|Year : 2022 | Volume
| Issue : 6 | Page : 841-848
Evaluation of color change before and after polymerization of laminate veneer restorations: A clinical study
O Ozisci1, HC Kucukesmen2
1 Department of Prosthodontics, Faculty of Dentistry, Başkent University, Ankara, Turkey
2 Department of Prosthodontics, Faculty of Dentistry, Süleyman Demirel University, Isparta, Turkey
|Date of Submission||14-Sep-2021|
|Date of Acceptance||28-Jan-2022|
|Date of Web Publication||16-Jun-2022|
Dr. O Ozisci
Department of Prosthodontics, Faculty of Dentistry, Başkent University, 06490, Çankaya, Ankara
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background and Aim: The purpose of this in vivo study was to investigate the effect of translucent adhesive resin cement on the final color of ceramic laminate veneer restoration before and after polymerization in intraoral conditions. Materials and Methods: This study was conducted in 92 ceramic laminate veneer restorations of 27 patients. The ceramic laminate veneer restorations in standard thickness lithium disilicate ceramic structure (IPS e.max Press HT, Ivoclar Vivadent) were cemented to the tooth with translucent light-polymerized resin cement (Choice 2 Starter Kit, Bisco). Results: It was observed a clinically noticeable color change between ΔE values before and after polymerization (ΔE >3.3). There was a statistically significant difference in b* values, ΔL value, and Δb value. Conclusion: Within the limitations of this in vivo study, the results suggest that light polymerization of the translucent resin cement (Choice 2, Bisco) used is an important factor for the final color of the restoration and should be considered during shade selection and fabrication.
Keywords: Ceramics, color, dental veneers, polymerization, resin cement
|How to cite this article:|
Ozisci O, Kucukesmen H C. Evaluation of color change before and after polymerization of laminate veneer restorations: A clinical study. Niger J Clin Pract 2022;25:841-8
|How to cite this URL:|
Ozisci O, Kucukesmen H C. Evaluation of color change before and after polymerization of laminate veneer restorations: A clinical study. Niger J Clin Pract [serial online] 2022 [cited 2022 Jul 5];25:841-8. Available from: https://www.njcponline.com/text.asp?2022/25/6/841/347611
| Introduction|| |
Ceramic veneers are one of the most favorable treatments for the conservative restoration of unaesthetic anterior teeth.,, It is possible to recreate the natural structure of the tooth by taking advantage of the improvements in ceramic systems and resin cements with different mechanical and physical properties.,
The challenges with ceramic laminate veneer restorations are to achieve maximum aesthetics, which frequently includes color change with limited preparation of the enamel which is described as 0.3 to 0.7 mm thick, and to obtain a durable bonding strength.,,, With the introduction of ceramic systems such as translucent lithium disilicate, which provides more light transmission, these ceramic systems have become more preferred in thin ceramic veneer restorations.,
The final color of ceramic veneer restorations is influenced by the ceramic fabrication technique, material, tooth structure thickness and color, shade and type of resin cement, and polymerization method., The final color of ceramic veneer restorations also depends on three main factors: the color of the tooth, thickness of the ceramic and resin cement, and ceramic system and the type of resin cement, and the interaction of these factors with each.
A wide variety of available cements are used in the cementation of ceramic restorations as they provide sufficient aesthetics, low solubility in oral environment, high bond strength to tooth structures, superior mechanical properties, and the management of the final color of ceramic restorations., After selecting the resin cement color to provide a suitable color match with the adjacent teeth, the final color of ceramic veneer restorations must remain the same after the polymerization of the resin cement. The resin luting agents shade may appear brighter after polymerization. Moreover, after polymerization, the color of some resin cements appears clinically significantly different from the shade guide color.
Color stability of cement can be influenced by several extrinsic factors, such as intensity and duration of polymerization, exposure to environmental factors, including ambient and UV irradiation, heat, water, and food colorants, and the intrinsic factors associated with their physical and chemical properties of the material.
