CATEGORY 52 AUSTRALASIAN DENTIST LINICAL On the Mandible u The mandible rotates downward and backwards due to the downward movement of the maxillary posterior teeth in a buccal direction. u The palatal cusps of the maxillary posterior teeth, which should ideally occlude in the occlusal grove of the mandibular posterior teeth, tend to occlude with the lingual slopes of the buccal cusps of these teeth, thereby giving the effect of opening the bite. On the Nasal Cavity and Adjacent Cranial Bones u The RME tends to increase the intranasal space as the outer walls of the nasal cavity move apart and the palatal shelves flatten out, making the nasal floor broader. u Improvement in the nasal breathing is almost universally accepted. u The parietal as well as the zygomatic bones show signs of some form of realignment at the sutures, especially in younger individuals. 8. Retention following RME Therapy u The objective of retention is to hold the expansion while the forces generated have decayed. u The same fixed RME appliance is used as retainer for first 3months.The hole of the screw is filled with self-cure acrylic to prevent accidental unwinding of the screw. fixed appliance treatment can proceed unhindered. u Selection of the appliance for the transverse correction required and skeletal age also plays an important role in retention. the reduced stress loads within the tissues u Least strain is exerted on anchored teeth. u The appliance is light and comfortable to the patient. u It can be used for sufficient retention after the expansion. u Relapse tendencies are less. u Time required for retention is less. u Less pain and discomfort due to light forces. iii. Disadvantage u Slow expansion produces predominantly tipping rather than bodily expansion of teeth. u Longer treatment duration compared to RME iv. Classification u The slow expansion appliances can be broadly classified as: u Removable and fixed appliances: Stabilised with self-cure acrylic u At the end of active expansion treatment, 80% skeletal and 20% dental expansion is achieved. Therefore when relapse occurs after active treatment, there is more skeletal relapse and dental correction is retained. u Relapse is highest during the first 6 weeks after expansion. u Removable retainers are given from the 4th month and are worn full time for about 9 months after expansion. After 9 months, half time wear is advised. u Alternatively, the expansion can be maintained using a trans-palatal arch (TPA) or any of the other appliances, The TPA has the advantage that the Selection of the appliance is important depending on the skeletal correction needed. i.e., transverse skeletal discrepancy between the mandible and maxilla and the skeletal age, determines the percentage of basal change of the mean jackscrew opening at the levels of the first permanent molar. SLOW MAXILLARY EXPANSION DEVICES Slow expansion was developed by the brainchild of the father of modern dentistry, Pierre Fauchard. Slow expansion involves the use of relatively lesser forces (2 to 4 pounds) over longer periods (2 to 6 months) to achieve the desired results. These appliances are designed primarily to produce dentoalveolar expansion or changes. In young children, slow expansion appliances might produce skeletal expansion with opening of mid-palatal suture. The effect of skeletal versus dental changes purely depends on the age of the patient and the magnitude of force applied. However, it was not until 1978 when Hicks with his cephalometric study used a fitted split acrylic plate to expand the maxillary arch and proved the effectiveness of slow palatal expansion. i. Indications of slow expansion u Correction of unilateral cross bites- Posterior dental crossbite u Correction of ‘V’ shaped arches as in “thumb suckers”. u Cleft palate cases with collapsed maxilla and preparation for bone grafts in cleft cases. u Minimal crowding in the upper arch (1-2 mm), i.e., < 4 mm inminimal space discrepancy cases u Elimination of a displacement u Constricted maxillary arch ii. Advantages u Slow expansion delivers a constant physiologic force until the required expansion is obtained. u Less damage to the teeth. u Produces skeletal effect in young children. u Requires minimal adjustment throughout its use, and allows easy adjustment when necessary. u Maintenance of sutural integrity and REMOVABLE APPLIANCES FOR SLOW EXPANSION Screw Appliances: These screws have a smaller pitch and are activated less frequently as compared to screws used for RME appliances. a. Expansion plate with screw The concept of active plate was introduced by Pierre robin in 1902 Appliance framework The appliance consists of a split acrylic palatal plate which is thoroughly adapted to the contours of the palate with a central expansion screw (jackscrew), retained by stainless steel clasps on the first primary and permanent molars. Expansion plate with screw Activation To expand the plate, the screw is activated one or two notches per week (0.2–0.4 mm).
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