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Table of Contents   
ORIGINAL RESEARCH  
Year : 2013  |  Volume : 24  |  Issue : 4  |  Page : 484-487
Maxillary repositioning according to Frankfort horizontal plane during orthognathic surgery


1 Department of Oral and Maxillofacial Surgery, Torabinejad Dental Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran
2 Department of Oral and Maxillofacial Surgery, School of Dentistry, Zahedan University of Medical Sciences, Zahedan, Iran
3 Department of Oral and Maxillofacial Surgery, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah, Iran

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Date of Submission19-Oct-2012
Date of Decision18-Jan-2013
Date of Acceptance06-Feb-2013
Date of Web Publication19-Sep-2013
 

   Abstract 

Context: There are a lot of disagreements among surgeons over controlling the maxillary position during orthognathic surgery.
Aim: To investigate maxillary repositioning according to Frankfort horizontal plane in orthognathic surgery.
Materials and Methods: Fourteen patients were selected who were submitted to maxillary or bimaxillary surgery. Maxillary model surgery was performed based on the treatment planning and an intermediate splint was made. The surgical technique in this study was based on maxillary osteotomy according to the findings of the model surgery, in a manner that the osteotomy line was parallel to the Frankfort horizontal plane. Intermediate splint was used for repositioning of the maxilla in the new position and the vertical position of that was determined according to external reference point and fixed on this position. The upper central incisor designed from prediction tracing and post-operative cephalometry on the first tracing. The new position of maxilla was evaluated horizontally and vertically.
Statistical Analysis Used: A paired t-test was used to compare the predicted maxillary position and the actual position. Association between these two groups of variables was evaluated with Pearson correlation.
Results: The mean difference between the maxillary planned position and post-operative cephalometric radiography varied between 0.3 mm and 0.9 mm vertically (P value = 0.315) and 0.0 mm and 0.9 mm horizontally (P value = 0.034). The averages of horizontally and vertically observed changes were 0.3 mm and 0.17 mm respectively (P < 0.001).
Conclusion: Good surgical accuracy in repositioning of the maxilla can be achieved according to Frankfort horizontal plane during the surgery. By eliminating the ramping effect the accuracy of surgery increases.

Keywords: Frankfort horizontal plane, maxillary repositioning, orthognathic surgery, osteotomy

How to cite this article:
Ghoreishian M, Hasheminia D, Hashemzehi H, Khazaei S. Maxillary repositioning according to Frankfort horizontal plane during orthognathic surgery. Indian J Dent Res 2013;24:484-7

How to cite this URL:
Ghoreishian M, Hasheminia D, Hashemzehi H, Khazaei S. Maxillary repositioning according to Frankfort horizontal plane during orthognathic surgery. Indian J Dent Res [serial online] 2013 [cited 2019 May 24];24:484-7. Available from: http://www.ijdr.in/text.asp?2013/24/4/484/118395
There are a lot of disagreements among surgeons over controlling the maxillary position during orthognathic surgery. Several techniques have been utilized by various individuals in this regard. Commonly, the most accurate technique is using the external reference point (ERP) along with intermediate splint. This technique however, does not make the accurate use of surgery in multidimensional movements of maxilla in three dimensional planes. [1],[2],[3]

It is essential to use a common reference plane (CRP) to relate the main parts of the presurgical databases to each other. It is not possible to unify the main parts of the presurgical databases without CRP. CRP in the orthognathic surgery is the Frankfort plane, which is used in the clinical examination, radiographic evaluation and dental model analysis. [4] The design of the osteotomy of the lateral maxillary wall should vary, depending on the patient's esthetic needs in which the line of osteotomy of the maxilla may not be parallel with the Frankfort plane of the patient. Ignoring this issue in maxillary multiplanar movements will result in major errors in the surgical results.

The aim of the present study was to determine the accuracy of maxillary repositioning according to Frankfort plane in maxillary surgery and on this ground the accuracy of upper incisors positioning in the vertical and horizontal dimensions were evaluated.


