The tunnel restoration - nine years of clinical experience using capsulated glass ionorner cements. Case report Geoffrey M. Knight
Key words: Capsulated glass ionomer cements, case report, cavity design, tunnel restorations. Abstract The clinical potential of the tunnel restoration is restrained by perceived difficultiesof access to proximal caries and lack of long-term clinical data. This paper describes a technique that affords proximal access similar to that of a standard Class II cavity preparation and provides an evaluation of a technique, using capsulated glass ionomer cements. It is supported by more than nine years of clinical experience that confirms the viability of this procedure as an alternative to conventional Class II cavity restorations for initial proximal lesions. (Received for publication December 1991. Revised January 1992. Accepted February 1992.)
Introduction The introduction of glass ionomer cements’ provided the dental profession with a reliable’ and predictable material for a number of specific restorative application^.^-^ In 1984 the tunnel restoration emerged as a conservative alternative to the conventional Class I1 preparation for initial carious lesions.6-8 The continuing integrity of the marginal ridge protects a tooth from inherent restorative problems that include occlusal and proximal instability, open contacts and weakening of associated CUSPS.~ Furthermore, the prolonged release and uptake of fluoride from the glass ionomer surface’o*llprovides a continuous fluoride presence that protects the margins of the restoration from caries and possibly the proximal surfaces of adjacent teeth. Marginal ridge fracture after placement is infrequent6-’ and Australian Dental Journal 1992;37(4):245-51.
the management of such is the simple repair of the defect with composite resin. The technique has since been modified to incorporate a composite overlay on the occlusal surface and this modification is receiving increasing interest in the literature.’’-’4 Widespread acceptance of this procedure is currently limited by the lack of longterm clinical information and perceived difficulties with access to proximal caries through a small occlusal preparation.” There is emerging evidence indicating that the technique is a viable restorative procedure.16 This paper addresses this situation by suggesting modifications to cavity design that improve access to increase clinical predictability and reports on more than nine years clinical experience with the tunnel technique using capsulated glass ionomer cements (Fig. 1, 2).
Cavity design As first reported, the tunnel preparation utilized a small oval access cavity in the occlusal fossa above the proximal lesion.6-8This access was limited and interfered with: (1) Determination of the extent of caries. Radiographs tended to underestimate the lesion size and were, therefore, clinically unreliable.” (2) Adequate mechanical preparation. (3) A practitioner’s judgment to ensure that caries had been removed. Improved access required in both the buccolingual and mesio-distal planes may be gained by extending the access cavity from the occlusal fossa bucco-lingually, parallel to the marginal ridge (2 mm in from the margin) and along the central fissure away from the margin to form a ‘T’pattern on the occlusal surface (Fig. 3). This improved access over the standard ‘tunnel’ cavity design in 245
Fig. 1.-Tunnel preparation in tooth 36. Fig. 2.-Restoration (Ketac-Fil) at nine years and seven months.
Fig. 3.-The ‘T’cavity modification compared with the original ‘ 0type. Fig. 4.-‘T’ preparation showing substantially better access than the original ‘0type in the mesio-distal plane. Fig. 5.-Better access with the ‘T’preparation in the bucco-lingual plane.
both the mesio-distal plane (Fig. 4) and bucco-lingual plane (Fig. 5) enhances the diagnosis of the carious involvement of the tooth. Removal of an existing occlusal restoration facilitates access, otherwise removal of some healthy tissue may be required to achieve the ‘T’ configuration. 246
Modification of the original tunnel access with a ‘T’preparation may increase the propensity of the marginal ridge to fail. A bonded composite overlay at the occlusal surface up to the marginal ridge will improve strength and abrasion resistance and should minimize future marginal ridge failure. FurtherAustralian Dental Journal 1992;37:4.
