Evaluation of continuous arch and segmented arch leveling techniques in adult patients ,a clinical study

Frank J. Weiland, DDS," Hans-Peter Bantleon, MD, DDS, PhD, b and Helmut Droschl, MD, DDS, PhD ~

Graz and Vienna, Austria

The purpose of this study was to compare the efficacy of overbite correction achieved by a conventional continuous arch wire technique and the segmented arch technique as recommended by Burstone. The sample comprised 50 adult patients (age 18 to 40 years) with deep bites. Twenty-five patients were treated with a continuous arch wire technique (CAW); in the second half of the sample, the segmented arch technique (Burstone) was used for correction of the vertical malocclusion. Lateral cephalograms and plaster cast models taken before and immediately after treatment were evaluated. Statistical analysis was performed on the collected data. The results showed that both techniques produced a highly significant overbite reduction (CAW: -3.17 mm, p < 0.001; Burstone: -3.56 mm, p < 0.001). The CAW group showed an extrusion in the molar area with subsequent posterior rotation of the mandible (6occI-ML: +1.30 mm; 6occI-NSL: +1.63 ram; ML/NSL: +1.94 ~ all p < 0.001). The Burstone group, however, showed overbite reduction by incisor intrusion without any substantial extrusion of posterior teeth (upper 1-NSL: -1.50 mm; lower 1-ML: -1.72 ram; both p < 0.001). As a consequence, no significant posterior rotation of the mandible took place (ML/NSL: +0.52 ~ n.s.). It is concluded that in adult patients the segmented arch technique (Burstone) can be considered as being superior to a conventional continuous arch wire technique if arch leveling by incisor intrusion is indicated. (Am J Orthod Dentofac Orthop 1996;110:647-52.)

Deep overbite is a common condition in adults. ' Because of potentially detrimental effects on mandibular and temporomandibular joint function, 2-4 and periodontal health, 5 as well as for esthetic reasons, 6 deep overbite correction is often a major component of orthodontic treatment. It has been shown that ortho- dontic correction of deep bite can be achieved in patients with no growth left. 7I~ This correction can be performed by extrusion of molars, intrusion of incisors, or by a combination of both.

In certain cases, intrusion of incisors is absolutely indicated to reduce deep overbite. One example is overerupted incisors, frequently seen in Class II, Divi- sion 2 malocclusions. 12''3 Moreover, if elongation of front teeth after loss of periodontal support has oc- curred, intrusion of these teeth is indicated. 9''4

It has been stated that arch leveling with continu- ous arch wires in both growing and nongrowing pa-

Supported by the Fonds zur Frrderung der Wissenschaftlichen Forschung, Vienna, Austria; grant P7477. aAssistant professor, Orthodontic Department, University Dental School, Graz, Austria. bProfessor and chairman, Orthodontic Department, University Dental School, Graz, Austria. "Professor and chairman, Orthodontic Department, University Dental School, Vienna, Austria. Reprint requests to: Dr. Frank ]. Weiland, Orthodontic Department, University Dental School, A-8036 Graz, Austria. Copyright 9 1996 by the American Association of Orthodontists. 0889-5406/96/$5.00 + 0 8/1/64369

tients will produce extrusion in the molar area, 8 whereas a segmented approach with bioprogressive mechanics predominantly produces incisor intrusion with molar extrusion to a lesser degreeff No data regarding a direct comparison between the effects of different types of bite-opening mechanics in adult patients were found in the literature. This study was performed to analyze the skeletodental changes occur- ring during deep bite correction with a conventional continuous arch wire technique and the segmented arch technique as recommended by Burstone. '5-'8

MATERIALS AND METHODS

The sample of this study consisted of 50 adult patients treated in the Department of Orthodontics at the University Dental School in Graz, Austria. All patients showed low- angle, deep bite (overbite greater than 4 mm) malocclusions and were at least 18 years old. Twenty-five patients were treated with a continuous arch wire (CAW) technique with a pretorqued and preangulated bracket system. Second-order bends were used when indicated. Mean age of this group was 23.3 years (range 18 to 35.3 years) at the beginning of treatment. There were 8 men and 17 women in this group. The other half of the sample (5 men and 20 women) was treated with the segmented arch technique as recommended by Burstone. '5-t8 The same preadjusted appliance was used in the second group. Intrusive mechanics were used in both arches in all 25 patients. The point of intrusive force appli- cation was individualized, depending on the desired tooth

