ACCURACY OF STO PREDICTION

Introduction:

Orthognathic surgery for the correction of facial deformities and severe malocclusions has

been performed more frequently and involves a much wider range of operative procedures

than in the past. The criteria for a successful surgical outcome is not only the correction of

skeletal and dental abnormalities but also an aesthetic improvement as judged by both

patients and practitioners.

Since Tweed (1954)1 first presented his ‘diagnostic triangle’, many orthodontists including

Steiner, Holdaway and Hilgers have developed the concept of using cephalometric tracings to

establish precise treatment objectives. Holdaway (1983)2 in particular, proposed a method of

overlay prediction tracing for a patient requiring orthodontic treatment. His analysis brought

together factors such as growth increments, stability and soft tissue balance to form a

Visualised Treatment Objective (VTO).

It was Wolford (1985)3 who used the VTO for surgical-orthodontic treatment planning and

coined the term Surgical Treatment Objective (STO).

Uses of an STO: (Taylor 1998)4

Plan dental movements.

Assess need for extractions

Plan mechanics.

Plan type of surgery and nature of osteotomies.

A basis for communication

A basis for informed consenting.

A basis for splint construction.

Provides a reasonable prediction of soft tissue changes, that can provide a basis for computer

imaging.

In recent studies, Kiyaki found that 53% of female patients and 41% of male patients listed

aesthetics as a major factor in their decision to proceed with orthognathic surgery. Other

studies report that 76% to 89% of patients rate aesthetics as a moderate to major factor in

their decision to pursue treatment. Clearly a treatment prediction technique that provides

both accurate diagnostic information required for treatment planning and a realistic

simulation of the aesthetic outcome is needed to maximize the chances of patient satisfaction.

Methods of surgical outcome prediction:

The objective of treatment simulation is to allow the clinician to visualize and manipulate the

skeletal and dental structures, so to compare different treatment alternatives.

There are five general methods of visualising, planning and predicting surgical-orthodontic

treatment outcomes.

1. The first method has been in use for the past 20 years.

Acetate tracings of skeletal structures are manually repositioned over the original

cephalometric tracing to simulate the proposed surgical movements.ii

The posttreatment soft tissue outcome is established by using acceptable guidelines for the

ratio of soft to hard tissue changes.

The two major weaknesses of this technique is that:

I. Variables in soft tissue thickness, tonicity, individual responses

II. Differences in the surgeon’s manipulation will introduce uncertainties that make soft tissue

prediction more of an ‘art’ form.

III. The ‘line drawing’ produced by this approach is an inadequate means by which to portray the

proposed result to the patient.

2. Manipulation of patient photographs (cut and past) to illustrate treatment goals. iii.

Traditionally, the lateral cephlogram was traced and superimposed onto a profile picture in a

ratio of 1:1; this has been called a "photometric plan". The photograph, with the hard tissue

points marked, was then cut-up to simulate the pre-surgical orthodontic phase of incisor

decompensation. The necessary surgical movements were then undertaken; followed by the

soft tissue response to the hard tissue movements. The end results sometimes looked a bit like

a Picasso picture!

3. Computerised diagnostic and planning software that produced a soft tissue profile ‘line

drawing’ as a result of manipulation of digitised structures of lateral cephalometric

radiographs. iv,v Using any of the commercially available programmes, the clinician can

simulate surgical movements on the screen and rapidly compare different treatment options.

Hard copies can then be used as visual aids in treatment planning. This method of prediction

is no more accurate than manual predictions as the computer predictions are based on the

same guidelines and the resultant line drawing is still lacking in providing a lifelike aesthetic

representation.

4. Computerised diagnostic and planning software that integrates video images with the

patient’s lateral cephalograph to aid in planning and predicting surgical orthodontic

procedures (Videocephalometrics). Visualisation of facial changes is enhanced as is

patient/clinician communication; alternative treatment plans can be evaluated with ease, and

realistic patient expectations may be achieved. (Harradine 1985, Sarver 1988, Sinclair 1995).

5. Three-dimensional computer technology for planning and predicting orthognathic surgery.

Moss et al (1988)vi expanded on the early methods of 3-D planning by including laser

scanning to model the soft tissue response to hard tissue movements.

