Th.e inteqolay between sagittal and vertical growth, factors

An implant study of activator treatment

Stephen Williams and Birte Melsen Aarhus. Denmark

Changes in sagittal jaw relationship are dependent on an interplay between a series of basal and dentoalveolar changes in both sagittal and vertical planes. The present article uses the implant method to examine and discuss this interrelationship as well as condylar growth and, in addition, comments on the relative value of accepted methods of expressing sagittal jaw relationship. The interplay between vertical and horizontal dentoalveolar, sutural, and condylar changes occurring relative to the occlusal plane in nineteen patients treated by means of the activator was studied quantitatively by means of the implant method. Changes in the sagittal jaw relationship were evaluated by means of the change in ANB angle and utilizing the “Wit& appraisal” with a modified occlusal plane construction. Change in sagittal jaw relationship was studied by means of a correlation analysis and shown to be largely dependent on the spatial development of the mandible; the latter was positively correlated to vertical condylar development and maxillary horizontal development but negatively correlated to increase in vertical sutural and dentoalveolar parameters. Vertical condylar development was also demonstrated to influence the rotational pattern of mandibular development. The clinical importance of controlling vertical development, sutural as well as dentoalveolar, in the treatment of sagittal discrepancies was stressed through the findings of the present study.

Key words: Activator, implant study, jaw relationship

T he relative position of the jaws in the sagit- tal plane, an important factor in the diagnosis and treatment of malocclusion, has frequently been ex- pressed as the angle formed between the points A and B described by Downs’ and the point nasion. Comment- ing on the dependency of the parameter on the inclina- tion and cranial relationship of the jaws, Jacobsen’* 3 suggested a metric approach based on the sagittal posi- tion of the jaws relative to the occlusal plane. The magnitude of the “Witts” appraisal of sagittal jaw re- lationship will, however, also be dependent on external biologic factors, namely, the inclination of the plane of reference. Thus, both methods, each with its own strength and weakness, should be considered in evalu- ation of sagittal jaw position.

While the sagittal position of the jaws is frequently assumed to be a factor in one plane of space, the inter- relationship between vertical and sagittal relationships was described by Isaacson.”

The purpose of the present study is to analyze, by means of the implant method, a series of sagittal and

From the Department of Orthodontics, Royal Dental College

vertical changes taking place during activator treatment and to study the relative contribution of sutural growth, dentoalveolar development, and condylar growth to these changes.

MATERIAL AND METHODS

The present analysis was carried out on pairs of lateral cephalograms of nineteen subjects (eleven boys and eight girls), all included in a study of the effect of activator treatment.5 The average age of the patients was 11 .O years, with a range from 9 years 3 months to 13 years 5 months. On the basis of an appraisal of their hand/wrist films, the skeletal age of the patients was estimated as being at least 1 year prior to the pubertal growth maximum. The lateral head films were taken with the patients placed in a cephalostat at a film- midsagittal plane distance of 180 cm. The resulting roentgenographic enlargement of 5.6 percent was not compensated for in the subsequent measurements. Be- fore the initiation of the study, each patient had con- sented to having tantalum implants inserted in both the maxilla (anterior = implant A, posterior = B), and mandible (posterior = C, anterior = D) in the manner and localization described by Bj6rk6 (Fig. 2). Implants

0002.9416/82/040327+06$00.60/O 0 1982 The C.V. Mosby Co 327

320 Williams and M&en Am. .i Orrhod. .4pri/ 1982

4 l

I ‘\

COP

l

02 i l

Fig. 1. Sagittal parameters measured perpendicular from im- plants A and B along COP. Superimposition: Anterior cranial base.

Fig. 2. Vertical parameters measured perpendicular to implants ABCD along COP. Superimposition: Anterior cranial base.

Fig. 3. Maxillary dentoalveolar development. Superimposition: Maxillary implants.

of different sizes were used in right and left sides of the jaws, facilitating identification and correction due to variations of the head position in the cephalostate.’ All patients presented prior to treatment with an excess overjet and overbite. On the basis of a morphologic structural analysis as described by BjGrk,’ the patients could be expected to exhibit a mandibular growth pat- tern of the anterior rotating type, resulting in more for- ward than downward movement of pogonion. During

Fig. 4. Mandibular dentoalveolar development. Superimposi- tion: Mandibular implants.

