A Prospective Study Comparing Adolescent and Post-Adolescent Periods Regarding Effects of Activator Appliance in Patients with Class II Mandibular Retrognathia by Using 3dMDface Analysis and Cephalometry

Background

Skeletal Class II anomalies exhibit maxillomandibular sagittal discrepancy and are more commonly associated with mandibular retrognathia [1–4]. Several methods and appliances have been used for decades for treating mandibular retrognathia in growing patients. One of the generic names of these kind of appliances is functional orthopedic appliances, which serve as mandibular advancement splints in the management of mandibular retrognathia. They refer to a variety of removable appliances designed to provide mandibular sagittal growth improvement by rearranging the masticatory muscle groups and are commonly used in growing Class II patients [5]. The effectiveness of this approach in treating mandibular retrognathia has been investigated for decades [6–17]. The conventional activator was the first appliance used for functional orthopedic treatment [18]. Subsequently, many appliances, such as twin block, Bionator, Frankel, or their modifications, were introduced for treating mandibular retrognathia in adolescent-period patients [6–9,19–22]. It has been targeted to increase the mandibular length by stimulating the condylar growth with any of these removable appliances and also to minimize the dental adverse effects. There has been considerable controversy about the skeletal effects of these appliances in treating mandibular retrognathia [23]. Some researchers have advocated that an increase in the mandibular length can be achieved with the functional orthopedic appliances rather than other fixed orthodontic appliances. However, others have suggested that the functional orthopedic therapy did not alter the mandibular length [8,24] and the overjet elimination can only be achieved by dental movement [25,26]. Treatment timing and the effectiveness of these appliances are another important factor as well as the appliance type. Various opinions have been expressed in the literature on the optimal treatment timing for the functional orthopedic treatment to obtain the best skeletal results. Most of the researchers have suggested that it is appropriate to perform functional orthopedic treatment at the beginning of the adolescent period or at the late mixed or permanent dentition to obtain more improvement in sagittal mandibular growth [22,27–29]. However, other researchers have suggested that functional orthopedic treatment may be performed in the post-adolescent period as an alternative to surgical treatment [30,31]. In studies conducted by Ruf and Pancherz, an increase in the mandibular length and mandibular sagittal activation were observed in young adult patients [30–32]. However, another study by the same authors reported undesirable mandibular growth following conventional activator therapy [33]. Therefore, the first purpose of this prospective study was to compare adolescent and post-adolescent periods regarding the effectiveness of conventional activator appliance in patients with Class II mandibular retrognathia by using lateral cephalometric radiographic analyses.

Evaluations of the hard and soft tissues and dentition have an essential role in the planning of orthodontic treatment, especially in patients who require skeletal corrections. Three-dimensional photogrammetry is a useful system for clinicians in assessing the soft tissues of patients [34,35]. Conventional two-dimensional evaluations have been supported by three-dimensional images to diagnose and evaluate outcomes, which has become more popular in the last decade [36–38]. Therefore, the second purpose of this prospective study was to evaluate the effects of conventional activator therapy on facial soft tissues in these Class II patients by using three-dimensional photogrammetry.

Material and Methods

THE CONVENTIONAL ACTIVATOR APPLIANCE DESIGN:

This study included patients with skeletal Class II mandibular retrognathia, and all of them were treated by the conventional activator appliance. The conventional activator appliances were used with one-step advancement (maximum jumping) of the mandible and were activated until the upper and lower incisors were in edge-to-edge position. The thickness of the posterior part of the appliance was approximately 4–5 mm. An ‘acrylic cap’ covering 3 mm of the labial surfaces of the mandibular incisors was used to prevent undesired protrusion of the mandibular incisors. The patients were instructed to wear the conventional activator appliance for 16–18 hours a day. Patients were examined at 4-week intervals. The treatment was continued until the mandible did not slide through backward in both groups (Figure 2).

