
Facilitates model trimming
Longer working time
Addition of whiteners (improve appearance of study model)

Question 7

What are elastic ligatures

Answer 7

Small rubber bands stretched around wings of the bracket slot.
These can be tied in specific ways to direct teeth in particular directions

Question 8

What are the disadvantages of heat cured acrlic resins?

Answer 8

• Production cost
• Technician time increased

Question 9

What material can be used to hold bent wires in place during base plate construction?

Answer 9

Sticky wax

Question 10

What are the advantages of heat cured acrylics compared to self cured?

Answer 10

• More robust (stronger)
• Less porous
• More resistant to abrasion
• Contains less monomer

Question 11

What form is PMMA when it is in the powder? How does it react with the MMA monomer in the liquid?

Answer 11

Found as PMMA polymer beads

These beads dissolve in the monomer

Question 12

Comment on how acrylic is applied to a cast model during base plate constuction

Answer 12

The acrylic (orthodonticresin) is applied
incrementally on the gypsum model to build up the acrylic resin base until the desired thickness is reached

Question 13

What type of reaction takes place when the acrylic resin mix is heat cured?

Answer 13

Free radical addition polymerisation reaction

Question 14

What is the primary function of the base plate?

Answer 14

To incorporate all the components together as a functional unit

Question 15

What is N,N-dimethyl-p-toluidine?

Answer 15

Activator found in liquid for self-cured acrylic resins

Question 16

Compare syntehtic rubber to natural rubber

Answer 16

Synthetic rubber (PU) has greater resistance to heat, cold and can withstand stresses, pressures and abrasion when compared with natural rubber

Question 17

What is an ideal thickness for a base plate?

Answer 17

1.5mm to 2mm

Question 18

What are the active components of a fixed orthodontic appliance?

Answer 18

• Separators (metal or elastic)
• Archwires
• Elastics
• Springs

Question 19

Why is benzoyl peroxide added to the powder component of a heat cured acrylic resin?

Answer 19

Acts as the initiator to heat cured reaction

Question 20

Explain why excess resin is easily removed if a gel is used rather than a powder/liquid sytem when making a base plate?

Answer 20

Since the gel form (UDMA) only cures when a light source (visible light) is directed on to it

Question 21

What are the passive components of a fixed orthodontic appliance?

Answer 21

• Brackets
• Bands
• Lock pins
• Ligature wires

Question 22

What are synthetic elastics made from?

Answer 22

Polyurethane rubber (PU)

Question 23

What are some disadvantages of latex elastics?

Answer 23

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

Question 24

Removable appliances generally consist of what two components?

Answer 24

Consists of wires and acrylic base plate

Question 25

What are the disadvantages of self cured acrlic resins?

Answer 25

• More prone to water uptake
• Residual monomer may cause hypersensitivity

Question 26

What is latex elastics?

Answer 26

Natural rubber from trees (isoprene)

Question 27

What are the disadvanteges of Synthetic rubber (PU)?

Answer 27

• They tend to distort permanently with time in the mouth and lose elasticity
• Chemical degradation with water (long-term)

Question 28

What type of acrylics can be used in a base plate?
What form do they come in and how do they cure?

Answer 28

PMMA
* Powder and liquid
* Heat cured / Room temp cured

UDMA
* Gel
* Light cured

UDMA - Urethane dimethacrylate

Question 29

What are some disadvantages of removable appliances?

Answer 29

• 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

Question 30

What are connected elastic ligatures and what is their function?

Answer 30

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.