Rapid Palatal Expansion Treatment Research Articles

Effects of Rapid Palatal Expansion on the Upper Airway Space in Children with Obstructive Sleep Apnea (OSA): A Case-Control Study

Obstructive Sleep Apnea (OSA) in children needs a multidisciplinary approach. Even if the first-line treatment of pediatric OSA is adenotonsillectomy, nowadays rapid palatal expansion (RPE) is considered a valid additional treatment. The aim of this study is to evaluate cephalometric changes in upper airways dimensions after rapid palatal expansion (RPE) in children suffering from Obstructive Sleep Apnea (OSA). A total of 37 children (range age 4-10 years) with diagnosis of OSA referred to Dentistry Unit of Bambino Gesù Children's Research Hospital IRCCS (Rome, Italy) were included in this pre-post study and underwent lateral radiographs at the start (T0) and at the end (T1) of a RPE treatment. Inclusion criteria were: diagnosis of OSA confirmed by cardiorespiratory polygraphy (AHI > 1) or pulse oximetry (McGill = >2), skeletal maxillary contraction evaluated by presence of posterior crossbite. A control group of 39 untreated patients (range age 4-11 years), in good general health, was set up. A paired T-test was used to investigate the statistical differences between T0 and T1 values in both groups. The results showed a statistically significant increase of nasopharyngeal width in the treated group after RPE treatment. Moreover, the angle that identifies mandibular divergence compared to palatal plane (PP-MP°) was significantly reduced. In the control group, no statistically significant differences were observed. The present study showed that RPE treatment determines a significant sagittal space increase in the upper airways space and a counterclockwise mandibular growth in children with OSA compared to a control group. These results suggest that a widening of the nasal cavities induced by RPE may support a return to physiological nasal breathing and promote a counterclockwise mandibular growth in children. This evidence confirms the crucial role of the orthodontist in the management of OSA in pediatric patients.

Evaluation of the Effects of Mandibular Lingual Arch on Dentoalveolar Structures in Orthopedic Face Mask with Rapid Palatal Expansion Treatment of Class III Malocclusions

Evaluation of the Effects of Mandibular Lingual Arch on Dentoalveolar Structures in Orthopedic Face Mask with Rapid Palatal Expansion Treatment of Class III Malocclusions

Impact of rapid palatal expansion on the size of adenoids and tonsils in children

IntroductionAdenoid and tonsillar hypertrophy in children often leads to adverse respiratory symptoms and obstructive sleep apnea (OSA). Current clinical guidelines from the American Academy of Pediatrics and American Academy of Otolaryngology–Head and Neck Surgery recommend tonsillectomy as the first line of pediatric OSA treatment for children with tonsillar hypertrophy. Rapid palatal expansion (RPE) performed by orthodontists improves obstructive sleep apnea in children by reducing nasal airway resistance, increasing nasal volume, raising tongue posture, and enlarging pharyngeal airway. However, the role of RPE in alleviating adenoid and tonsillar hypertrophy remains elusive. In this study, we aim to evaluate the changes in adenoid and palatine tonsil sizes following RPE using 3D volumetric analysis of cone beam computational tomography (CBCT) imaging. Materials and methodsIn this retrospective cohort study, a total of 60 pediatric patients (mean age: 8.00, range: 5–15, 32 females and 28 males) who had tonsillar hypertrophy (size 3 and 4) were included and divided into the control group (n = 20) and expansion group (n = 40). The control group did not undergo any treatment. The expansion group underwent RPE using a conventional Hyrax expander, activated 0.25 mm per day for 4–6 weeks. Final CBCT scans (T2) were performed 13.8 ± 6.5 months after the initial scan (T1). Pediatric sleep questionnaire (PSQ) and BMI were obtained at each timepoint. Volumetric analysis of adenoid and palatine tonsils was performed using a combination of bony and soft tissue landmarks in CBCT scans through Anatomage Invivo 6 imaging software. Paired t-tests were used to evaluate the difference between the initial and final adenoid and tonsil volumes. p values less than 0.05 were considered statistically significant. ResultsCompared to the control group, the expansion group experienced a statistically significant decrease in both adenoid and tonsil volume. There was non-statistically significant increase in volume from T1 to T2 for the control group. For the expansion group, 90.0% and 97.5% of patients experienced significant reduction in adenoid and tonsil volume, respectively. The average volume decrease of adenoids was 16.8% while that of tonsils was 38.5%. The patients had up to 51.6% and 75.4% reduction in adenoid and tonsil size, respectively, following RPE orthodontic treatment. Pearson correlation ranged from 0.88 to 0.99 for each measurement, representing excellent internal consistency. There was a significant reduction in the PSQ scores from 5.81 ± 3.31 to 3.75 ± 2.38 in expansion group (p < 0.001). ConclusionsOur results demonstrated that RPE significantly reduced the size of both adenoid and palatine tonsils and revealed another long-term benefit of RPE treatment. To our knowledge, this is the first study to quantify the changes of adenoids and tonsils following RPE. RPE treatment can be considered as a valid and effective treatment option for pediatric OSA population with narrow high arch palate and adenotonsillar hypertrophy.

