- Email: [email protected]
Depth of cure of visible light-cured resin: Clinical simulation
REFERENCES 1.
Coye RB: A study of the variability of setting a fully adjustable gnathologic articulator to a pantographic tracing. J PROSTHET
7.
DENT 37~460, 1977.
2.
Winstanley RG: Observation on the use of the Denar pantographic articulator. J PROSTHET DENT 38:660, 1977. 3. Watt DM: A study of the reproducibility of articulator settings from graphic records of mandibular movement. Dent Pratt Dent Ret 19:119, 1968. 4. Crispin BJ, Myers GE, Clayton JA: Elects of occlusal therapy on pantographic reproducibility of mandibular border movements. J PROSTHET DENT 40~29, 1978. 5. Beard CC, Clayton JA: Effects of occlusal splint therapy on TMJ dysfunction. J PROSTHET DENT 44~324, 1980. 6. Lamontagne PP: Pantographic Tracings Related to Setting of
8.
Articulator. Thesis, University of Michigan, School of Dentistry, 1970. p 44. Rea TJ: Human Variance in Adjusting a Fully Adjusted Articulator by Means of a Pantograph. Thesis, University of Michigan, School of Dentistry, 1972, p 65. Dorman CW: The Relationship of Hinge Axes to Pantographic Surveys. Thesis, University of Michigan, School of Dentistry, 1972, p 46
Kqmnl
H. b&#&mm&e,* J. E. Gres, D.DS.,** V. A. M&m, P&D.,*** J. L. Fexracaae, Ph.D.,*** and G. A. Harvey, D.Dd.***** Baylor
College of Dentistry,
Dallas,
T. 0
Tex.
L
@t-cured resins have the advantage of being one component system with a virtually infinite working time. H~wwer, the limited depth of cure in these systems has proved to be of conccrn.lW4 Two methods have commonly been used to determine the depth of cure in resins. One method used the optical rnicrw to detect changes in the translucency of the light-cured resins as a function of depth of polymerization.5,6 A second method involved measuring the microhardmz+s of the resir~.‘-~*‘-‘~ Apparently, several variabhs may play a role in determining depth of cure in light-a&vat& resins. Certain light sources failed to produce optimum cures in many resins.‘s4 In other research, darker shades seemed to require longer illumination times than did lighter shades to produce a high degree of polymeriaa&n.7-io The continued polymerization of &ghbctned m&s after il~~~~n has al= been reported.’ In ene study the ~&W&K&continued to
Presented at the International Association for Dental Dallas, Tex. *Visiting Scientist, Sunstar, Inc., Osaka Japan. **Private practice, Austin, Tex. ‘**Assistant Professor, Dental Materials. ****Professor and Chairman, Dental Matcrials. *****Assistant Professor, Operative Dentistry. 574
reyuest.r to:
DR. CHARLES C. BEARD UNIVERSITY OF MICHIGAN SCHOOL OF DENTISTRY ANN ARBOR, MI 48109
Research,
T&de I. Compites
stwbd IHiUmia&on
Material’ Aurafill yellow Aurafill gray-brown Aurafill light Command universal Prima+Fil light gray Primaa-Fil light gray Prisma-Fine light gray Ultra-Bond shade 62 Profile
40 (>4 mm) 40 (>4 mm) 40 (>4 mm) 30 (4 mm) 10 (2.5 mm) 40(4mm) 40 (2.5 mm) 15 (unlimited)
OlZU83 012083 012083 122382-1342 111092 111@92 1213831 q?Y5 052582
‘All resins were illuminated with a Prisma-Litc (L.D. Caulk) except for Ultra-Bond, which was illuminated with a Visar Liihc (Den-Mat). Depths listed under illumination times refer to maduifacmmn’ claims for depth of cure at the specified illumination period.
in~upto3moaths*tht&i4ikb@ia~ pit and fissurx! seabta.” A s&s@@+@ &&CJMX between the hardness measu& w,abr i#bmination and that W-a.& 1 dr)l w~.~~BJM&~ However, the hardness after 1 dq rnas~~~&~.~ to the ha&ess after 7 days.
MAY 19%
VOLUME
55
NUMBER 5
DEPTH
OF CURE OF VISIBLE
LIGHT-CURED
RESIN
25mm
_ 2mm
)
Compodts Resin
0
4.5mm
0 12mm
Gypsum
0 l!klT
I
(b)
(a
Fig. 1. a, Specimen configuration for Knoop hardness measurements. b, An enlarged view of composite shows measurement positions.
pylene and polytetrafluoroethylene molds. resulted in an overestimated depth of cure, thereby emphasizing the importance of the mold material in in vitro studies.14 The purpose of this study was to determine the depth of cure of light-activated composite restoratives placed under simulated clinical conditions in extracted teeth. The specimens were evaluated to determine the effects of aging the resins for 6 months at 37” C.
