Three-Dimensional Evaluation of Slow Maxillary Expansion with Leaf Expander Vs

applied sciences

Article Three-Dimensional Evaluation of Slow Maxillary Expansion with Leaf Expander vs. Rapid Maxillary Expansion in a Sample of Growing Patients: Direct Eﬀects on Maxillary Arch and Spontaneous Mandibular Response

Gianguido Cossellu 1,2 , Alessandro Ugolini 3, Matteo Beretta 4, Marco Farronato 1,2 , Alessandro Gianolio 5 , Cinzia Maspero 1,2 and Valentina Lanteri 1,2,* 1 Fondazione IRCCS Ca’ Granda, Ospedale Maggiore Policlinico, 20100 Milan, Italy; [email protected] (G.C.); [email protected] (M.F.); [email protected] (C.M.) 2 Department of Biomedical, Surgical and Dental Sciences, University of Milan, 20100 Milan, Italy 3 Department of Sciences Integrated Surgical and Diagnostic, University of Genova, 16100 Genova, Italy; [email protected] 4 Private Practice, 15033 Casale Monferrato (AL), Italy; [email protected] 5 Private Practice, 12042 Bra (CN), Italy; [email protected] * Correspondence: [email protected]; Tel.: +39-025-032-0241

Received: 9 April 2020; Accepted: 23 June 2020; Published: 29 June 2020

Abstract: The aim is to evaluate the effects of slow maxillary expansion on maxillary and mandibular arch, using a slow maxillary expander (SME-Leaf Expander) banded on primary second molar. Ninety patients with transverse maxillary deficiency and posterior crossbite were selected. Sixty-nine patients (33 males/36 females; 7.6 1.7 years old) who underwent SME and 21 patients (10 males/ ± 11 females; 7.4 1.2 years old) who were treated with rapid maxillary expander (RME). Digital ± models obtained pre- and post-treatment at appliance removal (9 to 11 months) were processed by means of a 3D scanner (Trios 3, 3Shape D250 laser, Copenhagen, Denmark). Interdental width in both maxilla and mandible were measured with 3 SHAPE Ortho Analyzer. Four Maxillary and four mandibular interdental width were traced and evaluated. The adequate Student’s t-test (dependent or independent) was used to compare intra and intergroups interdental width differences (p < 0.05). The efficacy of the SME was confirmed both on maxillary and mandibular arch. All the maxillary and mandibular interdental widths increased significantly (p < 0.001). The comparison with the RME group showed significant statistical differences between the two treatments with a greater increase in primary first and second intermolar and canine width for the test group (p < 0.001). SME with Leaf Expander produced statistically significant effects for the correction of transverse maxillary deficiencies with a significant indirect effect on the mandibular arch.

Keywords: maxillary expansion; palatal expansion; crossbite; digital dentistry; digital orthodontics; 3D imaging; slow maxillary expansion; clinical research

1. Introduction Maxillary transverse hypoplasia is commonly associated with uni- or bilateral posterior crossbite with an incidence ranging from 4% to 20% and, depending on the geographical area, even 50% of the population examined [1–5]. Posterior crossbite can result in many diﬀerent growth alterations, with asymmetrical condylar positioning, temporomandibular dysfunction and even more severe skeletal and myofunctional alterations [6–8].