LATERAL CEPHALOMETRIC RADIOGRAPHIC ANALYSIS (TWO-DIMENSIONAL):

The lateral cephalometric radiographic records of the patients were analyzed with NemoCeph NX (Nemotech, Madrid, Spain), a computerized lateral cephalometric radiographic analysis program. Twenty-one linear and 15 angular lateral cephalometric radiographic measurements were performed (Figure 3, Table 2) [43–47]. A basicranial line passing through the tuberculum sella (T) and the wing points of sphenoid (W) was used as a sagittal reference plane (TW) (Figure 3C, 3D). Another line constructed perpendicular to the basicranial line and passing through the point T was used as a vertical reference line (VRL) (Figure 3C, 3D). The sagittal distances from the A point and the pogonion were calculated. Maxillomandibular angular and linear measurements used in this study are shown in Figure 3. All measurements were repeated by the same orthodontist and the intraobserver variability was non-significant.

THREE-DIMENSIONAL PHOTOGRAMMETRIC ANALYSIS:

Three-dimensional photogrammetry can capture 3D images of the craniofacial complex in 2 milliseconds without ionizing radiation, and three-dimensional images can be formed by photographing with the help of 2 or more cameras from at least 2 different planes [35,48]. Volumetric measurements can be generated with three-dimensional photogrammetry in addition to linear and angular measurements, and these measurements improve diagnosis and evaluation of outcomes.

Three-dimensional images were obtained using the 3dMDface system (3dMDface LLC, Atlanta, GA, USA). The images were transferred to 3dMDface Vultus® software (3dMDface Vultus® software version 2.3.0.2, 3dMDface, Atlanta, GA, USA) and analyzed. After transferring these images to the 3dMDface Vultus® software, they were reoriented for the standardization in 3 dimensions. Unnecessary fields of the images were removed for ease of analysis. Fourteen linear, 7 angular, and 2 volumetric measurements were performed on the 3dMDface Vultus® software (Figures 4–6, Table 3) [46,49]. Perpendicular distances from menton (Me), pogonion (Pg), and sublabial (Sl) points to the coronal and axial planes were calculated (Figures 4, 7). The coronal plane (CP) was defined as the vertical plane passing through the outer canthi of both eyes and the axial plane (AP) was defined as the horizontal line passing through the outer canthi of both eyes, and were positioned parallel to the Frankfort horizontal plane (FH). The mandibular volume was measured from the right (Ch-R) and left lip-edge points (Ch-L) and menton (Me) point, as shown in Figure 6A. For measuring the total lip volume, a contour was formed by placing points at 2-mm intervals on the upper and lower vermilion lines. The volume of the region between these contours was calculated using the software program (Figure 6B).

STATISTICAL ANALYSIS:

All statistical analyses were performed using SPSS statistics 22.0 for Windows (Statistical Package for Social Science for Windows, version 22.0, SPSS Inc, Chicago, IL, US). The paired-sample t test was used to evaluate the intragroup changes after conventional activator therapy (T1-T0) for each group. Comparisons of the adolescent and the post-adolescent groups in terms of intergroup differences were performed using the independent-samples t test.

Results

LATERAL CEPHALOMETRIC RADIOGRAPHIC FINDINGS:

The results showed that the maxillary growth was restricted (decreased SNA°) and the sagittal mandibular growth was stimulated (increased SNB°). A significant improvement in the sagittal relationship of the jaws (decrease in the ANB° and the wits value) was obvious in both groups (p<0.05). Mandibular ramus length (Co-Gn) was increased by 2.97 mm and 2.68 mm in the adolescent and the post-adolescent groups, respectively (p<0.05). Moreover, convexity angles were increased in both groups. Statistically significant increases were observed in the FH⊥Na-Pg and the SN-GoGn° parameters, while a statistically significant decrease was found in the Pg-NB in both groups (p<0.05). No significant differences were observed between the groups in terms of these parameters, except for the gonial and the lower gonial angles. Increases in these angles were more significant in the adolescent group than in the post-adolescent group (p<0.05, Table 4).

