Before going in detail about the Palate Expansion Appliance, we should know why we need the palate expansion appliance. Some times the patient has the narrow upper arch because of that the teeth are crowded. There is not sufficient space for the teeth and moreover the back teeth does not meet the lower back teeth properly normally the upper back teeth are out side the lower back teeth but when the arch is narrow the upper back teeth are inside that is called as the posterior cross bite. So to correct the posterior cross bite and to adjust the teeth which are crowded because of the narrow arch we use the appliances which are called expansion appliances. They have a screw in that which is opened at regular intervals as directed by the dentist to expand the arch and these appliances can be removable or fixed.
The reliability of removable appliances in producing skeletal expansion is highly questionable. Although it is possible to split the sutures using removable plates, it nevertheless is unpredictable. Treatment during the deciduous or early mixed dentition is considered more favourable in producing appreciable skeletal effects.
A removable type of rapid maxillary expansion device consists of a split acrylic plate with a midline screw. The appliance is retained by using clasps on the posterior teeth. Jack screw is one of the most common removable appliances used for rapid maxillary expansion.
Description of a Typical Expansion Screw:
A typical expansion screw consists of an oblong body divided into two halves. Each half has a threaded inner side that receives one end of a double ended screw. The screw has a central bossing with four holes. These holes receive a key which is used to turn the screw. The turning of the screw by 90 degree (i.e. one turn) brings about a linear movement of 0.18mm. The pattern of threading on either side is of opposite direction. Thus turning the screw withdraws it from both sides simultaneously.
1. Posterior crossbite associated with real or relative maxillary deficiencies. A real maxillary deficiency is associated with an undersized/narrow maxilla.
2. Class III malocclusion of dental or skeletal cause. Improvement is seen in both anterior as well as posterior crossbite.
3. Cleft palate patients with collapsed maxillary arch.
4. In cases requiring face mask therapy, it is used along with face mask to loosen the maxillary sutural attachments so as to facilitate protraction.
5. The medical indications for rapid maxillary expansion include nasal stenosis, poor nasal airway, septal deformities, recurrent ear & nasal infection, allergic rhinitis, etc.
Various authors have advocated different activation schedules to achieve the desired results.
Schedule by Timms
For patients of up to 15 years of age, 90 degree rotation in the morning & evening. In patients over 15 years, timms recommends 45 degree activation 4 times a day.
Schedule by Zimring & Isaacson
In young growing patients, they recommend two turns each day for 4-5 days & later one turn per day till the desired expansion is achieved. In case of non-growing adult patients, they recommend two turns each day for first two days, one turn per day for the next 5-7 days & one turn every alternate day till desired expansion is achieved.
Clinically, the most noticeable feature during rapid maxillary expansion is the appearance of a midline distema. Studies by various authors show that the amount of incisor separation is roughly half the amount of jack screw separation. But the amount of distema should not be taken as a reliable factor in estimating the amount of expansion. Maxillary occlusal radiograph & P.A. cephalogram are more reliable in estimating the amount of maxillary expansion.
1. Single tooth cross bites.
2. In patients who are uncooperative, Rapid maxillary expansion is contraindicated as the appliance requires frequent activation & maintenance of good oral hygiene.
3. Rapid maxillary expansion is not carried out after ossification of the mid-palatal suture unless it is accompanied by adjunctive surgical procedures.
4. Skeletal asymmetry of maxilla & mandible & adult cases with severe antero-posterior skeletal discrepancies.
5. Vertical growers with steep mandibular plane angle are usually a contra-indication.
6. As the posterior teeth are used as anchors to move the bones apart, the procedure is not indicated in a periodontal weak dentition
Failure to retain the expansion results in relapse. Most authors recommend a retention period of not less than 3-6 months. Isaacson recommends the use of the rapid maxillary expansion appliance itself for the purpose of retention. The screw should be immobilized using cold cure acrylic. Alternatively, either a removable or fixed retainer can be used.
Clinical Tips for Expansion Screw
1. Oral hygiene instructions should be given to the patient & reinforced during the procedure.
2. The patient should be trained to use key. The key should be tied to a string & the free end should be secured around the patient’s wrist to avoid accidental swallowing.
3. Maxillary occlusal radiographs should be taken at regular intervals to monitor the expansion.
The possible immediate effects of premature appliance removal include dizziness, pressure at the bridge of nose, pressure under eyes, etc. These symptoms may occur on removal of the appliance for repair or re-cementation. The patients should therefore be kept seated & asked not to stand immediately after appliance removal.
Orthodontic movement of the anchor teeth should be avoided prior to rapid maxillary expansion, as mobile teeth do not offer adequate anchorage for palatal split. Recently moved teeth tend to tip.
Derichsweiler Type Palate Expansion Screw
The first premolars & the first molars are banded. Wire tags are soldered onto the palatal aspect of the bands. These wire tags get inserted into a split palatal acrylic plate incorporating a screw at the centre.
Hass Type Palate Expansion Screw
The first premolar & molar of either side are banded. A thick stainless steel wire of 1.2mm diameter is soldered on the buccal & lingual aspects connecting the premolar & molar bands. The lingual wire is kept longer so as to extend past the bands both anteriorly & posteriorly. These extensions are bent palatially to get embedded in the palatal acrylic. The split palatal acrylic has a midline screw. The plate does not extend over the rugae area.
Isaacson Type Palate Expansion Screw
This is a tooth borne appliance without any acrylic palatal covering. This design makes use of a spring loaded screw called a MINNE expander.
The first premolars & molars are banded. Metal flanges are soldered onto the bands on the buccal & lingual sides. The expander consists of a coil spring having a nut which can compress the spring. This coil spring is made to extend between the lingual metal flanges that have been soldered. The expander is activated by closing the nut so that the spring gets compressed.
Hyrax Type Palate Expansion Screw
This type of appliance makes use of a special type of screw called HYRAX ( Hygienic Rapid Expander ).The screws have heavy gauge wire extensions that are adapted to follow the palatal contour & are soldered to bands on premolars & molars.
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