Armamentarium

History of the Procedure

The first anterior segmental maxillary osteotomy (ASMO) was reported at the beginning of the twentieth century. Günther Cohn-Stock tried to surgically “correct a marked overjet and overbite of the central maxillary teeth.” In his pioneering article in 1921, he described the evolution of his idea to perform an osteotomy of the anterior segment of the maxilla while preserving the vestibular pedicle and, in a later design, also the palatal artery.

Cohn-Stock presented two surgical cases performed under local anesthesia in his Berlin practice in May and June 1920. In his definitive version, “Cohn III,” he described a transverse palatal wedge ostectomy palatal to the anterior teeth, performed through a subperiosteal tunnel, and then a manual manipulation to create a greenstick fracture at the ostectomy site to retract the anterior maxilla. Contemporary authors suggest that Cohn-Stock’s greenstick fracture method resulted in significant relapse after removal of the fixation splint because the anterior maxilla was not adequately mobilized.

After Cohn-Stock’s original report, three variations of the procedure were developed by Wassmund, Wunderer, and Cupar. These variations were designed to maintain sufficient blood supply to the maxilla while giving adequate access for instrumentation.

In 1927 Wassmund improved Cohn-Stock’s design by creating a direct approach to the labial premaxillary cortex using three vertical incisions and subperiosteal tunneling for completion of the labial osteotomy without reflection of labial or palatal flaps. Both the labial and palatal blood supply is maintained; however, the osteotomy is made in a relatively blind fashion. This method may be indicated for closure of multiple interdental spaces and for anteroposterior repositioning of the premaxilla. It was found to maintain the best vascularity of the repositioned segment in comparison to all other ASMO methods.

In 1954 Cupar described a different approach for down-fracture of the anterior maxilla: exposure of the labial aspect of the maxillary bone by a vestibular circumferential cut and labial flap to facilitate the labial osteotomy under direct vision. A palatal osteotomy was performed through a tunnel, maintaining the palatal blood supply. This technique is indicated for superior repositioning of the anterior maxilla in cases of vertical maxillary excess.

In 1963 Wunderer advocated reflection of a palatal flap with out-fracturing of the anterior maxilla and maintenance of the labial blood supply. Direct access for the palatal osteotomy is the main advantage of this technique, especially if posterior segments of the premaxilla must be removed. Therefore, this technique may be indicated for setback of the anterior part of the maxilla. Blood flow studies have demonstrated that the transpalatal approach causes the greatest decrease in blood supply to the anterior maxilla. However, transpalatal soft tissue incision and labial osteotomies impair blood supply to the anterior maxilla from the greater palatine vessels and the superior alveolar vessels, respectively, leaving the labial collaterals as the sole blood supply to the anterior maxilla.

In 1977 Epker modified the Cupar technique for down-fracture of the anterior maxilla. He used only labial flaps and vertical tunnels labial to the teeth to be extracted, which were usually premolars on both sides (this technique is described in detail later in the chapter). Epker’s modification enables repositioning of the anterior maxilla superiorly, posteriorly, and inferiorly. The main advantages of the Epker modification include preservation of the palatal pedicle, ease of placement of internal fixation, access to the nasal septal structures to prevent buckling of the nasal septum with superior repositioning of the maxilla, and a direct approach for removal of palatal bone. When required, bone grafting for stabilization of an inferiorly positioned anterior maxilla may also be done using this method.

History of the Procedure

The first anterior segmental maxillary osteotomy (ASMO) was reported at the beginning of the twentieth century. Günther Cohn-Stock tried to surgically “correct a marked overjet and overbite of the central maxillary teeth.” In his pioneering article in 1921, he described the evolution of his idea to perform an osteotomy of the anterior segment of the maxilla while preserving the vestibular pedicle and, in a later design, also the palatal artery.

Cohn-Stock presented two surgical cases performed under local anesthesia in his Berlin practice in May and June 1920. In his definitive version, “Cohn III,” he described a transverse palatal wedge ostectomy palatal to the anterior teeth, performed through a subperiosteal tunnel, and then a manual manipulation to create a greenstick fracture at the ostectomy site to retract the anterior maxilla. Contemporary authors suggest that Cohn-Stock’s greenstick fracture method resulted in significant relapse after removal of the fixation splint because the anterior maxilla was not adequately mobilized.

After Cohn-Stock’s original report, three variations of the procedure were developed by Wassmund, Wunderer, and Cupar. These variations were designed to maintain sufficient blood supply to the maxilla while giving adequate access for instrumentation.

