PREDICTING LOWER LIP AND CHIN RESPONSE TO MANDIBULAR ADVANCEMENT WITH GENIOPLASTY A CEPHALOMETRIC STUDY Dr. Deepthi T. Amanna Authors : Dr. Deepthi T. Amanna Assistant Professor Dr. E.T. Roy Professor Dr. K. Sadashiva Shetty Professor & Head Dr. Kiran Kumar, H.C. Reader Corresponding Author: Dr. Deepthi T. Amanna Assistant Professor E-mail: deepthi_dental@yahoo.com Ph:09886480164 ABSTRACT Background Patients seeking orthodontic treatment are usually eager to receive precise information about and objectives: the facial changes that surgical intervention may bring about. Predictions provide a realistic estimate of the outcome of anticipated surgery. It is also an important tool for treatment planning by the clinician. But there are only a few studies which have verified the accuracy of these predictions. Therefore, the aim of the present study was to analyze the accuracy of prediction for mandibular advancement with vertical reduction augmentation genioplasty using the ratios given in the previous studies. Method: Presurgical and postsurgical lateral cephalograms of 15 patients who had undergone mandibular advancement and vertical reduction augmentation genioplasty were obtained. Paired t-test was used to compare between presurgical prediction and postsurgical outcome. A P value of <0.05 was set for statistical significance. Results: Findings of this study demonstrate that there is no considerable difference between the predicted finding and the actual postsurgical outcome for mandibular advancement and genioplasty. Previous studies have shown that genioplasty along with mandibular advancement is a stable surgical procedure when rigid fixation is used. As the long term postsurgical changes are minimum, we can rely on these predictions to a greater extent. Keywords: Prediction accuracy, prediction ratios, mandibular advancement, vertical reduction augmentation genioplasty. 29
INTRODUCTION Throughout the recorded history, and even earlier as evidenced by archeological artifacts, humans have been aware of beauty and facial esthetics. Facial appearance plays a significant role in a person s wellbeing and social acceptance because the face is the most important part of the body in regulating social interactions. It is a living mirror held out to the world. The human face is a complex mosaic of lines, angles, planes, shapes, textures, and colours. The interplay of these elements produce an infinite variety of facial forms, from perfect symmetry to extreme disproportions. 1 When such facial disproportions occur, orthognathic surgeries are used as adjunctive procedures along with orthodontic treatment. These surgeries have the potential to change facial esthetics dramatically. Patients seeking orthodontic treatment in whom surgical correction is recommended are usually eager to receive precise information about the facial changes that surgical intervention may bring about. Hence presurgical predictions have become an integral part of the treatment process, aiming to provide a realistic estimate of the outcome of the anticipated surgery. This serves as a vehicle for communication with the patient and also acts as an important tool for treatment planning by the clinician. Since the patient s overall satisfaction could primarily depend on the final position of soft tissues, it is important to not only predict the dental and skeletal changes but also consider the soft tissue changes. The known ratios of soft to hard tissue movement can vary considerably in each individual and it is not so well known to what extent and in what direction these soft tissue changes occur. Therefore mean figures of soft to hard tissue ratios are utilized when designing prediction tracing of a facial profile. In studies that examined the hard to soft tissue response with a bilateral sagittal split osteotomy and mandibular advancement, most of the studies reported a ratio of 1:1 for pogonion. However these studies demonstrated great variability in soft tissue response of the lower lip. The present study was designed and undertaken to find out how accurately and reliably the lower lip and chin response to mandibular advancement and genioplasty could be predicted using the database provided by the previous studies. 2,3 Materials and Methods Pre-surgical and post-surgical lateral cephalograms of 15 adult patients who had been treated successfully at Department of Orthodontics and Dentofacial Orthopedics, Bapuji Dental College and Hospital, Davangere were obtained. The age group of these patients ranged from 18-25 years with a mean age of 20 years. Bilateral Sagittal Split Osteotomy for mandibular advancement procedure and vertical reduction augmentation genioplasty were carried out under the supervision of a single surgeon. Cephalograms were taken at two intervals: (a) Presurgical - one week before surgery; (b) Postsurgical - 1 to 6 months following surgery. Predictions were made using hard to soft tissue ratios given in the previous studies. Predictions were made independent of postsurgical cephalograms. Postsurgical