Comparative Evaluation of Contact Angle and Surface Roughness in Resin Based Dental Composites After Polishing – An In Vitro Study

Introduction

Clinicians routinely utilise dental composite resins as restorative materials. They are esthetic, offer easy application, economic, and have the potential to replace amalgam in terms of strength and longevity. Dental composites are primarily made of organic resin matrix, fillers (either organic or inorganic), initiators, and accelerators.¹ The four types of resin composites hybrid, microfilled, microhybrid, and nanofilled composites can be categorised according to the size of the filler particles. In contrast to macrofilled composites which are used in areas where strength is the primary concern, microfilled and nanofilled materials are highly concerned with aesthetics.^2,3 Both anterior and posterior teeth serve better with composite restorations.⁴ After ten years, the overall survival percentage for composite restorations is 75.6%.⁵ Color change, fracturing, and marginal degeneration resulting in secondary caries are the most frequent factors requiring replacement of composite restorations.⁶ The last stage of finishing and polishing is crucial for composite restorations' aesthetics and bio-integration. Finishing and polishing of restorations enhances appearance and protects patient's oral health.^7,8 Increased microleakage can result in sensitivity, discoloration at restoration margins, and the development of secondary caries.⁹ Multi-step discs, fine and superfine diamond burs, abrasive discs, diamond, silicon or aluminium oxide impregnated soft rubber cups are some of the polishing technologies that are available.¹⁰

Increased surface roughness enhances bacterial adhesion, according to in vitro studies.¹¹ Cell adhesion properties of biomaterials can be modulated by altering the surface properties of biomaterials. The wettability of solid surfaces is a different surface characteristic that is measured by the contact angle. The measurement of contact angles (ca) also enables the determination of surface free energies (SFE), which reveals the polarity or non-polarity of the interactions at the liquid/solid interface as well as the hydrophilicity or hydrophobicity of a surface.^12,13 Compared to hydrophobic surfaces, hydrophilic surfaces with high surface free energy values are more likely to exhibit bacterial adherence.¹⁴ In order to evaluate the two different filled resin-based dental composites, the contact angle and surface roughness both before and after finishing and polishing were assessed.

Materials and Method

Sample size calculation

Sample size was calculated with G power software version 3.1.9, with 80% power, keeping the level of significance at 5%, and effect size of 0.5 as 12 samples per group.

Specimens preparation

For surface roughness and contact angle analysis Twenty four composite slabs were prepared using Teflon moulds in dimensions of 6 mm in diameter and 2 mm in height. The composite blocks were polished using silicon carbide and aluminium oxide abrasives (Shofu mini snap kit, Japan) in the following order: coarse, medium, fine, and super fine.

The samples were divided into the following groups: (Table 1)

Group I (NH): Nanohybrid composite resin (Ivoclar tetric N ceram) (n=12)

Group II (MH): Microhybrid composite resin (Ivloclar Te-Econom Plus ) (n= 12) The samples were stored in light-proof container and subjected to surface roughness analysis using a stylus profilometer (Mitutoyo version 2.0) and contact angle measurement using a goniometer (Sessile drop method).

Statistical analysis

The data were tabulated on Excel sheet and statistically analysed using IBM SPSS software version 22. Test of normality was done using Kolmogorov-Sminrov test and data were found to be normal in distribution. Inter group comparison was done using independent t-test. Intra group comparison was done using paired t-test.

Results

Surface Roughness Analysis

Ra – Intergroup comparison

There was no significant difference in the Ra values of unpolished surfaces between nanohybrid and microhybrid composites (p=0.301).

There was a statistical significant difference in the Ra values of polished surfaces between nanohybrid and microhybrid composites (p <0.001) (Table 2).

Ra – Intragroup comparison

There was a statistical significant difference in the Rq values of group 1 and group 2 between unpolished and polished surfaces (p=0.001 and p=0.03, respectively) (Table 3).

Rq – Intergroup comparison

There was a statistical significant difference in the Rq values of both the unpolished and polished surfaces between group 1 and group 2 (p=0.024 and p <0.001, respectively) (Table 2).

Rq – Intragroup comparison

There was no statistical significant difference in the Rq values of group 1 and group 2 between unpolished and polished surfaces (p=0.620 and p=0.944, respectively) (Table 3).

