TENSILESTAENGTBOFRESINBOND
ically etched L&cast I3 alloy (Williams Gold Refining Co) bonded to enamel and achieved a mean tensile strength of 10.9 + 4.2 MPa. Sloan et ais reported simifar results with electrolytically etched Rexillum III alloy (Jeneric Gold Co. Wallingford, Conn.) bonded to enamel. These results do not agree with those of Livaditis.” He obtained tensile bond strengths in the range of 20 MPa for chemically etched non-noble alloy bonded to resin columns. Clinically, resin-bonded retainers are always bonded to enamel. Therefore, this study, which evaluates the etched metal bond to enamel, should relate more to the actual clinical situation. Of the four luting resins tested, Comspan Regular demonstrated the highest tensile bond strength. A disadvantage of Comspan Regular resin, however, is its low opacity, which results in metal show-through in the resin, especially at the incisal edges of anterior teeth. Chemical etching has several advantages over electrolytical etching. The restoration can be etched in the dental office, possibly saving a patient visit. The technique is also simpler, the equipment less costly and easier to use. Several restorations can be etched together, unlike electrolytic etching where only one retainer can be etched at a time. With electrolytic etching, the degree of etch depends on the distance of the metal surface from the electrode. This frequently results in surfaces closest to the electrode being overetched or the curved surfaces farthest from the electrode being underetched. The curvature of the restoration does not affect the uniformity of etch with chemical etching.
Influence of ceramic thickness light-cured resin cement
SUMMARY A model was made to represent the in vivo situation for resin-bonded restoration using metal bonded to enamel. The tensile bond strength of chemically etched metal bonded to enamel was compared to that obtained for electrolytically etched metal. Four resin luting agents were used. The results obtained were as follows: 1. The tensile bond strength of chemically etched nonnoble alloy bonded to enamel was lower than that obtained for electrolytically etched alloy, but the difference was not statistically significant. 2. Of the four resin luting agents used, Comspan Regular demonstrated the highest mean bond strength. REFERENCES 1. Rochette AL. Attachment of a splint to enamel of lower anterior J PROSTHET DENT 1973;30:418-23.
teeth.
2. Livaditis Cd, Thompson VP. Etched castings: an improved retentive mechanism for resin-bonded retainers. d PROSTHET DENT 1982;47:52-8. 3. Levine WA. Physical properties of resin futing cements [Abstract]. J Dent Res 1986;65:256. 4. Nykamp TL, Lorey RE, Myers GE. A comparison of the various mechanisms of etched resin-bonded bridges [Abstract]. J Dent Res 1984;63:331. 5. Sloan KM, Koray RE, Myers GE. Evaluation of laboratory etching of cast metal resin-bonded retainers [Abstract]. 3 Dent Res 1983;62:305. 6. Livaditis GJ. A chemical etching system for creating rnicrarn~h~~~l retention in resin-bonded retainers. J PROSTHET DENT 1986;56:181-8. Reprint
requests
to:
DR. WENDI A. LEVINE SCHOOL OF DENTISTRY, RM 337 GE~R~T~~TOWN UNIVERSITY WASHINGTON, DC 20007
on the polymerization
of
R. Blackman, D.D.S., M.S.D.,** N. Barghi, D.D.S., M.A.,** and E. Duke, D.D.S., M.S.D.*** The
University
of Texas
Health
Science
Center
at San Antonio,
Dental
School,
San Antonio,
Tex.
The curing of two light-activated resin cements under two ceramic materials was examined to assess the influence of ceramic thickness on polymerization. The degree of resin cure was determined by microhardness measurements (Snoop) on resin cement samples cured under five ceramic thicknesses with light exposures of 30 to 120 seconds. These cements cured under thin ceramic specimens with recommended exposures. With thick ceramics, both cements cured better under the glass-ceramic, but neither reached a level of maximum cure under the procelain. (J P~0S~B~~D~~~1990;63:295-300.)
Supported in part by Dentsply In~rnation~, York, Pa. *Clinical Assistant Professor, Department of Restorative Dentistry. **Professor, Department of Restorative Dentistry. ***Associate Professor, Department of Restorative Dentistry.
