This retrospective study aimed to assess the stability of Class II malocclusion treatment with the distal jet, followed by fixed appliances.
Seventy-five cephalograms of 30 subjects were divided into 2 groups. The treated group consisted of 15 patients who were evaluated at the pretreatment, posttreatment, and long-term posttreatment stages. The control group consisted of 15 subjects with normal occlusion, comparable to the experimental group at the long-term posttreatment period. Intergroup comparison of posttreatment changes was evaluated with t tests.
In the long-term posttreatment period, there was no significant change in the anteroposterior position of the maxilla and mandible to the cranial base. The lower anterior face height had a significantly smaller increase in the treated than in the control group. The maxillary molars in the treated group had significantly smaller vertical development, and the mandibular incisors had significantly greater labial tipping and protrusion than the control group. The treatment produced significant improvement in molar relationship and reduction of overbite and overjet, which remained stable in the long-term posttreatment period. There was greater upper lip protrusion in the experimental than in the control group in the long-term posttreatment period.
Treatment of Class II malocclusions with the distal jet, followed by fixed appliances, showed good long-term stability in molar relationship, overbite, and overjet.
Patients with Class II malocclusion were treated with distal jet and fixed appliances.
Significant improvements occurred in molar relationship, overbite, and overjet.
Results remained stable at the posttreatment stage.
Stability might depend on active retention after distalization.
Maxillary molar distalization for nonextraction treatment of patients with Class II malocclusions has been used for many years. Conventionally used appliances for molar distalization such as extraoral headgear, Cetlin removable plate, pendulum appliances, the recently popular Carriere appliance, and Wilson arches are dependent on patient compliance to correct molar relationship.
Patient compliance is the most important key to any treatment success and plays a major role in achieving the desired results. Lack of compliance is a common problem in the orthodontic clinic. Therefore, treatments that require minimal patient compliance may produce better and more predictable results. , , ,
By the end of the 1970s, intraoral distalizers began to be used, which are appliances with intramaxillary anchorage for distalization, described as an alternative to headgear. The advantages of these appliances are that they act permanently, do not affect facial esthetics and are independent of patient compliance. However, problems related to these appliances such as anchorage loss associated with great labial tipping of maxillary incisors have been reported on previous studies. , ,
Recently, modern anchorage systems for molar distalization were introduced, such as mini-implants and surgical plate supported distalization, and have become increasingly popular. Not only they provide effective anchorage, but also do not rely on patient compliance to retract the anterior teeth.
Developed by Carano and Testa, in 1996, the distal jet is one of the most frequently used noncompliance appliances for molar distalization. It is a lingual distalization appliance, consisting of an acrylic Nance button and stainless-steel wires and springs. This lingual appliance has 3 distinct advantages: the maxillary molars are distalized without the lingual movement that occurs with the pendulum; it can be easily converted into a regular Nance holding arch when the distalization is complete; and it produces less molar tipping, with more bodily movement.
As demonstrated, since the introduction of the distal jet, many studies have evaluated the dentoskeletal changes produced by this appliance and its efficiency, but what about the stability? Besides obtaining good treatment outcomes, maintaining teeth in their corrected positions is challenging, and a major objective of orthodontic treatment is to achieve long-term stability of the dental relationships. , , ,
In the literature, there is a lack of studies evaluating stability of the changes induced by the distal jet. Therefore, this study aimed to evaluate the long-term stability of Class II malocclusion treatment with the distal jet, followed by fixed appliances.
Material and methods
The sample size was calculated on the basis of an alpha significance level of 0.05 and a beta of 0.2 to detect a mean difference of 1.5 mm with a standard deviation (SD) of 1.43 in the changes in molar sagittal position between the posttreatment and long-term posttreatment stages. The results showed that a minimum of 15 patients were needed in each group.
Therefore, the sample consisted of 45 lateral cephalometric radiographs of 15 patients from the files of the Orthodontic Department at Bauru Dental School, University of São Paulo. The patients were selected according to the following inclusion criteria: Class II Division 1 malocclusion (minimum severity of one-fourth Class II molar relationship), in the permanent dentition, including or not fully erupted maxillary second molars, with records of at least 5 years after treatment with the distal jet, followed by fixed; absence of agenesis or loss of permanent teeth; dental arches with slight to moderate crowding; molar distalization achieved only with the distal jet in the first phase of treatment; without history of previous orthodontic treatment; and treated nonextraction. No cephalometric characteristic was considered as inclusion criteria.
