Evaluation of Sagittal Changes in Class II Div 2 Patients with Decelerating Phase of Growth by PowerScope Appliance: A Retrospective Cephalometric Investigation.

BACKGROUND: Restricted mandibular growth is observed in Class II Div 2 malocclusions. The fixed functional appliances are used to effect the skeletal changes in patients with end stages of skeletal maturity. AIM: This cephalometric study aimed to distinguish the skeletal and dental corrections done in the mandible on skeletal Class II Div 2 subjects when treated with PowerScope appliance (American Orthodontics, Sheboygan, WI).
MATERIALS AND METHODS: This is a cephalometric study based on the retrospective data. The patients selected for this study were with Class II Div 2 malocclusion and assessed to be in decelerating phase of skeletal growth. A total of 12 patients were selected after applying inclusion and exclusion criteria. A PowerScope was placed after incisor correction and followed up till Class I molar relation was achieved. The initial values (T1) at the time of placement of the appliance and the final values at the end of the molar correction (T2) were noted. The cephalometric parameters at T1 and T2 were assessed using sagittal occlusal (SO) analysis by Pancherz. The paired Student's t-test was used to analyze pre- and posttreatment changes.
RESULTS: There was sufficient lengthening of the mandible (4.38 mm). Both the dental and skeletal alterations were observed in the mandible. These changes were marked compared to the maxilla. The pre- and posttreatment changes were statistically significant for the mandibular skeletal changes (P < 0.001) as well as mandibular incisor proclination (P < 0.001).
CONCLUSION: The PowerScope can be used as a propeller for sagittal mandibular correction in Class II Div 2 patients.

INTRODUCTION

The Class II Div 2 malocclusion is a unique subclass of Class II malocclusion and is characterized by retroclination of two or more maxillary incisors with a Class II molar relation. It has distinctive dental and craniofacial features that differentiate it from other malocclusions. One of the most damaging features of this malocclusion is increased overbite brought about by retroclination of maxillary incisors. This condition becomes overly complex if overlapped on a Class II skeletal base.[1] According to McNamara,[2] the most common characteristic of Class II malocclusion is mandibular retrusion, rather than maxillary prognathism. It was suggested that the natural forward movement of point B was somehow to be inhibited by a deep incisal overbite.[3] According to him, unlocking of the deep bite would result in unimpeded mandibular dentoalveolar or skeletal growth and particularly in Class II Div 2 cases as long as the potential to grow exists. Behrents[4] from his growth studies has stated that the craniofacial growth does not stop in young adulthood but is a continuous process even into later ages. The correction of mild-to-moderate skeletal II conditions during the accelerating slope of growth phase can be effected with a removable myofunctional appliance. However, in cases where the growth potential is at the ebb, a fixed appliance is the obvious choice. In patients who have crossed the adolescent growth spurt and those who are in the late stages of puberty, fixed functional appliances such as fixed Twin Block,[5] Herbst,[67] Eureka Springs[8], and Forsus fatigue-resistant devices[9] would be given.

The successful correction of a Class II malocclusion by a functional appliance depends on its effectiveness from operator’s point of view and more comfort from the patient’s point of view. PowerScope is the latest innovation in the noncompliant Class II correctors developed by American Orthodontics in collaboration with Dr. Andy Hayes (www.americanortho.com/Powerscope.html)[10]. According to the manufacturer, this intermaxillary Class II corrector appliance was developed to meet the needs, such as reduced chair time, ease of fabrication and attachment, and minimum adjustments including patient comfort and acceptance, of an orthodontist.

The functional orthopedic appliances are indicated to correct Class II malocclusions associated with retrognathic mandible in the first phase of comprehensive orthodontic treatment. No studies have been reported on first phase of biphasic treatment plan of skeletal Class II, Angle’s Class II Div 2 involving fixed functional appliances. With this in mind, this study was designed to determine the range of likely sagittal changes of mandible brought about by PowerScope appliance in Class II Div 2 patients decelerating the slope of pubertal growth spurt.

Aim and objectives

This cephalometric study aimed to assess the efficacy of PowerScope in subjects with skeletal Class II Div 2 malocclusion in decelerating stages of adolescent growth. The objectives included determination of the skeletal changes in the maxillary and mandibular base and dentoalveolar changes in the corresponding arches. Finally, the objective was also to differentiate the magnitude of skeletal and dental corrections in the mandible achieved.

