SURGICAL TREATMENT OBJECTIVES

SEMINAR

1. SURGICAL TREATMENT OBJECTIVES (STO) DR. SHEHNAZ JAHANGIR FINAL YEAR MDS DEPT. OF ORTHODONTICS & DENTOFACIAL ORTHOPAEDICS NOORUL ISLAM COLLEGE OF DENTAL SCIENCE

2. CONTENTS INTRODUCTION DEFINITION METHODS CEPHALOMETRIC PREDICTION MANUAL METHOD COMPUTERIZED METHOD SOFTWARES VIDEO IMAGING 3D PREDICTION METHODS STEREOLITHOGRAPHY

3. THE INITIA STO PRE SURGICAL ORTHODONTIC GOALS INITIAL FINAL SURGICAL GOALS SINGLE JAW STO MANDIBLE MAXILLA DOUBLE JAW STO MANDIBLE MAXILLA CHIN STO AP HIN POSITION VERTICAL CHIN POSITION

4. THE FINAL STO MAND. ADVANCEMENT MAXILLARY SUPERIOR REPOSITIONING COMBINED MAX. AND MAND CASES SOFT TISSUE PREDICTION MAND. PROCEDURES MAX. PROCEDURES CHIN PROCEDURES CONCLUSION REFERENCES

5. INTRODUCTION Orthognathic surgery involves the surgical manipulation of the elements of the facial skeleton to restore the proper anatomic and functional relationship in patients with dentofacial skeletal anomalies. The word Orthognathic comes from the Greek word, “ Orthos ” meaning to straighten, and “ Gnathos ” meaning jaw. Orthognathic surgery thus means to straighten a jaw.

6. Over the past decade a growing number of adult patients are seeking orthodontic treatment. A noteworthy part of the adult population reporting for orthodontic treatment is associated with severe skeletal discrepancy. Correction of such skeletal discrepancy in adults cannot be achieved by growth modification procedures, as the patient is no longer growing.

7. This necessitates surgical repositioning of one or both the jaws and or the dento -alveolar segments. The goals of surgical management of malocclusion therefore should include structural integrity, functional balance and esthetic harmony.

8. The prediction of orthognathic treatment outcome is an important part of orthognathic planning and the process of patient’s inform consent. Cephalometric prediction plays an important role in orthognathic surgery by increasing patient understanding and acceptance of the recommended treatment.

9. In planning objectives for orthognathic surgery, predicting surgical outcomes by surgical treatment objective (STO) is mandatory. It is a vital tool for assessment, communication and patient education. STO helps the orthodontist in assessing the goals of pre surgical orthodontics. For the surgeon, it helps in deciphering the surgical sequence.

10. As for the patient, his perception of esthetics should be disregarded with prime importance, for which a visual aid to show the surgical outcome is mandatory. Therefore , the determination of the final surgical outcome should be compiled by predicting the results of a series of feasible treatment options.

11. There are five general methods of visualizing, planning, and predicting surgical orthodontic outcomes : Manual acetate tracing. Manipulation of patient photographs to illustrate treatment goals. Computerized diagnostic and planning software that produces a soft tissue profile "line drawing"; as a result of manipulation of digitized structures of lateral cephalometric radiographs.

12. 4. Computerized diagnostic and planning software that integrates video images with the patient's lateral cephalogram to aid in planning and predicting surgical orthodontic procedures (Video cephalometrics ). 5. Three-dimensional computer technology for planning and predicting orthognathic surgery.

13. SURGICAL TREATMENT OBJECTIVE Surgical treatment objective or prediction tracing is a two dimensional projection of the osseous, dental and soft tissue changes resulting from surgical orthodontic correction of orthodontic and orthopaedic deformities. Bell, Profitt, and White proposed the use of cephalometric prediction using templates. Wolford LM, Hilliard FW, Dugan DJ . Surgical Treatment Objective . 1985.

14. The purposes of the S.T.O. are threefold:- To establish orthodontic and presurgical orthodontic goals . To develop surgical objectives To create the predicted facial profile

15. The S.T.O. has significant importance in two phases of treatment planning. The initial S.T.O . It is prepared before treatment to determine orthodontic and surgical goals . The final S.T.O . It can be prepared after initial S.T.O using the pre-treatment cephalogram or it can be prepared after active orthodontic treatment and before surgery to determine the exact vertical and antero -posterior changes to be achieved.

16. Before performing the S.T.O. presurgical orthodontic goals must be established by, Clinical examination Dental model evaluation Cephalometric analysis.

17. METHODS

18. CEPHALOMETRIC PREDICTION Currently, there are three methods for cephalometric analysis: hand tracing and direct measurement of the desired angles and distances with the use of a protractor and ruler, and direct and indirect computer digitization of the radiograph.

19. For direct computer digitization the anatomical points are entered from the cephalometric radiograph into computer memory using an electronic pen or the crosshair cursor. For indirect digitization, a scanner or a video camera captures an image of the radiograph and stores it in the computer. The video camera is calibrated in co-ordination with the cephalometric radiograph.

20. Another method of cephalometric film entry into the computer and analysis is the use of digital radiology. Computerized cephalometric analysis is rapid and the clinician can run as many analyses as the computer program allows arriving at a diagnosis. Cephalometric prediction in orthognathic surgery can be performed, as well, manually or by computer. Several methods of prediction have been suggested.

21. MANUAL METHODS Traditionally, acetate tracings have been used for cephalometric determination of the movement of hard tissue and the prediction of the response of the soft tissue to those movements. Historically , the first method to determine the amount of posterior movement of the mandible needed to produce satisfactory facial esthetics following mandibular surgery was described by Cohen.

22. COHEN A tracing of the maxilla, maxillary teeth, mandible, mandibular teeth, and soft tissue profile was made from the original cephalogram . A divider was used to record the posterior movement of the mandible. A regional tracing of the lower face alone including only the mandible and mandibular teeth as well as the soft tissue outline of the upper throat, chin, and lower lip was made and cut-out.

23. This cut-out section was moved distally along the plane of occlusion following the amount of posterior movement of the mandible recorded with the divider. The soft tissue changes were then inspected. The cut-out section is outlined in a different colour than the original tracing and thus it was easier to visualize the soft tissue changes.

