Hyrax-type Expander Research Articles

Effect of treatment of transverse maxillary deficiency using rapid palatal expansion on oral health-related quality of life in children: complementary results for a controlled clinical trial.

To evaluate the effect of rapid palatal expansion (RPE) using Haas-type expanders on children's oral health-related quality of life (OHRQOL) and compare said effect with that previously reported for the use of Hyrax-type expanders. Forty participants aged 8-10 years with transverse maxillary deficiency were treated using Haas appliances. OHRQOL was measured using the CPQ8 - 10 before RPE, during RPE (T1), at the end of RPE (T2), and 1 month after appliance removal (T3). Generalized mixed models were fitted to assess the effect of the Haas-type expander compared to previously collected data (a nontreated and a Hyrax-type expander-treated group). RPE with Haas-type appliances had a negative impact on overall OHRQOL at T1 and T2 (P = 0.001), and a positive impact at T3 (P = 0.001). The Haas-type expander had a significantly greater negative impact on OHRQOL than the Hyrax-type appliance during RPE. At T1, overall scores using the Haas-type expander were 1.08 times the scores using the Hyrax-type expander (i.e., 8% increase; 95% CI, 1.01-1.17; P = 0.033). Patients using the Haas appliance had 1.24 times the scores of those using Hyrax-type devices for the oral symptoms domain at T1 (i.e., 24% increase; 95% CI, 1.06-1.46; P = 0.009). Correction of the transverse maxillary deficiency by RPE using the Haas appliance in children 8-10 years improves OHRQOL. The Haas- and Hyrax-type devices temporarily worsen OHRQOL during treatment, however, the negative impact is less with the Hyrax-type expander than with the Haas-type expander, because it causes fewer negative oral symptoms. From a patient-centered perspective, the use of the Hyrax over the Haas appliance may be suggested as it causes less negative oral symptoms during use.

Rapid maxillary expansion for maxillary atresia and mandibular alignment: A mixed dentition case report

Introduction: Posterior crossbite is a common malocclusion in orthodontics. It often accompanies maxillary atresia, leading to unilateral or bilateral posterior crossbite. Rapid maxillary expansion (RME) is an approach to treat atresia, correct transverse discrepancies, and increase the perimeter of the maxillary arch. Objective: To present the case of an 8-year-old patient with maxillary atresia, skeletal Class I, dental Class I, and no space in the maxillary anterior and mandibular regions for the alignment of the incisors. Clinical procedures: RME was performed using a HYRAX type expander. After 20 days of daily activations, there was a change in the morphology of the palate, an increase in the arch perimeter, facilitating the eruption of incisors and canines. Final considerations: RME is an effective and efficient orthopedic treatment, recommended for correcting transverse deviations, normalizing structural and functional problems. As positive side effects, the indirect action on the mandibular molars and canines allowed the alignment of the incisors.

Skeletal and Dentoalveolar Changes in Growing Patients Treated with Rapid Maxillary Expansion Measured in 3D Cone-Beam Computed Tomography.

The skeletal and dental effects of rapid maxillary expansion (RME) have been extensively studied, but high-quality research is still needed to determine the three-dimensional (3D) effects of RME. The aim of this study was to compare skeletal and dentoalveolar parameters through cone-beam computed tomography (CBCT) pre- (T1) and post-treatment (T2) with respect to RME. Twenty growing patients (mean age 10.7 years) were treated with a Hyrax-type expander. A 3D CBCT was performed at T1 and T2, measuring nasal width, maxillary width, palatal height, maxillary arch perimeter, angulation of the upper first molar, and intermolar width. The mean palatal suture opening was 2.85 ± 0.62 mm (p < 0.0001). Nasal width increased 1.28 ± 0.64 mm and maxillary width 2.79 ± 1.48 mm (p < 0.0001). In contrast, palatal height was reduced 0.65 ± 0.64 mm (p < 0.0001). Regarding arch perimeter, the radicular perimeter increased 2.89 ± 1.80 mm, while the coronal perimeter increased 3.42 ± 2.09 mm (p < 0.0001). Molar angulation increased 5.62 ± 3.20° for the right molar and 4.74 ± 2.22° for the left molar (p < 0.0001). Intermolar width increased 5.21 ± 1.55 mm (p < 0.0001). Treatment with Hyrax produced a significant opening in the mean palatal suture. Also, a significant increase in nasal width, maxillary width, arch perimeter, molar angulation, and intermolar width, and a decrease in palatal height, were observed.

