INTRODUCTION

Transverse maxillary deficiency is a common malocclusion that is often treated in adolescence using tooth-supported expanders.¹ The transmission of expansion forces to the mid-palatal suture through the anchoring teeth may result in unfavorable effects.² Miniscrew-supported maxillary expanders have offered orthodontists a viable treatment option to avoid such adverse effects³ and expand the maxilla in patients with periodontally involved teeth and partially edentulous patients.^4,5

Although previous studies^4,6–10 have demonstrated the effectiveness of maxillary expanders supported only by miniscrews, their optimal activation rate is still debatable. The decision to use a rapid or slow activation rate currently depends on the practitioner's clinical experience and personal preference.¹¹ Choi et al.¹² used a slow rate with miniscrew-supported expansion to reduce patient discomfort and tissue damage. Similarly, Zong et al.¹³ recommended using a slower rate of activation if patients reported moderate to severe pain. The rationale was that pain is affected by the magnitude of the applied force,¹⁴ which in turn varies according to the activation protocol. A single activation produces approximately three to 10 pounds of force.¹⁵

Pain is a common adverse effect of using maxillary expanders,^16,17 and the soreness resulting from their use may interfere with the patient's daily activities, such as speech, chewing, and swallowing.¹⁶ The perception of pain is subjective and shows individual variation. The numeric rating scale (NRS) can be used for grading pain and its effect on function.¹⁸ The most frequently used NRS is the 11-point scale ranging from 0 to 10, in which the patient chooses an integer that best denotes the intensity of the effect.¹⁹ A score of 0 to 4 represents mild intensity, a score of >4 to 7 represents moderate intensity, and a score of >7 to 10 represents severe intensity.²⁰

The objective of this study was to compare the adolescent patient-reported experience between a miniscrew-supported expander activated every other day vs twice per day. The hypothesis was that the rate of activation would affect the reported discomfort and interference with daily activities.

MATERIALS AND METHODS

Interventions

Patients were randomly allocated into two groups: slow maxillary expansion (SME), where the appliance was activated every other day, or rapid maxillary expansion (RME), with two turns of activation daily. All treatment procedures were carried out by the primary investigator. Four palatal miniscrews (1.6 × 10 mm, H-screw, Hubit Co Ltd, Ojeon-Dong, Korea) were inserted at the following sites bilaterally: between the first and second premolars and between the second premolar and the first molar (Figure 1). A miniscrew-supported acrylic expander was fabricated as shown in Figure 1 using a 9-mm expansion screw (Leone Orthodontic Products, Sesto Fiorentino, Firenze, Italy) with four holes accommodating the head of the miniscrews that were subsequently filled with light-cure flowable composite (Te-econom flow, Ivoclar Vivadent, Schaan, Liechtenstein). Expansion was considered sufficient when the transverse maxillary discrepancy measured on digital dental casts was corrected.²¹

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RESULTS

The flow of participants through the trial is shown in Figure 2. Sample demographic and clinical data are reported in Table 1. Descriptive statistics and box plots of the scores for each outcome are shown in Table 2 and Figure 3, respectively.

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Table 1.  Demographic and Clinical Data of Patients in the SME and RME Groups^a

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Table 2.  Medians and IQRs of Scores of Each Patient-Reported Outcome in the Two Groups^a

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Median scores approximated zero for all the variables measured after appliance placement before activation of the expansion screw except for swallowing, where median scores were 2 ± 4.8 and 2 ± 2.8 in the SME and RME groups, respectively, with some patients reporting a score of 10 at t₁ (Figure 3). All patients experienced some form of discomfort and functional limitation with the activation of the expanders. However, the median scores were in the two bottom quartiles of the NRS for all outcomes.

The general trend of change in scores in the SME group was a statistically significant increase in reported scores following activation that subsequently decreased significantly at the end of expansion. This was true for pressure, speech, and swallowing, where significantly higher scores were reported at t₂ and/or t₃ compared with t_1, with no statistically significant difference between scores at t₁ and t₄.

In the RME group, scores significantly increased from baseline to the subsequent time points, with a statistically significant increase at t₄ compared with t₁ for pain, pressure, and chewing difficulty scores. In contrast, speech scores demonstrated no statistically significant difference between t₁ and t₄: 0 ± 1.8 and 3 ± 4, respectively. It was interesting to note that, as the median score increased from baseline to the final activation, the IQR also increased, rendering the difference between the medians not statistically significant.

