Is Pain Stronger in Adults or in Adolescents During Semi-Rapid Maxillary Expansion (SRME) and Fixed Appliance (FA) Therapies?

Abstract

Rapid or semi-rapid maxillary expansion is a well-established method of treating severe transversal maxillary deficiency or transversal dental arch discrepancy. Pain is considered an inevitable undesirable adverse effect of orthodontic treatment. The aim of the present study was to compare pain levels experienced from the semi-RME (SRME) procedure between adults and adolescents and the lower fixed appliance (FA) procedure in the same patients. The study comprised 95 patients (51 adults and 44 adolescents) treated with a bonded acrylic Hass-type expander and the following month (after blocking the screw) with a lower fixed orthodontic appliance. Pain was assessed using a numerical rating scale from 0 to 10. During screw activation, adolescent patients reported a statistically significantly higher median pain level (5.00) compared to adults (3.00) [p = 0.009]. During the fixed appliance treatment, adolescent patients reported similar pain level to adults (4.5 and 4.0, respectively; p = 0.49). Interestingly, the median pain level for SRME in the whole group was 4, and was not different from the fixed appliance treatment sensations. Adolescent females had the highest pain sensation, while adult males had the lowest during both procedures, SRME and FA. The difference between the midpalatal suture opening (appearance of diastema) in adolescents (81.82%) vs. adults (64.71%) was not statistically significant (p = 0.062). The oldest patients with diastema were a 36y-2mo-old man and a 42-year-old woman, whereas the youngest patients without diastema were an 11y-11mo-old girl and a 13y-2mo-old boy. Moreover, all female patients between 30 to 42 years of age (eight women) had presented with diastema. In both age groups, the biggest disadvantage during SRME, reported by 50.53% of all patients (45.45% of adolescents and 54.9% of adults; p = 0.062), were speech problems, whereas only 18.95% of the total group (27.27% of adolescents vs. 11.76% of adults; p = 0.054) considered pain as the main disadvantage. During FA therapy, 32.63% of all patients reported pressure sores as the main disadvantage (29.55% of adolescents and 35.29% of adults; p = 0.551).

1. Introduction

It is well established that most patients undergoing different types of orthodontic treatment experience pain [1,2,3,4,5,6,7,8,9,10]. Pain perceived during orthodontic treatment is considered an inevitable undesirable adverse effect caused by stimulating the trigeminal nerve by inflammatory factors and cytokines [11,12]. In general, it usually begins 4 h after the onset of orthodontic force [13]. A significant effect on orthodontic pain arises from age and sex [14].

Semi-rapid maxillary expansion (SRME) has been defined as 1 mm to 1.5 mm expansion per week, producing lower forces than RME [6,15,16]. Activation of a Penn expander supported on four miniscrews resulted in discomfort and functional impairment that were higher in patients who had the appliance activated twice a day compared to those who had the screw activated once a day [17]. Similar results related to comparisons between one versus two turns daily were reported in other studies [5,6,16,17,18]. All of the above studies concluded that one turn a day was less painful than two turns a day for patients in different ages.

Pain experienced during rapid maxillary expansion (RME) has been investigated from different points of view [5,6,7,8,9,10,15,16,17,18,19,20]. Hasson et al. (2023), as well as Jawad and Alhashimi (2021), compared RME to a quadhelix appliance and found no difference in pain or discomfort levels [10,19]. A recent systematic review by Rutili et al. (2022) proved that pain was characterized by a lower intensity in SME than in RME, only during the first week of treatment [6]. A comparison between tooth-borne RME with special predetermined MEMORIA^® Leaf springs, calibrated with constant forces released by a nickel–titanium hybrid Hyrax expander showed no statistically significant difference in pain levels. According to Ugolini et al. (2020) and Nieri et al., the use of a Hyrax appliance was associated with a significantly higher pain than of the LEAF expander [6,7,8]. However, a recent systematic review showed inconclusive results regarding pain levels from various maxillary expansion appliances in growing patients [20].

Pain appears difficult to objectively quantify; moreover, pain level related to the same procedure can be sensed differently among people [21]. To our knowledge, no studies compared the pain perceived during two different orthodontic procedures in the same patients. Nevertheless, conducting a comparison between SRME and another orthodontic procedure performed on the same persons at the same time may provide the most reliable answer to the questions related to discomfort with the SRME procedure.

Thus, the aim of the present study was to analyze pain and discomfort related to SRME according to chronological age, gender, skeletal maturation and presence/absence of diastema, and comparing them to pain and discomfort related to the fixed appliance (FA) procedure. The null hypothesis was that to adults, both procedures (SRME and FA therapies) would be more painful than to adolescents. The second hypothesis was that SRME would be more painful than FA therapy.

2. Materials and Methods

The study group consisted of 95 patients who were treated between 2007 and 2021. The inclusion criteria for the study were age above 10 years; permanent dentition; transversal maxillary deficiency above 5 mm referring to the lower dental arch, visible as unilateral or bilateral cross-bite; Class II malocclusion (with maxillary deficiency) with upper airways constriction visible on lateral cephalograms; Class III malocclusion (with maxillary deficiency); and normal health status. The diagnosis of a sagittal malocclusion was confirmed via cephalometric analysis by Bjork. In the lower dental arch, the patients had a Little’s irregularity index between 2 and 3 mm. The exclusion criteria were previous orthodontic treatment, craniofacial deformities (including cleft lip or palate) and missing permanent teeth (except for the third molars).

The sample size was verified using a standard sample size calculator for two-sample t-tests for an estimated effect size of 0.83, power of 80%, level of significance (alpha) of 0.05, and the required sample size per group yielded 26.

All patients included were treated during one orthodontic practice by the same experienced orthodontist (MKM). The appliances used were bonded acrylic Hass-type expanders, with a Hyrax screw (Dentaurum, Phorzheim, Germany) bonded on permanent teeth from the first premolar to the first or second molar with a chemical-cure adhesive (Excel, Reliance, USA) and a fixed appliance with MBT 0.022 slot brackets (Carriere 2007, Henry Schein Orthodontics, Melville, NY, USA) as presented in Figure 1.