MATERIAL
AND METHODS
Cylindrical cavity preparations were drilled in occlusal surfaces of extracted second molars with a modified carbide bur mounted in a precision drill press. The cavity preparations were 2 mm in diameter and 4.5 mm in depth. Seven light-cured composites were studied including the yellow, gray-brown, and light shades of Aurafill (Johnson & Johnson, East Windsor, N.J.), Command universal (Sybron/Kerr, Romulus, Mich.), Prisma-Fil light gray and Prisma-Fine light gray (L.D. Caulk Co., Milford, Del.), and Ultra-Bond shade 62 (Den-Mat, Santa Maria, Calif.). Profile (S.S. White, Philadelphia, Pa.), a chemically cured composite, was used as a control. The resins were injected with a syringe into the preparations and were illuminated .according to manufacturers’ instructions (Table I). In addition, a second series of Prisma-Fil specimens was illuminated for 10 seconds to determine the effects of insufficient illumination time. Five specimens were tested for each resin. Specimens were retained at 37” C for 2 hours after illumination. They were subsequently embedded in gypsum and sectioned longitudinally with an Isomet low-speed saw (Buehler, Ltd., Lake Bluff, Ill.). The sectioned surfaces were polished with a 6 pm diamond polishing wheel to produce smooth surfaces. These specimens were stored at 37” C until tested. Rnoup hardness was measured with a Tukon Tester (Page-Wilson Corp., Bridgeport, Conn.) with a SOOgram load. Measurements of hardness were made at 48 hours and 6 months (except for resins Ultra-Bond and Prisma-Fine). The indentations were made at 0.5 and 1 THE JOURNAL
OF PROSTHETIC
DENTISTRY
Aurafill Aurafill
Command Ptisma-Fii Prism&Al
liiht
Prisma-Fine Ultra-Bond
yellow
gray-brown
universal liiht
gray
gray
- 40s
light
gray
shade
62
-20 -10 AH (KHNlmm)
60 loo H? (KHN)
Fig. 2. Changes in hardness values (AH) and hardness values at a depth of 1 mm (H,) for all composites at 48 hours and 6 months. (Asterisks indicate no measurements at 6 months.)
mm distances from the tooth/restoration interface and at depths of 1, 2, 3, and 4 mm, as shown in Fig. 1. The data were analyzed with analysis of variance and the Scheffe test for multiple comparisons between means at the p = 0.05 level of significance. Linear regression analysis was performed for each resin system to determine the variation of hardness with depth, according to the equation: H = H. + AH . d, where d = depth (in millimeters), H = &mop hardness at depth of d (in millimeters), H. = Knoop hardness extrapolated to the surface, and AH = change of Knoop hardness with 1 mm increase in depth.
RESULTS There were no significant differences between the hardness values measured at 0.5 and 1 mm distances from the tooth/restoration interface for any resin system. Therefore the results for each resin at each depth were 575
MATSUMOrO
AU: A 100): A (YI
100
AuM AudW Au&I
t-r
Al
Mf&ht ~+‘8y-kown VJbw
A(LI
l
AlOblO
t Y 3
2
1
0
m
4
mm)
0
Fig. 3. Graph of Knoop h&nversus depth for three shades of Au&IL Values represent mean of pooled results for 48 hours and 6 months.
:
:
J
:
-m(mm)
Fig 5. Graph of Knoop hardneaa versus depth for Profile, Ultra-Bond, Command, and PriuarrRne. Values represent mean of pooled resuJts for 48 hours and 6 months.
cxpcacd, a dccrea& illumination
0
:
;
1
:
Fig. 4. Graph of Knoop hardness veruus depth for Prisma-Fil (10 seconds and 40 seconds). Values represent mean of pooled results for 48 hours and 6 months.
