Accurate tooth-shade analysis means the color of the ceramic crown and reference teeth must show high similarity and consistency.[1,2] Even, a well-planned preparation and well-designed ceramic crown failed esthetically due to inaccurate tooth shade selection.[3,4]
Tooth-shade selection method must fulfill the ideal requirements for accurate shade. However, ideal requirements were not discussed in the literature. Hence, the present study mentioned the ideal requirements on a subjective basis, which are as follows: (1) tooth-shade selection method must provide accurate, reliable, and consistent shade; (2) tooth-shade selection method must be free of subjective errors; (3) tooth-shade selection method does not compromise by weather conditions and background illumination; (4) tooth-shade selection method must provide simple and easy shade communication to laboratory technician; (5) tooth-shade Selection method must produce equal shade matching on flat and curved tooth surface; (6) tooth-shade selection method must provide no variation on repeatable shade matching; and (7) tooth-shade selection method must be simple, cost-effective, and maintenance free.
Tooth shade is determined by visual shade system and instrumental method of shade evaluation. Visual system is most commonly preferred by the practitioner as it is a simple method, cost-effective, and easy to communicate with laboratory technicians. However, shade matching by visual system is compromised due to subjective and physical errors. Subjective errors[4–6] are operator’s variables such as variation of shade matching between two or many operators. Weather condition and surrounding illumination are major physical errors that interfere with reflection of optical properties of natural teeth and compromise shade quality.
Instrumental method provides objective tooth-shade analysis and eliminates subjective errors of visual-shade method. Instrumental method consisted of computer-assisted device and spectrophotometer. The computer-assisted device includes colorimeter[9,10] and digital camera photography, more recently, smartphone images and noncalibrated raw mobile photos with different light conditions. Spectrophotometer works on the principle that the amount of light absorbed by color solution is directly proportional to the concentration of the solution (Beer–Lambert’s Law); thereby, it measures the color and its accuracy. Instrumental methods provide accurate and reliable shade match than visual method and spectrophotometer provides more accurate and consistent shade matching than visual and other instrumental methods of tooth shade selection. However, spectrophotometer provides a limited quantitative measurement that captures the reading one tooth at a time, inaccurate shade matching on curved tooth surface. Digital photography provides an image to laboratory technicians but lacks of shade information.
Shade selection method was considered successful only when the fabricated ceramic crown provides complete replication of reference natural tooth. None of the above-mentioned methods satisfy the all requirements tooth shade. Hence, the present study developed mobile digital application for Android smartphone to overcome the drawback of both shade selection methods. It is based on CIELAB values of color. The objective of the present study is to evaluate and compare the shade matching by mobile digital application versus Vita Easyshade spectrophotometer and Vita Three-Dimensional (3D)-Master shade guide method for metal–ceramic and all-ceramic restorations. Null hypothesis for this study was divided into two parts: (1) no difference of shade matching of metal–ceramic or all-ceramic crowns and reference maxillary central incisor would exist between the mobile digital application, Vita Easyshade spectrophotometer, and Vita 3D Master shade guide and (2) no difference of clinical agreement of shade matching of metal–ceramic or all-ceramic crowns and reference maxillary central incisor, among two skilled operators and participants would exist between mobile digital application, Vita Easyshade spectrophotometer, and Vita 3D-Master shade guide.
Materials and Methods
The study was planned as a double-blind multicenter randomized clinical trial. The trial is registered under Clinical Trial Registry-India (CTRI: Acknowledgement number: REF/2021/03/042258). The study was approved by the institutional ethical committee subjected to Maharashtra University of Health Science Nashik (MUHS/Dental/MUHS/-014442/2019 dated: March 2, 2019). The participants of the study were informed about the clinical step according to the World Medical Association Declaration of Helsinki ethical principles as revised in 2013, each participant provided written informed consent.
Thirty participants between the age group of 20–40 years were selected for the study on the basis of effect size of previously published studies. The probability of type I error (α = 0.05) and type II error (1-β = 0.20) with an estimated power of 0.80. The participant who required full-coverage restorations in one of the central incisors with adjacent central incisor untouched was the main inclusion criteria. The exclusion criteria were the presence of gingival or periodontal inflammation, existing decay, existing restorations, discoloration, and any previous bleaching with adjacent central incisor.
The participant further divided as per the full-coverage restorations and tooth-shade method used for the study, which are as follows: Group I (n = 15): full-coverage metal–ceramic restoration (n = 45 crowns, each shade method has 15 crowns). Group II (n = 15): full-coverage all-Ceramic restoration (n = 45 crowns, each shade method used 15 crowns). A total of 90 crowns were fabricated using the metal–ceramic and all-ceramic restorations. The complete study protocol is mentioned with Figure 1.
