Assessing microleakage of composite restorations in class V cavities prepared by Er:YAG laser irradiation or diamond bur.

INTRODUCTION: The aim of this study was to make a comparison between microleakage of conventionally restored class V cavities using bur and acid etchant and, the ones prepared and conditioned by Er:YAG laser.
MATERIALS AND METHODS: 30 recently extracted intact caries and filling free human permanent molars were used for this study. Then, Cold cure acrylic resin was used to seal the apices. The samples were randomly assigned to 5 groups of six each. Class V cavities were prepared one on buccal and one on lingual surface of each sample. Group 1: cavity preparation by diamond bur and turbine + acid etch, Group 2: cavity preparation by Er:YAG laser + acid etch, Group 3: cavity preparation by Er:YAG laser + Laser etching, Group 4: cavity preparation by diamond bur and turbine + laser etching, Group 5: cavity preparation by Er:YAG laser with no conditioning procedure. The cavities restored with restorative composite resin. Samples were then immersed in 2% methylene blue solution for 24 hours. The data were then analyzed using Wilcoxon signed ranks test and Kruskal-Wallis statistical tests.
RESULTS: The Kruskal Wallis test showed a significant difference (P < 0.05) between enamel and cementum margin microleakage, while the higher microleakage was related to the cementum margin of restorations.
CONCLUSION: There was no significant difference in evaluating microleakeage degree of cavities prepared by Er:YAG laser and diamond bur.

INTRODUCTION

Recently there has been an increasing debate on the use of laser irradiation for preparing cavities and conditioning enamel and dentine as an alternative for routine chemical acid etching.[12] Despite the improvements achieved in decreasing composite resin shrinkage, this is still an important factor reducing success rate of direct composite fillings,[3] so it is important to obtain a strong bond between restoration and dental hard tissues by surface pretreatment.[4]

The erbium-doped yttrium aluminium garnet (Er:YAG) laser energy is highly absorbed by water, which is the well-absorbed energy by hydroxyapatite and therefore it is more effective than any other laser system in removing tooth hard tissues,[56] with minimal thermal damage and consequently one of Er:YAG laser first indications is preparing cavity for composite resin restoration[1] and surface pretreatment. So the efficacy of Er:YAG laser in dental procedures such as caries removal, preparing cavities,[57] and modifying surface specifications has been studied by many investigators;[89] and in the last years many studies are done around the microleakage of laser prepared cavities.[1011]

But the effect of laser irradiation on surface characteristics is not still completely revealed if it beneficially alters surface specifications or not, and needs more investigations to show if it results in increasing or decreasing the microleakage in comparison to conventional chemical acid etching procedures.[12]

The aim of this study was to make a comparison between microleakage of conventionally restored class V cavities using bur and acid etchant and the ones prepared and conditioned by Er:YAG laser. Besides, Er:YAG laser showed advantages such as minimal need for local anesthesia,[1314] producing rough surface with no demineralization, sterilizing surface of dentin and no smear layer production.[15]

MATERIALS AND METHODS

Thirty recently extracted intact caries and filling free human permanent molars were used for this study. The teeth surfaces were cleaned under tap water and any residual tissue removed by means of a sickle scaler (204s, Hu-Friedy Chicago, USA). The specimens were then pumiced and stored in distilled water at 4°C. Before any manipulation, samples were placed in 0.5% chloramine solution for a week at 4°C. Cold cure acrylic resin was used to seal the apices to prevent dye penetration through the pulp chamber during the study.

The samples were randomly assigned to five groups of six in each. Class V cavities were prepared one on buccal and one on lingual surface of each sample resulting 12 class V cavities in each group. Cavity specifications were the same in all specimens (3 mm width, 4 mm length, and 1.5 mm depth). Coronal margins of cavity were located on enamel and gingival margins on cementum.

Group characteristics were as following:

Group 1: Using a diamond bur (008) (Teezkavan, Tehran, Iran) and a turbine and conditioning with 37.5% phosphoric acid (Kerr, Italy).

