J Adv Prosthodont.  2014 Jun;6(3):185-193. 10.4047/jap.2014.6.3.185.

The reliability of an easy measuring method for abutment convergence angle with a computer-aided design (CAD) system

• Seo YJ
• Kwon TK
• Han JS
• Lee JB
• Kim SH
• Yeo IS

• KMID: 2118229
• DOI: http://doi.org/10.4047/jap.2014.6.3.185

Abstract

PURPOSE
The purpose of this study was to evaluate the intra-rater reliability and inter-rater reliability of three different methods using a drawing protractor, a digital protractor after tracing, and a CAD system.
MATERIALS AND METHODS
Twenty-four artificial abutments that had been prepared by dental students were used in this study. Three dental students measured the convergence angles by each method three times. Bland-Altman plots were applied to examine the overall reliability by comparing the traditional tracing method with a new method using the CAD system. Intraclass Correlation Coefficients (ICC) evaluated intra-rater reliability and inter-rater reliability.
RESULTS
All three methods exhibited high intra-rater and inter-rater reliability (ICC>0.80, P<.05). Measurements with the CAD system showed the highest intra-rater reliability. In addition, it showed improved inter-rater reliability compared with the traditional tracing methods.
CONCLUSION
Based on the results of this study, the CAD system may be an easy and reliable tool for measuring the abutment convergence angle.

Keyword

Computer-aided design; Convergence angle; Prosthodontic tooth preparation; Validation studies; Dental abutments

MeSH Terms

Computer-Aided Design*
Dental Abutments
Humans
Students, Dental
Tooth Preparation, Prosthodontic

Figure

• 

  Fig. 1 The images provided to the raters. (A) A printed image for measuring the mesio-distal convergence angle, and (B) A printed image for measuring the bucco-lingual convergence angle by tracing or CAD.

• 

  Fig. 2 Schematic diagram of the measuring methods. (A) The occlusal convergence angle was measured based on the inclination of the cervical third (red circles). In case of the lingual surface, the end of the cingulum was determined as a reference point (blue circle). Three different methods were used to measure the occlusal convergence angles. After tracing the images following the magnification of the pictures, the abutment occlusal convergence angles were measured using a drawing protractor (B) and a digital protractor (C). (D) represents measuring by CAD on the monitor.

• 

  Fig. 3 The definition of the abutment occlusal convergence angle in this study. The occlusal convergence angle is usually selected as shown in (A). However, the angle was defined in this study as in (B), based on the inclination of the cervical third. Comparison between (A) and (B) shows that the occlusal convergence angles are different from each other, depending on the selected portion of the prepared wall. α: abutment occlusal convergence angle.

• 

  Fig. 4 The measurement of the abutment occlusal convergence angle by CAD. The two tangent lines (red solid lines) are mesio-distally established to the cervical third of the abutment. The software virtually extends the tangent lines to converge (white dashed lines) and calculates the angle between the tangent lines. Therefore, additional space, which the tracing method requires, is unnecessary.

• 

  Fig. 5 Bland-Altman plots. (A) The distribution of the bucco-lingual convergence angle differences between the measurements by CAD and drawing protractor, (B) The distribution of the mesio-distal convergence angle differences between the measurements by CAD and drawing protractor, (C) The distribution of the bucco-lingual convergence angle differences between the measurements by digital protractor and drawing protractor, and (D) The distribution of the mesio-distal convergence angle differences between the measurements by digital protractor and drawing protractor are shown. The solid lines represent the mean values of the differences between the two methods. The dashed lines are ±2s of the measured value differences between two methods. s; standard deviation.

• 

  Fig. 6 Inter-rater reliabilities of the convergence angles measured at mesio-distal direction (A), and at bucco-lingual direction (B), according to the measuring methods (n = 72). The black rods show 95% of confidence intervals. All ICCs are over 0.80, which means perfect agreement. Especially notice that the ICCs calculated for the CAD group are over 0.90 both at mesio-distal and at bucco-lingual directions.

• 

  Fig. 7 The paired t-test results for the convergence angles measured between mesio-distally and bucco-lingually. Means and standard deviation (SD) of the abutment convergence angles are shown according to the measuring methods. Data are expressed as the mean ± SD (n = 216). *P<.05.

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