Long term results of double plate appliance and facemask combination in the treatment of Class III malocclusion: cephalometric analysis

Amac: Sinif III malokluzyonun tedavisinde kullanilan agiz-ici cift plak ile yuz maskesi (ACP-YM) kombine tedavisinin uzun donem sonuclarinin buyume potansiyeli bitmis ya da bitmekte olan hastalarda degerlendirilmesidir . Gerec ve Yontem: Calismanin materyali ACP-YM kombine tedavisi uygulanmis olan iskeletsel ve dissel Sinif III malokluzyona sahip 13 hastaya (5 kiz, 8 erkek; ortalama kronolojik yas: 11.1±1.40 yil) ait tedavi oncesi (T1), sonrasi (T2) ve uzun donem takip (T3) lateral sefalometrik ve el bilek radyografilerinden olusturuldu. Ortalama ACP-YM tedavi suresi 10.8±1.88 aydir. T3 doneminde, el bilek buyume ve gelisim safhasi, MP3u veya Ru donemidir. Ortalama takip suresi 5.0±1.98 yildir. Tedavi (T2-T1), takip (T3-T2) ve toplam (T3-T1) degisiklikleri degerlendirmek icin Friedman iki yonlu ANOVA ve Wilcoxon isaretli siralar testleri kullanildi . Bulgular: ACP-YM tedavisi ile SNA ve ANB acilarinda artis bulundu (p<0.001). Ancak bu parametrelerde T3-T2 doneminde onemli duzeyde bir degisiklik meydana gelmedi [p=0.655 (SNA), p=0.805 (ANB)]. N ┴ FH-A mesafesi tedavi (p<0.01) ve takip (p<0.05) donemlerinde onemli duzeyde artti. Molar iliskide, hem ACP-YM tedavisi sirasinda hem de toplam surede onemli duzeyde bir artis meydana geldi (p<0.001). Overjet ise, tedavi (p<0.001), takip (p<0.05) ve toplam surede (p<0.001) onemli duzeyde artti. Tedavi, takip donemlerinde ve toplam surede, ust keserlerde (U1/NA) onemli duzeyde protruzyon gozlendi (p<0.05). U6/PP ve L6/MP acilari ACP-YM tedavisi ile degismezken, takip periyodunda ve toplam surede bu parametrelerde onemli duzeyde azalma meydana geldi (p<0.05). Sonuc: ACP-YM kombine tedavisi, Sinif III malokluzyonun tedavisinde etkili bulundu. Bu ortopedik tedavi ile meydana gelen iskeletsel ve dissel sagital degisikliklerin uzun donem takip periyodunda korundugu gozlendi .


INTRODUCTION
Skeletal Class III malocclusions remain one of the most challenging problems due to the relapse of skeletal problem. The effects of maxillary protraction by facemask (FM) therapy on skeletal and dentoalveolar components of craniofacial region are well established in the treatment of skeletal Class III malocclusions characterized by maxillary hypoplasia. [1][2][3][4][5][6] Besides, successful outcomes of Class III malocclusion have been reported with the use of functional appliances, including Frankel III, double plate appliances (DPA), and reverse twin-block. 2,[7][8][9][10][11] The DPA was designed as an intraoral opposed angulated acrylic blocks. Sagittal skeletal changes during DPA treatment was less than FM therapy. 9 However, greater dental contribution to Class III treatment and more satisfying vertical dental and skeletal changes were shown in the DPA group. 9 In order to obtain more favorable dental effects with FM DOI: http://dx.doi.org /10.17214/gaziaot.345052 Original research article Long term results of double plate appliance and facemask combination in the treatment of Class III malocclusion: cephalometric analysis therapy, combined use of FM and DPA was offered. 2 Gencer et al. 2 reported significant changes in maxillary growth and position with DPA-FM combination and less effect on mandible than FM therapy.
In several follow-up studies of facemask, evaluations were done on growing subjects. [12][13][14][15] Shortterm improvements does not always assure longterm success. 5,16 There is still a risk for relapse due to substantial growth potential. A longer follow-up period is needed to understand the real growth alterations after Class III treatment.
The success of the orthopedic treatment, age at the beginning of the treatment, excessive mandibular growth, overcorrection, overbite, and overjet at the end of the treatment were the important factors in determining long term outcomes in Class III malocclusions. 4,6,13,17 In literature, long-term evaluations of FM were well documented; [3][4][5][6]13,14,16 however, there is no study evaluating the stability of DPA-FM combination therapy. Therefore, the aim of this study was to evaluate the long term results of DPA-FM combination in treating Class III malocclusions when growth potential of the patients was close to cease or ceased.