Appl. Sci. 2020, 10, 4512; doi:10.3390/app10134512 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, x FOR PEER REVIEW 2 of 9 Appl. Sci. 2020, 10, 4512 2 of 9 The maxillary deficit does not self-correct during the growth, thus, slow maxillary expansion (SME)The or maxillaryrapid maxillary deficit doesexpansion not self-correct (RME) could during be theperformed growth, with thus, the slow intent maxillary to correct expansion it. As (SME)reported or rapidby several maxillary authors, expansion widening (RME) couldthe maxilla be performed with withmaxillary the intent expansion to correct often it. As reportedleads to byspontaneous several authors, forward widening posturing the and maxilla to spontaneous with maxillary expansion expansion of the often mandible leads to [9–12]. spontaneous This is forwardbecause posturingthe palatal and expansion to spontaneous acts on the expansion balance of of the forces mandible between [9– the12]. tongue This is and because cheek the on palatal lower expansion arch. The actsaction on of the the balance tongue of on forces the betweenmandibular the tongueteeth might and cheek promote on lower the growth arch. The of actionthe mandibular of the tongue dental on thearch mandibular width [12,13]. teeth might promote the growth of the mandibular dental arch width [12,13]. Spontaneous enlargement inin the mandibular dentitiondentition under the influenceinfluence of RME or SME have been reported previouslypreviously [[14–18].14–18]. The LeafLeaf Expander Expander has has been been proposed proposed previously previously in 2016 in by2016 Lanteri by Lanteri et al. [19 et] andal. [19] is now and available is now withavailable two with different two measurementsdifferent measurements of the screw of the (6 sc orrew 9 mm) (6 or and9 mm) with and two with diff twoerent different types of types forces of generatedforces generated by the nickelby thetitanium nickel titanium leaf spring leaf (450 spring or 900 (450 g). or Recently 900 g). Recently the efficacy the of efficacy this new of expanderthis new hasexpander been reported has been byreported the same by authorsthe same in authors pilot studies in pilot based studies on based digital on models digital andmodels postero-anterior and postero- cephalometricanterior cephalometric study. However, study. However, the sample the of sample patients of patients treated was treated limited was tolimited only10 to subjectsonly 10 subjects [20,21]. [20,21].Few data based on 3D noninvasive analysis are available considering the indirect effects of SMEFew on mandibular data based on arch 3D and noninvasive all of those analysis have are been available done with considering a removable the indirect expansion effects plate of SME or a Quadon mandibular Helyx [22 –arch25]. and all of those have been done with a removable expansion plate or a Quad HelyxThe [22–25]. aim of this retrospective study is to quantitatively evaluate the maxillary and mandibular changesThe afteraim theof this SME retrospective treatment with study the is Leaf to quanti Expandertatively in patients evaluate with the maxillarymaxillary archand constrictionmandibular comparedchanges after with the a groupSME treatment of subjects with treated the Leaf with Expander RME. The in null patients hypothesis with maxillary is that the arch Leaf constriction Expander willcompared show lesswith increase a group in of the subjects amount treated of expansion with RM comparedE. The null with hypothesis the RME is group. that the Leaf Expander will show less increase in the amount of expansion compared with the RME group. 2. Materials and Methods 2. Materials and Methods Ninety Caucasian patients, 43 males and 47 females (mean age 7.5 1.5 years), presenting ± withNinety maxillary Caucasian transverse patients, deficiency 43 males and posteriorand 47 females crossbite, (mean were age selected 7.5 ± 1.5 from years), those presenting treated at with the Departmentmaxillary transverse of Biomedical deficiency Surgical and and posterior Dental cro Sciences,ssbite, Universitywere selected of Milan from fromthose June treated 2018 at until the DecemberDepartment 2019. of Biomedical The study Surgical was approved and Dental by the Scie Ethicnces, Committee,University of Fondazione Milan from IRCCS June 2018 Ospedale until Maggiore-Policlinico,December 2019. The Milanstudy (Prot.was approved n◦573). by the Ethic Committee, Fondazione IRCCS Ospedale Maggiore-Policlinico,Inclusion criteria Milan were: (Prot. early n°573). or midmixed dentition with upper primary second molars (E) preserved,Inclusion cervical criteria vertebral were: early stage or 1 throughmidmixed 3 (CVSdenti methodstion with 1–3)upper [26 primary], Angle second Class I ormolars Class (E) II malocclusion,preserved, cervical no previous vertebral orthodontic stage 1 through treatments, 3 (CVS transverse methods maxillary 1–3) [26], hypoplasia, Angle Class digital I or Class records II obtainedmalocclusion, before no activation previous and orthodontic at appliance treatments, removal. transverse Exclusion maxillary criteria were: hypoplasia, presence digital of craniofacial records deformities,obtained before tooth activation extraction and or at surgical appliance treatment, removal. temporomandibular Exclusion criteria were: disorders, presence absence of craniofacial or caries ofdeformities, E. tooth extraction or surgical treatment, temporomandibular disorders, absence or caries of E. Sixty-nine patients (33 males/36 females), mean age 7.6 1.7 years old, treated with SME ± (LeafSixty-nine Expander) patients were selected (33 males/36 according females), to the mean inclusion age 7.6 criteria. ± 1.7 years The appliances old, treated were with banded SME (Leaf by a uniqueExpander) operator were selected on the E. according The expanders to the inclusion presented criteria. a 6 mm The screw appliances (450 g) were with banded an anterior by a armunique till canines;operator no on other the E. orthodontic The expanders treatment presented was applied a 6 mm before screw the (450 removal g) with of thean anterior appliance. arm The till expander canines; wasno other activated orthodontic as described treatment previously was applied by Lanteri before et al.the [ 19removal] (Figure of1 theand appliance. Table1). The expander was activated as described previously by Lanteri et al. [19] (Figure 1–Table 1).

