Rapid Maxillary Expansion with the Hyrax Appliance

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Karina Santos Mundstock, DDS, MS, PhD1 RAPID MAXILLARY EXPANSION WITH

Gustavo Barreto, DDS, MS, THE HYRAX APPLIANCE: AN OCCLUSAL PhD2 RADIOGRAPHIC EVALUATION STUDY Aparecida Fernanda Meloti, DDS3 Aim: To evaluate, via occlusal radiographs, transversal alterations that result from rapid maxillary expansion with the Hyrax appliance. Methods: Milena Andrade Araújo, DDS3 The sample consisted of 14 children of both genders, in mixed dentition, with unilateral or bilateral posterior crossbite. Occlusal radiographs were Ary dos Santos-Pinto, MS, PhD4 taken at the beginning and at the end of maxillary expansion. The following variables were measured: intermolar distance, interincisal distance, Dirceu Barnabé Raveli, MS, incisor interapex distance, interbase distance, interarm distance, and inter- PhD4 incisor inclination. The interapex and interbase distances had their radiographic amplification corrected. Results: A mean opening of 7.65 mm of the expansion screw resulted in an increase of the intermolar distance of 7.40 mm, progressively smaller increases of the interarm distance of the appliance of 6.6 mm, and of the incisor interapex distance of 5.5 mm. The distance between the maxillary incisors increased 1.9 mm, which indicated more posterior than anterior expansion. In addition, some buccal inclination of the molars was found, but the apexes of the incisors opened 1.9 mm less than the intermolar distance. Incisor inclination changed 9.7 degrees as a result of the rapid maxillary expansion therapy. Conclusions: Analyzing the occlusal radiographs, the dental arch showed more posterior than anterior opening and a change of 9.72 degrees in incisor angulation as a result of rapid maxillary expansion. World J Orthod 2007;8: 277–284.

1Clinical Instructor, Department of Orthodontics, Federal University of n 1839, Le Foulon1 described the which can be identified clinically as: (1) Rio Grande do Sul (UFRGS), and maxillary expansion of a 12-year-old unilateral or bilateral posterior crossbite Adjunct Professor, Department of I Orthodontics, Lutheran University of patient, in a period of 5 months, where with normal inclination of the dentoalve- Brazil (ULBRA), Porto Alegre, Rio the molar region expanded 14 mm. olar processes; (2) unilateral or bilateral Grande Do Sul, Brazil. Angell, in 1860,2 reported expansion of crossbite with retrusion of the middle 2Clinical Instructor of Orthodontics, the maxillary suture using a fixed appli- third of the face (Class III tendency); and Brazilian Association of Dentistry in ance; after 2 weeks of treatment, the (3) total crossbite. Sergipe (ABO - Sergipe), Sergipe, Brazil. patient presented a diastema between RME is characterized by a widening of 3Graduate student, Department of the maxillary central incisors that was the midpalatal suture by forcing a lateral Orthodontics, São Paulo State Uni- the clinical sign of the separation of the shift of the 2 horizontal processes of the versity – UNESP, Araraquara, Brazil. maxillary bones. This procedure was maxilla. Such widening is greater in the 4 Associate Professor, Department of popularized by the clinical studies per- anterior than in the posterior segment, Orthodontics, São Paulo State Uni- versity – UNESP, Araraquara, Brazil. formed by Haas. Rapid maxillary expan- forming a V-shaped expansion of the sion (RME) is the treatment of choice to suture in the horizontal plane.5–9 The CORRESPONDENCE correct skeletal maxillary deficiency.3,4 midpalatal suture opening is called the Dr Karina Santos Mundstock According to Haas5 and Silva Filho et al,6 orthopedic effect, in which clinical evi- Rua Ramiro Barcelos, 1056/501 Porto Alegre – RS 90035-002 RME is indicated in the primary and dence is the diastema between the max- Brazil mixed dentition whenever a crossbite is illary central incisors. The radiographic E-mail: [email protected] associated with a skeletal constriction, evidence of this effect can be observed

