RESEARCH ARTICLE
Effect of Preoperative Occlusal Matrices on the Vickers Microhardness of Composite Disks Polymerized with QTH and LED Lamps RAQUEL CASTILLO-OYAGÜE, DDS, PHD*, PAUL J. MILWARD, MPHIL, MIMPT, LCGI/MARK WATERS, BSC, PHD†, ALICIA MARTÍN-CERRATO, DDS, PHD‡, CHRISTOPHER D. LYNCH, BDS, PHD, MFD, RCSI, FDS (REST DENT)§
ABSTRACT Purpose: This study aimed to assess the reliability of the preoperative occlusal matrix technique in terms of the surface Vickers microhardness (VMH) of the underlying composite restorative material. Materials and Methods: Two hundred microhybrid composite cylinders were built up and light-cured in a single-layer step, forming two experimental groups (N = 100) according to their heights (1.5 mm/2 mm). Each group was divided into five subgroups (N = 20) depending on the matrix thickness (no matrix/0.5 mm/1 mm/2 mm/3 mm). Half the specimens per subgroup (N = 10) were randomly polymerized with a quartz-tungsten-halogen (QTH) light-curing unit (LCU).The remaining half were cured using a light-emitting diode lamp.The top and bottom samples’ sides were tested for VMH at 1 hour and 24 hours post-curing using a universal VMH machine. A multiple analysis of variance with repeated measurements for the “surface” factor and the Student–Newman–Keuls test were run (α = 0.05). Bottom/top microhardness ratios were compared with the empirically accepted limit (0.8). Surface topography was analyzed under a scanning electron microscope. Results: The thinnest matrices provided the significantly best VMH values. LCU, disc height, and time also contributed to VMH. At 24 hours, 2-mm high discs polymerized with QTH resulted in inadequate microhardness ratios when 1-mm thick to 3-mm thick matrices were used. Conclusion: The thinnest matrices are the most recommendable ones.
CLINICAL SIGNIFICANCE The esthetics and occlusal reproducibility achieved with customized occlusal matrices fabricated before cavity preparation have been widely demonstrated. However, their effect on the physical properties of the restorations deserves further investigation. Although more studies are necessary, the thinnest matrices seem to be the most suitable to preserve the composite surface VMH and the curing depth. (J Esthet Restor Dent 27:203–212, 2015)
INTRODUCTION The reestablishment of an adequate anatomy is still a matter of concern in the case of posterior composite restorations in order to get harmonious esthetics and
cusp–fossa relationships with opposing teeth without the requirement of time-consuming adjustments.1–3 The chairside fabrication of a clear occlusal matrix before cavity preparation has been proposed for the obturation of “hidden” caries that keep the tooth morphology
*Professor, Department of Buccofacial Prostheses, Faculty of Dentistry, Complutense University of Madrid (U.C.M.), Pza. Ramón y Cajal, s/n, Madrid 28040, Spain † Senior lecturer in dental technology and biomaterial sciences, Department of Prosthetic Dentistry, University Dental School, Heath Park, Cardiff CF14 4XY, UK ‡ Associate professor, Department of Dentistry for Adults, European University (U.E.), C/ Tajo, s/n, Villaviciosa de Odón, Madrid 28670, Spain § Senior lecturer/consultant in restorative dentistry, Department of Adult Dental Health, University Dental School, Heath Park, Cardiff CF14 4XY, UK
© 2015 Wiley Periodicals, Inc.
DOI 10.1111/jerd.12156
Journal of Esthetic and Restorative Dentistry
Vol 27 • No 4 • 203–212 • 2015
203
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
intact.3 The matrix is placed over the occlusal cavity to light-cure the last composite layers. This device allows the final restoration to replicate the original structure and occlusion, require no or minimal finishing, diminish the incidence of superficial voids, reduce the flash at the interphase, and be optimally polymerized due to the anaerobic environment.2,3
Switzerland) were light-cured in a single phase and divided into two experimental groups (N = 100) according to their final height: group 1 had 1.5 mm (curing depth stated by the ISO-4049) (www.aenor.es), and group 2 had 2 mm (maximum depth of composite to be polymerized in a single-layer step, as recommended by manufacturers).