The semi-rapid maxillary expansion (SRME) protocol included one quarter turn of the screw per day [22,23], carried out just before bedtime. It was recommended to activate the screw with a slow movement. Opening of the palatal suture was checked clinically by the presence of a diastema and radiologically via intraoral radiographs (Figure 2a,b).

The minimum expansion included 10 turns of the screw, and the maximum was 28 turns. Expansion was considered as sufficient when the palatal cusps of the upper permanent first molars approximated the buccal cusps of the lower permanent first molars (stop of activation). The appliance was kept on the teeth as a passive retainer for 5 months.

The course of the study is presented in Figure 3.

The questionnaires, delivered one month after debonding the Haas-type expanders, concerned pain and other discomfort related to the RME and fixed appliance procedures, as presented in Figure 4.

No patient refused to fill in the questionnaire, and drop-out during the treatment phases described was noted only for one 11-year-old boy (who moved to another country just after bonding a Haas-type appliance). Informed consent was signed by all patients and/or their relatives before the proposed treatment. The distributions of the study group, according to age, sex and type of sagittal skeletal classes, are presented in

Table 1. Characteristics of the study group according to age, sex and type of skeletal sagittal morphology.

Characteristic	N (%)	Age Group		p
		Adolescents,	Adults,
female	60 (63.16%)	25 (56.82%)	35 (68.63%)	0.234 (Pearson’s chi-square test)
male	35 (36.84%)	19 (43.18%)	16 (31.37%)
total	95 (100%)	44 (46.32%)	51 (53.68%)
age, years. Mdn (Q1, Q3):	18.34 (16.08, 25.61)	15.77 (13.26, 16.60)	25.23 (21.51, 29.03)	<0.001 (Mann–Whitney U test)
skeletal class:
Class I	9 (9.47%)	6 (13.64%)	3 (5.88%)	0.222 (Fisher’s exact test)
Class II	18 (18.95%)	8 (18.18%)	10 (19.61%)
Class III	68 (71.58%)	30 (68.18%)	38 (74.5%)

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The age ranged from 10y 1m to 41y 11m. The cohort was almost evenly split between adults (equal and above 18 years) and pediatric patients (between the age of 10 to under 18 years), with a preponderance of females in both age groups. The difference in sex distribution, with 68.63% females in the adult subgroup compared to 56.82% in the pediatric subgroup, was statistically insignificant (p = 0.234). The distribution of skeletal classes enrolled in the study was 9.47% Class I patients, 18.95% Class II patients and 71.58% Class III patients, as presented in Table 1.

In order to assess pain, an NRS—numerical rating scale—from 0 to 10 was used, where 0 was no pain, and 10 was an extreme amount of pain [21]. The patients were asked to report the highest pain perceived.

3. Statistical Analysis

Analyses were performed using the R Statistical language (version 4.3.1; R Core Team, 2023) on Windows 10 pro 64 bit (build 19045), using the packages sjPlot (version 2.8.15; Lüdecke D, 2023), report (version 0.5.7; Makowski D et al., 2023), ggstatsplot (version 0.12.1; Patil I, 2021), gtsummary (version 1.7.2; Sjoberg D et al., 2021), MASS (version 7.3.60; Venables WN, Ripley BD, 2002) and dplyr (version 1.1.3; Wickham H et al., 2023).

The threshold for significance was set at 0.05. The Shapiro–Wilk test was used to assess the distribution of parametric variables. The median and first and third quartiles were presented for variables not conforming to a normal distribution. For non-parametric variables, frequencies and percentages were reported.

For the analysis of two independent groups with parametric data that did not adhere to a normal distribution, the Mann–Whitney U test was employed. The association between two categorical variables was examined using Pearson’s chi-square test or Fisher’s exact test, depending on the cell frequencies expected in the contingency tables.

When analyzing differences among more than two groups with non-normally distributed numerical data, the Kruskal–Wallis test was applied, followed by Dunn’s test for post hoc analysis, adjusting the p-values using Holm’s method to control for the type I error rate.

Differences between two proportions from a dichotomous variable were analyzed using Pearson’s goodness-of-fit test. For multivariate analyses with a numeric outcome, a robust linear regression model was employed, while for binary outcomes, we used a generalized linear model with a logit link function.

4. Results

The distributions of clinical variables in the study groups are presented in

Table 2. Comparative analysis of clinical parameters and adverse effects associated with the use of Haas-type expanders and fixed orthodontic appliances for overall cohort and stratified by age groups.

Characteristic	Overall Cohort (N = 95)	Age Group		p c
		Adolescents n1 = 44 a	Adults n2 = 51 a
Skeletal stage: Mdn (Q1, Q3) b	6.00 (4.00, 6.00)	4.00 (3.00, 5.00)	6.00 (6.00, 6.00)	<0.001 d
Diastema occurrence	69 (72.63%)	36 (81.82%)	33 (64.71%)	0.062
Level of pain on NRS during the SRME activation: Mdn (Q1, Q3) b	4.00 (2.50, 6.00)	5.00 (4.00, 7.00)	3.00 (2.00, 5.50)	0.009  d
Main disadvantage reported:
pain	18 (18.95%)	12 (27.27%)	6 (11.76%)	0.054
pressure sores	14 (14.74%)	7 (15.91%)	7 (13.73%)	0.765
speech difficulties	48 (50.53%)	20 (45.45%)	28 (54.90%)	0.358
headache	2 (2.11%)	0 (0.00%)	2 (3.92%)	0.497 e
other ailments	12 (12.63%)	4 (9.09%)	8 (15.69%)	0.335 e
no ailments	2 (2.11%)	1 (2.27%)	1 (1.96%)	1.000 e
Level of pain on the NRS during fixed appliance therapy: Mdn (Q1, Q3) b	4.00 (2.00, 6.00)	4.50 (3.00, 6.00)	4.00 (2.00, 6.00)	0.493 d
pain	19 (20.00%)	12 (27.27%)	7 (13.73%)	0.100
pressure sores	31 (32.63%)	13 (29.55%)	18 (35.29%)	0.551
speech difficulties	2 (2.11%)	1 (2.27%)	1 (1.96%)	1.000 e
eating difficulties	5 (5.26%)	1 (2.27%)	4 (7.84%)	0.369 e
other ailments	19 (20.00%)	8 (18.18%)	11 (21.57%)	0.681
no ailments	20 (21.05%)	10 (22.73%)	10 (19.61%)	0.710

Note: N—cohort size; n—group size; Mdn—median; Q1—first quartile (25%); Q3—third quartile (75%); p—p-value of statistical test. ^a n (%); ^b Mdn (Q1, Q3); ^c Pearson’s chi-square test; ^d Mann–Whitney U test. ^e Fisher’s exact test.

