Pulp reaction to a tri-cure resin-modified glass ionomer

17ol. 85 No. 6 June 1998

ENDODONTICS

Editor." Richard E. Walton

Pulp reaction to a tri-cure resin-modified glass ionomer Mustafa Demirci, DMD, a Mete 1]~ok, DMD, b Nazan Kti~tikkele~, DMD, c and N a m i k Soydan, DMD, d Istanbul, Turkey UNIVERSITY OF ISTANBUL

Objective. This study evaluated the pulp response to a tri-cure resin-modified glass ionomer cement and compared this response to those elicited by a zinc oxide-eugenol cement and a silicate cement. Materials were placed in nonexposed class V cavity preparations on human teeth. Study Design. Sixty premolars were selected in orthodontic patients in a voluntary group of teenagers. All cavities were prepared according to International Dental Federation specifications. Resin-modified glass ionomer and silicate applications were carried out according to the manufacturers' instructions. Result. All teeth were asymptomatic. Pulp responses to the resin-modified glass ionomer cement were slightly greater than to the zinc-oxide-eugenol cement. Bacterial staining attempts were inconclusive with regard to time intervals and pulp responses. No necrotic pulps were seen in any teeth. Conclusion. The tri-cure resin-modified glass ionomer cement elicited a slightly greater adverse pulp response than did the zincoxide-eugenol cement with respect to the healing process of the pulp. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;85:712-19)

Resin-modified glass i o n o m e r ( R - M G I ) cements are used as lining c e m e n t s or bases, core b u i l d - u p materials, and restorative m a t e r i a l s in n o n - s t r e s s b e a r i n g areas. R e s t o r a t i v e uses include, but are not l i m i t e d to, class III and class V restorations, cervical erosion lesions, areas prone to high caries incidence, and areas involving esthetic considerations. T h e s e c e m e n t s c o m b i n e the m a j o r benefits of glass ionomer cements with the easy handling of lightcuring composites. R - M G I has a coefficient o f thermal e x p a n s i o n similar to that o f tooth structure, 1,2 offers i m p r o v e d esthetics (translucency) 3-5 and has r e l a t i v e l y high bond strength, 6-1° an ability to release fluoride,IllS and complementary curing mechanisms. 16 R - M G I s are classified on a c o n t i n u u m a c c o r d i n g to their aDoctor of Conservative Dentistry, University of Istanbul, Department of Conservative Dentistry. bprofessor, University of Istanbul, Department of Conservative Dentistry. CAssociateProfessor, University of Marmara, Faculty of Dentistry, Department of Orthodontics, Istanbul, Turkey. aProfessor, University of Istanbul, Departments of Histology and Embryology. Received for publication May 5, 1997; returned for revision July 18, 1997, and Dec. 4, 1997; accepted for publication Jan. 20, 1998. Copyright © 1998 by Mosby, Inc. 1079-2104/98/$5.00 + 0 7/15/89280 7/2

Table I. Histologic evaluation criteria Pulp tissue response and inflammation scale 1. Normalor uneven odontoblastic layer below tubules of remaining dentin with subjacent slight inflammatory changes. 2. Peripheral pulp disorganizationbeneath remaining dentin wall associated with moderate acute or chronic inflammatory changes. 3. Reaction involving coronal pulp associated with severe acute or chronic inflammatory changes. 4. Necrotic pulp. Reparative dentin deposition (R)1. No additional reparative dentin deposition. (R)2. Layer of reparative dentine seen below cavity preparation. (R)3. Reparative dentin anywhere on dentin wall. curing reactions, with conventional glass i o n o m e r s at one end and composite resins at the other. 1 Some important clinical characteristics of any particular R - M G I material are dictated b y its location on this continuum. 1 Vitremer (3M), which is near the glass ionomer end, possesses a third curing mechanism and is considered a true R-MGI. 17-19 R - M G I cements have only recently received biological evaluation with respect to their effect on the integrity o f the adjacent tissue. Previous studies in tissue culture, 2° pulp testings on animal 21,22 and human teeth, 23,24 and in vitro microleakage investigations25-29 have reported acceptable in vivo and in vitro responses

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Fig. 1. Test material (Vitremer) at 3 days. Almost-even cell distribution at odontoblastic layer (cut at a slightly oblique angle) is evident; slight inflammatory changes are present within cell-rich zone. Remaining dentin thickness = 600 gin.