pooted (n - 10). The means aad SDs for hardnus valua atadepthoflmmfor48hoursand6mcmthsarc iUuu.1~dhFig.2.Graphsdthehard1xave~sdepth for c.& resin art preuntcd in F&s. 2 through 5. nctladaeadAwa6tlgr8y-txownwaaththighQlc of the light-curad #ystam and was apIi*t to that of the dumicdty cured min Pro&. For each light-cured min, ha&ess decrwxd with increased depth (i.e., the chmgcinlwdamfor~1mm~iadephwas n4qptive) (Fii. 2). The efkct was kwt et for Au&ill Li&t and Ultra-Bond (F&a. 3 and 5). As
576
tim for P&ma-Fil lightgray~uadaminwithareducuiharbssat inaeaaai deph (Fig. 4). The chemi&y cured cap&x& Profile, showed a slight inuzasc in hordnas with increaxd depth (Fig. 5). Cbrrclation betw~ reduced hardness at incrcasai depths was strong (r 2 0.95 for all except Ultra&ad 10.85) and Aurafill [email protected] 10.75)) and significant for the tigtw!ured r&M but in@&ant fix the chemically curat mat. Id IcJloop hardncss vahtcs were obearved bttwecn 48 houn and 6 monthsfor~uatrk@hsd334nun(Fig. 2). This was most &dent for the Riaaa-FIL k@ py spccimm that were itiunkutal for 40 sax&s. Holwever, the slopa of the rqrusion lines for 48 hours and 6 months were stabtially compared at the p = 0.05 kvcl.“ No differenas were found for any of the resins.
The insignificant diffcrcnces between the hardness values at 0.5 and 1 mm dbnces fmn the tooth/ ralawionintafaainliewthatthedcgteof~was cwutMt~tbe~crof~-~ve -Y material. Appmnly, tk optical popeties d the tooth stn@uredomiue-ttKdq5n!cdcurenem.rthc intufauin~dthiarh.
MAY
1%
VOLUME
5s
NUMBER
5
DEPTH
OF CURE OF VISIBLE
LIGHT-CURED
RESIN
polymerization was relatively constant at all depths for these composites. Their constant hardness is in accord with claims made by the manufacturers for the illumination times used. However, it should be noted that Ultra-Bond possessedone half of the hardness of Aurafill light at all depths. The relatively uniform hardness of Ultra-Bond may be explained by a variation in its catalyst chemistry, compared with other light-cured resins. This light-cured resin, which behaved like the chemically cured control Profile, is thought to contain a chemical-curing component as well as a visible light-activated catalyst. For all resins, except Aurafill light, Aurafill graybrown, and Ultra-Bond, the hardness values at the depth of 3 mm were less than 70% of the values measured at a depth of 1 mm, despite manufacturers’ claims for complete cure at these depths. Command universal was not cured sufficiently at 4 mm to record a hardness value. In general, it appears that the manufacturers’ designated illumination times for specific depths of cure are inadequate. Fig. 3 indicates the relationships between depth and Knoop hardness for the three Aurafill shades tested after 48 hours and 6 months. The hardness of Aurafill yellow was not significantly different from that of Aurafill light or Aurafill gray-brown at 1 mm depth after 48 hours @ = 0.05). However, the hardness of Aurafill yellow was significantly lower than that of the light and gray-brown shades at 3 and 4 mm depths after 48 hours (p = 0.05). Visually, Aurafill yellow appears to be less translucent than Aurafill light and Aurafill gray-brown, suggesting that the increased opacity of the yellow shade allows less illumination from the light source to penetrate to greater depths. Apparently, translucency of the resin is more important than shade for predicting depth of cure. Fig. 4 shows the relationship between depth and Knoop hardness after 48 hours and 6 months for Prisma-Fil light resins illuminated for IO and 40 seconds. Measurements of Knoop hardness at 4 mm depths were not possible because of the insufficient polymerization in the resin illuminated for only 10 seconds. The higher hardness value at 1 mm of the Prisma-Fil illuminated for 40 seconds was probably due to an increased concentration of free radicals formed during the longer illumination period. When the illumination time is prolonged, the amount of light reaching the lower depths to form free radicals that initiate polymerization is increased. The total number of photons of light reaching the lower depths for the Prisma-Fil illuminated for 10 seconds is much less than that for the material exposed for 40 seconds. The hardness of the former at 4 mm is negligible. Therefore the increase in illumination time for the latter produces a relatively large increase in
THE JOURNAL
OF PROSTHETIC
DENTISTRY
hardness at the lower depths. These results indicate that the longer exposure time should always be used to cure this composite regardless of the depth of the restoration. The tendency for Knoop hardness values at depths of 3 or 4 mm to be larger at 6 months than at 48 hours may be the result of evaporation or leaching of low molecular weight plasticizing components in the dry 37” C atmosphere or the effects of a continued polymerization during storage. The differences were not always significant, however. The results suggest that the uncured material may undergo physical or chemical changes during aging. CONCLUSIONS 1. Light-activated resins cured in natural teeth exhibited a reduction in hardness with increased depth of the restoration. These results are comparable to tests of different types of curing molds. 2. The difference in catalyst chemistry of Ultra-Bond may explain the uniform hardness profile of this material. 3. The uniform hardness profile of Aurafill (light) may be due to a higher degree of translucency compared with the other shades (yellow and gray-brown). Shade was not the determining factor for depth of cure in Aurafill resin material. 4. In general, manufacturers’ designated illumination times for specific depths are inadequate to ensure complete polymerization. Layering the composite may still be the best method for filling cavity preparations that extend 3 to 4 mm in depth. We thank all the manufacturers for supplying material used in this project.
