Análisis de datos laborales

A cephalometric appraisal of nonextraction Begg treatment of Class II malocclusions

Malcolm E. Meistrell, Jr., D.D.S., Thomas J. Cangialosi, D.D.S., Jose E. Lopez, D.D.S., and Angelica Cabral-Angeles, D.D.S.

New York. N.Y.

Initial and final cephalometric evaluations are compared in a sample of 42 patients with Class II malocclusions treated in a nonextraction manner with the Begg appliance. The sample was analyzed as a group. Subgroups of patients with Division 1 and Division 2 characteristics were analyzed separately. To depict skeletal and dental changes, measurements were made using the sella nasion, palatal, and mandibular planes as reference planes. The findings show that on the average:

(1) The upper first molar maintained its anteroposterior position at the same time that SNA was reduced. This suggests a restriction of anterior maxillary growth. (2) The mandibular first molar moved forward by 1.2 mm. Part of this change was attributed to anchorage consumption. (3) Vertical changes in both the maxilla and the mandible were found to be within the normal range. (4) No significant change in occlusal or mandibular plane angles was observed except for the Division 1 subgroup in whom a mild increase in the mandibular plane angle was observed. (AM J ORTHOD DENTOFAC ORTHOP 90:

286-295, 1986)

A basic principle underlying the Begg treatment method is, "Occlusion is never static. It is in a constant state of flux.''1 Occlusion should change simultaneously in a horizontal direction (mesial migration) and a vertical direction (continuous eruption) throughout life. P. Raymond Begg based his philosophy of treatment on his studies of the occlusion of

Australian aborigines. The corase diet of the aborigines abraded the teeth not only incisally and occlusally but also interproximally from the moment of their eruption into the dental arches. He concluded that the average loss of tooth mass as a result of attrition over the period of a lifetime was 14 mm. This has a tendency to prevent crowding as teeth migrate mesially. Attrition in modern man is minimal. In light of the horizontal and vertical changes that were observed in stone Age man's dentition, moving the maxillary dental arch distally in the correction of Class II malocclusion is

biologically unsound, according to Begg.

Although numerous articles in the orthodontic literature address different aspects of the Begg technique, it is evident that the use of this technique in the nonextraction treatment of patients with Class II malocclusions requires further clarification with regard to the movements that contribute to the Class II correction.

REVIEW OF THE LITERATURE

Originally, the Begg method was primarily an extraction technique. However, it has been observed that excellent results may be achieved using the Begg appliance for nonextraction treatment. In nonextraction treatment, some adjuncts to

38 Begg mechanics have been used, such as bite plates, extraoral force, lip bumpers, and the Margolis ACCO appliance.

However, in 1975, Cadman2 reported nonextraction treatment without these adjuncts, using pure Begg mechanics. His indications far nonextraction treatment were minimum tooth movement required, maximum intraarch space or substantial freedom to reposition the lower incisors labially in relation to the A-Po line, the presence of a good skeletal pattern, a satisfactory relationship of tooth size to arch length, and good growth potential. If these factors are present, Cadman believed it should be possible to complete nonextraction treatment within profile and denture base

requirements.

The mechanics of nonextraction treatment are essentially the same as for extraction therapy with the exception of Stage II. During the second stage of extraction treatment, the excess extraction space is closed. In nonextraction treatment, there is usually little ar no residual space remaining so that Stage II is either very short or unnecessary. Cadman suggested that the premolars should be left unbanded early in treatment to permit their extrusion during bite opening in Stage I.

Cadman theorized that unlike overbite correction by leveling with a full-banded appliance, the change from distocclusion to neutrocclusion occurs in less time and with less anchorage loss if premolars are free to adjust to the transitional occlusion. Any arch wire engagement of the premolars will interfere with occlusal correction because of increased cuspal interference, which impedes efficient bite opening and prolongs Class II elastic wear with resultant anchorage loss.

Cadman did not support this with specific data. He advised banding of premolars for the alignment of rotations and marginal ridge heights at the end of Stage I.

However, Barrer3 stated that all teeth should be banded, especially if the malocclusion is severe. Premolars are banded when the case requires a specific positional change such as rotation or alignment of marginal ridge heights. If premolars are not banded, he suggested placing an activated coil spring between the molar and canine. stage III is greatly reduced because extensive root positioning is not required. The use of Class II mechanics is minimized in the last two stages since it is needed only to maintain an edge-to-edge relationship of the anterior teeth. Therefore, anchor bends are reduced progressively as the need for elastic wear is decreased.

