ORIGINAL ARTICLES DERIVED FROM RESEARCH

OCCLUSAL PLANE INCLINATION IN CHILDREN BETWEEN 9 AND 10 YEARS OF AGE WITH POSTURAL ASYMMETRY. A STUDY ON THE FRONTAL PLANE

Juan Pablo Rebolledo Uribe¹, Patricio Andrés Pincheira Barbé², Verónica Bittner Schmidt³, Raúl Ernesto Frugone Zambra⁴

¹ Kinesiologist, private office, Chile
² Professor at the Department of Academic Outreach and Continuous Education Coordination. Universidad del Desarrollo, Concepción, Chile
³ Bioestadistics Professor, Universidad del Desarrollo, Concepción, Chile
⁴ Professor of Oral Physiology and Occlusion, Universidad del Desarrollo, Concepción, Chile

SUBMITTED: DECEMBER 6/2011-ACCEPTED: MAY 22/2012

ABSTRACT

INTRODUCTION: with the purpose of establishing the relationship between side and direction of occlusal plane inclination in children with postural asymmetry of the suprascapular unit, an observational study was conducted in 34 subjects aged 9 to 10 years.
METHODS: both postural asymmetry and occlusal plane inclination using a fox plate were measured by means of photograph analysis standardized with the Kinovea 0.7.10 software version 2.
RESULTS: 18 subjects presented a minor occipital middle cervical-scapular waist angle (MOMCSWA) to the left, with a minimum angle of 87.4°; 4 of them presented elevated occlusal plane (EOP) in the same side in relation the bipupillary plane; in 11 patients this plane was elevated to the right, and 3 did not present occlusal plane inclination. 16 of the subjects presented (MOMCSWA) to the right with a minimum angle of 87.13°; 5 of them showed EOP to the same side, in 7 patients the plane was elevated to the left, and 4 did not present occlusal plane inclination. The variables used were average and standard deviation.
CONCLUSION: this study allowed concluding that healthy kids with postural asymmetry present a tendency to have a lower occlusal plane to the side of head inclination, pr obably due to factors related do dentoalveolar growth.

Key words: occlusal plane, postural asymmetry, cranial inclination.

INTRODUCTION

The relationship between postural asymmetry and occlusal plane inclination is still an unanswered question although several studies on similar topics have been conducted.

There exists some evidence on the relationship between malocclusion and overactivation of postural musculature. This might be observed after balancing occlusion, as it produces a significant reduction of muscle activation rates as measured by surface electromyography.¹ Another study suggests repercussion of dental occlusion on visual proprioception and stabilization,² which therefore might affect posture control and its balance.

There are numerous speculations on postural asymmetry and occlusal plane inclination. Considering the close relationship between posture and stomatognathic system,³ as well as between form and function, one could infer that occlusal plane inclination in the frontal plane might vary due to changes of the suprascapular unit's general biomechanics. In 1979, Rocabado said:

[...] in presence of head and neck inclination, the mandible shifts toward the opposite side of the movement due to a mandibular compensatory effect. This produces contacts at critical apexes of the opposite side of the movement, and just slight contacts at the homolateral side [sic].⁴

On the other hand, diverse analyses on growth and development in relation to neuro-occlusal rehabilitation,⁵ as well as on the theory of functional matrices,⁶ allow explaining how occlusal plane inclination occurs as a response to functional stimuli since effects on the matrices produce structural changes in both the basal bone and the dentoalveolar region. These changes usually result in vertical growth (either as enlargement or resorption) of the basal component.⁵

Therefore, both postural/functional asymmetries and parafunctions developed by a given patient could produce structural modifications of basal bone height; a parafunctional stimulus producing severe occlusal deterioration may eventually produce a reduction of maxillary basal bone height.⁷

Based on this concept, as well as on functional matrices concepts and postural biomechanics, we suggest that if the stimulus were asymmetrical, the occlusal plane could produce functional asymmetry of its inclination at the frontal plane. This study seeks to prove the existence of a relationship between the direction of cranial inclination and the direction of occlusal plane inclination in the frontal plane of children with postural asymmetry.