a b c

Figure 1. Test Group:Group: Leaf Expander bandedbanded on primary second molars withwith an anterior arm till the canine before ((aa),), afterafter activationactivation ((bb)) andand toto thethe removalremoval ((cc).).

The RME control group consisted of 21 subjects (10 males/11 females); mean age 7.4 ± 1.2 years old (Table 1). These appliances were banded by a unique operator on the primary second molars. The

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Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 9 Table 1. Starting form comparison (T0 RME vs. T0 slow maxillary expander—SME). expander (Haas type) presented an anterior arm till canines and a posterior till the first permanent molars (Figure 2).Sample Screw Group activation Control was done Group—RME three times per Test day Group—SME for ten days (0.2p Values mm × 3 × 10).

Male b10 c 33 - Female 11 36 - a Age (years) 7.4 1.2 7.6 1.7 - ± ± 16–26 (mm) 43.36 2.34 44 2.17 0.273 ± ± 55–65 (mm) 39.93 2.01 38.85 2.13 0.042 ± ± 54–64 (mm) 34.52 1.99 33.52 1.84 0.054 ± ± 53–63 (mm) 31.51 2.61 30.52 2.23 0.122 ± ± SD = standard deviation. Test t for independent samples, p value < 0.05 were considered to indicate statistical signiﬁcance.Figure 2. Control Group: rapid maxillary expander (RME) banded on primary second molars before (a), after activation (b) and to the removal (c). The RME control group consisted of 21 subjects (10 males/11 females); mean age 7.4 1.2 years ± oldAppl. (TableSci. 20201,). 10Table These, x FOR 1. StartingPEER appliances REVIEW form were comparison banded (T0 by RME a unique vs. T0 slow operator maxillary on theexpander—SME). primary second molars.3 of 9 The expander (Haas type) presented anControl anterior Group— arm till caninesTest Group— and a posterior till the ﬁrst permanent Sample Group p Values molarsexpander (Figure (Haas2). type) Screw presented activation an was anterior doneRME arm three till times canines per daySMEand for a posterior ten days (0.2till the mm first3 permanent10). × × molars (Figure 2). Screw Maleactivation was done10 thr ee times per day33 for ten days- (0.2 mm × 3 × 10). Female b 11 36c - aAge (years) 7.4 ± 1.2 7.6 ± 1.7 - 16–26 (mm) 43.36 ± 2.34 44 ± 2.17 0.273 55–65 (mm) 39.93 ± 2.01 38.85 ± 2.13 0.042 * 54–64 (mm) 34.52 ± 1.99 33.52 ± 1.84 0.054 *

53–63 (mm) 31.51 ± 2.61 30.52 ± 2.23 0.122 FigureSD = standard 2. Control deviation. Group: rapidTest t maxillary for independent expander samples, (RME (RME) )p banded value < on 0.05 primary were considered second molars to indicate before (statisticala), after activation significance; ((b)) *: andand Statistically toto thethe removalremoval significant. ((cc).).

