LAB Flashcards
What are the key components of URA appliance design?
Active Component(s): Apply the force for tooth movement.
Retentive Component: Prevent displacement of the appliance.
Anchorage: Resistance against unwanted tooth movement.
Baseplate: Connects all the components and provides stability.
What are the two components of the Index of Orthodontic Treatment Need (IOTN)?
Aesthetic Component (AC): Measures aesthetic impairment.
Dental Health Component (DHC): Evaluates occlusal traits affecting dental and surrounding structure morbidity.
What are the main reasons for stainless steel wire fractures in orthodontics?
Overwork: Excessive bending and straightening.
Mechanical Abrasion: Damage during finishing or fabrication.
Fatigue: Repeated strain at the same point.
Weld Decay: Corrosion at the grain boundaries due to overheating.
How is stainless steel made corrosion-resistant?
Chromium forms a passive oxide film over the surface, preventing corrosion.
What is the composition of 18/8 austenitic stainless steel used in orthodontics?
72% Iron
18% Chromium
8% Nickel
1.7% Titanium
0.3% Carbon
What is the Bauschinger effect, and how does it relate to orthodontic wires?
When a coil in a wire is activated in the same direction as its previous bending, its elastic recovery increases. This occurs because the outer surface becomes more work-hardened than the inner surface.
What is the key structural difference between austenite and martensite?
Austenite: Has a perfect cubic crystalline structure.
Martensite: Has a distorted cubic structure due to interstitial carbon atoms, causing hardness.
What are the three types of orthodontic retainers, and their key features?
Conventional Removable Retainers: Made of acrylic and wire.
Thermoplastic Retainers: Clear and aesthetic.
Bonded Retainers: Fixed to teeth, ensuring long-term retention.
How does titanium improve welding in stainless steel?
Titanium prevents the precipitation of chromium carbides, reducing grain boundary corrosion during welding or soldering.
What is the basic principle of orthodontic tooth movement?
If prolonged force is applied to a tooth, tooth movement occurs through bone remodeling, controlled by the periodontal ligament (PDL).
How does bone remodel during orthodontic treatment?
Bone is selectively removed in areas under pressure and added in areas under tension around the tooth.
What are the components of a URA appliance design?
Active Component: Moves teeth with force.
Retentive Component: Resists displacement forces (e.g., Adams clasps).
Anchorage Component: Resists unwanted tooth movement.
Baseplate: Connects all components, provides anchorage, and assists retention.
What components are used to retract canines with a URA appliance?
13 & 23 (Canines): Palatal finger springs (0.5mm HSSW).
16 & 26 (Molars): Adams clasps (0.7mm HSSW).
11 & 21 (Centrals): Southend clasp (0.7mm HSSW).
Baseplate Material: Self-cure PMMA.
List advantages of removable orthodontic appliances.
Tipping movement of teeth.
Excellent anchorage.
Shorter chairside time.
Easier oral hygiene maintenance.
Cheaper than fixed appliances.
Adaptability for overbite reduction.
What are the disadvantages of removable orthodontic appliances?
Less precise control of tooth movement.
Limited to moving 1-2 teeth at a time.
Easily removable by the patient.
Difficult to correct rotations.
What materials and wire dimensions are used for the Adams clasp?
Permanent Teeth: 0.7mm stainless steel round hard wire.
Deciduous/New Premolars: 0.6mm stainless steel round hard wire.
List the key advantages of the Adams clasp.
Small, neat, and unobtrusive.
Usable on deciduous or permanent teeth.
Suitable for partially erupted teeth.
Highly retentive if constructed well.
Modifiable for auxiliary springs, hooks, or facebows.
