A cephalometric study of Class H, treatment using differential torque

Division 1 mechanics

Athanasios T. Nasiopoulos, DDS, a Leo Taft, DDS, b and Saul N. Greenberg, DDS New York City, N.Y.

A pilot study was designed in which 19 growing patients with Class II, Division 1 malocclusions who were undergoing differential torque treatment were cephalometrically evaluated. No extraoral force or Class II elastics were used. Findings indicate that the 2 4 appliance can be useful in the treatment of selected Class II, Division 1 malocclusions in growing children. (AM J ORTHOD DENTOFAC ORTHOP 1992;101:276-80.)

The rationale for the correction of a Class II, Division 1 malocclusion in a growing patient is based on the following possibilities: (1) the maxillary first molar may actually be displaced distally; (2) it may be held in the same relative position in the maxilla while the mandibular first molar continues in its upward and forward eruption path in conjunction with the down- ward and forward growth of the mandible; (3) the for- ward growth component of the maxilla may be modified or even halted in the course of treatment. Any com- bination of these possibilities would result in the even- tual establishment of a normal Class I molar relation- ship, provided the mandible enjoys normal growth and development. 1.3

The purpose of this research is to investigate clin- ically and cephalometrically whether it is possible to correct aClass II, Division 1 malocclusion in a growing patient with properly directed moments and forces as described by Mulligan. 2

LITERATURE REVIEW

The forces and moments produced by a V bend on a 0.016-inch stainless steel round arch wire when placed between two brackets were analytically studied by Bur- stone and Koening. 4 It was found that a V bend placed between two brackets produces varying force systems depending on the centering or lack of centering of the apex of the V. The position of the apex of the V is conveniently described as the ratio of the distance of

From the New York University, College of Dentistry. aPostgraduate student, Program for Advanced Study for International Graduates in Orthodontics. bClinical Professor of Orthodontics; Director, Advanced Study for International Graduates in Orthodontics; and ABO Diplomate. cClinical Professor of Orthodontics and ABO Diplomate. 8 / 1 / 25845

the apex to one bracket to the total interbracket distance (a/L). Each a/L ratio has a characteristic force system: when the apex of the V bend is centered (a/L = 0.5), the moments at each bracket are equal and opposite in direction, and no forces are present in the system (Fig. 1). As the apex of the V bend is placed off center, intrusive and extrusive forces are introduced into the system, as well as moments of different magnitude and direction. If a/L = 0.4, the moments are of different magnitude and opposite in direction. An extrusive force and a downward and backward moment are present at the bracket close to the V bend, and an intrusive force and an upward and forward moment are present at the bracket farther from the V bend (Fig. 2). If a/L --- 0.33, an extrusive force and a substantial down- ward and backward moment are present at the bracket closest to the V, whereas at the bracket farthest from the V, there is only an intrusive force (Fig. 3). Finally, as the V bend is placed closer to the bracket (a/L = 0.2), moments are produced at both ends and in the same direction (downward and backward). It must be emphasized that the largest moment is always found at the bracket closest to the V bend. Intrusive and extrusive forces are also present (Fig. 4). The con- stant, regardless of where the V bend is placed within the system, is the equal and opposite intrusive and ex- trusive forces, except for the center bend when no ver- tical forces are present. The only changes in the system are the magnitude of the moments and th.eir direction.

The two by four (2 4) is a technique in which the four incisors and the two first permanent molars are engaged by an arch wire; tip-back bends (V bends) are placed in the arch wire. When an arch wire with V bends is inserted into the molar tubes and then engaged into the incisor brackets, a system of forces and mo- ments occurs similar to the previously described study by Burstone and Koenig. 4 When a/L is less than 0.33

276

Volume 101 Cephalometric study of Class H, Division 1 treatment 277 Number 3

;~ v ; , , 0 .33 0 .66 0.5 ' 0.5

Fig. 1, No forces are present in system, only equal and opposite moments.

I " , ! 0.4 ' 0.6 Fig. 2. An intrusive force and a forward and upward moment is present on incisor bracket. On the molar, an extrusive force and a downward and upward moment are applied.

and is toward the molar tube, an intrusive force and a small downward and backward moment are present on the incisors. These will reduce the overbite and overjet. On the molars, an extrusive force and a substantial downward and backward moment occur. This moment will produce distal crown torque on the molar. The larger moment on the molar and the frictional resistance in the buccal tube enhance the distalization of the four incisors. Because the treatment is applied to a growing patient with a large interbracket distance that reduces to a minimum the resultant vertical forces, the eruption of the molar under this treatment modality does not exceed normal limits of vertical growth.

