IDEAS AND INNOVATIONS

Evaluation of a 3D Stereophotogrammetric Technique to Measure the StoneCasts of Patients With Unilateral Cleft Lip and Palate

Chiarella Sforza, M.D., Marcio De Menezes, D.D.S., Elena Bresciani, B.Sc., Ana M. Ceron-Zapata, D.D.S.,

Ana M. Lopez-Palacio, D.D.S., Myriam J. Rodriguez-Ardila, D.D.S., Lina M. Berrio-Gutierrez, D.D.S.

Objective: To assess a three-dimensional stereophotogrammetric method for palatal castdigitization of children with unilateral cleft lip and palate.

Design: As part of a collaboration between the University of Milan (Italy) and the University CESof Medellin (Colombia), 96 palatal cast models obtained from neonatal patients with unilateral cleftlip and palate were obtained and digitized using a three-dimensional stereophotogrammetricimaging system.

Main Outcome Measures: Three-dimensional measurements (cleft width, depth, length) weremade separately for the longer and shorter cleft segments on the digital dental cast surfacebetween landmarks, previously marked. Seven linear measurements were computed. Systematicand random errors between operators’ tracings, and accuracy on geometric objects of known sizewere calculated. In addition, mean measurements from three-dimensional stereophotographswere compared statistically with those from direct anthropometry.

Results: The three-dimensional method presented good accuracy error (,0.9%) on measuringgeometric objects. No systematic errors between operators’ measurements were found (p . .05).Statistically significant differences (p , 5%) were noted for different methods (caliper versusstereophotogrammetry) for almost all distances analyzed, with mean absolute difference valuesranging between 0.22 and 3.41 mm. Therefore, rates for the technical error of measurement andrelative error magnitude were scored as moderate for Ag-Am and poor for Ag-Pg and Am-Pmdistances. Generally, caliper values were larger than three-dimensional stereophotogrammetricvalues.

Conclusions: Three-dimensional stereophotogrammetric systems have some advantages overdirect anthropometry, and therefore the method could be sufficiently precise and accurate on palatalcast digitization with unilateral cleft lip and palate. This would be useful for clinical analyses inmaxillofacial, plastic, and aesthetic surgery.

KEY WORDS: cleft lip, cleft palate, three-dimensional analysis

Cleft lip and palate (CLP) represents the most frequent

congenital malformation of the head and neck. Although

the treatment of children with CLP has improved over the

years, deficient growth of the maxilla is still common. The

reasons for abnormal facial morphology in treated cleft

individuals may involve two factors: intrinsic developmen-

tal deficiency or iatrogenic factors introduced by treatment

(Oberoi et al., 2008).

Treatment of children with complete unilateral CLP

(UCLP) can be achieved with diverse protocols (LaRossa,

2000; Rohrich et al., 2000; Kulewicz and Dudkiewicz,

2010). All protocols involve various surgical techniques

with different considerations such as patient age; sequence

of lip, soft palate, and hard palate closure; and treatment

with presurgical maxillary orthopedics and orthodontics

(Kulewicz and Dudkiewicz, 2010). Several papers have

investigated craniofacial morphology in children with cleft

disorders (Prahl et al., 2001; Yamada et al., 2003; Bugaighis

et al., 2010; Gursoy et al., 2010). In particular, quantitative

analyses of palatal morphology before, during, and at the

Dr. Sforza is Professor of Human Anatomy, Facolta di Medicina e

Chirurgia, Dipartimento di Morfologia Umana e Scienze Biomediche

‘‘Citta Studi,’’ Universita degli Studi di Milano, Milano, Italy. Dr. De

Menezes is Ph.D. student–Morphological Sciences, Facolta di Medicina e

Chirurgia, Dipartimento di Morfologia Umana e Scienze Biomediche

‘‘Citta Studi,’’ Universita degli Studi di Milano, Milano, Italy. Ms.

