- Email: [email protected]
Surgical accuracy in orthognathic surgery
Surgical accuracy in orthognathic surgery D. C. Bryan, N. P. Hunt Queen Elizabeth Military Hospital, Stadium Road, London; Eastman Dental Hospital, Grays Inn Road,
London
SUMMARY. This study investigated the accuracy with which the planned surgical change could be achieved during orthognathic surgery, based upon the retrospective cephalometric analysis of 62 patients who received correction of dentofacial deformity. It is concluded that, despite individual variation, no statistically significant difference could be demonstrated between the orthognathic prediction and the surgical outcome. This supports both the use of orthognathic profile planning and the surgeon’s ability to follow the plan.
INTRODUCTION
MATERIALS
Modern surgical and orthodontic techniques have to point where developed the combined orthodontic/surgical treatment can bc planned for almost all kinds of severe dcntofacial deformity. With this technical advance has grown a need to plan and predict accurately the outcome of treatment. Most reports have been of isolated casts but recently two papers have compared the relationship between orthognathic prediction/planning and the surgical outcome in a series of cases. Friede et al. (1987) reviewed a series of 30 orthognathic cases which had received one of six operative procedures. Prediction tracings were made before any treatment and were compared to radiographs taken at the review 6 months post-operatively. The results were reported as a series of individual tracings and showed considerable anteropostcrior and vertical variation both within and between the surgical groups. The authors concluded that vertical changes were the hardest to predict. However: they noted that the use of radiographs taken 6 months postoperatively may have allowed surgical relapse to influence their results. Pospisil (1987) compared prediction tracings against the 6 month post-operative radiographs for both hard and soft tissue movement in a series of 40 cases. He reported significant variation (defined as greater than 20% of planned movement) in 60% of his casts, but he did attempt to eliminate the effect of relapse upon the results by comparing six month post-operative cephalograms to radiographs taken before the removal of intermaxillary fixation. The aim of the present investigation was to examine the relationship between orthognathic prediction planning and the surgical outcome in a series of cases treated by a single Consultant surgeon and his surgical team.
All cases of facial deformity were assessed on a joint Orthognathic Planning Clinic under the care of one Consultant surgeon. Every patient on this clinic had standard records, involving radiographs (orthopantomogram, lateral cephalogram and P.A. cephalogram as required), facial and intra-oral photographs and study models. A face bow registration was only used if vertical height changes were anticipated. The patient assessment was systematic, based upon the methods summarised by Hunt and Rudge (1984). The Eastman Cephalometric Analysis (Mills, 1970, Lewis, 1981) was routinely employed and profile prediction was based upon a modification of the method described by Henderson (1974, 1976): in that hard and soft tissue detail was transferred from the ccphalogram to sheets of tracing paper or acetate prior to the construction of templates. The templates were adjusted to optimise facial aesthetics and to achieve a Class I incisor relationship, simulating both orthodontic and surgical treatment. Soft tissue profile changes were planned using known ratios of hard to soft tissue movement (Hunt and Kudge, 1984). In view of the known variability of soft tissue response after orthognathic surgery: this study concentrated upon the accuracy of hard tissue surgery. At final review before surgery, the details of the proposed operation were recorded, with an orthognathic prediction tracing. The surgical procedure was carried out under the supervision of a single Consultant surgeon. Intraoperative control of the maxilla during Le Fort 1 osteotomies used the mandible and/or an intermediate wafer for control of the anteroposterior and transverse dimensions. Control of the vertical dimension was by reference lines scribed upon the bone with a bur as described by Turvey ( 1982). The records of 296 cases of orthognathic surgery, carried out between 1984 and 1989 were examined. 343
AND METHODS
344
British Journal
of Oral and Maxillofacial
Surgcrq
Many of these case records were incomplete, often with radiographs absent. The records of 62 cases met the following criteria: 1. The patients received either a sagittal split or a vertical subsigmoid mandibular ostcotomy, a onepart IX Fort 1 level ostcotomy or a combination of these procedures, surgical movements 2. Full details of the planned were available with the prediction tracing and post-operative lateral cephalog3. Prc-operative rams were available (Table 1), did not show any apparent pos4. The radiographs turing of the mandible or misalignment of the subject’s head within the cephalostat, 5. The patients had no relevant medical history with no pathological or endocrine anomalies. Cleft deformities were excluded since previous surgery and soft tissue anomalies may have influenced the outcome of the ostcotomy. The patients received both rigid fixation and wire osteosynthcsis since the investigation was concerned only with the accuracy of the operative procedure itself. Where intermaxillary fixation was applied. this was with arch bars or cyclet wires. Cases treated with cast splints were excluded since the splints obscured some of the cephalometric landmarks used. Three surgical groups were identified; those who received (i) mandibular surgery only, (ii) maxillary surgery only and (iii) a bimaxillary procedure. Tracings were made of the facial hard tissues of each prc-operative and post-operative radiograph. Tracings wcrc used to allow the use of templates of upper and lower incisors made from the clearest incisor shadow and to allow construction of the Table 1 - Interval Middle of interval
hctween
Autorotation The assessment of mandibular autorotation following maxillary surgery is a common problem. It must be accurately predicted if the jaws are to occlude in the
and sur_ecq
Number 01 observations
Time intervals bctwccn surfer!; in weeks 0 3 1:
20 II
IS 20 25 30
II 6 4 6
3s 40
0 I
Mean
radiograph
mandibular gonion. On each tracing 14 ccphalometric landmarks (Fig. 1) in a set sequence were digitised. The sequence was then repeated. If a repeat measurement was more than 0.2 mm from the first, then that landmark was automatically rejected and new measurements taken. The tracings were automatically corrected for enlargement and superimposed, with allowance for the planned surgical movement, upon x and y axes constructed after the method of Burstone et ul. (1978) (Fig. 2). The x axis was taken as a line projected 7” clockwise from SN registcrcd at N to approximate to the normal head posture (a surrogate Frankfort horizontal plane). The y axis was a line perpendicular to the x axis passing through S. The planned surgical movement was recorded in the patient’s pre-operative notes and confirmed with the prediction tracing in terms of horizontal and vertical movements relative to normal head posture, which corresponded to the x and y axes. All mcasurements were made in millimetres. On superimposition: the displaccmcnt of the landmarks post-operatively could be measured and compared to their planned movement. Ideally, the preoperative tracing plus the surgical movement would equal the post-operative tracing. All discrepancies were recorded, labellcd surgical error, and formed the raw data of this study.
pre-opera&c
radiograph
\
and
*** ***:******I+ ******************** *********** **et** **** ****t* 1:
I4 weeks
Time interval between surgery radiograph in weeks 0 I7 I:, 17 15 20 25 30 35 40 45 50
and post-operative
: I 1 2 I
****a************ et*************** ************* ***** **** * * ** *
0 I
*
I3
Mean 9.5 weeks Fig. I - Cephalometric
landmarks
used in this study.