In 1927 Wassmund improved Cohn-Stock’s design by creating a direct approach to the labial premaxillary cortex using three vertical incisions and subperiosteal tunneling for completion of the labial osteotomy without reflection of labial or palatal flaps. Both the labial and palatal blood supply is maintained; however, the osteotomy is made in a relatively blind fashion. This method may be indicated for closure of multiple interdental spaces and for anteroposterior repositioning of the premaxilla. It was found to maintain the best vascularity of the repositioned segment in comparison to all other ASMO methods.

In 1954 Cupar described a different approach for down-fracture of the anterior maxilla: exposure of the labial aspect of the maxillary bone by a vestibular circumferential cut and labial flap to facilitate the labial osteotomy under direct vision. A palatal osteotomy was performed through a tunnel, maintaining the palatal blood supply. This technique is indicated for superior repositioning of the anterior maxilla in cases of vertical maxillary excess.

In 1963 Wunderer advocated reflection of a palatal flap with out-fracturing of the anterior maxilla and maintenance of the labial blood supply. Direct access for the palatal osteotomy is the main advantage of this technique, especially if posterior segments of the premaxilla must be removed. Therefore, this technique may be indicated for setback of the anterior part of the maxilla. Blood flow studies have demonstrated that the transpalatal approach causes the greatest decrease in blood supply to the anterior maxilla. However, transpalatal soft tissue incision and labial osteotomies impair blood supply to the anterior maxilla from the greater palatine vessels and the superior alveolar vessels, respectively, leaving the labial collaterals as the sole blood supply to the anterior maxilla.

In 1977 Epker modified the Cupar technique for down-fracture of the anterior maxilla. He used only labial flaps and vertical tunnels labial to the teeth to be extracted, which were usually premolars on both sides (this technique is described in detail later in the chapter). Epker’s modification enables repositioning of the anterior maxilla superiorly, posteriorly, and inferiorly. The main advantages of the Epker modification include preservation of the palatal pedicle, ease of placement of internal fixation, access to the nasal septal structures to prevent buckling of the nasal septum with superior repositioning of the maxilla, and a direct approach for removal of palatal bone. When required, bone grafting for stabilization of an inferiorly positioned anterior maxilla may also be done using this method.

Indications for the Use of the Procedure

• 1.

  Anterior vertical maxillary excess in cases with acceptable posterior occlusion

• 2.

  Sagittal maxillary excess with acceptable posterior occlusion

• 3.

  Maxillary anterior protrusion of anterior teeth with normal incisor axial inclination to bone and acceptable posterior occlusion

• 4.

  Excessive proclination of anterior teeth

• 5.

  Dentoalveolar bimaxillary protrusion when an acceptable posterior occlusion is performed in association with a mandibular subapical osteotomy

• 6.

  Anterior open bite without vertical maxillary excess and normal posterior occlusion

• 7.

  When retraction of anterior teeth is indicated but cannot be accomplished with conventional orthodontic treatment (e.g., because of root resorption as a result of previous orthodontic treatment, tooth ankylosis, malpositioned dental implants)

• 8.

  Reduction of upper lip prominence relative to the nose and lower face

• 9.

  Maxillary excess combined with wide interdental spaces (malformed teeth, oligodontia)

• 10.

  Preprosthetic procedure: augmentation and repositioning of anterior edentulous atrophic maxillary ridge for dental implants

• 11.

  Dental crowding and anterior maxillary hypoplasia

Limitations and Contraindications

The same principles for every orthognathic procedure apply to the anterior segmental maxillary osteotomy. Most authors advocate postponing the surgery until the craniofacial skeleton reaches full maturity. Orthodontic consultation and treatment should be scheduled well in advance (typically 9 to 12 months) to prepare the occlusion for the planned postoperative position of the anterior segment and the interdental or extraction sites. A useful application to accomplish this is a three-dimensional (3D) manipulation of the computed tomography (CT) scan, which can be used to predict ortho­dontic movement of teeth, subsequent segmental repositioning, and soft tissue changes.

Patient cooperation and compliance in the maintenance of good periodontal condition during the preoperative orthodontic treatment are crucial. Dental neglect, gingivitis, and periodontitis must be well controlled before the operation. Failure to do this is a relative contraindication and adversely affects the quality of the final outcome. Local factors and habits, such as tongue thrust and finger sucking, also impair treatment results if not diagnosed and addressed before intervention.