Remineralization of Artificial Dentin Lesion In vitro using Dental Nanomaterials.

BACKGROUND: Teeth in the human body are the most mineralized tissue, which contain both organic and inorganic components. Demineralization and remineralization of teeth occur continuously, but demineralization causes structural loss of a tooth. AIM: This study was done to find the effect of ceramic by adding mono-n-Dodecyl phosphate to ceramic in dentin remineralization.
MATERIALS AND METHODS: A total of sixty permanent intact tooth specimens were randomly divided into four equal groups: Group 1: control group, Group 2: dentin was etched and restored with plain ceramic restoration, Group 3: etched dentin restored with ceramic containing 2% mono-n-Dodecyl phosphate, and Group 4: etched dentin restored with ceramic containing 5% mono-n-Dodecyl phosphate. Each sample was immersed completely in simulated body fluid and was kept in an incubator at 37°C to simulate the human body environment. Knoop microhardness measurements were recorded at 10, 20, and 38 days.
RESULTS: Knoop microhardness of dentin (KHN) reduced to 32.6% after dentin was etched. No significant difference was found between group 2, 3 and 4 after 10 days. KHN value was increased and showed significant changes restored with group 2 and 3, group 3 showed nonsignificant changes.
CONCLUSION: Through this study, we found that Ceramic can be used as a remineralizing agent to restore marginal dentine around of the cavity and root lesions from secondary caries. Copyright:

INTRODUCTION

Teeth are the highly mineralized tissue in the human body, which contain both organic and inorganic components. Wear and remineralization of teeth occur continuously, but demineralization causes structural loss of a tooth.[1] Many dietary carbohydrates undergo fermentation, which produces acidogenic bacteria. Which further produces lactic acid, propionic acid, acetic acid leads to demineralization of enamel and dentine.[23] As dentine undergo ageing, numerous changes takes place to alter biomechanics and biochemistry of tissue.[45]

Many approaches have been implicated for remineralizing demineralized dentin. Recently, fluoride, amorphous calcium phosphate (ACP), or resin-based adhesives containing bioactive glass are novel approaches introduced to improve the resistance of bonded restorations to secondary caries.[6] However, many of the studies focused on remineralizing partially demineralized carious dentin, which was based on the concept of epitaxial deposition of calcium and phosphate ions over the existing apatite seed crystallites.[7]

In this study, dentin remineralization was evaluated by altering microhardness of dentin surface around ceramic.

MATERIALS AND METHODS

Sixty permanent, noncarious, upper and lower, anterior and posterior teeth were selected, which underwent extraction for orthodontic or periodontic reasons and stored in 0.5% chlorophyll solution. Carious teeth were excluded.

Before the initiation of study, all teeth were cleaned by a ultrasonic scaler and casted in self-cure dental acrylic resin, only exposing the buccal and lingual surfaces of the tooth. Then, the buccal/lingual surfaces were wet grounded to obtain a smooth dentin by using grits, and final polishing was done by using alumina powder to obtain a smooth and polished surface. The mean Knoop hardness number [KHN] microhardness value was calculated by making four indentations in the dentin surface.

Demineralization and cavity preparation

To evaluate the outcome, initially, the dentin was demineralized and etching was done by 37% phosphoric acid for 5 s to expose the dentin collagen. All the specimens were soaked in deionized water and then dried, after which, KHN of the etched dentin was evaluated.

A total of sixty tooth specimens were randomly divided into four equal groups as follows:

Group 1: Control group

Group 2: Dentin was etched and restored with plain ceramic restoration

Group 3: Etched dentin restored with Ceramic containing 2% mono-n-Dodecyl phosphate

Group 4: Etched dentin restored with Ceramic containing 5% mono-n-Dodecyl phosphate.

Ceramic capsules were mixed using an amalgamator for 5 s according to manufacturer's instructions. For Groups 3 and 4, 2% and 5% surfactant i.e. mono-n-dodoecyl phosphate mixed with ceramic. Then, mono-n-Dodecyl phosphate (surfactant) powder was weighed at 2% and 5% concentration and mixed with ceramic paste.

For keeping the specimen simulated, body fluid (SBF) was prepared according to the instructions of the International Organization for Standardization. Table 1 lists the reagents which were required for the SBF solution. SBF was kept in a plastic bottle, and each sample was immersed entirely and was kept in an incubator at 37°C to simulate the human body environment.

Table 1

Change in Knoop values at different intervals

Restoration type	Baseline KHN (SD)	Postetching filling KHN (SD)	Post 10 days KHN (SD)	Post 20 days KHN (SD)	Post 38 days KHN (SD)
Control group	104.2 (20)	72.2 (14.2)	72.2 (15.0)	73.2 (14.4)	74.1 (16.2)
Ceramic			100.1 (22.3)	116.6 (21.4)	125.0 (17.1)
Ceramic with 2% surfactant			90.1 (21.4)	112.4 (18.1)	126.1 (23.4)
Ceramic with 5% surfactant			92.2 (17.5)	101 (20.0)	111.4 (19.3)

KHN: Knoop hardness number, SD: Standard deviation

KHN test was done at 10, 20, and 38 days of interval. At each test, four indentations were made on the sample of approximately 75 μm area away from the filling margin in the dentin surface.

