Three-Year Clinical Evaluation of CAD/CAM Restorations Barry P . Isenberg, D.M.D., M.A.* Milton E . Essig, D.M.D. Karl F . Leinfelder, D.D.S., M.S.
'
This study dealt with the clinical evaluation of 121 inlays and onlays generated from both Dicor ceramics and Vita porcelains. These two different types of ceramic materials were cemented using three different duo-cured composite resin luting agents, which differed in particle size. At the end of 3 years, no difference could be detected between the clinical performance of the Dicor and Vita restorations. Both exhibited the same degree of color matching characteristics, marginal integrity, and general clinical performance; however, seven of the restorations exhibited fracture through the isthmus, which was shown to be due to insuficient cavity depth. The balance of the restorations exhibited excellent clinical performance when evaluated against the United States Public Health Service System.
T
Although a number of CAD/CAMs have been investigated for the purpose of developing various forms of dental restorations, one that has been marketed for general practice and undergone extensive clinical research testing is identifled as the CEREC CAD/CAM system. This novel process was designed for generating ceramic inlays and onlays as well as facial veneers. Although a number of publications have been generated as it relates to dental CAD/CAM systems, little or no information exists concerning long-term clinical performan~e.~-~ The purpose of this study, then, was to evaluate a series of carefully placed posterior restorations for specific clinical performance over an extended period of time.
he CEREC CAD/CAM system was introduced to the dental profession over 7 years ago. Since that time it has been marketed in Europe, the United States, Canada, Mexico, and South America. The concept of this novel technique has been extremely stimulating to a large number of dentists because it offers a number of unique advantages. These, of course, include a one appointment operation, no impressions and no assistance by the laboratory technician. In addition, this particular system offers a potential for fabricating facial veneers.' Presently, patients are more demanding for esthetic restorations in posterior teeth. While amalgam has long been the standard restorative material for most patients, the initial color or the result of all the changes occurring in the corrosion process cause the patient to demand something more esthetic. Posterior composite resins are used by numerous dentists to rectify this problem. However, the posterior composite resin is extremely technique sensitive and furthermore, it is far less stable than the ceramic restorative material. In addition to the inadequacies in terms of marginal adaptation, the direct fUled posterior composite resin commonly exhibits problems related to proximal contour and contact. The results are characterized by rather high incidences of postoperative sensitivity. In this regard then, the ceramic inlay/onlay restorative material is considered by many to be a superior alternative.
METHODS AND MATERIALS A total of 121 inlay/onlay restorations were generated by means of the CEREC CAD/CAM system and inserted into a series of patients. In this study, two different types of ceramic materials, Dicor (Dentsply Int.) and Vita (Vita Zahnfabrik), were included as restorative agents. Two different types of duo-cured composite resin luting agents were employed. These included two hybrids and a microfill. The list of the cementing materials included in the study is presented inTable 1. AU the restorations included in the study were generated and inserted by three different clinicians over a 6-month period. Use of the ceramic material as well as the luting agent was carried out on a randomized basis. After cementation, the restorations were surfaced and flnished using a series of finishing diamonds followed by a 12-bladed fluted carbide bur, rubber polishing
'Professor. Department of Restorative Dentistry: t Associate Professor. Department of Restorative Dentistry: $Professor and Acting Chairman, Department of Biomaterials. University of Alabama at Birmingham, School of Dentistry. Birmingham. Alabama Address reprint requests to Barry P. Isenberg. D.M.D., M.A., University of Alabama at Birmingham. Schwl of Dentistry. SDB Box 82. Birmingham. AL 35294-0007 0 1992 Decker Periodicals Inc.
173
JOURNAL OF ESTHETIC DENTISTRY VOLUME 4. NUMBER 5 September/October 1992
Table 1. Ceramic Luting Agents Luting Agent
Type
Manufacturer
Batch #
Caulk
Hybrid
L.D. Caulk Co.
ERVH1514-1 C-100489
Kulzer
Hybrid
Kuker. Inc.
5022 C-029
Vivadent
Microfill
Vivadent Co.