Although the occlusal reproducibility achieved with such appliances has been widely studied,2–4 their effect on the physical properties of the polymerized restoration remains unknown.2 Microhardness describes the wear resistance of resin composite and its ability to abrade or be abraded by opposing teeth or restorative materials.5 To date, the evaluation of microhardness has been widely used for testing the quality of polymerization and thus the efficiency of different light sources for stimulating the photoinitiators of composite resins.5,6 To define the “depth of cure” of light-curing units (LCUs), it is also common to calculate the ratio of bottom/top surface microhardness.7 Minimum values of 0.8 are empirically accepted to consider the bottom composite surfaces adequately polymerized.8,9
Each group of composite samples was divided into five subgroups (N = 20) depending on the thickness of the preoperative occlusal matrix utilized: subgroup 1 (control: no matrix), subgroup 2 (0.5 mm), subgroup 3 (1 mm), subgroup 4 (2 mm), and subgroup 5 (3 mm).
This is the first study that investigates the Vickers microhardness (VMH) of a composite restorative material to indirectly assess the reliability of the preoperative occlusal matrix technique. Several clinical parameters (matrix thickness, LCU, composite film height, and post-curing period) were simulated and combined in the experiment.
The respective matrices were put over the composite discs contained in nylon washers before being polymerized. A microscope slide was used as a support to obtain a flat bottom surface. A mirror beneath the glass slide reproduced the clinical reflection of the dentine.10
Preparation of Specimens
Half the specimens per subgroup (N = 10) were randomly light-cured using a second-generation lamp (QTH: quartz-tungsten-halogen; output: 850 mW/cm2, 40 seconds) (Smartlite PS, Dentsply De-Trey Gmbh, Konstanz, Germany), and the remaining half were polymerized with a third-generation unit (LED: light-emitting diode; output: 950 mW/cm2, 40 seconds) (Ultra Lume 5, Ultradent Products Inc., South Jordan, UT). The operator checked the light source with a radiometer during the experiment and found the above-mentioned irradiance values. The light-curing tip was positioned in direct contact with the matrix surface in groups 2 to 5. When no matrix was used, the light-curing tip was positioned directly over and in contact with a mylar strip (group 1).
Two hundred microhybrid resin composite discs (Ø 8 mm) (Herculite XRV, KerrHawe S.A., Bioggio,
Composite cylinders were stored in the dark at 37°C and 100% relative humidity. The relevant data of the
The null hypotheses tested were that (1) the thickness of the preoperative occlusal matrix, the LCU, the height of the composite layer, and the storage period do not affect the top and bottom surface VMH of composite films, and that (2) the bottom/top microhardness ratios for the tested groups are within the empirically accepted limit (0.8).
MATERIALS AND METHODS
204
Matrices were prepared with vinylpolysiloxane bite registration material (Memosil 2, Heraeus Kulzer, Hanau, Germany) simulating the clinical procedure. This was delivered from the automix tips to customized silicon molds (which had different heights depending on the group of matrix thickness).
Vol 27 • No 4 • 203–212 • 2015
Journal of Esthetic and Restorative Dentistry
DOI 10.1111/jerd.12156
© 2015 Wiley Periodicals, Inc.
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
TABLE 1. Materials and equipment used in the study Material/equipment
Classification
Main features of composition and performance
Herculite XRV Batch No. 07-1179 KerrHawe S.A., P.O. Box 268, 6934 Bioggio, Switzerland
Microhybrid composite restorative material
• •
• Memosil 2, Batch No. 315485, Heraeus, Kulzer, Germany
Polyvinyl siloxane bite registration material
• •
Shade: A2 Chemical composition: Bis-GMA, Bis-EMA, TEGDMA, camphorquinone (photoinitiator), stabilizers, barium aluminium borosilicate (mean particle size 800 mW/cm2 • Peak wavelength range of 370–500 nm
LCU = light-curing unit; QTH = quartz-tungsten-halogen; LED = light-emitting diode.
materials and equipment employed in the experiment are outlined in Table 1.
VMH Test The top (T) and bottom (B) surfaces of the composite samples were tested for VMH at 1 hour and 24 hours post-curing. At each time point, five measurements were taken on each sample surface. These measurements were equally distributed along the circumference, being equidistant between the circle center and the periphery. Hence, the measuring points were previously marked on the discs’ surfaces halfway along their radius with an indelible marking pen in order to standardize the procedure and minimize the operator bias. This resulted in 50 top and 50 bottom VMH values per experimental subgroup of matrix thickness, LCU, disc height, and storage time (N = 10 specimens per subgroup). The VMH test was carried out using a calibrated Universal Vickers Microhardness indenter (Mitutoyo MVK-G1, Sakato, Kawasaki, Japan) with a load of 1 kg (1,249 MPa) and a dwell time of 15 seconds (Figure 1).