MATERIALS AND METHODS

Sample source

This was an observational study based on the retrospective data. The sample for this study was drawn from treatment records including lateral cephalograms of Class II Div 2 cases registered as outpatients in the Department of Orthodontics, Narayana Dental College and Hospital, Nellore, Andhra Pradesh, India, during 2012–2017. Ethical clearance from institutional regulatory board was obtained for the study (application dated 27 December 2018). Patient consent forms were available, which were procured at the commencement of the treatment. Patients in the age group of 13–16 years and who were under decelerating growth phase as assessed by cervical vertebrae maturation index (CVMI) stages 4 and 5[11] were included. Full complement of teeth, Class II skeletal bases as assessed by Wits appraisal,[12] overbite of more than 50% with retroclination of incisors, and overjet of less than 2° were the inclusion criteria. Nongrowing patients and those with temporomandibular joint and periodontal problems, those with severe transverse (or) vertical problems, and those with syndromic diseases were not considered in the study.

A manual search of the permanent patient database identified all subjects seen for initial records between August 1, 2012, and July 31, 2017. A total of 14 records of Class II Div 2 patients were selected after filtration by inclusion and exclusion criteria. All the lateral cephalometric radiographs obtained as a part of their treatment convention were collected. All the radiographs were taken with the Cephalostat (model no. mr05, type 84086511; Villa sistemi medicali, Italy). The magnification error was found to be 8%, which is clinically acceptable. All the radiographs were traced manually in a standardized manner by a single observer to avoid errors due to interexaminer variability. The sagittal occlusal (SO) analysis of Pancherz[13] was used to calibrate the cephalometric data for the skeletal and dentoalveolar parameters. The linear measurements were made by using a set square with an accuracy of 0.5 mm.

The treatment protocol for the selected subjects comprised a biphasic orthodontic treatment with a fixed functional appliance therapy in the initial phase [Figure 1]. Standard MBT (Masters series; American Orthodontics) brackets with 0.022 × 0.028 slot was bonded on the upper and lower arches to align the teeth. Alignment and incisor inclination correction were brought about by using 0.014-in NiTi archwire, 0.018-in NiTi, followed by 17 × 25-in NiTi, and 19- × 25-in NiTi archwires, respectively. Upper and lower arches were stabilized using the 19 × 25 SS wire with transpalatal arch and lingual arch in upper and lower arches before proceeding to the functional appliance phase. PowerScope appliance was attached to the archwire distal to mandibular canine and mesial to maxillary first molars on both sides. All the patients received a single-step advancement protocol, and the mandible was positioned in an edge-to-edge relation. There were regular follow-ups at 1-month interval period to check for breakups or any missing components. Lateral cephalograms taken just before the placement of PowerScope (T1) and after its removal following the attainment of a Class I molar relationship (T2) were used for this study. These cephalograms were analyzed for skeletal and dentoalveolar changes and from T1 to T2 using various cephalometric parameters. For analysis purposes, the final data of only 12 patients were considered as two of the patients were found to be inconsistent in their appointments [Figure 2].

Figure 1

Clinical steps of the study: (A) pretreatment, (B) prefunctional, (C) PowerScope insertion, (D) postfunctional

Figure 2

Flowchart showing the steps in the study

The saggital occlusal analysis

The SO analysis by Pancherz [13] can effectively apportionate the skeletal and dentoalveolar components in the maxilla and mandible to the alterations in SO (overjet, molar relationship) brought about by the functional appliance. This is a reference grid comprising an occlusal reference line (RL). A line perpendicular to that of RL passing through Sella (RLp) is defined, and all the sagittal measurements are done parallel to RL plane [Figure 3].

Figure 3

Analysis of skeletal and dental changes by SO (sagittal occlusal) analysis of Pancherz. RL = horizontal reference line; RLp = a perpendicular line to Rl drawn through Sella; SS = corresponds to point A on Maxilla; Pg = Pogonion; is = incisal edge of maxillary incisor; ii = incisal edge of mandibular incisor; ms = mesiobuccal cusp tip of maxillary first molar; mi = mesiobuccal cusp tip of mandibular first molar.

