heilsa
Rotter
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When it comes to facial analaysis reference planes like the so called frankfurt horizontal line are used to analyse the face
However this isnt a acurate in many cases due to individual variability.
Therefore It is therefore necessary to reduce the limitations of using the Frankfurt plane while maintaining the advantages of the overall concept. This may be achieved by evaluating the patient in natural head position and constructing a true horizontal plane (THP)
Natural head positon:
Now with the natural head position we are able to determine the true horizontal plane:
http://ejo.oxfordjournals.org/content/30/5/532
http://www.scielo.br/scielo.php?pid=S1415-54192006000100012&script=sci_abstract
http://lookism.net/showthread.php?tid=228


However this isnt a acurate in many cases due to individual variability.


Therefore It is therefore necessary to reduce the limitations of using the Frankfurt plane while maintaining the advantages of the overall concept. This may be achieved by evaluating the patient in natural head position and constructing a true horizontal plane (THP)
Natural head positon:
Natural head position (NHP) was introduced into orthodontics in the late 1950s (Downs, 1956; Bjern, 1957; Moorrees and Kean, 1958). Broca (1862) defined this head position as ‘when man is standing and his visual axis is horizontal, he is in the natural position’ (cited by Moorees and Kean, 1958). A typical method of registering NHP is based on the work of Solow and Tallgren (1971), who cited Mølhave (1958) in which subjects are asked to stand in an ‘orthoposition’ and look into their own eyes in a mirror after a series of neck flexion exercises. Other methods of NHP registration include instructing subjects to look at a small light (Cleall, 1965), the use of a fluid level device (Showfety et al., 1983), an operator-estimated ‘natural head orientation’ (Lundström et al., 1995), and the use of an inclinometer (Preston et al., 1997). NHP can be recorded radiographically (Bjern, 1957; Moorrees and Kean, 1958) or photographically, which is preferred to allow the most freedom in producing a natural position (Lundström and Lundström, 1989).

Now with the natural head position we are able to determine the true horizontal plane:
A plumb line was used to define the vertical plane (VER) on the photographs, and a line connecting soft tissue glabela and pogonion were transfered from the photograph to the lateral teleradiograph. A true horizontal line (HOR) at a right angle to the vertical plane with the intracranial reference Frankfurt horizontal plane (HF) was used to assess the variability in relation between HF and NHP.
Craniofacial reference planes investigated. HOR, true horizontal constructed perpendicular to the vertical plumb line (VER); FH, Frankfort Horizontal; SN, sella–nasion; StN, sella tangent–nasion (Sassouni, 1955); NHA, neutral horizontal axis (McCarthy and Lieberman, 2001); KW line, Krogman–Walker line (Rothstein and Yoon-Tarlie, 2000); P plane, palatal plane; FML, foramen magnum line; AtPt, anterior tubercle to posterior tubercle of C1; FOP, functional occlusal plane; Md plane, mandibular plane, PM plane, posterior maxillary plane (Enlow and Azuma, 1975); PM vertical, pterygomaxillary vertical (Enlow et al., 1969).
http://ejo.oxfordjournals.org/content/30/5/532
http://www.scielo.br/scielo.php?pid=S1415-54192006000100012&script=sci_abstract
http://lookism.net/showthread.php?tid=228