The expansion,expansion, inin bothboth groups, groups, was was considered considered clinically clinically obtained obtained when when the the intercuspation intercuspation of the of Table 1. Starting form comparison (T0 RME vs. T0 slow maxillary expander—SME). lingualthe lingual cusp cusp of the of firstthe first permanent permanent upper upper molar molar laid onlaid the on occlusal the occlusal aspect aspect of the of vestibular the vestibular cusp of cusp the Control Group— Test Group— lowerof the lower first permanent first permanentSample molar. Group molar. p Values Dental casts were done pretreatmentRME and at applianceSME removal with a meanmean comprehensive treatment durationduration (active(activeMale phasephase and and retention) retention)10 of of 9 9 to to 11 11 months months33 and and were were processed- processed by by means means of anof intraoralan intraoral scanner scanner (Trios (Trios 3,Female 3Shape 3, 3Shape D250 laser,D25011 3 laser, Shape, 3 Copenhagen, Shape, 36Copenhagen, Denmark). Denmark).- The sample The comprised sample 180comprised cast models 180 cast (90 models ofAge the (years) maxillary (90 of the and maxillary 907.4 of ± the1.2 and mandibular 90 of the 7.6 mandibular arch). ± 1.7 arch). - Digital landmarks16–26 were (mm) traced by means43.36 ± of 2.34 3Shape3S hape OrthoOrtho 44 ± AnalyzerAnalyzer2.17 softwareso 0.273ftware (version(version 1.7).1.7). Each patient was 55–65 randomly (mm) identified identified39.93 with ± 2.01 a numb number er and and38.85 eight eight ± 2.13 linear linear variables0.042 variables * were were considered, considered, traced and analyzed by54–64 a single (mm) blindedblinded 34.52 examiner.examiner. ± 1.99 33.52 ± 1.84 0.054 * Permanent intermolar, 53–63 (mm) primary canine, 31.51 and± 2.61 firstfirst and 30.52 second ± 2.23 intermolar 0.122 width were measured for allSD subjects. = standard The The deviation. reference Test points t for independentwere set for samples, the molars p value at thethe< 0.05 mesio-palatalmesio-palatal/lingual were considered/lingual to indicate cusps and the intercaninestatistical significance; width was*: Statistically traced between significant. the two caninecanine cuspscusps tipstips (Figures(Figures3 3–6).–6). WhenWhen eithereither thethe deciduous or the permanent teeth were missing or not fully erupted, the measurements for that deciduousThe expansion, or the permanent in both teeth groups, were was missing considered or not fullyclinically erupted, obtained the measurements when the intercuspation for that variable of variable were not traced. werethe lingual not traced. cusp of the first permanent upper molar laid on the occlusal aspect of the vestibular cusp of the lower first permanent molar. Dental casts werea done pretreatment band at appliance removalc with a mean comprehensive treatment duration (active phase and retention) of 9 to 11 months and were processed by means of an intraoral scanner (Trios 3, 3Shape D250 laser, 3 Shape, Copenhagen, Denmark). The sample comprised 180 cast models (90 of the maxillary and 90 of the mandibular arch). Digital landmarks were traced by means of 3Shape Ortho Analyzer software (version 1.7).

Each patient was randomly identified with a number and eight linear variables were considered, tracedFigure and analyzed3. TestTest Group—Leaf: by a single Maxillary Maxillary blinded arch examiner. before ( a ), after after the the expansion expansion ( (b) and and the the superimposition superimposition ofPermanent the two digital intermolar, casts (c) withprimary traced canine, interdentalinterdental and width.firstwidth. and second intermolar width were measured for all subjects. The reference points were set for the molars at the mesio-palatal/lingual cusps and the intercanine width was traced between the two canine cusps tips (Figures 3–6). When either the deciduous or the permanent teeth were missing or not fully erupted, the measurements for that variable were not traced.

a b c

Figure 3. Test Group—Leaf: Maxillary arch before (a), after the expansion (b) and the superimposition of the two digital casts (c) with traced interdental width.

Appl. Sci. 2020,, 10,, x 4512 FOR PEER REVIEW 4 of 9 Appl. Sci. 2020, 10, x FOR PEER REVIEW 4 of 9 Appl. Sci. 2020, 10, x FOR PEER REVIEW 4 of 9 a b c a b c a b c

Figure 4. Test Group—Leaf: Mandibular arch before (a), after the expansion (b) and the Figure 4. Test Group—Leaf: Mandibular arch before (a), after the expansion (b) and the superimpositionFigure 4.4.Test Test Group—Leaf: ofGroup—Leaf: the two digital Mandibular Mandibular casts arch(c). beforearch (abefore), after the(a), expansion after the (b )expansion and the superimposition (b) and the superimposition of the two digital casts (c). ofsuperimposition the two digital of casts the (twoc). digital casts (c). a b c a b c a b c

