Use of Yellow Plastic Food Wrap to Retard Composite Resin Polymerization

MARK S. HAGGE, DMD' SCOTT C. DI LORENZO, DDSt JAMES S. LINDEMUTH, DDS* MARK A. LATTA, DMD, MSS JAMES W. SMITH, PHD"

ABSTRACT Background: Dental chair lights can rapidly polymerize light-reactive composites beyond the point of workability, preventing adequate time for the shaping and sculpting of large direct com- posite restorations.

Purpose: The purpose of this study was to determine whether yellow plastic food wrap placed over a dental chair light would perceptibly retard the polymerization rate of a light-cured com- posite ( Esthet-XTM, shade Al , Dentsply/Caulk, Milford, DE, USA). Materials and Methods: Zero, one, and two thicknesses of yellow plastic food wrap (Reynolds Metals Company, Richmond, VA, USA) were, in turn, used in the following scenarios: (1) placed in a spectrophotometer and compared for percentage transmission of 470 nm light; (2) placed over a curing unit light wand and compared for milliwatts of output on a radiometer; (3) placed over a den tal chair light positioned 64 cm from 0.22 mm thick composite specimens, with Fourier Transform Infrared Spectrometry readings made every 40 seconds to measure degree of composite polymeriza- tion; (4) placed over a dental chair light positioned 64 cm from a direct veneer preparation (clinical simulation), which was then restored by four experienced clinicians who reported working times.

Results: Results for the scenarios were as follows: (1) zero sheets loo%, one sheet 34%, two sheets 6%; (2) zero sheets 580 mW, one sheet 190 mW, two sheets 20 mW; (3) percent conver- sion at 80 seconds-zero sheets 8%, one sheet 0.65%, two sheets 0.76%; percent conversion at 120 seconds-zero sheets 19.11%, one sheet 12.22%, two sheets 0.42%; (4) mean working times-zero sheets 34 seconds, one sheet 72 seconds, two sheets 155 seconds.

Conclusions: Yellow plastic food wrap placed over a dental chair light markedly extended the working time of a light-cured composite in each of four assessments performed. Two sheets of plastic wrap were more than twice as effective as one sheet.

CLINICAL SIGNIFICANCE The suggested filtering technique with yellow plastic wrap placed over a dental chair light is a highly effective, expedient, and inexpensive method for increasing the working time of light- cured composites.

(J Esthet Restor Dent 15:370-376,2003)

'Associate professor of restorative dentistry, University o f the Pacific School of Dentistry, San Francisco, CA, USA tAssistant professor of fixed prosthodontics, Creighton University School of Dentistry, Omaha, NE, USA #Colonel, United States Air Force, Lackland Air Force Base, TX, USA; previously director of clinical research, Travis Air Force Base, CA, USA $Associate dean for research, Creighton University School of Dentistry, Omaha, NE, USA "Lieutenant colonel, United States Air Force, and director, Clinical Investigation Facility, Travis Air Force Base, CA, USA

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ental manufacturers have D recently focused considerable attention on increasing the poly- merization rate of light-cured com- posites. Claims have been made that improvements in clinical pro- ductivity result from reduced curing light Two principal approaches have been used to achieve this goal-the use of curing lights with increased output and the use of more reactive composites.

The curing rate of composites is affected by many factors, including the type of filler as well as the shade, thickness, and temperature of the material.’ If these factors are rendered equivalent, the type and amount of photoinitiator in each composite is a major determinant of polymerization rate. By increas- ing the amount of photoinitiators, manufacturers are able to claim that their composites require half the amount of curing time previ- ously required.1.2

The potential of significantly improved efficiency with these materials carries with it an atten- dant disadvantage-a shorter work- ing time.’l2 Operatory lights have been shown to induce a preliminary setting reaction in photoinitiated composites, with the amount of premature curing dependent upon light intensity and duration of exposure to the operatory light.3>4 In addition, different composites are known to vary in their sensitiv- ity to ambient light.S*6 This behav- ior is clinically significant when substantial sculpting is required

(with direct anterior veneer or large posterior restorations) and is fur- ther compounded if the operator has relatively little experience with the material, which is the case with dental students.

Several methods of varying intri- cacy may be carried out to retard the composite’s set. The most obvi- ous and common solution is to move the dental chair lamp farther away or to turn it off completely. Unfortunately, this causes the oper- ator to lose much of his or her abil- ity to precisely locate margins or to develop desired anatomic features. The attention subsequently required for margin refinement, additional characterization, shaping, and pol- ishing might easily counteract any savings made with decreased poly- merization time.

An expensive solution to this prob- lem is to purchase a head-mounted lamp with the sensitizing wave- lengths of light removed by inline filters. Additionally, one dental manufacturer (Midmark Corp., Versailles, OH, USA) has developed a dental chair light with a “com- posite safe’’ setting. This is achieved by decreasing both the Kelvin tem-

perature and output wattage of the dental chair light bulb.