Parental Satisfaction with Their Children's Rapid Palatal Expansion Treatment Provided by Orthodontists and Pediatric Dentists.

BackgroundDentofacial problems have a definitive impact on patients’ psychological well-being, quality of life, and satisfaction. Therefore, patients’ satisfaction with their dentition should be an essential goal for dental caregivers.AimTo compare parental satisfaction with their children’s rapid palatal expansion treatment outcome provided by orthodontists and pediatric dentists.Materials and MethodsThe authors reviewed 605 medical records and contacted 134 parents whose children received early orthodontic treatment from orthodontists and pediatric dentists using a rapid palatal expander. Eighty-eight parents (65.7%) responded to a validated questionnaire about patients’ satisfaction with orthodontic treatment outcomes.ResultsAt baseline; there were no significant differences in relation to parent-related demographic variables. However, there were statistically significant differences between patients’ ages and treatment duration (p < 0.001). Independent t-tests showed statistically significant differences in the means for the subscales of doctor–patient relationship and situational aspects (p < 0.05). Spearman’s rho correlation coefficients and multivariate linear regression analysis showed that the overall satisfaction is significantly related to, and can be predicted by, parents’ educational level, child’s gender, and the specialty of the dentist who provided the treatment (p < 0.05).ConclusionOverall parental satisfaction with their children’s rapid palatal expansion treatment is significantly higher when provided by pediatric dentists as compared with orthodontists. Factors related to doctor–patient relationship and situational aspects (ie, office location and design, appointment waiting, and treatment duration) significantly impacted parental satisfaction.

The assessment of rapid palatal expansion using a remote monitoring software

ObjectiveDental Monitoring (DM) is a software system that allows orthodontists to remotely monitor a patient's treatment. This study evaluated the accuracy of DM software in assessing the achievement of treatment goals in patients undergoing rapid palatal expansion treatment and patient acceptance of DM. MethodsConsecutively treated patients undergoing rapid palatal expansion were invited to participate. Participants were trained to capture intraoral photos/videos using the DM app. Maxillary intermolar width (mm) and posterior crossbite correction measured by DM were compared with digital models and intraoral measurements. Patient acceptance of the DM app was evaluated with a survey. ResultsOf the 30 patients enrolled, 20 patients completed the study. DM accurately assessed the correction of posterior crossbite. There was no significant difference in intermolar width measurements obtained with DM, digital model, or intraoral examination. Overall, 71% of the participants found the DM app “easy” to work with and 43% of the patients preferred DM over a clinical visit. ConclusionIn-person evaluation of maxillary expansion with a Hyrax expander can be replaced with remote monitoring using the DM software, yet challenges associated with digital imaging hinder the use of this remote evaluation for some patients.

Rapid palatal expansion (RPE): Meta-analysis of long-term effects.

