- Email: [email protected]
Evaluating CAD-CAM Generated Ceramic Veneers
P E R N G -R U LIU, D .D .S ., M .S .; B A R R Y R. IS E N B E R G , D .M .D ., M .A .; K A R L F. LEIN F ELDER, D .D .S , M .S.
he proper cosmetic appearance of anterior teeth is A s th e CAD-CAM an important social require ment for today’s patients. In the t e c h n iq u e h a s b e e n past, restoring unesthetic e x p a n d e d to in c lu d e anterior teeth has generally p o r c e la in fa c in g s , o f involved removal of consider p a r tic u la r in t e r e s t is able amounts of sound tooth a d a p tin g th e v e n e e r to : structure. Occasionally, this th e p r e p a r e d s u r fa c e . In a procedure has adverse effects on the pulp and gingival tissue. c o m p a r is o n o f th e g a p The use of ceramic veneers d im e n s io n o f CAD-CAM has added a new dimension to g e n e r a te d v e n e e r s to restorative esthetic dentistry. It th o s e p r o d u c e d in th e is now possible to change the la b o ra to ry , no appearance, color, size and s t a t is t ic a lly s ig n ific a n t ; spacing of teeth with minimum surface preparation. The d iffe r e n c e s w e r e functional strength and d e te c te d . potential longevity of ceramic use has some disadvantages. ; veneers are quite acceptable. These include multiple When veneers are properly appointments, repair difficulty placed, the periodontal response and need for laboratory has been excellent.12 assistance. Regardless of these Although many articles disadvantages, porcelain about ceramic veneers have veneers are considered to be the been published, most are “state-of-the-art.” technique oriented.3'6 Only a few When the CEREC computerstudies have investigated aided design and computermarginal adaptation of the aided manufacture techniques ; veneer to the prepared tooth : surface.6,7 Although facial veneers have been constructed from polymers and ceramic, the latter currently is the preferred material. In general, ceramic veneers are more stain: and wear-resistant and their clinical longevity : is appreciably : greater.2,3'5'8Although porcelain appears to be gaining steadily as the Figure 1. A custom-made cavity preparation preferred material, its template for a CAD-CAM veneer.
were first introduced into dentistry, they were used primarily for inlays and onlays.912 Subsequently, they were recommended for veneers.13Thereafter, an advanced milling system with an electronic milling device was introduced th a t increased the accuracy of the veneers. In this study, we compare the gap dimension of veneers generated by a CAD-CAM (CEREC, Siemens) system to those produced in the laboratory using conventional methods. We also evaluated the clinical performance of the veneers produced. MATERIALS AND METHODS
Thirty human maxillary central incisors were used. All teeth were disinfected in 10 percent formaldehyde for one month and then stored in normal saline solution at room tem perature except during veneer preparation, impression making and cementation. Two veneer systems were included in the investigation: one using the CAD-CAM method with a relatively porefree dental ceramic (Dicor-MGC, L.D. Caulk) or a feldspathic porcelain (Vita Mark II, Vident) supplied in standardized blocks; the other, a conventional porcelain veneer m aterial (Vita VMK 68, Vident) laboratory-fired with the refractory method. DicorJADA, Vol. 124, April 1993
59
MGC (machinable glass ceramic) is a ceramic consisting of 70 percent fine interlocked array of tetrasilicic fluoromica crystals precipitated in a 30 percent non-porous glass matrix consisting principally of silica.14 The composite resin luting system used was Mirage FLC (Chameleon Dental Products). After pooling all of the prepared teeth, we randomly determined the particular technique—either CAD-CAM or laboratory—to fabricate the ceramic veneer. Ten samples were also generated with the new modified milling device. During the study, the new electric version (E-drive) of the CEREC system became available. This model superseded the traditional hydro unit (H-drive) th at milled the ceramic restoration by a pump-generated water jet, which turned the high-speed turbine. The new E-drive milling unit uses an electric motor to drive the milling wheel. Teeth were prepared with a 0.5-millimeter depth cutting
