ing effectiveness Sidhu,
BDS,
of light-cured
glass ionomer
cem
MSc”
National University of Singapore,Singapore Glass ionomer materials have been used as liners or bases beneath restorations, but light-cured varieties have recently been introduced. Microleakage at the restoration/tooth interface in cervical cavities was used to test the adhesion to dentin of two new light-cured glass ionomer cement lining materials, XR-Ionomer and Fuji Lining LC. Wedge-shaped cervical cavities were prepared on extracted teeth with a gingival cavosurface margin involving dentin, and the specimens were assigned randomly to three groups. The experimental groups were restored with two light-cured glass ionomer cements, the controls were restored with a chemically cured glass ionomer cement; and marginal leakage was assessed by dye penetration. The two light-cured glass ionomer cements displayed some adhesion to dentin in class V test cavities, but there was no significant diEerence between the two materials. (J PROSTHET DENT 1992;68:891-4.)
major goal of restorative dentistry is control of intraoral marginal leakage. Marginal leakage can occur because of dimensional changes and lack of adaptation of the restoration to the cavity wal1s.l These interfacial gaps may lead to recurrent caries and pulpal pathosis. New materials are often subjected to a barrage of rigorous testing that includes tests of bond strength, but the microleakage performance for a specific material is critical. Because no dental material is completely exempt from this phenomenon of microleakage, microleakage information is useful for comparative assessment of different materials.3 The potential for microleakage of various restorative materials has been extensively examined. Marginal microleakage of amalgam restorations diminishes with aging and after the initial application of cavity varnish.4 Conversely, etching of enamel margins controls microleakage of composite resin restorations, but the microleakage is more evident if margins are located in cementum or dentin. Pulpal protection is also important in the use of a base to seal dentin. Traditional liners and bases are chemically cured, but a variety of light-cured materials have been introduced, including glass ionomer cements. Glass ionomer cements develop their strength by a hardening reaction between ion-leachable glasses and an aqueous solution of homopolymer and copolymers of acrylic acid.5 The glass ionomer cements are adhesive dental materials with fluoride-leaching properties that bond to both enamel and dentin.6, 7 Light-cured glass ionomers are now available for liners or bases in restorative dentistry, and they compensate for the limited working time of the conventional chemically cured glass ionomer. This study tested the bonding to dentin of two light-
aTeachingFellow,
Department
of Restorative
1Q/1/4105Q
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Dentistry.
cured glass ionomer lining materials. Microleakage at the glass ionomer/dentin interface was recorded to evaluate the bonding of the materials. MATERIAL
AND
METHODS
Sixty intact extracted human teeth were selected for this study and stored in isotonic saline. Cavity
preparation
and restoration
Wedge-shaped cavities were prepared in the cervical third of the facial and lingual surfaces of the teeth to simulate abrasive lesions. Identical cavities 3 mm x 2 mm and 2 mm in depth were prepared with a tungsten carbide bur in a high-speed handpiece with constant water spray. The preparations were positioned at the cementoenamel junction so that the occlusal margins were in enamel and the gingival margins were in dentin or cementurn. The prepared cavities were then pumiced with a rubber polishing cup in a slow-speed handpiece and washed thoroughly with water. The cavities were then randomly assigned to three groups of 40. Specimens in the control group (group I) were restored with chemically-cured Fuji II glass ionomer cement (G-C Dental, Tokyo, Japan) according to the manufacturer’s instructions. The restorations were covered with a varnish and stored in normal saline for 24 hours prior to the finishing procedures. Cavities in the experimental groups or groups II and III were restored with light-cured glass ionomer lining materials, XR-Ionomer (Kerr Mfg. Co., Romulus, Mich.) and Fuji Lining LC (G-C Dental) respectively, according to the manufacturer’s instructions. The cavities were restored with the light-cured materials in 1 mm increments, with each increment cured with a Coltolux visible light-curing unit (Coltene AG, Altstatten, Switzerland). The restorations were than covered with varnish and stored in normal saline at 37’ C. Half of the specimens in 891
SIDHU
Table
I.