Rapid palatal expansion (RPE) is a widespread orthopaedic procedure used in several clinical situations. The aim of the study was to provide a systematic review and meta-analysis of transverse intercanine and intermolar width changes after RPE and long-term effects. A systematic literature search was conducted until January 2018 on original studies with RPE treatment. Intercanine and intermolar distance were measured at the start of RPE (T1, median age 9.2years) and at the end of treatment (T2). The long-term evaluation was conducted on a subset of articles with 5-year follow-up (T3). Eighteen studies T1-T2 and 5 studies T3 were selected. Regarding the intercanine distance, the RPE resulted in a gain of space T1-T2 of 3.73mm with a significant heterogeneity (P<0.0001; I2 =94.21%) and a relapse T2-T3 of -0.81mm with a significant heterogeneity (P<0.0001; I2 =95.8%); the overall gain of space was 2.91mm. Regarding the intermolar distance, the RPE resulted in a gain of space T1-T2 of 4.85mm with a significant heterogeneity (P<0.0001; I2 =92.41%) and a relapse T2-T3 of -0.47mm with a significant heterogeneity (P<0.0001; I2 =87.5%); the overall gain of space was 4.38mm. Meta-regression analysis showed that at younger age, the amount of anterior expansion is similar to posterior. With increasing age, the anterior opening diminishes significantly more than the posterior, being half of the posterior at 15years. Because long-term results were obtained with simultaneously fixed appliances and long upper retention, RPE should be carefully considered before using.

Ultrasonography in the evaluation of the mid-palatal suture in rapid palatal expansion.

Orthodontists usually evaluate the mid-palatal sutural opening with occlusal radiography. The purpose of this article is to evaluate the sutural opening with ultrasonography (USG) in a series of patients undergoing rapid palatal expansion (RPE). The study included 87 USG images and 87 occlusal radiographs from 29 healthy patients (mean age, 13.9 years; range, 11-20 years; boys, 12; girls, 17) who required RPE treatment. The sutural opening was assessed with USG, and the amount of sutural expansion as mesiodistal length was measured immediately after appliance practice (T0), 10 turns (T1) and 20 turns (T2) during the expansion period. Sutural expansion evaluated by occlusal radiographs was scored at every stage. Measurements obtained by USG and scores observed in the occlusal radiographs were compared by non-parametric Kendall's tau test. Both USG and radiographic images revealed normal anatomical structure during pre-expansion (stage T0). On USG, sutural expansion was seen in 19 patients at stage T1. There was no expansion at this stage in ten patients. At stage T2, on USG and radiography, an increase in the amount of expansion was observed in 19 patients with sutural expansion at stage T1 and sutural expansion was observed in 5 patients without sutural expansion at stage T1. No expansion was observed at both stages T1 and T2 in five patients. USG measurements and occlusal scores in both T1 and T2 turns showed statistically significant correlation (p < 0.001). The results indicate that USG might be a useful method to assess mid-palatal sutural opening in patients undergoing RPE.

Effects of rapid palatal expansion on the sagittal and vertical dimensions of the maxilla: A study on cephalograms derived from cone-beam computed tomography

The purpose of this study was to use cone-beam computed tomography imaging to examine the skeletal and dental changes in the sagittal and vertical dimensions after rapid palatal expansion. Twenty-eight healthy children (mean age, 9.9 years; range, 7.8-12.8 years; 17 boys, 11 girls) who required rapid palatal expansion treatment were included. For each patient, a bonded Haas-type expander with full occlusal and palatal acrylic coverage was cemented in place. Cone-beam computed tomography images were obtained as part of the pretreatment orthodontic records and at the completion of rapid palatal expansion for all patients. The mean interval between pretreatment and completion of rapid palatal expansion was 52 days (range, 19-96 days). The average skeletal age of the patients, determined from hand-wrist films also obtained before treatment, was 10.1 years. The mean expansion of the expander was 8.0 mm (range, 5.9-9.6 mm). Each cone-beam computed tomography image was compressed from the outer portion of the right side of the patient's head to the center of the left central incisor into a 2-dimensional synthesized cephalogram, which was then traced and measured. The results showed that from pretreatment to completion of rapid palatal expansion, SNA, FH-NA, and A-Nperp increased by means of 1.04°, 0.92°, and 0.87 mm, respectively (P <0.05). In addition, 1/-NA, 1/-SN, 1/-NA, 1/-Nperp, and 1/-PP showed mean decreases of 3.74°, 2.53°, 1.17 mm, 0.49 mm, and 2.69°, respectively (P <0.05). Both ANS and PNS moved significantly downward (ANS, 2.05 mm; PNS, 1.16 mm). There was forward movement of the maxilla as a result of rapid palatal expansion treatment. Bonded rapid palatal expansion treatment resulted in downward displacement of the maxilla with a greater displacement of ANS than PNS and posterior movement of the maxillary central incisors.