VENEER
diamond bur, No. LVS - 1 (Brasseler USA), to uniformly reduce the enamel. Special twogrit diamond burs (LVS No. 3 and 4) were used to remove the remaining excess enamel to the depth of the original grooves. The final preparation was completed with the entire surface in enamel. The chamfer margins, 0.5 mm in depth, were placed cervically 0.5 mm away from the cementoenamel junction and one-third of the faciolingual dimension interproximally with a welldefined margin. All preparations were divided into three groups: conventional laboratory, CEREC H-drive and CEREC E-drive. The preparations in the conventional veneer group were impressed with a vinyl polysiloxane impression material, Reprosil (L.D. Caulk Co.). The impressions were poured with a vacuum-mixed die stone (Vel-Mix, Kerr) using recommended water/powder ratios. Ten master dies were divided into two groups (specimens 1 to 5 and 6 to 10) before being sent to two different commercial laboratories to fabricate the porcelain veneers. In the CEREC veneer group, the teeth were prepared and
verified with a special custommade preparation template (Figure l).15Possessing the same curvature of the milling disk (30 mm in diameter for the H-drive and 40 mm in diameter for the E-drive), the instrum ent was used to confirm th a t the radius of the prepared labial surface was within the limits of the disk. This process was necessary to ensure th a t the milling machine could cut the restoration properly. After a thin coating of lightreflecting powder was applied to the surface of the prepared tooth, the preparation was imaged. When an acceptable optical impression was imaged, the three-dimensional image was displayed on the monitor. At this point the restoration was computer designed on the monitor (Figure 2). After an appropriately sized block of ceramic was selected, the milling machine produced a veneer in accordance with the electronic instructions placed into the computer. In most instances the entire milling process required less than 10 minutes. The thickness of the completed veneer ranged from 0.5 to 1.0 mm as predetermined in the software program. The internal surfaces were then adjusted to remove
TABLE
MATERIALS AND METHODS. Material
B O T T O M !.IN E
Figure 2. Design of the veneer on the computer screen.
60
JADA, Vol. 124, April 1993
Manufacturer
Method
Dicor ]VIGO
L.D. C aulk
CAD-CAM
V ita M ark II
V id en t
CAD-CAM
V ita VM K 68
V id en t
Lab
TOOTH
VENEER;
Figure 3. Diagram of incisal, gingival and proximal measurement points.
the interferences or high spots th at may have prevented the facing from seating properly. Since the Dicor MGC material is monochromatic, a Dicor shading porcelain kit (Dentsply) was used to shade, stain and glaze the veneer after the labial surface had been shaped to proper contour. This procedure may not be totally necessary since shade modifiers can be placed under the veneers to alter the gingival and incisal shades. After final surfacing and polishing or shading, the pre cemented interfacial gaps between the veneer and the margin of the preparation were determined. Each veneer was held in position with sticky wax at the midpoint of the mesial and distal veneer/tooth interface. The impressions for replica were made with vinyl polysiloxane (Reprosil, L.D. Caulk) according to the manufacturer’s recommendation. In each case, the actual measurements were conducted on epoxy resin replicas of the veneered tooth. Measurements were done at two predetermined sites for each incisal, gingival and proximal margin (Figures 3, 4). This process was performed with a microscope (Gaertner
Figure 4. Diagram of marginal geometry for measuring marginal gap (MG).
