AN OUTLINE OF
“LATERAL CEPHALOMETRICS”
BY
DR. ULFAT BASHIR RAJA MCPS, FCPS (Orthodontics)
de’ Montmorency College of Dentistry, Lahore
PREFACE It was a nutshell to compile this manuscript but ALHAMDLILLAH somehow it is in black & white. Because you have to start somewhere and enough is never enough. I would be highly obliged for any suggestion / amendment to improve such endeavors in future. ULFAT 23.07.02.
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Introduction to Cephalometrics: It is one of the branches of Orthodontics that deals with the study of skull in different aspects in order to determine the skeletal, dental or soft tissue changes that can effect the occlusion and is one the mandatory record to diagnose the orthodontic problems. It is also an important tool in research and clinical orthodontics. It is a 2-dimensional study of a 3-dimensional object. The prime uses of Cephalometrics are: Classification of malocclusion Studying growth of the jaws or soft tissues Diagnosis of the orthodontic problem Treatment planning for such problems Evaluating the treatment brought about by orthodontics orthognathic surgery Predicting the treatment outcome or prognosis of the results Detecting the morphology of the orthodontic problem Detecting the extent or degree of the orthodontic problem
or
Broadly can be divided into 3 sub-branches: 1) 2) 3)
Cephalometric Radiology (information before getting an image) Practical Cephalometrics (manipulating with the cephalometric image) Interpretation of Cephalograms (the detail of the data collected to be utilized in order to diagnose and treat the orthodontic problem)
The details of 1) are more important at postgraduate level but some basic information is required at undergraduate level.
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Brief History: Craniometry was the study of dried skulls used before cephalometry. Paciniin in 1922 introduced teleroentgenographic lateral head film radiography Broadbent in USA and Hofrath in Germany in 1931 started with cephalostat machine
BASIC REQUIREMENTS FOR CEPHALOGRAMS: X-Ray source A specialized machine called as “Cephalostat” A patient It is different from conventional skull radiography in terms of standardized technique. THE BASIC VIEWS OF CEPHALOGRAMS ARE Lateral view (the most common used view to study in sagittal & vertical planes of space) PA view (to study in transverse plane) Oblique view (the rays given in 350 or 1350 to study the mixed dentition stages)
THE X-RAY SOURCE: The X-ray tube is a high vacuum tube comprising of three basic components that generate the X-rays are, a cathode, an anode and the electrical power supply.
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Numerics: Tube voltage = 60-90 KV Tube current = 4-14 mA Exposure time = 0.01-4 sec. Source-patient distance (mid sagittal) = 5 feet (152.4 cm) Patient-film distance = 1 ft Extra-oral film size = 8” x 10” (203mm x 254mm) = 10” x 12” (254mm x 305mm) CEPHALOSTAT (fig. 1): Ear rods inserted in the external auditory meatuses Head is oriented horizontally with the Frankfort plane parallel to floor Mid sagittal plane vertically parallel to the cassette or film A forehead clamp positioned at nasion A chin rest Natural head position or True Horizontal plane is achieved by placing a mirror in front of the patient in which he has to look directly in his eyes Teeth in centric occlusion and lips in repose, but may be taken in centric relation e.g. in case of TMJ problems
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Practical Aspect: REQUIREMENTS FOR CEPHALOMETRIC TRACING: A lateral cephalogram An acetate matte tracing paper of 0.03” thickness & 8” x 10” dimension A sharp 3H drawing pencil Masking tape A geometry box with eraser & sharpener A viewing box or illuminator with covered black sheets except the ceph. image Dental casts of the same patient Tracing templates (optional) It is the left lateral view that is mostly used in orthodontics, but right lateral view is equally important. The PA and Oblique views are rarely used radiographs and will be considered separately. After getting a cephalometric image, an experienced one can directly understand or read the cephalometric norms from the image and can utilize the information received for clinical use. But for detailed analysis it has to be traced manually or digitized. Radiographic structures.