Six months prior to start of the study, centers were informed about protocol and inclusion and exclusion criteria for the participant. A total of 36 patients were screened those meet with search criteria; however, six participants were excluded due to moderate-to-severe periodontitis with gingival recession. The preparation and shade evaluation for metal–ceramic crown and all-ceramic crowns were completed at center I and center II, respectively. The computer-generated sequence (https://www.randomizer.org/) was prepared to select the participant randomly at the time of shade selection and tooth preparation. Allocation concealments were done by investigators on while paper sheet in an opaque well-sealed envelope till the date of shade selection and tooth preparation. Each participant received opaque sealed envelope with an allocation number.
Three shade selection methods were used: (1) Group 1: VITA 3D Master (VITA Zhanfabrik, Bad Sackingen Germany); (2) Group 2: mobile digital Application (DENTHUE); and (3) Group 3: Vita Easyshade spectrophotometer (VITA Zhanfabrik, Bad Sackingen Germany). Shade selection [Figure 2] was performed by investigators only, operators and participants were completely blind for shade selection. Shade selection was performed at morning hours between 10 am and 12 am. The adjacent maxillary central incisor was cleaned with mixture pumice and water to remove accumulated plaque and debris. Investigators were examined for defective color vison tests and none of them had defective vision. Investigators have taken enough time to get adjusted with surrounding lightening conditions of both centers. The participants were sited upright on the dental chair. Vita 3D Master (VITA Zhanfabrik, Bad Sackingen Germany) shade evaluated individually for each participant. Shade guide was positioned at the eye level of investigator and at the level maxillary central incisor of the participant. In Vita Easyshade spectrophotometer (VITA Easy Shade V, VITA Zhanfabrik, Bad Sackingen Germany), the manufacturer’s instructions were followed for the calibration of the device. The measuring tip (probe) was covered by anti-infection cover and placed on the middle third of maxillary central incisor at an angle of 90°. Two consecutive identical readings were recorded by VES spectrophotometer for each participant.
Mobile digital application (copyright number: 8085/2021-CO/SW under DENTHUE™)
Smartphone with installed DENTHUE mobile digital application was used for shade selection. Mobile applications have two options, either select the tooth image which was already stored in the gallery or start the camera option for a new photo of tooth image [Figure 3]; however, while taking the photo of tooth image, mobile was held perpendicular to the desired tooth surface for proper surface reading and eliminate background illumination. Mobile application crops the tooth image and scans the tooth in nine areas from misodistally to cervico-incisally. Mobile-shade analysis determined the L*A*B* values and ΔE values for the tooth along with tooth image and percentage shade in nine parts of the tooth surface.
The abutment maxillary central incisor in each participant was prepared for all ceramic and metal–ceramic crown. In all-ceramic crowns, 1.5–2 mm of tooth structure was reduced and 1-mm deep radial shoulder was placed slightly beneath the gingiva. Metal–ceramic preparation was done by removing 1.5 mm of tooth structure axially, 1 mm deep shoulder with bevel placed labially beneath the gingiva and chamfer finish line lingually. Definitive impressions were made using low viscosity vinyl polysiloxane material (Putty and wash; Aquasil ultra Dentsply Sirona) and Stock metal tray. The working cast and silicon impressions were submitted to investigators. The investigators further handover to laboratory technician with the work authorization form. Impressions and working cast of both metal ceramic and all ceramic crowns were sent to two different laboratories. For each participant, three crowns were fabricated with the selected shade. Both the metal–ceramic and all-ceramic crowns received from the laboratories were collected by an investigator for coding. The coding was done to hide the information of selected shade, which is as follows: “X” for shade selection of all-ceramic crowns (X1: Visual Shade selection, X2: Vita Easyshade Spectrophotometer, and X3 Mobile Digital application) and “Y” for metal–ceramic crowns (Y1 Visual Shade selection, Y2 Vita Easyshade Spectrophotometer, Y3 Mobile Digital Application).
Vita easyshade spectrophotometer was used to records the color difference between ceramic crowns and reference maxillary central incisor. The tip (probe) of the VITA Easyshade was projected at right angle to the labial surface of crown, as per the manufacturer’s instructions. Three consecutive readings were taken and average of three was accepted as a final ΔE.