Two significant advantages of video imaging over other prediction techniques are:

The image facilitates communication between clinician and patient by establishing

visual treatment goals for orthodontics and surgery. By involving the patient in the decision

of treatment options, acceptance of the treatment outcome should be improved.

Valuable aid in treatment planing decisions by providing a maniputable image for the

orthodontist and surgeons to decide on the best soft tissue outcome. This technique is also

helpful on deciding the necessity of adjunctive soft tissue procedures.

Radiographic Analysis

In order to use a computer programme to plan orthognathic treatment, the radiograph needs to

be digitised prior to analysis. Two methods are described (Travess and Juggins, 2007):

1. Direct computer digitisation of the radiograph:

• The radiograph is placed onto a digitising light box

• Anatomical points are entered into computer using a cursor or electronic pen

2. Indirect computer digitisation of the radiograph:

• Image is captured (scanned image or true digital image) and stored on the computer.

• Image displayed in orthognathic programme and digitised using a cursor.

Studies have shown that the direct and indirect methods of cephalometric analysis are

comparable (Richardson, 1981; Oliver, 1991; Sarver, 1998).

There are advantages to using the indirect method:

• Digital storage of radiographs allows easy access when required

Use of magnification, alteration of brightness and contrast allow more detailed visualisation

of the image

Orthognathic Prediction Software

There are numerous programmes available for the analyses and prediction of orthognathic

treatment:

• OPAL image version 2.2

• Dolphin imaging 10

• Dentofacial Planner 8.05

• Quick Ceph Image

• Computer assisted simulation system for Orthognathic surgery (CASSOS)

There have been several studies evaluating the accuracy of digitisation and validity of

computerised prediction of surgical outcome.

Power et al. (2005) compared the accuracy of cephalometric digitisation and orthognathic

prediction of Dolphin Imaging 8 with manual tracing (the "gold standard"). Both methods

were reliable at identifying cephalometric points. Of note, manual tracing was more reliable

for SNA, SNB, SNMx and MxMd. In contrast Dolphin imaging 8 was more reliable for

UIMx and LIMd, although systematic error in the software meant that LAFH% was 4%

larger than manual tracing (this has been corrected in Dolphin Imaging 10).

Loh et al. (2001) analysed the accuracy and reliability of Quick Ceph Image software

(version 3). There was good correlation between repeated digitisation for all measurements.

The only variables to show statistically significant differences were ANB, FMA, SN-Mx1

and Wit's but only the Wit's analysis showed clinically relevant differences between the two

measurements. The authors concluded that clinicians should be cautious when using this

system; it may not be possible to achieve the planned surgical result based upon this system's

information.

CASSOS prediction of hard tissue profiles was evaluated in a retrospective analysis by Loh

and Yoe (2002). Results showed good correlation between repeated digitisation for all

measurements. The differences that were statistically significant were in angular

measurements for SNA, U1-Mx, U1-L1, U1-SN. None of the measurements demonstrated a

clinically relevant difference.

More recently CASSOS was evaluated for its validity in planning surgical correction of Class

III deformities (Jones et al., 2007). Two groups were compared, maxillary advancement and

bimaxillary surgery. For the maxillary advancement group there were statistically significant

differences in three horizontal landmarks: superior labial sulcus, labrale superius and the

labiomental fold. In the bimaxillary group only the landmark labrale superius (in the vertical

direction) showed a statistically significant difference. The authors commented that CASSOS

produced useful predictions; however there was wide interindividual variation, mainly for the

lips.

Smith et al. (2004) investigated the ability of prediction imaging software to simulate the

actual outcome of orthognathic surgery. Five programmes were compared - Dentofacial

Planner Plus, Dolphin imaging, Orthoplan, Quick Ceph Image and Vistadent. Ten difficult

vertical discrepancy cases were chosen and "retreated" with the programmes using the actual

surgical changes. Dentofacial Planner Plus was judged the best default simulation. The

authors also noted that programme choice is not only related to simulation ability but also

performance, cost, ease of use, compatibility, image and and for some practitioners the

inclusion of a practice management tool.