24. McNeill et al . Another cephalometric prediction technique for the soft tissue profile after surgical repositioning of the mandible has been proposed by McNeill et al. including the following steps : (a) Use of dental casts to establish the tentative post-treatment dental relationship. This could be done easily by using an articulator on which the casts could be mounted. Sometimes a diagnostic set-up before repositioning of the casts was necessary.

25. (b) Construction of an overlay cephalometric tracing that included the outlines of the hard and soft tissues, which would not be affected during treatment . ( c) Sliding of the overlay tracing until the parts that are to be changed in the treatment, duplicate their desired position as shown on the pre oriented casts. Molar and incisor relationships on the casts serve as guides for correct overlay positioning.

26. The preferable skeletal relationship is traced in a different colour , on the overlay. ( d) Completion of the prediction tracing by adding soft tissue profile outlines. According to this technique lip thickness will vary inversely with changes in facial vertical dimension and soft tissue chin thickness will not be affected by treatment.

27. Hohl et al. A photo cephalometric technique for the prediction and evaluation of skeletal and soft tissue changes following dentofacial and craniofacial surgery was advocated by Hohl et al. Lateral and frontal cephalograms and photographs were taken. Photographic negatives were enlarged allowing the photographic images to be superimposed upon the radiopaque images on the cephalograms .

28. Transparent photographs were produced from the projection of the enlarged negatives that can be superimposed over the cephalometric films. By drawing the line from nasion to pogonion onto the photograph, soft tissue measurements could be made directly in vertical and horizontal directions. This technique allowed detailed soft tissue analysis in the lateral projection that was difficult to obtain by standard cephalometric techniques.

29. Fish and Epker Another method of surgical-orthodontic cephalometric soft tissue prediction tracing for mandibular advancement, maxillary superior repositioning and combined maxillary and mandibular surgery was proposed by Fish and Epker . Their method was adapted in part from Ricketts’ cephalometric analysis, growth prediction and visual treatment objective construction as presented by Bench et al.

30. The Frankfort horizontal and a perpendicular line from nasion were drawn to indicate the optimum facial depth as a guide to begin the prediction for either mandibular advancement or set-back surgery. The teeth were placed as described by Bench et al. The change in lower incisor position was found and marked by superimposing the mandible on corpus axis at pterygo -maxillary fissure. The prediction tracing for maxillary superior repositioning, auto-rotates the mandible clockwise around the condyle.

31. Proffit . The use of cephalometric prediction to forecast changes in bony relationships and associated soft tissue changes has been also systematically advocated by Proffit . According to the author, cephalometric prediction can be done manually by moving templates or by repositioning an overlay tracing of the patient’s cephalogram .

32. The template method should be used in any case where vertical maxillary surgical movement is planned and it is very useful when large dental movements are planned, as well as in chin repositioning. It is not widely used because it is time-consuming. Typically, this method is used in maxillary osteotomies and in double surgeries (bi-maxillary surgery). In one- or two-piece osteotomies, the entire maxilla outline is drawn. In three-piece osteotomies, the outlines of anterior and posterior maxillary pieces, as well as two mandibular outlines (extraction and non-extraction) are drawn. During the prediction course, the mandible rotates around the condyle.

33. The overlay method is the simplest prediction method for mandibular osteotomies. Its use is limited to surgeries that do not affect vertical maxillary position and the method is not time consuming. For this method there is no need for intermediate tracings. Steps to be followed by using the overlay method are:

34. (a) The initial cephalogram is traced and the surgical reference line is drawn . (b) All structures that will not be affected by the mandibular osteotomy are traced on a second paper placed over the original pre-surgical tracing, so called the overlay tracing. (c) The overlay tracing is held stable and the underlying pre-surgical tracing is moved backwards until desired overjet , overbite and proper occlusion are achieved. The mandible and lower teeth as well as the surgical reference line are drawn.

35. (d) The two tracings are superimposed on the cranial base and the distance of mandibular incisor backward movement is measured in mm. Data regarding ratios of soft tissue changes relative to respective skeletal movements is used to estimate the predicted lower lip position relative to surgical incisor movement. The distance between surgical references line will be measured to determine the surgical movement in mm. (e) Tracings are superimposed on the mandible and lower lip outline and soft tissue chin are drawn.

36. (f) Superimposition on the cranial base and completion of predicted soft tissue profile by using the data from Jensen et al. Wolford and Proffit have presented the most systematic approaches for prediction tracings. In these prediction methods the cephalogram is obtained, in natural head position, teeth at maximum intercuspation and with the patient’s lips in repose.

37. However, acetate tracings are of lesser value for visualization of the profile outcome. The final esthetic outcome is heavily dependent on the experience and the artistic skill of the clinician who makes the treatment plan. Moreover, the manual methods of cephalometric prediction of the orthognathic outcome are time consuming.

38. COMPUTERIZED METHODS Prediction of the orthognathic surgery outcome can also be done by computer, using various available software programs, alone or in combination with video images. Historically the first computer program designed by Bhatia and Sowrayto aid diagnosis and treatment planning in orthognathic surgery and prediction of postoperative soft tissue profile.

39. The general software could collect, store and analyze graphic data such as radiographs of the skull and photographs of the face and dentition . The operator manipulated graphics to attempt different possible surgical procedures and was able to produce different predicted profiles . To predict soft tissue changes, the program first produced a bodily movement of the soft tissues corresponding to the hard tissue movement and then produced a change in the soft tissue shape.

40. Later, Harradine and Burnie described a computer program that was capable of providing the user with superimposition tracings in order to visualize where and how much the patient deviates from “Bolton’s standard” and with quantitative measurement of the hard and soft tissue changes for comparison. Prediction could be carried out after the user selects the surgical procedure and enters the required vertical and horizontal dimensions of change. Soft tissue change predictions were performed automatically using hard to soft tissue ratios.

41. Another computerized program for the planning of maxillofacial osteotomy and its applications was developed by Walters and Walters . A suggested operation was generated spontaneously by the computer. The computer then adjusted the position of the soft tissue according to the degree of the bone movements as suggested by Freihofer and produced the predicted soft tissue profile. The surgeon or the patient had the option to accept or reject the suggestion of the computer in part or whole by altering the esthetic prediction generated by the computer.