10/l/15847 THEJOURNALOFPROSTHETIC~~NTIS~Y
eramic onlay and inlay veneer restorations are luted with light-activated composite resin cements.The degreeof polymerization of thesecementamay be influenced by the ceramic material placed between the curing light and the resin. c
commonly
295
BLACKMAN,
DIRECTION LIGHT i 1
METHODS
Of
I ----CERAMIC
BLOCK
METAL FORMER 0.5mm THICK
1 Q-RESIN
SAN~PLE
! # ;
GLASS, CLEAR
RESIN SAMPLE
FORMINQ
EXPANDED
MOLD
VIEW
Fig. 1. Diagram of sample-forming
mold.
In their study on the curing of composite resin restorations, Chan and Boyerl noted that the degree of polymerization was reduced when the activating light passed through dentin. Onose et al.,2 also found that resin hardness at deep cavity Ievefs was significantly improved by additional light delivered directly to sectioned specimen surfaces. Strang et a1.,3reported setting times of resin cements used for luting etched porcelain resin-bonded veneers, but their study did not include thick porcelain samples (3 to 4 mm) as may occur in posterior resin-bonded restorations. They showed that porcelain absorbs 40% to 50% of the curing light and that increased porcelain thicknesses required increased exposure times for resin curing. In addition, they found that a visible light-curing resin cement performed better than a light- and ~hemic~-curd (dual curing) resin. Although there are pol~erization factors common to composite resins used for restorations and those used for luting, the influence of thickness and type of overlying ceramic material used for luting should be considered. This study examined and compared the influence of material thickness by using two commercially available ceramic materials (a feldspathic porcelain and a cast glassceramic) on curing resin cements used for luting etched ceramic resin-bonded restorations. 296
AND
BARGHI,
AND
DUKE
MATERIAL
Ceramic specimens, 11 mm square, were made in five thicknesses (O&l, 2,3, and 4 mm) with two materials: Vita VMK68 porcelain (Vident, Baldwin Park, Calif.) and Dicer cast glass-ceramic (Dentsply International, York, Pa.). These ceramic materials were processed according to manufacturers’ instructions, and all were shaded to match the Vita Lumin A3 porcelain shade. Resin samples, 0.5 mm x 6 mm in dimeter, were made in a metal former sandwiched between a ceramic specimen and glass (Fig. 1). A release agent, dry Teflon spray lubricant (Dymon Inc., Kansas City, Kan.), was used on the metal and ceramic surfaces. For this study, two types of resin cement were used, (1) light-curing Porcelite yellow (Kerr M~ufact~ing Co., Romulus, Mich.) and (2) dual curing Dicer translucent (Dentsply International). Resin samples were light-cured with a Coe-lite model 4000 (Coe Laboratories, Inc., Chicago, Ill.). Exposure times varied from 30 to 120 seconds with intervals of 30 seconds. The two ceramic materials, two resin cements, five ceramic thicknesses, and four exposure times provided 80 different combinations. Three resin samples were made for each combination. The samples were mounted on glass slides so that surfaces cured against glass were exposed for microhardness rne~~ernen~. Mounted resin samples were stored in room temperature water for 7 days before measurements were taken. The degree of polymerization was determined by Knoop microhardness measurements in the manner of other studies,4* 5 using a Micromet model 16001001 inst~ment (Buehler, Inc., Evanston, Ill.) with a 5 gm load. Four microhardness measurements were made on each resin sample, one in each quadrant. Thus, 80 different combinations of ceramic types, cements, thicknesses, and exposure times provided 240 resin samples and 960 measurements. Data were analyzed before conversion to Knoop hardness numbers (KHNs) with three-way analysis of variance and Fisher’s least significant difference post-hoc analysis. A value of p < 0.05 was considered statistically significant.