OPAL software (Orthodontic planning and analysis) was developed by Nigel Harradine and

David Birnie and George Chauvet in 1983. It has undergone numerous revisions since its

initial presentation. Cousley et al. (2003) investigated the accuracy of OPAL in the

calculation of the total treatment hard tissue and dental changes. Prediction of the majority of

the variables was acceptable, however there was large interindividual variation for most

measurements; prediction of Wits, MxP/MdP, LAFH and LPFH were prone to systematic

error. There was also a tendency towards over-prediction of the surgically-induced backward

mandibular rotation. A follow-on study was carried out which assessed the accuracy of

OPAL preoperative prediction in relation to immediate and long term changes in mandibular

advancement (Cousley and Grant, 2004). Overall the wafer had a limited anterior

displacement (0.1mm) but 2.1mm of bite-opening measured at the incisor level. There was

little difference in actual and predicted values for LAFH%, SNA, ANB, OJ and OB. The

most pronounced inaccuracies were in L1/MdP. The vertical skeletal measurements

(MxP/MdP, LAFH and LPFH) were significantly under-estimated in both the immediate and

long term predictions. In essence the programme underestimated the amount of backward

rotation of the mandible as it was advanced.

However, it is important to ask ourselves if the use of 2D prediction software is more useful

to clinicians than to patients and whether patients ever look at themselves in profile?

Phillips et al. (2001) investigated the effects of computerized treatment simulation on patient

expectations of orthognathic treatment. One hundred and forty-six patients requiring

combined orthodontic and orthognathic treatment were randomly allocated to two groups:

presurgical consultation with, and without, computerised treatment simulation software.

Viewing a prediction did not have a significant effect on the anticipation of social relations

and general health in the first month after surgery. Psychologically distressed patients,

whether or not they saw a simulation, expected significantly more problems in social

interaction and general health in the first month after surgery. Treatment simulation did affect

patients' overall expectations of problems in the first month after surgery and their concerns

about symptom recovery

VIDEO IMAGING vii

Does the prediction image create an unrealistic expectation of the final result?

Does sharing the image with the patient represent an implicit warranty as to the treatment

outcome?

Phillips et al (1995)1010 found that the presentation of video images appears to be a valuable

adjunct for conveying treatment options to patients, but warned that caution may be needed to

avoid elevated or unrealistic treatment expectations. Video imaging was found to heighten

patients’ expectations of improvement in self-image following treatment.

Kiyak (1991)5 showed that fewer than 45% of non-imaged patients were satisfied with their

aesthetic result.

However, Sarver et al (1988)9 found that 89% of the patients believed that the image

predictions were realistic and that desired results were achieved.

Furthermore, 83% believed that the imaging process helped them in deciding whether to have

surgery or not,

72% believed the process allowed them to take part in specific treatment decisions.

Fear that the patients expectations may be too high do not appear to be supported.

How accurate is the prediction?

There are few studies investigating the validity of methods predicting the soft tissue

outcomes after orthognathic surgery.

Pospisil (1987)viii evaluated manual acetate tracings and found 60% inaccuracy when

compared to 6-month postoperative radiographs. He stated that soft tissue profiles in 83% of

2-jaw and 40% of single jaw cases were inaccurately predicted. The magnitude and direction

of discrepancy was not reported.

Hing (1989)ix and Sinclair (1995)14 used records of patients who had mandibular

advancement surgery to investigate the accuracy of computerised soft tissue line drawings.

Sinclair et al (1995) also compared the accuracy of line drawings of patients who had

mandibular advancement with those who had both mandibular advancement and

advancement genioplasty. Sample of 56 patients from the office of one of the authors (D.

Sarver), who had completed treatment involving orthodontics and orthognathic surgery to

advance the mandible a minimum of 5mm. 41 had mandibular advancement only and 15 had

an additional advancement genioplasty. All patients were over 18 years old, white and

selected on the basis of the availability of presurgical and posttreatment lateral cephalograms

and lateral profile photographs. All records were taken with teeth together in centric

occlusion and lips in repose. By superimposing the computerized hard tissue prediction

(using Prediction Planner/Portrait imaging system) with the actual hard tissue result, it was

possible to compare and analyze the accuracy of the soft tissue outline.

To assess the accuracy of the video image predictions, the actual initial, the actual final and

the predicted final images were displayed simultaneously on the monitor. These three images

were evaluated and scored independently by an oral surgeon and an orthodontist, for the

similarity between the actual final and the predicted final images.

