Orthodontic materials 1

What are orthodontic materials/appliances used for?

• Align teeth in their most aesthetic and functional positions

• Moves teeth and affect growth in the maxilla and mandible

2 Types of appliances?

• Removable and fixed

Removable appliances are used in what arch?

removable?

consist of 2 things

• Used in the upper arch

• Removed from the mouth by the patient for cleaning

• Wires and acrylic base plate

Removable appliances can be what 2 categories in terms of what they do?

e.g P and A

• Passive: for retention after tx

• Active: Designed to achieve only simple tooth movement via active components such as wires, springs and screws

Base plate:

Made of what - be specific - cure?

Primary function and other functions (4)

thickness?

• Acrylic resin, room temp cured

• Primary - incorporate all the components together as a functional unit

• Provide support to wire components

• Helps in anchoring appliance in place

• helps in distributing forces over a larger area

• 1.5-2mm

In the production of acrylic base plates, what dental materials are involved? (3 main materials for each stage)

• Impression materials

• Gypsum products

• Acrylic based materials

What material could be used but isn’t used and why?

• Elastomer based impression materials can be used but these are more expensive

• Precision is not a requirement

• Alginates commonly used

What is the name of the gypsum product used to pour casts for appliance construction?

• Orthodontic stone

Properties of orthodontic stone? (4)

• Not as strong as dental stone - doesn’t need to be

• Facilitates model trimming

• Longer working time

• Addition of whiteners to improve appearance of study models

Base plate construction:

after the stone sets what happens?

• Separate the alginate from the mould

• The bent wires are held in place by sticky wax

• Separator applied to the gypsum model

• Then acrylic (orthodontic resin) is applied incrementally on the gypsum model to build up the acrylic resin base until the desired thickness is reached

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How is the acrylic dispensed? (2)

• Powder and liquid system or in a gel form

The method of dispensing is based on what monomers and how are they cured

• Powder and liquid: PMMA

• UDMA presented as gel that is light cured (photocured)

Removal of excess resin is eaier in powder liquid form or gel form?

• Excess resin is easily removed if a gel is used rather than P/L system

• As the gel only cures when a light source (visible light) is directed on to it

Powder/liquid acrylic resins for base plate:

when powder and liquid are mixed, they are either x or x cured?

• heat cured or self cured

What is found in powder for heat and self cured resins? (3)

• PMMA polymer beads

• Benzoyl peroxide - initiator

• Colour pigments

Liquid for heat and self-cured contains what? (4)

• MMA

• EGDMA

• HQ - inhibitor

• In self cure - activator - DMPT

P:L ratio, what happens to the polymer when mixed with the monomer?

• 2.5:1

• Polymer beads dissolve in the monomer

What reaction occurs in both heat cured and self-cured?

• Free radical polymerisation reactions

• What components of the P:L are involved in the HC ?

• Under what conditions?

• cooling process and why?

• MMA + BP + heat - to form HC PMMA

• 10 hours to cure in water bath

• 7 hours at 70 degrees and 3hrs at just below 100 degrees

• slow cooling process

• reduces stress?

What components of the P:L are involved in the SC ?

How long does it take?

• MMA + BP + tertiary amine - self cured PMMA

• 20 minutes

MMA - PMMA

Gel for light cured contains what? (5)

UDMA

pigments

fillers

CQ

DMPT or DHPT

What is the reactions that occurs in light cured resins?

• Free radical addition polymerisation

What components of the gel are involved in the LC?

How long does the presence of light?

• UDMA + DMPT + CQ + visible light - light cured poly(UDMA)

• 5 minutes of visible light

ADV of heat cured compared with self cured orthodontic resins? (4)

• More stronger/robust

• Less porous

• More resistant to abrasion

• Contains less monomer

Adv of self cure compared to heat cured? (2)

• Cheaper to produce

• less technician time

DIS of:

heat cured

self cured:

• HC: cost, technician time increased

• More prone to water uptake, residual monomer may cause hypersensitivity

DIS of removable appliances? (5)

• Pt can leave them out for long periods of times

• Affect speech

• Technician input required

• Inefficient for multiple tooth movements

• Lower removable appliances are more difficult to tolerate

What do fixed appliances in orthodontics consist of?

• Arch wires attached to teeth by brackets and band and ligatures

• Brackets and bands attached to teeth using cements

What are fixed orthodontic devices and what can they do (2)?

• Attached to the teeth - cannot be removed by the patient

• capable of causing precise tooth movements and multiple teeth movement in an arch

When might fixed appliances be used? (4)

• Correct moderate skeletal discrepancies

• closure of spaces

• intrusion/extrusion

• overbite reduction

Two types of components of fixed appliances?

• active and passive compoenets

Name some active components? (4)

• separators - metal or elastic

• arch wires

• elastics

• springs

Passive components of fixed appliances? (4)

• Brackets

• Bands

• Lock pins

• Ligature wires

• Other accessories

What is the definition of an elastomer?

• A material that stretches easily to several times its length and returns to its original shape

What are the rubber bands used for?

forces from the bands?

• Used to apply forces to teeth

• Changed by the pt several times a day

• the force of the rubber decays overtime

Elastic ligatures:

What are they for?

• Small and used to secure the arch wire into the slots on the bracket

• Stretched around wings of bracket

• look liek small o rings

Uses of elastic ligatures?

• Direct teeth in a particular direction-

Materials ligatures can be?

• elastic or metal

2 groups of ligatures - not material?

• Single elastic ligatures - variety of colours, size uniform - lose strength overtime

• Connected elastic ligatures - power chains or c-chain ligatures - variety of colours and strengths

• Used to close spaces between teeth, or move specific groups of teeth together at the same time

2 types of elastics? - materials

• Latex elastics and synthetic elastics

What is the source and chemical name of latex elastics?

• Poly cis-isoprene - natural rubber from trees

3 dis to latex elastics?

• Oxygen atoms in the air can attach to the carbon atoms making them brittle and lose elasticity - antioxidants can be incorporated to prevent this from happening

• Contact with oils and sunlight harms them

• Patient may have latex allergy

what does oxygen attack in the poly-isoprene molecules?

What is the synthetic elastics made form?

• polyurethane rubber

What linkage do they contain and what polymerisation is it - C or A?

• C

• urethane link

• di-isocyanate NCO and polyether glycol

Synthetic rubber vs natural rubber?

• greater resistance to heat, cold, withstand stresses, pressure and resist abrasion

Dis of synthetic rubber PU?

• Tend to distort permanently with time in the mouth and lose elasticity

• Chemical degradation with water - long term

Elastics and ligatures

the o rings are changed by the orthodontist

the rubber band - changed by pt multiple times a day