Specimen groups and treatment procedures
involved Materials
Group
Ia Ib IIa IIb IIIa IIlb
Fuji
used
II glass
ionomer Fuji II glass ionamer Kerr XR ionomer Nerr XR ionomer Fuji lining LC Fuji lining LC
Treatment procedure
No. of specimens
Thermocycled
20
Not thermocycled
20
Thermocycled Not thermocycled Thermocycled Not thermocycled
20 20 20 20
gival margins, but this was not a feature of the control specimens. The results were analyzed by the Kruskal-Wallis one-way analysis of variance by ranks. A comparison of the three materials (group I versus group II versus group III) disclosed a significant difference at the 0.05 level (H value 10.42). There was no significant difference in microleakage within groups before and after thermocycling, but further analysis revealed a significant difference between the control and experimental groups at p < 0.05. However, there was no significant difference between the two experimental groups at the 0.05 significance level (H value 0.04).
DISCUSSION each group were subjected to thermocycling. Table I lists the various specimen groups and the treatment.
Thermocycling
and dye immersion
Groups Ia, Ha, and IIIa were subjected to thermocycling. The regime was a modification of similar investigations,s g that is, the cycles consisted of 500 times between baths of 5’ + 2” C, and 55’ F 2’ C, with a dwell time of 30 seconds in each bath. The apices of the roots were sealed with glass ionomer cement and all external surfaces of the teeth were coated with nail varnish except an area within 2 mm of the periphery of the restoration. The teeth were then submerged in 0.5 % aqueous fuchsin dye for 24 hours at room temperature. After removal from the dye solution, the teeth were cleaned, rinsed with tap water, and sectioned longitudinally through the center of the restorations with a diamond blade.
Assessment
of dye penetration
The degree of marginal leakage was evaluated by the penetration of the dye stain from the gingival cavosurface margin to the base of the cavity preparation. The readings were recorded in the sectioned plane of the teeth, that is, one reading per specimen. Each specimen was reviewed with a dissecting microscope (Olympus CO 11, Olympus Co., Tokyo, Japan) at x40 magnification and graded according to the dye penetration. The scoring criteria was: O-No l-Dye 2-Dye &Dye
evidenceof dye penetration at tooth/restoration interface penetration along the interface to 5 ‘/z depth of cavity penetration to full depth of cavity penetration to base of cavity and beyond
Scoring was done by an independent examiner and the specimens photographed.
RESULTS The adhesion of the glass ionomer cements to dentin was the purpose of the experiment; therefore only the dye penetration at the cervical margins was recorded. The scores for all groups are listed in Table II. Specimens in the experimental groups displayed limited leakage from the gin892
The new light-cured liners are commonly subjected to a variety of tests, notably bond strength tests. However, the advantage of high bond strengths listed by manufacturers is often negated by other limitations and unreliable predictors of the clinical performance. The microleakage may be a more accurate assessment of dental materials than in vitro bond strengths.3 In this study the control group was restored with a traditional chemically cured glass ionomer cement. Studies on clinical and simulated abrasive lesions restored with glass ionomer cement exhibited an almost perfect seal between the cement and tooth structure.lO-l2 In a similar radioisotope study,rs no leakage was noted at the gingival and occlusal margins of cervical abrasion cavities restored with glass ionomer cement. This study investigated the microleakage of two new liners compared with an established cavity sealing material. Thermocycling was used to simulate clinical situations, but only half the number of specimens restored with each material was subjected to thermocycling. This was designed to eliminate the possibility that the results merely reflected a function of the thermocycling. Microleakage can be defined as the clinically undetectable passage of bacteria, fluids, molecules, or ions between a cavity wall and the restorative materialI Several methods have been introduced for evaluating in vitro microleakage, including radioisotopes, dyes, air pressure, neutron activation analysis, bacterial penetration, pH changes, and scanning electron microscopy, but dyes and radioisotopes are most common. In a previously combined dye and radioisotope leakage study, comparison of the two techniques indicated that the dye penetration was a more valuable test with direct inspection under a dissecting microscope, because it was more flexible, less complicated, and provided more information. I5 Basic fuchsin dye was selected as a measure of microleakage because of ease of manipulation, and the scoring criteria for the microleakage was similar to a former study.ra The results disclosed significant differences in microleakage between the control and test specimens. In general, the dental materials tested exhibited little or no microleakage at the dentin/glass ionomer cement interface. DECEMBER
1.992
VOLUME
68
NUMBER
6
MARGINAL
LEAiXAGE
OF LIGHT-CURED
GIC LINERS
Table II. Dye penetration scores at dentimcementum
margin Degree
Trwtment
procedure/groups
la (GIC/TC) Ib (GIC/NTC) IIa (XR ionomer/TC) liIb (XR ionomer/NTC) IIIa (Lining LC/TC) Klb (Lining LCYNTC) TC,Thermocycled; NTC,
not
JOURNAL
leakage
0
1
2
Total No. of restorations
10 10
6
16 17 16 18
4 3 4 2
4 2 0 0 0 0
20 20 20 20 20 20
8
thermocycled.
