J Indian Soc Pedod Prev Dent - June 2007 82

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Comparative evaluation of shear bond strength of conventional composite resin and nanocomposite resin to sandblasted primary anterior stainless steel crownKHATRI A.a, NANDLAL B.b, SRILATHAc

Abstract

To evaluate and compare the shear bond strength of conventional composite resin and nanocomposite resin to sandblasted primary anterior stainless steel crown. The study samples consisted of 30 primary anterior stainless steel crowns (UnitekTM, size R4), embedded in resin blocks with crown, in test groups of 15 samples each. Mounting of the crown was done using resin block with one crown each. Sandblasting was done and the bonding agent Prime and Bond NT (Dentsply) was applied on the labial surface of the primary anterior sandblasted crown. The composite resin and nanocomposite resin were placed into the well of Tefl on jig and bonded to Stainless Steel Crowns. The cured samples were placed in distilled water and stored in incubator at 37°C for 48 hours. Shear bond strength was measured using universal testing machine (Hounsefi eld U.K. Model, with a capac-ity of 50 KN). Independent sample ‘t’ test revealed a nonsignifi cant (P < 0.385) difference between mean shear bond strength values of conventional and nanocomposite group. The bond strength values revealed that nanocomposite had slightly higher mean shear bond strength (21.04 ± 0.56) compared to conventional composite (20.78 ± 0.60). It was found that conventional composite resin and nanocomposite resin had statistically similar mean shear bond strength, with nanocomposite having little more strength compared to conventional composite.

Key words: Anterior stainless steel crowns, composite, nanocomposite

aP.G. Student, bHead of Department, cReader, Department of Pedodontics and Preventive Dentistry, J.S.S. Dental College and Hospital, Mysore - 570 015, India

Introduction

Esthetic restorations on primary teeth have long been a challenge for the pediatric dentist. The small size of teeth, patient cooperation and parental expectations are major challenges in the restoration of primary incisors.[1,2]

Numerous techniques for restoring primary teeth have been attempted over the years. Different types of restorations for complete coronal coverage include polycarbonate crowns, acid etched resin crowns, stainless steel crowns, open-faced stainless steel crown with veneers placed on the chair side and commercially veneered stainless steel crowns. Each of these techniques presents technical, functional or esthetic compromises that complicate its efficient and effective usage.[3,4]

Polycarbonate crowns are associated with common clinical problems of fracture, debonding and dislodgement.[5,6]

Acid-etched resin or strip crown depends on the amount of enamel and dentin remaining after removal of caries and this procedure is technique sensitive.

Stainless steel crowns are retentive, easy to place and durable; but the metallic appearance may be displeasing to both the

parent and child.[7]

To improve esthetics, the facial surface was removed by high speed bur to create a window, which was filled with tooth-colored resin. It results in some metal being exposed, which is an esthetic concern.[8]

Commonly available veneered Stainless Steel Crowns are often difficult to fit due to the problem encountered with crimping and trimming of preveneered surface and due to problems regarding color stability and high cost compared to nonveneered crowns.[2]

Advances in the fields of restorative materials and metal bonding procedures have made possible, new restorative techniques that combine the advantage of stainless steel crown with cosmetics of composite restorative materials.[2]

Nanocomposite resin using advanced methacrylate resin has esthetic properties required for anterior restorations and mechanical properties required for posterior restorations. Nanofillers are different from traditional fillers. Milling procedure cannot reduce the filler particle size to below 100 nm (1 nm = 1/1000 µm). Synthetic chemical processes are used to produce building blocks on molecular scale. The nanomeric particles are monodispersed nonaggregated and nonagglomerated silica nanoparticles.[9] This study was conducted to evaluate the shear bond strength of composite resin and recently introduced nanocomposite resin to sandblasted primary anterior stainless steel crown.

ISSN 0970 - 4388

J Indian Soc Pedod Prev Dent - June 200783

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Materials and Methods

The study samples consisted of 30 primary anterior stainless steel crowns (UnitekTM, size R4), embedded in resin blocks with crown, in test groups of 15 samples each.

Mounting of the crown was done using resin block with one crown. Mould was designed with silicon duplicating material of specific dimensions.

Crown was placed in the mould and since all crowns were of the same size, mesiodistal and buccolingual positions were standardized [Figure 1].

Self-cure acrylic powder was sprinkled on the primary anterior stainless steel crown and monomer added drop by drop (‘sprinkle’ method). The whole mould was filled and kept in a pressure pot to help in polymerization and minimizing any porosity.

The crown was sandblasted with a 50 µ aluminum oxide at a pressure of 75 psi in for approximately 20 seconds, which resulted in the labial surface of the crown to have dull frosty appearance. The bonding procedure was carried out within 30 minutes of sandblasting. Strength of sandblasted metal has been found to be affected adversely by more time interval between sandblasting and bonding composite.[10]

To standardize the amount and location of composite material on the primary anterior sandblasted crown, a jig was designed.

The bonding agent Prime and bond NT (Dentsply) was applied on the labial surface of the primary anterior sandblasted crown and light-cured for 20 seconds as per the manufacturer’s instructions. The composite resin and nanocomposite resin were taken on clean plastic (nonstick) instrument and placed

into the well of Teflon jig. The composite material was placed in increments. The light-cure gun was placed directly on the top of the well of jig and cured. The distance and direction of photo-curing was standardized.

The cured samples were placed in distilled water and stored in incubator at 37°C for 48 hours.

Shear bond strength was measured by using universal testing machine (Hounsefield U.K. Model, with a capacity of 50 KN). Testing was done in compression mode; in the lower jaw samples was placed and in the upper jaw, shearing jig was placed to shear the composite cylinder from the facial surface of primary anterior stainless steel crown [Figure 2].

With the use of a chisel-like rod, 0.5 mm thick at the edge and 8 mm wide, force was applied to debond the specimen with crosshead speed of 1 mm/min and the maximum value to debond the specimen was recorded in Newtons.[11] The values thus obtained were converted into MPa, using the known surface area of composite cylinder.

The site of fracture between the composite cylinder and the facial surface of the sandblast-treated primary anterior stainless steel crowns was determined. The debonded surface of all the specimens was examined to define the location of bond failure; the observations made were categorized into adhesive failure: bond failure at the resin/stainless steel crown interface; cohesive failure: bond failure within resin; combined (mixed) failure: bond failure at resin/stainless steel crown interface as well as within resin.

Results

Independent sample ‘t’ test revealed a nonsignificant (t = -0.882; P = 0.385) difference between mean shear bond

Comparative evaluation of shear bond strength of conventional composite resin and nanocomposite resin

Figure 1: Anterior Stainless Steel Crowns mounted on resin blocks

Figure 2: Force applied with a chisel-like rod to debond the specimen

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strength values of conventional and nanocomposite group. The bond strength values revealed that nanocomposite had slightly higher mean shear bond strength (21.04 ± 0.56) compared to conventional composite (20.78 ± 0.60).

The site of fracture between the composite cylinder and the facial surface of the sandblasted treated primary anterior stainless steel crowns was determined.

The debonded surfaces of all the specimens were examined to define the location of bond failure; the observations made were categorized into Adhesive failure: Bond failure at the resin /stainless steel crown interface. Cohesive failure: Bond failure within resin. Combined (mixed failure): Bond failure at resin /stainless steel crown interface as well as within resin.

In the conventional composite group, the fracture site distribution observed was - adhesive failure 6 (40%), cohesive failure 6 (40%) and combined failure 3 (20%).

In the nanocomposite group, the fracture site distribution observed was - adhesive failure 6 (40%), cohesive failure 4 (26.66%) and combined failure 5 (33.34%).

Discussion

Restoration of severely damaged primary anterior teeth presents a challenging problem to the clinicians. Baby bottle tooth decay can cause extensive damage to the teeth of infants and toddlers, which especially increases when the bottle is used as pacifier or for other non-nutritive reasons.[12]

Nursing bottle caries is also predominant in preschool children of India. A study was done to evaluate the prevalence of nursing bottle caries; anterior teeth constituted 47% of total DMFT in their study samples.[13]

The preformed stainless steel crown is the most durable and reliable restoration for severely carious or fractured incisors. These are the easiest type to place. These advantages, however, are overshadowed by the unsightly; stark silver metallic appearance of the restoration in the most cosmetically prominent region of mouth.[14]

A chair-side veneering technique was proposed, which has the advantage of being durable and providing esthetically pleasing result.[15,16]

For the success of the chair-side veneered primary anterior

stainless steel crown, the joint interface between the facial surface of the crown and composite resin plays a critical role.

There are various methods to increase the bond strength between the crown surface and the composite resin.

Laser surface treatment obtains the highest bond strength; but as sandblasting is easily available and not technique sensitive, in the present study sandblasting treatment was followed.

Advances in the fields of restorative materials, metal bonding procedures and surface treatment like sandblasting to enhance mechanical retention have made it possible to treat primary anterior teeth with durable and esthetically pleasing results.

The delivery of functional, esthetic, and durable restoration has been simplified by the introduction of contemporary cosmetic materials. The most recent innovation in composite resin technology is the revolutionary application of nanocomposite.

Contemporary nanocomposite material delivery increases esthetics, strength and durability, which are the scientific principles for increased longevity.[9]

Restorative composite systems using nanotechnology can offer high translucency, high polish and polish retention similar to that of microfilled composite while maintaining physical properties and wear equivalent to several hybrid composites.

Nanotechnology, also known as molecular nanotechnology or molecular engineering, is the production of functional materials and structures in the size range of 0.1 to 100 nanometers, - the nanoscale - by various physical or chemical methods.

Two types of nanofillers, nanomeric particles and nanoclusters, were developed. They used optimal combinations of these nanofillers in a proprietary resin matrix to prepare the nanocomposite system with a wide range of shades and opacities. The compressive, diametral tensile, flexural strengths were compared wear; fracture resistance; and polish retention to the conventional composite.[9]

The present study was planned to compare the shear bond strength of conventional composite resin with nanocomposite resin on primary anterior stainless steel crowns.

Table 1: Descriptive statistics of shear bond strength for conventional composite and nanocomposite groupDescriptive Conventional composite Nanocomposite Mean difference ‘ t’ value df PMean 20.78 21.04S.D 0.60 0.56 -0.1897 -0.882 28 0.385

Comparative evaluation of shear bond strength of conventional composite resin and nanocomposite resin

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Table 2: Fracture site distribution in both conventional composite group and nanocomposite groupGroups Adhesive Cohesive CombinedConventional composite 6 6 3Percentage % 40 40 20Nanocomposite 6 4 5Percentage % 40 26.66 33.34

Result of the present study showed nonsignificant difference between the shear bond strength of conventional composite resin and nanocomposite resin on sandblasted primary anterior stainless steel crowns.

Independent sample ‘t’ test revealed a nonsignificant (t = -0.882; P = 0.385) difference between mean shear bond strength values of conventional and nanocomposite group. The bond strength values revealed that nanocomposite had slightly higher mean shear bond strength (21.04 ± 0.56) compared to conventional composite (20.78 ± 0.60) [Table 1].

Fracture site distribution also reveals almost same pattern of fracture [Table 2]. In conventional composite group, adhesive failure 6 (40%), cohesive failure 6 (40%) and combined failure 3 (20%) were observed, whereas in nanocomposite group cohesive failure 6% values, adhesive failure 4% values and cohesive failure 5% values were observed.

References

Roberts C, Lee JY, Wright TJ. Clinical evaluation of and parental satisfaction with resin faced stainless steel crowns. Pediatr Dent 2001;23:28-31.Wiedenfeld KR, Draughn RA, Welford JB. An esthetic technique for veneering anterior stainless steel crowns with composite resin. ASDC J Dent Child 1994;61:321-6.

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Waggoner WF, Cohen H. Failure strength of four veneered primary stainless steel crowns. Pediatr Dent 1995;17:36-40.Helpin ML. The open face steel crown restoration in children. ASDC J Dent Child 1983;50:34-8.Braham RL. Restorative procedures for primary anterior teeth with proximoincisal caries. In Text book of Pediatric Dentistry, 2nd ed. Braham RL, Morris ME. Williams and Wilkin: Baltimore; 1985. p. 549-51.Stewart RE, Luke LS. Preformed polycarbonate crowns for the restoration of anterior teeth. J Am Dent Assoc 1974;88:103-7.Hartmann CR. The open face stainless steel crown: An esthetic technique. ASDC J Dent Child 1983;50:31-3.Waggoner WF. Restorative dentistry for primary dentition. In Pediatric dentistry: Infancy through adolescence, 2nd ed. Pinkham JR, editor. WB Saunders Co: Philadelphia; 1994. p. 298-325.Mitra SB, Homes BN. An application of nanotechnology is advanced dental material. J Am Dent Assoc 2003;134:1382-9.McCaughey AD. Sandblasting and tinplating-surface treatment to improve bonding with resin cements. Dent Update 1993;20:153-7.Salama FS, el-Mallakl BF. An in vitro comparison of four surface preparation techniques for veneering a compomer to stainless. Pediatr Dent 1997;19:267-72.McDonald RE, Avery DR, Stookey GK. Dental caries in the child and adolescent. In dentistry for the child and Adolescent, 6th ed. McDonalds RE, Avery DR. CV Mosby Co: St. Louis; 1994. p. 223-5.Chawla HS, Gauba K, Goyal A, Trends of dental caries in children of Chandigarh are the 1st sixteen years. J Indian Soc Pedo Prev Dent 2000;18:41-5.Croll TP, Helpin ML. Preformed resin veneered stainless crowns for restoration of primary incisors. Quintessence Int 1996;27:309-13.Baker LH, Moon P, Mowino AP. Retention of esthetic veneers on primary stainless crowns. ASDC J Dent Child 1996;63:185-9.Salama FS, el-Mallakl BF. An in vitro comparison of four surface preparation techniques for veneering a compomer to stainless. Pediatr Dent 1997;19:267-72.

Reprint requests to:Dr. Amit Khatri,Dept. of Pedodontics and Preventive Dentistry,J.S.S. Dental College and Hospital,Mysore - 570 015, India.E-mail: khatri9804@rediffmail.com

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Comparative evaluation of shear bond strength of conventional composite resin and nanocomposite resin