42. Currently there is a wide variety of computerized cephalometric software systems for orthognathic surgery prediction.  

43. Quick Ceph Quick Ceph was the first commercially available software for orthognathic surgery prediction. The Quick Ceph Image (Quick Ceph Systems, San Diego, California ). it is designed for Macintosh computers. It permits a wide range of functions based on a 28-point digitization. When orthodontic and surgical movements are simulated, horizontal and vertical changes are recorded by the computer. The soft tissue adjusts automatically according to predetermined ratios. The majority of these ratios are derived from Wolford et al.

44. Quick Ceph2000 Recently, the release of the latest version (Quick Ceph2000) incorporated many advantages, including capture and storage of high resolution images, treatment simulations, growth forecasts, compatibility with any operating system and digital image enhancement of tracing accuracy

45. dentofacial planner The dentofacial planner is a product of Dentofacial Software Inc. (Toronto, Canada). It has been designed for IBM-compatible computers. The program is capable to perform a variety of cephalometric analyses including Steiner, Downs, McNamara, Ricketts, Grummons , Harvold , Legan , and Jarabak . It is also capable to perform CO–CR conversions, to estimate facial growth, simulate any combination of orthognathic surgery procedures including one piece or segmental maxillary surgery, mandibular advancement or setback, total or anterior mandibular sub apical surgery and chin surgery.

46. When a surgical movement is manipulated, vertical and horizontal changes are calculated by the computer. The soft tissue profile is automatically displayed after each treatment planning manipulation, according to predetermined ratios.

47. Vistadent Vistadent (GAC International, Birmingham, AL) it has been developed by GAC Techno Center. It is an orthognathic surgical program that uses Ricketts, VTO for treatment simulations. It is compatible with all digital X-ray systems and digital cameras.

48. Orthodontic treatment planner (OTP) Orthodontic treatment planner (OTP) (Pacific Coast Software, Inc., Wayzata, MN) is a surgical prediction program distributed by ortho –vision technologies.

49. Dolphin imaging software Dolphin imaging software (Dolphin Imaging and Management Solutions, Chatsworth, CA) is another popular software orthognathic surgical program, presently commercially available. The version 11.0 software involves the indirect digitization of multiple dental, skeletal and soft tissue landmarks of the scanned cephalogram , using a mouse-controlled cursor.

50. An aid in landmark location is the capability of the image to be enhanced and enlarged. The program can also demonstrate landmarks expected position, thereby minimizing errors in landmark definition. The software links up the points to give a trace image, which can be manually manipulated for improved fit. The user can then select the analysis of choice.

51. ADVANTAGES OF COMPUTERIZED PREDICTION (1) The best available data on the soft tissue changes associated with each operation is always at the clinician's disposal . (2) Although there is the possibility of errors in landmark recognition which is inherent in any cephalometric technique, there are no measurement errors in the movement of hard and soft tissues during the prediction process or in the cephalometric analysis of any record.

52. (3) No artistic skill is required in smoothly progressing from one ratio of hard to soft tissue change to the next. (4) The records of stages in treatment and of predicted results are not easily lost. Back-up copies of the disc files are easily made and additional copies of the plot can be produced at any stage. (5) The program enforces a standardized method of recording data and performing predictions.

53. (6) The method is rapid in comparison with other techniques. This combination of speed and accuracy which is characteristic of all computerized processes, encourages the clinician to explore the predicted results of several different combinations of orthodontic and surgical procedures.

54. Disadvantages relatively expensive equipment is required, although a microcomputer linked to a digitizer and plotter can be used for many other purposes . software is required. However, as with computer hardware, the ability to write or purchase programs is becoming increasingly widespread and existing programs can be translated to conform to different hardware.

55. the graphic output is a silhouette rather than a picture. This is a potential disadvantage when discussing treatment options with patients, but not, in the authors' opinion, a large one. A further problem shared by all methods is the variability in ratio of hard to soft tissue change. For some procedures, this variability is small.

56. VIDEO IMAGING More recently, the introduction of computer software programs with video imaging by Sarver et al.

57. Orthographic software was first used in the mid 1980s. With this software an image of known size was capture and then calibrates the imaging software so that the computer was capable of internal software measurement of image on the screen in real size. However , direct visualization of the bony structures in coordination with soft tissue profile was not easily accomplished.

58. TRUE VISION IMAGE PROCESSING SYSTEM (TIPS) AND ORTHOGRAPHIC SOFTWARE The use of true vision image processing system (TIPS) and orthographic software in the superimposition of the lateral cephalometric tracing or cephalogram over a profile image as an aid of planning and predicting the orthognathic surgery outcome was further evaluated

59. main advantages the capability of the software to overlay images, the calibration of the images on the computer screen to actual dimensions and the quantification in x and y axis of the movement of defined areas.

60. Grubb Another computer software program with video imaging was used by Grubb . Preselected skeletal and soft tissue landmarks were digitized and then anatomic areas were traced. If desirable, an occlusogram could be created by digitizing the photocopy of the occlusal view of each dental arch.

61. After cephalometric and study cast data were entered into the system, a variety of analyses and treatment options could be selected and simulated. To simulate anatomic structures, electronic templates were created.

62. THREE-DIMENSIONAL PREDICTION METHODS Computer methodology integrating cephalometric data with three-dimensional (3D) computerized tomographic (CT) data has been found to aid in the clinical planning of orthognathic surgery, especially in craniofacial anomalies cases.

63. A patient’s 3D tracing is compared to a similarly generated “ideal” for every age and sex corresponding Bolton tracing. After the type and number of osteotomies to be performed have been selected, the program calculates the postoperative movements of all osteotomy fragments required to have the surgical outcome most closely approximate the Bolton “ideal” form. The user can modify the orientation and position of each osteotomy fragment, if needed. The surgical planning cephalometric treatment may be performed on 3DCT scan reconstructions for superior visualization of the planned surgical changes.

64. Today, three-dimensional prediction methods are available, such as three-dimensional computerized tomography (3DCT), 3D magnetic resonance imaging (3DMRI) and surface scan/cone-beam CT. The combination of surface scanning and cone-beam CT scan uses hard tissue imaging data from the tomogram and soft tissue data from the surface scan, which are processed through special software.