Sussex, UK) and observed under an SEM (JSM-6400LV, Jeol, Tokyo, Japan) at 20 kV, using a resolution of 4 nm and a working distance of 39 mm measured on the Z-axis. The T and B surfaces of the composite cylinders were examined for porosity and roughness at different magnifications (50×–1,000×) (Figures 1–3).
Statistical Analysis Since all structures were systematically fabricated under standardized procedures, an average VMH value was assigned to each subgroup of matrix thickness, LCU, disc height, storage period, and cylinder surface.11 Normal data distribution and homogeneity of variances were confirmed by the Kolmogorov–Smirnov and the Levene’s tests, respectively.
Scanning Electron Microscope (SEM) Evaluation
A multiple analysis of variance with repeated measurements for the “surface” factor (T/B) was performed for “Vickers microhardness (VMH),” which was considered the dependent variable. Matrix thickness, LCU, disc height, and storage time were the independent variables.12
Composite discs were coated using a special gold-sputtering machine (Emitech k550×, Emitech, East
The Student–Newman–Keuls test was run for further post-hoc comparisons.11
© 2015 Wiley Periodicals, Inc.
DOI 10.1111/jerd.12156
Journal of Esthetic and Restorative Dentistry
Vol 27 • No 4 • 203–212 • 2015
205
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
FIGURE 1. SEM images showing the mark left by the Vickers indenter on the T surface of a 2-mm high sample polymerized with QTH through a 0.5-mm thick matrix at 24 hours. A, 100 ×. B, 500 ×. C, 1K×. QTH = quartz-tungsten-halogen; SEM = scanning electron microscope.
FIGURE 2. SEM micrographs of the T surface of a 2-mm high sample cured with LED without a matrix at 24 hours. The microroughness is more evident at higher magnifications. A, 100 ×. B, 500 ×. C, 2K×. LED = light-emitting diode; SEM = scanning electron microscope.
RESULTS The microhardness ratios for the experimental groups were calculated as bottom/top VMH9 and compared with the empirically accepted limit of 0.8.8,9 Data were processed using the SPSS/PC+ v.20 statistical package software (SPSS Inc., Chicago, IL, USA) at α = 0.05.
206
Vol 27 • No 4 • 203–212 • 2015
Journal of Esthetic and Restorative Dentistry
The experimental results are presented in Tables 2 and 3. Matrix thickness, LCU, composite film height, and storage time were statistically significant predictors of composite surface VMH. Interactions among the factors were significant (p < 0.0001).
DOI 10.1111/jerd.12156
© 2015 Wiley Periodicals, Inc.
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
surfaces of 0.5-mm versus 3-mm thick matrix subgroups in all cases. Thus, the significantly lowest VMH values were associated with the use of 3-mm thick matrices (Table 2). Higher porosity was observed when these devices were utilized (Figure 3). Significant differences between 0.5-mm and 2-mm thick matrix subgroups were found among the T surfaces of 1.5-mm high discs cured with QTH at 1 hour among the T and B surfaces of QTH-cured samples and among the B surfaces of LED-polymerized cylinders at 24 hours, regardless of the disc height. The 1-mm and 3-mm thick matrix subgroups yielded significant VMH differences in the following cases: (1) T and B surfaces of 1.5-mm high QTH-cured samples at 1 hour and B surfaces of the same specimens at 24 hour, (2) T surfaces of 2-mm high QTH-cured samples at 1 hour and T and B surfaces of these samples at 24 hours, and (3) T and B surfaces of 2-mm high LED-cured discs at 1 hour. The thinnest matrices produced the highest VMH in all pair-wise comparisons, despite the lack of significant differences in several cases (Table 2). A higher porosity was detected in those samples that showed lower VMH values (Table 2, Figure 3).
FIGURE 3. SEM images of the B surface of a 1.5-mm high sample polymerized with QTH through a 3-mm thick matrix at 1 hour. Dispersed pores of different sizes may be observed on the flat surfaces of the composite discs. A, B, C, 100×. QTH = quartz-tungsten-halogen; SEM = scanning electron microscope.
