Reproducibility of natural head position in profile photographs in children aged 8 to 12 years old, with and without an auxiliary cephalostat

Abstracts

AIM: This study assessed the reproducibility of natural head position (NHP) in children. METHODS: 25 children, 12 female and 13 male, aged from 8 to 12 years old, patients of Dentistry School of the State University of Maringá were photographed. Photographs were taken in NHP, using a digital camera, with and without cephalostat. A vertical line (VL) was used as reference for measurements. The photographs were repeated after a 15-day interval respecting the same protocol. Reproducibility of NHP between both moments of photographs was evaluated using an angular measurement between the reference vertical line and a profile line, from soft pogonion and upper lip point. RESULTS AND CONCLUSION: Although some positional variations have suggested that patients in these ages should receive additional orientation on NHP photographs, there were no significant differences in reproducibility of NHP in this 15-day interval, with or without auxiliary cephalostat. NHP showed to be a good method of reproducibility in children.

Natural head position; True vertical line; Orthodontics; Children

OBJETIVO: este estudo avaliou a reprodutibilidade da posição natural da cabeça (PNC) em crianças. MÉTODOS: foram fotografados 25 pacientes da Clínica Infantil do Curso de Graduação em Odontologia da Universidade Estadual de Maringá com idades entre 8 e 12 anos, sendo 12 do gênero feminino e 13 do masculino. As tomadas fotográficas registraram a PNC com uma câmera digital e foram realizadas com e sem o uso de um cefalostato. Uma linha vertical (LV) foi usada como referência para as mensurações. Após um intervalo de 15 dias, as fotografias foram repetidas, respeitando-se o mesmo protocolo utilizado na primeira série de tomadas fotográficas. A reprodutibilidade da PNC entre os dois momentos das tomadas fotográficas foi avaliada utilizando-se a medida angular entre a linha vertical de referência e uma linha do perfil, passando pelo pogônio tegumentar e pelo ponto labial superior. RESULTADOS E CONCLUSÃO: embora algumas variações de posição tenham sugerido que os pacientes dessa idade devam receber orientações adicionais quanto à PNC, não foram observadas diferenças significativas quanto à reprodutibilidade das fotografias tomadas no intervalo de 15 dias, com ou sem a utilização do cefalostato auxiliar. Dessa forma, a PNC mostrou-se como um método de boa reprodutibilidade em crianças.

Posição natural da cabeça; Linha vertical verdadeira; Ortodontia; Crianças

ORIGINAL ARTICLE

^ISpecialist in Dentistry, Universidade Estadual de Maringá

^IISpecialist in Orthodontics and Master's Student in Integrated Dentistry, Universidade Estadual de Maringá

^IIISpecialist in Orthodontics, Centro Universitário de Maringá/Dental Press and Master's Student in Integrated Dentistry, Universidade Estadual de Maringá

^IVAdjunct Professor, Department of Dentistry and Coordinator of Postgraduate Program in Dentistry, Universidade Estadual de Maringá

Contact address

ABSTRACT

OBJECTIVES: The present study assessed the reproducibility of the natural head position (NHP) in children.

METHODS: Twenty-five children (12 females and 13 males) aged 8 to 12 years (patients at the School of Dentistry of the Universidade Estadual de Maringá PR, Brazil) were photographed. Photographs were taken in the NHP using a digital camera with and without the aid of a cephalostat. A vertical line (VL) was used as reference for the measurements. The photographs were taken again after a 15-day interval using the same protocol. Reproducibility of the NHP between both photograph sessions was evaluated using an angular measurement between the reference vertical line and a profile line passing through the soft pogonion and the upper lip point.

RESULTS AND CONCLUSION: Although positional variations have suggested that patients in this age group should receive additional orientation on NHP photographs, there were no significant differences in the NHP within a 15-day interval with or without the aid of a cephalostat. The NHP proved to be a method with good reproducibility in children.