Instrumental color analysis devices such as colorimeter and spectrophotometer offer accuracy, standardization, and mathematical expression of color. These electronic devices measure the color parameters using the Commission Internationale de l'Eclairage (International Commission on Illumination) CIE L*a*b* color space system., The perceivability of the Δ E values resulting from the CIE L*a*b* color system by the human eye is very important. In most of the studies on color, the clinically acceptable limit of color change has been accepted as 3.3 units.,
Color stability of composite resin cements depends on polymerization. Many factors such as color, thickness, opacity, polymerization type of adhesive cement, filler content, and type of light device affect the polymerization of composite resin cement. Today, these factors affecting the polymerization of composite resin cements are still being investigated in many clinical and in vitro studies. Clinical studies (in vivo) must evaluate the properties of restored materials due to some intraoral conditions that cannot be imitated in the laboratory. Although there are many in vitro studies examining intraoral conditions and polymerization effects, the absence of a similar in vivo study is of great importance in terms of reference to future studies. Although there are many in vitro studies investigating the effects of intraoral conditions and the polymerization reaction in adhesive resin cements, the fact that similar in vivo studies have not been reported is very important in terms of reference of this study to future studies. The null hypothesis of this in vivo study was that the color change before and after the polymerization of adhesive cement would not be observed, and after a certain period, intraoral conditions would not cause a color change.
| Materials and Methods|| |
This study was conducted in 92 incisors (46 central incisors and 46 lateral incisors) ceramic laminate veneer restorations of 27 patients (age range: 18–35 years; 15 females and 12 males) who applied to Süleyman Demirel University Faculty of Dentistry, Department of Prosthetic Dentistry, with aesthetic expectations, who were given an indication for laminate veneer and volunteered to participate in this study. Written information was obtained from all participants, and they signed informed consent form which was approved by the Ethical Board of the Süleyman Demirel University (no.: 2018/54). Patients with major morphological modifications like conoid teeth, fracture, diastema closure, irregular shape, and tooth position were included in this study. Participants with caries, restoration, endodontic treatment, bleaching, orthodontic treatment, and excessive coloration in their teeth to be treated were excluded from the study. Indications for laminate veneer restoration among patients participating in our study include diastema closure, conoid lateral teeth, crown fractures, correction of crown length and width, localized enamel loss due to abrasion or erosion, and the need to increase incisal length of teeth. The materials used in the study and their compositions are given in [Table 1].
|Table 1: The manufacturer and chemical composition of used ceramic material and resin cement|
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Preparation of the porcelain veneers
During the first diagnostic appointment, the color of the selected tooth was measured with a spectrophotometer (VITA Easyshade, VITA Zahnfabrik, Germany) and the unaffected portion of the teeth or adjacent or opposing teeth was used as a reference, followed by diagnostic waxing for further evaluation. From this wax-up, the silicone indexes were fabricated in order to construct the aesthetic pre-evaluative temporary (APT) method with bis-acrylic resin (Luxatemp, DMG). Once the patient accepted the mock-up, the same operator used the APT restoration as a precise guideline to prepare the tooth structure, considering that the thickness of the veneer was 0.3–0.5 mm. In this study, ceramic laminate veneer restorations in standard thickness (0.3–0.5 mm) lithium disilicate ceramic structure (IPS e.max Press HT, Ivoclar Vivadent, Schaan, Liechtenstein) were cemented to the tooth with translucent light-polymerized resin cement (Choice 2 Starter Kit, Bisco, Schaumburg, IL, USA). Preparation for laminate veneers was achieved at a depth of 0.3–0.5 mm guided by depth cut marks. Tapered round-ended diamond chamfer burs were used for uniform preparations, and at the cervical area, a shallow chamfer finish line was created epi- or supragingival to maintain good periodontal health. A final impression was made in a custom tray, using heavy-body and light-body addition silicone impression material (Elite HD + Putty Soft, Elite HD + Light Body, Zhermack, Italy), by putty-wash technique. One dental technician fabricated ceramic veneers using lithium disilicate ceramic structure (IPS e.max Press HT, Ivoclar Vivadent, Schaan, Liechtenstein). The restoration thicknesses of the prepared standard thickness (0.3–0.5 mm) ceramic laminate veneer (IPS e.max Press HT, Ivoclar Vivadent, Schaan, Liechtenstein) were controlled using a digital micrometer (Digimatic Caliper; Mitutoyo) [Figure 1].
|Figure 1: Determination of standard thickness (0.3–0.5 mm) ceramic laminate veneer by using a digital micrometer|
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Cementation procedure and measurement of CIELAB color coordinates
The teeth were cleaned before the trial. The quality of fit, gingival extension, and color match of the veneer were assessed. Try-in allowed contours and margins to be evaluated, and the patient requested to proceed with the final bonding procedures. Before the cementation process, while restoration was on the tooth, the color values of each restoration were measured using a spectrophotometer (VITA Easyshade, VITA Zahnfabrik, Germany) from the center side (middle third) of the facial surface of the restoration (color analysis 1). A single operator performed the color measurements in the same period (at 11:00–13:00 noon hours) and at the same dental unit [Figure 2].