Concerning the type of preoperative occlusal matrix, no significant differences were recorded among the T and B VMHs of the controls (Figure 2) and the samples polymerized through 0.5-mm thick matrices (except the B surfaces of 2-mm high discs cured with QTH at 24 hours). Scarce porosity was observed in these specimens (Figure 2). No significant differences were found in the comparison of the next subgroups of matrices: 0.5 mm/1 mm, 1 mm/2 mm and 2 mm/3 mm. Differences were significant among the T and B
© 2015 Wiley Periodicals, Inc.
DOI 10.1111/jerd.12156
Overall, the type of lamp (QTH or LED) did not affect the T and B VMH when the other variables were kept constant. Nevertheless, there were two exceptions in the control group in which the QTH showed significantly higher VMH than did the LED: B surfaces of 2-mm high samples at 24 hours, and T surfaces of 1.5-mm high samples at 1 hour. In the latter, the statistical differences disappeared in the 24-hour retest (Table 2). The composite T and B surface VMH values were not affected by the height of the composite cylinders within each experimental subgroup (Table 2). The T surfaces of the composite samples recorded higher VMH than their respective B surfaces within each experimental subgroup. Such differences were significant in 24 of the 40 possible pair-wise
Journal of Esthetic and Restorative Dentistry
Vol 27 • No 4 • 203–212 • 2015
207
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
TABLE 2. Mean and SD of Vickers microhardness (VMH) obtained in the experimental subgroups Matrix thickness No matrix Composite disc height
Lamp
1.5 mm
QTH
LED
2 mm
QTH
LED
0.5 mm
1 mm
2 mm
3 mm
Storage time
Vickers microhardness mean (SD) T
B
T
B
T
B
T
B
T
B
1 hour
84.75 (1.1) a34*
70.01 (1.63) bcd234
77.11 (1.33) ab23*
64.18 (1.47) def23
71.40 (1.54) bcd12
59.26 (1.58) ef23
66.01 (1.4) cde12
53 (1.58) fg234**
60.23 (1.58) ef123
45.32 (1.52) g23**
24 hours
95.14 (1.64) a12*
89.36 (1.42) ab1*
90.36 (1.39) ab1*
81.70 (0.96) bc1
81.1 (1.37) bc1
71.77 (1.97) cd1
76.08 (1.27) c1
63.60 (1.1) de12**
70.05 (1.42) cd1
56.01 (1.03) e12**
1 hour
73.01 (1.76) a5*
70.06 (1.79) a234*
71.05 (1.74) a3*
64.01 (1.34) ab23*
65.1 (1.33) ab2*
60.18 (1.72) bc123**
62.07 (1.71) abc2**
56.96 (1.66) bc123**
58.09 (1.57) bc23**
53.04 (1.74) c12**
24 hours
88.06 (1.40) a123*
80.07 (1.95)ab12*
82.52 (1.41) ab12*
77.05 (1.64) bc1
77.07 (1.73) bc1
71.97 (2.19) cd1
72.03 (1.82) bc12
67.04 (1.26) d1**
68.09 (1.34) cd12**
62.01 (1.77) d1**
1 hour
85.25 (1.46) a234*
60.40 (1.86) cd4
76.31 (1.33) ab23*
54.56 (1.48) cde3
72.04 (1.71) b12
50.59 (1.39) def3**
65.08 (1.37) bc2
45.17 (1.13) ef4**
59.78 (1.9) cd23
40.23 (1.67) f3**
24 hours
96.56 (1.19) a1*
85.60 (1.96) abc1*
89.5 (1.6) ab1*
72.59 (1.77) def12
82.07 (1.77) bcd1
62.71 (1.5) fg12
75.21 (2.01) cde1
54.24 (1.09) gh234**
67.10 (1.67) ef12
46.40 (1.29) h23**
1 hour
75.40 (1.33) a45*
63.32 (1.18) bcd34
70.26 (1.41) ab3*
59.52 (1.90) cd3
66.02 (1.8) abc2*
57 (1.7) d23
61.06 (1.98) bcd2
52.52 (1.43) de34**
56.28 (1.34) de3**
45.67 (1.64) e23**
24 hours
87 (1.82) a123*
73.94 (1.28) bc23
81.1 (1.23) ab123*
70.06 (1.48) bc12
76.08 (0.93) bc12
65.7 (1.29) cd12
71.02 (1.99) bc12
61.48 (1.96) d123**
66.43 (1.54) cd123
55.43 (1.54) d12**
T = top composite surface; B = bottom composite surface; QTH = quartz-tungsten-halogen; LED = light-emitting diode; LCU = light-curing unit. Different letters within the same row and different numbers within the same column indicate statistically significant differences (p < 0.05). Maximum (*) and minimum (**) top and bottom VMH values per experimental subgroup of LCU, composite-layer height, and post-curing time depending on the variation of the matrix thickness.