8-260 399 c-360 209
points, and lastly a fine diamond paste. In each case, all of the clinical operations were carried out in the presence of a rubber dam. All restorations were evaluated directly and indirectly at the time of insertion, at six months, and then annually for 3years. Each restoration was evaluated in accordance with the United States Public Health Service (USPHS)System by two evaluators trained and calibrated in the technique.6In addition, each restoration was impressed with a poly vinylsiloxane impression (Reprosil, L.D. Caulk Co., Milford, DE) material at the time of each recall. The impressions were then cast with a die stone material for the purpose of monitoring changes along the restoration-tooth interface. The die stone casts were used in conjunction with the MoffaLugassy (ML) Scale to determine the extent and rate of wear of the luting agent.’ Specifically,the optical standard was used to determine the width of the interfacial gap as well as the depth of the interfacial defect. This was accomplished after fist identifying three to four locations near the incline planes of the die stone cast. Finally. each restoration was photographed to an original magnification 1.5x at all periods of recall.
Figure 1. Cerec restoration at 3 years.
Dicor restorations exhibited some evidence of localized wear. Normally this wear was manifested by small wear facets on incline planes. The results of the direct clinical evaluation for marginal integrity is presented in Figure 2. Indicated are the percent Bravo ratings for all the restorations over a 3-year period. As can be seen, clinical evidence of a detectable margin increased rapidly during the first year but then tended to level off at values approaching 50%.In other words only 50%or less of the restorations exhibited gap dimensions sufficiently large to be detected by means of an explorer. The clinical ratings for margin detection as related to the individual cement is presented in Figure 3. As shown, there are appreciable differences among the cements. The two hybrid luting agents tended to exhibit higher levels of Bravo ratings than the microfill cement, the levels for which are appreciably lower.6For example, while the Bravo ratings for the hybrid cement ranged upwards to 70%. those for the microfill did not exceed 25%.
RESULTS Direct Over the 3-year period of evaluation, results for the color matching ability of both the Dicor and Vita ceramic restorations were the same. Specifically, none of the restorations, regardless of composition, exhibited an Alfa rating of less than 90%. Using the USPHS system of evaluation, the visual idenmeation of either ceramic material was virtually impossible. Throughout the course of 36 months, none of the restorations exhibited any evidence of interfacial staining or marghal discoloration. No caries were detected for any of the restored teeth over the 3-year period of investigation. A typical example of one of the restorations after 3 years of service is presented in Figure 1. Several of the restorations exhibited clinical evidence of wear or loss of anatomic form when evaluated in accordance with the USPHS evaluation criteria. While no more than 5% of the Vita restorations showed evidence of wear at the end of 3 years, up to 34% of the
Figure 2. Marginal integrlty-direct clinical evaluation.
1I 74
Three-Year Evaluation of CAD/CAM Restorations
Flgum 3. Margin detection-'Yo Bravo-USPHS Criteria.
5. Depth/width ratio of the interfacial gap.
Over the 3-year period no differences in surface texture for the two different ceramic materials could be detected. In fact, all restorations, regardless of the time period were found to exhibit a surface smoothness similar to that of the adjacent enamel. Incidentally, none of the evaluators was able to ascertain the identity of the ceramic material by means of direct clinical evaluation.
Comparison of gap width to the actual wear or loss of luting agent revealed an interesting relationship. Specifically, the vertical loss of cement was always less than the width of the interfacial gap. In fact the depth: width ratio generally did not exceed 50%. During the first 12 months, the ratio increased linearly but then tended to level off. At this point the ratio remained constant to the end of the third year. This relationship is illustrated in Figure 5.
Indirect The values for gap width as well as vertical loss of luting agent as determined by means of the optical standards are presented in Figure 4. The values shown represent the mean scores for two evaluators trained in the technique. As illustrated, the gap width (top curve) remained relatively constant through the entire period of clinical investigation. The vertical loss of cement is represented in the lower curve and indicates a linear rate ofwear during the first 12months. At the end of this time however, the wear rate tended to level off remaining constant over the 3-year period.
