This study aimed to investigate the relative efficacy of maxillary protraction combined with a modified alternate rapid maxillary expansion and constriction (Alt-RAMEC) protocol compared with conventional protocols in the early orthopedic treatment of skeletal Class III malocclusion.
A sample of 39 patients was divided into 3 groups on the basis of different interventions. Conventional facemask (FM) with splint-type intraoral devices was performed in the FM group (7 males and 5 females; mean age, 9.53 ± 1.37 years). Maxillary expansion with an activation rate of 0.5 mm/d (twice a day) followed by FM therapy was applied in the rapid maxillary expansion group (RME/FM) (6 males and 6 females; mean age, 9.31 ± 1.60 years). In the Alt-RAMEC/FM group (7 males and 8 females; mean age, 10.01 ± 1.31 years), Alt-RAMEC was started simultaneously and throughout the entire course of maxillary protraction, with repetitive alternations between activation and deactivation of expanders (0.5 mm/d for 7 days). The patients in all groups were instructed to wear FMs for a minimum of 12 h/d. Pretreatment and posttreatment lateral cephalograms were all traced and measured.
The Alt-RAMEC group showed statistically more significant maxillary advancement than other groups (A-VRP, 3.87 mm vs 3.04 mm [RME/FM], vs 2.04 mm [FM]; P <0.05). Analysis of variance did not reveal significant intergroup differences in palatal plane angulation changes ( P > 0.05). No pronounced mandibular clockwise rotations were noted in the Alt-RAMEC/FM group with distinct intergroup differences ( P < 0.05). There were more skeletal effects (88.7%) during overjet correction in the Alt-RAMEC/FM protocol.
A combination of the modified Alt-RAMEC protocol with FM revealed more favorable skeletal effects compared with FM and RME/FM protocols in treating prepubertal patients with maxillary deficiency.
Alternate rapid maxillary expansion and constriction (Alt-RAMEC) was studied.
Results were compared with facemask therapy and rapid maxillary expansion.
Alt-RAMEC was performed simultaneously with maxillary protraction.
Alt-RAMEC along with facemask therapy produced more favorable skeletal effects.
No short-term abnormal dental, periodontal, or craniofacial changes were observed.
Maxillary deficiencies with either normal or abnormal mandibles possessed the largest proportion in Class III malocclusion compared with other types. , Considering the exceeding uncontrollability of mandibular growth, Oppenheim firstly proposed maxillary advancement instead of mandibular inhibition in 1944. Further development based on this standpoint was made by Delaire. However, molar mesial movement, incisor tipping, maxillary counterclockwise rotation, and anterior constriction were confirmed to be the primary side effects of conventional facemask (FM) therapy. , In addition, maxillary forward displacement is based on skeletal reconstruction in the sutural area, more active bone remodeling is observed when circummaxillary sutures are repetitively weakened and opened. Rapid maxillary expansion (RME) was then combined with FM therapy for its validity in disarticulating circummaxillary sutures, effectively enhancing the therapeutic outcome of protraction.
Nevertheless, Liou et al emphasized the goal of maxillary expansion used in FM therapy, which should be the adequate disarticulation of the sutures and the displacement of the anterior maxilla, rather than expanding the width of the maxilla. A new protocol called alternate maxillary expansion and constriction (Alt-RAMEC) was then proposed in treating patients with cleft palates. More remarkable maxillary anterior movement was observed in the Alt-RAMEC/FM group, whereas palatal overexpansion was avoided. Subsequently, Yen et al modified the protocol and presented 8-week Alt-RAMEC followed by protraction; the patients were instructed for Class III intermaxillary elastics in the daytime and FM at night.
However, the enhancement of Alt-RAMEC in maxillary protraction for patients with noncleft palate remains controversial. Several relevant studies with inconsistent results have been reported, which varied in study designs, sample size, and research approaches. Masucci et al indicated that Alt-RAMEC/FM resulted in more skeletal effects compared with RME/FM. Inconsistently, Do-delatour et al found greater maxillary advancement in the latter protocol. In addition, unlike the simultaneous protocol we used in this study, most of the previous studies implemented Alt-RAMEC and maxillary protraction separately. , , A limited number of studies focused on the effectiveness of simultaneous Alt-RAMEC/FM therapy. , Baik claimed that protraction during palatal expansion would cause more counterclockwise rotation of the palatal plane. Although the latest study by Canturk and Celikoglu suggested no significant differences between FM treatment started simultaneously and after Alt-RAMEC, the former protocol was recommended to raise efficiency. The efficacy of protraction when simultaneously combined with Alt-RAMEC in tooth-borne FM therapy still needs to be confirmed. Hence, this retrospective study aimed to evaluate the skeletal and dental effect in a simultaneous Alt-RAMEC/FM protocol relative to conventional FM and RME/FM therapies.