Figure 5. ControlControl Group—RME: Group—RME: Mandibular Mandibular arch arch before before ( (aa),), after after the the expansion expansion ( (bb)) and the Figure 5. Control Group—RME: Mandibular arch before (a), after the expansion (b) and the superimpositionFigure 5. Control of theGroup—RME: two digital castsMandibular (c). arch before (a), after the expansion (b) and the superimposition of the two digital casts (c). superimposition of the two digital casts (c). a b c a b c a b c

Figure 6.6.Control Control Group—RME: Group—RME: Maxillary Maxillary arch beforearch (abefore), after the(a), expansion after the ( b)expansion and the superimposition (b) and the Figure 6. Control Group—RME: Maxillary arch before (a), after the expansion (b) and the superimpositionofFigure the two 6. digitalControl castsof theGroup—RME: (c )two with digital the digital castsMaxillary landmarks (c) with arch the traced beforedigital by means (landmarksa), after of 3Shape the traced Orthoexpansion by Analyzermeans (b )of softwareand 3Shape the. superimposition of the two digital casts (c) with the digital landmarks traced by means of 3Shape Orthosuperimposition Analyzer software. of the two digital casts (c) with the digital landmarks traced by means of 3Shape 2.1. EvaluationOrtho Analyzer of Reliability software. Ortho Analyzer software. 2.1. Evaluation of Reliability 2.1. EvaluationAll measurements of Reliability were traced by one expert operator that was blinded to the treatment. Measurements2.1. EvaluationAll measurements of were Reliability repeated were on traced 20 randomly by one selected expert dentaloperator casts that by thewas same blinded operator to the and treatment. a different All measurements were traced by one expert operator that was blinded to the treatment. Measurementsone—evenAll measurements he waswere blinded repeated were to traced theon 20 group randomlyby one allocation—to expert selected operator assessdental that intra-casts was andby blindedthe interoperator same to operator the variability.treatment. and a Measurements were repeated on 20 randomly selected dental casts by the same operator and a differentIntraclassMeasurements one—even correlation were herepeated coe wasfficients blinded on (ICC)20 randomlyto werethe group calculated selected allocation—to dental to compare casts assess by within-subject theintra- same and operator variabilityinteroperator and toa different one—even he was blinded to the group allocation—to assess intra- and interoperator variability.between-subjectdifferent one—even Intraclass variability. he correlation was blinded coefficients to the group (ICC) allocation—towere calculated assess to intra-compare and within-subject interoperator variability. Intraclass correlation coefficients (ICC) were calculated to compare within-subject variabilityvariability. to Intraclass between-subject correlation variability. coefficients (ICC) were calculated to compare within-subject 2.2.variability Statistical to between-subject Analysis variability. variability to between-subject variability. 2.2. StatisticalThe software Analysis MedCalc (v. 18.10.2) was used for the statistical analysis. 2.2. Statistical Analysis Descriptive statistics were expressed as mean value and standard deviation. The adequate Student’s 2.2. StatisticalThe software Analysis MedCalc (v. 18.10.2) was used for the statistical analysis. t-testThe (dependent software or MedCalc independent) (v. 18.10.2) was used wa tos compareused for intrathe statistical and intergroups analysis. interdental width differences. DescriptiveThe software statistics MedCalc were (v. 18.10.2) expressed was asused mean for thevalue statistical and standard analysis. deviation. The adequate Ninety-fiveDescriptive percent statistics confidence were interval expressed was also as calculatedmean value (Table and1 ).standard deviation. The adequate Student’sDescriptive t-test (dependent statistics were or independent) expressed as was mean used value to compare and standard intra and deviation. intergroups The interdental adequate Student’sAll the t-test interdental (dependent widths or independent) expressed in millimeters was used to were compare compared intra andand evaluated.intergroups The interdental Shapiro– widthStudent’s differences. t-test (dependent Ninety-five or percentindependent) confiden wasce usedinterval to compare was also intracalculated and intergroups (Table 1). interdental Wilkwidth test differences. for normality Ninety-five showed percent that data confiden werece normally interval distributed.was also calculated A p value (Table< 0.051). was set as widthAll differences. the interdental Ninety-five widths expressedpercent confiden in millimetce intervalers were was compared also calculated and evaluated. (Table 1). The Shapiro– statisticallyAll the significant.interdental widths expressed in millimeters were compared and evaluated. The Shapiro– Wilk Alltest the for interdental normality widths showed expressed that data in were millimet normallyers were distributed. compared Aand p evaluated.value < 0.05 The was Shapiro– set as Wilk test for normality showed that data were normally distributed. A p value < 0.05 was set as statisticallyWilk test for significant. normality showed that data were normally distributed. A p value < 0.05 was set as 3.statistically Results significant. statistically significant. 3. ResultsPosterior crossbite was clinically corrected in all the subjects with an improvement of the transversal 3. Results maxillary dimension. The ICC values for the intra- and interobserver agreement were always larger 3. ResultsPosterior crossbite was clinically corrected in all the subjects with an improvement of the thanPosterior 0.88. The meancrossbite error was was clinically less than 0.3corrected mm. The in methodall the subjects error was with considered an improvement negligible. of the transversalPosterior maxillary crossbite dimension. was clinically The ICC corrected values infor all the the intra- subjects and interobserverwith an improvement agreement of were the transversalDescriptive maxillary statistics dimension. and statistical The ICC results values of maxillary for the intra- and mandibular and interobserver measurements agreement at T0 were and alwaystransversal larger maxillary than 0.88. dimension. The mean The error ICC was values less thanfor the 0.3 intra- mm. andThe interobservermethod error agreementwas considered were T1always in the larger test and than control 0.88. groupThe mean are shownerror was in Tables less than2–5. 0.3 mm. The method error was considered negligible.always larger than 0.88. The mean error was less than 0.3 mm. The method error was considered negligible. negligible.