Traveling M Microscope, i c Scientific r Corp.) a t xlO o m magnification. c Values of gap t dimension were e r determined to s the nearest 2 microns. After all the Surfaces measurements A U , G R O U P S N = 10 > VNOV i> < « .0 5 were completed, the Figure 5. Gap measurements for the various systems studied. data were analyzed using a one-way drive system. In fact, the analysis of variances (ANOVA) differences between the and a Duncan Multiple Range laboratory preparations and Test to determine differences veneers generated with the Ebetween groups. All tests were drive were statistically performed at the 95 percent insignificant. confidence level. For all methods, the greatest R ESU LTS gap dimension between tooth surface and veneer occurred in M easurements of the mean the incisal region. Interfacial gaps between the ceramic gap dimension in this region veneers and the prepared teeth ranged from 103 to 117 microns are presented in Figure 5. The depending on the fabrication mean interfacial gap, regardless method. In the proximal and of location, generally was gingival regions, the amount greater for the H-drive veneer was considerably less. than for laboratory Regardless of how they were preparations. But the values developed, all veneers required associated with the new E-drive internal surface grinding to milling system were maximize adaptation. However, substantially better than those the CAD-CAM veneers required generated with the original HM tS lA f . D IS T A L
G IN C il' U .
IN C IS A I.
JADA, Vol. 124, April 1993
61
Figure 6a. Before placement of CAD-CAM veneers.
b. After veneer placement.
Figure 7a. Before placement of three CAD-CAM veneers.
b. After veneer placement. Note shade match to adjacent porcelain crowns.
more internal surfacing than the laboratory systems. By comparison, the E-drive milling device produced internal surfaces th a t required less modification than the H-drive system. During the adjustment process, several laboratory generated veneers fractured. However, none of the CADCAM veneers had this problem. We think the difference in fracture resistance can be attributed to differences in mechanical properties.1416 Examples of the colormatching effectiveness of the CAD-CAM processed veneers are shown in Figures 6 and 7. The first represents treatm ent of eight maxillary teeth affected 62
JADA, Vol. 124, April 1993
by fluorosis. The second represents treatm ent of darkened maxillary central incisors and a lateral incisor. In both cases, the teeth were restored with CAD-CAM veneers. Note the degree to which the veneers match the existing adjacent porcelain crown and natural teeth. DISCUSSION
The results of this study show th a t the ceramic veneers generated by the CAD-CAM system were as equally acceptable as those fabricated in the laboratory using conventional procedures. The laboratory-processed veneers, however, required contouring of the facial surfaces, approxi
mating the gingival and proximal margins. This is a common finding with most laboratory-processed veneers.4 The veneers produced by the CAD-CAM technique required modification of the internal surfaces of the veneer adjacent to the prepared tooth. This limitation can be attributed to the geometry of the diamond milling wheel. After the surface modifications were completed, we found th at the interfacial spaces between veneers and prepared tooth were the same. The interfacial gap for the laboratory-processed veneers averaged 66 microns and those for the CAD-CAM veneers after modification were 68 microns.
The differences, however, were statistically insignificant except for the Dr. Isenberg is incisal edge. professor, We noted Department of Restorative th at the only Dentistry, School of statistically Dentistry, University of Alabama at significant Birmingham, UAB differences in Station, Box 82, interfacial gap Birmingham, Ala. 35294-0007. related to the Address reprint incisal edge. requests to Dr. Isenberg. Specifically, the CAD-CAM system, regardless of milling drives, tended to produce incisal edge gaps somewhat larger than those fabricated in the laboratory. We think the discrepancy is related to the software design itself. The E-drive milling device generally produced better fitting or closer adapting margins than those created by the earlier Hdrive milling system. Lack of uniform water pressure with the previously used more flexible diamond disk may have been responsible for the performance differences. Either quartz-containing porcelains (Vita Mark II, Vident) or Dicor can be used for this veneer-generating process. One advantage of the Vita system over Dicor ceramic is that the latter is limited to only two veneer shades. This problem can be resolved somewhat by using internal shading with opaque luting agents.17 In addition, new computerized furnaces (Dentsply Multimat 99, Dentsply) permit the application of external characterization in about 20 minutes. As use of ceramic veneers
Dr. Liu is assistant
: Dr. Leinfelder is
professor,
: professor and acting
Department of
chairman,
Restorative
; Department of
Dentistry, School of
: Biomaterials, School
Dentistry, University
: of Dentistry,
of Alabama at Birmingham.