TABLE 3. Bottom/top microhardness ratios obtained in the experimental subgroups at 24 hours Bottom/top microhardness ratios for the experimental subgroups at 24 hours Composite disc height
Lamp
No matrix
0.5 mm
1 mm
2 mm
3 mm
1.5 mm
QTH
0.94
0.90
0.88
0.83
0.8
LED
0.91
0.93
0.93
0.93
0.91
QTH
0.89
0.81
0.76*
0.72*
0.69*
LED
0.85
0.86
0.86
0.86
0.83
2 mm
LED = light-emitting diode; QTH = quartz-tungsten-halogen. *Ratios below the accepted limit of 0.8.
208
Vol 27 • No 4 • 203–212 • 2015
Journal of Esthetic and Restorative Dentistry
DOI 10.1111/jerd.12156
© 2015 Wiley Periodicals, Inc.
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
FIGURE 4. Clinical application of the preoperative occlusal matrix technique. A, Occlusal surface of a molar before being restored. B, C, Impression of the molar occlusal surface, made with the matrix. D, Final composite restoration, with a perfect reproduction of the occlusal anatomy.
comparisons (Table 2). The T surfaces evidenced higher microroughness than the B surfaces in most groups (Figures 2 and 3).
clinical use of these matrices, which allow for obtaining a replica of the occlusal anatomy of a tooth that is going to be restored.1–3
The VMH of both the T and B surfaces was augmented within each subgroup at 24 hours, causing significant differences in 17 of the 40 possible pair-wise comparisons (Table 2).
The study results require the rejection of the first null hypothesis, as matrix thickness, LCU, composite film height, and time significantly affected the T and B surface VMHs (Table 2).
The B/T microhardness ratios are reported in Table 3. At 24 hours, all subgroups provided values within the empirically accepted limit of 0.8, except 2-mm high composite discs polymerized with the QTH LCU through 1-mm, 2-mm, and 3-mm thick occlusal matrices, which showed ratios below this limit (Table 3).
DISCUSSION
The thinnest matrices promoted the highest surface VMH values (Table 2). The matrix enlarges the distance from the light tip to the composite surface, which reduces the light intensity and hampers the physical properties of the composite resin.13,14 Moreover, the matrices were made of polyvinyl siloxane (Table 1), which is an addition-reaction silicon elastomer. All rubber polymers that were contained in the base material contracted during polymerization as they cross-linked.15
The goal of this investigation was to evaluate the reliability of the preoperative occlusal matrix technique in terms of the surface VMH of the underlying composite restorative material. Figure 4 illustrates the
The use of thin preoperative occlusal matrices may be recommended as a faster procedure that facilitates the reconstruction of the occlusal morphology without significantly decreasing the composite VMH when
© 2015 Wiley Periodicals, Inc.