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Palatal suture opening, confirmed by opening a diastema between the upper central incisors and being visible on intraoral radiographs, was successful in 69 patients (72.6% of total group of patients), including 36 growing patients (81.82% of adolescents) and 33 adults (66.67% of adult patients), as presented in Figure 2a,b. The difference in diastema occurrence between the adolescent group and the adult group was statistically insignificant (p = 0.062). The youngest patients without a diastema were an 11y-11mo-old girl and a 13y-2mo-old boy. The oldest male patient with a diastema was a 36y-2mo-old Class III male whose orthopedic nonsurgical treatment with an SRME Haas-type acrylic bonded expander, face mask and fixed appliance was associated with marked changes, both on the dental and skeletal level, as seen in Figure 5, whereas the oldest female patient was a 41y-11m-old Class III woman.

No statistically significant differences referred to pain or discomfort were found between patients with and without diastema, neither in the whole study group nor in the age subgroups.

The average pain level reported on the NRS in the whole group of patients during SRME screw activation and FA therapy was equal (4.00). A statistically significant difference (p = 0.009) was apparent in pain levels during the SRME screw activation of the Haas-type appliance between adolescent patients, who reported a significantly higher median pain level (5.00), compared to adults (3.00) (Figure 6a). When comparing pain levels during the treatment with an FA, a similar level was found for both age groups (NRS = 4.5 in adolescents and 4.0 in adults) (Figure 6b). Graphical visualizations of the comparisons are presented in Figure 6a,b.

Further analysis of pain revealed that merely 18 persons (18.95% of total group) considered pain during SRME as the main disadvantage. In the above group, the percentage of adolescent patients was 27.27% compared to 11.76% of adults; the difference was statistically insignificant (p = 0.054). The highest value of pain, equaling 10 in the NRS, was reported by two adolescent patients: an 11y-6m-old boy and a 13y-10m-old girl. In the whole study group, no statistically significant difference in pain level was found between the sexes in relation to Haas-type SRME or FA procedures.

However, when comparisons of pain/sex sensitivity during the SRME procedure were made separately for adolescents and adults, it showed that adolescent females felt the highest pain level (NRS = 6) among the four age and sex subgroups. Adult females reported a significantly higher mean pain level (NRS = 4.0) than adult males (NRS = 2.0) (p = 0.007). Additionally, the difference between adolescent females and adult males was highly statistically significant (p = 0.002) (Figure 7a–c).

A similar comparison of pain levels according to age and sex is presented for the FA treatment (Figure 8a,b).

Comparisons of pain level during FA therapy related to age and sex in the whole study group revealed no statistically significant differences in pain level reported by adolescents (NRS = 4.5) vs. adults (NRS = 4.0), as well as females (NRS = 5.0) vs. males (NRS = 4.0).

However, when the comparison of pain or sex sensitivity during FA therapy was conducted separately for adolescents and for adults, adolescent females felt insignificantly higher pain (NRS = 5.0) than adolescent males (NRS = 4.0), whereas adults females reported significantly higher mean pain (NRS = 5.0) than males (NRS = 2.5) (p = 0.003).

Interestingly, for adolescents during the period of peak pubertal growth (CS3–4), both treatment modalities were less painful in comparison to pre- and postpubertal stages, as presented in Figure 9a,b.

When examining other adverse effects, no significant differences were observed in the occurrence of pressure sores or speaking difficulties between the two age groups, indicating that these complications are similarly experienced across age demographics.

Specifically, speaking difficulties were reported by a substantial portion of the overall cohort (50.53%), suggesting that the Haas-type acrylic bonded appliance commonly impacts speech, regardless of the patient’s age.

Headaches were only reported by two adults: an 18-year-old female and a 21-year-old male with severe skeletal maxillary deficiency (Figure 10a,b).

5. Discussion

Contemporary indications for RME comprise maxillary deficiency, often concurrent with Class II or Class III malocclusion [24].

The data presented in the present study offer a comprehensive insight into the clinical parameters and discomfort associated with the use of Haas-type acrylic expanders and fixed orthodontic appliances, stratified by adolescent and adult age groups. This analytical approach facilitates a comprehensive understanding of the impact of orthodontic appliances on different age demographics within the cohort.

Our research describes one of few studies referring to pain and discomfort in patients treated with RME devices anchored on acrylic splints (bonded RME) with acrylic extensions on the palate [23,24,25,26,27]. It is important to underline that most studies refer to RME anchored on two or four separated bands overloading supported teeth [7,8,9,10,16,19,20,28,29,30,31]. Both the rate of screw turning and the design of the appliance might have an impact on the pain levels reported [5].

The findings of previous studies on pain reported during RME or SRME are presented in Table 3.

We decided to compare adolescents’ and adults’ pain perceptions during two potentially painful orthodontic procedures, i.e., SRME (semi-RME) and FA, in the same patients. To our knowledge, this is the first study reporting such a comparison.

No consistency exists in the literature referring to the definition of SRME. Baldini et al. [16] consider SRME as one quarter-turn activation per day, while Ramoglu and Sari (2010) defined SRME as two quarter turns per day for the first week followed by one quarter turn per day, every other day [23]. In contrast—rapid maxillary expansion (RME) is performed as two to four quarter-turn screw activations per day during the whole treatment [6,16,18,27,28,32].

