Dr.Rebin Ali Fixed Orthodontic Appliance Lec.4

Most orthodontic treatment is carried out using fixed appliances, directly attached to the teeth. Fixed orthodontic appliances are required for accurate tooth positioning. The brackets, archwires and auxiliary components that make up a fixed appliance are responsible for mediating tooth movement and this takes place at the tooth – bracket interface.

Fixed orthodontic appliances include orthodontic devices, which have attachments that are fixed on to the tooth surface, and forces are exerted via these attachments using arch wires and / or other auxiliaries. The appliances cannot and should not be adjusted or removed by the patient.

ADVANTAGES OF FIXED ORTHODONTIC APPLIANCES

1. Fixed appliances can bring about various types tooth movements including bodily movement, rotation, tipping, intrusion, extrusion & root movement.

2. Fixed appliances can be used to most malocclusions. 3. Multiple tooth movements are possible simultaneously. 4. More precise tooth movements & detailing of occlusion is possible using fixed

appliances.

DISADVANTAGES OF FIXED ORTHODONTIC APPLIANCES

1. Oral hygiene requirement Oral hygiene maintenance becomes more difficult. Food debris tend to accumulate around the attachments and their removal becomes difficult.

2. Esthetics Fixed appliances are generally made of metal that might not be esthetically acceptable to the patient. The advent of the lingual technique and tooth-colored brackets (made of ceramic/ composites / fiber glass) has helped overcome this disadvantage to a large extent.

3. Special training for operator Only orthodontists are trained to handle and monitor these appliances. Special training is a must to achieve acceptable results.

4. Increased cost of treatment Fixed orthodontic appliances are costly as compared to removable appliances. The attachments used with these appliances are expensive and hence, the cost of the treatment goes up.

5. Increased chair side time

All adjustments have to be made in the patient's mouth by the operator. This increases the chair side time. .

6. Anchorage control is more difficult as compared to removable appliances.

INDICATIONS OF FIXED APPLIANCES

1. Fixed Appliances are indicated when precise tooth movements are required.2. Correction of mild to moderate skeletal discrepancies3. Intrusion/ Extrusion of teeth4. Correction of rotation 5. Overbite reduction by intrusion of incisors6. Multiple tooth movements required in one arch7. Active closure of spaces: extraction spaces/hypodontia

Fig: Extrusion and intrusion of teeth by fixed orthodontic appliance

Space closure

Fig: Open bite and deep bite correction by fixed orthodontic appliance

CONTRAINDICATIONS TO FIXED ORTHODONTIC APPLIANCES

1. Poorly motivated patient The patient should understand that his/her cooperation will be required throughout treatment. The patient's responsibility is not limited to maintaining good oral hygiene but will also involve wearing elastics and/ or headgear and keeping appointments at regular intervals, etc.

2. Poor dental health A patient who does not maintain oral hygiene routinely, cannot be expected to maintain the stringent oral hygiene procedures required with fixed appliances in place.

3. Malocclusions beyond the scope of fixed orthodontic appliances Malocclusions that are skeletal in nature or otherwise beyond the scope of orthodontics should not be attempted.

COMPONENTS OF FIXED ORTHODONTIC APPLIANCES

The components which form any fixed orthodontic appliance system can be divided into two categories depending upon their ability to generate forces:

1. ACTIVE COMPONENTS

These include components which are capable of generating tooth moving forces. These include:

a. Separators b. Archwires c. Elastics d. Elastomerics e. Springs

A.Separators Separators are used to create spaces in between two adjacent teeth, generally for the purpose of banding them.

B. Archwire Archwires are available of variable dimensions and materials. Archwires are available in the prefabricated mould. They may be of various shapes depending upon the arch form type.

The ideal properties required of an orthodontic archwire will depend upon the stage of treatment and the type of tooth movements being carried out and no archwire material will offer all of these together. For this reason, a number of different archwires are required during a course of orthodontic treatment and these will vary in both the type of metal used and the dimensions.

C. Elastics Elastics can be of latex or non-latex material. Elastics are available in various strengths, which is dependent upon their diameter and thickness. The elastics are chosen according to the purpose of their use.

