The Behavior of Two Types of Upper Removable Retainers—Our Clinical Experience

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Article The Behavior of Two Types of Upper Removable Retainers—Our Clinical Experience

Luminita Ligia Vaida 1 , Eugen Silviu Bud 2,*, Liliana Gabriela Halitchi 3,*, Simona Cavalu 4 , Bianca Ioana Todor 1, Bianca Maria Negrutiu 1, Abel Emanuel Moca 1 and Florian Dorel Bodog 5 1 Department of Dentistry, Faculty of Medicine and Pharmacy, University of Oradea, 1 Universitatii Str., 410087 Oradea, Romania; [email protected] (L.L.V.); [email protected] (B.I.T.); [email protected] (B.M.N.); [email protected] (A.E.M.) 2 Department of Orthodontics, University of Medicine and Pharmacy Science and Technology G.E Palade, 38 Gh. Marinescu Str., 540139 Targu Mures, Romania 3 Department of Clinical Disciplines, Faculty of Dentistry, Apollonia University of Iasi, 2 Muzicii Str., 700399 Iasi, Romania 4 Department of Preclinical Sciences, Faculty of Medicine and Pharmacy, University of Oradea, 1 Universitatii Str., 410087 Oradea, Romania; [email protected] 5 Department of Surgery, Faculty of Medicine and Pharmacy, University of Oradea, 1 Universitatii Str., 410087 Oradea, Romania; [email protected] * Correspondence: [email protected] (E.S.B.); [email protected] (L.G.H.)

Received: 26 October 2020; Accepted: 14 December 2020; Published: 16 December 2020

Abstract: The Hawley retainer (HR) and the vacuum-formed retainer (VFR) are the most common removable retainers in orthodontic treatments. The aim of this retrospective study was to comparatively analyze the behavior of two types of removable retainers—HRs and VFRs—in terms of retainer damage, loss, and the rate of installation of mild or severe relapse that required recourse to certain therapeutic interventions. The study was performed on 618 orthodontic patients aged 11–17 years, average age 13.98 1.51, out of which 57% were patients having VFRs and the remaining ± 43% having HRs in the upper arch. We performed an analysis of the two groups of patients—HRs group and VFRs group—at 6 months (T1) and at 12 months (T2) after the application of the retainer. The results showed that 6% of all the retainers were damaged, mostly at T2 (54.1%). Seven percent of all the retainers were lost, mostly at T1 (58.1%). Of all the patients, 9.1% presented mild relapse, mostly at T1 (58.9%), while 2.6% presented severe relapse. The VFRs were signiﬁcantly more frequently associated with the occurrence of damage than the HRs (p < 0.001). Severe relapse was more frequently associated with the HRs rather than with VFRs (p < 0.05).

Keywords: Hawley retainer; vacuum-formed retainer; relapse; orthodontic treatment; children and adolescents

1. Introduction The aim of the orthodontic treatment is not only to improve oral functioning and health but also to enhance dento-facial esthetics, self-esteem, and oral health-related quality of life [1]. Retention is a sine-qua-non condition of orthodontic treatment and its aim is to maintain the teeth in the correct position obtained at the end of the active phase of the orthodontic treatment. The omission of the retention phase has as consequence the relapse, the tendency for the initial malocclusion to reappear [2,3]. Relapse may occur due to imbalances in the gingival ﬁbers, periodontal tissues, occlusion, or facial soft tissues [4,5]. Unwanted changes may also occur after the removal of the orthodontic ﬁxed appliance (at the end of the active phase of orthodontic treatment) in growing patients, due to unfavorable growth trends. Unfortunately, no prediction can be made regarding the risk of relapse in the event of giving

Children 2020, 7, 295; doi:10.3390/children7120295 www.mdpi.com/journal/children Children 2020, 7, 295 2 of 16 up the retention phase [6]. So far, the specialized literature has described several types of retainers that can be classified as removable retainers and fixed retainers [7–10]. There is no unanimous consensus for any of the existing types of retainers, each with advantages and disadvantages [11,12]. The Hawley retainer (HR) and the vacuum-formed retainer (VFR) are the most common removable retainers. The Hawley retainer was introduced 100 years ago by Charles Hawley (1919) and has been widely used over time. It consists of an acrylic mass applied to the palatal mucosa, in contact with the palatal surfaces of all the teeth on the dental arch, Stahl or Adams clasps, and a labial bow made of stainless-steel wire. The labial bow passes from 4 or 6 anterior teeth and its advantages can include controlling the incisor torque and allowing vertical movement of posterior teeth [11]. The main disadvantages of the HR are related to the large extension on the palate and the visibility of the labial bow. VFR is considered an alternative to HR and is also known as clear thermoplastic retainers. Sheridan et al. [13] introduced a removable retainer in 1993, a vacuum-formed retainer that has been extensively used in the last years under the commercial name of Essix (DENTSPLY Raintree Essix Glenroe, Sarasota, FL, USA). This retainer is made from polyvinyl siloxane sheets to cover all the surfaces of the teeth [14]. Other materials used for the thermoplastic retainers are the following: polypropylene polymer-based material (Invisacryl C, Essix C+), polyethylene copolymers (Essix ACE), and polyethylene terephthalate glycol copolymer—PETG (a hard sheet material) [14,15]. The advantage of polyethylene polymers is that they allow the acrylic to be bonded to them. Therefore, polyethylene polymers are preferred in cases where bite planes must be incorporated into the appliances. Polypropylene polymers are more durable and flexible, but esthetically speaking, they are inferior to polyethylene as they are translucent. Moreover, acrylic cannot be added to the polypropylene polymers [16]. The advantages of these VFRs include superior esthetics, low cost, and ease of fabrication. The most common disadvantages are fractures (poor wear resistance and durability), occlusal wear, and limited vertical settling of teeth [14,17,18]. Frequently, the thicknesses of VFRs are 0.75 mm (0.30 inch) or 1 mm (0.40 inch) [19,20]. Over the last decades, many studies have been published on the effectiveness, advantages, disadvantages of retainers, patient comfort (patient satisfaction, accommodation period, compliance, speech, mastication) [21–23], periodontal health [5], and the costs involved in the retention stage [8], but all these studies revealed much controversy about the risks of relapse. The aim of our study was to comparatively analyze the behavior of two types of removable retainers—HR and VFR—in terms of retainer damage (fracture, discoloration), loss, and the rate of installation of mild or severe relapse, requiring recourse to certain therapeutic interventions.

