Treatment effects of a modified palatal anchorage plate for distalization evaluated with cone-beam computed tomography


The purpose of this study was to evaluate the treatment effects of maxillary posterior tooth distalization performed by a modified palatal anchorage plate appliance with cephalograms derived from cone-beam computed tomography.


The sample consisted of 40 lateral cephalograms obtained from the cone-beam computed tomography images of 20 Class II patients (7 men, 13 women; average age, 22.9 years) who underwent bilateral distalization of their maxillary dentition. The lateral cephalograms were derived from the cone-beam computed tomography images taken immediately before placement of a modified palatal anchorage plate appliance and at the end of distalization. Paired t tests were used for comparisons of the changes.


The distal movement of the maxillary first molar was 3.3 ± 1.8 mm, with distal tipping of 3.4° ± 5.8° and intrusion of 1.8 ± 1.4 mm. Moreover, the maxillary incisors moved 3.0 ± 2.7 mm lingually, with lingual tipping of 6.2° ± 7.6° and insignificant extrusion (1.1 mm; P = 0.06). The occlusal plane angle was increased significantly ( P = 0.0001).


The maxillary first molar was distalized by 3.3 mm at the crown and 2.2 mm at root levels, with distal tipping of 3.4°. It is recommended that clinicians should consider using the modified palatal anchorage plate appliance in treatment planning for patients who require maxillary total arch distalization.

Extraoral appliances have been prescribed for maxillary molar distalization in nonextraction treatment of Class II malocclusion patients. However, these devices require patient cooperation. To effectively overcome this problem, intraoral noncompliance appliances have been developed. Nevertheless, the negative side effects of these appliances include anchorage loss at the reactive part, distal tipping, and extrusion of molars.

To reduce the drawbacks of noncompliance appliances, temporary skeletal anchorage devices (TSADs) have been applied to the buccal plate of the bone to achieve molar distalization. However, the buccal approach poses an increased risk of contacting the roots of adjacent teeth, and the range of action might be limited by the interradicular space. Sugawara et al placed plates at the zygomatic buttresses for distalization of the maxillary dental arch. However, their method involved surgical procedures and a latency time between the surgery and force application.

Recently, palatal bone thickness and density as well as palatal soft-tissue thickness have been evaluated in adults and adolescents. These studies have provided detailed information for the placement of the TSADs in the palate. In addition, the placement of the TSADs in the palate eliminates the need for reimplanting miniscrews as in the buccal approach.

Several appliances with TSADs have been reported to distalize the maxillary posterior teeth, but some were bulky and others contributed to distal crown tipping. Kinzinger et al proposed a distal jet appliance supported by dental and skeletal anchorages. Although it reduced the anchorage loss, it prevented movement of the premolars during the distalization period. Kircelli et al used a bone-anchored pendulum appliance. A large amount of distal tipping of the first molar (10.9°) was reported with this appliance; this could have been due to a force vector similar to the conventional appliance. On the other hand, the modified palatal anchorage plate (MPAP) appliance has been reported to effectively distalize the posterior teeth in adults and adolescents. Finite element analysis suggested that distalization with a palatal plate rather than buccally placed mini-implants provides bodily molar movement without tipping or extrusion. However, no clinical evaluation has been performed with the MPAP.

So far, most distalization studies have used 2-dimensional lateral cephalograms. The disadvantages of this approach include confounded images caused by superimposed anatomic structures, vertical and horizontal magnifications, and a lack of right and left side information. Although cone-beam computed tomography (CBCT) has disadvantages that include higher doses of radiation, higher cost, and limited availability, these limitations are overcome by the huge amount of data that is provided without distortion or superimposition.

The degree of difficulty and the prognosis of distalization are affected by the patient’s dental and chronologic ages. A high success rate with fewer complications occurs when the maxillary molars are distalized in the mixed dentition stage. Hence, most distalization studies have focused on adolescents, and there have been no studies, to the best of our knowledge, investigating the distalization effect in adults who have full eruption of their maxillary second molars.

Therefore, the purpose of this study was to evaluate the treatment effects of posterior tooth distalization in adults with an MPAP appliance using lateral cephalograms derived from CBCT images.

