Peter Ngan, D.M.D., Cert Orth, D. Ortho.
Professor and Chair
West Virginia University School of Dentistry
Department of Orthodontics

Christopher Ciambotti D.M.D., M.S.
Private practice
Tokyo, Japan

The incidence of posterior crossbites in American Caucasian children is approximately 7%.¹ Posterior crossbites due to a constricted maxilla in young patients are often treated by expansion of the maxilla. This expansion is accomplished by a combination of skeletal (orthopedic) expansion and dental (orthodontic) expansion. Skeletal expansion involves separation of the midpalatal suture while dental expansion results in buccal tipping of the maxillary posterior teeth. The proportion of skeletal and dental movement is dependent on the rate of expansion and the age of the patient during treatment.^2-3 The goal of palatal expansion is to maximize the skeletal movement and to minimize the dental movement, while allowing for physiological adjustment of the suture during separation.⁴

Rapid palatal expansion (RPE) produces large forces at the sutural site over a short period of time.^5,6 These heavy forces maximize skeletal separation of midpalatal suture by overwhelming the suture before any dental movement or physiological sutural adjustment can occur. However, traumatic separation of the midpalatal suture may induce patient discomfort. RPE appliance also requires patient or parent cooperation in appliance activation and labor-intensive laboratory procedures in fabrication of the appliance.

The slow expansion appliances allow for more physiologic adjustment to sutural separation. This in turn, produces greater stability and less relapse potential.⁷ Arndt,⁸ in 1993, developed a tandem-loop nickel titanium (NiTi), temperature-activated palatal expander with the ability to produce light, continuous pressure on the midpalatal suture. This appliance is also capable of correcting molar rotation and requires little patient cooperation or laboratory work.

The NiTi expansion appliance was a tandem-loop, temperature-activated expansion appliance as previously described by Arndt (GAC International, Central Islip, New York). The appliance consisted of two tandem, temperature sensitive, 0.035 inch diameter NiTi transpalatal loops which were connected bilaterally to the lingual sheaths of the maxillary molar bands. Anteriorly, an 0.032 inch diameter stainless steel wire formed a helical loop fingerspring designed for lateral expansion in the canine and premolar region (Figure 1). The appliance was manufactured in eight sizes in 3mm increments (Figure 2). The size was chosen based on measuring the intermolar width on the pretreatment study casts from the maxillary molar lingual groove at the gingiva to the opposite lingual groove and adding 3-4mm to the measurement (Figure 3). The NiTi transpalatal loops has a transition temperature of 94^oF. The martensitic transformation and superelastic properties of the NiTi wires helped the insertion of the expander into the lingual sheaths of prefitted maxillary molar bands. Expansion occurs after insertion when the appliance was warmed up to body temperature and the NiTi loops return to its original shape. Over expansion was built into the treatment to anticipate relapse (approximately 30%) due to uprighting of the maxillary molars after removal of appliance.

4. After the initial fitting of the appliance, both the maxillary molar bands and the expansion appliance are removed from the patient's mouth. A ligature wire is then tied from the helical loop of the appliance to the distal extension of the lingual sheath to secure the appliance with the molar bands prior to cementation (Figure 5).

Figure 5
A ligature wire is tied from the helical loop of the appliance to the lingual sheath of the molar bands to secure the appliance prior to cementation.

5. It is recommended that the inside of the maxillary molar bands be sandblasted to increase band retention.

6. Maxillary molars are pumiced, isolated with cotton roll to keep dry.

7. The appliance together with molar bands are cemented using the glass ionomer cements.

8. Just before placing the appliance, spray the NiTi expansion loops with the refrigerant.

9. Check the patient within 2-3 days for comfort in wearing the appliance. Patients with resting tongue posture that pushes the tongue against the roof of the mouth may have indenting mark on the tongue. For these patients, orthodontic rope wax may be used during this adjusting period. Pain medication is rarely needed in young patients. If necessary, children’s Tylenol can be prescribed as needed during the first 2-3 days.

10. Patients are checked every 6 weeks for the amount of expansion. An occlusal radiograph can be taken to check for median palatal sutural separation. If additional expansion is necessary, replace the expansion appliance that is one size larger. Expansion is usually considered adequate once the occlusal aspect of the maxillary lingual cusp of either the permanent first molar or primary second molar contacts the occlusal aspect of the mandibular facial cusp of either the permanent first molar or primary second molar. The appliance is then left in place for approximately 3 months for bone apposition in the median suture and uprighting of the maxillary molars.

11. The appliance can be converted to a fixed retainer by removing the anterior NiTi loop or replace with a removable Hawley retainer for retention.

A study was performed at the West Virginia University, Department of Orthodontics to evaluate the difference in maxillary dental and skeletal changes between a tandem-loop NiTi palatal expansion appliance and a rapid palatal expansion (RPE) appliance.

