orthognathic reconstruction the dental technician's role in

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ORTHOGNATHIC RECONSTRUCTION The Dental Technician’s Role in Orthognathic Surgery Orthognathic surgery involves the surgical manipulation of the facial skeleton to correct anatomical and functional deformities. The 3 main classifications of maxillofacial dysplasia are dental, skeletal, and dentoskeletal. The case presented in this article exhibits dentoskeletal dysplasia; the dentition is misaligned or malpositioned within each arch, along with an abnormal skeletal relationship of the upper and lower jaws. The following will describe the integral role of the dental lab technician within the process of orthognathic reconstructive surgery and the steps involved in the fabrication of an orthognathic surgical splint. Responsibilities of the reconstruction team The orthognathic reconstruction team chiefly consists of an orthodontist, a lab technician and a maxillofacial surgeon. If tooth extractions are deemed necessary, an oral surgeon may be required. Pre-surgical plans begin with orthodontically treating each arch independently. Corrections within each arch usually include tooth alignment, leveling the curve of Spee, and idealizing the anterior dentition without any attempt at correcting the occlusion. Because of this, the occlusion is frequently worsened before orthognathic surgery takes place. Next, a dental laboratory technician will be responsible for simulating the surgical outcome in the dental laboratory. The technician’s goal is to occlude the orthodontically corrected models as ideally as possible. This sometimes requires pre-sectioning of the models into segments. For the case presented in this article, the maxilla is too wide in the posterior region and skeletally insufficient in the anterior region. A wedge shaped portion of bone will be removed from the palate (figures 1, 2), and the dental segments will be repositioned more anterior. After the carefully positioned sections are based and models are articulated, a surgical splint is fabricated. An orthognathic surgical splint serves two purposes. During surgery, the surgeon will use it as a template guide for accurate placement of the dentoalveolar segments and after surgery it will provide the repositioned bones stability during the healing process. Finally, the maxillofacial surgeon will perform the osteotomy and coordinate the maxillary and mandibular segments or arches to their ideal dentoalveolar relationship. The sequence of operative procedures is based on the pre-operative planning and the model surgery performed in the dental laboratory. If a single jaw is being repositioned, the surgical splint is used to guide the occlusion of the jaw or a segment being moved relative to the remaining jaw and is then wired in place to the orthodontic appliances still on the teeth. If both maxillary and mandibular repositioning osteotomies are planned, two surgical splints are made. A primary or intermediate splint is used first, to guide the movement of one jaw relative to the position of the other jaw. Then, the secondary or final surgical splint is used to reposition the remaining jaw.

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Page 1: ORTHOGNATHIC RECONSTRUCTION The Dental Technician's Role in

ORTHOGNATHIC RECONSTRUCTION The Dental Technician’s Role in Orthognathic Surgery Orthognathic surgery involves the surgical manipulation of the facial skeleton to correct anatomical and functional deformities. The 3 main classifications of maxillofacial dysplasia are dental, skeletal, and dentoskeletal. The case presented in this article exhibits dentoskeletal dysplasia; the dentition is misaligned or malpositioned within each arch, along with an abnormal skeletal relationship of the upper and lower jaws. The following will describe the integral role of the dental lab technician within the process of orthognathic reconstructive surgery and the steps involved in the fabrication of an orthognathic surgical splint. Responsibilities of the reconstruction team The orthognathic reconstruction team chiefly consists of an orthodontist, a lab technician and a maxillofacial surgeon. If tooth extractions are deemed necessary, an oral surgeon may be required. Pre-surgical plans begin with orthodontically treating each arch independently. Corrections within each arch usually include tooth alignment, leveling the curve of Spee, and idealizing the anterior dentition without any attempt at correcting the occlusion. Because of this, the occlusion is frequently worsened before orthognathic surgery takes place. Next, a dental laboratory technician will be responsible for simulating the surgical outcome in the dental laboratory. The technician’s goal is to occlude the orthodontically corrected models as ideally as possible. This sometimes requires pre-sectioning of the models into segments. For the case presented in this article, the maxilla is too wide in the posterior region and skeletally insufficient in the anterior region. A wedge shaped portion of bone will be removed from the palate (figures 1, 2), and the dental segments will be repositioned more anterior. After the carefully positioned sections are based and models are articulated, a surgical splint is fabricated. An orthognathic surgical splint serves two purposes. During surgery, the surgeon will use it as a template guide for accurate placement of the dentoalveolar segments and after surgery it will provide the repositioned bones stability during the healing process. Finally, the maxillofacial surgeon will perform the osteotomy and coordinate the maxillary and mandibular segments or arches to their ideal dentoalveolar relationship. The sequence of operative procedures is based on the pre-operative planning and the model surgery performed in the dental laboratory. If a single jaw is being repositioned, the surgical splint is used to guide the occlusion of the jaw or a segment being moved relative to the remaining jaw and is then wired in place to the orthodontic appliances still on the teeth. If both maxillary and mandibular repositioning osteotomies are planned, two surgical splints are made. A primary or intermediate splint is used first, to guide the movement of one jaw relative to the position of the other jaw. Then, the secondary or final surgical splint is used to reposition the remaining jaw.

