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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 9  |  Issue : 1  |  Page : 29-33

Interfacial micro gaps between dentin bases and hard setting calcium hydroxide liner: A scanning electron microscopy study


1 Conservative Unit, School of Dental Sciences, Universiti Sains Malaysia, Health Campus, Kota Bharu, Kelantan, Malaysia
2 Klinik Pergigian Lekir, Klinik Kesihatan Lekir, Manjung, Perak, Malaysia
3 Klinik Pergigian Kangar, Klinik Kesihatan Kangar, Kangar, Perlis, Malaysia
4 Faculty of Dentistry, Lincoln University College, Kelana Jaya, Petaling Jaya, Selangor, Malaysia
5 Prosthodontics Unit, School of Dental Sciences, Universiti Sains Malaysia, Health Campus, Kota Bharu, Kelantan, Malaysia

Date of Submission10-Aug-2020
Date of Decision01-Oct-2020
Date of Acceptance21-Nov-2020
Date of Web Publication14-May-2021

Correspondence Address:
Rabihah Alawi
Conservative Unit, School of Dental Sciences, Universiti Sains Malaysia, Health Campus, Kota Bharu, Kelantan
Malaysia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/dmr.dmr_44_20

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  Abstract 


Objective: This study is aimed to investigate interfacial micro gaps between bases and hard setting calcium hydroxide liner. Materials and Methods: Twelve sound extracted human maxillary premolars were selected and immersed in 0.1% thymol solution. Samples were subjected to Class I cavity preparations with the width of 2.5 mm buccolingually, 3 mm mesiodistally, and 2 mm depth from the dentinoenamel junction (DEJ). The cavities were lined with hard setting calcium hydroxide lining (Dycal®), (Dentsply, USA) and then divided randomly into two groups. The cavities were restored with smart dentin replacement (SDR®), (Dentsply, Germany) and glass ionomer cement Ketac™ N100 (3M ESPE, USA) for Group 1 and 2, respectively, (n = 6 for each group) up to DEJ level. All samples were then packed with composite resin. Samples were cut longitudinally using a hard tissue cutter (Exact, Japan) and sanded with increasing grit sandpaper (#320, #500, #800, and #1200) for 30 s each and subjected for interfacial micro gaps analysis using scanning electron microscopy. Results: There was a significant difference of micro gap formation between two groups of base materials and hard setting calcium hydroxide (Dycal®) (P < 0.05). Conclusions: Lesser micro gap between Dycal® and SDR® compared to Dycal® and Ketac™ N100 suggested SDR® as a better base material to be used with Dycal® for deep caries management.

Keywords: Bulk-fill resin, calcium hydroxide, dental cavity lining, glass ionomer cement, interfacial micro gaps


How to cite this article:
Alawi R, Lotfy AM, Zakaria A, Masudi SM, Abdul Muttlib NA. Interfacial micro gaps between dentin bases and hard setting calcium hydroxide liner: A scanning electron microscopy study. Dent Med Res 2021;9:29-33

How to cite this URL:
Alawi R, Lotfy AM, Zakaria A, Masudi SM, Abdul Muttlib NA. Interfacial micro gaps between dentin bases and hard setting calcium hydroxide liner: A scanning electron microscopy study. Dent Med Res [serial online] 2021 [cited 2021 Dec 2];9:29-33. Available from: https://www.dmrjournal.org/text.asp?2021/9/1/29/315967




  Introduction Top


Tooth-colored restoration, such as composite resin has been well developed to improve strength and manipulation during its application on the tooth structure. However, it has high polymerization shrinkage, which causes microleakage over time.[1] Microleakage is a phenomenon which occurs between a cavity wall and the restorative filling material, whereby there is bacteria, fluids, molecules, or ions that may not be detectable clinically. The causes of microleakage include dimensional changes to the tooth structure following polymerization shrinkage, thermal contraction, absorption of water, or mechanical stress.[2] Microleakage in a restorative material causes staining at the margin of restorations, recurrent caries, hypersensitivity of the tooth, and pulp pathology.[3]

In a deep cavity, it is recommended to apply hard setting calcium hydroxide near the pulp or over the exposed pulp as pulp protection, followed by a liner or base and finally restorative material.[4] The function of this step is to prevent pulp inflammation.

