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 Table of Contents  
ORIGINAL RESEARCH
Year : 2019  |  Volume : 11  |  Issue : 5  |  Page : 293-298

Comparison and evaluation of color stability and flexural strength of various provisional restorative materials after bleaching: An in vitro study


Department of Prosthodontics, Manipal College of Dental Sciences, MAHE, Manipal, India

Date of Web Publication24-Sep-2019

Correspondence Address:
Dr. Veena Hegde
Department of Prosthodontics, Manipal College of Dental Sciences, MAHE, Manipal 576104.
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jioh.jioh_83_19

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  Abstract 

Aims: The purpose of this in vitro study was to evaluate and compare the effect of bleaching (16% carbamide peroxide) on color stability and flexural strength of DPI Self-Cure Tooth Moulding Powder, Protemp 4, and Revotek LC. Materials and Methods: Disc-shaped 10 samples were prepared for each of the materials DPI Tooth Moulding Powder, Protemp 4, and Revotek LC with a dimension of 10-mm diameter and 4-mm height. Similarly for flexural strength, 30 rectangular samples with a dimension of 25mm × 2mm × 2mm were made for each material. All the disc-shaped samples were dipped in bleaching agent and ΔE values were recorded before bleaching after 7 and 14 days of bleaching using spectrophotometer. For flexural strength, 10 rectangular samples of each material were kept in bleaching agent for 7 days and 10 samples were kept for 14 days. Remaining 10 without bleaching acted a control group. The data were subjected to repeated measures analysis of variance test. Result: No statistically significant difference was observed between the mean values of color change before bleaching and after 14 days of bleaching for all three materials. But statistically significant difference was observed in mean values of color change among the three materials (P < 0.001). For flexural strength, statistically significant difference was observed between the mean values of flexural strength before bleaching and after 14 days of bleaching for DPI (P = 0.007) and Revotek LC (P = 0.026). Conclusion: All the three materials showed noticeable color change after 7 and 14 days of bleaching when compared with color of specimen before bleaching. Maximum color change was observed in Protemp 4 and least color change was observed in Revotek LC. Flexural strength was significantly different among the material as well as there were significant changes in flexural strength of each material after bleaching.

Keywords: Bleaching, Color Stability, Flexural Strength


How to cite this article:
Kothari P, Hegde V. Comparison and evaluation of color stability and flexural strength of various provisional restorative materials after bleaching: An in vitro study. J Int Oral Health 2019;11:293-8

How to cite this URL:
Kothari P, Hegde V. Comparison and evaluation of color stability and flexural strength of various provisional restorative materials after bleaching: An in vitro study. J Int Oral Health [serial online] 2019 [cited 2021 Oct 18];11:293-8. Available from: https://www.jioh.org/text.asp?2019/11/5/293/267718


  Introduction Top


Esthetics plays a major role in the social and mental well-being of individual. Dental esthetics can be in any form, such as replacing missing anterior tooth/teeth, correcting the space between the teeth, correcting dental protrusion or retrusion, smile correction, and bleaching discolored tooth/teeth.

Although bleaching of teeth has been known for many years (first bleaching was performed in 1877), it has become popular in recent times. Discoloration of teeth varies with etiology. It varies in appearance, distribution over the teeth, severity of discoloration, etc. Tooth bleaching can be performed extracoronally or intracoronally. The term night guard vital bleaching (NGVB) or vital tooth bleaching is used for extracoronal bleach whereas non-vital tooth bleaching is performed intracoronally in root-filled teeth. NGVB is performed to improve the esthetics in which the patient uses a custom-fitted prosthesis to apply a solution at home to his vital teeth, which lightens the color of the teeth.[1]

In some instances, this bleaching procedure must be performed while a provisional restoration is in place. One reason is that there may have been an immediate need for a crown because of the traumatic fracture of an anterior tooth and at same time adjacent vital teeth are under bleaching treatment. Another reason for a provisional restoration during the bleaching process is when extensive caries requires an immediate full-coverage temporary crown.

Ease of manipulation, esthetics, and strength are some of the important factors that a clinician takes into consideration while selecting a material. Color stability of temporary restorative material is an important factor especially when prosthesis is given for longer duration.[2] Also flexural strength becomes an important factor for selection of material in long-span temporary bridges.[3] Thus the current study was performed to evaluate and compare the effect of bleaching on color stability and flexural strength of poly(methyl methacrylate) material, Bis acrylic resin, and urethane dimethacrylate material.