SS/RLp and Pg/RLp: Position of the maxillary and mandibular jaw base.

is/RLp and ii/RLp: Position of the maxillary and mandibular central incisor.

ms/RLp and mi/RLp: Position of the maxillary and mandibular first molar.

Overjet: is/RLp minus ii/RLp (a positive value indicates a proclination; a negative value indicates a retroclination).

Molar relation: ms/RLp minus mi/RLp(a positive value indicates a distal/Class II relation; a negative value indicates a normal relation or a class III relation).

The difference in the horizontal distances measured in relation to RLp at two different points of time is used to calculate the skeletal and dental changes.

The variance in parameter 1 represents skeletal changes. Variables 2–5 represent a combined effect of skeletal and dental changes, whereas the changes in dentoalveolar variables, that is, the dental changes within the maxilla and mandible (variables 6–9), were obtained by the following calculations:

is/RLp(d) minus ss/RLp(d): Change in position of the maxillary central incisor within the maxilla.

ii/RLp(d) minus pg/RLp(d): Change in position of the mandibular central incisor within the mandible.

ms/RLp(d) minus sp/RLp(d): Change in position of the maxillary permanent first molar within the maxilla.

mi/RLp(d) minus pg/RLp(d): Change in position of the mandibular permanent first molar within the mandible.

Data collection and statistical analysis

The direct data and derived data of the variables mentioned earlier were entered in an Excel sheet. The data were summarized as mean ± SD in the Excel spreadsheet (MS Windows, 2010). The data were then subjected to statistical analysis (SPSS, version 21.0; IBM, New York). The normal distribution of quantitative variables was verified using Shapiro–Wilk test. Treatment-related changes between T1 and T2 stages were analyzed by Student’s paired t-test. Mean differences with probabilities less than 5% (P <0.05) were considered statistically significant.

RESULTS

The demographic data of the records of the subjects analyzed for the study are given in Table 1. The sex, mean age, and the skeletal maturity status at the pretreatment stage are also given. However, the data were not analyzed based on the above variables. The results were obtained from measured and calculated data from functional (T1) and postfunctional treatment (T2) stages. Cephalometric findings are tabulated [Table 2].

Table 1

Demographic data of the subjects at the T1 stage

Gender wise
Sex	Male	Female
N	7	5
Mean age	13.8 ± 0.8	14.8 ± 0.4
Maturity status
Stage	Stage 4	Stage 5
N	5	7

Table 2

Comparison of pretreatment and posttreatment effects of PowerScope (sagittal occlusal [SO] analysis)

Parameters/linear measurements	Prefunctional (T1) n = 12		Postfunctional (T2) n = 12		Mean difference	t-value df = 22	P-value
	Mean	SD	Mean	SD
Maxillary base (SS/RLp)	81.26	3.45	80.78	3.25	−0.48	0.35	0.72 NS
Mandibular base (pg/RLp)	76.6	2.94	80.98	2.85	4.38	3.7	0.0012**
Maxillary incisor (is/RLp)	85.33	2.69	84.13	3.89	−1.2	0.87	0.38 NS
Mandibular incisor (ii/RLp)	76.36	3.43	82.3	3.18	5.94	4.4	0.0002**
Maxillary molar (ms/RLp)	52.42	3.57	51.24	3.56	−1.18	0.85	0.40 NS
Mandibular molar (mi/RLp)	50.4	3.23	55.12	2.95	4.72	3.73	0.0011**
Overjet	8.97	0.88	1.83	0.77	−7.14	21.15	0.0001**
Molar relation	2.02	1.18	−3.88	1.18	−5.9	12.24	0.0001**
Maxillary molar within maxilla	−28.84	0.42	−29.54	0.25	−0.7	4.911	0.0001**
Mandibular molar within mandible	−26.2	0.45	−25.86	0.24	0.34	2.3	0.03 NS
Incisor within the maxilla	4.07	0.85	3.35	0.76	−0.72	2.18	0.04 NS
Incisor within the mandible	−0.24	0.54	1.32	0.46	1.56	7.6	0.0001**

Incisors: Negative value indicates retroclination and positive value indicates proclination; molars: Positive value indicates class II /distal relation and negative value indicates a class I/mesial relation.