Surgical
y
mxis
x axis
Fig. 2 - x and y axes used in this study.
planned relationship post-operatively. IIowcvcr, unless the prediction rotates the mandible about the true axis of autorotation them will be a horizontal discrepancy between the predicted and the achieved position of the mandibular incisors which will bc proportional to the vertical movement. Three distinct points have been suggested to assess mandibular autorotation (Fig. 3).
accuracy
in orthognathic
surgery
345
Thompson (1946), Craddock (1948) and Posselt (1957) described the axis of rotation of the mandible from mandibular rest position to centric occlusion as being at, or close to: the ccntre of the condyle. Schcndcl et ul. ( 1976) evaluated a group of I4 cases of maxillary impaction against 30 non-surgical controls. They noted that the mandible rotated through an arc about the highest point on the head of the mandibular condylcs, the condylion, (Krogmann and Sassouni, 1957). This work was cited by Epker and Fish (1980, 1986) as justification for using the condylion as the centre of autorotation in maxillary surgery. Sperry et (11.( 1982) matched data from two edentulous patients with metallic implants embedded within wax bite blocks with data from 23 cases of maxillary impaction surgery. They found that autorotation occurred in the region of a point within the mastoid process. This point is found by establishing a coordinate system, with the ‘X’ axis being the line ST\j and the ‘Y’ axis a lint perpendicular to SN through S. The point lies 32 mm posteriorly on the ‘X’ axis and 28 mm inferiorly on the ‘Y’ axis. The authors did: however, note that a degree of individual variation was seen about this point. Grant (1973) supported the concept of an instantaneous centrc of rotation. This suggests that the mandible will translate as well as rotate for any movement, but that for any small movement a point can be found that can be taken as the ccntrc of rotation for that movement. A small pilot study compared the accuracy of autorotation about the following points (Fig. 3): (a) the ccntrc of the condylc (b) the condylion (c) Sperry’s mastoid point. Six cases of maxillary surgery were predicted and measured three times, each time a diflercnt point of autorotation was used in the prediction. The computer gave error values in x and y axes which were combined to give a resultant for each landmark which was then averaged (Table 2). The method which gave the smallest resultant error: Sperry’s Point, was taken as the least inaccurate and was applied to the rest of the study (Bryan, 1989).
ERROR
OF ‘THE METHOD
In any investigation based upon cephalomctrics, the error of the method must be assessed and considered when interpreting the results, since it estimates the Table 2 - Resultant
Case Cast Case Case Case Case Fig. 3 - Possible points of autorotation.
I 2 3 4 5 6
error values in millimctrcs
Centre of Condylc
Condylion
Sperry‘s Point
6.81 8.15 6.54 5.95 3.28 4.86
7.09 X.16 4.X2 6.21 3.41 5.34
4.13 5.30 3.33 5.80 2.6’) 3.84
346
British Journal
of Oral and Maxiltofdcial
Surgery
degree of precision with which a landmark can be identified and measured by a particular investigator. The method error will vary between studies, being influenced by the experience of the operator and the working conditions. The method error was found by retracing and remeasuring 20% of the sample (24 radiographs), taken at random, 4 months after the initial tracing. These were compared to the original measurements using the formula of Dahlberg (1940), Se2 = ,&d2!2n where d is the difference- between the two measurements of a given landmark. This will include both random and systematic error and is only identical with the error variance when there is no bias. In addition, Houston (1983) advised the USC of a coefficient of reliability, to assess the contribution of random error, which will increase the total variance of the measurement (St’), and can be expressed as 1 -Se*; St2 x lOO%, which was also calculated (Table 3).
RESULTS 62 patients met the criteria of this study. 25 received mandibular surgery only: 10 maxillary surgery only and 27 bimaxillary surgery. The average age of the patients at operation was 23.5 years with a range from 16.1 years to 42.3 years. Table 4 shows the surgical movement in these cases. The most common mandibular procedure was the sagittal split ramus osteotomy. a versatile procedure which allows either mandibular advance or set back. In this series mandibular set back accounted for 58% of mandibular procedures, and the advancement for 42%. In only three cases was the vertical subsigmoid osteotomy used to set back the mandible. Some degree of mandibular autorotation will accompany any maxillary movement. In the bimaxillary osteotomies this was incorporated into the planned mandibular movement. Only in cases of maxillary ostcotomy could the mandibular autorotation could be assessed as a discrete factor. The one piece Lc Fort I level osteotomy was the maxillary operation investigated. It was used mainly to advance and impact the maxilla, but differential anteropostcrior impaction was common. Table 3 - Error of the method,
x and y axes measured
Coeflicient of reliability
Standard error of the mean
0.34
S-N distance ANS A point Upper incisor apex IJpper incisor edge Maxillary molar Posterior nasal spine Lower incisor edge Lower incisor apex B point Pogonion Mcnton Gonion
x axis 0.77 0.74 0.61 0.76 0.99 I.21 0.77 0.91 1.12 1.17 1.50 0.59
in millimetres
97.8 y axis 0.77
I .03 0.82 0.59 0.65 0.43 0.67 0.60 1.79 I.19 I .O5 0.50
96.8 95.75 97.8 98.3 96.1 92.2 99. I 98.9 97. I 98.3 97.8 98.1
Table 4 - Operative
proccdurcs
in this study
25 IO 27 62
Mandibular surgery Maxillary surgery Bimaxillary surgery Total cases Mandihlar
Sagittal
prowdures
advance setback osteotomy, advance setback
22 27 0 3 IO
advance setback anlcrior intrusion posterior intrusion anterior sctdown posterior setdown
28 I 22 28 3
split ramus osteotomy.
Vertical subsignoid
ramus
Autorotation Muxillar_v
procedures
Le Fort I lcvcl osteotomy.
I
The study was intended to measure change at the time of operation, so that radiographs were sought as close to the time of surgery as possible. Preoperative radiographs were taken at least 8 weeks after the cessation of active orthodontics (to allow the archwires’ full expression). The first available post-operative radiograph was measured, except where an inter occlusal wafer was used, when the first radiograph after wafer removal was assessed. The mean time elapsed between the pre-operative film and operation was 14 weeks and between surgery and the post-operative film 9.5 weeks (Fig. 1). The analysis of surgical error showed it to be normally distributed which allowed parametric statistical analysis using a one sample Students’ t test (Table 5). Intra-group analysis included a one-way analysis of variance (Table 6) and where a statistical significance was noted the location of that sibmificance was identified through a two sample t test. Only four out of 12 landmarks were so identified (Table 7). Overall, the lcvcls of significance seen between the surgical groups studied was not high. No significant differences were found between the maxillary surgical group and the bimaxillary surgical group. Between the bimaxillary surgical group and the mandibular group, only the menton in the antcro-posterior plane showed a statistical significant difference, and then only at the 5% level. The major signilicant difTerence was seen in three landmarks between the mandibular and maxillary surgical groups. The lower incisor apex, pogonion and menton all showed significance antero-posteriorly. Only the menton showed a significant difference at the 5% level in the vertical plane.
DISCUSSION Any retrospective investigation of a series of cases is limited by its nature. It is unlikely to be a truly random selection and is dcpendcnt upon the quality of the records available. However, such a study can provide evidence to the merits of a particular technique. This study supports both the use of orthognathic prediction of hard tissue movement as an approximation of the complex events that occur to
Surgical Table 5 - Analysis of prediction deviations. significance) Mandibular N=25 Mean N-S ANS x Apt
1.