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on occlusal and posteroanterior (PA) radi- was, on average, more than twice as ographs. In the occlusal radiographs, it is large between the incisors as it was possible to see a triangular radiolucent between the molars. area where the base is turned toward the Most of the studies the authors found anterior region, where the resistance of in the literature used the occlusal radi- the facial structures is weaker.5,8,10–15 ograph to visualize the opening of the In 1968, Timms16 evaluated 19 midpalatal suture but not to perform any patients, 10 to 15 years of age, who measurements. Ciambotti et al18 com- underwent RME. He observed that the pared the effects of a palatal NiTi expan- maxillary and palatine bones were disar- sion appliance and RME in 25 patients in ticulated from each other and inclined mixed or early permanent dentition. laterally, with the largest sutural opening Occlusal radiographs were used to in the anterior region first and later pos- demonstrate suture opening. Both teriorly. However, only cases that required expanders were capable of correcting large amounts of expansion showed a posterior crossbites. They found that the complete opening of the midpalatal best predictors for intermolar changes in suture. Two years later, Wertz8 conducted the RME group were alveolar tipping, a similar study using lateral cephalo- palatal width change, and molar tipping. grams and posteroanterior and occlusal On the other hand, few authors used radiographs to evaluate the effects of the occlusal radiographs to study the RME. In the cephalograms, he found a effects of RME. Inoue et al14 indicated downward and forward maxillary move- the use of occlusal radiographs in all ment, an opening of the mandibular stages of RME to analyze the changes of plane angle, and an increase in the ANB the midpalatal suture. Initially, the angle. Posteroanterior radiographs occlusal radiograph shows a defined and showed opening of the maxillary halves uniform radiolucid line to the edge of the with the fulcrum at the maxillofrontal bone surfaces of both maxillary halves. suture, inclination and extrusion of the After RME, this image is more ample and maxillary teeth, and increase in the nasal frequently in a “V” shape (anteroposterior cavity and in the dental arch. In addition, direction). As soon as bone neoformation in the occlusal radiographs the mid- and mineralization starts, the suture has palatal suture opening was larger in the an increased radiopacity; after the reten- anterior region and decreased progres- tion period, a well-defined radiolucent sively to the posterior region. line is not normally seen, which is similar In a literature review about RME, to a pre-expansion image of the mid- Bishara and Staley17 concluded that the palatal suture. Revelo and Fishman19 maxillary splitting compresses the peri- used occlusal radiographs and hand-wrist odontal ligament and the alveolar radiographs to correlate the stages of processes, tips the anchor teeth, and ossification of the midpalatal suture with gradually opens the midpalatal suture. skeletal maturation indicators (Fishman’s From an occlusal view, the palatine standards). They concluded that the pos- processes of the maxilla separated in a terior part of the midpalatal suture corre- nonparallel manner, but in a wedge lates to Fishman’s stages of skeletal mat- shape in 75% to 80% of the cases.14 uration and recommended that more From a frontal view, the maxillary suture force should be applied in the posterior opened in a nonparallel manner and the part of the suture with the expander separation was pyramidal in shape, with because it ossifies before the rest of the base of the pyramid located at the the suture. Horst and Brucker20 studied oral side of the maxillary bone. the relationship between the opening of Krebs15 performed a study in which he the midpalatal suture and the opening of used implants to evaluate the effects of the expansion screw using occlusal radio- RME. Twenty of the 23 patients in the graphs. They found that older patients sample had an amount of sutural open- had a large difference between the ing equal to or less than half the amount amount of sutural opening and the of dental expansion. The sutural opening amount of screw opening, which confirms