anatomy
is
mandatory
to
understand
the
craniofacial
The outline is drawn from the image given keeping in view the radiographic anatomy. The outline of lateral view should comprise of at least of following parts, but may vary according to the particular analysis used. Base of skull with outer table of frontal bone, planum sphenoidale & ethmoidale, body of sphenoid with sella turcica, basi-occiput, nasal bone, latero-inferior margins of orbit, external auditory meatus, pterygo-maxillary fissure, hard palate, maxillary most labial central incisor, maxillary first molars or second molars, maxillary second premolars, mandibular condyle,
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posterior and inferior borders, whole contour of symphysis, same dentition as for maxilla, lateral soft tissue profile of soft tissue chin, lips, external nose, and front of scalp. The outline for cervical spine, hyoid bone, pharyngeal spaces, soft palate, throat etc. is optional. The landmarks or points are divided into anatomical landmarks and derived or constructed landmarks. The anatomical landmarks are present on the anatomy or outline taken while derived points are constructed by joining lines from anatomical points outside the anatomical outline. The anatomical landmarks are broadly divided into unilateral (sagittal) and bilateral landmarks. The landmarks are generally divided into cranium, naso-maxillary and mandibular landmarks (only important points that are used conventionally in the cephalometric analysis of de’Montmorency College of Dentistry are given). CRANIUM (fig. ): UNILATERAL: Nasion (Na) = the intersection point between outer table of frontal bone & nasal bone Sella (S) = the imaginary central point in the sella turcica Basion (Ba) = the intersection of superior & inferior borders of basiocciput BILATERAL: Orbitale (Or) = the mid point of inferior margin of the orbit Porion (Po) = the mid point on superior margin of external auditory meatus Ptergomaxillary fissure (Ptm) = the intersecting poing between anterior & posterior margings of ptergomaxillary fissure
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Articulare (Ar) = the intersecting point between inferior border of basiocciput & posterior border of condyle NASOMAXILLARY COMPLEX (fig. ): UNILATERAL: Anterior nasal spine (ANS) = the anterior most point on the anterior nasal spine or hard palate Posterior nasal spine (PNS) = the posterior most point on the contour of posterior nasal spine or hard palate Point A (sub-spinale) = the deepest point on the concavity of the contour between ANS & labial cortical plate of the most labially placed maxillary central incisor
MANDIBLE (fig. ): UNILATERAL: Point B (supra-mentale) = the deepest point on the concavity of labial cortical plate of most labially placed mandibular central incisor Pogonion (Pog) = the anterior most prominent point on the outer contour of the bony chin Menton (Me) = the inferior most point on the outer contour of the bony chin Gnathion (Gn) = the anterior & inferior point on the outer contour of the bony chin BILATERAL: Gonion (Go) = the posterior & inferior point on the contour of the angle of mandible Condylion (Co) = the mid point on the superior margin of the condyle
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SOFT TISSUE LANDMARKS (fig. ): Nasion (Ns) = soft tissue nasion at the intersection of outer contour of the scalp over frontal bone & skin over nasal bone Pronasale (Pn) = the point on the tip or apex of external nose Subnasale (Sn) = the point of intersection of lower border of nose with the outer contour of the upper lip Labrale superius (Ls) = the prominent point on the vermilion of the upper lip Labrale inferius (Li) = the prominent point on the vermilion of the lower lip Pogonion (SPog) = the soft tissue point on the prominent aspect of the soft tissue chin Steiner (S) = the point taken at the half of the distance between the points Pn & Sn There are two derived landmarks taken in this routine ceph. analysis that will be explained later. After demarcating these landmarks five lines or planes are drawn in horizontal plane by joining two points in the following fashion (fig. ):Sella nasion plane (SN) = by joining sella & nasion points Frankfort horizontal plane (FH) = by joining the orbitale & porion points Palatal plane or Maxillary plane (PP) = by joining the ANS & PNS points Functional occlusal plane (FOP) = by joining the distal occluding points of upper & lower first molars (or second molars) & mesial occluding points of second premolars Mandibular plane (MP) = joining the Go & Me or Go & Gn or a tangent drawn from Me to base of the jaw close to the Gonion point (fig. ).