  Materials and Methods Top


Total 30 disc-shaped samples (10-mm diameter and 4-mm height), 10 of each brand of provisional restorative material were fabricated using a metal mould [Figure 1] and [Figure 2]. Each material was processed according to manufacturer’s instruction and was polished with 600-Grit SiC paper.
Figure 1: Metal mould for disc-shaped sample

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Figure 2: Disc-shaped sample—labeled in bottles

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Each brand samples were recorded for color stability using spectrophotometer before bleaching, 7 days after bleaching, and 14 days after bleaching. Data recorded were grouped as dpiC0, dpiC7, dpiC14, proC1, proC7, proC14, revoC0, revoC7, and revoC14 [Table 1].
Table 1: Groups for color stability and flexural strength testing

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For applying the bleaching agent on the specimen, specific disc-shaped moulds of thermoplastic sheet of 0.5-mm thickness were made. Bleaching agent was filled in the mould and specimen was dipped into it [Figure 3]. Specimens were bleached for 10 minutes every day, and after every bleaching cycle, they were cleaned and stored in distilled water.
Figure 3: Disc-shaped samples dipped in bleaching agent

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For testing color change, specimen were kept in a custom-made mould made up of Type I gypsum product, which would provide a white background to material and would hold the specimen in a specific position under the spectrophotometer to record the color coordinates [Figure 4]. The values were recorded using Software Measure Tool 5.0 (Package Professional Profilemaker 5.0). These were digitally compared to the reference color coordinates provided by the company along with the device and readings were noted down for each coordinates.
Figure 4: Type II gypsum mould for specimen positioning

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Flexural strength was also evaluated with total 90 rectangular samples each with a dimension of 25mm × 2mm × 2mm (ISO 4049 American National Standards Institute/ADA specification no. 27) [Figure 5], 30 of each brand of provisional restorative material were fabricated and polished with 600-Grit SiC paper [Figure 6].
Figure 5: Metal mold for rectangular samples

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Figure 6: Samples for flexural strength testing

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Each brand samples were tested for flexural strength before bleaching, 7 days after bleaching, and 14 days after bleaching. Data recorded were grouped as dpiF0, dpiF7, dpiF14, proF1, proF7, proF14, revoF0, revoF7, and revoF14 [Table 1].

For applying the bleaching agent on the specimen, specific rectangular moulds were made. Bleaching agent was filled in the mould and specimen was dipped into it [Figure 7]. The specimens were subjected to a three-point bending test in Instron universal testing machine (Instron 3366, Norwood). The crosshead speed of 5mm/min and 20-mm support span was used.
Figure 7: Rectangular samples dipped in bleaching agent

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  Results Top


The data were subjected to repeated measure analysis of variance (ANOVA) and post hoc Tukey test for statistical analysis using statistical package SPSS version 22. When analyzed for color change within a material, there were no statistically significant difference observed between the mean values of color change before bleaching, 7 days after bleaching, and 14 days after bleaching for DPI (df = 2, confidence interval [CI] = 95, P = 0.802), Protemp 4 (df = 2, CI = 95, P = 0.118), and Revotek LC (df = 2, CI = 95, P = 0.415). But analysis performed among the materials showed statistically significant difference in mean values of color change between the three materials (df = 2, CI = 95, P < 0.001) [Table 2].
Table 2: Tests within the material and between the materials for color change

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To categorize the amount of color change observed, National Bureau of Standards (NBS) unit was calculated by multiplying mean of color differences at different stages of bleaching for each material with NBS factor 0.92 (NBS Unit = ΔE × 0.92).

After 7 days of bleaching, NBS unit was 1.31 (1.43 × 0.92) for DPI, 1.82 (1.98 × 0.92) for Protemp 4, and 1.26 (1.38 × 0.92) for Revotek LC. Similarly after 14 days of bleaching, NBS unit was 2.03 (2.21 × 0.92) for DPI, 2.3 (2.51 × 0.92) for Protemp 4, and 1.95 (2.12 × 0.92) for Revotek LC [Table 3].
Table 3: Mean difference in ΔE values of all the material before bleaching, 7 days bleaching, and 14 days of bleaching

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According to NBS classification, all the changes fall under noticeable category [Table 4].
Table 4: NBS classification

