A Comparison of the Effects of Rapid Maxillary Expansion and Fan-Type Rapid Maxillary Expansion on Dentofacial Structures

Rapid maxillary expansion (RME) is accomplished by applying a laterally directed force against the teeth or palatal mucosa, or both, resulting in a widening of the midpalatal suture.1 The RME appliance has been in the orthodontic literature since 1860 when Angell2 described its use in treating maxillary deficiency. Since then, numerous researchers have tried and discarded this method.

The RME expander as described by Haas3 is a tissue-borne fixed split acrylic maxillary expansion appliance. Because the appliance commonly produces orthopedic forces in the range of 3 to 10 pounds,4 the expansion was deemed to be skeletal and, therefore, more stable.3 

The Hyrax or Biederman RME appliance is a commonly used type of RME appliance.5 It is tooth borne and consists of a screw with heavy wire extensions that are soldered to the palatal aspects of the bands on the first molars and premolars.

Isaacson's Minne expander appliance is a special spring-loaded appliance adapted to the first permanent molar bands. It could be reduced in length to adapt narrow maxilla by shortening the spring, tube, and rod.6 

Derichsweiler7 claimed an increase in nasal width, lowering of the palatal vault, and straightening of the nasal septum due to the RME allowing many mouth breathers to adapt to the use of the nasal passages for respiration. The maxilla comprises the external walls of the nasal cavity laterally, and expansion results in an increase in the internasal capacity.

During expansion, bending of the alveolar structures and buccal tipping of the posterior maxillary teeth lead to posterior rotation of the mandible, open bite, and an increased vertical face dimension.3,8–14 

In orthodontic practice, there are often cases in which narrowing of the upper arch occurs only in the anterior region. Many kinds of appliances have been used to try to gain more expansion in the intercanine area. However, all these appliances were removable and only expand the maxilla dentally. In 1996, Schellino et al 15 designed a spider screw named “Ragno,” which works asymmetrically and allows “fan opening.” The development of a rapid-expansion appliance, which only affects the anterior region of the maxilla, certainly represents a significant improvement in conventional RME appliances. It avoids undesired expansion of the maxilla in the region of the upper first and second premolars, which creates an advantage in the future treatment of the case.

Levrini and Filippi16 used a Ragno appliance to expand the maxilla in a study involving a six-year-old male with bilateral cleft lip and palate that required RME only at the anterior region. Posttreatment plaster models revealed that the intercanine width increased more than intermolar width, which was different from previous studies.

Sadeddin17 evaluated the effect of a fan-type RME on anteriorly constricted cases. He found significantly greater expansion in the intercanine width than in the intermolar width, increase in upper arch parameter, and downward and forward movement of the upper arch in addition to clockwise movement of the mandible.

The aim of this study was to compare the sagittal, transverse, and vertical effects of an acrylic-bonded RME device on maxillary restricted cases with those of a fan-type acrylic-bonded RME device on anterior constricted maxillary cases with normal intermolar width.

The study involved 34 patients, 14 boys and 20 girls, who were treated in the Department of Orthodontics of Cumhuriyet University. Lateral and frontal cephalometric films and upper plaster models were obtained before treatment (T1), after treatment (T2), and after three months of retention (T3). The patients were selected without considering their skeletal properties or sex and were divided into two groups. Group I consisted of 17 patients (7 boys and 10 girls), who had an anteriorly constricted maxillary arch (V shaped), normal intermolar width, and no crossbite in the posterior region (Table 1).

A fan-type acrylic-bonded fully tooth- and tissue-borne RME appliance was used to correct the anterior narrowness (Figure 1). The Ragno screw (Leone, Florence, Italy) was placed in the acrylic plate parallel to the occlusal plane of the upper teeth. The hinge point of the screw was positioned tangent to the distal surfaces of the upper first permanent molars. The anterior arms of the screw were bent mesially, and the posterior arms were bent perpendicular to the screw body to standardize the position of the jackscrew (Figure 2).