When the face height measurements were examined, statistically significant increases were observed in the anterior and posterior facial heights (AFH, LAFH, and PFH) in both groups (p<0.05). However, there was no significant difference in the Jarabak ratio between the groups (Table 4).

Changes in the parameters related to the upper lip and the upper incisors (UL-S, U1-NA°, and nasolabial angle) were not statistically significant in either the adolescent or in the post-adolescent group. However, the parameters related to the lower lip and the lower incisors (LL-S, labiomental sulcus, labiomental angle, L1-NB°, IMPA°, Pg-VRL, and Ls-VRL) exhibited statistically significant increases in both groups (p<0.05). The mentocervical angle decreased by 5.03° and 2.75° in the adolescent and post-adolescent groups, respectively, and the differences were significant between the groups (p<0.05).

THREE-DIMENSIONAL PHOTOGRAMMETRIC FINDINGS:

Projections of menton, sublabial, and pogonion points showed statistically significant increases in both groups. Significant increases were observed in the anterior, posterior, and lower anterior facial heights, convexity angles, lower lip angle, and labiomental angle.

When the lip and the chin measurements were evaluated in the groups, the lip width, the upper lip length, and the chin height did not show any significant changes, while the lower lip length was significantly increased (p<0.05). The total lip volume was significantly decreased and the mandibular volume was significantly increased in both groups. No significant changes were observed between the groups regarding the treatment changes, except for the nose height and the anterior facial height; these 2 parameters showed greater increases in the adolescent group than in the post-adolescent group (p<0.05, Table 5).

Discussion

The issue of optimal timing for functional orthopedic treatment in Class II patients has been discussed for many years [27,29,50,51]. The discussion involved the age or the stages of dentition such as late mixed dentition and early permanent dentition. However, in the present study, groups were divided based on growth periods because substantial variations are presented in the orthodontic patients regarding dental, chronologic, and skeletal ages [31,32,52]. Most of researchers have stated that the adolescent growth spurt is the most appropriate time for the functional orthopedic treatment for mandibular growth modification [53,54]. However, others have reported that functional orthopedic treatment can be performed in the post-adolescent period as well, and patients with moderately severe mandibular retrognathia can be treated without orthognathic surgery [55,56]. Studies that did not advocate the orthopedic effects of the functional appliances have stated that it does not provide any mandibular stimulation and causes unfavorable growth of the mandible [7,57,58]. In addition to the concerns about the rate of the orthopedic effects of the functional appliances, concerns about patient compliance and certain adverse effects on the incisors have resulted in a very limited number of studies in patients in the late growth period or adulthood. Most of the late growth period studies are related to the effects of the Herbst appliance, which was found to be very effective in the post-adolescent and the young adulthood periods with respect to skeletal responses [32]. In the present study, effects of the conventional activator appliance in the adolescent group and the post-adolescent group were compared with respect to mandibular growth stimulation and soft tissue response, because the conventional activator appliance has been rarely studied in the subjects in late growth period [59].

Overjet correction with the functional orthopedic treatment has been reported by many studies [60–62]. However, there is still a lack of consensus regarding the contribution rates of the orthopedic and the orthodontic components for elimination of overjet using conventional activator therapy. Some clinicians believe that the changes are primarily dentoalveolar, with some maxillary orthopedic effects [8,22,26,60,63–65]. Others stated that functional appliance therapy results primarily in orthodontic changes, with increased mandibular length [28,66–69]. In the present study, the treatment effects for both growth periods were a combination of skeletal and dental improvements. The significant reductions of overjet were 4.57 and 4.13 mm in the adolescent and post-adolescent growth periods, respectively. The restriction of maxillary growth and the stimulation of mandibular growth resulted in significant reduction in the ANB° by 3.47° and 3.01° in the adolescent and the post-adolescent growth periods, respectively. This improvement was mainly due to advancement of the mandible (increase in the SNB° by 2.9° and 2.68°, respectively, in the 2 groups) and due to maxillary growth inhibition (decrease in the SNA° by 0.56° and 0.33°, respectively) to a lesser extent. These results were consistent with previous studies that showed the orthopedic effects of conventional activator therapy on mandibular growth [5,8,30,55,61,66,70,71]. In one of the few studies conducted on untreated Class II patients, SNB° was found to be almost stable (0.17°) compared to growing subjects treated with a functional appliance [66].