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Two planes are drawn in the vertical plane in the following way (fig. ):Facial plane = the anterior plane drawn by joining the Na & Pog Ramal plane = the posterior plane drawn by a tangent line from the articulare to the posterior border of the ramus close to the Go point DERIVED OR CONSTRUCTED POINTS (fig. ): These two vertical planes intersect with the mandibular plane (MP) at two points to form two constructed points:Constructed mandibular Constructed mandibular
Gnathion (CGn) = by intersection of facial plane & planes Gonion (CGo) = by intersection of ramal plane & planes
From these points and planes, the linear and angular measurements are being taken for further analysis and inferences. DIFFERENCE BETWEEN ANATOMICAL FUNCTIONAL OCCLUSAL PLANE:
OCCLUSAL
PLANE
&
The ideal or normal occlusal plane that passes through occluding surfaces of the posteriors as well as incisors while functional occlusal plane passes from the occluding posteriors (that are used in function) irrespective of the position of the incisors (that are mostly malaligned in case of orthodontic patients). DRAWBACKS IN THE RADIOGRAPHIC IMAGE: Sometimes, the image is not clear to be traced because of the changed position of the patient in the cephalostat during exposure or due to facial asymmetry, or greater magnification of the image of the skull facing towards the X-ray source or farthest from the film for the bilateral structures. So, the bilateral structures (e.g. , the rami and inferior borders of mandible are first drawn independently and then an average is drawn by a broken line (fig. ) .
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Cephalometric Analysis: There are many cephalometric analysis established in the world that are used for a variety of the orthodontic problems, research and clinical aspects. Some of famous and mostly used analysis are:Down’s analysis Steiner analysis Rickett’s analysis Mc Namara analysis Witt’s analysis Jaraback analysis Sassoni analysis Various institutes of the world have also established their own cephalometric analysis derived from these analysis or on the basis of the research at their part. de’ Montmorency College of Dentistry, orthodontic department have also compiled such analysis that have mainly derived its values from Down’s, Steiner’s and Rickets’ analysis. Stepwise method of tracing this analysis is described, however, author would recommend the practical demonstrations as well for the better understanding. The cephalometric image is placed on the viewing box and the tracing sheet is placed and the masking tape is applied on one left whole corner of the image. The name of the patient, his age & sex, and the date of tracing with the name of the tracer are written in the left upper corner of the tracing sheet (fig. ). Three registration crosses are drawn at three different sites of the tracing, e.g., one at the level of spine, one at anterior cranial fossa and one at the posterior cranial fossa. One can rearrange the tracing sheet if displaced during tracing procedure, with the help of these registration marks (fig. ).
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With the help of the pencil or colour markers, keeping in view the earlier described landmarks, draw the outline. The anatomical landmarks are taken as described earlier. The five horizontal planes are drawn from top to bottom, and then two vertical planes are drawn that also give the two constructive landmarks as is shown in fig. No. Now the tracing is ready for the detailed analysis, every analysis is consisted of skeletal, dental and soft tissue analysis. The skeleton is studied in sagittal & vertical aspects. SAGITTAL ANALYSIS (fig. ): This analysis is comprised of 4 angles and 3 linear measurements. Before this analysis, draw NA line by joining the nasion and A points, and NB line by joining the nasion and B points. The 4 angles are SNA, SNB, ANB (the difference between SNA & SNB) and SNPog (Facial Angle). These all angles can be measured at once by placing the protractor at nasion point. The 3 linear measurements are I) Anterior cranial base length (X) measured between points S & Na, II) Mandibular corpus length (MCL) measured between CGo & CGn, III), the Witt’s value or AO-BO distance (the perpendicular lines are drawn at occlusal plane from the points A & B respectively & the linear distance on occlusal plane is measured. The distance is considered positive if AO is ahead of BO line and is negative in opposite situation. All angles are measured in degrees while the linear measurements are taken in millimeters.