A Computerized Photographic Method to Evaluate Changes in Head Posture and Scapular Position Following Rapid Palatal Expansion: A Pilot Study

To assess the applicability of a computerized method to measure on digital photographs the changes in head and scapular posture following rapid palatal expansion (RPE) treatment. Randomized controlled trial. Twenty-three children (age 9.2 +/- 70.88 years) diagnosed with maxillary constriction were randomly divided into two groups: 1. Study group (n = 12): patients receiving RPE treatment; 2. Untreated controls (n = 11). Postural measurements were taken on frontal, lateral, and dorsal views of each subject. In the study group measurements were taken at T0 (the day orthodontic records were taken), T1 (end of RPE active phase), and T2 (RPE removal). In controls the same observations were conducted at T0 and T1(98.18 +/- 36.01 days after T0). Measurements were statistically analyzed (Intraclass Correlation Coefficient, t-tests, Signed Rank test, One-Way Repeated Measures Analysis of Variance, Tukey test; p < 0.05). In the study group a significant reduction in forward head posture (FHP) occurred between T0 and T1. Forward shoulder posture (FSP) decreased significantly between T1 and T2. At T1 treated patients exhibited significantly lower values of the measurements indicating FHP and FSP than controls. Changes in head and scapular posture following RPE treatment can be documented with computerized measurements on digital photographs.

Measurement of somatosensory-evoked potential to evaluate function of the trigeminal nerve after rapid palatal expansion treatment in a rabbit model

The aim of this study was to evaluate whether high force or stress response occurs in rapid palatal expansion (RPE) on the skull base would affect the function of trigeminal nerve and its branches by measuring trigeminal somatosensory-evoked potential (TSEP). Twenty-four male New Zealand white rabbits were selected when they were 12-13 weeks old with mean weight around 3.05 ± 0.33 kg. A modified acrylic-bonded RPE appliance was used as an expansion tool. Through a series of TSEP measurements performed before the expansion treatment (T0), on the third day of the expansion (T1), at the end of the expansion process (T2), and after 10 days of retention (T3), function of the trigeminal nerve was analyzed with statistical models, including the Kruskal-Wallis test and paired t tests. A stable short-latency response represented by a "W" waveform was consistently identified on the TSEP spectram analysis. Within-subject comparisons between the experimental group and control group did not show significant differences on TSEP of maxillary nerve and of mandibular nerve. TSEP is a valuable technique for a comprehensive evaluation of the trigeminal system. Our study demonstrates that rapid palatal expansion is a safe orthopedic method regarding function of the trigeminal nerve during expansion and short-term retention period in young rabbits.