Modifications of the chemical formulation of the glass ionomer cements to allow light-curing appeared to have an effect on adhesion compared with the chemically cured glass ionomer cements (Fuji II). Fuji II cement is marketed as a restorative material and has displayed adequate clinical retention for prolonged periods.16, l7 The impressive clinical retentive rates in class V restorations are related to the adhesive properties of glass ionomer cements. With improved marginal integrity between the chemically cured and light-cured glass ionomer cements illustrated in this study, perhaps the light-cured cements will also exhibit the same long-term clinical adhesion provided by the chemically cured glass ionomer cement. This is a critical feature because other light-activated bases are primarily resin based and exhibit polymerization shrinkage with contractive gaps. In a recent study of the microleakage of a composite resin light-activated base material, polymerization shrinkage caused severe leakage. This was minimally reduced by the application of a dentinal bonding agent before placement of the base.18 This study was completed in relatively ideal conditions. The lining/base materials were not subjected to the stress of placing a permanent restoration because the glass-ionomer/dentinal bond can be disrupted during the restorative process. Thermocycling did not significantly affect the sealing effectiveness of the three materials tested; therefore the coefficient of thermal expansion/contraction of these materials may have been similar to that for dentin. The clinical significance of the results is important. Glass ionomer liners are indicated for amalgam restorations and are also useful in the “sandwich” technique with composite resin restorations. The chemically cured glass ionomer liners have reduced leakage at gingival margins of cervical cavities.lg This study indicated that light-cured glass ionomer cements were also effective. The light-cured glass ionomer cements appear to reduce microleakage associated with composite resin restorations more effectively than conventional glass ionomer cements.20 Although this study closely simulated clinical conditions, the results may not be applicable to clinical situations. Although in vitro studies are useful, they may not THE
of marginal
OF PROSTHETIC
DENTISTRY
completely reflect an in vivo response, but merely indicate a possible clinical performance. Because the initial trials of new materials do not always reveal their limitations or attributes, clinical longitudinal data are commonly indicated. CONCLUSION The glass ionomer cements are an important contribution to restorative dentistry, but creating a hermetic seal for restorations remains elusive. In this study, the microleakage of the light-cured glass ionomer cements was investigated, and these conclusions were drawn: 1. The glass ionomer restorative materials in this study did not always provide a complete seal in cervical wedgeshaped cavities. 2. The twolight-curedglassionomerlinerstested bonded to dentin. 3. Microleakage tests revealed in most instances that the bond was complete but occasionally minimally disrupted. 4. There was no significant difference between microleakage of the two light-cured liners tested. REFERENCES
1. Nelson 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
R, WolcottR,Paffenbarger G.Fluidexchange at the margins of dental restorations. J Am Dent Assoc 1952;44:289-95. Brannstrom M, Nordenvall KJ. Bacterial penetration, pulpal reaction and the inner surface of Concise enamel bond. J Dent Res 1978;57:3-10. Douglas WH. Clinical status of dentin bonding agents. J Dent 1989;17:209-15. Swartz ML, Phillips RW. In vitro studies on the marginal leakage of restorative materials. J Am Dent Assoc 1961;62:141-51. Wilson AD, Kent BE. A new translucent cement for dentistry. The glass-ionomer cement. Br Dent J 1972;132:133-5. Hots P, McLean JW, Seed I, Wilson AD. The bonding of glass-ionomer cements to metal and tooth substrates. Br Dent J 1977;142:41-7. Forsten L. Fluoride release from a glass-ionomer cement. Stand J Dent Res 1977;89:509-12. Welsh EL, Hembree JH. Microleakage at the gingival wall with four Class V anterior restorative materials. J PROSTHET DENT 1985;54:370-2. Hembree JH. Microleakage at the gingival margin of class II composite restorations with glass-ionomer liner. J PROSTHET DENT 1989;61:28-30. Kidd EAM. Cavity sealing ability of composite and glass-ionomer cement restorations. Br Dent J 1978;144:139-42. Maldonado A, Swartz ML, Phillips RW. An in vitro study of certain properties of a glass-ionomer cement. J Am Dent Assoc 1978;96:785-91. Charbeneau GT, Bozell RR III. Clinical evaluation of a glass ionomer cement for restoration of cervical erosion. J Am Dent Assoc 1979; 98:936-9.