Group II consisted of 17 patients (7 boys and 10 girls), who had presented with posterior crossbites (Table 1). An acrylic-bonded fully tooth- and tissue-borne RME appliance (Figure 3) containing a Hyrax screw (Dentaurum, Pforzheim, Germany) was positioned parallel to the second premolars (Figure 4) and used to correct the posterior crossbite.

The acrylic part of the appliance extended over the occlusal and middle third of the vestibular surfaces of all teeth. The thickness of the occlusal acrylic surface was limited to the freeway space and was in contact with all lower teeth. Holes were opened for the escape of excess cement during cementation. The appliances were activated with one-fourth twice per day in both groups. Patients and parents were advised to discontinue expansion if pain or tissue swelling was felt.

In group I, expansion was considered complete when a premolar cusp of overcorrection at the first premolar area was achieved. In group II, expansion was considered complete when the occlusal aspect of the maxillary lingual cusp of upper first molars contacted the occlusal aspect of the facial cusp of the mandibular first molars. At that time the screw was fixed with 0.014-inch ligature wire, and the appliance was left for one week to minimize discomfort during removal. After removal, the appliance used in active treatment was cleaned and reused as a removable retention appliance. After a mean of 90.02 days of retention for group I and 90.47 days for group II, the postretention records were taken, and the patients' routine orthodontic treatment was continued.

The measurements used in the study are shown in Figures 5 through 7. The maxillary arch width was recorded between the right and left canines and permanent first molars on the T1, T2, and T3 models. Intermolar dimensions were measured between the deepest points of central sulci of the upper first molar teeth. The intercanine width was measured between the incisal tips of the canines.

To evaluate the measurement error in landmark identification and location, 20 randomly selected lateral and frontal cephalometric films and18 upper plaster models were remeasured. The same films and casts were measured after a one-month interval, and the method error was calculated according to Dahlberg's formula (√Σd2/2n).19 The d in the formula represents the difference between two measurements, and n represents the number of double measurements.

The results were calculated using the software SPSS for Windows (release 10.0.0, SPSS Inc., Chicago, Ill). The arithmetic mean and standard deviation between the pretreatment and posttreatment (T1 and T2) measurements, the posttreatment and postretention (T2 and T3) measurements, and the pretreatment and postretention (T1 and T3) measurements were all studied using the paired t-test. The time interval between T1 and T2 did not exceed 30 days, which virtually eliminated growth as a variable. The differences between the groups were evaluated using a Student's t-test.

The measurement errors were calculated to vary from 0.253 to 0.857 and were nonsignificant. The pretreatment (T1) and posttreatment (T2) measurements, the posttreatment (T2) and postretention (T3) measurements, and the pretreatment (T1) and postretention (T3) measurements are presented in Tables 2 through 4.

All the patients demonstrated sutural opening, which was confirmed by an occlusal radiograph. A median diastema between the central incisors developed during treatment, and no problems were reported by any of the patients in either group.

Differences between pretreatment and posttreatment are shown in Table 2. Group I showed increases for SNA, ANB, SN-MP, SV ⊥ A, N-ANS, U1P-SN, SN ⊥ U1, and SV ⊥ U1 (P < .001); SN-PP and ANS-Me (P < .01); and UL-E (P < .05). Treatment was associated with a reduction for SNB that was not significant (P < .01).

Group II presented with increases for SNA, ANB, and SN-MP (P < .001); MP-PP, SV ⊥ A, and ANS-Me (P < .01); and N-ANS (P < .05). Treatment was associated with reductions for SNB and SV ⊥ B (P < .05).

When the differences between the groups were compared using Student's t-test (Table 2), group I showed a significantly greater increment for U1P-SN and SN ⊥ U1 (P < .001) and SN-PP and SV ⊥ U1 (P < .01) when compared with group II.

Differences between posttreatment and postretention are shown in Table 3. Group I showed a reduction in SNA, ANB, SN-MP, and SV ⊥ A (P < .001); SN ⊥ U1 and SV ⊥ U1 (P < .01); MP-PP and N-ANS (P < .05); and an increase for SV ⊥ B (P < .05).

