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Successful treatment of the orthognathic surgical patient is dependent on careful diagnosis. Cephalometric analysis can be an aid in the diagnosis of skeletal and dental problems and a tool for simulating surgery and orthodontics by the use of acetate overlays. Cephalometric analysis also allows the clinician to evaluate changes after surgery. The first step in the diagnosis of the orthognathic surgical patient is to determine the nature of the dental and skeletal defects www.indiandentalacademy.com
Patients who require orthognathic surgery usually have facial bones as well as tooth positions that must be modified by a combined orthodontic and surgical treatment. For this reason, a specialized cephalometric appraisal system, called Cephalometrics for Orthognathic Surgery (COGS), was developed at the University of Connecticut. This appraisal is based on a system of cephalometric analysis that was developed at Indiana University, with the addition of clinically significant new measurements. www.indiandentalacademy.com
The COGS system describes the horizontal and vertical position of facial bones by use of a constant coordinate system; the sizes of bones are represented by linear dimensions and their shapes, by angular measurements. The standards are based on a sample obtained from the Child Research Council of university of Colorado School of Medicine. Although the sample of 16 females and 14 males is small, the mean measurement values closely correspond with those of other northern European populations. This longitudinal sample was selected to ensure consistent standards by age and rate of growth. www.indiandentalacademy.com
Cephalometric Analysis Sella (S), the center of the pituitary fossa. Nasion (N), the most anterior point of the nasofrontal suture in the midsagittal plane Articulare (Ar), the intersection of basisphenoid and the posterior border of the condyle mandibularis. Pterygomaxillary fissure (PTM), the most posterior point on the anterior contour of the maxillary tuberosity Subspinale (A), the deepest point in the midsagittal plane between the anterior nasal spine and prosthion, usually around the level of and ante足rior to the apex of the maxillary central incisors.足Pogonion (Pg), the most anterior point in the midsagittal plane of the contour of the chin www.indiandentalacademy.com
Supramentale (B), the deepest point in the midsagittal plane between infradentale and Pg, usually anterior to and slightly below the apices of the mandibular incisors. Anterior nasal spine (ANS), the most anterior point of the nasal floor; the tip of the premaxilla in the midsagittal plane. 足Menton (Me), the lowest point of the contour of the mandibular symphysis Gnathion (Gn), the midpoint between Pg and Me, located by bisecting the facial line N足Pg and the mandibular plane (lower border). Posterior nasal spine (PNS), the most posterior point on the contour of the palate. Mandibular plane (MP), a plane constructed from Me to the angle of the mandible (Go). Nasal floor (NF), a plane constructed from PNS to ANS. 足Gonion (Go), located by bisecting the posterior ramal plane and thewww.indiandentalacademy.com mandibular plane angle.
The baseline for comparison of most of the data in this analysis is a constructed plane called the horizontal plane (HP), which is a surrogate Frankfort plane, constructed by drawing a line 7째 from the line S to N. Most measurements will be made from projections either parallel to HP (11 HP) or perpendicular to HP ( 1 HP).
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CRANIAL BASE First, it is necessary to establish the length of the cranial base, which is a measurement parallel to HP from Ar to N. This measurement should not be considered an absolute value but a skeletal baseline to be correlated to other measurements, such as maxillary and mandibular length, to obtain a diagnosis of proportional dysplasia.