In the present study, an NRS was chosen for its simplicity compared to a VAS [21].

The NRS has been widely used in diverse populations, since pain cannot be directly measured and is believed to range across a continuum of values. The level of pain in the present study can be assumed as moderate grade, as it was equal to 4.00 on the NRS, and only 18.95% of the total group considered pain as the main disadvantage during SRME. The relatively moderate level of pain in our study could be related to a few factors.

The first factor might be the design of appliance. Connecting six to eight upper teeth (from first premolar to the first or second molar) increases the support for optimal distribution of the force, instead of devices anchored on two or four bands (as in most studies published), potentially overloading separated, supported teeth. Alpernern and Yurosko claim that acrylic splints counteract possible fracture of the buccal bone plate and gingival recessions usually described in the literature [33]. Moreover, the study by Altuhafy et al. reported that the Hyrax expander is more painful than the Haas appliance [20].

The second factor seems to be the rate of expanding the screw. In the present study, it was one quarter turn per day. The activation protocol was chosen following that used by Haas and Handelman [22]. Similarly to the present study, Handelman et al. used a typical Haas appliance on four bands and acrylic extensions on the palate and found pain or swelling only in 19.15% of patients. On the contrary, Capelozza et al. used a Hyrax expander on four bands turned four times a day and reported pain, swelling and ulceration in 68% of patients [32]. A more recent study by Baldini et al. used an RME device with a stainless-steel expander cemented to the maxillary first molars, comparing two protocols of expansion, and concluded that patients treated with two activations per day reported significantly higher pain levels compared to patients treated with one activation per day. The difference was more than twice as much between groups with one turn vs. two turns daily [16]. Similar findings were reported in other studies [5,6,17,18,34], whereas Halicioglu et al. reported no correlation between pain and activation protocols [35]. However, a more detailed insight into three protocols, described by Halicioglu et al., reveals that the first study group with a protocol of six turns daily had been treated with a memory screw combining intermittent and continuous force modules, while the second and third study groups had been treated with another type of appliance, i.e., the conventional Hyrax screw. Moreover, the groups with Hyrax turned the screw in the same protocol two times a day during the most painful period, i.e., the first ten turns [16,28]. Thus, the results, despite the three different protocols, were not statistically different.

Table 3. Previous studies on pain reported during RME or SRME.