|Figure 2: Spectrophotometric color measurement of ceramic laminate veneers|
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Before the cementation process, tooth surfaces were cleaned with pumice slurry, rinsed, and dried. Then, the teeth were etched with phosphoric acid (Uni-Etch, Bisco, Schaumburg, IL, USA) for 15 seconds, followed by rinsing, air-drying, and application of bonding agent (All Bond, Bisco, Schaumburg, IL, USA), gently air-dried, and light-polymerized for 10 seconds. The porcelain veneers were etched with 9.5% buffered hydrofluoric acid gel (Porcelain Etchant, Bisco, Schaumburg, IL, USA) for 20 seconds, rinsed with water, and carefully air-dried. Ceramic veneers were silanated (Bis-Silane part A and B, Bisco, Schaumburg, IL, USA), and dentin-bonding agent (porcelain bonding resin, Bisco, Schaumburg, IL, USA) was applied following manufacturer's instructions. Translucent light-polymerized resin luting cement (Choice 2, Bisco, Schaumburg, IL, USA) was used for the cementation of the porcelain laminate veneers. The restorations were seated with finger pressure of only one examiner, and before the polymerization process, measurement was taken with a spectrophotometer (VITA Easyshade, VITA Zahnfabrik, Germany) to determine the color measurement values (color analysis 2). After color measurement, the cement was polymerized with the light intensity of 480 nm and a power of 1100 mW/cm2 for 5 seconds. Then, the excess cement was removed to simulate the real intraoral conditions. The specimens were polymerized for 40 seconds on all surfaces. The finishing and polishing of the cement line were performed using flexible aluminum oxide disks (Sof-Lex XT Pop-on, 3M ESPE, St. Paul, MN, USA). After the polymerization process was completed, the tooth surface was cleaned so that there was no residual substance that could affect the color, and the color measurement values after the polymerization process were measured using a spectrophotometer (VITA Easyshade, VITA Zahnfabrik, Germany) (color analysis 3). The patient was given oral hygiene and home care instructions for the adequate care of the porcelain laminate veneers. Patients were called for follow-up 1 day (color analysis 4) and 1 month (color analysis 5) later for the control of ceramic laminate veneer restorations and color measurement.
The tooth selected for measurement was brushed for 3 minutes by the subject with toothpaste (Colgate Total, Colgate-Palmolive, İstanbul, Turkey) and a toothbrush (Oral-B Complete, Procter & Gamble, İstanbul, Turkey). The surface was wiped with clean paper for saliva and moisture before the measurement. Immediately after the cleaning procedure, the color of the tooth was measured by a spectrophotometer (VITA Easyshade, VITA Zahnfabrik, Germany). Before measurements in every volunteer, an infection control shield (VITA Easyshade Infection Control Shield, Vita Zahnfabrik, Bad Säckingen, Germany) was placed on the probe tip and the lamp was calibrated on its own white ceramic block. After calibration, the probe tip was placed in contact with and perpendicular to the middle third of the facial surface of the restorations. The color was determined on the middle third of the restorations, which is the area that best illustrates tooth shade. Measurements were taken in “tooth single” mode with a spectrophotometer (VITA Easyshade, VITA Zahnfabrik, Germany). The measurements were performed using the CIE L*a*b* system three times for each tooth, and the average was recorded.
Five color measurement times were measured with ceramic laminate veneer restorations of our volunteer patients who participated in our experimental study, and L *, a *, b * values were calculated [Table 2]. The groups given in [Table 3] were used to determine the color difference between these measurement times.
|Table 3: Groups determining the color difference between measurement times|
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Color differences (ΔE*) between the teeth of the same individual were calculated using the following formula: ΔE = [(ΔL*)2 +(Δa*)2 + (Δb*)2]½.
The degree of color difference between two objects is expressed in ΔE * units, and in the literature, there are different color change values for perceptible and acceptable thresholds under in vitro/in vivo conditions. ΔE ≤ 2.0 represents the clinically acceptable color difference limit; ΔE ≥ 3.3 represents a poor match. In this study, the ΔE of 3.3 was selected as the clinically unacceptable color difference threshold.