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VERTICAL ANALYSIS (fig. ): This analysis is comprised of 8 angles and 2 linear measurements or ratios of linear measurements. The 8 angles are SN-MP >, SN-OP >, SN-PP >, N-S-Gn (Y-Axis growth >), MMA (maxillary-mandibular >), Upper-Occlusal (PP-OP >), Lower-Occlusal (MP-Occlusal >) and Sum of Posterior (inner) angles {Saddle > (N-S-Ar) + Articulare > (S-Ar-CGo) + Gonial > (Ar-CGo-Me)}. The 2 linear ratios are i) Jaraback ratio i.e. ratio of posterior face height to total anterior facial height {posterior facial height is taken from point S to CGo, and anterior facial height is taken between points Na & Me}& ii) ratio of lower anterior facial height to total anterior facial height {lower face height is taken between ANS to Me points}. DENTAL ANALYSIS (fig. ): This analysis is consisting of 6 angles and 3 linear measurements. Practically only 2 lines have to be drawn i.e. upper incisor & lower incisor lines drawn by joining their apices and tip of incisal edges. The 6 angles are Upper incisor to SN plane > (U.I-SN), Upper incisor to palatal plane > (U.I-PP), Inter-incisal > (IIA), Incisor-mandibular plane angle (IMPA), Upper incisor to NA > (U.I-NA), Lower incisor to NB > (L.I-NB). The 3 linear measurements are I) Upper incisor to NA line distance. II) Lower incisor to NB line distance III) Holdaway Ratio (the ratio between L.I. – NB: Pog – NB distances).
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SOFT TISSUE ANALYSIS (fig. ): This analysis consists of 5 measurements including 4 linear and one angular measurement. Two lines are drawn from soft tissue Pogonion, one is esthetic line (E plane) joining SPog & Pn, and other line is Steiner line (S line) joining SPog & S points. The linear distances are measured from Ls of upper & Li of lower lip to these lines to get 4 linear measurements of this analysis. The distance is taken in minus if lines are ahead of the lips & is taken in plus in vice versa situation. One angle is naso-labial angle that is drawn by two tangent lines. One line is from Sn to base of nose and other is from Sn to upper lip.
Interpretation: There are many ways for interpretation of lateral cephalograms but one should know the basic radiographic anatomy of the lateral view and be able to understand the changes that occur with the passage of age. One way can be directly comparing the two images provided, these two images can be of the same patient at different ages or before or after the treatment or one image can be of the patient of some particular age and the other can be of a person of same age, who has excellent / ideal skeletal & dental & soft tissue structures. The other way is to get some craniofacial norms in terms of angles or linear measurements by tracing the cephalometric image and then comparing these norms of a particular patient with some standardized / ideal / normal established norms. Standard norms for each race and country vary significantly. Standard norms that can apply all the population groups of the world are not available or possible so, it is recommended that each of the country should have its own standard norms by which they can compare the malocclusion levels. In our country we are still in the process of establishing the cephalometric norms and hence believe the established American norms for the utility in orthodontic research and clinical purpose for our patients.
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The composite analysis used at orthodontic department de’Montmorency College of Dentistry, has mainly derived its norms from the Down’s, Steiner’s and Rickett’s analysis (American) and it is assumed that it is practically applicable for the population of this area. There are some terminologies that are important to discuss before elaborating the interpretation of lateral cephalometry in detail. PLANES OF ORIENTATION: These are the planes by which one is oriented in cephalostat while taking the cephalometric image. E.g. the Frankfort horizontal plane or True horizontal plane (both have already been explained). PLANES OF SUPERIMPOSITION OR REFERENCE: These are the planes of reference taken from the relatively more stable anatomical landmarks. Absolutely there is no such plane or landmark that may be considered the stable but SN plane or Frankfort Horizontal plane may be used for such purpose. Subsequent tracings of the same person or with some standard of a particular age can be superimposed by placing on these reference planes and treatment changes or growth changes may be compared. By taking these planes as reference the angular or linear measurements of a tracing are executed. COMPARISON OF FRANKFORT HORIZONTAL PLANE & SN PLANE:
FRANKFORT HORIZONTAL PLANE is formed by Porion & Orbitale. Porion is relatively less stable, because the image of ear rods gives the machine landmark rather than anatomical. In these days flexible ear rods are being used which give relative more stable position of porion. Otherwise anatomical porion is posterior & superior to the machine porion. The orbitale is also relatively less stable because it goes on growing after puberty (a part of nasomaxillary complex), and secondly it is one of the bilateral points, which is again less stable. SN PLANE is formed by two relatively more reliable sagittal (unilateral) points than the bilateral points and secondly the Sella to Nasion is anterior cranial base length, which completes its growth by 6 years of age, hence is more reliable than Frankfort Horizontal Plane.