2. Materials and Methods

2.1. Patients A retrospective study was performed on 900 orthodontic patients aged 11–17.9 years, randomly selected, for whom removable retainers—HRs and VFRs—were used on the upper arch during the retention phase. Of these, 469 patients (52.11%) were girls, and 431 patients (47.89%) were boys. The study was conducted in accordance with the World Medical Association (WMA) Declaration of Helsinki—Ethical Principles for Medical Research Involving Human Subjects, approved by the Ethics Committee of the University of Oradea, Romania (Project identiﬁcation code: 10/15.10.2020). All patients were included in the study with their parents or legal tutors’ consent. All subjects gave their informed consent for inclusion before they participated in the study. The inclusion criteria in this retrospective study were as following: (1) patients to whom the phase of active orthodontic treatment at the upper arch was performed with ﬁxed orthodontic appliances; (2) patients to whom a correct dental alignment/correct three-dimensional positioning was achieved, and inclination within normal limits of the upper frontal group; (3) patients who could be monitored for a period of at least 1 year in the retention phase; (4) crowding at the start of the orthodontic treatment, good alignment and clinically acceptable outcome at the end of the active treatment (zero values of the irregularity index for Children 2020, 7, x FOR PEER REVIEW 3 of 16

Children 2020, 7, 295 3 of 16 within normal limits of the upper frontal group; (3) patients who could be monitored for a period of at least 1 year in the retention phase; (4) crowding at the start of the orthodontic treatment, good thealignment 6 anterior and superior clinically teeth); acceptable (5) no systemic outcome or at oral the disease.end of the The active exclusion treatment criteria (zero were values the following: of the (1)irregularity patients who index did for not the present 6 anterior for superior consultation teeth); for (5) a no period systemic of at or least oral onedisease. year The in the exclusion retention phase;criteria (2) were patients the following: who could (1) not patients achieve who the did correct not present three-dimensional for consultation alignment for a period and of positioning at least ofone the year teeth; in (3) the patients retention with phase; cleft (2) lip patients or palate, who sectional could not ﬁxed achieve orthodontic the correct treatment three‐dimensional in the upper arch,alignment severe rotationsand positioning or midline of diastemathe teeth; suggesting (3) patients the needwith forcleft a bondedlip or palate, retainer, sectional poor periodontal fixed orthodontic treatment in the upper arch, severe rotations or midline diastema suggesting the need condition; (4) patients with a restorative need in the labial segment (e.g., implant, bridges, veneers) or for a bonded retainer, poor periodontal condition; (4) patients with a restorative need in the labial missing teeth. segment (e.g., implant, bridges, veneers) or missing teeth. Following the application of the inclusion/exclusion criteria, 618 patients remained in the study, out Following the application of the inclusion/exclusion criteria, 618 patients remained in the study, of which 352 were patients with vacuum-formed retainers (VFRs group). Out of these 352 patients with out of which 352 were patients with vacuum‐formed retainers (VFRs group). Out of these 352 VFRs, 181 patients (51.42%) were girls and 171 patients (48.57%) were boys. The remaining 266 patients patients with VFRs, 181 patients (51.42%) were girls and 171 patients (48.57%) were boys. The woreremaining Hawley 266 retainers patients (HRs wore group), Hawley of retainers these 137 (HRs patients group), (51.50%) of these were 137 girlspatients and (51.50%) 129 patients were (48.49%) girls wereand boys. 129 patients Patients (48.49%) in both groupswere boys. were Patients advised in to both wear groups the retainers were advised full-time to for wear 3–4 the months retainers (except duringfull‐time meals) for 3–4 and months then night-only. (except during We performed meals) and an then analysis night‐only. of the We two performed batches at an 6 analysis months of (T1) the and 12two months batches (T2) at after 6 months the application (T1) and 12 of months the retainer. (T2) after the application of the retainer.

2.2.2.2. Measurements Measurements TheThe assessment assessment of of thethe correctcorrect teeth positioning at at the the end end of of the the active active orthodontic orthodontic treatment treatment waswas made made by by clinicalclinical observation, observation, measuring measuring irregularity irregularity index index using using study study models models (Figure (Figure 1a), and1 a), andby bycephalometric cephalometric assessment assessment of the of inclination the inclination of the upper of the incisors. upper Thus, incisors. we assessed Thus, we the assessed anterior‐ the anterior–posterior–posterior position position of the of upper the upper incisors incisors at the at end the endof the of theorthodontic orthodontic treatment treatment by bymeasuring measuring 1—A-Pog1—A‐Pog (upper (upper central central incisor incisor to to A-Pog) A‐Pog) angle angle (angle (angle formed formed by by the the extension extension of of the the longitudinal longitudinal axis ofaxis maxillary of maxillary incisor incisor to the A-Pog to the line, A‐Pog with line, normal with values normal of values 3 5 degrees) of 3 ± 5 on degrees) the lateral on cephalograms.the lateral ± Tocephalograms. measure the 1—A-PogTo measure values, the 1—A we used‐Pog avalues, computerized we used defalcation a computerized software defalcation entitled software OnyxCeph versionentitled 69 OnyxCeph (open software version license) 69 (open (Figure software1b). In license) order to (Figure analyze 1b). the In correct order alignmentto analyze of the the correct anterior maxillaryalignment teeth of the at theanterior end of maxillary the orthodontic teeth at activethe end treatment of the orthodontic (prior to the active application treatment of (prior the removable to the retainer),application but alsoof the during removable the ﬁrst retainer), year of but the also retention during phase the first in cases year with of the changes retention in the phase position in cases of the upperwith teethchanges (respectively in the position the cases of the with upper relapse), teeth irregularity (respectively indexes the cases (similar with to therelapse), index irregularity introduced by indexes (similar to the index introduced by Little R.M. [24] for the six anterior mandibular Little R.M. [24] for the six anterior mandibular teeth—Little’s irregularity indexes) were measured on teeth—Little’s irregularity indexes) were measured on dental casts. The irregularity index was dental casts. The irregularity index was calculated based on the linear measurement of displacements calculated based on the linear measurement of displacements in the anatomical contact points of in the anatomical contact points of upper anterior teeth, parallel to the occlusal plane (Figure1a). upper anterior teeth, parallel to the occlusal plane (Figure 1a). We used a digital caliper with a 0.01 We used a digital caliper with a 0.01 mm sensitivity for these measurements. All cephalometric analyses mm sensitivity for these measurements. All cephalometric analyses and dental cast measurements andwere dental performed cast measurements by the same investigator were performed to avoid by inter the same‐operator investigator bias. to avoid inter-operator bias.