Actual versus predicted line drawings

The mean differences on the posttreatment soft tissue profile was small and statistically

insignificant for measures other than the lower lip. The computer predicted lip was

significantly more retrusive when compared with the E-line and a vertical through subnasale

(SNV-line). The lower lip was also predicted to be thinner than it actually was.

For 11 of the 18 measurements taken, a 2mm of greater discrepancy was found in at least

20% of the patients. Differences at the chin point were higher than would be expected from

mean changes alone. For the majority of patients the 2mm discrepancy was an

underprediction.

Actual versus predicted video images

1. Mandibular advancement only: predicted and actual images agreed most often in the upper

lip area; poorest agreement in the labiomental fold and submental areas.

2. Genioplasty group: agreement most frequent in upper and lower lip areas.

The percentage of acceptable images was higher in submental areas but lower for

labiomental fold and chin.

71% of mandibular group and 53% of genioplasty group had acceptable predictions at the

chin.

Results:

more than 20% of patients had >2mm discrepancy at lower lip and chin. Current prediction

algorithms based of ratios of averages do not reflect the variability of responses and the

interrelationships of horizontal, vertical and transverse dimensions. To improve accuracy of

computer line drawings, better data is needed for soft tissue changes that accompany vertical

and horizontal skeletal and dental changes.

all video image predictions were considered acceptable for patient education.

in all cases the actual final images were superior in aesthetics to the prediction images.

the greater the mandibular advancement and the greater the vertical change, the poorer the

lower lip prediction.

Hing used the Quick-Ceph diagnostic software programme and he found that the largest

amount of discrepancy between the computer predicted profile outline and the posttreament

radiographic tracing was in the horizontal position of the lower lip and the vertical position

of soft tissue Pogonion.

predicted position of lower lip was more anterior

predicted position of soft tissue pogonion was more superior

Konstiantos et al (1994)x investigated the accuracy of computer predictions of patients who

had LeFort 1 osteotomy, using the Dentofacial Planner imaging system.

nasal tip (pronasale) and nasal base (subnasale) were more posterior on the prediction

position of lower lip was more retrusive on the prediction

Upton et al (1997) evaluated the accuracy of soft tissue profile ‘line drawings’ predicted by

Quick-Ceph in combined maxillary and mandibular orthognathic surgery procedures. In this

study preoperative and posttreament lateral cephalographs of 40 white patients (10 males, 30

females) who had undergone LF1 and BSSO advancement with or without genioplasty were

used. 45 hard and soft tissue landmarks were digitised for each readiograph. Results

indicated variability among several of the landmark positions when comparing prediction

tracings with posttreament radiographs, with more variability in vertical measurements than

in horizontal or angular measurements. This current study revealed more measurements that

were statistically significantly different from posttreatment tracings than did previous validity

studies. One explanation may be that in this study patients had 2-jaw surgery whereas other

study samples had only single jaw procedures. Other reasons include the different soft and

hard tissue ratios used in different software packages and different statistical methods

employed. The Quick-Ceph programme uses soft and hard tissue ratios published by

Wolford (1985)3 and Epker and Fish (1986)xi.

amount and direction of soft tissue changes differed between predicted and actual tracings

most differences were in the horizontal and vertical positions of the lower lip

lower lip was predicted to be more inferior, shorter and more protrusive

upper lip was predicted to be shorter

soft tissue pogonion was predicted to be more inferior

Gerbo (1997)xii in a retrospective study of the accuracy of a prediction algorithm from Quick-

Ceph, digitised lateral cephalographs of 35 adult patients. Results showed good correlation

between repeated digitisation of all variables except soft tissue B point and the E-plane.

Comparison of predicted and actual changes showed that all differences were less than

1.8mm or 3.1 degrees. 10 of the 16 measurments did not differ significantly and were judged

to be within clinically acceptable limits.

Can the surgeon actually produce the suggested outcome?

Donatsky et al (1997)xiii applied a computerised cephalometric, orthognathic surgical

programme (TIOPS) in simulation, treatment planning and postsurgical records, to assess

precision and stability of bimaxillary surgery. This prospective study included 40

consecutive patients requiring maxillary superior repositioning combined with mandibular

advancement or setback. All were managed with rigid wire fixation. Planned, 5-week

postsurgical and 1-year postsurgical cephalometric positions were compared.

