Accuracy and Reliability of Intraoral Scanners for Tooth Shade Determination in Comparisons with Intraoral Spectrophotometer: In Vitro Study

Abstract

Objective This study aimed to compare the accuracy and repeatability of shade determination using an intraoral spectrophotometer (SP) and two intraoral scanners, hypothesizing no significant differences in performance.

Materials and Methods A computer-aided design/computer-aided manufacturing-designed right upper central incisor was manufactured in multiple shades using feldspathic ceramic. Shade determination was performed using the CEREC Primescan (CP), Trios V scanners, and an intraoral SP, with multiple scans taken for each.

Statistical Analysis Measurement accuracy was evaluated using the Cochran Q test and pairwise comparisons with Bonferroni's correction. Reliability was assessed through Cronbach's α, with a significance level set at 0.05 for all tests.

Results The SP achieved 84% accuracy, while the CP and 3Shape Trios V (T5) recorded 66 and 71%, respectively. None of the instruments reached 100% accuracy, with the SP displaying an accuracy range of 80 to 90%, and both scanners achieving between 60 and 80%. Statistically significant differences indicated that the SP outperformed the scanners (p < 0.05). False shade readings showed shades 3M2 and 4M2 as having the highest erroneous results. Reliability scores ranged from 92% for the scanners to 94% for the SP, with a Cronbach's α coefficient of 0.839, indicating high reliability.

Conclusion Intraoral SP displayed superior accuracy over the intraoral scanners, while their reliability in shade assessment was comparable. Thus, dental SPs are preferred for precise shade matching, suggesting potential reliability issues with intraoral scanners for consistent dental shade assessment.

Keywords

accuracy - intraoral scanner - shade determination

Introduction

Dental professionals employ intraoral scanners for a variety of applications, including caries detection, creating digital impressions, orthodontic imaging, dental education, guided implant surgery, diagnosing periodontal defects, and shade matching. These devices enhance communication between dentists and laboratories, improve patient comfort, reduce chair time, and ensure the production of high-quality and accurate impressions. By capturing digital impressions of prepared teeth, the workflow for fabricating restorations is streamlined. As aesthetics remain a priority for dental practitioners, a comprehensive treatment strategy, effective communication, and a systematic approach are essential to achieving the desired aesthetic results.[1] [2] Accurately matching the color of restorative materials with adjacent natural teeth is a critical clinical step.[1] [2] [3] Tooth color can be assessed clinically through visual or instrumental methods. The visual method often involves the use of shade guides, which are commonly employed to determine tooth color. However, this approach is subjective and can vary based on factors such as the light source, viewing angle, previous visual exposure, metamerism, eye fatigue, and the experience and education of the examiner.[1] [2] [4] The VITA Classic shade guide (VITA Zahnfabrik, Bad Säckingen, Germany) is one of the most commonly used tools and is formulated based on natural tooth color, although its color distribution is not uniform. The VITA 3D-Master (VITA Zahnfabrik) features an arrangement utilizing the CIE LCh color scale, which is reportedly more reliable than the classic guide.[3] Despite advancements, visual methods can still result in shade-matching errors due to the complexities of color perception.[4]

To address these issues, spectrophotometric shade assessment has been proposed. Research indicates that spectrophotometers (SPs) provide higher accuracy and reliability compared with visual inspection, establishing them as a recommended standard for tooth shade measurement.[3] [5] [6] For instance, the Vita Easyshade Advance 4.0 SP (VITA Zahnfabrik) showed an estimated accuracy of 92.6% and precision of 96.4% in a study conducted by Kim-Pusateri et al.[5]

Recently, some intraoral scanners have included shade determination capabilities since 2015.[5] These digital solutions are anticipated to enhance the accuracy and consistency of shade assessments by reducing human errors. However, different scanners utilize various acquisition technologies and light sources, which may affect their accuracy in shade determination.[7] Consequently, their effectiveness has not been fully established. This study seeks to compare the accuracy and repeatability of an intraoral SP with various intraoral scanners. The null hypothesis states that there is no difference in the accuracy and repeatability of shade determination between intraoral scanners and the intraoral SP.