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Table 2. Paired t-test comparing the mean interdental maxillary width (mm) increase after SME

treatment—Test Group (n◦69).

Interdental T0 Mean SD CI 95% T1 Mean SD CI 95% Increase SD CI 95% Significance Maxillary Width 16–26 width 44 2.17 43.46–44.54 46.51 2.46 45.97–47.05 2.51 1.58 2.14–2.88 <0.001 55–65 width 38.85 2.13 38.36–39.33 43.91 2.13 43.43–44.40 5.06 0.98 4.84–5.28 <0.001 54–64 width 33.52 1.84 33.00–34.04 38.93 2.44 38.41–39.46 5.41 1.8 5–5.84 <0.001 53–63 width 30.52 2.23 29.95–31.10 35.75 2.73 35.17–36.33 5.22 1.91 4.77–5.41 <0.001 SD = standard deviation CI = confidence interval; p value < 0.05 were considered to indicate statistical significance.

Table 3. Paired t-test comparing the mean interdental mandibular width (mm) increase after SME

Treatment—Test Group (n◦69).

Interdental Mandibular T0 Mean SD CI 95% T1 Mean SD CI 95% Increase SD CI 95% Significance Width 36–46 width 45.58 2.61 44.99–46.17 46.82 2.51 46.23–47.40 1.24 1.09 0.992–1.49 <0.001 75–85 width 39.62 2.36 39.06–40.19 41.23 2.63 40.66–41.79 1.63 1.57 1.25–1.95 <0.001 74–84 width 32.16 1.95 31.70–32.61 33.09 2.01 32.63–33.54 0.93 1.08 0.684–1.18 <0.001 73–83 width 25.46 2.03 25.03–25.89 26.46 1.75 26.03–26.89 1.03 1.25 0.719–1.28 <0.001 SD = standard deviation CI = confidence interval; p value < 0.05 were considered to indicate statistical significance.

Table 4. Paired t-test comparing the mean interdental maxillary width (mm) increase after RME

treatment—Control Group (n◦21).

Interdental T0 Mean SD CI 95% T1 Mean SD CI 95% Increase SD CI 95% Significance Maxillary Width 16–26 width 43.36 2.34 42.4–44.4 47.17 2.1 46.3–48.1 3.81 1.43 3.2–4.44 <0.001 55–65 width 39.93 2.01 35.4–41.6 43.12 1.78 42.3–43.9 3.2 1.1 2.74–3.68 <0.001 54–64 width 34.52 1.99 33.6–35.4 37.82 1.63 37.1–38.5 3.3 1.22 2.77–3.83 <0.001 53–63 width 31.51 2.61 30.4–32.6 35.15 2.45 34.2–36.3 3.63 1.51 2.99–4.29 <0.001 SD = standard deviation CI = confidence interval; p value < 0.05 were considered to indicate statistical significance.

Table 5. Paired t-test comparing the mean interdental mandibular width (mm) increase after RME

treatment—Control Group (n◦21).