REFERENCES 1. Skeeters TM, Timmons JH, Mitchell RJ: Curing depth of visible-light cured composite resins. J Dent Res 62~219, 1983 (Abstr No. 448). 2. Stillwater JC, Louka AN: A study on the depth and postexposure polymerization of light-cured composite resins. J Dent Res 62~218, 1983 (Abstr No. 444). 3. Watts DC, Amer 0, Combe EC: Characteristics of visible-light activated composite systems. Br Dent J 156:209, 1984. 4. Hansen EK: After-polymerization of visible light-activated resins: Surface hardness vs. light source. Stand J Dent Res 91:406, 1983. 5. Murray GA, Yates JL, Newman SM: Ultraviolet light and ultraviolet light-activated composite resins. J PROSTHET DENT 46~167, 1981. 6. Newman SM, Murray GA: Visible lights and visible lightactivated composite resins. J PROSTHETDENT 50~31, 1983. 7. Swartz ML, Phillips RW, Rhodes BF: Visible light-activated resins-Depth of cure. J Dent Res 61:270, 1982 (Abstr No. 823). 8. Swarm ML, Phillips RW, Rhodes B: Visible light-activated resins-Depth of cure. J Am Dent Assoc 106:634, 1983.
577
MATSUMQTO
9.
10.
11.
12. 13. 14.
Leung RL, Fan FL, Johnston WM: Post-irradiation polymerization of visible light-activated composite resin. J Dent Res 62:363, 1983. Leung R, Fan PL, Johnston WM: Exposure time and thickness on polymerization of visible light composite. J Dent Res 61:248, 1982 (Abstr No. 623). Young KC, Cummings A, Main C, Gillespie FC, Stephen KW: Microhardness studies on the setting characteristics of fissure sealants. J Oral Rehab 5187, 1978. Lange CD, Bausch JR, Davidson CL: The curing pattern of photo-initiated dental composite. J Oral Rehab 7:369, 1980. Salako NO, Cruickshanks-Boyd DW: Curing depths of materials polymerized by ultra-violet light. Br Dent J 146~375, 1979. Denyer R, Shaw D J: Cure evaluation of visible light composites
fStm&q L. Wadt,
Jzs, D,D$.,* oad
s. co
ET AL
by Knoop hardness measurements. J Dent Res 63:271, 1982 (Abstr No. 833). 15. Cook WD: Factors affecting the depth of cure of UV-polymerized composites. J Dent Res 59~800, 1980. 16. Tirtha R, Fan PL, Dennison JB, Powers JM: In vitro depth of cure of photo-activated composites. J Dent Res 61:11&4, 1982. 17. Sokal RR, Rohlf FJ: Biometry, ed 2. San Francisco, 1981, WH Freeman & Co Publishers, p 499. Refirint requests to: DR. V. A. MARKER BAYLORCOLLEGEOF DENTISTRY 3302 GASTONAVE. DALLAS, TX 75246
D8Ds.+
University of Tennessee Center for the Health Sciences, College of Dentistry, Memphis, Tenn
T
he use of &d-etched &red partial dentures for the replacementof missing teeth is well documented.‘” The teehniq~e has also been describedby Tkmmpsonet al.4 Bond strengths and teebniques for bond&g acid-etched fixed partial dentures have l3ccnreported for the chemically cured compositesnormally used.5The literature doesnot include researchwith light-cured cxxnpositesto bond the solid retainers of acid-etched fixed partial dentures. With the introduction of perforated retainers, the use of visible light guns to cure light-cured composites could be used in bonding the restoratiion. The solid retainers of the acid-etched fixed partial denture make conventional methods of bonding with ligbxred cornposites difficult. The purpcse of this study was to devisea technique to use light-cured compositesas a bonding medium for the solid retainer and to test the strength of the bonds.
Fig, 1. Fabticated retabers used to represf+nt s&d retainers of fixed partial &m.
retainers: Sikx (384 fill (K&m, Irvine,
L AND M-05 In this study, retainers were fabricated out of Rexillium III &neric Gold Co., Wallingford, C&n.) metal (a aiekel~andberyIlium~tainmg alley} and bandedto the f&al su&ces of 60 bevine teeth. Ibvine teeth have been used as an acceptablesubstitute for human teeth becauseof the clese resemblanceof the enamel surface.6 Thrce~~~com~tcswcre~to~the *Assistant Professor, Division of Biomaterials.