Analysis of maxillary arch expansion in growing patients treated with early Class III protocol versus RME.

To evaluate and compare the maxillary arch expansion obtained in growing patients treated with Class III early treatment protocol (the modified SEC III protocol), or rapid maxillary expansion (RME). This retrospective observational study included patients in the mixed dentition with maxillary constriction and/ or dental crowding. The first group consisted of 30 patients (11 males and 19 females, mean age 9.4 ±1.7 years) with dentoskeletal Class III malocclusion treated with the modified SEC III protocol. The second group of 30 patients (14 males and 16 females, mean age 9.3 ±1.5 years) with Class I or II malocclusion was treated with a Hyrax-type expander applied to bands on the first upper molars. For each subject, initial (T0) and post expansion (T1) digital dental casts were collected. The intermolar and intercanine widths, the arch lengths at both cusp and gingival levels, the anteroposterior length and the palatal depth were measured at T0 and T1. At T1 there were statistically significant differences for 3-3 occlusal (OC) (P < 0.009), arch-length OC (P <0.030), anteroposterior arch-length (AP) (P <0.003), Depth (P <0.030) and Ap (P <0.000). No statistically significant T0-T1 changes were found between the modified SEC III and Hyrax groups except for Depth (P <0.011) with a mean difference of 2.3 mm between the two groups. Both bonded and banded expanders, used in the modified SEC III protocol and RME treatment respectively, produced similar changes in the upper arch. The different initial dentoskeletal malocclusions of the two sample groups were not relevant to the post-expansion arch changes.

CBCT Analysis of Dento-Skeletal Changes after Rapid versus Slow Maxillary Expansion on Deciduous Teeth: A Randomized Clinical Trial.

The aim of the present study was to compare skeletal and dental changes after rapid maxillary expansion (RME) and slow maxillary expansion (SME) performed by a Leaf Expander (LE) with upper deciduous teeth as anchorage and using 3D CBCT (Cone Beam Computed Tomography) analysis. Mixed dentition patients were randomly divided in two groups, according to the different expansion used anchored on maxillary primary second molars: the RME group (n = 16) was treated with a Hyrax type expander, whereas the SME group (n = 16) was treated with an LE expander. CBCT scans were performed before (T1) and after treatment (T2) and analyzed with a custom landmarks system. A paired t-test was used for intragroup analysis between T1 and T2, and a Student t-test was used for intergroup analysis; statistical significance was set at 0.05. Both RME and SME groups showed a statistically significant increase in dental and skeletal diameters. Group comparisons between T1 and T2 showed a significant expansion rate in the RME group for upper permanent molars (p = 0.025) but not for deciduous molars (p = 0.790). Moreover, RME showed higher increases for skeletal expansion evaluated at nasal walls (p = 0.041), whereas at pterygoid plates did not show any significant differences compared with the SME group (p = 0.849). A significant transverse expansion could be achieved with the expander anchored on deciduous teeth. RME and SME produced effective both skeletal and dentoalveolar transverse expansion; RME produced more anterior expansion than SME but less control regarding the permanent molar decompensation. SME by LE therefore could be an efficient and helpful alternative in the treatment of transverse maxillary deficiency in growing patients.

A Modified Hyrax-Type Expander Is Effective for Distal Bodily Movement of the Maxillary First Molar

Impaction and eruption disturbance of permanent teeth are frequently encountered in orthodontic practice. The canine teeth play an important role both functionally and esthetically. Eruption disturbance of a maxillary canine, if left untreated, can cause not only disturbed jaw movement and esthetic problems, but also root resorption of adjacent permanent teeth, and thus should be diagnosed and treated appropriately. In this report, we present a case of a patient with eruption disturbance of the maxillary left canine in which the maxillary left second molar was extracted and the maxillary left first molar was distally moved with a Hyrax-type expander (Veltri Monolateral Screw®; Leone, Firenze, Italy) designed to enable the distal movement of a unilateral first molar in order to create eruption space for the maxillary left canine, resulting in smooth distal molar movement and alignment of the left maxillary canine in the dental arch. Furthermore, the maxillary third molar was also aligned to achieve a good occlusal relationship without reducing the number of teeth.