cephalograms were given at a later date to be compared with the presurgical predictions. The primary selection criteria were: Patients were non-growing adults. had natural dentition supporting the lips. had class II skeletal malocclusion due to retrognathic mandible with an ANB of more than 5 degrees and a retrognathic chin for which surgical intervention was necessary. Underwent Mandibular advancement procedure by bilateral sagittal split osteotomy and vertical reduction augmentation genioplasty. Among the various cephalometric analyses for estimating the amount of hard and soft tissue changes, the Burstone s, Steiner s, McNamara and Rickett s analyses were employed in this study. These analyses include certain angular and linear measurements for both hard and soft tissues, which were easily applicable for the study. (fig 1, fig 2, & fig 3) Prediction ratios: For mandibular advancement- Soft tissue chin moves 1:1 with hard tissue chin and lower lip moves 2/3 rd the distance with lower incisors. 2 For genioplasty- Soft tissue chin moves in a 1:1 ratio with the hard tissue chin. 3 30
Fig. 1. Landmarks Fig. 2. Linear Parameters for Soft Tissue Evaluation. S N G S N G C IIE Si B Sn Li Pg Pg Me Gn Gn Me Ls Cm C Cm Sn Ls IIE Si Li B Pg Gn Me Gn Me Fig. 3. Angular Parameters for Soft Tissue Evaluation. G 1. G-Pg 2. G-Sn and Sn-Me 3. Sn-Gn and C-Gn 4. Li to( Sn-Pg ) 5. Si to (Li-Pg ) 6. E line. 7. IIE-Li 8. Pt B Si 9. Pg-Pg 10. Gn-Gn 11. Me-Me 1. G-Sn-Pg (Angle of facial convexity) S 2. Sn-Gn -C (Lower face throat angle) 3. Cm-Sn-Ls (Nasolabial angle) C N Cm Sn Ls Stms Stmi Si Li B Pg Gn Me RESULTS The present study was undertaken to analyse how accurately and reliably the lower lip and chin response to mandibular advancement and genioplasty could be predicted using the database provided by the previous studies. Presurgical and post-surgical lateral cephalograms of 15 adult patients who had undergone mandibular advancement and vertical reduction augmentation genioplasty were taken. Presurgical prediction tracings and analyses were done independent of post-surgical tracings and were later compared. Descriptive Data that included means and standard deviations were calculated for the linear and angular parameters. A total of 14 parameters were used in this study. Paired t-test was used to compare between presurgical prediction findings and actual post-surgical changes. A P value of <0.05 was set for statistical significance (tables I, II,III and IV), (graphs 1 and 2) 31
DISCUSSION Orthognathic surgeries bring about a dramatic change in facial esthetics and this change should be predictable if the results are to be satisfactory. Predicting the soft tissue profile from orthognathic surgery was first described in 1972 by McNeill et al. Today, the process of predicting orthognathic treatment outcomes has evolved from manual tracings and manipulations to computer manipulation of digitized lateral cephalograms. Whatever the method for establishing these predictions, the accuracy of the prediction depends on the ratios used to define the response of soft tissue to the bony change. Many studies have formulated ratios based on soft tissue responses to hard tissue changes following orthognathic surgeries and predictions have been done based on these ratios. But the soft to hard tissue movement can vary considerably in each individual and it is reasonable to assume that in certain cases an inaccuracy of prediction tracing could be inevitable. Accuracy of tracings depends on many factors. Variable factors influencing prediction tracing are type of surgery, accuracy of surgery, methods of fixation, degree of soft tissue stripping, presurgical soft tissue thickness, degree of relapse, accuracy and reproducibility of tracing including difficulty in identification of some landmarks. 4 Literature presents with only a few studies where the accuracy and reliability of presurgical predictions was verified. Therefore, the present study was undertaken in an attempt to study the accuracy of predictions using the ratios given by the earlier authors. 2,3 The discussion is put forth under the following headings. Lips - Previous studies have noted a variable response of lower lip in relation to the inferior incisal edge ranging from 0.26:1 to 0.85:1 when mandibular advancement surgical procedure was carried out. Reasons suggested were that in most of the cases, the preoperative measurement was made with a pseudo position of lower lip. After the mandibular advancement, the lower lip had a more correct relationship to the lower teeth and alveolus. 5 Ewing and Ross made a similar observation stating that a difference of 2-3mm in the position of lower lip in either direction can be expected when the often everted lower lip is allowed to unfurl as the jaw relation is normalized. 