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Ar足pterygomaxillary fissure (Ar足PTM) is measured parallel to HP to determine the horizontal distance between the posterior aspects of the mandible and maxilla. The greater the distance between Ar足PTM, the more the mandible will lie posterior to the maxilla, assuming that all other facial dimensions are normal. Therefore, one causal factor for prognathism or retrognathism can be evaluated by this measurement of the cranial base. www.indiandentalacademy.com
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HORIZONTAL SKELETAL PROFILE A few simple measurements should be made on the skeletal profile to assess the amount of disharmony. We call this the horizontal skeletal profile analysis because all the measurements are made parallel to HP. This is very practical because most surgical corrections. primarily made in the anteroposterior direction. The first measurement quantitatively describes the degree of skeletal convexity in the patient. The angle of skeletal facial convexity is measured by the angle formed by the line N足A and a line A to Pg. The N足A足Pg (angle) gives an indication of the overall facial convexity, but not a specific diagnosis of which is at fault 足the maxilla or mandible www.indiandentalacademy.com
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A perpendicular line from HP is dropped through N and the inferior anatomic point is horizontally measured in relation to the superior structures The horizontal position of A is measured to this perpendicular line (N足A). This measurement describes the apical base of the maxilla in relation to N and enables the clinician to determine if the anterior part of the maxilla is protrusive or retrusive. The measurement and related measurements are important in the planning of treatment of anterior maxillary horizontal advancement or reduction, and of total maxillary horizontal advancement or reduction. Point B and PG[ pogonion ] are measured in the same way.
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VERTICAL SKELETAL AND DENTAL A vertical skeletal discrepancy may reflect an anterior, posterior, or complex dysplasia of the face. Therefore, the vertical skeletal cephalometric measurements are divided into anterior and posterior components.
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MAXILLA AND MANDIBLE The total effective length of the maxilla is the distance from PNSANS that is projected on a line parallel to the HP. The ANSPNS distance, with the previous measurements NANS and PNSN, give a quantitative description of the maxilla in the skull complex. Four measurements relate to the mandible Ar to Go GoPg Go angle [represents the relationship between the ramal plane and MP] BPg, [Distance from B point to a line perpendicular to MP through Pg.]
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DENTAL In the assessment of de anomalies cephalometrically, one must attempt to relate the teeth to each other through a common plane, such as the occlusal plane (OP) or to a plane in each jaw, the MP, or the NF plane.
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Table
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Discussion: A cephalometric appraisal is only one step in diagnosis and planning of treatment. It gives the clinician insight into the quantitative nature of the skeletal足dental dysplasia. If surgery' is planned to produce cephalometric changes that make the face approach the normative standards, usually a more typical and desirable face is produced. It is a mistake, however, to treat to a standard that avoids other considerations. The soft tissues can and do mask the underlying bone and teeth; therefore one must compensate for this variations. www.indiandentalacademy.com
ADVANTAGES: A cephalometric analysis for patients who have orthognathic surgery It is based on the landmarks that can be altered by various surgical procedures. These rectilinear measurements examine critical facial components that can be readily transferred to acetate overlays and study casts for detailed planning of treatment and post surgical evaluation. www.indiandentalacademy.com
SOFT
TISSUE
CEPHALOMETRIC
ANALYSIS
FOR
ORTHOGNATHIC SURGERY: Treatment planning for patients who require orthognathic surgery should include both a hard tissue and soft tissue cephalometric analysis. The hard tissue will show the nature of the existing skeletal discrepancy, it is incomplete in providing the information concerning the facial form and proportions of patient. The soft tissue covering the teeth and bone is highly variable in its thickness and this www.indiandentalacademy.com
variation may be greater.
In
planning
surgery
on
patients
with
vertical
discrepancies, lip length is an important factor. Sometime lips may be short,allowing the patient to close with great difficulty. Amount of incisor exposure will be more during speaking.
Therefore,
the
diagnosis
of
vertical
discrepancies will be depend upon both soft and hard tissues factor. Therefore, Charles J. Burstone in 1980 developed a soft tissue cephalometric analysis for orthognathic surgery. www.indiandentalacademy.com
Cephalometric landmarks: Soft tissue landmarks used are; Glabella (G) : The most prominent midsagittal plane of the forehead.
point
in
the
Columella point (Cm) : The most anterior point on the columella of nose. Subnasale (Sn) : The point at which the nasal septum merges with the upper cutaneous lip in the midsagittal plane. Labrale superiors (Ls) : A point mucocutaneous border of upper lip.