FigureFigure 1. 1.( a()a) Dental Dental cast cast measurements: measurements: Irregularity index index (A (A ++ BB + +C C+ +D D+ +E);E); (b) ( bCephalometric) Cephalometric analysisanalysis using using OnixCeph OnixCeph software. software.

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Children 2020, 7, x FOR PEER REVIEW 4 of 16 Children 2020, 7, x FOR PEER REVIEW 4 of 16 2.3. Procedure 2.3. Procedure The Hawley retainers had Adams clasps attached, labial bow with vertical loops, and palatal The Hawley retainers had Adams clasps attached, labial bow with vertical loops, and palatal acrylic.The The Hawley acrylic partretainers of the had Hawley Adams retainer clasps hadattached, a uniform labial thickness bow with (2–3 vertical mm), loops, and it and was palatal trimmed acrylic. The acrylic part of the Hawley retainer had a uniform thickness (2–3 mm), and it was intoacrylic. a horseshoe The acrylic shape. part The of labialthe Hawley bow extended retainer had to the a posterioruniform thickness region (molar-to-molar) (2–3 mm), and it and was was trimmed into a horseshoe shape. The labial bow extended to the posterior region (molar‐to‐molar) solderedand was to soldered the Adams to the clasps. Adams It can clasps. be eﬀ Itective can be in controllingeffective in incisorcontrolling torque incisor and thetorque position and the of the caninesand was and soldered premolars to asthe well Adams (Figure clasps.2). It can be effective in controlling incisor torque and the position of the canines and premolars as well (Figure 2).

Figure 2. (a) Hawley retainer (HR); (b) HR view in the oral cavity. FigureFigure 2. 2. ((aa)) Hawley retainer retainer (HR); (HR); (b (b) )HR HR view view in in the the oral oral cavity. cavity. The VFRs were manufactured from polyethylene terephthalate glycol copolymer (PETG) 1 mm The VFRs were manufactured from polyethylene terephthalate glycol copolymer (PETG) 1 mm thicknessthickness (0.040”) (0.040″) sheet sheet materials materials accordingaccording to to the the manufacturer’s manufacturer’s instructions, instructions, and and these these maxillary maxillary retainersretainers were were trimmed trimmed into into a a horseshoe horseshoe shape. To To obtain obtain the the VFRs, VFRs, we we used used a vacuum a vacuum machine machine that that adaptsadapts heat-softened heat‐softened plastic plastic byby negativenegative pressure, creating creating a avacuum, vacuum, and and pulls pulls the the plastic plastic onto onto a a workingworking cast cast (Figure (Figure3). 3).

Figure 3. (a) Vacuum‐formed retainer (VFR); (b) VFR view in the oral cavity. FigureFigure 3. 3. ((aa)) Vacuum-formedVacuum‐formed retainer retainer (VFR); (VFR); (b (b) )VFR VFR view view in in the the oral oral cavity cavity..

TheThe e ﬃefficiencyciency of of both both typestypes ofof removableremovable retainers retainers was was evaluated evaluated according according to tothe the following following criteria:criteria: ‐ Damage of the retainers (fractures—perforated and cracked, loss, unfitting and obvious - ‐ DamageDamage ofof thethe retainersretainers (fractures—perforated(fractures—perforated and and cracked, cracked, loss, loss, unfitting unﬁtting and and obvious obvious discolorations) as a result of which the respective retainers could no longer be used, requiring discolorations)discolorations) as a a result result of which of which the respective the respective retainers retainers could no could longer nobe used, longer requiring be used, restoration. requiring restoration. ‐ Loss of the retainer. - Loss of the retainer. ‐ The rate of installation of mild or severe relapse of dento‐maxillary anomalies, requiring the use - The rate of installation of mild or severe relapse of dento-maxillary anomalies, requiring the use of various therapeutic interventions. of various therapeutic interventions.

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We considered as mild relapse situations where the irregularity index had values of maximum 1 mm (these cases can be solved with the same Hawley retainer or with a new VFR on the set-up model) or changes in the inclination of the upper incisors (1 to A-Pog) were maximum 2 degrees from the value at the end of the active phase of the orthodontic treatment. Cases with mild relapse can be solved by activating the Hawley retainer or by manufacturing a thermoplastic retainer on the setup model. We considered as severe relapse the cases where the irregularity index was over 1 mm or with 1 to A-Pog value diﬀerences of over 2 degrees compared to the value at the end of the active phase of the orthodontic treatment; these situations required the reapplication of ﬁxed orthodontic appliances or the use of clear aligners.

2.4. Data Analysis All the data were analyzed using IBM SPSS Statistics 25. Quantitative variables were expressed as averages with standard deviations and medians with interquartile ranges. Shapiro–Wilk test was used for distribution testing. Qualitative variables were expressed as counts with percentages and were tested using Fisher’s Exact Test for evaluating statistical diﬀerences between groups. Quantitative variables with non-parametric distribution were tested using the Mann–Whitney U test.

3. Results Data presented in Table1 show the characteristics of the studied patients. The average age was 13.98 1.51 years with a median age of 13.7 years. VFRs were applied to 57% of the patients and HRs ± to 43% of them. Six percent of all the retainers were damaged, mostly at T2 (54.1%), while 7% of all retainers were lost, mostly at T1 (58.1%). Of all the patients, 9.1% presented mild relapse, mostly in the ﬁrst 6 months (58.9%), while 2.6% presented severe relapse, mostly in the ﬁrst 6 months (62.5%).

