Journal of Indian Society of Pedodontics and Preventive Dentistry
Journal of Indian Society of Pedodontics and Preventive Dentistry
                                                   Official journal of the Indian Society of Pedodontics and Preventive Dentistry                           
Year : 2012  |  Volume : 30  |  Issue : 3  |  Page : 201--205

Effect of light-emitting diode and halogen light curing on the micro-hardness of dental composite and resin-modified glass ionomer cement: An in vitro study


M Bhalla1, D Patel2, ND Shashikiran3, RM Mallikarjuna4, TM Nalawade5, HK Reddy6,  
1 Department of Pedodontics and Preventive Dentistry, Inder Prastha Dental College and Hospital, Ghazizbad 46/1 Site No. IV, Industrial Area, Sahibabad, Ghazizbad, India
2 Department of Orthodontics, Inder Prastha Dental College and Hospital, Ghazizbad 46/1 Site No. IV, Industrial Area, Sahibabad, Ghazizbad, India
3 People's College of Dental Sciences and Research Centre, People's Campus Bhanpur, Bhopal, India
4 Department of Pedodontics and Preventive Dentistry, K. M. Shah Dental College and Hospital, Sumandeep Vidyapeeth, Piparia, Waghodia, Vadodara, India
5 Department of Pedodontics and Preventive Dentistry, Manubhai Patel Dental College and Charitable Dental Hospital, Vishwajyoti Ashram, Nr. Vidyakunj School, Munjmahuda, Vadodara, India
6 Department of Pedodontics and Preventive Dentistry, HKDET Dental College and Hospital, Humnabad, India

Correspondence Address:
M Bhalla
Department of Pedodontics and Preventive Dentistry, Inder Prastha Dental College and Hospital, 46/1 Site No. IV Industrial Area, Sahibabad, Ghaziabad- 201 010
India

Abstract

Aims : This in vitro study was conducted to evaluate and compare the micro-hardness of composite resin and resin-modified glass ionomer cement using light-emitting diode (LED) and halogen curing and also to inter-compare the effect of LED and halogen curing. Materials and Methods : The study sample comprised of 4 stainless steel plates with a thickness of 2 mm. For these stainless steel plates, holes were made to a diameter of 3 mm. The samples were divided into 4 groups of 8 each and labeled as group I, group II, group III, group IV, thus making provision for the two different modes of light exposure. In each group, the hole was restored with its respective restorative material and cured with light-curing unit according to manufacturer instructions. The results were statistically analyzed using Mann-Whitney test. Results and conclusion: It was concluded that the curing efficacy of the LED lamp was comparable to that of conventional halogen lamp, even with a 50% reduction in cure time, and resin composite (Filtek Z-250) presented the highest hardness values, whereas complete hardening of resin-modified glass ionomer cement (RMGIC) (Vitremer) was observed because of its self-curing system even after the removal of light source.



How to cite this article:
Bhalla M, Patel D, Shashikiran N D, Mallikarjuna R M, Nalawade T M, Reddy H K. Effect of light-emitting diode and halogen light curing on the micro-hardness of dental composite and resin-modified glass ionomer cement: An in vitro study.J Indian Soc Pedod Prev Dent 2012;30:201-205


How to cite this URL:
Bhalla M, Patel D, Shashikiran N D, Mallikarjuna R M, Nalawade T M, Reddy H K. Effect of light-emitting diode and halogen light curing on the micro-hardness of dental composite and resin-modified glass ionomer cement: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2012 [cited 2019 Dec 6 ];30:201-205
Available from: http://www.jisppd.com/text.asp?2012/30/3/201/105011


Full Text

 Introduction



Dental profession now embraces the concept of minimal intervention and conscious effort to practice maximum conservation of tooth structure. This has been very true in case of pediatric dentistry too where the esthetically pleasing materials like composite, compomer, and resin-modified glass ionomer cement (RMGIC) have tremendously changed the concept of today's practice. Advantages of resin other than cosmetic include relatively low thermal conductivity, preservation of tooth structure in cavity preparation, and advances in the stability of compositional properties of the material.