A less expensive solution consists of attaching an orange plastic filter over the dental chair 1amp.l Although accomplished relatively easily for a limited number of dental chairs, this solution might prove overwhelming for a facility the size of a dental school. An inex- pensive and more pragmatic solu- tion would be beneficial.

Recently, assorted colors of plastic food wrap have been introduced (Figure 1; Reynolds Metals Com- pany, Richmond, VA, USA). Among these are yellow and rose-colored varieties. We speculated that the yellow or a combination of the yellow and rose plastic wraps might block adequate amounts of the sensitizing wavelengths of light and provide a very inexpensive solution to this problem. If success- ful, the wrap could simply replace the existing clear plastic film cur- rently used as an infection control barrier. Therefore, the purpose of this study was to determine whether colored plastic food wrap reduced the polymerization rate of a light-cured composite.

Figure 1 . Commercially available yellow plastic food wrap.

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U S E O F YELLOW P L A S T I C F O O D WRAP T O RETARD COMPOSITE RESIN POLYMERIZATION

MATERIALS A N D M E T H O D S

Esthet-X" (shade A1 , Dentsplyj Caulk, Milford, DE, USA), a micro- hybrid composite, was selected for use in this study. It is the principal composite used by dental students at the University of the Pacific School of Dentistry and, in our pre- clinical courses and clinics, has often been reported to polymerize before desired shaping and sculpt- ing can be completed.

Examination of the effect of the colored plastic wraps was divided into four phases. In the first phase, one and two thicknesses of yellow and rose-colored wraps in addition to a yellow-rose combination were analyzed in a spectrophotometer (Spectronic@ 1201, Milton Roy Co., Rochester, NY, USA), scanning first at 470 nm to determine the most effective combination, and then from 420 to 500 nm for a more complete examination.

Based upon results from the spectro- photometer, effective plastic wrap combinations were applied directly over the tip of a visible curing light (Optilux@ 500, Kerr Dental, Orange, CAY USA) and measurements of light transmission were taken using the incorporated radiometer.

Next, a clinical simulation was devised. Four dentists (mean experi- ence level = 18.5 yr) manipulated the composite, performing a mock direct veneer restoration on a typodont tooth (Figure 2) while being timed with a stODwatch. The dental chair

light was placed 64 cm from the sur- face of the preparation and in suc- cession covered with zero, one, and two layers of yellow plastic wrap (Figure 3). The clinicians reported findings at two intervals: when the composite first became difficult to manipulate, and when the composite had undeniably set beyond a work- able condition. The clinicians each made three attempts under all of the filtration conditions; the times were averaged separately for each partici- pant and for the group as a whole.

Finally, 0.22 mm thick specimens of the composite were examined using Fourier Transform Infrared (FTIR) Spectrometry (model 560 E.S.P. FT-IR, Thermo Nicolet Corp., Madison, WI, USA) to determine the degree of composite polymer- ization. Results obtained using this recently devised method have been shown to correlate well with mea- surements of composite hardness and depth of Degree of conversion (DC) was computed using a single bounce diamond

attenuated total reflectance acces- sory mounted in the spectrometer. Direct DC values were determined using the percentage of carbon double bonds (1,638 cm-l) present before and after polymerization compared with a reference aromatic peak of 1,608 cm-*.

A dental chair light was again placed 64 cm away from the speci- mens, and conversion was mea- sured at 40,80,120,160, and 200 seconds with no filtration and with one and two layers of yellow plastic wrap. DC measurements were made from the bottom of each specimen ( n = 3) for each group.

RESULTS

A single sheet of rose-colored wrap demonstrated limited ability to block 470 nm light, allowing 62.8% of the light to penetrate. Because of this, the rose-colored wrap was not used further in the investigation. In comparison, one sheet of the yellow wrap permitted just 34% of the light to penetrate. The addition of a

Figure 2. Clinical simulation of anterior direct composite veneer restoration.

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transmission at this bandwidth.

Figure 3. Dental chair light covered with yellow plastic wrap.

second yellow sheet reduced 470 nm light transmission to just 6.1%. Results of the spectrophotometric testing with one and two sheets of yellow wrap are shown in Figure 4. The curing light developed 580 mW with no filtration (100% baseline). Using one sheet of the yellow wrap, the power dropped to 190 mW (32.75% of baseline). With two sheets power dropped to just 20 mW (3.75% of baseline).

The results of the clinical simula- tion are shown in Table 1. When all four clinicians’ results were averaged, use of one sheet of yellow plastic wrap more than doubled the composite’s working time. With the use of two sheets, it more than quadrupled.