With this technique, it is suggested that 0.5 to 2 mm of space can be gained in each quadrant. In addition, Mulligan 2 speculates that the tipped molar teeth, while uprighting, are continuing to erupt along a new longitudinal axis, and thus achieve a further net gain when they finally attain their upright position. An extra 1 to 1.5 mm is gained in this process. 2 At the same time, the mandible is growing downward and forward, with the mandibular first molars erupting in a

Fig. 3. No moments are present on incisor, only intrusive forces. On the molar, an extrusive force and a substantial downward and backward moment are applied.

, i

0.2' 0.8

Fig. 4. An intrusive force and a small downward and backward moment are applied on incisor. A large downward and backward moment and an extrusive force are present on the molar.

forward direction, thus helping to achieve a normal Class I molar relationship.

MATERIALS AND METHODS

For this study, all registrations and superimpositions are adopted from Mills et al. 5

Our 2 x 4 treatment group consisted of 19 patients, 6 boys (mean age 10.5 years) and 13 girls (mean age 10.7 years). Patient records were obtained from the files of ortho- dontists in private practice (Saul N. Greenberg, Albert Gil- mon, and Wayne Prigoff), as well as from the clinic of the Department of Advanced Study of Orthodontics for Foreign Dental Graduates at New York University, College of Den- tistry. All patients in this study were treated with the 2 x 4 appliance using the differential torque concept. No extraoral force or Class 1I elastics were used. All patients had Class II, Division 1 malocclusions with a distocclusal lower molar relationship, an excessive overjet and overbite, and no con- genitally missing teeth. The lower dental arches were rea- sonably normal. All patients were still growing during the active treatment time, and the cephalometric films that were

278 Nasiopoulos, Taft, and Greenberg Am. J. Orthod. Dentofac. Orthop. March 1992

Frankfort Horizontal

Fig. 6. Typical O.020-inch working wire with molar tip back.

Fig. 5. To evaluate forward or distal movements, a vertical reference plane was constructed, through sella turcica perpen- dicular tO Frankfort horizontal. 5

taken at the beginning and at the end of active treatment were of good quality.

In serial superimpositions, a best fit over the anterior cranial base was used, taking into consideration the detailed individual anatomy of the cranial base. Anatomic landmarks used were the anterior wall of sella turcica, the anterior con- tours of the middle cranial fossae, the contours of the crib- riform plate, the cerebral surfaces of the orbital roofs, and the cortical layers of the frontal bone (after Bjork6). A vertical reference plane, which is named "sella plane" as used by Graber, 5 was constructed through sella perpendicular to the Frankfort horizontal on the first (pretreatment) film. This plane was transferred onto the second (posttreatment) film in the series. It was used to evaluate the forward or backward (distal) movements in the horizontal plane of selected land- marks. Only linear measurements were used in this study. The anatomic landmarks that were measured were A point and anterior nasal spine (ANS), defined as the most anterior point on the inferior contour of the image of the anatomic ANS at which the vertical thickness of the structure was 3 mm (after Harvold6). The sagittal change in the crown of the maxillary first molar was measured by recording the dis- tance of the distal cementoenamel junction (CEJ) to sella plane. Also, the overbite and overjet correction were evalu- ated (Fig. 5).

Pretorqued and preangulated siamese edgewise brackets were bonded to the four maxillary incisors. Molar bands with a 0.022 0.028-inch buccal tube were cemented on the maxillary first permanent'molars.

Leveling and alignment were achieved with the use of an 0.016 inch or an 0.018-inch nitinol arch wire, when necessary;

otherwise treatment was started with an 0.016-inch stainless steel arch wire and progressed to an 0.020-inch stainless steel arch wire, which was used as the basic working wire (Fig. 6). No Class lI elastics or extraoral force was used. After Class I molar relationship was achieved, as well as overbite and overjet correction, brackets were placed on the maxillary canines and premolars to align these teeth, if necessary (Figs. 7 to 9). Class I canine relationship was established, and final detailing and finishing was achieved with a 0.021 0.028- inch nitinol arch wire or stainless steel arch wire.

DISCUSSION AND CONCLUSIONS

The 2 4 method did correct the Class II, Division 1 malocclusion. It is postulated that the technique achieves an "orthopedic effect" since it apparently mod- ifies (retards) the forward component of maxillary

growth. In the 2 x 4 method, this is due to the strong down-

ward and backward moment applied to the maxillary molars and the continuous retrusive and intrusive force on the maxillary incisors.

Although the 2 x 4 method does not appear to achieve an absolute distal displacement of the maxillary molars, it considerably retards their mesial migration. Since the mandible continues an uninhibited downward and forward growth, this retardation is the significant determinant in the correction of the Class II molar re-

lationship? Relative to overjet and overbite correction, the

2 x 4 method appears to be effective. This is due to the continuous intrusive force applied to the maxillary incisors, thus reducing the overbite, while at the same time a large downward and backward moment applied from the molars helps to reduce the overjet. The pos- sibility of elimination of functional retrusion, concur- rent with reduction of overbite and maxillary arch wid- ening, also exists.