In the Begg technique, anchorage is a function of arch wire design and degree of tip-back or anchorage bend. To quote Swain,4

One of the paradoxical but pleasant suprises of Begg nonextraction mechanics is that the anchorage potential is often enhanced if the anchor molars have a mesial axial inclination at the commencement of treatment. The combination of normal anchorage bend force with light Class II elastic force brings about a beneficial distal tipping of the molar crowns into an upright position. Provided that the force of the Class II elastics is sufficiently light, the lower as well as the upper molar crowns actually tend to move distally. This net distal movement occurs because, although the influence of the anchorage bend simultaneously tends to tip the crown distally and the roots forward, the resistance to crown tipping is low while the resistance to root tipping is high. Consequently, crown tipping occurs rapidly and root tipping slowly. Such net distal movement of mesially inclined anchor molars can be important in non-extraction treatment because it provides more arch length for teeth anterior to the molars.

One should consider the differential response to magnitude and duration of forces. Light Class II elastic forces should be used over the shortest period of time to prevent forward drag of the lower posterior teeth, keeping anchorage loss to a minimum. One to two ounces of elastic traction is usually sufficient. Rapid bite opening that results in minimal occlusal interference is helpful in the reduction of treatment time. Patient cooperation is imperative. Lastly, the rate, amount, timing, and direction of growth can be factors for a favorable result. Therefore, success depends on a delicate balance of anchorage control, the magnitude of Class II elastic force, and the duration of the force and growth, if present.

Lateral cephalometric x-ray films taken before, during, and after treatment are useful in observing the changes that have taken place. Williams5 made a cephalometric appraisal of the characteristic responses of patients who had been treated

39 with the Begg technique. He observed the following: the lower incisors moved bodily lingually within the alveolar process of the mandible; SN-GoGn increased during the third stage; at posttreatment Point B moved forward as SN-GoGn

decreased, reducing ANB; the occlusal plane angle increased more than SN-GoGN because the heights of the posterior and anterior teeth were influenced by treatment; and as SN-GoGn decreased, Ul and SN decreased. Ll to APo is critical to lip balance and overbite reduction is stable because of torquing of the maxillary incisors.

Little can be found in the literature concerning changes taking place in nonextraction Begg treatment, specifically those changes that cause a correction from Class II to Class I. Cadman2 believed that there is distal tipping of the upper molar caused by the amount of anchor bend and the distal component of the Class II elastic force transmitted through the molar stop. He theorized that a restriction of normal maxillary growth was present. He also believed that the lower molar moved in an occlusal and slightly mesial direction because of the vertical and horizontal components of the Class II mechanics. Class II mechanics may also facilitate a functional positional change of the jaw.

Napolitano6 made a similar study. His results showed distal movement of the upper molars and mesial movement of the lower molars. He concluded that growth and appliance manipulation determined his results.

Levin7 in a review of the literature on treatment results of the Begg technique stated, "There is disagreement regarding the manner in which treatment changes are attained.''

OBJECTIVES OF THE STUDY

The purpose of this study was to determine cephalometrically the changes that occur in the dentition and supporting structures during the correction of a Class II malocclusion to a Class I relationship with nonextraction Begg mechanics.

It is expected that the findings obtained will provide a better understanding of the different factors affecting treatment, and give the clinician a better understanding of the technique and the proper indications and contraindications for its use.

MATERIALS AND METHODS

Forty-two patients treated at the clinic of the Orthodontic Department of Columbia University or at the private office of two of the authors were selected for this study. All patients had been classified as having Class II malocclusions. There were 23 girls and 19 boys in the sample. The age range at the start of treatment was 10 to 16 years with a mean of 12 years 9 months. The sample was not separated by sex because the rate of change with age for skeletal measurements used in the study is similar for both boys and girls.8 The molar relation ranged from a cusp-to-cusp relation to a full cusp, Class II relation. The overjet ranged from 0 to 14 mm with a mean of 6.5 mm and a standard deviation of 2.79 mm.

Initially, first molars, canines, and anterior teeth molars were banded (or bonded if preferred). The arches were leveled and aligned with a multiple-loop arch wire or a plain arch wire with a coaxial auxillary wire if crowding was present.

Anchorage bends were placed anterior to the molar tubes to initiate bite opening. If no bracket or cuspal interferences were observed, Class II elastics were started to consolidate interdental spaces in the maxillary arch and to begin anterior retraction. Otherwise, in order to conserve anchorage, Class II elastics should be delayed until the interferences are no longer present.