Table I. Measured and calculated parameters

1. The change in sagittal jaw relationship-ss-n-sm 2. Change in sagittal jaw relationship-The distance from AX-D,

subtracted from A,-D, (Fig. 1) Variables related to the maxilla

3.

4.

5.

6.

I.

8. 9.

Maxillary sagittal development-The distance between the im- plants A, and A, projected perpendicularly on COP (Fig. I) Maxillary vertical development (anterior)-The distance be- tween the implants A, and A, projected perpendicularily on COPV (Fig. 2) Maxillary vertical development (posterior)-The distance be- tween the implants B, and B, projected perpendicularily on COPV (Fig. 2) Maxillary vertical dentoalveolar development (anterior)-The distance A, <-> Op, subtracted from the distance A, <p> OP, (Fig. 3) Maxillary vertical dentoalveolar development (posterior&The distance B,-Op, subtracted from B,-Op, (Fig. 3) Maxillary total vertical development (anterior)-Variable 4 + 5 Maxillary total vertical development (posterior)-Variable 5+7

Variables related to the mandible 10. Mandibular sagittal development-The distance between the

implants D, and D, projected perpendicularily on Cop (Fig. 1) 1 1. Mandibular vertical development (anterior)-The distance be-

tween implants D, and D, projected perpendicularily on COpV (Fig. 2)

12. Mandibular vertical development (posterior)-The distance be- tween the implants C, and C, projected perpendicularily on COpV (Fig. 2)

13. Mandibular vertical dentoalveolar development (anterior)-The distance from D,-Op, subtracted from D,-Op, (Fig. 4)

14. Mandibular vertical dentoalveolar development (posterior)- The distance C,-Op, subtracted from C,-Op, (Fig. 4)

Condylar development 15. Condylar sagittal development-The distance Ar,-Ar, pro-

jected perpendicularily on COP (Fig. 5) 16. Condylar vertical development-The distance Ar,-Ar, pro-

jected perpendicularily on COpV (Fig. 5)

the observation period of 10 months and 2 weeks, the patients were treated with an activator of the type de- scribed by Harvold.” The activators were produced from construction bites, the heights of which exceeded the freeway space by 2 to 3 mm., and with the incisors in a sag&al edge-to-edge position. An attempt was made at preventing eruption of the maxillary molar teeth by means of a lateral bite plane, whereas free

Qjfects of’uctivutor treatment 329

Table II. Statistical description of the measured and calculated parameters

.r Min. Max. S.D. S.E.

1. Change in sagittal jaw ss-n-sn -0.84 -3.5 0.5 1.09 0.25 2. Reduction in relative sagittal jaw position (A,-D,) ~ (AZ-D,) 0.92 -1.0 3.0 1.19 0.27 3. Maxillary sagittal development AI-A,* 0.82 -0.5 2.0 0.65 0.15 4. Maxillary vertical development, sutural (anterior) A,-A,** 1.18 0.0 2.5 0.75 0.17 5. Maxillary vertical development, sutural (posterior) B,-B,** 0.97 0.0 2.5 0.86 0.20 6. Maxillary vertical dentoalveolar (anterior) (A,-Op,) - (A,-Op,) 1.08 0.0 3.0 0.93 0.21 7. Maxillary vertical dentoalveolar (posterior) (B,-Op,) - (B,-Op,) 1.11 0.0 3.0 1.09 0.25 8. Maxillary total vertical development (anterior) (var. 4 + 6) 2.21 I.0 4.5 1.15 0.26 9. Maxillary total vertical development (posterior) (var. 5 + 7) 2.08 0.0 5.5 I .46 0.33

10. Mandibular sagittal development D,-D,* 1.76 - I.0 4.0 I .44 0.33 1 1. Mandibular vertical (anterior) D,-D,** 2.71 1 .o 6.0 1.64 0.38 12. Mandibular vertical (posterior) C,-C, (COpV)** 2.97 0.0 7.0 1.77 0.41 13. Mandibular vertical dentoalveolar (anterior) (D,-Op,) - (D,-Op,) 0.55 0.0 1.5 0.60 0. 14 14. Mandibular vertical dentoalveolar (posterior) (C,-Op,) - (C,-Op,) 0.86 0.0 5.0 1.35 0.32 15. Articulare sagittal development Ar,-Ar,** - 1.53 2.0 -7.0 2.13 0.52 16. Articulare vertical development Ar,-Ar,* 4.03 0.0 9.0 2.18 0.53

*Projected on Cop. **Projected on COpV

eruption of the lower buccal teeth was encouraged by the removal of acrylic in these areas.