At each interval, the mean KHN of all teeth in each group was calculated. Scanning electron microscope (SEM) was used to evaluate dentin surface after every testing period.

Data were expressed in KHN, and ANOVA was applied to analyze repeated measure amongst group using SPSS 21.0 Armonk (2012). Statistical significance was set at P = 0.05.

RESULTS

ANOVA showed the increase in KHN values of Group 2, that is, plain ceramic, which was not significant after 10 days of postrestoration, but after 20 and 38 days of restoration, the KHN value depicted a significant increase in hardness values compared to the etched values. In addition, a significant change was found in the values between 10 and 38 days.Table 2 showed KHN value significance over different time period for plain ceramic in group 2, 3 and 4. Follow up for 10 days, 20 days and 38 days showed no statistical significance as depicted in Table 3. KHN values of Group 3 were statistically not significant (P < 0.05) after 10 days of restoration. After 20 and 38 days of restoration, a statistically significant increase in hardness values versus etched values. Also, 10 versus 20 versus 38 days, shows statistically significant change. Group 4 showed increase in KHN values which were statistically not significant after 10 days of restoration. After 20 and 38 days of restoration, there was a significant increase in hardness values versus etched values. 10 days versus 20 days, 20 days versus 38 days showed no statistical significance as depict in Table 3.

Table 2

Knoop hardness number value significance over different time periods for plain ceramic in Groups 2, 3, and 4

Time period	Significance of KHN
	Group 2	Group 3	Group 4
Etching versus 10 days	NS	NS	NS
Etching versus 20 days	S	S	S
Etching versus 38 days	S	S	S
10 days versus 20 days	NS	NS	NS
10 days versus 38 days	S	S	NS
20 days versus 38 days	NS	NS	NS

S: Significant, NS: Not significant, KHN: Knoop hardness number

Table 3

Microhardness values from baseline and etched dentin with time interval in percentage

Restoration type	Baseline (%)			Etched dentin (%)
	10 days	20 days	38 days	10 days	20 days	38 days
Control group	32.68	31.5	30.5	0.03	0.7	1.38
Plain ceramic	6.56	9.1	18.1	17.47	30.30	36.6
Ceramic with 2% surfactant	13.65	8.5	22.95	13.95	30.5	39.1
Ceramic with 5% surfactant	13.76	3.48	4.6	15.55	21.76	28.66

DISCUSSION

This study shows that restoring dentin lesions with ceramic remineralizes dentin by about 75 μm from the margins of the restoration. For this study, etching was done by using 37% phosphoric acid gel to demineralize the dentine surface. The semi-electron micrographs of a specimen which were restored with ceramic restoration showed a nano-size particle covering the dentine surface and filling the dentinal tubules partially.

In our study, we found adding 2% surfactant to ceramic increases the remineralization over time in comparison to plain ceramic restoration, whereas adding 5% surfactant to ceramic does not show significant results as it might decrease the effect of ceramic.

Zhang S et al., (2013)8 suggested that there are various ways to estimate dentine mineralization, such as SEM and transmission electron microscopy,[9] Raman spectroscopy,[10] X-ray diffraction,[11] microcadiography,[12] micro-computed tomography scanning,[13] and nano-indentation, to evaluate microhardness.[14]

Resistance to local deformation is known as microhardness. For dental materials, two microhardness tests are commonly used, that is, Knoop and Vickers hardness tests. Both tests can evaluate fracture resistance,[14] modulus of elasticity, and yield strength.[15]

As mineral content increases, Knoop hardness value also increases and vice versa. In our study, KHN was evaluated at a site close to [DEJ], and the results were similar to that of Mahoney et al.[16] Cavalcanti et al.[17] used bio-active glass and polyacrylic acid-modified bioactive glass powders in white spot lesion of enamel and showed that when mineral content increases Knoop hardness value increases. Knoop microhardness values of dentine for baseline measurements range from 70 up to 90 depending on the location of tooth and the area of indentation. Anterior teeth have lower hardness value than posterior teeth. Chanya et al. studied the microhardness of superficial and deep sound human dentin using a Knoop indenter.[18]

In our study, we used SBF to mimic saliva for providing phosphate, which is used widely for biomineralization. Human saliva was not used for two reasons – first, the duration of the study was long, so sterility might get hampered, and second a large amount of saliva was required, which was difficult to obtain.

CONCLUSION

In our study, we found that ceramic can remineralize, demineralized dentin and the rate of remineralization increases by adding 2% surfactant to plain ceramic, while adding 5% surfactant to ceramic cement decreases the remineralization process. Through this study, we found that Ceramic can be used as a demineralizing agent to restore root lesions and marginal dentine which helps to reduce secondary caries. CPP-ACP material has the highest amount of evidence to support its use as a demineralizing agent. Ceramic use still needs to be verified.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.