DISCUSSION From the results of this 3-year study it is apparent that the clinical restorations generated by means of the CEREC CAD/CAM system were quite successful. Specifically, none of the restored teeth exhibited any evidence of secondary caries, postoperative sensitivity, or microleakage. In addition, the gap dimension was sufficiently narrow that after 3 years, only 50% of these could be detected clinically by means of a sharp explorer. In terms of material selection, little difference could be detected in the clinical performance of Dicor and Vita. Interestingly however, considerable differences were detected in the wear resistance of the two materials. Specifically, more Dicor restorations were found to possess occlusal wear facets than the harder Vita ceramic restorations. The higher incidence of wear facets would suggest that the Dicor material may be more compatible with natural tooth structure than the harder quartz-containing Vita ceramic material. During the course of 3 years, seven of the restorations underwent bulk fracture. In each case, the fracture occurred in the isthmus portion of the occlusal surface. A careful examination of the preparation revealed that the finalized cavity preparation was less than 2.0 mm from the occlusal cavosurface margin to the pulpal floor. Under such conditions, the bulk of the ceramic restoration apparently was insumcient to resist
Figure 4. Gap dimension as a function of time.
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JOURNAL OF ESTHETIC DENTISTRY VOLUME 4. NUMBER 5 September/October 1992
CONCLUSIONS
occlusal loading. The depth of these cavity preparations in some cases actually was 2.0 mm or more. After application of the glass ionomer liner, however, the finalized preparation was sometimes less than this amount. Further examination of the restorations also revealed a rather deep depression in the occlusal contact area to accommodate the antagonist cusp. Coupled with an insufficiently deep cavity preparation as well as excessive removal of occlusal material to accommodate the antagonist cusp, an insufficient bulk of material resulted. Most of these fractures occurred in restorations that were inserted early in the study. Generally, the failures happened within 9 months of insertion. As a result, the problems could be attributed to lack of experience associated with the generation of ceramic restorations. Interestingly, none of the restorations exhibited secondary caries throughout the 3-year period. Apparently then, the mean interfacial gap associated with all the restorations in this study was sufficiently acceptable to preclude the occurrence of secondary caries. An examination of the depth/width values suggest that the vertical loss of the luting agent was insufficient to support leakage and/or caries. Regardless of the gap dimension, both horizontally and vertically, none of the restorations showed any clinical evidence of marginal discoloration or microleakage. It was noted that the wear rate of the cementing agent continued in a linear fashion during the first 12 months. The wear rate then leveled off. In fact, at the end of the year and throughout the 36 months, no further wear of the luting agent could be measured. The cessation of wear can be attributed to the inability of the bolus of food to contact the cement surface.
On the basis of this information generated from this 3-year study, it is apparent that the CEREC CAD/CAM system is most effective in developing ceramic restorations of excellent clinical quality. If the marginal gap can be kept to a reasonably small dimension, the clinical success of these ceramic restorations seems assured.
REFERENCES 1. Leinfelder KF, Isenberg BP, Essig ME. A new method for generatingceramicrestorations:a CAD/CAM system. JAm Dent Assoc 1989: 118:703-707. 2. Duret F. Blouin J L . Buret B. CAD-CAM in dentistry. J Am Dent Assoc 1988; 117:715-720. 3. Rekow D. Computer-aided design and manufacturing in dentistry: a review of the state of the art. J Prosthet Dent 1987: 58:512-516. 4. Brandestini M, Moermann W, Lutz F, Krejci I. Computer machined ceramic inlays: in vitro marginal adaptation. Dent Res 1985: 64:208 (Abstr). 5. Bayne S. What is the future of CAD/CAM materials and techniques? Symposium on Esthetic Restorations. American Dental Association, Chicago, IL, February, 1992. 6. Cvar J R , Ryge G . Criteria for the clinical evaluation of dental restorative materials. US. Department of Health, Education and Welfare, Publication No. 790:244. 1971. 7. Lugassy AA, Moffa JP. Laboratoly model for quantification of clinical occlusal wear. J Dent Res 1985; 64:181 (Abstr 63). 8. Isenberg BP. Kawai K, Leinfelder KF. Effect of gap dimension on composite resin cement wear. J Dent Res 1992: 72: 1402 (Abstr).