UIA
:
UIE
: Y x
M
LIE
:
LIA
;
Bpt PO
t: Y x
Me
;
Go
: y
Significance
group SD
0.02 0.02 -0.11 -. 0.03 -0.11 0.46 - 0.46 -0.08 -0.55 0.16 ---0.55 0.32 0.12 -0.16 -0.22 -1.01 0.23 -0.92 0.82 - 1.68 0.44 -2.26 0.59 0.64 0.80
PKS :
surgical
error for individual
Maxillary N=lO Mean
Sig
0.43 I .29 0.93 1.29 2.68 I.04 1.23 1.52 1.20 2.24 I.15 1.49 0.66 2.17 1.33 2.39 2.29 2.43 2.68 3.27 3.65 3.80 1.92 5.83 2.69
* *
*
+ **
Table 6 - Analysis of variance maxillary : bimaxillary groups)
unless marked:
(ANOVA)
F ratio Maxillary
landmarks
ANS A point UIA UK! M PNS
Mandibular
landmarks
LIE l.IA B point PO Me Go
Significance-surgical is marked *: p~O.01
x y x y x y x v x y x y x y x y x y x y x y x y
error not significant is marked **.
the patient at surgery, follow that plan.
landmarks
0.61 0.57 0.11 0.81 0.40 0.75 0.32 0.73 0.15 1.28 0.53 1.67 0.07 0.41 2.50 0.07 1.93 0.59 3.70 0.74 6.01 2.20 0.65 0.03
SD
p ~0.05
*
* *
is marked
in millimctrcs
Bimaxillary N=27 Mean 0.20 -0.35 ---0.21 0.10 0.23 0.53 -0.41 I .oo -0.11 0.92 -0.24 -- 0.04 0.48 - 0.26 0.23 0.10 0.17 0.04 0.25 1.05 0.57 I.50 -0.20 0.39 0.79
*; p
in orthognathic
surgery
341
(one sample ‘t’ test: means, standard
group SD 0.57 2.71 1.84 3.05 1.56 2.92 1.53 3.82 1.83 3.64 1.74 3.17 I .58 2.60 2.51 2.80 2.75 2.87 2.84 3.41 2.36 3.52 2.20 5.83 2.70
Sig
*
**; p
***.
event, but involves groups of landmarks. Interpretation of changes to individual landmarks must be made with caution. The measurement of surgical change involves error which may be inherent in the cephalometric technique, the surgery and fixation may alter or obscure radiographic landmarks and post-operative ocdema may reduce the film quali ty (Baumrind and Fran tz, 197 1; Gravely and Murray Benzies, 1974; Baumrind et ul., 1976; Houston, 1983; et al.: 1987). Careful radiographic techHouston niques, rigid definitions of landmarks used and the use of electronic measuring and recording devices will help to reduce the error. Willmar ( 1974) used cephalometric analysis with metallic implants to assess surgical change and showed a method error similar to that of conventional cephalomctric assessment. Unfortunately implants arc not routinely available and surgery will often affect cephalometric landmarks, particularly the gonion and those of the maxilla. Conventional ccphalometric landmarks used for surgical assessment will have a method error greater than that of nonsurgical cephalomctric analysis.
Significance
*
** ** *
and the surgeon’s
Sig
0.30 2.70 3.25 2.33 3.65 3.43 3.23 3.88 3.29 2.93 2.40 2.49 1.58 0.04 1.55 1.78 1.57 I .43 1.86 2.55 I.61 3.09 I .63 3.90 1.10
(mandibular:
unless marked:
measured
group
0.01 0.31 0.06 -0.38 -0.09 - 0.43 0.21 --0.15 0.49 0.06 0.64 - 0.42 -0.55 -0.30 0.29 I .09 0.11 0.77 -0.48 1.82 -0.63 2.37 -0.97 -0.08 0.52
*
error not signilicant
cephalometric
accuracy
p < 0.05
Autorotation ability
to
The method Surgical change to cephalometric landmarks in the maxillofacial region does not occur as an isolated
Autorotation of the mandible will follow surgical movement of the maxilla. Unless the prediction is perfect, the mandible will not adopt the planned position post-operatively and the condyles may bc distracted from the glenoid fossae when achieving an intercuspal relationship. The increasing use of intermediate wafers has increased this problem, since the
34x
Hritish Journal
of Oral and _Maxillofacial
I‘able 7 - C’npaircd
I.IA PO Me MC
x x x >
Significance-stqical
‘t’ test significant
Surgcr)
landmarks
Mand : Max ‘1’value
signilicance
Mand : Himax ‘L’value
2.61 3.10 3.55 2.14
* ** ** *
I.19 1.94 2.64 1.37
error not significant
unless marked:
thickness inherent in the wafer may result in a degree of autorotation after wafer removal. Nat&tad et ul. ( 1991) showed that a discrepancy of 2 mm anteropostcriorly between the planned result and the operative result could result from an autorotation of 5 mm if there was a discrepancy of 20 mm between the true ccntre of autorotation and the ccntre of autorotation used in the prediction. The autorotation point of Sperry et ul. (1982) appeared to be more accurate than the ccntre of the condyle or condylion, but the pilot study sample was very small. A larger series of maxillary surgical cases is being investigated currently. The significant differences seen between the mandibular and maxillary surgical groups suggests that inadequate prediction of mandibular autorotation may be responsible.
Max : Rimax ‘1‘value
significance
I.21 0.88 0.94 0.95
,:
p
signifcance
*; ~~0.01
is marked
**
LIE
.
.
Emm.
Training Training and experience will affect the accuracy of both the prediction and the surgical procedure. Kvam and Krogstad (1969) showed that training and experience with cephalometric techniques will improve accuracy. while the use of rigid definitions of the landmarks used (Hixon, 1956; Baumrind & Frantz, 1971) and a ‘two pass’ measuring technique (Houston, 1983) will reduce variation in landmark identification. Experience both increases the accuracy of an operative technique (Adcll et al.? 1970; Barer ef al.: 1987) and enlarges the data base of past operations (Harradine & Birnie: 1985) allowing increasingly accurate estimations of the hard and soft tissue response. In the present study, each landmark investigated showed an expected individual and non-circular pat1971). tern of error (Baumrind and Fran& Scattcrgrams of the incisal edges from all three surgical groups (Fig. 4) indicated an even distribution about zero, though there was a small tendency for the upper incisal edge to be placed slightly behind the planned position. This observation supports the suggestion of Van Sickcls ef al. ( 1986) that the incisal edges arc valid surgical landmarks. The Le Fort 1 level ostcotomy was noted by Frcide et ul. (1987) as being particularly variable in the vertical plane. This view is not supported by this study where the greatest variation was seen in the horizontal plant. The prediction technique, the surgical procedure and the assessment of operative change, all involve inherent errors which limit our ability to measure reliably small changes. This, with the patient’s indi-
2mm. b
Fig. 4 - Scattergrams:
I
incisal edges of all surgical
groups.
vidual response to treatment will demand increasingly sophisticated research techniques to distinguish between minute changes due to treatment and the error inherent in the method.
COSCLUSION An orthognathic prediction is only as good as the surgeon’s ability to transfer it to the patient. If the landmarks of the mandible and maxilla are considered as a group, the results of this study indicate that, though there was individual variation, the means of the surgical groups studied showed no statistically significant difference between the planned postsurgical position of the jaws and the position actually achieved at surgery. Acknowledgments We wish to thank Professor M. Harris for allowing us to evaluate his patients and records at the Eastman Dental Hospital and Mr I’. Furniss for his work upon the computer program used in this study.