Statistical analysis was performed on IBM SPSS v20 (SPSS Inc., Chicago, IL, USA). Data obtained were analyzed using one-way analysis of variance (ANOVA) followed by Duncan's significant difference tests for comparisons among groups. Significance level was taken as P ≤ 0.05. Changes on color coordinates L*, a*, b* with color measurement time were compared using the related samples' Wilcoxon signed-rank test with a Bonferroni correction (level of significance P ≤ 0.003).
| Results|| |
Mean values of chromatic coordinates CIE L*, a*, b* for all incisors, as well as the central and lateral incisors separately, for different color measurement times, are shown in [Table 4]. Changes with color measurement (color analysis) time were registered for all chromatic coordinates. For the CIE L*, a*, b* coordinate, a tendency to decrease was found for the three study groups (all teeth, central incisors, and lateral incisors), with a more pronounced decrease in the central incisor group when compared to the lateral incisors.
|Table 4: Mean values of the chromatic coordinates L*, a*, and b* at different color analysis times for all teeth (A), central (C), and lateral (L) incisors|
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One-way analysis of variance (ANOVA) was used to detect the L*, a*, b* color measurement value change of the recorded measurements and the experimental groups created. Descriptive statistics of L *, a *, b *, ΔE, ΔL, Δa, Δb values, F and P values of one-way analysis of variance are given in [Table 5]. In the one-way analysis of variance, it was seen that there was no statistically significant difference between L *, a * values (p > 0.05), but there was a statistically significant difference between b * values (p ≤ 0.05). The mean b * values after 24 h were statistically significantly different from the non-cemented, before polymerization and after polymerization color measurement values (p ≤ 0.05) [Figure 3].
|Table 5: Statistical evaluation of the L*, a*, b*, ΔE, ΔL, Δa, Δb values at five different color measurement times (one-way ANOVA)|
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|Figure 3: Box plot graph of the multiple comparison test results of b* values at five different color measurement times|
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The highest ΔE value was observed in group 1, while the lowest ΔE value was observed in group 2. Visible color difference (ΔE > 3.3) was observed in Δ E values of group 1 (ΔE = 4.359) and group 3 (ΔE = 4.132). The polymerization process was observed to affect ΔE values.
In the one-way analysis of variance, it was seen that there was a statistically significant difference between ΔL experimental groups (p ≤ 0.05). There was a statistically significant difference between the mean ΔL values of the measurements in group 1 and the mean ΔL values of group 2 and group 4 measurements (p ≤ 0.05) [Figure 4]. In the one-way analysis of variance, it was seen that there was no statistically significant difference between Δ a values (p > 0.05), but there was a statistically significant difference in Δ b values (p ≤ 0.05). Although Δ a difference in all groups tended to show a more reddish color change in a positive direction, the differences obtained were not statistically significant. It was seen that Δ b color difference in all groups tended to show a more yellowish color change in the positive direction. The maximum mean Δ b color difference was observed in group 1, while the minimum mean Δ b color difference was observed in group 2 [Figure 5].
|Figure 4: Box plot graph of the multiple comparison test results of ΔL values|
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|Figure 5: Box plot graph of the multiple comparison test results of Δb values|
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| Discussion|| |
The results of this study showed that before and after the polymerization of the adhesive cement, the color coordinates were different from each other and the oral conditions had a significant effect on the color values. There were significant differences in color changes within groups. According to these results, the null hypothesis that groups did not show the statistical difference for the color change was rejected.
In dentistry, spectrophotometers have been considered the most accurate, useful, and applicable instruments for color matching, and the color is recorded in the CIELAB system. In a study in which color measurement device measured the accuracy and reliability, the reliability rate and accuracy rate of Vita Easyshade was found to be higher than other color selection devices. The Commission Internationale de l'Eclairage (CIE) defines the L * a * b * color space (CIELAB), the parameters in which color is expressed and measured, and the color difference formula as three coordinate values (L*, a*, b*). L* represents the lightness of the color, a* represents the green (negative a*) to red (positive a*) colors, and b* represents the blue (negative b*) to yellow (positive b*) chroma.,,,,,,,,
In this study, the ceramic laminate veneer restorations were prepared from IPS e.max Press HT blocks. IPS e.max Press, which is lithium disilicate glass ceramic, due to its high optical and aesthetic properties and more light transmission, has been preferred in the fabrication of thin ceramic laminate veneer restorations recently.,,, The thickness of the ceramic restoration is limited by the amount of tooth preparation and is an important factor to achieve accurate color matching. As a conservative restoration, ceramic veneers should adhere to the enamel for a durable bonding interface and longer clinical durability, so the recommended amount of preparation is 0.5–0.7 mm., The literature also reports that ceramic restorations have various opacities and therefore resin cement discoloration could be masked., In this in vivo study, to evaluate the intraoral conditions of a light-curing translucent cement, the restoration thickness was between 0.3 and 0.5 mm. With minimally invasive ceramic laminate veneer restorations, only shape modifications were intended without the need to hide the underlying substrate color.