In mandibular advancement group:

anterior maxilla was placed too far superiorly, with an inaccuracy of 0.4mm. Posterior

maxilla and anterior mandible were placed in the planned positions.

Lower posteior part of mandibular ramus was placed too far anteriorly with inaccuracy of

2.0mm. However condyles were in correct positions.

In mandibular setback group:

anterior maxilla was too far superiorly and posteriorly with a vertical and horizontal

inaccuracy of 1.0mm and 0.7mm respectively.

Lower posteior part of mandibular ramus was placed too posteriorly with inaccuracy of

0.9mm. Again, condyles were in correct positions.

Stability:

1-year data showed maxilla had moved 0.3mm posteriorly in the advancement group and

0.8mm superiorly in the setback group. No significant positional changes were observed in

the mandibular ramus.

They concluded that the TIOPS progamme is useful in orthognathic surgical simulation,

planning and prediction, and also in evaluation of surgical precision and stability. The

simulated treatment plan can be transferred to model surgery and then on to surgical

procedures. The results suggest that this technique yields acceptable postoperative precision

and stability.

In a review of the current capabilities and limitations of video imaging, Grubb et al

(1996)1111 discusses the factors affecting the accuracy of video imaging. He considers the

accuracy of the predictions is dependent on three components:

accuracy of the computerized cephalometric VTO. Researchers have shown a reasonable

accuracy in the A/P plane when compared to manual tracings, and slightly poorer but still

acceptable accuracy in the vertical plane. All the software tested had problems predicting the

position of the lips, especially the morphology of the lower lip.

ability of the program to fit the facial image onto the corresponding soft tissue cephalometric

outline. All programs tested differed; an optimal system is yet to be developed.

image morphing. Sinclair (1995) reports that 70% of video images produced are accurate

enough for clinical use without any additional operator influence in blending or smoothing

the profiles. Less than 50% of images predicting the position and contour of the lower lip

showed acceptable accuracy.

Soft Tissue Profile Changes Associated with Surgical Movement

The recognition of the importance of aesthetic factors in orthognathic treatment is a very

important part of the planning process. Knowledge of the relationship between hard tissue

changes and the effect this has on the overlying soft tissues is essential when planning and

predicting facial changes.

Moss et al. (1988) noted that the various type of orthognathic procedures and the anatomical

morphology of the patient must be considered when predicting the outcome of facial surgery.

Mandibular setback procedures

The first studies on the effects of surgery on the soft tissues were associated with mandibular

reduction procedures (Knowles 1965). It was found that for each 1mm of posterior movement

of the mandible, soft tissue pogonion moved posteriorly between 0.9-1mm while the soft

tissue lip moved back 0.6-0.75mm (Shiu-Shiung et al. 1998).

Mandibular advancement:

Veltkamp et al (2002) confirmed that the direction of surgical movement and preoperative

soft tissue thickness have a definitive effect on the post-operative lower lip position. As the

mandible advances the lower lip contour straightens and the vermillion thins. The authors

confirmed that the effect of maxillary surgery in conjunction with anterior mandibular

advancement on the soft tissue contour of the lower lip is similar to an isolated single jaw

procedure.

Mobarak et al. (2001) investigated changes in soft tissue profiles following mandibular

advancement surgery. In a sample of 61 patients with retrognathic mandibles the authors

confirmed that the soft tissue chin and labio-mental fold followed their underlying skeletal

structures in a 1:1 ratio. They did however suggest that more realistic long term projection

may be achieved if ratios incorporating mean relapse values were used rather than relying on

a 1:1 relationship.

Mandibular advancement with genioplasty:

Ewing and Ross (1992) carried out a study on 31 patients investigating the soft tissue

response to mandibular advancement and genioplasty. The results showed a consistent 1:1

ratio of soft tissue to hard tissue movement at pogonion and point B; with accurate

predictions in both antero-posterior directions. When a genioplasty was added to the

advancement, however, the results became much less consistent. The mean ratio was 0.9:1

but had a variation of +/- 2.6mm which was not sufficiently accurate for predictive purposes.

After genioplasty the soft tissue pogonion moved inferiorly relative to the underlying hard

tissue pogonion. The behaviour of the lip was also variable between the two groups.