Patient selection
This study was approved by the Ethical Committee of Gazi University (#77082166-604.01.02).This retrospective study was carried out on the pretreatment (T1), posttreatment (T2), and long-term (T3) lateral cephalometric and hand-wrist radiographs of 13 patients (5 females, 8 males; mean chronological age: 11.1±1.40 years) with Angle Class III malocclusion characterized by an anterior cross-bite and/or Class III molar relationship with skeletal Class III malocclusion (ANB angle≤0°) due to maxillary retrusion or a combination of maxillary retrusion and mandibular protrusion. None of the patients had a congenital anomaly in the craniofacial region. All patients were treated with DPA-Delaire type FM combination ( Figure 1).

Appliance design
The DPA-FM combination was designed as in studies previously reported. 2,18 Construction bites for DPA were taken without sagittal activation and with a 5-6 mm. vertical opening at the molar region. The appliances had modified Adams clasps at the molar region and F clasps between upper lateral incisors and canines. Inclination between the acrylic blocks was 30°. 2 The protraction elastics were attached to the F clasps and a force of 350-400 g per side was applied and the patients were instructed to wear it approximately 16 hours a day. At the beginning of treatment and every 3 weeks during treatment, 2 mm was trimmed from the posterior region of the lower angulated acrylic block and the anterior region of the upper angulated acrylic block. The aim of this trimming was to facilitate the free sliding of the upper and lower pieces of the appliance along the angulated surfaces. The mean treatment time was 10.8±1.88 months.

Radiographic evaluation
Lateral cephalograms and hand-wrist radiographs were taken at the beginning of DPA-FM (T1), after achieving at least a positive overjet and/or Class I molar occlusion (T2) and long-term period (T3). The mean follow-up period was 5.0±1.98 years. The hand-wrist growth and developmental stages were MP3u or Ru at T3. Fixed therapy was performed in all patients between T2 and T3 periods. Remaining growth potential was assessed with hand-wrist radiographs according to Grave & Brown 19 at T3 to determine whether the growth potential was close to cease or ceased.
Ten linear and 10 angular measurements were evaluated ( Figure 2). The lateral cephalometric radiographs of 8 subjects were retraced, and measurements were repeated after 15 days. Method error coefficients were calculated and found to be within acceptable limits (range 0.98-1.00).

Statistical analysis
Statistical analysis was performed with IBM SPSS Statistics Version 20.0 (SPSS Inc., Armonk, NY, USA). The normality of the data was tested with Shapiro Wilk's test. Because the data were not normally distributed, Friedman's Two-Way ANOVA and Wilcoxon signedrank tests were used. The level of significance used was p<0.05.

RESULTS
Descriptive data, treatment changes and long term results of DPA-FM combination therapy were given in Table 1.
PP/MP angle showed a significant increase during DPA-FM therapy (p<0.01) and a significant decrease during follow-up period (p<0.01). By the evaluation of the overall changes (T3-T1), a significant decrease was observed in this angle (p<0.05). A significant decrease during DPA-FM therapy (p<0.01) and a significant increase (p<0.05) during follow-up were determined in SN/PP angle. There were significant increases in ANS-Me during therapy (p<0.01), follow-up (p<0.01) and overall periods (p<0.001).

