The Journal of the American Dental Association
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

J Am Dent Assoc, Vol 138, No 7, 978-984.
© 2007 American Dental Association
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Polydorou, O.
Right arrow Articles by Auschill, T. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Polydorou, O.
Right arrow Articles by Auschill, T. M.
Related Collections
Right arrow Restoratives

RESEARCH

JADA Continuing Education

The effect of at-home bleaching on the microhardness of six esthetic restorative materials

Olga Polydorou, DDS, Dr med dent, Elmar Hellwig, DDS, Dr med dent, PhD and Thorsten Mathias Auschill, DDS, Dr med dent, PhD


   ABSTRACT
TOP
 ABSTRACT
AT-HOME BLEACHING
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Background. The authors conducted an in vitro study to evaluate the effect of an at-home bleaching product on the microhardness of six restorative aterials under different surface treatments.

Methods. Four resin-based composite materials (a hybrid, flowable, microhybrid and nanohybrid), an ormocer (organic modified ceramic) material and a ceramic material were bleached with 15 percent carbamide peroxide. The authors prepared two groups of samples (polished and unpolished) (n = 7) from each resin-based composite material and the ormocer. The authors polished all of the samples in the ceramic group. Two samples from each group served as negative controls. The authors measured the microhardness of the samples before bleaching, after eight hours and 56 hours of bleaching, and 24 hours and one month after the end of bleaching.

Results. The statistical analysis showed that the at-home bleaching technique did not have a statistically significant effect on the microhardness of any of the restorative materials tested (hybrid, P = .0679; flowable, P = .5088; microhybrid, P = .0601; nanohybrid, P = .6166; ormocer, P = .2154; ceramic, P = .9943).

Conclusion. At-home bleaching with 15 percent carbamide peroxide did not cause any harmful changes to the microhardness of tooth-colored restorative materials.

Clinical Implications. Clinicians do not need to replace resin-based composite, ormocer or ceramic restorations after at-home bleaching treatment when the restorations are in posterior teeth.

Key Words: At-home bleaching; carbamide peroxide; microhardness; dental restorative materials

Abbreviations: SiO2: Silicon dioxide

Several factors may alter the appearance of smiles, including alterations in the form, texture, position and color of teeth. These alterations can occur frequently and are easily noticeable. Up until about 30 years ago, teeth exhibiting these anomalies received invasive treatments, which invariably involved prosthetic solutions. However, new esthetic treatments that do not wear out the dental structure have been introduced.1,2


   AT-HOME BLEACHING
TOP
 ABSTRACT
 AT-HOME BLEACHING
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Bleaching of vital teeth has become one of the most popular esthetic dental services offered to patients. Haywood3 reported that bleaching has been an esthetic treatment option since 1898. Bleaching is the most conservative treatment for discolored teeth compared with other treatments, such as veneers, crowns or composite bonding.4,5 A plethora of bleaching products and techniques are available. Different products and systems have appeared on the market for in-office use, containing up to 38 percent hydrogen peroxide, as well as for over-the-counter use. However, 10 to 15 percent carbamide peroxide bleaching agents are the most widely used at-home products. The literature contains several reports of their safety and effectiveness.6,7

Although at-home vital bleaching has been researched widely since 1989, it is a relatively new treatment and some doubts remain with regard to its use. Researchers have shown that at-home bleaching is a safe technique with regard to its effect on tooth structure,8–12 but some concerns remain regarding its possible effect on restorative materials.13–15

Patients commonly have restorations in posterior teeth, made of resin-based composite, amalgam or glass ionomer or another material. Questions remain concerning the need for replacement of posterior restorations after bleaching. Some factors involved in the chemical process of bleaching might accelerate the hydrolytic degradation of the composite materials described by Soderholm.16 Chemical softening resulting from bleaching might affect the durability of tooth-colored restorations.17 Softening of the composite materials by chemicals in the bleach is believed to occur in vivo, contributing to resin wear in both stress-bearing and non–stress-bearing areas.18,19 However, it is not clear if the bleaching agents exert some effect on the restorative materials that could harm the quality and longevity of these restorations.

