[Table/Fig-12].

Various methods followed by researchers for the measurement of curve of Spee.

Authors	Method and Measurements
Marshall SD et al., [17] Ahmed I et al., [18]	Digital caliper vertically mounted on a dental surveyor used to measure the maximum depth on leveled study models. The sum of the right and left greatest perpendicular distances divided by 2 where the reference line is from the central incisors to the distal cusp tip of the most posterior tooth.
Cheon CH et al., [19]	Used computer software, 3D models and lateral cephalograms. The measurements of the curve of Spee were taken from the occlusal plane to the deepest perpendicular point to the buccal cusp tip and these distances were averaged between the right and left sides. The occlusal plane was defined as the midpoint of the centers of the right and left incisor edges as well as the distobuccal cusp tips of the right and left molars.
Dager MM et al., [20]	Measured the curve of Spee from dental casts using digital calipers. A flat plane was constructed over the incisal edges of the mandibular incisors to the mandibular first molar cusps and perpendicular distances were then measured from this plane to the most inferior aspect. This was repeated on both sides and an average taken.
Bernstein RL et al., [21]	Used lateral cephalometric radiographs to create a perpendicular for curve depth analysis, similar to methods utilizing study models.
Lie F et al., [22]	Standardized photographs of mandibular study models were used. Photographs were taken in a plane perpendicular to the occlusal plane tangent to the buccal surface of the first molar and canine and centered on the first premolar, from the left and right sides. Magnification was determined by a ruler incorporated in all the photographs. Measurements of fixed landmarks on the photographs, to determine the curve of Spee were carried out on both left and right sides.
Xu H et al., [3]	Standardized digital images of the right side of the maxillary and mandibular dental casts were made and transferred to a computer. The cusp tips of canines, premolars and molars of the maxillary and mandibular arches were recognized. The radius and the depth of the curve of Spee were calculated on the images of dental casts with the help of a computer software Occlcircle.
De Praeter J et al., [23]	Utilized photographs of study models and the creation of reference lines from the incisal edge of the central to the distal cusp tip of the first molar. This reference line served as a reference point from which perpendicular reference planes could be constructed to the lateral incisor, canine, first and second premolar and the mesio-buccal cusp of the first molar. These lines served as a means of measuring the depth of the curve.
Farella M et al., [24]	Dental casts and lateral cephalograms were used for the study. Second-order quadratic interpolation of buccal cusp tips obtained from lateral digital photographs of the teeth were used to determine the extent of concavity of the curve of Spee.
Ferrario VF et al., [6,7]	Analyzed digitized dental casts (3D method), excluding the third molars with three coordinates of cusp tips, recorded with a three-dimensional digitizer and used to derive a spherical model of the curvature of the occlusal surfaces. The radii of the left and right curves of Spee and the molar curve of Wilson were computed from the best interpolating sphere.
Braun S et al., [25]	Used study models. Measured the depth of the curve of Spee from a flat plane, which was formed by the tips of the mandibular incisors anteriorly and the distal cusp tips of the second molars. The greatest depths of both the right and left sides were measured using a Brown and sharp precision coordinate measuring machine, where the touch trigger probe has a precision of 0.006 mm.
Bishara SE et al., [26]	Used study models. The mean of perpendicular distances from the cusp tips of the canine, premolars and mesio-buccal cusp of the first molar to a reference line drawn from the incisal edge of the central incisor to the distal cusp tip of the second molar were considered for the measurement of curve of Spee.
Sondhi A et al., [27]	Used integrated data from lateral cephalometric radiographs and study models. The sum of the perpendicular lengths from cusp tips of canine, premolars and mesio-buccal cusp tip of the first molar to the occlusal plane (line joining disto-buccal cusp of the first molar and incisor) from the right side was considered.