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Effects of preparation designs and adhesive systems on retention of class II amalgam restorations
Effects of preparation designs and adhesive systems on retention of class II amalgam restorations Jale Giiriicii, DDS, PhD, a Meserret Tiritoglu, DDS, PhD, a and Giil Ozgiinaltay, DDS, PhD b
Faculty of Dentistry, University of Hacettepe, Ankara, Turkey P u r p o s e . This study evaluated the effects of three preparation designs and the influence of an adhesive system in Class II amalgam restorations when a load was applied directly to the marginal ridge. M a t e r i a l a n d m e t h o d s . Seventy-two sound caries-free maxillary molars were divided into 6 groups of 12 teeth. In groups i and 4, the preparation had an extension through the occlusal groove, whereas the other four groups used a proximal slot (box-only) preparation. Groups 2 and 5 had facial and lingual retention grooves that extended from the gingival floor to the occlusal surface, and groups 3 and 6 had slots without grooves. Teeth in groups 1, 2, and 3 were restored with amalgam and groups 4, 5, and 6 were restored with resin bonded amalgam. The marginal ridges of the restorations were loaded at an angle of 13.5 degrees to the long axis of the tooth in an Instron testing machine until failure. Results. Analysis of mean failure loads indicated that proximal slot preparations with retention grooves or occlusal extensions were statistically equivalent but significantly greater than proximal slots without grooves. The addition of an adhesive system improved fracture values for all three types of preparations. Conclusions. When proximal caries was diagnosed and no occlusal caries was evident, a proximal slot amalgam restoration combined with retention grooves and an adhesive system was the appropriate choice. (J Prosthet Dent 1997;78:250-4.)
Attention has focused on the strength o f teeth after preparation for rcstorative treatment as it relates directly to their long-term longevity in the oral environmcnt. Class I and class I I cavity preparations have been based on Black's principles, ~ which require an occlusal width o f one third o f the buccolingual intercuspal distance. Current equipment and restorative materials permit m o r e conservative geometric forms. Reductions in bur dimensions have allowed a minimal removal o f tooth structure in intracoronal operative dentistry preparations.2-s Vale 6 studied the effect o f the buccolingual width o f M O D cavity preparations prepared in sound teeth and his stress studies encouraged conservative cavity preparations. When proximal caries has been diagnosed and there is no occlusal caries, a proximal slot amalgam restoration may be the restoration of choice. Sealants have permitted noncarious fissures to be sealed rather than be included in amalgam preparations. ~ The benefits o f the slot amalaAssistant Professor, Department of Conservative Dentistry. bAssociate Professor, Department of Conservative Dentistry. 250
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gam restoration such as maintenance of tooth strength, maintenance o f occlusal enamel, and limiting the extent of restoration margin length have been pubfished. 7-9Clinical studies have clearly demonstrated the increased longevity and the service of narrow preparations for amalgam, when compared with wider preparations? °-12 Adhesive systems designed to bond amalgam to enamel and dentin have been introduced in an effort to compensate for some o f the disadvantages presented by amalgam, particularly microleal~ag@ 3,14 and the need for additional retentive devices, a3-1sThese systems may obviate the need for protective bases and to strengthen remaining tooth tissues weakened by disease and cavity preparation. 16,17Eakle et al?6 assessed the effects of bonded amalgam in relation to resistance to tooth fracture and reported that a tooth restored with a bonded amalgam requires a significantly greater load to fracture than a tooth restored with amalgam and no adhesive. This result suggests the possibility that the adhesive technique is more conservative. Although many in vitro studies have assessed the effectiveness o f the use o f retention grooves in class I I amalgam restorations, studies on the retention to occlusal VOLUME 78 NUMBER 3
G(~IROC0,TIRITOGLU, AND OZGUNALTAY
loading of the proximal portions of class II amalgam restorations with adhesive systems have been conducted by a small number of investigators, ls'18-21 The purpose of this study was to evaluate the effect of three preparation designs and the influence of an adhesive system in class II amalgam restorations when a load was applied directly to the marginal ridge.
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MATERIAL AND METHODS Seventy-two extracted, intact, noncarious, human maxillary molars of approximately the same size were selected. The teeth were stored in tap water at room temperature after extraction and during restorative and testing procedures. The widest faciolingual and mesiodistal dimensions for each tooth crown were measured and recorded. The sum of these two dimensions was used in the distribution of specimens among groups to provide uniformity of tooth size in each group. Specimens were divided into 6 groups o f l 2 teeth. After roots were notched, they were e m b e d d e d in autopolymerizing acrylic resin blocks (Major, Major Prodotti Dentari, 1Vfincelieri,Italy), which were confined by cubic Plexiglass holders (Far Glass, Istanbul, Turkey) (i5 x 15 x 15 mm) (Fig. 1). The specimens were positioned with the long axis, paralleled to the sides on the holder for momating. The groups were assigned as follows: Group I: Occlusal extension and without adhesive system; Group 2: Slot with retention groove and without adhesive system; Group 3: Slot without retention groove and adhesive system; Group 4: Occlusal extension and with adhesive system; Group 5: Slot with retention groove and adhesive system; and Group 6: Slot without retention groove and with adhesive system.