Author, Year (Ref. No.)	Study Group—Number, Age, Gender	Type of Appliance (Rate of Activation)	Pain Level (Scale Used) and Other Discomfort
Capelozza F et al. 1996 [32]	38 patients No data referring to age and gender	RME appliance of the Haas design 4× daily	Mild discomfort to significant pain Subjective pain assessment—no scale was used
Handelman et al. 2000 [22]	Adults 94 patients 47 adults 19 M, 28 F 47 children as CG	a Haas-type palatal expander followed by edgewise appliance therapy 1× daily	9 of the 47 subjects (19%) reported palatal swelling and pain, and 1 subject reported headaches Subjective pain assessment—no scale was used
Needleman et al. 2000 [18]	Children and adolescents 80 patients 38 M, 59 F 5 to 13 years (median 7.7 years)	RPE procedures with the Hyrax (Dentaurum, Newtown, PA, USA) 1× daily or 2× daily	the Facial Pain Scale and the Color Analog Scale (0–10). Two turns/day—pain stronger than those expanding once/day. No statistically significant difference between females and males.
Önçağ G et al. 2011 [27]	Adolescents 30 patients 16 M, 14 F between the ages of 13 and 15 years (mean 14.4 years).	Acrylic bonded Hyrax expander 2× daily during a period of 10 days (0.5 mm/day)	A color pain scale (0–10) Pain was found to be most severe in the dental arch, while it decreases with the distance from the activation region No significant differences in pain perception between males and females (p > 0.05)
Gecgelen M et al. 2012 [25]	Adolescents 40 patients 20 F, 20 M aged 10.9–14.7 y	RME an acrylic-bonded RME appliance 1× daily for 36 days	Pressure pain threshold (PPT) Male = 8.84, Female = 7.43
Halicioglu K et al. 2012 [35]	Adolescents 60 patients 32 F, 28 M (mean age 13.5 y)	RME 1. The memory screw (9 F, 9 M), combining intermittent and continuous force modules, 6× daily 2. The second group (10 F, 10 M), conventional Hyrax appliance, activated 2× daily until the mid-palatal suture opened, after which activation was reduced to 1× daily 3. The third group (13 F, 9 M), a conventional Hyrax screw 2× daily during the entire expansion phase	Numerical rating scale (NRS) 98% of the patients reported pain during RME to a mild degree The majority of the patients undergoing RME suffered pain and pressure sensations especially after the fifth activation Patients who were treated with RME appliances experienced headache and slight dizziness No activation-related differences were found No gender-related differences were found
Baldini A, Nota A 2015 [16]	Children 112 prepubertal patients (54 M, 58 F) m.a. 11.00 ± 1.80 y	A stainless-steel banded expander cemented to the maxillary first molars. RME with two different activation protocols Group 1: 1× daily Group 2: 2× daily	NRS and the Faces Pain Scale (FPS) RME at 2×/day reported significantly greater amounts of pain than subjects treated with RME at 1×/day Pain reported during RME: F = 2.5, M = 2.2 Younger and female patients were more sensitive to the activation protocol
Feldman I, Bazargani F. 2017 [28]	Children 54 patients 28 F, 26 M age: 9.8 ± 1.28	Conventional Hyrax with 2 bands and metal bar from 6 to IV vs. Hybrid Hyrax	The VAS Median values for pain were 8.0 (range 0–50) Hyrax and 3.0 (0–82) HH No statistically significant differences in pain Age was positively correlated with overall pain and discomfort
Cossellu G et al. 2019 [31]	Children Phase 1: 101 patients. KLS G: 28 p: 7 F, 11 M, m.a. 8.5 ± 1.8 y. PG: 35 p (17 F, 18 M), m.a. 8.7 ± 1.8 y. CTRL G: 35 p: 17 F, 19 M, m.a. 8.9 ± 1.2 y. Phase 2: added KLS-B 31 p: 15 F, 16 M, m.a. 8.7 ± 1.6 y.	Haas-expander, bonded through bands on the maxillary first permanent molars 2× daily	VAS associated with a numeric rating scale (NRS) Ketoprofen lysine salt vs. paracetamol on pain perception during RME KLS is more effective than P during the fourth, fifth and sixth days
Ugolini A et al. 2020 [7] RCT	101 patients (48 RME G, 53 LE G) RME G: 26 F, 23 M. m.a. 9.4 years LE G: 28 F, 25 M m.a. 9.1. years	Leaf expander vs. Hyrax LE: 2× at chairside, followed by two 1/4 turns/d (1 in the morning and 1 in the evening, 0.40 mm/d)	Wong–Baker FPS (0–10) from the 1st to the 7th d of screw activation, with a double registration/d (morning and evening) Pain is influenced by clinical activation protocol and by the screw type. Patients treated with Leaf expander reported significantly lower pain level in the first 7 days of treatment
Abed Al Jawad FH, Alhashimi NA. 2021 [19]	Adolescents 55 patients 43 F, 12 M aged 10.2 to 15 y	Quadhelix group (QG) vs. Hyrax on 4 bands	Hyrax group reported significantly higher scores for difficulty in swallowing (moderate to severe) during the first 6 days. No differences in pain between QG vs. HG. No correlations between age, gender or malocclusion type
Nieri M et al. 2021 [8]	Children (CS 1–2) 56 patients 28 LE: 61% F, 39% M. 8 y 28 RME: 43% F, 57% M. m.a. 8.4 y RME: 8.4 ± 1.0 y SME: 8.0 ± 1.3 y RME: 12 F, 16 M MSME: 17 F, 11 M RME: 21 subjects in CS 1; 6 subjects in CS 2 SME: 24 subjects in CS 1; 4 subjects in CS 2	Butterfly expander anchored with bands on second primary molars LE activation protocol: initial expansion of 4.5 mm in about 2–3 m, followed by ten 1/4 turns/m for spring reactivation (1 mm) RME activation protocol: 1/4 turn/d (0.2 mm) until the desired expansion was achieved	VAS and Wong–Baker Faces Pain Scale for pain assessment with a complementary NRS from 0 to 10 VAS scale (0–10 pt) once/w for 12 w VAS for pain was 0.3 ± 0.4 in the Leaf group and 0.6 ± 0.5 in the RME group - After the first week of beginning of treatment RME and SME, difficulty in speaking was highly prevalent (85–90%) - Patients in the Leaf group experienced a lower degree of pain, especially during the first week
Rutili V et al. 2022 [10] Systematic review and meta	Children and adolescents 157 patients between 5.7 and 13 years	RME vs. SME	NRS and VRS - SME patients (GRADE very low) - Pain intensity was significantly lower in SME compared to RME during the first week of treatment
Yacout YM et al. 2022 [17] RCT	Adolescents 30 patients aged 12–16 years SME group (n = 12, mean age = 14.30 ± 1.37 years) RME group (n = 12, mean age = 15.07 ± 1.59 years)	Penn expanders anchored by four palatal miniscrews (HH) (SME) group activated the appliance once every other day (RME) group activated the appliance twice daily	NRS at the following four time points: before appliance insertion (t1), after first activation (t2), after 1 week of activation (t3) and after last activation (t4) - Outcome measures were pain, pressure, headache, dizziness, speech difficulty, chewing difficulty, swallowing difficulty - Slow activation resulted in a better overall patient experience compared with rapid activation
Barone M et al. 2023 [5] Systematic Review.		RME different types RME vs. SME	Different pain scales - Gender and age differences in pain perception are not clear Perceived pain is influenced by the expander design and expansion protocol used - A slower expansion protocol (i.e., fewer screw activations per day) correlates with less pain perceived by the patient
Pasqua et al. 2023 [13]	Adolescents 42 patients 17 F, 25 M aged 11–14 years Female sex presenting higher scores for pain and functional limitation	Hybrid Hyrax (12 F and 9 M, m.a. 13.3 ± 1.3 years), and TB GROUP (tooth-borne expander), treated with Hyrax (5 F and 16 M, m.a 13.3 ± 1.4 years)	NRS and the instrument MFIQ (Mandibular Functional Impairment Questionnaire). - Pain and discomfort were assessed two times: after the first day of activation (T1) and four days after - The scores obtained were of low intensity, and no significant differences were observed between the groups
Hasson S et al. 2023 [10]	Children 35 patients in each group 13 F, 22 M Age: 9.3 F, 9.6 M	Quad Helix (QH) vs. RME (Marco Rosa Hyrax-type)	VAS and VRS - Patients with QH experienced more chafe and pain from tongue on the first days than the RME group - Speech was more affected in patients with RME on days 4 and 7 - The levels of pain were to be considered as low to moderate in both groups the first week
Altuhafy M et al. 2023. [20] Syst Rev.	Growing patients The number of participants in the included RCTs ranged between 34 to 114 and included both male and female growing patients	Hyrax vs. other maxillary expansion orthodontic appliances (Leaf expander, Haas appliance)	Graphic rating scale for pain, the Wong–Baker Faces Pain Scale, the NRS, VAS and a questionnaire - Pain intensity in patients treated with the Hyrax was higher than with the Haas appliance (one study) - Pain intensity in patients treated with the Leaf expander was lower than in the Hyrax during the first 7 days of treatment (2 studies) Two RCTs: no significant differences in pain intensity between the Hyrax and other RME appliances
El Naghy R et al. 2023 [34]	Adolescents 30 patients aged between 12 to 16 y total of 24 patients (12 patients in each group)	Miniscrew-supported Penn expanders allocated (ratio 1:1) into two groups based on the activation protocol SME = 1×/daily or RME = 2×/day	NRS at 4 time points: t1 = before appliance insertion, t2 = after first activation, t3 = after 1 week of activation, t4 = after last activation. - Pain, headache, pressure, dizziness, speech, chewing and swallowing difficulties - Median scores were in the bottom quartiles of NRS for all reported outcomes - Headache and dizziness had no statistical difference between the two group - SME protocol provided a better overall patient experience compared to RME protocol

Table 3. Previous studies on pain reported during RME or SRME.

