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| Year : 2007 | Volume
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| Issue : 1 | Page : 38-42 |
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| Fourier transform infrared spectroscopic evaluation - Degree of conversion of a packable, hybrid and flowable composite resin cured using a light transmitting post |
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Sridhar Vishnu, Sowmya Natesh Kumar, Deivanayagam Kandaswamy, Nagendrababu Venkateshbabu
Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Maduravoyal, Chennai, India
Click here for correspondence address and email
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 Abstract | | |
The introduction of light transmitting post paved the way for the composite resin to invade the root canal systems. Aim of the study was to evaluate the degree of conversion of a flowable, hybrid and packable composite resin after polymerizing the resin by using light transmitting post by using the Fourier transform infrared spectroscopy. Packable composite resin showed significantly lower degree of conversion values when compared to hybrid and flowable at the apical and middle third. Coronal third showed better conversion than middle third and apical third. Even though degrees of conversion values in the apical samples were low they fall well within the range of 50 - 70% which is considered adequate. A higher degree of conversion can be obtained for hybrid and flowable resin composite up to 14 mm length, if a light transmitting post is used along with an increased light curing time of 4 minutes.
How to cite this article:
Vishnu S, Kumar SN, Kandaswamy D, Venkateshbabu N. Fourier transform infrared spectroscopic evaluation - Degree of conversion of a packable, hybrid and flowable composite resin cured using a light transmitting post. J Conserv Dent 2007;10:38-42 |
How to cite this URL:
Vishnu S, Kumar SN, Kandaswamy D, Venkateshbabu N. Fourier transform infrared spectroscopic evaluation - Degree of conversion of a packable, hybrid and flowable composite resin cured using a light transmitting post. J Conserv Dent [serial online] 2007 [cited 2023 Jun 4];10:38-42. Available from: https://www.jcd.org.in/text.asp?2007/10/1/38/42279 |
| Introduction | |  |
Loss of dentin inside the root can lead to root fracture. The root dentin can be lost due to various factors like root caries, dentin defects, iatrogenic cause, and root resorption. Reinforcing the weakened root structure is an ideal method of rehabilitating the weakened tooth. Strengthening of the weakened portion would render the root capable of supporting a restoration, thereby continuing the usefulness of the tooth. With the advent of light transmitting post, the possibility of restoring the lost root dentin with composite resin became a reality [1] [2] . Composite resins with new bonding systems may prove to be an ideal alternative as their modulus of elasticity (5.7 - 25 GPA) is close to that of dentin (20 GPA). The composite resins bonds by hybridization with dentin on one side and bonds to the resin cement on the other side, which in turn bonds to the fiber reinforced composite post. Being made of same material with the modulus of elasticity being same as dentin, the whole tooth acts as a single unit [3] and thus helps in preventing fracture, by equally distributing stress over the entire bonded interface [4] [5] .
The most important factor to be considered in restoring root dentin is the selection of type of composite. A packable composite resin has improved strength [6],[7] , depth of cure and can be condensed like amalgam. This property may allow for good condensation of composite into the root canal. The handling properties of this material also allows for placement of this material in one particular area if need be. The flowable composite resin is low in filler content and hence has good flow properties. This material due to its low modulus of elasticity effectively dissipates stress. Hybrid resin composites have good strength neither too much flow nor too much of bulk. But the most important consideration should be that composite undergoes adequate polymerization. Incomplete polymerization could lead to inferior physical properties, higher solubility [8],[9] and monomer leaching which in turn leads to carcinogenicity and mutagenicity [10],[11] .
Hence a study was undertaken to evaluate the degree of conversion of a flowable, hybrid and packable - composite resin after polymerizing the resin by using light transmitting post by using the Fourier transform infrared spectroscopy (FTIR).
To study the degree of polymerization methods like FTIR [12],[13],[14] , Raman spectroscopy [15] , Knoop hardness [16] , magnetic resonance imaging [17] and differential scanning calorimeter [18] are available. In all the above methods FTIR is the only method to directly evaluate the carbon - carbon double bond conversion rate which is the true measure of the degree of conversion. Different kinds of composites need different time and intensity of light exposure for complete polymerization. The difficulty encountered in polymerizing the composite inside the root canal up to the apical third is the biggest challenge
| Materials and Methods | | |
Ten separable hollow dies were made with an uniform internal diameter of 4 mm and a length of 14 mm. The dies were made of highly polished steel. The die could be split exactly into two halves. These dimensions were chosen to evaluate the full range of possible light transmitting capabilities of the light transmitting post. The length 14mm was chosen so that the top 2mm could be sectioned and used as control, because light will fall on the exposed composite resin at the sites of the post. This will transmit more light and aid in better curing. So this 2mm can be used as control. The remaining 12mm was uniformly divided into coronal, middle and apical thirds. An internal diameter of4mm was used to simulate the worst possible clinical scenario, a tooth with weak, parallel walls.