893
SIDHU
13. Bembree storative
JH, Andrews JI. Microleakage materials: a laboratory study.
class V composite resin restorations with glass ionomer liners in vitro. J PROSTHET DENT 1990;63:522-5. 20. Tjan AHL, Dunn JR, Grant BE. Microleakage of light-cured glass-ionomer under Class V composite restorations [Abstract]. J Dent Res 1989;945:1015.
of several Class V anterior reJ Am Dent Assoc 1978;97:179-
83.
14. Kidd EAM. Microleakage in relation to amalgam and composite restorations. A laboratory study. Br Dent J 1976;141:305-10. 15. Crim GA, Swartz ML, Phillips RW. Comparison of four thermocycling techniques. J PROSTHET DENT 1985;53:50-3. 16. Mount GJ. The longevity of glass ionomer cements. J PROSTHET DENT 1986;55:682-5. 17. Tyas MJ, Alexander SB, Beech DR, Brackhurst PJ, Cook WD. Bonding-retrospect and prospect. Aust Dent J 1988;33:364-74. 18. Ghan KC, Swift EJ Jr. Leakage of a light-activated base: effect of dentin bonding agents. J PROSTHET DENT 1991;65:790-2. 19. Mathis RS, Dewald JP, Moody CR, Ferracane JL. Marginal leakage in
Reprint
ntion properties of a split-shaft ff erent apical lengths . Cohen, PhD,a and Allan S. Deutsch, Essential
Dental
Laboratories,
Spyridon DMW South
Condos, Hackensack,
DDS,b
requests
to:
DR. 5. K. SIDHU DEPARTMENT OF CONSERVATIVE DENTAL SURGERY UNITED MEDICAL AND DENTAL SCHOOLS GUY’S HOSPITAL LONDON BRIDGE LONDON SE1 9RT UNWED KINGDOM
Barry
threaded Lee
Musikant,
post: Cut a DMD,”
N.J.
The retention of the post to the root of an endodontically treated tooth is critical for a successful restoration. Modification of the post length to accommodate a specific clinical situation is common. This study compared the retention of No. 1 and No. 2 Flexi-Post restorations shortened apically from 1 to 5 mm with that reported for full-length control No. 1 and No. 2 Flexi-Post dowels. The experimental material was divided into 10 groups with 10 samples in each group. Retentive values were recorded in pounds with a universal testing machine. Analysis of variance with a Tukey-Student range, multiple-comparison test showed no statistical differences from apical reductions of 1,2, 3, and 5 mm including the full-length control FlexiPost No. 1 system. With 4 mm of apical shortening statistically greater retention was recorded. No statistical differences resulted with apical reductions of 1 to 4 mm or with the full-length control Flexi-Post No. 2 system, but 5 mm of apical shortening caused significantly less retention. (J PROSTHET DENT 1992;68:894-8.)
post and core restoration provides a substructure for anchoring the final restoration to the root; thus post retention is critical.l, 2 Clinical observations confirmed that cements adhered to dentin and posts, but the inherent weaknesses of cement caused failure.3-5 This deterioration of the cement can result in loosening of the post, leading to possible fracture of the root. Artificial crowns are subject to micromovement during normal occlusion. Dislodgment can follow, causing the post to transmit the masticatory forces to the dentin and the cement sustaining the post. Cements are brittle and susceptible to disintegration during continual cyclic loading. When the cement deteriorates and remains located
aVice President of Dental Research. bPrivate practice, New York, N.Y. %odirector of Dental Research. 10/1/4P170
894
around the most coronal part of the post during failure, the fulcrum of the post descends along the root, increasing the lever arm associated with the post. This elevated lever arm magnifies the stress transmitted to the surfaces of the post that remain cemented to the root. This can result in a defective restoration because greater stresses are then directed to the unsupported post and either dislodge the cement or concentrate the stress at the apical surface of the root, with possible root fracture.6-8 Failure rates can be increased in most prefabricated post systems, because there is poor adaptation between the post and the post hole, particularly in the coronal 2 mm.3, s, g Retention is a convenient method to evaluate the stability of a specific post system. Posts that possess greater retention exhibit greater resistance to dislodgment from lateral occlusal stresseslO-l3 The split-shank Flexi-Post system (Essential Dental Systems, Inc., South Hackensack, N.J.) has demonstrated excellent retention in the root.10-12*14,15 Hopwood and
DECEMBER
1992
VOLUME
68
NUMBER
6
BDS,
of light-cured
glass ionomer
cem
MSc”
National University of Singapore,Singapore Glass ionomer materials have been used as liners or bases beneath restorations, but light-cured varieties have recently been introduced. Microleakage at the restoration/tooth interface in cervical cavities was used to test the adhesion to dentin of two new light-cured glass ionomer cement lining materials, XR-Ionomer and Fuji Lining LC. Wedge-shaped cervical cavities were prepared on extracted teeth with a gingival cavosurface margin involving dentin, and the specimens were assigned randomly to three groups. The experimental groups were restored with two light-cured glass ionomer cements, the controls were restored with a chemically cured glass ionomer cement; and marginal leakage was assessed by dye penetration. The two light-cured glass ionomer cements displayed some adhesion to dentin in class V test cavities, but there was no significant diEerence between the two materials. (J PROSTHET DENT 1992;68:891-4.)