Author, Year (Ref. No.)	Study Group—Number, Age, Gender	Type of Appliance (Rate of Activation)	Pain Level (Scale Used) and Other Discomfort
Capelozza F et al. 1996 [32]	38 patients No data referring to age and gender	RME appliance of the Haas design 4× daily	Mild discomfort to significant pain Subjective pain assessment—no scale was used
Handelman et al. 2000 [22]	Adults 94 patients 47 adults 19 M, 28 F 47 children as CG	a Haas-type palatal expander followed by edgewise appliance therapy 1× daily	9 of the 47 subjects (19%) reported palatal swelling and pain, and 1 subject reported headaches Subjective pain assessment—no scale was used
Needleman et al. 2000 [18]	Children and adolescents 80 patients 38 M, 59 F 5 to 13 years (median 7.7 years)	RPE procedures with the Hyrax (Dentaurum, Newtown, PA, USA) 1× daily or 2× daily	the Facial Pain Scale and the Color Analog Scale (0–10). Two turns/day—pain stronger than those expanding once/day. No statistically significant difference between females and males.
Önçağ G et al. 2011 [27]	Adolescents 30 patients 16 M, 14 F between the ages of 13 and 15 years (mean 14.4 years).	Acrylic bonded Hyrax expander 2× daily during a period of 10 days (0.5 mm/day)	A color pain scale (0–10) Pain was found to be most severe in the dental arch, while it decreases with the distance from the activation region No significant differences in pain perception between males and females (p > 0.05)
Gecgelen M et al. 2012 [25]	Adolescents 40 patients 20 F, 20 M aged 10.9–14.7 y	RME an acrylic-bonded RME appliance 1× daily for 36 days	Pressure pain threshold (PPT) Male = 8.84, Female = 7.43
Halicioglu K et al. 2012 [35]	Adolescents 60 patients 32 F, 28 M (mean age 13.5 y)	RME 1. The memory screw (9 F, 9 M), combining intermittent and continuous force modules, 6× daily 2. The second group (10 F, 10 M), conventional Hyrax appliance, activated 2× daily until the mid-palatal suture opened, after which activation was reduced to 1× daily 3. The third group (13 F, 9 M), a conventional Hyrax screw 2× daily during the entire expansion phase	Numerical rating scale (NRS) 98% of the patients reported pain during RME to a mild degree The majority of the patients undergoing RME suffered pain and pressure sensations especially after the fifth activation Patients who were treated with RME appliances experienced headache and slight dizziness No activation-related differences were found No gender-related differences were found
Baldini A, Nota A 2015 [16]	Children 112 prepubertal patients (54 M, 58 F) m.a. 11.00 ± 1.80 y	A stainless-steel banded expander cemented to the maxillary first molars. RME with two different activation protocols Group 1: 1× daily Group 2: 2× daily	NRS and the Faces Pain Scale (FPS) RME at 2×/day reported significantly greater amounts of pain than subjects treated with RME at 1×/day Pain reported during RME: F = 2.5, M = 2.2 Younger and female patients were more sensitive to the activation protocol
Feldman I, Bazargani F. 2017 [28]	Children 54 patients 28 F, 26 M age: 9.8 ± 1.28	Conventional Hyrax with 2 bands and metal bar from 6 to IV vs. Hybrid Hyrax	The VAS Median values for pain were 8.0 (range 0–50) Hyrax and 3.0 (0–82) HH No statistically significant differences in pain Age was positively correlated with overall pain and discomfort
Cossellu G et al. 2019 [31]	Children Phase 1: 101 patients. KLS G: 28 p: 7 F, 11 M, m.a. 8.5 ± 1.8 y. PG: 35 p (17 F, 18 M), m.a. 8.7 ± 1.8 y. CTRL G: 35 p: 17 F, 19 M, m.a. 8.9 ± 1.2 y. Phase 2: added KLS-B 31 p: 15 F, 16 M, m.a. 8.7 ± 1.6 y.	Haas-expander, bonded through bands on the maxillary first permanent molars 2× daily	VAS associated with a numeric rating scale (NRS) Ketoprofen lysine salt vs. paracetamol on pain perception during RME KLS is more effective than P during the fourth, fifth and sixth days
Ugolini A et al. 2020 [7] RCT	101 patients (48 RME G, 53 LE G) RME G: 26 F, 23 M. m.a. 9.4 years LE G: 28 F, 25 M m.a. 9.1. years	Leaf expander vs. Hyrax LE: 2× at chairside, followed by two 1/4 turns/d (1 in the morning and 1 in the evening, 0.40 mm/d)	Wong–Baker FPS (0–10) from the 1st to the 7th d of screw activation, with a double registration/d (morning and evening) Pain is influenced by clinical activation protocol and by the screw type. Patients treated with Leaf expander reported significantly lower pain level in the first 7 days of treatment
Abed Al Jawad FH, Alhashimi NA. 2021 [19]	Adolescents 55 patients 43 F, 12 M aged 10.2 to 15 y	Quadhelix group (QG) vs. Hyrax on 4 bands	Hyrax group reported significantly higher scores for difficulty in swallowing (moderate to severe) during the first 6 days. No differences in pain between QG vs. HG. No correlations between age, gender or malocclusion type
Nieri M et al. 2021 [8]	Children (CS 1–2) 56 patients 28 LE: 61% F, 39% M. 8 y 28 RME: 43% F, 57% M. m.a. 8.4 y RME: 8.4 ± 1.0 y SME: 8.0 ± 1.3 y RME: 12 F, 16 M MSME: 17 F, 11 M RME: 21 subjects in CS 1; 6 subjects in CS 2 SME: 24 subjects in CS 1; 4 subjects in CS 2	Butterfly expander anchored with bands on second primary molars LE activation protocol: initial expansion of 4.5 mm in about 2–3 m, followed by ten 1/4 turns/m for spring reactivation (1 mm) RME activation protocol: 1/4 turn/d (0.2 mm) until the desired expansion was achieved	VAS and Wong–Baker Faces Pain Scale for pain assessment with a complementary NRS from 0 to 10 VAS scale (0–10 pt) once/w for 12 w VAS for pain was 0.3 ± 0.4 in the Leaf group and 0.6 ± 0.5 in the RME group - After the first week of beginning of treatment RME and SME, difficulty in speaking was highly prevalent (85–90%) - Patients in the Leaf group experienced a lower degree of pain, especially during the first week
Rutili V et al. 2022 [10] Systematic review and meta	Children and adolescents 157 patients between 5.7 and 13 years	RME vs. SME	NRS and VRS - SME patients (GRADE very low) - Pain intensity was significantly lower in SME compared to RME during the first week of treatment
Yacout YM et al. 2022 [17] RCT	Adolescents 30 patients aged 12–16 years SME group (n = 12, mean age = 14.30 ± 1.37 years) RME group (n = 12, mean age = 15.07 ± 1.59 years)	Penn expanders anchored by four palatal miniscrews (HH) (SME) group activated the appliance once every other day (RME) group activated the appliance twice daily	NRS at the following four time points: before appliance insertion (t1), after first activation (t2), after 1 week of activation (t3) and after last activation (t4) - Outcome measures were pain, pressure, headache, dizziness, speech difficulty, chewing difficulty, swallowing difficulty - Slow activation resulted in a better overall patient experience compared with rapid activation
Barone M et al. 2023 [5] Systematic Review.		RME different types RME vs. SME	Different pain scales - Gender and age differences in pain perception are not clear Perceived pain is influenced by the expander design and expansion protocol used - A slower expansion protocol (i.e., fewer screw activations per day) correlates with less pain perceived by the patient
Pasqua et al. 2023 [13]	Adolescents 42 patients 17 F, 25 M aged 11–14 years Female sex presenting higher scores for pain and functional limitation	Hybrid Hyrax (12 F and 9 M, m.a. 13.3 ± 1.3 years), and TB GROUP (tooth-borne expander), treated with Hyrax (5 F and 16 M, m.a 13.3 ± 1.4 years)	NRS and the instrument MFIQ (Mandibular Functional Impairment Questionnaire). - Pain and discomfort were assessed two times: after the first day of activation (T1) and four days after - The scores obtained were of low intensity, and no significant differences were observed between the groups
Hasson S et al. 2023 [10]	Children 35 patients in each group 13 F, 22 M Age: 9.3 F, 9.6 M	Quad Helix (QH) vs. RME (Marco Rosa Hyrax-type)	VAS and VRS - Patients with QH experienced more chafe and pain from tongue on the first days than the RME group - Speech was more affected in patients with RME on days 4 and 7 - The levels of pain were to be considered as low to moderate in both groups the first week
Altuhafy M et al. 2023. [20] Syst Rev.	Growing patients The number of participants in the included RCTs ranged between 34 to 114 and included both male and female growing patients	Hyrax vs. other maxillary expansion orthodontic appliances (Leaf expander, Haas appliance)	Graphic rating scale for pain, the Wong–Baker Faces Pain Scale, the NRS, VAS and a questionnaire - Pain intensity in patients treated with the Hyrax was higher than with the Haas appliance (one study) - Pain intensity in patients treated with the Leaf expander was lower than in the Hyrax during the first 7 days of treatment (2 studies) Two RCTs: no significant differences in pain intensity between the Hyrax and other RME appliances
El Naghy R et al. 2023 [34]	Adolescents 30 patients aged between 12 to 16 y total of 24 patients (12 patients in each group)	Miniscrew-supported Penn expanders allocated (ratio 1:1) into two groups based on the activation protocol SME = 1×/daily or RME = 2×/day	NRS at 4 time points: t1 = before appliance insertion, t2 = after first activation, t3 = after 1 week of activation, t4 = after last activation. - Pain, headache, pressure, dizziness, speech, chewing and swallowing difficulties - Median scores were in the bottom quartiles of NRS for all reported outcomes - Headache and dizziness had no statistical difference between the two group - SME protocol provided a better overall patient experience compared to RME protocol