Preparations Class II mesioocclusal (MO) cavities were prepared with tapered fissure burs, (835/012, Northbel SRL, Milan, Italy) and round burs (FG 001/010, FIS, Finzler Schrock and Kimmel GmbH, Bad Ems, Germany) in a high-speed handpiece by one operator. Groups 1 and 4 received an MO preparation that extended through the central groove into the central fossa (Fig. 2, a). The faciolingual width of the occlusal extension was 2.00 ± 0.25 mm and the pulpal depth of the occlusal extension was 1.80 -+0.30 mm. Faciolingual dimensions of the proximal box were 2.25 -+ 0.25 mm occlusally and 2.75 ± 0.25 mm gingivally. The occlusogingival height of the axial wail was 1.75 ± 0.25 mm and the pulpoaxial line angle was rounded. Groups 2 and 5 received an MO slot preparation (slightly divergent facial and lingual walls, perpendicular to the external tooth surface), with retention grooves SEPTEMBER 1997
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Fig. I. Positioned tooth under simulated occlusa[ load; a, Plexiglass holder; b, steel mold; and c, screw.
that extended from the gingival floor to the occiusal surface at the axiofacial and axiolingual line angles (Fig. 2, b). The depth of the box or slot gingivally from the marginal ridge was 3.25 ± 0.25 mm. Axially, the gingival floor was 1.25 + 0.25 mm wide. The retention grooves were 0.33 mm (approximately a half to a third the diameter of the No. 001/0.10 bur) deep. Groups 3 and 6 received an MO slot preparation as in groups 2 and 5, but without retention grooves (Fig. 2, c). During cavity preparation, the fissure bur was replaced every five teeth.
Restorative procedure The teeth in groups 1 through 3 were restored with amalgam (SDI, GS 80, Bayswater, Victoria, Australia). The preparation was rinsed with water spray and dried for 15 seconds with an air syringe. A matrix band with a Tofflemire retainer (Union Broach Corp., Long Island City, N.Y.) was placed. Amalgam was triturated according to the manufacturer's instructions and condensed into the preparation by using vertical and lateral pressure with condensers. Carving was completed in accordance with the external contour of the tooth, but the marginal ridge was left slightly more bulky than normal. The restoration was thoroughly burnished. An adhesive system (Amalgambond Plus, Parketl, Farmingdale, N.Y.) was applied to the cavity walls of teeth in groups 4, 5, and 6 and then restored with amalgam. The preparation was rinsed with water spray and dried for 15 seconds with air syringe. Dentin activator 251
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Fig. 2. Class II amalgam preparation designs used in this study; a, group 1 and 4 with extension through occlusal groove; b, groups 2 and 5 with slot retention grooves; c, grooves 3 and 6 without retention grooves. Table I. Average force required to dislodge amalgam restorations (n = 12) Type of preparation design
Occlusal extension (Groups 1 and4) Slot with retention grooves (Groups 2 and 5) Slot without retention grooves (Groups 3 and 6)
Without adhesive system Mean ± SD
With adhesive system Mean ± SD
196_+45"
233_+44*
166 ___29
216 _+47
87 -+ 24
129 -+ 35
*According toTukey test, groups 1 and 4, both with and without adhesive,were not significantly different atp < 0.05.
was dispensed into a mixing well, applied to enamel and dentin walls for 30 seconds, and then rinsed and air dried. Three drops of base, one drop of catalyst, and one scoop of High Performance Additive (HPA) were dispensed into a mixing well and gently stirred. The mixture was applied in a thin layer to the cavity walls and then let dry for 60 seconds. A matrix band with a Tofflemire retainer was placed on the tooth and the amalgam was condensed, carved, and burnished in the same manner as for the other groups. After restoration, all groups of teeth were rinsed with water and stored in tap water at room temperature for 14 days before testing. 252
Testing A special steel mold was prepared to provide the long axis of the teeth at a 13.5 degree angle to the vertical plane (Fig. 1). This mold had a socket (16 x 16 x 14 mm) suitable for the dimensions of the cubic holder. The teeth, which were embedded in a Plcxiglass cubic holder, were placed in this socket and fixed by a screw (Fig. 1). A fissure bur (FG 107/008, Dental Diamant) in a straight handpiece (Bell International, Burlingame, Calif.), mounted in a paralleling device was used to flatten the center of the restored marginal ridge to 0.5 x 1.3 mm. Specimens were positioned in the same mold and held at a 13.5 degree angle for loading (Fig. 1). A blunt stainless steel testing point (0.5 x i mm) was used to load the flattened amalgam in compression with an Instron testing machine (model 4301, Instron Corp., Attleboro, Mass.) at a crosshead speed of 1 m m / m i n u t e until the restoration was dislodgcd from the tooth. The force required to dislodge (Newtons) the restoration and the type and location of failure were recorded. The data were analyzed with two-way analysis of variance (ANOVA) and Tukey multiple comparison tests. The level of significance was set at # < 0.05. RESULTS The mean forces required to dislodge the restorations arc presented in Table I. Two-way ANOVA indicated VOLUME 78 NUMBER 3