Dentin replacement material is recommended to be placed before final restorative material to protect the pulp and overcome the micro gap problem in between the incremental layer of the restoration by reducing the bulk of composite restoration.[5] In addition, dentin replacement material functions as dentine substitute, which improves the strength of the tooth with a significant amount of tooth structure loss.[6] Nowadays, there are various materials available in the market for dentin replacement. One of them is glass ionomer cement (GIC). GIC was introduced by Wilson and Kent in the 1960s and this material was indicated for restorative, lining, and luting material.[7] GIC is water-based cement, also known as polyalkenoate cement. It has the anticariogenic effect due to its ability to release fluoride.

All commercial GIC's can be divided into two categories; conventional GIC and resin-modified GIC (RMGIC).[8] With the advancement of new molecular engineering, nano-filled particles were added to the resin-modified glass ionomer restorative material, namely, Ketac™ N100 (3M ESPE, USA) to improve the esthetic and mechanical properties.[9],[10]

Previous studies reported less gap formation between Ketac™ N100 and the tooth structure compared to other types of GICs.[9],[11] Based on a study by Sengupta et al.,[12] Ketac™ N100 showed no microleakage on 40% of the polished samples and 20% of the non-polished samples. However, there was no significant difference of the microleakage between these two groups. They claimed that Ketac™ N100 showed a rapid initial shrinkage due to the free-radical polymerization of resin monomers. However, the setting stress on the bond of this material was not significant to result in gap formation and microleakage.

Another product that is available in the market that can be used as base material has been introduced by Dentsply Company named as Smart Dentin Replacement (SDR®) (Dentsply, Germany). It is a modified urethane dimethacrylate resin which has a photoactive group. SDR has 60%–70% less shrinkage stress in comparison to the conventional methacrylate-based resin. The effect of SDR® on microleakage was investigated and compared with conventional composite resin by Arslan et al.[3] The study showed that there was no significant difference between SDR® and conventional composite resin.

Another study investigated on the penetration of SDR® in dentin substructure in comparison with Tetric®flow (Ivoclar-Vivadent-Liechtenstein) in Class II cavities prepared mechanically and kinetically, using laser.[13] They found that the hybrid layer was formed better in the specimens prepared using mechanical technique restored with SDR®.

Up to this date, no study has compared interfacial micro gaps between hard setting calcium hydroxide liner and dentin replacement material. Therefore, the objective of this study was to measure and compare the interfacial micro gaps between SDR® and Ketac N100 used as base materials in relation to hard setting calcium hydroxide liner (Dycal®) using scanning electron microscopy (SEM). The null hypothesis would be there was no significant difference of micro gap formation between two groups of base materials and hard setting calcium hydroxide liner.


  Materials and Methods Top


Materials used in this study were SDR® (Dentsply, Germany), Ketac™ N100 (3M ESPE, USA) and hard setting calcium hydroxide (Dycal®) (Denstply, USA). Details of the materials are shown in [Table 1].
Table 1: Materials used in this study

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Twelve extracted human permanent maxillary premolar teeth were randomly selected and stored in 0.1% thymol solution until the beginning of the procedures. The inclusion criteria were sound teeth extracted due to orthodontic treatment and periodontal disease and the exclusion criteria were teeth with caries lesion and tooth wear.

All specimens were washed in running water to eliminate thymol residues and examined at ×10 stereoscopic magnifying glass (Carl Zeiss-Jena, Germany), those with structural defects were discarded. Then, all the specimens were subjected to Class I cavity preparations and restorations that were performed by one operator for standardization. Class I cavities were prepared according to the previous study[14] with modifications. The cavities were cut using round diamond bur ISO 010 with a diameter of 1.0 mm on the occlusal surface with the width of 3.5 mm mesiodistally, 2.5 mm buccolingually, and 2 mm depth measured using a periodontal probe from the dentinoenamel junction (DEJ). The samples were randomly divided into two groups of six teeth according to the materials used (Group 1: SDR® and Dycal®; Group 2: nano-glass ionomer Ketac™ N100 and Dycal®).