Contact Angle Analysis

Intergroup comparison

There was no statistical significant difference in the contact angle of both the unpolished and polished surfaces between group 1 and group 2 (p=0.076 and p=0.582, respectively) (Table 4).

Intragroup comparison

There was no statistical significant difference in the contact angle of group 1 and group 2 between unpolished and polished surfaces (p=0.265 and p=0.821, respectively ) (Table 5).

Discussion

Finishing and polishing continues to be the most neglected part of composite restoration despite the researchers emphasising its significance. According to a study, 99% of dental clinicians understand the value of polishing and finishing composites but only 59.8% of practitioners use the proper protocol of finishing and polishing.¹⁵ The particle size, shape, filler, and resin utilised, together with the polishing mechanism, are some of the variables that determine the polishability of composite resin.

Microhybrid composites and nanocomposites are two types of commonly used direct composite resin materials based on filler content. Microhybrid composites consist of both microscale and nanoscale (~20 nm) glass fillers, while nanocomposites are made of either individual (5– 20 nm) or clustered (0.6–1.4 μm) nanoscale glass fillers.¹⁶ Tetric N ceram comprises of Barium glass, ytterbium triflouride, 80-81 wt% mixed oxide and copolymers, whereas Te Econom Plus contains Barium glass, Barium-Aluminium fluoro-silicate glass, ytterbium trifluoride, highly dispersed silicon dioxide and spheroid mixed oxide (81 wt%).¹⁷

In the current investigation, contact stylus profilometer was used to assess the specimens for surface roughness. Low surface roughness improves the aesthetic appearance and endurance of the restoration in the oral environment, whereas rough surfaces encourage the buildup of plaque, jeopardize periodontal health, and result in discoloration.¹⁰ One of the key elements affecting the restoration's aesthetic performance, increasing plaque buildup, and biofilm formation is the resin composite's surface roughness.¹⁸ Even though the surface roughness of both nanohybrid and microhybrid composites were similar before polishing, finishing and polishing rendered the nanohybrid surface smoother than microhybrid.

Goniometer was used to quantify the specimen contact angles using the sessile drop method. Contact angle is a crucial factor in determining the wettability of dental materials. Surface wettability is a crucial factor in predicting the capacity of microbial adsorption and colonisation on the composite surface in a biological environment.¹⁹ The most accurate way to assess the hydrophobicity of cell surfaces is probably using the contact angle method, which is derived from drop profile image analysis.²⁰ The hydrophilic/hydrophobic makeup of the composite surface affects the contact angle as well. Plaque buildup is reduced in proportion to observed contact angle. While polishing removes minor imperfections, finishing removes a significant amount of material.²¹

A study conducted by Xu L, Siedlecki CA showed that for polymers, contact angles between 40° and 70° are reported as most suitable for cell adhesion. In our study, the contact angle values obtained where within the agreeable range for both nanohybrid and microhybrid composites.²²

Composite resins must be able to be polished since a smooth surface improves the restoration's aesthetics and patient comfort.²³ The hydrophilic/hydrophobic makeup of the composite surface affects the contact angle as well. Plaque buildup is reduced in proportion to observed contact angle. The abrasive particle and polishing technique, both have a significant impact on the final result. Modern resin-based composite materials can be polished using a variety of methods, such as multistep discs, fine and superfine diamond burs, abrasive discs, and soft rubber cups that have been infused with diamond, silicon, or aluminium oxide. While some polishing systems are simpler and need fewer therapeutic processes, others demand more time and a series of abrasive tools that must be used sensibly.²⁴ The abrasive particles need to be comparatively tougher than the fillers for a polishing system to work well. In the alternative, the polishing chemical will only remove the soft resin matrix, leaving the filler particles sticking out of the surface.²⁵

According to the present study findings, composites surface characteristics improved with finishing and polishing, and their surface roughness decreased by surface wettability. It is important not to undervalue the importance of finishing and polishing of composites because these processes are an essential component of the restoration.

Conclusion

Nanohybrid composites owing to their smaller filler particle size renders high polishability to the resin composites making them ideal material of choice for restoration in the aesthetic zone. The surface wettability of both nanohybrid and microhybrid were not different from each other. The long term effects of these surface characteristics is a subject for future research.

Conflicts of Interest

Nil