Surgical
References Adell. R.. Hansson.
B. 0.; Brinemark, P. I. & Brcine, U. (1970). Intra-osseous anchorapc ofdcntal prostheses. IT. Review of clinical approaches. Scur~tkmariu~~ Joztr~a/ o/‘P/crsric and Rrwn.~tructive Surgz~r~~4, 19. Barer. P. G.. Wallcn. T. R.. McNcill, R. W. & Reitzik, M. (19X7). Stability of mandibular advancement osteotomy using rigid internal fixation. Awericcm .Jourtznl ~~fOrr/zudonrics and Derztqf~zrial Orrhopwdics. 92,403. Baumrind, S. & FrantJ. R. C. (1971). The reliability ofheadfilm measurements. I Landmark identification 2 Conventional angular and linear mcasurcs. iittzericun Journnl of Orfhodonrics. 60, I I I & 505, Baumrind; S.. Miller, D. & Molthcn. R. (1976). The reliability of hcadtilm measurements. 3 Tracing superimposition. .&nrricun .Journul u/Orthodontics, 70, 6 17. Bryan; D. C.. (198’)). The accuracy of prediction in ortho_eathic surgery. MSc Report. University of London. Burstone. C. J., James, R. B.. Lcgan. H.. Murphy. G. A.. Sorton: L. A. (,lY78). Ccphalometrics for orthognathic surgery. Journal of Orul Surgety. 36, 269. Craddock. F. W. (1948). The muscles of mastication and mandibular movements. ,I’rw Zcwlr~zd h7k7/ Journal, 44,233. Dahlbcrg. G.: (1940). Statistical Methods for Medical and Biological Students. Interscience Publishers. New York. Fpkcr, B. N. & Fish. L. C.. ( 1980). Surgical superior repositioning of the maxilla: what to do with the mandible? Anzericun .Jourtzul qJ‘O~hodonri~s, 78, 164. Epkcr, B. N. L Fish, L. C. (1986). Dentofacial Deformities: lntcgrated orthodontic and surgical correction. Vols 1 and II. C. V. Mosby Co, St Louis. Frcide. H.. Kahnberg. K. E., Adcll, R. & Ridcll, A. (1987). Accuracy of cephalometric prediction in orthognathic surgery. .Journul of Oral and Musillof~z~iul Surgery. 45, 754. Grant, P. G. (1973). Biomcchanical significance of the instantaneous centre of rotation: the human temporomandibular joint. Jozrnzol ol‘Biotllrcllmzics. 6, 109. Gravch. J. F. & Bcnrics. P. MM.( 19741. The clinical sienificancc of t&in2 error in ccphalomctry. British Jozrrrral of Orrhudonrics. 1.95. Harrddine. N. W. & Birnie, D. J. ( 3985). Computcrised prediction of the results of orthognathic surgery. Journu/ of .Musi//ojr,c iczl Szzrgery, 13, 245. I lcnderson. D. (1974). The assessment and management of bony deformities of the middle and lower face. Rrirkh Journaiof Plustic Surger),. 27. 287. Henderson, L). (1976). Photoccphalometric prediction and its influence on the surgical management of symmctricdl Facial deformity. I luntarian Lecture, Royal College of Surgeons of England. llixon. E. 11. (1956). The norm concept and cephalomctrics. Awwricun Jozrrnul q/ Orrhodotzfic.c, 42, X9X. Houston, W. J. ( lY83). The analysis of errorsin orthodontic measurements. Am&-an Journul of Orrhodutztics. 83, 3X2. Houston. W. J.. Jones, I!. & James. D. R. (1987). A method of recording change in maxillary position following orthognathic surgery. Europun Jnurnul of Orrhodotztics, 9. 9. Hunt. N. P. & Rudge, S. J. (1954). l:acial profile and orthognathic surgery. British Journal yf‘Orthodotztics. II, 126.
accuracy
in orthognathic
sur_gery
349
Krogman. W. M. & Sassouni, V. (1957). A syllabus of roentgenographic crphalomctry. Philadelphia Centrc for Research in Child Growth. Kvam: E. & Krogstad. 0. (1969). Variability in tracings of lateral head plates for diagnostic orthodontic purposes. A mcthodologic study. Acru Odontologicd Sc&dinuvicu, 27, 359. Lewis. D. H. (19Xla). Basic tracing for lateral skull radioeranhs. - . Dental C$dute. b, 45. L&s. D. H. ( I98 I b). Lateral skull radiographs: using SNA and SNB. Detuul L’l,dute.8, 123. Mills, J. R. ( 1970). The application and importance of ccphalometry in orthodontic treatment. The Orthodonrisr, 2, 32. Nattcstad. A., Vedtoftc. I’. & Mosekilde. E. (1991). ‘The significance of an erroneous recording of the centrc of mandibular autorotation in orthognathic surgery. Jounzul o/ Cr~zttiotnaxillo~i~iul Surpy. 19, 254. Pospisil, 0. A. (1987). Reliability and feasibility ofprcdiction tracing in orthogathic surgery. Journul of ~ratziomuxillojirciul Surger). 15, 7Y. Posscl~. U. L. l-‘. ( 1957). Movement arcas of the mandible. .Journa/ 0fProsrhetir Iknri.slry. 7, 375. Schendcl. S. A.. Eisenfeld. J. H., Bell. W. H. & Epkcr, B. N. (1976). Superior repositioning of the maxilla: stability and soft tissue osseous relations. American Jozrrtza/ of Orrhudontirs. 70,663. Sperry. T. I’.. Steinberg, 41. J. & Gans. B. J. (19X2). Mandibular as a result of maxillary movcmcnt during autorotation impaction surgery. Atnrricun .Journul of 0rthodontic.r. 81, I 16. Thompson, J. R. (lY46). Rest position of the mandible and its significance to dental science. Journal q/the ,4nzericun Denrul Aswciuzion. 33, I5 I. Turwy. T. A. ( 1982). Simultaneous mobilisation of the maxilla and mandible: Surgical technique and results. Journul of Orul utzd ;Mrrxillofirciul Surgq~. 40, 96. Van Sickles, J. E., Larsen. A. J. & Triplett. Ii. G. (lY86). of internal Predictability of maxillary surgery: a comparison and external refcrcncc marks. Oral Szrrgq~, Oral Medicine, Orui Paiholog),. 61, 542. Willmar. K. (1974). On the Le Fort I ostcotomy: A follow-up study of 106 operated patients with maxillo&cial deformity. .ScundunuGm Journul of Plu.rtic and Recotzsrrucfive Surgery, 12, (Suppl I).
The Authors D. C. Bryan Senior S&alist in Orthodontics Oueen Elizabeth Militarv Hosuital Siadium Road . * London SE18 4011 N. P. Hunt Consultant and Senior Lecturer Eastman Dental llospital GrdvS Inn Road London WC I Correspondence
and requests
for oiTprints to D. C. Bryan
Paper rcccivcd 18 April 1992 Accepted 13 May 1993
Invited comment Surgical
accuracy
in orthognathic
surgery 19~D. C. Bryn
Authors of the article accept in their summary and throughout the Paper that there are individual variations between planned and achieved surgical results. The article concentrates only on study of the hard tissue (dental and skeletal refcrencc points)
& N P. Zlunt
planned and achieved changes after surgery. Failure to concentrate on soft tissue/profile changes is justilied by the statement that these are known. Literature is littered with numerous papers all of which demonstrated quite clearly that there is a vast
London
SUMMARY. This study investigated the accuracy with which the planned surgical change could be achieved during orthognathic surgery, based upon the retrospective cephalometric analysis of 62 patients who received correction of dentofacial deformity. It is concluded that, despite individual variation, no statistically significant difference could be demonstrated between the orthognathic prediction and the surgical outcome. This supports both the use of orthognathic profile planning and the surgeon’s ability to follow the plan.