   Materials and Methods Top


In this prospective study, fourteen patients (9 female and 5 male) between 18 to 25 years old with mean age of 20 years were selected among the patients who referred to oral and maxillofacial surgery clinic in Alzahra hospital Isfahan University of Medical Sciences and were submitted to maxillary surgery during 2008. The inclusion criteria were: access to cephalometric radiography before and after surgery, prediction tracing, model surgery casts, hospital records regarding the amount of the planned movements for maxillary surgery, one piece Le Fort ² osteotomy in any direction, absence of craniofacial abnormalities or cleft lip and palate and absence of pervious maxillary surgery. This study was submitted to and approved by the Ethical Committee for Research in Isfahan University of Medical Sciences, Isfahan, Iran and had no conflict with declaration of Helsinki.

Laboratory procedure

The casts of patients were mounted on a semi-adjustable articulator with face-bow transfer and centric relation (CR), based on the model by Ellis et al. [5] Maxillary casts were made on the Erickson model surgery platform; [6] they were measured with digital caliper (Batch No. 5120-150. Mainland, China). In each case, the distance between canine and maxillary first molar mesiobuccal cusp and axis orbital plane of the articulator was measured in each side. The difference between the distance of two teeth and articulator plane in each side was measured and recorded. After this stage, maxillary model surgery was performed based on the treatment planning and in the final stage, an intermediate splint was made.

Surgical technique

Among 14 patients, 10 of them had class III malocclusion and four had class II malocclusion. The surgical technique in this study was based on maxillary osteotomy according to the findings of the model surgery. A point, five millimeters from the bottom of the canine root was selected and marked on the bone by a fissure bur. To determine a point above the upper first molar root, the derived number in model surgery stage was considered (the distance of the canine and mesiobuccal cusp of the maxillary first molar mesiobuccal cusp to axis-orbital plane articulator) [Figure 1]. In a manner that the distance between this point and mesiobuccal cusp of the first maxillary molar were equals with selected point above the canine and that tooth. In this method, the osteotomy line was parallel to the Frankfort plane. Maxillary advancement, impaction and push back were the movements which performed during the surgery. After the separation of the maxilla, intermediate splint was used for repositioning that in the new position and using ERP on glabellas, the vertical position of maxilla was determined and fixed on this position. All the surgical and laboratory procedures were done by one person.
Figure 1: Maxillary casts mounted on articulator and the difference between the distance of the canine and mesiobuccal cusp of the first maxillary molar to axis orbital plane of the articulator measured and during the surgery

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Cephalometric analysis

Cephalometric radiographs were taken one week before and after surgery. All the radiographs were traced and analyzed by one person and same X-ray machine. Tracing of all cranial structures was performed with preoperative cephalograms and was superimposed on the post-operative cephalometric films and prediction tracing. The upper central incisor was designed from post-operative cephalometry and prediction tracing on the first tracing. In this stage, the new position of maxilla was evaluated horizontally and vertically. Frankfort plane and nasion perpendicular were used horizontally and vertically to record the new position of the upper central incisors. Nasion perpendicular was defined as a vertical line on Frankfort plane from nasion. In order to prevent bias, seven patients were randomly selected and tracing measurements were performed on them again.

Statistical analysis

For determining the accuracy of the operative technique, the difference between the predicted and actual maxillary position was analyzed. All measurements were converted to positive numbers for statistical analysis to remove directional differences between subjects. A paired t-test was used to compare the predicted maxillary position and the actual position. Any association between these two groups of variables was evaluated with Pearson correlation.


   Result Top


[Table 1] shows the mean difference between the maxillary planned position in the treatment planning stage and its post-operative actual position based on cephalometric analysis. In most cases, the difference between predicted and actual central maxillary incisors position in horizontal and vertical dimensions was less than 0.8 mm and 1.0 mm, respectively. [Figure 2] and [Figure 3] indicate the association between planned horizontal and vertical changes and post-operative actual changes in these dimensions.
Figure 2: Scatter plot shows the relationship between predictive vertical position of central maxillary incisor (PTV) and actual surgical position (POV) of that in the cephalometric tracing.

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Figure 3: Scatter plot shows the relationship between predictive horizontal position (PTH) of central maxillary incisor and actual surgical position (POH) of that in the cephalometric tracing.