The patients were instructed to use their activators every night while sleeping, advice that was not always followed.

MEASUREMENTS ON RADIOGRAPHS

Sixteen variables were measured, all in relation to the occlusal plane. An occlusal plane was, therefore, constructed for both the first (OP,) and second (OP,) films as a line through the tip of the distobuccal cusp of the maxillary first molar and a point bisecting the verti- cal overbite in the anterior region.

The first and second radiographs were super- imposed on stable structures on the cranial base (lamina cribrosa, the anterior contour of sella turcica, and the medial delineation of the roof of the orbit) and a com- mon occlusal plane (COP) was constructed as an angu- lar bisector between the two occlusal planes OPi and OP,. To this, a perpendicular (COPV) was constructed from the anterior implant of the mandible on the pre- treatment radiograph, establishing a coordinate system (Fig. 2).

Sutural growth of the maxilla as well as mandibular displacement was analyzed as the change in position of the implants in relation to stable structures of the cra- nial base (variables 3, 4, 5, 10, 11, and 12) (Table I, Figs. 1 and 2). Dentoalveolar development of the maxilla and the mandible was measured relative to OP, and OPZ (variables 6,7,13, and 14) with the implants as stable references (Table I, Figs. 3 and 4).

Condylar development (Fig. 5) was expressed in the vertical and horizontal planes as movement of the point

Fig. 5. Condylar (articulare) development. Superimposition: Mandibular implants.

articulare (Ar) relative to the common occlusal plane COP (variables 15 and 16). For this purpose, the man- dibles of each pair of pictures were superimposed on their implants.

The measured parameters are described fully and illustrated in Table I and Figs. 1 to 5. All measurements were recorded to the nearest 0.5 mm./0.5”and repeated in order to estimate the error of the measurement.

STATISTICAL ANALYSIS

A statistical description of the distribution of the variable (Table II) as well as the correlation matrix between all variables was developed (Table III). The forward movement of the mandible is determined by translation and rotation. In order to evaluate the influence of the factors determining the relationship be- tween rotation and translation, namely, the vertical

An. J Orrhod. Aprrl 1982

Table III. Correlation matrix

Variable 1 2 -0.55* 3 0.26 0.16 4 -0.41 0.20 -0.55* 5 -0.66** -0.21 -0.28 0.44 6 -0.18 -0.27 -0.08 -0.14 7 -0.18 -0.07 -0.14 0.29 8 -0.43 -0. I1 -0.45* 0.61** 9 -0.52* -0.25 ~0.27 0.48”

10 PO.33 0.90** 0.57** -0.09 11 -0.41 0.07 -0.39 0.44 12 ~0.52* 0.21 -0.16 0.28 13 -0.25 0.12 -0.11 0.23 14 -0.08 0.04 0.00 -0.09 15 0.34 -0.39 0.02 -0.05 16 -0.28 0.26 0.19 0.21

I 2 3 4

*p < 0.05. **p < 0.01.

0.28 0. I 1 0.33 0.45* 0.67** 0.51* 0.67** 0.42 0.81** 0.65**

-0.12 -0.29 -0.20 -0.23 -0.08 0.29 0.63** 0.71** 0.85** 0.71** -0.14 0.57** 0.50* 0.40 0.59** 0.62** 0.07 0.06 0.36 0.54* 0.48* 0.44 0.03

-0.08 0.08 -0.51* 0.02 -0.42 0.02 0.17 PO.04 -0.46* -0.06 -0.24 -0.29 0.64** PO.05 PO.07 0.08 0.31 0.29

5 6 7 8 9 10

Table IV. Multiple regression analysis-Dependent variable: Mandibular sagittal development (Var. 10)