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that RME is affected by patient age. MATERIAL AND METHODS Another study performed by David et al21 used a sample of 17 patients, ranging in A sample of cases was selected from the age from 7 to 22.8 years, in which they records of the Orthodontic Department of evaluated and quantified the midpalatal the State University of São Paulo–UNESP suture using occlusal radiographs taken Araraquara. This sample had subjects before and after RME. They found a sig- with unilateral or bilateral posterior cross- nificant opening of the suture in the max- bite, included both genders, and had an illary central incisor area. A diastema age range from 7 years 7 months to 10 between the maxillary central incisors years 1 month. occurred in 69.8% of the sample. In addi- Complete orthodontic records were tion, it was found that a distance of 3 mm taken from the sample of 14 patients. from the screw of the RME appliance to The posterior crossbite was treated using the posterior of the midpalatal suture Hyrax expanders that were activated 2 increased in 69.38% of the cases, and in turns (one-quarter turn each) per day (0.5 35.97%, a distance of 10 mm from bone mm) for about 3 weeks. The expansion crest to posterior of the midpalatal suture was finished when transversal overex- was also increased. pansion was obtained. The expander was In addition, some animal studies were then stabilized with a ligature wire tied in done to evaluate the effects of RME. Vardi- the expansion screw. mon et al22 studied the closure mineraliza- The Hyrax appliance was left in place tion pattern of the midpalatal suture after for retention, resulting in a total treat- RME treatment. This study used 12 cats, ment period of 4 to 9 months (mean, and the measurements were performed 5.43). Routine occlusal radiographs were on magnified occlusal radiographs. They taken, using the maxillary occlusal plane compared the anterior and posterior parallel to the floor and the x-ray cone suture width, which related the suture positioned at a 60-degree angle to the region anterior to the expansion screw. film and parallel to the patient’s facial The results revealed that the typical “V” midline. The occlusal radiographs were expansion pattern was not maintained in obtained at the beginning and at the end the anterior region, but appeared in the of this period. To evaluate the changes in region obscured by the RME appliance. the midpalatal suture from before RME to Furthermore, they concluded that the after RME, the authors studied the anterior suture region requires longer occlusal radiographs. retention than the posterior suture region. The occlusal radiographs were Murray and Cleall23 conducted a study in scanned using an Agfa scanner (Snap- monkeys in which they evaluated the bone scan 1236; Agfa, Mortsel, Belgium) and and connective tissue response of the data were obtained through a personal- palatal sutures after short periods of RME. ized analysis using the software Radiocef They used occlusal radiographs to check Studio 1.0 version 4.0 (Radiocef, Minas the relative degree of bone mineralization Gerais, Brazil). The following variables of the midpalatal suture, followed by a his- were measured on the occlusal radio- tological exam. They concluded that the graphs: intermolar distance (IMD), dis- actual opening of the suture took place tance between the maxillary first molars, between the 4th and 7th day of expan- measured in occlusobuccal surface of sion, that more dental tipping occurred the molars; interincisal distance (IID), during the initial stages of expansion, and distance between the incisal edge of the that bodily movement occurred by the maxillary incisors and measured at the 14th day of RME. mesioincisal angle of the central The objective of this study was to eval- incisors; interapex distance (IAD), dis- uate, using occlusal radiographs, the tance between the apices of the maxil- maxillary transversal alterations that lary incisors and measured at the apex result from RME performed with the of the central incisors; interbase dis- Hyrax appliance. tance (IBD), considered the opening of the Hyrax screw of the expander (this

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Fig 1 Occlusal radiographs before and after rapid maxillary expansion.

Fig 2 Points used to perform the measurements on the occlusal radiographs.

was the measurement of the extreme RESULTS central medium base of the appliance screw); and interarm distance (IARD), dis- The results are shown in Tables 1 tance between the anterior arms of the through 4, which contain the mean, stan- appliance, measured at the extreme dard deviation, and minimum and maxi- anterior extension of the appliance. In mum values of all measurements per- addition, the interincisor angulation was formed on the occlusal radiographs. All measured as the angle formed by the measurements taken were found to be mesioincisal points of the incisal edges statistically significant. A mean opening of the central incisors and apices of the of 7.65 mm of the expander was found, central incisors (Figs 1 and 2). resulting in an almost equivalent The measurements of IAD and IBD increase of the intermolar distance (7.40 had their radiographic amplification cor- mm). The other analyzed variables had rected, using the real size of the base of progressively smaller increases, such as: the appliance (Hyrax screw) as a refer- IARD, increased 6.6 mm; IAD, increased ence and then compared to the size 5.5 mm; and IID, increased 1.9 mm. In obtained in the occlusal radiograph. The addition, the measured interincisal angle rest of the measurements did not have was 9.72 degrees, which indicated that to be corrected due to the proximity of the incisor crowns converged as a result the reference structures to the radio- of RME (Fig 3). When the authors com- graphic film. pared the increase of the IMD (7.4 mm) to The measurements were digitized in the IID (5.5 mm), a difference of 1.9 mm the Excel program, and statistical analy- was found, which may be a result of more sis was performed using SPSS program posterior than anterior expansion. It is version 10.1. important, however, to remember that in Descriptive statistics were used to the molar region, there was molar inclina- evaluate the results. Mean and standard tion in addition to the translation move- deviation were calculated for all mea- ment of the molars. When the movement surements. Confidence interval, Student of the incisors as a consequence of the t test, and the level of significance were maxillary expansion was analyzed, the set at P < .05. authors realized that the IAD was 5.5 mm