Fig. 6.-Tooth 16 with an initial carious lesion present on the mesial aspect. Fig. 7. -Rubber dam placed for good moisture control. Existing amalgam restoration removed and caries accessed by a ‘T’type preparation on the mesial aspect of the tooth. Fig. 8.-The ‘T’type preparation showing excellent access to diagnose and remove remaining caries. Fig. 9.-The ‘smear layer’ removed with a mild acid and matrix band placed and wooden wedge inserted proximally.
more, composite resins have been shown to be a viable occlusal restorative material.18.19 The author has used a ‘sandwich’ technique of overlaying an etched capsulated glass ionomer base with a bonded composite resin in association with the ‘T’ cavity design for over four years. A minimum of 40 restorations have been placed during this time without observing a single fractured composite bonded marginal ridge at recall visits. Operative technique The operative technique for the modified ‘Ttunnel restoration is set out below. The clinical case chosen depicts the restoration of a first permanent molar. Case report
1. A young adult presented with mesial caries on tooth 16. The hypoplasia on the buccal aspect was pigmented but not carious and, as it had been present for over 20 years, it was left intact (Fig. 6). Australian Dental Journal 1992;37:4.
2. Rubber dam was applied to facilitate moisture control. The broken-down amalgam on the occlusal surface was removed to facilitate access. The cavity was prepared with a cylindrical diamond bur (541) to the width of the marginal ridge, parallel to, and about 2 mm in from the margin. The central fissure was removed, to form the neck of the ‘T,to the old amalgam margin and to the fill depth of the enamel on the occlusal surface (Fig. 7). 3. Carious dentine was removed with a slow speed round bur (6 round) and small excavators accessing the lesion at each of the ‘T’extensions. This preparation affords similar visual and instrumental access to the cavity as a standard Class I1 cavity preparation (Fig. 8). As caries occurs below the contact area, protection of the proximal enamel surface of the adjoining tooth is seldom needed. 4. After removal of the smear layer with a weak acid solution (Mounts currently recommends a 10 per cent solution of polyacrylic acid for 10 seconds), the preparation was washed thoroughly and dried with 247
Fig. 10.-Glass ionomer cement at the gelatinous setting stage is packed into the preparation with a ball burnisher to eliminate voids and maximize the integrity of the proximal margin. Fig. 11.-Set glass ionomer base prepared back to the dentino-enamel margin. Fig. 12.-The composite resin overlay placed incrementally over the etched glass ionomer base. Fig. I3.-The occlusal surface developed and continuity of the proximal surface created with finishing strips. Fig. I4.-Dam removed, occlusion adjusted. Note centric stops on mesial and distal marginal ridges. Fig. 15.-Final contouring and polishing. (Note: Patient was recalled for review one week later.)
oil free air. A matrix band was placed and wedged firmly (Fig. 9). Wooden wedges adapt much better to the proximal margin than plastic ones. A small increment of calcium hydroxide lining may be placed at the base of deep cavities. 5. Capsulated Ketac-Bond,* a Type I11 glass 248
ionomer cement, as classified by Wilson and McLean" was used to restore the tooth up to the level of the dentino-enamel junction on the occlusal surface. A powder liquid ratio of4.2:l gives capsulated Ketac-Bond similar properties to capsulated Ketac-Fil" but with higher early resistance to water Australian Dental Journal 1992;37:4.
Fig. 16. -Clinical criteria for evaluatingtunnel restorations. Occlusul A, Occlusal surfaces demonstrating no clinical evidence ofwear. B, Those with some wear but still considered clinically acceptable. Margins: A, Clinically intact margins. B, Those with some pitting but still clinically acceptable. war:
Table 1. Clinical features of occlusal surface wear Occlusal wear
No. %
A No clinical wear B Clinical wear not affecting function C Clinical wear requiring replacement
43 8 Nil
84 16 0
Table 2. Clinical features of marginal integrity No. 70 A No evidence of marginal breakdown B Marginal pitting not affecting function C Marginal pitting requiring replacement Evidence of recurrent occlusal caries Marginal ridge failures
47 4 Nil Nil 2
92 8 0 0
4
contamination, faster setting time and greater tensile and compressive strengths. Furthermore, KetacBond is radiopaque and as such is recommended for externalized ‘sandwich’ re~torations.~ Hand-mixed Ketac-Bond with unpredictable powder liquid ratios is not suitable for use as a base material in the ‘sandwich technique.’’ The use of a capsule enables the glass ionomer to be placed in the depths of the cavity, minimizing the chance of air inclusions. When the glass ionomer cement had reached the gelatinous stage of setting it was further compacted with a ball burnisher to eliminate voids and maximize the integrity of the proximal marginzo (Fig. 10). Compacting the glass ionomer cement at this stage of the setting process has been carried out for many Australian Dental Journal 1992:37:4