Dental Arch Changes with Two Different Trans-Palatal Arch

Background: Rapid maxillary expansion (RME) is a dentofacial orthopedic treatment often used to treat patients with narrow palate and transverse maxillary growth deficiency. Introduction: This treatment leads to correction of posterior dental crossbites, coordination of the upper and lower arches and gaining arch perimeter in patients with tooth size/arch size discrepancies. To stabilize the results obtained with RME and to limit or avoid the relapse, the use of Transpalatal Arch (TPA) would be recommended. Objectives: The aim of this study is to evaluate short-term maxillary changes in patients treated with RME followed by TPA with and without palatal arms. Materials and Methods: 30 patients, 16 females and 14 males (mean age of 9.7 yrs ranging between 9 and 12), were treated by expansion with palatal Hyrax-type expander. After this period, it was removed and one of the two different types of TPA was used. The two different TPA were a 0.036-inch stainless steel wire with a loop directed mesially in the middle, one maintained the original design (TPA), the second one presented arms extended to canines (TPAa). Dental casts were collected for each patient for each treatment step; before (T0), after expansion (T1) and after TPA or TPAa (T2). To assess differences in dental arches after the two treatment phases, three-dimensional (3D) dental casts were used to make more predictable measurements compared with caliper measurements that presented intra-examiner and inter-examiner measurements errors. Results: In TPAa group, differences between the value at the end of the retention period and at the end of expansion showed no statistical significance. Instead in TPA group, the same measurements suggested a reduction of value in almost all dental transverse diameters. Statistically significant differences in dental measurements were found between TPAa and TPA. Conclusion: Results confirm the hypothesis that TPAa can allow to better maintain dental transverse dimensions.

CBCT Comparison of Dentoskeletal Effects of Haas-Type and Hyrax-Type Expanders Using Deciduous Teeth as Anchorage: A Randomized Clinical Trial

The aim of this study was to compare the three-dimensional dentoskeletal effects of Haas-type and Hyrax-type expanders using primary teeth as anchorage for rapid palatal expansion (RPE). Thirty-four subjects in mixed dentition were divided according to their expander’s type: Hyrax (n = 16; 6F, 10M; mean age 8 ± 3 years) or Haas (n = 18; 14F, 4M; mean age 8 ± 2 years). Each patient underwent CBCTs before (T0) and after RPE (T1). Dentoskeletal changes were collected. A paired sample t-test and independent t-test were used to compare each variable within the same group and between groups, respectively, with a 5% significance. The Hyrax group showed an increase in all dentoskeletal parameters; skeletal expansion was significantly increased anteriorly (1.76 mm) and posteriorly (1.93 mm). The greatest dental expansion was observed in the anchorage unit (6.47 mm), about twice as much as permanent molars (3.42 mm). The same statistical significance of Haas group measurements was observed; anteriorly skeletal expansion (2.97 mm) was greater than posteriorly (1.93 mm) and dental expansion was greater on anchored teeth (6.80 mm) than non-anchored teeth (4.57 mm). No statistical significance was observed between Hyrax and Hass groups. CBCT analysis showed that, in RPE, the dental expansion was greater than skeletal expansion. No significant or clinical changes were observed between Hyrax and Haas appliances anchored to primary teeth.

Classe II, divisão 1 – da dentição mista à permanente com aparelho ortopédico funcional e fixo

Orthodontic treatment of Class II, division 1 malocclusion in one or two phases is still controversial in contemporary Orthodontics. The present clinical case presents the orthodontic treatment of a 6-year-old patient with aesthetic complaint regarding the smile and bullying, presenting skeletal Class II, Class II malocclusion, Angle division 1, overjet with exaggerated protrusion of the maxillary incisors, exaggerated overbite with the lower incisors touching the palatal mucosa, absence of lip sealing and concave inferior face profile. In Phase I, rapid maxillary expansion was performed with Hyrax-type expander together with the Herbst fixed functional orthopedic device for 11 months. In Phase II, the fixed orthodontic appliance associated with intermaxillary elastics was used for 13 months. The two-phase treatment of Class II malocclusion, division 1 showed to be effective after 24 months, establishing adequate occlusal and functional results and improving the aesthetics of the lower third of the face.