DOI 10.1111/jerd.12156
Journal of Esthetic and Restorative Dentistry
Vol 27 • No 4 • 203–212 • 2015
209
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
compared with the no-matrix values (Table 2). Furthermore, matrices have the advantage of isolating the resin composite from oxygen in the air, which is beneficial because oxygen disturbs polymerization.16 This technique may also minimize direct handling, thus reducing possible porosities.17,18 Conversely, the utilization of occlusal matrices that are thicker than 1 mm would reduce the VMH of posterior composite restorations (Table 2). Moreover, low VMH scores appeared to be coupled with high porosity in this research (Figure 3), which could result in a weaker and more permeable composite construction that would lead to failure. Efficient curing may also depend on the irradiance and wavelength emitted by the lamp, such that the spectrum irradiated by the light source is higher than the absorption range of the composite photoinitiator.14,16,19 Until recently, QTH was the most commonly used LCU. Lamps of this type require fans and optical filters, which make them less energy-efficient.19 To overcome such drawbacks, blue LED LCUs with minor heat production and increased life expectancy were introduced.19 New LEDs have even higher light intensities (500–1,400 mW/cm2) and wavelengths coinciding with the absorption peak of camphorquinone (470 nm).6 Recently marketed LEDs are still compared with conventional QTHs, as the latter are considered the gold standard for LCUs. Whereas some studies attribute better top and bottom VMH values to resin composites polymerized with LEDs,7,20 other studies, including our experiment, confirm that the type of LCU does not affect the composite VMH.21,22 The QTH resulted in a higher B VMH than the LED only when polymerizing 2-mm high composite samples in the absence of a matrix (Table 2). Differences in the spectral emission of both lamps may produce variations in light scattering, which in turn may cause differences in the depth of penetration.23 However, methodological disparities among the study protocols make comparisons difficult. The fact that the VMH was not influenced by the height of the composite discs when the other variables were kept constant (Table 2) was somewhat predictable,
210
Vol 27 • No 4 • 203–212 • 2015
Journal of Esthetic and Restorative Dentistry
since “1.5 mm” is the maximum desirable depth for the incremental curing of resin composites stated by the ISO-4049 (www.aenor.es), and manufacturers recommend polymerizing composite resin in layers of “2 mm.” These dimensions were selected to emulate the clinical procedure. Due to the lack of interference with light transmission,13 it is reasonable that the T surfaces of the composite discs registered significantly higher VMH values than did the respective B surfaces in most of the experimental subgroups, as occurred in previous research22 (Table 2). Since light passes through the mass of the matrix and the composite, its intensity is greatly decreased due to the light absorption and spreading by the restorative material, reducing its potential to cure.13 This is consistent with the gradual reduction in B surface microhardness produced when thicker matrices were used regardless of the type of LCU (Table 2). The SEM analysis revealed that the B surfaces (Figure 3) of the composite cylinders were flatter than the T surfaces (Figure 2), which may be due to the glass slide used as a support.10 The compression of the composite layer with the occlusal matrix generally resulted in higher surface microroughness of the T surfaces. However, this can be clinically solved by polishing the restoration. The T and B VMHs augmented after 24 hours in all subgroups; the differences were significant in almost half of the cases (Table 2). This supports previous findings, as the composite surface VMH is linearly correlated with the degree of conversion of the composite material;24 which successively increases over time.14 The second null hypothesis was rejected because not all the B/T microhardness ratios obtained were within the empirically accepted limit of 0.8 (Table 3). This limit may ensure adequate polymerization of the bottom surfaces of composite films.8,9 All samples verified this condition except 2-mm high composite discs cured with QTH when matrices of 1 mm to 3 mm were used (Table 3). The LED LCU demonstrated a better depth of penetration in the above-mentioned subgroups, probably due to differences in light intensity among both lamps.25
DOI 10.1111/jerd.12156
© 2015 Wiley Periodicals, Inc.
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
Future studies should analyze the influence of other relevant factors, such as resin composition, filler size and loading, shade, light intensity, and/or exposure time.14,23,24
5.
CONCLUSIONS
7.
Within the limitations of this research, it may be concluded that the entire polymerization process is somehow compromised when preoperative occlusal matrices are used. Despite the type of LCU, height of the composite layers, and storage period, the thinnest matrices are the most recommendable ones as they preserve the composite surface VMH and the curing depth more than do the thickest devices.
6.
8.
9.
10.
DISCLOSURE AND ACKNOWLEDGEMENTS The authors do not have any financial interest in the companies whose materials are included in this article. The authors would like to express their special and sincere gratitude to their friend, Dr. Carlos Oteo Calatayud, for selflessly offering them the clinical case of Figure 4 in order to illustrate and facilitate the understanding of this in vitro experiment. Dr. Carlos Oteo Calatayud is a professor at the Department of Restorative and Aesthetic Dentistry of the Faculty of Odontology of the Complutense University of Madrid (U.C.M., Spain).
2.
3.
4.
Lynch CD, Opdam NJ, Hickel R, et al. Guidance on posterior resin composites: Academy of Operative Dentistry—European section. J Dent 2014;42:377– 83. Hamilton JC, Krestik KE, Dennison JB. Evaluation of custom occlusal matrix technique for posterior light-cured composites. Oper Dent 1998;23:303–7. Geddes A, Craig J, Chadwick RG. Preoperative occlusal matrix aids the development of occlusal contour of posterior occlusal resin composite restorations—clinical rationale and technique. Br Dent J 2009;206:315–7. Trushkowsky RD. Use of a clear matrix to minimize finishing of a posterior resin composite. Am J Dent 1997;10:111–2.