Material and methods
This study was ratified by Shandong University Medical Science Research Ethics Committee (no. 20190403). The sample consisted of 39 subjects, 20 males and 19 females, who started treatments in the Department of Orthodontics at Stomatological Hospital of Shandong University between February 2015 and September 2018. The inclusion criteria were as follows: (1) prepubertal or pubertal stage according to the cervical vertebral maturation method, ranging from 7-12 years old; (2) anterior crossbite or edge-to-edge incisor relationship; (3) ANB <0°; (4) a Wits appraisal of ≤−2 mm ; (5) no functional shift (absence of pseudo–Class III malocclusion) ; (6) no permanent teeth congenitally missing before treatment or lost during treatment; and (7) midface deficiency diagnosed by the following specifications: concave profile (straight or concave contour in soft-tissue analysis) ; convexity (A-Np) <0°; decreased maxillary depth (FH-NA); negative NA-PA angle.
The exclusion criteria were as follows: (1) orthodontic treatment history; (2) systemic disease; (3) congenital craniofacial malformation, such as cleft lip or palate; (4) temporomandibular joint diseases; and (5) cooperation disability.
The treated sample was divided into 3 groups according to different treatment protocols. The FM group included 12 patients (7 males, 5 females), with an average age of 9.53 ± 1.37 years. Another 12 patients (6 males, 6 females) were included in the RME/FM group, with a mean age of 9.31 ± 1.60 years. The Alt-RAMEC/FM group was composed of 15 patients (7 males, 8 females), with a mean age of 10.01 ± 1.31 years. The pretreatment (T1) growth periods for all patients were assessed on the basis of Baccetti’s modified cervical vertebral maturation. All patients showed Class I to Class III malocclusion, and the consistency among the 3 groups was then tested by statistical analysis.
Pretreatment (T1) and posttreatment (T2) lateral cephalograms and panoramic radiographs for all subjects were taken under natural head postures with the same magnification factors. Root resorption of posterior teeth in T2 was evaluated by panoramic radiographs and periapical films.
Intraoral devices with acrylic splint were used in the FM group ( Fig 1 , A ). All appliances were uniformly bonded to the anchorage teeth by glass ionomer (first molars and 2 deciduous molars, or the first premolars and second deciduous molar). Adam clasps and embrasure clasps were used for supplementary retention. The thickness of the splint was properly designed to separate the maxillary and mandibular incisors with a −1 to 0 mm overbite obtained. Protraction hooks were designed around canines and lateral incisors. Follow-up of patients were completed every 4-6 weeks.
In the RME/FM group, tooth-borne soldered maxillary expanders with acrylic splint were bonded to posterior teeth ( Fig 1 , B ). The protraction hooks were placed in the area around canines for the attachments of elastics. The patients in the RME/FM group underwent expansion with an activation rate of 0.5 mm/d (twice a day) until the appropriate overcorrection was achieved. The expansion procedure was subsequently followed by FM therapy.
The intraoral devices in the Alt-RAMEC/FM group were identical to those in the RME/FM group ( Fig 1 , B ). A simultaneous Alt-RAMEC protocol accompanied by FM therapy was applied. The expander screw was activated at a rate of twice a day (0.5 mm/d) for 7 days and then converted into a 7-day deactivation period (0.5 mm/d). Alt-RAMEC was performed throughout the whole treatment course. The guardians of the patients in both the RME/FM and Alt-RAMEC/FM groups were informed to complete customized forms to record daily treatments. The patients were followed up with at the second week to ensure the stability of devices and correct operation. The patients were notified to follow-up after the completion of every 7-week circulation.
The FM therapies in the 3 groups followed the same protocol, which required the patients to wear the FM for a minimum of 12 h/d. The FM was examined and firmly adjusted by investigators. Protraction forces were imposed via elastics, delivering magnitudes of 300-500 g of force per side. In addition, with the objective of approaching the force vector to the center of resistance of the maxilla, the elastic direction was 30°-45° downward from the occlusal plane. All patients in the 3 groups used fully adjustable FMs for maxillary protraction (Delaire-type, Hangzhou Westlake Biomaterial, Hangzhou, Zhejiang, China).
During the routine assessment conducted by investigators, overjet, intercanine anteroposterior relationship, maxillary width, and soft-tissue changes were observed and recorded by chair-side examinations and photographs. The splints were gradually ground once the anterior crossbite was corrected. Any soft-tissue injury or damage on oral devices and the FM received treatment and repair in time. The completion criterion was a neutral or Class II occlusal relationship, along with the overjet reaching 3 mm. An overcorrection was pursued as compensation for growth and the reduction in relapse.
All lateral cephalograms were traced by the same investigator (Y.L.). Cephalometric analysis was based on previously described methods, in which a coordinate system containing a horizontal reference plane (HRP) and a vertical reference plane (VRP) was used. , A line rotated clockwise 7° from the Sella-Nasion plane at the sella was defined as HRP, whereas VRP was perpendicular to HRP through point sella. Cephalometric landmarks were based on a combination of Ricketts, Jacobson, and Downs analyses. A total of 36 variables were selected, including 20 skeletal, 9 dental, and 7 soft-tissue landmarks ( Fig 2 ). Ten angular and 23 linear measurements were used to evaluate changes before and after treatments. All tracing and measuring procedures were carefully performed and checked. For evaluating the measurement errors, 10 cephalograms were randomly selected, traced, and superimposed, and subsequently repeated 2 weeks later by the same investigator. The paired t test was performed to detect the difference between the 2 measurements ( P >0.05). Measurement error was tested by Dahlberg formula. , The Dahlberg standard variations showed that the error in angular measurements was <0.68°, and the linear measurements error was <0.81 mm, indicating the reliability of measurements.