years and does not appear to have an adverse effect upon the clinical properties of the set cement. Mount favours incremental placement, tamping in the unset ionomer with a foam plastic pledget whilst the cement is still very wet.z2 Once set, excess glass ionomer cement was trimmed from the enamel margins with a high speed bur and the cement was removed to the depth ofthe dentino-enamel junction (Fig. 11). 6. The glass ionomer and enamel were etched with 37 per cent phosphoric acid for 15 seconds, washed and dried with oil free air. Etching also removes tags of glass ionomer remaining on the enamel surface. Enamel bond was brushed over the occlusal preparation and interproximal surface and then cured. A small increment of posterior composite resin was placed into the preparation, spread thinly over the floor and walls and light-cured for 20 seconds. Polymerization shrinkage is minimized and the possibility of post-operative sensitivity reduced, as well as assuring that the cavo-surface margins are sealed. A second increment of posterior composite was placed to fill the preparation and cured for 40 seconds (Fig. 12). 7. The restoration was then contoured with fine diamonds, carbides and stones and polished with silicone rubber discst and Soflex discs.$ Interproximal regions were finished with abrasive strips and checked with dental floss for overhangs (Fig. 13). ‘ESPE CmbH, Fabrik Pharmazeutischer, SeefeldOkrbay Germany. tIvoclar, Schaan, Liechtenstein. $3M Dental Products Division, St Paul, Minn., USA. 249
3-9year tunnel restorations
YO
7
100
0 Zero Functional
40 30
20 10
0
Occlusal wear
Marginal wear
Fig. 17. -Percentage occlusal wear and marginal integrity.
8. The rubber dam was removed, the occlusion checked with articulating paper and adjusted as necessary. Note the centric stops on the mesial and distal marginal ridges (Fig. 14). 9. A final polishing completed the restoration and the patient was recalled for review one week later (Fig. 15).
Method of review A rating scale based upon that proposed by RygeZ3 was adopted for its ability to distinguish between criteria of clinical significance. A three-scale rating was used (A) Restorations deemed to be clinically excellent. (B) Restorations that showed minor deviations from the ideal but remained clinically acceptable. (C) Restorations that should be replaced to avoid the likelihood of imminent failure or those requiring immediate replacement. The clinical features of occlusal wear and marginal integrity were evaluated as demonstrated in Fig. 16 and Table 1, 2. Further to this, any evidence of recurrent caries or marginal ridge failure was noted (Table 2). All results were recorded by the author. Results A total of 51 restorations was evaluated, 41 in molars and ten in bicuspids. The average age of the restorations was five years and three months. The range was between three years and nine years and seven months. Capsulated Ketac-Silver*was used for 14 restorations (12 molars and two bicuspids with an average restoration age of four years and two months). 250
The remaining restorations were filled with capsulated Ketac-Fil (prior to 1984 capsulated Ketac-Silver was not available). The use of a radiopaque glass ionomer cement facilitates radiographic evaluation of the restoration. All tunnel restorations placed for three years or longer were evaluated in patients during recall visits over a twelvemonth period. Tunnel restorations that had been overlaid with composite resin were omitted due to the small number of observations. Specific patients were not recalled for review to try to achieve a random sampling of restorations and minimize the bias of the results. Figure 16 presents a graphical representation of the above data. When Ketac Fil and Ketac Silver restorations were compared separately the results were as follows: (1) 84 per cent of Ketac Fil restorations had no occlusal wear compared with 86 per cent of Ketac Silver restorations. (2) 89 per cent of Ketac Fil restorations showed no marginal wear compared with 100 per cent of Ketac Silver restorations. All observations of occlusal wear and marginal pitting occurred in molar teeth. In a clinical environment, despite diligent efforts at drying and probing, evaluation of the interproximal surfaces relied upon deduction. There were no detectable deficiencies with probing and no catching with dental floss. As the occlusal surfaces had withstood the masticatory loads without significant wear, it was assumed that wear of the proximal surfaces was similar to the occlusal surfaces and was, therefore, clinically acceptable. Also, the absence of caries at the occlusal surfaces and the proven cariostatic of glass ionomer cement suggest that no recurrent caries had occurred at the proximal margins.