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statistically significant differences among all preparation designs whether they had an adhesive system or not (F = 51,887; p = 0.000). Significant differences were also found between each cavity design with and without an adhesive system (F = 23.028; p = 0.00). The Tukey multiple comparison tests indicated that the mean forces required to dislodge the restorations were not significantly different in groups 1 and 4, with restorations that included an occlusal extension of the MO preparation through the central groove to the central fossa, or in groups 2 and 5, with restorations included the proximal slot preparation with retention grooves (>0.05). However, restorations in groups 1 and 4 and groups 2 and 5 were significantly more resistant to dislodging forces than those in groups 3 and 6, which included the proximal slot preparations without retention grooves (p < 0.05) Table I. According to the Tukey multiple comparisons test, application of the adhesive systems for each cavity design revealed a significant difference between the mean failure loads (p < 0.05). DISCUSSION Slot restorations involve only the interproximal box without opening of the occlusal fissure if the latter is not affected by caries. Opening of the occlusal fissure has been advised in dental school, which is in line with Black's ~famous concept of "extension for prevention". However, as early as 1951, Markley22proposed its abandonment but only for the maxillary first premolar and for esthetic reasons. Almquist et al. 7proposed the omission of the opening of the occlusal fissure except to treat a carious lesion, The old axiom of "extension for prevention" was thus discarded. A series of instruments suitable for preparing a technically perfect slot restoration has been developed to save the hard dental tissues.>s Studies of proximal slot cavity preparation have concentrated mainly on the amount of necessary undercut. 21,23,24 In their study of class II proximal slot amalgam restorations, Summit* et al.2~were determined that the long grooves and conventional grooves were more retentive than the short ones. Sturdevant et al.2a completed a clinical study of three cavity designs and concluded that only box form preparations can be successful, provided that full-length retention grooves are placed, rather than the short conventional type. Summitt et al. 24 evaluated the load applied to the marginal ridge required to produce failure in class 1I posterior composite restorations with four preparation designs and found that mean failure loads with restorations, including an occlusal extension of the MO preparation and the proximal slot preparation with retentive grooves, were not significantly different. In these groups, restorations were significantly more resistant to failure than the other two groups, which included the proximal slot preparation without retentive grooves. SEPTEMBER 1997
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The results of this study indicated that class II amalgam restorations that extended through occlusal grooves were not significantly more resistant to failure than proximal slot restorations with retention grooves. Restorations in these groups were significantly more resistant to failure than the other groups, which included the proximal slot preparations without retentive grooves. Summit* et al.24presented similar findings, although both studies used different restoration material. The effectiveness of adhesive agents used in proximal slot cavity preparations has been studied by a small number of investigators. Staninec~s compared the in vitro retention of class II amalgam restorations mediated either by an adhesive agent proximal slot preparation without retentive grooves or by conventional mechanical retention (boxes and grooves). The restorations retained in cavities by means of an adhesive exhibited twice the resistance to dislodge restorations in similar cavities with conventional mechanical retention. In this study, the results demonstrated that the preparations with adhesive systems indicated higher resistance to dislodging load than the preparations without adhesive systems. When compared with a study by Staninec, is the bond strengths of the adhesive system revealed greater values than those in this study that may be due to the bond strengths of adhesive systems. From the results of this study, it may appear to be unnecessary to extend class II preparations across the occlusal surfaces to obtain adequate resistance form and they should not routinely be extended into noncarious occlusal grooves. Under the conditions of this vitro study, a slot type preparation should be used for proximal caries. A retention form must be built into the slot preparation for dental amalgam. Because there is no occlusal extension to provide some of that retention, distinct retention grooves should be placed in the facial and lingual walls of the preparation to retain the restoration. The resistance of restorations would also be increased by the adhesive system. However, these findings must be validated with clinical research. CONCLUSIONS Results of this study indicate that the failure load of class II amalgam restorations, which extended through occlusal grooves, was comparable to proximal slot restorations with retention grooves. Restorations in these groups were significantly more resistant to vertical forces than slot restorations without retention grooves. The restorations with an adhesive system were significantly more resistant to vertical forces than the restorations without an adhesive system. This study evaluated only one aspect of potential failure. The decision regarding extension depends on many factors. 253
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REFERENCES 1. Black GV. Operative dentistry. Chicago: Medico Dental; 1908. 2. Bell BH, Grainger DA. Basic operative dentistry procedures. 2nd ed. Philadelphia: Lea and Febiger; 1971. 3. Markley MR. Restorations of silver amalgam. J Am Dent Assoc 1951 ;43:133-46. 4. Charbeneau GT. Principles and practice of operative dentistry. Philadelphia: Lea and Febiger; 1975. 5. Summitt JB, Obsorne JW. Initial preparations for amalgam restorations: extending the longevity of the tooth-restoration unit. J Am Dent Assoc 1992;123:67-73. 6. Vale WA. Cavity preparation and further thoughts on high speed. Br Dent J 1959;107:333-40. 7. Almquist TC, Cowan RD, Lambert RL. Conservative amalgam restorations. J Prosthet Dent 1973;29:524-8. 8. El Mowafy OM. Fracture strength and fracture patterns of maxillary premolars with approximal slot cavities. Oper Dent 1993;18:160-6. 9. Mondel[i J, Steaga]l L, Ishikiriama A, de Lima Navvarro MF, Soares FB. Fracture strength of human teeth with cavity preparations, l Prosthet Dent 1980;43:419-22. 10. Osborne JW, Gale EN. Relationship of restoration width, tooth position, and alloy to fracture at the margins of 13- to 14-year old amalgams. J Dent Res 1990;69:1599-601. 12. Berry TG, Laswell HR, Osborne JW, Gale EN. Width of isthmus and margina[ fail ure of restorations of amalgam. Oper Dent 1981 ;6:55-8. 13. Char]ton DG, Moore BK, Swartz ML. In vitro evaluation of the use of resin liners to reduce microleakage and improve retention of amalgam restoration. Oper Dent 1992;17:112-9. 14. Staninec M, Holt M. Bonding of ama]gam to tooth structure: tensile adhesion and microleakage tests. J Prosthet Dent 1988;59:397-402. 15. Staninec M. Retention of amalgam restorations: undercuts versus bonding. Quintessence Int 1989;20:347-51. 16. Eakle WS, Staninec M, Lacy AM. Effect of bonded amalgam on the fracture resistance of teeth. J Prosthet Dent 1992;68:257-60.