Vuriuhle Multiple r I’ square r .squarr change Signl$cunre

Posterior maxillary development (Var. 9) 0.55 0.30 0.30 0.076 Vertical condylar growth (Var. 16) 0.84 0.70 0.39 0.001 Sagittal condylar growth (Var. 15) 0.94 0.89 0.18 0.001 Vertical development, maxillary alveolar (Var. 7) process 0.98 0.96 0.07 0.001

sutural and dentoalveolar development in the molar re- gion and condylar growth sagittally as well as verti- cally, a stepwise regression analysis of these factors with the mandibular sagittal development (variable 10) as the dependent variable was carried out (Table IV).

RESULTS

The error of the method was of the same magnitude as previously described in implant studies carried out by one of us.iO

The changes observed in the measured variables are seen in Table II. The sagittal jaw relationship, ex- pressed as the angle ANB diminished during the period of observation by, on average, 0.84 degree, with the individual values ranging from a decrease of 3.5 de- grees to an increase of 0.5 degree (variable 1). The observed change in the relative sagittal position of the jaws (variable 2), when measured along the COP, showed an average reduction of 0.92 mm., ranging from an increase of 1.0 mm. to a decrease of 3.0 mm. The sagittal displacement of the anterior maxillary im- plant (A) as measured along the COP (variable 3) re- vealed an average forward displacement of 0.82 mm., ranging from 2.0 mm. forward to a 0.05 mm. posterior

displacement. The sagittal movement of the anterior mandibular implant (D) (variable 10) varied between a forward displacement of 4.0 mm. and a posterior dis- placement of 1 .O mm., the average being a forward displacement of 1.76 mm.

The measured components reflecting vertial de- velopment (Figs. 2, 3, and 4) reveal in like manner a high degree of variation. The total maxillary vertical development (basal and dentoalveolar) varied between 1 .O mm. and 4.5 mm. anteriorly (variable 8) and 0 mm. and 5.5 mm. posteriorly (variable 9)) the average being 2.21 and 2.08 mm., respectively. The observed vertical changes could be ascribed to roughly equal amounts of sutural growth, measured through the displacement of the implants (Fig. 2), and dentoalveolar development (Fig. 3) (anterior variables 4 and 6; posterior variables 5 and 7). The sutural vertical growth appeared slightly greater anteriorly than posteriorly. Mandibular vertical dentoalveolar development measured from the implants to the occlusal plane (Fig. 4) (variables 13 and 14) was only half that of the corresponding maxillary compo- nent (variables 6 and 7).

The interrelationship between these factors was demonstrated by the analysis of correlation (Table III).

Effects of activutor treatment 331

0.54* 0.x1** 0.34 0.15 0.27 -0.13

-0.39 -0.06 -0.62** 0.22 -0.16 0.38 -0.42 -0.09 0.59**

II 12 13 14 15

The change in the relative sagittal position of the jaws (variable 2) was considerably more closely related to the sagittal development of the mandible (variable 10, r = 0.90, P < 0.01) than to that of the maxilla (vari- able 3, r = 0.16). The analysis of correlation revealed further that forward development of the mandible (vari- able 10) was positively related to the forward develop- ment of the maxilla (variable 3, r = 0.57, P < 0.05). Likewise, a large vertical displacement of the anterior mandibular implant (variable 11) seemed to imply a large vertical growth component of the anterior maxilla (variable 4, r = 0.44). In general, a negative correla- tion was observed between sagittal and vertical growth components. Large vertical development of the man- dible (variable 11) was thus negatively correlated to forward growth of the maxilla (variable 3, r = -0.39), the latter being in like manner negatively correlated to vertical basal development of the maxilla (variable 5, r = -0.28; variable 4, r = -0.55, P < 0.05).

The vertical development of the condyle (variable 16) was, as could be expected, positively although not significantly correlated to the vertical development of the posterior part of the mandible (variable 12, r = 0.38) and negatively to the vertical development of the anterior part of the mandible (variable 11, r = -0.16). The forward positioning of the mandible (variable 10) was positively related to the amount of vertical condy- lar growth (variable 16, r = 0.29) and inversely corre- lated to the maxillary vertical dentoalveolar growth (variable 6, r = -0.29).