578
3 minutes in an ultr-rasQnEc dcaner in a s&r&m -of It%
Coye RB: A study of the variability of setting a fully adjustable gnathologic articulator to a pantographic tracing. J PROSTHET
7.
DENT 37~460, 1977.
2.
Winstanley RG: Observation on the use of the Denar pantographic articulator. J PROSTHET DENT 38:660, 1977. 3. Watt DM: A study of the reproducibility of articulator settings from graphic records of mandibular movement. Dent Pratt Dent Ret 19:119, 1968. 4. Crispin BJ, Myers GE, Clayton JA: Elects of occlusal therapy on pantographic reproducibility of mandibular border movements. J PROSTHET DENT 40~29, 1978. 5. Beard CC, Clayton JA: Effects of occlusal splint therapy on TMJ dysfunction. J PROSTHET DENT 44~324, 1980. 6. Lamontagne PP: Pantographic Tracings Related to Setting of
8.
Articulator. Thesis, University of Michigan, School of Dentistry, 1970. p 44. Rea TJ: Human Variance in Adjusting a Fully Adjusted Articulator by Means of a Pantograph. Thesis, University of Michigan, School of Dentistry, 1972, p 65. Dorman CW: The Relationship of Hinge Axes to Pantographic Surveys. Thesis, University of Michigan, School of Dentistry, 1972, p 46
Kqmnl
H. b&#&mm&e,* J. E. Gres, D.DS.,** V. A. M&m, P&D.,*** J. L. Fexracaae, Ph.D.,*** and G. A. Harvey, D.Dd.***** Baylor
College of Dentistry,
Dallas,
T. 0
Tex.
L
@t-cured resins have the advantage of being one component system with a virtually infinite working time. H~wwer, the limited depth of cure in these systems has proved to be of conccrn.lW4 Two methods have commonly been used to determine the depth of cure in resins. One method used the optical rnicrw to detect changes in the translucency of the light-cured resins as a function of depth of polymerization.5,6 A second method involved measuring the microhardmz+s of the resir~.‘-~*‘-‘~ Apparently, several variabhs may play a role in determining depth of cure in light-a&vat& resins. Certain light sources failed to produce optimum cures in many resins.‘s4 In other research, darker shades seemed to require longer illumination times than did lighter shades to produce a high degree of polymeriaa&n.7-io The continued polymerization of &ghbctned m&s after il~~~~n has al= been reported.’ In ene study the ~&W&K&continued to
Presented at the International Association for Dental Dallas, Tex. *Visiting Scientist, Sunstar, Inc., Osaka Japan. **Private practice, Austin, Tex. ‘**Assistant Professor, Dental Materials. ****Professor and Chairman, Dental Matcrials. *****Assistant Professor, Operative Dentistry. 574
reyuest.r to:
DR. CHARLES C. BEARD UNIVERSITY OF MICHIGAN SCHOOL OF DENTISTRY ANN ARBOR, MI 48109
Research,
T&de I. Compites
stwbd IHiUmia&on
Material’ Aurafill yellow Aurafill gray-brown Aurafill light Command universal Prima+Fil light gray Primaa-Fil light gray Prisma-Fine light gray Ultra-Bond shade 62 Profile
40 (>4 mm) 40 (>4 mm) 40 (>4 mm) 30 (4 mm) 10 (2.5 mm) 40(4mm) 40 (2.5 mm) 15 (unlimited)
OlZU83 012083 012083 122382-1342 111092 111@92 1213831 q?Y5 052582
‘All resins were illuminated with a Prisma-Litc (L.D. Caulk) except for Ultra-Bond, which was illuminated with a Visar Liihc (Den-Mat). Depths listed under illumination times refer to maduifacmmn’ claims for depth of cure at the specified illumination period.
in~upto3moaths*tht&i4ikb@ia~ pit and fissurx! seabta.” A s&s@@+@ &&CJMX between the hardness measu& w,abr i#bmination and that W-a.& 1 dr)l w~.~~BJM&~ However, the hardness after 1 dq rnas~~~&~.~ to the ha&ess after 7 days.
MAY 19%
VOLUME
55
NUMBER 5
DEPTH
OF CURE OF VISIBLE
LIGHT-CURED
RESIN
25mm
_ 2mm
)
Compodts Resin
0
4.5mm
0 12mm
Gypsum
0 l!klT
I
(b)
(a
Fig. 1. a, Specimen configuration for Knoop hardness measurements. b, An enlarged view of composite shows measurement positions.
pylene and polytetrafluoroethylene molds. resulted in an overestimated depth of cure, thereby emphasizing the importance of the mold material in in vitro studies.14 The purpose of this study was to determine the depth of cure of light-activated composite restoratives placed under simulated clinical conditions in extracted teeth. The specimens were evaluated to determine the effects of aging the resins for 6 months at 37” C.