Bresciani, Facolta di Medicina e Chirurgia, Dipartimento di Morfologia

Umana e Scienze Biomediche ‘‘Citta Studi,’’ Universita degli Studi di

Milano, Milano, Italy, and Dipartimento di Bioingegneria, Politecnico di

Milano, Milano, Italy. Dr. Ceron-Zapata is Professor, Postgraduate

Program, Pediatric Dentistry and Preventive Orthodontics, Universidad

CES, and Specialist, Pediatric Dentistry and Preventive Orthodontics,

Universidad CES, Medellın, Colombia. Dr. Lopez-Palacio is Professor,

Postgraduate Program, Pediatric Dentistry and Preventive Orthodontics,

Universidad CES, and Specialist, Comprehensive Dentistry for Children,

Universidad de Antioquia, Medellın, Colombia. Dr. Rodriguez-Ardila

and Dr. Berrio-Gutierrez are Residents, Postgraduate Program, Pediatric

Dentistry and Preventive Orthodontics, Universidad CES, Medellın,

Colombia.

Submitted September 2010; Accepted March 2011.

Address correspondence to: Prof. Chiarella Sforza, Dipartimento di

Morfologia Umana e Scienze Biomediche Citta Studi, via Mangiagalli 31,

I-20133 Milano, Italy. E-mail chiarella.sforza@unimi.it.

DOI: 10.1597/10-207

The Cleft Palate-Craniofacial Journal 49(4) pp. 477–483 July 2012’ Copyright 2012 American Cleft Palate-Craniofacial Association

477

end of the treatment are necessary to better appreciate the

actual effect of the various protocols (Prahl et al., 2001;

Yamada et al., 2003; Kulewicz and Dudkiewicz, 2010).

The palate and its three-dimensional (3D) reproductions

with stone casts are complex structures that cannot be

analyzed easily with conventional two-dimensional methods

(photographs, radiographs) (Ferrario et al., 1998; Restrepo

et al., 2008). The problem is particularly important for CLP

patients, where the quantitative assessment of the depth of

the cleft can be better done with 3D imaging methods

(Braumann et al., 1999; Baek and Son, 2006; Restrepo et al.,

2008; Boldt et al., 2009). Previous investigations used

methods like the reflex microscope (Prahl et al., 2001; Krey

et al., 2009), magnetic resonance imaging (Benacerraf et al.,

2006), or contact digitizers (Ferrario et al., 1998; Yamada et

al., 2003; Restrepo et al., 2008) to determine the 3D

characteristics of cleft palates (Baek and Son, 2006; Proff

et al., 2006). Although these methods were shown to be very

accurate and to provide clinically relevant information, they

all have several limitations, either requiring large and well-

equipped measurement setups or providing only the 3D (x, y,

z) coordinates of selected reference points, neglecting the

surface characteristics of the palate.

Currently, palatal models of patients can be scanned by

laser to obtain 3D virtual models that can be used to

perform measurements needed for treatment planning

(Baek and Son, 2006). Additionally, virtual models allow

an easier communication between clinical areas and

specialties due to the facility of sharing files. Biological

structures can be scanned also by other optical instruments,

like stereophotogrammetry, a method that is used most for

the imaging of soft tissues (de Menezes et al., 2010; Rosati

et al., 2010) but may be used efficaciously for stone casts

also (Littlefield et al., 2005).

Although 3D virtual palatal models may be an advanta-

geous tool in CLP patient analysis and planning, a necessary

prerequisite is that measurements performed on these 3D

virtual models are reliable and valid. Therefore, this study

has the aim to assess a 3D stereophotogrammetric method

for palatal cast digitization of children with UCLP. Data

obtained with the 3D method will also be compared with

conventional caliper measurements. In a first step, only

conventional measurements of selected landmarks pairs will

be made: The assessment of more complex information

(surfaces, geodesic distances, angles) will be done only afterdemonstration of the suitability of stereophotogrammetry

for simple palatal measurements.