Cone-beam computerized tomography evaluation of the maxillary dentoskeletal complex after rapid palatal expansion

Rapid palatal expansion (RPE) is routinely used to correct transverse deficiencies in the maxilla, but its effects on the dentoalveolus are uncertain. The purpose of this study was to compare measurements made on cone-beam computerized tomography scans between patients with RPE treatment and controls to determine transverse dimension increases and the amounts of alveolar and dental tipping. Twenty-five patients with posterior crossbite who required RPE treatment and 25 sex- and age-matched controls (no crossbite) were orthodontically treated and received cone-beam computerized tomography scans at the beginning and middle of treatment. Transverse widths and several angulations were measured, and matched paired t tests used. RPE treatment produced a significant increase in all measured transverse dimensions. Analysis of posttreatment angulation changes in the RPE group showed that the alveolus substantially tipped buccally by nearly 5.6° (measured from a horizontal reference, the base of the hard palate). The angulations of the dentition, however, remained constant before and after treatment (<1° of change) in both groups. These data showed no statistically significant amount of relative dental tipping after RPE treatment but significant alveolar tipping compared with the controls.

Three-dimensional computed tomography comparison of the maxillary palatal vault between patients with rapid palatal expansion and orthodontically treated controls

The aim of this study was to use cone-beam computed tomography to compare changes of skeletal and dental structures of the maxillary palatal vault in a group of growing patients treated for posterior crossbite before and after rapid palatal expansion (RPE) with changes over time in a control group. The sample for this retrospective study included 19 patients treated with a hyrax palatal expander at a graduate orthodontic clinic and 19 control subjects who received no RPE. Beginning and progress cone-beam computed tomography scans of all patients were analyzed to measure the anatomic volume, width, height, and anteroposterior dimensions of the palatal region. Progress scans (after RPE treatment for cases) showed, the mean percentages of change in palatal volume were 10.8% in the controls and 21.7% in the RPE group (P = 0.038); however, there were no statistically significant differences in palatal volume at baseline or at progress scan between the RPE patients and controls. Absolute first molar-to-molar width changes at progress scan were 0.57 mm in the controls and 3.27 mm in the RPE group (P = 0.022). Absolute canine-to-canine width changes at progress scan were 0.45 mm in the controls and 2.79 mm in the RPE group (P = 0.007). There were significant differences in percentage and absolute changes in maxillary width measured from molar to molar and canine to canine between RPE group and controls, but no significant differences in maxillary vault height or anteroposterior dimension changes. At progress scan, canine-to-canine width, first molar-to-molar width, and anteroposterior length of the palatal maxillary volume in the RPE group approached the measurements of the controls. Palatal volumes (at baseline and progress scan) were not statistically significantly different between the groups.

Effects of bonded rapid palatal expansion on the transverse dimensions of the maxilla: A cone-beam computed tomography study

The purpose of this study was to examine the maxillary response on the transverse dimensions to rapid palatal expansion (RPE) by using cone-beam computed tomography (CBCT). Twenty-four children (average age, 9.9 years) who had RPE treatment with a bonded expander were included. Pretreatment orthodontic records (T1) and immediately after expansion (T2) CBCT images were taken for all patients. For each patient, the width of the nasal cavity at the level of the maxillary first permanent molar and second deciduous molar (or second permanent premolar), the width of the maxillary basal bone, and the width of the midpalatal suture at the level of the second deciduous molar (or the second permanent premolar), the first deciduous molar (or first permanent premolar), and the deciduous canine (or permanent canine) at T1 and T2 were measured. In addition, the amount of tipping for both the maxillary right and left first permanent molars was measured. From T1 to T2, mean increases in nasal width, related to the mean jackscrew opening (8.19 mm), occurred at the levels of the first permanent molars of 33.23% (2.73 mm, P <0.05) and the second deciduous molars of 37.32% (3.06 mm, P <0.05). Significant increases in basal bone of the maxilla were found at all levels (P <0.05), with mean increases of 40.65% (3.33 mm), 44.08% (3.49 mm), 46.73% (3.83 mm), and 46.83% (3.62 mm) of the mean jackscrew opening at the levels of the first permanent molars, and the second deciduous molars, first deciduous molars, and deciduous canines, respectively. Significant openings in the midpalatal sutures was found at all levels (P <0.05), with mean increases of 52.82% (4.33 mm), 53.23% (4.36 mm), 54.35% (4.46 mm), and 52.77% (4.33 mm) of the jackscrew opening at the levels of the first permanent molars, and the second deciduous molars, first deciduous molars, and deciduous canines, respectively. The right first molar tipped buccally an average of 6.2 degrees (P <0.05), and the left first molar tipped buccally 5.6 degrees (P <0.05). After RPE, significant increases in the transverse dimensions of the nasal cavity, the maxillary basal bone, and the midpalatal suture opening occurred, with the greatest increase in the midpalatal suture followed by basal bone and nasal cavity. The midpalatal suture opened in a parallel fashion. Moreover, significant buccal tipping occurred on both maxillary first molars.