Three types of composite resins were chosen as Group I,II,III respectively.
1) Packable, 63 % Filler Volume (Tetric Ceram HB)A3 Filler Size 0.04-3 Micrometer
2) Hybrid (Solitaire) A3, 60 65 % Filler Volume Filler Size 0.4-1 Micrometer
3) Flowable (3M ESPE Filltek) A3 47 % Filler Volume, Filler Size 0.6 -1 Micrometer
Light transmitting posts used.
a) Smooth post (Dentatus Luminex), Size 6 (1.8mm diameter)
The serrated post was eliminated from the study because it could not be removed once the composite resin was polymerized.
The composite resin was packed into the hollow die with a plastic instrument and the die was placed on a glass slab. The post was placed in the center using the centering hole in the die as a guide. Heraeus, transluxcllight curing unit with a power setting of 180 w was placed at the protruding 2mm of the light transmitting post. Exposure time was standardized to 4 minutes. Thirty samples were divided into three groups (Group I packable, Group II hybrid, Group III flowable), each group having 10 samples. Once the curing was completed the light trasmitting post was removed with a haemostat using a rotational force. The cured resin composite block was stored in a light proof container for 24 hrs. The samples were then sectioned using a diamond saw under water coolant. The top 2 mm of every block was used as a control. The remaining 12mm was sectioned into 3 equal parts of 4mm each (A - Coronal, B - Middle, C - Apical) From each of the sectioned disc a sample of less than 1 mm was sectioned approximately from the outer half. The sectioned sample was pulverized in a mortar and pestle. The powdered sample was mixed with potassium bromide powder in a ratio of 1: 1 00. This sample was put into a hydraulic pellatesir to make pellets of 13mm under a 7-ton hydrolic pressure. Infrared rays (4000 400cm-1) were passed through a pure potassium bromide pellet for 32 seconds to obtain a background value. Potassium bromide is used as it allows 100% infrared rays to pass through without any distortion. Then the pellet containing sample and potassium bromide was placed in the line of infrared waves (4000 - 400cm) for 32 seconds. The percentage of unreacted carbon - carbon double bonds (% C=C) was determined from the absorption intensities of carbon - carbon double bond (1638 cm - 1) These values are represented as graph values by the computer , that is connected to the FTIR machine. The degree of conversion was determined by subtracting the percentage of carbon carbon double bond from 100%.
Mean and standard deviation were estimated from the sample for each study group. Mean values were compared by one way ANOVA. Multiple range test by Tukey HSD procedure was employed to identify the significant, further one sample T-test was employed to compare the control value with other group means. In this study p < 0.05 was considered as the level of significance.
| Results | | |
Comparison of mean values of each subgroup with control group within each study group [Table 1].
In the study the degree of conversion values were the lowest in the apical third of all groups and between Group II and Group III there was no significant difference in the degree of conversion at all three levels.
Group I showed significant, lower degree of conversion values when compared to Group II and Group III at the apical and middle third. Coronal third of Group II showed better conversion than Group I.
| Discussion | | |
In this study a die that was 14mm long with an internal diameter, of 4mm was made. The average length of the root of a maxillary central incisor is 13mm. A minimum of 3mm apical seal is needed. Considering that curing is done from the area near the cingulum and the cingulum is located 4mm from the cervical area and additional 4mm was added and so a 14mm long die was made, to simulate the length of the post space. The top 2mm was used as a control and the remaining 12mm was sectioned into 3 disks of 4mm each. The diameter was made to 4mm because the average diameter of the root at the cementoenamel junction is 6mm. In case of canal diameter of 4mm, it can be assumed that the remaining root walls of only 2mm will need reinforcement. This 4mm internal diameter simulates the worst possible clinical scenario.
Pilot study was done with three samples for each group. During pilot study when reduced light curing time (90 sec) was tried out there was inadequate polymerization from the middle to apical third of the die, but the composite resin that had flown into the centring hole was adequately cured when clinically seen. This could be because the light rays that may have been internally reflected could have caused this to happen. With an increasing distance from the light source, the number of light rays available at the desired angle to get refracted may be less in number. Since Intensity = Energy x Exposure Time to compensate for the loss in intensity, exposure time can be increased [19] . In order to achieve a clinically well-cured sample, curing time was gradually increased. (Till 4 min where a good, hard sample could be obtained).