MATERIALS AND METHODS

Experimental Design

A total of 96 palatal cast models obtained from neonatal

patients with UCLP attending the Fundacion Clınica Noel

de Medellın (Colombia) were analyzed. Palatal casts were

collected during a clinical study performed to evaluate the3D morphological effects of various treatments on the

growing segments of dental arches of patients with UCLP.

The institutional ethics committee of the University CES

approved this study.

Anatomical References (Landmarks) on Cleft Dental Casts

Before the digitization, landmarks were marked on each

palatal cast. The anatomical reference landmarks assessed

the two cleft segments separately. Landmarks were identified

according to Prahl et al. (2001) and Yamada et al. (2003)

(Table 1; Fig. 1).

Dental Cast Digitization

Using a commercial 3D stereophotogrammetry system

(VECTRA-3D; Canfield Scientific, Inc., Fairfield, NJ), the

palatal casts were digitized and the appropriate files were

analyzed using the stereophotogrammetric software (de

Menezes et al., 2010). The 3D coordinates of the selected

landmarks were obtained. Overall, the 3D stereophoto-

grammetry system has already been found to assess thecoordinates of soft tissue facial landmarks with good

precision and reproducibility, without systematic errors

among operators, calibration steps, and repeated acquisi-

tions (de Menezes et al., 2010).

TABLE 1 Reference Points

Segment Landmarks Abbreviation Description

Greater Postgingivale Pg Posterior endpoint of the alveolar crest (at the junction of the crest of the

ridge with the outline of the tuberosity)

Greater Anterior alveolar Ag Anterior endpoint of the alveolar crest (where the continuation of a line

marking the crest of the ridge turns from the oral side to the nasal side at

the anterior end of the segment)

Greater Canine Cg Crossing point of the canine groove and alveolar ridge

Greater Deep cleft Dg Deepest point of the cleft

Minor Postgingivale Pm Posterior endpoint of the alveolar crest (at the junction of the crest of the

ridge with the outline of the tuberosity)

Minor Anterior alveolar Am Anterior endpoint of the alveolar crest (where the continuation of a line

marking the crest of the ridge turns from the oral side to the nasal side at

the anterior end of the segment)

Minor Canine Cm Crossing point of the canine groove and alveolar ridge

Minor Deep cleft Dm Deepest point of the cleft

478 Cleft Palate–Craniofacial Journal, July 2012, Vol. 49 No. 4

Digital Dental Cast Measurements

Using the landmark coordinates, anterior-posterior,

transverse, and vertical linear distances were obtained as

described in Table 2. All the measurements were made with

the ‘‘point-to-point’’ distance tool of the stereophotogram-

metric software (de Menezes et al., 2010).

Digitization Error

To investigate the reproducibility of the operators’

tracings, the same landmarks were assigned and referenced

twice by the same operator (A1 and A2).

Caliper Measurements

Using the landmarks described above, the same linear

distances were measured on the palatal casts using a caliper

with a 0.05-mm precision. The obtained values were

compared with the 3D measures provided by the stereo-

photogrammetric system.

Accuracy on Objects of Known Size

To assess the accuracy of the 3D stereophotogrammetry

instrument, a set of measurements were made using objects

of known size and simple geometry (cubes and cylinders of

different dimensions). Images of the geometric objects were

taken with a measuring grid with a 1-mm resolution (Fig. 2),

and measurements were performed for linear distances (unit:

millimeter), angles (unit: degree), and areas (unit: centimeter

squared). Data were saved and analyzed using the processing

software of the 3D stereophotogrammetry instrument (de

Menezes et al., 2010; Rosati et al., 2010).

Statistical Analysis

For the assessment of system accuracy, means and

standard deviations were computed for distances, angles,

and areas calculated on the objects of known size. Accuracy

errors (AE, unit: percentage) were used to compare the

measurements with the reference values.