INTRODUCTION
MATERIALS
Modern surgical and orthodontic techniques have to point where developed the combined orthodontic/surgical treatment can bc planned for almost all kinds of severe dcntofacial deformity. With this technical advance has grown a need to plan and predict accurately the outcome of treatment. Most reports have been of isolated casts but recently two papers have compared the relationship between orthognathic prediction/planning and the surgical outcome in a series of cases. Friede et al. (1987) reviewed a series of 30 orthognathic cases which had received one of six operative procedures. Prediction tracings were made before any treatment and were compared to radiographs taken at the review 6 months post-operatively. The results were reported as a series of individual tracings and showed considerable anteropostcrior and vertical variation both within and between the surgical groups. The authors concluded that vertical changes were the hardest to predict. However: they noted that the use of radiographs taken 6 months postoperatively may have allowed surgical relapse to influence their results. Pospisil (1987) compared prediction tracings against the 6 month post-operative radiographs for both hard and soft tissue movement in a series of 40 cases. He reported significant variation (defined as greater than 20% of planned movement) in 60% of his casts, but he did attempt to eliminate the effect of relapse upon the results by comparing six month post-operative cephalograms to radiographs taken before the removal of intermaxillary fixation. The aim of the present investigation was to examine the relationship between orthognathic prediction planning and the surgical outcome in a series of cases treated by a single Consultant surgeon and his surgical team.
All cases of facial deformity were assessed on a joint Orthognathic Planning Clinic under the care of one Consultant surgeon. Every patient on this clinic had standard records, involving radiographs (orthopantomogram, lateral cephalogram and P.A. cephalogram as required), facial and intra-oral photographs and study models. A face bow registration was only used if vertical height changes were anticipated. The patient assessment was systematic, based upon the methods summarised by Hunt and Rudge (1984). The Eastman Cephalometric Analysis (Mills, 1970, Lewis, 1981) was routinely employed and profile prediction was based upon a modification of the method described by Henderson (1974, 1976): in that hard and soft tissue detail was transferred from the ccphalogram to sheets of tracing paper or acetate prior to the construction of templates. The templates were adjusted to optimise facial aesthetics and to achieve a Class I incisor relationship, simulating both orthodontic and surgical treatment. Soft tissue profile changes were planned using known ratios of hard to soft tissue movement (Hunt and Kudge, 1984). In view of the known variability of soft tissue response after orthognathic surgery: this study concentrated upon the accuracy of hard tissue surgery. At final review before surgery, the details of the proposed operation were recorded, with an orthognathic prediction tracing. The surgical procedure was carried out under the supervision of a single Consultant surgeon. Intraoperative control of the maxilla during Le Fort 1 osteotomies used the mandible and/or an intermediate wafer for control of the anteroposterior and transverse dimensions. Control of the vertical dimension was by reference lines scribed upon the bone with a bur as described by Turvey ( 1982). The records of 296 cases of orthognathic surgery, carried out between 1984 and 1989 were examined. 343
AND METHODS
344
British Journal
of Oral and Maxillofacial
Surgcrq
Many of these case records were incomplete, often with radiographs absent. The records of 62 cases met the following criteria: 1. The patients received either a sagittal split or a vertical subsigmoid mandibular ostcotomy, a onepart IX Fort 1 level ostcotomy or a combination of these procedures, surgical movements 2. Full details of the planned were available with the prediction tracing and post-operative lateral cephalog3. Prc-operative rams were available (Table 1), did not show any apparent pos4. The radiographs turing of the mandible or misalignment of the subject’s head within the cephalostat, 5. The patients had no relevant medical history with no pathological or endocrine anomalies. Cleft deformities were excluded since previous surgery and soft tissue anomalies may have influenced the outcome of the ostcotomy. The patients received both rigid fixation and wire osteosynthcsis since the investigation was concerned only with the accuracy of the operative procedure itself. Where intermaxillary fixation was applied. this was with arch bars or cyclet wires. Cases treated with cast splints were excluded since the splints obscured some of the cephalometric landmarks used. Three surgical groups were identified; those who received (i) mandibular surgery only, (ii) maxillary surgery only and (iii) a bimaxillary procedure. Tracings were made of the facial hard tissues of each prc-operative and post-operative radiograph. Tracings wcrc used to allow the use of templates of upper and lower incisors made from the clearest incisor shadow and to allow construction of the Table 1 - Interval Middle of interval
hctween
Autorotation The assessment of mandibular autorotation following maxillary surgery is a common problem. It must be accurately predicted if the jaws are to occlude in the
and sur_ecq
Number 01 observations
Time intervals bctwccn surfer!; in weeks 0 3 1:
20 II
IS 20 25 30
II 6 4 6
3s 40
0 I
Mean
radiograph
mandibular gonion. On each tracing 14 ccphalometric landmarks (Fig. 1) in a set sequence were digitised. The sequence was then repeated. If a repeat measurement was more than 0.2 mm from the first, then that landmark was automatically rejected and new measurements taken. The tracings were automatically corrected for enlargement and superimposed, with allowance for the planned surgical movement, upon x and y axes constructed after the method of Burstone et ul. (1978) (Fig. 2). The x axis was taken as a line projected 7” clockwise from SN registcrcd at N to approximate to the normal head posture (a surrogate Frankfort horizontal plane). The y axis was a line perpendicular to the x axis passing through S. The planned surgical movement was recorded in the patient’s pre-operative notes and confirmed with the prediction tracing in terms of horizontal and vertical movements relative to normal head posture, which corresponded to the x and y axes. All mcasurements were made in millimetres. On superimposition: the displaccmcnt of the landmarks post-operatively could be measured and compared to their planned movement. Ideally, the preoperative tracing plus the surgical movement would equal the post-operative tracing. All discrepancies were recorded, labellcd surgical error, and formed the raw data of this study.
pre-opera&c
radiograph
\
and
*** ***:******I+ ******************** *********** **et** **** ****t* 1:
I4 weeks
Time interval between surgery radiograph in weeks 0 I7 I:, 17 15 20 25 30 35 40 45 50
and post-operative
: I 1 2 I
****a************ et*************** ************* ***** **** * * ** *
0 I
*
I3
Mean 9.5 weeks Fig. I - Cephalometric
landmarks
used in this study.