Group 2: Using Er:YAG laser (Smart 2940 plus, DEKA, Italy) accompanied by water and air spray and conditioning with acid etch.

Group 3: Using Er:YAG laser for cavity preparation and conditioning.

Group 4: Using a diamond bur (008) and a turbine and conditioning with Er:YAG laser.

Group 5: Using Er:YAG laser for cavity preparation with no conditioning procedure.

The laser parameters for cavity preparation were as following: Energy of 450 mJ, frequency of 10 Hz, and output power of 4.5 W for enamel removal; energy of 300 mJ, frequency of 10 Hz, and output power of 3 W for dentine and cementum removal; and the parameters for surface conditioning was energy of 50 mJ, frequency of 10 Hz, and output power of 0.5 W.

After rinsing for 30 s, each cavity was treated with resin adhesive system (Kerr, Optibond Solo Plus, Italy) following manufacture's instruction. The adhesive system used is (5th generation ternary solvent: Acetone, water, and ethanol) one component photoactivated bonding agent. This was light cured for 20 s followed by 2 s gentle air drying. The cavities then restored incrementally with restorative composite resin (Kerr, Premise, Italy). Each layer with 2 mm thickness light cured for 40 s.

After 24 h of storing restored samples in distilled water at 25°C, restorations were accurately polished with Soflex polishing discs (3 M Dental Products, USA).

The specimens were then thermocycled for 500 cycles between 5 and 55°C through water baths with a 20 s dwell time in each. All tooth surfaces were coated with two layers of nail varnish leaving 1 mm wide border, around restoration margins. Samples were then immersed in 2% methylene blue solution for 24 h.

To visualize the extent of dye penetration, the teeth were bisected into two equal longitudinal buccal and palatal/lingual halves by means of a low speed air cooled diamond disc. The sectioned samples evaluated using a light microscope (Olympus CX 31, Olympus America Inc) at ×30 magnification.

The microleakage evaluation based on degree of dye penetration was scored via a graded qualitative scale under a blinded manner[16] [Table 1].

Table 1

Qualitative dye penetration scale

The data were then analyzed (Statistical Package for Social Sciences (SPSS) 16) using Wilcoxon signed-rank test and Kruskal-Wallis statistical tests.

RESULTS

To assess the microleakage using dye penetration technique in enamel and cementum margins of restorations separately and also to compare these two groups with each other, results were categorized into two groups, enamel and cementum [Tables 2 and 3].

Table 2

Microleakage results in enamel margin of restorations

Table 3

Microleakage results in cementum margin of restorations

Test results in enamel margin of restorations (coronal to cementoenamel junction (CEJ))

In Group 1, dye penetrated through floor of cavities in three of 12 restorations, through axial dentine walls in four of them, and only in one restoration dye penetration limited to enamel. There was no dye penetration in the remaining four restorations.

In Group 2, dye penetrated through floor of cavities in five restorations and only in one sample dye penetration limited to enamel. There were no dye penetrations in six samples.

In Group 3, in four samples dye reached to floor of cavities, in two restorations reached to axial dentine walls, and in six fillings dye penetrated only through enamel.

In Group 4, dye penetrated through floor of cavities in four samples and in the eight remaining restorations dye penetrated only through enamel margins.

In Group 5, only in one restoration dye reached up to floor of cavity, in four of restorations dye penetrated through dentine axial walls, and dye penetration was seen only through enamel in the rest of restorations.

Test results in cementum margin of restorations (apical to CEJ)

In none of five groups there was not any restoration scoring ‘0’ or ‘1’. But in Groups 1 and 5 the results were the same; in nine restorations dye penetrated up to the floor of cavities and in the three remaining dye penetration was seen through axial dentine walls.

The results were also the same in Groups 2 and 3; while dye penetrated through floor of cavities in 10 restorations and it penetrated through axial dentine walls in the rest of restorations.