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When analyzed among the materials, statistically significant difference was observed in mean values of flexural strength between the three materials (df = 2, CI = 95, P < 0.001). Also the analysis performed within the material at different time points of bleaching showed statistically significant difference between the mean values of flexural strength before bleaching, 7 days after bleaching, and 14 days after bleaching for DPI (df = 2, CI = 95, P = 0.007) and Revotek LC (df = 2, CI = 95, P = 0.026). No statistically significant difference was observed between the mean values of flexural strength at different time period of bleaching for Protemp 4 (df = 2, CI = 95, P = 0.195) [Table 5].
Table 5: Tests between materials and within material for flexural strength

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Repeated measures ANOVA with post hoc Tukey test indicated statistically significant difference in overall mean values for flexural strength between DPI and Protemp 4, between DPI and Revotek LC as well as the between Protemp 4 and Revotek LC [Table 6] and [Table 7].
Table 6: Difference in mean values of flexural strength between three materials

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Table 7: Descriptive table for mean values of flexural strength of different materials at different time points of bleaching

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  Discussion Top


The arrival of newer composite resin-based provisional restorative materials to the field of dentistry, which has been dominated by Poly methyl methacrylate (PMMA) for long, has let practitioners to have a freedom of choice. It has yet added to the conundrum of doubt regarding their performance in vivo. These variations with regard to their mechanical parameters are likely to be due to the differences in their method of polymerization, filler composition, and monomer type. Thus, provisional restorative materials need to fulfill the mechanical and esthetic demands with newer advancements.

Dental bleaching has gained popularity in this new era of esthetic demands. This procedure is noninvasive. Different concentration of gels is available commercially and differs in their time of application accordingly.[4] Carbamide peroxide is an oxidizing agent. When it comes into contact with the oral tissues and saliva, it dissociates into its constituent parts, hydrogen peroxide and urea.[5] The hydrogen peroxide further degrades into oxygen and water, and the urea breaks down into ammonia and carbon dioxide. Free radicals are generated by the bleaching agents via oxidation reaction.[6]

Although newer resin-based provisional materials provide esthetic with the advent of variety of shades and better fit, their mechanical durability is still questionable. The importance of mechanical durability adds on when the prosthesis provided is a long-span bridge. Also the esthetic aspect of the materials needs to be checked for cases where prosthesis needs to be in service for longer duration.[7] Thus, this study has aimed to evaluate the effect of 16% carbamide peroxide bleaching agent on the color stability and flexural strength of three common types of provisional restorative material.[8],[9]

In this study, color difference ΔE was calculated before immersion, after 7 days of immersion, and after 14 days of immersion in bleaching agent. It was seen that mean color difference ΔE when multiplied with NBS unit (0.92) for materials after 7 days of bleaching (ΔE7−ΔE0) was 1.31 for DPI, 1.82 for Protemp 4, and 1.26 for Revotek LC. These ΔE values for all materials after 7 days of bleaching were in noticeable range. Further, the mean color difference ΔE values for materials after 14 days of bleaching were also in noticeable range [Table 3].

Color was assessed with spectrophotometer using the CIE (Commission Internationale de l′Eclairage) L*a*b system. Spectrophotometer is basically a standardized colorimetric equipment for matching and measuring color. Change in color is expressed mathematically as the difference between the CIE L*a*b coordinates of different specimens or the same specimen at different instances relative to the CIE standard illuminant D50, against a white background.[10]

Study showed that bleaching had very mild effect on the color change as difference in mean values of color change between time period before bleaching, 7 days of bleaching, and 14 days of bleaching was very minimal. This is in accordance with study conducted by Pereddy et al.,[11] which evaluated the color stability of four provisional crown and bridge materials and concluded that Revotek LC was the most color stable provisional restorative material followed by Protemp II, Systemp, and DPI. The change in color for all the individual material differed significantly from one another.

This study also evaluated flexural strength of three materials viz. PMMA, Bis acrylic resin, and Urethane Dimethacrylate groups. In this study, flexural strength was calculated before immersion in bleaching agent, 7 days after bleaching, and 14 days after bleaching. Statistically significant difference observed between the mean values of flexural strength before bleaching, 7 days after bleaching, and 14 days after bleaching for DPI (F2,18 = 6.58, P = 0.007) and Revotek LC (F2,18 = 4.52, P = 0.026). No statistically significant difference was observed between the mean values of flexural strength at different time period of bleaching for Protemp 4 (F2,18 = 1.793, P = 0.195) [Table 5].