5 In the present study, a ratio of 0.66:1 has been used to predict the lower lip response to movement in the lower incisor region. When the lower lip distance was measured from the Sn-Pg line, there was a statistically insignificant difference suggesting that there could be some amount of post surgical edema which has brought the lower lip closer to the Sn-Pg line. The distance between the inferior incisal edge and the lower lip which indicates the thickness of the lower lip was slightly more than predicted value which again indicates the possibility of edema, but this was statistically insignificant. This possibility was in agreement with the study done by Dolce et al who noted that the greater advancement at lip could be most likely due to greater edema from additional surgical manipulation involved in genioplasty. 6 But the mean difference of the above mentioned parameters was statistically insignificant suggesting that the lower lip can be quite accurately predicted with a ratio of 0.66:1. Chin - Previous studies have reported a ratio of 1:1 of soft to hard tissue advancement at pogonion and point B after mandibular advancement. In cases with genioplasty as well as mandibular advancement, mean ratios of soft to hard tissue advancement at pogonion and point B were approximately 1:1, but were very inconsistent. Predictions could be expected to err by as much as 3mm in either direction and a variation of plus or minus 3mm could represent a considerable disappointment to the patient and clinician. 5 Explanations given were that, the cases requiring genioplasty were often the more severe cases and soft tissue drape in severe retrognathia is usually abnormal and minor variations in the surgical management of tissues occur from patient to patient, so that variation in results in the sensitive chin should not be surprising. When minimal reflection of soft tissue from the segment was done during genioplasty only enough to allow visualization and access to the level of the osteotomy, a ratio of 1.0 to 0.9 could be used to predict the softtissue-to osseous movement when advancement genioplasty was performed. According to Bell et al, more predictable changes in soft tissue chin are achieved by maintaining as much soft tissue attachment as possible to the repositioned segment. 7 In patients who had both vertical reduction of the chin and anterior repositioning augmentation, the soft tissue advancement was greater than in patients who had only straight anterior repositioning of the segment. Reason is the increase in bulk of soft tissue associated with the vertical movement, provided that the periosteum had not been reflected from the bony chin segment especially in case of simultaneous anterior and superior movement of the segment. When the height of the chin 32
was significantly reduced (6-8mm) the soft tissue advancement exceeded the amount of anterior repositioning of the segment. 8 This might explain the mild difference of increase in thickness in the pogonion region which was observed in the present study. Overall, the difference between the predicted value and the actual surgical outcome in the chin region was negligible and was statistically insignificant and predictions can be done with accuracy when a 1:1 ratio is used. Vertical dimension of the lower face - vertical dimensions couldn t be very accurately predicted. Lower face measured from subnasale to menton was more than what was seen in the prediction. Similarly, the distance measured from subnasale to gnathion was also slightly more but was statistically insignificant. Both these findings suggest that the vertical dimensions cannot be very accurately predicted. Since the vertical reduction genioplasty is combined with mandibular advancement, the final vertical dimension might be difficult to predict. The other parameters used in this study showed minimum difference postsurgically when compared with the prediction values. The present study was carried out with a 6 months follow up and predictions were found to be quite accurate. But if the purpose of predicting hard and soft tissue is to provide an accurate estimate of actual long term postoperative profile, then relapse has to be considered. Shaugnessey et al noted that advancement genioplasty was a fairly stable procedure and there was a mean relapse of only 8.2% at Pg, 3 years after surgery. Part of this change was due to bone remodeling and after 6 months and upto 3 years postsurgical follow up, there were only minor soft tissue changes. 9 LINEAR PARAMETERS A study conducted by Talebzadeh N and Pogrel MA showed that after a 12 months follow up, there was no statistically significant relapse for genioplasty alone or when combined with mandibular advancement even with different amounts of advancement, when rigid internal fixation was used. The changes were minimal and hard to detect clinically. They reported that genioplasty with or without mandibular advancement is a stable surgical procedure when used in conjunction with rigid internal fixation and the minimum relapse which occurred was clinically hard to detect. 