Materials and Methods

To prepare the ceramic control shade teeth, a right-upper central incisor (tooth number 11) of the typodont model (Nissin Dental Products INC, Kyoto, Japan) was removed and scanned with CEREC Primescan (CP) AC intraoral scanner (CEREC, Dentsply Sirona, Bensheim, Germany). Using computer-aided design software, a copied tooth of the upper right central incisor was designed and subsequently manufactured using computer-aided manufacturing with machinable feldspathic ceramics (VITABLOCS Mark II, VITA Zahnfabrik), ensuring precision in shape and dimensions. The control tooth shades selected for the study were 0M1, 1M1, 1M2, 2M1, 2M2, 2M3, 3M1, 3M2, 3M3, and 4M2. Measurements of the ceramic teeth's size and shape were conducted using a vernier caliper to ensure accuracy. The samples were polished according to the manufacturer's guidelines, with each polishing step lasting 60 seconds at 300 revolutions per minute, conducted by a single operator.

Color calibration for all ceramic control shade teeth was performed using a SP (Vita Easyshade Advance 4.0, VITA Zahnfabrik), where the L* a* b* values were recorded three times per tooth to calculate color differences. The mean color difference between (∆E21) the ceramic control shade teeth (E2) and their corresponding VITABLOCS Mark II block (E1), with identical manufacturing lot numbers, was compared using a specific formula:

The color difference, ∆E21, less than or equal to 1.7 ∆E units, is considered negligible and acceptable for study standardization.[8] A single operator conducted all measurements to minimize error, with standard calibration supervised by a senior lecturer in the prosthetics department at Prince of Songkla University's Faculty of Dentistry. The color difference (∆E21) within the ceramic control shade teeth ranged from 0.33 to 0.73 units, falling below the established acceptable threshold from previous experiments. [9] [10] [11] [12]

For the shade determination process, each tooth was individually placed in a box, with the true shade labeled underneath and randomly assigned numbers from 1 to 10 by an individual who was not participating in the study to ensure unbiased record-keeping. Initially, the edentulous area in the typodont was replaced with the ceramic control tooth from box number 1. The upper right lateral to upper left lateral teeth were scanned using the CP intraoral scanner (Dentsply Sirona) from labial, palatal, and incisal perspectives. The scanning process was performed at room temperature and ambient light. The scanned impression data were displayed, and shade determination of the ceramic control shade tooth was performed using the VITA 3D master shade selection menu, with results recorded. This procedure was repeated 10 times for each control tooth shade. The same scanning process was performed on the ceramic control shade tooth number 1 using another intraoral scanner, the Trios V (3Shape, Copenhagen, Denmark), and the results were documented. Additionally, the Vita Easyshade Advance 4.0 SP (VITA Zahnfabrik) was used to determine the shade of the ceramic control shade tooth number 1 according to the manufacturer's instructions, and the findings were noted. For SP use, it was activated via the On/Off button, with its tip positioned perpendicularly to the tooth surface, near the center. Upon pressing the test button, a sound indicated completion, and the shade result was displayed. Following shade determination of the ceramic control shade tooth number 1, using all three instruments, the process was repeated for control tooth shades numbered 2 through 10, repeating the same steps. Every shade-matching process was conducted in a consistent environment by the same trained operator to ensure consistency. Both intraoral scanners and the SP were calibrated with a calibration block before each subsequent tooth measurement to ensure accuracy.

The accuracy of the instruments was evaluated by comparing the reference shade of each test tooth to the shades that were determined. The accuracy percentage was calculated by dividing the number of agreements by the total number of comparisons made. To assess the repeatability of the instruments, the repeatability percentage was calculated by dividing the total number of shade measurements in each group by the number of repeated shades. If the shade selected by the instruments matched the control shades, it was classified as “true,” whereas nonmatching shades were considered “false.” A power analysis was conducted with an α level of 5% and a β level of 20% using data from a pilot study. Categorical data were reported as frequencies (n) and percentages (%). Measurement accuracy was evaluated using the Cochran Q test, followed by pairwise comparisons with Bonferroni's correction. The reliability of instrumental measurements was assessed through Cronbach's α, with a significance level set at 0.05 for all statistical tests.[13]

Results

This study found that the SP achieved 84%, the CP 66%, and the 3Shape Trios V (T5) 71% of accuracy in shade determination. These findings have been summarized in [Table 1].