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indicating
the
Stomion superius (Stms) : Lower most point on the vermilion of the lower lip. Labrale inferius (stml) : The upper most point on the vermilion of the lower lip. Labrale
inferius
(Li):
A
point
indicating
the
mucocutaneous border of lower lip. Mentolabial sulcus (Si) : The point of greatest concavity in the midline between the lower lip and chin. Soft tissue pogonion (Pg) : The most anterior point on soft tissue chin www.indiandentalacademy.com
soft tissue gnathion (Gn) : The constructed midpoint between soft tissue pogonion and soft tissue menton.
Soft tissue menton (me) : Lowest point on the soft tissue chin, found by dropping a perpendicular from horizontal plane through menton. Cervical
point
(C):
Innermost
point
between
the
submental area and neck located at the intersection of lines drawn tangent to neck and submental areas. Horizontal reference plane (HP): Constructed by drawing a line through nasion 7° up from sella  nasion line. www.indiandentalacademy.com
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Facial form To describe the soft tissue profile of patient angle of facial convexity, or facial contour angle, G Sn Pg is evaluated. GSn Pg : 12°+/ 4° A line perpendicular to horizontal plane (HP) is dropped from glabella and the relationship of the maxilla and mandible is related to it to determine if the problem is maxillary or mandibular. www.indiandentalacademy.com
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G足Sn (Hp): The distance from subnasal (Sn) to vertical line parallel to the horizontal plane is measured maxillary
which
describes
protrusion
or
the
amount
retrusion
of in
anteroposterior dimension. Negative number is maxillary retrusion, large positive number,is maxillary procumbency. G 足 Sn 足 (HP): 0 +/足 3 mm www.indiandentalacademy.com
G Pg (HP) : The position of pogonion is measured parallel to HP from the Perpendicular line dropped from glabella. This measurement gives an indication of maxillary prognathism or retrognathism. G Pg : 0 +/ 4 mm
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Vertical height ratio - G - Sn / Sn - Me (HP): In
vertical
dimension,
anterior
facial
proportionality is assessed by taking the ratio of middle third facial height to lower third facial height measured perpendicular to HP. The ratio less than 1 to 1 connote a disproportionality large lower third of face . Normal: 1 mm
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Lower face - throat angle (Sn - Gn - C): It is formed by intersection of the lines Sn 足 Gn and Gn 足 C. an obtuse lower face neck angle warns the clinician not to use procedures that reduce the prominence of chin.
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Nasolabial angle (Cm - Sn - Ls) : 4 +/- 2mm It is important in assessing anteroposterior maxillary dysplasia. An acute nasolabial angle will often allow us to surgically retract the maxilla or retract the maxillary incisors. Obtuse nasolabial angle suggests a degree of maxillary hypoplasia. Cm Sn Ls: 102° +/ 8° www.indiandentalacademy.com
Upper lip protrusion Ls to (Sn Pg) : 3 +\1 mm Lower lip protrusion Li to (Sn Pg) : 2+\ 1 mm It is evaluated by drawing a line from subnasal to soft tissue pogonion and amount of lip protrusion or retrusion is measured by perpendicular linear distance from this line to the most prominent point of both lips. Labio-mental sulcus Si to (Li – Pg) 4 +/ 2 mm It
is
measured
from
the
depth
of
the
sulcus
perpendicular to Li Pg line. Sulcus of about 4 mm is average in pleasing lower lip t0 chin contour. www.indiandentalacademy.com
Vertical lip chin ratio - Sn - Stms / Stms - Me: 0.5 mm: Lower third of face (Sn Me) is divided into length of upper Sn Stms. It should be approximately 1/ 3rd the total and distance Stms Me is about 2/3rd. Sn Stms/Stms Me should be 1: 2 ratio becomes smaller than one half vertical reduction genioplasty considered. Distance of upper lip to the maxillary incisor (Stms 1) is key factor in determining the vertical position of maxilla. Patient with vertical maxillary excess tend to show a large amount of upper incisors with the lip in response. www.indiandentalacademy.com
Interlabial gap - 3 mm: Vertical distance between the upper lip and lower lip with then lip in rest position is normally 3mm. If vertical maxillary excess tend to have large Interlabial gap, lip In competency.
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www.indiandentalacademy.com Leader in continuing dental education
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