The second shade analysis was the clinical agreement for shade matching between metal–ceramic and all-ceramic crowns and selected maxillary central incisor. The shade analysis was performed by two skilled operators and participant. To increase significance of agreement, visual analog scale (VAS) was used. VAS has been interpreted on a horizontal scale from 0 to 10 readings. 0–3 noted as accurate shade matching with adjacent central incisor, 4–5 noted as an acceptable shade match, 6–7 mismatch shade with adjacent central incisor, and 8–10 definite shade mismatch (>5 not accepted and <5 accepted). The coded crown individually presented in front of 2 skilled operators and participants, at the time cementation stage. Each operator interpreted VAS horizontal scale independently and was blinded to other operators and participants. Operators and participants submitted their VAS score to investigators for disclosure of coding of the crown. The clinical agreement among the operators and participants was evaluated with the kappa test. If the multiple agreements fall on one scale, then closet delta E value was taken for consideration as a final shade, but participant (patient) preference was considered as a final decision prior to cementation of the crown and cemented crown was taken into the account of shade match. All statistical analyses were performed using SPSS version 21 for window (SPSS 21.0 windows; SPSS Inc, Chicago, III).
ANOVA statistics and Turkey’s post hoc analysis of color difference are mentioned in Table 1 and Figure 4. Group 1 (Vita 3D) showed highest color difference (ΔE) value for all-ceramic and metal–ceramic crowns (P < 0.01). Group II (mobile digital) observed a slightly lower ΔE value than Group III (Vita Easyshade), whereas ΔE value of Group III was lower than Group II. However, Group II and III do not show a significant color difference. Pairwise comparison recorded statistically significant difference among Group 1 and the remaining two groups for all-ceramic crowns (P = 0.007 and P < 0.01) and highly significant (P < 0.001 and 0.003) metal–ceramic crowns. There is a significant color difference for Group II and III.
Clinical agreement among two operators and participant is mentioned in Table 2 and Figure 5. No agreement was reported for Vita 3D in all-ceramic crowns whereas slight agreement (13.3%) in metal–ceramic crowns. Mean kappa agreement was significant for Vita Easyshade (k = 0.581, P < 0.05) in all-ceramic crowns, whereas mobile digital was highly significant (k = 0.809, P < 0.001) in metal–ceramic crowns. Acceptable and rejected crown summary is mentioned in Figure 5. All-ceramic crowns showed a higher acceptance (<5, VAS score) rate than metal–ceramic crowns.
The present study has been developed mobile digital application for Android phone and evaluated its role in shade selection. The Vita Easyshade was used for comparison, as it is the most reliable instrument for accurate and consistent shade matching among other instrumental methods. Similarly, Vita 3D Master has chosen for comparison because it has more uniform color space, less coverage error, and more ordered color distribution than other commercially available shade guides.
Based on the observation of the result, both parts of the Null hypothesis were partially retained and partially rejected. The color difference values of Vita 3D Master were highest and significant for both metal–ceramic and all-ceramic crowns than the remaining two methods. However, mobile digital and Vita Easyshade methods observed no significant color difference clinically and statistically. Both methods reported a closer shade match than Vita 3D Master. VAS was used to determine clinical agreement. Although operators may have experienced in clinical shade matching, their judgment may vary while shade evaluation; therefore, VAS can be helpful as it is simple, reliable, and was found to be a valid measure for multiple readings Participant was included in shade evaluation due to increase in esthetic awareness in the current scenario. Kappa statistics was used to determine the robust agreement between operators and participants as per the graded system used by Landis etal. Clinical agreement showed moderate agreement for Vita Easyshade in all-ceramic crowns, in metal–ceramic, mobile digital observed substantial agreement, and no-slight agreement for Vita 3D Master.
The study findings experienced similar observation of previous studies which compared the instrumental method versus visual method for shade selection. Instrumental method has more accuracy than human eye, reported by the present study and more consistent with Polo etal. that spectrophotometer has a closet match on midpoint or halfway on tooth surface, which is impossible for human eye to detect. Metal–ceramic shade agreement between spectrophotometer and visual methods was reported by Paul etal. and Da Silva etal. Both studies observed higher agreement for spectrophotometer shade evaluation. Furthermore, Todorovic etal. and Ozat etal. disagree with visual shade guide system and both authors agree that instrumental method is more accurate and reliable. Similarly, in vitro agreement of all-ceramic shade matching using spectrophotometer has more accuracy than visual shade selection.[27,28] In contrast to our result, in vitro agreement shade comparison reported that visual method has higher agreement than spectrophotometer. However, agreement has questionable clinical validity since it was performed by 10 examiners, but which scale used for agreement, as per the criteria mentioned by Landies etal., was not mentioned in the study. Miyajiwala etal. stated that operator experience under standardized conditions can improve visual shade matching. In contrast recently, Bai etal. believe that visual method has high subjectivity despite experienced effort, clinical difference value was higher than instrumental method. The present study observed that ΔE value of Vita 3D (<2) was less than averaged ΔE value of clinical agreement reported by previous studies.[25,26,31] However, Ongul etal. suggested that color difference value smaller than 2 ΔE was not perceived intraorally by an observer while using visual shade guide system and that could be the reason why repeatable shade evaluation has a significant variation with visual shade guide.