Dycal® was mixed according to the manufacturer's instructions and then placed on the deepest part of the cavity floor using Dycal applicator to a depth of 0.5 mm guided by the diameter of the Dycal® instrument.[14] For specimens in Group 1, the cavities were restored with SDR® up to the DEJ level, and light cured for 20 s using LED light cure unit (Elipar Freelight 2, 3M ESPE, Germany) according to manufacturer's instructions, whereas for specimens in Group 2, the cavities were restored with Ketac™ N100 up to the DEJ level and light cured for 20 s using LED light cure unit (Elipar Freelight 2, 3M ESPE, Germany) according to manufacturer's instructions. All the cavities were then packed with composite resin according to the manufacturer's recommendation. After the restoration, all the specimens were kept in wet gauze at 37°C for 24 h, and then their crowns were sectioned perpendicular to the long axis, in parallel sections using the Exakt cutting system (Exakt, Germany), obtaining discs of approximately 3 mm thick. The discs were sanded using Exakt grinding system (Exakt, Germany) with increasing grit sandpaper (#320, #500, #800, and #1200) for 30 s each and prepared for SEM analysis. The specimens were metalized with a fine gold overlay (gold sputter machine, Leica EM SCD005, Germany), submitted to SEM laboratory and photographed at different magnifications so that the SDR®/Dycal® and Ketac™ N100/Dycal® interfaces could be analyzed. Three measurements were taken at the most uniform gap on each sample and recorded.[13] The gaps were selected by two examiners to reach a consensus.[14]

The specimens were viewed under SEM (FEI Quanta FEG 450, USA) at different sections. The sections of the tooth were photographed using SEM and the morphological interface characterization of each section was described accordingly on the photomicrographs.

The statistical analysis was performed using the Statistical software IBM SPSS statistics 20.0 (IBM Corporation, Chicago, USA), and the results were analyzed using Mann–Whitney U test. The P value was set as statistically significant at P < 0.05.


  Results Top


The images were viewed under SEM (FEI Quanta FEG 450, USA) at magnifications of × 100, ×500 and ×1000. The micro gaps between Dycal® and Ketac™ N100 were observed at ×500. However, the close adaptation between Dycal® and SDR® required higher magnification which was ×1000.

The results showed significant difference of micro gap formation between two groups of base materials and hard setting calcium hydroxide (Dycal®) (P < 0.05) [Table 2].
Table 2: Median, interquartile range and P value of the interfacial micro gap between Dycal® and base materials

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A wider interfacial micro gap formation observed between Dycal® and Ketac™ N100 as shown in the SEM photomicrograph [Figure 1] and superior adaptation between Dycal® and SDR® was shown in SEM photomicrograph [Figure 2].
Figure 1: Scanning electron microscopy image of Dycal®-Ketac™ N100 interface at × 500

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Figure 2: Scanning electron microscopy image of Dycal®-SDR® interface at × 1000

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  Discussion Top


A deep caries management is the last step of restoring a tooth before a root canal treatment is indicated. This is a viable option when constructing a treatment plan. Up to this date, several materials have been introduced for pulp protection in deep caries management, such as hard setting calcium hydroxide, mineral trioxide aggregate, Emdogain, and Biodentin. These materials have their own advantages and disadvantages. In this study, we only focused on the hard setting calcium hydroxide. The hard setting calcium hydroxide can help in laying down reparative dentin, which is the goal in deep caries management, preventing bacteria from invading the pulp, causing pulp pathology. The biggest concern in deep caries management is hard setting calcium hydroxide exhibits poor sealing properties, which resulted into microleakage.[15] Therefore, good restorative material is required to seal over the hard setting calcium hydroxide.[16]

Our study compared the micro gaps between two different types of base materials; SDR and Ketac N100 in relation to Dycal®. These materials have similar degrees of viscosity with approximately equal filler load: SDR® has 68% by weight of filler,[13] whereas Ketac™ N100 consisted of approximately 69% by weight filler load.[9],[11] The viscosity of the material influenced the formation of the hybrid layer and the high filler content resulted in lower polymerization shrinkage.[13]