With respect to the effective mandibular length, the Co-Gn parameter presented a significant increase of 2.97 mm and 2.68 mm in the adolescent and the post-adolescent groups, respectively. This increase was not statistically different between the groups. In previous studies, the range of the increase in the growth of the mandible in the late growth period was reported to be 1–4.15 mm following treatment with functional appliances [22,31,71,72]. Most researchers have found that craniofacial growth may extend to the late stages of growth and development in both males and females [73–77]. Björk (1963) revealed that an increase in the condylar growth was recorded even, after age 20 years [78]. Ruf and Pancherz (2006), in their study with the Herbst appliance, reported that the stimulation of mandibular growth in the young adult group was probably due to reactivation of the cells in the chondroblastic region [62]. Uematsu et al. (2002) found a significant increase in the ramus length in both growing and mature patients after 6–8 months of treatment with the conventional activator appliance [59], consistent with the present study. Similarly, McNamara (1985) found that the Frankel appliance resulted in an average increase of 1.2 mm per year in mandibular growth [53]. Cozza et al. (2006) demonstrated that the untreated Class II subjects exhibited significantly lesser improvement in mandibular length when compared with the treated ones (2 mm) [5]. In light of the previous studies and based on our findings, overjet elimination appears to be partly achieved by the skeletal response of the mandible. The remaining part of the correction of the increased overjet was provided by the dentoalveolar compensation with retrusion of the upper incisors and protrusion of the lower incisors. In the present study, more than two-thirds of the overjet correction were skeletal and less than one-third were dental. The results were consistent with previous studies [32,60,61]. Interestingly, the skeletal contribution was greater than the dental contribution in the post-adolescent growth period, with a higher rate of correction than the expected value. The amount of skeletal changes contributing to the overjet elimination was larger in the adolescent group (76%) than in the post-adolescent group (66%). One of the important reasons for this favorable outcome may be good compliance of the patients by considering orthognathic surgical therapy as a possible alternative treatment to functional orthopedics. Another reason may be the nighttime and (partly) the daytime use of the appliance (16–18 hours/day) in the present study. The treatment duration for mandibular advancement was significantly longer (10.12±0.99 months) in the post-adolescent group when compared with the adolescent group (7.33±2.02 months). This difference may have resulted from slower condylar adaptation to the new mandibular position in the late growth period.

Conventional activators have been typically associated with maxillary and mandibular molar extrusion. Although the vertical eruption of maxillary teeth is impeded by the occlusal acrylic part, the eruption of the mandibular posterior teeth is allowed for occlusal settling. This can result in an unfavorable increase in lower anterior facial height [75]. In the present study, lower facial height was significantly increased in both growth periods, and the increase was statistically similar between the groups. However, the Jarabak ratio remained stable with an increase in the posterior facial height, demonstrating that primarily translational mandibular growth occurred even in the post-adolescent group. When the rotational change of the mandible (SN-GoGn°) was evaluated, an approximate increase by 1.5° was observed in both groups. This increase might be related to the increased lower gonial angle, which was one of the remarkable differences between the 2 growth periods. This increase was more prominent in the adolescent group than in the post-adolescent group (p<0.05). This increase might be due to an unstable occlusion or the primary contacts after the conventional activator therapy. Although this change was statistically significant, it may be clinically negligible due to the lack of interdigitation immediately following the conventional activator therapy.

The change in the mentocervical angle in the present study was notable [79]. It was decreased significantly after the conventional activator therapy and returned to normal values (80–95°). The decrease was statistically significant in both groups following the treatment, and it was more prominent in the adolescent group (p<0.05). The natural head posture might have changed with the mandibular advancement.