Discussion Tunnel preparations restored with glass ionomer cements have been shown to achieve a strength at the marginal ridge of 92 per cent of that of the original Similar observations have been made using composite resin as an occlusal restorative material for tunnel restoration^.^^ The failure of two marginal ridges was probably due to fractures that occurred during cavity preparation. Subsequent observations have detected cracked margins that remained in place but were easily dislodged with a hand instrument. Practitioners are encouraged to check the marginal ridge prior to placing a restoration for fine fault lines. This is facilitated by the use of magnlfling loupes. A fractured marginal ridge can usually be restored with composite resin bonded onto the remaining enamel and glass ionomer cement. Australian Dental Journal 1992;37:4.
The small number of teeth restored with Ketac Silver in this evaluation, made it statistically unwise to conclude that there were any differences in performance between Ketac Silver and Ketac Fil. The survey results showed that both Ketac Fil and Ketac Silver demonstrated acceptable occlusal wear and marginal integrity for at least three years and possibly for much longer periods when used as occlusal restorative materials in either molar or bicuspid teeth. This supported previous observations.’ A glass ionomer cement restoration exhibiting unacceptable occlusal wear or marginal breakdown is most unlikely to predispose a tooth to recurrent caries. In such cases, the placement of a bonded composite overlay (‘sandwich restoration’) or amalgam can be achieved with minimal preparation to the remaining glass ionomer cement and without removing existing tooth structure.’ The use of the ‘T preparation requires a little more removal of healthy tissue than the original ovoid design but enhances diagnosis and access to caries and thus the predictability of the restoration. The rationale for overlaying the glass ionomer base in the ‘T design with composite resin is twofold. Firstly, the bonded resin adheres more strongly to enamel than to glass ionomer cement, thus affording better protection to the unsupported enamel at the marginal ridge. Secondly, the greater occlusal surface generated by the ‘Tconfiguration is afforded better wear resistance with composite resin than with glass ionomer cement. Conclusions There are dentists who remain hesitant to attempt the tunnel restoration because of lack of long-term data and concerns over complete caries removal. This paper has aimed to establish that the technique does provide a viable long-term restoration that enjoys many benefits over a conventional Class I1 preparation for the initial lesion, primarily because of the conservative cavity design and the ability to utilize the cariostatic properties and oral stability of capsulated glass ionomer cement. The difficulties that dentists may have encountered gaining adequate access to the cavity have been addressed by describing a cavity design that affords similar access to that of a conventional Class I1 preparation whilst maintaining the benefits of the tunnel restoration. The continuing improvement of dental materials will see firther advancements in the strength and predictability of this technique. Acknowledgements The author wishes to acknowledge the assistance Australian Dental Journal 1992;37:4.
given by Dr Graham Mount AM, Dr John McLean OBEYand Dr Lennart Forsten for their advice and critical evaluation during the preparation of this paper. References 1. Wilson AD, Kent BE. A new translucent cement for dentistry: the glass ionomer cement. Br Dent J 1972;132:133-5. 2. Mount GJ. Longevity of glass ionomer cements. J Prosthet Dent 1986;55:682-5. 3. McLean JW:Aesthetics in restorative dentistry: The challenge for the future. Br Dent J 1980;149:36872. 4. Wilson AD, McLean JW.Glass ionomer cement. Chicago: Qwntessence, 1988 Ch.9-14. 5. Mount GJ. An atlas of glass ionomer cements: a clinician’s guide. London: Manin Dunitz, 1990 Ch.2-6. 6. Knight GM. Tunnel restorations. Dent Outlook 1984;1053-7. 7. Knight GM. The use of adhesive materials in the conservative restorations of selected posterior teeth. Aust Dent J 19&1,29:32431. 8. Hunt PR. A modified Class I1 cavity preparation for glass ionomer restorativematerials. Qumtessence Int 1984,101011-8. 9. McLean JW.Limitations of posterior composite resins and extending their use with glass ionomer cements. QULntessence Int 1987;10517-29. 10. Swam ML, PhillipsRW, Clark HE.Long-term fluoride release from glass ionorner cements. J Dent Res 1984,63:15860. 11. Forsten L. Fluoride release and uptake by glass ionomers. Stand J Dent Res 1991;99:241-5. 12. McLean JW. New concepts in cosmetic dentistry using glass ionomer cements and composites. J Calif Dent Assoc 1986;21:20-7. 13. Clinical Research Associates. Tooth preparation, tunnel preparation. CRA Newsletter 1987;11:7. 