Postero anterior cephalometry

Postero anterior cephalometryProf : maher foudaBy : Ameen qulah Om Prakash Kharbanda (Diagnosis and M anagement of Malocclusion and Dentofacial Deformities)Basavaraj Subhashchandra Phula (an atlas on CephalometriC landmarks)

Postero anterior cephalometry

The PA cephalogram offers an effective tool in evaluating the craniofacial structures in transverse and vertical dimensions. It allows us to look at the facial skeleton in relative view of the right-left face and upper-lower face. First attempts towards analyzing the craniofacial skeleton on PA cephalograms were limited to absolute linear ^measurements such as face widths and heights and later ratio and volumetric comparisons were added to evaluate relative asymmetries.

Set-up for PA cephalometry

Patients correct orientation is of utmost importance before exposing the patient to X-ray radiation. The cephalostat head holder is rotated 90 so that the subject will face the X-ray cassette and the central X-ray beam passes through the skull in a posteroanterior direction bisecting the transmeatal axis perpendicularly. Patient is fixed in a headholder with the use of ear rods. The standard distance from X-ray source to the ear post axis is 5 feet. The reproduction of the head position is crucial because if the head is tilted all vertical dimensional measurements will change.

Reproducing correct head orientation1. Conventionally, head can be positioned with the tip of the nose and forehead in light contact with the cassette holder. This position is good for evaluation of craniofacial anomalies which require special attention to the upper face.2. The standard method is by keeping the Frankforts horizontal plane parallel to the floor, while the patient is facing the X-ray film cassette as close as permissible within the limits of nose prominence.

Reproducing correct head orientation3. To ensure correct orientation of head in FH plane, a guided patient positioning as follows: A line is scribed on the ear rod assembly at a point 1^5 mm above the ear rod. The height of the orbit is about 3 cm, and the lateral canthus is essentially at the centre of the orbit, or 15 mm. The patient should be oriented such that his ear canals tuck snugly against the top of the ear rods with the head positioned so that the lateral canthus of the eye is located in level with that line

4- Orienting the head in natural head position (NHP).6 5- Cephalograms are taken with the mouth of the patient slightly open for cases with significant mandibular displacement.

Signs of good head position on PA cephalogram X-ray film

1. The head position and the intermaxillary occlusal relationship that appear in X-ray should be first confirmed using patients photographs, study casts or clinical evaluation as a guideline.2. In a properly oriented frontal head film, the top of the petrous portion of the temporal bone will lie near the centre of the orbit.

Evaluation of PA cephalogramImportant featuresOrbits - whether normally inclined or oblique and size of orbits whether equal or disparate. 2. Ramus of the mandible - whether present or absent or underdeveloped as seen in unilateral or bilateral hypoplasia cases.3. Angle of mandible - whether obtuse or acute. Obtuse angle is usually seen on the unaffected side in ankylosis. 4. Body of mandible - whether present or absent and developed on both sides to an equal extent or not. May be deviated to either side in certain situations.

5- Chin - whether present in centre or deviated to one side as seen in cases of asymmetry of mandible. 6- Malar bones - whether equally prominent on either sides or one side as in craniofacial syndromes. 7- Maxillary antra - whether equal on both sides and whether the development is normal or not.

8- Width.of dental arches - may be underdeveloped or over developed on either sides.9. Cant of occlusal plane - can be compared at a single glance in PA cephalogram. Cant may be tilted to the affected side in TMJ ankylosis cases.10. Nasal widths - may be equal or unequal as in unilateral hypoplasia.

PA cephalometric landmarks/points related to specific bones are listed below:

1. Cephalometric landmarks (points) related to ethmoid bone.2. Cephalometric landmarks (points) related to nasal bone. 3. Cephalometric landmarks (points) related to zygomatic bone. 4. Cephalometric landmarks (points) related to maxillary bone. 5. Cephalometric landmarks (points) related to dentition. 6. Cephalometric landmarks (points) related to mandible.

PA Cephalometric Landmarks Related to Ethmoid Bone

).

Cg. Critsta galli :

Neck of crista galli, most constricted point of the projection of the perpendicular lamina of the ethmoid (almost at the level of planum

PA Cephalometric Landmarks Related to Nasal Bone

Top of Nasal Septumaccording to athanasios E athanasiou (tns)The highest point onto the superior aspect of the nasal septum TypeTop of nasal septum is a unilateral, anatomic, hard tissue PA cephalometric landmark.

Nasal cavity (NC)according to Robert M RickettsLateral most point on inside surface of the bony nasal cavity Type: NC is a unilateral, anatomic, hard tissue PA cephalometric landmark.

Pa Cephalometric Landmarks Related to zygomatic Bone

(Zyg ) zygomaaccording to Viken Sassouni :Most lateral and superior point of the shadow of the zygomatic archType:Zygoma is a bilateral, anatomic, hard tissue PA cephalometric landmark.