Table 1 Accuracy of shade matching by instruments

Control shade	Spectrophotometer (SP)		CEREC Primescan (CP)		Trios 5 (T5)
	T	F	T	F	T	F
0M1	8	2	6	4	7	3
1M1	9	1	7	3	7	3
1M2	8	2	6	4	8	2
2M1	9	1	8	2	7	3
2M2	8	2	7	3	7	3
2M3	9	1	6	4	8	2
3M1	8	2	7	3	7	3
3M2	8	2	6	4	6	4
3M3	9	1	7	3	8	2
4M2	8	2	6	4	6	4
Summary (%)	84	16	66	34	71	29

Note: Frequency of agreement of each control shade. If the shade selected by the instruments matched the control shades, it was classified as (T) whereas nonmatching shades were considered false (F).

The accuracy of repeated measurements for 10 different shades of ceramic control tooth specimens is illustrated in [Fig. 1]. None of the instruments achieved 100% accuracy for each shade. The SP showed an accuracy range of 80 to 90%, while the two intraoral scanners, CP and 3Shape Trios V, demonstrated an accuracy between 60 and 80%. When assessing the overall instrumental percentage of accuracy (%) for all ceramic control shade specimens ([Fig. 2]), there were statistically significant differences between the SP VITA Easyshade Advance 4.0 (84%) and the two intraoral scanners, 3Shape Trios V (71%; p = 0.015) and CP (66%; p = 0.000). The SP outperformed intraoral scanners in shade determination accuracy.

Fig. 1 Accuracy of shade matching “T” means true, and “F” means false for all ceramic control shades.

Fig. 2 Accuracy of all shade determination by all instruments (the “asterisk bracket” with different numbers of asterisk marks indicates significant differences between groups).

False shade readings of all instruments were displayed in [Table 2]. For shades 1M1, 1M2, and 4M2, each instrument recorded only one false reading (1M1 read as 1M2, 1M2 read as 1M1, and 4M2 read as 4R2.5). Other shades exhibited more than one false result. Specifically, 3M2 and 4M2 control shades had the highest false readings for both intraoral scanners, whereas 2M1 and 3M3 had the fewest false readings. All false results for the instruments shared the same level of lightness (L* parameter) and closely matched the control shades; in the Vita 3D-Master shade guide, the first digit (0–5, where 0 = lightest and 5 = darkest) corresponds to the lightness level.

Table 2 False shade reading of all instrument

Control shade	False shade reading
	Spectrophotometer (SP)	CEREC Primescan (CP)	Trios 5 (T5)
0M1	0M1, 0M2	0M2, 0M2, 0M2, 0M3	0M2, 0M2, 0M3
1M1	1M2	1M2, 1M2, 1M2	1M2, 1M2, 1M2
1M2	1M1	1M1, 1M1, 1M1, 1M1	1M1, 1M1
2M1	2R1.5	2R1.5,2R1.5,2R1.5	2R1.5, 2R1.5, 2R1.5, 2L1.5
2M2	2L1.5	2L1.5,2L1.5,2R1.5	2L1.5, 2L1.5, 2L1.5
2M3	2R2.5	2L2.5, 2L2.5, 2R2.5, 2L2.5	2R2.5, 2L2.5
3M1	3L1.5, 3M2	3M2, 3L1.5, 3L1.5	3M2, 3L1.5, 3M2
3M2	3L1.5, 3L1.5	3R1.5, 3M1, 3L1.5, 3L1.5	3M1, 3L1.5, 3L1.5, 3R1.5
3M3	3R2.5	3R2.5, 3R2.5, 3L2.5	3R2.5, 3L2.5
4M2	4R2.5, 4R2.5	4R2.5, 4R2.5, 4L2.5, 4R2.5	4R2.5, 4R2.5, 4R2.5, 4R2.5

For the assessment of reliability, a shade reading classified as true or false that occurred more than once was considered indicative of consistent performance. Each shade was measured consecutively 10 times with each instrument. Reliability assessment was conducted in two phases. Initially, identical measurements recorded across all attempts for each instrument were utilized to evaluate reliability, independent of whether the measurements corresponded to the actual tooth shade. For instance, an instrument that consistently reported the same result for shade 1M1 across all 10 measurements would achieve a reliability score of 100%, even if the reading did not match the true shade of 1M1. Any singular occurrence of either an incorrect or correct result for each control shade and instrument was excluded from the calculation of the reliability score. The overall reliability scores ranged from 92% for the two intraoral scanners to 94% for the SP. Statistical analysis of reliability was performed using Cronbach's α coefficient. No significant statistical differences were identified in the overall reliability scores ([Fig. 3]) among the devices, which ranged from 92% for both intraoral scanners to 94% for the SP, and the calculated Cronbach's α coefficient was 0.839.