647

648 Weiland, Bantleon, and Droschl American Journal of Orthodontics and Dentofacial Orthopedics December 1996

34 35

.2

1 36

Fig. 1. Cephalometric landmarks used in study.

movement, according to data in the literature. 19 An intrusive force of 10 to 15 gm per tooth was used. After correction of the vertical malocclusion with intrusive mechanics, treatment was continued with continuous arch wire mechanics similar to those in the first group. Mean pretreatment age of this sample was 25.6 years (range 18.7 to 40.3 years). The treatment period of the Burstone group was 4 months longer than that of the continuous arch wire group (Table I). A transpalatal arch wire was applied in all patients to enhance posterior stabilization. No headgear was used in either group. In 12 patients (eight from the CAW group, four from the Burstone group) teeth were congenitally missing, already extracted before, or were extracted during treatment.

Lateral cephalograms and plaster cast models were made before and immediately after treatment. Each cephalogram was traced by two investigators independently on acetate paper with a 0.3 mm lead pencil. Forty-two reference points were marked on each radiograph (Fig. 1). All bilateral structures were located midway between the two images. The points were digitized, and the mean coordinates of the two tracings stored in a computer for analysis. The midpoint between the incisal edge and the apex of the upper and lower incisors was calculated and used for analysis of vertical incisor position. Seven angular and nine linear measurements were selected for cephalometric analysis (Fig. 2). No correc- tion for linear enlargement was made. Dental changes were assessed by superimposing pretreatment and posttreatment cephalograms on the nasion-sella line (upper dental changes) and the mandibular plane (lower dental changes). Overbite reduction was analyzed by the change inthe vertical overlap of the upper and lower incisors, measured on the pretreat- merit and posttreatment plaster cast models, perpendicular to the occlusal plane.

Statistical analysis involved comparison of the pretreat- ment values of the two groups by means of Student's t test to assure comparable samples. Means and standard devia- tions for each variable were calculated. The changes that occurred during treatment were compared within each group,

. . . . . . . . . . . . . . ir

t i

, I

16

,5 !! t t I i

i i r t 1

;i . . . . . . J . _ . t _

Fig. 2. Linear and angular cephalometric measurements. Var. 3 (Bj6rk polygon) = a + b + var. 2

as well as between the groups. The p < 0.05 confidence level was considered significant.

RESULTS

Analysis of the pretreatment data revealed no sta- tistically significant difference between the two groups. Comparison of pretreatment and posttreatment values of each group, as well as treatment changes between the groups are shown in Tables II to IV. Composite tracings showing the mean treatment effects in both groups are shown in the Figs. 3 and 4.

Cast analysis

Treatment-induced reduction in overbite was simi- lar and highly significant in both groups (CAW group =-3 .17 mm, Burstone group =-3 :56 mm; both p < 0.001). Resulting posttreatment overbite was 2.2 and 2.5 ram, respectively; this intergroup difference was not significant.

Maxillary dental changes

The CAW group showed some upper incisor up- righting (upper 1/NSL=-2.35 ~ n.s.) and retraction (upper 1-NPg = -1.61 mm, p < 0.01), whereas the Bur- stone group showed minor bodily retraction of the upper incisors. This change, however, was not signif- icant. Intrusion of the upper incisors in the Burstone group (p < 0.001) was significantly different (p < 0.05) from the stable vertical position these teeth displayed in the CAW group. Upper molar extrusion occurred in the CAW group (6occl-NSL = +1.63 mm, p < 0.001). This was in contrast to the stable position in the Burstone group (intergroup difference: p < 0.01).

American Journal of Orthodontics and Dentofacial Orthopedics Weiland, Bantleon, and Drosch l 64g Volume 110, No. 6

Table I. Description of the sample

Groups N

CAW 25 Burstone 25

Se)c

M W

8 17 5 20

Malocclusion Age O'rs. I

Class 11, Class 11, I Class l Division 1 Division 2 N Mean Minimum Maximum

9 10 6 25 23.3 18.0 35.3 3 13 9 25 25.6 18.7 40.3

Treatment time (yrs., mos.) "[ .....