65. STEREOLITHOGRAPHY Stereolithography has become a well known technique in the rapid prototyping sector. In preoperative model planning and surgery simulation, this technique has been used in the field of craniofacial surgery, tumour surgery, reconstructive surgery, orthognathic surgery, preprosthetic surgery and dental implants. ( Lambrecht , 1989; Kärcher , 1992; Millesi et al., 1994; Ono et al., 1994; Wolf et al., 1994; Bill et al., 1995; Kermer et al., 1998).

66. THE INITIAL STO It is prepared before treatment to determine the orthodontic and surgical goal. It is both a diagnostic aid and a treatment planning aid. This part will discuss the development of the initial STO. It is divided into two sections. Presurgical orthodontic goals Surgical goals

67. PRESURGICAL ORTHODONTIC GOAL Before constructing an initial STO, presurgical orthodontic treatment must be established by clinical examination, dental model evaluation . cephalometric analysis.

68. Initial presurgical orthodontic goal Position the long axis of the maxillary incisor at 22 degrees tonasion -point A (NA) line with the labial face of the incisor 4anterior to that line (Fig. 2-1, A). Position the long axis of the mandibular incisor at 20 degrees to nasion -point B (NB) line with the labial face of the incisor 4 mmanterior to that line (Fig. 2-1, B).   Satisfy arch length requirements (crowding or spacing).

69. Removal of dental compensations is necessary before surgery for maximal skeletal correction . Surgical skeletal correction to an ideal 2-degree ANB angle will produce an ideal interincisal angle of 136 degrees when the proper incisor positionareachieved presurgically . Anincrease or decrease in the ANB angle will require changes in incisor angulation to maintain the ideal interincisal angle of 136 degrees. As the ANB angle is increased, it is necessary to decrease the upper incisor angle to the NA line and the distance from the labial face to that line. It is also necessary to increase the lower incisor angle to the NB and the distance from its labial face to that line (Fi g. 2-2, C).

70. . Relocation of the molar teeth will depend on the arch length requirements and mechanics used by the orthodontist to achieve the ideal incisor position. The original cephalometric radiograph is traced in black pencil on manual acetate. Once the initial orthodontic goals are established, the teeth must be redrawn on the original CT. we prefer to do this with colored pencil, since the CT is traced in the black. A mandibular advancement was planned for the patient in fig 2-3 A. Relocation of the incisors to satisfy ideal presurgical orthodontic goals is demonstrated in fig 2-3,B.

71. After the teeth have been relocated on the CT tracing, the initial STO is constructed. The technique used is the same as that used for the final STO. The initial STO is helpful to: Establish the final presurgical orthodontic goals Establish the surgical dentoskeletal objective Establish the genioplastic procedure with chin evaluation Establish the soft tissue facial profile objective

72. Final presurgical orthodontic goal After the completion of the initial STO, the relationship of the lower incisor to the NB line is changed because predominant clockwise movement of the body of the mandible (fig 2-4, B) The lower incisor is now 5mm anterior to the NB line at 29 degrees and thus the initial presurgical goal may be modified to upright the incisor and move it distally 1mm. unless extreme skeletal movement with the STO, usually only slight modification (if any) of the initial goal is necessary.

73. In the maxillary segmental surgical procedures abnormal incisor angulation may be partially or totally corrected with the surgical procedure to properly align that segment . Completion of the initial STO will establish the final presurgical preorthodontic goal. Usually only slight adjustment of the initial goal is necessary.

74. SURGICAL GOAL Accurate determination of skeletal movements is very important in treatment planning. It not only affects the presurgicalmachanics but will have definite effects on the functional and esthetic results. This section is divided into three parts: Single jaw STO Double jaw STO Chin STO

75. Single jaw STO Surgical repositioning of single jaw units greatly depends on the opposite jaw position, occlusion and presurgical orthodontic goals. Establishing surgical reference lines on the CT is very important to determine accurate movement of the single jaw or parts thereof.

76.   Mandible NON SEGMENTAL. The presurgical position of the maxillary and mandibular teeth dictates the vertical and AP position of the mandible. An appropriate reference line is placed in the area of osteotomy to determine the AP change.

77. A vertical reference line is drawn in the area of the vertical buccal osteotomy. A short horizontal reference line is drawn 2 to 3 mm below the alveolar crest.

78. SEGMENTAL. Mandibular segments can be repositioned in all three dimensional planes via subapical or bilateral body osteotomies and depend on: Occlusion Angulation of lower incisors Arch length requirements Lower dental height

79. MAXILLA Alterations in position of the maxilla in single jaw surgery depend on the position of the mandible, the occlusion and presurgical orthodontic goals, upper tooth relation to lip, and upper lip length. The primary decision that the clinician must make is the desired vertical position of the maxillary central incisor. The vertical position of the central incisor is based on normal interrelationships from Burstone Lip length measured from subnasale to upper lip stomion ; men, 22 mm +/-2 mm; women,20 mm +/- 2 mm; upper tooth to lip relation, 1to 4 mm.

80. VERTICAL POSITION OF MAXILLA. Aftertracing all stable skeletal and tissue structures on the STO, a horizontal line is drawn to indicate the desired incisor level (Fig. 2-9). As the maxillary incisor is moved more superiorly, the maxilla must move more anteriorly to accommodate the mandibular autorotation.

81. Itis difficult to alter upper lip length and maintain optimal upper esthetics. Therefore with abnormal lip lengths the upper tooth to lip relationcan be altered tomaximize esthetic balance. If the upper lip is excessively long,we usually minimize the upper tooth to lip relation (0 to 2 mm). If theupper lip is short, we will maximize the tooth to lip relation (3 to 5 mm).

82. NONSEGMENTAL When a deformity is to be corrected with isolated nonsegmental maxillary surgery , the only option available to the clinician is the vertical position of the maxillary incisor. The resultant AP position of the Maxilla and the maxillary teeth is dictated by the autorotation of the maxillary and the mandibular teeth.