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Table 1 Descriptive analysis for the variables at the start of treatment Age IBD IMD IARD IAD IID IIA (mo) (mm) (mm) (mm) (mm) (mm) (degrees) Mean 105.4 2.53 55.07 23.16 6.65 2.46 11.77 SD 9.2 0.56 3.48 2.01 1.39 0.96 5.78 95% Confidence interval LB 100.1 2.20 53.06 21.99 5.84 1.91 8.43 UB 110.8 2.85 57.08 24.32 7.45 3.02 15.11 Minimum 93.0 1.92 49.27 20.42 4.05 1.40 1.04 Maximum 121.0 3.64 61.98 28.02 8.77 4.52 21.89

IBD, interbase distance; IMD, intermolar distance; IARD, interarm distance; IAD, interapex distance; IID, interincisal distance; IIA, interincisal angle.

Table 2 Descriptive analysis for the variables obtained at the end of treatment Age IBD IMD IARD IAD IID IIA (mo) (mm) (mm) (mm) (mm) (mm) (degrees) Mean 110.9 10.18 62.47 29.73 12.12 4.35 21.49 SD 9.8 1.28 3.04 3.03 2.29 1.53 9.07 95% Confidence interval LB 105.2 9.44 60.72 27.98 10.80 3.47 16.26 UB 116.5 10.91 64.23 31.48 13.44 5.23 26.73 Minimum 97.0 8.39 59.07 24.50 8.41 1.35 8.62 Maximum 129.0 13.11 68.49 35.59 15.07 6.77 39.78

IBD, interbase distance; IMD, intermolar distance; IARD, interarm distance; IAD, interapex distance; IID, interincisal distance; IIA, interincisal angle.

Table 3 Descriptive analysis for the variables as a result of the treatment Age IBD IMD IARD IAD IID IIA (mo) (mm) (mm) (mm) (mm) (mm) (degrees) Mean 5.4 7.65 7.40 6.57 5.48 1.89 –9.72 SD 1.3 1.48 2.07 2.21 2.08 1.40 8.78 95% Confidence interval LB 4.7 6.79 6.21 5.30 4.28 1.08 –14.78 UB 6.2 8.51 8.60 7.85 6.68 2.69 –4.67 Minimum 4.0 4.85 2.34 2.36 2.13 -0.16 –30.93 Maximum 9.0 11.18 10.34 10.85 9.05 4.40 –0.56

IBD, interbase distance; IMD, intermolar distance; IARD, interarm distance; IAD, interapex distance; IID, interincisal distance; IIA, interincisal angle.

Table 4 Student t test to verify the significance of treatment effect Variable tP IBD 19.306s .000 IMD 13.364s .000 IARD 11.120s .000 IAD 9.851s .000 IID 5.061s .000 IIA -4.155s .001

Test value = 0. S, significant; IBD, interbase distance; IMD, intermolar distance; IARD, interarm distance; IAD, interapex distance; IID, interincisal distance; IIA, interincisal angle.

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70 10

Initital phase Final phase 8 60

6 50

4 40

30 0

20 –2

10 –4

–6 IBDC MD IARD ID IADC IIA

Fig 3 (above) Mean results observed at the beginning and –8 at the end of expansion.