Interdental Mandibular T0 Mean SD CI 95% T1 Mean SD CI 95% Increase SD CI 95% Significance Width 16–26 width 44.81 2.08 43.9–45.7 46.84 2.02 45.9–47.7 2.02 1.33 1.46–2.6 <0.001 55–65 width 39.45 2.37 38.5–40.5 41.2 2.52 40.1–42.3 1.75 1.38 1.21–2.31 <0.001 54–64 width 32.34 1.57 31.66–33 33.74 1.88 32.9–34.5 1.39 1.18 0.891–1.91 <0.001 53–63 width 26.43 2.14 25.5–27.3 27.38 2.18 26.5–28.3 0.95 1.1 0.484–1.42 <0.001 SD = standard deviation CI = confidence interval; p value < 0.05 were considered to indicate statistical significance.

Statistically significant differences were found in all of the intragroup comparisons of the test group (p < 0.05). SME—test group: all the interdental widths of the maxilla (Table2) increased significantly: first permanent molars +2.51 mm (SD 1.58 mm), second primary molar +5.06 mm (SD 0.98 mm), first primary molar +5.41 mm (SD 1.81 mm), primary canine +5.22 mm (SD 1.91 mm). As shown in Table3, even the mandibular interdental width of the test group increased significantly: intermolar width increased by 1.24 mm (SD 1.09 mm), first primary intermolar 1.63 mm (SD 1.57 mm), second primary intermolar by 0.93 mm (SD 1.08 mm), intercanine width 1.03 mm (SD 1.25 mm). RME—control group: all the interdental widths increased significantly in both arches and are shown in Tables4 and5. Appl. Sci. 2020, 10, 4512 6 of 9

Treatment comparison between the control and the test group (Tables6 and7) showed statistically significant differences indicating a greater increase in patients treated with the Leaf Expander in the upper first and second primary intermolar (p < 0.001) and primary canine width (p < 0.001). The control group presented a greater expansion only in the first permanent molar (p < 0.05). The other interdental width showed no significant statistical differences.

Table 6. T test for independent samples comparing the net (∆T1 T0) interdental width (mm) increase − after Leaf (n◦69) or RPE treatment (n◦21)—maxillary arch.

Interdental Leaf Group RPE Group CI 95% CI 95% Significance Maxillary Width Mean SD Mean SD 16–26 width 2.51 1.58 2.14–2.88 3.8 1.4 3.22–4.4 <0.001 55–65 width 5.06 0.98 4.84–5.28 3.2 1.1 2.61–3.85 <0.001 54–64 width 5.41 1.8 4.98–5.84 3.3 1.2 2.82–3.86 <0.001 53–63 width 5.22 1.91 4.78–5.66 3.6 1.5 2.98–4.28 <0.001 SD = standard deviation CI = confidence interval; NS = not significant p value < 0.05 were considered to indicate statistical significance.

Table 7. T-Test for independent samples comparing the net (∆T1 T0) interdental width (mm) increase − after Leaf (n◦69) or RPE treatment (n◦21)—mandibular arch.

Interdental Leaf Group RPE Group CI 95% CI 95% Significance Mandibular Width Mean SD Mean SD 36–46 width 1.24 1.09 0.992–1.49 2.02 1.43 1.41–2.63 0.009 75–85 width 1.63 1.57 1.25–1.95 1.75 1.38 1.16–2.34 NS–0.753 74–84 width 0.93 1.08 0.692–1.18 1.39 1.18 0.885–1.9 NS–0.098 73–83 width 1.03 1.25 0.717–1.28 0.95 1.10 0.482–1.42 NS–0.792 SD = standard deviation CI = confidence interval; NS = not significant p value < 0.05 were considered to indicate statistical significance.

