This in-vitro experimental study was conducted in the Department of Conservative Dentistry and Endodontics, Bharati Vidyapeeth Deemed to be University, Dental College and Hospital, Sangli in collaboration with Department of Mechanical Engineering, Walchand College of Engineering, Sangli, Maharashtra, India. The study was approved by Institutional Ethical Committee on December 7^th 2017 (Letter number -BVDUMC and H/Sangli IEC/ Dissertation 2017-18/251) and duration was about 8 months in the calendar year 2019.

In this study, a nanofilled composite resin (Filtek Z350 XT {Universal Restorative, 3M ESPE St.Paul, MN, USA}) and three polishing systems (Sof-Lex XT {3M do Brasil Ltda. Sumare, SP, Brasil}, Enhance and PoGo {DENTSPLY Caulk}, KerrHawe and OptiDisc {Kerr, Switzerland}) were used. The sample size was determined from data obtained from previous research by Scheibe KG et al. (2009), journal of applied sciences and using Gpower 3.0.10 [11].

Sample size estimation:

Sixty six acrylic resin (DPI RR cold cure, Mumbai) blocks measuring 2 cm in diameter and 2 cm in height were prepared from plastic mould. Circular cavity measuring 8 mm in diameter and 3 mm in depth was prepared in each acrylic resin block using high speed airotor (>2,00,000 rpm) with round and straight fissure burs. Dimensions were confirmed with digital vernier caliper. Acrylic resin was used to prepare the specimens because of ease of manipulation, stability and durability [Table/Fig-1,2].

[Table/Fig-1]:

Acrylic resin blocks.

[Table/Fig-2]:

After cavity preparation.

Nanofilled composite resin i.e., Filtek Z350 XT (3M ESPE, St. Paul, MN, USA) indicated for direct restoration was inserted into the prepared cavities using composite packing instruments (GDC) in three increments. Each increment was activated using LED curing unit (Ivoclar vivadent, Austria) for 20 seconds. The last layer was cured against a mylar strip (SHOFU DENTAL GmbH, Japan) with pressure being applied to the ends in order to produce extravasation of the material and the excess material was trimmed. The specimens were stored in distilled water at 37°C for 24 hours [Table/Fig-3,4] [11].

[Table/Fig-3]:

Last layer cured against matrix strip.

[Table/Fig-4]:

After curing of the samples.

All the specimens were finished with fine grit diamond burs using a high speed hand piece under water cooling and the specimens were divided into three groups (n=22 each).

Group I: 22 Specimens were polished using aluminium oxide- impregnated discs (Sof-Lex XT) polishing system. Sequence of coarse to superfine discs were used for 30s with high speed hand piece on each specimens with light intermittent pressure in the planar motion.

Group II: 22 Specimens were polished using disc-shaped aluminium oxide-impregnated silicon points and cups (Enhance and PoGo) polishing system. Polishing procedure was same as mentioned in group I.

Group III: 22 Specimens were polished using durable polyester discs impregnated with aluminium oxide particles (KerrHawe and OptiDisc) polishing system. Polishing procedure was same as mentioned in group I.

Following are the recommended cut-offs (ISO 4288-1966) for different surface finish [Table/Fig-5] [12].

All the procedure was performed by a single trained investigator to avoid operator bias and no blinding was done as it was an in-vitro study and there was one composite resin material tested and the operator was aware of the group to be polished respectively by polishing system. Each specimen was polished with a new polishing disc. All the specimens were washed with an air/water spray to remove debris and air dried and subjected to surface roughness measurement [Table/Fig-6,7 and 8].

[Table/Fig-6]:

Sof-Lex XT discs.

[Table/Fig-7]:

Enhance and PoGo.

[Table/Fig-8]:

KerrHawe and OptiDisc.

The surface texture of individual specimen in each group was measured by surface profilometer (Surtronic 25, Taylor Hobson Ltd, Leicester, England). A single measurement was recorded for each specimen at the center and the reading was noted by a trained laboratory technician. The surface texture (Ra, in μm) for each specimen was directly observed on the LCD screen connected to surface profilometer [Table/Fig-9,10].