Advancement thinned the lip by an average of 1.7mm. Changes in the vertical dimension

were also more variable with a range of 4mm recorded depending on the operator. This

variation means that surgeons must assess the soft tissue reaction pertaining to their

technique.

Maxillary procedures at Le Fort I level:

There have been many studies attempting to assess the soft tissue changes that occur with Le

Fort I surgical procedures. Initial ratios proposed by Lines and Stenhauser (1974) stated that

there was a 2:3 soft tissue: hard tissue ratio in the maxilla although the number of patients

included in this study was very small.

Costa et al. (1986) investigated 25 cases of Le Fort I maxillary advancement and naso-labial

reconstruction and found a lip to osseous ratio of 0.9:1. This is a higher ratio than in other

studies but may be due to the naso-labial reconstruction process.

Stella et al. (1989) followed 21 maxillary advancement patients for at least 6 months post-

operatively and found no reliable correlations between bony advancement and soft tissue

position. However they did find that tissue changes varied with different lip thicknesses.

Hack et al. (1992) collected cephalometric data from 25 patients who underwent either a Le

Fort l or a bimaxillary procedure. They aimed to establish the long term stability and

prediction of soft tissue changes after Le Fort I surgery and found that the short term soft:

hard tissue correlations were in the range suggested by previous authors.

They concluded that soft tissue settling and maturation may take several years to complete.

Bimaxillary Procedures

Jensen at al. (1992) investigated the response of simultaneous maxillary impaction and

mandibular advancement. They suggested that the soft tissue responses seen were similar to

single jaw procedures, with the exception of changes to the naso-labial angle and the labio-

mental fold. With maxillary advancement and impaction, the upper lip advanced 90% of the

underlying hard tissue change and moved superiorly by 20% of the hard tissue movement.

The naso-labial angle changed about 60% of the rotation of the maxilla.

Shiu-Shiung et al. (1998) aimed to clarify the soft tissue changes that occur with maxillary

advancement and mandibular set back when correcting Class III malocclusions, using the V-

Y closure technique and alar-base cinch suture. In a sample of 17 patients undergoing

bimaxillary osteotomy, superimposition cephalometric analysis was carried out post-

operatively. They found similar results to previous studies in that the mandibular hard tissue

to soft tissue ratio was 1:1 at pogonion and point B. The maxillary ratios correlated less

strongly with maxillary advancement. The ratio of the superior labial sulcus and A point was

less than that of the lower lip and chin, ranging from 0.4:1 to 0.82:1.

This wide variation may be due to the modification of various cephalometric landmarks such

as ANS.

Vertical movements of the mandible showed a strong correlation in the lower lip and chin but

vertical movement of the maxilla showed a weak correlation at the level of the nasal base and

upper lip.

Advancement genioplasty

Shaughnessy et al. (2006) aimed to assess the skeletal stability of advancement genioplasty 3

years after surgery and to evaluate the predictability of soft tissue changes in 21 patients

underwent genioplasty advancement only. At 3 years the soft tissue of the chin was found to

follow the bony movement in a ratio of 0.9:1 but great individual variability was observed.

CONCLUSION:

“ In any creative endeavour, orthodontics included, one must have an idea, a mental image

of his objective.” King12 12

The integration of video imaging into the counseling of patients on aesthetics considerations

of treatment offer several advantages:

a higher level of communication

more precision in this communication

improved visualisation of individual treatment plans, resulting in greater precision in

planning a desired outcome

a template is provided for decision-making among patient, orthodontist and oral surgeon,

with greater participation by the patient

Quantitates surgical movements

allows facial planing and provided quantitative feedback as to what is required to attain a

particular treatment plan.

It is clear that surgical treament prediction methods are a valuable tool in planning and

simulating treatment objectives. From the literature it appears that manual acetate tracings

alone were more inaccurate in predicting treatment outcomes than the more advanced

technology of video imaging. Different degrees of inaccuracy are reported in different

studies assessing the validity of videocephalometrics, mainly due to different soft /hard tissue

ratios used in various software. With continued technological advancements and the

development of more accurate soft /hard tissue ratios, we can look forward to more accurate

prediction methods that facilitate greater success in orthognathic surgery and greater patient

satisfaction.

_____________________________________

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