The material used for dental restorations must have long-term durability in the mouth.20 One of the most important physical properties of restorations is surface hardness.20 The hardness of a material is a relative measure of its resistance to indentation when a specific and constant load is applied.21 In addition, surface hardness is the mechanical property used most frequently to characterize the wear resistance of materials. Microhardness has been shown to be an adequate indicator of the degree of conversion of resin-based composite. The degree of polymerization may be associated with the clinical performance of resin-based composite materials.22 Changes in hardness may reflect the curing stage of a material and the presence of an ongoing setting reaction or maturity of the restorative material.23

Studies that evaluated the interaction between bleaching and the microhardness of restorative materials have reported conflicting results.1,2,24–28 Some studies have shown that resin-based composites are unaffected by bleaching agents.2,28 Bailey and Swift24 found that the microhardness of hybrid and microfilled resin-based composite materials decreased after bleaching. Turker and Biskin25 reported that exposure (eight hours per day for four weeks) to a 16 percent carbamide peroxide (Nite White, Discus Dental, Culver City, Calif.) produced an increase in mean microhardness for a microfilled resin-based composite material, while the same exposure to two 10 percent carbamide peroxide bleaching gels (Opalescence, Ultradent Products, South Jordan, Utah, and Rembrandt, Den-Mat, Santa Maria, Calif. [now manufactured by Personal Products, a division of McNeil-PPC, Skillman, N.J.]) resulted in a decrease in microhardness.

The conflicting results of the data published to date and the large number of restorative materials that are introduced into the market each year are further reasons for more research on the subject.

Therefore, we conducted an in vitro study to evaluate the effect of at-home bleaching on the microhardness of six dental restorative materials, under different surface treatments.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 AT-HOME BLEACHING
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
We selected for this study four resin-based composite materials, an ormocer (organic modified ceramic) material and a ceramic material, which represent the commonly used types of esthetic restorative materials. Carbamide peroxide (Opalescence PF 15%, Ultradent Products) was the bleaching agent, which is the most common material used for at-home bleaching. Table 1Go lists the materials tested.


View this table:
[in this window]
[in a new window]

  		TABLE 1 Materials tested.

 
To prepare the samples, we used the A3 color (Vitapan Classic, VITA, Bad Säckingen, Germany) or the color corresponding to A3 for each material. We used transparent thermoforming disks that were 2 millimeters thick to produce the resin-based composite and ormocer samples. We drilled 4.5-mm–diameter holes into the disks and positioned the disks on a transparent plastic matrix strip lying on a glass plate. We then filled the holes with the restorative materials. The samples were built up in a single 2-mm thick increment. After inserting the materials into the disks, we placed a transparent plastic matrix strip over them and a glass slide on top of the strip to flatten the surface. In this way, the flattened upper surface of the samples was parallel to the flat lower surface. We light-cured each sample for 40 seconds with a halogen curing light (Elipar Highlight, 3M ESPE, Seefeld Germany).

We produced the ceramic samples from Vitablocs Mark II for CEREC (VITA) by using the CEREC 3D system (Sirona Dental Systems GmbH, Bensheim, Germany). We cut these samples in the dimensions described above.

In all, we produced 77 samples, consisting of 14 samples each of the four resin-based composite and ormocer materials and seven samples of the ceramic material. We randomly divided each resin-based composite and ormocer group (n = 14 samples) into two groups of seven samples each. We polished one group of samples and left the other group unpolished. We polished all of the ceramic samples. To polish the samples (that is, the resin-based composite, ormocer and ceramic materials), we used medium, fine and superfine disks (Sof-Lex Discs, 3M ESPE) on a slow-speed handpiece in accordance with the manufacturer’s instructions. We randomly selected two samples from each group to serve as negative controls (n = 22).

Bleaching procedure. We stored all of the samples in distilled water at room temperature for 24 hours before any treatment. We bleached the top surface of each sample, applying the agent according to the manufacturer’s instructions. We used 15 percent carbamide peroxide to bleach the samples for eight hours and 56 hours (48 plus eight hours). For the second treatment period, we replaced the bleaching agent every eight hours, thus simulating the daily eight-hour application period typically used by patients for the at-home bleaching technique. Between applications of the bleaching agent, we stored the samples in water for 24 hours. At the end of each bleaching period, we used a soft toothbrush to wash the treated specimens under running distilled water and then placed them in fresh distilled water until the next application of bleach or the end of the 56-hour period. We replaced the distilled water every seven days to minimize the effect of the monomer, which leaches into the storage medium over time.