The treated group included 15 patients (10 females and 5 males) who were treated with the distal jet for a mean period of 1.20 (SD, 0.32) years, followed by fixed appliances for a mean time of 2.93 (SD, 0.67) years. The average total treatment time was 4.13 (SD, 0.99) years. The pretreatment mean age was 12.63 (SD, 1.31) years, the posttreatment mean age of 16.76 (SD, 1.55) years, and the long-term posttreatment mean age was of 23.26 (SD, 1.33). The mean long-term posttreatment period was of 6.49 years (SD, 0.59; Table I ).
|SNA (°)||Angle between SN and A point|
|SNB (°)||Angle between SN and B point|
|ANB (°)||NA to NB angle|
|LAFH (mm)||Lower anterior face height-distance between ANS and Me|
|FMA (°)||Frankfort mandibular plane angle|
|SN.GoGn (°)||Angle between SN line and mandibular plane (GoGn)|
|SN.PP (°)||Angle between SN and Palatal plane|
|Mx1.NA (°)||Angle between the maxillary incisor long axis to NA line|
|Mx1-NA (mm)||Distance between the maxillary incisor crown and NA line|
|Mx1.SN (°)||Angle between the maxillary incisor long axis to SN line|
|Mx1-PTV (mm)||Distance between the maxillary incisor long axis to pterigomaxillary vertical (PTV)|
|Mx1-PP (mm)||Distance between the maxillary incisor crown tip and palatal plane|
|Mx4.SN (°)||Angle between the maxillary first premolar long axis to SN line|
|Mx4-PTV (mm)||Distance between the maxillary first premolar long axis to pterigomaxillary vertical (PTV)|
|Mx4-PP (mm)||Distance between the maxillary first premolar crown tip and palatal plane|
|Mx6.SN (°)||Angle between the maxillary first molar long axis to SN line|
|Mx6-PTV (mm)||Perpendicular distance between the centroid of the maxillary first molar to the pterigomaxillary vertical (PTV)|
|Mx6-PP (mm)||Perpendicular distance between the centroid of the maxillary first molar to the palatal plane|
|Mx7.SN (°)||Angle between the maxillary second molar long axis to SN line|
|Mx7-PTV (mm)||Perpendicular distance between the centroid of the maxillary second molar to the pterigomaxillary vertical (PTV)|
|Mx7-PP (mm)||Perpendicular distance between the centroid of the maxillary second molar to the palatal plane|
|Md1.NB (°)||Angle between the mandibular incisor long axis to NB line|
|Md1-NB (mm)||Distance between the mandibular incisor tip and NB line|
|Md6-PogPerp (mm)||Distance between the mandibular first molar and a line perpendicular to the mandibular plane (GoGn), tangent to Pg point|
|Molar relationship (mm)||Distance between mesial points of maxillary and mandibular first molars, parallel to Frankfort plane|
|Overbite (mm)||Distance between incisal edges of maxillary and mandibular central incisors, perpendicular to Frankfort plane|
|Overjet (mm)||Distance between incisal edges of maxillary and mandibular central incisors parallel to functional occlusal plane|
|NLA (°)||Nasolabial angle|
|UL-E (mm)||Distance between the upper lip to the esthetic plane|
|LL-E (mm)||Distance between the lower lip to the esthetic plane|
The long-term posttreatment control group comprised 15 untreated subjects (10 female and 5 male) with normal occlusion and initial mean age of 16.40 (SD, 0.97) years, and final mean age of 24.09 (SD, 2.49) years. The long-term posttreatment period of 7.69 (SD, 2.32) years was comparable to the experimental group. This group was selected from the longitudinal growth study sample of the Iowa Facial Growth Study (Department of Orthodontics, College of Dentistry, University of Iowa, Iowa City, IA) and The Oregon Growth Study (Department of Orthodontics, School of Dentistry, Oregon Health and Science University, Portland, Ore) obtained from the online American Association of Orthodontists Foundation Craniofacial Growth Legacy Collection ( Table I ).
The treatment protocol consisted in the use of the distal jet appliance, constructed with 2 bilateral tubes embedded in a modified acrylic Nance palatal button according to the recommendations of Carano and Testa ( Fig 1 ). The appliances were used until an over-correction of 2 mm in Class I molar relationship was achieved. Once the first molars had been moved into an overcorrected relationship, the distal jet appliance was converted into a modified Nance holding arch. Subsequently, preadjusted orthodontic fixed appliances were placed to retract the maxillary anterior segment, align the teeth, and detail the occlusion. All patients were instructed to wear a headgear and Class II elastics at night as active retention and to recover the side effects of the distal jet, until the end of treatment. At the end of the orthodontic treatment, all patients were instructed to wear a maxillary Hawley retainer for a total of 1 year, with recommended use of 20 h/d during 6 months, and additional 6 months of night wear. A fixed canine-to-canine lingual retainer was used for retention in the mandibular arch with recommended use of 3 years. At the long-term stage (T3) none of the patients were wearing their Hawley retainers, but 14 of 15 patients in the experimental group were still wearing the canine-to-canine lingual retainer.
Lateral cephalometric radiographs were taken of each patient at the pretreatment (T1), posttreatment (T2), and long-term posttreatment stages (T3). They were digitized and had the landmarks identified by a single operator (S.C.R.P) in the Dolphin Imaging software (version 11.5; Dolphin Imaging and Management Solutions, Chatsworth, Calif), which also corrects the image magnification factors of the different radiographic machines in which the lateral cephalograms were taken. The cephalometric variables are shown in Table I and in Figures 2 to . Long-term posttreatment changes were calculated as T3-T2.