Mean Minimum Maximum

2,2 0.8 5,2 2,5 0,9 4,3

Table II. Comparison of pretreatment and posttreatment values of continuous arch wires

Variables Unit

1, Overbite (cast) mm 2. S-At-Go degrees 3. Bj6rk polygon degrees 4, Y-axis degrees 5, ML-NSL degrees 6. Anterior face height mm 7. Lower anterior face height mm 8, Upper I -NSL degrees 9, Lower I -ML degrees

10. Upper 1-NPg mm 11. Lower l-NPg mm 12. Upper 1-NSL mm 13, Lower I-ML mm 14. Lower l-Occlusal plane mm 15. 6occl-ML mm 16, 6occl-NSL mm 17. Occlusal plane-XiPm degrees

7"1 T2

Mean ] SD Mean l SD Mean

5.39 1.37 2.22 1.01 -3.17 142.16 7.15 143.51 7.36 +1.35 388.03 7.43 389.90 7.39 +1.87 65.79 3.59 67.20 3.62 +1.41 28.04 7.41 29.98 7.45 + 1.94

119.80 6.66 122.30 6.55 +2.50 66.07 5.56 68.42 5.69 +2.35

101.69 9.30 99.34 805 -2.35 91.60 7.90 97.31 7.12 +5.71 6.34 5.24 4.73 396 -1.61 0.98 4.39 2.07 3.90 + 1.09

70.18 4.57 69.92 4.12 0.26 29.96 5.19 28.93 4.91 - 1.03

3.83 2.33 1.13 1.31 -2.70 31.06 2.80 32.36 2.88 +1.30 70.72 4.11 72.35 4.95 +1.63 18.04 6.09 16.57 5.21 - 1.47

T2- T1

I SD Significance 1.67 *** 2.52 ** 1.17 *** 0.94 *** 1.28 *** 2.71 ** 2.22 ** 9.58 ns 8.90 ** 3.17 ** 2.18 ** 1.55 ns 1.55 ** 2.52 *** 1.43 *** 1.90 *** 5.64 ns

T1, Pretreatment; T2, posttreatment; *significance at p < 0.05 level; **significance at p < 0.01 level: ***significance at p < 0.001 level.

Table IlL Comparison of pretreatment and posttreatment values of segmented arch wires (Burstone)

Variables Unit

1. Overbite (cast) mm 2. S-Ar-Go degrees 3. Bj6rk polygon degrees 4. Y-axis degrees 5. ML-NSL degrees 6. Anterior face height mm 7. Lower anterior face height nun 8. Upper 1-NSL degrees 9. Lower 1-ML degrees

10. Upper I-NPg mm 11. Lower I-NPg mm 12. Upper I-NSL mm 13. Lower I-ML mm 14. Lower l-Occlusal plane mm 15. 6occl-ML mm 16. 6occt-NSL mm 17. Occlusal plane-XiPm degrees

TI T2 T2-TI

Mean SD Mean [ SD Mean

6.10 1.76 2.54 1.14 -3.56 143.99 6.85 144.60 7.04 +0.61 389.11 5.35 389.62 5.74 +0.51 66.92 3.41 67.01 3.44 +0.09 29.12 5.38 29.64 5.74 +0.52

121.47 9.25 122.25 9.95 +0.78 66.52 6.90 66.90 7.35 +0.38 99.82 8.86 99.72 4.24 -0.10 92.38 9.72 96.32 7.90 +3.94 5,82 6.17 4.30 3.49 - 1.52 0.16 4.19 0.44 3.01 +0.28

71.64 5.58 70.14 5.80 - 1.50 30.19 4.13 28.47 4.58 -1.72 3.08 1.63 1.21 1.46 -1.87

32.32 2.69 32.88 2.59 +0.56 73.19 529 73.05 5.54 -0.14 17.05 5.49 15.72 4.74 -1.33

SD Significance

1.76 *** 1.94 ns 1.62 ns 2.04 ns 1.62 ns 2.13 * 1.94 ns 7.20 ns 7.70 ** 5.08 ns 3.54 ns 1.28 *** 1.90 *** 2.08 *** 1.06 ** 1.50 ns 4.76 ns

T1, Pretreatment; T2, posttreatment; *significance a! p < 0.05 level; **significance at p < 0.01 level; ***significance at p < 0.001 level.