NoteworthyAbstracts of the Current Literature
GOROC0,TIRITOGLU, AND OZGUNALTAY
17. Bakland T, Tjan AHL, Li T, Francis M. Fracture resistance of MOD-restored teeth: Effects of bonding agents. J Dent Res 1992;71:635 (abstract 955). 1B. Caplan DJ, Denehy GE, Reinhart JW. Effect of retention grooves on fracture strength of Class II composite resin and amalgam restorations. Oper Dent 1990;15:48-52. 19. Summitt JB, Osborne JW, Burgess JO, Howell ML. Effect of grooves on resistance form of Class 2 amalgams with wide occ[usal preparations. Oper Dent 1993;18:42-7. 20. Summitt JB, Howell ML, Burgess JO, Dutton FB, Osborne JW. Effect of grooves on resistance form of conservative class II amalgams. Oper Dent 1992;17:50-6. 21. Summitt JB, Osborne JW, Burgess JO. Effect of grooves on resistance/ retention form of Class 2 approximal slot amalgam restorations. Oper Dent 1993;18:209-13. 22. Markley MR. Restorations of silver amalgam. J Am Dent Assoc 1951;43:133-46. 23. Sturdevant JR, Wilder AD, Roberson TM, eta[. Clinical study of conservative designs for class II amalgams. J Dent Res 1988;67:306 (abstract 1549). 24. Summitt JB, Del]a Bona A, Burgess JO. The strength of Class I1 composite resin restorations as affected by preparation design. Quintessence Int 1994;25:251-7. Reprint requests to: DR. JALEGOR0C0 HACETTEPEUNIVERSITESI DISHEKIMLfGIFAKULTESI KONSERVATIFDIS TEDAVlS[ B D
06100 ANKARA TURKEY Copyright © 1997 by The Editorial Council of The Journal of Prosthetic Dentistr~ 0022-3913/97/$5.00 + 0. 10/1/83632
The reasons for replacement and the age o f failed restorations in general dental practice Mj6r I. Acta Odontol Scand 1997"55:58-63.
Purpose. Since marked changes have occurred in the use of restorative materials (composite, amalgam, and glass ionomer) in Sweden over the past 15 to 20 years, the aim of this study was to evaluate the reasons for replacement of these types of restorations. Any significant differences in the mode of failure of these types of restorations were also evaluated. Material and M e t h o d s . A cross-sectional survey among 177 general dental practitioners treating adult patients in Sweden was undertaken to record the reason for replacement of composite (2431), amalgam (1062), and glass ionomer (538) restorations and to compare these findings to a similar survey conducted 16 years ago. Data, including the age of the failed restoration, on these three types of restorations were recorded and analyzed. The results were statistically analyzed with a random effect logistic regression model clustering on dentists by use of an epidemiologic statistical software package to evaluate the reasons for restoration replacement. An odds ratio (OR) was calculated--that is, the odds of having a specific failure of a restoration after it is placed compared with the odds of the same failure of another type of restoration. If the ORis near one, no association exists, if it is less than one, an inverse or negative association is established. Results. The clinical diagnosis of secondary caries was the main reason to replace all three types of restorations and this diagnosis was significantly higher for amalgam restorations than for composite or glass ionomers. There was a relative decrease in the frequency of replacement of composite restorations from the initial survey but replacement was due to composite degradation/wear and bulk and marginal fractures. The most surprising result was the diagnosis of secondary caries of glass ionomer restorations in more than 50% of the restorations placed. While the age of failure of restorations was noted but limited, the median age was 6 years of composite, 9 years for amalgam, and 3 years for glass ionomer. 36 references. - - R P Renner 254
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Faculty of Dentistry, University of Hacettepe, Ankara, Turkey P u r p o s e . This study evaluated the effects of three preparation designs and the influence of an adhesive system in Class II amalgam restorations when a load was applied directly to the marginal ridge. M a t e r i a l a n d m e t h o d s . Seventy-two sound caries-free maxillary molars were divided into 6 groups of 12 teeth. In groups i and 4, the preparation had an extension through the occlusal groove, whereas the other four groups used a proximal slot (box-only) preparation. Groups 2 and 5 had facial and lingual retention grooves that extended from the gingival floor to the occlusal surface, and groups 3 and 6 had slots without grooves. Teeth in groups 1, 2, and 3 were restored with amalgam and groups 4, 5, and 6 were restored with resin bonded amalgam. The marginal ridges of the restorations were loaded at an angle of 13.5 degrees to the long axis of the tooth in an Instron testing machine until failure. Results. Analysis of mean failure loads indicated that proximal slot preparations with retention grooves or occlusal extensions were statistically equivalent but significantly greater than proximal slots without grooves. The addition of an adhesive system improved fracture values for all three types of preparations. Conclusions. When proximal caries was diagnosed and no occlusal caries was evident, a proximal slot amalgam restoration combined with retention grooves and an adhesive system was the appropriate choice. (J Prosthet Dent 1997;78:250-4.)
