Principles of removable appliancesBy Dr Rop Lecturer: Dr Ngesa

1

Introductiony Two broad categories of appliances: REMOVABLE and

FIXED. y ACTIONy As a general rule, removable appliances tilt (or tip) the teeth,

providing mainly a movement of the crown, possibly followed (and only to a certain extent)- by the apices. y Extrusion y Controlled movement of the roots cannot be easily achieved with removable appliances.

2

Indicationsy Growth modification during mixed dentition stage

(functional appliances) y Limited tooth movement (tipping) y Arch expansion y Retention after comprehensive orthodontic treatment.

3

Advantagesy Removable for socially sensitive occasions y Uncompromised oral hygiene y Short chair time

4

Disadvantagesy Heavily dependent upon patient compliance y Affects speech y Unable to perform complex tooth movements as it is difficult

to produce the two-point contacts on teeth.

5

General principles in selection and construction

6

Retentivey Describes the mechanisms by which an appliance stays in the

mouth. y U/Jacksons clasp y Triangular clasp y Adams claspy Constructed from 0.7mm ss round wire. y The arrow head engage the MB & DB undercuts are connected

to each other by a bridge.

7

Modifications of Adams claspy With: y A single arrowhead y J hook y Helix y Buccal tube y Distal extension y Modified on anterior teeth

8

Active componentsy The force should be applied at right angles to the long axis of y y y y y

the tooth. It should be applied through a surface that is parallel to the long axis of the tooth. Bows Springs Elastics Screws

9

Acrylic base platey It is about 1.8 to 2mm thick to offer adequate strength while

being tolerated by the patient. y Should fit closely around the necks of the teeth that are not to be moved. y In the maxilla it covers the entire palate and ends distal to the 1st molar.

10

Wiresy Properties:y Give low constant forces that are biologically desirable. y Good working range i.e. flexible y Cost y Ductile y Easily joined by soldering and welding to the wires y Corrosion resistant y Biocompatible

11

Stainless steely Austenitic type because it has good corrosion resistance. y Chromium 18% Nickel 8% carbon 0.15% iron 73%. y Also known as 18:8 ss

12

Cobalt chromiumy Good corrosion resistance y Can be welded and soldered y Not as flexible as ss y Cobalt 40% chromium 20% nickel 15% iron 15.8%

13

Nickel titaniumy Fabrication of fixed appliances y It is flexible y Has a high working range y Nickel 54% ti 44% cobalt 2%

14

Beta-titaniumy Has ti 79% molybdenum 11% zirconium 6% y Has good corrosion resistance and is biocompatible

15

Cold cure acrylic(base plate)y Powder:y PMMA, copolymer ethylacrylate, benzoyl peroxide as initiator

y Liquid :MMA y Inhibitor: hydroquinone y Cross linking agent y Activator : NN dimethyl P-toluidine.

16

Removable applince for tooth movement in children

y Active plates for arch expansion y Removable appliances with springs for tooth movement.

17

Active plates for arch expansiony The framework of an active platey a baseplate that serves as a base y in which screws or springs are embedded y and to which clasps are attached

y The active element is almost always a jackscrew. y Advantagesy Amount of movement can be controlled y Base plate remains rigid

18

Active plates for arch expansiony Disadvantagesy Production of heavy force that decays rapidly. y Rapid rectivation has the potential of damaging the teeth. y If the force level is too high, the appliance is likely to be

displaced.

19

Removable appliances with springs for tooth movementy Nearly optimum light continuous forces can be produced. y The springs, however, contact the tooth surface at only one

point. y It is difficult to use them for anything but tipping movements. y Root control is needed for more than 3 to 4 mm of crown movement.

20

Removable appliances with springs for tooth movementy In designing springs for tooth movement, two important

principles must be kept in mind:y The design must ensure adequate springiness and range while

retaining acceptable strength. This usually means using recurved or looped wires for additional length. y The spring must be guided so that its action is exerted only in the appropriate direction.y It is better to use a larger wire for its(considerably) greater

strength, and then gain springiness and range by increasing the length of the spring, than to use a smaller wire initially.

21

Appliance designy Considerationsy What movement is desired y Acceptability of the appliance to the patient y Cost

22

Referencesy S.I. Bhalaji. Orthodontics the art and science y William R. Proffit. Contemporary orthodontics. Fourth

edition.

23

Thank you

24