As soon as anterior segments were leveled and aligned, and all maxillary interdental spaces were closed, Australian 0.016 inch plain arch wires were prepared making sure that the intermaxillary circles were against the canine brackets. At this stage the premolars were not banded or bonded. A piece of coil spring or plastic tubing may be placed between the molar tube and the canine bracket to maintain premolar space and to protect the cheek from irritation.

The anchor bends were made of sufficient magnitude to carry the anterior segment of the arch wire to the depth of the muccobuccal fold when passive. Class II elastic traction in the range of 1 to 2 ounces was used.

40 Once Class I molar and canine relationships were achieved, the premolars were banded and engaged onto the arch wire.

Subsequently, Stage III mechanics were instituted as required. A brief torquing period was usually necessary to establish the correct axial relationship of the maxillary central incisors.

Initial and final cephalometric x-ray films were taken using a standard cephalometric technique. Pretreatment and posttreatment cephalometric evaluations were compared.

The analysis consists of three separate groups of measurements. The first group used sella as registration point and the sella-nasion line as the reference plane. From this configuration the following angular measurements were recorded:

sella nasion to Point A (SNA), sella nasion to Point B (SNB), the difference between SNA and SNB (ANB), the long axis of the most anterior maxillary central incisor to the sella-nasion plane (U1-SN), mandibular plane (a line drawn from Go to Gn) to the sella-nasion Plane (SN-MP), occlusal plane to the sella-nasion plane (SN-OP), the sella-nasion plane to pogonion (SN-Po), interincisal angle (U1-L1), and the distance in millimeters from the tip of the most anterior lower central incisor along a perpendicular to the line connecting Point A to pogonion (L1-APo).

The second group of measurements used the palatal curvature as registration point and the palatal plane as the reference plane. For this purpose the palatal plane was defined as a Cartesian x axis, and the intersection between the palatal plane and the perpendicular line from the tip of the maxillary first molar of the initial headplate was defined as the origin. Relative to this system, the initial and final positions of the mesial cusp of the maxillary first molar were measured. Measurements were made in millimeters, perpendicular and parallel to the palatal plane, to determine the X and Y coordinates.

The third group of measurements was made using the mandibular symphysis as registration and the mandibular plane as reference plane. Again the reference plane (mandibular) was used as the Cartesian x axis and the intersection between the mandibular plane and a perpendicular line to the tip of the mesial cusp of the lower first molar of the initial headplate was defined as the origin. Relative to this position, the initial and final positions of the tip of the mesial cusp of the

mandibular first molar were measured perpendicular and parallel to the mandibular plane (X and Y coordinates) in millimeters.

All measurements were made for each of the 42 cases whenever possible. The computations were made for the whole sample group and for a 15-case subgroup of Class II, Division 1 malocclusions and a 10-case subgroup of Class II, Division 2 malocclusions.

The data were analyzed using a DEC 10 computer and the SPSS program. Mean, standard deviation, standard error, and t test for the difference of the means between initial and final values were computed for all angular measurements and for the difference in X and Y positions for upper and lower first molars.

In addition, each cephalogram was superimposed on millimeter graph paper. To make the superimposition, sella was defined as the origin (point o,o) and the sella-nasion plane was defined as the x axis. X and Y coordinate values were recorded for each of the following landmarks: nasion, anterior nasal spine, posterior nasal spine, Point A, Point B, tips of the crown and root of the most anterior maxillary central incisor, tip of the mesial cusp of the maxillary first molar, tips of the crown and root of the most anterior mandibular incisor, tip of the mesial cusp of the mandibular first molar,

pogonion, gnathion, and gonion. The values of the X and Y coordinates for each of the landmarks were averaged in total, and for Division 1 and Division 2 subgroups separately. These averages were used to construct composite graphic representations of the changes that occurred during treatment.

RESULTS

Figs. 1 and 2 graphically summarized Table I, which shows the changes observed in the relationship of the maxillary and mandibular first molars to their respective basal bones.

41 Table II shows the average changes computed for each of the measurements using the complete sample of 42 cases.

Tables III and IV show the average changes for the Class II, Division 1, and Class II, Division 2 subgroups, respectively.

Fig. 3 is a composite graphic representation of the average changes that were recorded for the complete sample. Figs. 4 and 5 are composite graphic representations of the average changes observed in the Division 2 and Division 1 subgroups, respectively.