Surgical
y
mxis
x axis
Fig. 2 - x and y axes used in this study.
planned relationship post-operatively. IIowcvcr, unless the prediction rotates the mandible about the true axis of autorotation them will be a horizontal discrepancy between the predicted and the achieved position of the mandibular incisors which will bc proportional to the vertical movement. Three distinct points have been suggested to assess mandibular autorotation (Fig. 3).
accuracy
in orthognathic
surgery
345
Thompson (1946), Craddock (1948) and Posselt (1957) described the axis of rotation of the mandible from mandibular rest position to centric occlusion as being at, or close to: the ccntre of the condyle. Schcndcl et ul. ( 1976) evaluated a group of I4 cases of maxillary impaction against 30 non-surgical controls. They noted that the mandible rotated through an arc about the highest point on the head of the mandibular condylcs, the condylion, (Krogmann and Sassouni, 1957). This work was cited by Epker and Fish (1980, 1986) as justification for using the condylion as the centre of autorotation in maxillary surgery. Sperry et (11.( 1982) matched data from two edentulous patients with metallic implants embedded within wax bite blocks with data from 23 cases of maxillary impaction surgery. They found that autorotation occurred in the region of a point within the mastoid process. This point is found by establishing a coordinate system, with the ‘X’ axis being the line ST\j and the ‘Y’ axis a lint perpendicular to SN through S. The point lies 32 mm posteriorly on the ‘X’ axis and 28 mm inferiorly on the ‘Y’ axis. The authors did: however, note that a degree of individual variation was seen about this point. Grant (1973) supported the concept of an instantaneous centrc of rotation. This suggests that the mandible will translate as well as rotate for any movement, but that for any small movement a point can be found that can be taken as the ccntrc of rotation for that movement. A small pilot study compared the accuracy of autorotation about the following points (Fig. 3): (a) the ccntrc of the condylc (b) the condylion (c) Sperry’s mastoid point. Six cases of maxillary surgery were predicted and measured three times, each time a diflercnt point of autorotation was used in the prediction. The computer gave error values in x and y axes which were combined to give a resultant for each landmark which was then averaged (Table 2). The method which gave the smallest resultant error: Sperry’s Point, was taken as the least inaccurate and was applied to the rest of the study (Bryan, 1989).
ERROR
OF ‘THE METHOD
In any investigation based upon cephalomctrics, the error of the method must be assessed and considered when interpreting the results, since it estimates the Table 2 - Resultant
Case Cast Case Case Case Case Fig. 3 - Possible points of autorotation.
I 2 3 4 5 6
error values in millimctrcs
Centre of Condylc
Condylion
Sperry‘s Point
6.81 8.15 6.54 5.95 3.28 4.86
7.09 X.16 4.X2 6.21 3.41 5.34
4.13 5.30 3.33 5.80 2.6’) 3.84
346
British Journal
of Oral and Maxiltofdcial
Surgery
degree of precision with which a landmark can be identified and measured by a particular investigator. The method error will vary between studies, being influenced by the experience of the operator and the working conditions. The method error was found by retracing and remeasuring 20% of the sample (24 radiographs), taken at random, 4 months after the initial tracing. These were compared to the original measurements using the formula of Dahlberg (1940), Se2 = ,&d2!2n where d is the difference- between the two measurements of a given landmark. This will include both random and systematic error and is only identical with the error variance when there is no bias. In addition, Houston (1983) advised the USC of a coefficient of reliability, to assess the contribution of random error, which will increase the total variance of the measurement (St’), and can be expressed as 1 -Se*; St2 x lOO%, which was also calculated (Table 3).
RESULTS 62 patients met the criteria of this study. 25 received mandibular surgery only: 10 maxillary surgery only and 27 bimaxillary surgery. The average age of the patients at operation was 23.5 years with a range from 16.1 years to 42.3 years. Table 4 shows the surgical movement in these cases. The most common mandibular procedure was the sagittal split ramus osteotomy. a versatile procedure which allows either mandibular advance or set back. In this series mandibular set back accounted for 58% of mandibular procedures, and the advancement for 42%. In only three cases was the vertical subsigmoid osteotomy used to set back the mandible. Some degree of mandibular autorotation will accompany any maxillary movement. In the bimaxillary osteotomies this was incorporated into the planned mandibular movement. Only in cases of maxillary ostcotomy could the mandibular autorotation could be assessed as a discrete factor. The one piece Lc Fort I level osteotomy was the maxillary operation investigated. It was used mainly to advance and impact the maxilla, but differential anteropostcrior impaction was common. Table 3 - Error of the method,
x and y axes measured
Coeflicient of reliability
Standard error of the mean
0.34
S-N distance ANS A point Upper incisor apex IJpper incisor edge Maxillary molar Posterior nasal spine Lower incisor edge Lower incisor apex B point Pogonion Mcnton Gonion
x axis 0.77 0.74 0.61 0.76 0.99 I.21 0.77 0.91 1.12 1.17 1.50 0.59
in millimetres
97.8 y axis 0.77
I .03 0.82 0.59 0.65 0.43 0.67 0.60 1.79 I.19 I .O5 0.50
96.8 95.75 97.8 98.3 96.1 92.2 99. I 98.9 97. I 98.3 97.8 98.1
Table 4 - Operative
proccdurcs
in this study
25 IO 27 62
Mandibular surgery Maxillary surgery Bimaxillary surgery Total cases Mandihlar
Sagittal
prowdures
advance setback osteotomy, advance setback
22 27 0 3 IO
advance setback anlcrior intrusion posterior intrusion anterior sctdown posterior setdown
28 I 22 28 3
split ramus osteotomy.
Vertical subsignoid
ramus
Autorotation Muxillar_v
procedures
Le Fort I lcvcl osteotomy.
I
The study was intended to measure change at the time of operation, so that radiographs were sought as close to the time of surgery as possible. Preoperative radiographs were taken at least 8 weeks after the cessation of active orthodontics (to allow the archwires’ full expression). The first available post-operative radiograph was measured, except where an inter occlusal wafer was used, when the first radiograph after wafer removal was assessed. The mean time elapsed between the pre-operative film and operation was 14 weeks and between surgery and the post-operative film 9.5 weeks (Fig. 1). The analysis of surgical error showed it to be normally distributed which allowed parametric statistical analysis using a one sample Students’ t test (Table 5). Intra-group analysis included a one-way analysis of variance (Table 6) and where a statistical significance was noted the location of that sibmificance was identified through a two sample t test. Only four out of 12 landmarks were so identified (Table 7). Overall, the lcvcls of significance seen between the surgical groups studied was not high. No significant differences were found between the maxillary surgical group and the bimaxillary surgical group. Between the bimaxillary surgical group and the mandibular group, only the menton in the antcro-posterior plane showed a statistical significant difference, and then only at the 5% level. The major signilicant difTerence was seen in three landmarks between the mandibular and maxillary surgical groups. The lower incisor apex, pogonion and menton all showed significance antero-posteriorly. Only the menton showed a significant difference at the 5% level in the vertical plane.
DISCUSSION Any retrospective investigation of a series of cases is limited by its nature. It is unlikely to be a truly random selection and is dcpendcnt upon the quality of the records available. However, such a study can provide evidence to the merits of a particular technique. This study supports both the use of orthognathic prediction of hard tissue movement as an approximation of the complex events that occur to
Surgical Table 5 - Analysis of prediction deviations. significance) Mandibular N=25 Mean N-S ANS x Apt
1.