All patients showed an improved soft tissue profile with significantly increased convexity angles based on lateral cephalometric radiographic and three-dimensional photogrammetric analyses. Lip balance was achieved with the conventional activator therapy in both groups. Some of the previous studies in late growth subjects have also reported that the soft tissue convexity and the total facial convexity angles were significantly increased by the Bionator and the Herbst appliance [30,55,80]. Decreased upper lip projection and increased lower lip projection were reported by Remmer et al. (1985), Almeida et al. (2004), and Cozza et al. (2004) [66,81,82]. Other three-dimensional photogrammetric measurements showed certain favorable results in the post-adolescent group as well. The labiomental angle showed a statistically significant increase in lateral cephalometric radiographic and three-dimensional photogrammetric analyses in both groups. Varlık et al. (2008) reported that the labiomental angle was increased by the twin block and the conventional activator therapies due to relaxation of the lower lip with the decrease of overjet [83]. Another reason for this finding may be a reduction in the depth of labiomental sulcus following twin block therapy, as reported by Singh and Clark (2003) [84]. Labiomental sulcus depth, which exhibited higher values before the treatment, showed a statistically significant decrease after treatment. Total lip volume was slightly decreased in both groups (0.29±0.39 cm3 and 0.36±0.22 cm3 in the adolescent and the post-adolescent groups, respectively). Although the change was statistically significant, it may be negligible clinically. The overjet elimination, the increase of lip closure in the resting position, the decrease in the labiomental sulcus depth, the increase of pogonion projection (Pg-VRL), and the increase in the labiomental angle might have caused a decrease in total lip volume. In accordance with the profile convexity, the H angle showed a significant decrease by 2.37° in the adolescent group and by 2.24° in the post-adolescent group. Morris et al. (1998) found a significant decrease in the H Angle with the three-dimensional laser scanning system using the Bass appliance, the Bionator, and the twin block appliances in the adolescent period [85]. Erdem et al. (2009) also reported a similar decrease in the H Angle following treatment with the conventional activator appliance [86]. Mandibular volume was significantly increased in the adolescent group (mean 0.59 cm3) and the post- adolescent group (mean 0.73 cm3). The decreased H Angle might have resulted in the increased mandibular volume. Consequently, the soft tissue convexity, the lip positions, and the mandibular measurements were favorably affected by the conventional activator therapy, even in the late growth period. The conventional activator therapy may be considered as an alternative treatment approach to camouflage therapy or, to a certain extent, to orthognathic surgery in the post-adolescent period. However, the main disadvantage of this type of removable appliance is patient cooperation. Although outcomes of this treatment approach were satisfactory in both growth periods based on these data, it should be kept in mind that the patient cooperation in use of removable appliances tends to decrease in the post- adolescence period and in young adulthood. Further research is needed to compare the removable appliance to fixed orthodontic appliances in treating Class II anomalies in the post-adolescent period to understand the degree of skeletal effects of these appliances. Another limitation of the present study may be the small sample size, and studies with larger sample sizes are needed.

Conclusions

Favorable outcomes were achieved with the conventional activator therapy in patients with Class II mandibular retrognathia in both growth periods. The contribution of the skeletal changes was greater in the adolescent group than in the post-adolescent group. Conventional activator appliance on a short-term basis was found also to be effective to a certain extent for mandibular growth stimulation in patients in late growth period. However, the treatment duration was significantly longer in the post-adolescent group. This study suggests that conventional activator therapy can be an alternative treatment approach in the late growth period, since it induces considerable skeletal changes. Regarding the soft tissue changes, significant increases in the anterior facial height and the nose height were observed in the three-dimensional photogrammetric measurements in both growth groups. These changes were found to be higher in the adolescent group when compared with the post-adolescent group. The total lip volume was significantly reduced following the treatment, while the mandibular volume was significantly increased in all patients. The present study may serve as the basis for future studies on this subject regarding volumetric measurements.