10 Mobarak et al in their long term follow up of soft tissue changes found that the soft tissue chin and mentolabial fold followed the underlying skeletal structures in a 1:1 ratio but when skeletal relapse was accounted for, the ratios dropped. But they also mentioned that the discrepancies between the predicted and actual soft tissue profile as a result of minor to moderate skeletal relapse may be too small to be noticed, especially since the patient rarely views himself or herself in a profile view. 11 Bailey et al conducted a study where comparison was made between the patients who underwent bilateral sagittal split osteotomy and patients who underwent only orthodontic treatment. They analysed the soft tissue changes that occurred between 1 year and 3 to 5 years postsurgery and found that although soft tissue changes occur, there were no significant differences in the average annualized soft tissue changes seen in both the groups. 12 The present study shows that prediction for mandibular advancement in combination with vertical reduction augmentation genioplasty is quite accurate. As the long term postsurgical changes are minimum, we can to a greater extent, rely on these predictions. Table I DESCRIPTIVE STATISTICS OF STUDY GROUPS Parameters Pre surgical prediction Post surgical findings Mean SD Mean SD G-Pg -2.83 6.20-3.83 7.28 G-Sn & Sn-Me 1.07 0.08 1.00 0.13 Sn-Gn & C-Gn 1.32 0.20 1.47 0.29 Li to (Sn-Pg ) 4.43 2.07 4.37 2.36 Si to (Li-Pg ) -4.50 1.48-5.50 1.31 E Line Upper Lip -3.36 2.38-2.56 2.5 Lower Lip 1.43 2.09 0.93 3.05 IIE-Li 14.87 2.82 16.47 2.38 Pt B-Si 13.93 2.87 14.33 2.41 Pg-Pg 11.60 2.32 11.87 2.00 Gn-Gn 9.67 2.23 9.13 1.96 Me-Me 6.93 2.22 6.60 1.35 33
Table II DESCRIPTIVE STATISTICS OF STUDY GROUPS ANGULAR PARAMETERS Parameters Pre surgical prediction Post surgical findings Mean SD Mean SD G-Sn-Pg 16.60 5.26 16.80 4.33 Sn-Gn -C 112.87 6.31 112.67 7.66 Cm-Sn-Ls 124.60 9.55 125.07 10.83 LINEAR PARAMETERS * Student s paired t test Parameters Table III INTRA GROUP COMPARISON (LINEAR PARAMETERS) Pre surgical prediction Post surgical findings Mean Difference P* Value, Sig G-Pg -2.83-3.83 1.00 P>0.05 NS G-Sn & Sn-Me 1.07 1.00 0.07 P<0.05S Sn-Gn & C-Gn 1.32 1.47-0.15 P>0.05 NS Li to (Sn-Pg ) 4.43 4.37 0.07 P>0.05 NS Si to (Li-Pg ) -4.50-5.50 1.00 P>0.05 NS E Line Upper Lip -3.36-2.56-0.8 P>0.05NS Lower Lip 1.43 0.93 0.50 P>0.05 NS IIE-Li 14.87 16.47-1.6 P>0.05 NS Pt B-Si 13.93 14.33-0.40 P>0.05 NS Pg-Pg 11.60 11.87-0.27 P>0.05 NS Gn-Gn 9.67 9.13 0.53 P>0.05 NS Me-Me 6.93 6.60 0.33 P>0.05 NS Table IV INTRA GROUP COMPARISON (ANGULAR PARAMETERS) ANGULAR PARAMETERS Parameters Pre surgical prediction Post surgical findings Mean Difference P* Value, Sig % accuracy G-Sn-Pg 16.60 16.80-0.20 P>0.05 NS 102.4 Sn-Gn -C 112.87 112.67 0.20 P>0.05 NS 100.5 Cm-Sn-Ls 124.60 125.07-0.47 P>0.05 NS 100.2 * Student s paired t test 34
Graph 1: Linear Parameters Mean (mm) 20.00 15.00 10.00 5.00 0.00 1.07 1.00 1.32 1.47 4.43 4.37 1.43 0.93 14.87 16.47 13.93 14.33 11.60 11.87 9.67 9.13 6.93 6.60-5.00-10.00-2.83-3.83 G-Pg' G-Sn & Sn-Me' -4.50-5.50-3.36-2.56 Sn-Gn' Li to (Sn- Si to (Li- E Line-U E Line-L & C-Gn' Pg') Pg') Lip Lip IIE-Li Pt B-Si Pg-Pg' Gn-Gn' Me-Me' Pre Surgical Prediction Post Surgical Findings Graph 2: Angular Parameters 150.00 112.87 112.67 124.60 125.07 Mean(Deg) 100.00 50.00 16.60 16.80 0.00 G-Sn-Pg' Sn-Gn'-C Cm-Sn-Ls Pre Surgical Prediction Post Surgical Findings CONCLUSION Presurgical prediction serves as a vehicle for communication with the patient and also acts as an important tool for treatment planning by the clinician. The present study with a 6 months follow-up verified the accuracy of prediction after mandibular advancement and vertical reduction augmentation genioplasty and found no significant difference between the presurgical prediction and the postsurgical outcome, indicating that the predictions can be quite accurate when a ratio of 0.66:1 for lower lip and 1:1 for chin is used when predicting changes after mandibular advancement and genioplasty. Both upper and lower lip were positioned a little ahead than what was anticipated. This could largely be due to postsurgical edema. There was an insignificant difference between the prediction and actual postsurgical outcome in the chin region. There was a mild increase in nasolabial angle. The mentolabial sulcus was a little deeper than what was anticipated. Vertical dimensions showed a significant difference, suggesting that it could be difficult to predict the vertical change. The present study was a short term study and we can expect further changes in the hard and soft tissues. These postsurgical changes could be due to resolution of edema, remodeling changes, relapse or the normal aging process. Postsurgical relapse was less with rigid internal fixation. Though some studies suggest using alternative ratios after taking into account the relapse factor, long term studies on soft tissue changes show no appreciable changes up to 3 years of follow-up. The minimum changes seen were almost similar to the average annualized changes seen in the nonsurgical group. Therefore, we can rely on these predictions even on a long term basis. 35
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