Sagittal chin rotation of the prognathic edentulous mandible

Sagittal chin rotation of the prognathic edentulous mandible

lilt, J. Oral Surgery 1981: 10: 161-167 (Key words: surgery, orthognothlc; surgery, preprosthetic: chin correction; prognath ism t Sagittal chin rota...

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lilt, J. Oral Surgery 1981: 10: 161-167 (Key words: surgery, orthognothlc; surgery, preprosthetic: chin correction; prognath ism t

Sagittal chin rotation of the prognathic edentulous mandible J. VAN DER ZWAN AND G. BOERING Department of Oral and Maxillofacial Surgery, University Hospital, Groningen, The Netherlands

ABSTRACT - In edentulous patients with a prognathic mandible, a pronounced chin and extensive resorption of the lower alveolar ridge, the commonly used techniques of ramus osteotomy and chin reduction will not give optimal results in the majority of cases. The solution of this problem can be obtained by a mandibular body ostectomy and a sagittal rotation of the frontal part of the lower jaw. By this operation the originally horizontally orientated upper plane of the chin area is placed in a more vertical position, This operative technique gives a better predictable facial contour than the conventional methods. It causes no unfavorable displacement of the lower lip and, which is very important, it gives an absolute increase of height of the lower alveolar ridge and a more favorable inclination of the frontal part of the alveolar process from a prosthetic point of view. The problems encountered and the results obtained by this technique will be demonstrated by a short case presentation.

(Received for publication 26 October 1979, accepted 20 March 1980)

Little attention has been paid in the literature to the surgical correction of the prognathic edentulous patient who has extensive resorption of the lower alveolar ridge. Operative techniques which would as a rule be successful in patients with a natural dentition will, on closer consideration, be found unsuitable for cases in which the natural dentition has already been lost for a long time. In these edentulous patients the following corrections are generally necessary: - correction of the facial contour - reduction of the prominent chin - creation of a normal intermaxillary relationship

- creation of better retention for the lower denture The following problems may arise: - the risk of a dropping chin in the case of extensive elevation of the mucoperiosteum in the chin area, for example after chin reduction - a higher risk of disturbed bone healing and occurrence of a pseudarthrosis due to only slight bone contact of the cut surfaces caused by the reduced height of the mandible, in combination with: - difficulties in getting a sufficiently rigid fixation of the fragments and by a diminished blood circulation

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difficulties in orientation of the fragments due to lack of natural occlusal interdigitaHan higher risks of complications in general health due to the older age of these patients. The principles of the correction of the prognathic edentulous patient and the problems encountered will be discussed by means of a short case presentation.

Case report A 32-year-old woman CPk 78/4854) was referred by her dentist to the Department of Oral and Maxillofacial Surgery of the University of Groningen because of a very prominent chin and an ill-fitting lower denture. During her lifetime she had already had a secret wish to have her protruding chin corrected, but recently this desire was enhanced by the remarks of her children's schoolfriends that at their school she was known by her nickname "the witch". Her desire to have her chin corrected was so intense that she tried to keep it a secret that her health was not too good. Her family doctor, however, informed us about the bad condition of her lungs. The lung specialist reported chronic inflammation of the respiratory system due to bronchiectases since 1957. In 1959 the middle lobe of the right lung was removed. In 1966 a radical operation was performed on the maxillary sinuses because of recurrent sinusitis. The vital capacity of the lungs turned out to be two-thirds of the normal and expiration was somewhat obstructive. The ever recurring lung inflammations reacted favorably to treatment by drugs. The lung specialist advised us to give protection by antibiotics and prednisolone in case of operation, in combination with daily physiotherapy. When her face is examined, the prominent chin is striking (Fig. 1). The labiomental fold is lacking. The mandibular angle is stretched. The relationship between upper and lower lip is normal. The eversion of the upper lip is normal when the denture is in place. The slight overclosure of the lips is probably due to the resorption of the maxillary alveolar process under the 12-year-old denture. Examination of the middle third of the face reveals a sagittal underdevelopment of the zygomatic bone on both sides. This, however, does not occur to such a degree that too much of the white

.... t Fig. 1. Profile of a 32-year-old woman with a prognathic mandible lind a chin prominence of

21 mm. of the eyeball is shown. When the patient is talking, the tip of the nose is turned down, causing a curved back of the nose and slight movements of the tip. The inferior margin of the nose is horizontal. The face shows a normal division in height of the different parts. In full face a slight assymmetry was seen at the lower margin of the chin running parallel to the lip slit which has a downward inclination on the right side. Intraoral inspection reveals an ill-fitting denture with insufficient retention due to resorption of the inferior alveolar ridge. In the lower front area only a horizontal plane is left, offering no contribution to the retention of the prosthesis. The mucosa over the inferior alveolar ridge is normal except for a slight indication of a flabby ridge. The panoramic X-ray shows no abnormality except for a root remnant of the 36; there are no signs of inflammation. Cephalometric analysis reveals an angle SNA of 77° and an angle SNB of 83 0 • The top of the inferior alveolar process protrudes 10 mm in front of the top of the upper alveolar ridge. The chin prominence extends 21 rnrn in front of the perpendicular dropped from the inner side of the upper lip. The following diagnosis was made:

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Rigid intermaxillary fixation wa s not a llowed because of the necessary physiotherapy fo r the pr evention of lung co mplicatio ns. Based on the data of the ccphalograrn, orthopan tomograrn and black a nd white photographs, the vari ous possibi lities for co rrection were evalu ated. As none of the convent ion al techniques would give the des ired effect , however, (see dis cussion ) the cep halograrn was analyzed aga in (Fig. 3) and the idea occurred to place the horizontal ventral part of the mand ibl e in a vertical po sitio n (F ig. 4). The part of the chin is rotated in a s agittal direction around a transverse axis. Mor e or less automatically we retu rn ed to a mod ification of th e simple body ostec tomy as was already described by BLAJR 3 in 18B6. This modification oE Blair's operation is charac terized by removing a tr apezoid p iec e of the man-

Fig. 2. Same patient 1 year after a sagittal chin

rotation.

-

mandibular prognathism rnacrogenia maxillary retrognathism hypoplasia of zyg omatic bones straining of the tip of the nose by the up per lip - insuff icient retentio n for the lower denture - chronic respiratory insufficien cy and rec u rrent pneumonia. The treatment plan based on this diagnosis has to be in theory: maxillary advancement, retropos itioning of the mandib le, reduction of the rnacrogenia and heightening of the anterior lower ridge for a better reten tion of the prosthesis . Taking into consideration the risk of lung complications, the bad con dition of the maxillary sinuses and th e chan ce of relapse of maxillary advancements, due to lack of natural occlusion, it was decided to opt for a limited program. T he three main topics that n eed correction are the mandibular prognathism, macrogenia and the insufficient retention of the prosthesis.

Fig. 3. Preoperative tracing of the cephalog rarn

DE the patient of Fig. 1 showing a prognathic mandible, macrogenia and a flat upper surface of the chin area. The bone cuts for a sagitta l chin rotation are indicated by dotted lines.

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Fig. 5. A nice, smooth alveolar process has al-

ready been formed in the lower front with a vertical slope.

tected. This was done by removing first part of the buccal cortical plate by vertical splitting, from a bur cut in the inferior mandibular margin. The nerve was taken out of the canal and placed distally into a newly created mental foramen. The buccal bone cuts were now extended

4. Preoperative tracing indicating the planned situation after body ostectomy and chin rotation showing correction of the prognatism, the prominent chin and a more favorable inclination of the chin area.

Fig.

dibular body on both sides, backward displacement and backward rotation of the chin. In April 1979 the operation was performed in accordance with the above-described planning under endotracheal anesthesia. The habitual submandibular incisions for an extraoral approach were made and connected over the midline, submentally resulting in a horseshoeshaped incision. The mandibular body was now made accessible by elevation of the periosteum, except for the chin area, to prevent a dropping chin. With a reciprocating saw, oblique bone cuts were made ventrally and dorsally of the mental foramen on both sides so that a trapezoid piece of bone could be removed. To make the ostectomy on both sides identical, a preformed model of leadfoil from a dental film package was used. In order to prevent damage to the inferior alveolar nerve, the mandibular canal was de-

Fig. 6. Preoperative cephalogram. Note the un-

favorable sagittal relationship between upper and lower alveolar ridge and the nearly horizontal slope of the upper aspect of the bony chin.

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and adaptation of the soft tissues, a nice smooth alveol ar process had alre ady been formed in the lower front (Fig. 5). The patient and her family were very much satisfied with the results (Fig. 2). A new prosthesis will be made after the fourth postoperative month . The residual swollen soft tissue up and under the chin is expected to reduce spontaneously in due time.

Discussion

Fig. 7. Postoperative cephalogram . Correction

of tbe unfavor able relationship between upper and lower alveolar ridge. There is an increase in height of the frontal part of the denturebearing area and a more favorable slope in the chin area.

lingually. A total of 21 mm of bone was removed. Now the loose part of the chin was rotated around a transversal axis in a more dorsocaudal position so that its upper horizontal plane was placed in a vertical position (Fig. 4). It was fixed rigidly to the left and right half of the mandibular body by two wire osteosyntheses- and two eight ligatu res in the buccal cortical plate. The excess of soft tissue as a result of the backward displacement of the chin was removed. After this the wound was closed in layers. Postoperative healing was undisturbed; there were no respiratory complications. Sensibility and funct ion of the mand ibular branch of the facial nerve were normal. The displacement of the tongue muscles gave no problems. The fourth postoperative day the patient was sufficiently recovered to go home. The X-rays give a good insight into the differences between the pre- and postoper ative situation (Figs. 6, 7). At a follow-up visit 6 weeks postoperatively, due to remodelling of the bone at the saw cuts