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Table 1: The mean difference between the maxillary planned position in the treatment planning stage and its postoperative actual position

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The mean difference between the maxillary planned position and post-operative cephalometric radiography varied between 0.3 mm and 0.9 mm vertically which was not statistically significant (P value = 0.315), but the Pearson correlation showed a strong and significant relations between vertical position of the central maxillary incisor in the prediction tracing and post-operative position of that in the cephalometric tracing (P < 0.001, r = 0.903). Also, the mean difference between the maxillary planned position and post-operative cephalometric tracing varied between 0.0 mm and 0.9 mm horizontally which was statistically significant (P value = 0.034) and the Pearson correlation showed a strong and significant relations between horizontal position of the central maxillary incisor in the prediction tracing and post-operative position of that in the cephalometric tracing (P < 0.001, r = 0.959).

The average of the horizontally and vertically observed changes was 0.3 mm and 0.17 mm respectively. There were noticeable correlations between maxillary planned position and its post-operative position. The difference of those two measures was less than 1.0 mm in all cases.


   Discussion Top


Because of the nature of the orthognathic surgery, the surgeon should perform the positioning of the jaws as accurately as possible. Any error in positioning the central upper incisor, even few millimeters, causes the patient's dissatisfaction and specially will be awkwardly demonstrated in vertical plane.

The accuracy of orthognathic surgery depends on two major stages; transfer from prediction tracing to model surgery and transfer from model surgery to actual surgery. Any error in the preoperative face bow transfer and the model surgery will influence the surgical accuracy. During surgery, the main focus is on how to transfer the movements from model surgery to surgical environment. [7]

In this study, the results after surgery were compared with predicting tracing using cephalometric radiography. Model surgery was performed on Erickson model surgery platform [8] which has a digital caliper (Batch No. 5120-150. Mainland, China) accuracy of 0.01 mm and digital caliper (Batch No. 5120-150. Mainland, China) with same accuracy was used for the comparison between prediction tracing and post-operative cephalogram analysis.

Ellis introduced a kind of model surgery in which intermediate splint was used for repositioning maxilla in the horizontal and vertical planes. [6] In this study, intermediate splint was used for positioning maxilla in the horizontal and vertical dimensions; likewise the position of maxilla in vertical plane was determined with ERP.

The key point in the method used in this study was determining the line of osteotomy of maxilla parallel to Frankfort plane which is easily accessible with the performed measurements on articulator and their transfer to maxilla during surgery. Various studies have analyzed the various techniques of maxillary positioning during orthognathic surgery. Van Sickles and et al.,[9] compared internal reference point (IRP) and ERP and reported better results with ERP. Stanchina and et al.,[3] as well compared IRP and ERP and reported much difference in the accuracy between these two techniques. Polido and et al.,[2] compared ERP and IRP and did not find any difference in the accuracy between two groups in the horizontal positioning of maxilla but the difference in the accuracy of the two techniques in the vertically positioning of maxilla was significant and in this regard, the results of ERP were more accurate. These three studies compared the position of maxilla in the prediction tracing with postoperative results on cephalometric radiography. The accuracy of the horizontally maxilla positioning was 0.2 mm and with ERP, the accuracy of the vertically maxilla positioning was 0.5 to 1.0 mm. [1],[3],[8] The technique used in this study is based on manual tracing. Although it is possible to perform tracing with both manual and digital style, in both techniques points is determined manually, therefore there is the possibility of human error in both technique. Power et al.,[10] compared manual and digital tracing and concluded that digital tracing may not have high calculation accuracy.

Usually the line of osteotomy on the maxilla has a posterior slope. This slope is made due to the high length of canine root compared to posterior molar teeth; this form of osteotomy line design causes the ramping effect. If this anatomic ramp is accompanied by anterior or posterior movements, in case it is ignored, it will affect the results negatively. [11] With this ramp planning if maxilla is moved forward, it will move up too. Since the maxilla simultaneously goes up when moved forward, mandible will rotate upward and forward. Creating change in the ramp angle encounter anatomical limitations resulting from maxillary bone and roots. Controlling ramp angle has useful effects which can be applied in the surgical procedure. The key point here is its accurate planning based on the prediction tracing and model surgery. With maxillary osteotomy, according to the previously mentioned slanted ramp, maxillary backward movement will be accompanied by downward movement and the posterior height of the face will increase.