DISCUSSION
The real success of a therapy is the long-term stability of the results achieved by treatment. A tendency toward Class III relapse was reported when the mandible rotated downward and backward with FM therapy. [3][4][5] The main purpose of the DPA was to withstand the possible tendency toward posterior rotation of the mandible. 9,18 Though similar vertical skeletal changes were reported in DPA-FM and FM treatments; sagittal skeletal and dental changes in the mandible showed significant differences between these treatment The significant increase in SNA during DPA-FM therapy was maintained during follow-up period, and overall improvement in this angle was found significant. In concomitant with this, similar results have been reported with FM therapy. 6,16,[23][24][25] The results indicated that there were no significant changes in SNB angle and horizontal movement of pogonion (N┴FH-Pg) during DPA-FM therapy. That might be defined as the less effect of this appliance on the mandible. In contrast with this, backward rotation associated with a reduction in mandibular growth was reported with FM appliance which was attributed to the chincap effect. 2,13,26 During follow-up in the present study, the position of mandible did not change which can be defined as a stability. In contrast with this, anterior rotation of the mandible was reported due to a return to previous growth pattern during FM. 4,16,17,23 Wells et al. 27 also observed that posterior rotation of the mandible with FM appliance increased the chance of long term failure of treatment.
The significant improvement in maxillomandibular relation during DPA-FM combination treatment was mainly caused by the maxilla in this study. This result was in agreement with the findings of several studies on treatment of Class III malocclusion. 25,28,29 No significant change was found in ANB angle during long-term period (T3-T2) and this can be interpreted as the stability of maxillomandibular relationship. Nevertheless, in follow-up studies regarding FM therapy non-significant increase in SNB angle and a significant decrease in ANB angle were reported. 12,30 Mandall et al. 21 reported that changes in SNA, SNB and ANB angles with FM therapy did not show long term differences compared to a control group, but pointed out that this kind of treatment reduced the need for orthognathic surgery.
Both CoA and CoGn lengths showed significant increases during follow-up period. Janson et al. 20 emphasized that the significant increase in mandibular length during the posttreatment period was compensated by a significant increase in maxillary length. So, apical base relationship was found to be similar to the control group. 20 Increase in lower facial height (ANS-Me) was significant during all periods which might be due to the significant anterior rotation of the maxilla during treatment (SN/PP) and continued vertical growth in all periods. 12 During follow-up period, maxillary rotation changed into a clockwise direction. As, SN/GoGn angle showed no significant changes in any of the periods, no rotational changes occurred in mandible. Changes in palato-mandibular angle in all periods seemed to be related to the rotational changes in palatal plane. Thus, it could be suggested that vertical stability after DPA-FM therapy was successful. This finding is consistent with the long-term results of FM studies. 16,20 However, Hägg et al. 5 reported significant posterior rotation and increases in vertical dimensions. Mandall et al. 21 emphasized that the clockwise rotation of maxilla and mandible during protraction of maxilla provides a more favorable facial profile compared to control group which have an anti-clockwise growth direction.
In several facemask studies, proclination of the upper incisors and retroclination of the lower incisors by the effect of maxillary protraction were reported. 18,25,31 In this study, proclination of upper incisor was significant both during treatment and follow-up periods. However, no significant change was found in lower incisors, as the contact to the acrylic surface of DPA prevent retrusion effect of the facemask. Cozza et al. 30 also reported no changes in mandibular incisors both during the treatment and long-term period of bite-block and FM study. On the contrary, significant retrusion of the mandibular incisors was reported with other removable appliances. 7,8,32 Both overjet and molar relationship improved significantly due to the dental and skeletal changes achieved by DPA treatment. A significant relapse in overjet was occurred during follow-up period (T3-T2), but eventually the positive overjet was maintained (T3-T1). This finding was in accordance with previous literature with data ranging from 67% to 72% of patients having a positive overjet. 5,33 In a previous study, the decrease in overjet during posttreatment was found to be correlated with the increase in mandibular length. In this study, both maxillary and mandibular lengths showed significant increases, but increase in mandibular length was greater and might have played an important role in the decrease of overjet. 20 U6/PP and L6/MP angles did not change during DPA-FM treatment; however, significant decreases were observed during T3-T2 period. Upper molar tipping seems to be prevented by the guidance of the angulated surfaces with DPA-FM. Mesial tipping of upper and lower molars during follow-up period was possibly due to both the transition from mixed to permanent dentition and the effect of fixed appliances.
In a meta-analysis study, 29 it was concluded that there was insufficient evidence to assess the long term stability of early Class III treatment. The limitations of this study were lack of control group and small sample size. However, both because of ethical purposes and difficulties relating to the follow-up period, it is not easy to set up the long term studies. Nevertheless, being the first study that evaluated the long term stability of DPA-FM therapy provides a unique contribution to literature.

CONCLUSION
In the treatment of Class III malocclusion, DPA-FM appliance was effective. The skeletal and dental sagittal changes achieved by orthopedic treatment were preserved during long-term period. Vertical stability was maintained both during DPA-FM combination treatment and follow-up periods.