176
'
This study dealt with the clinical evaluation of 121 inlays and onlays generated from both Dicor ceramics and Vita porcelains. These two different types of ceramic materials were cemented using three different duo-cured composite resin luting agents, which differed in particle size. At the end of 3 years, no difference could be detected between the clinical performance of the Dicor and Vita restorations. Both exhibited the same degree of color matching characteristics, marginal integrity, and general clinical performance; however, seven of the restorations exhibited fracture through the isthmus, which was shown to be due to insuficient cavity depth. The balance of the restorations exhibited excellent clinical performance when evaluated against the United States Public Health Service System.
T
Although a number of CAD/CAMs have been investigated for the purpose of developing various forms of dental restorations, one that has been marketed for general practice and undergone extensive clinical research testing is identifled as the CEREC CAD/CAM system. This novel process was designed for generating ceramic inlays and onlays as well as facial veneers. Although a number of publications have been generated as it relates to dental CAD/CAM systems, little or no information exists concerning long-term clinical performan~e.~-~ The purpose of this study, then, was to evaluate a series of carefully placed posterior restorations for specific clinical performance over an extended period of time.
he CEREC CAD/CAM system was introduced to the dental profession over 7 years ago. Since that time it has been marketed in Europe, the United States, Canada, Mexico, and South America. The concept of this novel technique has been extremely stimulating to a large number of dentists because it offers a number of unique advantages. These, of course, include a one appointment operation, no impressions and no assistance by the laboratory technician. In addition, this particular system offers a potential for fabricating facial veneers.' Presently, patients are more demanding for esthetic restorations in posterior teeth. While amalgam has long been the standard restorative material for most patients, the initial color or the result of all the changes occurring in the corrosion process cause the patient to demand something more esthetic. Posterior composite resins are used by numerous dentists to rectify this problem. However, the posterior composite resin is extremely technique sensitive and furthermore, it is far less stable than the ceramic restorative material. In addition to the inadequacies in terms of marginal adaptation, the direct fUled posterior composite resin commonly exhibits problems related to proximal contour and contact. The results are characterized by rather high incidences of postoperative sensitivity. In this regard then, the ceramic inlay/onlay restorative material is considered by many to be a superior alternative.
METHODS AND MATERIALS A total of 121 inlay/onlay restorations were generated by means of the CEREC CAD/CAM system and inserted into a series of patients. In this study, two different types of ceramic materials, Dicor (Dentsply Int.) and Vita (Vita Zahnfabrik), were included as restorative agents. Two different types of duo-cured composite resin luting agents were employed. These included two hybrids and a microfill. The list of the cementing materials included in the study is presented inTable 1. AU the restorations included in the study were generated and inserted by three different clinicians over a 6-month period. Use of the ceramic material as well as the luting agent was carried out on a randomized basis. After cementation, the restorations were surfaced and flnished using a series of finishing diamonds followed by a 12-bladed fluted carbide bur, rubber polishing
'Professor. Department of Restorative Dentistry: t Associate Professor. Department of Restorative Dentistry: $Professor and Acting Chairman, Department of Biomaterials. University of Alabama at Birmingham, School of Dentistry. Birmingham. Alabama Address reprint requests to Barry P. Isenberg. D.M.D., M.A., University of Alabama at Birmingham. Schwl of Dentistry. SDB Box 82. Birmingham. AL 35294-0007 0 1992 Decker Periodicals Inc.
173
JOURNAL OF ESTHETIC DENTISTRY VOLUME 4. NUMBER 5 September/October 1992
Table 1. Ceramic Luting Agents Luting Agent
Type
Manufacturer
Batch #
Caulk
Hybrid
L.D. Caulk Co.
ERVH1514-1 C-100489
Kulzer
Hybrid
Kuker. Inc.
5022 C-029
Vivadent
Microfill
Vivadent Co.