In this study, we used ERP for maxillary repositioning. In cases the cut on maxilla contains ramp during surgery, it will cause many error regarding the ERP limitation, even it is noticed, preventing ramp with parallel cut lines on the articulator in the model surgery stage and maxilla during surgery will eliminate the error. The comparison of the results of maxillary repositioning, according to the technique used in this study, with the outcome methods that used ERP and IRP indicate that the previously mentioned technique showed the greater accuracy. The main reason of the high accuracy of this technique is eliminating the problems of the ramping effect; because the reference point that used in model surgery are different from that is used in the surgery if we did not consider the ramping effect the accuracy of maxillary repositioning will reduce.

The technique used in this study has very good results but like any other technique used in this field; correct patients selection, the accuracy of face bow transfer, mounting in articulator, model surgery and making splint manufacture are the major factors in the success of orthognathic surgery and any preoperative error with any of the current techniques for maxillary repositioning will result in inadequate findings.


   Conclusion Top


Good surgical accuracy in repositioning of the maxilla can be achieved according to Frankfort horizontal plane during the surgery. By eliminating the ramping effect the accuracy of surgery increases.

 
   References Top

1.Polido WD, Ellis E, 3rd, Sinn DP. An assessment of the predictability of maxillary surgery. J Oral Maxillofac Surg 1990;48:697-701.  Back to cited text no. 1
    
2.Polido WD, Ellis E 3rd, Sinn DP. An assessment of the predictability of maxillary repositioning. Int J Oral Maxillofac Surg 1991;20:349-52.  Back to cited text no. 2
[PUBMED]    
3.Stanchina R, Ellis E 3rd, Gallo WJ, Fonseca RJ. A comparison of two measures for repositioning the maxilla during orthognathic surgery. Int J Adult Orthodon Orthognath Surg 1988;3:149-54.  Back to cited text no. 3
[PUBMED]    
4.Fonseca R. Oral and maxillofacial surgery. 2 ed. Missouri: Saunders; 2009.  Back to cited text no. 4
    
5.Ellis E 3rd, Tharanon W, Gambrell K. Accuracy of face-bow transfer: effect on surgical prediction and postsurgical result. J Oral Maxillofac Surg 1992;50:562-7.  Back to cited text no. 5
[PUBMED]    
6.Ellis E, 3rd. Accuracy of model surgery: Evaluation of an old technique and introduction of a new one. J Oral Maxillofac Surg 1990;48:1161-7.  Back to cited text no. 6
    
7.Kwon TG, Mori Y, Minami K, Lee SH. Reproducibility of maxillary positioning in Le Fort I osteotomy: A 3-dimensional evaluation. J Oral Maxillofac Surg 2002;60:287-93.  Back to cited text no. 7
[PUBMED]    
8.Erickson K, Bell W, Oldsmith D. Analytical model surgery. In: WH Bell, editor. Modern practice in orthognathic and reconstructive surgery. Philadelphis: PA: Saunders; 1992.  Back to cited text no. 8
    
9.Van Sickels JE, Larsen AJ, Triplett RG. Predictability of maxillary surgery: A comparison of internal and external reference marks. Oral Surg Oral Med Oral Pathol 1986;61:542-5.  Back to cited text no. 9
[PUBMED]    
10.Power G, Breckon J, Sherriff M, McDonald F. Dolphin Imaging Software: An analysis of the accuracy of cephalometric digitization and orthognathic prediction. Int J Oral Maxillofac Surg 2005;34:619-26.  Back to cited text no. 10
[PUBMED]    
11.Betts NJ, Vanarsdall RL, Barber HD, Higgins-Barber K, Fonseca RJ. Diagnosis and treatment of transverse maxillary deficiency. Int J Adult Orthodon Orthognath Surg 1995;10:75-96.  Back to cited text no. 11
    

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Correspondence Address:
Dariush Hasheminia
Department of Oral and Maxillofacial Surgery, Torabinejad Dental Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.118395

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