Mandibular dental changes

Significant proclination of the lower incisors oc- curred in both groups (CAW: +5.71 ~ , p

650 Weiland, Bantleon, and Droschl American Journal of Orthodontics and Dentofacial Orthopedics December 1996

i CONTINUOUSARCH WIRES T1 T2 . . . . .

Fig. 3. Composite tracing of treatment changes in CAW group.

Table IV. Comparison of treatment changes between the two groups continuou

Variables Unit

arch versus segmented arch (Burstone)

Continuous arch Segmented arch

T2-T1 T2-T1

Mean SD Mean SD Significance

1. Overbite (cast) mm -3.17 1.67 -3.56 1.76 ns 2. S-At-Go degrees +1.35 2.52 +0.61 1.94 ns 3. Bjtirk polygon degrees +1.87 1.17 +0.51 0.93 ** 4. Y-axis degrees +1.41 0.94 +0.09 2.04 ** 5. ML-NSL degrees +t.94 1.28 +0.52 1.63 ** 6. Anterior face height mm +2,50 2.71 +0.78 2.13 * 7. Lower anterior face height mm +2.35 2.22 +0,38 1.94 ** 8. Upper 1-NSL degrees -2.35 9.58 -0.10 7.20 ns 9. Lower 1-ML degrees +5.71 8.90 +3.94 7.71 ns

10. Upper 1-NPg mm -1.61 3.17 -1.52 5.08 ns 11. Lower 1-NPg mm +1.09 2.18 +0.28 3.54 ns 12. Upper 1-NSL mm -0.26 1.55 -1.50 1.28 ** 13. Lower 1-ML mm -1.03 1.55 -1.72 1.91 ns 14. Lower 1-Occlusal plane mm -2.70 2.52 -1.87 2.08 ns 15. 6occl-ML mm +1.30 1.43 +0.56 1.07 * 16. 6occl-NSL mm +1.63 2.11 -0.14 1.49 **

17. Occlusal plane-XiPm degrees -1.47 5.64 -1.33 4.76 ns

T1, Pretreatment; T2, posttreatment; *significance at p < 0.05 level; **significance at p < 0.01 level.

in the Burstone group. The group difference was not significant. The mandibular molars were extruded sig- nificantly in the CAW group (+1.30 mm, p < 0.001), and to a much lesser extent in the Burstone group (+0.56 mm, p < 0.01). Group comparison showed sig- nificance at p < 0.05 level.

More treatment effects

The molar extrusion in the CAW group produced some posterior rotation of the mandible. This is shown by the increase of the Bj/3rk polygon (+1,87~ y-axis (+1.41~ and ML/NSL (+1.94 ~ all p < 0.001). As a

consequence, total and lower anterior face height were increased by 2 to 2.5 mm. In contrast, the vertical dimension of the face in the Burstone group did not change substantially. The intergroup differences were significant at p < 0.01 level, with exception of total anterior face height (p < 0.05).

The inclination of the occlusal plane did not change significantly in both groups.

DISCUSSION

It is possible to correct deep overbite with two differing orthodontic mechanics in adult patients. The

American Journal of Orthodontics and Dentofacial Orthopedics Weiland, Bantleon, and Droschl 651 Volume 110, No. 6

I l t l l l~rom ~

Fig. 4. Composite tracing of treatment changes in segmented arch wire (Burstone) group.

only difference between the groups regarding the treat- ment regimen was in the first phase of treatment, during which the vertical malocclusion was corrected. Whereas, in the first group of patients, the arches were leveled with continuous arch wires, in the second group, intrusive segmented arch mechanics, as recom- mended by Burstone, were used. Mean overbite reduc- tion did not differ significantly between the two groups of our sample. Absolute values (3 to 3.5 mm) corre- spond with previous reports . 7"8'm'11 Apart from some intrusion (1 ram) and flaring of the lower anterior teeth, the continuous arch wire treatment predomi- nantly caused correction of the deep bite by extrusive tooth movement in the molar area, concomitant with posterior (bite opening) rotation of the mandible. Other authors report similar results by using a straight wire appliance in adults. 7,s Possibly, the high initial vertical force levels that are generated when using continuous arch wires" in deep bite cases result in an overloading of the vertical anchorage.