University of : Alabama at : Birmingham.
increases, they have become an acceptable conservative alternative for resin veneers. The computerized approach offers advantages over the conventional laboratory method of processing: a oneappointment process as well as the ability to fabricate an additional veneer if fracture occurs during placement or cementation. CONCLUSION
This study shows th at a CADCAM system is quite effective in generating high-quality ceramic veneers. We found th at the marginal adaptations of these veneers were essentially the same as those produced by conventional methods. When used with inlay/onlay generating capability, its role in restorative dentistry is apparent. ■ The opinions expressed are those of the authors and do not necessarily reflect the opinion or official policy of the American D ental Association. Inform ation about the m anufacturers of the products m entioned in this article may be available from the authors. N either the authors or the American D ental Association has any commercial interest in the products mentioned.
porcelain lam inate veneers. JADA (Special Issue) 1987;83-7 E. 2. Calam ia JR . Clinical evaluation of etched porcelain veneers. Am J D ent 1989;2:9-15. 3. Calam ia JR. Etched porcelain veneers: the current sta te of the art. Quintessence Int 1985;16:5-12. 4. N athanson D. Etched porcelain restorations for improved esthetics, P a rt 1: anterior veneers. Compend Contin Educ Dent 1986;7:706-13. 5. Clyde JS , Gilm our A. Porcelain veneers: a preliminary review. B r D ent J 1988;164:9-14. 6. H arasani MH, Isidor F, K aaber S. M arginal fit of porcelain and indirect composite lam inate veneers under in vitro condition. Scand J D ent Res 1991;99:262-8. 7. Sorensen JA, S trutz JM , Avera SP, Materdomini D. M arginal fidelity and microleakage of porcelain veneers made by two techniques. J P rosthet D ent 1992;67:16-
22.
8. H orn HR. Porcelain lam inate veneers bond to etched enam el. D ent Clinics North Am 1983;27:671-84. 9. M orm ann WH, B randestini M, Lutz F, Barbakow F. C hairside com puter-aided direct ceramic inlays. Q uintessence In t 1989;20:32939. 10. Leinfelder KF, Isenberg BP, Essig ME. A new m ethod for generating ceramic restorations: a CAD-CAM system . JADA 1989;118:703-7. 11. Isenberg BP, Essig ME, Leinfelder KF, M ueninghoff LA. Clinical evaluation of CEREC CAD-CAM restorations (A bstract no. 1597). J D ent Res 1990;69:1597. 12. Isenberg BP, Essig ME, Leinfelder KF, M ueninghoff LA. Clinical evaluation of m arginal integrity: 2 year results. International Symposium on Com puter Restorations. Chicago: Quintessence; 1991:163-72. 13. C erutti A, Salgarello S, G astaldi G. M arginal adaptation of CEREC veneers in vivo. International Symposium on Com puter Restorations. Chicago: Quintessence; 1991:553-7. 14. Grossm an DG. S tructure and physical properties of Dicor/MGC glass-ceramic. International Symposium on Com puter Restorations. Chicago: Quintessence; 1991:103-13. 15. Essig ME, Isenberg BP, Leinfelder KF, Liu PR. In vitro evaluation of CEREC veneer utilizing standardized preparation template. International Symposium on Com puter Restorations. Chicago: Quintessence; 1991:547-52. 16. Kelly JR , L uthy H, Gougoulakis A, Pober RL, M orm ann WH. M achine effects on feldspathic porcelain and glass ceramic: fractographic analysis. International Symposium on Com puter Restorations. Chicago: Quintessence; 1991:253-73. 17. Siervo S, Pam palone A, Valenti G, B andettini B, Siervo R. Porcelain CAD-CAM veneers: some new uses explored. JADA 1992;123(4):63-7.