Group II showed reductions for ANB and SN-MP (P < .01) and an increase for SV ⊥ B (P < .01).

When the differences between the groups were compared using Student's t-test (Table 3), group I showed a significant reduction for the values SNA and ANB (P < .001) and SN-MP and SV ⊥ A (P < .05) when compared with group II.

Differences between pretreatment and postretention are shown in Table 4. Group I presented with increases in SNA, ANB, SV ⊥ A, U1P-SN, SN ⊥ U1, and SV ⊥ U1 (P < .001) and SN-MP, SN-PP, N-ANS, SV ⊥ L1, and UL-E (P < .01).

Group II presented with increases in SNA, ANB, and SN-MP (P < .001); MP-PP, SV ⊥ A, and ANS-Me (P < .01); and N-ANS (P < .05); and reduction for SNB (P < .05) (Table 4).

The differences between the groups were compared using Student's t-test (Table 4). The mean differences for group I were larger than the means for group II for the values U1P-SN (P < .001); SV ⊥ U1 (P < .01); and SN-PP, ANS-Me, SN-U1, and UL-E (P < .05).

The differences between pretreatment and posttreatment are shown in Table 2. Group I showed increases for both nasal cavity width (+2.41 mm) (P < .001) and maxillary width (+0.41 mm) (P < .01).

Group II showed increases for nasal cavity width (+3.5 mm) and maxillary width (+4.94 mm) (P < .001).

The differences between the groups were compared using Student's t-test (Table 2). Group II showed a significantly greater increase for both nasal cavity width and maxillary width when compared with group I (P < .001).

Differences between posttreatment and postretention are shown in Table 3. Group I showed a reduction for nasal cavity width (−0.47 mm) (P < .01).

Differences between posttreatment and postretention are shown in Table 4. Group I showed an increase for nasal cavity width (+1.94 mm) (P < .001) and maxillary width (+0.29 mm) (P < .05). Group II showed an increase for nasal cavity width (+3.35 mm) and maxillary width (+4.86 mm) (P < .001).

The differences between the groups were compared using Student's t-test (Table 4). Group II showed significantly greater increase for both nasal cavity width and maxillary width when compared with Group I (P < .001).

Differences between pretreatment and posttreatment are shown in Table 2. Group I showed an increase for both upper intercanine width (+8.12 mm) and intermolar width (+2.65 mm) (P < .001). In group II, the posttreatment values also were greater than the pretreatment values for both upper intercanine width (+6.06 mm) and intermolar width (+6.77 mm) (P < .001).

The differences between the groups were compared using Student's t-test (Table 2). Group I presented with significantly greater increments for upper intercanine width (P < .01) and conserved the upper intermolar width (P < .001) when compared with group II.

Differences between posttreatment and postretention are shown in Table 3. Group I showed a decrease for both upper intercanine width (−1.94 mm) and intermolar width (−0.76 mm) (P < .001). No statistically significant differences were found between posttreatment and postretention for the upper intercanine width and intermolar width in group II.

Differences between posttreatment and postretention are shown in Table 4. Group I showed an increase for both intercanine width (+6.18 mm) and intermolar width (+1.88 mm) (P < .001). Group II showed an increase for intercanine width (+5.91 mm) and intermolar width (+6.68 mm) (P < .001).

The differences between the groups were compared using Student's t-test (Table 4). The amount of increase in maxillary width was significantly greater in group I when compared with group II (P < .001).

Acrylic-bonded fully tooth- and tissue-borne expanders provide effective palatal expansion for patients, without the use of orthodontic bands. Although banded expansion appliances are also effective, they are more complicated to fabricate. Occasional failure in delivery may result from inaccurate band placement before the pouring and soldering steps. However, the acrylic-bonded fully tooth- and tissue-borne expander is easily fabricated and does not require orthodontic bands. All acrylic appliances have the potential for palatal mucosa ulceration. We did not report any unusual symptoms such as pain or dizziness in any of the patients. When we removed the appliance, we noticed hyperemia on the palatal mucosa and gums in all patients; however, it disappeared spontaneously in few days soon after appliance removal.