Table 1. Characteristics of the studied patients.

Parameter Value Age (Average SD, Median–IQR) 13.98 1.51, 13.7 (12.7–15.1) ± ± Retainer type (No./%) 266 (43%) HR/352 (57%) VFR Damage (No./%) 37 (6%) Damaged retainers Type of damage (No./%) Fracture at T1 14 (37.8%) Fracture at T2 20 (54.1%) Severe discoloration at T1 3 (8.1%) Loss (No./%) 43 (7%) Lost retainers Type of loss (No./%) Loss at T1 25 (58.1%) Loss at T2 18 (41.9%) Mild relapse (No./%) 56 (9.1%) Type of mild relapse (No./%) Mild relapse in the ﬁrst 6 months 33 (58.9%) Mild relapse after 6 months 23 (41.1%) Severe relapse (No./%) 16 (2.6%) Type of severe relapse (No./%) Severe relapse in the ﬁrst 6 months 10 (62.5%) Severe relapse after 6 months 6 (37.5%) HR: The Hawley retainer; VFR: the vacuum-formed retainer; SD: standard deviation; IQR: interquartile ranges.

Table2 and Figure4 present a comparison of patients’ age according to the type of retainer applied. The distribution of the patients’ age was detected to be non-parametric according to the Shapiro–Wilk Children 2020, 7, 295 6 of 16

Children 2020, 7, x FOR PEER REVIEW 6 of 16 test (p < 0.001). According to the Mann–Whitney U test, the diﬀerences in the patients’ age according to agethe typeaccording of retainers to the was type not of signiﬁcant retainers was (p = 0.983),not significant and the median(p = 0.983), age inand both the groups median was age 13.7 in years.both groups was 13.7 years. Table 2. Comparison of patients’ age according to the type of retainer. Table 2. Comparison of patients’ age according to the type of retainer. Retainer Average SD Median (IQR) Average Rank p * ± HR (p < 0.001Retainer **) 13.98Average1.53 ± SD 13.7 (12.7–15.1)Median (IQR) 309.33Average Rank p * ± 0.983 VFR (pHR< 0.001 (p < **)0.001 **) 13.97 13.981.49 ± 1.53 13.7 (12.7–15.07)13.7 (12.7–15.1) 309.63 309.33 ± 0.983 VFR (p < 0.001 **) 13.97* Mann–Whitney ± 1.49 U Test,13.7 ** (12.7–15.07) Shapiro–Wilk Test. 309.63 * Mann–Whitney U Test, ** Shapiro–Wilk Test.

Figure 4. Comparison of patients’ age according to the type of retainer. Figure 4. Comparison of patients’ age according to the type of retainer. The distribution of the patients according to the occurrence of damage and the type of retainer is The distribution of the patients according to the occurrence of damage and the type of retainer presented in Table3 and Figure5. Di fferences between groups were detected as significant according to is presented in Table 3 and Figure 5. Differences between groups were detected as significant Fisher’s Exact Test (p < 0.001), emphasizing that the VFRs are significantly more frequently associated according to Fisher’s Exact Test (p < 0.001), emphasizing that the VFRs are significantly more with the existence of damage compared with the HRs. The odds ratio is 5.22 (95% C.I: 2.006–13.587), frequently associated with the existence of damage compared with the HRs. The odds ratio is 5.22 which shows that it is 5.22 times more probable that VFRs would be damaged. (95% C.I: 2.006–13.587), which shows that it is 5.22 times more probable that VFRs would be damaged.Table 3. Distribution of the patients according to the occurrence of damage and type of retainer.

Table 3. Distribution of the patientsHawley according Retainer to the occurrence Vacuum-Formed of damage and type Retainer of retainer. Type of Retainer/Damage p * NoHawley Retainer % Vacuum No‐Formed Retainer % Type ofNo Retainer/Damage damage 261 98.1% 320 90.9% p * No % No % <0.001 NoDamage damage 5261 98.1% 1.9% 320 3290.9% 9.1% <0.001 Damage 5 * Fisher’s1.9% Exact Test. 32 9.1% * Fisher’s Exact Test.

Children 2020, 7, 295 7 of 16 Children 2020, 7, x FOR PEER REVIEW 7 of 16 Children 2020, 7, x FOR PEER REVIEW 7 of 16

Figure 5. Distribution of the patients according to the existence of damage and type of retainer. FigureFigure 5.5. DistributionDistribution ofof thethe patientspatients accordingaccording toto thethe existenceexistence ofof damagedamage andand typetype ofof retainer.retainer. Data from Table4 and Figure6 show the distribution of the patients according to the type of DataData fromfrom TableTable 44 andand FigureFigure 66 showshow thethe distributiondistribution ofof thethe patientspatients accordingaccording toto thethe typetype ofof damage and type of retainer. Diﬀerences between groups were detected as not signiﬁcant according damagedamage andand typetype ofof retainer.retainer. DifferencesDifferences betweenbetween groupsgroups werewere detecteddetected asas notnot significantsignificant accordingaccording to Fisher’s Exact Test (p = 1.000), as no type of retainer was associated with some particular type of toto Fisher’sFisher’s ExactExact TestTest ((pp == 1.000),1.000), asas nono typetype ofof retainerretainer waswas associatedassociated withwith somesome particularparticular typetype ofof damage. However, it is worth mentioning that the damaged retainers were mostly fractured at T2. damage.damage. However,However, itit isis worthworth mentioningmentioning thatthat thethe damageddamaged retainersretainers werewere mostlymostly fracturedfractured atat T2.T2. Table 4. Distribution of the patients according to the type of damage and type of retainer. TableTable 4.4. DistributionDistribution ofof thethe patientspatients accordingaccording toto thethe typetype ofof damagedamage andand typetype ofof retainer.retainer. HawleyHawley Retainer Retainer Vacuum Vacuum-Formed‐Formed Retainer Retainer TypeType of RetainerRetainer/Damage/Damage Hawley Retainer Vacuum‐Formed Retainer p * p * Type of Retainer/Damage No % No % p * NoNo %% NoNo %% FractureFracture at atat T1 T1T1 222 4%4%4% 1212 1237.5%37.5% 37.5% Fracture at T2 3 60% 17 53.1% 1.000 FractureFracture atat T2T2 33 60%60% 1717 53.1%53.1% 1.0001.000 Severe discoloration at T1 0 0% 3 9.4% SevereSevere discolorationdiscoloration atat T1T1 00 0%0% 33 9.4%9.4% * Fisher’s Exact Test. T1: after 6 months of retention; T2: after 12 months of retention. ** Fisher’sFisher’s ExactExact Test.Test. T1:T1: afterafter 66 monthsmonths ofof retention;retention; T2:T2: afterafter 1212 monthsmonths ofof retention.retention.