14. Croll TP. Glass ionomer-silvercermet bonded composite resin Class I1 tunnel restorations. Quintessence Int 1988;19:533-9. 15. Hickel R, Vob A. Untersuchungen zur Tunnelpraparation. Dtsch Zahnarztl 198542545-8. 16. Hasselrot AV. Tunnelpreparationer. Traditionella och alternativa metoder. Tandlakartidningen 1990;21: 1114-26. 17. Kleier DJ, Hicks MJ, Flaitz CM.A comparison of Ultraspeed and Ektaspeed dental x-ray film: in witto study of the r a d b graphic and histologic appearance of interproximal lesions. Quintessence Int 1987;18:623-31. 18. Leinfelder KF. Posterior composite resins J Am Dent Assoc 1988,117:21E-8E. 19. Wilson NHF, Wilson MA, Wastell DG, Smith GA. A clinical trial of a visible light cured posterior composite resin Int 1988;19: restorative m a t d fiveyear results. Quint675-81. 20. Wilson AD, McLean JW. Glass ionomer cement. Chicago: QULntessence, 1988224. 21. Welbury RR, Murray JJ. A clinical trial of the glass ionomer cement-comwsite resin “sandwich”techniaue in Class I1 cavities in pe-ent premolar and molar teeth. Qluntessence Int 1990;2 1507-12. 22. Mount GJ. An atlas ofglass ionorner cements. Martin Dunitz. op. cit.: 90-6. 23. Ryge G. Clinical criteria. Int Dent J 1980;30347-58. 24. Hill FJ, Halaseh FJ. A laboratory investigationof tunnel restct rations in premolar teeth. Br Dent J 1988;165:364-7. 25. Covey D, Schulein TM, Kohout FJ. Marginal ridge strength of restored teeth with modified Class I1 cavity preparations. J Am Dent Assoc 1989;I 18199-202.
Address for correspondendreprints: 20 Carpenter Street, Brighton, Victoria, 3186. 251
Key words: Capsulated glass ionomer cements, case report, cavity design, tunnel restorations. Abstract The clinical potential of the tunnel restoration is restrained by perceived difficultiesof access to proximal caries and lack of long-term clinical data. This paper describes a technique that affords proximal access similar to that of a standard Class II cavity preparation and provides an evaluation of a technique, using capsulated glass ionomer cements. It is supported by more than nine years of clinical experience that confirms the viability of this procedure as an alternative to conventional Class II cavity restorations for initial proximal lesions. (Received for publication December 1991. Revised January 1992. Accepted February 1992.)
Introduction The introduction of glass ionomer cements’ provided the dental profession with a reliable’ and predictable material for a number of specific restorative application^.^-^ In 1984 the tunnel restoration emerged as a conservative alternative to the conventional Class I1 preparation for initial carious lesions.6-8 The continuing integrity of the marginal ridge protects a tooth from inherent restorative problems that include occlusal and proximal instability, open contacts and weakening of associated CUSPS.~ Furthermore, the prolonged release and uptake of fluoride from the glass ionomer surface’o*llprovides a continuous fluoride presence that protects the margins of the restoration from caries and possibly the proximal surfaces of adjacent teeth. Marginal ridge fracture after placement is infrequent6-’ and Australian Dental Journal 1992;37(4):245-51.
the management of such is the simple repair of the defect with composite resin. The technique has since been modified to incorporate a composite overlay on the occlusal surface and this modification is receiving increasing interest in the literature.’’-’4 Widespread acceptance of this procedure is currently limited by the lack of longterm clinical information and perceived difficulties with access to proximal caries through a small occlusal preparation.” There is emerging evidence indicating that the technique is a viable restorative procedure.16 This paper addresses this situation by suggesting modifications to cavity design that improve access to increase clinical predictability and reports on more than nine years clinical experience with the tunnel technique using capsulated glass ionomer cements (Fig. 1, 2).
Cavity design As first reported, the tunnel preparation utilized a small oval access cavity in the occlusal fossa above the proximal lesion.6-8This access was limited and interfered with: (1) Determination of the extent of caries. Radiographs tended to underestimate the lesion size and were, therefore, clinically unreliable.” (2) Adequate mechanical preparation. (3) A practitioner’s judgment to ensure that caries had been removed. Improved access required in both the buccolingual and mesio-distal planes may be gained by extending the access cavity from the occlusal fossa bucco-lingually, parallel to the marginal ridge (2 mm in from the margin) and along the central fissure away from the margin to form a ‘T’pattern on the occlusal surface (Fig. 3). This improved access over the standard ‘tunnel’ cavity design in 245
Fig. 1.-Tunnel preparation in tooth 36. Fig. 2.-Restoration (Ketac-Fil) at nine years and seven months.