Volume 101 Cephalometrie study of Class H, Division 1 treatment 279 Number 3

Fig, 7. Patient K.B. A, Pretreatment photograph. Note overbite and overjet. B, Bite opening, anterior retrusion, and Class I occlusion accomplished without the use of headgear or Class II elastics. C, Final result.

The question of whether the effects of the 2 x 4 method are significantly better than other techniques has yet to be investigated in a more substantive and systematic research project. A larger number of con- secutively treated 2 x 4 technique patients must be assessed. A more comprehensive cephalometric anal- ysis, evaluating both linear and angular measurements, is desirable. However, it can be suggested after this preliminary cephalometric assessment of the 2 x 4 method that the application of differential torque might be of great importance in the correction of the less severe Class II, Division 1 malocclusions. It seems to deliver beneficial results without the need for patient cooperation from extraoral force or Class II elastics.

The distance upper molar to sella plane increased less than 0.5 mm on average. The distance of ANS to sella plane was reduced on average of -0 .24 mm. The distance of A point to sella plane increased by 0.12 mm on average. These results are in contrast to most growth studies of untreated persons indicating these distances increase on average of 3 mm during the age span stud- ied. 70verjet reduction of 4 mm and overbite reduction of almost 3 mm showed the effectiveness of this ap- proach in establishing normal overjet and overbite (Table I).

SUMMARY

A pilot study was designed i n which 19 growing patients with Class II, Division 1 malocclusions who

Fig. 8. Patient J.B. A and B, Pretreatment photographs, 100% overbite, and Class II posterior occlusion.

280 Nasiopoulos, Taft, and Greenberg Am. J. Orthod. Dentofac. Orthop. March 1992

Fig. 9. Patient J.R. A, Bite opening with upper and lower 2 x 4 appliance. B, Note beginning im- provement in posterior occlusion and canine relationship. C, Open molar contact points due to molar crown distallization.

Table I. Posttreatment cephalometric results

Variable Mean J (mm) SD

6 to sella plane + 0.415 (2.174) ANS to sella plane -0 .242 (1.644) A to sella plane + 0.121 (1.765) Overjet reduction - 4.068 (3.158) Overbite reduction - 2.821 (1.96)

underwent 2 x 4 appliance therapy were studied cephalometrically to determine whether there is merit in applying differential torque in treatment, without extraoral force or Class II elastics.

The pretreatment and posttreatment lateral head films of these patients (6 boys and 13 girls) were traced by postgraduate students in the Advanced Study of Orthodontics for Foreign Dentists at New York Uni- versity.

Findings indicate that the 2 x 4 method presents encouraging results, according to linear measurements of A point, ANS, distal CEJ of the maxillary first per- manent molar, and overjet and overbite reduction.

Since the 2 x 4 method requires minimal patient cooperation it may be suggested that it could be an alternative treatment method or at least an initial treat- ment regimen. The findings of the preliminary cepha-

lometric assessment justify the design of a more thor- ough research project to evaluate the results of the 2 x 4 method in more detail.

We thank Dr. Eugene Hittleman, Associate Professor of the Department of Behavioral Science Programs at New York University, Col lege of Dentistry, who supplied the statistical analysis and evaluation for our study.

REFERENCES 1. Klein PL. An evaluation on cervical traction on the maxilla and

the upper first permanent molar. Angle Orthod 1957;27:100-61. 2. Mulligan TF. Common Sense Mechanics. Phoenix: CSM, 1982. 3. Jacobson A. A key to the understanding of extraoral forces. AM

J ORTHOD 1979;75:361-86. 4. Burstone CJ, Koenig HA. Creative wire bending- The force sys-

tem from step and V bends. AM J ORTHOD DENTOFAC ORTHOP 1988;93:59-67.

5. Mills CM, Holman RG, Graber TM. Heavy intermittent cervical traction in Class II treatment: a longitudinal cephalometric as- sessment. AM J ORTHOD 1978;74:361-79.

6. Ghafari J, Engel FE, Laster LL. Cephalometric superimposition on the cranial base: a review and comparison of four methods. AM J ORTHOD DENTOFAC ORTHOP 1987;91:403-13.

7. Poulton DR. A three-year survey of Class II malocclusion with and without headgear therapy. Angle Orthod 1964;34:181-93.

Reprint requests to: Dr. Leo Taft Advanced Study of Orthodontics N.Y.U. Dental Center, 8th Floor 345 E. 24th St. New York, NY 10010