It has been suggested that low, continuous forces should be applied to achieve intrusion. 2~ Proffit 2~ states that to correct a deep overbite "in the absence of growth absolute intrusion (of the incisors) is required and segmented arch mechanics must be used to achieve this." Indeed, it could be shown that seg- mented bite opening mechanics, as recommended by Burstone, result in a substantial intrusion of the upper and lower incisors. Although the vertical position of the upper molars stays approximately stable and the lower molars show an extrusive movement that is less than 40% of that seen in the CAW group, the intrusive movement of the incisor teeth accounts for the overbite correction almost completely. The low force levels

used (totaling 40 to 50 gm for four incisors) appear to have little (lower arch) or no substantial (upper arch) effect on vertical posterior anchorage, although no anchorage enhancement with a high-pull headgear, as advocated in the literature, ~7 was performed. We hy- pothesize that occlusal forces are able to prepare sufficient vertical anchorage in cases with very low extrusive force. The extent of incisor intrusion found in our sample (maxilla: 1.50 rnm, mandible: 1.71 mm) is somewhat lower than those found in patients in whom utility arches are used in the lower jaw. Several authors "'2~ state that with utility arches, it is reason- able to expect about 2 mm of incisor intrusion. The difference in our results might be explained by the fact that in all our "Burstone" patients, intrusive mechanics were applied in both the upper and the lower jaws. Therefore we hypothesize that maximum intrusion was not needed to correct the deep overbite. Great latitude exists regarding the amount of intrusion seen, which is shown by the standard deviations. This is in accor- dance with data from the literature. '~ In addition to individual biologic reactions, this may be due partly to the differing amounts of intrusive tooth movement needed in individual patients. Maximum intrusion seen was 6.6 mm in the mandible of a female patient.

These individual variations are even stronger re- garding changes in incisor inclination. This is due to the compilation of the pretreatment malocclusions, including Class I; Class II, Division 1; and Class II, Division 2 cases. Depending on the original inclina- tion, flaring of incisors can be desirable (Class II, Division 2), undesirable, or even contraindicated, as is the case in most Class II, Division 1 malocclusions. A change of incisor inclination, however, has a distinct

652 Weiland, Bantleon, and Droschl American Journal of Orthodontics and Dentofacial Orthopedics December 1996

effect on overbite. 24 As genuine intrusion of a tooth is defined as apical movement of the center of resistance in relation to a reference plane 17 an approximation of the center of resistance, defined as the midpoint be- tween the incisal edge and the apex of the upper and lower incisor, respectively, was used for analysis of the vertical position of the incisors, rather than the incisal edge.

Factors that are said to be responsible for relapse of deep bite in adult patients include, among others, molar extrusion during treatment ~4'25-27 and intrusion of incisors. 2s As the two groups of patients described in this study reacted very characteristically in one of these two ways to the differing bite opening mechan- ics, it would be very interesting to reevaluate the long-term results. A report is planned in due time.

CONCLUSIONS AND CLINICAL IMPLICATIONS

Deep overbite malocclusion can be corrected in non- growing patients by orthodontic treatment. With a conven- tional continuous arch wire technique, overbite reduction will be due mainly to extrusion of molars and some intrusion and flaring of the lower incisors. Posterior rotation of the man- dible may result. Incisor intrusion with little extrusive move- ment in the molar area, however, is found with the segmented arch technique as recommended by Burstone. In certain cases, intrusion of incisors is absolutely indicated. This holds true particularly in patients showing elongation of incisor teeth, e.g., in Class II, Division 2 cases 12'13 or after periodon- tal bone 10ss. 9'14'23'25 However, intrusion of teeth may aggra- vate the periodontal breakdown in the presence of plaque and inflammation. 293' Experiments on dogs clearly showed that orthodontic movement can shift supragingival plaque into a subgingival position, producing infrabony pockets. 32 On the other hand, though, it has been shown that orthodontic treatment, including intrusion of teeth, does not result in decrease of the marginal bone level, provided the gingival inflammation is kept to a minimum. 23'3t'32 Therefore, in periodontally involved patients, as in all adults, gingival inflammation should be brought to a minimum before start- ing orthodontic treatment and the periodontal condition su- pervised meticulously during the orthodontic procedure.

From this study, it may be concluded that the arch leveling technique, according to Burstone, can produce genu- ine intrusion of the incisors with little vertical effect in the molar area in adult patients. The application of this tech- nique, rather than using continuous arch wires therefore is indicated if correction of deep overbite by intrusion is desired.

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