Comparative Evaluation of Internal Margin Adaptation and Integrity of Class I Preparations using Two Composites: An In Vitro Study.

AIM AND
OBJECTIVES: The aim of this study is to evaluate the internal margin adaptation and integrity of Class 1 preparations using two composites types (bulk fill/conventional) with two placement methods (4/2 mm increments).
MATERIALS AND METHODS: Class 1 preparations of 4 mm × 4 mm dimensions were made on 30 extracted human mandibular molars. They were randomly divided into three groups; among them, in Group 1 (n = 10), cavities were filled with SureFil SDR Bulk Fill, Group 2 (n = 10) cavities were filled with Filtek Bulk Fill of 4 mm increments in both groups, and in Group 3 (n = 10), cavities were filled with conventional composite Filtek Z350 with 2 mm increments. Samples were sectioned occlusogingivally. Then, dye was on internal margins, and images of each specimen were recorded using a digital camera to evaluate the marginal integrity and adaptation of restorative material to the tooth surface with image analysis software. Then, collected data were put under the statistical analysis with analysis of variance test and post hoc Tukey's test.
RESULTS: There was no significant difference in overall dye penetration in bulk fill and conventional (incremental fill) composite resins; however, when dye penetration was evaluated at different locations, within enamel and mid-dentin, significantly more gap-free margins were found than at the pulpal interface. Filtek Bulk Fill and conventional composite (Filtek Z350) showed comparatively more dye penetration toward the pulpal interface compared to SDR Bulk Fill.
CONCLUSION: There were no significant differences in percentage of gap-free margins between fill types for any of the composite materials. The proportions of gap-free margin were less at the pulpal interface and mid-dentin portions and enamel when filled with 4 and 2 mm increments. Copyright:

INTRODUCTION

Composite resins are material of choice in restorative dentistry for the reason that they have high esthetic results in routine practice. The material is composed of a polymer resin matrix with filler particles. Bowen in 1962 developed the resin which contained bis-GMA in its composition. Furthermore, the presence of filler particles improved the translucency, reduced the coefficient of thermal expansion, and increased the wear resistant.[1234] Regardless of the continuous evolution of these resins, complications such as polymerization shrinkage and marginal microleakage still occur.[5] To minimize the polymerization shrinkage stresses, various restoration placement techniques have been introduced. To overcome the clinical consequences of polymerization shrinkage, incremental filling techniques are usually preferred over the bulk filling method to acquire effective marginal integrity. In incremental techniques, the stresses developed within the tooth-restoration system reduce to compensate the polymerization shrinkage of composites. In various studies, it was reported that the incremental technique for composite placement had better marginal quality, marginal integrity, and marginal adaptation.[67] Many clinicians, however, have adopted an incremental cure philosophy since long when placing light-cured composites. Recently, numerous new restorative materials have been marketed as “bulk fill” composites. The concept of “bulk filling,” preparation, is not a novel idea and has been evaluated numerous times in the literature.[89] The newly introduced “bulk-filled” resins claim to offer superior results with 4–6 mm single-increment placement thicknesses, instead of the conventional 2 mm value frequently used for incremental fill resins.[810] Hence, the purpose of this research study is to evaluate the potential for marginal integrity within the enamel, mid-dentin, and pulpal floor areas in controlled-size, Class I preparations made in extracted human mandibular molars when restored using a variety of the newly marketed “bulk-filled” products compared to increment fill resins. The null hypothesis states that there was no significant difference among the bulk fill and increment fill composite resins when the marginal integrity was analyzed.

MATERIALS AND METHODS

Thirty freshly extracted, intact, noncarious, and nonrestored, human mandibular molars were used in the study. Teeth with caries, restoration, fracture, and intact tooth fractured during decoronation were excluded from the study. Only the root portions of the extracted teeth were embedded in resin blocks of 1cm × 1cm × 1 cm dimensions. A precise removal of enamel on the occlusal surface was accomplished, to provide a flat occlusal surface which resulted in having centrally located enamel while dentin was slightly exposed at the cusp tips. An outline of cavity preparation which has dimensions of 4.0 mm (L) × 4.0 mm (B) × 4.0 mm deep (±0.2 mm) was marked using metallic scale and marker, and the cavity was prepared using a high-speed airotor handpiece with copious water irrigation and equipped with a flat-ended diamond bur. The dimensions of each preparation were measured using a periodontal probe. Then, all samples were randomly divided into three groups (Group 1 and Group 2 – bulk fill and Group 3 – increment fill) and restored with the following composites:

Group 1 (n = 10): SureFil SDR Bulk Fill (Dentsply DeTrey, Germany)

Group 2 (n = 10): Filtek Bulk Fill (3M ESPE, Germany)

Group 3 (n = 10): Filtek Z 350 XT (3M ESPE, Germany).