RESULTS Figs. 2 through 5 depict the results of microhardness measurements obtained from this study for the two cements with the various ceramic thicknesses and curinglight exposure times. As judged by these measurements, a maximum cure level was reached at 19.3 KI-IN with Dicor translucent and at 18.7 KHN with Porcelite yellow materials. Porcelite/VMK68 porcelain combinations (Fig. 2) cured to a maximum level within 30 seconds when the porcelain specimens were thin, 0.5 to 1 mm. When specimens were 4 mm thick, a state of maximum cure was not reached with up to 120 seconds of light exposure. A similar curing pattern developed with Dicer cement/ VMK68 porcelain combinations (Fig. 3). Thus, neither cement reached a highly cured state under porcelain specimens 4 mm thick. In contrast, as seen in Figs. 4 and 5, both MARCH
1990
VOLUME
63
NUMBER
3
INFLUENCE
OF CERAMIC
THICKNESS
Fig, 2. Porcelite cement/porcelain tal hne are statistically similar.
Fig. 3. Dicor cement/porcelain line are statistically similar.
ceramic group. All columns extending above borizon-
ceramic group. All columns extending above horizontal
cements developed better curing patterns under Dicer glass-ceramic. Porce~i~~icor glass combinations showed resin cured to a maximum level within the recommended 60 seconds with all Dicer glass specimens except the 4 mm specimens, where more than recommended light exposure THE
JOURNAL
OF PROSTHETIC
DENTISTRY
time was required to bring Porcelite material to a highly cured state {Fig. 4). The curing pattern for Dicer cement/Dicer glass was the best of the four cement/ceramic combinations. In this combination, Dicer cement cured within the recommended 297
BLACKMAN,
BARGHI,
AND
DUKE
Fig. 4. Porcelite cement/Dicer glass-ceramic group. All columns extending above horizontal line are statistically similar.
Fig. 5. Dicer cement/Dicer glass-ceramic group. All columns extending above horizontal line are’statistically similar.
298
MARCH
1990
VOLUME
69
NUMBER
9
INFLUENCE
i
OF CERAMIC
THICKNESS
Fig. 6. Curing pattern comparison for all groups of 80 cement and ceramic combinations studied. Shaded areas include statisticallv similar combinations that cured to maximum level. light exposure time of 60 seconds with all Dicor glass comresins cured under ceramic materials may generally apply to light-curing resins as a group. binations (Fig. 5). Figs. 2 through 5 display the general pattern of Porcelite Statistically significant differences are noted in Figs. 2 and Dicer cements reaching maximum cures more satisthrough 5 by horizontal lines placed through the vertical columns. Those columns extending above the horizontal factorily under thin ceramic specimens than under thick lines represent statistically similar values. These differspecimens. In many instances the level of resin cure ences are also shown in the composite diagram (Fig. 6) improved with light exposure increased up to twice the where shaded areas represent a level of maximum cure for recommended time. A highly cured state was reached with the various exposure times and ceramic thickness (the 30all four cement/ceramic combinations by using thin cesecond exposure time has been separately marked to indiramic specimens (Figs. 2 through 5). These were the maximum levels obtained in this study and no improvement cate that this interval was below the manufacturers’ was found with increased exposure time. Consequently, recommendations). they constitute the study controls. Because the thin ceDISCUSSION ramic specimens represent thicknesses found in most When light-curing composite resin cements are used for ceramic veneer restorations, it is reasonable to expect bonding etched ceramic restorations, there appear to be maximum resin curing under etched-ceramic, resin-bonded veneers with the use of any of the four cement/ceramic distinct differences in what can be expected from different combinations studied. cement/ceramic combinations. The ceramic material under With thick ceramic specimens, the curing pattern which a resin cement is cured seems to exert a considerable changes. These dimensions (3 to 4 mm) are common for influence on the degree