MATERIALS AND METHODS

34 subjects from Escuela Santa Eufrasia in Concepción, Chile, were recruited regardless of their sex, and were evaluated at Kinesiology School of the Universidad del Desarrollo, Concepción, Chile

This study was conducted in compliance with the Helsinki Declaration. The school principal and the parents of the participating kids were properly informed, and they signed a consent form once they were aware of the characteristics of this study. Inclusion criteria comprised healthy kids aged nine to ten years with postural asymmetry of the suprascapular unit. Exclusion criteria included suprascapular pain, bruxism experience, and subjects with psychopathological conditions. The main objective was to establish the relationship between side and direction of the occlusal plane inclination in children with postural asymmetry of the suprascapular unit.

Of a total of 39 children, 34 complied with the inclusion criteria and accepted to participate in the study. Each of them was taken a standardized photograph which served as the basis for measuring the occipital middle cervical-scapular waist angle (OMCSWA) both right and left, and for observing both side and direction of the occlusal plane inclination in relation to the bipupillary plane. Once illumination adjustments had been completed, as well as camera calibration and location of the adequate implements for optimum photograph procedures, the patients were instructed on how to maintain right posture and to correctly hold a fox plate in their hands.

Round adhesive reflective markers of 1.5 cm in diameter were glued on barefoot, undressed subjects in the upper fourth.

For the posterior view four markers were used: One marker was placed 3 cm over the external occipital protuberance, the second one was located on the spinous process of the seventh cervical vertebra, and the remaining two markers were placed over each acromion process. For the photographs, each subject was requested to adopt a relaxed biped posture staring at the horizon and with their back to the camera. For the frontal view, the markers were placed on the external edge of each eye as well as on the end of the fox plate, which was previously disinfected. The fox plate was placed against the occlusal surfaces of the upper maxilla. The patients were requested to adopt a relaxed biped posture staring at the horizon facing the camera.

In order to mark the planes and to measure the angles, each photograph was analyzed by using the Kinovea 2 software, version 0.7.10. Each OMCSWA was measured in sexagesimal degrees. Each angle was established between a vertical line determined by the marker situated 3 cm over the external occipital bulge and by the one located over the seventh cervical vertebra and one horizontal line determined by the marker located over the seventh cervical vertebra and the marker situated over the spinous process. The same software was used to evaluate the occlusal plane inclination provided by the fox plate in relation to the bipupillary plane. The condition of parallelism between the occlusal plane and the bipupillary one was evaluated by measuring the perpendicular distance from the bipupillary plane and the occlusal plane under each marker of the fox plate. The measurements were given in centimeters with two decimals, and parallelism was defined when the measurements were exactly the same. Elevated occlusal plane (EOP) was defined according the shortest measure.

After the process of data collection, the figures were analyzed by means of Microsoft Office Excel 2004 and the statistical package SPSS, version 11.5 for Windows. The variables used were average and standard deviation.

RESULTS

Concerning OMCSWA, the obtained minimum angle measure on the right side of the sample was 87.13°, while the one on the left side was 87.4° (table 1).

Sixteen subjects presented a minor right MOMCSWA five of them showed EOP on the same side, seven patients presented EOP on the left side, and four of them did not present occlusal plane inclination at all (table 2).

Eighteen subjects presented left MOMCSWA, four of them showed EOP on the same side, eleven patients presented EOP on the right side, and three of them did not present occlusal plane inclination at all (table 2).

DISCUSSION

This study was performed on healthy individuals, with no parafunctional activities, and with asymmetry of the cranium's static position in relation to the pectoral girdle. It verified the ascending tendency of the contralateral occlusal plane to MOMCSWA, and therefore an ipsilateral reduction of it. Out of the total sample (34), 18 (52.94%) of the patients presented contralateral EOP to MOMCSWA (table 2 shows that 11 patients presented left MOMCSWA with right EOP, while 7 of them presented right MOMCSWA with left EOP), and 9 of them (26.47%) presented ipsilateral EOP (table 2 shows that 4 patients presented left MOMCSWA with ipsilateral EOP, while 5 of them presented right MOMCSWA with ipsilateral EOP).