AE~Real value{measured value

Real value|100

For palatal cast measurements, together with the descrip-

tive statistics (mean and standard deviation), the mean

absolute difference (MAD) across each data set was

calculated. The MAD is the average of absolute differences

between the values of two sets of measurements. Paired

Student’s t tests were used to compare the systematic errors

between the replicate measurements. A p value of .05 or less

was used to assess statistical significance. The technical error

of measurement (TEM) was used to evaluate the random

error. The TEM or Dahlberg’s error is calculated as

TABLE 2 Distances Measured in All Casts

Distances (mm) Definition

Ag-Am Anterior transverse cleft gap between the

greater and the minor segments

Cg-Cm Intercanine width between the greater

and the minor cleft segments

Pg-Pm Posterior transverse distance between the

greater and the minor cleft segments

Ag-Pg Length of the greater cleft segment

Am-Pm Length of the minor cleft segment

Dm-Cm Height of the greater cleft segment

Dg-Cg Height of the minor cleft segment

FIGURE 1 Landmark position.

Sforza et al., 3D STEREOPHOTOGRAMMETRY FOR STONE CAST DIGITIZATION 479

TEM~

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiXD2=2n

s,

where D is the difference between each pair of replicate

measurements, and n is the number of pairs.

Finally, another accuracy estimator, an error magnitude

relative to the size of the measurement (REM), was

obtained by dividing the MAD by the grand mean for

that variable, represented as a percentage. Thus, smaller

percentages correspond to more precise measurements.

According to Weinberg et al. (2004), REM scores were

divided into five precision categories: Values less than 1%

were considered excellent; from 1% to 3.9%, very good;

from 4% to 6.9%, good; from 7% to 9.9%, moderate, and

those exceeding 10% were considered poor.

The same calculations (MAD, TEM, and REM) and

statistical tests (paired Student’s t tests) were made to

compare linear distances obtained by stereophotogramme-

try and by caliper.

RESULTS

Objects of Known Size

Table 3 reports the measurements obtained on the

objects of known size for linear distances, angles, and

areas. The differences between measurements obtained on

the geometric objects were quite low and were nearly

similar to the resolution of the grid. Thus, except for small

round objects (with an error of 1.21%), the AE when

measuring geometric objects was lower than 0.9%.

Digitization Error

No systematic errors between measurements obtained on

two different occasions by the same operator (A1 and A2)

were found (Table 4; all p values from the paired Student’s

t tests were larger than .05). All mean differences were

lower than 0.2 mm, with MADs ranging between 0.05 mm

(Dg-Cg distance) and 0.32 mm (Cg-Cm distance). Accord-

ingly, the lowest TEM was found for the Dg-Cg, Ag-Pg,

and Am-Pm distances, and the largest, for Cg-Cm. Lower

TEM values correspond to more repeatable measurements:

The random error was lower than 0.7 mm for all distances.

According to the ranking described by Weinberg et al.

(2004), all REM values were considered excellent or to have

very good precision.

Palatal Measurements: Caliper Versus

Stereophotogrammetry

In Table 5, data obtained by two different methods

(caliper versus stereophotogrammetry) were compared. For

all distances, except for Cg-Cm distances, significant

systematic errors were found (all p values of paired Student’s

t tests were smaller than 5%), with MAD values ranging

between 0.22 and 3.41 mm. Consequently, REM rates were

scored as moderate for Ag-Am and poor for the Ag-Pg and

Am-Pm distances. Indeed, apart from the Ag-Pg and Am-

Pm distances, all TEMs had small random errors (lower than

1.06 mm). Caliper measurements were larger than 3D

stereophotogrammetry measurements for distances Pg-Pm,

Am-Pm, Dm-Cm, and Dg-Cg and lower for distances Ag-

Am and Ag-Pg (Fig. 3).

FIGURE 2 Geometric objects of known size with the measuring grid.