of resin polymerization achievable, posterior ceramic inlay and onlay restorations (Fig. 6). It much the same as thickness does with direct composite can be seen that neither Porceiite nor Dicer cement cured resin restorations cured by light.6*7 as well under thick VMK68 porcelain as they did under For this study, the materials selected are representative thin VMK68 porcelain specimens. Twice the recommended of those available for the etched ceramic resin bonding light exposure (120 seconds) was inadequate for producing technique. Although comments are specific for the cement/ a highly cured state with these two resin cements. However, ceramic combinations examined, general characteristics of
TEE
JOURNAL
OF PROSTHETIC
DENTISTRY
299
BLACKMAN,
both Porcelite and Dicer cements cured better under thick Dicer glass-ceramic specimens compared with thick VMK68 porcelain. In Fig. 6 it is also apparent that Dicer cement cured well within the recommended 60 seconds of curing-light exposure, whereas Porcelite cement required more exposure to attain a similar level of cure in 4 mm specimens. From a clinical standpoint, curing cements under thick (3 to 4 mmf porcelain restorations may present a problem. In these situations both cements could be expected to reach their maximum cure only under thick Dicer glass-ceramic restorations-Dicer cement within recommended exposure time and Porcelite cement with slightly longer than recommended exposure. Here our findings agree with Strang et aL3 who stated that cement manufacturers’ exposure times “should be treated with caution.” Composite resins as used for direct dental restorations have been studied extensively in recent years, and there may be a great deal of valuable ~formation applicable also to composite resin cements in these studies. In this regard, some investigators have noted that reductions in’ physical properties and performance characteristics accompany incomplete polymerization of light-cured composite resins.8*g Because these restorative resins are chemically similar to the resin cements studied, it is logical that the loss of potential properties and characteristics during the curing process should be avoided. In addition, the consequences of resin fully cured at the margins of etchedceramic, resin-bonded restorations and partially cured at the depths of the restoration have not been explored. Therefore, it seems prudent to use systems that will ensure resin cement curing to a maximum level.
CONCLUSIONS 1. Porcelite yellow and Dicer translucent cements reach maximum cure levels within the recommended 60 seconds of light exposure under thin, 0.5 and 1 mm, specimens of VMK68 porcelain and Dicer glass-ceramic.
300
BARGHI,
AND
DUH
2. Under thin specimens of both ceramics, Dicer yell01 cement cured to its maxims in less than the recon: mended exposure time. 3. Both cements studied cured better under thick, 3 an 4 mm, specimens of Dicer glass-ceramic: Dicer cemen cured within the recommended 60 seconds and Porcelit cement required slightly longer light exposure. 4. Neither resin cured well under thick, 3 and 4 mn VMK68 porcelain, even with light exposures of two time the recommendations. 5. When ceramic restorations having thick dimension are cemented with the resin cements studied, maximum curing would be expected under the glass-ceramic Dice but not under the feldspathic porcelain VMK68. REFERENCES 1. Chan KC, Boyer DR. Curing light-activated composite resins throug dentin. J PROST~ DENT 1985;54:643-5. 2. Onose H, Sano H, Kanto H, et al. Selected curing characteristics < light-activate composite resins. Dent Mater 1985;1:48-54. 3. Strang R, McCrosson J, Muirhead M, Richardson SA. The setting I visible-light-cured resins beneath etched porcelain veneers. Br Dent 1987;163:149. 4. Watts DC, Amar 0, Combe EC. Characteristics of visible-light-act vated composite systems. Br Dent J 1984;156:209-15. 5. Watts DC. Surface hardness development in light-cured composite Dent Mater 1987;3:256. 6. Matsumoto H, Gres JE, Marker VA, Okabe T, Ferracane JL, Harve GA. Depth of cure of visible light-cured resin: clinical simulation. PROSTHET
DENT
1986;55:574-8.