As may be observed, the maxillary first molar had an average change of 0.22 mm mesially. The standard deviation was 2.24 and the range was 5.0 mm distally to 5.0 mm mesially. The maxillary first molar had a mean movement of 2.1 mm occlusally or away from the palatal plane. The standard deviation was 2.32 mm with a range of 6.0 mm gingivally to 9.0 mm occlusally.

The mandibular first molar showed an average change of 1.2 mm mesially. The standard deviation was 2.76 mm and the range was 7.5 distally to 7.0 mm mesially. The mandibular first molar had a mean occlusal movement of 2.6 mm. The standard deviation was 3.01 mm and the range was 6.0 mm gingivally to 9.0 mm occlusally.

There was a mean decrease in SNA of – 0.73° with a standard deviation of 2.77 and standard error of 0.43. The t value was 1. 73, indicating a nonsignificant change in SNA with P = 0.091. SNB displayed a mean increase of 0.58° with a standard deviation of 2.22 and a standard error of 0.34. The t value was 1.71 with P = 0.096, indicating the change in SNB was not significant. However, the mean change in the ANB angle of – 1.27 with standard deviation of 2.27, a standard error of 0.35, and a t value of 3.64 (P = 0.001) shows a statistically significant change for the entire sample. The change in the ANB angle was not significant for the Division 1 subgroup, but was statistically significant in the Division 2 subgroup (P

= 0.008) (Tables II, III, and IV).

As shown in Table II, the average initial value for Sn-GoGn was 28.69°. The average final value was 28.61°. This value shows a nonsignificant difference of – 0.08° with standard deviations (SD) of 5.69 and 6.46 for the initial and final values, respectively. The standard errors (ER) were 0.00 and 0.99. The Student t test gave a value of 0.16 and P = 0.876.

The average change in the mandibular plane angle in the Division 1 subgroup, as presented in Table III, was 1.2° with a standard deviation of 2.5 and a standard error of 0.6. The Student t test value of 1.91 indicates a nonsignificant change (P

= 0.077). The Division 2 subgroup had a mean change in the mandibular plane angle of – 0.05°. The Student t value was 0.05 (P = 0.077), indicating that the change was not significant.

The SN-OP angle had an average change of – 0.37°. Student t value of 0.63 failed to show a significant change with treatment (P = 0.531). The average change in the Division 1 subgroup was 1.5°. The Student t test value of 1.85 shows a nonsignificant increase (P = 0.085). The Division 2 subgroup also showed a nonsignificant change of 0.2°. The t value was 0.12 (P = 0.909).

The SN-Po angle, which was used as an indicator of growth during treatment, had a mean change for the entire sample of 0.92° with a standard deviation of 1.79, a standard error of 0.27, and a t test value of 3.32 (P = 0.010). This change is statistically significant. However, the changes found for SN-Po for the Division 1 and Division 2 subgroups were not statistically significant. See Tables III and IV.

The maxillary central incisor did not show a statistically significant change in relation to SN for the total sample (P = 0.537). However, when the individual subgroups were examined, there were significant changes in U1-SN. The change for the Division 1 subgroup was – 5.03 with a standard deviation of 5.19, a standard error of 1.34, and a t value of 3.76 (P = 0.002). The change in the Division 2 subgroup was 9.25 with a standard deviation of 8.34, standard error of 2.64, and a t value of 3.51 (P = 0.007). See Tables III and IV.

The mandibular incisors showed statistically significant changes in both their angular relations to the mandibular plane and their spacial relations in terms of the A-Po line. For the entire sample, L1-MP increased 3.67° with a standard

42 deviation of 6.49, standard error of 1.00, and a t value of 3.66 (P = 0.001). The change for the Division 1 subgroup was 3.87° with a standard deviation of 6.16, standard error of 1.59, and a t value of 2.43 (P = 0.029). The Division 2 subgroup increased 5.40° with a standard deviation of 6.35, standard error of 2.01, and a t value of 2.66 (P = 0.025). The spatial relation of the mandibular incisors changed significantly for the entire sample. L1-APo increased 1.68 mm with a standard

42 deviation of 6.49, standard error of 1.00, and a t value of 3.66 (P = 0.001). The change for the Division 1 subgroup was 3.87° with a standard deviation of 6.16, standard error of 1.59, and a t value of 2.43 (P = 0.029). The Division 2 subgroup increased 5.40° with a standard deviation of 6.35, standard error of 2.01, and a t value of 2.66 (P = 0.025). The spatial relation of the mandibular incisors changed significantly for the entire sample. L1-APo increased 1.68 mm with a standard