Korean J Orthod.  2016 Nov;46(6):356-363. 10.4041/kjod.2016.46.6.356.

Reference points suitable for evaluation of the additional arch length required for leveling the curve of Spee

• Cho YH
• Lim SH
• Gang SN

• KMID: 2426679
• DOI: http://doi.org/10.4041/kjod.2016.46.6.356

Abstract

OBJECTIVE
The additional arch length required for leveling (AALL) the curve of Spee (COS) can be estimated by subtracting the two-dimensional (2D) arch circumference, which is the projection of the three-dimensional (3D) arch circumference onto the occlusal plane, from the 3D arch circumference, which represents the arch length after leveling the COS. The purpose of this study was to determine whether the cusp tips or proximal maximum convexities are more appropriate reference points for estimating the AALL.
METHODS
Sixteen model setups of the mandibular arch with COS depths ranging from 0 mm to 4.7 mm were constructed using digital simulation. Arch circumferences in 2D and 3D were measured from the cusp tips and proximal maximum convexities and used to calculate the AALL. The values obtained using the two reference points were compared with the paired t-test.
RESULTS
Although the 3D arch circumference should be constant regardless of the COS depth, it decreased by 3.8 mm in cusp tip measurements and by 0.4 mm in proximal maximum convexity measurements as the COS deepened to 4.7 mm. AALL values calculated using the cusp tips as reference points were significantly smaller than those calculated using the proximal maximum convexities (p = 0.002).
CONCLUSIONS
The AALL is underestimated when the cusp tips are used as measurement reference points; the AALL can be measured more accurately using the proximal maximum convexities.

Keyword

Digital models; Dental cast analysis; 3-Dimensional diagnosis and treatment planning; Curve of Spee

MeSH Terms

Dental Occlusion

Figure

• 

  Figure 1 The three-dimensional (3D) arch circumference is calculated as the sum of the 3D tooth widths, corresponding to the distances between adjacent reference points, which are shown as dots in A and B. A, 3D tooth widths measured using the cusp tip as a reference; B, 3D tooth widths measured using the proximal maximum convexity as a reference.

• 

  Figure 2 The two-dimensional (2D) arch circumference is calculated as the sum of the 2D tooth widths, which are projections of the three-dimensional tooth widths onto the occlusal plane. A, 2D tooth widths measured using the cusp tip as a reference; B, 2D tooth widths measured using the proximal maximum convexity as a reference.

• 

  Figure 3 Changes in three-dimensional (3D) and two-dimensional (2D) arch circumferences according to the use of cusp tips and proximal maximum convexities as references. The 3D arch circumference decreased by 3.8 mm in the cusp tip measurements and by 0.4 mm in the proximal convexity measurements as the curve of Spee (COS) increased from 0 mm to 4.7 mm. The difference between the 3D arch circumference and 2D arch circumference is the AALL. Data are mean and standard deviation values. AALL, The amount of additional arch length required for leveling the COS.

• 

  Figure 4 Measurements of the three-dimensional (3D) tooth width minus the two-dimensional (2D) tooth width for each tooth. In the cusp tip measurements, the widths were measured between the cusp tips of adjacent teeth, while in the proximal maximum convexity measurements, they were measured between the mesial and distal maximum convexities. Mean values from 16 setup models are shown.

• 

  Figure 5 A comparison of estimations of the AALL from various studies is shown. AALL, The amount of additional arch length required for leveling the COS; COS, curve of Spee.

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