7. Ferracane JL, Aday P, Matsumoto H, Marker VA. Relationshi between shade and depth of cure for light-activated dental composil resins. Dent Mater 1986,2:80-4. 8. Asmusaen E. Restorative resins: hardness and strength vs. quantity ( remaining double bonds. Stand 3 Dent Res l~~~:~-Q. 9. Ruyter IE. Methac~late-based polymeric dental materials: conversio and related properties. Summary and review. Acta Odontol Scan 1982;40:359-76. Reprint
requests
DR. ~NALD
to:
BLACKEN
WNTAL SCHOOL THE ~NI~~~Y OF TEXAS 7703 FLOYD CURL DR. SAN ANTONIO, TX 16284
HEALTH
MARCH
SCBNCE
1990
CENTER
VOLUME
AT SAN ANTONIO
03
KUMBER
ically etched L&cast I3 alloy (Williams Gold Refining Co) bonded to enamel and achieved a mean tensile strength of 10.9 + 4.2 MPa. Sloan et ais reported simifar results with electrolytically etched Rexillum III alloy (Jeneric Gold Co. Wallingford, Conn.) bonded to enamel. These results do not agree with those of Livaditis.” He obtained tensile bond strengths in the range of 20 MPa for chemically etched non-noble alloy bonded to resin columns. Clinically, resin-bonded retainers are always bonded to enamel. Therefore, this study, which evaluates the etched metal bond to enamel, should relate more to the actual clinical situation. Of the four luting resins tested, Comspan Regular demonstrated the highest tensile bond strength. A disadvantage of Comspan Regular resin, however, is its low opacity, which results in metal show-through in the resin, especially at the incisal edges of anterior teeth. Chemical etching has several advantages over electrolytical etching. The restoration can be etched in the dental office, possibly saving a patient visit. The technique is also simpler, the equipment less costly and easier to use. Several restorations can be etched together, unlike electrolytic etching where only one retainer can be etched at a time. With electrolytic etching, the degree of etch depends on the distance of the metal surface from the electrode. This frequently results in surfaces closest to the electrode being overetched or the curved surfaces farthest from the electrode being underetched. The curvature of the restoration does not affect the uniformity of etch with chemical etching.
Influence of ceramic thickness light-cured resin cement
SUMMARY A model was made to represent the in vivo situation for resin-bonded restoration using metal bonded to enamel. The tensile bond strength of chemically etched metal bonded to enamel was compared to that obtained for electrolytically etched metal. Four resin luting agents were used. The results obtained were as follows: 1. The tensile bond strength of chemically etched nonnoble alloy bonded to enamel was lower than that obtained for electrolytically etched alloy, but the difference was not statistically significant. 2. Of the four resin luting agents used, Comspan Regular demonstrated the highest mean bond strength. REFERENCES 1. Rochette AL. Attachment of a splint to enamel of lower anterior J PROSTHET DENT 1973;30:418-23.
teeth.
2. Livaditis Cd, Thompson VP. Etched castings: an improved retentive mechanism for resin-bonded retainers. d PROSTHET DENT 1982;47:52-8. 3. Levine WA. Physical properties of resin futing cements [Abstract]. J Dent Res 1986;65:256. 4. Nykamp TL, Lorey RE, Myers GE. A comparison of the various mechanisms of etched resin-bonded bridges [Abstract]. J Dent Res 1984;63:331. 5. Sloan KM, Koray RE, Myers GE. Evaluation of laboratory etching of cast metal resin-bonded retainers [Abstract]. 3 Dent Res 1983;62:305. 6. Livaditis GJ. A chemical etching system for creating rnicrarn~h~~~l retention in resin-bonded retainers. J PROSTHET DENT 1986;56:181-8. Reprint
requests
to:
DR. WENDI A. LEVINE SCHOOL OF DENTISTRY, RM 337 GE~R~T~~TOWN UNIVERSITY WASHINGTON, DC 20007
on the polymerization
of
R. Blackman, D.D.S., M.S.D.,** N. Barghi, D.D.S., M.A.,** and E. Duke, D.D.S., M.S.D.*** The
University
of Texas
Health
Science
Center
at San Antonio,
Dental
School,
San Antonio,
Tex.
The curing of two light-activated resin cements under two ceramic materials was examined to assess the influence of ceramic thickness on polymerization. The degree of resin cure was determined by microhardness measurements (Snoop) on resin cement samples cured under five ceramic thicknesses with light exposures of 30 to 120 seconds. These cements cured under thin ceramic specimens with recommended exposures. With thick ceramics, both cements cured better under the glass-ceramic, but neither reached a level of maximum cure under the procelain. (J P~0S~B~~D~~~1990;63:295-300.)
Supported in part by Dentsply In~rnation~, York, Pa. *Clinical Assistant Professor, Department of Restorative Dentistry. **Professor, Department of Restorative Dentistry. ***Associate Professor, Department of Restorative Dentistry.