Figure 6. Distribution of the patients according to the type of damage and type of retainer. FigureFigure 6.6. DistributionDistribution ofof thethe patientspatients accordingaccording toto thethe typetype ofof damagedamage andand typetype ofof retainer.retainer. Data from Table5 and Figure7 show the distribution of the patients according to the existence Data from Table 5 and Figure 7 show the distribution of the patients according to the existence of lossData and from type Table of retainer. 5 and Figure Diﬀerences 7 show between the distribution groups were of the detected patients as according not signiﬁcant to the according existence of loss and type of retainer. Differences between groups were detected as not significant according to ofto loss Fisher’s and type Exact of Test retainer. (p = 0.750), Differences as such between no type groups of retainer were was detected associated as not with significant a higher according frequency to Fisher’s Exact Test (p = 0.750), as such no type of retainer was associated with a higher frequency of Fisher’sof loss. Exact Test (p = 0.750), as such no type of retainer was associated with a higher frequency of loss.loss.

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ChildrenTable 2020, 5.7, xDistribution FOR PEER REVIEW of the patients according to the existence of loss and type of retainer.8 of 16

Children 2020, 7, x FOR PEER REVIEW 8 of 16 Table 5. Distribution of the patientsHawley according Retainer to the existence Vacuum-Formed of loss and type of Retainer retainer. Type of Retainer/Loss p * Table 5. Distribution of theNo patientsHawley according Retainer % to the existenceVacuum of No loss‐Formed and type Retainer of retainer. % Type of Retainer/Loss p * Without loss 246No % 92.5% No 329% 93.5% Hawley Retainer Vacuum‐Formed Retainer 0.750 TypeWith Withoutof lossRetainer/Loss loss 20246 92.5% 7.5% 329 2393.5% 6.5% p * No % No % 0.750 With loss 20 7.5% 23 6.5% Without loss 246 * Fisher’s92.5% Exact Test. 329 93.5% * Fisher’s Exact Test. 0.750 With loss 20 7.5% 23 6.5% * Fisher’s Exact Test.

Figure 7. Distribution of the patients according to the existence of loss and type of retainer. Figure 7. Distribution of the patients according to the existence of loss and type of retainer. Figure 7. Distribution of the patients according to the existence of loss and type of retainer. DataData from from Table Table6 and 6 Figureand Figure8 show 8 show the distributionthe distribution of theof the patients patients according according to to the the type type of of loss and typeloss ofand retainer. type of Diretainer.ﬀerences Differences between between groups groups were detected were detected as not as signiﬁcant not significant according according to Fisher’s to Data from Table 6 and Figure 8 show the distribution of the patients according to the type of ExactFisher’s Test (p =Exact1.000), Test as (p the= 1.000), retainers as the were retainers not associatedwere not associated with any with particular any particular type of type loss. of However, loss. loss and type of retainer. Differences between groups were detected as not significant according to it is worthHowever, mentioning it is worth that mentioning the lost retainersthat the lost were retainers mostly were lost mostly at T1. lost at T1. Fisher’s Exact Test (p = 1.000), as the retainers were not associated with any particular type of loss. However, it is worth mentioning that the lost retainers were mostly lost at T1. TableTable 6. Distribution 6. Distribution of of the the patients patients according according to the type type of of loss loss and and type type of retainer. of retainer. Table 6. Distribution of the patientsHawley according Retainer to the type ofVacuum loss and‐Formed type of retainer. Retainer Type of Retainer/Loss Hawley Retainer Vacuum-Formed Retainer p * Type of Retainer/Loss No % No % p * NoHawley Retainer % Vacuum No‐Formed Retainer % Type ofLoss Retainer/Loss at T1 12 60% 13 56.5% p * No % No % 1.000 LossLoss at T1 at T2 128 60%40% 1310 56.5%43.5% Loss at T1 12 60% 13 56.5% 1.000 Loss at T2 8* Fisher’s 40% Exact Test. 10 43.5% 1.000 Loss at T2 8 40% 10 43.5% * Fisher’s Exact Test. * Fisher’s Exact Test.

Figure 8. Distribution of the patients according to the type of loss and type of retainer. Figure 8. Distribution of the patients according to the type of loss and type of retainer. Figure 8. Distribution of the patients according to the type of loss and type of retainer.

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Children 2020, 7, x FOR PEER REVIEW 9 of 16 Data from Table7 and Figure9 show the distribution of the patients according to the existence Data from Table 7 and Figure 9 show the distribution of the patients according to the existence of mild relapse and type of retainer. Diﬀerences between groups were detected as not signiﬁcant of mild relapse and type of retainer. Differences between groups were detected as not significant according to Fisher’s Exact Test (p = 0.480), as no particular type of retainer was associated with a according to Fisher’s Exact Test (p = 0.480), as no particular type of retainer was associated with a higher frequency of a mild relapse. higher frequency of a mild relapse. Table 7. Distribution of the patients according to the existence of mild relapse and type of retainer. Table 7. Distribution of the patients according to the existence of mild relapse and type of retainer. Hawley Retainer Vacuum-Formed Retainer Type of Retainer/Mild Relapse Hawley Retainer Vacuum‐Formed Retainer p * Type of Retainer/Mild Relapse No % No % p * No % No % Without mild relapse 239 89.8% 323 91.8% Without mild relapse 239 89.8% 323 91.8% 0.480 With mild relapse 27 10.2% 29 8.2% 0.480 With mild relapse 27 10.2% 29 8.2% * Fisher’s Exact Test. * Fisher’s Exact Test.