In this study, we found that SDR® has the capability of adapting closely to hard setting calcium hydroxide (Dycal®) and showed lesser gap interface with Dycal® when compared to Ketac™ N100. This finding was explained by the fact that SDR® was designed to be used as a base in Class I and II restorations due to its superior curing efficiency and low polymerization shrinkage. A study by Van Ende et al.[17] found that SDR® was able to maintain the adhesive interface integrity and exhibited excellent bond strength at the cavity bottom with high C-factor class I cavities. In addition, SDR® was a recommended material for base material due to its self-leveling property, which contributed to the superior adaptation to the cavity walls.[18]

Abd El Halim and Zaki[9] in their study found that Ketac™ N100 had the lowest microleakage scores compared to other resin-modified glass ionomers. Nandana et al.[19] also reported less microleakage for the cavities restored with Ketac™ N100. This could be explained by the fact that bonded nanofillers and nanoclusters have better bonding properties. In addition, polymerization shrinkage was reduced when the filler loading was increased, and the size of the filler was decreased.

However, in this study, we found that all samples of Ketac™ N100 showed gap formation with Dycal®. This finding was supported by Peliz et al.[20] who found that hard setting calcium hydroxide did not adhere to Vitrebond or dentin. Later, Oliveira et al.[21] also found an increased polymerization shrinkage stress at the adhesive interface when RMGIC was used as a stress-absorbing layer in composite restorations. With increased polymerization shrinkage stress, there was gap formation at the RMGIC-adhesive interface. Therefore, in this study, we found that no hybrid layer was formed between Dycal® and Ketac™ N100. Magdy et al.[22] claimed that the primary goal of restoration was a tight marginal seal as demineralization may occur along its cavity wall and stated that when a gap was formed it can provide a pathway for bacteria to invade underlying dental tissue and resulted in the failure of restoration and secondary caries.

This study only assessed the interface between the two materials using SEM. This technique provided a more critical assessment of the efficiency of the restorative materials on the tooth structure. However, it did not show a direct relationship between visible fissure size and depth of leakage.[23] Using SEM also may lead to an increased number of cracked tooth samples or other artifacts in comparison to other alternative microscopic techniques. This was probably due to the drying process of the tooth samples before assessing them under SEM. Therefore, the findings from our study must be carefully applied clinically as SEM was used to evaluate microleakage, which could also cause dehydration that resulted in micro cracks and gap formation between Dycal®-Ketac™ N100 interfaces.

In addition, other factors may influence the formation of micro gap between the materials assessed in this study such as the direction of light curing and the technique for the placement of the materials. Class 1 cavity exhibits high configuration factor which tends to increase polymerization stress if the adhesive restorative material is placed in bulk placement and thick layer. To minimize this effect, the standardization in the thickness of the material has been done, which was approximately 1.5 mm. In terms of the technique for placement of the materials, both materials were dispensed according to the manufacturer's instructions. SDR® was dispensed using the capsule tip, whereas the nozzle tip was used for Ketac™ N100. Therefore, there was no issue of pulling the material away from the cavity with the instrument.

In this study, only the interfacial micro gaps were assessed using SEM. Therefore, in a future study, we would like to suggest other properties of these materials should be assessed as well.


  Conclusions Top


From this study, we concluded that SDR® showed lesser gap formation with hard setting calcium hydroxide (Dycal®) as compared to Ketac™ N100 suggesting SDR® as a better base material in deep caries management. Within the limitations of this study, SDR® is recommended to be used to seal over the hard setting calcium hydroxide (Dycal®) liner in deep caries management due to its superior adaptation to this material.

Acknowledgment

We would like to extend our greatest appreciation and gratitude to School of Dental Sciences, USM, for providing us funding (USM Short term grant 304/PPSG/61313110) and laboratory facilities. We also would like to thank all laboratory staff for guiding us through the entire process, including all the laboratory procedures and Assoc. Prof. Dr. Wan Muhamad Amir W Ahmad for statistical consultation.

Financial support and sponsorship

USM Short term grant 304/PPSG/61313110.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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    Tables

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