[Table/Fig-9]:

Surface profilometer.

[Table/Fig-10]:

Reading of surface profilometer.

The data was analysed using SPSS v.20 IBM Corp. USA and the surface roughness between groups was compared by ANOVA. When the difference was statistically significant, Post-hoc tuckey test was used for intergroup comparison. The p-value was kept statistically significant at ≤0.05.

The present in-vitro study was conducted to evaluate and compare the effect of three polishing systems on the surface texture of nanofilled composite resin. When polishing was done by Sof-Lex XT, Enhance and PoGo, KerrHawe and OptiDisc the surface roughness for individual system was 0.35 μm, 0.56 μm, 0.59 μm respectively. The standard deviation was as follows: 0.09, 0.14 and 0.15 [Table/Fig-11].

The mean difference between Sof-Lex XT and Enhance and PoGo was 0.2109 μm, between Enhance and PoGo and KerrHawe was 0.0263 μm, between Sof-Lex XT and KerrHawe was 0.2372 μm [Table/Fig-12].

Hence, it can be inferred that surface texture of Filtek^TM Z350 XT polished with Sof-Lex XT polishing system produced significantly smoother surface than the one obtained with Enhance and PoGo and KerrHawe and OptiDisc polishing systems. Results of one-way ANOVA test for surface roughness showed p=0.001 which is statistically significant.

Proper finishing and polishing of composite resin restorations are important steps to increase the longevity and aesthetics of restoration. Poorly polished restoration surfaces are susceptible to discoloration, gingival irritation and secondary caries [4]. In the present study, we investigated the surface roughness of nanofilled composite (Filtek Z350 XT) using three polishing systems (Sof-Lex XT, Enhance and PoGo, KerrHawe and OptiDisc) and Sof-Lex XT showed lowest surface roughness value. Surtronic 25 profilometer was used to evaluate surface roughness (Ra). The Ra value was defined as the arithmetic average height of roughness component irregularities from the mean line measured within the sample length [9]. Surtronic 25 is a contact-type (Stylus) surface roughness tester. Even though it has disadvantages like stylus wear and creation of scratches on specimen’s surface, it provides reliable measurements as it directly touches the specimen. Also, it is portable and suitable for use both in the workshop and laboratory [12]. Scanning probe microscopy, atomic force microscopy and electron microscopy are the other methods for evaluation of surface roughness. However, these techniques are tedious, time consuming, expensive, requires a trained technician etc., [13].

Regarding the surface roughness, Sof-Lex XT produced the smoothest surface in all groups tested. This can be attributed to the fact that flexible discs of aluminium oxide was more efficient in removing particulate inorganic filler at the very surface of the organic matrix of the biomaterial [14].

The results of present study are in accordance with the results of Chour RG et al., Barbosa SH et al., Gulati GS and Gulati NK, Nair VS et al., Abzal MS et al., who showed that aluminium-oxide discs are superior than other systems [3,6-9]. However, results of this study are in contrast to the study by Patel B et al., who found that Enhance and PoGo was better polishing system than Sof-Lex spiral [4]. [Table/Fig-13] depicts a comparative evaluation of this study with other similar studies [3,6-9].

Clinical implication of this study are that the results of the present study must also be understood with caution since in clinical practice; the use of composite restorative material and polishing systems could be limited to the real accessibility and unvarying nature of the surfaces to be finished [15].

The specimens made in this in-vitro studies are relatively flat, uniform as compared to intra oral restorations. The presence of factors like saliva, location of the tooth, temperature, accessibility etc., influence the process of finishing and polishing which were not accounted in this in-vitro study. The study was self-funded and due to financial implications, only experimental groups were involved.

Within the limitations of the study, it was concluded that for the nanofilled composite resin (Filtek Z350 XT), among the tested polishing systems, Sof-Lex XT produced better surface texture as compared to Enhance and PoGo and KerrHawe and OptiDisc. Although companies recommend the protocol to use the material/instruments, the dentist need to evaluate and optimise the material/instruments depending on patient’s perfection and clinical situation. This being an in-vitro study, future studies should simulate oral conditions to determine the surface texture of composite resin polished by polishing system.