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Compressive strength recovery by composite onlays in primary teeth
journal of dentistry 34 (2006) 478–484
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/jden
Compressive strength recovery by composite onlays in primary teeth Substrate treatment and luting agent effects Ana Fla´via Sanches Borges *, Gisele Maria Correr, Ma´rio Alexandre Coelho Sinhoreti, Simonides Consani, Lourenc¸o Correr Sobrinho, Regina Maria Puppin Rontani Dental Materials and Pediatric Dentistry Departments of the Piracicaba Dental School, State University of Campinas, Piracicaba, Av. Limeira, 901, Piracicaba, SP 13414-903, Brazil
article info
abstract
Article history:
Objectives: To evaluate 1% NaOCl treatment and two resin luting agent effects on com-
Received 15 July 2005
pressive strength recovery in composite onlays on primary teeth and to analyze the
Received in revised form
fractures type.
9 November 2005
Methods: Forty sound primary molars crowns were prepared in the standard machine and
Accepted 11 November 2005
randomly divided into four groups (n = 10): G1 (1% NaOCl/ 30 min + EnForce); G2 (without 1% NaOCl EnForce); G3 (1% NaOCl/ 30 min + Rely X); G4 (without 1% NaOCl + Rely X). The onlays were made using Z250 composite on plaster models. Ten sound teeth were used as control
Keywords:
group (CG). All groups were submitted to compression mechanic test in a universal test
Composite resins
machine INSTRON at 1 mm/min cross-head speed. After that, the data (kgf) were submitted
Onlays
to ANOVA test (a = 0.05). Finally, the fracture types were classified in a crescent scale (1–5)
Sodium hypochlorite
related with severity degree and submitted to Fisher’s Exact Test ( p < 0.05). Scanning
Luting agents
electronic microscope analysis was done in order to illustrate the fractures sites.
Compressive strength
Results: The values of compressive strength of experimental groups did not differ each others neither from control group ( p > 0.05). The results from fracture type showed that types 5 and 4 fractures (most severe) present the highest percentage to experimental groups. Conversely, the CG showed higher percentage of fracture types 2 and 3. Conclusions: This research found that the composite onlays recovered the compressive strength compared to sound teeth, regardless of the substrate treatment and cement agent used. Nevertheless, no group showed similar type of fractures to CG, which had more frequency of less severe fracture types. # 2005 Elsevier Ltd. All rights reserved.
1.
Introduction
The restorative composites have been improved markedly concerning the esthetic and mechanical properties;1 therefore, they have been indicated for application in stress bearings areas in posterior teeth. In Pediatric Dentistry, when atypical prepares are present because of caries extension, the
better option is the indirect composite restoration that provide a shorter clinical section and less contamination risk.2 The indirect composite restorations show many advantages compared to direct technique such as the replacement of natural convexities of teeth and control of occlusal and proximal contact points, better marginal fit especially in the gingival wall,3,4 minimal shrinkage polymerization only due to
* Corresponding author. Tel.: +55 19 3412 5286; fax: +55 19 3412 5218. E-mail address: [email protected] (R.M.P. Rontani). 0300-5712/$ – see front matter # 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2005.11.003
journal of dentistry 34 (2006) 478–484
cement agents1 and good polishing and finishing possibilities. Furthermore, in pediatric dentistry the additional cure of composite in indirect technique is not necessary because this could increase the wear resistance of some composites commercially available.5 The increased wear resistance of composite restorations is not required to primary teeth since restorative composite materials have to follow the physiologic wear of deciduous dentition.6,7 Primary teeth present structural and compositional differences from permanent teeth, as lesser thickness of dentin and degree of mineralization.8 Secondary dentin secretion and pulpar repair activity decreases with aging in primary teeth. This promotes a favorable condition to caries process reach the coronary pulp.9 Consequently, a great number of teeth that require onlay indirect restorations need previous endodontic treatment. There is a widely held belief that root-treated teeth are weakened and more susceptible to fracture than the vital ones specially because during the endodontic treatment there is a reduction of inner cuspal slopes that support cuspal angles from coronal tooth structure.10 Intracanal irrigants may also play a role in influencing the physical and mechanical properties of dentin. Sodium hypochlorite (NaOCl) is widely recommended as a root canal irrigant due to its antibacterial and organic tissue disintegration properties.11,12 Since dentin is composed of 22% by weight of organic material, NaOCl solution could potentially affect the penetration of resin into the dentin structure and/or the monomer polymerization13,14 from adhesive systems when composite restorations are used. There is no information in the literature about mechanical properties of indirect composite restorations placed on endodontically treated primary teeth. The purpose of this study was to evaluate the compressive strength of composite onlay restorations in primary teeth, submitted to 1% NaOCl treatment, using two resin luting agents and to verify the fracture types. The hypothesis tested was that the treatment with 1% NaOCl solution would decrease the compressive strength recovery of onlay restorations in primary teeth, regardless the luting agents used.
2.
Materials and methods
This study was submitted to the Research Ethics Committee of FOP/UNICAMP (approval no. 108/2003) according to the Resolution of the National Commission of Ethics in Research. Fifty freshly-extracted primary molars were cleaned, disinfected and frozen stored until experiment. The teeth were distributed into five groups (n = 10), according to the treatment: G G G G G
1—1% sodium hypochlorite + EnForce (Dentsply); 2—EnForce (Dentsply); 3—1% sodium hypochlorite + Rely X (3M/ESPE); 4—Rely X (3M/ESPE); C (control group)—sound teeth.
Each group was comprised by five mandibular first molars, two maxillary first molars, two maxillary second molars and one mandibular second molar.
479
Fig. 1 – Sequence of tooth cavity preparation using a high speed handpiece. (A) A first maxillary primary molar positioned into a machine in order standardize the cavity dimensions of each tooth. (B) Oclusal box was made beginning with grinding in a slot shape. (C) The proximal boxes were made in the machine followed by manual additional grinding of the biggest cusp.
2.1.
Specimen preparation
Each tooth was embedded in PVC cylinders (21 mm in diameter and 25 mm in height) using polystyrene resin (Piraglass Ltda., Piracicaba, SP, Brazil). The crowns were positioned 1 mm below the cement-enamel junction and totally out of the resin. The teeth were prepared in a machine in order to standardize some areas of cavities (Fig. 1) using diamond trunk-conic burs with a six degree inclination (KG Sorensen, Sa˜o Paulo, SP, Brazil) specially designed for this experiment, that were changed after every 5th preparation. The teeth were prepared with the following characteristics: Oclusal box: the isthmus width was approximately half the buccal-lingual distance without cavosurface grind and the depth ranged according to the anatomy of teeth. To first molars, the depth of pulpar wall was 2.0 mm below the tallest cuspid present. To second molars, the depth of pulpar wall was 2.5 mm below the tallest cuspid. Proximal box: the depth was determined according to the remaining distance of each tooth with polystyrene resin base due to the cervical-occlusal height variation. The inner angles of prepared teeth were rounded. All teeth had an additional grinding of the greatest cusp: distal-lingual cusp in the mandibular first molars, palatine
480
journal of dentistry 34 (2006) 478–484
Table 1 – Description of materials used in this study Compositiona
Manufacturer—batch no.
37% phosphoric acid Bis-GMA; Bis-EMA;UDMA; zirconia/silica filler (82 wt.%) Bis-GMA; TEGDMA dymethacrylate monomers; filler (67 wt.%) UDMA; PENTA; toluen and dymetil aminbenzoate, cetilamine fluoridate acetone; photoinitiators Bis-GMA; TEGDMA zirconia/silica filler (67.5 wt.%) dymethacrylate monomers HEMA; Bis-GMA; dimethacrylates; methacrylates; polyacrilic acid and poli-itaconic copolymers ethanol; water; photoinitiators
FGM, Joinville, SC, Brazil—101103 3M/ESPE, St. Paul, MN, USA—2KX Dentsply, Petro´polis, RJ, Brazil—55612b, 54925c Dentsply, Petro´polis, RJ, Brazil—55684
Materials Cond ac 37 Filtek Z250 (C4) EnForce (A2) Prime e Bond 2.1 Rely X (A3) Single Bond
3M/ESPE, St. Paul, MN, USA—CXCY 3M/ESPE, St. Paul, MN, USA—3HW
Abbreviations: Bis-GMA, bisphenol A glycidyl methacrylate; Bis-EMA, ethoxylated bisphenol A glycol dimethacrylate; UDMA, dimethacryloyloxyethyl 2,2,4(3,3,5)-timethylhexamethylene dicatbamate; PENTA, pentaacryloydipentaerythrtol phosphoric acid; TEGDMA, triethyleneglycol dimethacrylate; HEMA, 2-hydroxyethyl methacrylate. a Material compositions according to manufactures´ technical profile. b Matized paste. c Catalyzed paste.
cusp in the maxillary first molars, distal-lingual cusp in the mandibular second molars and mesial-palatine cusp in the maxillary second molars. The treatment with 1% NaOCl solution (PRODERMA LTDA, Piracicaba, SP, Brazil) in G1 and G3 groups was done in order to simulate irrigation during the pulp therapy. Each tooth was placed in a plastic recipient while the solution was flushed out through a disposable pipette during 30 min simultaneously with vibration using the Multi-Sonic-s ultrasson (Gnatus, Ribeira˜o Preto, SP, Brazil). The commercial trades of restorative materials, their composition, manufacturers and batch # are described in Table 1. Impressions from the preparations were taken using addition silicon putty and soft (Express—3M Dental Products, St. Paul, MN, USA). The casts were poured in hard plaster (Herostone—Vigodent, Rio de Janeiro, RJ, Brazil) and isolated with the Isolant Gel (KG So¨rensen, Sa˜o Paulo, SP, Brazil). Indirect restorations (onlays) were made using a hybrid composite (Filtek Z-250, C4 shade, 3M/ESPE), by incremental technique beginning with proximal box followed by oclusal box. Each increment was photocured for 40 s using the Elipar Trilight curing unit (ESPE Made in Germany; Norristown, AMERICA INC.). The bonding procedure of restorations on the teeth surfaces was made according to the manufacturer’s instructions, which is acid phosphoric etching (Cond ac 371—FGM, Joinville, SC, Brazil) followed by one bottle primer and adhesive application. The resin luting agents were inserted upon inner surface of onlays after they had been cleaned with phosphoric acid. The onlay was fixed by finger pressing, simulating a clinical situation, and excess cement was removed with a cut instrument. Then, each face (buccal, lingual, mesial, and distal) was photocured for 40 s. After that, the restoration/tooth set was stored in 100% relative humidity at 37 8C during 24 h followed by finishing with Soflex (3M, St. Paul, MN, USA) discs.
2.2.
Compression test
All groups were submitted to compression mechanic test in a universal testing machine (model 4411, INSTRON Corp.,
Canton, MA) at a crosshead speed of 1 mm/min. A stainless steal sphere was placed on the center of occlusal surface and loaded until fracture. The diameters of the spheres were determined according to teeth anatomy to ensure they touched only the restoration, so a 4 mm diameter sphere was chosen with exception to mandibular second molars that were tested using a 5 mm sphere. Data (kgf) were transformed into logarithm function and analyzed by ANOVA test (a = 0.05).
2.3.
Fracture types analysis
After the compression test, the set (tooth/fractured restoration) was observed in a stereomicroscope in order to classify the failure sites. The failure pattern classification described by Burke et al.15 was adaptated to onlay as follows in Fig. 2. The results of failure mode classification were submitted to Fisher’s Exact Test ( p < 0.05). Ninety percent of experimental group’s specimens were observed in scanning electronic microscopic (SEM) in order to illustrate the fracture sites. The work distances ranged between 30 to 15 mm, according to specimens height. Then, each specimen was classified according to the predominant remaining structure upon its surfaces as interface tooth/ restoration adhesive failure, resin luting agent cohesive failure, composite cohesive failure, dentin cohesive failure, mixed (adhesive and cohesive failure into dentin substrate or resin materials).
3.
Results
The means of compressive test values are displayed in Fig. 3. The ANOVA test showed there were no significant differences of the compressive force averages among the groups ( p > 0.05). Regarding fracture types, the most frequent type of fracture found was type 5 (G1—70%, G2—70%, G3—40%, and G4—50%). G2 showed a homogeneous distribution of the other kinds of fractures compared to G1. This kind of distribution was also observed in G3 and G4.
journal of dentistry 34 (2006) 478–484
481
Fig. 3 – Compressive strength means (kgf) and confidence intervals of the experimental and control groups.
2% composite cohesive failure. The most representative samples are shown in Figs. 5 and 6.
4.
Fig. 2 – Types of fracture patterns illustrated from the mandibular first molar designs. Type 1—minimal fracture of tooth and/or onlay, both in the interface area; type 2—fracture in less than half meson-distal distance of tooth and/or onlay; type 3—fracture in the middle of distal-distal distance of tooth and/or onlay; type 4—fracture in more than half distal-distal distance of tooth and/or onlay; type 5—severe fracture in tooth and/or onlay (fracture in reconstructed cusp).
CG presented no type 5 fracture. The highest frequency of fracture found in CG was type 2, followed by type 3 as showed in Fig. 4. The Fisher’s Exact Test showed that there was a significative association between substrate treatment with NaOCl and luting agent regarding the fracture types ( p = 0.0207). The SEM analysis reveled predominance of mixed failures for all experimental groups. The area of the examined specimens showed 90% resin luting agent cohesive failure with some areas showing cohesive failure in the adhesive system, 6% adhesive failure, 2% dentin cohesive failure, and
Discussion
The challenge of restorative procedures is to give back the physical and mechanical properties to restored teeth, especially fracture strength, because sound tooth structure is a complex system with components that protect each other and do not easily allow the dissipation of fracture.13,16,17 In this study, the experimental groups were not statistically different from sound teeth concerning fracture strength, showing that similar compressive forces are required to fracture the restored teeth and sound ones. Ausiello et al.18 and Wendt et al.19, affirmed that the efficacy of the bonding to dentin be based on hybridization, although their studies were carried out in permanent teeth. Ausiello et al.20 using the finite element analysis (FEA) described the importance of adhesive systems on stress distribution in direct composite restorations (MOD) because the stress difference is transferred to adhesive layer, generating a deformation. Despite technique differences, both adhesive systems used in this study contributed to compressive force in experimental groups become similar to that of sound teeth (CG). Regarding endodontic treatment it is prudent to select a suitable concentration of irrigant, which has minimal effects on the physical properties of the tooth whilst achieving the desired debridement effect.21 In this study, the 1% NaOCl
Fig. 4 – Fracture types distribution to each group.
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journal of dentistry 34 (2006) 478–484
Fig. 5 – (a) Specimen surface showing cohesive failure in the resin luting agent. (b) Cohesive failure in the adhesive system present in some areas of any specimens with resin luting agent cohesive. Note remaining material left inside the dentin tubules. (c) Specimen surface with composite cohesive failure.
solution was used during 30 min under vibration in order to simulate a root instrumentation section as usually used. This study showed that the groups treated with 1% NaOCl were not different, concerning the forces required to fracture the set, from the ones that were not treated even related to the control group, not validating the hypothesis tested. Similarly, Ari et al.22 did not found significant statistical difference on shear bond strength of the resin luting agents C&B Metabond, Panavia F, and Rely X bonded to root dentin after applied or not 5% NaOCl. Sim et al.21 evaluated changes in strain of ‘‘whole’’ teeth submitting them to 0.5% NaOCl and 5.25% NaOCl irrigation cycles. The 5.25% NaOCl caused more changes in the strain of teeth. In our study, the methodology was developed in a macro environment, which did not allow identifying the alterations that really occurs in primary dentin treated with 1% NaOCL and its influence in force required to fracture the tooth/ restoration set. Nevertheless, the irrigation during 30 min is
very near to clinical situation, opposing Sim et al.21 that tested the ‘‘whole’’ teeth under the worst case scenario and unlikely to match that of many clinicians. The sodium hypochlorite breaks down to sodium chloride and oxygen, which provides oxidation of some components in the dentin matrix14 and consequently decreases the elastic modulus and flexural strength of dentin.21 Allied to that it could affect the resin penetration into the dentin structure and/or the polymerization of monomer in the demineralized dentin and also could influence the restorations quality.21 It would suggest that less force would be required for the cohesive bonds within dentin to fail. More studies should be done concerning morphological and biochemical alterations in dentin substrate submitted to 1% NaOCl as well other bond strength methodologies, which could give additional information about tooth/ restoration interface in primary teeth endodontically treated.
journal of dentistry 34 (2006) 478–484
Fig. 6 – (a) Adhesive failure. Note the plane surface with opened tubules without remaining materials. (b) Dentin cohesive failure. Note the stratificated dentin layers opposing adhesive failure (white arrows).
The hybrid restorative composite (Filtek Z250) could be responsible for results close to those of sound teeth as well, because of its great volume and intrinsic properties; consequently, a greater part of the load could have been absorbed by restorative composite. The Filtek Z250 composite consists of Bis-GMA, Bis-EMA, UDMA resin polymer, with rounded zircon/ silicon micro-particle fillers (0.6 mm in mean particle size) in a mono-module distribution. A correlation exists between filler content and mechanical properties, particularly for modulus of elasticity. The higher the filler content,23 the higher the elasticity modulus and the resistance to deformation.24 Other points related with modulus of elasticity are the monomer type, polymer network formation, as well as resin/filler interaction, that affect the composite elastic-plastic properties.25 The composite pointed out the significantly highest strength fracture values26 besides high flexural modulus,27 which is another property also required for onlays restorations to maintain its shape under load.
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The results of compressive force required to fracture the specimens observed in this study are supported by Rees and Jacobsen,28 who showed that dentin is an elastic and isotropic material while enamel is an elastic and anisotropic material from a mechanical point of view, since the values of compressive force required to fracture the specimens in the experimental group were statistically similar to those from sound teeth showing that restorative resin materials perform as an isotropic structure. On the other hand, when type of fracture was examined, all the experimental groups were statistically different from the control one concerning the fractures severity. These groups (experimental) showed a more unpredictable type distribution as also showed by Ausiello et al.20 Under the same oclusal loading condition, the sound tooth exhibits a mechanical behavior quite different from that of restored teeth because the rigid enamel does not deform significantly, but transfer the deformation to lower, more resilient dentin, and thus can rigidly ‘‘move’’ over it. Conversely, in the restored teeth, as observed in our study, the cavity restoration could interrupt the tooth bi-elastic structure and cause stress where the applied force component is maximal, resulting in other type of fractures related to composition and consequently mechanic properties of both composite and resin luting cements as stated by Ausiello et al. 20 Considering the fracture severity, types 4 and 5 can be considered the most severe because they involve the reconstructed cuspid and the biologic space. All experimental groups showed the highest percentage of severe fracture. These results are similar to those found by Burke et al.29 who observed the highest frequency of severe fractures when composite inlays were bonded with the composite Brilliant Dentin (Co`ltene). Despite having lower filler content than Filtek Z250 composite, both luting agents used in this study present bifunctional monomers TEGDMA/Bis-GMA, which result in high number of double bonds per unit of weight that create high degree of crosslinking, producing a very rigid polymeric network.30,31 In Filtek Z250 composite, the majority of TEGDMA has been replaced with a blend of UDMA and BisEMA, which show higher molecular weight. Therefore, they have fewer double bonds per unit of weight leading to lesser crosslinking density than that of TEGDMA/Bis-GMA resin matrix.32 Then, resultant forces of compressive load led to more drastic fracture types affecting great part of ‘‘onlay’’ since resin luting agents probably behaved as materials with greater modulus of elasticity than Filtek Z250 composite, that is, more ‘‘rigid’’ and less resilient materials. The SEM analysis illustrated in Fig. 4 showed high quantity of remaining resin luting agents upon specimen surfaces, supporting the explanation concerning fracture types found. To avoid severe types of fractures, the resin luting systems should have more resilient behavior to minimize fracture type due to restored tooth condition when used to lute Filtek Z250 composite indirect restorations, and then approach sound teeth since in the deep dentine, the modulus of elasticity is lower than in dentine from other regions.33 Although the bite force in primary teeth can not provide sufficient compressive load to cause fractures as seen in this study, since the compressive force averages found were much
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journal of dentistry 34 (2006) 478–484
greater than means of maximum bite force that did not exceed 30 kgf in posterior teeth in children aged 3–5 years34 and 7–9 years,35 the failures types in restored teeth are always unfavorable,20 regardless of the substrate treatment and luting agent used.
5.
Conclusions
Within the limitations of this study, it can be concluded that the 1% NaOCl solution did not decrease the indirect composite compressive strength recovery, regardless the luting agents used.
references
1. Peutzfeldt A. Indirect resin and ceramic systems. Operative Dentistry 2001;(Suppl. 6):153–76. 2. Rabeˆlo RTS, Caldo-Teixeira AS, Puppin-Rontani RM. An alternative aesthetic restoration for extensive coronal destruction in primary molars: indirect restorative technique with composite resin. The Journal Clinical of Pediatric Dentistry 2005;29:277–84. 3. Gladys S, Van Meerbeek B, Inokoshi S, Willems G, Braem M, Lambrechts P, et al. Clinical and semiquantitative marginal analysis of four tooth-coloured inlay systems at 3 years. Journal of Dentistry 1995;23:329–38. 4. van Dijken JW, Horstedt P. Marginal breakdown of 5-year-old direct composite inlays. Journal of Dentistry 1996;24:389–94. 5. Peutzfeldt A, Asmussen E. The effect of postcuring on quantity of remaining double bonds, mechanical properties, and in vitro wear of two resin composites. Journal of Dentistry 2000;28:447–52. 6. Vann Jr WF, Barkmeier WW, Mahler DB. Assessing composite resin wear in primary molars: four-year findings. Journal of Dental Research 1988;67:876–9. 7. Cunha MRB. Avaliac¸a˜o in vitro do desgaste por abrasa˜o de materiais restauradores e do esmalte em dentes decı´duos. [tese] Piracicaba: UNICAMP/FOP; 2003. 8. Arau´jo FB, Moraes FF, Fossati ACM. A estrutura da dentina do dente decı´duo e sua importaˆncia clı´nica. Revista Brasileira de Odontologia 1995;52:37–43. 9. Garcı´a-Godoy F, Donly KJ. Dentin/enamel adhesives in pediatric dentistry. Pediatric Dentistry 2002;24:462–4. 10. Camp JH. Tratamento endodoˆntico em odontopediatria. In: Cohen S, Burns RC, editors. Caminhos da polpa. 7th ed. Rio de Janeiro: Editora Guanabara Koogan S.A; 2000, p. 680. 11. Czonstkowsky M, Wilson EG, Holstein FA. The smear layer in endodontics. Dental Clinic of North American 1990;34:13–25. 12. Tasman F, Cehreli ZC, Ogan C, Etikan I. Surface tension of root canal irrigants. Journal of Endodontics 2000;26:586–7. 13. Marshall Jr, Grayson W. Dentin: microstructure and characterization. Quintessence International 1993;24:439–41. 14. Nikaido T, Takano Y, Sasafuchi Y, Burrow MF, Tagami J. Bond strengths to endodontically-treated teeth. American Journal of Dentistry 1999;12:177–80. 15. Burke FJ, Wilson NH, Watts DC. The effect of cavity wall taper on fracture resistance of teeth restored with resin composite inlays. Operative Dentistry 1993;18:230–6.
16. Urabe I, Nakajima S, Sano H, Tagami J. Physical properties of the dentin-enamel junction region. American Journal of Dentistry 2000;13:129–35. 17. Shimada Y, Tagami J. Effects of regional enamel and prism orientation on resin bonding. Operative Dentistry 2003;28: 20–7. 18. Ausiello P, De Gee AJ, Rengo S, Davidson CL. Fracture resistance of endodontically-treated premolars adhesively restored. American Journal of Dentistry 1997;10:237–41. 19. Wendt Jr SL, Harris BM, Hunt TE. Resistance to cusp fracture in endodontically treated teeth. Dental Materials 1987;3: 232–5. 20. Ausiello P, Apicella A, Davidson CL. Effect of adhesive layer properties on stress distribution in composite restorations— a 3D finite element analysis. Dental Materials 2002;18:295– 303. 21. Sim TP, Knowles JC, Ng YL, Shelton J, Gulabivala K. Effect of sodium hypochlorite on mechanical properties of dentine and tooth surface strain. International Endodontic Journal 2004;34:120–32. 22. Ari H, Yasar E, Belli S. Effects of NaOCl on bond strengths of resin cements to root canal dentin. Journal of Endodontics 2003;29:248–51. 23. Kim KH, Ong JL, Okuno O. The effect of filler loading and morphology on the mechanical properties of contemporary composites. Journal of Prosthetic Dentistry 2002;87:642–9. 24. Attar N, Tam LE, McComb D. Mechanical and physical properties of contemporary dental luting agents. Journal of Prosthetic Dentistry 2003;89:127–34. 25. Tantbirojn D, Versluis A, Cheng Y, Douglas WH. Fracture toughness and microhardness of a composite: do they correlate? Journal of Dentistry 2003;31:89–95. 26. Lohbauer U, von der Horst T, Frankenberger R, Kramer N, Petschelt A. Flexural fatigue behavior of resin composite dental restoratives. Dental Materials 2003;19:435–40. 27. Yap AU, Tan AC, Quan C. Non-destructive characterization of resin-based filling materials using Electronic Speckle Pattern Interferometry. Dental Materials 2004;20:377–82. 28. Rees JS, Jacobsen PH. Modelling the effects of enamel anisotropy with the finite element method. Journal of Oral Rehabilitation 1995;22:451–4. 29. Burke FJ, Wilson NH, Watts DC. Fracture resistance of teeth restored with indirect composite resins: the effect of alternative luting procedures. Quintessence International 1994;25:269–75. 30. Asmussen E. Factors affecting the quantity of remaining double bonds in restorative resin polymers. Scandinavian Journal of Dental Research 1982;90:490–6. 31. Van Noort R. Resin composites and polyacid-modified resin composites. In: Van Noort R, editor. Introduction to dental materials. St. Louis: Mosby; 2003. p. 98. 32. TECHNICAL Product Profile Filtek Z250. 3M Dental Products. p. 7–10. 33. Angker L, Swain MV, Kilpatrick N. Micro-mechanical characterization of the properties of primary tooth dentine. Journal of Dentistry 2003;31:261–7. 34. Rentes AM, Gaviao MB, Amaral JR. Bite force determination in children with primary dentition. Journal of Oral Rehabilitation 2002;29:1174–80. 35. Maki K, Nishioka T, Morimoto A, Naito M, Kimura M. A study on the measurement of occlusal force and masticatory efficiency in school age Japanese children. International Journal of Paediatric Dentistry 2001;11:281.
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/jden
Compressive strength recovery by composite onlays in primary teeth Substrate treatment and luting agent effects Ana Fla´via Sanches Borges *, Gisele Maria Correr, Ma´rio Alexandre Coelho Sinhoreti, Simonides Consani, Lourenc¸o Correr Sobrinho, Regina Maria Puppin Rontani Dental Materials and Pediatric Dentistry Departments of the Piracicaba Dental School, State University of Campinas, Piracicaba, Av. Limeira, 901, Piracicaba, SP 13414-903, Brazil
article info
abstract
Article history:
Objectives: To evaluate 1% NaOCl treatment and two resin luting agent effects on com-
Received 15 July 2005
pressive strength recovery in composite onlays on primary teeth and to analyze the
Received in revised form
fractures type.
9 November 2005
Methods: Forty sound primary molars crowns were prepared in the standard machine and
Accepted 11 November 2005
randomly divided into four groups (n = 10): G1 (1% NaOCl/ 30 min + EnForce); G2 (without 1% NaOCl EnForce); G3 (1% NaOCl/ 30 min + Rely X); G4 (without 1% NaOCl + Rely X). The onlays were made using Z250 composite on plaster models. Ten sound teeth were used as control
Keywords:
group (CG). All groups were submitted to compression mechanic test in a universal test
Composite resins
machine INSTRON at 1 mm/min cross-head speed. After that, the data (kgf) were submitted
Onlays
to ANOVA test (a = 0.05). Finally, the fracture types were classified in a crescent scale (1–5)
Sodium hypochlorite
related with severity degree and submitted to Fisher’s Exact Test ( p < 0.05). Scanning
Luting agents
electronic microscope analysis was done in order to illustrate the fractures sites.
Compressive strength
Results: The values of compressive strength of experimental groups did not differ each others neither from control group ( p > 0.05). The results from fracture type showed that types 5 and 4 fractures (most severe) present the highest percentage to experimental groups. Conversely, the CG showed higher percentage of fracture types 2 and 3. Conclusions: This research found that the composite onlays recovered the compressive strength compared to sound teeth, regardless of the substrate treatment and cement agent used. Nevertheless, no group showed similar type of fractures to CG, which had more frequency of less severe fracture types. # 2005 Elsevier Ltd. All rights reserved.
1.
Introduction
The restorative composites have been improved markedly concerning the esthetic and mechanical properties;1 therefore, they have been indicated for application in stress bearings areas in posterior teeth. In Pediatric Dentistry, when atypical prepares are present because of caries extension, the
better option is the indirect composite restoration that provide a shorter clinical section and less contamination risk.2 The indirect composite restorations show many advantages compared to direct technique such as the replacement of natural convexities of teeth and control of occlusal and proximal contact points, better marginal fit especially in the gingival wall,3,4 minimal shrinkage polymerization only due to
* Corresponding author. Tel.: +55 19 3412 5286; fax: +55 19 3412 5218. E-mail address: [email protected] (R.M.P. Rontani). 0300-5712/$ – see front matter # 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2005.11.003
journal of dentistry 34 (2006) 478–484
cement agents1 and good polishing and finishing possibilities. Furthermore, in pediatric dentistry the additional cure of composite in indirect technique is not necessary because this could increase the wear resistance of some composites commercially available.5 The increased wear resistance of composite restorations is not required to primary teeth since restorative composite materials have to follow the physiologic wear of deciduous dentition.6,7 Primary teeth present structural and compositional differences from permanent teeth, as lesser thickness of dentin and degree of mineralization.8 Secondary dentin secretion and pulpar repair activity decreases with aging in primary teeth. This promotes a favorable condition to caries process reach the coronary pulp.9 Consequently, a great number of teeth that require onlay indirect restorations need previous endodontic treatment. There is a widely held belief that root-treated teeth are weakened and more susceptible to fracture than the vital ones specially because during the endodontic treatment there is a reduction of inner cuspal slopes that support cuspal angles from coronal tooth structure.10 Intracanal irrigants may also play a role in influencing the physical and mechanical properties of dentin. Sodium hypochlorite (NaOCl) is widely recommended as a root canal irrigant due to its antibacterial and organic tissue disintegration properties.11,12 Since dentin is composed of 22% by weight of organic material, NaOCl solution could potentially affect the penetration of resin into the dentin structure and/or the monomer polymerization13,14 from adhesive systems when composite restorations are used. There is no information in the literature about mechanical properties of indirect composite restorations placed on endodontically treated primary teeth. The purpose of this study was to evaluate the compressive strength of composite onlay restorations in primary teeth, submitted to 1% NaOCl treatment, using two resin luting agents and to verify the fracture types. The hypothesis tested was that the treatment with 1% NaOCl solution would decrease the compressive strength recovery of onlay restorations in primary teeth, regardless the luting agents used.
2.
Materials and methods
This study was submitted to the Research Ethics Committee of FOP/UNICAMP (approval no. 108/2003) according to the Resolution of the National Commission of Ethics in Research. Fifty freshly-extracted primary molars were cleaned, disinfected and frozen stored until experiment. The teeth were distributed into five groups (n = 10), according to the treatment: G G G G G
1—1% sodium hypochlorite + EnForce (Dentsply); 2—EnForce (Dentsply); 3—1% sodium hypochlorite + Rely X (3M/ESPE); 4—Rely X (3M/ESPE); C (control group)—sound teeth.
Each group was comprised by five mandibular first molars, two maxillary first molars, two maxillary second molars and one mandibular second molar.
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Fig. 1 – Sequence of tooth cavity preparation using a high speed handpiece. (A) A first maxillary primary molar positioned into a machine in order standardize the cavity dimensions of each tooth. (B) Oclusal box was made beginning with grinding in a slot shape. (C) The proximal boxes were made in the machine followed by manual additional grinding of the biggest cusp.
2.1.
Specimen preparation
Each tooth was embedded in PVC cylinders (21 mm in diameter and 25 mm in height) using polystyrene resin (Piraglass Ltda., Piracicaba, SP, Brazil). The crowns were positioned 1 mm below the cement-enamel junction and totally out of the resin. The teeth were prepared in a machine in order to standardize some areas of cavities (Fig. 1) using diamond trunk-conic burs with a six degree inclination (KG Sorensen, Sa˜o Paulo, SP, Brazil) specially designed for this experiment, that were changed after every 5th preparation. The teeth were prepared with the following characteristics: Oclusal box: the isthmus width was approximately half the buccal-lingual distance without cavosurface grind and the depth ranged according to the anatomy of teeth. To first molars, the depth of pulpar wall was 2.0 mm below the tallest cuspid present. To second molars, the depth of pulpar wall was 2.5 mm below the tallest cuspid. Proximal box: the depth was determined according to the remaining distance of each tooth with polystyrene resin base due to the cervical-occlusal height variation. The inner angles of prepared teeth were rounded. All teeth had an additional grinding of the greatest cusp: distal-lingual cusp in the mandibular first molars, palatine
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Table 1 – Description of materials used in this study Compositiona
Manufacturer—batch no.
37% phosphoric acid Bis-GMA; Bis-EMA;UDMA; zirconia/silica filler (82 wt.%) Bis-GMA; TEGDMA dymethacrylate monomers; filler (67 wt.%) UDMA; PENTA; toluen and dymetil aminbenzoate, cetilamine fluoridate acetone; photoinitiators Bis-GMA; TEGDMA zirconia/silica filler (67.5 wt.%) dymethacrylate monomers HEMA; Bis-GMA; dimethacrylates; methacrylates; polyacrilic acid and poli-itaconic copolymers ethanol; water; photoinitiators
FGM, Joinville, SC, Brazil—101103 3M/ESPE, St. Paul, MN, USA—2KX Dentsply, Petro´polis, RJ, Brazil—55612b, 54925c Dentsply, Petro´polis, RJ, Brazil—55684
Materials Cond ac 37 Filtek Z250 (C4) EnForce (A2) Prime e Bond 2.1 Rely X (A3) Single Bond
3M/ESPE, St. Paul, MN, USA—CXCY 3M/ESPE, St. Paul, MN, USA—3HW
Abbreviations: Bis-GMA, bisphenol A glycidyl methacrylate; Bis-EMA, ethoxylated bisphenol A glycol dimethacrylate; UDMA, dimethacryloyloxyethyl 2,2,4(3,3,5)-timethylhexamethylene dicatbamate; PENTA, pentaacryloydipentaerythrtol phosphoric acid; TEGDMA, triethyleneglycol dimethacrylate; HEMA, 2-hydroxyethyl methacrylate. a Material compositions according to manufactures´ technical profile. b Matized paste. c Catalyzed paste.
cusp in the maxillary first molars, distal-lingual cusp in the mandibular second molars and mesial-palatine cusp in the maxillary second molars. The treatment with 1% NaOCl solution (PRODERMA LTDA, Piracicaba, SP, Brazil) in G1 and G3 groups was done in order to simulate irrigation during the pulp therapy. Each tooth was placed in a plastic recipient while the solution was flushed out through a disposable pipette during 30 min simultaneously with vibration using the Multi-Sonic-s ultrasson (Gnatus, Ribeira˜o Preto, SP, Brazil). The commercial trades of restorative materials, their composition, manufacturers and batch # are described in Table 1. Impressions from the preparations were taken using addition silicon putty and soft (Express—3M Dental Products, St. Paul, MN, USA). The casts were poured in hard plaster (Herostone—Vigodent, Rio de Janeiro, RJ, Brazil) and isolated with the Isolant Gel (KG So¨rensen, Sa˜o Paulo, SP, Brazil). Indirect restorations (onlays) were made using a hybrid composite (Filtek Z-250, C4 shade, 3M/ESPE), by incremental technique beginning with proximal box followed by oclusal box. Each increment was photocured for 40 s using the Elipar Trilight curing unit (ESPE Made in Germany; Norristown, AMERICA INC.). The bonding procedure of restorations on the teeth surfaces was made according to the manufacturer’s instructions, which is acid phosphoric etching (Cond ac 371—FGM, Joinville, SC, Brazil) followed by one bottle primer and adhesive application. The resin luting agents were inserted upon inner surface of onlays after they had been cleaned with phosphoric acid. The onlay was fixed by finger pressing, simulating a clinical situation, and excess cement was removed with a cut instrument. Then, each face (buccal, lingual, mesial, and distal) was photocured for 40 s. After that, the restoration/tooth set was stored in 100% relative humidity at 37 8C during 24 h followed by finishing with Soflex (3M, St. Paul, MN, USA) discs.
2.2.
Compression test
All groups were submitted to compression mechanic test in a universal testing machine (model 4411, INSTRON Corp.,
Canton, MA) at a crosshead speed of 1 mm/min. A stainless steal sphere was placed on the center of occlusal surface and loaded until fracture. The diameters of the spheres were determined according to teeth anatomy to ensure they touched only the restoration, so a 4 mm diameter sphere was chosen with exception to mandibular second molars that were tested using a 5 mm sphere. Data (kgf) were transformed into logarithm function and analyzed by ANOVA test (a = 0.05).
2.3.
Fracture types analysis
After the compression test, the set (tooth/fractured restoration) was observed in a stereomicroscope in order to classify the failure sites. The failure pattern classification described by Burke et al.15 was adaptated to onlay as follows in Fig. 2. The results of failure mode classification were submitted to Fisher’s Exact Test ( p < 0.05). Ninety percent of experimental group’s specimens were observed in scanning electronic microscopic (SEM) in order to illustrate the fracture sites. The work distances ranged between 30 to 15 mm, according to specimens height. Then, each specimen was classified according to the predominant remaining structure upon its surfaces as interface tooth/ restoration adhesive failure, resin luting agent cohesive failure, composite cohesive failure, dentin cohesive failure, mixed (adhesive and cohesive failure into dentin substrate or resin materials).
3.
Results
The means of compressive test values are displayed in Fig. 3. The ANOVA test showed there were no significant differences of the compressive force averages among the groups ( p > 0.05). Regarding fracture types, the most frequent type of fracture found was type 5 (G1—70%, G2—70%, G3—40%, and G4—50%). G2 showed a homogeneous distribution of the other kinds of fractures compared to G1. This kind of distribution was also observed in G3 and G4.
journal of dentistry 34 (2006) 478–484
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Fig. 3 – Compressive strength means (kgf) and confidence intervals of the experimental and control groups.
2% composite cohesive failure. The most representative samples are shown in Figs. 5 and 6.
4.
Fig. 2 – Types of fracture patterns illustrated from the mandibular first molar designs. Type 1—minimal fracture of tooth and/or onlay, both in the interface area; type 2—fracture in less than half meson-distal distance of tooth and/or onlay; type 3—fracture in the middle of distal-distal distance of tooth and/or onlay; type 4—fracture in more than half distal-distal distance of tooth and/or onlay; type 5—severe fracture in tooth and/or onlay (fracture in reconstructed cusp).
CG presented no type 5 fracture. The highest frequency of fracture found in CG was type 2, followed by type 3 as showed in Fig. 4. The Fisher’s Exact Test showed that there was a significative association between substrate treatment with NaOCl and luting agent regarding the fracture types ( p = 0.0207). The SEM analysis reveled predominance of mixed failures for all experimental groups. The area of the examined specimens showed 90% resin luting agent cohesive failure with some areas showing cohesive failure in the adhesive system, 6% adhesive failure, 2% dentin cohesive failure, and
Discussion
The challenge of restorative procedures is to give back the physical and mechanical properties to restored teeth, especially fracture strength, because sound tooth structure is a complex system with components that protect each other and do not easily allow the dissipation of fracture.13,16,17 In this study, the experimental groups were not statistically different from sound teeth concerning fracture strength, showing that similar compressive forces are required to fracture the restored teeth and sound ones. Ausiello et al.18 and Wendt et al.19, affirmed that the efficacy of the bonding to dentin be based on hybridization, although their studies were carried out in permanent teeth. Ausiello et al.20 using the finite element analysis (FEA) described the importance of adhesive systems on stress distribution in direct composite restorations (MOD) because the stress difference is transferred to adhesive layer, generating a deformation. Despite technique differences, both adhesive systems used in this study contributed to compressive force in experimental groups become similar to that of sound teeth (CG). Regarding endodontic treatment it is prudent to select a suitable concentration of irrigant, which has minimal effects on the physical properties of the tooth whilst achieving the desired debridement effect.21 In this study, the 1% NaOCl
Fig. 4 – Fracture types distribution to each group.
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Fig. 5 – (a) Specimen surface showing cohesive failure in the resin luting agent. (b) Cohesive failure in the adhesive system present in some areas of any specimens with resin luting agent cohesive. Note remaining material left inside the dentin tubules. (c) Specimen surface with composite cohesive failure.
solution was used during 30 min under vibration in order to simulate a root instrumentation section as usually used. This study showed that the groups treated with 1% NaOCl were not different, concerning the forces required to fracture the set, from the ones that were not treated even related to the control group, not validating the hypothesis tested. Similarly, Ari et al.22 did not found significant statistical difference on shear bond strength of the resin luting agents C&B Metabond, Panavia F, and Rely X bonded to root dentin after applied or not 5% NaOCl. Sim et al.21 evaluated changes in strain of ‘‘whole’’ teeth submitting them to 0.5% NaOCl and 5.25% NaOCl irrigation cycles. The 5.25% NaOCl caused more changes in the strain of teeth. In our study, the methodology was developed in a macro environment, which did not allow identifying the alterations that really occurs in primary dentin treated with 1% NaOCL and its influence in force required to fracture the tooth/ restoration set. Nevertheless, the irrigation during 30 min is
very near to clinical situation, opposing Sim et al.21 that tested the ‘‘whole’’ teeth under the worst case scenario and unlikely to match that of many clinicians. The sodium hypochlorite breaks down to sodium chloride and oxygen, which provides oxidation of some components in the dentin matrix14 and consequently decreases the elastic modulus and flexural strength of dentin.21 Allied to that it could affect the resin penetration into the dentin structure and/or the polymerization of monomer in the demineralized dentin and also could influence the restorations quality.21 It would suggest that less force would be required for the cohesive bonds within dentin to fail. More studies should be done concerning morphological and biochemical alterations in dentin substrate submitted to 1% NaOCl as well other bond strength methodologies, which could give additional information about tooth/ restoration interface in primary teeth endodontically treated.
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Fig. 6 – (a) Adhesive failure. Note the plane surface with opened tubules without remaining materials. (b) Dentin cohesive failure. Note the stratificated dentin layers opposing adhesive failure (white arrows).
The hybrid restorative composite (Filtek Z250) could be responsible for results close to those of sound teeth as well, because of its great volume and intrinsic properties; consequently, a greater part of the load could have been absorbed by restorative composite. The Filtek Z250 composite consists of Bis-GMA, Bis-EMA, UDMA resin polymer, with rounded zircon/ silicon micro-particle fillers (0.6 mm in mean particle size) in a mono-module distribution. A correlation exists between filler content and mechanical properties, particularly for modulus of elasticity. The higher the filler content,23 the higher the elasticity modulus and the resistance to deformation.24 Other points related with modulus of elasticity are the monomer type, polymer network formation, as well as resin/filler interaction, that affect the composite elastic-plastic properties.25 The composite pointed out the significantly highest strength fracture values26 besides high flexural modulus,27 which is another property also required for onlays restorations to maintain its shape under load.
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The results of compressive force required to fracture the specimens observed in this study are supported by Rees and Jacobsen,28 who showed that dentin is an elastic and isotropic material while enamel is an elastic and anisotropic material from a mechanical point of view, since the values of compressive force required to fracture the specimens in the experimental group were statistically similar to those from sound teeth showing that restorative resin materials perform as an isotropic structure. On the other hand, when type of fracture was examined, all the experimental groups were statistically different from the control one concerning the fractures severity. These groups (experimental) showed a more unpredictable type distribution as also showed by Ausiello et al.20 Under the same oclusal loading condition, the sound tooth exhibits a mechanical behavior quite different from that of restored teeth because the rigid enamel does not deform significantly, but transfer the deformation to lower, more resilient dentin, and thus can rigidly ‘‘move’’ over it. Conversely, in the restored teeth, as observed in our study, the cavity restoration could interrupt the tooth bi-elastic structure and cause stress where the applied force component is maximal, resulting in other type of fractures related to composition and consequently mechanic properties of both composite and resin luting cements as stated by Ausiello et al. 20 Considering the fracture severity, types 4 and 5 can be considered the most severe because they involve the reconstructed cuspid and the biologic space. All experimental groups showed the highest percentage of severe fracture. These results are similar to those found by Burke et al.29 who observed the highest frequency of severe fractures when composite inlays were bonded with the composite Brilliant Dentin (Co`ltene). Despite having lower filler content than Filtek Z250 composite, both luting agents used in this study present bifunctional monomers TEGDMA/Bis-GMA, which result in high number of double bonds per unit of weight that create high degree of crosslinking, producing a very rigid polymeric network.30,31 In Filtek Z250 composite, the majority of TEGDMA has been replaced with a blend of UDMA and BisEMA, which show higher molecular weight. Therefore, they have fewer double bonds per unit of weight leading to lesser crosslinking density than that of TEGDMA/Bis-GMA resin matrix.32 Then, resultant forces of compressive load led to more drastic fracture types affecting great part of ‘‘onlay’’ since resin luting agents probably behaved as materials with greater modulus of elasticity than Filtek Z250 composite, that is, more ‘‘rigid’’ and less resilient materials. The SEM analysis illustrated in Fig. 4 showed high quantity of remaining resin luting agents upon specimen surfaces, supporting the explanation concerning fracture types found. To avoid severe types of fractures, the resin luting systems should have more resilient behavior to minimize fracture type due to restored tooth condition when used to lute Filtek Z250 composite indirect restorations, and then approach sound teeth since in the deep dentine, the modulus of elasticity is lower than in dentine from other regions.33 Although the bite force in primary teeth can not provide sufficient compressive load to cause fractures as seen in this study, since the compressive force averages found were much
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greater than means of maximum bite force that did not exceed 30 kgf in posterior teeth in children aged 3–5 years34 and 7–9 years,35 the failures types in restored teeth are always unfavorable,20 regardless of the substrate treatment and luting agent used.
5.
Conclusions
Within the limitations of this study, it can be concluded that the 1% NaOCl solution did not decrease the indirect composite compressive strength recovery, regardless the luting agents used.
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