Material and methods

Forty lateral cephalograms were obtained from CBCT images of 20 consecutively treated Class II adult patients (7 men, 13 women; average age, 22.9 years; range, 17.4-33 years) who underwent bilateral distalization of their maxillary dentition at the Department of Orthodontics at Seoul St. Mary’s Hospital, Catholic University of Korea. Of the 40 lateral cephalograms, 15 sides had one quarter cusp, 12 had one half cusp, 7 had three quarters cusp, and 6 had full cusp Class II molar relationships.

The inclusion criteria for this retrospective study were (1) dental Class II relationship, (2) 3-dimensional CBCT images taken immediately before and after distalization, (3) exclusive use of the MPAP appliance for distalization, and (4) age over 17 years. The exclusion criteria were (1) extraction treatment (except for third molars) and (2) unilateral distalization. Approval was obtained from the institutional review board of the Catholic University of Korea (KC11RASI0790), and informed consent was provided according to the Declaration of Helsinki.

The MPAP appliance ( Fig 1 ) and its installation method have been described in previous articles. The MPAP was fitted on the dental cast to the shape of the palate, extending its arms to the area between the first molar and the second premolar and leaving enough space between the arms and the palatal slopes. The transfer from the cast to the patient’s mouth was made with a jig by the same operator (Y.-A.K.) using 3 miniscrews (length, 8 mm; diameter, 2 mm: Jeil, Seoul, Korea). Then a palatal bar with 2 hooks extending along the gingival margins of the teeth was banded to the right and left maxillary first molars. Immediately after placement, distalization can be initiated by engaging elastics or nickel-titanium closed-coil springs between the MPAP arm notches and the hooks on the palatal bar, applying approximately 300 g of force per side.

Fig 1
The palatal plate is connected to the hooks of the palatal wire via power elastics or nickel-titanium closed-coil springs. The direction of force can be changed according to the notches on the arms of the palatal plate ( A , B , and C ).

Along with the MPAP appliance, 0.022-in slot brackets and bands (Tomy, Tokyo, Japan) were placed on the maxillary and mandibular teeth including the second molars. The interval between appointments was 3 to 4 weeks. The distalization periods were calculated from the patients’ records.

CBCT images (before and after distalization) were taken with an iCAT scanner (Imaging Science International, Hatfield, Pa). The scanning parameters were 120 kV, 47.7 mAs, 20 seconds per revolution, 170 × 130 mm field of view, and voxel size of 0.4 mm. Each seated subject’s head position was oriented so that the Frankfort plane was parallel to the floor, and the images were taken at the intercuspal position.

The CBCT data were exported in a digital imaging and communications in medicine (DICOM) multifile format and imported into InVivo software (version 5.2; Anatomage, San Jose, Calif) for 3-dimensional volume rendering. Reorientation of the head position of each scan was performed as follows. The horizontal plane (x) was defined through the right and left orbitales and the left porion, and the midsagittal plane (y) was defined as the perpendicular plane passing through nasion and anterior nasal spine. The vertical plane (z) was perpendicular to both x and y. Then, using the super-ceph module in the InVivo software, a lateral cephalometric image was created for each right and left side independently and saved in JPG format. Each image was then traced and superimposed using V-Ceph software (version 5.5; Cybermed, Seoul, South Korea) with the manual geometric method. The horizontal reference line was the Frankfort horizontal plane, and the vertical reference line was the perpendicular at pterygoid. All tracings and digitizations were made by 1 examiner (V.T.T.T.) to minimize operator-generated variation in the measurements.

The software calculated the linear and angular dimensions between certain landmarks according to the definitions given in Figures 2 through 4 .

Fig 2
Cephalometric landmarks and maxillary dental sagittal, vertical, and angular measurements. Landmarks: Or , Orbitale; Po , porion; Pt , pterygoid; ANS , anterior nasal spine; PNS , posterior nasal spine; FH , Frankfort horizontal; VRL , vertical reference line; U1 , incisal tip of the maxillary central incisor; U1r , root tip of the maxillary central incisor; U5 , cusp tip of the maxillary second premolar; U5r , root tip of the maxillary second premolar; U6 , distobuccal cusp of the maxillary first molar; U6r , distobuccal root tip of the maxillary first molar. Measurements: 1 , U6-VRL; 2 , U6r-VRL; 3 , U6-FH; 4 , U6r-FH; 5 , angle between U6-U6r and FH; 6 , U5-VRL; 7 , U5r-VRL; 8 , U5-FH; 9 , U5r-FH; 10 , angle between U5-U5r and FH; 11 , U1-VRL; 12 , U1r-VRL; 13 , U1-FH; 14 , U1r-FH; 15 , angle between U1-U1r and FH.