Attention has focused on the strength o f teeth after preparation for rcstorative treatment as it relates directly to their long-term longevity in the oral environmcnt. Class I and class I I cavity preparations have been based on Black's principles, ~ which require an occlusal width o f one third o f the buccolingual intercuspal distance. Current equipment and restorative materials permit m o r e conservative geometric forms. Reductions in bur dimensions have allowed a minimal removal o f tooth structure in intracoronal operative dentistry preparations.2-s Vale 6 studied the effect o f the buccolingual width o f M O D cavity preparations prepared in sound teeth and his stress studies encouraged conservative cavity preparations. When proximal caries has been diagnosed and there is no occlusal caries, a proximal slot amalgam restoration may be the restoration of choice. Sealants have permitted noncarious fissures to be sealed rather than be included in amalgam preparations. ~ The benefits o f the slot amalaAssistant Professor, Department of Conservative Dentistry. bAssociate Professor, Department of Conservative Dentistry. 250
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gam restoration such as maintenance of tooth strength, maintenance o f occlusal enamel, and limiting the extent of restoration margin length have been pubfished. 7-9Clinical studies have clearly demonstrated the increased longevity and the service of narrow preparations for amalgam, when compared with wider preparations? °-12 Adhesive systems designed to bond amalgam to enamel and dentin have been introduced in an effort to compensate for some o f the disadvantages presented by amalgam, particularly microleal~ag@ 3,14 and the need for additional retentive devices, a3-1sThese systems may obviate the need for protective bases and to strengthen remaining tooth tissues weakened by disease and cavity preparation. 16,17Eakle et al?6 assessed the effects of bonded amalgam in relation to resistance to tooth fracture and reported that a tooth restored with a bonded amalgam requires a significantly greater load to fracture than a tooth restored with amalgam and no adhesive. This result suggests the possibility that the adhesive technique is more conservative. Although many in vitro studies have assessed the effectiveness o f the use o f retention grooves in class I I amalgam restorations, studies on the retention to occlusal VOLUME 78 NUMBER 3
G(~IROC0,TIRITOGLU, AND OZGUNALTAY
loading of the proximal portions of class II amalgam restorations with adhesive systems have been conducted by a small number of investigators, ls'18-21 The purpose of this study was to evaluate the effect of three preparation designs and the influence of an adhesive system in class II amalgam restorations when a load was applied directly to the marginal ridge.
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I l |
MATERIAL AND METHODS Seventy-two extracted, intact, noncarious, human maxillary molars of approximately the same size were selected. The teeth were stored in tap water at room temperature after extraction and during restorative and testing procedures. The widest faciolingual and mesiodistal dimensions for each tooth crown were measured and recorded. The sum of these two dimensions was used in the distribution of specimens among groups to provide uniformity of tooth size in each group. Specimens were divided into 6 groups o f l 2 teeth. After roots were notched, they were e m b e d d e d in autopolymerizing acrylic resin blocks (Major, Major Prodotti Dentari, 1Vfincelieri,Italy), which were confined by cubic Plexiglass holders (Far Glass, Istanbul, Turkey) (i5 x 15 x 15 mm) (Fig. 1). The specimens were positioned with the long axis, paralleled to the sides on the holder for momating. The groups were assigned as follows: Group I: Occlusal extension and without adhesive system; Group 2: Slot with retention groove and without adhesive system; Group 3: Slot without retention groove and adhesive system; Group 4: Occlusal extension and with adhesive system; Group 5: Slot with retention groove and adhesive system; and Group 6: Slot without retention groove and with adhesive system.