Fig. 3.-The ‘T’cavity modification compared with the original ‘ 0type. Fig. 4.-‘T’ preparation showing substantially better access than the original ‘0type in the mesio-distal plane. Fig. 5.-Better access with the ‘T’preparation in the bucco-lingual plane.
both the mesio-distal plane (Fig. 4) and bucco-lingual plane (Fig. 5) enhances the diagnosis of the carious involvement of the tooth. Removal of an existing occlusal restoration facilitates access, otherwise removal of some healthy tissue may be required to achieve the ‘T’ configuration. 246
Modification of the original tunnel access with a ‘T’preparation may increase the propensity of the marginal ridge to fail. A bonded composite overlay at the occlusal surface up to the marginal ridge will improve strength and abrasion resistance and should minimize future marginal ridge failure. FurtherAustralian Dental Journal 1992;37:4.
Fig. 6.-Tooth 16 with an initial carious lesion present on the mesial aspect. Fig. 7. -Rubber dam placed for good moisture control. Existing amalgam restoration removed and caries accessed by a ‘T’type preparation on the mesial aspect of the tooth. Fig. 8.-The ‘T’type preparation showing excellent access to diagnose and remove remaining caries. Fig. 9.-The ‘smear layer’ removed with a mild acid and matrix band placed and wooden wedge inserted proximally.
more, composite resins have been shown to be a viable occlusal restorative material.18.19 The author has used a ‘sandwich’ technique of overlaying an etched capsulated glass ionomer base with a bonded composite resin in association with the ‘T’ cavity design for over four years. A minimum of 40 restorations have been placed during this time without observing a single fractured composite bonded marginal ridge at recall visits. Operative technique The operative technique for the modified ‘Ttunnel restoration is set out below. The clinical case chosen depicts the restoration of a first permanent molar. Case report
1. A young adult presented with mesial caries on tooth 16. The hypoplasia on the buccal aspect was pigmented but not carious and, as it had been present for over 20 years, it was left intact (Fig. 6). Australian Dental Journal 1992;37:4.
2. Rubber dam was applied to facilitate moisture control. The broken-down amalgam on the occlusal surface was removed to facilitate access. The cavity was prepared with a cylindrical diamond bur (541) to the width of the marginal ridge, parallel to, and about 2 mm in from the margin. The central fissure was removed, to form the neck of the ‘T,to the old amalgam margin and to the fill depth of the enamel on the occlusal surface (Fig. 7). 3. Carious dentine was removed with a slow speed round bur (6 round) and small excavators accessing the lesion at each of the ‘T’extensions. This preparation affords similar visual and instrumental access to the cavity as a standard Class I1 cavity preparation (Fig. 8). As caries occurs below the contact area, protection of the proximal enamel surface of the adjoining tooth is seldom needed. 4. After removal of the smear layer with a weak acid solution (Mounts currently recommends a 10 per cent solution of polyacrylic acid for 10 seconds), the preparation was washed thoroughly and dried with 247
Fig. 10.-Glass ionomer cement at the gelatinous setting stage is packed into the preparation with a ball burnisher to eliminate voids and maximize the integrity of the proximal margin. Fig. 11.-Set glass ionomer base prepared back to the dentino-enamel margin. Fig. 12.-The composite resin overlay placed incrementally over the etched glass ionomer base. Fig. I3.-The occlusal surface developed and continuity of the proximal surface created with finishing strips. Fig. I4.-Dam removed, occlusion adjusted. Note centric stops on mesial and distal marginal ridges. Fig. 15.-Final contouring and polishing. (Note: Patient was recalled for review one week later.)
oil free air. A matrix band was placed and wedged firmly (Fig. 9). Wooden wedges adapt much better to the proximal margin than plastic ones. A small increment of calcium hydroxide lining may be placed at the base of deep cavities. 5. Capsulated Ketac-Bond,* a Type I11 glass 248
ionomer cement, as classified by Wilson and McLean" was used to restore the tooth up to the level of the dentino-enamel junction on the occlusal surface. A powder liquid ratio of4.2:l gives capsulated Ketac-Bond similar properties to capsulated Ketac-Fil" but with higher early resistance to water Australian Dental Journal 1992;37:4.