Results of the FTIR Spectrometry analysis are shown in Figure 5 . As with the other test phases, successively greater retardation of the composite’s polymerization occurred as sheets of the yellow wrap were added.

DISCUSSION

Readings made from the curing light radiometer aligned closely with those obtained from spectro- photometric analysis. In both tests one sheet of the yellow wrap reduced 470 nm photoinitiating wavelength light transmission by two-thirds. The addition of a second yellow sheet in both tests resulted in more substantial reductions, block- ing approximately 95% of light

During the clinical simulation, the subjective impressions of working time varied between clinicians and increased with successive layers of the yellow plastic wrap. The clini- cians were requested to work with the composite at maximal thickness to simulate a gingival-coronal incre- mental application technique. How- ever, one of the clinicians (clinician no. 1) later reported that he had unintentionally reverted to his usual clinical technique of thinning and spreading the composite over the entire axial wall. This thinning of the composite was thought to be responsible for the comparatively decreased working times he reported when using two sheets of the yellow plastic wrap (see Table 1).

All four clinicians firmly stated that unfiltered light did not permit adequate working time with this

. ” 60 A

420 430 440 450 460 470 480 490 500

Light Wavelength (nrn)

I -0- 1 sheet + 2 sheets

Figure 4 . Percentage light transmission at 420 to 500 nrn by one and two sheets of yellow plastic wrap.

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U S E OF YELLOW PLASTIC FOOD WRAP TO RETARD COMPOSITE RESIN POLYMERIZATION

TABLE 1. WORKING TIMES OF COMPOSITE DURING DIRECT ANTERIOR VENEER RESTORATION O N A TYPODONT.*

Reported Working Time (s) Clinician 4 Average Composite No. of Sheets Clinician 1 Clinician 2 Clinician 3

Workable 0 31 37 32 36 34

1 78 78 69 65 72

2 112 200 155 154 155

0 44 39 37 44 41

1 88 85 77 78 82 2 132 215 173 187 177

Definitely set

“As reported by four clinicians using zero, one, and two thicknesses of yellow plastic wrap over the dental chair light.

composite. Similarly, they all felt that two layers provided sufficient working time for any conceivable size of composite restoration, and that one layer of the colored plastic wrap should provide enough work- ing time for most restorations. These clinicians also reported that two layers of colored wrap provided more than enough total illumina-

tion to adequately view cavosurface margins and surface details of the composite restoration.

One potential concern expressed by the clinicians while using this tech- nique was ensurance of accurate color perceptiodshade prescription following exposure to filtered light, that is, if a ceramic shade prescrip-

35

30

25 E .o 20 E 0 2 15

s 8 lo

5

5

-5 0 40 80 120 160 200

Time (8)

I --C Osheets 1 sheets -k 2sheets I ~~

Figure 5. Fouriu Transform Infrared Spectrometry analysis o f percent conversion under three conditions. Second-order polynomial trend lines (dotted lines) have been calculated for each data set.

tion had to be made immediately in an adjacent operatory. Minimal research has been reported on this subject, although considerable work has been done with respect to dark adaptation. Even though the dominant retinal cell type differs for light sensitivity (rods) and color perception (cones), the chemical pathways for recovery are infinitely more similar than they are different. Interpolating reviews of photo- receptor light adaptation research, a recovery time of 15 to 20 seconds is probably adequate, and 45 sec- onds should provide a more than safe interval for recovery of color sensitivity.*lJ2 The topic of color sensitivity and its associated recov- ery time might provide a subject for subsequent clinical investigation.

Correlation of the FTIR Spectrome- try results with those of the clinical simulation is speculative to some degree; however, one potential asso- ciation was noted after second- order polynomial trend lines were constructed for each test condition

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(see Figure 5 ) . When the averaged data regarding workability (see Table 1) was transposed onto each of the trend lines, decreased worka- bility was seen to occur at approxi- mately 4% conversion for all three test conditions. The clinical impli- cations of this finding are unknown at present, but if this relationship were proven to be valid, FTIR Spectrometry might permit a more quantitative comparison of differ- ent composites’ photosensitivity.

Although not specifically examined in this study, the results obtained would be expected to be relevant for photoinitiated luting cements. Use of the yellow plastic wrap should provide extended time for confirmation of correct seating and the removal of excess cement prior to the photoinitiation of the com- posite luting cements used with indirect tooth-colored restorations such as porcelain veneers.

CONCLUSIONS

Yellow plastic food wrap placed over a dental chair light consider- ably extended the working time of a light-cured composite in each of four assessments performed. Two sheets of plastic wrap were more than twice as effective as one sheet.

Filtering dental chair light with yel- low plastic food wrap proved to be a highly effective, expedient, and cost-effective method that markedly delayed the polymerization onset of a light-cured composite. When clin-

icians require extended working time with photocured composites (eg, large direct veneers), the sug- gested filtering technique extends working time appreciably while providing adequate illumination for visualization of surface detail and cavosurface margins.

