Removable appliances Flashcards
What are removable appliances
Orthodontic devices that are designed to apply force to the teeth by means of a spring, screw or another mechanical component and can be taken out by the patient for cleaning
What are the actions of removable appliances
Active
Passive
What do passive removable appliances do
Maintain the position of the teeth
What do active removable appliances do
Bring about tooth movement via incorporation of active forces within the appliance
What type of movement can be achieved with removable appliances
Tipping movement
Movement of blocks of teeth
What are the indications for removable appliances
- Active treatment of simple malocclusions
- Passively as a space maintainer or retainer post op
List the occlusal discrepancies that can be treated with removable appliances
- Tipping teeth mesially/distally along arch
- Tipping teeth labially/buccal
- Reduction of overbite
- Reduction of overjet
- Expansion of the arch
Instructions for patients for removable appliance prescription
- Wear appliance all day and night
- Remove for contact sports
- Clean teeth and appliance after every meal and at night
- Avoid sticky foods
- Know how to insert and remove
- Return to dentist if it breaks
When to monitor progress of removable appliance
Every 4 weeks for reactivation if active appliance
Advantages of removable appliances
Can be removed for brushing Easy to adjust Passive or active Bite planes can be incorporated Lower risk of iatrogenic damage than fixed appliances
Disadvantages of removable appliances
Issue with compliance Only tilting movement possible - limited to certain indications Good technician required Initially affects speech LRA hard to tolerate due to tongue Palatal inflammation
Ideal properties of a removable appliance
Comfortable and well tolerated Durable under oral function Hygienic Adequate retention Force and anchorage components
What should be included in the laboratory prescription for removable appliances
Active components and the diameters for each component
Retentive factors and their diameters
Layout of the baseplate
Modifications where required e.g. bite planes
List the components of removable appliances
Active components
Retentive components
Anchorage components
Baseplate components
What are the types of active components
Springs
Bows
Screws
Elastics
What is the most commonly used active component
Springs
How much force is required to tip a single rooted tooth
25-50 grams
What is the diameter of palatal and buccal springs? What activation is required
Palatal - 0.5mm with 3mm activation
Buccal - 0.7mm with 1-2mm activation
Describe the action of springs
Point of application is adjusted to give desired movement
The further the spring is from centre of resistance of the tooth, the greater the degree of tilting
Ideal requirements of springs
Continuous force
Correct magnitude
Exert force over full range of tooth movement
List the palatal springs
Finger spreader
Z spring
T spring
Coffin spring
Indications for a finger spreader spring
Movement of teeth in line of the arch e.g. mesial/distal movement of incisors, premolars or canines
Indications for a Z spring
Proclination of incisors over the bite
Indications of T spring
Move premolars buccally over the bite
Indications for a coffin spring
Transverse upper arch expansion
What is the wire diameter for coffin springs
Heavy wire - 1.25mm
What is the buccal spring?
Buccal canine retractor
Indications for buccal canine retractor
Retract buccally placed canines
Relate the flexibility of bows to the action
More flexible = can reduce larger overjets
List the common types of Bows
Labial bow
Roberts retractor
Describe labial bow construction
- 0.7mm wire (less flexible)
- U loops 3-3
- Adjustment via 1mm activation
Indications for labial bow
- Minor OJ reduction
- Align irregular alignment of incirors
- Passive in retainers
Indications for Roberts retractor
- Reduction of large overjet due to flexibility
Construction of Roberts retractor
- 0.5mm with buccal arms sheathed in tubing
- 3mm activation required
What is the disadvantages of screw appliances
Less versatile Bulkier More expensive Requires patient cooperation with turning screw Movement limited by width of PDL
What does the direction of movement depend on with screw appliances
The position of the screw in the appliance
How much tooth movement is achieved by a turn of the key in a screw appliance
0.2mm movement per turn
Describe the type of forces applied by screw appliances
Large intermittent forces
What is movement limited by in screw appliances
Width of the pdl
What happens if pdl width is exceeded in screw appliances
Crushes pdl cells and hinders tooth movement
Indications for use of screw appliance
Procline upper incisors (labial movement of incisors)
Distal movement of molars
Expansion fo upper buccal segments (crossbites)
Buccal movement of an individual tooth or segment
What are the types of retentive components in URA
Adams clasp for posterior retention
Labial bow or southend clasp for anterior retention
What is an adams clasp? And describe its construction
Major retentive component
It is 0.7mm SS wire
Used on 6s mainly and has arrowheads engaging undercuts mesiobuccal and distobuccal
Where is a southend clasp placed?
0.7mm wire on upper 1-1 to utilise interproximal undercut
Where is a labial bow used?
0.7mm wire on upper 2-2
When is additional retention (anterior) required?
When there is active displacement forces e.g. springs
What are the additional retention components
- Anterior retention (adams clasp or southend)
- Adams clasp anterior to the 6 (e.g. on primary molar or premolar)
What is anchorage?
Source of resistance to the forces (and unwanted movement) generated in reaction to the active components of an appliance
What is Newotn’s third law of motion?
Every force produces an equal and opposite reaction to the forces applied
What are the sources of anchorage in an URA?
- Palate
- Teeth in contact with the URA
- Use of EOT
What are the types of anchorage?
Simple - small tooth moved using a big tooth
Compound - tooth is moved by two or more teeth
Reciprocal - two teeth pitted against each other
How can the URA baseplate be modified?
- Anterior bite plane
- Buccal capping (posterior bite plane)
What are anterior bite planes?
- Flat layer of acrylic built up behind upper incisors to form a plane to which they can occlude
What are posterior bite planes?
- Coverage of occlusal surfaces of relevant buccal teeth allowing for disclusion of anterior teeth and eruption of lower incisors
When to use anterior bite planes?
- Used when overbite needs to be reduced by eruption of lower buccal segment
When are posterior bite planes used?
- Where occlusal interferences need to be eliminated to allow tooth movement BUT reduction of overbite is undesirable
In the treatment of which malocclusion would you use posterior capping?
Unilateral anterior crossbite
Describe the malocclusion that is still commonly treated with URA and describe the appliance design
Anterior crossbite in mixed dentition
- Z spring with posterior bite planes
Describe an appliance used to expand the upper arch (with bilateral crossbite)
- Screw appliance with posterior bite planes
Why may an appliance not fit when you try it in?
- Teeth have erupted/moved since impression was taken
- Delay in impression taking
What are the causes of frequent breakage of URAs?
- Poor compliance
- Pt habitually clicks appliance in and out of place
- Eating inappropriate food with appliance in place
What can result in anchorage loss?
- Patient factors - part time wear, breakage of appliance, failure to attend check ups
- Operator factors - poorly designed, over activation of components
How long should active URA treatment last? How often are the recalls?
- 4-6 week recall
- Total treatment time 4-6 months
What happens if URA has not solved the malocclusion within 6 months?
Move on to another option - you should not exceed >6 months
How may anterior teeth can be moved with an URA?
1-2 ONLY
How may you determine lack of compliance with an URA?
- No wear or tear of appliance
- Pt still lisping +/- excess saliva production
- Frequent breakages
- No marks around palatal mucosa
- No movement of tooth/teeth
