ORIGINAL RESEARCH ARTICLE

 

Clinical effectiveness of light-curing units of the School of Dentistry of the Federal University of Goias

 

 

Laís Santos Gonçalves^I; Mércia Bráulio Gonçalves^I; Marília Morais Martins^I; Gersinei Carlos de Freitas^I; Lawrence Gonzaga Lopes^I; Terezinha Jesus Esteves Barata^I

^IDepartment of Prevention and Oral Rehabilitation, School of Dentistry, Federal University of Goias – Goiânia – GO – Brazil.

Corresponding author

 

 

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ABSTRACT

Introduction: The clinical longevity of the procedures is directly associated to the adequate activation (photopolymerization) of adhesive restorative materials.
Objective: To evaluate and compare by allocation the conservation status and power density of the light-curing units available at the School of Dentistry of the Federal University of Goias (FO/FUG) for clinical care.
Material and methods: The following information and specific techniques of all light sources existing at FO/UFG, available for clinical care in 2011, were collected: dental/ambulatory clinic where they are located, type of source [device of halogen light and light-emitting diode (LED)], brand, parallelism test (halogen light sources), state of conservation of the light transmitter tip, density of the potency/intensity/irradiance in mW/cm2 and acquisition date. The data obtained were submitted to one-way ANOVA (Analysis of Variance) and Turkey test for multiple comparisons (P < 0.05).
Results: In the second half of 2011, FO/UFG had 20 light sources (04 halogens and 16 LEDs), of which 90% were found in inadequate condition and 55% of those with power density less than 300 mW/cm2. There was no statistically significant difference in the power density between halogen and LED sources tested (P = 0.526). Likewise, no statistical difference was observed between the power density of the light sources (LED) placed at the Clinic II and III (P = 0.479). Also there was no statistically significant difference between the light sources (LED Halogen X) at the Clinic I (P = 0.943).
Conclusion: The light sources regardless of the clinic in which they were located presented mostly with inadequate clinical effectiveness in terms of their conservation status and power density.

Keywords: Endodontics; root canal preparation; gutta-percha.

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Introduction

The advancement of aesthetical Dentistry is inter-related to the improvement of both the adhesive restorative materials and the light-curing systems for activation of these materials ^3,15,22.

Among the adhesive materials available in dental market, resin composites have been increasingly used in current oral rehabilitation because they attend the function and aesthetical expectations ^3,13.

Resin composites are composed by three main components: organic matrix, inorganic filler and bonding agent ¹⁴. Bis-GMA (bisphenol A-glycidyl methacrylate) and/or UDMA (urethane dimethacrylate), associated with monomers of low molecular weight as TEGDMA (triethylene glycol dimethacrylate) and EGDMA (ethylene glycol dimethacrylate), comprised the components of the organic matrix ⁷. The inorganic filler particles within the organic matrix aim to ameliorate the mechanical properties, viscosity and degree of conversion of the resin composites ²³. The silane, on the other hand, is the bonding agent most common in the composition of resin composites with the aim of linking the filler particles to the organic matrix. The accelerator/initiator system completes the composition of the resin composites, which can be chemically or physically activated by this system. The chemical activation occurs through a reaction between the benzoyl peroxide and the tertiary amine respectively within the base paste and the catalyst paste ¹². On the other hand, the physical activation occurs when the photoinitiators within the resin composites are sensitized by the light sources or light-curing devices ⁷. Among the photoinitiators, camphorquinone can be emphasized which exhibits a wavelength around 450 to 500 nanometers, with absorption peak at the 460 nm band of light ²¹.

Among the light sources available in dental market, the light emitting diode devices (LEDs) have been an alternative to the halogen light sources ¹⁶. They emit light at specific and narrow wavelength bands, generally at the range between 440 and 500 nanometers, making them an efficient light source for resin composites ^15,19,24.

Additionally to the efficiency in photoactivation, LEDs are also a light source of longer clinical durability, lower cost, and lower maintenance than other light sources ^8,15,19.