Fig 4 (right) Mean values of the changes induced by treat- –10 ment. IBDC MD IARD ID IADC IIA

and the IID increased only 1.9 mm. This DISCUSSION result was likely related to the fact that the maxillary central incisor crowns Most of the literature used the occlusal tipped toward each other by 9.76 degrees radiographs to evaluate the opening of instead of closing the space in a bodily the midpalatal suture as a result of movement during the retention period RME.6,8,16–18,24 Ciambotti18 used maxil- (Fig 4). The mean initial diastema lary occlusal radiographs to evaluate the between the maxillary central incisors evidence of sutural opening, which was was 2.5 mm; after the retention period considered a radiolucent widening of the the measurement was 4.3 mm, which suture. The same procedure was used in means that the midline diastema the studies performed by Silva et al.6,24 increased to about twice the initial mea- The present authors found a mean surement. During the retention period, opening of the expansion screw of 7.65 the authors found an increase in the max- mm, and an equivalent increase in the illary midline diastema in 78.6% of the IMD (7.4 mm) and progressively smaller sample; in 35.7%, the diastema was increases in the IARD (6.6 mm), IAD (5.5 more than 2 mm (from 2.24 to 4.46 mm). mm), and IID (1.9 mm). The interincisal

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angulation increased 9.7 degrees, which sample and here an increase in the means that the angulation between the diastema was found in 78.6% of the sam- long axes of the maxillary central incisors ple. The present sample was younger increased by 9.7 degrees. This result may than the sample analyzed by David et al, be a consequence of the opening of the and this fact may explain the difference midpalatal suture, nonparallel movement in results. of the maxillary incisors, and approxima- The results of this investigation tion of the dental crowns due to the showed a greater posterior than anterior action of the periodontal fibers.23 The widening of the maxillary dental arch, buccal inclination changes found agreed indicating that a posterior alveolar incli- with the literature, ie, alveolar process nation has occurred. This effect counter- tipping during expansion. This tipping acts the skeletal opening of the mid- results from the initial bending of the palatal suture, which was greater in the alveolus, followed by a triangular separa- anterior than in the posterior (known as tion of the maxilla into 2 halves, with the the “V opening”). These findings give the apex located near the frontomaxillary impression that the effect of RME is suture and the base located near the larger in the posterior region of the den- alveolar region.6,8,11,15,24 tal arch, confirmed when the authors per- Krebs15 found that the amount of formed a clinical examination of the sutural opening was equal to or less than patient after RME therapy. half the amount of dental arch expan- The posterior alveolar inclination, sion, and also that this opening was, on along with the molar widening, repre- average, more than twice as large sents a possible instability area that between the molars, which means that should be considered in the treatment the posterior region expands more than planning and retention protocol of RME the anterior region of the palate. This therapy. study agreed with the present results; however, Krebs’s study was performed on casts. CONCLUSIONS The present findings pointed in an opposite direction, to the “V” opening of 1. The dental arch showed more poste- the midpalatal suture reported in the lit- rior expansion than anterior opening. erature by other authors. This finding 2. In addition to the translation expan- shows that the posterior opening of the sion, some degree of buccal inclina- dental arch was larger than the anterior tion was found, because the apices of opening, which can be explained by the the incisors opened 1.9 mm less than larger degree of posterior alveolar inclina- the molars. tion and a smaller anterior dental effect, 3. Incisor crowns converged in relation to as well as more orthopedic effect occur- their apices by 9.7 degrees (IID, 1.9 ring in the anterior region than in the mm; IAD, 5.5 mm) at the end of reten- posterior region of the midpalatal tion period. suture.3,17,18,24 Vardimon et al22 studied the occlusal radiographs taken from cats, measuring the closure mineralization pat- REFERENCES tern of the midpalatal suture, and found that the typical “V” expansion pattern 1. Le Foulon, 1839. In: Rinderer L. The Effects of was not maintained in the anterior region Expansion of Palatal Suture. Congress of Euro- 21 pean Orthodontic Society, 41. Transactions of the maxilla. Furthermore, David et al 1966:365. used occlusal radiographs to measure 2. Angell EC. Treatment of irregularities of the per- the results of RME therapy and found manent adult teeth. Dent Cosmos 1860;1: results that were similar to the present 540–544. findings, including the measurement of 3. Bell RA. A review of maxillary expansion in relation to rate of expansion and patient’s age. Am the midline diastema as a consequence J Orthod 1982;81:32–37. of RME. David et al21 found an opening of the midline diastema in 69.8% of their

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