Changes in pharyngeal aerobic microflora in oral breathers after palatal rapid expansion

BackgroundThe purpose of this study was to investigate in oral breathing children the qualitative and quantitative effects on aerobic and facultatively anaerobic oropharyngeal microflora of respiratory function improved by rapid palatal expansion (RPE).MethodsIn an open clinical trial, we studied 50 oral breathers, aged 8 to 14 years and suffering from both maxillary constriction and posterior cross-bite. At baseline, patients were examined by a single otorhinolaryngologist (ENT), confirming nasal obstruction in all subjects by posterior rhino-manometric test. Patients were evaluated three times by oropharyngeal swabs:1) at baseline (T = 0); 2) after palatal spreading out (T = 1); and 3) at the end of RPE treatment (T = 2). With regard to the microbiological aspect, the most common and potentially pathogenic oral microrganisms (i.e. Streptococcus pyogenes, Diplococcus pneumoniae, Staphylococcus aureus, Haemophilus spp, Branhamella catarrhalis, Klebsiella pneumoniae, Candida albicans) were specifically detected in proper culture plates, isolated colonies were identified by means of biochemical tests and counted by calibrated loop. The data were analyzed by means of the following tests: Chi-square test, Fisher's exact test and Wilcoxon's test.ResultsAfter the use of RME there was a statistically significant decrease of Staphylococcus aureus stock at CFU/mLat T1(P = 0.0005; Z = -3,455 by Wilcoxon Rank test) and T2 (P < 0.0001; Z = -4,512 by Wilcoxon Rank test) vs T0. No significant changes were found for the other examined microrganisms.ConclusionOur data suggest that RPE therapy in oral breathers may strongly reduce the pathogenic aerobic and facultatively anaerobic microflora in the oral pharynx after a normalization of the upper airways function, and may reduce the risk of respiratory infections.

Maxillary incisor root resorption after rapid palatal expansion in Felis catus

Root resorption after rapid palatal expansion (RPE) treatment was found in anchored teeth but has not been studied on non-anchored incisors. This study evaluated root resorption, root tipping, and root proximity of maxillary incisors after RPE treatment. Fourteen cats were divided into treated (n = 10) and untreated (n = 4) groups. The RPE treatment consisted of active, retention, and relapse phases, lasting 25, 60 and 60 d, respectively. Standardized occlusal radiographs were taken to measure tipping and root proximity before and after each treatment phase. Maxillary incisors were analysed histologically by fluorescent microscopy for root resorption. Data was analysed statistically with anova with repeated measures, t-test and Pearson's coefficient of correlation. Root resorption was confined to the first incisors and was 750-fold greater in the treated vs. the control group. Root tipping and root proximity were significantly greater (2.5- and 17-fold, respectively) in the first than in the second maxillary incisor and highly correlated with root resorption (r = -0.927 and 0.723, respectively). This suggests a cause (tipping and root proximity) and effect (root resorption) relationship. Data suggest that first maxillary incisor susceptibility to root resorption during RPE is associated with severe tipping and root proximity.

