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.
What is the typical treatment goal when designing a URA for a patient with a 6mm overjet and extracted first premolars?
The aim is to retract the canines using palatal finger springs and guards while maintaining anchorage with Adams clasps on molars.
Why are removable appliances considered to provide “excellent anchorage,” and what is their main limitation compared to fixed appliances?
Excellent anchorage: Because they engage multiple teeth for stability.
Main limitation: Less precise control of tooth movement, mainly causing tipping rather than bodily movement.
What biological process allows teeth to move under orthodontic force, and what structures mediate this movement?
Process: Bone remodeling (osteoclasts resorb bone on the pressure side, and osteoblasts deposit bone on the tension side).
Mediators: Periodontal ligament (PDL) fibers respond to force application and direct remodeling.
Match the following components to their respective stainless-steel wire gauges:
(A) Adams Clasp
(B) Finger Spring
(C) Z-Spring
(D) Buccal Canine Retractor
(E) Southend Clasp
(A) 0.7mm
(B) 0.5mm
(C) 0.5mm
(D) 0.5mm (with tubing for support)
(E) 0.7mm
What are the essential checks before fitting a URA in a patient’s mouth?
- Confirm patient identity
- Check appliance specifications.
- Inspect for sharp edges or defects.
- Check wire integrity (damage, work-hardening, deformation).
- Insert the appliance and assess tissue blanching or trauma.
- Verify posterior retentionn
- Verify anterior retention (engagement of clasps).
- Activate the appliance (typically 1mm movement per month).
- Teach the patient correct insertion, removal, and maintenance.
- Book review apt 4-6 weeks
What common initial side effects might a patient experience with a URA, and how can they be managed?
- Appliance will feel big & bulky (this is perfectly normal, and they will get used to it quickly).
- My cause initial excessive salivation (this will pass in 24 hours).
- May impinge speech for a short period of time (practise reading a book aloud at home and this will subside).
- May cause initial discomfort or ache (this is perfectly normal, and indicates that the appliance is working).
- To be worn 24/7 including meal times & sleep.
- Remove after every meal and clean with a soft brush.
- Remove and store in a protective container when participating in contact or active sports.
- Avoid hard or sticky foods that may damage the appliance and be cautious with hot food or drinks.
- Missing appointments and non-compliance will significantly lengthen the treatment time.
- Provide emergency contact details in case any problems arise.
What modifications are made to a URA when treating a patient with anterior crossbite of the upper right lateral incisor?
Active Component: Z-spring (0.5mm HSSW) to push 12 labially.
Retention: Adams clasps on molars (16, 26) and premolars (14, 24).
Baseplate: Posterior bite plane to disclude anterior teeth and facilitate movement.
What is the primary function of a Z-spring in a URA?
In which orthodontic case is a Z-spring commonly used?
To move a single tooth labially by applying controlled, light force.
Anterior crossbite correction (e.g., pushing the upper lateral incisor forward).
Why is a posterior bite plane often used alongside a Z-spring?
To disclude the anterior teeth, allowing free movement of the tooth being pushed forward.
What is the function of a posterior bite plane in orthodontics?
How does a posterior bite plane help correct a deep bite?
To disclude anterior teeth, allowing them to move freely while reducing overbite.
It prevents anterior teeth from occluding, which encourages posterior tooth eruption and opens the bite.
How does an anterior bite plane reduce overbite?
When is an anterior bite plane indicated?
By preventing posterior teeth from occluding, leading to posterior eruption and bite opening.
When treating patients with deep overbites
How does the anterior bite plane interact with the lower incisors?
The lower incisors contact the flat acrylic surface, preventing them from further over-erupting.
What are the two key structural features of an Adams clasp?
Arrowhead clasps that grip the undercut.
Flyovers that provide additional retention on the buccal surface.
Name three types of active components used in a URA and their function.
Buccal Canine Retractors – Used for retracting buccally placed canines.
Roberts Retractor – Used to reduce overjet by moving incisors posteriorly.
Z-Spring – Used to correct anterior crossbites by pushing the affected tooth labially.
What is the purpose of retentive components in a URA? Provide two examples.
Retentive components keep the appliance in place by engaging undercuts in the teeth. Examples:
Adams Clasp – Engages the undercuts of molars for strong retention.
Southend Clasp – Used on central incisors for additional stability.
What is the function of anchorage in a URA, and how can it be reinforced?
Anchorage prevents unwanted tooth movements during activation. It can be reinforced by:
Using multiple clasps (e.g., Adams clasps on molars).
Utilizing reciprocal anchorage (e.g., using a midline palatal screw to balance forces).
What is the function of the baseplate, and name two types used in a URA.
The baseplate provides structural support and maintains the overall appliance shape.
Flat Anterior Bite-Plane (FABP) – Used to reduce overbite by preventing incisor contact.
Posterior Bite-Plane (PBP) – Used in crossbite correction to create space for tooth movement.
How does a URA reduce overjet, and what active component is used?
Overjet is reduced by retracting upper incisors using a Roberts Retractor (0.5mm HSSW + 0.5mm I.D tubing). A Flat Anterior Bite-Plane (FABP) is often included to aid overbite reduction.
What component is used to correct an anterior crossbite, and how does it work?
A Z-Spring (0.5mm HSSW) is used to apply a light force on the lingually displaced tooth (e.g., 12) to move it labially. A Posterior Bite-Plane is often included to disocclude the bite.
How is a URA used to expand the upper arch?
A midline palatal screw is incorporated into the appliance. When activated, it applies lateral forces to the maxillary arch, gradually widening it. Reciprocal anchorage helps balance the forces.
