ortho - the international C.E. magazine of orthodontics

ortho1_201308 I I C.E. article_ orthognathic surgery Range of motion should be between 45 mm and 55 mm on opening and includes assessing move- ment. We’re looking for a symmetrical mandible motion—meaningthechinshouldnotdeviatetothe left or right on opening — and it should be relatively free of dental interference. Now check for palpation of the muscles of masti- cation. If you don’t check the muscles that move the mandible,thenthere’sagoodchancethatyou’llmiss some sort of functional bite issue. Wealsolistentothejointwithastethoscope,and we apply some anterior pressure to the disc through external auditory meatus to make sure the disc is functioning properly. When trying to manipulate the mandible, one can feel the muscles. If the muscles will not let you obtain a centric joint position, then we cannot do a diagnosis because the muscles aren’t holding the condyleoutofthesocket.Thisisusuallyduetosome inflammation. Finally, we’ll check what we call the centric rela- tion position, which you should be able to feel. It should feel solid and the patient should be able to open from this position with relative ease, and there should be no noises. _Imaging Theclinicalexaminationwilltellusalotaboutthe joint status. The use of imaging will help us build our baseofcase-specificintelligence.We’llusetwotypes of imaging: MRI and cone beam. LCBCT Mostofthetime,westartwithconebeambecause it’s easy to obtain a 3-D image of the joints. Thanks totheworkofRicketsandDr.Ikeda,wehaveawayto measure joint position and get an idea if the condyle is basically seated. With cone beam, we can measure the health of the condyles. 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 asymmetricalopeningwherethechindeviatestothe affectedside.Inallthreeviews(saggital,coronaland axial), we have a condyle that is actually changing, especially when you make a comparison to the left condyle (Fig. 4). In a side-by-side presentation, you can see that theleftsideisdefinitelyinalotbettershape,havinga moreroundedeffecttoit.Thesizeofthecoronalview isonethatshowsadefinitesymmetricoutlinetoitas compared to the other side. The axial view confirms this; you see that the shape is better and has a more dense outline. Thus,ourbasicimagingsystemhelpsusdetermine that, in this case, one side is going to be the problem side,especiallyasitpertainstoorthognathicsurgery. If we go to the two-dimensional 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. 5, 6). In the coronal view, we can even see that there may be some sort of cyst formation. When you com- paretherightsidetotheleftsideinthecoronalview, yougetamoretraditionalimage,whichiswhatwe’d like to see. However, there have been some changes 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 determining if we should proceed with any kind of a surgical cor- rection. In the saggital view, the right side, the joint looks prettynormal.However,ifwelookatitinatransverse direction,you’llseelessjointspacelaterallythanyou do medially, something we see in both the left and rightjoints(amuchbiggerjointspace).That’swhyit’s important that you not only look at a saggital view, butyoualsoneedtolookatthecoronalviewtoseeif youhaveatransverseproblemoccurringinthejoints. _Soft-tissue analysis Whenwe’retrainedinorthodontics,we’retrained in hard-tissue analysis, otherwise all of our cephalo- metric analysis are based on hard structures. If you use hard structure to determine soft-tissue correc- tions,thenyou’llcomeupshortofgoodfacialesthet- ics. That’s why a soft-tissue analysis is so important. Fig. 4 Fig. 4_A state of degeneration: a condyle that is actually changing.