Figure 9. Distribution of the patients according to the existence of mild relapse and type of retainer. Figure 9. Distribution of the patients according to the existence of mild relapse and type of retainer. Data from Table8 and Figure 10 show the distribution of the patients according to the type of mild Data from Table 8 and Figure 10 show the distribution of the patients according to the type of relapse and type of retainer. Diﬀerences between groups were detected as not signiﬁcant according to mild relapse and type of retainer. Differences between groups were detected as not significant Fisher’s Exact Test (p = 1.000), as the retainers were not associated with any particular type of mild according to Fisher’s Exact Test (p = 1.000), as the retainers were not associated with any particular relapse. However, it is worth mentioning that patients that had a mild relapse, usually had mild type of mild relapse. However, it is worth mentioning that patients that had a mild relapse, usually re-lapse at T1. had mild re‐lapse at T1. Table 8. Distribution of the patients according to the type of mild relapse and type of retainer. Table 8. Distribution of the patients according to the type of mild relapse and type of retainer. Hawley Retainer Vacuum-Formed Retainer Type of Retainer/Mild Relapse Hawley Retainer Vacuum‐Formed Retainer p * Type of Retainer/Mild Relapse No % No % p * No % No % Mild relapse at T1 16 59.3% 17 58.6% Mild relapse at T1 16 59.3% 17 58.6% 1.000 Mild relapse at T2 11 40.7% 12 41.4% 1.000 Mild relapse at T2 11 40.7% 12 41.4% * Fisher’s Exact Test. * Fisher’s Exact Test.

ChildrenChildren 20202020,, 77,, 295x FOR PEER REVIEW 1010 of 16 Children 2020, 7, x FOR PEER REVIEW 10 of 16

Figure 10. Distribution of the patients according to the type of mild relapse and type of retainer. Figure 10. Distribution of the patients according to the type of mild relapse and type of retainer. Data fromfrom TableTable9 9and and Figure Figure 11 11 show show the the distribution distribution of of the the patients patients according according to theto the existence existence of Data from Table 9 and Figure 11 show the distribution of the patients according to the existence severeof severe relapse relapse and typeand oftype retainer. of retainer. Differences Differences between between groups weregroups detected were asdetected significant as significant according of severe relapse and type of retainer. Differences between groups were detected as significant toaccording Fisher’s to Exact Fisher’s Test (Exactp = 0.042); Test ( datap = 0.042); show data that theshow HRs that are the significantly HRs are significantly more frequently more associatedfrequently according to Fisher’s Exact Test (p = 0.042); data show that the HRs are significantly more frequently withassociated the existence with the of severeexistence relapse of severe than the relapse VFRs. than The oddsthe VFRs. ratio 0.334 The (95%odds C.I: ratio 0.115–0.973) 0.334 (95% shows C.I: associated with the existence of severe relapse than the VFRs. The odds ratio 0.334 (95% C.I: that0.115–0.973) it is 3 times shows more that probable it is 3 thattimes HRs more retainers probable would that be HRs associated retainers with would severe be relapse. associated with severe0.115–0.973) relapse. shows that it is 3 times more probable that HRs retainers would be associated with severeTable relapse. 9. Distribution of the patients according to the existence of severe relapse and type of retainer. Table 9. Distribution of the patients according to the existence of severe relapse and type of retainer. Table 9. Distribution of the patients accordingHawley to Retainer the existence of severe Vacuum-Formed relapse and Retainer type of retainer. Type of Retainer Severe Relapse Hawley Retainer Vacuum‐Formed Retainer p * Type of Retainer Severe Relapse No % No % p * HawleyNo Retainer% VacuumNo ‐Formed Retainer% TypeWithout of Retainer severe Severe relapse Relapse 255 95.9% 347 98.6% p * Without severe relapse 255No 95.9%% 347No 98.6%% 0.042 With severe relapse 11 4.1% 5 1.4% 0.042 WithoutWith severe severe relapse relapse 25511 95.9%4.1% 3475 98.6%1.4% * Fisher’s Exact Test. 0.042 With severe relapse * Fisher’s11 Exact4.1% Test. 5 1.4% * Fisher’s Exact Test.

Figure 11.11. DistributionDistribution of of the the patients patients according according to the to existencethe existence of severe of severe relapse relapse and type and of retainer.type of retainer.Figure 11. Distribution of the patients according to the existence of severe relapse and type of Dataretainer. from Table 10 and Figure 12 show the distribution of the patients according to the type of severe relapse and type of retainer. Diﬀerences between groups were detected as not signiﬁcant Data from Table 10 and Figure 12 show the distribution of the patients according to the type of according to Fisher’s Exact Test (p = 1.000), as such the retainers were not associated with any particular severeData relapse from andTable type 10 andof retainer. Figure 12 Differences show the distribution between groups of the werepatients detected according as not to thesignificant type of accordingsevere relapse to Fisher’s and type Exact of retainer.Test (p =Differences 1.000), as suchbetween the groupsretainers were were detected not associated as not significant with any according to Fisher’s Exact Test (p = 1.000), as such the retainers were not associated with any

Children 2020,, 7,, 295x FOR PEER REVIEW 1111 of of 16 particular type of severe relapse. However, it is worth mentioning that patients who had a severe typerelapse of severeusually relapse. had it in However, the first it6 ismonths. worth mentioning that patients who had a severe relapse usually had it in the ﬁrst 6 months. Table 10. Distribution of the patients according to the type of severe relapse and type of retainer. Table 10. Distribution of the patients according to the type of severe relapse and type of retainer. Vacuum‐Formed HawleyHawley Retainer Retainer Vacuum-Formed Retainer Type of of Retainer Retainer/Severe/Severe Relapse Relapse Retainer pp ** NoNo %% NoNo % SevereSevere relapse relapse at T1at T1 77 63.6%63.6% 33 60% 1.0001.000 SevereSevere relapse relapse at T2at T2 44 36.4%36.4% 22 40% ** Fisher’s Fisher’s Exact Test. Test.