10/l/15847 THEJOURNALOFPROSTHETIC~~NTIS~Y
eramic onlay and inlay veneer restorations are luted with light-activated composite resin cements.The degreeof polymerization of thesecementamay be influenced by the ceramic material placed between the curing light and the resin. c
commonly
295
BLACKMAN,
DIRECTION LIGHT i 1
METHODS
Of
I ----CERAMIC
BLOCK
METAL FORMER 0.5mm THICK
1 Q-RESIN
SAN~PLE
! # ;
GLASS, CLEAR
RESIN SAMPLE
FORMINQ
EXPANDED
MOLD
VIEW
Fig. 1. Diagram of sample-forming
mold.
In their study on the curing of composite resin restorations, Chan and Boyerl noted that the degree of polymerization was reduced when the activating light passed through dentin. Onose et al.,2 also found that resin hardness at deep cavity Ievefs was significantly improved by additional light delivered directly to sectioned specimen surfaces. Strang et a1.,3reported setting times of resin cements used for luting etched porcelain resin-bonded veneers, but their study did not include thick porcelain samples (3 to 4 mm) as may occur in posterior resin-bonded restorations. They showed that porcelain absorbs 40% to 50% of the curing light and that increased porcelain thicknesses required increased exposure times for resin curing. In addition, they found that a visible light-curing resin cement performed better than a light- and ~hemic~-curd (dual curing) resin. Although there are pol~erization factors common to composite resins used for restorations and those used for luting, the influence of thickness and type of overlying ceramic material used for luting should be considered. This study examined and compared the influence of material thickness by using two commercially available ceramic materials (a feldspathic porcelain and a cast glassceramic) on curing resin cements used for luting etched ceramic resin-bonded restorations. 296
AND
BARGHI,
AND
DUKE
MATERIAL
Ceramic specimens, 11 mm square, were made in five thicknesses (O&l, 2,3, and 4 mm) with two materials: Vita VMK68 porcelain (Vident, Baldwin Park, Calif.) and Dicer cast glass-ceramic (Dentsply International, York, Pa.). These ceramic materials were processed according to manufacturers’ instructions, and all were shaded to match the Vita Lumin A3 porcelain shade. Resin samples, 0.5 mm x 6 mm in dimeter, were made in a metal former sandwiched between a ceramic specimen and glass (Fig. 1). A release agent, dry Teflon spray lubricant (Dymon Inc., Kansas City, Kan.), was used on the metal and ceramic surfaces. For this study, two types of resin cement were used, (1) light-curing Porcelite yellow (Kerr M~ufact~ing Co., Romulus, Mich.) and (2) dual curing Dicer translucent (Dentsply International). Resin samples were light-cured with a Coe-lite model 4000 (Coe Laboratories, Inc., Chicago, Ill.). Exposure times varied from 30 to 120 seconds with intervals of 30 seconds. The two ceramic materials, two resin cements, five ceramic thicknesses, and four exposure times provided 80 different combinations. Three resin samples were made for each combination. The samples were mounted on glass slides so that surfaces cured against glass were exposed for microhardness rne~~ernen~. Mounted resin samples were stored in room temperature water for 7 days before measurements were taken. The degree of polymerization was determined by Knoop microhardness measurements in the manner of other studies,4* 5 using a Micromet model 16001001 inst~ment (Buehler, Inc., Evanston, Ill.) with a 5 gm load. Four microhardness measurements were made on each resin sample, one in each quadrant. Thus, 80 different combinations of ceramic types, cements, thicknesses, and exposure times provided 240 resin samples and 960 measurements. Data were analyzed before conversion to Knoop hardness numbers (KHNs) with three-way analysis of variance and Fisher’s least significant difference post-hoc analysis. A value of p < 0.05 was considered statistically significant.
RESULTS Figs. 2 through 5 depict the results of microhardness measurements obtained from this study for the two cements with the various ceramic thicknesses and curinglight exposure times. As judged by these measurements, a maximum cure level was reached at 19.3 KI-IN with Dicor translucent and at 18.7 KHN with Porcelite yellow materials. Porcelite/VMK68 porcelain combinations (Fig. 2) cured to a maximum level within 30 seconds when the porcelain specimens were thin, 0.5 to 1 mm. When specimens were 4 mm thick, a state of maximum cure was not reached with up to 120 seconds of light exposure. A similar curing pattern developed with Dicer cement/ VMK68 porcelain combinations (Fig. 3). Thus, neither cement reached a highly cured state under porcelain specimens 4 mm thick. In contrast, as seen in Figs. 4 and 5, both MARCH
1990
VOLUME
63
NUMBER
3
INFLUENCE
OF CERAMIC
THICKNESS
Fig, 2. Porcelite cement/porcelain tal hne are statistically similar.
Fig. 3. Dicor cement/porcelain line are statistically similar.
ceramic group. All columns extending above borizon-
ceramic group. All columns extending above horizontal
cements developed better curing patterns under Dicer glass-ceramic. Porce~i~~icor glass combinations showed resin cured to a maximum level within the recommended 60 seconds with all Dicer glass specimens except the 4 mm specimens, where more than recommended light exposure THE
JOURNAL
OF PROSTHETIC
DENTISTRY
time was required to bring Porcelite material to a highly cured state {Fig. 4). The curing pattern for Dicer cement/Dicer glass was the best of the four cement/ceramic combinations. In this combination, Dicer cement cured within the recommended 297
BLACKMAN,
BARGHI,
AND
DUKE
Fig. 4. Porcelite cement/Dicer glass-ceramic group. All columns extending above horizontal line are statistically similar.
Fig. 5. Dicer cement/Dicer glass-ceramic group. All columns extending above horizontal line are’statistically similar.
298
MARCH
1990
VOLUME
69
NUMBER
9
INFLUENCE
i
OF CERAMIC
THICKNESS
Fig. 6. Curing pattern comparison for all groups of 80 cement and ceramic combinations studied. Shaded areas include statisticallv similar combinations that cured to maximum level. light exposure time of 60 seconds with all Dicor glass comresins cured under ceramic materials may generally apply to light-curing resins as a group. binations (Fig. 5). Figs. 2 through 5 display the general pattern of Porcelite Statistically significant differences are noted in Figs. 2 and Dicer cements reaching maximum cures more satisthrough 5 by horizontal lines placed through the vertical columns. Those columns extending above the horizontal factorily under thin ceramic specimens than under thick lines represent statistically similar values. These differspecimens. In many instances the level of resin cure ences are also shown in the composite diagram (Fig. 6) improved with light exposure increased up to twice the where shaded areas represent a level of maximum cure for recommended time. A highly cured state was reached with the various exposure times and ceramic thickness (the 30all four cement/ceramic combinations by using thin cesecond exposure time has been separately marked to indiramic specimens (Figs. 2 through 5). These were the maximum levels obtained in this study and no improvement cate that this interval was below the manufacturers’ was found with increased exposure time. Consequently, recommendations). they constitute the study controls. Because the thin ceDISCUSSION ramic specimens represent thicknesses found in most When light-curing composite resin cements are used for ceramic veneer restorations, it is reasonable to expect bonding etched ceramic restorations, there appear to be maximum resin curing under etched-ceramic, resin-bonded veneers with the use of any of the four cement/ceramic distinct differences in what can be expected from different combinations studied. cement/ceramic combinations. The ceramic material under With thick ceramic specimens, the curing pattern which a resin cement is cured seems to exert a considerable changes. These dimensions (3 to 4 mm) are common for influence on the degree of resin polymerization achievable, posterior ceramic inlay and onlay restorations (Fig. 6). It much the same as thickness does with direct composite can be seen that neither Porceiite nor Dicer cement cured resin restorations cured by light.6*7 as well under thick VMK68 porcelain as they did under For this study, the materials selected are representative thin VMK68 porcelain specimens. Twice the recommended of those available for the etched ceramic resin bonding light exposure (120 seconds) was inadequate for producing technique. Although comments are specific for the cement/ a highly cured state with these two resin cements. However, ceramic combinations examined, general characteristics of
TEE
JOURNAL
OF PROSTHETIC
DENTISTRY
299
BLACKMAN,
both Porcelite and Dicer cements cured better under thick Dicer glass-ceramic specimens compared with thick VMK68 porcelain. In Fig. 6 it is also apparent that Dicer cement cured well within the recommended 60 seconds of curing-light exposure, whereas Porcelite cement required more exposure to attain a similar level of cure in 4 mm specimens. From a clinical standpoint, curing cements under thick (3 to 4 mmf porcelain restorations may present a problem. In these situations both cements could be expected to reach their maximum cure only under thick Dicer glass-ceramic restorations-Dicer cement within recommended exposure time and Porcelite cement with slightly longer than recommended exposure. Here our findings agree with Strang et aL3 who stated that cement manufacturers’ exposure times “should be treated with caution.” Composite resins as used for direct dental restorations have been studied extensively in recent years, and there may be a great deal of valuable ~formation applicable also to composite resin cements in these studies. In this regard, some investigators have noted that reductions in’ physical properties and performance characteristics accompany incomplete polymerization of light-cured composite resins.8*g Because these restorative resins are chemically similar to the resin cements studied, it is logical that the loss of potential properties and characteristics during the curing process should be avoided. In addition, the consequences of resin fully cured at the margins of etchedceramic, resin-bonded restorations and partially cured at the depths of the restoration have not been explored. Therefore, it seems prudent to use systems that will ensure resin cement curing to a maximum level.
CONCLUSIONS 1. Porcelite yellow and Dicer translucent cements reach maximum cure levels within the recommended 60 seconds of light exposure under thin, 0.5 and 1 mm, specimens of VMK68 porcelain and Dicer glass-ceramic.
300
BARGHI,
AND
DUH
2. Under thin specimens of both ceramics, Dicer yell01 cement cured to its maxims in less than the recon: mended exposure time. 3. Both cements studied cured better under thick, 3 an 4 mm, specimens of Dicer glass-ceramic: Dicer cemen cured within the recommended 60 seconds and Porcelit cement required slightly longer light exposure. 4. Neither resin cured well under thick, 3 and 4 mn VMK68 porcelain, even with light exposures of two time the recommendations. 5. When ceramic restorations having thick dimension are cemented with the resin cements studied, maximum curing would be expected under the glass-ceramic Dice but not under the feldspathic porcelain VMK68. REFERENCES 1. Chan KC, Boyer DR. Curing light-activated composite resins throug dentin. J PROST~ DENT 1985;54:643-5. 2. Onose H, Sano H, Kanto H, et al. Selected curing characteristics < light-activate composite resins. Dent Mater 1985;1:48-54. 3. Strang R, McCrosson J, Muirhead M, Richardson SA. The setting I visible-light-cured resins beneath etched porcelain veneers. Br Dent 1987;163:149. 4. Watts DC, Amar 0, Combe EC. Characteristics of visible-light-act vated composite systems. Br Dent J 1984;156:209-15. 5. Watts DC. Surface hardness development in light-cured composite Dent Mater 1987;3:256. 6. Matsumoto H, Gres JE, Marker VA, Okabe T, Ferracane JL, Harve GA. Depth of cure of visible light-cured resin: clinical simulation. PROSTHET
DENT
1986;55:574-8.
7. Ferracane JL, Aday P, Matsumoto H, Marker VA. Relationshi between shade and depth of cure for light-activated dental composil resins. Dent Mater 1986,2:80-4. 8. Asmusaen E. Restorative resins: hardness and strength vs. quantity ( remaining double bonds. Stand 3 Dent Res l~~~:~-Q. 9. Ruyter IE. Methac~late-based polymeric dental materials: conversio and related properties. Summary and review. Acta Odontol Scan 1982;40:359-76. Reprint
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DR. ~NALD
to:
BLACKEN
WNTAL SCHOOL THE ~NI~~~Y OF TEXAS 7703 FLOYD CURL DR. SAN ANTONIO, TX 16284
HEALTH
MARCH
SCBNCE
1990
CENTER
VOLUME
AT SAN ANTONIO
03
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