Skeletal and dental changes in the sagittal, vertical, and transverse dimensions after rapid palatal expansion

The purpose of this study was to examine the maxillary and mandibular responses to rapid palatal expansion (RPE) in all 3 dimensions. Twenty children (average age, 11.7 years) who required RPE treatment were included in this study. Pre- (T1) and post-RPE (T2) lateral and posteroanterior (PA) cephalograms and study models were taken for all patients. For each patient, lateral and PA cephalograms at T1 and T2 were traced, and the sagittal, vertical, and transverse measurements were made. In addition, on the pre- and postexpansion models, the widths between the first premolars, the first molars, and the two acrylic halves of the Haas-type expander were measured. Results showed that from T1 to T2, the mean SNA increased 0.35 degrees (P < .05) and ANB increased 1.00 degrees (P < .05). Both the ANS and PNS moved downward (1.30 mm and 1.43 mm, respectively, P < .05), and the mandibular plane angle (MP-SN) increased 1.72 degrees (P < .05). The maxillary and mandibular incisors did not change significantly after RPE. After RPE, the mean increase of maxillary interpremolar width, maxillary intermolar width, maxillary width (J-J), nasal width, and interorbital width were found to be 110.7%, 104.5%, 30.1%, 23.1%, and 3.3% of the screw expansion, respectively. After RPE treatment in children, the maxilla displaced slightly forward and downward (P < .05); the mandible rotated downward and backward, and the anterior facial height increased significantly (P < .05); and the widths of the maxilla and nasal cavity increased significantly (P < .05).

Rapid palatal expansion in the absence of crossbites: added value?

As noted in a recent article, 1 interest in rapid palatal expansion (RPE), which has traditionally been used to resolve crossbites, has increased markedly in the past 2 decades. Orthodontists using this procedure might be seeking to gain arch perimeter to avoid extractions. This treatment, which is most often started in the mixed dentition, raises some interesting questions. One question is this: In the absence of a crossbite, is RPE necessary to gain arch width to avoid extraction treatment? If so, then is the maxillary arch perimeter the determinant in the extraction-nonextraction decision? These questions are fundamental, because using the maxillary arch to decide whether to extract challenges the concept of mandibular arch-based diagnosis and treatment planning. For this reason, it might be useful to evaluate the rationale for RPE treatment in the correction of crowding. RPE increases the perimeter of the maxillary arch and can provide space to correct moderate (3-4 mm) amounts of crowding. Because no treatment occurs in the mandibular arch, a logical question is this: How is space to be gained to resolve crowding in the mandibular arch? One view is that expansion of the maxillary arch is accompanied by spontaneous transverse expansion of the mandibular arch, with the implication that space would be available to resolve any lower arch-tooth size discrepancy. This supposition is easy to assess because there are adequate data; the conclusion is that any spontaneous expansion provides almost no space to resolve crowding. Brust and McNamara, in a 2-phase treatment protocol, evaluated both mandibular intercanine and intermolar expansion and noted that, immediately after RPE, both dimensions increased approximately 1 mm. However, the intercanine distance decreased before phase 2 treatment, and the net intercanine gain was only 0.3 mm. The 1-mm intermolar increase remained stable. These results are similar to those noted by others who recorded spontaneous mandibular arch change incident to RPE treatment. The increase in intercanine width in these studies was less than 1 mm. As an example, the increase observed by Grayson was only 0.22 mm and led the author to conclude that “the use of rapid palatal expansion as a method of increasing lower arch length cannot be justified.” Interestingly, Brust and McNamara observed that the mandibular arch perimeter decreased 1.3 mm from phase 1 to the beginning of phase 2 treatment. In an investigation of 17 subjects whose comprehensive treatment included RPE, the intercanine dimension increased 2.2 mm during treatment and relapsed 50% postretention, to yield a net long-term gain of only 1.1 mm. In this study, there were no recordings of the intercanine width immediately after RPE to indicate the amount of spontaneous expansion that occurred. Also, variation in response was remarkable, ranging from 0.3 to 3.8 mm. (This large variation is a reason that anecdotal information can be misleading—if one cites only the extreme positive response.) One motive for focusing on the mandibular intercanine dimension in the preceding descriptions is that, in the transverse plane of space, an increase in this area provides the most space to resolve mandibular incisor crowding. Specifically, Germane et al determined that a 1-mm increase in intercanine dimension provides 0.73 mm of space to correct incisor position. In contrast, 1 mm of molar expansion provides only 0.27 mm of space. (Subsequent increases in width provide slightly more space per millimeter. For instance, expansion of 2 mm yields 0.27 mm for the first millimeter and 0.31 mm for the second millimeter, for a total of 0.58 mm.) Clearly, the available data indicate that spontaneous expansion of the mandibular arch usually does not supply adequate space to align crowded incisors. Because spontaneous expansion of the mandibular arch is extremely limited, appliances, such as the Schwartz appliance, have been placed to expand it Professor and chairman, Boston University School of Dental Medicine, Boston, Mass. Reprint requests to: Dr Anthony A. Gianelly, Boston University, Goldman School of Dental Medicine, Department of Orthodontics, 100 E Newton St, Boston, MA 02118-2392; e-mail, gianelly@bu.edu. Submitted and accepted, June 2003. Am J Orthod Dentofacial Orthop 2003;124:362-5 Copyright © 2003 by the American Association of Orthodontists. 0889-5406/2003/$30.00 0 doi:10.1016/S0889-5406(03)00568-7