Fig. 3 Repeatability score (%) of all instruments (the “asterisk bracket” with the same number of asterisk marks indicates no significant differences between groups).

Discussion

In the reliability evaluation, the null hypothesis positing that all devices possess equal reliability was accepted. However, when assessing accuracy, the null hypothesis that all devices are equally accurate was rejected for the two intraoral scanners and the SP. The SP demonstrated superior accuracy in shade matching, achieving an accuracy rate of 84%, compared with 71% for the 3Shape Trios V and 66% for the CP. These findings corroborate previous studies indicating that SPs tend to outperform intraoral scanners in terms of accuracy.[3] [14] [15] [16] [17]

Contrary to certain studies suggesting that visual assessment, intraoral scanners, and SPs are comparably effective,[18] our investigation utilized manufacturing ceramic control shades (VITA blocks Mark II) to define accuracy. This methodological difference may elucidate the discrepancies observed in this result.

Notably, the accuracy of the SP significantly surpassed that of the CP (p < 0.001) and the 3Shape Trios V (p < 0.05), which may be attributed to their differing methodologies for color evaluation. Intraoral scanners necessitate a high level of proficiency in color imaging and data processing. Although they excel in capturing tooth color and three-dimensional (3D) surface data, these devices may face challenges with color matching due to the inherent limitations of their systems.[14]

In contrast to the shade guides employed by intraoral scanners, which do not record laboratory color parameters, the VITA Easyshade Advance 4.0 utilizes a D65 illuminant and a halogen bulb to convert light into tristimulus values.[8] [14] The CP relies on video capture to generate 3D images, employing confocal microscopy and triangulation techniques, whereas the 3Shape Trios V uses optical sectioning methods similar to confocal laser scanning microscopy.[19] [20]

The accuracy of digital imaging is significantly influenced by the quality of the camera and the image processing techniques employed, as well as by the lighting conditions present during VITA Classical and 3D-Master mode evaluations. Yoon et al reported that the 3Shape Trios recorded higher a* values and lower L* and b* values compared with the ShadeEye colorimeter, indicating discrepancies between devices.[14] Additionally, factors such as the mode of the shade guide used and the environmental conditions can further impact the performance of intraoral scanners. This underscores the potential advantages of utilizing supplementary instruments to enhance shade identification accuracy. When comparing intraoral scanners to visual methods, the shade selection appears to be quite similar. Czigola et al suggest that the Trios 3 effectively utilizes a 3D-Master color system.[1] Ebeid et al found that expert visual shade matching ranges from 65 to 90%, which aligns with the results obtained from our scanners. Some studies indicate that visual and instrumental methods yield comparable outcomes,[21] although combining both approaches is believed to achieve optimal accuracy. A study by Yilmaz and Karaagaclioglu, which utilized distinct shades (A1, B1, C3, D3, A3.5 from the VITA Classic), indicated a preference for the effectiveness of visual methods over instrumental techniques.[22] However, the differences in shades employed in their study may have biased the results toward visual discernibility. The inferior accuracy of the VITA Classical system compared with the 3D-Master adds complexity to clinical accuracy contexts.[1] [3]

This study found no significant differences in reliability among the instruments tested; both intraoral scanners and SPs demonstrated high reliability rates, exceeding 92%. This finding aligns with acceptable standards (> 75%),[23] with a reliability range of 92% for scanners and 94% for the SP. The calculated Cronbach's α of 0.839 indicates strong internal consistency, exceeding the accepted threshold of 0.70.[24] While both types of devices exhibited similar reliability, SPs offered superior accuracy. The complexity involved in tooth shade selection significantly influences the visual outcomes of restorations. The variability inherent in visual methods, which can be affected by environmental conditions, eye fatigue, and subjective experiences, underscores the importance of digital systems. These systems play a vital role in enhancing communication between dentists, technicians, and patients, thereby improving the shade determination process in conjunction with human evaluation.[20]

Conclusion

Despite the limitations of this study, the findings suggest that the VITA Easyshade Advance 4.0 demonstrates superior accuracy compared with both the 3Shape Trios V and the CP. As a result, intraoral scanners may not be consistently reliable for dental shade assessment, while dental SPs prove to be well-suited for precise shade matching. However, regarding reliability, there was no significant difference observed between the two intraoral scanners and the SP, indicating that they are comparable in this aspect.

Conflict of Interest

None declared.

Acknowledgment

None.

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Artikel online veröffentlicht:
27. Januar 2025