Preparations Class II mesioocclusal (MO) cavities were prepared with tapered fissure burs, (835/012, Northbel SRL, Milan, Italy) and round burs (FG 001/010, FIS, Finzler Schrock and Kimmel GmbH, Bad Ems, Germany) in a high-speed handpiece by one operator. Groups 1 and 4 received an MO preparation that extended through the central groove into the central fossa (Fig. 2, a). The faciolingual width of the occlusal extension was 2.00 ± 0.25 mm and the pulpal depth of the occlusal extension was 1.80 -+0.30 mm. Faciolingual dimensions of the proximal box were 2.25 -+ 0.25 mm occlusally and 2.75 ± 0.25 mm gingivally. The occlusogingival height of the axial wail was 1.75 ± 0.25 mm and the pulpoaxial line angle was rounded. Groups 2 and 5 received an MO slot preparation (slightly divergent facial and lingual walls, perpendicular to the external tooth surface), with retention grooves SEPTEMBER 1997
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Fig. I. Positioned tooth under simulated occlusa[ load; a, Plexiglass holder; b, steel mold; and c, screw.
that extended from the gingival floor to the occiusal surface at the axiofacial and axiolingual line angles (Fig. 2, b). The depth of the box or slot gingivally from the marginal ridge was 3.25 ± 0.25 mm. Axially, the gingival floor was 1.25 + 0.25 mm wide. The retention grooves were 0.33 mm (approximately a half to a third the diameter of the No. 001/0.10 bur) deep. Groups 3 and 6 received an MO slot preparation as in groups 2 and 5, but without retention grooves (Fig. 2, c). During cavity preparation, the fissure bur was replaced every five teeth.
Restorative procedure The teeth in groups 1 through 3 were restored with amalgam (SDI, GS 80, Bayswater, Victoria, Australia). The preparation was rinsed with water spray and dried for 15 seconds with an air syringe. A matrix band with a Tofflemire retainer (Union Broach Corp., Long Island City, N.Y.) was placed. Amalgam was triturated according to the manufacturer's instructions and condensed into the preparation by using vertical and lateral pressure with condensers. Carving was completed in accordance with the external contour of the tooth, but the marginal ridge was left slightly more bulky than normal. The restoration was thoroughly burnished. An adhesive system (Amalgambond Plus, Parketl, Farmingdale, N.Y.) was applied to the cavity walls of teeth in groups 4, 5, and 6 and then restored with amalgam. The preparation was rinsed with water spray and dried for 15 seconds with air syringe. Dentin activator 251
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Fig. 2. Class II amalgam preparation designs used in this study; a, group 1 and 4 with extension through occlusal groove; b, groups 2 and 5 with slot retention grooves; c, grooves 3 and 6 without retention grooves. Table I. Average force required to dislodge amalgam restorations (n = 12) Type of preparation design
Occlusal extension (Groups 1 and4) Slot with retention grooves (Groups 2 and 5) Slot without retention grooves (Groups 3 and 6)
Without adhesive system Mean ± SD
With adhesive system Mean ± SD
196_+45"
233_+44*
166 ___29
216 _+47
87 -+ 24
129 -+ 35
*According toTukey test, groups 1 and 4, both with and without adhesive,were not significantly different atp < 0.05.
was dispensed into a mixing well, applied to enamel and dentin walls for 30 seconds, and then rinsed and air dried. Three drops of base, one drop of catalyst, and one scoop of High Performance Additive (HPA) were dispensed into a mixing well and gently stirred. The mixture was applied in a thin layer to the cavity walls and then let dry for 60 seconds. A matrix band with a Tofflemire retainer was placed on the tooth and the amalgam was condensed, carved, and burnished in the same manner as for the other groups. After restoration, all groups of teeth were rinsed with water and stored in tap water at room temperature for 14 days before testing. 252
Testing A special steel mold was prepared to provide the long axis of the teeth at a 13.5 degree angle to the vertical plane (Fig. 1). This mold had a socket (16 x 16 x 14 mm) suitable for the dimensions of the cubic holder. The teeth, which were embedded in a Plcxiglass cubic holder, were placed in this socket and fixed by a screw (Fig. 1). A fissure bur (FG 107/008, Dental Diamant) in a straight handpiece (Bell International, Burlingame, Calif.), mounted in a paralleling device was used to flatten the center of the restored marginal ridge to 0.5 x 1.3 mm. Specimens were positioned in the same mold and held at a 13.5 degree angle for loading (Fig. 1). A blunt stainless steel testing point (0.5 x i mm) was used to load the flattened amalgam in compression with an Instron testing machine (model 4301, Instron Corp., Attleboro, Mass.) at a crosshead speed of 1 m m / m i n u t e until the restoration was dislodgcd from the tooth. The force required to dislodge (Newtons) the restoration and the type and location of failure were recorded. The data were analyzed with two-way analysis of variance (ANOVA) and Tukey multiple comparison tests. The level of significance was set at # < 0.05. RESULTS The mean forces required to dislodge the restorations arc presented in Table I. Two-way ANOVA indicated VOLUME 78 NUMBER 3
GORUCCI,TIRITOGLU, AND OZGUNALTAY
statistically significant differences among all preparation designs whether they had an adhesive system or not (F = 51,887; p = 0.000). Significant differences were also found between each cavity design with and without an adhesive system (F = 23.028; p = 0.00). The Tukey multiple comparison tests indicated that the mean forces required to dislodge the restorations were not significantly different in groups 1 and 4, with restorations that included an occlusal extension of the MO preparation through the central groove to the central fossa, or in groups 2 and 5, with restorations included the proximal slot preparation with retention grooves (>0.05). However, restorations in groups 1 and 4 and groups 2 and 5 were significantly more resistant to dislodging forces than those in groups 3 and 6, which included the proximal slot preparations without retention grooves (p < 0.05) Table I. According to the Tukey multiple comparisons test, application of the adhesive systems for each cavity design revealed a significant difference between the mean failure loads (p < 0.05). DISCUSSION Slot restorations involve only the interproximal box without opening of the occlusal fissure if the latter is not affected by caries. Opening of the occlusal fissure has been advised in dental school, which is in line with Black's ~famous concept of "extension for prevention". However, as early as 1951, Markley22proposed its abandonment but only for the maxillary first premolar and for esthetic reasons. Almquist et al. 7proposed the omission of the opening of the occlusal fissure except to treat a carious lesion, The old axiom of "extension for prevention" was thus discarded. A series of instruments suitable for preparing a technically perfect slot restoration has been developed to save the hard dental tissues.