83. SEGMENTAL. In addition to vertical incisor position, the clinician controls the angulation of the maxillary teeth with segmental procedures, but the AP position of the maxillary incisal edge is still dictated by the mandibular auto-rotation. More angulation control is available with a four-tooth anterior seg­ment that a six-tooth anterior segment. The curve of the dental arch limits the surgical correction of overangulated incisors in a six- tooth . segment be­cause the more the incisors are uprighted , the more superior the cuspids become (Fig. 2-10).

84. DOUBLE JAW STO Mobilization of both jaws requires predetermination of following relations in the STO that must also correlate with the clinical examination and model surgery: Vertical position of maxillary incisor AP position of maxilla Occlusal plane angulation These factors will dictate the position of the mandible and will affect to functional and esthetic results.

85. Mandible NONSEGMENTAL . Mandibular position is dictated by the reposition. maxilla, maxillary teeth, and occlusal plane angulation. SEGMENTAL.Additional control of mandibular segments is available as previously discussed.

86. Maxilla. In double jaw surgery the vertical and AP positions of the maxilla and the occlusal plane angulation can be selected. The desired position determined from clinical and cephalometric evaluations.

87. VERTICAL, POSITION OF THE MAXILLA. As in single jaw maxillary surgery the vertical position of the maxilla is determined by the upper tooth to lip relation . After the stable cranial base and soft tissue landmarks are traced on the STO, the desired vertical position of the Maxillary incisor marked with a horizontal reference line .

88. AP POSITION OF THE MAXILLA AP position of the maxilla is determined from cephalometric analysis and clinical examination .

89. Cephalometric measurements helpful in determining AP maxillary position are, maxillary depth, McNamara's nasion perpendicular and SNA. Maxillary depth: the angle formed by Frankfort horizontal and a line from the nasion to point A; average: 90 degrees = 3.

90. McNamara's nasion perpendicular: the distance (in mm) from point- A, to a line from nasion constructed perpendicular to Frankfort horizon tal ; average: 0 mm, ±-2 min . SNA: the angle formed by the sella-nasion (SN) and NA lines; average: 82 degrees, 2 degrees.

91. OCCLUSAL PLANE ANGULATION. The average relationship of Frankfort horizontal to the occlusal plane is 8 degrees +5 degrees. If alteration of the maxillary occlusal plane is desired, the posterior maxillary position may be selected- before the mandibular movement.

92. A summary of the options available for the double jaw STO is presented in Table

93. Chin STO The chin position should be evaluated after major skeletal relocation has been completed on the STO , but before completion of the soft tissue projection. For the STO the chin position is evaluated in two dimension: AP and vertical. Average soft tissue thickness of the upper lip, lower lip, and chin is approximately 11 to 14 mm, but more important is an equal balance between the structures.

94. Normally there should be approximately a 1 : 1 : 1 relation in the AP soft tissue thick­ness of the upper lip, lower lip, and chin (Fig. 2-13). The CT must reflect the soft tissues of the lips and chin in the relaxed position to adequately evaluate thickness. If the AP and vertical soft tissue thickness of the chin is less than desired, then the osseous tissues of the chin can be positioned in a more anterior relation than determined by the osseous analyses to add support to the deficient soft tissues.

95. However, if the mandible and/or maxilla are to be repositioned, the chin analysis is performed on the STO after the repositioning of those structures and after the soft tissues of the forehead, nose , and upper lip have been completed.

96. AP Chin Position The determination of AP chin position can be analyzed relative to the osseous or soft tissue structures. The object of analysis is to position the soft tissue chin in the most desirable position, and the osseous chin position is adjusted accordingly.

97. The hard and soft tissues of the chin should be carefully evaluated in the AP dimension. We found the following analyses to be most helpful in con­struction of the STO . NB line (Fig. 2-14): Distance from NB line to lower incisor arid to pogonion Average: Lower incisor and pogonion equal distance from NB line (4 to 6 mm)

98. Apo line (Fig. 2-15) Distance from A pogonion line to lower incisor Average: 2 mm +/- 2 mm

99. Angle of facial convexity (Fig 2-16) Angle between soft tissue glabella – subnasale ( GaSn ) line and subnasale – soft tissue pogonion ( SnPo ’) line. Average: 11 degrees +4 degrees

100.   Subnasale vertical (Fig 2-17) Distance from soft tissue chin to a line perpendicular to Frankfort horizontal through subnasale . Average: -3 mm +/- 3 mm

101. 0-degree meridian (fig 2-18) Distance from soft tissue chin to line perpendicular to Frankfort horizontal through soft tissue nasion   Average: 0 mm +/- 2 mm

102.   E line (Fig 2-19) Distance between lower lip and esthetic (nose-chin) plane   Average: 2 mm +2 mm

103. Vertical Chin Position The vertical chin position is determined primarily analysis of anterior vertical mandibular dental height and correlated upper lip length, vertical facial proportions, and vertical soft tissue length the chin.  

104. If the upper lip length is greater than normal, then vertical chin position should be greater than normal to maintain appropriate vertical balance in the lower third of the face. If the upper lip is long and chin is positioned vertically in a normal dimension, the vertical length of lower lip and chin will be out of balance with the upper lip.

105. To evaluate the hard and soft tissues of the chin in the vertical demission, we find the following analyses most useful : 1.Lower anterior dental height (Fig. 2-20): Distance from incisal edge of lower incisor to lower border of mandible

106. 2.Lower anterior soft tissue (lower lip length) Distance from lower lip stomion to soft tissue mention

107. A summary of chin evaluations is presented in table.

108. THE FINAL STO OVERLAY METHOD Various surgical procedures for which S.T.O can be used Mandibular advancement Mandibular setback Maxillary impaction Maxillary advancement Maxillary setback Combined Maxillary and mandibular procedures Adjunctive Genioplasty

109. I. Cephalometric Prediction Tracing for Mandibular Advancements. The basic reasons for doing predictions for isolated mandibular surgery (advancement or set-back) are: To accurately assess the profile esthetic results this will result from the proposed surgery,

110. To consider the desirability of simultaneous adjunctive procedures such as genioplasty , suprahyoidmyotomy , etc., To help determine the sequencing of surgery and orthodontics (i.e., if the surgery is done first will it be more difficult or easier to do the indicated orthodontics),

111. To help decide what type of orthodontics might best be employed (i.e., extraction versus non-extraction) and To determine the anchorage requirements

112. Step 1 - Trace the Stable Structures. The first step in producing a prediction tracing is to overlay a piece of acetate paper on the original cephalometric tracing and trace all structures which will not be significantly altered by the surgery and/or orthodontics . For mandibular surgery, these structures will include the deep cranial features, the maxilla, the maxillary occlusal plane, the mandibular ramus and the profile to the base of the nose.