Fig. 16. -Clinical criteria for evaluatingtunnel restorations. Occlusul A, Occlusal surfaces demonstrating no clinical evidence ofwear. B, Those with some wear but still considered clinically acceptable. Margins: A, Clinically intact margins. B, Those with some pitting but still clinically acceptable. war:
Table 1. Clinical features of occlusal surface wear Occlusal wear
No. %
A No clinical wear B Clinical wear not affecting function C Clinical wear requiring replacement
43 8 Nil
84 16 0
Table 2. Clinical features of marginal integrity No. 70 A No evidence of marginal breakdown B Marginal pitting not affecting function C Marginal pitting requiring replacement Evidence of recurrent occlusal caries Marginal ridge failures
47 4 Nil Nil 2
92 8 0 0
4
contamination, faster setting time and greater tensile and compressive strengths. Furthermore, KetacBond is radiopaque and as such is recommended for externalized ‘sandwich’ re~torations.~ Hand-mixed Ketac-Bond with unpredictable powder liquid ratios is not suitable for use as a base material in the ‘sandwich technique.’’ The use of a capsule enables the glass ionomer to be placed in the depths of the cavity, minimizing the chance of air inclusions. When the glass ionomer cement had reached the gelatinous stage of setting it was further compacted with a ball burnisher to eliminate voids and maximize the integrity of the proximal marginzo (Fig. 10). Compacting the glass ionomer cement at this stage of the setting process has been carried out for many Australian Dental Journal 1992:37:4
years and does not appear to have an adverse effect upon the clinical properties of the set cement. Mount favours incremental placement, tamping in the unset ionomer with a foam plastic pledget whilst the cement is still very wet.z2 Once set, excess glass ionomer cement was trimmed from the enamel margins with a high speed bur and the cement was removed to the depth ofthe dentino-enamel junction (Fig. 11). 6. The glass ionomer and enamel were etched with 37 per cent phosphoric acid for 15 seconds, washed and dried with oil free air. Etching also removes tags of glass ionomer remaining on the enamel surface. Enamel bond was brushed over the occlusal preparation and interproximal surface and then cured. A small increment of posterior composite resin was placed into the preparation, spread thinly over the floor and walls and light-cured for 20 seconds. Polymerization shrinkage is minimized and the possibility of post-operative sensitivity reduced, as well as assuring that the cavo-surface margins are sealed. A second increment of posterior composite was placed to fill the preparation and cured for 40 seconds (Fig. 12). 7. The restoration was then contoured with fine diamonds, carbides and stones and polished with silicone rubber discst and Soflex discs.$ Interproximal regions were finished with abrasive strips and checked with dental floss for overhangs (Fig. 13). ‘ESPE CmbH, Fabrik Pharmazeutischer, SeefeldOkrbay Germany. tIvoclar, Schaan, Liechtenstein. $3M Dental Products Division, St Paul, Minn., USA. 249
3-9year tunnel restorations
YO
7
100
0 Zero Functional
40 30
20 10
0
Occlusal wear
Marginal wear
Fig. 17. -Percentage occlusal wear and marginal integrity.
8. The rubber dam was removed, the occlusion checked with articulating paper and adjusted as necessary. Note the centric stops on the mesial and distal marginal ridges (Fig. 14). 9. A final polishing completed the restoration and the patient was recalled for review one week later (Fig. 15).