>s Studies of proximal slot cavity preparation have concentrated mainly on the amount of necessary undercut. 21,23,24 In their study of class II proximal slot amalgam restorations, Summit* et al.2~were determined that the long grooves and conventional grooves were more retentive than the short ones. Sturdevant et al.2a completed a clinical study of three cavity designs and concluded that only box form preparations can be successful, provided that full-length retention grooves are placed, rather than the short conventional type. Summitt et al. 24 evaluated the load applied to the marginal ridge required to produce failure in class 1I posterior composite restorations with four preparation designs and found that mean failure loads with restorations, including an occlusal extension of the MO preparation and the proximal slot preparation with retentive grooves, were not significantly different. In these groups, restorations were significantly more resistant to failure than the other two groups, which included the proximal slot preparation without retentive grooves. SEPTEMBER 1997
THE JOURNAL OF PROSTHETIC DENTISTRY
The results of this study indicated that class II amalgam restorations that extended through occlusal grooves were not significantly more resistant to failure than proximal slot restorations with retention grooves. Restorations in these groups were significantly more resistant to failure than the other groups, which included the proximal slot preparations without retentive grooves. Summit* et al.24presented similar findings, although both studies used different restoration material. The effectiveness of adhesive agents used in proximal slot cavity preparations has been studied by a small number of investigators. Staninec~s compared the in vitro retention of class II amalgam restorations mediated either by an adhesive agent proximal slot preparation without retentive grooves or by conventional mechanical retention (boxes and grooves). The restorations retained in cavities by means of an adhesive exhibited twice the resistance to dislodge restorations in similar cavities with conventional mechanical retention. In this study, the results demonstrated that the preparations with adhesive systems indicated higher resistance to dislodging load than the preparations without adhesive systems. When compared with a study by Staninec, is the bond strengths of the adhesive system revealed greater values than those in this study that may be due to the bond strengths of adhesive systems. From the results of this study, it may appear to be unnecessary to extend class II preparations across the occlusal surfaces to obtain adequate resistance form and they should not routinely be extended into noncarious occlusal grooves. Under the conditions of this vitro study, a slot type preparation should be used for proximal caries. A retention form must be built into the slot preparation for dental amalgam. Because there is no occlusal extension to provide some of that retention, distinct retention grooves should be placed in the facial and lingual walls of the preparation to retain the restoration. The resistance of restorations would also be increased by the adhesive system. However, these findings must be validated with clinical research. CONCLUSIONS Results of this study indicate that the failure load of class II amalgam restorations, which extended through occlusal grooves, was comparable to proximal slot restorations with retention grooves. Restorations in these groups were significantly more resistant to vertical forces than slot restorations without retention grooves. The restorations with an adhesive system were significantly more resistant to vertical forces than the restorations without an adhesive system. This study evaluated only one aspect of potential failure. The decision regarding extension depends on many factors. 253
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REFERENCES 1. Black GV. Operative dentistry. Chicago: Medico Dental; 1908. 2. Bell BH, Grainger DA. Basic operative dentistry procedures. 2nd ed. Philadelphia: Lea and Febiger; 1971. 3. Markley MR. Restorations of silver amalgam. J Am Dent Assoc 1951 ;43:133-46. 4. Charbeneau GT. Principles and practice of operative dentistry. Philadelphia: Lea and Febiger; 1975. 5. Summitt JB, Obsorne JW. Initial preparations for amalgam restorations: extending the longevity of the tooth-restoration unit. J Am Dent Assoc 1992;123:67-73. 6. Vale WA. Cavity preparation and further thoughts on high speed. Br Dent J 1959;107:333-40. 7. Almquist TC, Cowan RD, Lambert RL. Conservative amalgam restorations. J Prosthet Dent 1973;29:524-8. 8. El Mowafy OM. Fracture strength and fracture patterns of maxillary premolars with approximal slot cavities. Oper Dent 1993;18:160-6. 9. Mondel[i J, Steaga]l L, Ishikiriama A, de Lima Navvarro MF, Soares FB. Fracture strength of human teeth with cavity preparations, l Prosthet Dent 1980;43:419-22. 10. Osborne JW, Gale EN. Relationship of restoration width, tooth position, and alloy to fracture at the margins of 13- to 14-year old amalgams. J Dent Res 1990;69:1599-601. 12. Berry TG, Laswell HR, Osborne JW, Gale EN. Width of isthmus and margina[ fail ure of restorations of amalgam. Oper Dent 1981 ;6:55-8. 13. Char]ton DG, Moore BK, Swartz ML. In vitro evaluation of the use of resin liners to reduce microleakage and improve retention of amalgam restoration. Oper Dent 1992;17:112-9. 14. Staninec M, Holt M. Bonding of ama]gam to tooth structure: tensile adhesion and microleakage tests. J Prosthet Dent 1988;59:397-402. 15. Staninec M. Retention of amalgam restorations: undercuts versus bonding. Quintessence Int 1989;20:347-51. 16. Eakle WS, Staninec M, Lacy AM. Effect of bonded amalgam on the fracture resistance of teeth. J Prosthet Dent 1992;68:257-60.