major goal of restorative dentistry is control of intraoral marginal leakage. Marginal leakage can occur because of dimensional changes and lack of adaptation of the restoration to the cavity wal1s.l These interfacial gaps may lead to recurrent caries and pulpal pathosis. New materials are often subjected to a barrage of rigorous testing that includes tests of bond strength, but the microleakage performance for a specific material is critical. Because no dental material is completely exempt from this phenomenon of microleakage, microleakage information is useful for comparative assessment of different materials.3 The potential for microleakage of various restorative materials has been extensively examined. Marginal microleakage of amalgam restorations diminishes with aging and after the initial application of cavity varnish.4 Conversely, etching of enamel margins controls microleakage of composite resin restorations, but the microleakage is more evident if margins are located in cementum or dentin. Pulpal protection is also important in the use of a base to seal dentin. Traditional liners and bases are chemically cured, but a variety of light-cured materials have been introduced, including glass ionomer cements. Glass ionomer cements develop their strength by a hardening reaction between ion-leachable glasses and an aqueous solution of homopolymer and copolymers of acrylic acid.5 The glass ionomer cements are adhesive dental materials with fluoride-leaching properties that bond to both enamel and dentin.6, 7 Light-cured glass ionomers are now available for liners or bases in restorative dentistry, and they compensate for the limited working time of the conventional chemically cured glass ionomer. This study tested the bonding to dentin of two light-
aTeachingFellow,
Department
of Restorative
1Q/1/4105Q
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Dentistry.
cured glass ionomer lining materials. Microleakage at the glass ionomer/dentin interface was recorded to evaluate the bonding of the materials. MATERIAL
AND
METHODS
Sixty intact extracted human teeth were selected for this study and stored in isotonic saline. Cavity
preparation
and restoration
Wedge-shaped cavities were prepared in the cervical third of the facial and lingual surfaces of the teeth to simulate abrasive lesions. Identical cavities 3 mm x 2 mm and 2 mm in depth were prepared with a tungsten carbide bur in a high-speed handpiece with constant water spray. The preparations were positioned at the cementoenamel junction so that the occlusal margins were in enamel and the gingival margins were in dentin or cementurn. The prepared cavities were then pumiced with a rubber polishing cup in a slow-speed handpiece and washed thoroughly with water. The cavities were then randomly assigned to three groups of 40. Specimens in the control group (group I) were restored with chemically-cured Fuji II glass ionomer cement (G-C Dental, Tokyo, Japan) according to the manufacturer’s instructions. The restorations were covered with a varnish and stored in normal saline for 24 hours prior to the finishing procedures. Cavities in the experimental groups or groups II and III were restored with light-cured glass ionomer lining materials, XR-Ionomer (Kerr Mfg. Co., Romulus, Mich.) and Fuji Lining LC (G-C Dental) respectively, according to the manufacturer’s instructions. The cavities were restored with the light-cured materials in 1 mm increments, with each increment cured with a Coltolux visible light-curing unit (Coltene AG, Altstatten, Switzerland). The restorations were than covered with varnish and stored in normal saline at 37’ C. Half of the specimens in 891
SIDHU
Table
I.