Figure 12. Distribution of the patients according to the type of severe relapse and type of retainer. Figure 12. Distribution of the patients according to the type of severe relapse and type of retainer. 4. Discussion 4. Discussion The study we conducted shows that VFRs are less resistant than HRs, suffering much more fracturesThe comparedstudy we toconducted HRs (p < 0.001)shows (Table that 3VFRs). Mild are relapses less resistant were reported than HRs, in both suffering groups withoutmuch more any statisticalfractures compared significance, to being HRs ( morep < 0.001) frequently (Table at 3). T1 Mild in both relapses groups—due were reported to inadequate in both wearing, groups damage,without orany loss statistical of retainer. significance, Mild relapses being could more befrequently remediated at T1 by in activating both groups—due the HRs or to by inadequate manufacturing wearing, the VFRsdamage, on theor setuploss models.of retainer. However, Mild severerelapses relapses could were be significantlyremediated moreby activating frequent inthe the HRs HRs groupor by (manufacturingp < 0.05) (Table 9the), especially VFRs on duethe setup to improper models. wearing. However, These severe situations relapses required were significantly the resumption more of thefrequent active in orthodontic the HRs group treatment (p < 0.05) with (Table a fixed 9), appliance especially or due clear to aligners. improper wearing. These situations requiredFor the resumption retention phase, of the we active most orthodontic often use treatment removable with retainers a fixed in appliance the upper or arch clear and aligners. fixed retainersFor the in theretention lower phase, arch [10 we,25 most]. Despite often alluse the removable disadvantages retainers of in the the need upper for arch proper and patient fixed compliance,retainers in wethe arelower most arch often [10,25]. forced Despite to use removable all the disadvantages retainers in theof upperthe need arch for as proper fixed retainers patient cancompliance, generate we occlusive are most interference. often forced In to our use practice, removable we retainers used HRs in in the the upper upper arch arch as for fixed a long retainers time, butcan duegenerate to dissatisfaction occlusive interference. with the use In our of HRs, practice, we decided we used to HRs apply in the thermoplastic upper arch retainers.for a long Thus,time, thebut usedue of to VFRs dissatisfaction as upper retainers with the has use predominated of HRs, we decided in our practice to apply for thermoplastic the last five years. retainers. Of course, Thus, therethe use were of VFRs various as upper drawbacks retainers in the has use predominated of VFRs, which in led our us practice to this retrospectivefor the last five study years. that Of analyzes course, thethere behavior were various of the two drawbacks types of retainersin the use in termsof VFRs, of certain which clinical led us and to this paraclinical retrospective aspects. study VFRs that are consideredanalyzes the to behavior be less resistant of the intwo time, types and of their retainers durability in oftenterms is of limited certain to clinical a few months. and paraclinical However, Gardneraspects. VFRs et al. [ 14are] demonstratedconsidered to thatbe less polyethylene resistant in terephthalate time, and their glycol durability copolymer often (PETG) is limited is harder to a andfew hasmonths. greater However, resistance Gardner to wear thanet al. Invisacryl [14] demonstrated C and Essix Cthat+, which polyethylene are softer, polypropylene-basedterephthalate glycol thermoplastics.copolymer (PETG) We alsois harder prefer and to use has PETG greater as removableresistance retainerto wear materials.than Invisacryl In this C study, and theEssix slight C+, occlusalwhich are wear softer, of thepolypropylene VFRs was not‐based considered thermoplastics. as damage We becausealso prefer it did to notuse aPETGffect the as stabilityremovable of theretainer teeth materials. position. In In this our study, opinion, the the slight fact occlusal that a slight wear degree of the VFRs of wear was is installednot considered in the as areas damage with morebecause intense it did occlusal not affect contact the stability points allows of the teeth a continuation position. In of theour settlingopinion, phase, the fact which that hasa slight a beneficial degree of wear is installed in the areas with more intense occlusal contact points allows a continuation of the settling phase, which has a beneficial effect on the occlusal stability. One of the important

Children 2020, 7, 295 12 of 16 effect on the occlusal stability. One of the important advantages of polyethylene polymers used for VFRs retainers is that it allows acrylic pads to be bonded to the material in the anterior region (near the upper lateral incisors) on the upper retainer and in the posterior region on the lower VFRs, which allows application in the retention phase of light class II elastics (or light class III elastics, with a reverse orientation) in patients who have used class II or class III mechanics and present the risk of relapse of mandibular-maxillary relationships [26,27]. We inform patients that VFRs may change their translucency after one year of use, color changes may occur, so it is often necessary to restore them after the first year of retention. The literature presents various protocols for wearing these mobile retainers during the retention phase. Some authors recommend prolonging the retention phase for a period of one year, with full-time wearing in the first 3–4 months of retention, followed by night-only wearing for a period of up to one year [28], or full-time wearing of VFRs in the first week, followed by night-only wearing [29], while other authors have demonstrated that full-time wearing is not beneficial compared to night-only wearing [11]. Shawesh et al. [30] conducted a study starting from the idea that it is still unclear whether it may be clinically acceptable for patients to wear their retainers for 1 year at night only or whether it is necessary for an initial period of full-time wear followed by night-only wear. Their study demonstrated that there were no statistically significant differences between the two retention protocols (full-time versus night-only wear) for labial segment irregularity or crowding and thus the patients may be advised to wear their retainers at night only. On the other hand, in a study conducted by Meade and Millett (2014) on a sample of orthodontic specialists, most of the respondents from their study (70–76%) preferred a full-time followed by part-time wear protocol of removable retainers, and almost all respondents (93%) agreed to full occlusal coverage design. The authors found that VFRs were the most chosen retainers, recommended by 53% of the respondents in the maxilla and 33% in the mandible [19]. In our practice in adult patients, we recommend that the removable retainers be worn two years after the completion of the active phase of the orthodontic treatment. In contrast, in children and adolescent patients at the end of the active orthodontic treatment, we recommend that retention be continued until the end of growth. We instructed our patients to wear their retainers full-time (except during meals) for a period of 3–4 months and then only while sleeping. The retention protocol we use provides a gradual reduction in wear time in the last 4–6 months of the retention period (alternative wearing, one night yes–one night no, then wearing only two nights/week, and finally wearing only one night/week). In this way, the risk of relapse can be investigated, signaled by the fact that the removable retainer begins to fit perfectly no longer on the teeth. Other authors did not find statistically significant differences between the two types of retainers. Kaya Y. et al. (2019) did not obtain statistically significant differences between two groups of patients who used the Hawley retainer and the Essix retainer for a period of 12 months in terms of overbite, overjet, arch length, maxillary, and mandibular intercanine widths, and intermolar widths [2]. In a systematic review, the authors found that, in terms of occlusal contacts and survival time, there was insufficient evidence to distinguish the effectiveness between HRs and VFRs. Some authors reported higher numbers of occlusal contacts for patients wearing HRs and higher patient satisfaction associated with VFRs [12]. It is well-known that the best orthodontic results are related to good occlusal contacts (centric stops) and intercuspation, and hence, various studies in the literature have reported changes in the occlusion, respectively increased the number of occlusal contacts after orthodontic treatment with conventional retention devices [31,32]. However, different results were obtained by Dinçer and Aslan [33], as the expected increase of occlusal contacts was not observed at the end of the retention period when using thermoplastic retainers. The authors also concluded that both ideal and non-ideal posterior contacts increased in the long term, but the number of non-ideal contacts was greater than the ideal contacts. In a study performed by Tecco et al. [34], the authors showed that upper removable retainers, unlike positioners, did not have a relevant effect on the activity of masticatory and neck muscles. Children 2020, 7, 295 13 of 16