113. Draw in Frankfort Horizontal and a line from nasion to indicate the optimum facialdepth , i.e., 89° in females, 90° in males (Fig. 2A ). optimum facial depth is a convenient guide forbeginning a prediction for either mandibular advancement or set-back surgery. Nasal esthetics and sex have a directinfluence on optimum chin prominence .

114. Step 2 - Add Skeletal Portion Changed by Surgery Slide the prediction tracing to the left and rotate it slightly to position bony pogonion at the optimum facial depth, keeping the mandibular occlusal plane in proper relation to the maxillary occlusal plane. Once a satisfactory position is achieved. Trace the distal portion of the mandible, the corpus axis, and the soft tissue chin in this position (Fig. 2B). There is little change in soft tissue chin thickness, so the soft tissue chin may be drawn in just as it was originally . However , this isso only if the original cephalometric radiograph is taken with the lips in repose.

115. Step 3 - New A-Po Line. Construct a new line from Point A to pogonion . If a genioplasty is to be included in the procedure, the anterior portion of this altered chin, be it bone or alloplast , is now construed to be pogonion for purposes of placing the teeth.

116. Step 4 - Placing the Teeth. The teeth are placed exactly as described by Bench, et al . First the lower incisor is placed in its optimum position 1 millimetre ahead of the A-Po line, 1 millimetre above the occlusal plane, and at 22 degrees to the A-Po line. Old and new mandibles are then superimposed on Corpus Axis at PM and the change in lower incisor position is noted.

117. The upper first molar is then placed in the desired occlusion and the upper incisor is likewise placed in the optimum position with its long axis 5 degrees more upright than the new facial axis (dotted line on the prediction tracing).

118. Step 5 - Tracing the New Lip Contours. Once the teeth are placed, the lip contours are traced to correspond to the new incisor positions. The result of Steps 4 and 5 are shown in Figure 2D which is the completed prediction tracing. Once completed, the prediction tracing must be viewed as a goal toward which one is working.

119. II. Cephalometric Prediction for Maxillary Superior Repositioning. Step 1 - Trace the Stable Structures. As is the case with all prediction tracings, we again begin by tracing the structures which will not be modified either surgically or orthodontically (Fig. 4A) . This should include point A

120. Step 2 - Determination of Ideal Vertical Position for the Upper Incisor. Regardless of how accurate your cephalometric technique, we recommend that the measurement of the amount of upper central incisor exposed, i.e., that from stomion of the upper lip to incisal edge, be made clinically with the patient standing in a relaxed posture.

121. This is the single most important measurement in preparation for superior repositioning of the maxilla and can be confirmed cephalometrically . Once the amount of incisor exposed beneath the upper lip is determined, the "ideal" amount of superior repositioning of the upper incisor can be determined by the formula:X = (y-2)/0.8 where X is the amount of superior repositioning necessary and Y is the amount of upper incisor showing . Once the desired amount of vertical incisor repositioning is determined, draw a line parallel to Frankfort horizontal on the prediction tracing to represent the desired vertical position (Fig. 4B).

122. Step 3 - Autorotation of the Mandible. Superimpose the original and prediction tracings and, keeping the mandibular condyle in the same position, rotate the prediction tracing clockwise until the occlusal plane is 1 mm above the line indicating the desired position of the upper incisor. Trace the mandible in this position. The corpus axis and the occlusal plane are also traced in at this time (Fig. 4C).

123.   Step 4 - Genioplasty Determination. The second feature which must be noted is the new soft tissue chin position. If the chin is adequate, then genioplasty is not necessary. However, if the chin is still weak, as in our example either mandibular advancement or some type of genioplasty must be added to the treatment plan for optimum esthetics .

124. Step 5 - Placement of Teeth in Ideal Positions. This step is carried out exactly as described by Bench, et al. After placing the teeth in their ideal position (Fig. 4E), we are now ready to trace the new profile. ( The excessive overjet in this patient is produced by a missing lower incisor.)

125. Step 6 - Nasal Outline. With superior repositioning of the maxilla, the nasal tip is generally elevated slightly. This is more pronounced if the maxilla is moved upward and forward, less pronounced if upward and backward. The lower border of the nose is relatively unchanged though it too may be elevated a small amount. Accordingly, the prediction tracing should be placed on the original with the fixed landmarks superimposed and the nasal outline traced with the aforementioned alterations (Fig. 4F).

126. Step 7 - Upper Lip. The upper lip reacts to superior repositioning in the following ways: 1 ) the length from subnasale to upper lip stomion shortens 1/5 of the amount of superior repositioning, 2 ) the thickness increases by 1/3 of the amount of incisor retraction, and 3 ) the lip thins out slightly if the upper incisor is moved forward, but in all but the most extreme instances this is unnoticeable. To trace the new upper lip one should superimpose on the fixed cranial structures and study the change in incisor position.

127. Step 8 - Lower Lip. In most instances the lower lip vermillion is traced in the same relation to the lower incisors as existed prior to treatment. Superimpose the lower incisor on the prediction tracing over that on the original and trace the lower lip.

128. Step 9 - Chin. If no genioplasty is projected, the soft tissue chin will be relatively unaffected by treatment and should be traced bysimply superimposing on the mandibular symphysis . If a sliding genioplasty is done, the chin is traced by first superimposing on the original symphysis and then sliding the prediction tracing back 6/10 of the amount of the genioplasty and tracing the new chin contour.

129. III. Cephalometric prediction tracing for combined maxillary and mandibular cases. The basic technique involved is to trace the stable structures, place the maxilla in the desired position both vertically and anterior-posteriorly and then place the mandible in its desired position .