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ANATOMICAL PLANES: These are the planes formed by joining two anatomical landmarks and have been explained. The composite analysis is studied for skeletal, dental and soft tissues. The skeleton is studied in lateral view in sagittal (horizontal / anteroposterior) and vertical aspects.
THE SAGITTAL ANALYSIS: It is for the studying jaws in sagittal direction in relation with each other as well as with reference to the cranial base (SN Plane – the plane of reference in this composite analysis). The detailed analysis is described as follows: SNA (800-840) This angle describes the antero-posterior relationship of maxilla with cranial base. Raised values than normal show the prognathic maxilla and reduced than normal would show retrognathic maxilla. The change in these values can be due to magnitudinal or directional change in maxilla. The increase in mass or upward rotation of the maxilla with the fixed cranial base raises this value while downward rotation or decreased mass lowers this value. SNB (780-820) This angle describes the antero-posterior relationship of mandible with cranial base. Raised values than normal show the prognathic mandible and reduced than normal would show retrognathic mandible. The change in these values can be due to magnitudinal or directional change in mandible. The increase in mass or upward rotation of the mandible with the fixed cranial base raises this value while downward rotation or decreased mass lowers this value.
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ANB (0-40) The SNB value is subtracted from SNA value to get this angle. The reason is because normally SNA value is more than SNB value. If this value is in range of 0-40, it is skeletal class I case. If it is more than 40, it is skeletal class II and value is written in positive (+5, +6 values show mild problem, +7, +8 values show moderate & +9, +10 values show severe problem). Skeletal II may be due to prognathic maxilla, or retruded mandible or the combination of these two (composite class II). If it is less than 0, it is skeletal class III and value is written in negative (-1, -2 values show mild problem, -3, -4 values show moderate & -5, -6 values show severe problem). Skeletal III may be due to prognathic mandible, or retruded maxilla or the combination of these two (composite class III). LIMITATIONS OF ANB: If cranial base is fixed and do not have any change, this angle is reliable, but if SN plane (cranial base) gets by any change in the position of the Nasion or Sella points, may lead to pseudo presentation of the case. Hence the normal case may show increased or decreased values of the SNA or SNB. (Sella can change its location by any Pituitary tumor & Nasion can also change by some trauma or other environmental factors). Both SNA and SNB may show very small or very large values by the involvement of SN changed inclination, in such cases rest of the readings may be noticed to make an exact image of sagittal discrepancy. This problem is overcome by correcting the ANB value. True Horizontal Plane or Frankfort Horizontal Plane can correct the ANB value. True Horizontal Plane is a perpendicular line drawn on the vertical anterior hanged chain from Sella point. The angle between True Horizontal & SN Plane must be 60 – 80. So, if value of this angle is increased (show relative decreased values of SNA or SNB), the increased value is added p in the SNA or SNB to correct them & vice versa.