Other studies have shown that Essix retainers are more effective than Hawley retainers only in the mandibular arch, preventing the recurrence of crowding to a greater extent [25,35]. In another comparative study on Hawley and vacuum-formed retainers, performed by Barlin et al. (2011) [9], there were no statistically significant differences between the two types of retainers, and the authors suggested that the degree of relapse is unlikely to be affected by the choice of retainer. On the contrary, our study compared the two types of retainers only in the upper arch and it demonstrated that HR was associated with an increased risk of severe relapse in the first year of the retention phase. Barlin et al. [9] suggested that, when deciding on the type of retainer to be fitted following fixed appliance therapy, other factors such as cost may play a more significant role when deciding what type of retainer should be used. In our praxis, the costs with HRs are double compared to those with VFRs. Most of the patients (8 patients) with severe relapse in our study, belonging to the HRs group, initially showed severe canine abnormalities (accentuated ectopia or impactions) [36] that suggests that HR are associated with a higher risk of relapse in patients who have been orthodontically treated for severe canine malposition. Two of the patients in the VFRs group with severe relapse initially presented canine abnormalities associated with severe dental crowding, while three patients initially presented severe protrusions. The removable retainers are efficient in the orthodontic practice in terms of maintaining the stability of the result of the active orthodontic treatment. They have many advantages related to the possibility of maintaining proper oral hygiene [37], are easy to perform [38], are acceptable in terms of aesthetics (especially the VFRs), and have a satisfactory resistance [39]. Their main disadvantage is related to the need for optimal collaboration of the patient. Many children and adolescents in our study did not present at regular check-ups during the retention phase and did not exactly follow our recommendations. Therefore, like other authors, we consider it particularly important to have optimal communication with pediatric patients [40]. In the current context of young patients’ education and their participation in social media activity, several studies have pointed out various aspects related to patient compliance and have suggested strategies to obtain the best patient engagement in order to reduce the occurrence and degree of relapse [41]. The use of social networks or regular communication, written or through shots, with patients on WhatsApp has a beneficial role in stimulating patient compliance in terms of increasing the quality of oral hygiene, increasing regularity in wearing removable retainers, participation in the follow-up program to achieve better long-term results of the orthodontic stability [41,42]. This study and others that we have carried out previously lead us toward giving special importance to stimulating patient compliance [43], training patients on how to store and properly maintain these removable retainers, trying to always make them aware of the fact that non-compliance retention favors relapse, the treatment instituted being thus in vain. However, given the increased prevalence of malocclusions, their early onset often in early childhood, involving several factors (e.g., dental caries and its complications, vicious oral habits), the high risk of relapse of malocclusions and that many children and adolescents are not aware of the importance of the retention phase, we consider it very important to implement a prevention program in pedodontics and orthodontics starting with pre-school children, program that requires close collaboration between parents, educators, and the professional team—pedodontists, orthodontists, and pediatricians [44,45]. The limitations of the study are primarily related to the inconsistency of the information provided by children and adolescents on the regular wearing of retainers, with the information provided being often irrelevant. Relapse in the upper arch also involves a complex set of factors such as gingival fibers, periodontal tissues, oral habits, occlusion, lower arch relapse, facial soft tissues, and the impossibility of establishing exactly the factors that contributed to its occurrence. Our study was limited to analyzing the behavior of the two types of retainers and the relapse rate over a limited retention period (one year), but the retention phase often extends over a longer period, sometimes life-long retention is necessary. Therefore, further studies are needed, on a larger sample size, with the investigation of the various parameters involved in relapse, over an extended period. Children 2020, 7, 295 14 of 16

5. Conclusions Following the study and being aware that there is no perfect device that can be used as a retainer in orthodontic practice, we can conclude that the two types of removable retainers, namely, the Hawley retainer and the thermoplastic retainer, are effective in the upper arch in the retention phase. However, the thermoplastic retainer has lower resistance in time compared to the Hawley retainer. No differences between groups were found in the rates of loss of the retainers. The risk of severe relapse during the first year of the retention phase is higher when using Hawley retainers.

Author Contributions: Conceptualization, L.L.V.; data curation, L.L.V., E.S.B., L.G.H. and B.I.T.; formal analysis, B.I.T. and B.M.N.; funding acquisition, F.D.B.; investigation, B.M.N. and A.E.M.; methodology, L.L.V., E.S.B. and L.G.H.; software, A.E.M.; supervision, S.C. and F.D.B.; writing—original draft, L.L.V., E.S.B. and L.G.H.; writing—review and editing, L.L.V. and S.C. 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.

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