Overview of Orthodontics, Cephalometric Analysis
Cephalometric analysis is a technique used to study the position and relationship of the skull and teeth. The process uses side-on X-rays of the head, taken using a specialized machine called a cephalostat. This technique is helpful, especially if there’s a need to plan forward or backward movements of teeth. However, it’s not needed for all types of braces or teeth-straightening treatments. Cephalometric analysis is most valuable if the position of the front teeth, known as incisors, needs to be significantly changed.
The roots of cephalometric analysis go back to the late 19th century when X-rays first started being used to study the head and neck. A significant leap in the field occurred in the 1930s when Holly Broadbent, an orthodontics professor at the University of Michigan, used it to understand how teeth relate to the skull. He developed the technique of measuring different angles and distances on X-ray images, laying the groundwork for cephalometric analysis.
In the years that followed, scientists built upon Broadbent’s initial findings, creating other methods like the Wits analysis. Nowadays, cephalometric analysis plays an important role in modern orthodontics. It’s a critical tool that helps in diagnosing and treating various dental and skeletal issues.
Anatomy and Physiology of Orthodontics, Cephalometric Analysis
Cephalometric analysis is a technique used to measure the angles and distances among various points in the head, especially in the jaw and teeth area. This helps doctors understand the upper and lower jaw’s position as related to your skull and each other. Not only that, but they can also detail how well your upper and lower teeth relate to each respective jaw. It’s done with the reference of an image and involves comparing a specific patient’s measurements to the general population’s averages. These measurements are normally done manually or through digital methods.
That being said, these measurements are not perfect and could encounter problems due to wrong projections or variations in measurements. These measurements could also differ based on who is doing the analysis. As a result, your doctor must consider these measurements, keeping in mind your entire facial structure, as sometimes one’s face or skull features may balance any differences from average values.
There are a lot of terms used to describe the various points and areas that the doctors consider in cephalometric analysis. These specific terms refer to different parts of your skull, and while they may sound difficult to understand, they’re very straightforward! Here are some of them explained in simpler terms:
1. Sella (S): This refers to the midpoint of a small depression in the skull where the pituitary gland resides.
2. Nasion (N): This is the most frontward point where the nasal and frontal bones meet.
3. Orbitale (Or): This is the lowest point on the eye socket’s edge.
4. Porion (Po): This is the highest point of your ear canal.
5. Anterior nasal spine (ANS) and Posterior nasal spine (PNS): These are the terminal points of the bones found in the nasal passage.
6. A-point (A) and B-point (B): These are different points on the jaws.
7. Menton (Me): This is the lowest point on your chin situated in the mid-line.
8. Pogonion (Pog): This is the most frontward point on the contour of your chin.
9. Gnathion (Gn): This is the lowest and most forward point on your chin’s outline.
10. Condylion (Cd): This is the highest point on the curvature of your jaw bone.
There are also specific areas or planes used as reference points in this analysis. Here’s what they are in simpler terms:
1. Sella-Nasion (SN): a plane that’s drawn from the Sella to the Nasion, used for measuring the jaws’ and facial structures’ relationship.
2. Frankfort plane: a plane formed by joining the Porion and the Orbitale, used as a reference to evaluate the vertical relationship between the jaws and facial structures.
3. Mandibular plane: a line through the lower border of the lower jaw joining two points: gonion and menton.
4. Maxillary plane: a line joining the front and back nasal spines.
5. Occlusal plane: a plane that touches the edge of the upper and lower front teeth and the tips of the back teeth.
6. Camper plane: a plane passing through the bottom edge of the nasal opening and the top edge of the earlobe. This helps evaluate the upper lip’s inclination and the teeth’s placement.
Why do People Need Orthodontics, Cephalometric Analysis
Cephalometric analysis is a tool used to spot issues with the alignment of your teeth and jaw. It plays a key role in figuring out what kind of dental issues you might have, planning the right treatments to correct these problems, and checking to see if the treatment has worked. It can also help track any changes in your jaw growth over time.