MATERIAL
AND METHODS
Cylindrical cavity preparations were drilled in occlusal surfaces of extracted second molars with a modified carbide bur mounted in a precision drill press. The cavity preparations were 2 mm in diameter and 4.5 mm in depth. Seven light-cured composites were studied including the yellow, gray-brown, and light shades of Aurafill (Johnson & Johnson, East Windsor, N.J.), Command universal (Sybron/Kerr, Romulus, Mich.), Prisma-Fil light gray and Prisma-Fine light gray (L.D. Caulk Co., Milford, Del.), and Ultra-Bond shade 62 (Den-Mat, Santa Maria, Calif.). Profile (S.S. White, Philadelphia, Pa.), a chemically cured composite, was used as a control. The resins were injected with a syringe into the preparations and were illuminated .according to manufacturers’ instructions (Table I). In addition, a second series of Prisma-Fil specimens was illuminated for 10 seconds to determine the effects of insufficient illumination time. Five specimens were tested for each resin. Specimens were retained at 37” C for 2 hours after illumination. They were subsequently embedded in gypsum and sectioned longitudinally with an Isomet low-speed saw (Buehler, Ltd., Lake Bluff, Ill.). The sectioned surfaces were polished with a 6 pm diamond polishing wheel to produce smooth surfaces. These specimens were stored at 37” C until tested. Rnoup hardness was measured with a Tukon Tester (Page-Wilson Corp., Bridgeport, Conn.) with a SOOgram load. Measurements of hardness were made at 48 hours and 6 months (except for resins Ultra-Bond and Prisma-Fine). The indentations were made at 0.5 and 1 THE JOURNAL
OF PROSTHETIC
DENTISTRY
Aurafill Aurafill
Command Ptisma-Fii Prism&Al
liiht
Prisma-Fine Ultra-Bond
yellow
gray-brown
universal liiht
gray
gray
- 40s
light
gray
shade
62
-20 -10 AH (KHNlmm)
60 loo H? (KHN)
Fig. 2. Changes in hardness values (AH) and hardness values at a depth of 1 mm (H,) for all composites at 48 hours and 6 months. (Asterisks indicate no measurements at 6 months.)
mm distances from the tooth/restoration interface and at depths of 1, 2, 3, and 4 mm, as shown in Fig. 1. The data were analyzed with analysis of variance and the Scheffe test for multiple comparisons between means at the p = 0.05 level of significance. Linear regression analysis was performed for each resin system to determine the variation of hardness with depth, according to the equation: H = H. + AH . d, where d = depth (in millimeters), H = &mop hardness at depth of d (in millimeters), H. = Knoop hardness extrapolated to the surface, and AH = change of Knoop hardness with 1 mm increase in depth.
RESULTS There were no significant differences between the hardness values measured at 0.5 and 1 mm distances from the tooth/restoration interface for any resin system. Therefore the results for each resin at each depth were 575
MATSUMOrO
AU: A 100): A (YI
100
AuM AudW Au&I
t-r
Al
Mf&ht ~+‘8y-kown VJbw
A(LI
l
AlOblO
t Y 3
2
1
0
m
4
mm)
0
Fig. 3. Graph of Knoop h&nversus depth for three shades of Au&IL Values represent mean of pooled results for 48 hours and 6 months.
:
:
J
:
-m(mm)
Fig 5. Graph of Knoop hardneaa versus depth for Profile, Ultra-Bond, Command, and PriuarrRne. Values represent mean of pooled resuJts for 48 hours and 6 months.
cxpcacd, a dccrea& illumination
0
:
;
1
:
Fig. 4. Graph of Knoop hardness veruus depth for Prisma-Fil (10 seconds and 40 seconds). Values represent mean of pooled results for 48 hours and 6 months.
pooted (n - 10). The means aad SDs for hardnus valua atadepthoflmmfor48hoursand6mcmthsarc iUuu.1~dhFig.2.Graphsdthehard1xave~sdepth for c.& resin art preuntcd in F&s. 2 through 5. nctladaeadAwa6tlgr8y-txownwaaththighQlc of the light-curad #ystam and was apIi*t to that of the dumicdty cured min Pro&. For each light-cured min, ha&ess decrwxd with increased depth (i.e., the chmgcinlwdamfor~1mm~iadephwas n4qptive) (Fii. 2). The efkct was kwt et for Au&ill Li&t and Ultra-Bond (F&a. 3 and 5). As
576
tim for P&ma-Fil lightgray~uadaminwithareducuiharbssat inaeaaai deph (Fig. 4). The chemi&y cured cap&x& Profile, showed a slight inuzasc in hordnas with increaxd depth (Fig. 5). Cbrrclation betw~ reduced hardness at incrcasai depths was strong (r 2 0.95 for all except Ultra&ad 10.85) and Aurafill [email protected] 10.75)) and significant for the tigtw!ured r&M but in@&ant fix the chemically curat mat. Id IcJloop hardncss vahtcs were obearved bttwecn 48 houn and 6 monthsfor~uatrk@hsd334nun(Fig. 2). This was most &dent for the Riaaa-FIL k@ py spccimm that were itiunkutal for 40 sax&s. Holwever, the slopa of the rqrusion lines for 48 hours and 6 months were stabtially compared at the p = 0.05 kvcl.“ No differenas were found for any of the resins.