TABLE 3 Accuracy of the Stereophotogrammetric System

Cubic Box Small Cylindrical Object Big Cylindrical Object

Distances (mm) Angles (u) Area (cm2) Distances (mm) Angles (u) Area (cm2) Distances (mm) Angles (u) Area (cm2)

Real values 10 90 1 3 90 3 34 90 68

Measured values 10.02 89.96 1.01 3.02 88.95 2.99 34.02 89.23 67.59

Accuracy error (%) 0.20 0.04 0.10 1.21 1.17 0.28 0.05 0.86 0.60

480 Cleft Palate–Craniofacial Journal, July 2012, Vol. 49 No. 4

DISCUSSION

The variety of methods for facial analyses using 3D

reconstructions is offering a significant change in the

process of diagnosis, providing information for planning

and evaluating medical procedures and treatments (He

et al., 2010). The stereophotogrammetric systems are being

spread into the anthropometric laboratories as good-

quality instruments for morphologic facial examinations;

they have with several advantages over previous methods,

such as fast acquisition, limited cost, and lack of dangerous

procedures, thus becoming the leading tool for surface

investigations (Weinberg et al., 2004; Wong et al., 2008; de

Menezes et al., 2010).

At the same time, dental casts can be digitized using laser

scanners (Oosterkamp et al., 2006; Kecik and Enacar, 2009),

and the digital models can be used in association with the 3D

facial images, allowing the clinician to analyze the relation-

ships between soft tissues and dental arches without

submitting the subjects to radiographic scans (Rosati et al.,

2010). Independently of the technique used, the precision

and validity of the method are essential for a reliable analysis

of craniofacial deformities (Weinberg et al., 2004). The

present study showed that a commercial stereophotogram-

metric system can be used to digitize the palatal casts of

children with UCLP. There are several other anthropometric

studies that analyzed palatal cleft deformity using highly

sophisticated, computerized analytical methods (Bilwatsch

et al., 2006; Chen et al., 2010), but these methods are not

usually available outside the center that developed them.

Measurements on the geometric objects of known size

showed a good accuracy; the obtained values were close to

the real values, ranging from 0.04% to 1.21%, with a mean

accuracy error of 0.50%. Actually, the minimal differences

found might be associated with the operator digitization or

the printed grid used.

To evaluate the reproducibility of measuring 3D virtual

models, a set of linear distances was selected among those

most used for the quantitative analysis of UCLP. All

reference landmarks were marked on the palatal cast

surface prior to stereophotogrammetric imaging. Indeed,

previous investigations found that sets with marked

landmarks were associated with smaller errors than were

unmarked ones (Weinberg et al., 2004; Wong et al., 2008).

The used method was reproducible in measuring the

studied linear distances. No systematic errors were found;

on average, the differences (MAD) between repeated

measurements were lower than 0.32 mm. The MAD and

the REM are reported as an accuracy assessment, with a

simple calculation and interpretation (Weinberg et al.,

2004; Wong et al., 2008).

In analyzing the errors between the two different systems

of acquisition, systematic errors were found for all measures

(p , .05) except for Cg-Cm. This could be because the

landmarks Cg and Cm are located on the crest of the

alveolar segments in an anatomical position that allows an

‘‘easy’’ positioning of the caliper. The differences found

between the two measurement methods are in agreement

with previous studies that performed linear measurements

between reference points with digital calipers directly on cast

models (Suzuki et al., 1999; Naidu et al., 2009). In both

studies, this procedure was found to produce errors not only

during the positioning of the landmarks but also during

distance measurement and when transferring the data into

TABLE 4 Differences Between Repeated Acquisitions*

Distances

A1 A2 Comparison

Mean SD Mean SD p Value MAD TEM REM (%)