The prospective study consisted of 12 patients treated consecutively with RPE appliance and 13 patients treated with tandem loop NiTi expansion appliance. The average age of the patients was 11.1 years in the RPE group and 9.4 years in the NiTi expansion group. All patients had either a unilateral or bilateral posterior crossbite at the start of the treatment. The average treatment time in the RPE group was 127 days and 153 days in the NiTi group. Study casts were taken before treatment and after treatment for analyzing the difference in changes between the two appliances in intermolar width (total expansion), palatal width (sutural or skeletal expansion), maxillary alveolar tipping, maxillary molar tipping, maxillary molar rotation, and palatal depth.

Table 1 compares the changes between the RPE and the NiTi expansion groups. Both the NiTi expansion and RPE groups produced significant increases in maxillary intermolar width of 6.26 mm and 4.76 mm, respectively, with the NiTi expansion group producing on average 1.5 mm more than the RPE group. Both the NiTi expansion and RPE groups produced significant increases in palatal width of 0.99 mm and 1.41 mm, respectively, with the RPE group producing 0.42 mm more than the NiTi expansion group. The ratio of skeletal to total expansion was found to be greater in the RPE group (0.28) than in the NiTi expansion group (0.16).

Table 1. Comparison of Changes between the NiTi Expansion Group and the REP Group

Both the NiTi expansion and the RPE group produced significant increases in alveolar tipping (6.61 degrees and 5.08 degrees, respectively) and molar tipping (11.69 degrees and 6.08 degrees, respectively) with the NiTi expansion group producing twice as much tipping of the molars than the RPE group. A difference between the groups was also found in the ability to rotate molars during expansion. The change in molar rotation in the NiTi expansion and RPE groups was 26.61 degrees and 1.58 degrees, respectively. Both the NiTi expansion and RPE groups demonstrated no significant changes in palatal depth (-0.04 mm and -0.07 mm, espectively).

These results demonstrate that both the NiTi and RPE expansion appliances are clinically capable of expanding the maxilla and correcting posterior crossbites. Median sutural separation can be obtained in 85% of the cases treated by NiTi expansion appliances and 100% with RPE appliances. More skeletal expansion can be expected using RPE appliance whereas more dental tipping of the molars are expected when using the NiTi expansion appliance. The NiTi expansion appliances have the ability to correct mesiolingually rotated molars. The RPE appliance is a rigid appliance and is not capable of producing molar rotations.

A 5-year-old female patient in the primary dentition presenting with a unilateral right posterior crossbite and a mandibular shift to the right on closure. Clinically, she also presented with lingually inclined maxillary primary incisors and an anterior crossbite on closure (Figure 6). Molar bands were fitted on the maxillary second primary molars. A tandem-loop NiTi expansion appliance (size 26) was used to correct the posterior crossbite (Figure 7). An occlusal radiograph was taken after 2 weeks of expansion. A median sutural separation of 2-3 mm was noted when compared with the pre-treatment occlusal radiograph (Figure 8). After 120 days of treatment, the posterior crossbite was corrected (Figure 9). The appliance was left in place for 3 months as a retainer. A removable Hawley with anterior fingersprings was placed to correct the anterior crossbite.

Increases in arch width with slow expansion appliances such as a quadhelix and Porter arch type of expansion appliance are thought to result from buccal tipping of the maxillary molars. By contrast with RPE appliance, only 400 to 600 g of force is generated, which may not be sufficient to separate the median palatal sutures.^3,9 However, clinical studies with slow expansion appliances in young patients with primary or early mixed dentition show that skeletal contribution to maxillary expansion ranges from 16% to 64%.^10,11 In the West Virginia University Study, radiographic analysis of occlusal films taken two weeks after expansion with tandem-loop NiTi expansion appliance showed sutural separation in 85% of the cases. These results suggest that NiTi expansion appliances are effective for transverse expansion in young patients with primary or early mixed dentition.

Another group of patients that can be benefited from this type of appliance is the cleft lip and palate patients.¹² Early surgical soft tissue repair of the palate often creates constriction of the maxillary arch and contributes to posterior crossbite. Maxillary expansion is needed around mixed dentition period to approximate the anterior and posterior alveolar segments in preparation for the alveolar bone graft. Due to the presence of an alveolar and palatal cleft, low level of force is actually desirable for maxillary expansion so as not to tear the repaired soft palate.

An advantage of the tandem-loop NiTi expansion appliance is the ability to rotate maxillary molars prior to expansion. In most of the patients with Class II division 1 malocclusions, the shape of the maxillary arch is tapered with mesiolingually rotated maxillary permanent first molars. The NiTi expansion appliance is capable of rotating the maxillary molars on an average of 26 degrees. The rotation of the maxillary molars help in the correction of the Class II molar relationship.

Finally, the tandem-loop NiTi expansion appliances do not require laboratory fabrication. The prefabricated appliances eliminate the necessity to take another maxillary impression and save chair time.

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