A vertical pl acement of a horizontal frontal part of the mandible in edentulous prognathism patients with macrogenia gives opti mal esthetic and functional results. This result can not be obtained with the conventional opera tions. Step body ostectomy performed on the cephalogram does not provide a good profile, especially the lip relation will be unfavorable. The inferior alveolar n erve will certainly be damaged when taking into consideration the height of the mandibular body, the course of the mandibular canal and the degree of disp lacement that is needed. The step body ostectomy is also not the method of choice because of insuffic ient correction of the prominent chi n . If the chin is also reduced the result will still not be optimal. By sagittal reduction of the bony chin only, a reduction of the chin of 5 mm can be obtained maximally. Disadvantages are a weakening of the frontal part of the mandible, irregular resorption of the opened spongiosa and the risk of a dropping chin and no contribution to a better f un ction of the lower denture. Sliding genioplasty also holds the risk of a dropping chin, but the main objection is that it doe s not contribute to a better base fo r the prosthesis. A sagittal split osteotomy according to Obwegeser-Dal Pont with fixation of the loose fragments with screws" would normally be t he first operation that has to be taken into consideration. Disadvantages

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of this method in a case like the one presented are, however, a too large displacement of the lower lip and a too small correction of the prominent chin as can be shown on the tracing. There is no contribution to a better retention of the lower denture. The risks are damage of the inferior alveolar nerves. 7 and extensive postoperative swelling in the oropharynx in a patient with a high risk of respiratory complications and infections. - The combination of a sagittal split osteotomy and a genioplasty, a combination which is mostly used in cases like this, has almost the same disadvantages as the sagittal split osteotomy alone. Our modification of the simple body ostectomy, first described by BLAIRs, with a vertical rotation of the chin part of the mandible has the following advantages in edentulous prognathism and macrogenic cases: correction of the rnacrogenia with a predictable contour correction of the soft tissues without the risk of a dropping chin because of the fact that the mentalis muscle is not loosened from the bone. If a double chin should occur, the surplus of tissue is easily accessible. correction of the prognathic mandible even in the case of extensive malformations is easy with the possibility to give the chin, the lower alveolar process and the lower lip the right place. absolute raising of the frontal part of the alveolar process and creation of a more favorable vertical slope labially in the lower front for a better retention of the lower denture. elongation of the face is possible by a more caudal fixation of the medial part. Other advantages are the absence of contamination of the wound with oral flora, the possibility to correct a double chin, no

risk of damage to the inferior alveolar nerve, no swelling in the oropharynx, and no intermaxillary fixation. Disadvantages of the method are: - certain risk of damage to the mandibular branch of the facial nerve - scar formation due to the extraoral approach - heavy demands on stability of the fixation of the fragments. The best fixation of the fragments is in theory obtained by a stable plate osteosynthesis, but in this case would certainly mean damage to the inferior alveolar nerve due to the position of the mandibular canal. It was concluded that a stable wire osteosynthesis of 0.6 mm as described by BRONS & BOERINo4 in combination with a buccally placed eight ligature served our purpose best because it would fix the bone fragments sufficiently to make the mandible one rigid body again, but it made extraoral approach necessary. At first it was thought that maintenance of the lingual cortical plate might contribute to the stability by overlapping the bone cut. Later, however, this suggestion was rejected because of the expectation that it would weaken the extremities of the bone fragments too much for stable wire osteosyntheses, which were chosen ultimately.

Conclusion In edentulous patients with mandibular prognathism, macrogenia and almost complete resorption of the lower alveolar ridge, good results may be obtained by a modification of Blair's body ostectomy, followed by rotation of the chin fragment in a vertical position, resulting in a good facial contour and a more favorable base for the lower denture. The risk of non- or delayed union of the straight bone cuts, which was a problem in Blair's days, is less serious now because of better instruments, better fixation techniques and antibiotics.

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References

5. IRBY, D.: Current advances in oral surgery. Mosby, St. Louis 1974, pp , 109-143.

1.

6. SPIESSL, B.: Rigid internal fixation after sagittal split osteotomy of the ascending ramus. In: New concepts in maxillofacial bone surgery . Springer, Berlin 1976, pp. 115-122. 7. TtnNZlNG, D. B. : Kaakosteotomieen. Thesis, Amsterdam 1979, pp. 44-45.

ARANJO, A., SCHENDEL, S. A., WOLFORD, L. R. & EPKER, D. N .: Total maxillary advancement with and without bone grafting. J. Oral Surg, 1978: 36: 849-858. 2. BEHRMAN, S. J., In: Surgical treatment of developmental jaw deformities. ed. H!:NDs, E. C. & KENT, 1. N. Mosby, 81. Louis 1972, pp. 50-56. 3. BLAIR, V. P.: Report of a case of double resection of the correction of protrusion of the mandible. Dent. Cosmos 1906: 48: 817-820. 4. BRONS, R. & BOERING, G.: Fractures of the mandibular body treated by stable internal fixation: a preliminary report. J. Oral Surg, 1970: 28: 407-415.

Address : Department of Oral and Maxillofacial Surgery University Hospital Oosterslngel 59 9713 EZ Groningen The Netherlands