Rapid palatal expansion. Part 3: Strains developed during active and retention phases

Patterns of strain accumulation/dissipation during the active and retention phases of rapid palatal expansion treatment were studied in a preliminary animal model (5 cats) followed by clinical study (14 patients). Two uni-axial strain gauges were bonded to the arms of a hyrax screw. The strain gauges were wired intraorally to a common male connector and protected against salivary assault. For strain registration, the connector was hooked to a switch and balance instrument and a digital strain indicator. The screw was activated (4 × 1/4 turn) every 3 to 4 days and strain and interarch distances were measured during rapid palatal expansion active and retention phases. Interarch distances were also measured during the relapse phase. Both studies share the same results. Strains and expansion increased progressively during active and retention phases of rapid palatal expansion. No difference between anterior and posterior strain was found. An immediate dental strain response that occurred during screw activations (intrasession strain) was related to tooth compression in the PDL. During the 3 to 4 day pause, a delayed skeletal strain response (intersession strain) developed that was inverted or continuous to the preceding intrasession strain. Complete dissipation of residual strains was limited to the first 1 to 3 active phase sessions. Strain accretion resulted essentially from intersession strain build-up. Strain level was preserved during the retention phase, apparently due to relapse strains. Relapse strains could not be measured but are inferred from the predominant interarch rebound measured during the relapse phase. Clinically, an extension of the intersession intervals and the retention phase are recommended. (Am J Orthod Dentofacial Orthop 1998;114:123-33)

Rapid palatal expansion: Part 1. Mineralizationpattern of the midpalatal suture in cats

The mineralization pattern of the midpalatal suture after rapid palatal expansion was investigated in 10 treated and 2 control cats, in light of the tendency of RPE to relapse. The rapid palatal expansion treatment consisted of active (25 days), retention (60 days), and relapse (60 days) phases. Standardized occlusal radiographs were taken periodically and analyzed for suture width, suture optical density in anterior vs. posterior regions, and suture area measurements of radiopaque vs. radiolucent zones. Nine cats exhibited suture splitting. During the active phase, the radiolucent zone (nonmineralized tissue) increased 12-fold and the increase in optical density was 50% greater in the anterior over the posterior suture region, demonstrating increased formation of loose connective tissue at the anterior region. During the retention period, the suture's radiopaque zone (mineralized tissue) increased by 62%, the radiolucent zone declined (64%) and the suture width decreased (65%) indicating reorganization of mineralized tissue. The decrease in optical density (increased mineralization) was 2.5 times greater in the posterior over the anterior suture region, indicating that the remineralization (closure) pattern of the expanded suture is analogous to a zipper closed in a posteroanterior direction. During the relapse phase, the reduction in total suture area (41%) and in the radiopaque zone (32%) indicates medial convergence of the maxillary horizontal processes. From our findings we extrapolated that the retention of the suture anterior region should be longer than the posterior region to catch up the lag in rebuilding and maturation of the newly deposited hard tissue.