Zygion (zy)according to Robert M RickettsZygion is the most lateral point of each zygomatic arch .TypeZygion is a bilateral, anatomic, hard tissue PA cephalometric landmark

zygomatic arch (ZA)according to Robert M RickettsCenter of zygomatic arch by inspection for frontal.TypeZygomatic arch is a bilateral, anatomic, hard tissue PA cephalo-metric landmark.

zygomatic Suture Point - Zaccording to Robert M RickettsMedial and anterior junction of the zygomatic bone with the frontal boneTypeZygomatic suture point is a bilateral, anatomic, hard tissue PA cephalometric landmark.

Jugal Process ( J) Bilateral points on the jugal process at the intersection of the outline of the tuberosity of the maxilla and zygomatic buttress (left and right).according to Robert M RickettsLowest point on the curve of zygomatic bone used in the lateral film, also the point on the jugal process of the maxilla at a crossing with the tuberosity of the maxilla (in the frontal)

Pa Cephalometric Landmarks Related to Maxilla

Maxillare (Mx)Maximum concavity on the contour of the maxilla between the first molar and malare . Maximum concavity on the contour of the maxilla between malare (Ma) and the maxillary first molar (U6).Closely corresponds to the key ridge. The intersection of the lateral contour of the maxillary alveolar process and the lower contour of the maxillozygomatic process of the maxilla (left and right).

Pa Cephalometric Landmarks Related to Dentition

Incision Superius Incisalis (Isi)Incision superius incisalis is the incisal edge of the maxillary central incisor. according to arne Bjork Incision superius incisalis is the mid-point of the incisal edge of the most prominent upper central incisor.according to Robert E MoyersIncision superius incisalis is the incisal tip of the most anterior maxillary central incisor.

Incision Superius apicalis Incision superius apicalis (Isa (Upper incisor apex (UIA)Incision superius apicalis is the root apex of the most anterior maxillary central incisor; if this point is needed only for defining the long axis of the tooth, the midpoint on the bisection of the apical root width can be used.according to Michael L RioloThe upper incisor apex is the root tip of the maxillary central incisor. In cases where the root is not yet completed, the midpoint of the growing root tip is marked.SN Bhatia and BC LeightonThe upper incisor apex is the root apex of the most prominent upper incisor.

Maxillary Molar (um)Definitionaccording to athanasios E athanasiouThe most prominent lateral point on the buccal surface of the second deciduous or first permanent maxillary molar

Maxillary First MolarU6Maxillary first molar A6Maxillary first molarDefinitionMaxillary first molar is the tip of the mesiobuccal cusp of the maxillary first permanent molar.

Tracing of Maxillary First Molar on Lateral CephalogramThe labial and lingual and cuspal outlines of the crown of the maxillary permanent first molar appears as radio-opaque lines on the lateral cephalogram. Trace these outlines of crown of the maxillary permanent first molar, the tip of the mesiobuccal cusp of the maxillary permanent molar is the point of maxillary first molar.

Cuspid AbbreviationA3Cuspid Definitionaccording to Carl F guginoTip of the upper permanent canine .TypeCuspid is a bilateral, hard tissue cephalometric landmark.

Incision Inferius Incisalis (Iii) DefinitionIncision inferius incisalis is the incisal edge of the most prominent mandibular central incisor.according to arne BjorkThe incision inferius is the incisal point of the most prominent medial mandibular incisor.according to Robert E MoyersThe incision inferius is the incisal tip of the most labial mandibular central incisor.

Incision Inferius apicalis (Iia)DefinitionIncision inferius apicalis is the root apex of the most anterior mandibular central incisor; if this point is needed only for defining the long axis of the tooth, the midpoint on the bisection of the apical root width can be used.SN Bhatia and BC Leighton The lower incisor apex is the root apex of the most prominent lower incisor.

Incision Inferius Frontale (iif)Definitionaccording to athanasios E athanasiouThe midpoint between the mandibular central incisors at the level of the incisal edges .TypeIncision inferius frontale is a unilateral, hard tissue cephalometric landmark.

Mandibular First Molar (L6)Definition Mandibular first molar is the tip of the mesiobuccal cusp of the mandibular first permanent molar.TypeMandibular first molar is a unilateral, anatomic, hard tissue cephalometric landmark.

miDefinition mi is the mesial contact of the lower molar projected normal to the plane of occlusion. Significance mi is used as one of the reference points in the construction of plane and angle in the Bjork cephalometric analysis.

Mandibular Molar (Im) Definitionaccording to athanasios E athanasiouThe most prominent lateral point on the buccal surface of the second deciduous or first permanent mandibular molar Type Mandibular molar is a bilateral, hard tissue cephalometric landmark.