130. Step 1 - Trace the Stable Structures (Fig. 7A). Step 2 - Determine the Ideal Vertical Position for the Upper Incisor. In the patient with an obtuse nasolabial angle, where the maxilla will come forward to increase lip support, slightly more shortening of the lip will be produced than might otherwise be expected.

131. Superimpose the original and the prediction tracings and draw a line parallel with Frankfort horizontal to indicate the desired vertical position of the upper incisor. Trace a line from original point A tangent to the labial of the upper incisor as a reference for the original upper lip support (Fig. 7B).

132. Step 3 - Autorotation of the Occlusal Plane. Keeping the condyle in the same position, rotate the prediction tracing clockwise until the occlusal plane is 1mm above the line indicating the desired position of the upper incisor. Trace the occlusal plane and the mandibular ramus in this position.

133. Step 4 - Mandibular Movement. This is done exactly as was done in Step 2 under mandibular advancement (Fig. 7D).

134. Steps 5-10 - Completing the Tracing. Once the new position of the mandible has been traced, the balance of the tracing is done as outlined in Steps 4-9 under Maxillary Superior Repositioning. The finished prediction tracing is seen in Figure 7E . In Figure 7F the superimposed tracings are illustrated.

135. SOFT TISSUE PREDICTION Soft tissue changes are very important in the determination of final profile results and should be projected as accurately as possible. The soft tissue may move significantly different than the osseous structures, creating difficulties in determining accurate soft tissue changes on the STO. These differences are more apparent in maxillary surgery.

136. The more commonly soft tissue landmarks are. P( pronasale ): The most prominent or anterior point of the nose. Sn : The most posterior-superior point on the nasolabial curvature. A’(soft tissue A point) : The point of greatest concavity of the upper lip between subnasale and labralesuperius . UL( labralesuperius ): The most anterior point on the upper lip. St ( stomion -upper lip) :The most inferior on the upper lip LL ( labraleinferius ) :The most anterior point on the lower lip. B’(soft tissue B point) : the point of greatest concavity of the lower lip between labraleinferius and soft tissue pogonion . PO’ (soft tissue pogonion ): The , ost anterior point on the soft tissue chin. Me’ (soft tissue menton ) :The most inferior point on the soft tissue chin.

137. The soft tissue discussion will be divided in to three sections : Mandibular procedures Maxillary procedures Chin procedures

138. Mandibular procedures A summary of the following material can be seen in the following table and in the figure Soft tissue changes expressed as percentage of dentoosseous movement for linear change degrees per millimetre for angular change. +LL- Most anterior point onlower lip +/- H – Horizontal UL – Most anterior point on upper lip

139. Procedure Soft tissue anatomic points Dimension measured % change Advancement LL+ B’ Po’ H+ H H 67-85 100 100 Setback UL LL B’ Po’ H H H H 20 90 90 90 Subapical development   LL   H   60 Subapical setback LL H 75

140. Total Advancement In mandibular advancement the soft tissue change at pogonion and labiomental fold is approximately 100% relative to the bone . Although no data are available, if dental interferences are present preoperatively , the lower lip should assume a more superior position relative to the mandibular incisors after advancement.

141. Total setback. Posterior repositioning of the mandible via ramus procedures yields a 90 % soft tissue change at the chin, labiomental fold, and lower lip relative to the AP bone change. The upper lip may also move posteriorly 20%. Bilateral mandibular body ostectomies should produce the same soft tissue change.

142. Subapical Advancement. A study of two patients showed that a mandibular subapical brought the lower lip forward by 60% and that the soft tissues of the chin remained relatively stable. In this type of procedure the labiomental fold will decrease in prominence. Careful soft tissue management is necessary to maintain good lower lip to mandibular incisor vertical relationship.

143. Subapical setback. An anterior or total subapical setback brings the lip posterior 75% and the soft tissues of the chin remain relatively unchanged. The labiomental fold will increase in prominent. Careful soft tissue management is necessary to maintain good lower mandibular incisor vertical relationship.

144. Subapical inferior repositioning. The horizontal soft tissue effect subapical inferior repositioning will depend on the AP dentoalveolar change relative to lower lip support. The vertical relationship of the lower lip mandibular incisor relationship should be improved.

145. Maxillary Procedures Soft tissue change with maxillary surgery depends on the dental-osseous movements and the management of the soft tissue . Superimposition of preoperative and postoperative tracings demonstrates the change in lip support. The maxilla was moved straight superiorly. Although the incisal edge was also moved straight superiorly, the resultant postoperative support is more anterior. Preoperative lip support was in the cervical area of the incisor, and the incisal edge was well below the inferior margin of the upper lip.

146. . Because of the incisor angulation, the lip support becomes more anterior as the tooth is repositioned. As expected, the soft tissue in the superior labial sulcus area reflects the AP change.

147. Superimposition of preoperative and postoperative tracing of superoposterior maxillary movement shows no change in the AP position of the superior labial sulcus. Although the incisal edge was moved significantly superiorly and lightly posteriorly, the lip support has changed from the cervical area of the incisor to an area closer to the incisal edge.

148. The use of the alar base cinch suture has significantly improved the quality of results. Previously, flaring of the alar bases was common in maxillary surgery. After base flaring occurs because of detachment of muscles and periosteum in the area, oedema , and changes in the osseous support to the nasal structures. Passing a “figure 8’ suture intraorally through the lateral aspect of the alar bases will control the width, narrow the alar bases, minimize the shortening of the lip, and improve the AP thickness of the lip . In addition, closing the vestibular incision in a V-Y fashion also helps minimize lip shortening and increases the AP thickness if the lip.

149. A summary of the following material can be seen in the below table and in the figure.

150. Advancement The classic soft tissue management techniques for maxillary advancement move the upper lip forward 50% of the dental-osseous movement. The nasal tip advances approximately 30% (significant variability), and the nasolabial angle decreases .1.2 degrees per 1mm, upper lip length is unpredictable. The greater the maxillary advancement is, the less percentage AP change of the upper lip occurs.

151. Setback Soft tissue changes for maxillary setback by either anterior or total maxillary osteotomy are similar. The upper lip moves posteriorly50% to 65% of the dentoosseous movement, the base of the nose and superior labial sulcus move posteriorly approximately 30% and the nasolabial angle increases 1.2 degrees per 1mm . although the tip of the nose may move posteriorly, no quantitative values have been established.