Specimen groups and treatment procedures
involved Materials
Group
Ia Ib IIa IIb IIIa IIlb
Fuji
used
II glass
ionomer Fuji II glass ionamer Kerr XR ionomer Nerr XR ionomer Fuji lining LC Fuji lining LC
Treatment procedure
No. of specimens
Thermocycled
20
Not thermocycled
20
Thermocycled Not thermocycled Thermocycled Not thermocycled
20 20 20 20
gival margins, but this was not a feature of the control specimens. The results were analyzed by the Kruskal-Wallis one-way analysis of variance by ranks. A comparison of the three materials (group I versus group II versus group III) disclosed a significant difference at the 0.05 level (H value 10.42). There was no significant difference in microleakage within groups before and after thermocycling, but further analysis revealed a significant difference between the control and experimental groups at p < 0.05. However, there was no significant difference between the two experimental groups at the 0.05 significance level (H value 0.04).
DISCUSSION each group were subjected to thermocycling. Table I lists the various specimen groups and the treatment.
Thermocycling
and dye immersion
Groups Ia, Ha, and IIIa were subjected to thermocycling. The regime was a modification of similar investigations,s g that is, the cycles consisted of 500 times between baths of 5’ + 2” C, and 55’ F 2’ C, with a dwell time of 30 seconds in each bath. The apices of the roots were sealed with glass ionomer cement and all external surfaces of the teeth were coated with nail varnish except an area within 2 mm of the periphery of the restoration. The teeth were then submerged in 0.5 % aqueous fuchsin dye for 24 hours at room temperature. After removal from the dye solution, the teeth were cleaned, rinsed with tap water, and sectioned longitudinally through the center of the restorations with a diamond blade.
Assessment
of dye penetration
The degree of marginal leakage was evaluated by the penetration of the dye stain from the gingival cavosurface margin to the base of the cavity preparation. The readings were recorded in the sectioned plane of the teeth, that is, one reading per specimen. Each specimen was reviewed with a dissecting microscope (Olympus CO 11, Olympus Co., Tokyo, Japan) at x40 magnification and graded according to the dye penetration. The scoring criteria was: O-No l-Dye 2-Dye &Dye
evidenceof dye penetration at tooth/restoration interface penetration along the interface to 5 ‘/z depth of cavity penetration to full depth of cavity penetration to base of cavity and beyond
Scoring was done by an independent examiner and the specimens photographed.
RESULTS The adhesion of the glass ionomer cements to dentin was the purpose of the experiment; therefore only the dye penetration at the cervical margins was recorded. The scores for all groups are listed in Table II. Specimens in the experimental groups displayed limited leakage from the gin892
The new light-cured liners are commonly subjected to a variety of tests, notably bond strength tests. However, the advantage of high bond strengths listed by manufacturers is often negated by other limitations and unreliable predictors of the clinical performance. The microleakage may be a more accurate assessment of dental materials than in vitro bond strengths.3 In this study the control group was restored with a traditional chemically cured glass ionomer cement. Studies on clinical and simulated abrasive lesions restored with glass ionomer cement exhibited an almost perfect seal between the cement and tooth structure.lO-l2 In a similar radioisotope study,rs no leakage was noted at the gingival and occlusal margins of cervical abrasion cavities restored with glass ionomer cement. This study investigated the microleakage of two new liners compared with an established cavity sealing material. Thermocycling was used to simulate clinical situations, but only half the number of specimens restored with each material was subjected to thermocycling. This was designed to eliminate the possibility that the results merely reflected a function of the thermocycling. Microleakage can be defined as the clinically undetectable passage of bacteria, fluids, molecules, or ions between a cavity wall and the restorative materialI Several methods have been introduced for evaluating in vitro microleakage, including radioisotopes, dyes, air pressure, neutron activation analysis, bacterial penetration, pH changes, and scanning electron microscopy, but dyes and radioisotopes are most common. In a previously combined dye and radioisotope leakage study, comparison of the two techniques indicated that the dye penetration was a more valuable test with direct inspection under a dissecting microscope, because it was more flexible, less complicated, and provided more information. I5 Basic fuchsin dye was selected as a measure of microleakage because of ease of manipulation, and the scoring criteria for the microleakage was similar to a former study.ra The results disclosed significant differences in microleakage between the control and test specimens. In general, the dental materials tested exhibited little or no microleakage at the dentin/glass ionomer cement interface. DECEMBER
1.992
VOLUME
68
NUMBER
6
MARGINAL
LEAiXAGE
OF LIGHT-CURED
GIC LINERS
Table II. Dye penetration scores at dentimcementum
margin Degree
Trwtment
procedure/groups
la (GIC/TC) Ib (GIC/NTC) IIa (XR ionomer/TC) liIb (XR ionomer/NTC) IIIa (Lining LC/TC) Klb (Lining LCYNTC) TC,Thermocycled; NTC,
not
JOURNAL
leakage
0
1
2
Total No. of restorations
10 10
6
16 17 16 18
4 3 4 2
4 2 0 0 0 0
20 20 20 20 20 20
8
thermocycled.