RMGIC is an important advancement in glass ionomer technology that has influenced dentistry for children. [1] Resin-modified glass ionomer, which was introduced to decrease sensitivity, decreases initial hardening time and handling difficulties, but substantially increases wear resistance and physical strength of the cement and improve early weak mechanical strength of conventional glass ionomer, while preserving their clinical advantages i.e., esthetics, self-adhesion to dental tissue, fluoride release, and thermal insulation. [1]

Halogen-curing light, broad emission spectrum initiates polymerization of all known photo-activated resin-based dental materials. However, the principle output from these lamps is infrared energy, with the generation of high heat. The relatively inefficient emission typically requires corded hand pieces with noisy fans. [2] The halogen bulb generates high heat, which degrades the bulb's components over time. Therefore, halogen bulbs have a limited effective lifetime of approximately 100 hours. [3] LEDs have lifetimes of more than 10,000 hours and undergo little degradation of output over this time. LEDs do not require filters to produce blue light, are resistant to shock and vibration, and consume little power in operating. [3] This current study is designed in vitro with an aim to evaluate and compare the micro-hardness of composite resin and resin-modified glass ionomer cement using LED and halogen-curing and also to inter-compare the effect of LED and halogen-curing on the micro-hardness during curing of composite resin and resin-modified glass ionomer cement.

 Materials and Methods



In the present study, micro-hardness of composite resin (Filtek Z 250) and resin-modified glass ionomer (Vitremer) are compared. 32 sound single-rooted premolar teeth, which were extracted for orthodontic purpose and stored in saline till the study was done. The study sample comprised of 4 stainless steel plates with a thickness of 2 mm. For these stainless steel plates, holes were made to a diameter of 3 mm. In each group, the hole was restored with its respective restorative material and cured with light-curing unit according to manufacturer instructions.

The samples were divided into 4 groups and labeled as Group I, Group II, Group III, Group IV, thus making provision for the two different modes of light exposure.

Group I : Holes filled with composite and cured with halogen LCU.Group II : Holes filled with RMGIC and cured with LED LCU.Group III : Holes filled with composite and cured with LED LCU.Group IV : Holes filled with RMGIC and cured with halogen LCU.

The metal plate was placed on a glass slab, and the hole was overfilled with composite material and RMGIC, respectively. After placement of a cellophane strip, a glass plate was applied and held under finger pressure to allow excess material to escape. Group II and group III holes were cured by LED LCU for 20 sec. Group I and group IV holes were cured by halogen LCU for 40 sec. Micro-hardness test was conducted with the surface closest to and furthest from the light source i.e., the top surface and bottom surface, respectively, were subjected to a Vickers micro-hardness test by using micro-hardness tester machine at a load of 100 g for 10 sec., and the data was obtained. Results are expressed as mean ± standard deviation. Mann-Whitney test was used for comparing micro-hardness between the groups. For the entire test, a P value of 0.05 or less was considered for statistical significance.

 Results



[Table 1] shows range, mean, and standard deviation for the micro-hardness values of composite and Vitremer at the top and bottom surfaces after curing with LED and halogen light-curing units. Composite top surface micro-hardness value after curing with LED ranged from 61.0 to 75.5 VHN with a mean value of 68.9 VHN and a standard deviation of ±6.0, and the bottom surface showed the range from 32.0 to 58.9 VHN with a mean value of 43.3 VHN and a standard deviation of ±7.5. After curing with halogen LCU composite top surface, micro-hardness value ranged from 60.0 to 82.1 VHN with a mean value of 75.2 VHN and a standard deviation of ±7.4, and the bottom surface showed the range from 35.3 to 58.0 VHN with a mean value of 45.5 VHN and a standard deviation of ±9.4. Similarly, vitremer top surface micro-hardness value after curing with LED ranged from 39.0 to 51.0 VHN with a mean value of 46.0 VHN and a standard deviation of ±3.8, and the bottom surface showed the range from 36.1 to 55.0 VHN with a mean value of 43.4 VHN and a standard deviation of ±6.3. After curing with halogen LCU vitremer top surface, micro-hardness value ranged from 40.0 to 55.4 VHN with a mean value of 49.6 VHN and a standard deviation of ±5.1, and the bottom surface showed the range from 35.0 to 52.4 VHN with a mean value of 45.0 VHN and a standard deviation of ±6.7.{Table 1}

[Table 2] shows the comparison between the top surface and the bottom surface micro-hardness value for composite, and it also shows the inter-comparison between the LED and halogen LCU. In case of LED composite, top surface showed the mean value of 68.9 VHN and the bottom surface showed the value of 43.3 VHN with a difference of 25.6 and a significant P value < 0.01. In case of halogen LCU, composite top surface showed the mean value of 75.2 VHN and the bottom surface showed the value of 45.5 VHN with a difference 29.7 and a highly significant P value < 0.001. When LED and halogen LCU were inter-compared, the top surface and the bottom surface showed the P value of 0.07 and 0.95, respectively, which were non-significant.{Table 2}