Pa Cephalometric Landmarks Related to Mandible

Menton ( Me)according to Viken SassouniLower most point of the contour of the chin.according to Carl F gugino Menton is the point on inferior border of symphysis directly inferior to mental protuberance and below center of trigonium mentali.

Articulare (Ar)DefinitionArticulare is the point of intersection the dorsal contours of the processus articularis mandibulare and os tempoarle.The midpoint, a is used where double projection gives rise to two pointsSignificance Constructions of posterior/ramus border of the mandible i.e. the line joining the point articulare and gonion. Growth pattern is assessed using Go and Go angles. Rotation of the mandible is also assessed using the S-Ar-Go angle.

.

Malare (Ma)Definitionaccording to Viken SassouniMidpoint of intersection between the projection of the coronoid process and the lower contour of the malar bone

antegonial Tubercles (Ag)Definitionaccording to Robert M RickettsIntersection of the outline of the dense bone of the trihedral eminence with the lower border of the ramus.

Antegonion (Ag)Definitionaccording to athanasios E athanasiouThe highest point in the antegonial notch (left and right)

Planes in PA cephalogramVarious horizontal and vertical planes are drawn in PA cephalogram in different analyses for the determination of asymmetry, linear dimensions and angles.

Median sagittal reference (MSR) planeIt has been selected as a key reference line because it closely follows the visual plane formed by subnasale and the midpoints between the eyes and eyebrows. The median sagittal reference plane normally runs vertically from crista galli (Cg) through the anterior nasal point (ANS) to the chin area, and is typically nearly perpendicular to the Z plane (line joining zygomaticofrontal suture of one side to the other).

44

If the location of Cg is in question, an alternative method of drawing MSR is to draw a line from the midpoint of the Z plane through ANS. The position of anterior nasal spine will be altered in facial asymmetry involving the maxilla.

If there is upper facial asymmetry, MSR can be drawn as a line from the midpoint of the Z plane through the midpoint of the Fr-Fr line (foramen rotundum of one side to the other). To avoid any such bias, a best-fit vertical line is drawn in the center connecting the midpoints of lines joining zygomaticofrontal sutures (Z-Z), the centres of the zygomatic arches (ZA), the medial aspects of the jugal processes (J) and antegonial notch (AG-GA) of both the sides.

The best-fit line and all lines constructed as perpendiculars through midpoints between pairs of orbital landmarks have shown excellent validity.Besides vertical reference lines, horizontal best-fit lines have to be constructed to know the asymmetry in vertical plane. All horizontal lines connecting bilateral cranial landmarks can adequately serve as reference lines in the analysis of vertical asymmetry from PA cephalograms, if landmark identification error is acceptable.

Grummons analysisGrummons analysis is a comparative and quantitative PA cephalometric analysis and is not related to normative data. The analysis consists of different components:1. Horizontal planes2. Mandibular morphology3. Volumetric comparisonMaxillomandibular comparison of asymmetry5. Linear asymmetry assessment6. Maxillomandibular relation7. Frontal vertical proportions.

Horizontal planesFour planes are drawn to show the degree of parallelism and symmetry of the facial structures. Three planes connect the medial aspects of the zygomatic frontal sutures (Z-Z), the centres of the zygomatic arches (ZA), and the medial aspects of the jugal processes (J). Another plane is drawn at menton parallel to the Z plane. MSR has been selected as a true vertical reference line.

Mandibular morphologyLeft and right triangles are formed from the heads of the condylar processes or the condyles (Co), the antegonial notches (AG), and menton. These are split by the ANS-ME line and compared. ANS-ME parallels the visual dividing line from subnasale to soft tissue menton in the lower face.Linear values and angles can be measured while the anatomy can be determined. Like the horizontal planes, this data is quite sensitive to head rotation.

Volumetric comparisonTwo volumes (polygons) are calculated from the area defined by each Co-GA-ME and the intersection with a perpendicular from Co to MSR. A computer can superimpose one polygon upon the other to provide a percentile value of symmetry.

GACOME

Maxillomandibular comparison of asymmetry Perpendiculars are drawn to MSR from J and GA, and connecting lines from Cg to J and GA. This produces two pairs of triangles, each pair bisected by MSR. If perfect symmetry is present, the four triangles become two, J-Cg- J and AG-Cg-GA.

Linear asymmetries

The vertical offset as well as the linear distances are measured from MSR to Co, C, J, AG and ME.

Maxillomandibular relation

To allow tracing of the functional posterior occlusal plane, a .014" wire is placed across the mesio-occlusal areas of the maxillary first molars. The wire should extend about 3 mm buccally to make it easy to recognize on the head film.Distances are measured from the buccal cusps of the upper first molars (on the occlusal plane) along the J perpendiculars. The AG plane, MSR, and the ANS-ME plane are also drawn to depict the dental compensations for any skeletal asymmetries in the horizontal or vertical planes (maxillomandibular imbalance). Midline asymmetries of the upper and lower incisors and ME-MSR are also provided.