The insignificant diffcrcnces between the hardness values at 0.5 and 1 mm dbnces fmn the tooth/ ralawionintafaainliewthatthedcgteof~was cwutMt~tbe~crof~-~ve -Y material. Appmnly, tk optical popeties d the tooth stn@uredomiue-ttKdq5n!cdcurenem.rthc intufauin~dthiarh.
MAY
1%
VOLUME
5s
NUMBER
5
DEPTH
OF CURE OF VISIBLE
LIGHT-CURED
RESIN
polymerization was relatively constant at all depths for these composites. Their constant hardness is in accord with claims made by the manufacturers for the illumination times used. However, it should be noted that Ultra-Bond possessedone half of the hardness of Aurafill light at all depths. The relatively uniform hardness of Ultra-Bond may be explained by a variation in its catalyst chemistry, compared with other light-cured resins. This light-cured resin, which behaved like the chemically cured control Profile, is thought to contain a chemical-curing component as well as a visible light-activated catalyst. For all resins, except Aurafill light, Aurafill graybrown, and Ultra-Bond, the hardness values at the depth of 3 mm were less than 70% of the values measured at a depth of 1 mm, despite manufacturers’ claims for complete cure at these depths. Command universal was not cured sufficiently at 4 mm to record a hardness value. In general, it appears that the manufacturers’ designated illumination times for specific depths of cure are inadequate. Fig. 3 indicates the relationships between depth and Knoop hardness for the three Aurafill shades tested after 48 hours and 6 months. The hardness of Aurafill yellow was not significantly different from that of Aurafill light or Aurafill gray-brown at 1 mm depth after 48 hours @ = 0.05). However, the hardness of Aurafill yellow was significantly lower than that of the light and gray-brown shades at 3 and 4 mm depths after 48 hours (p = 0.05). Visually, Aurafill yellow appears to be less translucent than Aurafill light and Aurafill gray-brown, suggesting that the increased opacity of the yellow shade allows less illumination from the light source to penetrate to greater depths. Apparently, translucency of the resin is more important than shade for predicting depth of cure. Fig. 4 shows the relationship between depth and Knoop hardness after 48 hours and 6 months for Prisma-Fil light resins illuminated for IO and 40 seconds. Measurements of Knoop hardness at 4 mm depths were not possible because of the insufficient polymerization in the resin illuminated for only 10 seconds. The higher hardness value at 1 mm of the Prisma-Fil illuminated for 40 seconds was probably due to an increased concentration of free radicals formed during the longer illumination period. When the illumination time is prolonged, the amount of light reaching the lower depths to form free radicals that initiate polymerization is increased. The total number of photons of light reaching the lower depths for the Prisma-Fil illuminated for 10 seconds is much less than that for the material exposed for 40 seconds. The hardness of the former at 4 mm is negligible. Therefore the increase in illumination time for the latter produces a relatively large increase in
THE JOURNAL
OF PROSTHETIC
DENTISTRY
hardness at the lower depths. These results indicate that the longer exposure time should always be used to cure this composite regardless of the depth of the restoration. The tendency for Knoop hardness values at depths of 3 or 4 mm to be larger at 6 months than at 48 hours may be the result of evaporation or leaching of low molecular weight plasticizing components in the dry 37” C atmosphere or the effects of a continued polymerization during storage. The differences were not always significant, however. The results suggest that the uncured material may undergo physical or chemical changes during aging. CONCLUSIONS 1. Light-activated resins cured in natural teeth exhibited a reduction in hardness with increased depth of the restoration. These results are comparable to tests of different types of curing molds. 2. The difference in catalyst chemistry of Ultra-Bond may explain the uniform hardness profile of this material. 3. The uniform hardness profile of Aurafill (light) may be due to a higher degree of translucency compared with the other shades (yellow and gray-brown). Shade was not the determining factor for depth of cure in Aurafill resin material. 4. In general, manufacturers’ designated illumination times for specific depths are inadequate to ensure complete polymerization. Layering the composite may still be the best method for filling cavity preparations that extend 3 to 4 mm in depth. We thank all the manufacturers for supplying material used in this project.