Intergroup comparisons showed statistically significantly higher pain and chewing difficulty scores after 1 week of rapid activation compared with slow activation. Significantly higher scores for all variables were reported in the RME group after t₄ except for dizziness and headache. Headache scores showed no statistically significant difference between RME and SME at any time point. The reported median dizziness score at all time points for both groups was zero.

DISCUSSION

It was hypothesized that a slower rate of activation of miniscrew-supported maxillary expanders would result in a better patient experience. With miniscrews serving as anchorage, the rationale of using a rapid activation rate of conventional expanders to minimize dentoalveolar adverse effects²⁴ no longer seems valid. A slow activation rate has been advocated with miniscrew-supported expanders to allow dissipation of stresses,^25,26 avoid palatal bone fracture,⁴ and, therefore, in addition to other benefits, reduce pain and discomfort.¹²

An 11-point NRS was used for grading patient self-reported outcomes.¹⁸ The numeric pain rating scale was shown to be both reliable and valid.¹⁸ In addition, it was considered more straightforward for patients and more practical for the purpose of research compared with other methods.¹⁸

Median scores for most variables were near zero at t₁, with narrow IQRs from 0 to 1.8. However, swallowing scored a median of 2 in both groups. In addition, the IQRs were wider for swallowing (4.8) as well as for chewing (3.8) in the SME group. Initial scores were taken after miniscrew insertion. Although at least 7 days were allowed following miniscrew insertion to ensure that the procedure had no effect on the patient response, the presence of miniscrews may have interfered with swallowing and chewing. Discomfort resulting from contact between the tongue and the palatal miniscrews was reported previously.²⁷

Participants in both groups reported higher median scores following appliance activation for most of the measured variables. Previous research showed increased pressure and pain following the placement of expansion appliances^17,28 as well as difficulties with chewing and swallowing.¹⁶ Maxillary expansion has been associated with speech problems.¹⁶ The presence of palatal appliances may restrict tongue movements during speech, thus affecting alveolar consonants /t/ and /d/.²⁹

Median pain scores significantly increased immediately and 1 week following appliance activation in the RME group. Conversely, Altieri et al.³⁰ reported higher pain scores on the first day of activation that declined to lower scores after 1 week of activation of rapid bone-borne expanders. Unlike the present study, Altieri et al.³⁰ inserted the miniscrews, inserted the appliance, and activated it in the same visit as the first score was measured. Also, the rate of screw activation was four times on the first day followed by activation three times per day. In contrast, in the current study, appliance insertion and pain assessment were performed after a minimum of 7 days of miniscrew insertion, and the appliances were activated only twice per day in the RME group.

At the end of expansion, SME patients reported mild pain scores. Lagravère et al.⁴ showed that bone-borne expanders activated every other day resulted in pain scores in the lower quartile of the visual analog scale at different time points. RME patients reported mild pain at t₁ and t₂ that increased to moderate pain at t₄ as classified by Brailo et al.²⁰ In contrast, moderate to severe pain has been reported in association with tooth-supported maxillary expanders.^16,28,31,32 The compression of the periodontal ligaments of anchor teeth may have added to the pain experienced due to the inflammation response during the opening of the mid-palatal suture.¹⁴ Using miniscrews in tooth-bone-borne expanders has been shown to reduce pain from maxillary molars.¹⁷

Comparing both activation rates, the difference in patient-reported outcomes was demonstrated following 1 week of activation. Patients in the RME group experienced more pain and chewing difficulty than patients in the SME group. At the end of expansion, the RME group reported higher scores than the SME group for all measured variables except headache and dizziness.

Several studies reported greater pain associated with RME compared with SME.^31–33 In addition, the higher pain scores in the RME group may have resulted in greater difficulty to chew food.³⁴ The association of pain and pressure may be attributed to the histological proximity of mechanoreceptors to nociceptors.²⁸ The greater speech difficulty at the end of expansion may be attributed to the larger median diastema in RME patients compared with SME.³⁵ In addition, the longer duration of expansion in the SME group may have allowed a longer time for the patients to adapt and for interference with daily activities to return to baseline values.^16,36 Hence, the null hypothesis can be rejected.

There were no statistically significant differences in the reporting of headache and dizziness between the RME and SME patients at any time point. However, patients treated by tooth-supported maxillary expanders have previously reported slight headache and dizziness.²⁸ It may be postulated that both headache and dizziness are more associated with increased pressure on the teeth from tooth-borne expanders.

CONCLUSIONS

• All patients experienced some form of discomfort and functional limitation with the activation of miniscrew-supported expanders. However, it was generally mild to moderate.

• A slow activation rate of miniscrew-supported maxillary expanders resulted in a better patient experience compared with a rapid activation rate.