Use of Elastics:a. Closure of space (Class I elastics).b. To correct open bite (Box elastics).c. Treatment of cross bite (Cross bite elastics).d. Correction of inter arch relationship (Class II elastics, Class III elastics, Diagonal elastics).

1. 2.

D. Elastomerics

These are generally made of synthetic polyeurythane materials. The various forms of elastomerics used are:

Elastic chains More commonly referred to as E-chains. These are mainly used for space closure.These are available in three different strengths based on the distance between the rings as continuous or closed short and long.

Elastic thread Made of special elasticized cotton, it is used to exert forces, which are used to correct derotations, consolidation of anterior spacing.

Elastic ligatures

These are used to secure the archwire in brackets. These can be easily engaged under bracket tie wings. They are available in various attractive colors.

E. Springs Various types of springs are used as auxiliaries to generate tooth moving forces. Springs may be used to open spaces (open coil springs) or to close spaces (closed coil springs).

PASSIVE COMPONENTS

These are those components of the fixed appliances which are not capable of generating tooth moving forces but help in providing attachment for other auxiliaries to the tooth or retaining other active components of the appliances. These include:

A. Bands

B. Brackets

C. Buccal tubes

D. Lingual attachments

E. Ligature wires

Bandsa. Bands are passive components that help in fixing the various attachments into the teeth like buccal tube, lingual bottons, etc (by welding).b. They are available in various sizes to suit different teeth & made of soft stainless steel.c. The outer surface of band material is smooth & glossy. The inner surface is comparatively rough & dull which helps to aid in retentions of the cement.

d. It is either preformed or custom made. Nowadays mostly preformed type is used.

BracketsOrthodontic brackets are fixed to the tooth crown and mediate forces applied by the archwire and auxiliaries on the tooth.Bonding techniques rely on a physical interaction being established between the bracket base and an etched enamel tooth surface. Function: To transmit the force arch wire to teeth.

Figure:Mesh design bracket base toImprove bond strength.

Buccal TubesBuccal tubes are horizontal hollow tubes, round, rectangular or oval in shape, they are generally used on molars and help provide better three dimensional control of these anchor teeth. They can be classified as:a. Classification based on mode of attachment• Weldable-can be welded on-to bands • Bondable-bonded directly to the tooth surface

B. According to the number of tubes• Single

Double used for auxiliary wires or headgear

• Triple three tubes-two rectangular and one large round for headgear or lip bumper.

Lingual AttachmentsThese are accessory attachments other than brackets and tubes which are placed on the lingual aspect of teeth (bonded) or bands (welded). These include:

Ligature Wires

Ligature wires are soft stainless steel wires of 0.008 to 0.010 inch in diameter. These may be used to hold / ligate the archwire in brackets (Fig. 39.44A) or to tie segments of teeth together.

Stages of fixed appliance treatment

Treatment with fixed orthodontic appliances can be separated into a number of phases, each with a list of specific objectives.

1. Levelling and aligning

The first phase in all fixed appliance treatment is to align and level the dentition.

Levelling means the correction of marginal ridge discrepancies as opposed to definitive overbite control. To achieve this, small-diameter flexible nickel titanium or multistranded steel arch wires are used.

The aligning archwires are initially ligated into all the brackets, either fully or partially, unless a tooth is severely crowded and short of space.

2. Overbite control

A number of techniques for facilitating overbite reduction are available and these vary between appliance systems. Edgewise and preadjusted edgewise appliances begin the process of overbite reduction following initial tooth alignment and use continuous rigid archwires, often with a reverse curve of Spee in the lower archwire. The working archwire is usually rectangular and composed of stainless steel.

3. Space closure and overjet correction

4. FinishingWith the introduction of preadjusted systems, the bracket prescription does a lot of the work in achieving the correct in/out position, angulation and torque for each tooth relative to its neighbours within the dental arch. Finishing has become less reliant upon wire bending and more of a reflection of correct bracket positioning. However, even with precise bracket positioning, a period of finishing to achieve an optimal aesthetic and

occlusal result is often required. This usually involves removing the heavy rectangular steel working archwires, and replacing them with lighter wires that allow some occlusal settling.