1. Friedm an M. M ultiple potential of etched
JADA, Vol. 124, April 1993
63
he proper cosmetic appearance of anterior teeth is A s th e CAD-CAM an important social require ment for today’s patients. In the t e c h n iq u e h a s b e e n past, restoring unesthetic e x p a n d e d to in c lu d e anterior teeth has generally p o r c e la in fa c in g s , o f involved removal of consider p a r tic u la r in t e r e s t is able amounts of sound tooth a d a p tin g th e v e n e e r to : structure. Occasionally, this th e p r e p a r e d s u r fa c e . In a procedure has adverse effects on the pulp and gingival tissue. c o m p a r is o n o f th e g a p The use of ceramic veneers d im e n s io n o f CAD-CAM has added a new dimension to g e n e r a te d v e n e e r s to restorative esthetic dentistry. It th o s e p r o d u c e d in th e is now possible to change the la b o ra to ry , no appearance, color, size and s t a t is t ic a lly s ig n ific a n t ; spacing of teeth with minimum surface preparation. The d iffe r e n c e s w e r e functional strength and d e te c te d . potential longevity of ceramic use has some disadvantages. ; veneers are quite acceptable. These include multiple When veneers are properly appointments, repair difficulty placed, the periodontal response and need for laboratory has been excellent.12 assistance. Regardless of these Although many articles disadvantages, porcelain about ceramic veneers have veneers are considered to be the been published, most are “state-of-the-art.” technique oriented.3'6 Only a few When the CEREC computerstudies have investigated aided design and computermarginal adaptation of the aided manufacture techniques ; veneer to the prepared tooth : surface.6,7 Although facial veneers have been constructed from polymers and ceramic, the latter currently is the preferred material. In general, ceramic veneers are more stain: and wear-resistant and their clinical longevity : is appreciably : greater.2,3'5'8Although porcelain appears to be gaining steadily as the Figure 1. A custom-made cavity preparation preferred material, its template for a CAD-CAM veneer.
were first introduced into dentistry, they were used primarily for inlays and onlays.912 Subsequently, they were recommended for veneers.13Thereafter, an advanced milling system with an electronic milling device was introduced th a t increased the accuracy of the veneers. In this study, we compare the gap dimension of veneers generated by a CAD-CAM (CEREC, Siemens) system to those produced in the laboratory using conventional methods. We also evaluated the clinical performance of the veneers produced. MATERIALS AND METHODS
Thirty human maxillary central incisors were used. All teeth were disinfected in 10 percent formaldehyde for one month and then stored in normal saline solution at room tem perature except during veneer preparation, impression making and cementation. Two veneer systems were included in the investigation: one using the CAD-CAM method with a relatively porefree dental ceramic (Dicor-MGC, L.D. Caulk) or a feldspathic porcelain (Vita Mark II, Vident) supplied in standardized blocks; the other, a conventional porcelain veneer m aterial (Vita VMK 68, Vident) laboratory-fired with the refractory method. DicorJADA, Vol. 124, April 1993
59
MGC (machinable glass ceramic) is a ceramic consisting of 70 percent fine interlocked array of tetrasilicic fluoromica crystals precipitated in a 30 percent non-porous glass matrix consisting principally of silica.14 The composite resin luting system used was Mirage FLC (Chameleon Dental Products). After pooling all of the prepared teeth, we randomly determined the particular technique—either CAD-CAM or laboratory—to fabricate the ceramic veneer. Ten samples were also generated with the new modified milling device. During the study, the new electric version (E-drive) of the CEREC system became available. This model superseded the traditional hydro unit (H-drive) th at milled the ceramic restoration by a pump-generated water jet, which turned the high-speed turbine. The new E-drive milling unit uses an electric motor to drive the milling wheel. Teeth were prepared with a 0.5-millimeter depth cutting
