Please activate JavaScript!
Please install Adobe Flash Player, click here for download

Dental Tribune Middle East & Africa Edition

11Dental Tribune Middle East & Africa Edition | November-December 2014 mCME > Page 37 < Page 10 Fig. 5. Establishing the true vertical line based on natural head position. Fig. 8. Surgical treatment objective. Fig. 6. Glabella to subnasale (SN). Fig. 9. Completed the extrusion of the max- illary segment and balanced the occlusal plane. Fig. 7. Establish the horizontal position. Fig. 10. Establishing the true vertical line. LCBCT Most of the time, we start with cone beam because it’s easy to obtain a 3-D image of the joints. Thanks to the work of Rickets and Dr Ikeda, we have a way to measure joint position and get an idea if the condyle is basically seated. With cone beam, we can measure the health of the con- dyles. Our imaging showed a joint that is in a state of degeneration. The condylar head has changed in vertical height. Therefore, we would expect to see an asym- metrical opening where the chin deviates to the affected side. In all three views (saggital, coronal and axial), we have a condyle that is actually changing, espe- cially when you make a compar- ison to the left condyle (Fig. 3). In a side-by-side presentation, you can see that the left side is definitely in a lot better shape, having a more rounded effect to it. The size of the coronal view is one that shows a definite sym- metric outline to it as compared to the other side. The axial view confirms this; you see that the shape is better and has a more dense outline. Thus, our basic imaging system helps us determine that, in this case, one side is going to be the problem side, especially as it pertains to orthognathic surgery. If we go to the two-dimension- al images created in the cone beam, we can see that the right joint has definitely lost vertical height, and we definitely have a joint spacer that is excessive (Figs. 4 & 5). In the coronal view, we can even see that there may be some sort of cyst formation. When you compare the right side to the left side in the coronal view, you get a more traditional image, which is what we’d like to see. Howev- er, there have been some chang- es that have occurred, because we’re starting to see a “bird- beaking” effect in the left joint. The images of the joint are ones that are important in determin- ing if we should proceed with any kind of a surgical correction. In the saggital view, the right side, the joint looks pretty nor- mal. However, if we look at it in a transverse direction, you’ll see less joint space laterally than you do medially, something we see in both the left and right joints (a much bigger joint space). That’s why it’s important that you not only look at a saggital view, but you also need to look at the coronal view to see if you have a transverse problem occurring in the joints. Soft-tissue analysis When we’re trained in ortho- dontics, we’re trained in hard- tissue analysis, otherwise all of our cephalometric analysis are based on hard structures. If you use hard structure to determine soft-tissue corrections, then you’ll come up short of good fa- cial aesthetics. That’s why a soft- tissue analysis is so important Using soft-tissue markers with 3-D facial mapping, we are able to diagnose the soft tissue, and we can also relate it to the hard tissue. In Figure 4, we’ve overlaid the soft tissue on top of the hard tis- sue. With the markers on, after we convert it to a two-dimen- sional X-ray, we can see where the sub-pupal area is, where the cheekbones are and where the alar base is. In addition, you will see a marker that we call a hinge access marker, which comes from establishing the true hinge axis of the patient. There is also a marker that’s placed on the nose that we call the horizontal point. We are going to analyze every- thing from a basic coordinate system of a true vertical to an axis horizontal. The image is orientated from the axis horizontal plane and the true vertical plane, which is based on the patient’s natural head position. Figure 5 shows how these two corners are at 90 degrees from each other. In this analysis, we’re going to record all the soft- tissue measurements, both hori- zontal and vertical, and we’re going to base them on the line that runs through the subnasale (SN). This establishes the true vertical line based on natural head position. Furthermore, we’re including a few hard-tissue measurements that will tell us about the archi- tecture of the mandible. These come from Rickets and from the Jarabak analysis. With this anal- ysis, we can cover the basis that we need for orthodontics, but we can also cover what we need in a surgical workup. We also need a frontal analysis, which is taken from the patient’s face. Most of the frontal workup is done in examining the patient clinically. This enables us to look at the orbital rim, cheekbone, sub-pupil, alar bases, nasal bas- es and canthus of the eyes. All of this enables us to assess if we have transverse asym- metries, where the occlusal plane is