152. Superior repositioning Soft tissue changes from the literature report approximately 20% to 40% shortening of the upper lip, the base of nose moves up 20%, the nasal tip moves up 20%, and the upper labial superioris moves 60% to 70% of the AP change in lip support position. Usually with vertical maxillary excess, dental-osseous support to the lip is located higher on the dentoalveolus . When the maxilla is moved superiorly the lip support shifts lower on the dentoalveolus or incisor but subsequently more anteriorly because the incisors are angulated forward. Therefore, with straight superior movement of the maxilla, the lip support will be more anterior.

153. Inferior repositioning Inferior repositioning of the maxilla usually has a lengthening effect on the upper lip. The closer the incision is made towards the attached gingiva, the greater the increase in length. The nasal tip usually drops inferior slightly. When the maxilla is inferiorly repositioned, the lip support area on the dentoalveolus moves superiorly and also posteriorly. If the maxilla is repositioned directly downward, the lip should assume a more posterior position.

154. Chin procedure Chin procedure can affect both the AP and vertical soft tissue dimensions and the AP and vertical position of the lower lip. A summary of the following material is presented in the table below depicts simplified diagrammatic representations of average soft tissue changes.

155. Augmentation Genioplasty The chin can be augmented in two dimensions on the STO: AP and vertical. In augmentation procedures the soft tissue thickness in the pogonion are will decrease in the AP dimension.

156. Osseous AP Augmentation Reports in the literature vary from 60% to 75% soft tissue advancement relative to bony advancement. Also, it is the best to avoid a pressure dressing directly over the pogonion area. With this type of soft tissue management, we project 75% to 90% soft tissue chin change. The labiomental fold will become more prominent.

157. Alloplastic AP Augmentation Proplast and silastic implants are the most commonly used materials, and both provide approximately the same soft tissue change. The literature reports an 80% to 85% soft tissue change relative to the AP dimension of proplast implants but with significant variability. larger the implant is, the less the soft tissue percentage change.

158. Osseous vertical Augmentation Vertical mandibular deficiency can be corrected by an anterior horizontal osteotomy with downgrafting of the chin. This procedure usually requires stripping the periosteum off the inferior border of the mandible to decrease shortening of the lower lip relative to the mandibular teeth. the vertical soft tissue change will be approximately 100% relative to the osseous change. The labiomental fold will lose some of its prominence.

159. Alloplastic Vertical Augmentation Alloplastic implants can be used to augment the inferior border of the mandible. To place the implant the soft tissues must be stripped from the inferior border of the mandible. This technique should provide approximately 100% vertical soft tissue change relative to the vertical height of the implant.

160. Reduction Genioplasty Chin excesses in the vertical and AP direction can be reduced by osteotomy or ostectomy . Predictability of results depends or the surgical procedure selected.

161. VERTICAL REDUCTION Removal of the inferior border by a horizontal ostectomy yields only about a 30% vertical and 25%. AP soft tissue change, but this is significantly variable. By maintaining a maximal soft tissue attachment to the inferior segment, approximately 90% vertical soft tissue change relative to the bone can be expected.

162. AP REDUCTION Decreasing the AP prominence of the chin can be accomplished by two techniques. An ostectomy that removes the anterior portion of the chin is quite unpredictable, resulting in only about 25% soft tissue change relative to the bone in the AP direction. A horizontal osteotomy moving the inferior segment posteriorly is predictable when the soft tissue remain attached to the inferior segment. With this technique the soft tissue change is approximately 90% relative to the bone. The labiomental fold will become more obtuse.

163. CONCLUSION Cephalometric prediction in orthognathic surgery can be performed manually or by computer, using several currently available software programs, alone or in combination with video images. The manual methods of cephalometric prediction of the orthognathic outcome are time consuming, whereas, computerized methods facilitate and speed the performance of the visualized treatment objective. Both manual and computerized cephalometric prediction methods are two-dimensional and will always have limitations, because they are based on correlations between single cephalometric variables and cannot fully describe a three-dimensional biological phenomenon.

164. Today, three-dimensional prediction methods are available, such as three-dimensional computerized tomography (3DCT), 3D magnetic resonance imaging (3DMRI) and surface scan/cone-beam CT. Despite the promising capabilities of 3D technology there is not yet a reliable technique for orthognathic prediction. Although , the different method of prediction are useful tools for orthognathic surgery planning and facilitates patient communication.

165. REFERENCES Sarver DM.Videocephalometric treatment prediction. In: Sarver DM, editor.  Estetics orthodontics and orthognathic surgery. St Louis: Mosby Inc ; 1998. Fish LC, Epker BN. Surgical-orthodontic cephalometric prediction tracing. J Clin Orthod.1980;14:36-52 .  McNeill RW, Proffit WR, White RP.Cephalometric prediction for orthodontic surgery. Angle Orthod . 1972; 42:154–164.  Wolford LM, Hilliard FW, Dugan DJ. Surgical treatment objective.A systematic approach to the prediction tracing. St Louis: Mosby Year Book; 1985. pp. 54–74.

166. Sarver DM, Johnston MW. Video imaging: techniques for superimposition of cephalometric radiography and profile images.  Int J Adult OrthodonOrthognath Surg.  1990 Sarver DM.Videocephalometric treatment prediction. In: Sarver DM, editor.  Estetics orthodontics and orthognathic surgery.  Sarver DM. Video imaging, a computer facilitated approach to communication and planning in orthognathic surgery. Br J Orthod .  1993;20:187–191 Grubb JE. Computer assisted orthognathic surgical treatment planning: a case report. Angle Orthod

167. Proffit WR. Treatment planning: The search for wisdom. In: Proffit WR, White RP, editors. Surgical orthodontic treatment. St Louis: Mosby Year Book; 1991. pp. 142–191. Bhatia SN, Sowray JH. A computer-aided design for orthognathic surgery. Br J Oral Maxillofac Surg. 1984;22:237–253. Walters H, Walters HD. Computerized planning of maxillofacial osteotomies: The program and its clinical applications. Br J Oral Maxillofac Surg. 1986

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