Composite restoration was done according to the manufacturer's instructions [Table 1]. After composite restoration, roots were resected in all the samples, and crown portions of all the teeth were sectioned buccolingually as it provides a complete visualization of enamel–dentin–pulp complex to assess the marginal integrity at all the levels. All the sectioned samples were then embedded in elastomeric impression material for stability. Caries indicator dye (Sable Sleek) was used by tracing the internal margins of restoration with the help of ball burnisher [Figures 1a, 2a, and 3a]; the pooling dye was then immediately wiped off with the help of tissue paper. Images were taken by a digital single-lens reflex camera of 90 mm focal length and macro 1:1, and the photographs were processed in image analysis software (ImageJ v1.46r, National Institutes of Health, Bethesda, MD, USA) [Figures 1b, 2b, and 3b]. Using this software, the area of the marginal interface was determined at specific locations along the internal tooth/restoration interface: (1) the interface between enamel/composite, (2) within the mid-dentin, and (3) along the pulpal floor.

Table 1

Monomers and filler contents of materials used in the study

Resin cement	Type	Manufacturer	Increment thickness	Composition according to the manufacturer’s information
				Monomer	Filler
SDR	Flowable bulk fill composite	Dentsply DeTrey	4 mm	Barium-alumino-fluoro borosilicate glass, strontium alumino-fluorosilicate glass, modified urethane dimethacrylate resin, ethoxylated bisphenol adimethacrylate, triethyleneglycol dimethacrylate, camphorquinone, photoaccelerator, butylated hydroxyl toluene, UV stabilizer, titanium dioxide, iron oxide pigments, fluorescing agent	Barium glass Strontium glass (68 wt%, 45 vol%)
Filtek Bulk Fill Posterior Restorative	Flowable bulk fill composite	3M ESPE	4 mm	Silane-treated ceramics, diurethane dimethacrylate, substituted dimethacrylate, bisphenol apolyethylene glycol diether dimethacrylate-6, Ytterbium fluoride-3, bisphenol Adiglycidyl ether dimethacrylate, benzotriazole, triethylene glycol dimethacrylate	Ethyl 4-dimethyl aminobenzoate (64.5% wt/42.5%vol)
Filtek Z350 XT	Conventional increment fill	3M ESPE	2 mm	Bisphenol adiglycidyl ether dimethacrylate, bisphenol apolyethylene glycol diether dimethacrylate, diurethane dimethacrylate, triethylene glycol dimethacrylate	Silica-zirconia particles (82% wt/60%vol)

SDR: Smart Dentin Replacement

Figure 1

Buccolingual tooth sections restored with SureFil SDR – (a) Stained tooth images, (b) images analyzed using Image J Software

Figure 2

Buccolingual tooth sections restored with Filtek bulkfill – (a) Stained tooth images, (b) images analyzed using Image J Software

Figure 3

Buccolingual tooth sections restored with Filtek Z350 XT – (a) Stained tooth images, (b) images analyzed using Image J Software

Statistical analysis

The data were put under Kolmogorov–Smirnov test which was applied to verify that the data were normally distributed. The statistical analysis was accomplished using SPSS, version 23 (SPSS Inc., Chicago, IL, USA) with two-way analysis of variance (ANOVA) and post hoc Tukey's test. The statistical significance level was set at P < 0.05.

RESULTS

The two-way repeated-measures ANOVA when applied to evaluate the marginal leakage of bulk fill composite resin and increment fill composite resin, it was reported that there was no significant difference noted among the two bulk fill (SureFil SDR and Filtek Bulk Fill) and one increment fill (Filtek Z350) groups. Although there was no significant difference in the technique for composite placement using bulk fill or increment fill, SureFil SDR Bulk Fill showed better results when compared to Filtek Z350 and Filtek Bulk Fill as seen in figures. The second measure of one-way ANOVA test was applied for location to evaluate the significant difference between the location of the three different composite resins (enamel, mid-dentin, and pulpal floor interfaces), and it was reported that there was a significant difference stating the highest marginal dye penetration in the pulpal floor interface when compared to enamel and mid-dentin interfaces in all the three composite resins (SureFil SDR, Filtek Z350 XT, and Filtek Bulk Fill), and the lowest marginal dye penetration was noted in the enamel interface [Table 2]. In enamel–dentin interface, P value was reported to be 0.187, 0.153, and 0.146 for SureFil SDR, Filtek Z350 XT, and Filtek Bulk Fill, respectively. In dentin–pulp interface, P value was reported to be 0.073, 0.034, and 0.024 for SureFil SDR, Filtek Z350 XT, and Filtek Bulk Fill, respectively, suggestive of significant difference. In enamel–pulp interface, P value was reported to be 0.0038, 0.002, and 0.0009 for SureFil SDR, Filtek Z350 XT, and Filtek Bulk Fill, respectively, suggestive of significant difference as shown in Table 3.