canted instead of level. This also holds true with the mandibular plane, which we may also find is canted. This is especially true in cases where there’s a degenerative process happening in one joint. Head position, profile and frontal analysis The natural head position is different for each individual patient. This will make the dis- tance recorded for Glabella to the true vertical line different. To measure how far Glabella is from SN (true vertical line), we first need to establish the pa- tient’s natural head position (Fig. 6). To do so, we have the patient stand in front of a mirror. First, the patient is asked to close his eyes and bob his head up and down three times. After this is complete, the pa- tient is asked to open his eyes and look himself directly in the eyes in the mirror. After we have established the natural head po- sition, we then use the measure- ment gauge. Our goal is to make sure the leveling bubble is in the lines. This will allow us to take a measurement from the true ver- tical line to Glabella. Keep in mind that everybody’s head position is a bit different. The further that Glabella is from the true vertical line will affect how we look at the lower third of the face. Now we need to establish the axis-horizontal plane (Fig. 7). First, we establish the horizontal position using the ear bow. We’ll use the pointer on the ear bow to make a mark on the nose when the bow is level. We have previously established, through axiopath tracing, the hinge axis position on the pa- tient’s right and left sides. In combining the horizontal point with the two axis points, the axis-horizontal plane can be es- tablished. The axis-horizontal plane is then transferred to the articulator. This allows us to ori- entate the CBCT data with the articulator mounting. Now we have the true axis- horizontal plane and the true vertical line combined, and now facial, skeletal and functional is- sues can be assessed. In the example we are using, the patient has a mandible that has an architecture problem, which causes her to occlude only on the molars with an anterior open bite. This is precisely the kind of case where you should be looking for degenerative joint disease. All of the above enables us to establish the parameters and coordinates we need to analyze the face and occlusion and then apply the correct treatment so the patient will have a functioning stable occlusion with the necessary fa- cial improvements. Soft-tissue analysis The treatment objectives are based on the soft tissue. You per- form the surgical treatment ob- jective in this order. 1) Establish the position of the upper lip to the true vertical line in a vertical and horizontal man- ner. 2) Determine what you need to do with the anterior teeth to cre- ate the correct upper lip posi- tion. 3) Once you established the an- terior part of the maxilla, then proceed to the posterior part of the maxilla and determine if you need to do an intrusion or extru- sion of the posterior segments to level the occlusal plane. In most cases where there’s a retrusive chin and a skeletal open-bite, the patient has an oc- clusal plane, measured from the true vertical line that is some- where between 102 and 108 de- grees. By leveling the occlusal plane, based on the anterior tooth position, you can set the mandible to the maxilla. This will usually balance the lower third of the face. If you still find the chin is too far forward or too far back, you may need to do genioplasty. In the example case (Fig. 8), we have performed a surgical treat- ment objective, established the true vertical line and we have our axis-horizontal plane. In this patient, we need to move the anterior teeth up because in the frontal analysis the patient showed too much tooth struc- ture and too much gingival tis- sue. To fix this, we balance the maxillary anterior teeth based on the upper lip position. Once we’ve established the cor- rect tooth position in the an- terior, we’re able to set up our occlusal plane at 95 degrees, showing us what we need to do with the posterior segment. In the example case, we need to extrude the posterior segment. Figure 9 shows how we’ve completed the extrusion of the maxillary segment, and we’ve balanced the occlusal plane. The next objective is to place the mandible with the correct overbite. This is not 2 mm but 4 mm. This is because you want to have an adequate overbite to create adequate disclusion. In establishing the mandible, you can see in our example how the lower part of the face is placed normally enough with the true vertical line (Fig. 10). Inestablishingthesurgicaltreat- ment objective, we see that we want to place the anterior sec- tion in the superior direction and the posterior in the inferior di- rection. These are all the meas- urements we need to establish a surgical setup. Hopefully, this is performed pre-treatment so the patient has a good idea of what needs to be done. Pre-surgical and surgical set- ups The pre-surgical and surgical setups are techniques that do require the clinician’s time. It’s

Pages Overview