Page 2: ORTHOGNATHIC RECONSTRUCTION The Dental Technician's Role in

Fabricating an Orthognathic Surgical Splint Model prep 1) Inspect the models. Impressions for this type of bite splint will have been taken with orthodontic brackets still in place. This causes the impression material to tear on the facial surface, cervical to the brackets. This will not interfere with the accuracy of the splint. However, models must be inspected for distortion since the brackets that cause the impression material to tear can also cause the material to pull or elongate, if not fully set before the impression’s removal. The models need to be accurate on the lingual, occlusal and occlusal-buccal 1/3 of the posterior teeth. The brackets must also be visible enough to identify each bracket’s location for the precise placement of the splint’s ligature loops. 2) Carefully remove bubbles and clarify the occlusal surfaces. Accurate occlusal intercuspation will be essential to the success of the orthognathic surgical splint. Block-out any sharp edges or undercuts for ease of duplication. Duplicate the prepared models. The duplicate model will be used for sectioning. The original models should be preserved and then returned to the Doctor. 3) Review the Rx, or pre-surgical notes, to determine if there are other model prep steps required. For this case, the instructions require the upper model to be segmented along the mid-palatal suture, narrowed interpalatally, and the dentoalveolar segments reset more anteriorly. 4) After sectioning the model and narrowing the palatal scope, carefully balance the right and left dentoalveolar segments onto the mandibular cast, in ‘the corrected occlusal relationship‘, and wax in place (figures 3, 4, 5). The occlusion will not be ideal. Compromises will have to be made. Generally, ‘the ideal occlusion’ refers to a Class I skeletal and dental relationship (anteriors set to 1 mm. OB and 1 mm. OJ and most of the posteriors aligned in the correct cusp/fossa positions), it is understood that finalizing cusp/fossa contacts and interdigitation will be achieved with orthodontic finishing, post-surgically. 5) Make a new model base to stabilize the segments by mixing a stone patty and inverting the mandibularly retained segments gently into the patty. Trim the base and then fill inside the palatal cuts with wax, to normal anatomical contours (figures 6, 7). This is now considered the surgical model and must be duplicated to provide a fabrication model. 6) Carefully seat the finished splint on the preserved cut and waxed surgical model and check the surgical splint against the original opposing model for balanced internal and occlusal fit. Occlude the new upper fabrication model to the mandibular duplicate model and mount on an articulator (figure 8). Set the amount of vertical opening by estimating just enough space to suspend a ligature wire framework interocclusally, usually 2-3 mm. clearance in the posterior segments (at the thinnest point). Bending the ligature wire framework 7) The wire framework is not so precise or challenging that you need to possess expert wire bending skills. Begin by cutting a straight length of .032 stainless steel round wire, approximately twice the length of a posterior upper segment. Using a #139 plier or a three-prong plier, bend a ‘swimming recurve’ framework for each side of the arch. This recurve design allows for a one-piece construction that provides better retention within the acrylic and is more comfortable to the patient than other post or hook designs. Bend the ligature loops long enough to span from the central dissectional groove outward to approx. 3 mm. past the buccal cusps. Each loop should be bent to lie directly over each bracket on the upper segmented model. It is important that every tooth in the sectioned arch be wired in a singularly vertical direction to the splint (figure 9). It is not critical that the ligature loops be aligned with the lower brackets. With the splint in place, this arch is considered to be stable from all directions. Wiring the splint to the mandible from various angles will not alter its dental or alveolar stability.

Page 3: ORTHOGNATHIC RECONSTRUCTION The Dental Technician's Role in

9) Check the right and left frameworks for clearance by resting them on the occlusal and closing the articulator. Remember that the frames will be suspended between the posterior teeth. As such, they should follow the contours of the occlusal plane. If they contact the opposing in some places, bend that area out of the way of the interferences. It is not necessary that the loops be aligned horizontally to each other. Acrylicing 10) Check the Rx to determine if the splint should have anteriors and posteriors covered with acrylic. In this case, only posterior coverage with a full palate is needed. Draw the intended borders onto the maxillary model and apply acrylic separator on the models. 11) Suspend the wire frameworks interocclusally by waxing a temporary holding wire, connecting the frame to the model. Fill in the 3 mm. buccal overhanging loops with wax to prevent being buried in acrylic and to facilitate easier finishing (figures 10, 11). 12) The acrylic process used is the salt & pepper method using clear, hard, cold-cure resin. Wet the occlusion with monomer and sprinkle a thin layer of polymer onto the monomer (figures 12, 13). Wet with another layer of monomer and apply another layer of polymer. Work quickly to keep the acrylic moist, prevent dry spots and to prevent slumping. Continue this process until you have built up and covered the frameworks and have built up the buccal and lingual surface walls (figure 14). Gently try to close the articulator into the occlusal acrylic while moist. Add to areas until you have an even impression of the entire opposing registration. Use an elastic to insure the articulator remains closed during curing (figure 15). Place into a heated pressure pot to cure. Finishing 13) After removing the cured splint from the model, steam or flush the wax clean and remove the anchor wires. 14) Remove excess bulk and shape the borders with a grinding wheel. Use a large egg-shaped carbide bur to thin and contour the palate (figure 16). A series of smaller burs are used on the buccal surfaces to expose the loops and to smooth the acrylic around the loops (figure 17). A small bristle brush works well to remove unwanted acrylic from the wires without damage (figure 18). 15) Maxillary and mandibular outside borders should be finished to just above the brackets on the upper and lower buccal surfaces (figure 19). All brackets have four tie wings. The impression may not always pick these up completely, or you may have chipped them off during the acrylic process. Use your best judgment to allow for the presence of two occlusal tie wings. As for the occlusal surface, the splint should completely encapsulate all of the opposing buccal and lingual cusps for a solid, locked-in position. These indents should be approx. 2-3 mm. deep fossae. 16) Finally, sand all external surfaces, pumice and polish. Carefully seat the finished splint on the preserved cut and waxed surgical model and check the splint against the original opposing model for balanced internal fit and solid occlusion. The finished orthognathic surgical splint should remain on the surgical model and made ready for delivery (figure 20).