Ag-Am 7.44 3.85 7.37 3.89 .11 0.09 0.27 1.18

Cg-Cm 21.73 4.76 21.65 4.89 .45 0.32 0.67 1.49

Pg-Pm 31.62 3.10 31.67 3.05 .35 0.27 0.35 0.86

Ag-Pg 30.19 3.18 30.15 3.13 .10 0.15 0.19 0.62

Am-Pm 22.00 2.63 22.04 2.64 .13 0.07 0.19 0.33

Dm-Cm 13.84 2.25 13.74 2.22 .07 0.19 0.38 1.40

Dg-Cg 15.10 2.34 15.13 2.33 .21 0.05 0.19 0.32

* All values are mm. MAD 5 mean absolute difference; TEM 5 Technical error of measurement; REM 5 relative error magnitude. p values from paired Student’s t tests.

TABLE 5 Comparison Between Linear Distances Obtained by Stereophotogrammetry (VECTRA System) and by Caliper*

Distances

VECTRA Caliper Comparison

Mean SD Mean SD p Value MAD TEM REM (%)

Ag-Am 7.44 3.85 7.10 3.76 .00 0.56 0.49 7.66

Cg-Cm 21.73 4.76 21.85 4.85 .24 0.54 0.70 2.49

Pg-Pm 31.62 3.10 31.76 3.09 .00 0.22 0.26 0.68

Ag-Pg 30.19 3.18 27.13 4.68 .00 3.28 3.78 11.44

Am-Pm 22.00 2.63 25.60 5.17 .00 3.41 3.90 14.31

Dm-Cm 13.84 2.25 14.80 2.45 .00 0.80 1.06 5.60

Dg-Cg 15.10 2.34 15.33 2.25 .04 0.68 0.76 4.45

* All values are mm. MAD 5 mean absolute difference; TEM 5 Technical error of measurement; REM 5 relative error magnitude. p values from paired Student’s t tests.

Sforza et al., 3D STEREOPHOTOGRAMMETRY FOR STONE CAST DIGITIZATION 481

the computer (Nagy and Mommaerts, 2007). Indeed, we also

observed that the contact of the caliper tip on the palatal cast

landmark often canceled the dot, inducing imprecision in the

measurements. In a global analysis, caliper measurements of

linear distances were larger than relevant values obtained by

3D stereophotogrammetry.

Considering the MAD computed between the two

different methods, on most occasions the values were lower

than 0.8 mm; hence, almost all measurements seemed to

have a good accuracy. A different trend was found for the

anterior-posterior distances Ag-Pg and Am-Pm, which had

MADs of 3.28 and 3.41 mm, respectively. Actually, these

same distances, followed by Ag-Am, showed moderate and

poor scores, respectively, according to the classification

used by Weinberg et al. (2004). The REM analysis was

important because it offered an estimate of the relative

magnitude of errors independently of the absolute dimen-

sions (Weinberg et al., 2004). Both anterior-posterior

distances showed very large relative errors, which prevent

the use of caliper in clinical practice or research. All the

other linear distances had TEM values lower than 1.06 mm.

The largest reproducibility was found for the distance Pg-

Pm, with a TEM of 0.22 mm. However, the distances Ag-

Pg and Am-Pm showed somewhat larger errors. It could be

presumed that a large inaccuracy during the positioning of

the caliper tip might be due to the point location: Ag and

Am are cleft-edge points of the alveolar segments, located

near the deformities.

CONCLUSION

Measurements recorded by the 3D stereophotogram-

metric system appear to be sufficiently accurate and reliable

for assessing stone casts of newborn patients with UCLP.

The 3D stereophotogrammetric systems have several

advantages over direct anthropometry and gradually are

becoming more affordable, replacing classical methods to

quantify surface topography. The present study found that

the method could, therefore, be useful for clinical analyses

in maxillofacial, plastic, and aesthetic surgery.

Further investigations will assess more complex palatal

measurements and structural information (surface areas

and curvature, geodesic distances and angles) starting fromthe images recorded by the 3D stereophotogrammetric

system.

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