Fig 3
Cephalometric landmarks and mandibular dental sagittal, vertical, and angular measurements. Landmarks: Or , Orbitale; Po , porion; Pt , pterygoid; FH , Frankfort horizontal; VRL , vertical reference line; L1 , incisal tip of the mandibular central incisor; L1r , root tip of the mandibular central incisor; L5 , cusp tip of the mandibular second premolar; L5r , root tip of the mandibular second premolar; L6 , distobuccal cusp of the mandibular first molar; L6r , distal root tip of the mandibular first molar. Measurements: 1 , L6-VRL; 2 , L6r-VRL; 3 , L6-FH; 4 , L6r-FH; 5 , angle between L6-L6r and FH; 6 , L5-VRL; 7 , L5r-VRL; 8 , L5-FH; 9 , L5r-FH; 10 , angle between L5-L5r and FH; 11 , L1-VRL; 12 , L1r-VRL; 13 , L1-FH; 14 , L1r-FH; 15 , angle between L1-L1r and FH.

Fig 4
Cephalometric midsagittal measurements. Landmarks: S , Sella turcica; N , nasion; Or , orbitale; Po , porion; Pt , pterygoid; FH , Frankfort horizontal; ANS , anterior nasal spine; A , A-point; Ls , labrale superior; Li , labrale inferior; B , B-point; Pog’ , soft-tissue pogonion; Me , menton; VRL , vertical reference line. Measurements: 1 , SNA; 2 , ANB; 3 , palatal plane angle; 4 , occlusal plane angle; 5 , mandibular plane angle; 6 , ANS-Me; 7 , nasolabial angle; 8 , mentolabial fold; 9 , Ls-VRL; 10 , Li-VRL; 11 , Pog’-VRL.

The maxillary third molar was present in 31 sides and extracted or missing from 9 sides during treatment.

Ten randomly selected subjects were reprocessed 4 weeks later to evaluate intraoperator reliability. The intraclass correlation coefficient showed that the measurements were reliable (>0.997).

Statistical analysis

Statistical evaluation was performed using SPSS software (version 16.0; SPSS, Chicago, Ill). Normal distribution of the parameters was assessed with the Kolmogorov-Smirnov test. The paired t test was used to evaluate the skeletal, dental, and soft-tissue changes from before to after distalization. The comparison between subjects who had third molars during distalization and those with missing or extracted ones was performed by an independent sample t test. The statistical significance was determined at α = 0.05.


Clinically successful distalization was achieved using the MPAP appliance for an average of 12.5 months.

There were significant changes in the sagittal and vertical positions ( P <0.0001) and angulations ( P = 0.001) of the maxillary first molars after distalization. The mean amount of first molar distalization was 3.30 ± 1.80 mm, with distal tipping of 3.42° ± 5.79° and intrusion of 1.75 ± 1.35 mm. The maxillary second molar showed 2.66 ± 1.90 mm of distalization, 1.28 ± 1.61 mm of intrusion, and 2.03° ± 7.49° of distal tipping. The maxillary second premolars moved distally 3.05 ± 2.14 mm and tipped distally 8.38° ± 6.80°, with no significant change in the crown vertical position. The maxillary central incisors were retracted by 2.99 ± 2.73 mm, with a retroclination angle of 6.21° ± 7.64° and no significant change in the vertical position ( Table I , Fig 5 ).