FTIR [12],[13],[14] was undertaken to assess the degree of conversion, though other methods like raman spectroscopy [15] , knoop hardness [16] , water sorption, magnetic resonance imaging [17] , differential scanning calorimeter [18] are available. This is because Raman Spectroscopy produces fluorescence which affects the conversion in the sample [15] , water sorption doesn't measure the degree of conversion directly, knoop hardness values and FITR values differ considerably as depth increases, magnetic resonance imaging can be used only for experimental purpose and not for regular study purposes and differential scanning calorimeter checks the thermal emission during a reaction [18] . These above mentioned methods do not directly evaluate the carbon - carbon double bond conversion rate which is the true measure of the degree of conversion. Since only FTIR does this, this was chosen in our study. FTIR is a way to determine the true conversion as it measures the residual double bond in the resin based composite and it is highly specific in determining degree of conversion [14] . The degree of conversion is a measure of the percentage of carbon - carbon double bonds that have been converted to single bonds, to form a polymeric resin. The higher the degree of conversion, better the strength. The unreacted carbon-carbon double bond in the sample will absorb infrared rays between the ranges of 1630 - 1730 cm-1. So in the samples tested, the value that lies between 1630 - 1730 cm-1 is chosen as the peak value of absorption.
The potassium bromide pellets are used as potassium bromide allows the infrared rays to pass through without any distortion. This can be kept as a background value, against which the amount of light absorbed is calculated by the computer and a graphical value is given depicting the percentage of light transmission against the wave numbers passed in 32 seconds. Earliest studies to check polymerization in root canals used KHN. Though the knoop hardness testing correlates with the degree of conversion testing, it has been shown that the degree of conversion values declines more rapidly than hardness, with increasing sample depth [20]
The reason for the decrease in the degree of conversion as the depth increased could be because of the increasing distance from the light source [9] . Though a light transmitting post is claimed to pass light along its length it doesn't sufficiently cure the resin composite at the sides. This is because lighttransmitting posts acts in a manner, similar to optical fibers, (total internal reflection) and carries some light rays to a focused area deep down its length. Since the light diffusing out through the sides of the post due to refraction may be less, and as intensity falls with increasing distance from the source, a short exposure time is not sufficient. (Intensity = Energy x Exposure time). Increasing the exposure time, in this study could be the reason for the degree of conversion of the composite resin in Group-II and Group III to fall within the acceptable range of43% 78% [21]
Degree of conversion of packable composite resin was less when compared to the other two groups. The reason for this could be the increase in filler loading of packable composites. The packable composite used in this study (tetric ceram HB) has a filler loading of 63 % by volume. Studies show that if there is an increase in the filler loading there will be a decrease in the degree of conversion . The relationship between monomer conversion and inorganic filler loading is inversely proportional as light transmission decreases with increasing filler loading. It has been shown in studies that smaller filler particles are most likely to scatter light especially those similar in size to wavelengths of light emitted from the curing source Since the packable composite used in this study not only has high filler loading (63% by volume) it also has microfiller particles (0.04mm), which may scatter light and hence hinder light penetration.
In the groups (II & III) the filler loading in both the composites are low (60 - 650/0 and 47% respectively) when compared to the packable (63% by vol). The flowable composite (Filltek) has 47% of filler by volume and the size of the fillers range between 0.6 - 1 mm. The decrease in the filler, the resin ratio proportionately increases the degree of conversion, and also the filler particle is a midfiller size particle and it can be assumed that light scattering is less compared to micro fills. Due to this reason the flowable has a better degree of conversion than the packable.
Since the filler particle size is almost similar to the flowable in the hybrid composite and the filler loading is also lesser, the hybrid too had better degree of conversion when compared to packable. All the samples showed better degree of conversion towards the coronal end. This is obviously because of the increasing proximity to the light source. Since the exposure time was increased to 4 minutes in this study it can be considered that more light penetration could have happened resulting in greater amount of polymerization in the coronal and middle thirds. Though the degrees of conversion values in the apical samples were low they fall well within the range of 43% - 78%, which is considered adequate.
The degree of conversion values for the packable in the coronal and middle third also falls within this range. Since, in this study the sample was taken from the outer portion of the 4mm disks in each group; it can be considered that the degree of conversion will be better towards the post.
| Conclusion | | |
From the results of our study, flowable and hybrid composite can be used to rehabilitate the dentin structure.
Adequate degree of conversion can be obtained for hybrid and flowable resin composite up to 14mm length, if a light transmitting post is used along with an increased light curing time of 4 minutes.
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Correspondence Address:
Sridhar Vishnu
Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Maduravoyal, Chennai
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0972-0707.42279
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