© 2015 Wiley Periodicals, Inc.
12.
13.
14.
15.
REFERENCES 1.
11.
DOI 10.1111/jerd.12156
16. 17.
18. 19.
20.
Anusavice JK. Phillip’s science of dental materials. 11th ed. St. Louis (MO): Elsevier Science; 2003. Gaglianone LA, Lima AF, Araújo LS, et al. Influence of different shades and LED irradiance on the degree of conversion of composite resins. Braz Oral Res 2012;26:165–9. Yaman BC, Efes BG, Dörter C, et al. The effects of halogen and light-emitting diode light curing on the depth of cure and surface microhardness of composite resins. J Conserv Dent 2011;14:136–9. Bala O, Olmez A, Kalayci S. Effect of LED and halogen light curing on polymerization of resin-based composites. J Oral Rehabil 2005;32:134–40. Lombardini M, Chiesa M, Scribante A, et al. Influence of polymerization time and depth of cure of resin composites determined by Vickers hardness. Dent Res J (Isfahan) 2012;9:735–40. Ray NJ, Lynch CD, Burke FM, et al. Early surface microhardness of a resin composite exposed to a pulse-delayed curing exposure: a comparison of a tungsten halogen and a plasma arc lamp, in vitro. Eur J Prosthodont Restor Dent 2005;13:177–81. Castillo Oyagüe R, Sánchez-Jorge MI, Sánchez Turrión A. Influence of CAD/CAM scanning method and tooth-preparation design on the vertical misfit of zirconia crown copings. Am J Dent 2010;23:341–6. Lucey S, Lynch CD, Ray NJ, et al. Effect of pre-heating on the viscosity and microhardness of a resin composite. J Oral Rehabil 2010;37:278–82. Rueggeberg FA, Jordan DM. Effect of light-tip distance on polymerization of resin composite. Int J Prosthodont 1993;6:364–70. Zhu S, Platt JA. Curing efficiency of three different curing lights at different distances for a hybrid composite. Am J Dent 2009;22:381–6. Mandikos MN. Polyvinyl siloxane impression materials: an update on clinical use. Aust Dent J 1998;43:428–34. Phillips RW. Skinner’s science of dental materials. 10th ed. Philadelphia (PA): WB Saunders; 1996. Jörgensen KD, Hisamitsu H. Porosity in microfill restorative composites cured by visible light. Scand J Dent Res 1983;91:396–405. Ironside JG, Makinson OF. Resin restorations: causes of porosities. Quintessence Int 1993;24:867–73. Rahiotis C, Kakaboura A, Loukidis M, et al. Curing efficiency of various types of light-curing units. Eur J Oral Sci 2004;112:89–94. Oberholzer TG, Du Preez IC, Kidd M. Effect of LED curing on the microleakage, shear bond strength and surface hardness of a resin-based composite restoration. Biomaterials 2005;26:3981–6.
Journal of Esthetic and Restorative Dentistry
Vol 27 • No 4 • 203–212 • 2015
211
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
21. Ritter AV, Cavalcante LM, Swift EJ Jr, et al. Effect of light-curing method on marginal adaptation, microleakage, and microhardness of composite restorations. J Biomed Mater Res B Appl Biomater 2006;78:302–11. 22. Lima AF, de Andrade KM, da Cruz Alves LE, et al. Influence of light source and extended time of curing on microhardness and degree of conversion of different regions of a nanofilled composite resin. Eur J Dent 2012;6:153–7. 23. Kumar CN, Gururaj M, Paul J. A comparative evaluation of curing depth and compressive strength of dental composite cured with halogen light curing unit and blue light emitting diode: an in vitro study. J Contemp Dent Pract 2012;13:834–7.
212
Vol 27 • No 4 • 203–212 • 2015
Journal of Esthetic and Restorative Dentistry
24. Santini A, Miletic V, Swift MD, et al. Degree of conversion and microhardness of TPO-containing resin-based composites cured by polywave and monowave LED units. J Dent 2012;40:577–84. 25. Tanthanuch S, Ruengsri P, Kukiattrakoon B. Optimal depth of cure for nanohybrid resin composite using quartz tungsten halogen and new high intensity light-emitting diode curing units. Gen Dent 2013;61:14–7.