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Fig. 2. Positive control (silicate) at 4 days. Typical acute pulp response to silicate and severe tissue changes throughout the pulp can be noted. Remaining dentin thickness = 1000 [am,

Table II. Distribution of teeth and meterial groups with their respective pulp responses

Material

R-MGI (Vitremer)

ZOE (Kalzinol)

Silicate (Fritex)

Time interval (day)

Remaining dentin thickness average (tim)

Pulp tissue response and i n f l a m m a t i o n scale* 1 2 3

~Reparative dentin d~osition R(1) R(2) R(3)

5 30 90

510-710 350-800 110-700

7 8 7

2(a) 2(c) l(c)

0 0 0

5 5 5

0 0 0

0 0 0

5 30 90 5 30 90

300-900 350-870 100-740 240-1000 260-950 320-780

3 4 4 0 0 0

l(a) l(c) l(c) 0 0 2(c)

0 0 0 4(a) 5(c) 3(c)

5 5 3 5 0 0

0 0 2 0 5 4

0 0 0 0 0 l

a, Acuteinflammation,c, chronicinflammation. *No necroticpulp was seen.

to R - M G I cements. To date, there h a v e b e e n few publications on the histologic evaluation of this material with respect to the h u m a n pulp. T h e purpose o f our study was to determine, by means

of a conventional 3° histologic positive-negative control p r o t o c o l , the p u l p r e s p o n s e to Vitremer, an R - M G I cement, in class V cavities on noncarious vital h u m a n p e r m a n e n t teeth.

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Fig. 3. Higher magnification of Fig. 2. Odontoblastic layer disruption with lack of peripheral pulp definition is evident; nuclei in cut tubules, dilated vessels, and infiltration of neutrophil polymorphs (dense nuclei) can also be noted.

MATERIAL AND METHODS Sixty healthy human permanent premolars (in 24 patients) scheduled for orthodontic extraction were used in this study. With the patients under local anesthesia and with a rubber dam in place, class V cavities were prepared through the use of intermittent pressure with inverted-cone diamond burs (ISO 314) at high speed under water coolant. The preparation dimensions were approximately 2 mm axially, 3 mm mesiodistally, and 2 mm occlusogingivally. Both occlusal and gingival margins were in enamel. The smear layer was left intact. After preparation the cavities were cleaned with a stream of water and then dried with sterile cotton pellets and gentle air spray. Each cavity was restored with one material. For each time interval, 20 teeth (10 test material, 5 positive control, and 5 negative control) were used. All materials were mixed and placed directly into the cavities without lining or acid pretreatment according to the manufacturers' recommendations. For the tri-cure R-MGI (Vitremer) a thin layer of

Fig. 4. Test material (Vitremer) at 30 days. Moderate (grade 2) pulp response (also seen in one specimen filled with ZOE at same cavity depth) is evident; odontoblastic loss and leucocyte infiltration can also be noted. Remaining dentin thickness = 350 gm.

primer was applied on both enamel and dentin surfaces for 30 seconds before application of the material. Teeth were air-dried for 15 seconds and cured for 20 seconds. Vitremer was mixed and then placed in the cavities as a bulk and cured for 40 seconds. After finishing, the surfaces were coated with a thin layer of finishing gloss and cured for 20 seconds. The negative control material was a zinc oxideeugenol (ZOE) cement, Kalzinol (De Trey Division, Dentsply Ltd., Weybridge, Surrey, U.K.); the positive control material was a silicate cement, Fritex (Spofa Dental, Prague, Czech Republic). Control materials were placed directly into the cavities, and ZOE specimens were covered with amalgam for reinforcement. After evaluation periods of 5, 30, and 90 days, teeth were carefully extracted, fixed in 10% formalin, decalcified in 9% ethylenediamine tetraacetic acid solutions,

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Fig. 5. Negative control (Kalzinol) at 30 days. Even odontoblastic layer and a few inflammatory changes (grade 1) under cavity preparation are evident. Remaining dentin thickness = 500 ~tm.

and processed for routine paraffin embedding. They were serially sectioned in a buccolingual plane at 8 mm and stained with hematoxylin and eosin and Masson's tri-chrome. Selected slides were stained according to the modified Brown-Brenn method 31 for histologic demonstration of bacteria. Evaluation of the severity of the histologic reaction in any given specimen was based primarily on the most severe finding, which in most instances occurred under the deepest area in serial sections. Therefore the degree of response was first analyzed separately for each filling material with respect to the different depths of the cavities. Consideration was given to similarity of cavity depth in comparing time intervals within the same group or in comparing one material group with another. Pulp reactions were classified according to the criteria shown in Table I (a modification of the work of Cox et al.32,33).

Fig. 6. Positive control (silicate) at 30 days. Severe inflammation with dense inflammatory cell infiltration at dentin margin and a more diffuse infiltrate throughout pulp can be observed; there is no reparative dentin. Remaining dentin thickness = 700 gin.

RESULTS Five of the 60 teeth were unusable because of technical problems or pulpal exposure. The results of the histologic evaluation are summarized in Table II.

Five-day observation In teeth filled with ZOE cement (the negative controls) and Vitremer, no observable histologic differences were noted. Seven Vitremer- and three Kalzinolapplied teeth showed only slight (grade 1) odontoblastic and subodontoblastic layer changes below the cut tubules. There was a reduction in the number of odontoblasts, as evidenced by displacement of nuclei into the dentinal tubules and vacuolization, as well as by varying degrees of acute inflammatory reaction within the cell-rich layer (Fig. 1); no cell infiltration occurred in the cell-free zone. Three moderate (grade 2) changes were observed after 5 days under both

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Fig. 7. Test material (Vitremer) at 90 days. Disruption of odontoblast and predentin layers toward gingival wall of cavity can be noted; a few vascular and cellular changes are present; occlusal two thirds of pulp horn and opposite dentin wall are normal. Remaining dentin thickness = 100 gin.

Fig. 8. Gingival region of Fig. 7 manifests lack of predentin and odontoblast layer and subjacent slight inflammatory changes. Adjacent to zone of reaction is unaffected pulpal tissue with intact odontoblastic layer; opposite dentin wall is also normal.

Vitremer and Kalzinol, suggesting a cavity depthtissue response relationship. At 5 days, severe reactions (grade 3) were observed in four of the teeth filled with silicate cement (positive controls). An acute inflammation was seen under the cavity in every depth, extending throughout a large area of the coronal pulp (Figs. 2 and 3). The odontoblastic layer was damaged and infiltrated with inflammatory cells. Nuclei were displaced into the cut tubules. A marked vascular reaction involving the entire pulp tissue was characteristic.

cement specimens demonstrated severe pulp reactions with widespread, marked inflammation (Fig. 6). No abscesses, necrosis, or reparative dentin (except in a small area of the silicate group) was seen.

Thirty-day observation At 30 days, 10 teeth restored with Vitremer showed pulp response; it was slight in 8 of these and moderate in the other 2 (Fig. 4). Similarly, pulp tissue under cavities filled with Kalzinol exhibited four slight (Fig. 5) reactions and one moderate reaction. There .was no observable histologic difference between the two groups within the same level of response. All silicate

Ninety-day observation Vitremer and Kalzinol elicited a slight pulp response. The odontoblastic layer was reduced to some extent beneath the dentin wall with a few inflammatory changes subjacent. At similar cavity depths in teeth applied with Vitremer, the odontoblast reduction was greater, with no evidence of ensuing inflammatory consequence (Figs. 7 and 8). Reparative dentin was seen under the cut tubules of two specimens filled with ZOE. In contrast, no newly formed dentin was seen under Vitremer. At 90 days two moderate and three severe pulp responses were observed in the silicate cement group. A diffuse peripheral or widespread infiltrate consisting predominantly of mononuclear leukocytes was present.

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Fig. 9. Positive control (silicate) at 90 days. Peripheral moderate chronic inflammation and reparative dentin formation (arrows) under cavity preparation can be observed. Remaining dentin thickness = 500 gm.

All teeth showed a relatively thick reparative dentin layer (Figs. 9 and 10). No necrosis was seen.

Bacterial findings Vitremer and Kalzinol specimens were free of bacteria at all time intervals. With the silicates, only occasional bacteria were found--at the cavity-restoration interface of two specimens (at 30 days) and within the cut tubules of one specimen (at 90 days).

DISCUSSION This study showed that Vitremer, a tri-cure R-MGI cement, had a different slight reaction pattern to the pulp in comparison with the negative control, Kalzinol. Both groups, except for the few cases attributed to iatrogenic factors, were free of the sort of true, materialbased inflammation that was induced beneath the silicate cement. Both Vitremer and Kalzinol demonstrated a variety of slight tissue and inflammatory changes. When the 90-day findings were compared, odontoblastic irritation and dentin repair were observed to be

Fig. 10. Higher magnification of area indicated by arrows in Fig. 9. Reparative dentin layer and diffuse chronic inflammatory cell infiltration under cavity preparation can be noted; opposite dentin wall appears normal.

more pronounced in the Vitremer specimens, suggesting that it lacks both biocompatibility and the ability to stimulate the pulp to form hard tissue repair, as reported in some previous in vitro studies. 2°,34 Cox et al. 21 observed new odontoblasts adjacent to reparative dentin at 21 and 97 days on nonexposed and exposed pulps at or near the tri-cured interface; the pulpal reaction we observed for Vitremer was slightly different. Two possible explanations for pulp irritation from a restorative material are acidity of the cement and bacterial leakage. Several authors have reported initial pulpal responses to the new dental restorative materials, generally followed by complete resolution. Different toxicity potentials have been elaborated. However, this initial pulp response is generally attributed to bacterial invasion. 35-37 In previous studies bacteria have been considered a probable cause of the pulpal inflammation beneath glass ionomer cements, 38-41 composites, 35,42 and silicate. 35,42-44 Furthermore, microleakage was reported to be more prevalent beneath animal experi-

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mental m o d e l s than on h u m a n teeth. 44 In our study no s t a i n a b l e b a c t e r i a w e r e d e t e c t e d u n d e r any c a v i t i e s c o v e r e d with V i t r e m e r or K a l z i n o l that s h o w e d s o m e degree of i n f l a m m a t o r y reaction. The silicate group also d e m o n s t r a t e d a l a c k o f correlation b e t w e e n bacterial p r e s e n c e and p u l p i n f l a m m a t i o n , w h i c h c o n t r a d i c t s p r e v i o u s reports 35,43,44 T h e s e v e r e i n f l a m m a t o r y

8. Pawlus MA, Swift Jr EJ, Vargas MA. Shear bond strengths of resin ionomer restorative materials [abstract[. J Dent Res 1994;73:328. Abstract 1812. 9. Stattmiller SP, Burgess JO. Shear bond strengths of two glass ionomers to contaminated dentin [abstract]. J Dent Res 1994;73:328. Abstract i814. 10. Swift EJ Jr, Pawhis MA, Vargas MA. Shear band strength of resin-modified glass-ionomer restorative materials. Operative Dentistry •995;20:138-43. 11. Cao DS, Hollis RA, Hicken CB, Christensen RP. Fluoride release from glass ionomers, glass ionomer/resins and composites [abstract]. J Dent Re s 1994;73:184. Abstract 657. 12. Dunne SM, Goolnik JS, Millar BJ, Seddon RP. Caries inhibition by a resin-modified and a conventional glass ionomer cement, in vitro. J Dent 1996;24:91-4. 13. Forss H. Release of fluoride and other elements from light-cured glass ionomers in neutral and acidic conditions. J Dent Res 1993;72:1257-62. 14. Mitra SB. In vitro fluoride release from a light-cured glassionomer liner/base. J Dent Res 1991;70:75-8. 15. Momoi Y, McCabe JR Fluoride release from light-activated glass ionomer restorative cements. Dental Materials 1993;9:151-4. 16. Hammesfahr PD. Developments in resionomer systems. In: Hunt PR, editor. Glass ionomers--the next generation: proceedings of the 2nd international symposium on glass ionomers. Philadelphia: International Symposia in Dentistry, PC; 1994. p. 47-56. 17. 3M Vitremer tri-cure glass ionomer system: technical product profile. St. Paul, Minn.: 3M Dental Products; 1992. 18. Mitra S. Curing reaction of glass ionomer materials. In: Hunt PR, editor. Glass ionomers--the next generation: proceedings of the 2nd international symposium on glass ionomers. Philadelphia: Intemational Symposia in Dentisu'y, PC; 1994. p. 13-22. 19. Sidhu SK, Watson TE Resin-modified glass ionomer materials: a status report for the American Journal of Dentistry. American Journal of Dentistry 1995;8:59-67. 20. Chen RCS. Cytotoxicity of light-cured glass ionomer cements on two cell culture systems [abstract]. J Dent Res 1994;73:133. Abstract 253. 21. Cox CF, Erickson RL, Glasspoole E. Histologic pulp response of a new tri-cure glass ionomer [abstract]. J Dent Res 1993;72:348. Abstract 1960. 22. Gaintantzopoulou MD, Willis GP, Kafrawy AH. Pulp reactions to light,cured glass-ionomer cements. American Journal of Dentistry 1994;7:39-42. 23. Bazzucchi M, Mori G, Goracci G. Pulpal response to direct capping of adhesive resins and glass ionomer cements [abstract]. J Dent Res 1995;74:555. Abstract 1240. 24. Lasfargues JJ, Goldberg M. Human pulpal response to a lightcured glass ionomer cement [abstract]. J Dent Res 1995;74:945. Abstract 277. 25. Brackett WW, Gunnin TD, Johnson WW, Conkin JE. Microleakage of light-cured glass-ionomer restorative materials. Quintessence International 1995;26:583-5. 26. Cooley RL, Barkmeier WW. Dentinal shear bond strength, microleakage, and contraction gap of visible light-polymerized liners/bases. Quintessence International 199l;22:467-74. 27. Quinn E An in-vitro investigation into the sealing ability of two fourth generation dentine bonding agents and two resin modified glass polyalkenoate restoratives. European Journal of Prosthodontics and Restorative Dentistry 1995;3:119-25. 28. Sidhu SK. Sealing effectiveness of light-cured glass ionomer cement liners. J Prosthet Dent 1992;68:891-4. 29. Tjan AHL, Dunn JR. Microleakage at gingival dentin margins of class V composite restorations lined with light-cured glass ionomer cement. J Am Dent Assoc 1990;121:706-10. 30. Stanford JW. Recommended standard practices for biological evaluation of dental materials. Int Dent J 1980;30:140-88. 31. Taylor RD. Modification of the Brown and Brenn gram stain for the differential staining of gram-positive and gram-negative bacteria in tissue sections. Am J Clin Pathol 1966;46:472-4.

r e s p o n s e u n d e r all c a v i t i e s that w e r e m o s t l y free o f b a c t e r i a l c o n t a m i n a t i o n , a l o n g w i t h a net h e a l i n g t e n d e n c y and d e n t i n repair b e t w e e n s u c c e s s i v e intervals, supports f i n d i n g s r e p o r t e d b y o t h e r i n v e s t i g a tors, 45,46 w h o considered that pulp response is m a i n l y material-related, R - M G I cements were reported to have g o o d sealing properties 21,24 but to be cytotoxic. 34,47 S o m e o f their components w e r e implicated in the adverse response o f the pulp4~; the direct relationship is hard to establish, i n a s m u c h as differences in species and methods m a k e comparison rather difficult. In general the b i o c o m p a t i bility o f R - M G I was reported to be lower in c o m p a r i s o n with conventional glass ionomers, 34,48,49 s o m e of w h i c h revealed cytotoxic effects in cell culture. 34,49 A n adverse effect on the cell growth was reported. 49,5° In contrast, o t h e r studies in h u m a n teeth 21-24,51 r e p o r t e d a g o o d biocompatibility with little evidence o f cytotoxicity. Our study demonstrated that a direct adverse effect on pulp healing is likely to occur under cavities filled with R - M G I . C h e m i c a l toxic factors, such as acidity and the 2 - h y d r o x y e t h y l methacrylate content o f the restorative material per se, m a y cause pulpal injury; this m a y be as i m p o r t a n t as bacterial l e a k a g e around the restoration margins. Our findings, w h i c h support those o f previous studies, 52-54 d i s p u t e that the m i c r o l e a k a g e o f t h e bacteria is a p r i m e cause o f pulpal injury. 35-37

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Reprint requests: Namik Soydan, DMD Department of Basic Sciences Faculty of Dentistry Istanbul University ~apa-Istanbul 34390 Turkey