**P < 0.001 = very significant; *P < 0.05 = significant; P > 0.05; NS = not significant

There is a mean net molar correction of −5.9 mm, indicating a shift from Class II to Class I relation. This was effective by way of both skeletal and dental changes. The changes were observed in both the jaws. There was a significant mandibular base shift in the mesial direction with a difference in the mean value of 4.38 mm between T1 and T2 (P < 0.0012). There was also a restriction of maxillary skeletal growth (−0.48 mm), which was not statistically significant. The dentoalveolar changes of molar correction were effective by mesial movement of mandibular molar by 0.34 mm and also by the distal movement of maxillary molar by −0.7 mm.

Overjet decreased by a mean of −7.14 mm. Maxillary central incisor retroclined marginally by −0.72 mm whereas the proclination of the mandibular central incisors was 1.56 mm. The mean difference in the incisor inclination within the maxilla was not statistically significant whereas the proclination of mandibular incisors was statistically significant (P < 0.0002).

The opposite results were obtained when the effects of the molar movements within the individual basal bones were analyzed. There was a statistically significant change in the distal movement of the maxillary molar within the maxilla (P < 0.0001).

DISCUSSION

Treatment of Class II Div 2 malocclusion in noncomplaint patients continues to pose a great challenge to the technical abilities of the orthodontist. It involves a biphasic treatment with a fixed appliance phase to correct the associated mandibular retrognathism. Few of the noncompliance Class II correctors are studied for their efficiency.[1415] One of the appliances that has gained popularity in recent years is PowerScope Class II corrector. Its proclaimed advantages are patient-friendly design, no laboratory setup, and reduced chair-side time as there is no need of assembling the parts as it is supplied use-ready mode. It has a simple attachment system with a durable telescopic mechanism, a Ni–Ti internal spring system that reduces the treatment time compared to the other Class II correctors, and a ball and socket joint system that maximizes lateral movement for patient comfort.[10] The data set of the Class II Div 2 patients treated by PowerScope were retrieved from the preexisting patient records. A final analysis of the changes was performed on 12 subjects.

The correction of the molar relationship was done by a significant contribution from the mesial advancement of the mandibular base. The molar correction was affected both by skeletal growth (82.37%) and dentoalveolar (17.63%) segments. Distal driving of the molars within the maxilla (0.7 mm) is statistically significant compared to the mean differences in the mesialization of the mandibular first molar (0.34 mm) within the jaw base. However, the opposite was found to be true in case of overjet reduction where the mandibular incisors have contributed by way of proclination (56 mm), which is almost double the value compared to retroclination of the maxillary incisors (0.72 mm). Relatively, the skeletal factor (68.06%) has contributed less toward incisor correction. Thus, the dentoalveolar component (31.84%) has a profound effect on the incisor reduction. The increased movements of the maxillary molars and the mandibular molars may be due to the direct attachment of the PowerScope components to the archwire at these points [Figures 4 and 5].

Figure 4

Skeletal and dental changes in effecting molar correction

Figure 5

Skeletal and dental changes in effecting overjet correction

The results show that the PowerScope is effective in correcting the mandibular retrognathia originating from the functional mandibular retrusion as seen in Class II Div 2 patients [Table 1 and Figure 6]. The significant features of this study were the skeletal and dental evaluation of patients in Class II Div 2 treated by the PowerScope, which was not previously published. There was no control group in this study to compare the results of the study.

Figure 6

Showing the superimposition of the cephalograms at T1 and T2 stages at Nasion point on the Nasion–Basion line