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FACIAL ANGLE (SN-Pog) (770+40) This angle determines the chin position in relation with cranial base in sagittal plane. Raised values describe the protruded chin and decreased value show retruded chin. It is not always coinciding with the raised or lower value of SNB because it is a separate entity that shows the independent remodeling of the chin button in space and it depends upon a number of factors. E.g. in class II cases with deep bite, chin button is more prominent and gives increased value of this angle. This angle also like ANB can have limitations of pseudo presentation due to the fact of change in inclination of SN Plane. ANTERIOR CRANIAL BASE LENGTH (X): It has variable values from individual to individual but it is considered in relation with mandibular corpus length. MANDIBULAR CORPUS LENGTH (MCL) (X+7): For a normal profile person the value of MCL should be X+7. Relatively lower values would show mandibular deficiency and larger values show enlarged mandible. So, MCL may confirm the ANB values. E.g. if ANB shows class II due to mandibular deficiency, MCL value will show relatively decreased value. Like ANB or Facial angle, this value may have drawback due to the involvement of SN Plane. AO – BO DISTANCE (WITT’S VALUE) (Male = -1 mm, Female = 0) If the jaws have just linear change in growth, Witt’s value shows some significance and can confirm the ANB value of the same person. E.g. in skeletal class II cases, Witt’s shows raised positive values than normal, and in skeletal class III cases, Witt’s show negative values. As Witt’s value also depend upon the inclination of the occlusal plane, so any rotational factor may pseudo interpret the skeletal II or III situations. E.g. two different cases with similar ANB value may have different Witt’s value, making clinically more difficult cases to be handled with more changed Witt’s values (fig. )
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CORELATION OF SAGITTAL AND VERTICAL RELATIONSHIP: Any change in vertical plane by some rotational effect either in clockwise or counterclockwise direction, may have affect in the sagittal relation of the jaws. E.g. in skeletal III cases, clockwise rotation of the jaws, may have a masking affect, and counter clockwise rotation has an aggravating effect. This is vice versa for class II problems. Sometimes, ANB, Witt’s and other sagittal values do not clear the picture, that problem lies in which of the jaw, due to the compensatory change in the vertical aspect. Such situation can be elaborated through Mc Namara analysis, in which maxillary and mandibular lengths can be compared according to the lower anterior facial heights. Mc Namara has formulated a table of this data, by which a person’s norms can be compared to see which jaw is at fault.
OVERALL FINDING: This analysis shows skeletal class (I / II / III) and which jaw is sagittaly at fault. An overall impression is noticed by all these norms to find the sagittal discrepancy the jaw involved and what appropriate treatment may be adopted to resolve this problem. E.g. a sagittaly deficient lower jaw may be treated by functional appliances if case in growing stage and may be treated by surgical advancement in adults.
VERTICAL ANALYSIS: This analysis elaborates the jaws in relation with the cranial base in vertical direction. The detail of this analysis is as under: *SN-MANDIBULAR PLANE ANGLE (32 + 4) This is one of the important angles that determine the mandibular rotation in relation with SN Plane. Raised value than normal show high angle case (skeletal open bite) and decreased values than normal show low angle case (skeletal deep bite).
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SN – PALATAL PLANE ANGLE (6 + 4): This angle determines the palatal rotation in relation with SN Plane. Raised value than normal show high angle case and decrease value than normal show low angle case. SN – OCCLUSAL PLANE ANGLE (17 + 4): This angle determines the occlusal plane rotation in relation with SN Plane. Raised value than normal show high angle case and decrease value than normal show low angle case. Relative intrusion or extrusion of teeth may change this angle because of the change in the occlusal plane. *MAXILLARY-MANDIBULAR ANGLE (MMA) (25 + 4): This is also one of the important angles that determine the mandibular rotation in relation with palatal plane (maxillary plane). Raised value than normal show high angle case (skeletal open bite) and decreased values than normal show low angle case (skeletal deep bite). This angle is more reliable than SN-Mandibular plane angle because of the involvement of SN plane. UPPER OCCLUSAL (11 + 4): This angle demonstrates the changes that occur between maxillary plane and occlusal plane in vertical plane. Normally this angle is changed in relative intrusion or extrusion of the upper teeth. LOWER OCCLUSAL (14 + 4): This angle demonstrates the changes that occur between mandibular plane and occlusal plane in vertical plane. Normally this angle is changed in relative intrusion or extrusion of the lower teeth.