A significant percentage of transverse maxillary deficiency cases have anterior rather than posterior transverse narrowness. In these cases, expansion should be achieved in the intercanine area without expanding the intermolar region, in order not to create posterior buccal crossbites that are hard to correct. For a correct approach to the resolution of such cases, we consider a thorough knowledge of the mechanism of the expansion device to be appropriate.

The fan-type RME, Ragno, generates differential expansion of the transverse diameters of the arch. Studies to date have shown that RME appliances separate the midpalatal suture greatest anteriorly rather than posteriorly. However, the interarch changes did not mimic the sutural separation pattern because the intermolar changes were dimensionally greater than the intercanine changes.3,12,14,20 The fan-type Ragno screw permits a more rational management of expansion by differentiating between the treatments of the anterior and posterior diameters. A fan-type appliance is effective in expanding the anterior rather than the posterior part of the upper arch.15–17 However, does this screw have a skeletal effect or does it create only dental expansion without affecting the facial structures? The principal goal of this study was to determine the effects of the fan-type RME and to compare them with those of the more conventional RME.

Biederman18 explained the angular displacement of maxilla in the horizontal plane in two ways (Figure 8). In the schematic diagram, semicircle represents the halves of the maxilla, and the rectangle represents the bony complex with which it articulates posteriorly. The tangent to the semicircle defines point A at the point of tangency (Figure 8A). He concluded that if the center of rotation be any where in the midline, lateral points B and C must move backward, which entail the resorption of bone (the shaded area). He also noted that point A would also move slightly backward (Figure 8B). However, he found this consequence was unlikely to occur in so short a time as two weeks. His second theory was that the angular displacement must occur with centers of rotation at B and C, which results in the advance of point A (Figure 8C).

We also have three proposed hypotheses of the biomechanics of fan-type rapid expansion in the horizontal plane using a schematic diagram similar to that of Biederman (Figure 9). In the first theory, although the appliance, as designed, tries to alter the force system affecting intermolar region, the posterior part of the midpalatal suture must open slightly. This angular opening may occur with centers of rotation at points B and C. This opening is more V shaped than with the RME. This means that the displacement is mostly rotational and with a minimally parallel response (Figure 9A).

In the second theory, the effect of the mechanism of the appliance inhibits the separation of the whole midpalatal suture. The center of angular opening is anywhere in the midline that is distal to the hinge point (point X). However, the maxilla again rotates on points B and C in addition to point X and consequently point A advances (Figure 9B). The third theory is a resorption theory. The point of opening was moved to the hinge point because of the effect of the mechanism of the fan-type appliance. A contraction must occur in the part of maxilla that is distal to the hinge point, and this would entail the resorption of posterior maxillary bone (the shaded area) (Figure 9C). However, this consequence was not likely to occur in so short a time as three weeks. Although one of the center of rotation was in the midline (point H), the lateral points B and C could not move backward as previously mentioned by Biederman, when point A moved forward in all patients in our study group. That means an angular opening may occur with centers of rotation at points B, C, and H.

While considering the position of the maxilla sagittally, we observed that the SNA and SV ⊥ A distance increased significantly in both groups. Although a significant reduction in SNA and SV ⊥ A distance was noted during retention in group I, a statistically significant increase was found at the end of the retention in both groups. Many investigators have reported that the maxilla moves forward and downward with the use of different RME appliances.3,11,12,14,18,21–24 Our findings show that fan-type RME also forces the maxilla forward more than the RME. This means the fan-type RMEs also have a buttressing effect on the skeletal structures behind the maxilla because of the rotational opening.

Many investigators have reported that an RME results in a downward movement of the maxilla, more at ANS than at PNS, which creates an increase in the palatal plane angle and upper face dimensions.3,11,12,14,21,25–27 In our study, we also noted that the values of N-ANS were increased in both groups. We observed that fan-type RME also moves maxilla downward just as the RME.

The decrease in SNB angle was significant in group II and nonsignificant in group I, reflecting the downward rotation of the mandible, which could be the result of the downward movement of the maxilla. Although the decrease in group II was greater than in group I, there was no statistical difference between the groups at the end of the retention.