DISCLOSURE AND ACKNOWLEDGMENT

None of the authors has any financial interest in the materials or testing equipment used in this study and will not be compensated by any manufacturer upon publi- cation of this work.

The views expressed in this article are solely those of the authors and should not be construed as reflect- ing the official policy of the Department of the Air Force, the Department of Defense, or any other agency of the United States government. The work reported herein was performed under United States Air Force Surgeon General-approved Clinical Investi- gation No. FDG 20020020E.

REFERENCES Albers H. Tooth-colored restorations. 9th Ed. Lewiston, NY: BC Decker, 2002: 81-110.

Kanca J 111. Is it the light or is it the mater- ial? J Dent Res 2001; 80(Spec Issue):134. (Abstr)

Pagniano RP, Longenecker S, Chandler H. Effect of unit and operatory lights on the consistency of light-activated composites. J Prosthet Dent 1989; 61:150-152.

4. Dlugokinski MD, Caughman WF, Ruegge- berg FA. Assessing the effect of extraneous light on photoactivated resin composites. J Am Dent Assoc 1998; 129:1103-1109.

5. Dionysopoulous P, Watts DC. Sensitivity to ambient light of visible light-cured com- posites. J Oral Rehabil 1990; 17:9-13.

6. Lane DA, Watts DC, Wilson NH. Ambi- ent light working times of visible light- cured restorative materials. Does the IS0 standard reflect clinical reality? Dent Mater 1998; 14:353-357.

7. DeWald JP, Ferracane JL. A comparison of four modes of evaluating depth of cure of light-activated composites. J Dent Res 1987; 66:727-730.

8. Murdock CM, Latta MA, Barkmeier WW, Hammesfahr PD, Wang X. Barcol hard- ness vs. direct degree of conversion mea- surement by FTIR. J Dent Res 2001; 8O(Spec 1ssue):llO. (Abstr)

9. Di Lorenzo SC, Latta MA, Murdock CM, Wilwerding TM. Comparison of compos- ite polymerization using different curing light intensities. J Dent Res 2001; 8O(Spec Issue):253. (Abstr)

10. Yap AU, Soh MS, Siow KS. Effectiveness of composite cure with pulse activation and soft-start polymerization. Oper Dent 2002; 27:44-49.

11. Pugh EN Jr, Nikonov S, Lamb TD. Molec- ular mechanisms of vertebrate photorecep- tor light adaptation. Curr Opin Neurobiol 1999; 9:410-418.

12. Common unrecognized factors affecting dark adaptation. Southern Deep Sky 1999; 2( 1):3-7.

Reprint requests: Mark S . Hagge, DMD, University of the Pacific School of Dentistry, 21 55 Webster Street, Suite 522B, San Francisco, CA, USA 941 15; e-mail: mhagge@sf,uop.edu 02003 BC Decker Inc

This article fits the description in the US Copyright Act, Title 17, United States Code, of a “United States Government Work. ” It was written as part o f one or more of the authors’ official duties as government employees, who do not have rights to assign. The article “Use of Yellow Plastic Food Wrap to Retard Composite Resin Polymer- ization” is therefore freely available to the Journal of Esthetic and Restorative Dentistry for pubfiation.

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COMMENTARY

U S E OF YELLOW PLASTIC FOOD WRAP TO RETARD COMPOSITE RESIN POLYMERIZATION

Annie J. St-Georges, DMD, MS*

When placing composite resin restorations, dentists understand the importance of moving the operatory light away from the working area, or simply turning it off, to avoid premature polymerization of this light-sensitive material. However, working in a confined environment without appropriate lighting is not pleasant for the clinician and can compromise the dentist’s ability to generate proper anatomic morphology and marginal adaptation of the final restoration.

Over the years various means have been proposed to retard premature composite resin polymerization, but most of these solutions are expensive and some require the purchase of a filtered head-mounted lamp. The present article by Hagge and colleagues shows how an inexpensive and simple device can improve visibility for the operator and gain more time to place and sculpt a composite resin restoration, even when using the available operatory light.

By placing two sheets of yellow plastic food wrap over this dental chair light, the authors demonstrated that an extended working time was made possible. The placement of the two sheets blocked a significant amount of the pho- toinitiating wavelength (470 nm) responsible for the excitement of the photoinitiators in composite resins, thereby delaying the beginning of polymerization.

The fact that four dentists performed direct composite veneer restorations in a clinical simulation to test the efficacy of this new method affords reliability to the results. With this novel study, a simple technique using inexpensive yellow plastic food wrap has been revealed that can be of significant benefit to all dentists doing composite resin restorations.

‘Assistant professor, Department of Restorative Dentistry, Faculty of Dental Medicine, University of Montreal, Quebec, Canada

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