The third factor is the time of screw expansion. The Haas-type acrylic splint appliance in our study was expanded in the evening, just before going to bed, in order to reduce the pain sensation. In general, pain usually starts 4 h after the onset of the orthodontic force [13]; thus, screw turning before going to bed drives the pain into sleep time. Additionally, pain during the RME procedure might be related to the level of cortisol, a critical regulator of metabolism [36] that has its lowest level after lights off, at the onset of sleep, with peak levels occurring in every individual around waking [37,38]. An inhibition of proliferation of the periosteal cells, which gives rise to osteoblasts, is a primary effect of cortisol on bone growth [39] and down-regulation of the synthesis of collagen [40]. Therefore, small amounts of cortisol are necessary for normal bone development to reduce the initial resistance to expansion, while glucocorticoid excess inhibits bone formation and calcium absorption from the gut and increases bone resorption and osteoporosis [36,41,42]. Thus, there is a circadian turnover of the bone, with bone resorption in the morning and increasing formation at night [43]. Therefore, pain sensation during RME is opposite to the pain sensation related to treatment with fixed appliances, which is proved to be lower in the morning than in the evening [44] and achieves the lowest level during the afternoon [14].

In the present study, the average pain level reported on the NRS in the whole group of patients during SRME screw activation was compared with the pain during FA therapy, considered as a perfectly matching control group, and was equally moderate for both procedures. However, a comparison carried out between two age groups revealed that pain levels during the SRME screw activation of the Haas-type acrylic appliance in adolescent patients was more painful (NRS = 5.00) compared to adults (NRS = 3.00) with statistical significance (p = 0.009), contrary to the common opinion that for adults, the RME procedure might be more painful. A similar comparison between adolescents and adults carried out for lower FA therapy resulted in a similar moderate grade level for both age groups. During the leveling phase of orthodontic treatment, higher pain levels were reported in the lower arch compared to the upper arch at 6 h and at day 7 [45]. Lower pain levels were reported in the evening than in the morning for days 2–6, independent of patients’ age, sex and irregularity [45], which is in disagreement with the study by Satpal S et al. [44].

