Mundstock 8/21/07 3:05 PM Page 277 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 follow- ing 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 radio- graphic 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 indi- cated 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 poste- rior than anterior opening and a change of 9.72 degrees in incisor angula- tion 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 277 Mundstock 8/21/07 3:05 PM Page 278 Mundstock et al WORLD JOURNAL OF ORTHODONTICS 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 278 Mundstock 8/21/07 3:05 PM Page 279 VOLUME 8, NUMBER 3, 2007 Mundstock et al 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.