Keywords: Natural head position. True vertical line. Orthodontics. Children.

INTRODUCTION

The natural head position (NHP) is considered the most appropriate reference for orthodontic diagnoses and the planning of treatment. The NHP is a standardized, reproducible position, with the head in an upright posture and eyes focused on a point in the distance at eye level such that the visual axis is horizontal.¹⁹

There are two methods for obtaining the NHP. In the first method, the patient's head is orientated to his or her NHP and a mark or plumb line is used as a reference point in radiographs or photographs. In the second method, known as the Estimated Natural Head Position (ENHP), a conventional cephalogram or profile photograph is taken and then rotated to the patient's NHP under the judgment of an experienced specialist, if necessary.^14,19

A number of studies have found evaluations of the NHP required in photographs and lateral radiographs to be reasonably stable.^20,26,27 However, few studies have investigated the reproducibility of these imaging methods using a similar methodology, especially regarding photographs of children.^{4,11,12,13,22,24}

According to Moorrees,¹⁹ orthodontists have disregarded the statement Downs made in 1956 that discrepancies between cephalometric facial typing and photographic facial typing disappear when a correction is made for persons in whom the Frankfurt plane does not correspond to the true horizontal line observed in the NHP. As the inclination of intracranial reference lines varies significantly, these lines may also be used as variables in cephalometric analyses. The advantage of recording the NHP resides in the fact that an either horizontal or vertical extra-cranial reference line can be used.^9,17

One of the aims of orthodontic treatment is to improve the patient's profile and not merely correct numbers based on intracranial lines. Thus, a number of authors stress that facial profile analyses obtained using the NHP should be more reliable, with anterior-posterior corrections consistent with the patient's habitual image; this is especially true for patients who are in the growth phase.^14,17,19

The aim of the present study was to evaluate the reproducibility of the natural head position in standard photographs of male and female Brazilian children from 8 to 12 years of age with and without the aid of a cephalostat.

METHODS

Profile photos were taken of twenty-five children (12 females and 13 males) aged 8 to 12 years, patients at the School of Dentistry of the Universidade Estadual de Maringá (PR, Brazil). Parents/guardians authorized the participation of their children by signing terms of informed consent. All procedures were carried out in compliance with the principles established in Resolution n° 196/96 of Brazilian National Health Council. The study received approval from the ethics committee of the Universidade Estadual de Maringá.

A digital camera (Nikon Coolpix 4500) was used in manual mode, with aperture value F 4.2 and speed adjustment 1/60, normal quality and flash positioned 90 cm from the patient. The camera was attached to a tripod (Vivitar/VPT-15) with its height adjusted such that the center of the lens was aligned with the sub nasal point of the patient. An auxiliary light source was set up in a box (32 cm³) on a metal support (132 cm in height). The box was lined with aluminum foil on the sides, black TNT fabric on the posterior portion and a white TNT fabric on the anterior portion. A 100-watt incandescent light bulb (GE) was installed in the box, positioned 68 cm from the patient.

The portable cephalostat was specifically confected for this study and consisted of a metal structure with an acrylic part to which the ear rods were attached. These structures were adjustable in the horizontal and vertical directions for the correct adaptation to the patient's ears. An adjustable device on the anterior portion of the structure parallel to floor contained a red cotton string (0.5 mm thick), which was attached to a plumb. This string was used as the vertical reference line (VL).

A mirror (83 x 100 cm) was positioned 90 cm from the floor and 190 cm from the patient to assist in maintaining posture, allowing the patient to look into his/her own eyes while the photograph was being taken. As a background for the photographs, a light box (61 x 82 cm) with four fluorescent bulbs (Phillips do Brasil _ SP, Brazil), covered with white TNT fabric was placed 70 cm from the patient. Figure 1 illustrates the arrangement of the equipment used for the photography.

The NHP was obtained following the method proposed by Solow and Tallgren²⁷ adapted to photographs with and without the aid of a cephalostat. The patient was instructed to stand in front of the mirror with his/her feet a short distance apart, back straight and looking into his/her eyes in the mirror. There was no direct influence from the operator regarding posture during the instructions and photography. The operator was limited to giving the instructions orally.

Once the patient remained stable in the NHP, the ear rods were inserted with light skin contact. At this time, the first photograph was taken (T1 with cephalostat). Next, the ear rods were removed and the patient was again instructed not to move, maintain his/her feet a short distance apart, with back straight and looking into his/her eyes in the mirror while the second photograph was taken (T1 without cephalostat). New photographs were taken after 15 days of all the children in the sample using these same procedures (T2 with and without cephalostat). The digital photographs were unaltered, stored and printed. The angle between the VL (vertical reference line) and soft tissue line Ls _ Pog' (upper lip _ tegumentar pogonium) was manually measured by a single operator (Fig 2).

To evaluate the error of method, the described angle was measured again on all photographs by the same evaluator after a period of ten days. There were no statistically significant differences between first and second measurements, as determined by the paired Student's t-test. The mean value between these values was used for statistical purposes. The Shapiro-Wilk revealed that these data exhibited normal distribution.

STATISTICAL ANALYSIS

The Shapiro-Wilk and Kolmogorov-Smirnov tests demonstrated that the variables did not exhibit normal distribution. Therefore, non-parametric tests were applied, with the level of significance set at 5%. Wilcoxon's test was used to compare the first (T1) and second (T2) means of the measurements with and without the cephalostat. The Mann-Whitney test was used to compare absolute angular differences between T1 and T2 with and without the cephalostat. The Kruskal-Wallis test was used to compare all groups.

RESULTS

Table 1 displays the results of the measurements made with and without the cephalostat and with a 15-day interval between the photo sessions. Wilcoxon's test revealed no statistically significant differences between the angle values in T1 and T2 when the photos taken with the cephalostat (p = 0.484) or without the cephalostat (p = 0.425). Table 2 displays the absolute angular differences between T1 and T2 for the photos taken with and without the cephalostat. The Mann-Whitney test revealed no statistically significant differences between the absolute angles on the images obtained with and without the cephalostat (p = 0.313). The Kruskal-Wallis test revealed no statistically significant differences between T1 and T2 values with and without the cephalostat (comp = 0.998).

DISCUSSION

The importance of the reproducibility of the NHP is justified by the fact that facial analysis is essential to orthodontic diagnoses.¹ According to Moorrees,¹⁹ little attention has been given in orthodontic publications regarding the appropriate facial orientation during photographic recording. In some cases, patients with malocclusion Class II are documented before treatment with the head tilted down and after treatment with the head tilted up in order to highlight the correction of mandible retrognathia.

The Frankfurt horizontal plane (parallel to soil) is the most commonly used reference for positioning patients during photographic or radiographic records, as recommended by Burstone.⁵ However, according to Viazis²⁸ and subsequently confirmed by Arnett and Bergman,¹ people do not assume this posture in their day-to-day life. Viazis²⁹ states that a variation of as much as 4° could be tolerated in the records based on the NHP. This margin was found in most cases in the present study. Lin and Arild¹⁵ found a large variation in the NHP of children between six and nine years of age assessed longitudinally. Few studies have evaluated children in orthodontic treatment.⁹ Angular variations tend to decrease in adult patients.²¹

Arnett and Bergman² prefer the NHP in facial analysis, stating that it does not exhibit the same variation as intercranial points. This lesser variation has been confirmed by a number of authors.^6,7,9,15,17 Thus, the NHP has been a preferred reference position for assessing facial morphology, as it is the position individuals naturally assume. Arnett et al³ detailed the analysis of soft tissues based on the philosophy of "Facial Keys", which reinforces the need for the use of the NHP.

Although the NHP is recognized in the literature as a reliable position, different methods for obtaining this position are cited.^{7,8,18,20,28,29} There are few studies on profile photographs, which hinders the discussion of what method is best for obtaining the NHP. The use of the mirror promotes better reproducibility regarding this position when compared with images obtained without the aid of a mirror.^8,14 There are divergences regarding the need for the use of a cephalostat, especially when recording the NHP in children. Cooke and Wei⁸ analyzed the use of the ear rods of the cephalostat and found no significant influence regarding the obtainment of the NHP.

The present study found that the NHP is a method with good reproducibility, corroborating previous studies.^7,8,21 It was also confirmed that the NHP can be safely used in profile photography involving children. As there was no increase in accuracy when obtaining the NHP with the assistance of the cephalostat, this device seems unnecessary. Moreover, the children reported discomfort caused by the ear rods.

In 1971, Solow and Tallgren²⁷ found a standard deviation of 2.48° in the natural position when using the self-balance method, while the standard deviation with the aid of the mirror was 1.43°. A mirror was used in the present study and the standard deviation was 1.67° without the aid of the cephalostat and 3.26° with the cephalostat.

Another situation that caused discomfort in the patients was the presence of the string representing the true vertical line (VL), which was located in front of the patient. This suggests that it would be better to position the line simulating the VL alongside rather than in front of the patient in order to avoid this possible nuisance when photographing children. Another alternative would be to attach the string to the light box.

While there were cases in which the NHP did not vary with the use of cephalostat (Fig 3), there were also cases in which the mean values were different between the two photo sessions (initial and after 15 days) (Fig 4). A similar situation occurred when the photographs were taken without the use of the cephalostat, with some cases exhibiting no significant differences between photo sessions (Fig 5) and others exhibiting considerable variation (Fig 6). In most cases, however, the measures exhibited little variability in the photographs with and without the cephalostat (Fig 7).

Foster et al,¹⁰ Ludström and Ludström¹⁷ and Rino Neto et al²⁵ all report that slight differences in the recording of the natural head position is a smaller problem than the variation in intracranial reference lines. However, clinicians should assess whether the photography was really carried out with the patient in the NHP prior to performing the facial analysis. According to Reche et al,²³ the analysis of the facial profile using standardized photographs is valid and reliable for orthodontic documentation.

Based on the protocol of the present study, the researcher did not interfere in the positioning of the patient, as the intention of the study was to observe the reproducibility of the NHP in children. However, it should be noted that, in everyday practice, there is a need for trained technicians to record the photographs in the NHP. The cases in Figures 4B and 6B clearly show that the patients were in incorrect positions, requiring a new supervised photograph record. Thus, there should be technicians trained in obtaining photos in the NHP at centers for orthodontic exams, as suggested by Rino Neto et al.²⁵ Thus, the proposal made by Lundström et al¹⁶ regarding the natural head position (NHP) is confirmed, as previously suggested by Moorrees and Kean.²⁰ This position is also reinforced by Halazonetis,¹³ who stresses the need for the calibration of technicians, since more or less prognathous facial types could be positioned wrongly. It would therefore be ideal to take repeated photos in order to certify that the patient is in the NHP. This procedure has become more feasible with the popularization and routine use of digital cameras.

CONCLUSION

Although positional variations have suggested that patients in this age group should receive additional orientation on NHP photographs, there were no significant differences in the NHP within a 15-day interval with or without the aid of a cephalostat in the present study. Thus, the NHP proved to be a method with good reproducibility in children.

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Reproducibility of natural head position in profile photographs of children aged 8 to 12 years with and without the aid of a cephalostat

Adriana Likes Pereira^I; Luciana Manzotti De-Marchi^II; Paula Cabrini Scheibel^III; Adilson Luiz Ramos^IV

Publication Dates

• Publication in this collection
  03 May 2010
• Date of issue
  Feb 2010

History

• Received
  Jan 2007
• Accepted
  Sept 2009