Frontal vertical proportions

Skeletal and dental measurements are made along the Cg- ME line with divisions at ANS, Al, and Bl. The following ratio are calculated.1. Upper facial ratio Cg-ANS/Cg-ME 42 % 2. Lower facial ratio ANS-ME/Cg-ME 58%3. Maxillary ratio ANS-A1/ANS-ME 54%4. Total maxillary ratio ANS-Al/Cg-ME 31%5. Mandibular ratio B1 -ME/ANS-ME 55%6. Total mandibular ratio B 1 -ME/Cg-ME 32 %7. Maxillomandibular ratio ANS-A1/B1- ME 97%

Ricketts analysis

Ricketts analysis gives a normative data of parameters measured, which is helpful in determining vertical, transverse dental and skeletal problems. It has five components:1. Dental relations2. Skeletal relations3. Dental to skeletal4. Jaw to cranium5. Internal structure.

Dental relations

Dental relations1. Molar relation left (A6-B6). 2. Molar relation right (A6-B6). A differences in width between the upper and lower molars measured at the most prominent buccal contour of each tooth. Used to describe the buccal/lingual occlusion of first molars.

2 mmClinical deviation1.5 mmnorm

2mmClinical deviation1.5mmnorm

Intermolar width (B6-B6). It is measured from the buccal surface of the mandibular left first molar to the buccal surface of the mandibular right first molar. This is helpful in determining the aetiology of a crossbite.

Intercanine width (B3-B3). It is measured from the tip of the mandibular right canine to the tip of the mandibular left canine.Denture midline. It is measured from the midline of the upper arch to the midline of lower arch

Skeletal relations

Maxillomandibular width right. It is measured from the jugal process to the frontal facial plane (constructed from the medial margins of the zygomaticofrontal sutures to AG point). Used to measure skeletal crossbite. Maxillomandibular width left. It is measured on left side

Maxillomandibular midline. It is measured by the angle formed by the ANS-ME plane to a plane Perpendicular to ZA-AZ plane.Interpretation: Determines the mandibular midline deviation with respect to the midsagittal plane. This asymmetry might be the consequence of functional or skeletal problems

4. Maxillary width (J-J). It is measured as transverse distance from J-J.Mandibular width (AG-GA). It is measured as transverse distance from AG-GA.

Dental to skeletal

Clinical deviation

1. Lower molar to jaw left (B6 to J-GA left).Lower molar to jaw right (B6 to J-AG right). It is measured from the buccal surface of the lower molars to a plane from the jugal process to the antegonial notch. Norm: 6.3 mm, clinical deviation: 1.7 mm.increased measure indicates the likelihood of a buccal mandibular expansion

Clinical deviation

3. Denture-jaw midline. It is measured from the midline of the denture to the midline of the jaws (ANS-ME).

Clinical deviation

Occlusal plane tilt. It describes the difference in the height of the occlusal plane to the ZL-ZR plane.

Clinical deviation

Jaw to cranium

Clinical deviation

Postural symmetry. It is measured by the difference inthe angles (left and right) formed by a plane from the zygomatic suture to antigonion andantigonion to the zygomatic arch. Used to determine cause of asymmetries.Interpretation: Used for the diagnosis of asymmetry

Clinical deviation

Internal structure

Clinical deviation

Nasal width. It is measured from the widest aspects of the nasal cavity. May be used to determine the cause of mouth breathing.

Clinical deviation

2.Nasal height. It is measured by the distance from the ZL-ZR plane to the anterior nasal spine.Facial width. It is measured at AZ-ZA points. It essentially describes width at zygomatic arches and can be useful in maxillary expansion decision making.

Maxillomandibular differential values and ratioMaxillomandibular differential values and ratios obtained from PA cephalogram help us in estimating the transverse deficiency and also the amount of expansion required.Maxillomandibular differential value is the difference between mandibular width (AG-GA, antigonion - antigonion) and maxillary width (J- J). A differential in total width of about 20 mm was considered satisfactory

A definite ratio exists between maxillary and mandibular width and also nasal cavity to maxilla, which will help us in determining the relative transverse problem in the arches. The value of ratio of maxilla to mandible is about 80%, and the ratio of nasal cavity to maxilla ranges from 40 to 42%.

Summary

PA cephalogram is an essential diagnostic aid in cases with facial symmetry. It can answer the important aspects of facial symmetry like maxillomandibular width, occlusal plane level, dental to skeletal midline, skeletal midlines and chin location. It is helpful in determining true asymmetry from the apparent.The PA cephalogarms are used to assess location and its quantification of transverse problem, skeletal class III, and for prediction of upper canine impactions.PA cephalogram is used to measure the amount of maxillary expansion required and that has occurred with treatment.

Thank you