In an earlier article, I discussed the soft tissue profile analysis as an important factor in esthetic treatment planning. We are fully aware of how restorative care can influence esthetics from a frontal facial view.
Our starting point for esthetic planning is evaluating the maxillary central incisor position with the lip at rest and with a full smile. By considering the profile in esthetic planning, you add the third dimension of esthetics to achieve the most ideal results.
A cephalometric analysis can provide a deeper view into the support system of facial esthetics that can assist in planning restorative treatment and predicting the result.
Hidden underneath the facial profile photo lies another world of information that may help you with important details for your treatment planning. A cephalometric image can portray the skeletal and dental components that give the face its form. (Figures 1 and 2)
Not every restorative case will need the facial, skeletal and dental analysis that cephalometrics can provide. A general understanding of what contributes to facial esthetics and facial form can help you to include or exclude potential treatment options.
Cephalometric measurements, like all numerical evaluations we use to plan our patient's treatment, are norm values or guidelines that can be used to compare to our patient's measurements. Let’s take tooth height to width ratios as an example. (Figure 3)
Our ideal ratio may be 80 percent, yet we can accept a range from 77 percent to 85 percent if the individual patient circumstances prevent us from following the ideal ratio.
It is important to know the ideal or “norm” measurement to give you a perspective in making decisions and recommendations that will lead to an esthetic, stable and successful result. Similarly, the cephalometric analysis can provide a more detailed and focused guideline to support your restorative treatment planning.
Cephalometric analysis was introduced by Broadbent in 1931 and was initially used to study growth and development of the facial and dental complex. The exact numbers of measurement are not as important as our understanding how the numbers contribute to the current skeletal and dental problem list or treatment goals.
Like the tooth height and width ratio, cephalometric analysis numbers will include a wide range of clinically acceptable numbers. Usually they are reported as a “norm” with a plus or minus range.
These numbers provide a road map for identifying potential issues, and are a guideline for an acceptable range in treatment planning. Keep in mind that there are acceptable ethnic and cultural differences in cephalometric numbers that should be considered when treatment planning.
In this article, we will look at three of the dental components of the cephalometric analysis. Our focus will be on the position of the maxillary central incisors, since our esthetic treatment planning always begins there. The position of the incisors within the maxilla is a factor that can influence the lip position, lip drape and exposure of the vermillion border. What follows is a reference guide to esthetic restorative treatment planning.
1. Upper and lower incisor angle (Inter-incisal angle)
The upper and lower incisor positions intersect and form a norm angle of 131 degrees +/- nine degrees. This measurement gives you a relative degree of the proclination (forward or backward tip) of the incisors.
Looking at Figure 4, it would be difficult to know the position of the incisors without the aid of the cephalometric image. The inter-incisal angle is 150 degrees, indicating a more reclined or upright position of the incisors relative to each other. The drawback of the inter-incisal angle is that we can’t determine how much the upper, lower or both incisors are contributing to the angle (Figure 5).
2. Maxillary incisor angle
An alternative option is to take the upper and lower incisors individually. For repeatability, the upper incisors are compared to a stable base line in the skeletal cranial base: the Sella- Nasion line.
Sella (S) is the midpoint of the U shaped sella tusica in the mid cranium.
Nasion (N) is the junction of the frontal and nasal bone suture.
The average range for the maxillary incisor angle to Sella-Nasion line is 104 degrees +/- six degrees. In Figure 6, the maxillary incisor measures 104 degrees so it falls within the normal range. Based on the previously noted 150-degree inter-incisal angle, we can conclude that it is the lower incisor that is more upright or reclined than normal.
It is because individual skeletal landmarks can vary with each patient that the angle of the upper incisor to Sella-Nasion has a wide range of acceptable.
As a restorative dentist, this angle can be used to discover or confirm if there is a significant proclination angle to the upper incisor. Remembering that the maxillary central incisor position is our first point of reference for facially generated treatment planning, upper incisor proclination is a key component of planning the central incisor position.
In a conversation with your orthodontist, they might refer to the labial crown torque or lingual root torque instead of tip or proclination angle.
The angle or torque of the incisor can influence the lip position and the amount of tooth display at rest. A tooth with excess proclination will tend to show less of the crown at rest and with a full smile.
Yet esthetics is not the only consideration when evaluating the incisor position. The amount of proclination in the incisor can influence the amount of tooth reduction that is needed to re-orient the crown restoratively.
Also, when considering an anterior implant the proclination of the upper incisor is a significant consideration. If there is an excess proclination, there is a greater risk for a lack of labial bone to support an implant.
An evaluation of the cephalometrics can give you an early indication if this will be a limitation for your patient.
3. Maxillary incisor A-P position
In addition to the degree of tip (proclination), the anterior-posterior (A-P) position of the upper incisor also plays a role in esthetics. When we are looking at the upper incisor A-P position, it is important to think about what structure (the maxilla or the mandible) it is compared to.
If either the maxilla or mandible are protruded or reclined, it can alter the perception of the upper incisor position. We are used to thinking of the mandible in a retrognathic position, while the maxilla can also be recessive more often than we used to think.
With the growing understanding of airway, our focus is tuned into maxillary position. We need to be cautious about retracting upper incisors until we have confirmed a true protrusive position.
Using skeletal and facial landmarks like Nasion (N) and Glabella (G) (the most prominent point of the forehead) we can assess whether the incisor is bodily protruded or retruded.
Note in Figure 7 that the upper incisors are positioned forward A-P but are not proclined or tipped forward outside the normal range (degrees). During the extraction treatment plan with retraction into the extraction sites, the tooth change was primarily by bodily movement of the upper incisors rather than by tipping back during retraction. (Figure 8)
The superimposition of the maxillary central incisor position during treatment shows more clearly the change in bodily movement as compared to the change in tooth angulation. (Figure 9)
The facial profile photo shows the changes that the patient will see as a result of the change in maxillary incisor movement.
Treated differently with more lingual tipping during retraction rather than bodily movement, the facial esthetic result could be very different and offer less support to the lips and potentially a less esthetically ideal finish.
In a restorative case, the same potential consequences can be evaluated using the cephalometric dental analysis when you plan to restore the maxillary anterior teeth. In a severe anterior wear case, we know that as compensatory eruption progresses, the maxillary teeth erupt down and backward. That compensatory retracted tooth position is a factor to consider when restoring worn anterior teeth. Not only is adding back length important, adding back proper inclination and A-P position will provide the more ideal esthetic facial result. (Figure 11,12)
Interdisciplinary treatment planning that includes cephalometric evaluation can be a helpful adjunct to achieving ideal esthetic results.