Repeated measure ANOVA showed statistically significant difference in flexural strength among the three materials ([Table 6], P < 0.001). Post hoc Tukey test indicated statistically significant difference in mean values for flexural strength between DPI and Protemp 4 (P < 0.001), between DPI and Revotek LC (P < 0.001) as well as the between Protemp 4 and Revotek LC (P < 0.001) [Table 6]. Also statistically significant difference was observed between the mean values of flexural strength at different bleaching times (before bleaching, 7 days of bleaching, and 14 days bleaching) for DPI ([Table 5], P = 0.007) and Revotek LC ([Table 5], P = 0.026). But no statistically significant difference was observed between the mean values of flexural strength at different bleaching times (before bleaching, 7 days of bleaching, and 14 days bleaching) for Protemp 4 ([Table 5], P = 0.195). This is in accordance with the study conducted by Jo et al.[12] to evaluate and compare the flexural strength and hardness of five resins used for the fabrication of interim fixed partial dentures. And he concluded that statistical difference was found among all the groups.


  Conclusion Top


All the three materials showed noticeable color change after 7 days and 14 days of bleaching when compared with color of specimen before bleaching. Maximum color change was observed in Protemp 4 and least color change was observed in Revotek LC. Flexural strength was significantly different among the material as well as within the material before and after 14 days of bleaching. Protemp 4 showed maximum over all flexural strength (23.915 Mpa) followed by PMMA (19.358 Mpa), and Revotek LC (12.984 Mpa). DPI Tooth Moulding Powder showed the most significant change in flexural strength after 14 days of bleaching.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Ali A, Razooki A-S In-home bleaching effect on compressive strength values of some direct restorative materials. J Int Dent Med Res 2010;3:15-8.  Back to cited text no. 1
    
2.
Kohli S, Bhatia S, Sexana K, Kalsi R, Rajeshwari K, Arora M Discolouration of polymethyl methacrylate versus Bisâ Acrylic based provisional crown and bridge dental resins: Effect of storage media and duration. Annals of Med and Health Sci Res 2017;7:195-9.  Back to cited text no. 2
    
3.
Mazaro JV, Minani LM, Zavanelli AC, Mello CC, Lemos CA Evaluation of color stability of different temporary restorative materials. Rev Odontol UNESP 2015;44:262-7.  Back to cited text no. 3
    
4.
Llena C, Esteve I, Forner L Effect of hydrogen and carbamide peroxide in bleaching, enamel morphology, and mineral composition: in vitro study. J Contemp Dent Pract 2017;18:576-82.  Back to cited text no. 4
    
5.
Nakahara T, Harada A, Yamada Y, Odashima Y, Nakamura K, Inagaki R, et al Influence of a new denture cleaning technique based on photolysis of H(2)O(2) the mechanical properties and color change of acrylic denture base resin. Dent Mater J 2013;32: 529-36.  Back to cited text no. 5
    
6.
Turker SB, Biskin T Effect of three bleaching agents on the surface properties of three different esthetic restorative materials. J Prosthet Dent 2003;89:466-73.  Back to cited text no. 6
    
7.
da Cunha LF, Fernandes AB, Mushashe AM, Correr GM, Gonzaga CC Physical properties of two bis-acryl interim materials: color stability, flexural strength and shear bond strength to flowable composite resin as add-on material. Brazilian J Oral Sci 2017; 16:1-8.  Back to cited text no. 7
    
8.
Sarac D, Sarac YS, Yuzbasioglu E, Bal S The effects of porcelain polishing systems on the color and surface texture of feldspathic porcelain. J Prosthet Dent 2006;96:122-8.  Back to cited text no. 8
    
9.
Zaid A-J. Interdisciplinary approach for full mouth rehabilitation: A case report. Asian J Pharm Clin Res 2016;9:9-11.  Back to cited text no. 9
    
10.
Uchida H, Vaidyanathan J, Viswanadhan T, Vaidyanathan TK Color stability of dental composites as a function of shade. J Prosthet Dent 1998;79:372-7.  Back to cited text no. 10
    
11.
Pereddy MR, Janani S, Gupta B, Gajula VM Comparative evaluation of hardness of four provisional restorative materials: An in vitro study. Eur J Prosthodont 2016;4:51-5.  Back to cited text no. 11
    
12.
Jo LJ, Shenoy KK, Shetty S Flexural strength and hardness of resins for interim fixed partial dentures. Indian J Dent Res 2011;22: 71-6.  Back to cited text no. 12
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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