VENEER
diamond bur, No. LVS - 1 (Brasseler USA), to uniformly reduce the enamel. Special twogrit diamond burs (LVS No. 3 and 4) were used to remove the remaining excess enamel to the depth of the original grooves. The final preparation was completed with the entire surface in enamel. The chamfer margins, 0.5 mm in depth, were placed cervically 0.5 mm away from the cementoenamel junction and one-third of the faciolingual dimension interproximally with a welldefined margin. All preparations were divided into three groups: conventional laboratory, CEREC H-drive and CEREC E-drive. The preparations in the conventional veneer group were impressed with a vinyl polysiloxane impression material, Reprosil (L.D. Caulk Co.). The impressions were poured with a vacuum-mixed die stone (Vel-Mix, Kerr) using recommended water/powder ratios. Ten master dies were divided into two groups (specimens 1 to 5 and 6 to 10) before being sent to two different commercial laboratories to fabricate the porcelain veneers. In the CEREC veneer group, the teeth were prepared and
verified with a special custommade preparation template (Figure l).15Possessing the same curvature of the milling disk (30 mm in diameter for the H-drive and 40 mm in diameter for the E-drive), the instrum ent was used to confirm th a t the radius of the prepared labial surface was within the limits of the disk. This process was necessary to ensure th a t the milling machine could cut the restoration properly. After a thin coating of lightreflecting powder was applied to the surface of the prepared tooth, the preparation was imaged. When an acceptable optical impression was imaged, the three-dimensional image was displayed on the monitor. At this point the restoration was computer designed on the monitor (Figure 2). After an appropriately sized block of ceramic was selected, the milling machine produced a veneer in accordance with the electronic instructions placed into the computer. In most instances the entire milling process required less than 10 minutes. The thickness of the completed veneer ranged from 0.5 to 1.0 mm as predetermined in the software program. The internal surfaces were then adjusted to remove
TABLE
MATERIALS AND METHODS. Material
B O T T O M !.IN E
Figure 2. Design of the veneer on the computer screen.
60
JADA, Vol. 124, April 1993
Manufacturer
Method
Dicor ]VIGO
L.D. C aulk
CAD-CAM
V ita M ark II
V id en t
CAD-CAM
V ita VM K 68
V id en t
Lab
TOOTH
VENEER;
Figure 3. Diagram of incisal, gingival and proximal measurement points.
the interferences or high spots th at may have prevented the facing from seating properly. Since the Dicor MGC material is monochromatic, a Dicor shading porcelain kit (Dentsply) was used to shade, stain and glaze the veneer after the labial surface had been shaped to proper contour. This procedure may not be totally necessary since shade modifiers can be placed under the veneers to alter the gingival and incisal shades. After final surfacing and polishing or shading, the pre cemented interfacial gaps between the veneer and the margin of the preparation were determined. Each veneer was held in position with sticky wax at the midpoint of the mesial and distal veneer/tooth interface. The impressions for replica were made with vinyl polysiloxane (Reprosil, L.D. Caulk) according to the manufacturer’s recommendation. In each case, the actual measurements were conducted on epoxy resin replicas of the veneered tooth. Measurements were done at two predetermined sites for each incisal, gingival and proximal margin (Figures 3, 4). This process was performed with a microscope (Gaertner
Figure 4. Diagram of marginal geometry for measuring marginal gap (MG).