UIA
:
UIE
: Y x
M
LIE
:
LIA
;
Bpt PO
t: Y x
Me
;
Go
: y
Significance
group SD
0.02 0.02 -0.11 -. 0.03 -0.11 0.46 - 0.46 -0.08 -0.55 0.16 ---0.55 0.32 0.12 -0.16 -0.22 -1.01 0.23 -0.92 0.82 - 1.68 0.44 -2.26 0.59 0.64 0.80
PKS :
surgical
error for individual
Maxillary N=lO Mean
Sig
0.43 I .29 0.93 1.29 2.68 I.04 1.23 1.52 1.20 2.24 I.15 1.49 0.66 2.17 1.33 2.39 2.29 2.43 2.68 3.27 3.65 3.80 1.92 5.83 2.69
* *
*
+ **
Table 6 - Analysis of variance maxillary : bimaxillary groups)
unless marked:
(ANOVA)
F ratio Maxillary
landmarks
ANS A point UIA UK! M PNS
Mandibular
landmarks
LIE l.IA B point PO Me Go
Significance-surgical is marked *: p~O.01
x y x y x y x v x y x y x y x y x y x y x y x y
error not significant is marked **.
the patient at surgery, follow that plan.
landmarks
0.61 0.57 0.11 0.81 0.40 0.75 0.32 0.73 0.15 1.28 0.53 1.67 0.07 0.41 2.50 0.07 1.93 0.59 3.70 0.74 6.01 2.20 0.65 0.03
SD
p ~0.05
*
* *
is marked
in millimctrcs
Bimaxillary N=27 Mean 0.20 -0.35 ---0.21 0.10 0.23 0.53 -0.41 I .oo -0.11 0.92 -0.24 -- 0.04 0.48 - 0.26 0.23 0.10 0.17 0.04 0.25 1.05 0.57 I.50 -0.20 0.39 0.79
*; p
in orthognathic
surgery
341
(one sample ‘t’ test: means, standard
group SD 0.57 2.71 1.84 3.05 1.56 2.92 1.53 3.82 1.83 3.64 1.74 3.17 I .58 2.60 2.51 2.80 2.75 2.87 2.84 3.41 2.36 3.52 2.20 5.83 2.70
Sig
*
**; p
***.
event, but involves groups of landmarks. Interpretation of changes to individual landmarks must be made with caution. The measurement of surgical change involves error which may be inherent in the cephalometric technique, the surgery and fixation may alter or obscure radiographic landmarks and post-operative ocdema may reduce the film quali ty (Baumrind and Fran tz, 197 1; Gravely and Murray Benzies, 1974; Baumrind et ul., 1976; Houston, 1983; et al.: 1987). Careful radiographic techHouston niques, rigid definitions of landmarks used and the use of electronic measuring and recording devices will help to reduce the error. Willmar ( 1974) used cephalometric analysis with metallic implants to assess surgical change and showed a method error similar to that of conventional cephalomctric assessment. Unfortunately implants arc not routinely available and surgery will often affect cephalometric landmarks, particularly the gonion and those of the maxilla. Conventional ccphalometric landmarks used for surgical assessment will have a method error greater than that of nonsurgical cephalomctric analysis.
Significance
*
** ** *
and the surgeon’s
Sig
0.30 2.70 3.25 2.33 3.65 3.43 3.23 3.88 3.29 2.93 2.40 2.49 1.58 0.04 1.55 1.78 1.57 I .43 1.86 2.55 I.61 3.09 I .63 3.90 1.10
(mandibular:
unless marked:
measured
group
0.01 0.31 0.06 -0.38 -0.09 - 0.43 0.21 --0.15 0.49 0.06 0.64 - 0.42 -0.55 -0.30 0.29 I .09 0.11 0.77 -0.48 1.82 -0.63 2.37 -0.97 -0.08 0.52
*
error not signilicant
cephalometric
accuracy
p < 0.05
Autorotation ability
to
The method Surgical change to cephalometric landmarks in the maxillofacial region does not occur as an isolated
Autorotation of the mandible will follow surgical movement of the maxilla. Unless the prediction is perfect, the mandible will not adopt the planned position post-operatively and the condyles may bc distracted from the glenoid fossae when achieving an intercuspal relationship. The increasing use of intermediate wafers has increased this problem, since the
34x
Hritish Journal
of Oral and _Maxillofacial
I‘able 7 - C’npaircd
I.IA PO Me MC
x x x >
Significance-stqical
‘t’ test significant
Surgcr)
landmarks
Mand : Max ‘1’value
signilicance
Mand : Himax ‘L’value
2.61 3.10 3.55 2.14
* ** ** *
I.19 1.94 2.64 1.37
error not significant
unless marked:
thickness inherent in the wafer may result in a degree of autorotation after wafer removal. Nat&tad et ul. ( 1991) showed that a discrepancy of 2 mm anteropostcriorly between the planned result and the operative result could result from an autorotation of 5 mm if there was a discrepancy of 20 mm between the true ccntre of autorotation and the ccntre of autorotation used in the prediction. The autorotation point of Sperry et ul. (1982) appeared to be more accurate than the ccntre of the condyle or condylion, but the pilot study sample was very small. A larger series of maxillary surgical cases is being investigated currently. The significant differences seen between the mandibular and maxillary surgical groups suggests that inadequate prediction of mandibular autorotation may be responsible.
Max : Rimax ‘1‘value
significance
I.21 0.88 0.94 0.95
,:
p
signifcance
*; ~~0.01
is marked
**
LIE
.
.
Emm.
Training Training and experience will affect the accuracy of both the prediction and the surgical procedure. Kvam and Krogstad (1969) showed that training and experience with cephalometric techniques will improve accuracy. while the use of rigid definitions of the landmarks used (Hixon, 1956; Baumrind & Frantz, 1971) and a ‘two pass’ measuring technique (Houston, 1983) will reduce variation in landmark identification. Experience both increases the accuracy of an operative technique (Adcll et al.? 1970; Barer ef al.: 1987) and enlarges the data base of past operations (Harradine & Birnie: 1985) allowing increasingly accurate estimations of the hard and soft tissue response. In the present study, each landmark investigated showed an expected individual and non-circular pat1971). tern of error (Baumrind and Fran& Scattcrgrams of the incisal edges from all three surgical groups (Fig. 4) indicated an even distribution about zero, though there was a small tendency for the upper incisal edge to be placed slightly behind the planned position. This observation supports the suggestion of Van Sickcls ef al. ( 1986) that the incisal edges arc valid surgical landmarks. The Le Fort 1 level ostcotomy was noted by Frcide et ul. (1987) as being particularly variable in the vertical plane. This view is not supported by this study where the greatest variation was seen in the horizontal plant. The prediction technique, the surgical procedure and the assessment of operative change, all involve inherent errors which limit our ability to measure reliably small changes. This, with the patient’s indi-
2mm. b
Fig. 4 - Scattergrams:
I
incisal edges of all surgical
groups.
vidual response to treatment will demand increasingly sophisticated research techniques to distinguish between minute changes due to treatment and the error inherent in the method.
COSCLUSION An orthognathic prediction is only as good as the surgeon’s ability to transfer it to the patient. If the landmarks of the mandible and maxilla are considered as a group, the results of this study indicate that, though there was individual variation, the means of the surgical groups studied showed no statistically significant difference between the planned postsurgical position of the jaws and the position actually achieved at surgery. Acknowledgments We wish to thank Professor M. Harris for allowing us to evaluate his patients and records at the Eastman Dental Hospital and Mr I’. Furniss for his work upon the computer program used in this study.
Surgical
References Adell. R.. Hansson.