Microhardness test. We used a Knoop microhardness tester (Leitz Miniload 2, Ernst Leitzt GmbH, Wetzlar, Germany) to test the surface microhardness of the samples. A load of 300 grams was used for the ceramic samples and a load of 50 g was used for the resin-based composite and ormocer samples. The loading time was 30 seconds for all groups. We obtained five microhardness measurements from five positions on the upper surface of each sample at the following times: before bleaching (baseline), after eight hours and 56 hours of bleaching, and 24 hours and one month after the end of the bleaching procedure. We used the mean values of these five measurements at each testing period for the statistical analysis. Table 2Go shows the length of time of water storage and bleaching for a typical sample (Tetric Ceram, Ivoclar Vivadent AG, Schaan, Liechtenstein).


View this table:
[in this window]
[in a new window]

  		TABLE 2 Length of time of water storage and bleaching for a typical sample.*

 
Statistical analysis. We performed the statistical analysis using a significance level of .05. We used SPSS statistical software (SPSS, Chicago) for the statistical analyses. We used the repeated-measures analysis of variance (ANOVA) with two between factors (polishing and bleaching) and one within factor (time) (five levels, four degrees of freedom) to assess the effect of at-home bleaching on the microhardness of each of the six restorative materials. We tested each restorative material separately. In addition, we examined the effect of polishing in interaction with the effect of bleaching on the microhardness of the restorative materials.

We proceeded with the statistical analysis until attaining the simplest meaningful model. For example, when the first step of the repeated-measures ANOVA showed no sign of an interaction between polishing and bleaching, we removed this interaction from the model at the second step. After completing the study, we calculated a power of 84.6 percent by using the sample size and results for Tetric Ceram (the most representative material).


   RESULTS
TOP
 ABSTRACT
 AT-HOME BLEACHING
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Table 3Go shows the mean Knoop hardness values for the restorative materials. Table 4Go (page 983) provides a summary of the ANOVA results.


View this table:
[in this window]
[in a new window]

  		TABLE 3 Knoop hardness values after bleaching with 15 percent carbamide peroxide.

 

View this table:
[in this window]
[in a new window]

  		TABLE 4 Statistical evaluation of restorative materials.*{dagger}

 
According to the repeated-measures ANOVA, the effect of bleaching with 15 percent carbamide peroxide on the microhardness of Tetric Ceram (P = .0679), Tetric Flow (Ivoclar Vivadent AG) (P = .5088), Enamel Plus HFO (GDF gmbH, Rosbach, Germany) (P = .0601), Filtek Supreme (3M ESPE) (P = .6166), Definite (Dentsply DeTrey GmbH, Konstanz, Germany) (P = .2154) and the ceramic (Vitablocs Mark II for CEREC) (P = .9943) was not statistically significant.

The results also showed that polishing did not have a significant influence on bleaching with regard to the microhardness of any of the restorative materials tested (Tetric Ceram, P = .783; Tetric Flow, P = .069; Enamel Plus HFO, P = .215; Filtek Supreme, P = .255; Definite, P = .230). The polished and unpolished samples of all the restorative materials tested exhibited the same behavior as a result of bleaching.

According to the univariate tests of hypotheses for within-subject effects, no significant difference was found in microhardness values between the different periods for any of the restorative materials tested (Tetric Ceram, P = .127; Tetric Flow, P = .712; Enamel Plus HFO, P = .068; Filtek Supreme, P = .087; Definite, P = .870; ceramic, P = .706). The microhardness of each of the materials remained at levels similar to the initial baseline values throughout the bleaching and storage periods.


   DISCUSSION
TOP
 ABSTRACT
 AT-HOME BLEACHING
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
Bleaching agents lighten discolored tooth structure through the decomposition of peroxide into free radicals.26 The free radicals break down large pigmented molecules—which reflect a specific wavelength of light and are responsible for the color stain in enamel—into smaller, less-pigmented molecules through oxidation and reduction of molecules.26,29

We performed the bleaching procedures for eight and 56 hours, which represent one day and one week, respectively, of bleaching with an at-home bleaching product. The 56 hours of at-home bleaching have been shown to achieve six shades of lightening according to the shade guide (Vitapan Classic, VITA).10

In this study, we used loads of 300 g and 50 g to test the microhardness of the ceramic and resin-based composite materials, respectively. Many different loads have been reported in the literature25,27,30–32 for resin-based composite materials. As in our study, Turker and Biskin25 used a load of 50 g to test resin-based composite materials. If any changes were to occur, they probably would be on the surface of the restorative materials. The aim of our study was to detect even small changes and, therefore, we used small loads (50 g and 300 g). We evaluated both loads during the pilot studies to achieve stable and reproducible results.