Regardless of the activation system (chemical or physical) of a resin composite, its activation aims to obtain a uniformly and deeply high conversion of the material, associated with low stress of contraction therefore assuring the clinical longevity of the restoration ⁶. Thus, the success of the restorative procedure using resin materials is directly related to the adequate activation of the restorative procedure [25]. Concerning to the physical activation (photopolymerization) of resin composite, some factors are essential: density of potency/intensity/irradiance, time of exposure, distance from the light transmitter tip to the material to be light-cured, and properties of the resin composites ^1,6.

To obtain the adequate characteristics of the resin composites, most of the manufactures recommend the use of an intensity of light/irradiance or minimum power density of 400 mW/cm² ^5,11 associated with an exposure time between 20 and 40 seconds ⁹.

Still regarding to the distance from the transmitter tip to the resin material to be light-cured, it is emphasized that the distance should be as close to the material as possible because the light intensity tend to decrease as the tip is moved away ⁶.

Consequently, the lack of photoactivation is one of the main factors limiting the clinical success of the restorations with resin composites ^3,19,20. This occurs because the lack of photoactivation of the resin composite mostly causes the superficial staining and marginal microleakage ¹⁸.

These aspects are related to the improper polymerization of the resin composite and to the increase in the content of the residual monomers ². Thus, the conservation of the light sources, and consequently, their power density may influence negatively on the mechanical and physical properties of the resin materials. In this context, the aim of this present study is to evaluate the conservation and compare the power density of the light sources available in the School of Dentistry of the Federal University of Goias (FO/UFG) used in the clinical care. The null hypothesis is that the light sources existing in the clinics of FO/UFG had similar conservation and power density.

 

Material and methods

The following information and technical specifications of all light sources existing in the clinics of FO/UFG and available for clinical care were gathered: the clinic where the device was located, type of source (halogen and LED), brand, parallelism test (halogen light sources), state of conservation of the light transmitter tip, density of the potency/intensity/irradiance in mW/cm2 and acquisition date.

The parallelism test was conducted for the halogen light sources. This test assess the performance of the optical fiber through the contact of the light transmitter tip onto a text printed, when it is possible to visualize it with distinctness the parallelism is considered as positive; if the text is blurred the text is considered as negative ³.

The light intensity or power density of each light source was verified through a radiometer (Curing Radiometer Model 100 p/n – 10503, Demetron Research Corp., USA), according to the protocol proposed by Marson et al. ¹⁵ in mW/cm². To measure the power density, the active tip of the light source was placed centrally and perpendicularly to the radiometer and then three readings were performed, so that an arithmetic average was obtained. The first reading was executed for 10 seconds after the light source was switched on, the second and third readings were carried out consecutively with intervals of 30 seconds between each other.

The data obtained were submitted to descriptive statistical analysis, one-way analysis of variance (Anova), and Tukey test for multiple comparisons. The level of significance adopted was 5% (P < 0.05).

 

Results

In the second semester of 2011, FO/UFG had 20 light sources, of which 4 were halogens (Dabi Atlante) and 16 were LEDs [DMC (4), Schuster (9) and Sanders (3)]. These light sources were used in the Dentistry graduation and post-graduation courses and were located at 4 dental clinics (figure 1).

 

 

 

The light sources were employed in nine disciplines of graduation: Primary Care Clinic I and II, Children's Clinic I and II, Internship in Integrated Clinical I, II, III and IV and Emergency Clinic. Of these disciplines, the Emergency Clinic is taught in its own clinic, two disciplines are taught in Clinic I (Children's Clinic I and II), two in Clinic II (Primary Care Clinic I and II) and four disciplines in Clinic III (Integrated Clinic I, II, III and IV). This totalized about 100 hours per week of usage of the clinics for the graduation activities. Eventually, the discipline of Surgery and the Extension projects as well as the post-graduation courses utilized the clinics and consequently the light sources when necessary. Concerning to the time of acquisition, it was observed that all light sources of FO/UFG were acquired for more than six months prior to the study, and there had not been any program of periodical preventive maintenance.

In relation to the conservation state, it was observed that 90% of the light sources of FO/UFG showed an inappropriate conservation state, with cracks and/or fractures, as well as residues of resin composite and/or adhesive agent in the light transmitter tip. This study still revealed that 75% of the halogen transmitter light tip exhibited a negative parallelism.

Concerning to the power density, 55% of the light sources showed density lower than 300 mW/cm2 (50-225 mW/cm2) and 35% of the sources exhibited density greater or equal to 400 mW/cm2 (400 – 625 mW/cm2) (figure 2).