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*Y-AXIS / GROWTH AXIS ANGLE (66 + 4): The decreased values than normal show the low angle tendency (chin is forward & upward) and high values than normal show high angle tendency (chin is downward & backward). This angle also shows the normal growth pattern of the lower jaw i.e. forward & downward or in other words the jaw grow in the direction of this angle. *SUM OF INNER / POSTERIOR ANGLES (396 + 4): I)
SADDLE ANGLE (123 + 5):
This angle determines any change in the SN Plane inclination or at the level of the pituitary gland or any change in the remodeling between middle & posterior cranial fossa. II)
ARTICULARE ANGLE (143 + 6):
This angle mainly tells about the changes that occur at or around the condyle during growth or by some pathology. III) GONIAL ANGLE (128 + 7): This angle is mainly the determinant of mandibular rotation or the remodeling between the ramus & corpus. *JARABACK RATIO (RATIO OF POSTERIOR FACIAL HEIGHT TO TOTAL ANTERIOR FACIAL HEIGHT) (65% + 4%): This ratio is reverse to the rest of the measurements of the vertical analysis, that it is decreased than normal in high angle cases and increases than normal in the low angle cases. As there are more chances of changes in the anterior facial height, it determines the high or low angle cases.
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RATIO OF LOWER ANTERIOR FACIAL HEIGHT TO TOTAL ANTERIOR FACIAL HEIGHT (54% + 4%): This ratio like the Jaraback ratio increased in low angle cases & vice versa. As more changes occur in the lower anterior facial height, so this ratio confirms the high or low angle tendency.
OVERALL FINDING: Overall image of high or low angle is calculated by * readings. This analysis shows relative high or low angle case. High angle cases are difficult to treat in orthodontics, as anchorage demands are increased, otherwise good for the extraction cases as the spaces are closed spontaneously, while opposite to it, the extractions in the lower arch in low angle cases are extremely difficult to handle as it is hell of job to close the spaces.
DENTAL ANALYSIS: This analysis describes the sagittal positioning of the upper and lower incisors in relation with cranial base and upper and lower apical bases. The norms are described as follows. UPPER INCISOR TO SN PLANE ANGLE (1020 + 50): More than normal range demonstrates the proclination of upper incisors & less than normal show retroclination of upper incisors. Like other angles it may have pseudo presentation due to involvement of SN Plane as already described. UPPER INCISOR TO PALATAL PLANE ANGLE (1080 + 50): More than normal range demonstrates the proclination of upper incisors & less than normal show retroclination of upper incisors. When these two measurements are compared for proclination or retroclination of incisors, upper incisor to its own apical base reading is more reliable.
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INCISOR MANDIBULAR PLANE ANGLE (IMPA) (900 + 50): It shows the inclination of lower incisor to its apical base, if increased than normal, shows proclination of lower incisors, and if less than normal shows retroclination. This angle markedly compensates by the underlying status of the skeleton i.e. in class II cases with mandibular deficiency, IMPA is increased by the dento alveolar compensation, and in class skeletal III cases, it may reduce, in order to establish normal overjet. This angle is quite significant in predicting the prognosis of the orthodontic treatment, as the uprighted lower incisors (normal IMPA) is a requisite of long-term stable results. In the same way it also tells about the space deficiency in the lower arch. Each degree of reduction in this angle would require 0.8 mm of space in the arch. INTER INCISAL ANGLE (IIA) (1350 + 50): This angle decreases with the proclination of the either of the two incisors or is raised with retroclination of either of the two. But it may show a significant change if both incisors are proclined (bimaxillary proclination) or retroclined (bimaxillary retroclination). So, this reading would support the idea picked by the inclination of the incisors by their apical bases (e.g. proclined lower incisors would show reduced value of this reading). UPPER INCISOR TO NA LINE ANGLE (220 ): This angle is increased in case of proclination and decreased in retroclination of upper incisors supporting the idea framed by upper incisor angles to the palatal plane or SN Plane. LOWER INCISOR TO NB LINE ANGLE (250 ): This angle is increased in case of proclination and decreased in retroclination of lower incisors supporting the idea framed by IMPA.