In Group 4, dye penetration to the floor of cavities was seen in all of the restorations.

The Kruskal-Wallis test showed a significant difference (P < 0.05) between enamel and cementum margin microleakage, while the higher microleakage was related to the cementum margin of restorations. The Wilcoxon signed-rank test showed no significant difference between microleakage of five groups neither in enamel or cementum margin.

DISCUSSION

The aim of this study was to make a comparison between the microleakage of cavities which were prepared by Er:YAG laser or diamond bur and followed by two different acid or laser conditioning techniques. The present study used the common standardized dye penetration method used in the microleakage studies.

It is known that the microleakage occurred in cavities with cementum margins located on root surface is a concerning fact affecting class II and V composite restorations.[16]

Palma Dibb et al.,[17] used different adhesive systems in cavities prepared by Er:YAG laser and regardless of the material used, showed higher microleakage in cervical margins which were located on cementum and dentine in comparison with the enamel margins. This higher microleakage values seen in cervical margins may be related to the lower ability of hybrid layer formation on cementum and is also related to technique sensitivity of bonding to dentine in comparison with bonding to enamel.[15] The other factor resulting in higher leakage seen at cervical margins may because of the lack of dentinal tubules in the first 100 mm of cervical margins and higher organic content of the dentine.[18] Kimyai et al.,[19] also showed higher microleakage degree in gingival margins rather than occlusal margins, while using three different adhesive systems in cavities prepared by means of erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser; whereas, Kimyai et al., and Moldes et al., showed lower microleakage level through cervical margins when using self-etched adhesive system rather than etch and rinse two step (total etch) in class V cavities prepared by means of Er,Cr:YSGG[1920] and Er:YAG lasers; they showed no significant difference in microleakage of enamel margins when using these two different adhesive systems. So, in the present study the same adhesive system (total etch) was used for all groups to eliminate the effect of bonding system as a confounding factor.

There are different reasons introduced causing microleakage, including the marginal gap at the tooth-restoration interface and alteration of interfacial pressure. This pressure alteration is because of difference in thermal expansion coefficient of the tooth structures and the restorative material shrinkage.[1021] In the present study, specimens were thermocycled for 500 periods between 5 and 55°C to simulate the thermal changes taking place in oral environment resulted in gap formation at tooth-restoration interface.

Although acid etching of enamel margins significantly reduces the composite resin restoration microleakage,[21] there are no exact similar findings for acid etching of dentin for microleakage reduction when margins of restoration are located in dentin.[22]

On the other hand, acid etching of dentine eliminates smear layer and alters the surface topography which is helpful for mechanical retention and consequently may result in less gap formation and microleakage.[23]

During acid etching of dentin, peritubular dentin is mostly etched and produces cone-shaped openings through dentin tubules and this will let the restorative composite resin pull out due to its shrinkage.[24]

Both peri- and intertubular dentine demineralize during acid etching of dentin results in collagen exposure. This demineralized collagen and the adhesive resin both take part in hybrid layer formation.[2] This procedure needs enough surface moisture after etchant removal; otherwise hybrid layer formation will be decreased because of the collapse of collagen fibers. This is while the Er:YAG laser does not demineralize dentin surface and no collagen will be exposed which is important in hybrid layer formation.[15] Visuri et al., showed, remaining of peritubular dentin after Er:YAG laser irradiation, in return of collagen fibers, may be helpful to obtain stronger adhesion to the dentin, due to its more mineral content in comparison with intertubular dentin.[25]

Er:YAG laser irradiation vaporizes the water content of hard immediately which results in irregular surface. These irregularities work as a mechanical retention increasing adhesion of restoration to tooth hard tissue[15] which can be a substitution for acid etching technique, not only in microscopic dimensions, but also in macroscopic and clinical appearance.

CONCLUSION

There was no significant difference in evaluating microleakeage degree of cavities prepared by Er:YAG laser and diamond bur. The results showed a significant difference in microleakage degree between enamel and cementum margins.