Method of review A rating scale based upon that proposed by RygeZ3 was adopted for its ability to distinguish between criteria of clinical significance. A three-scale rating was used (A) Restorations deemed to be clinically excellent. (B) Restorations that showed minor deviations from the ideal but remained clinically acceptable. (C) Restorations that should be replaced to avoid the likelihood of imminent failure or those requiring immediate replacement. The clinical features of occlusal wear and marginal integrity were evaluated as demonstrated in Fig. 16 and Table 1, 2. Further to this, any evidence of recurrent caries or marginal ridge failure was noted (Table 2). All results were recorded by the author. Results A total of 51 restorations was evaluated, 41 in molars and ten in bicuspids. The average age of the restorations was five years and three months. The range was between three years and nine years and seven months. Capsulated Ketac-Silver*was used for 14 restorations (12 molars and two bicuspids with an average restoration age of four years and two months). 250
The remaining restorations were filled with capsulated Ketac-Fil (prior to 1984 capsulated Ketac-Silver was not available). The use of a radiopaque glass ionomer cement facilitates radiographic evaluation of the restoration. All tunnel restorations placed for three years or longer were evaluated in patients during recall visits over a twelvemonth period. Tunnel restorations that had been overlaid with composite resin were omitted due to the small number of observations. Specific patients were not recalled for review to try to achieve a random sampling of restorations and minimize the bias of the results. Figure 16 presents a graphical representation of the above data. When Ketac Fil and Ketac Silver restorations were compared separately the results were as follows: (1) 84 per cent of Ketac Fil restorations had no occlusal wear compared with 86 per cent of Ketac Silver restorations. (2) 89 per cent of Ketac Fil restorations showed no marginal wear compared with 100 per cent of Ketac Silver restorations. All observations of occlusal wear and marginal pitting occurred in molar teeth. In a clinical environment, despite diligent efforts at drying and probing, evaluation of the interproximal surfaces relied upon deduction. There were no detectable deficiencies with probing and no catching with dental floss. As the occlusal surfaces had withstood the masticatory loads without significant wear, it was assumed that wear of the proximal surfaces was similar to the occlusal surfaces and was, therefore, clinically acceptable. Also, the absence of caries at the occlusal surfaces and the proven cariostatic of glass ionomer cement suggest that no recurrent caries had occurred at the proximal margins.
Discussion Tunnel preparations restored with glass ionomer cements have been shown to achieve a strength at the marginal ridge of 92 per cent of that of the original Similar observations have been made using composite resin as an occlusal restorative material for tunnel restoration^.^^ The failure of two marginal ridges was probably due to fractures that occurred during cavity preparation. Subsequent observations have detected cracked margins that remained in place but were easily dislodged with a hand instrument. Practitioners are encouraged to check the marginal ridge prior to placing a restoration for fine fault lines. This is facilitated by the use of magnlfling loupes. A fractured marginal ridge can usually be restored with composite resin bonded onto the remaining enamel and glass ionomer cement. Australian Dental Journal 1992;37:4.
The small number of teeth restored with Ketac Silver in this evaluation, made it statistically unwise to conclude that there were any differences in performance between Ketac Silver and Ketac Fil. The survey results showed that both Ketac Fil and Ketac Silver demonstrated acceptable occlusal wear and marginal integrity for at least three years and possibly for much longer periods when used as occlusal restorative materials in either molar or bicuspid teeth. This supported previous observations.’ A glass ionomer cement restoration exhibiting unacceptable occlusal wear or marginal breakdown is most unlikely to predispose a tooth to recurrent caries. In such cases, the placement of a bonded composite overlay (‘sandwich restoration’) or amalgam can be achieved with minimal preparation to the remaining glass ionomer cement and without removing existing tooth structure.’ The use of the ‘T preparation requires a little more removal of healthy tissue than the original ovoid design but enhances diagnosis and access to caries and thus the predictability of the restoration. The rationale for overlaying the glass ionomer base in the ‘T design with composite resin is twofold. Firstly, the bonded resin adheres more strongly to enamel than to glass ionomer cement, thus affording better protection to the unsupported enamel at the marginal ridge. Secondly, the greater occlusal surface generated by the ‘Tconfiguration is afforded better wear resistance with composite resin than with glass ionomer cement. Conclusions There are dentists who remain hesitant to attempt the tunnel restoration because of lack of long-term data and concerns over complete caries removal. This paper has aimed to establish that the technique does provide a viable long-term restoration that enjoys many benefits over a conventional Class I1 preparation for the initial lesion, primarily because of the conservative cavity design and the ability to utilize the cariostatic properties and oral stability of capsulated glass ionomer cement. The difficulties that dentists may have encountered gaining adequate access to the cavity have been addressed by describing a cavity design that affords similar access to that of a conventional Class I1 preparation whilst maintaining the benefits of the tunnel restoration. The continuing improvement of dental materials will see firther advancements in the strength and predictability of this technique. Acknowledgements The author wishes to acknowledge the assistance Australian Dental Journal 1992;37:4.
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