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UPPER INCISOR TO NA LINE DISTANCE (4 mm): This distance is normally increased in case of proclination and decreased in retroclination of upper incisors supporting the idea framed by upper incisor angles to the palatal plane or SN Plane or to NA line. LOWER INCISOR TO NB LINE DISTANCE (4 mm): This distance is normally increased in case of proclination and decreased in retroclination of lower incisors supporting the idea framed by IMPA or Lower incisor to NB line angle. NORMALLY UPPER INCISOR TO NA LINE ANGLE & DISTANCE COINCIDE THAT MEAN IF ONE IS INCREASED THE OTHER ALSO INCREASES & VICE VERSA. IT IS ALSO SAME FOR LOWER INCISOR TO NB LINE ANGLE AND DISTANCE. BUT SOMETIMES THIS IS NOT APPLICABLE IN SOME SITUATIONS SO THAT DISTANCE CAN VARY WITH SAME ANGULATIONS & DISTANCE CAN BE SAME WITH DIFFERENT ANGULATIONS (fig. ). HOLDAWAY RATIO (1 : 1): As described earlier, this ratio is between lower incisor inclination and prominence of the chin. Ideally this ratio should be 1:1 (4:4), but it may be disturbed by one of these two. E.g. 8:4 means lower incisors are relatively more proclined and need to be retracted orthodontically to match this ratio. In other case if it is 4:8, it shows the chin relatively more prominent and need to be reduced surgically by genioplasty. If difference between these two distances is in the range of 2 mm, it is not significant, but significant if difference is more than 4 mm, sometime, ratio is such that both orthodontic and surgical intervention is required. The chin button prominence is seen by Facial Angle and Holdaway ratio in sagittal direction and by Y-axis Angle in vertical direction (e.g. in those cases where due to locked bite chin button becomes prominent even in class I cases).
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OVERALL FINDING: This analysis concludes whether a particular case is with upper incisors are proclined or retroclined, in the same way lower incisors or to find bimaxillary proclination or retroclination.
SOFT TISSUE ANALYSIS: This analysis in orthodontics determines whether soft tissue is changed by the underlying skeleton or dentition and the extent to which the profile of the person is changed. Soft tissues can independently be changed and cause a change in the soft tissue profile. So, this analysis is a comparative study of one’s profile with the standard norms. Like other aspects of the cephalometrics, the soft tissue norms vary with the different population groups. The underlying skeleton & dentition may affect the profile of the patient or it can be affected by the different soft tissue growth patterns or a patient may exhibit the combination of the two. Soft tissue can be studied in the population with balanced occlusion & skeleton or the population with some underlying skeletal / dental malocclusion. There are a number of soft tissue analyses available in the world, but we will discuss some of the important norms according to the composite analysis. Soft tissues can be studied in horizontal (antero- posterior / sagittal) or vertical planes. But here are mentioned only horizontal measurements. UPPER LIP TO E LINE DISTANCE (-3 + -2 mm): The positive distance shows the protrusive upper lip (e.g. in prognathic maxilla or protruded upper incisors) and negative distance within range show normal lip but negativity more than the range will show retrusive lip (e.g. in case of cleft lip or palate or hypoplastic maxilla or retroclined incisors). LOWER LIP TO E LINE DISTANCE (-2 + -2 mm): The positive distance more than normal shows the protrusive lower lip (e.g. in protruded lower incisors or prognathic lower jaw) and negative distance within range show normal lip but negativity more than the range will show retrusive lip (e.g. retroclined lower incisors).
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UPPER LIP TO S LINE DISTANCE (0 + 2 mm): It shows same results as the upper lip to E line distance, but this measurement rules out any growth changes in the nasal tip. LOWER LIP TO S LINE DISTANCE (0 + 2 mm): It shows same results as the lower lip to E line distance, but this measurement rules out any growth changes in the nasal tip. NOTE: All these linear measurements may give pseudo presentation in case of any abnormal growth of soft tissue chin or nasal tip / nasal base. Incompetent lips are a clinical term, that may be related with protrusive or retrusive lips. NASOLABIAL ANGLE (1020 + 80): In case of prognathic maxilla or proclined maxillary incisors, this angle becomes more acute (less than lower range) and in retrognathic maxilla or retroclined incisors, this angle becomes more obtuse (more than upper range). This angle supports the above said norms. Again this angle cannot differentiate the nasal part of this angle (only can rule out the change in upper lip), one of the drawbacks of this angle.
OVERALL FINDING: Show relative protrusivenes or retrusiveness of the lips and can describe the lip competency or profile of the patient.
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