Stress Pattern and Deformation in Mid-palatal Suture and Posterior Dentoalveolar Area With Two Different Types of Rapid Maxillary Expansion Appliances: A Finite Element Method Study

Objective: The study was conducted to evaluate stress pattern and deformation in mid-palatal suture and posterior dentoalveolar area during maxillary expansion therapy with two different types of rapid maxillary expansion by finite element method study. Methods and Methodology: The finite element analysis was performed on a model of maxilla, with narrow maxillary base and teeth digitally reconstructed, based on CBCT images, acquired by child (age 12.5 years) but not in permanent dentition stage from available pool data. Result: More amount of stress was observed in mid-palatal suture and posterior dental alveolar area by using the Hyrax appliance as compared to the Haas appliance. Stress pattern evaluated in mid-palatal suture depicts maximum stress concentration on the anterior region of mid-palatal suture at the position of incisive papilla. Deformation in maximum quantity is observed in central incisors. Maximum stress generation and deformation are observed in lingual region of premolar and molar areas. Minimum stress generation and deformation are observed in the posterior part of last molars. Conclusion: Hyrax produces more stress and deformation in mid-palatal suture as well as in the posterior alveolar segment in comparison to Haas appliance. Better results in the immediate skeletal response were obtained by the Hyrax-type expander as compared to the Haas type.

Tomographic evaluation of dentoskeletal effects of rapid maxillary expansion using Haas and Hyrax palatal expanders in children: A randomized clinical trial.

BackgroundRapid maxillary expansion (RME) is a usual procedure for correcting the transversal maxillary deficiency. Among the most used appliances are the Haas type (tooth-tissue-borne) and Hyrax (tooth-borne) whose main difference is the design. This study aimed to evaluate the dentoskeletal effects of RME using two different expanders in children. Material and MethodsThe sample was composed of 42 children of both gender presenting unilateral or bilateral posterior crossbite with mean age 9.49 (SD± 1.35). Patients were randomized into two groups according to the type of expander: Hyrax (n= 21, 9 boys and 12 girls) and Haas (n= 21, 11 boys and 10 girls). Multiplanar coronal and axial slices obtained from cone-beam computed tomography images (i-Cat, Hartsfield, PA, USA) were used at pretreatment (T1) and after 6 months when the expander was removed (T2). Measurements were performed on Dolphin Imaging Systems 11.7 software (Chatsworth, California, USA). The following variables were evaluated: inclinations of the posterior teeth, transverse skeletal widths, length of maxillary dental arch, buccal bone thickness and level of buccal alveolar crest. Statistical analysis performed using chi-squared test to compare the sex ratios between groups and independent t test with the Bonferroni correction for multiple tests. ResultsRME increased all maxillary transverse dimensions, regardless of the type of expanders used. Subjects in the Hyrax group experienced significantly increase in the lingual bone thickness (0.94 mm) compare to Haas group (0.21 mm). ConclusionsThe Hyrax-type expander produced greater increase in the lingual bone thickness than did the Haas-type expander, but this effect might not be clinically significant. Both appliances presented similar transversal gain and tended to produce similar orthopedic and orthodontic effects. Key words:Cone-beam computed tomography, palatal expansion technique, palate.

Rapid Arch Expansion in Cleft Lip and Palate Children: Comparison Between Fan-Shaped Expander and Hyrax-Type Expander by Using Cone Beam Computed Tomography

Purpose: The aim of the current study was to evaluate the skeletal and dentoalveolar effects of rapid palatal expansion (RPE) in children with cleft lip and palate (CLP), ages 8 to 12 years treated with 2 expanders. Methods: Twenty Egyptian children with complete bilateral CLP exhibiting maxillary transverse deficiency were divided randomly into 2 groups according to the appliance used for expansion: (A) fan expander group. (B) hyrax expander group. Cone-beam computed tomography (CBCT) images were taken before and immediately after expansion procedure. Results: There was non-significant vertical movement of the maxilla for the 2 groups. On the transverse plane, there was more anterior expansion and posterior restriction for the fan group. However, the hyrax group showed significant posterior as well as anterior expansion. Both groups showed significant tipping between both sides posteriorly and anteriorly. Mandibular expansion was non-significant. Conclusion: Fan expander showed better results for children with cleft palate requiring anterior expansion only. Hyrax expander is better used for cases seeking for posterior and anterior expansion.

Rapid arch expansion in cleft lip and palate children: comparison between fan-shaped expander and hyrax-type expander by using cone beam computed tomography

Purpose: The aim of the current study was to evaluate the skeletal and dentoalveolar effects of rapid palatal expansion (RPE) in children with cleft lip and palate (CLP) treated with 2 expanders. Methods: Twenty Egyptian children with complete unilateral or bilateral CLP exhibiting maxillary transverse deficiency were divided randomly into 2 groups according to the appliance used for expansion: (A) fan expander group and (B) hyrax expander group. Cone-beam computed tomography (CBCT) images were taken before and immediately after expansion procedure. Results: There was non-significant vertical movement of the maxilla for the 2 groups. On the transverse plane, there was more anterior expansion and posterior restriction for the fan group. However, the hyrax group showed significant posterior as well as anterior expansion. Both groups showed significant tipping between both sides posteriorly and anteriorly. Mandibular expansion was non-significant. Conclusion: Fan expander showed better results for children with cleft palate requiring anterior expansion only. Hyrax expander is better used for cases seeking for posterior and anterior expansion.