Twenty-two radiographs were randomly selected, retraced, redigitized and remeasured again by the same examiner (S.C.R.P), after a month of the first measurements. The random errors were calculated according to the Dahlberg formula (Se 2 = ∑d 2 /2n), in which Se 2 is the error variance and d is the difference between 2 determinations of the same variable. The systematic errors were evaluated with paired t tests, at P <0.05.
Normal distribution of the variables was evaluated with Kolmogorov-Smirnov tests, which showed that they had normal distribution. Intergroup comparability regarding ages at T2, T3, and posttreatment period was evaluated with t tests.
Repeated measures ANOVA, followed by Tukey tests were used to compare the experimental group variables at the 3 evaluation stages. t tests were used to compare changes during the long-term posttreatment period (T3-T2) in the experimental group with the changes during a comparable period for the control group.
All statistical tests were performed with Statistica software (version 10.0; Statsoft, Tulsa, Okla). Results were considered statistically significant at P <0.05.
The range of random errors varied from 0.14° (ANB) to 2.53° (Mx7.SN) and from 0.20 mm (UL-E) to 1.14 mm (Mx1-PP) and were within acceptable range. Only 2 (Overbite and LL-E) of 30 evaluated variables showed statistically significant systematic errors. The groups were comparable for ages at T2 and T3 and for the posttreatment period ( Table II ).
|Stage and/or period||Experimental group (n = 15)||Control group (n = 15)||P|
|Treatment period (T2-T1)||4.13||0.99|
|Posttreatment period (T3-T2)||6.49||0.59||7.69||2.32||0.062|
During treatment there was a significant increase in lower anterior facial height (LAFH), which remained stable in the posttreatment stage ( Table III ). The functional mandibular advancer increased significantly during treatment, but also decreased significantly in the posttreatment period. The maxillary incisors had significant vertical development, which remained stable in the posttreatment period. The maxillary first premolars showed significant mesial angulation, remaining stable in the posttreatment period. There was also significant maxillary first premolars extrusion between the pretreatment and follow-up stages. The maxillary first molars showed significant mesial tipping of the crown mesial crown tip and mesialization between the pretreatment and follow-up stages, and extrusion, during treatment, which remained stable in the posttreatment period. The maxillary second molars showed significant mesial angulation, mesialization, and extrusion during treatment, which remained stable in the posttreatment period. The mandibular incisors presented with significant labial inclination and protrusion that remained stable in the posttreatment period. Treatment produced significant improvement in molar relationship, overbite, and overjet, which remained stable at the posttreatment stage. There was significant upper lip significant retrusion that remained stable in the posttreatment period. The lower lip had significant retrusion between the pretreatment and follow-up stages.
|Variable||Pretreatment (T1)||Posttreatment (T2)||Follow-up (T3)||P|
|Maxillary skeletal component|
|Mandibular skeletal component|
|LAFH (mm)||62.69 a||6.86||67.37 b||8.82||67.40 b||9.47||<0.001 ∗|
|FMA (°)||25.82 a||3.85||27.12 b||4.42||25.76 a||4.18||0.012 ∗|
|Maxillary dentoalveolar component|
|Mx1-PP (mm)||72.76 a||3.04||75.87 b||5.43||77.08 b||5.61||0.005 ∗|
|Mx4.SN (°)||54.55 a||3.62||60.69 b||5.94||60.69 b||6.98||<0.001 ∗|
|Mx4-PP (mm)||34.42 a||3.60||35.44 ab||3.93||36.45 b||4.14||0.003 ∗|
|Mx6.SN (°)||19.20 a||3.42||20.30 ab||3.50||21.20 b||3.66||0.002 ∗|
|Mx6-PTV (mm)||10.50 a||3.10||11.00 ab||3.72||12.16 b||3.42||<0.011 ∗|
|Mx6-PP (mm)||27.14 a||3.11||29.19 b||4.32||29.42 b||4.32||<0.001 ∗|
|Mx7.SN (°)||20.48 a||2.29||22.59 b||3.21||22.96 b||3.52||<0.001 ∗|
|Mx7-PTV (mm)||17.42 a||2.26||19.89 b||2.78||20.40 b||2.86||<0.001 ∗|
|Mx7-PP (mm)||12.31 a||3.19||16.82 b||2.57||17.62 b||2.78||<0.001 ∗|
|Mandibular dentoalveolar component|
|Md1.NB (°)||24.53 a||5.96||28.29 b||6.45||29.16 b||7.73||0.008 ∗|
|Md1-NB (mm)||4.71 a||2.30||6.00 b||2.68||6.42 b||2.65||<0.001 ∗|
|Molar relationship (mm)||0.36 a||0.71||−1.28 b||1.24||−1.27 b||0.76||<0.001 ∗|
|Overbite (mm)||2.79 a||1.73||1.68 b||1.00||1.90 ab||1.02||0.016 ∗|
|Overjet (mm)||4.91 a||1.40||2.90 b||0.56||2.87 b||0.63||<0.001 ∗|
|UL-E (mm)||1.77 a||2.74||−0.51 b||2.49||−0.14 b||2.34||<0.001 ∗|
|LL-E (mm)||1.78 a||2.53||0.96 ab||2.88||0.63 b||2.84||0.037 ∗|