There is no consensus in the literature on whether different colors of adhesive cement affect the final color of ceramic veneer restorations. Some studies have identified that resin composite cement color affects the final color of ceramic restorations,, while others have shown a minimal effect of the shade of a cement on the final color of a restoration, which might be instrumentally detectable but clinically not relevant.,, In this in vivo study, translucent light-cure composite resin cement was used to eliminate the effect of cement color on the final restoration color and to investigate the effects of factors, such as the polymerization reaction, and oral conditions on the final color of veneer restorations. The Δ E value between the color measurement of the ceramic laminate veneer restoration without the application of adhesive resin cement and the color measurement before polymerization after translucent light-cure composite resin cement application was determined as 4.35, and there was a clinically noticeable color change (ΔE ≥3.3). This finding was in agreement with previous authors who reported that the final color of all-ceramic restorations was affected by the shade of the resin cement used., When compared with the results of other studies, it can be thought that the most frequently used translucent resin cement among the lighter shades of resin cements shows more color change than the darker ones.
Giti et al. reported that the final color of Choice 2 translucent shade was significantly different from that in A2 and opaque shades and reported that the Δ E values were higher than the clinically acceptable threshold in all groups except for Choice 2 translucent. In the present study, a clinically detectable color change was not observed at the ΔE value (ΔE = 2.16) before and after the polymerization of the translucent Choice 2 light cure composite cement. These findings were in agreement with what was found by the previous study. This may be because the translucent resin cement allows more light to pass through, reducing the amount of residual monomer formed as a result of polymerization. Light exposure increases the conversion, and increased conversion causes higher color stability.
Küçükeşmen et al. reported that direct shade matching of resin cement beneath ceramic restoration should be performed using the polymerized material to obtain a precise shade match. Because the resin-based luting agents shade gets lighter after polymerization, the color change of resin composites after polymerization causes characteristic chromatic change, making the composite appear lighter., During the first 24 h after light polymerization, resin cement polymers present appear yellowish, because unreacted camphorquinone molecules return to their initial state, that is, yellow. In this study, it was observed that the restorations showed a statistically significant difference in the b* value during the first 24 h after polymerization, and the Δ b value after 24 h was measured as 4.99, a significantly higher value than other measurement groups. This behavior can be explained by unreacted or oxidized molecules during the polymerization process.
Various studies have shown that the color stability of resin-based composites can be affected by various extrinsic and intrinsic factors.,, In this in vivo study, the color stability of ceramic laminate veneer restorations in the oral conditions after 1 month was investigated. In this study, when the color difference of ceramic laminate veneer restorations was examined at the end of 1 month, it was observed that the Δ L value was significantly different from the Δ L value after polymerization. This change in lightness was significant 1 month after polymerization. It can be considered that resin cements tend to darken, especially with high pigment content and unreacted components.
In in vitro studies evaluating the color stability of composite resins, maximum water absorption occurs during the first 24 h. For in vivo studies, this period is the first day. For this reason, in this study, the color measurement data of the cemented ceramic laminate veneer restorations were recorded on the first day after the maximum water absorption in the mouth. Many studies on the color stability of resin cements have used accelerated aging procedures to better simulate oral conditions. However, with this accelerated aging protocol, the exact simulation of aging in the oral cavity is difficult to replicate. Therefore, more clinical studies are required, such as the current in vivo study.
This study did not compare the color stability of different resin cements and different ceramic systems. A future objective is to measure the effects of different types of resin cement on the final color of other new ceramic systems. Due to the absence of a similar in vivo study, further studies are proposed to reveal differences.
| Conclusion|| |
Within the limitation of the present in vivo study, the following conclusions were drawn: The polymerization procedure resulted in an appreciable increase in b* values, which created a more yellow shade. We observed that the ΔL and Δb values of ceramic laminate veneer restorations were significantly different after 1 month.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]