8-260 399 c-360 209
points, and lastly a fine diamond paste. In each case, all of the clinical operations were carried out in the presence of a rubber dam. All restorations were evaluated directly and indirectly at the time of insertion, at six months, and then annually for 3years. Each restoration was evaluated in accordance with the United States Public Health Service (USPHS)System by two evaluators trained and calibrated in the technique.6In addition, each restoration was impressed with a poly vinylsiloxane impression (Reprosil, L.D. Caulk Co., Milford, DE) material at the time of each recall. The impressions were then cast with a die stone material for the purpose of monitoring changes along the restoration-tooth interface. The die stone casts were used in conjunction with the MoffaLugassy (ML) Scale to determine the extent and rate of wear of the luting agent.’ Specifically,the optical standard was used to determine the width of the interfacial gap as well as the depth of the interfacial defect. This was accomplished after fist identifying three to four locations near the incline planes of the die stone cast. Finally. each restoration was photographed to an original magnification 1.5x at all periods of recall.
Figure 1. Cerec restoration at 3 years.
Dicor restorations exhibited some evidence of localized wear. Normally this wear was manifested by small wear facets on incline planes. The results of the direct clinical evaluation for marginal integrity is presented in Figure 2. Indicated are the percent Bravo ratings for all the restorations over a 3-year period. As can be seen, clinical evidence of a detectable margin increased rapidly during the first year but then tended to level off at values approaching 50%.In other words only 50%or less of the restorations exhibited gap dimensions sufficiently large to be detected by means of an explorer. The clinical ratings for margin detection as related to the individual cement is presented in Figure 3. As shown, there are appreciable differences among the cements. The two hybrid luting agents tended to exhibit higher levels of Bravo ratings than the microfill cement, the levels for which are appreciably lower.6For example, while the Bravo ratings for the hybrid cement ranged upwards to 70%. those for the microfill did not exceed 25%.
RESULTS Direct Over the 3-year period of evaluation, results for the color matching ability of both the Dicor and Vita ceramic restorations were the same. Specifically, none of the restorations, regardless of composition, exhibited an Alfa rating of less than 90%. Using the USPHS system of evaluation, the visual idenmeation of either ceramic material was virtually impossible. Throughout the course of 36 months, none of the restorations exhibited any evidence of interfacial staining or marghal discoloration. No caries were detected for any of the restored teeth over the 3-year period of investigation. A typical example of one of the restorations after 3 years of service is presented in Figure 1. Several of the restorations exhibited clinical evidence of wear or loss of anatomic form when evaluated in accordance with the USPHS evaluation criteria. While no more than 5% of the Vita restorations showed evidence of wear at the end of 3 years, up to 34% of the
Figure 2. Marginal integrlty-direct clinical evaluation.
1I 74
Three-Year Evaluation of CAD/CAM Restorations
Flgum 3. Margin detection-'Yo Bravo-USPHS Criteria.
5. Depth/width ratio of the interfacial gap.
Over the 3-year period no differences in surface texture for the two different ceramic materials could be detected. In fact, all restorations, regardless of the time period were found to exhibit a surface smoothness similar to that of the adjacent enamel. Incidentally, none of the evaluators was able to ascertain the identity of the ceramic material by means of direct clinical evaluation.
Comparison of gap width to the actual wear or loss of luting agent revealed an interesting relationship. Specifically, the vertical loss of cement was always less than the width of the interfacial gap. In fact the depth: width ratio generally did not exceed 50%. During the first 12 months, the ratio increased linearly but then tended to level off. At this point the ratio remained constant to the end of the third year. This relationship is illustrated in Figure 5.
Indirect The values for gap width as well as vertical loss of luting agent as determined by means of the optical standards are presented in Figure 4. The values shown represent the mean scores for two evaluators trained in the technique. As illustrated, the gap width (top curve) remained relatively constant through the entire period of clinical investigation. The vertical loss of cement is represented in the lower curve and indicates a linear rate ofwear during the first 12months. At the end of this time however, the wear rate tended to level off remaining constant over the 3-year period.