Traveling M Microscope, i c Scientific r Corp.) a t xlO o m magnification. c Values of gap t dimension were e r determined to s the nearest 2 microns. After all the Surfaces measurements A U , G R O U P S N = 10 > VNOV i> < « .0 5 were completed, the Figure 5. Gap measurements for the various systems studied. data were analyzed using a one-way drive system. In fact, the analysis of variances (ANOVA) differences between the and a Duncan Multiple Range laboratory preparations and Test to determine differences veneers generated with the Ebetween groups. All tests were drive were statistically performed at the 95 percent insignificant. confidence level. For all methods, the greatest R ESU LTS gap dimension between tooth surface and veneer occurred in M easurements of the mean the incisal region. Interfacial gaps between the ceramic gap dimension in this region veneers and the prepared teeth ranged from 103 to 117 microns are presented in Figure 5. The depending on the fabrication mean interfacial gap, regardless method. In the proximal and of location, generally was gingival regions, the amount greater for the H-drive veneer was considerably less. than for laboratory Regardless of how they were preparations. But the values developed, all veneers required associated with the new E-drive internal surface grinding to milling system were maximize adaptation. However, substantially better than those the CAD-CAM veneers required generated with the original HM tS lA f . D IS T A L
G IN C il' U .
IN C IS A I.
JADA, Vol. 124, April 1993
61
Figure 6a. Before placement of CAD-CAM veneers.
b. After veneer placement.
Figure 7a. Before placement of three CAD-CAM veneers.
b. After veneer placement. Note shade match to adjacent porcelain crowns.
more internal surfacing than the laboratory systems. By comparison, the E-drive milling device produced internal surfaces th a t required less modification than the H-drive system. During the adjustment process, several laboratory generated veneers fractured. However, none of the CADCAM veneers had this problem. We think the difference in fracture resistance can be attributed to differences in mechanical properties.1416 Examples of the colormatching effectiveness of the CAD-CAM processed veneers are shown in Figures 6 and 7. The first represents treatm ent of eight maxillary teeth affected 62
JADA, Vol. 124, April 1993
by fluorosis. The second represents treatm ent of darkened maxillary central incisors and a lateral incisor. In both cases, the teeth were restored with CAD-CAM veneers. Note the degree to which the veneers match the existing adjacent porcelain crown and natural teeth. DISCUSSION
The results of this study show th a t the ceramic veneers generated by the CAD-CAM system were as equally acceptable as those fabricated in the laboratory using conventional procedures. The laboratory-processed veneers, however, required contouring of the facial surfaces, approxi
mating the gingival and proximal margins. This is a common finding with most laboratory-processed veneers.4 The veneers produced by the CAD-CAM technique required modification of the internal surfaces of the veneer adjacent to the prepared tooth. This limitation can be attributed to the geometry of the diamond milling wheel. After the surface modifications were completed, we found th at the interfacial spaces between veneers and prepared tooth were the same. The interfacial gap for the laboratory-processed veneers averaged 66 microns and those for the CAD-CAM veneers after modification were 68 microns.
The differences, however, were statistically insignificant except for the Dr. Isenberg is incisal edge. professor, We noted Department of Restorative th at the only Dentistry, School of statistically Dentistry, University of Alabama at significant Birmingham, UAB differences in Station, Box 82, interfacial gap Birmingham, Ala. 35294-0007. related to the Address reprint incisal edge. requests to Dr. Isenberg. Specifically, the CAD-CAM system, regardless of milling drives, tended to produce incisal edge gaps somewhat larger than those fabricated in the laboratory. We think the discrepancy is related to the software design itself. The E-drive milling device generally produced better fitting or closer adapting margins than those created by the earlier Hdrive milling system. Lack of uniform water pressure with the previously used more flexible diamond disk may have been responsible for the performance differences. Either quartz-containing porcelains (Vita Mark II, Vident) or Dicor can be used for this veneer-generating process. One advantage of the Vita system over Dicor ceramic is that the latter is limited to only two veneer shades. This problem can be resolved somewhat by using internal shading with opaque luting agents.17 In addition, new computerized furnaces (Dentsply Multimat 99, Dentsply) permit the application of external characterization in about 20 minutes. As use of ceramic veneers
Dr. Liu is assistant
: Dr. Leinfelder is
professor,
: professor and acting
Department of
chairman,
Restorative
; Department of
Dentistry, School of
: Biomaterials, School
Dentistry, University
: of Dentistry,
of Alabama at Birmingham.