Resin-based composites. According to the literature, the hardness of resin-based composites exposed to bleaching products has been reported to increase,25–30 decrease24,25 and remain unchanged.1,33

We found that bleaching with 15 percent carbamide peroxide did not have any statistically significant effect on the microhardness of any of the four resin-based composite materials tested. These results are in agreement with those of other studies.1,33 Campos and colleagues1 reported that treatment with carbamide (10 and 15 percent) did not alter the microhardness of the composite materials tested (Charisma, Heraeus Kulzer, Hanau, Germany, and Durafill VS, Heraeus Kulzer). Garcia-Godoy and colleagues33 also found that the microhardness of the composite material tested was not affected by bleaching with carbamide (10 to 30 percent).

Although we did not find this in our study, we expected a more noticeable reduction in microhardness in resin-based composites owing to their greater organic matrix content, which, according to many authors, is the probable site of the oxidation reaction.24,34,35 The difference in study results relates to the differences between specific bleaching products, the restorative materials used and the experimental test procedures.13,25,26 For example, Turker and Biskin25 reported that the microhardness of a particular resin-based composite was increased or decreased depending on the bleaching agents that were used.

</b></b>Such wide variations in data suggest that some tooth-colored restorative materials may be more susceptible to alterations in microhardness, while certain bleaching agents are more likely to cause the alterations.13 The latter result may be attributed to different pH values of the bleaching agents.36 Fortunately, the pH of most bleaching agents is close to neutral. The pH of the bleaching agent used in this study (Opalescence PF 15%) is 6.5.

As shown in Table 3Go, immediately after 56 hours of bleaching, we observed no decrease in microhardness after comparing the mean values of the control group with those of the bleached groups. On the contrary, almost all of the bleached samples exhibited an increase in microhardness. Only the Tetric Flow samples exhibited the same microhardness levels as those at baseline. Because of these findings, the microhardness of restorative materials immediately after bleaching is not a concern, and no risk of cracks exists. An increase in the microhardness of the materials does not pose any harm.

Ceramic. We used only polished ceramic samples in this study, which reflects clinically relevant conditions. We found that the bleaching material did not affect the microhardness of the ceramic. However, these findings are in conflict with those of Turker and Biskin,25 who concluded that the bleaching materials they used decreased the microhardness of the feldspathic porcelain. These authors measured the surface composition of the feldspathic porcelain samples by using energy-dispersive X-ray microanalysis, the results of which revealed a reduction in the feldspathic porcelain surface silicon dioxide (SiO2) content. The SiO2 forms the matrix,37 thus affecting surface hardness. However, this small amount of released SiO2 is not believed to be of clinical significance.

Ormocer. Our study results also showed that the microhardness of the ormocer samples was not affected by bleaching with 15 percent carbamide peroxide. This is in agreement with the results of Taher,26 who reported that the ormocer used in his study (Admira, Voco, Germany) exhibited no statistically significant changes in surface hardness after being bleached with 15 percent carbamide peroxide. Until recently, only a few reports26,27 have been published regarding the effect of bleaching agents on such restorative materials.

Polishing and bleaching. Another objective of this study was to examine the effect of polishing on bleaching with regard to microhardness. We found no difference between the polished and unpolished samples for all of the restorative materials tested. The low concentration of the active oxidizing agent in the bleach may explain these results. Park and colleagues38 reported that the hardness of composite surfaces covered with a celluloid strip before curing was lower than that of polished surfaces for the first few days after light-curing. However, the authors found no difference in microhardness between the polished and unpolished samples six days after light-curing.38 The effect of polishing procedures on surface hardness appears to depend on the material and technique used.39,40


   CONCLUSIONS
TOP
 ABSTRACT
 AT-HOME BLEACHING
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
Considering the experimental limitations of this in vitro study, we can conclude that bleaching with 15 percent carbamide peroxide did not alter the microhardness of hybrid, flowable, microhybrid and nanohybrid resin-based composite materials, or of ormocer and ceramic materials, which represent a wide range of the esthetic restorative materials used in clinical practice. On the basis of these findings, as well as those of other studies conducted to date, we can conclude that there is no sufficient reason to recommend replacement of posterior restorations after at-home bleaching with 15 percent carbamide peroxide.