Modifications of the chemical formulation of the glass ionomer cements to allow light-curing appeared to have an effect on adhesion compared with the chemically cured glass ionomer cements (Fuji II). Fuji II cement is marketed as a restorative material and has displayed adequate clinical retention for prolonged periods.16, l7 The impressive clinical retentive rates in class V restorations are related to the adhesive properties of glass ionomer cements. With improved marginal integrity between the chemically cured and light-cured glass ionomer cements illustrated in this study, perhaps the light-cured cements will also exhibit the same long-term clinical adhesion provided by the chemically cured glass ionomer cement. This is a critical feature because other light-activated bases are primarily resin based and exhibit polymerization shrinkage with contractive gaps. In a recent study of the microleakage of a composite resin light-activated base material, polymerization shrinkage caused severe leakage. This was minimally reduced by the application of a dentinal bonding agent before placement of the base.18 This study was completed in relatively ideal conditions. The lining/base materials were not subjected to the stress of placing a permanent restoration because the glass-ionomer/dentinal bond can be disrupted during the restorative process. Thermocycling did not significantly affect the sealing effectiveness of the three materials tested; therefore the coefficient of thermal expansion/contraction of these materials may have been similar to that for dentin. The clinical significance of the results is important. Glass ionomer liners are indicated for amalgam restorations and are also useful in the “sandwich” technique with composite resin restorations. The chemically cured glass ionomer liners have reduced leakage at gingival margins of cervical cavities.lg This study indicated that light-cured glass ionomer cements were also effective. The light-cured glass ionomer cements appear to reduce microleakage associated with composite resin restorations more effectively than conventional glass ionomer cements.20 Although this study closely simulated clinical conditions, the results may not be applicable to clinical situations. Although in vitro studies are useful, they may not THE
of marginal
OF PROSTHETIC
DENTISTRY
completely reflect an in vivo response, but merely indicate a possible clinical performance. Because the initial trials of new materials do not always reveal their limitations or attributes, clinical longitudinal data are commonly indicated. CONCLUSION The glass ionomer cements are an important contribution to restorative dentistry, but creating a hermetic seal for restorations remains elusive. In this study, the microleakage of the light-cured glass ionomer cements was investigated, and these conclusions were drawn: 1. The glass ionomer restorative materials in this study did not always provide a complete seal in cervical wedgeshaped cavities. 2. The twolight-curedglassionomerlinerstested bonded to dentin. 3. Microleakage tests revealed in most instances that the bond was complete but occasionally minimally disrupted. 4. There was no significant difference between microleakage of the two light-cured liners tested. REFERENCES
1. Nelson 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
R, WolcottR,Paffenbarger G.Fluidexchange at the margins of dental restorations. J Am Dent Assoc 1952;44:289-95. Brannstrom M, Nordenvall KJ. Bacterial penetration, pulpal reaction and the inner surface of Concise enamel bond. J Dent Res 1978;57:3-10. Douglas WH. Clinical status of dentin bonding agents. J Dent 1989;17:209-15. Swartz ML, Phillips RW. In vitro studies on the marginal leakage of restorative materials. J Am Dent Assoc 1961;62:141-51. Wilson AD, Kent BE. A new translucent cement for dentistry. The glass-ionomer cement. Br Dent J 1972;132:133-5. Hots P, McLean JW, Seed I, Wilson AD. The bonding of glass-ionomer cements to metal and tooth substrates. Br Dent J 1977;142:41-7. Forsten L. Fluoride release from a glass-ionomer cement. Stand J Dent Res 1977;89:509-12. Welsh EL, Hembree JH. Microleakage at the gingival wall with four Class V anterior restorative materials. J PROSTHET DENT 1985;54:370-2. Hembree JH. Microleakage at the gingival margin of class II composite restorations with glass-ionomer liner. J PROSTHET DENT 1989;61:28-30. Kidd EAM. Cavity sealing ability of composite and glass-ionomer cement restorations. Br Dent J 1978;144:139-42. Maldonado A, Swartz ML, Phillips RW. An in vitro study of certain properties of a glass-ionomer cement. J Am Dent Assoc 1978;96:785-91. Charbeneau GT, Bozell RR III. Clinical evaluation of a glass ionomer cement for restoration of cervical erosion. J Am Dent Assoc 1979; 98:936-9.
893
SIDHU
13. Bembree storative
JH, Andrews JI. Microleakage materials: a laboratory study.
class V composite resin restorations with glass ionomer liners in vitro. J PROSTHET DENT 1990;63:522-5. 20. Tjan AHL, Dunn JR, Grant BE. Microleakage of light-cured glass-ionomer under Class V composite restorations [Abstract]. J Dent Res 1989;945:1015.
of several Class V anterior reJ Am Dent Assoc 1978;97:179-
83.
14. Kidd EAM. Microleakage in relation to amalgam and composite restorations. A laboratory study. Br Dent J 1976;141:305-10. 15. Crim GA, Swartz ML, Phillips RW. Comparison of four thermocycling techniques. J PROSTHET DENT 1985;53:50-3. 16. Mount GJ. The longevity of glass ionomer cements. J PROSTHET DENT 1986;55:682-5. 17. Tyas MJ, Alexander SB, Beech DR, Brackhurst PJ, Cook WD. Bonding-retrospect and prospect. Aust Dent J 1988;33:364-74. 18. Ghan KC, Swift EJ Jr. Leakage of a light-activated base: effect of dentin bonding agents. J PROSTHET DENT 1991;65:790-2. 19. Mathis RS, Dewald JP, Moody CR, Ferracane JL. Marginal leakage in
Reprint
ntion properties of a split-shaft ff erent apical lengths . Cohen, PhD,a and Allan S. Deutsch, Essential
Dental
Laboratories,
Spyridon DMW South
Condos, Hackensack,
DDS,b
requests
to:
DR. 5. K. SIDHU DEPARTMENT OF CONSERVATIVE DENTAL SURGERY UNITED MEDICAL AND DENTAL SCHOOLS GUY’S HOSPITAL LONDON BRIDGE LONDON SE1 9RT UNWED KINGDOM
Barry
threaded Lee
Musikant,
post: Cut a DMD,”
N.J.
The retention of the post to the root of an endodontically treated tooth is critical for a successful restoration. Modification of the post length to accommodate a specific clinical situation is common. This study compared the retention of No. 1 and No. 2 Flexi-Post restorations shortened apically from 1 to 5 mm with that reported for full-length control No. 1 and No. 2 Flexi-Post dowels. The experimental material was divided into 10 groups with 10 samples in each group. Retentive values were recorded in pounds with a universal testing machine. Analysis of variance with a Tukey-Student range, multiple-comparison test showed no statistical differences from apical reductions of 1,2, 3, and 5 mm including the full-length control FlexiPost No. 1 system. With 4 mm of apical shortening statistically greater retention was recorded. No statistical differences resulted with apical reductions of 1 to 4 mm or with the full-length control Flexi-Post No. 2 system, but 5 mm of apical shortening caused significantly less retention. (J PROSTHET DENT 1992;68:894-8.)
post and core restoration provides a substructure for anchoring the final restoration to the root; thus post retention is critical.l, 2 Clinical observations confirmed that cements adhered to dentin and posts, but the inherent weaknesses of cement caused failure.3-5 This deterioration of the cement can result in loosening of the post, leading to possible fracture of the root. Artificial crowns are subject to micromovement during normal occlusion. Dislodgment can follow, causing the post to transmit the masticatory forces to the dentin and the cement sustaining the post. Cements are brittle and susceptible to disintegration during continual cyclic loading. When the cement deteriorates and remains located
aVice President of Dental Research. bPrivate practice, New York, N.Y. %odirector of Dental Research. 10/1/4P170
894
around the most coronal part of the post during failure, the fulcrum of the post descends along the root, increasing the lever arm associated with the post. This elevated lever arm magnifies the stress transmitted to the surfaces of the post that remain cemented to the root. This can result in a defective restoration because greater stresses are then directed to the unsupported post and either dislodge the cement or concentrate the stress at the apical surface of the root, with possible root fracture.6-8 Failure rates can be increased in most prefabricated post systems, because there is poor adaptation between the post and the post hole, particularly in the coronal 2 mm.3, s, g Retention is a convenient method to evaluate the stability of a specific post system. Posts that possess greater retention exhibit greater resistance to dislodgment from lateral occlusal stresseslO-l3 The split-shank Flexi-Post system (Essential Dental Systems, Inc., South Hackensack, N.J.) has demonstrated excellent retention in the root.10-12*14,15 Hopwood and
DECEMBER
1992
VOLUME
68
NUMBER
6