How is Orthodontics, Cephalometric Analysis performed
Lateral skull x-rays, also known as lateral cephalometric radiographs, give us a two-dimensional look at your head and neck. These images let us measure your skull from front to back and top to bottom. They tell us about the position and angle of your upper and lower jaw, and the height of your face. X-rays taken from the front of the head give us a different view, allowing us to measure the width of your face and how your jaws line up from side to side. But, these front view images are harder to interpret, so we usually rely on the side view x-rays.
To get the best and most accurate images, it’s important that you’re positioned correctly during the x-ray process. You’ll be asked to sit or stand with your head level, with supports placed against your ears. We’ll line up the x-ray machine with the bridge of your nose and make sure your teeth are in their natural resting position. The x-ray machine will be approximately 5 feet away from the middle of your face, but don’t worry, the technician will take care of all the precise measurements to ensure a good image. We include a ruler in each x-ray to make sure we get precisely calibrated readings.
Once the x-rays are taken, we “trace” the images. This means we identify certain important points on the x-ray and connect them to make lines and angles. These give us the measurements we need to understand more about your skull and face. Traditionally, this is done manually using a clear overlay and a precise pencil. However, these days, we usually use specialized computer software that does this automatically. It can even give us other useful information based on your sex, age, and ethnicity, and can help us predict changes, growth, and outcomes after surgery. Both manual and digital tracing methods are helpful and appropriate in assessing these images.
What Else Should I Know About Orthodontics, Cephalometric Analysis?
Cephalometrics is a science that measures your skull and facial bones to help orthodontists plan your treatment.
Typical measurements and proportions are usually used as a guideline, but they can fluctuate based on your age, gender, and ethnicity. Each assessment will take into account your unique bone and dental structure, as well as the results of the cephalometric analysis.
One part of the evaluation looks at the positioning of your upper and lower jaw bones (maxilla and mandible) in proportion to the front part of your skull.
– The ‘SNA angle’ checks the position of your maxilla. On average, this angle is about 81 degrees. If this angle is greater than 81, your maxilla is more forward to your skull than others, if less, then your maxilla is set back.
– The ‘SNB angle’ checks the position of your mandible. On average, this angle is about 78 degrees. If the angle is more than 78, then your mandible is more forward than average. If it’s less, then your mandible is set back.
– The ‘ANB angle’ checks the positional relationship between your maxilla and mandible. Under normal situations, this should be 2 degrees. An angle greater than 4 suggests that your maxilla is too far forward (class II); an angle less than 2 suggests that your maxilla is too far back (class III).
But, the ANB angle can change based on the position of the ‘nasion'(a point on the skull), and how protruding your lower face is. If this happens, a method called ‘Wits Analysis’ can be used.
Wits Analysis is another way of checking the positional relationship between your upper and lower jaws. Measurements from points A and B (found on your upper and lower jaws) to the line which connects the topmost part of your back teeth are taken. The normal range varies based on gender.
The next part of the evaluation looks at the vertical relationship between your maxilla and mandible with an ‘MMPA’ measurement. The average value for this is 27 degrees, with higher values indicating an open bite, and lower values indicating a closed bite.
The position of your teeth (incisors) is also evaluated. If your incisors are angled more forward, it’s called ‘proclination’. If they’re tilted backward, it’s called ‘retroclination’. The average angle measuring incisor position in your upper jaw to the ‘nasion’ is 22 degrees, and for the lower jaw, it’s 25 degrees. An increased angle means your incisors are proclined, a decreased angle means they’re retroclined.
The placement of your lower incisors is studied by calculating the angle formed between your tooth and the lower jawline, a normal angle here is 87 degrees.
Lastly, distances from your incisor to the ‘nasion’ are evaluated. This helps in understanding whether your tooth is in a normal position or too far forward (procumbent) or too far backward (recumbent). The average distance from your incisor to the ‘nasion’ is around 4 mm.