The ANB angle increased significantly in both groups because of a combination forward movement of point A and the backward rotation of the mandible. Sarver and Johnston,28 Haas,3,25 and Wertz14 found that SNA and ANB increase after RME treatment, similar to our findings.

When considering the mandibular position vertically, the SN-MP angle increased significantly in both groups but more in group II. This difference between the groups was statistically significant. Also ANS-Me increased in group II; however, there was no change in group I. Our findings indicate that vertical dimension control was better with the fan-type RME than with the RME. Northway and Meade29 evaluated the different expansion modalities and concluded that none of them resulted in appreciable buccal flaring or tipping. Extrusion of the maxillary posterior teeth or a downward displacement of the maxilla has been suggested as a possible mechanism that leads to clockwise mandibular rotation. In anterior maxillary restricted cases, the fan-type RME increases the intercanine width without increasing the intermolar width so the molars would not tip. Thus, the vertical dimension could be better controlled in group I.

In our study, a palatal movement of the maxillary incisors was noted in group II, in agreement with previous reports.14,28,30 However, in group I, the buccal tipping of the maxillary incisors differed from previous studies. Because the angular opening of the midpalatal suture with the fan-type RME is more rotational than with the RME, the anterior teeth were moved laterally and anteriorly with the fan-type RME, whereas they were uprighted with the RME.

Studies to date have shown the RME to be associated with various degrees of increase in the nasal cavity dimension and a decrease in nasal obstruction.11,14,21,24,25,31,32 Derichsweiler7 reported that suture opening allowed many mouth breathers to adapt to the use of the nasal passages for respiration. Group II presented with significantly greater increments for both nasal cavity width and maxillary width when compared with group I.

The difference in maxillary width changes between the two groups was not surprising. The design of the fan-type RME screw limited expansion in the posterior region of the maxilla, so a slight expansion of maxillary width in group I was an expected result. We had expected to observe increments of nasal cavity width increase in group I at least similar to those in group II. However, group II presented with significantly greater increments of nasal cavity width increase. All RME appliances in use today push below the center of resistance as viewed from the frontal plane. We hypothesized that fan-type RME appliance required a lower orthopedic force range than the RME appliance. Therefore, the center of rotation may be as high as the frontomaxillary suture with the RME and somewhere within nasal airway or below in the fan-type RME. We concluded that the fan-type RME appears to induce expansion at a more at dentoalveoler level; however, the RME was associated with significant widening of the maxilla at a skeletal level.

There was no difference between the groups in intercanine width; however, group II presented with significantly greater increments for the final intermolar width at the end of the retention period. Timms,33 Haas,3 Bell and LeCompte,20 Wertz,14 and Adkins et al30 all observed that the ratio of intercanine-intermolar width is nearly 50%. However, results from this study show that the ratio between the intercanine width and intermolar widths was nearly 3:1 in group I. This is a great difference and reproducible as long as a device opens in a V shape, causing more expansion in the anterior part of the maxilla. A fan-type RME can expand the maxillary arch more anteriorly rather than posteriorly. These findings may be of a great benefit in the treatment of certain patients exhibiting anterior maxillary narrowness with normal intermolar width.

The fan-type RME appliance separated the midpalatal suture like the conventional RME appliances. In addition, the action of the appliances showed more results:

• Intermolar width showed a slight expansion with fan-type RME when compared with the conventional RME.

• There were no differences for intercanine width between the groups.

• Opening of the midpalatal suture is more parallel in RME than in fan-type RME when viewed from the coronal and frontal plane.

• The changes achieved in dentofacial structures with a conventional RME were more stable than that achieved with the fan-type RME.

• The maxilla moved downward and forward in both groups.

• Both groups I and II demonstrated significant increase in vertical dimension. However, the fan-type RME avoided expanding and tipping the posterior teeth, which causes increase in vertical facial height.

• The upper incisors were tipped palatally in group II and tipped buccally in group I.

• Nasal cavity width increased more in group II than in group I.