4. Discussion This study aimed to confirm the efficacy of a new Slow Maxillary Expander—The Leaf Expander— in a large sample of growing patients and to compare the results obtained with those of patients treated with a RME. The first main clinical effect achieved is that the maxillary crossbite was corrected in all the patients. We obtained also significant statistical results for the lower dental measurements. Recently in a study by Di Ventura et al. [14], it was observed that there are no differences when comparing mono or bilateral crossbites; thus, we considered as a unique group all the patients presenting mono or bilateral crossbites. Few studies have been reported about SME effects both on the maxillary and the mandibular arches [18–21]. In 2018, Bukhari et al. [27] evaluated transversal interdental increase in a group of 30 patients treated with a banded Haas-Type appliance activated one quarter-turn every two days. The mean intercanine width increased 4.65 mm with values comparable with those reported also by Wong et al. [27,28]. These results were greater than those reported for other patients in mixed dentition treated with SME and RME such as Hyrax appliance, expansion plates, or quad helix [23,25,29]. However, our values are even higher than those with an increase in the intercanine width of more than 5 mm in accordance with the preliminary results published on the Leaf Expander appliance [20]. Bucci et al. published a review in 2016 reporting the dental effects of different slow maxillary expansion appliances. From these data, it has been confirmed with moderate evidence the efficacy of the Quad Helix for the increase of the maxillary intermolar and intercanine width [22,30,31]. Appl. Sci. 2020, 10, 4512 7 of 9

From these reviews it has been reported that there is not a significative difference comparing dentoalveolar transversal effects of the SME with the RME. Contrariwise in our study we have noticed significant differences comparing the test group with the RME. The Leaf Expander produced a significative greater expansion for maxillary intercanine and primary intermolar width. However, the interdental change for the first permanent molars was greater in the RME group. This might be explained also considering that the RME was banded with a posterior arm that is not placed on the Leaf Expander. Despite this, all the interdental widths in the test group were significantly improved when comparing the pre and post-treatment values. Minimal data has been already published about the SME effects on the mandibular arch: an increase of 0.49 mm was previously found on the lower molars and considered as clinically not relevant, thus indicating a lesser spontaneous adaptation of the lower dentition [22,30]. Indeed, in the test group we observed a significant increment of all the interdental width that was higher than those previously reported for the SME and comparable with those of the RME. Moreover, unlike previous studies, deciduous teeth such as primary molars were included in our study. Almost all the lower interdental width in the test group increased more than 1 mm (except for the lower first primary molar +0.93 mm). Mandibular intermolar width (1.19 mm) and intercanine (0.9 mm) inter second primary molar (0.7 mm) were found to be increased in the patients treated with Hyrax or Haas expander in previous studies [28]. The results of the control group were in accordance with this data confirming a spontaneous response of the lower arch after RME. The interdental width increment in the lower arch should be considered as the result gained from the increase of tongue pressure and the reduction of lip pressure and new occlusal intercuspation [32]. Moreover, the tongue lowers its position due to the presence of the expander (the Leaf Expander has the same structure as the RME of the control group) influencing and promoting the enlargement in the position of the lower teeth. Another important consideration is that the new intercuspation during the action of chewing might also promote expansive forces in the mandibular dental arch. Patients were selected in order to be far from their puberty growth peek and the measurements have been taken after a short period (not more than 11 months) from baseline in order to be able to consider the expansion obtained as the direct consequence of the treatments with no or insignificant influence of the spontaneous physiological growth. Posterior crossbite correction and stability of the expansion by other SME such as the Quad-Helyx has shown more than 90% of stability during the retention phase confirming the long-term effectiveness of SME [31,33]. The main limitation of the study is the lack of a long-term follow-up and the retrospective design of the study. Randomized controlled clinical trials are needed to confirm our results.

5. Conclusions Therapy with Leaf Expander anchored on primary molars is an effective treatment option to correct maxillary transverse deficiencies and crossbites. Within the limitations of this study, the mandibular and maxillary interdental arch widths increased significantly in both groups. A significant greater improvement resulted considering the primary canine and molars interdental width in the SME compared with those of the RME group. These results demonstrated also a statistically significant mandibular spontaneous response with RME and SME whose clinical influence should be better studied.

Author Contributions: Conceptualization, V.L. and G.C.; methodology, V.L. and G.C.; software, M.B. and A.G.; validation, V.L. and M.B.; formal analysis, G.C. and A.U. and M.B.; investigation, V.L and M.B. and A.G.; resources, V.L. and A.U.; data curation, G.C. and M.B.; writing—original draft preparation, G.C.; writing—review and editing, M.B., V.L. and A.U.; supervision, V.L.; project administration, V.L. and G.C., M.F. and C.M. made the investigation and supervision of the article. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂict of interest. Appl. Sci. 2020, 10, 4512 8 of 9

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