REFERENCES 1. Skeeters TM, Timmons JH, Mitchell RJ: Curing depth of visible-light cured composite resins. J Dent Res 62~219, 1983 (Abstr No. 448). 2. Stillwater JC, Louka AN: A study on the depth and postexposure polymerization of light-cured composite resins. J Dent Res 62~218, 1983 (Abstr No. 444). 3. Watts DC, Amer 0, Combe EC: Characteristics of visible-light activated composite systems. Br Dent J 156:209, 1984. 4. Hansen EK: After-polymerization of visible light-activated resins: Surface hardness vs. light source. Stand J Dent Res 91:406, 1983. 5. Murray GA, Yates JL, Newman SM: Ultraviolet light and ultraviolet light-activated composite resins. J PROSTHET DENT 46~167, 1981. 6. Newman SM, Murray GA: Visible lights and visible lightactivated composite resins. J PROSTHETDENT 50~31, 1983. 7. Swartz ML, Phillips RW, Rhodes BF: Visible light-activated resins-Depth of cure. J Dent Res 61:270, 1982 (Abstr No. 823). 8. Swarm ML, Phillips RW, Rhodes B: Visible light-activated resins-Depth of cure. J Am Dent Assoc 106:634, 1983.
577
MATSUMQTO
9.
10.
11.
12. 13. 14.
Leung RL, Fan FL, Johnston WM: Post-irradiation polymerization of visible light-activated composite resin. J Dent Res 62:363, 1983. Leung R, Fan PL, Johnston WM: Exposure time and thickness on polymerization of visible light composite. J Dent Res 61:248, 1982 (Abstr No. 623). Young KC, Cummings A, Main C, Gillespie FC, Stephen KW: Microhardness studies on the setting characteristics of fissure sealants. J Oral Rehab 5187, 1978. Lange CD, Bausch JR, Davidson CL: The curing pattern of photo-initiated dental composite. J Oral Rehab 7:369, 1980. Salako NO, Cruickshanks-Boyd DW: Curing depths of materials polymerized by ultra-violet light. Br Dent J 146~375, 1979. Denyer R, Shaw D J: Cure evaluation of visible light composites
fStm&q L. Wadt,
Jzs, D,D$.,* oad
s. co
ET AL
by Knoop hardness measurements. J Dent Res 63:271, 1982 (Abstr No. 833). 15. Cook WD: Factors affecting the depth of cure of UV-polymerized composites. J Dent Res 59~800, 1980. 16. Tirtha R, Fan PL, Dennison JB, Powers JM: In vitro depth of cure of photo-activated composites. J Dent Res 61:11&4, 1982. 17. Sokal RR, Rohlf FJ: Biometry, ed 2. San Francisco, 1981, WH Freeman & Co Publishers, p 499. Refirint requests to: DR. V. A. MARKER BAYLORCOLLEGEOF DENTISTRY 3302 GASTONAVE. DALLAS, TX 75246
D8Ds.+
University of Tennessee Center for the Health Sciences, College of Dentistry, Memphis, Tenn
T
he use of &d-etched &red partial dentures for the replacementof missing teeth is well documented.‘” The teehniq~e has also been describedby Tkmmpsonet al.4 Bond strengths and teebniques for bond&g acid-etched fixed partial dentures have l3ccnreported for the chemically cured compositesnormally used.5The literature doesnot include researchwith light-cured cxxnpositesto bond the solid retainers of acid-etched fixed partial dentures. With the introduction of perforated retainers, the use of visible light guns to cure light-cured composites could be used in bonding the restoratiion. The solid retainers of the acid-etched fixed partial denture make conventional methods of bonding with ligbxred cornposites difficult. The purpcse of this study was to devisea technique to use light-cured compositesas a bonding medium for the solid retainer and to test the strength of the bonds.
Fig, 1. Fabticated retabers used to represf+nt s&d retainers of fixed partial &m.
retainers: Sikx (384 fill (K&m, Irvine,
L AND M-05 In this study, retainers were fabricated out of Rexillium III &neric Gold Co., Wallingford, C&n.) metal (a aiekel~andberyIlium~tainmg alley} and bandedto the f&al su&ces of 60 bevine teeth. Ibvine teeth have been used as an acceptablesubstitute for human teeth becauseof the clese resemblanceof the enamel surface.6 Thrce~~~com~tcswcre~to~the *Assistant Professor, Division of Biomaterials.
578
3 minutes in an ultr-rasQnEc dcaner in a s&r&m -of It%