University of : Alabama at : Birmingham.
increases, they have become an acceptable conservative alternative for resin veneers. The computerized approach offers advantages over the conventional laboratory method of processing: a oneappointment process as well as the ability to fabricate an additional veneer if fracture occurs during placement or cementation. CONCLUSION
This study shows th at a CADCAM system is quite effective in generating high-quality ceramic veneers. We found th at the marginal adaptations of these veneers were essentially the same as those produced by conventional methods. When used with inlay/onlay generating capability, its role in restorative dentistry is apparent. ■ The opinions expressed are those of the authors and do not necessarily reflect the opinion or official policy of the American D ental Association. Inform ation about the m anufacturers of the products m entioned in this article may be available from the authors. N either the authors or the American D ental Association has any commercial interest in the products mentioned.
porcelain lam inate veneers. JADA (Special Issue) 1987;83-7 E. 2. Calam ia JR . Clinical evaluation of etched porcelain veneers. Am J D ent 1989;2:9-15. 3. Calam ia JR. Etched porcelain veneers: the current sta te of the art. Quintessence Int 1985;16:5-12. 4. N athanson D. Etched porcelain restorations for improved esthetics, P a rt 1: anterior veneers. Compend Contin Educ Dent 1986;7:706-13. 5. Clyde JS , Gilm our A. Porcelain veneers: a preliminary review. B r D ent J 1988;164:9-14. 6. H arasani MH, Isidor F, K aaber S. M arginal fit of porcelain and indirect composite lam inate veneers under in vitro condition. Scand J D ent Res 1991;99:262-8. 7. Sorensen JA, S trutz JM , Avera SP, Materdomini D. M arginal fidelity and microleakage of porcelain veneers made by two techniques. J P rosthet D ent 1992;67:16-
22.
8. H orn HR. Porcelain lam inate veneers bond to etched enam el. D ent Clinics North Am 1983;27:671-84. 9. M orm ann WH, B randestini M, Lutz F, Barbakow F. C hairside com puter-aided direct ceramic inlays. Q uintessence In t 1989;20:32939. 10. Leinfelder KF, Isenberg BP, Essig ME. A new m ethod for generating ceramic restorations: a CAD-CAM system . JADA 1989;118:703-7. 11. Isenberg BP, Essig ME, Leinfelder KF, M ueninghoff LA. Clinical evaluation of CEREC CAD-CAM restorations (A bstract no. 1597). J D ent Res 1990;69:1597. 12. Isenberg BP, Essig ME, Leinfelder KF, M ueninghoff LA. Clinical evaluation of m arginal integrity: 2 year results. International Symposium on Com puter Restorations. Chicago: Quintessence; 1991:163-72. 13. C erutti A, Salgarello S, G astaldi G. M arginal adaptation of CEREC veneers in vivo. International Symposium on Com puter Restorations. Chicago: Quintessence; 1991:553-7. 14. Grossm an DG. S tructure and physical properties of Dicor/MGC glass-ceramic. International Symposium on Com puter Restorations. Chicago: Quintessence; 1991:103-13. 15. Essig ME, Isenberg BP, Leinfelder KF, Liu PR. In vitro evaluation of CEREC veneer utilizing standardized preparation template. International Symposium on Com puter Restorations. Chicago: Quintessence; 1991:547-52. 16. Kelly JR , L uthy H, Gougoulakis A, Pober RL, M orm ann WH. M achine effects on feldspathic porcelain and glass ceramic: fractographic analysis. International Symposium on Com puter Restorations. Chicago: Quintessence; 1991:253-73. 17. Siervo S, Pam palone A, Valenti G, B andettini B, Siervo R. Porcelain CAD-CAM veneers: some new uses explored. JADA 1992;123(4):63-7.
1. Friedm an M. M ultiple potential of etched
JADA, Vol. 124, April 1993
63