Table I
Comparisons of predistalization and postdistalization positions of the maxillary dentition (n = 40)
Variable Predistalization Postdistalization Change P value
Mean SD Mean SD Mean SD
Central incisor crown horizontal distance (mm) 55.22 5.32 52.23 5.52 2.99 2.73 <0.001
Central incisor root horizontal distance (mm) 47.21 3.77 46.89 3.97 0.33 2.08 0.327
Central incisor crown vertical distance (mm) 54.52 4.57 55.61 4.20 −1.09 3.51 0.056
Central incisor root vertical distance (mm) 35.17 3.46 35.72 3.43 −0.55 1.92 0.077
Central incisor inclination (°) 68.15 10.47 74.36 10.34 −6.21 7.64 <0.001
Second premolar crown horizontal distance (mm) 33.14 5.21 30.09 4.94 3.05 2.14 <0.001
Second premolar root horizontal distance (mm) 33.61 3.87 33.26 4.03 0.34 2.21 0.332
Second premolar crown vertical distance (mm) 49.88 4.69 50.04 4.13 −0.16 3.91 0.798
Second premolar root vertical distance (mm) 33.26 5.20 32.75 3.63 0.51 3.61 0.381
Second premolar angulation (°) 92.11 7.22 100.49 8.66 −8.38 6.80 <0.001
First molar crown horizontal distance (mm) 18.43 4.42 15.13 4.17 3.30 1.80 <0.001
First molar root horizontal distance (mm) 22.99 3.48 20.82 3.53 2.17 1.85 <0.001
First molar crown vertical distance (mm) 45.51 4.08 43.76 4.63 1.75 1.35 <0.001
First molar root vertical distance (mm) 31.53 3.74 29.98 3.78 1.55 1.96 <0.001
First molar angulation (°) 109.30 6.05 112.72 7.83 −3.42 5.79 0.001
Second molar crown horizontal distance (mm) 9.23 3.93 6.57 3.74 2.66 1.90 <0.001
Second molar root horizontal distance (mm) 16.00 3.13 13.88 3.19 2.12 1.90 <0.001
Second molar crown vertical distance (mm) 42.56 4.75 41.28 5.15 1.28 1.61 <0.001
Second molar root vertical distance (mm) 30.97 3.91 29.67 4.03 1.30 1.45 <0.001
Second molar angulation (°) 120.67 10.05 122.71 9.36 −2.03 7.49 0.118
Positive values indicate distal movement, retraction, intrusion, and mesial tipping. P values were obtained by paired t test.

Fig 5
Summary of mean maxillary dental changes after distalization by the MPAP appliance.

The occlusal plane angle was significantly ( P = 0.001) increased by 2.81°. However, the palatal plane angle was not changed. The upper and lower lips showed about 1.5 mm of retraction ( P = 0.016 and 0.008, respectively). The nasolabial angle was significantly ( P = 0.008) increased to 101.9° ( Table II ).

Table II
Skeletal and soft-tissue cephalometric measurements before and after distalization (n = 20)
Variable Predistalization Postdistalization Change P value
Mean SD Mean SD Mean SD
SNA (°) 81.18 3.35 80.42 3.22 0.76 1.95 0.097
ANB (°) 4.38 2.11 3.36 1.80 1.01 1.46 0.006
Palatal plane angle (°) 5.96 17.50 9.31 3.08 −3.35 16.81 0.384
Occlusal plane to SN (°) 18.78 6.33 21.60 5.94 −2.81 3.37 0.001
Mandibular plane angle (°) 23.90 8.96 24.46 9.00 −0.55 2.58 0.351
ANS-Me (mm) 67.43 6.01 68.62 6.44 −1.19 3.26 0.120
Overjet (mm) 4.71 1.67 3.54 0.90 1.17 1.90 0.013
Overbite (mm) 3.28 1.44 3.16 1.15 0.13 1.64 0.735
Nasolabial angle (°) 98.64 7.69 101.90 8.38 −3.26 4.87 0.008
Mentolabial fold (°) 135.53 9.74 133.36 9.02 2.17 6.39 0.145
LS-VRL (mm) 67.22 5.04 66.04 5.01 1.18 1.99 0.016
LI-VRL (mm) 63.70 5.86 62.16 5.87 1.54 2.33 0.008
Pog′-VRL (mm) 42.38 9.77 41.82 9.92 0.56 2.91 0.398
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Apr 6, 2017 | Posted by in Orthodontics | Comments Off on Treatment effects of a modified palatal anchorage plate for distalization evaluated with cone-beam computed tomography
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