NoteworthyAbstracts of the Current Literature
GOROC0,TIRITOGLU, AND OZGUNALTAY
17. Bakland T, Tjan AHL, Li T, Francis M. Fracture resistance of MOD-restored teeth: Effects of bonding agents. J Dent Res 1992;71:635 (abstract 955). 1B. Caplan DJ, Denehy GE, Reinhart JW. Effect of retention grooves on fracture strength of Class II composite resin and amalgam restorations. Oper Dent 1990;15:48-52. 19. Summitt JB, Osborne JW, Burgess JO, Howell ML. Effect of grooves on resistance form of Class 2 amalgams with wide occ[usal preparations. Oper Dent 1993;18:42-7. 20. Summitt JB, Howell ML, Burgess JO, Dutton FB, Osborne JW. Effect of grooves on resistance form of conservative class II amalgams. Oper Dent 1992;17:50-6. 21. Summitt JB, Osborne JW, Burgess JO. Effect of grooves on resistance/ retention form of Class 2 approximal slot amalgam restorations. Oper Dent 1993;18:209-13. 22. Markley MR. Restorations of silver amalgam. J Am Dent Assoc 1951;43:133-46. 23. Sturdevant JR, Wilder AD, Roberson TM, eta[. Clinical study of conservative designs for class II amalgams. J Dent Res 1988;67:306 (abstract 1549). 24. Summitt JB, Del]a Bona A, Burgess JO. The strength of Class I1 composite resin restorations as affected by preparation design. Quintessence Int 1994;25:251-7. Reprint requests to: DR. JALEGOR0C0 HACETTEPEUNIVERSITESI DISHEKIMLfGIFAKULTESI KONSERVATIFDIS TEDAVlS[ B D
06100 ANKARA TURKEY Copyright © 1997 by The Editorial Council of The Journal of Prosthetic Dentistr~ 0022-3913/97/$5.00 + 0. 10/1/83632
The reasons for replacement and the age o f failed restorations in general dental practice Mj6r I. Acta Odontol Scand 1997"55:58-63.
Purpose. Since marked changes have occurred in the use of restorative materials (composite, amalgam, and glass ionomer) in Sweden over the past 15 to 20 years, the aim of this study was to evaluate the reasons for replacement of these types of restorations. Any significant differences in the mode of failure of these types of restorations were also evaluated. Material and M e t h o d s . A cross-sectional survey among 177 general dental practitioners treating adult patients in Sweden was undertaken to record the reason for replacement of composite (2431), amalgam (1062), and glass ionomer (538) restorations and to compare these findings to a similar survey conducted 16 years ago. Data, including the age of the failed restoration, on these three types of restorations were recorded and analyzed. The results were statistically analyzed with a random effect logistic regression model clustering on dentists by use of an epidemiologic statistical software package to evaluate the reasons for restoration replacement. An odds ratio (OR) was calculated--that is, the odds of having a specific failure of a restoration after it is placed compared with the odds of the same failure of another type of restoration. If the ORis near one, no association exists, if it is less than one, an inverse or negative association is established. Results. The clinical diagnosis of secondary caries was the main reason to replace all three types of restorations and this diagnosis was significantly higher for amalgam restorations than for composite or glass ionomers. There was a relative decrease in the frequency of replacement of composite restorations from the initial survey but replacement was due to composite degradation/wear and bulk and marginal fractures. The most surprising result was the diagnosis of secondary caries of glass ionomer restorations in more than 50% of the restorations placed. While the age of failure of restorations was noted but limited, the median age was 6 years of composite, 9 years for amalgam, and 3 years for glass ionomer. 36 references. - - R P Renner 254
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