Cephalometric Tracing App
Azalee Freas
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Lydia Harris graduated from Bristol dental school in 2012 and is currently working as a Maxillofacial SHO in Bath. This article discusses the uses, indications and basic anatomical features present on a Lateral Cephalometric Radiograph, as well as discussing the basic definitions of points and planes used in cephalometric analysis.
The LCR is used primarily in orthodontic diagnosis and treatment planning, particularly when considering orthognathic surgery. It is a useful record prior to treatment and can be used during treatment to assess progress. It is used to assess the aetiology of malocclusion; to determine whether the malocclusion is due to skeletal relationship, dental relationship or both. These radiographs can also be used for research purposes, although the radiographs must be clinically justified.
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Cephalometric analysis is the clinical application of cephalometry. It is analysis of the dental and skeletal relationships of a human skull.[1] It is frequently used by dentists, orthodontists, and oral and maxillofacial surgeons as a treatment planning tool.[2] Two of the more popular methods of analysis used in orthodontology are the Steiner analysis (named after Cecil C. Steiner) and the Downs analysis (named after William B. Downs).[3] There are other methods as well which are listed below.[4]
Cephalometric analysis depends on cephalometric radiography to study relationships between bony and soft tissue landmarks and can be used to diagnose facial growth abnormalities prior to treatment, in the middle of treatment to evaluate progress, or at the conclusion of treatment to ascertain that the goals of treatment have been met.[5] A Cephalometric radiograph is a radiograph of the head taken in a Cephalometer (Cephalostat) that is a head-holding device introduced in 1931 by Holly Broadbent Sr. in USA.[6] The Cephalometer is used to obtain standardized and comparable craniofacial images on radiographic films.
To carry out cephalometry, the X-ray source is placed a steady five feet away from the mid sagittal plane, with film situated just 15 cm from there. This allows for accurate measurements to be taken and recorded.[7] Distance has a direct impact on cephalometric image magnification. With an object-to-film interval of 15 cm and a source-to-object span of 5 feet, magnification of anatomical landmarks will be reduced in all three dimensions.When attempting to analyze a patient's anatomy through lateral and frontal cephalograms, the challenge arises due to these images being two-dimensional projections of three-dimensional structures. Magnification and distortion as an outcome of traditional radiography further complicates the process by blurring important details.[8]
Lateral cephalometric radiograph is a radiograph of the head taken with the x-ray beam perpendicular to the patient's sagittal plane. Natural head position is a standardized orientation of the head that is reproducible for each individual and is used as a means of standardization during analysis of dentofacial morphology both for photos and radiographs. The concept of natural head position was introduced by Coenraad Moorrees and M. R Kean in 1958[9][10] and now is a common method of head orientation for cephalometric radiography.[11][12]
Registration of the head in its natural position while obtaining a cephalogram has the advantage that an extracranial line (the true vertical or a line perpendicular to that) can be used as a reference line for cephalometric analysis, thus bypassing the difficulties imposed by the biologic variation of intracranial reference lines. True vertical is an external reference line, commonly provided by the image of a free-hanging metal chain on the cephalostat registering on the film or digital cassette during exposure. The true vertical line offers the advantage of no variation (since it is generated by gravity) and is used with radiographs obtained in natural head position.
A radiograph of the head taken with the x-ray beam perpendicular to the patient's coronal plane with the x-ray source behind the head and the film cassette in front of the patient's face.[13] PA ceph can be evaluated by following analyses that have been developed through the years:
A cephalometric tracing is an overlay drawing produced from a cephalometric radiograph by digital means and a computer program or by copying specific outlines from it with a lead pencil onto acetate paper, using an illuminated view-box. Tracings are used to facilitate cephalometric analysis, as well as in superimpositions, to evaluate treatment and growth changes. Historically, tracings of the cephalometric radiographs are done on an 0.003 inch thick matte acetate paper by using a #3 pencil. The process is started by marking three registration crosses on the radiograph which are then transferred to the acetate paper.
Anatomical structures are traced first and some structures are bilateral and have tendency to show up as two separate lines, should have an "average" line drawn which is represented as a broken line. These landmarks could include inferior border of mandible.
The basic elements of analysis are angles and distances. Measurements (in degrees or millimetres) may be treated as absolute or relative, or they may be related to each other to express proportional correlations. The various analyses may be grouped into the following:
SNA and SNB is important to determine what type of intervention (on maxilla, mandible or both) is appropriate. These angles, however are influenced also by the vertical height of the face and a possible abnormal positioning of nasion.[14] By using a comparative set of angles and distances, measurements can be related to one another and to normative values to determine variations in a patient's facial structure.[15]
The name Wits is short for Witwatersrand, which is a University in South Africa. Jacobsen in 1975 published an article called "The Wits appraisal of jaw disharmony".[16] This analysis was created as a diagnostic aid to measure the disharmony between the AP degree. The ANB angle can be affected by multitude of environmental factors such as:
Therefore, it measured the AP positions of the jaw to each other. This analysis calls for 1. Drawing an Occlusal Plane through the overlapping cusps of Molars and Premolars. 2. Draw perpendicular lines connecting A point and B Point to the Occlusal Plane 3. Label the points as AO and BO.[17]
In his study, Jacobsen mentioned that average jaw relationship is -1mm in Males (AO is behind BO by 1mm) and 0mm in Females (AO and BO coincide). Its clinical significance is that in a Class 2 skeletal patient, AO is located ahead of BO. In skeletal Class 3 patient, BO is located ahead of AO. Therefore, the greater the wits reading, the greater the jaw discrepancy.
Prof. Jean Delaire started developing his analysis along with Dr M. Salagnac back in the 70's. [citation needed] This analysis is still developed and improved by his pupils. This analysis is based on reciprocal proportion and balance and doesn't use standard deviation. It gives the ideal architecture the patient should have, based on his skull shape, posture and functions.[19]
This analysis by Arne Bjork was developed in 1947 based on 322 Swedish boys and 281 conscripts. He introduced a facial polygon which was based on 5 angles and is listed below. Bjork also developed the 7 structural signs which indicates the mandibular rotator type.[20]
Charles H. Tweed developed his analysis in the year 1966.[21] In this analysis, he tried describing the lower incisor position in relation to the basal bone and the face. This is described by 3 planes. He used Frankfurt Horizontal plane as a reference line.[22][23]
In a patient who has a clockwise growth pattern, the sum of 3 angles will be higher than 396 degrees. The ratio of posterior height (S-Go) to Anterior Height (N-Me) is 56% to 44%. Therefore, a tendency to open bite will occur and a downward, backward growth of mandible will be observed.[25]
This analysis, developed by Viken Sassouni in 1955,[26][27] states that in a well proportioned face, the following four planes meet at the point O. The point O is located in the posterior cranial base. This method categorized the vertical and the horizontal relationship and the interaction between the vertical proportions of the face. The planes he created are:
The more parallel the planes, the greater the tendency for deep bite and the more non-parallel they are the greater the tendency for open bite. Using the O as the centre, Sassouni created the following arcs
This analysis was developed by Egil Peter Harvold in 1974.[28] This analysis developed standards for the unit length of the maxilla and mandible. The difference between the unit length describes the disharmony between the jaws. It is important to know that location of teeth is not taken into account in this analysis.