Finally, 7 patients (20.58%) did not show inclined occlusal plane (table 2 shows that 3 patients presented left MOMCSWA, while 4 of them presented right MOMCSWA).

Mastication with functional loads produces tensile forces of the musculature on the periosteum, a place where communication between osteoclasts and osteoblasts occur,⁸ the latter being in charge of generating osseous growth as a result of such tension. On the contrary, one would expect that, in presence of extreme compressive forces, some loss of maxillary basal bone would occur.⁷

Tensile forces themselves serve as a growing stimulus and correspond to a periosteal matrix.⁴If a person performed masticatory functions on one side only, without producing squeezing and grinding overloads, there would be a greater growing stimulus on that side, and therefore a decrease of the occlusal plane, instead of a contralateral increase. If that person presented a bilateral mastication tendency, the occlusal plane would be more balanced in relation to the bipupillary plane. Consequently, one would think that 52.94% (18) of the sample in this study had unilateral mastication on the MOMCSWA side, and that only 26.47% (9) had contralateral mastication.

Unilateral mastication habits may be acquired for different reasons, such as lost or missing teeth, chronic pain, growth and development alterations, such as unilateral cross bite,⁹ or head inclination, to name just a few.

Concerning cranial inclination, in 1979 Rocabado suggested the possibility of the mandible contralateral shifting to the head and neck inclination side as a compensatory effect, thus producing an occlusal contact of greater strength.⁴ Under physiological conditions, the functional stimulus provokes that the occlusal plane remains relatively stable,⁵ but in presence of a postural asymmetry such as the one described in this study, asymmetric information occurs so both hemibodies would react differently before different tendonous, muscular, and proprioceptive tensions. The final result presents as structural differences of osseous units.

Biomechanically, due to gravity the mandible shifts towards the side that the cranium inclines. In case of cranium anteposition, the mandible condyle moves towards distal, and eventually also the mandible does and therefore the first occlusal contact. In case of cranium flexion, the contacts become anterior; in case of extension they become posterior, ¹⁰ and if inclination occurs they should become ipsilateral. The biomechanical logics suggest that if a body shifts towards an area, its function would move towards the same side in order to prevent additional energy waste. However, it is also possible that, given certain functional requirements, the neuromusculature system responds differently and occlusal contacts do not always follow biomechanical patterns.^{11, 12} This is why it has been suggested that in individuals with cranium inclination the mandible would tend to shift towards the same side and would function in an ipsilateral way thus producing greater ipsilateral maxillary basal bone growth and therefore occlusal plane reduction.

In the present study, although pain was included as a criterion, other dental parameters such as teeth loss were not included, and this could have altered the results. On the other hand, this study observed what occurred with the OMCSWA on both sides, taking MOMCSWA as a variable related to occlusal plane inclination. Nevertheless, one-side MOMCSWA may be due to cranium inclination as well as to ipsilateral pectoral girdle rise. Similarly, in this study parallelism was considered to be 100% equivalent in terms of the distances between the bipupillary plane and the occlusal plane. All this may have generated a tendency of the occlusal plane to drop on the side of the ipsilateral work to MOMCSWA rather than an evident difference.

This study allowed concluding that healthy kids with postural asymmetry present a tendency to have a lower occlusal plane to the side of head inclination, probably due to factors related do dentoalveolar growth. Future studies would require a larger sample in order to improve the results and to obtain greater significance.

CORRESPONDING AUTHOR

Juan Pablo Rebolledo Uribe
Benito Pérez Galdoz 1846
Villa los Castaños
Concepción, Chile
Phone number: +56 9 77 98 35 61
email addresses: jprebolledou@gmail.com, raul@frugone.com

REFERENCES