   FOOTNOTES
 

Dr. Polydorou is an assistant professor, Department of Operative Dentistry and Periodontology, Dental School and Hospital, Albert-Ludwigs University of Freiburg, Hugstetter St. 55, 79106 Freiburg, Germany, e-mail "olga.polydorou{at}uniklinik-freiburg.de". Address reprint requests to Dr. Polydorou.


Dr. Hellwig is a professor and the head, Department of Operative Dentistry and Periodontology, Dental School and Hospital, Albert-Ludwigs University of Freiburg, Germany.


Dr. Auschill is an associate professor, Department of Operative Dentistry and Periodontology, Dental School and Hospital, Albert-Ludwigs University of Freiburg, Germany.


   REFERENCES
TOP
 ABSTRACT
 AT-HOME BLEACHING
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 

  1. Campos I, Briso AL, Pimenta LA, Ambrosano G. Effects of bleaching with carbamide peroxide gels on microhardness of restorative materials. J Esthet Restor Dent 2003;15(3):175–82.[Medline]

  2. Haywood VB, Heymann HO. Nightguard vital bleaching: how safe is it? Quintessence Int 1991;22(7):515–23.[Medline]

  3. Haywood VB. History, safety, and effectiveness of current bleaching techniques and applications of the nightguard vital bleaching technique. Quintessence Int 1992;23(7):471–88.[Medline]

  4. Barghi N. Making a clinical decision for vital tooth bleaching: at home or in-office? Compend Contin Educ Dent 1998;19(8):831–8.[Medline]

  5. Al Shethri S, Matis BA, Cochran MA, Zekonis R, Stropes M. A clinical evaluation of two in-office bleaching products. Oper Dent 2003;28(5):488–95.[Medline]

  6. Haywood VB. The Food and Drug Administration and its influence on home bleaching. Curr Opin Cosmet Dent 1993(1):12–8.

  7. de Freitas PM, Basting RT, Rodrigues JA, Serra MC. Effects of two 10% peroxide carbamide bleaching agents on dentin microhardness at different time intervals. Quintessence Int 2002;33(5):370–5.[Medline]

  8. Al-Qunaian TA, Matis BA, Cochran MA. In vivo kinetics of bleaching gel with three-percent hydrogen peroxide within the first hour. Oper Dent 2003;28(3):236–41.[Medline]

  9. Auschill TM, Hellwig E, Schmidale S, Hannig M, Arweiler NB. Effectiveness of various whitening techniques and their effects on the enamel surface [in German]. Schweiz Monatsschr Zahnmed 2002;112(9):894–900.[Medline]

  10. Auschill TM, Hellwig E, Schmidale S, Sculean A, Arweiler NB. Efficacy, side-effects and patients’ acceptance of different bleaching techniques (OTC, in-office, at home). Oper Dent 2005;30(2):156–63.[Medline]

  11. Matis BA, Cochran MA, Eckert G, Carlson TJ. The efficacy and safety of a 10% carbamide peroxide bleaching gel. Quintessence Int 1998;29(9):555–63.[Medline]

  12. Zekonis R, Matis BA, Cochran MA, Al Shetri SE, Eckert GJ, Carlson TJ. Clinical evaluation of in-office and at-home bleaching treatments. Oper Dent 2003;28(2):114–21.[Medline]

  13. Swift EJ Jr, Perdigao J. Effects of bleaching on teeth and restorations. Compend Contin Educ Dent 1998;19(8):815–20.[Medline]

  14. Fay RM, Servos T, Powers JM. Color of restorative materials after staining and bleaching. Oper Dent 1999;24(5):292–6.[Medline]

  15. Polydorou O, Hellwig E, Auschill TM. The effect of different bleaching agents on the surface texture of restorative materials. Oper Dent 2006;31(4):473–80.[Medline]

  16. Soderholm KJ. Influence of silane treatment and filler fraction on thermal expansion of composite resins. J Dent Res 1984;63(11):1321–6.[Abstract/Free Full Text]

  17. Yap AU, Wattanapayungkul P. Effects of in-office tooth whiteners on hardness of tooth-colored restoratives. Oper Dent 2002;27(2):137–41.[Medline]