Digital evaluation of nasal changes induced by rapid maxillary expansion with different anchorage and appliance design

BackgroundScientific evidence showed that rapid maxillary expansion (RME) affects naso-maxillary complex, increasing nasal width and volume. This study aimed to evaluate nasal changes induced by rapid maxillary expansion with different anchorage and appliance design by using low dose and cone beam computed tomography.MethodsA total of 44 patients (20 males, mean age 8y 8 m ± 1y 2 m; 24 females mean age 8y 2 m ± 1y 4 m) were included in the investigation and divided into three groups according to the appliance: Hyrax-type expander anchored to permanent teeth, modified Hyrax-type expander anchored to deciduous teeth, modified Haas-type expander anchored to deciduous teeth. Maxillary expansion was performed until overcorrection and the expander was passively kept in situ for 7 months at least. All patients had three-dimensional imaging before expansion (T0) and after the retention period (T1). Nasal floor width, nasal wall width, maxillary inter-molar width were measured by means of Mimics software. The paired sample t-test was employed to assess the significance of the differences between the time points; the analysis of variance test (ANOVA) was used to compare differences between groups.ResultsThe statistical analysis revealed significant differences between T0 and T1 for each recorded measurement in each group; no significant differences were found by comparing groups.ConclusionsRapid maxillary expansion produces a significant skeletal transverse expansion of nasal region in growing patients. No significant differences in nasal effects are expected when the appliance is anchored onto deciduous teeth, with or without the palatal acrylic coverage.

Correction of Transverse Discrepancy with Slowly Maxillary Expansion by Hyrax type expander in Adult Patient

Approximately 30% of adult patients who want orthodontic treatment have transverse discrepancy with insufficient width of the maxilla. Particularly, in Class III patients requiring orthognathic surgery, the frequency of insufficient width of the maxillary arch related to respiratory problems is high. We report a case of non-surgical maxillary expansion using a Hyrax type expander with an orthognathic surgery, based on the reports that the ratio of non-fused midpalatal suture is not high in adults. A 30 years and 2 months old woman with a long face showed an Angle Class III with a vertical growth pattern. Class III molar and canine relation, anterior edge bite, and mandibular incisor compensatory lingual inclination were observed. The posterior buccal overjet seemed to be appropriate, but I diagnosed that there was a transverse discrepancy, for the following reasons. The inter-canine and inter-molar widths were sufficient but excessive lingual inclination of the mandibular molars was observed when assessing the bucco-lingual inclination based on the center of resistance of the maxillary and mandibular first molar. For this reason, it was expected that intercuspal interference would occur during orthodontic decompensation. Therefore, slow maxillary expansion using Hyrax type expander was performed and 2-jaw rotation surgery was performed to improve aesthetic and occlusion. Adults can also improve width discrepancy by non-surgical methods, which can avoid SARPE requiring additional surgery or segmental surgery lacking stability and predictability.

Cone-beam computed tomography evaluation of bone density of midpalatal suture before, after, and during retention of rapid maxillary expansion in growing patients

ObjectiveTo analyze changes in bone density of the midpalatal suture after rapid palatal expansion (RME) with the Hyrax-type expander in growing subjects using cone-beam computed tomography (CBCT). MaterialsFourteen patients (nine girls and five boys; mean age, 11.7 ± 2.4 years) who required RME as part of their orthodontic treatment and had preexpansion (T0) and postexpansion (at the end of active expansion [T1], after a retention period of 3 months [T2], and after 6-month [T3] retention period) CBCT scans. On the axial CBCT images, four regions of interest in the midpalatal suture were analyzed. Bone density (BD) was measured in voxel gray-scale histogram. BD measurements were compared by using Friedman ANOVA with post hoc tests. A P value less than 0.05 was considered statistically significant. ResultsBD values in all regions of interest in the midpalatal suture decreased significantly after active expansion (T0-T1) and significantly increased during the retention periods (T1-T2 and T1-T3). According to the density values 3 months after expansion (T0-T2), the remineralization was incomplete. At 6 months of the retention, nonsignificant differences in BD were observed in comparison with the pretreatment values (T0-T3). ConclusionsActive phase of RME produced effective opening of the midpalatal suture with significant decreases in BD levels. The results revealed that are necessary more than 3 months for complete sutural recovery after RME, thus indicating in prepubertal patients, the recommendation to extend the retention time to 6 months to achieve the midpalatal suture remineralization.