 

 

 

The power density values in mW/cm² of the light sources of the clinics of FO/UFG are seen in tables I and II and are divided per type of source and location in the clinic.

 

 

 

 

 

There were no statistical significant differences in the power density among the LED light sources located at the Clinics II and III (P = 0.479). Additionally, there were no statistically significant differences between LED and halogen light sources at Clinic I (P = 0.943). Based on these results, the null hypothesis was accepted.

 

Discussion

This present study revealed an inadequate conservation state of the light sources available for the clinical care at FO/UFG. Similar situation was observed by Baldi et al. ³ in the School of Dentistry of the State University of Ponta Grossa, in which 69.23% of the light sources were inadequate for use. Likely, in the Dentistry Clinic of the State University of Londrina, Beltrani et al. ⁴ observed that, regarding to the conservation state of the light transmitter tips, 91.7% exhibit debris, 83.3% were not capable of transmitting light and 16.7% showed any type of fracture.

It is important to emphasize that the performance of the halogen light sources can be decreased by the inadequate maintenance of the optic fiber and light transmitter tip ^4,17. It is important to consider that the inadequate conservation of the light sources is related to a smaller intensity of light emission ^3-5,15,27. This premise was corroborated by the results obtained by this present study. It can be affirmed that the conservation state of the light sources was directly related to the power density observed. Pascotto et al. ¹⁷ still emphasized that the adequate photopolymerization of a resin composite is linked to the light intensity and to the exposure time. It is known that the halogen light devices demand a minimum light intensity of 400 mW/cm² for the adequate photoactivation of the resin composites. On the other hand, LED sources required a minimum light intensity of 300 mW/cm² and at least 20 seconds of exposure time ²⁶.

This present study observed that 65% of the light sources of FO/UFG exhibited power density smaller than 400 mw/cm² (figure 2). Similar condition was found by Borges et al. ⁵ in the dental clinics of the Federal University of Maranhao. The authors verified that 68% of the light sources tested showed power density smaller than 400 mw/cm².

Likely, studies on the evaluation of the power density in private dental offices have observed these same outcomes, such as those by Freitas et al. ¹⁰ in the city of São Luís (MA) and Marson et al. ¹⁵ in Maringá (PR). Freitas et al. ¹⁰ observed that 46.01% of LED light sources tested exhibited power density smaller than 100 mW/cm²; 44.17% showed power density between 100-400 mW/cm²; and 9.82% presented density greater or equal to 400 mW/cm². For the halogen sources, the authors verified a density between 100 and 400 mW/cm² in 94.73% of the sources tested, while in 5.27% they found an intensity lower than 100 mW/cm²; none light source showed intensity greater than 400 mW/cm². Marson et al. ¹⁵ found that 50% of the halogen light sources exhibited power density above 300 mW/cm², 20% between 200-300 mW/cm² and 30% lower than 200 mW/cm².

The literature has described that this clinical situation can result in aesthetic involvement, marginal microleakage, and decrease of the physical and biological properties of the resin composites ⁷.

Based on this aforementioned discussion, it can be affirmed that the conservation state of the light source directly interfered in the photoactivation effectiveness. Baldi et al. ³, Beltrani et al. ⁴, Borges et al. ⁵ and Freitas et al. ¹⁰ affirmed that it is necessary the periodical maintenance of the light sources, once their conservation state is related to the power intensity and consequently with the polymerization effectiveness. Therefore, the clinic staff must be aware of these requirements regarding the use of the light sources and the need of a preventive maintenance protocol to achieve the photopolymerization effectiveness.

 

Conclusion

• The clinical effectiveness of the light sources was dependent on their conservation state and power density, which were inadequate for most of the sources tested;

• The light sources in clinical use exhibited similar conditions of conservation state and power density, regardless the clinic where they were located.

 

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Corresponding author:
Terezinha Jesus Esteves Barata
Avenida Universitária, esquina com 1.ª Avenida, s/n, Setor Universitário
CEP 74605-220 – Goiânia – GO – Brasil
E-mail: terezinhabarata@yahoo.com.br

Received for publication: February 14, 2013
Accepted for publication: February 22, 2013