Removable applliances Flashcards
Why should the apex location of teeth be diagnosed prior to using a removable appliance to tip teeth?
To determine if intrusion is necessary. Tiipped teeth are generally over-erupted and hence should be intruded while uprighting.
How to removable appliances move teeth and what does this response depend on?
Moves teeth by tipping.
Response depends on force magnitude, point of force application, tooth anatomy and patients age
What are the types of removable appliances?
1) Passive
- Space maintainners, orthodontic retainers, bite planes
2) Active
- springs, expansion screws
3) Functional
- tooth-borne
- tissue borne
WHat are the design rules when designing a URA?
1) Simplicity
2) COmfort
3) Retention
4) Accuracy of fit
5) Activation
What is the significance of simplicity when designing a URA?
If too complex:
- patient tolerance tends to be poor
- difficult to clean
- tends to break
- loss of anchorage
How can URAs be designed to optimise patient comfort?
1) Smooth polished base of minimum thickness
2) Avoid sharp ends of wire e.g. clasps and springs
What are the components of a URA?
1) Retenntive:
- clasps
- wire work and acrylic base when carefully made (labial bow, use of undercuts)
2) Active:
- protected and self supporting springs
- expansion screws
3) Passive:
- connectors
- acrylic base
- barriers (wires, shields)
- bite planes
What is the importance of the acrylic base with regards to a URA?
1) Supports the active and retentive components
2) Adds retention and stability
3) Can facilitate certain tooth movements i.e. opening the bite, guided eruption
4) Can function as anterior and posterior bite planes
How should the acrylic base be designed for a normal URA?
- > 2-3mm thickness to reduce bulk
- > Butt joint to palatal surfaces of teeth to provide frictional grip to enhance stability and retention, resist edge fracture and avoid damage to gingiva
- > Does not extend to the soft palate and the distal of 6s
What are the functions of bite planes?
Posterior bite plane: assists in crossbite correction
Anterior bite plane: Assissts in buccal segment eruption
Describe the construction of an Adams crib
1) Usually made from 0.7mm round steel wire
2) Arrowheads provide retention by engaging undercuts
3) Bridge. Its length determines the arrowhead engaging thee undercut
4) Tags. These adapt across embrasures to lock into the base
What are the principles of spring design?
1) Determine the range of action. A long range and light fore is preferrable
2) Point of action. This determines thhe direction of movement
3) Simplicity. Avoid moving more than 1or 2 teeth at a time.
4) Avoid overactivation of springs. Ideal movement is about 1mm a month.
5) Guards to protect delicate springs of smaller diameter.
What is the rationale for using coils with finger springs and how can they be incorporated?
Coils increase the wire length and hence deflection for a given force value.
1) Simple cantilever
2) One coil
3) Two coils
Coils should be ccompressed when activated
What kind of tooth movements can be achieved using finger springs?
1) Tooth extrusion
2) Molar uprighting
What are the tooth movements achievable using removable appliannces?
1) Tipping
2) Overbite correction
- anterior bite plane
3) Crossbite correction
- anterior x-bites: removable appliance with an activated palatal spring or screw to attempt to create a positive overbite on the corrected teeth
- post. x-bites: Midline expansion screw or spring to expand maxillary arch. Good for posterior crossbites in mixed dentition of dental origin.
4) Extrusion
- whip spring or elastic from a removable appliance to a fixed attachment on the tooth
5) Instrusion
- elasic run underneath a bracket via a removable appliance
6) Can be used in conjuction with headgear to produce distal movement of maxilary buccal segments