A few studies are available in the literature comparing the efficacy of PowerScope in Class II Div 1 malocclusion. Arora et al.[16] compared the treatment effects of Forsus and PowerScope in Class II Div 1 adolescent patients in the late stages of skeletal maturity. The changes in the forward movement of the mandibular molar and incisors were greater in the PowerScope group patients (2.3 and 2.80 mm) than in the Forsus group patients (1.9 and 2.38 mm). Dentoalveolar changes were more marked with PowerScope. They found that both the Powerscope and Forsus were effective in correcting Class II malocclusion. In their study, the changes in the sagittal transposition of the mandible were found to be 2.9 mm in the PowerScope group compared to the Forsus group (3.7 mm). In contrast, this study revealed more of skeletal magnitude changes brought about by the PowerScope appliance in the mandible, which is approximately 4.38 mm in effecting the molar correction and the overjet reduction. The dental changes were 0.34 mm of mandibular first molar mesialization and proclination of mandibular incisors by 1.56 mm. The apical base change (maxillomandibular differential change) was 3.0 mm in the Forsus participants and 2.2 mm in the PowerScope subjects (2.2 mm) from the previous study.[16] In this study, there was a net apical base change of 4.90 mm that included the restraining effect of the maxillary skeletal base by 0.48 mm and forward thrust of the mandible by 4.38 mm.

Antony et al.[17] conducted a study to evaluate the effects of PowerScope on patients in the age group of 15–19 years (CVMI stages 5 and 6). The total duration of the time taken for correction of a Class II molar relation to a Class I relation was on average 5.5 ± 1.2 months and the average rate of molar correction achieved was 0.92 mm/month in this study, which is greater than that of the previous study, which was 0.73 mm/month.

Another study by Malhotra et al.[18] evaluated the effects of PowerScope in adolescents with CVMI stages 5 and 6. There was a significant lengthening of the mandible and the changes brought about were both dentoalveolar and skeletal in nature. The authors found that there was no substantial change in the maxillary skeletal parameters whereas the SNB angle increased by 1.067° and there was an increase in the effective length of the mandible by 1.6 mm. The total molar correction achieved was 4.73 mm and an overjet reduction of 5.9 mm. This is in tune with the present study; however, the magnitude of changes in the mandibular parameters is less compared to our study. However, the split between the skeletal and dentoalveolar contribution was not done in their study.

There are controversial results available on the effects of the functional appliance on maxillary restriction. The restraining effect on the maxilla is seen in this study with PowerScope similar to the findings of Aras et al.[19] on Forsus appliance but are discordant with the studies of Pancherz[20] on the Herbst. Arora et al.[16] also noted a slight forward transformation of the maxilla (0.7 mm) on patients of both PowerScope and Forsus group. The restraining effect of the functional appliance was explained by the action of muscle forces transmitted in a posterior direction, thus withholding the forward growth of the maxillary skeleton. These muscle forces were generated due to distension of the musculature holding the mandible in an advanced position.[21]

The dentoalveolar effects on the mandibular arch were due to less of mesial movement of the lower molars (0.34 mm) and more of proclination of the incisors (1.56 mm). These findings are similar to those reported in various other studies of fixed functional appliances.[69]

The patient comfort and the operator’s convenience were not evaluated in this study compared to the study of Arora et al.[16] However, from the treatment records, it was evident that 3 of the 12 cases had a complaint of breakage of archwire at canine region and 2 of them had dislodgment at the molar area. However, this was not a frequent occurrence.

One of the significant features of this study was the magnitude of the skeletal changes in the mandible found Class II Div 2 persons with the application of the PowerScope. The amount of skeletal transformation was found to be 1.5 times higher compared to other studies on various functional appliances as well as PowerScope. Most of these studies were conducted on Class II Div 1 subjects. This study is unique in the sense that the effects of PowerScope after unlocking of the incisor relation in Class II Div 2 patients were evaluated. The difference in the greater scale of mandibular growth might have been due to the rebound catch-up growth of the mandible that was held due to the inclination of the maxillary incisors. However, the amount of incisor correction was not standardized for all the patients before the functional appliance therapy was started. This study attempted not to delineate the changes that were caused by normal skeletal growth. The data were also not analyzed gender-wise and stage-wise according to skeletal maturity. No existing studies on Class II Div 2 patients are available evaluating the effects of the functional appliances in general and PowerScope in particular. However, the results of this study have to be cautiously used in relation to other clinical findings until the findings are substantiated on large sample size.

CONCLUSION

PowerScope appliance in postpubertal Class II Div 2 patients like any other functional appliance has the following effects:

There were significant changes seen in mandibular skeletal base with minimal maxillary skeletal effects.

Molar correction and the overjet reduction were due to both the skeletal and dentoalveolar effects.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest