Natural head position


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Natural head position

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. INTRODUCTION: Cephalometrics has given us a different prespective of interpreting various skeletal problems in the dentofacial complex. However, the promise of the cephalometrics as a diagnostic and prognostic tool is yet to be fulfilled.
  3. 3. Limitations of cephalometry:  Errors of projection: Magnification Distortion  Errors of identification Radiograph quality Reproducibility  Unpredictability of growth  Limitations in suerimpositioning
  4. 4. Errors due to 1.use of intracranial reference planes 2.patient positioning in the cephalostat
  5. 5. Intracranial reference planes:  Indv. variations in reference lines - different interpretation of subjects with similar profiles.
  6. 6.  Variations in the reln. bet. reference lines - different evaluation of facial skeletal pattern  Does not always reflect the clinical appearance of the individual subject.
  7. 7.
  8. 8. CAMPER’S LINE: First orientation plane to orient cranium on a horizontal from the middle of EAM to ANS
  9. 9. Sella- Nasion Plane :  Antero posterior extent of ant. cranial base.  Steiner – the S & N points move only minimally when head deviates from the true profile position & even when head is rotated in the cephalostat
  10. 10. Inclination of SN plane: Bjork AO 1951 – earliest to report unreliability Drawbacks of S-N plane: Downward- facial angles decrease Upward- facial angles increase
  11. 11. Mcnamara AO 1981 – Cephalometric maxillary retrusion in cl.II cases is due to low inclination of the skull base
  12. 12. The anterior skull base (S-N) is unstable in growing persons. • Nasion - landmark on an actively growing suture, - moves forward, upward, or downward in growing children • Sella- its geometric center is unstable since the pituitary gland enlarges during growth.
  13. 13. • The S-N line may therefore rotate slightly over time - results in a considerable back or forward swing of the chin.
  14. 14. Sella is totally unrelated to the structures of the face and therefore cannot be used to measure facial development ( ELLIS & MC NAMARA)
  15. 15. Frankfort horizontal plane The plane through left and right porion and left orbitale , (in 1884 by craniologists), - the best compromise for orientation of crania.
  16. 16. Drawbacks of FH plane: Downs(1956) - the discrepancies between Cephalometric and photographic facial typing disappear when a correction is made for those persons in whom the "Frankfurt plane" is not horizontal.
  17. 17.
  18. 18. Anatomical location of porion Machine porion Anatomic porion Individual variation Vertical relationships with other intracranial landmarks – biologic variation
  19. 19.
  20. 20. Occlusal plane: Drawn thru’ the region of overlapping cusps of I premolar & I molars (Jacobson Wit’s Appraisal) • To eliminate the effect of rotation of the jaws • Variation in the A-P relation of the jaws with respect to cranium
  21. 21. Disadvantages: • Affected by occlusal plane angle & vertical alveolar relationships • Affected by vertical distance between points A & B
  22. 22. • Any change in occlusal plane during treatment allows variation • Growth related changes cannot be determined
  23. 23. Patient positioning in a cephalogram: Patient aligned within ear rods of the cephalostat exerting moderate pressure on EAM. Patient’s FH placed parallel to the floor canthomeatal line placed 10 degrees to floor Locking nasal positioner against bridge of nose
  24. 24.
  25. 25. Disadvantage of ear rods: Greenfield AJO 1989 Fixed position of cephalostat - cannot be adjusted forward, backward, sidewise, or rotated. - The subject moves his head to fit the ear rods, ( altering the angulation of the head and neck ).
  26. 26. If the transmeatal axis is not perpendicular to the midsagittal plane- immobilization of the head with ear rods introduces asymmetry Moorrees and Kean(1958).
  27. 27.
  28. 28. Definition : AJO 1994 Moorrees - A standardized and reproducible position of the head, in an upright posture, the eyes focused on a point in the distance at eye level, which implies that the visual axis is horizontal.
  29. 29. Advantages of NHP: It provides the use of an extracranial reference line (true vertical or horizontal) for cephalometric analysis. NHP should be the preferred for profile evaluation as it reflects the everyday true life appearance of people. (COOKE 1986)
  30. 30.
  31. 31. The natural head position is relatively constant over time. (MOORREES &KEAN 1958) Facial photograph and cephalometric radiograph in NHP - direct correlation bet. real-life appearance and tracing.
  32. 32. Natural head posture: Developed by Molhave for studying the biodynamics of the human body. Natural head posture is a physiologic position -"orthoposition" - characteristic for a person and reproducible, but differs among persons.
  33. 33. defined as a small range of positions oscillating around the subject's mean NHP. (Lundstrom EJO 1991) Head posture is a dynamic concept and ideally its measuration should be performed in a dynamic and continuous manner.
  34. 34. Postural control of the head is influenced by Resistance to gravity Respiration Deglutition Sight (visual axis) Vestibular balance mechanism Hearing
  35. 35. For Cephalometric analysis, the standardized NHP is preferable to natural head posture (MOORREES)
  36. 36. Ortho position: ―The momentary interim position when taking the first step forward from a standing to a moving or walking posture.― Ortho position is the most reproducible habitual symmetrical standing position. Solow and Tallgren
  37. 37. NATURAL HEAD ORIENTATION: ― The head orientation of the subject perceived by the clinician, based on general experience, as the NHP in a standing, relaxed body and head posture, when the subject is looking at a distant point at eye level.‖
  38. 38. Lundström and Lundström AJO1995 The NHO related horizontal line standardized to a line through Sella is the best reference for clinical cephalometric analysis when head positions registered at NHP are unnaturally flexed
  39. 39.
  40. 40.
  41. 41. Readily registered by instructing the subject standing or sitting in the cephalostat to look at a point on the wall in front, exactly at eye level. A small mirror (diameter no more than 10 cm), the midpoint of which also at eye level, can be used also for head orientation.
  42. 42. •The wire plumb line – record the true vertical Plumb line bisects the reflection of the subject's face in the mirror and minimize lateral head rotation.
  43. 43. The location of the central x-ray beam -determined by a projected light cross ("+"). Magnification standardized by the plumb line bisecting the reflection of the subject's face in the mirror.
  44. 44. To prevent the swaying , define the feet position as "a comfortable distance apart and slightly diverging― (Cooke 1986)
  45. 45. Solow & Tallgren Acta Odontol. Scand. 1971
  46. 46. REHEARSAL PHASE: • Patients placed facing a neutral wall (nothing to distract ). • Carefully observe the patient's posture before the actual rehearsal takes place, • The patient walks from the waiting area to the radiographic room.
  47. 47. BODY POSTURE. Mølhave(1958) -the most reproducible natural standing position is the orthoposition Small children - to place heels together and let the arms hang. Older and tense patients - "walk on the spot'' & to raise and drop shoulders to ease tension.
  48. 48. HEAD POSTURE. - two methods (SOLOW 1971)  The subject's own feeling of a natural head position ―the self-balance position.‖  Based on visual cues from external reference
  49. 49.  Positioning according to external reference - carried out only after the head has been placed in the self-balance position.  In adults the head is kept, on the average, 3 degrees higher in the mirror position than in the self-balance position.
  50. 50.
  51. 51. If the earrods are not aligned, place the operator’s foot in front of or behind the patient's feet and ask the patient to move slightly until he hits the operator's foot POSITIONING OF THE FEET.
  52. 52. BODY-POSITIONING & HEAD-POSITIONING. Patient instructed to ''hold your head so that you can look into your own eyes in the miror". ADJUSTMENT FOR SYMMETRY. carried out with guidance by the light-beam cross
  53. 53. THE FLUID LEVEL DEVICE AJO 1983 Showfety The ends of the air bubble aligned with the ends of an 0.030 inch diameter wire The fluid consists of a mixture of radiopaque liquid, blue dye, and a silicone suspension, rendering the air bubble visible on the cephalometric radiograph.
  54. 54.
  55. 55.
  56. 56.
  57. 57. The ideal location - between the eyebrow and the hairline behind the prominent temporal crest of the frontal bone. The patient instructed to stand in an ''intention position‖. The fluid level is rotated on the pivot until the bubble is aligned with the ends of the wire. PROCEDURE:
  58. 58. The patient is placed in the cephalometric head holder & the patient's head is tilted up or down until the bubble is aligned with the wire. A vertical reference chain & wire in the fluid- level device will be aligned at 90 degrees to each other
  59. 59.
  60. 60. Inclinometer AJO 1991 Murphy  uses a contactless precision potentiometer to continuously measure changes in inclination around a single axis of rotation  the inclinometer was calibrated  Spectacles attach the inclinometer to the head in a stable manner .
  61. 61.
  62. 62.
  63. 63. AJO1985 Archer and Vig Wood 1981 Leveling device consisting of a fluid-filled plastic ring mounted on a protractor.
  64. 64. Other methods: • Schmidt (1876) made use of a frame that encircled the skull, a plumb line and a protractor. • Moorrees and Kean projected the image of a plumb line of stainless steel ligature wire onto cephalometric radiographs • Von Baer and Wagner instructed subjects to look directly at the reflection of their eyes on a a mirror fixed to a wall.
  65. 65. • Cinefluorography may be used to measure head posture over a period but exposes subjects to irradiation for relatively long periods.(Cleall, AO 1966)
  66. 66. Importance of NHP: (Solow and Kreiborg 1977) ―Soft tissue stretching hypothesis'' Head extension - stretch of the soft tissues - increase in the forces of the lips and other faciocervical muscles .
  67. 67. Extended head posture – Facial retrognathism Retroclination of lower incisors AFH and PFH A-P craniofacial dimension Larger inclination of the mandible to SN Larger cranial base angle Small nasopharyngeal space SOLOW & TALLGREN 1976
  68. 68. RESPIRATION &NHP • Woodside and Linder-Aronson(EJO1976) - children with nasal obstruction had a more extended head posture(6°) . • Extended head posture after induced mouth breathing - Hellsing,(EJO1987)
  69. 69. • Oral respiration - produce an altered mandibular posture and changes in the shape of the mandible with development of an anterior open-bite (Harvold,1973)
  70. 70. Nasal obstruction Craniocervical postural adaptations Mandibular postural adaptation Skeletal growth modification Dentoalveolar compensation/adaptation
  71. 71. Dentoalveolar height and occlusal plane inclination showed a set of positive correlations with the craniocervical and sella -nasion to vertical angulations (SOLOW &TALLGREN 1977)
  72. 72. Goldstein and associates(1984)  Evaluated the mandibular trajectory of closure with a mandibular kinesiograph  Four postural attitudes: natural sitting posture (NP), forward head posture (FHP), maximal forward head posture (MFHP), and military posture (MP).
  73. 73. • Alterations of the A-P head and neck posture have an immediate effect on the trajectory of mandibular closure. • As the head moved anteriorly - the vertical distance of mandibular closure decreased. • When the head moved posteriorly - the anterior excursion of the mandible through the interocclusal space
  75. 75.
  76. 76. NSL/OPT - represent tilting of the head at occipitoatloid joint OPT/CVT -represent change in cervical curvature OPT/HOR & CVT/HOR- Cervical inclination in relation to the true horizontal NSL/VERT -the total change in head position
  77. 77. Large craniocervical angle- an extension of the head -the height of the posterior arc of the atlas is reduced -Also related to adenoid airway obstruction and a vertical facial development (Huggare, EJO 1985)
  78. 78. Various analysis using NHP:
  79. 79. Reference planes in NHP: Down’s & Tweed- Drop perpendicular thru’ Orbitale Test difference between true horizontal & FH & include in the analyses Bjork & Steiner- Draw horizontal thru’ nasion S-N made 10 degrees to horizontal
  80. 80. Growth prediction from posture Solow & Nielson AJO 1992 41 reference points and 4 fiducial points
  81. 81. Points N and S on the first film - fiducial points in the anterior cranial base- REFcrb. In the mandible - fiducial points located arbitrarily in the middle of the symphysis and one below the first molars- REFml.
  82. 82.
  83. 83.
  84. 84. A backward inclination of the cervical column & small craniocervical angle  reduced backward displacement of TMJ  increased growth in maxillary length,  increase in max. and mand. prognathism,  forward true rotation of the mandible .
  85. 85. Upright position of the cervical column & large craniocervical angle  large backward displacement of TMJ  reduced growth in maxillary length  reduction of max.and mand. Prognathism  less forward true rotation of the mandible
  86. 86. A small craniocervical angle was associated with a horizontal facial growth pattern A large craniocervical angle was associated with a vertical facial development.
  87. 87. Five-factor cephalometric summary analysis Horizontal line Reference-  drawn parallel to the border of the radiograph constructed at right angles to the registered true vertical.  drawn in any vertical position.  BEST -close to the Frankfort plane Cooke and Wei AJO 1988
  88. 88.
  89. 89. Angle 1 - anteroinferior angle bet. Y axis & true horizontal. Angle 2 - angle bet. upper incisor & true horizontal. Angle 3 - NHP equivalent of the facial angle Angle 4 - angle bet. AB line & true horizontal. Angle 5 - angulation of the lower incisor & true
  90. 90. "Normal" AB/horizontal values for clinical use  Skeletal Class I 12° to 18°  Skeletal Class II > 18°  Skeletal Class III < 12°
  91. 91. Advantages: Requires no new sets of "norms" or figures.  Only the reference plane has been changed to eliminate the errors inherent in analyses. Conventional methods are subject to errors in describing true life appearance.
  92. 92. Normal - focus on the profile from the nose down The A-P position of the forehead -not a major factor The size of the nose -alter clinician's impression of the convexity of the profile & the position of the lips. A new measurement of profile esthetics JCO, 1991 VIAZIS
  93. 93.
  94. 94. A line drawn through the middle of the nose (No), parallel to the true vertical- the ― V‖ line. The ― V‖ angle - the angle between this line and Steiner's ― S‖ line. for adults - -12.5° for adolescents -13.0 °
  95. 95. FCA - + 3° prognathic ― E‖ line -normal lower lip V‖ angle - -1.5° - supports clinical impression of prognathic profile .
  96. 96. FCA - -8° indicates retrognathic profile. ― E‖ line I- retrusive ― V‖ angle - -11° in accordance with clinical impression of orthognathic profile.
  97. 97. Cephalometric Analysis based on NHP: JCO 1991 VIAZIS Defines the A-P & vertical position of the maxilla and mandible relative to the true horizontal plane, then relates the position of the dentition to its skeletal substrate. Only two soft-tissue measurements. No linear measurements.
  98. 98.
  99. 99.
  100. 100. Comprehensive Assessment of Anteroposterior Jaw Relationships JCO1992 VIAZIS Describe an assessment of the anteroposterior position of the jaws based on measurements that use TH as their reference line.
  101. 101.  Size of Mand. relative to Ant. Cranial Base (SN- GoGn)  Maxillomandibular Ratio (PNS-ANS:ArGn)  Linear and Angular Measurements (A, B, Pg to N^TH; NA, NB, NPg to TH)  Relative A-P Position ( TH Wits & ANB)  Anteroposterior Chin Position (Chin Length and BNPg)
  102. 102. 1. Size of Mandible Relative to Anterior Cranial Base (SN-GoGn) 1:1 ratio -indicate a well-balanced mandible relative to the cranial base . SN should be 0- 5mm greater than GoGn before puberty, and about 0-5mm less than GoGn after puberty.
  103. 103. 2. Maxillomandibular Ratio (PNS- ANS:ArGn) The length of the mandible is exactly double the length of the maxilla for all age groups and both sexes
  104. 104. 3. Linear and Angular Measurements (A, B, Pg to N^TH; NA, NB, NPg to TH) Three linear measurements— from A, B, and Pg to nasion perpendicular to TH The angles between NA and NPg and TH - evaluate the anteroposterior position of the jaws . NB provides an additional assessment
  105. 105.
  106. 106. 4. Relative Anteroposterior Position (TH Wits and ANB)  Points A and B projected on perpendiculars to TH, (a and b). The distance ab - "TH Wits‖ - provides a clearer picture of the anteroposterior relationship of the jaws
  107. 107.
  108. 108. 5. Anteroposterior Chin Position (Chin Length and BNPg) The BNPg angle assesses the prominence of the chin relative to the body of the mandible
  109. 109.  Projections of B and Pg to a line parallel to TH and tangent to the mandible at menton define the chin length,- bp
  110. 110.
  111. 111. Optic plane: SASSOUNI the supraorbitale plane (a line tangent to anterior clinoid and the roof of the orbit) the infraorbital plane (line tangent to the inferior of sella turcica and the floor of the orbit)  bisect the angle formed by their intersection - the optic plane
  112. 112. Natural head position in photographs
  113. 113. Camera - mounted on a tripod & leveled with the optical axis of the lens horizontal and the film plane vertical. 20 × 100 cm mirror mounted at eye level on the wall Subject – camera –150 cm 2.55 m. Mirror- subject – 120cm. Recording of NHP:
  114. 114. Assume and maintain a "natural and normal" erect posture of head and shoulders, with both arms hanging free beside the trunk. On each photograph, a reference line placed perpendicular to the ground by using a small spirit level (true vertical) was drawn.
  115. 115. AJO 1994 Ferrario, Developed a photographic technique - associated with standard radiograph & a computerized method allowing an easy and fast superimposition of the two recordings was introduced
  116. 116.
  117. 117. the angle between the N'-Pg' line and the true vertical was calculated on the photograph & cephalometric films The difference - compute the position of the soft and hard tissue Frankfurt planes, and of the sella-nasion plane in NHP. These new values were compared with the values observed in the standard cephalometric orientation.
  118. 118.  Angle N'-Pg' line/true vertical was fed to a computer program - provided a rotation of all the landmarks until the cephalometric N'-Pg' line coincided with the photographic one. Rotation was performed around the Bolton point
  119. 119. Craniofacial morphometry by photographic evaluation AJO 1993 –Ferrario  Frontal standing, rest & clenching a Fox plane  Lateral standing, rest &clenching a Fox plane  Lateral sitting, rest 16 points were located by careful inspection & palpation and traced on the face of each subject
  120. 120.  Median points -soft tissue nasion ,nasal apex ,soft tissue subnasale ,upper lip ,lower lip ,soft tissue pogonion .  Lateral points - supraorbital foramen , infraorbital foramen , soft tissue orbitale , soft tissue gonion .
  121. 121.
  122. 122.  Face center of gravity (CG) coordinates--- used as the new origin of coordinate axes - the points were translated. on the frontal image using the areas of eyes ,nose and mouth on the lateral image as center of the polygon N- Pog-Go-Tr  In the frontal plot, the N-CG axis -used as a new reference y-axis - points were rotated.
  123. 123.
  124. 124.
  125. 125. A proportional analysis of the soft tissue facial profile Lundström, AO 1992
  126. 126.
  127. 127.
  128. 128. DISADVANTAGE OF NHP AJO 1980 Frankel  Functional appliance treatment- changes in posture ( functional and physiologic)- distorts data base  Fu.A. alters muscle form and function. Adjoining muscle groups experience reciprocal changes and treatment-related head posture changes could result.
  129. 129. Did not consider NHP modifications during treatment, but proposed to refer all longitudinal radiograms to the first NHP recording – missed the important information. Ferrario, AJO 1994
  130. 130. CONCLUSION: ― THE SEARCH FOR AN IDEAL‖ -Cephalometrics is constantly undergoing refinements in its techniques & analyses to improve the clinical applications. NHP , a long proposed modification, yet not fully into practice, can be an ―ideal‖ reference for us to improve our cephalometric interpretation……
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  132. 132. For more details please visit