DISCUSSION From the results of this 3-year study it is apparent that the clinical restorations generated by means of the CEREC CAD/CAM system were quite successful. Specifically, none of the restored teeth exhibited any evidence of secondary caries, postoperative sensitivity, or microleakage. In addition, the gap dimension was sufficiently narrow that after 3 years, only 50% of these could be detected clinically by means of a sharp explorer. In terms of material selection, little difference could be detected in the clinical performance of Dicor and Vita. Interestingly however, considerable differences were detected in the wear resistance of the two materials. Specifically, more Dicor restorations were found to possess occlusal wear facets than the harder Vita ceramic restorations. The higher incidence of wear facets would suggest that the Dicor material may be more compatible with natural tooth structure than the harder quartz-containing Vita ceramic material. During the course of 3 years, seven of the restorations underwent bulk fracture. In each case, the fracture occurred in the isthmus portion of the occlusal surface. A careful examination of the preparation revealed that the finalized cavity preparation was less than 2.0 mm from the occlusal cavosurface margin to the pulpal floor. Under such conditions, the bulk of the ceramic restoration apparently was insumcient to resist
Figure 4. Gap dimension as a function of time.
175
JOURNAL OF ESTHETIC DENTISTRY VOLUME 4. NUMBER 5 September/October 1992
CONCLUSIONS
occlusal loading. The depth of these cavity preparations in some cases actually was 2.0 mm or more. After application of the glass ionomer liner, however, the finalized preparation was sometimes less than this amount. Further examination of the restorations also revealed a rather deep depression in the occlusal contact area to accommodate the antagonist cusp. Coupled with an insufficiently deep cavity preparation as well as excessive removal of occlusal material to accommodate the antagonist cusp, an insufficient bulk of material resulted. Most of these fractures occurred in restorations that were inserted early in the study. Generally, the failures happened within 9 months of insertion. As a result, the problems could be attributed to lack of experience associated with the generation of ceramic restorations. Interestingly, none of the restorations exhibited secondary caries throughout the 3-year period. Apparently then, the mean interfacial gap associated with all the restorations in this study was sufficiently acceptable to preclude the occurrence of secondary caries. An examination of the depth/width values suggest that the vertical loss of the luting agent was insufficient to support leakage and/or caries. Regardless of the gap dimension, both horizontally and vertically, none of the restorations showed any clinical evidence of marginal discoloration or microleakage. It was noted that the wear rate of the cementing agent continued in a linear fashion during the first 12 months. The wear rate then leveled off. In fact, at the end of the year and throughout the 36 months, no further wear of the luting agent could be measured. The cessation of wear can be attributed to the inability of the bolus of food to contact the cement surface.
On the basis of this information generated from this 3-year study, it is apparent that the CEREC CAD/CAM system is most effective in developing ceramic restorations of excellent clinical quality. If the marginal gap can be kept to a reasonably small dimension, the clinical success of these ceramic restorations seems assured.
REFERENCES 1. Leinfelder KF, Isenberg BP, Essig ME. A new method for generatingceramicrestorations:a CAD/CAM system. JAm Dent Assoc 1989: 118:703-707. 2. Duret F. Blouin J L . Buret B. CAD-CAM in dentistry. J Am Dent Assoc 1988; 117:715-720. 3. Rekow D. Computer-aided design and manufacturing in dentistry: a review of the state of the art. J Prosthet Dent 1987: 58:512-516. 4. Brandestini M, Moermann W, Lutz F, Krejci I. Computer machined ceramic inlays: in vitro marginal adaptation. Dent Res 1985: 64:208 (Abstr). 5. Bayne S. What is the future of CAD/CAM materials and techniques? Symposium on Esthetic Restorations. American Dental Association, Chicago, IL, February, 1992. 6. Cvar J R , Ryge G . Criteria for the clinical evaluation of dental restorative materials. US. Department of Health, Education and Welfare, Publication No. 790:244. 1971. 7. Lugassy AA, Moffa JP. Laboratoly model for quantification of clinical occlusal wear. J Dent Res 1985; 64:181 (Abstr 63). 8. Isenberg BP. Kawai K, Leinfelder KF. Effect of gap dimension on composite resin cement wear. J Dent Res 1992: 72: 1402 (Abstr).
176