[Table 3] shows the comparison between the top surface and the bottom surface micro-hardness value for Vitremer, and it also shows the inter-comparison between the LED and halogen LCU. In case of LED, Vitremer top surface showed the mean value of 46.0 VHN and bottom surface showed the value of 43.4 VHN with a difference of 2.6 and a non-significant P value of 0.27. In case of halogen, Vitremer top surface showed the mean value of 49.6 VHN and the bottom surface showed the value of 45.0 VHN with a difference of 4.6 and a non-significant P value of 0.08. When LED and halogen LCU were inter-compared, the top surface and the bottom surface showed the P value of 0.10 and 0.75, respectively, which were statistically non-significant.{Table 3}

[Table 4] shows the inter-comparison of micro-hardness between composite and vitremer at the top and bottom surface, cured with LED and halogen LCU. In case of LED, composite top surface showed the micro-hardness value of 68.9 VHN, whereas vitremer top surface showed the value of 46.0 VHN with the significant P value < 0.01. And, the composite bottom surface showed the value of 43.3 VHN, whereas vitremer bottom surface showed the value of 43.4 VHN with a non-significant P value 0.96.{Table 4}

In case of halogen, composite top surface showed the micro-hardness value of 75.2 VHN, whereas vitremer top surface showed 49.6 VHN with the highly significant P value < 0.001. And, the composite bottom surface showed the value of 45.5 VHN, whereas vitremer bottom surface showed 45.0 VHN with the non-significant P value 0.99.

 Discussion



A great deal of dental research has led to the development of various newer light-curing restorative materials and curing units that provide us long-term clinical success. [4]

This in vitro study was carried out to evaluate the effect of light-emitting diode and halogen light-curing on micro-hardness of composite resin (FILTEK Z-250) and RMGIC (Vitremer).

As the occlusal surface of teeth is considered to be one of the susceptible surfaces for caries assault, and the occlusal cavities could be easily standardized, class I restorations were thought to be more practical for this study. [5] Micro-hardness is a typical parameter for indicating the degree of polymerization of resin composites. However, adequate surface hardness does not ensure proper polymerization throughout the restoration. Thus, hardness analysis must also be performed on the bottom surface of the specimens, since insufficient polymerization of this area may increase the risk of bulk and marginal fracture. Other possible complications associated with the inadequate curing of resin composite and RMGIC include secondary caries and adverse tissue reactions. [6]

Several methodologies have been proposed in order to evaluate the polymerization of light-curing units. Yearn [7] has presented a review on three main methods to evaluate curing depth of the material: Scrape test, hardness test (Barcol, Vicker's and Knoop), and degree of conversion (multiple internal reflection spectroscopy and Laser Raman Spectroscopy). The author concluded that the hardness test provides the convenient and efficient method for evaluating curing depth. [6]

The resin composite presented the highest micro-hardness values after being cured by both the light source (Halogen or LED). The probable reason could be the size and content of filling particles in the organic matrix of microhybrid resin composites might have accounted for the highest micro-hardness values reported. [8],[9]

The resin composite showed the significant decrease in micro-hardness value from top to the bottom surface. A possible explanation for such performance would be the fact that the polymerization of these materials rely exclusively upon light activation. So, the surface closest to the light source showed more value. [10] Other reason could be, because of their small filler particles, which causes light to scatter, decreasing the effectiveness of the curing light, [11],[12],[13] whereas vitremer did not show any significant decrease in micro-hardness from top to the bottom surface, possibly due to the acid-base reaction and chemical-free radical polymerization that continue after the removal of the light-source and, therefore, ensure a complete hardening of the material. [10]

LED uses a single high intensity LED for light generation. This high intensity LED uses a substantially larger semi-conductor, which increases both the illuminated area and light intensity, enabling a 50% reduction in curing time. [14] The performance of this light was also comparable to that of halogen lamps that is micro-hardness values and offers the advantage of a 50% reduction in cure time. [14] A possible explanation for these results may be the fact that LED LCUs present a specific pattern of light emission, which is similar to the absorption spectrum of the camphoroquinone photoinitiator of resin composites and RMGIC. [15],[16],[17] This spectral purity allows total usage of the emitted light by LED, which does not happen with halogen. [18]

Polymerization of light-activated resin composites and glass ionomer cement causes temperature increase by an exothermic reaction process and by energy absorbed during irradiation. [19],[20]

 Conclusion



Based on the findings and within the limitations of this in-vitro study, it may be concluded that,

The second generation LED is an improvement over conventional halogen. The curing efficacy of the LED lamp was comparable to that of conventional halogen lamp, even with a 50% reduction in cure time.Resin composite (Filtek Z-250) presented the highest hardness values, whereas complete hardening of RMGIC (Vitremer) was observed because of its self-curing system, even after the removal of light source.

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