The finding that adolescents experience greater discomfort during the initial stages of SRME treatment may be attributed to a lower tolerance for pain or the higher sensitivity of developing tissues in midpalatal sutures during maxillary expansion. Our study supports previous findings that adolescence is a developmental period when pain is highly prevalent, and girls experience pain more often than boys [46,47,48]. Nevertheless, in the literature, there is no agreement referring to pain during RME in relation to age and sex. Some studies reported an association with patients’ age [16,25,28,44], while others showed no correlation to age [19,35].

The present finding that both treatment modalities were less painful for adolescents during the period of peak pubertal growth (CS 3–4) in comparison to pre- and postpubertal stages is opposite to the results presented in a study based on the Turkish population by Gecgelen et al. 2012, where they found that the mean pressure pain threshold values of post-peak subjects were significantly higher than the mean pressure pain threshold values of pubertal-peak subjects [25]. It might be supposed that the lack of statistical significance in the present study might be related to the sizes of the skeletal-stage subgroups. The authors suppose that prepubertal growth stage is associated with higher pain. Similarly, the finding by Almallah et al. of 2020 that younger patients reported stronger pain relief after low-level laser treatment compared to older patients is possibly due to differences in tissue response or pain perception [49].

The questionnaire filled in by the patients at the appointment following RME debonding aimed to cover all possibly painful procedures, including debonding (the last procedure associated to SRME), which sometimes is inconvenient for the patients. However, it is difficult to assess if the delayed description of experienced pain could influence the reported pain level experienced during screw turning. In the literature, there is no agreement on the influence of time on describing pain intensity [50]; however, it seems a very interesting issue (within the field of psychology—useful for clinical orthodontics), whether and how the memory on pain changes with time.

Referring to the lack of significant differences between the sexes in the whole group, in the literature, there is no agreement related to pain during RME in relation to sex. Some studies showed that pain was more intense in girls [9,16,25], whereas other research showed no correlation to sex [18,19,27,35]. Referring to the comparison of pain sensitivity during SRME procedures between the sexes carried out separately for adolescents and adults that showed that adolescent females felt the highest pain level among the four age and sex subgroups, our finding is in agreement with some studies [9,16,25]. As far as statistically significantly higher pain levels reported by adult females than by adult males (who had the lowest pain levels among the four age/sex subgroups), and similar results for FA therapy in separated age groups, no suitable studies could be found in the literature for comparison. The biggest significant difference was observed between adolescent females and adult males. The highest pain threshold in adult males in both procedures (SRME or FA, average NRS = 2.25) is in agreement with the study by Gecgelen et al. [25].

The success rates of palatal suture openings in adults in the literature are 54% in the Polish population treated with the Biderman appliance on four bands [51]; 82% in the Brazilian population treated with typical Haas appliance [32]; and 100% in the American population also treated with Haas appliance [22]. In our study, it was 64.71%. All female patients between 30 and 42 years of age (8 women) presented with diastema, which is in agreement with the study by Chamberland (2023), who claimed that “the success rate decreases in males older than 25 years, whereas females in their 30s have a favorable response” [52]. Palatal suture opening in the oldest (36-year-old) male patient included was probably due to a remarkable plasticity of the facial skeleton, visible during the treatment with RME and facemask. Also, in the study which established the classification of midpalatal suture maturation the researchers found a great variability in sutural maturation in adolescents and adults (53). The greater percentage of subjects in stage C was during adolescent group (25% of girls at the age 11–14 y, 26.32% of girls at the age 14–18 y; 29.16% of boys at the age 11–14 y and 53.84% of boys at the age of 14–18%) than in adult group (15.8% of females and 7.7% of males). Even early fusion of the midpalatal suture (stages D and E) was detected in adolescent girls (20.83% at the age 11–14 y and 42.1% at the age of 14–18 y). On this account our results suports the uncertainty in the literature of the strict correlation between the metrical age and palatal suture resistance to opening (54–56). Therefore, more research is essential to determine the dilemma related to the relationship between palatal suture opening and metrical age of patients.

Thus, it can be assumed that the present protocol of screw activation, i.e., one quarter turn per day, just before going to sleep, allows the patients to manage the screw activation period of treatment relatively comfortably. Probably, the design of the expander, i.e., Haas-type expander with acrylic splints and acrylic palatal extension, also helped reduce pain levels, which is consistent with the study by Altuhafy et al., who reported a lower pain intensity in patients treated with the Haas appliance compared to the Hyrax [20].

Overall, the data indicate that the Haas-type appliance does pose moderate pain and discomfort; however, pain is experienced more strongly by adolescent patients. Thus, the use of ketoprofen lysine salt (KLS) could be recommended for adolescents, as KLS is considered to be more effective in reducing pain than paracetamol [31].

Finally, the null hypothesis that SRME and FA therapies are more painful to adults than to adolescents is rejected, similarly as is the other hypothesis that SMRE is more painful than FA therapy.

A possible limitation of the present study refers to the subjective assessment of pain, as well as still insufficient numbers (44 patients) of adolescent patients to achieve statistically significant results of pain related to skeletal stages.

6. Conclusions

Based on above findings, the following can be assumed:

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SRME with activating the screw in Haas-type acrylic splint expander by one turn daily just before going to bed is a relatively untroublesome procedure.

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SRME is more painful for adolescents than for adults.

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Adult males reported the lowest pain level, whereas adolescent females reported the highest pain level, both during SRME and FA treatments.

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Both SRME and FA therapies seemed to be less painful for adolescents during peak pubertal growth than during other stages.

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The relation between palatal suture opening and metrical age of patients needs more research on larger groups of adult and adolescent patients.

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Speaking difficulties were most pronounced during the treatment with the Haas-type acrylic splint expander, while pressure sores were most uncomfortable during FA therapy.