The result of the stepwise analysis of regression relating total maxillary vertical development of the

molar region (variable 9), condylar development sagit- tally (variable 15) and vertically (variable 16) to the forward displacement of the mandible (variable 10) can be seen in Table IV. It will be noted that the vertical development of the posterior part of the maxilla ac- counted for 30 percent of the variance in the sagittal displacement of the anterior mandibular implant. It should also be noted that vertical dentoalveolar devel- opment of the maxilla posteriorly and the development of the condyle expressed as the movement of the point articulare are factors of importance, although it must be stressed that none of these factors accounted for more than 40 percent of the total variance in sagittal move- ment of the pogonion area.

DISCUSSION

The objective of the present study was to analyze the influence of individual growth components on the changes in the interjaw relationship during activator treatment.

At the end of the observation period it was obvious that cooperation had failed completely in some of the patients, but since the present study aimed at illustrat- ing the interplay between sutural, dental, and condylar development, irrespective of mode of treatment, pool- ing the material irrespective of the degree of patient cooperation, differences of appliance design, etc. was considered valid.

Treatment effect has frequently been evaluated as change in the sagittal jaw relationship expressed as the angle ANB. Since activator treatment tends to result in a change in inclination of both the maxilla and the mandible,” the reliability of this parameter is not suffi- cient for the study of treatment effect. The Witts ap- praisal,‘, a on the other hand, is influenced by changes in the slope of the occlusal plane. As one of the objec- tives of the Harvold activator was (through selective molar extrusion) to change the slope of the occlusal plane, ‘, ii the value of this parameter also has limita- tions. In order to minimize the effect of the change in the slope of the occlusal plane, a bisector between the original and the final occlusal plane was used in this study (COP). The correlation between the changes in ANB and in the modified Witts appraisal was found to be 0.55, equivalent to a determinant coefficient of 0.30. The findings indicate that only 30 percent of the total variation in one of the parameters is determined by the other and thus confirms previous findings by Rotberg.”

The activator was constructed for the purpose of preventing upper molar eruption. Measurements of the individual components participating in the vertical de- velopment of the craniofacial complex revealed that

332 Williams rmd Melserz

vertical dentoalveolar growth, in spite of the treatment, was pronounced in the maxillary molar region. Vertical sutural growth (variables 4 and 5) was, furthermore, of the same magnitude as the maxillary dentoalveolar de- velopment (variables 6 and 7). The larger vertical dis- placement of the maxillary implants anteriorly (variable 4) than posteriorly (variable 5) indicated that a posterior tipping of the maxilla had taken place during treatment, a finding which has been reported previously.” Simul- taneously, there was a slight anterior rotation of the mandible, indicating that the vertical component of the articular displacement (variable 16) exceeded the total vertical, sutural, and dentoalveolar growth.

The forward positioning of the mandible, aiding the correction of the skeletal discrepancy, was found to be positively correlated to the vertical development of the posterior part of the mandible, a finding in agreement with Bergersen’” and Bjork and Skieller.’ When this finding is seen in relation to the demonstrated negative correlation to vertical development anteriorly, the ef- fect of the vertical condylar development on the man- dibular rotation as first illustrated by Bjork’” is clearly illustrated. When a stepwise regression analysis was applied for the purpose of determining the factors influencing the forward displacement of the anterior mandibular implant in relation to the anterior cranial base, and measured along the COP, it was found that the maxillary sutural and dentoalveolar development had a higher priority than the condylar growth.

While the movement of the point articulare relative to the mandibular implants is not synonymous with condylar growth, it has previously been used as an expression of the latter” and was considered defensible in this project, not least because of the difficulty in defining the condyle on the radiographs.

An increase in face height in the first molar region disturbs the balance of vertical development and thereby influences the displacement of pogonion in a backward direction. Variations in the vertical dimen-

Am J Orthod. April 1982

sions of the maxilla are thus highly related to sagittal discrepancies.

On this basis and in the light of the present findings, it would appear that control of the vertical dimension is imperative for an optimal forward displacement of the mandible in the correction of Class II skeletal maloc- clusions.

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