B. 0.; Brinemark, P. I. & Brcine, U. (1970). Intra-osseous anchorapc ofdcntal prostheses. IT. Review of clinical approaches. Scur~tkmariu~~ Joztr~a/ o/‘P/crsric and Rrwn.~tructive Surgz~r~~4, 19. Barer. P. G.. Wallcn. T. R.. McNcill, R. W. & Reitzik, M. (19X7). Stability of mandibular advancement osteotomy using rigid internal fixation. Awericcm .Jourtznl ~~fOrr/zudonrics and Derztqf~zrial Orrhopwdics. 92,403. Baumrind, S. & FrantJ. R. C. (1971). The reliability ofheadfilm measurements. I Landmark identification 2 Conventional angular and linear mcasurcs. iittzericun Journnl of Orfhodonrics. 60, I I I & 505, Baumrind; S.. Miller, D. & Molthcn. R. (1976). The reliability of hcadtilm measurements. 3 Tracing superimposition. .&nrricun .Journul u/Orthodontics, 70, 6 17. Bryan; D. C.. (198’)). The accuracy of prediction in ortho_eathic surgery. MSc Report. University of London. Burstone. C. J., James, R. B.. Lcgan. H.. Murphy. G. A.. Sorton: L. A. (,lY78). Ccphalometrics for orthognathic surgery. Journal of Orul Surgety. 36, 269. Craddock. F. W. (1948). The muscles of mastication and mandibular movements. ,I’rw Zcwlr~zd h7k7/ Journal, 44,233. Dahlbcrg. G.: (1940). Statistical Methods for Medical and Biological Students. Interscience Publishers. New York. Fpkcr, B. N. & Fish. L. C.. ( 1980). Surgical superior repositioning of the maxilla: what to do with the mandible? Anzericun .Jourtzul qJ‘O~hodonri~s, 78, 164. Epkcr, B. N. L Fish, L. C. (1986). Dentofacial Deformities: lntcgrated orthodontic and surgical correction. Vols 1 and II. C. V. Mosby Co, St Louis. Frcide. H.. Kahnberg. K. E., Adcll, R. & Ridcll, A. (1987). Accuracy of cephalometric prediction in orthognathic surgery. .Journul of Oral and Musillof~z~iul Surgery. 45, 754. Grant, P. G. (1973). Biomcchanical significance of the instantaneous centre of rotation: the human temporomandibular joint. Jozrnzol ol‘Biotllrcllmzics. 6, 109. Gravch. J. F. & Bcnrics. P. MM.( 19741. The clinical sienificancc of t&in2 error in ccphalomctry. British Jozrrrral of Orrhudonrics. 1.95. Harrddine. N. W. & Birnie, D. J. ( 3985). Computcrised prediction of the results of orthognathic surgery. Journu/ of .Musi//ojr,c iczl Szzrgery, 13, 245. I lcnderson. D. (1974). The assessment and management of bony deformities of the middle and lower face. Rrirkh Journaiof Plustic Surger),. 27. 287. Henderson, L). (1976). Photoccphalometric prediction and its influence on the surgical management of symmctricdl Facial deformity. I luntarian Lecture, Royal College of Surgeons of England. llixon. E. 11. (1956). The norm concept and cephalomctrics. Awwricun Jozrrnul q/ Orrhodotzfic.c, 42, X9X. Houston, W. J. ( lY83). The analysis of errorsin orthodontic measurements. Am&-an Journul of Orrhodutztics. 83, 3X2. Houston. W. J.. Jones, I!. & James. D. R. (1987). A method of recording change in maxillary position following orthognathic surgery. Europun Jnurnul of Orrhodotztics, 9. 9. Hunt. N. P. & Rudge, S. J. (1954). l:acial profile and orthognathic surgery. British Journal yf‘Orthodotztics. II, 126.
accuracy
in orthognathic
sur_gery
349
Krogman. W. M. & Sassouni, V. (1957). A syllabus of roentgenographic crphalomctry. Philadelphia Centrc for Research in Child Growth. Kvam: E. & Krogstad. 0. (1969). Variability in tracings of lateral head plates for diagnostic orthodontic purposes. A mcthodologic study. Acru Odontologicd Sc&dinuvicu, 27, 359. Lewis. D. H. (19Xla). Basic tracing for lateral skull radioeranhs. - . Dental C$dute. b, 45. L&s. D. H. ( I98 I b). Lateral skull radiographs: using SNA and SNB. Detuul L’l,dute.8, 123. Mills, J. R. ( 1970). The application and importance of ccphalometry in orthodontic treatment. The Orthodonrisr, 2, 32. Nattcstad. A., Vedtoftc. I’. & Mosekilde. E. (1991). ‘The significance of an erroneous recording of the centrc of mandibular autorotation in orthognathic surgery. Jounzul o/ Cr~zttiotnaxillo~i~iul Surpy. 19, 254. Pospisil, 0. A. (1987). Reliability and feasibility ofprcdiction tracing in orthogathic surgery. Journul of ~ratziomuxillojirciul Surger). 15, 7Y. Posscl~. U. L. l-‘. ( 1957). Movement arcas of the mandible. .Journa/ 0fProsrhetir Iknri.slry. 7, 375. Schendcl. S. A.. Eisenfeld. J. H., Bell. W. H. & Epkcr, B. N. (1976). Superior repositioning of the maxilla: stability and soft tissue osseous relations. American Jozrrtza/ of Orrhudontirs. 70,663. Sperry. T. I’.. Steinberg, 41. J. & Gans. B. J. (19X2). Mandibular as a result of maxillary movcmcnt during autorotation impaction surgery. Atnrricun .Journul of 0rthodontic.r. 81, I 16. Thompson, J. R. (lY46). Rest position of the mandible and its significance to dental science. Journal q/the ,4nzericun Denrul Aswciuzion. 33, I5 I. Turwy. T. A. ( 1982). Simultaneous mobilisation of the maxilla and mandible: Surgical technique and results. Journul of Orul utzd ;Mrrxillofirciul Surgq~. 40, 96. Van Sickles, J. E., Larsen. A. J. & Triplett. Ii. G. (lY86). of internal Predictability of maxillary surgery: a comparison and external refcrcncc marks. Oral Szrrgq~, Oral Medicine, Orui Paiholog),. 61, 542. Willmar. K. (1974). On the Le Fort I ostcotomy: A follow-up study of 106 operated patients with maxillo&cial deformity. .ScundunuGm Journul of Plu.rtic and Recotzsrrucfive Surgery, 12, (Suppl I).
The Authors D. C. Bryan Senior S&alist in Orthodontics Oueen Elizabeth Militarv Hosuital Siadium Road . * London SE18 4011 N. P. Hunt Consultant and Senior Lecturer Eastman Dental llospital GrdvS Inn Road London WC I Correspondence
and requests
for oiTprints to D. C. Bryan
Paper rcccivcd 18 April 1992 Accepted 13 May 1993
Invited comment Surgical
accuracy
in orthognathic
surgery 19~D. C. Bryn
Authors of the article accept in their summary and throughout the Paper that there are individual variations between planned and achieved surgical results. The article concentrates only on study of the hard tissue (dental and skeletal refcrencc points)
& N P. Zlunt
planned and achieved changes after surgery. Failure to concentrate on soft tissue/profile changes is justilied by the statement that these are known. Literature is littered with numerous papers all of which demonstrated quite clearly that there is a vast