An instrumental method of shade selection reported no color difference exists between Vita Easyshade and mobile application. Similarly, moderate-to-substantial agreement was experienced by both operators and participants for metal–ceramic and all-ceramic crowns. That means, shade selection performed by both methods was identical with minor difference, which was not clinically significant. However, all-ceramic group observed three crowns higher agreement for Vita Easyshade than mobile digital application, out of that two crowns showed A3.5 shade and mobile digital application does not scan A3.5 shade. Mobile digital application has technical sensitivity to judge the yellow hue between A3.5 and A4 shade; hence instead of A3.5, it shows A4 shade. Moreover, Douglus etal. experienced that A3.5 shade has more sensitivity to change in ceramic surface thickness. Apart from accurate shade selection, mobile application has several benefits such as it is simple, cost-effective, completely eliminates subjective errors, and definite control on background illumination. Mobile application scanned tooth surface from incisal to cervical and mesial to distal, in nine areas, regardless of flat or curved tooth surface. Hence, mobile application may provide similar shade matching for flat or curved tooth surfaces. However, the above-mentioned error often associated with Vita Easyshade was convex surface light reflection, noted as a “edge-loss error” effect. Since the probe tip of Vita Easyshade cannot make direct contact with curved tooth surface, particularly canine tooth (larger curvature) leads to reflection of light and incorrect shade match.[20,27] Similarly, improper positioning of probe tip leads to reduced L* value of shade matching. Furthermore, mobile application has better control on “hawthorn effect” related to laboratory technician ceramic buildup and its outcome on tooth shade, as reported by Da’silva etal. Acceptance and rejection ceramic crown analysis of the present study observed a prominent relation among laboratory ceramic buildup and final shade. Although metal–ceramic and all-ceramic work was submitted to two different experienced and well-skilled technicians, respectively, final shade variation still occurred in ceramic crowns. Accurate scale (0-3) match of ceramic crowns observed excellent esthetic with a lifelike appearance from closer distance; in addition, color, contour, surface thickness, translucency at incisal third, and surface stain simulate with reference central incisor. Rejection scale (6-10) observed improper ceramic buildup, uneven ceramic thickness, high opacity in metal–ceramic crowns, bulky crowns with uneven contours, and lack of surface characterization. Furthermore, metal–ceramic (21/45) showed high rejection than all ceramic crowns (14/45), reason probably due to mismatch of metal coping versus ceramic coping. Mobile application provides tooth image along with shade to laboratory technician and if technician downloads the mobile application, he or she can evaluate the ceramic buildup for acceptable shade match, color, and contour of ceramic crown with reference tooth.
Mobile applications related to shade selection are available on the Google Android platform, but these applications were product advertise applications developed by manufacturer of concern product. Recently, smile shade application based on IOS software with extension sensor device has been emerged for iPhone or iPad. Extension sensor device was a separate part which captured tooth image and transfer to smile shade application via Bluetooth for shade determination.
Present mobile application is a newly emerging advanced digital technique registered under “DENTHUETM” trademark for Android smartphone with no software or scanning device. Furthermore, the study observed that mobile application accomplished all the requirements of tooth shade selection. However, there are a few limitations of mobile application. Since it was performed only on a single reference maxillary central incisor, the factors of anterior esthetic rehabilitation such as shape, surface texture, contour, translucency, emergence profile at marginal area, and gingival configuration of remaining anterior teeth were not taken into the consideration. Hence, more clinical studies of anterior esthetic rehabilitation such ceramic or composite laminates, direct or indirect composite restorations, and CADCAM smile design are required to determine the role of mobile application. Furthermore, comparative studies between mobile application and computer-assisted device such as digital photography of shade matching and other commercially available shade systems are also required for better shade matching.
It has been observed from the study that Vita 3D Master shade guide reported inferior shade selection than Vita Easyshade and mobile digital application. Vita Easyshade observed marginally superior shade matching for all-ceramic crowns followed by mobile application, whereas mobile application was marginally higher than Vita Easyshade for metal–ceramic crowns. Clinically, both method has no significant difference in shade evaluation. Hence, the present study concluded that mobile digital application may indeed become a more alternative to visual shade guide and cost-efficient option for shade selection.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
The authors acknowledge the Department of Physics affiliated to Savitribai Phule University, Pune, for providing guidance and support of basic spectrophotometer during mobile digital application development. ORCID number: https://orcid. org/0000-0002-8375-4494.
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