  18. Wu W, Toth EE, Moffa JF, Ellison JA. Subsurface damage layer of in vivo worn dental composite restorations. J Dent Res 1984;63(5):675–80.[Abstract/Free Full Text]

  19. van Groeningen G, Jongebloed W, Arends J. Composite degradation in vivo. Dent Mater 1986;2(5):225–7.[Medline]

  20. Okada K, Tosaki S, Hirota K, Hume WR. Surface hardness change of restorative filling materials stored in saliva. Dent Mater 2001;17(1):34–9.[Medline]

  21. Mandikos MN, McGivney GP, Davis E, Bush PJ, Carter JM. A comparison of the wear resistance and hardness of indirect composite resins. J Prosthet Dent 2001;85(4):386–95.[Medline]

  22. Vargas MA, Cobb DS, Schmit JL. Polymerization of composite resins: argon laser vs conventional light. Oper Dent 1998;23(2):87–93.[Medline]

  23. Bourke AM, Walls AW, McCabe JF. Light-activated glass polyalkenoate (ionomer) cements: the setting reaction. J Dent 1992;20(2):115–20.[Medline]

  24. Bailey SJ, Swift EJ Jr. Effects of home bleaching products on composite resins. Quintessence Int 1992;23(7):489–94.[Medline]

  25. Turker SB, Biskin T. The effect of bleaching agents on the microhardness of dental aesthetic restorative materials. J Oral Rehabil 2002;29(7):657–61.[Medline]

  26. Taher NM. The effect of bleaching agents on the surface hardness of tooth colored restorative materials. J Contemp Dent Pract 2005;6(2):18–26.[Medline]

  27. Polydorou O, Moenting JS, Hellwig E, Auschill TM. Effect of in-office tooth bleaching on the microhardness of six dental esthetic restorative materials. Dent Mater 2007;23(2):153–8.[Medline]

  28. Dishman MV, Baughan LW. Vital tooth bleaching: home use review and evaluation. Va Dent J 1992;69(2):12–21.[Medline]

  29. Oltu U, Gurgan S. Effects of three concentrations of carbamide peroxide on the structure of enamel. J Oral Rehabil 2000;27(4):332–40.[Medline]

  30. Müjdeci A, Gökay O. Dental effects of home bleaching gels and whitening strips on the surface hardness of resin composites. Am J Dent 2005;18(5):323–6.[Medline]

  31. Calheiros FC, Kawano Y, Stansbury JW, Braga RR. Influence of radiant exposure on contraction stress, degree of conversion and mechanical properties of resin composites. Dent Mater 2006;22(9):799–803.[Medline]

  32. Felix CA, Price RB, Andreou P. Effect of reduced exposure times on the microhardness of 10 resin composites cured by high-power LED and QTH curing units. J Can Dent Assoc 2006;72(2):147.[Medline]

  33. Garcia-Godoy F, Garcia-Godoy A, Garcia-Godoy F. Effect of bleaching gels on the surface roughness, hardness, and micromorphology of composites. Gen Dent 2002;50(3):247–50.[Medline]

  34. Cullen DR, Nelson JA, Sandrik JL. Peroxide bleaches: effect on tensile strength of composite resins. J Prosthet Dent 1993;69(3):247–9.[Medline]

  35. Swift EJ Jr. Restorative considerations with vital tooth bleaching. JADA 1997;128(supplement):60S–64S.

  36. Price RB, Sedarous M, Hiltz GS. The pH of tooth-whitening products. J Can Dent Assoc 2000;66(8):421–6.[Medline]

  37. Philips RW, Skinner EW. Skinner’s science of dental materials. 8th ed. Philadelphia: Saunders; 1982.

  38. Park SH, Krejci I, Lutz F. Hardness of celluloid strip-finished or polished composite surfaces with time. J Prosthet Dent 2000;83(6): 660–3.[Medline]

  39. Yap AU, Lye KW, Sau CW. Surface characteristics of tooth-colored restoratives polished utilizing different polishing systems. Oper Dent 1997;22(6):260–5.[Medline]

  40. Yap AU, Sau CW, Lye KW. Effects of finishing/polishing time on surface characteristics of tooth-coloured restoratives. J Oral Rehabil 1998;25(6):456–61.[Medline]





This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Polydorou, O.
Right arrow Articles by Auschill, T. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Polydorou, O.
Right arrow Articles by Auschill, T. M.
Related Collections
Right arrow Restoratives

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS