1 comparative evaluation of bond · intraoral compressive and tensile forces that are produced in...

ABSTRACT: The aim of the study is to evaluate the bond strength of nanohybrid composite resin and

Cention N to enamel and dentin with and without etching

Materials And Method: 80 extracted human molar teeth were taken, cleaned and stored in distilled water.

Acrylic blocks were prepared by cold cure acrylic resin. The selected molars were embedded into the

blocks. Half of the samples the buccal surfaces of teeth were grinded with a straight fissured bur to prepare

flat surfaces at a depth of 1.5 mm exposing the dentinal surface. The other half samples were grinded at a

depth of 0.5 mm to observe the enamel surfaces. Half of the enamel and dentinal surfaces were acid etched

with 37% phosphoric acid. With the help of a 4 mm diameter straw, cut to 3 mm in length, cylinder shaped

mould were fixed to the samples. Composite resin and Cention N were inserted into the moulds,

polymerized with a light cure unit. Plastic moulds were cut out with a scalpel. The specimens were stored in

distilled water for 24hrs. All the specimens were transferred to the universal testing machine individually

and subjected bond strength analysis. Load required to debond the specimen were recorded.

Result: Cention N showed higher bond strength value than composite resin. Among etching groups, etched

specimen showed more bond strength than unetched specimens, enamel surfaces showed greater bond

strength with the materials than dentin surfaces.

Conclusion: Among both the materials, Cention n showed better bond strength than nanohybrid

composite.

1 2 3Paromita Mazumdar , Abiskrita Das, Debarpan Mandal1.Professor and H.O.D, Department of Conservative Dentistry & Endodontics , Guru Nanak

Institute of Dental Sciences and Research, Kolkata2,3 Post Graduate student, Department of Conservative Dentistry & Endodontics ,Guru Nanak,

Institute of Dental Sciences and Research, Kolkata

INTRODUCTION: The clinical success of restorative

material depends upon a good adhesion with dentinal surface

so as to resist various dislodging forces acting within the oral

cavity. The need for restorative material, with better bond

characteristics and strength to withstand the stress of

masticatory forces, leads to the recent advances in the

restorative dentistry[1]. Compressive strength is the ability of

a material to resist compression[2]. It is one of the most

important mechanical properties of a restorative material

which restores the structure of a tooth in posterior region. A

restorative material should have the same mechanical

properties as tooth structure. A material with higher or lower

amount of a property will adversely affect on longevity of the

tooth structure and the restoration and a premature failure of

each will happen.[3]

Since 1954 that Buonocore introduced acid etching procedure

as a pretreatment method that enhances the strength bonding

of composite resins to enamel for the first time , and then it's

clinical application presented in 1976 by Cueto and

Buonocore, many trials have been done to improve the quality

of composites and adhesives and several pretreatment

methods were discovered and presented.[4]

In fact, adhesive generations from first to seventh, are the

results of these studies that became more modified and their

COMPARATIVE EVALUATION OF BOND STRENGTH OF

COMPOSITE RESIN & CENTION N TO ENAMEL AND

DENTIN WITH AND WITHOUT ETCHING UNDER

UNIVERSAL TESTING MACHINE

Journal of Dental Sciences

University

University Journal of Dental Sciences, An Official Publication of Aligarh Muslim University, Aligarh. India 1

University J Dent Scie 2018; Vol. 4, Issue 3

ResearchArticle

Key words:

Bond strength,

compressive strength,

Cention n, nanohybrid

composite resin.

Conflict of interest: Nil

No conflicts of interest : Nil

application became easier step by step, so that along with

sixth generation of adhesives, the term self-etch came into the

world of restorative dentistry[3].

The composite resins are one of the commonest restorative

material used now a days. It is used mainly because of its

aesthetic appearance but they have some imperfections such

as shrinkage after polymerization. As these composites are a

mixture of different methacrylate monomers that polymerize

linearly, their shrinkage can negatively compromise the

longevity of resin-based restorations, resulting in

unsatisfactory marginal adaptation, marginal discoloration,

decrease in surface texture, secondary caries and excessive

loss of anatomic form[4].

With the purpose of overcome this imperfection, scientists

introduced a new restorative material that is Cention N which

is an alkasite restorative material. It is self-curing with

optional additional light-curing. Cention N is available in the

tooth shade A25. It is radiopaque, and releases fluoride,

calcium and hydroxide ions. As a dual-cured material it can be

used as a full volume (bulk) replacement material.

The aim of this study was to evaluate the bond strength of

nanohybrid composite resin and Cention N to the enamel and

dentin with and without etching.

MATERIALS AND METHOD: 80 sound mandibular first

molars, with neither carious lesions nor restorations, which

were recently extracted for periodontal or orthodontic reason,

were selected for this in vitro study. Each tooth underwent

scaling and root planing with an ultrasonic device to remove

residual organic tissue. Then, the teeth were immersed in

2.6% sodium hypochlorite solution and rinsed with running

water for 10 min.

Acrylic blocks were prepared by cold cure acrylic resin

material. The selected molars were embedded into the blocks.

The blocks were then put in water to avoid expansion of the

material.

In half of the samples the buccal surfaces of teeth were

grinded with the help of a straight fissured diamond bur to

prepare flat surfaces at a depth of 1.5 mm exposing the

dentinal surface. The other half samples were grinded at a

depth of 0.5 mm to observe the enamel surfaces.

Half of the enamel and dentinal surfaces will be acid etched

with 37% phosphoric acid

RESTORATIVE PROCEDURES: All the prepared

samples were divided into 2 experimental groups, and 4

subgroups and 8 subdivisions with 10 teeth in each group

according to the restorative material used: Group I-; Group II-

Cention N

With the help of a 4mm diameter straw, already cut to 3mm in

length, cylinder shaped mould will be fixed to the samples.

Nanohybrid composite resin (Tetric N Ceram) and Cention N

were inserted into the moulds and polymerized with a light

cure unit. Plastic moulds were then cut out with a scalpel.

STUDY DESIGN

EXTRACTED HUMAN MOLAR TEETH

The specimens were stored in distilled water for 24hrs then

were thermo-cycled for 500 cycles at 5-55°C for 60 seconds.

The interval time between each thermo-cycling phase was 30

seconds. Specimens were transferred to the universal testing

machine with a crosshead speed of 0.5 mm until fracture with

tip diameter 1.5mm and subjected to bond strength analysis.

Subjected to compressive test determination which created

buckling of the restoration which results in formation of a

tensile stress in enamel and dentinal walls.

The load required to debond the specimen was recorded.

Placed in the lower assembly of the machine and the force was

applied with the help of a knife-like mandrel which engaged

the blocks and dislodged it. Bond strength was calculated

according to the following formula and expressed in kilo

newton (KN):

Stress = Failure

load (N)/surface area (mm²?)

Data were subjected to statistical analysis and analyzed using

one-way anova analysis of variance using the SAS.



SPECIMEN SUBJECTED TO BOND STRENGTH

TESTING

UNIVERSAL TESTING MACHINE

RESULT:

Comparing among nanohybrid composite resin and Cention

N, the bond strength of Cention N was much higher than

nanohybrid composite resin level. In terms of significance it is

again significant with a confidence of more than 99.996% (p

value=0.004%).

Comparing among etched and non etched samples, the bond

strength of etched samples showed a much higher bond

strength when compared to non etched samples. In terms of

significance it is again significant with a confidence of more

than 99.772 %. (p value=0.228%)

Comparing among enamel and dentin samples, the bond

strength of enamel samples were much higher than dentin. In

terms of significance it was again significant with a

confidence of more than 99.965%. (p value=0.035%).

The mea bond strength of the two restorative materials

evaluated to enamel and dentin substrates are summarized in

the table below.

DISCUSSION: The selection of material is based primarily

on ease of handling with due consideration being given for

mechanical properties and manipulative variables. Among

mechanical properties bond strength of restorative materials

is important because it usually replace a large bulk of tooth

structure and they should provide sufficient strength to resist

intraoral compressive and tensile forces that are produced in

function and parafunction[6].

Cention N is a tooth coloured “alkasite” restorative material

used for filling for direct restorations. The organic, monomer

part of Cention N consists of four different dimethacrylates

which represent 21.6% wt. of the final mixed material. A

combination of UDMA, DCP, an aromatic aliphatic-UDMA

and PEG-400 DMA, interconnects (cross-links) during

polymerization resulting in strong mechanical properties and

good long-term stability[7].

Due to the sole use of cross-linking methacrylate monomers

in combination with a stable, efficient self-cure initiator,

Cention N exhibits a high polymer network density and

degree of polymerization over the complete depth of the

restoration.

The inorganic fillers comprise a barium aluminum silicate



glass filler, ytterbium trifluoride, an Isofiller, a calcium

barium aluminum fluorosilicate glass filler and a calcium

fluorosilicate glass filler, with a particle size of between 0.1

µm and 35 µm.

The silanes bonded to the filler particles improve the bond

strength as they are able to establish a chemical bond between

the glass surface and the matrix.[8]

They are responsible for imparting restorative materials with

the adequate strength to withstand the stresses and strains of

the oral cavity and to achieve acceptable clinical longevity.

During the last decades, the increasing demand for esthetic

dentistry has led to the development of resin composite

materials for direct restorations with improved physical and

mechanical properties, esthetics and durability.

Nano filled materials are believed to offer excellent wear

resistance, strength and ultimate esthetics due to their

excellent polishability, polish retention and lustrous

appearance. Nano filled resin composites show mechanical

properties at least as good as those of universal hybrids and

could thus be used for the same clinical indications along with

anterior restorations due to their high esthetic properties.[8]

Tetric N-Ceram is a light-curing, radiopaque nano-hybrid

composite based on nano-optimized technology for direct

restorative procedures. It can be universally applied to restore

teeth in the anterior and posterior region. Its nano-optimized

filler technology is responsible for the material's unique

chameleon effect and natural esthetic results.

Monomer of Tetric N-Ceram contains Bis-GMA, Bis-EMA

and UDMA which are converted into a cross-linked polymer

matrix during the polymerization process. Bis-GMA, Bis-

EMA and UDMA exhibit low polymerization shrinkage by

volume.

Tetric N-Ceram incorporates several different types of filler

(barium aluminum silicate glass with two different mean

particle sizes, an Isofiller, ytterbium fluoride and spherical

mixed oxide) in order to achieve the desired composite

properties.[7]

In this study, bond strength testing was done using a constant

crosshead speed and the samples were continuously loaded

such that the crack will propagate at increasing speed until

separation.

Mandibular molar was selected due to higher forces of

mastication over molars

In a clinical situation, the propagation kinetics of the crack is

completely different. During function, an assembly is

submitted to a series of brief loads. If these loads are high

enough, small extensions of cracks ensure sub-critical crack

growth in bonded area as explained by A. A. Griffith.

According to Griffith's theory of brittle solid it is stated that

the low fracture strength observed in experiments, as well as

the size-dependence of strength, were due to the presence of

microscopic flaws in the bulk material.[9]

Our analysis revealed the role of ethching enamel and dentin

on bond strength of Nano hybrid composite and Cention N.

The analysis also showed a definite difference of bond

strength between etched and without etched enamel and

dentin which might be explained by various reasons.

Surface area significantly affects the bond strength of Nano

hybrid composite and Cention N. An inverse relationship

between bond strength and bonded surface area has been

recently shown, confirming previous studies.

It has been shown that additional etching of enamel and dentin

can improve the bond strength of Nano hybrid composite and

Cention N

The acid etching time recommended for both enamel and

dentin with 37% phosphoric acid gels commonly employed

with etch-and-rinse systems has been 15 seconds.

Ustunkol et al., Batra et al. and Taschner et al. claimed etching

process has a significant effect on bond strength of

methacrylate-based composite

Adebayo et al., and showed higher bond strengths of the nano

hybrid composite.[10]

Although some researchers did not found any significant

difference between bond strength of etched and not-etched

enamel and dentin.

Koliniotou-Koumpia et al, Sampaio et al. said there is no

difference of bond strength between nano hybrid composite

and bulk fill composite on etching.

Part of the challenge in bonding to dentin when compared to

enamel is the difference in the substrates.

Enamel is homogeneous in nature and is primarily composed

of hydroxyapatite. Etchants dissolve hydroxyapatite crystals

in enamel, creating pits by which the adhesive resin is readily

absorbed by capillary attraction creating macrotags of resin

that envelop the individually exposed hydroxyl appetite

crystals. Additionally resin microtags extend within tiny etch

pits in the enamel prism cores. Resin tags in the interprismatic

spaces provide for the majority of micromechanical

adhesion.[11]

In comparison, dentin is heterogeneous, consisting of

hydroxyapatite and collagen. The degree of mineral content in

dentin is quite variable, depending on whether it is near the

DEJ or deeper in close proximity to the pulp. Overall, the

water content of dentin is significantly higher than enamel,



posing another challenge to adhesive bonding. Acidity of

monomer also caused change in surface chemistry and

morphology of dentin, which in turn can influence bonding. A

significantly thicker hybrid layer was noted in areas with

perpendicular tubule orientation than in areas with parallel

tubule orientation.[12]

For evaluating the bond strength, the study samples were

stored in distilled water with few thymol crystals, to maintain

aseptic conditions before cavity system, with hydrophilic

components, which can dislodge moisture from the

conditioned dentin and attain an intimate interaction at the

demineralized intertubular and peritubular dentin, creating

the hybrid layer, which is essential for an ideal bond to dentin.

The studies conducted by Kallenos et al. and Gupta et al.[13]

Mechanical behavior depends upon the concentration and

particle size of the inorganic filler. Owing to the reduced

dimension of the particles and to a wide size distribution, an

increased filler load can be achieved in Cention N, without

increasing their viscosity and increasing the mechanical

properties such as tensile strength, compressive strength and

other mechanical properties.[14]

The filler particle size of Cention is 0.1 µm, which is lower in

comparison with the filler particle size of Tetric N Ceram

which is 0.7ìm. A spherical shape is known to have many

advantages such as to allow an increased filler load in Cention

and also enhance their fracture strength since mechanical

stresses tend to concentrate on the angles and protuberances

of the filler particles. Also the spherical shaped filler particle

is seen in Cention N which have the advantage of increased

filler load, which is not seen in Tetric Ceram which has

irregular shaped filler particles.[15]

Though both etched Cention N and nano hybrid composite

resin has improved mechanical properties than unetched

samples it is hypothesized that Cention N will better resist to

occlusal loads than a nano composite. Cention N has better

bond strength comparable to Tetric N Ceram. From the above

results, it can thus be expected that the Cention N are able to

resist these stresses better than nano hybrid composite resin.

CONCLUSION: Within the limitations of this in vitro study;

it can be concluded that

1. Cention N have shown better bond strength than Nano

hybrid Composite Resin (Tetric N Ceram).

2. The bond strength of enamel is much higher than that of

dentin.

3. The bond strength of etched samples showed a much

higher bond strength when compared to non-etched

samples

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CORRESPONDING AUTHOUR:

Dr. Abiskrita Das

Guru Nanak Institute Of Dental Sciences And Research

157/f Nilgunj Road, Panihati, West Bengal -700114

Email: [email protected]

Phone No. 9477288361



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