Sample size calculation
Power Analysis and Sample Size software (version 15.0; NCSS, LLC, Kaysville, Utah) was applied to calculate the sample size. Previous data from a study by Liou and Tsai were used as a reference, in which A-VRL increased by 1.6 mm in the RME/FM group and 3 mm in the Alt-RAMEC/FM group, with standard differences of 1 mm and 0.9 mm, respectively. Considering the unequal number of patients, investigators designed the sample size ratio as 1:1:1.5 (FM: RME: Alt-RAMEC). A minimum sample size of 9 and 14 patients was severally required to detect significant differences (significance level of 0.05; 90% power). The present study increased the sample size.
SPSS (mac OS, version 25.0; IBM, Armon, NY) was used to perform all statistical analyses. The boxplot displayed no outliers. The Shapiro-Wilk test indicated a normal distribution of chronological ages and treatment duration ( P > 0.05). Levene test showed intergroup equal variance in these 2 aspects, and analysis of variance was subsequently performed to detect differences among the groups at T1. Because of the abnormal distribution of skeletal ages, a Kruskal-Wallis test was performed to test whether significant intergroup differences existed. All variables showed a normal distribution. A paired t test was performed to evaluate the significance of intragroup T1-T2 changes. ANOVA was also used to assess discrepancies in the initial values and T1-T2 changes among the 3 groups. Least significant difference tests were conducted to implemented multiple comparisons of T1-T2 changes among groups. A significance level of 0.05 was used in the statistical analysis.
As shown in Table I , both the chronological age ( P = 0.425) and skeletal age ( P = 0.703) in the 3 groups showed no significant differences, which exhibited consistency in the maturation stage among groups in T1. The nonsignificant intergroup difference of maxillary arch width demonstrated that patients were not assigned according to width. Variables in T1 presented no significant differences among groups, as shown in Table II . T1-T2 changes are reported in Table III by listing the descriptive statistics. Multiple comparison results with intergroup mean differences in changes are displayed in Table IV .
|Characteristics||FM (n = 12)||RME/FM (n = 12)||Alt-RAMEC/RM (n = 15)||Differences between groups|
|Chronological age (y)||9.53||1.37||9.31||1.60||10.01||1.31||NS|
|Treatment duration (m)||7.99||1.69||7.35||1.08||6.04||0.95||FM vs RME/FM †|
|FM vs Alt-RAMEC/FM ∗∗|
|RME/FM vs Alt-RAMEC/FM ∗|
|Maxillary skeletal measurements|
|Convexity (A-Np) (mm)||−1.63||1.15||−1.83||1.76||−0.70||1.80||NS|
|Maxillary depth (FH-NA) (°)||80.08||3.10||81.79||2.84||81.13||3.09||NS|
|Mandibular skeletal measurements|
|Intermaxillary skeletal measurements|
|Wits appraisal (mm)||−10.42||2.60||−9.38||2.32||−8.73||3.20||NS|
|Maxillary arch width (mm)||46.47||3.07||47.17||3.73||46.83||3.21||NS|
|UL-E line (mm)||−1.04||1.20||−0.46||1.96||−1.33||1.81||NS|
|LL-E line (mm)||2.21||1.80||3.04||1.47||2.30||1.31||NS|
|Mean||SD||P value||Mean||SD||P value||Mean||SD||P value|
|Convexity (A-Np) (mm)||2.33||0.58||∗∗∗||3.38||0.98||∗∗∗||3.40||1.72||∗∗∗|
|Maxillary depth (FH-NA) (°)||2.83||1.32||∗∗∗||2.92||1.95||∗∗∗||3.03||0.88||∗∗∗|
|Wits appraisal (mm)||3.46||1.29||∗∗∗||3.04||1.53||∗∗∗||3.97||2.26||∗∗∗|
|Actual U1-HRP (mm)||1.75||1.56||∗∗||1.34||1.45||∗∗||0.80||2.16||NS|
|Actual U1-VRP (mm)||2.29||1.54||∗∗∗||−0.25||2.68||NS||−1.40||3.49||NS|
|Actual L1-VRP (mm)||0.68||1.68||NS||−1.30||2.44||NS||−2.10||1.90||∗∗|
|Actual U6-HRP (mm)||1.55||1.85||∗||0.67||1.51||NS||0.60||2.10||NS|
|Actual U6-VRP (mm)||1.26||1.50||∗||0.04||0.86||NS||−0.98||1.43||NS|
|Maxillary arch width (mm)||0.42||2.09||NS||3.30||1.25||∗∗∗||1.63||1.24||∗∗∗|
|UL-E line (mm)||2.17||1.29||∗∗∗||2.33||1.11||∗∗∗||2.50||2.46||∗∗|
|LL-E line (mm)||−1.08||1.43||∗||−0.83||1.27||NS||−0.23||1.46||NS|