Table 2

Mean and standard deviation of marginal dye penetration measured at enamel, dentin, and pulp for all the tested composite resins

Groups	Enamel	Dentin	Pulp
SureFil SDR
Mean	62.57	72.84	89.11
SD	15.24	18.21	20.28
Filtek Bulk Fill
Mean	66.24	80.63	112.24
SD	16.79	24.73	33.20
Filtek Z350
Mean	63.25	77.76	109.83
SD	19.66	23.70	37.55

SD: Standard deviation

Table 3

Intragroup comparison using post hoc Tukey’s test

Groups	SureFil SDR (P)	Filtek Bulk Fill (P)	Filtek Z350 (P)
Enamel-dentin	0.187	0.146	0.153
Dentin-pulp	0.073	0.024	0.034
Enamel-pulp	0.0038	0.0009	0.002

SDR: Smart Dentin Replacement

DISCUSSION

Bulk fill resin-based composites due to their developing trend are materials of interest nowadays among practitioners because of their new technology and easy manipulation and application. The composite resin tested in this study characterizes a new range of bulk fill composites currently available in the market to restore the teeth function and strength.[511] In the present study, we evaluated the marginal leakage and adaptation of Class I cavities restored with two bulk fill composites (SureFil SDR and Filtek Bulk Fill) and one conventional fill composite (Filtek Z350 XT) at enamel, mid-dentin, and pulpal interfaces of the restoration. When marginal leakage was evaluated, the results showed that there was no significant difference among the Class I cavities restored using two bulk fill and one incremental fill composite resins (P > 0.05). The probable reason for this could be the development in photoinitiator dynamics and increased translucency of bulk fill-resined composites, which allow additional light penetration and a deeper cure to the thicker increments, hence giving similar results as compared to increment fill resin composites.[810] According to Scotti et al. and Roggendorf et al., the SureFill SDR showed the best marginal integrity and adaptation when compared to the groups using incrementally layered resin composites, which was not in favor of the study done by Juloski et al.[121314] According to the studies done by Cadenaro et al. and Ikeda et al., it was observed that the bulk fill composite resins have low modulus of elasticity, which causes lower wettability than the conventional composites, and hence, because of their low viscosity, they can be easily inserted into cavities with proper adaptation and marginal integrity. The results of these studies were in accordance with the results of the present study while comparing the marginal integrity of bulk fill with the conventional composite resin.[151617] Although there was no significant difference among the composites, interestingly, there was a significant difference reported when the three composite resins were evaluated at three different levels, i.e., enamel, mid-dentin, and pulp interfaces. At enamel and mid-dentin interface, SureFil SDR, Filtek Bulk Fill, and Filtek Z350 XT showed no statistically significant difference for marginal leakage, yet the proportion reported at pulpal interface was statistically significant as compared to other two levels. These differences which result from polymerization shrinkage indicate that when composite resins were inserted and polymerized in bulk, shrinkage stresses were observed less at the enamel and dentin interfaces, which could be because of the ability of unpolymerized composite to “feed” the resulting stress development from the strain of composite curing at shallower depths and causes deformation in deep composite restorations (near dentin–pulpal interface).[818] During cavity preparation, there is the presence of moist environment near pulpal interface due to the dentinal fluid efflux, which leads to difficulty in dentin bonding and adhesion of composite resins and causes gap formation which results in leakage and compromised marginal integrity and adaptation. Excessive contraction stresses at the tooth-restoration interface cause the gap formation, which can be a result of the polymerization rate of the material and the extent of polymerization contraction. The development of stresses is influenced by curing depth of the material, which also affects the dentin bonding at the interface. Gap formation is apparent if the interfacial stresses exceed the stresses which can be supported by the adhesive layer, thus compromising the adhesive reinforcement of the tooth structure.[1920] Similar to our study, Furness et al. evaluated the effect of bulk fill and increment fill on the internal gap formation, and it was concluded that composite placement methods did not affect the marginal integrity and adaptation. SDR Bulk Fill reported the higher gap-free margins at pulpal floor interface than enamel level when compared to Filtek Bulk Fill and Filtek Z350 XT. Percentages of gapfree margins were not significantly different for any of the composite material at the enamel and mid-dentin interfaces. Remarkably, within enamel and mid-dentin, significantly more gap-free margins were found than at the pulpal floor interface.[81720] Within the limitation of our study, it can be concluded that there was no significant difference noted when the marginal integrity of three composite resins was evaluated (two bulk fill and one increment fill), whereas there was a statistically significant difference noted when marginal integrity and adaptation at enamel, mid-dentin, and pulpal floor interfaces were analyzed, indicating more gap-free margins at enamel and mid-dentin as compared to pulpal floor interface.

CONCLUSION

Bulk fill composite resins could be the better alternative of the increment fill for the restoration of the Class I cavities. As it is a less time-consuming procedure, photoinitiator dynamics increase translucency of bulk fill resin composites, which allows additional light penetration and a deeper cure to the thicker increments, hence giving similar results as compared to increment fill resin composites.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.