Immediate effects of rapid maxillary expansion on the nasal cavity using Haas-type and Hyrax-type expanders in CBCT

Immediate effects of rapid maxillary expansion on the nasal cavity using Haas-type and Hyrax-type expanders in CBCT

Effects of low-level laser therapy on bone regeneration of the midpalatal suture after rapid maxillary expansion

This study evaluated the effect of low-level laser therapy (LLLT) on bone regeneration at the midpalatal suture (MPS) after rapid maxillary expansion (RME), using cone beam computed tomography. Fourteen 8-14-year-old patients with transverse maxillary deficiency underwent RME with a Hyrax-type expander activated with one full turn after installation and two half turn daily activations until achieving overcorrection. Patients were randomly assigned to either a control group (RME alone, n = 4) or an experimental group (n = 10) in which RME was followed by 12 LLLT sessions (GaAlAs, p = 70mW, λ = 780nm, Ø = 0.04cm(2)). Two tomographic images of the MPS were obtained-T0, after disjunction and T1, after 4months. Bone regeneration was evaluated by measuring the optical density (OD) on the tomographic images using InVivo Dental 5.0 software. Data were analyzed by the paired Student's t test (α = 0.05%). A statistically significant difference between T0 and T1 OD values was observed in the laser-treated group (p = 0.00), but this difference was not significant in the control group (p = 0.20). Intergroup comparison of OD values at T1 revealed higher OD in the laser-treated group (p = 0.05). In conclusion, LLLT had a positive influence on bone regeneration of the midpalatal suture by accelerating the repair process.

Mandibular arch dimensions following bonded and banded rapid maxillary expansion

BackgroundThe purpose of this study was to examine changes in mandibular arch dimensions of subjects submitted to either bonded or banded maxillary expansion. MethodsThe sample comprised of two groups, one with patients who underwent maxillary expansion with banded, Haas-type expanders, retrospectively selected (banded group), and the other patients carefully matched in sex, age, and malocclusion, prospectively observed with bonded, Hyrax-type expanders (bonded group). Each group was composed of 29 subjects evaluated at T1, before maxillary expansion, and T2, after expansion and stabilization. The mandibular arches were evaluated for changes in arch width, depth, and perimeter. Paired and independent Student's t tests were used to compare groups. ResultsPatients in the banded group experienced significantly more mandibular arch width expansion in the molar region. Both groups experienced a decrease in arch depth; however, the bonded group showed significantly greater loss. ConclusionRapid maxillary expansion is an effective method for achieving a gain in arch width and space in the maxillary arch and, depending on the type of expander, banded or bonded, it produces a different response on an untreated mandibular arch.

Immediate effects of rapid maxillary expansion with Haas-type and hyrax-type expanders: A randomized clinical trial

The purposes of this study were to evaluate and compare the immediate effects of rapid maxillary expansion (RME) in the transverse plane with Haas-type and hyrax-type expanders by using cone-beam computed tomography. A sample of 33 subjects (mean age, 10.7 years; range, 7.2-14.5 years) with transverse maxillary deficiency were randomly divided into 2 groups: Haas (n= 18) and hyrax (n= 15). All patients had RME with an initial activation of 4 quarter turns followed by 2 quarter turns per day until the expansion reached 8 mm. Cone-beam computed tomography scans were taken before expansion and at the end of the RME phase. Maxillary transversal measurements were compared by using the mixed analysis of variance (ANOVA) model and the Tukey-Kramer method. RME increased all maxillary transverse dimensions (P<0.0001). There was less expansion at skeletal than dental levels. The hyrax group had greater statistically significant orthopedic effects and less tipping tendency of the maxillary first molars compared with the Haas group. Both appliances were efficient in correcting a transverse maxillary deficiency. The pure skeletal expansion was greater than actual dental expansion. The hyrax-type expander produced greater orthopedic effects than did the Haas-type expander, but this effect was less than 0.5 mm per side and might not be clinically significant.