Reprint requests: Raquel Castillo-Oyagüe, DDS, PhD, Department of Buccofacial Prostheses, Faculty of Dentistry, Complutense University of Madrid (U.C.M.)., Pza. Ramón y Cajal s/n, Madrid 28040, Spain; Tel.: 0034607367903; Fax: 0034913942029; email: [email protected]
DOI 10.1111/jerd.12156
© 2015 Wiley Periodicals, Inc.
Effect of Preoperative Occlusal Matrices on the Vickers Microhardness of Composite Disks Polymerized with QTH and LED Lamps RAQUEL CASTILLO-OYAGÜE, DDS, PHD*, PAUL J. MILWARD, MPHIL, MIMPT, LCGI/MARK WATERS, BSC, PHD†, ALICIA MARTÍN-CERRATO, DDS, PHD‡, CHRISTOPHER D. LYNCH, BDS, PHD, MFD, RCSI, FDS (REST DENT)§
ABSTRACT Purpose: This study aimed to assess the reliability of the preoperative occlusal matrix technique in terms of the surface Vickers microhardness (VMH) of the underlying composite restorative material. Materials and Methods: Two hundred microhybrid composite cylinders were built up and light-cured in a single-layer step, forming two experimental groups (N = 100) according to their heights (1.5 mm/2 mm). Each group was divided into five subgroups (N = 20) depending on the matrix thickness (no matrix/0.5 mm/1 mm/2 mm/3 mm). Half the specimens per subgroup (N = 10) were randomly polymerized with a quartz-tungsten-halogen (QTH) light-curing unit (LCU).The remaining half were cured using a light-emitting diode lamp.The top and bottom samples’ sides were tested for VMH at 1 hour and 24 hours post-curing using a universal VMH machine. A multiple analysis of variance with repeated measurements for the “surface” factor and the Student–Newman–Keuls test were run (α = 0.05). Bottom/top microhardness ratios were compared with the empirically accepted limit (0.8). Surface topography was analyzed under a scanning electron microscope. Results: The thinnest matrices provided the significantly best VMH values. LCU, disc height, and time also contributed to VMH. At 24 hours, 2-mm high discs polymerized with QTH resulted in inadequate microhardness ratios when 1-mm thick to 3-mm thick matrices were used. Conclusion: The thinnest matrices are the most recommendable ones.
CLINICAL SIGNIFICANCE The esthetics and occlusal reproducibility achieved with customized occlusal matrices fabricated before cavity preparation have been widely demonstrated. However, their effect on the physical properties of the restorations deserves further investigation. Although more studies are necessary, the thinnest matrices seem to be the most suitable to preserve the composite surface VMH and the curing depth. (J Esthet Restor Dent 27:203–212, 2015)
INTRODUCTION The reestablishment of an adequate anatomy is still a matter of concern in the case of posterior composite restorations in order to get harmonious esthetics and
cusp–fossa relationships with opposing teeth without the requirement of time-consuming adjustments.1–3 The chairside fabrication of a clear occlusal matrix before cavity preparation has been proposed for the obturation of “hidden” caries that keep the tooth morphology
*Professor, Department of Buccofacial Prostheses, Faculty of Dentistry, Complutense University of Madrid (U.C.M.), Pza. Ramón y Cajal, s/n, Madrid 28040, Spain † Senior lecturer in dental technology and biomaterial sciences, Department of Prosthetic Dentistry, University Dental School, Heath Park, Cardiff CF14 4XY, UK ‡ Associate professor, Department of Dentistry for Adults, European University (U.E.), C/ Tajo, s/n, Villaviciosa de Odón, Madrid 28670, Spain § Senior lecturer/consultant in restorative dentistry, Department of Adult Dental Health, University Dental School, Heath Park, Cardiff CF14 4XY, UK
© 2015 Wiley Periodicals, Inc.
DOI 10.1111/jerd.12156
Journal of Esthetic and Restorative Dentistry
Vol 27 • No 4 • 203–212 • 2015
203
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
intact.3 The matrix is placed over the occlusal cavity to light-cure the last composite layers. This device allows the final restoration to replicate the original structure and occlusion, require no or minimal finishing, diminish the incidence of superficial voids, reduce the flash at the interphase, and be optimally polymerized due to the anaerobic environment.2,3
Switzerland) were light-cured in a single phase and divided into two experimental groups (N = 100) according to their final height: group 1 had 1.5 mm (curing depth stated by the ISO-4049) (www.aenor.es), and group 2 had 2 mm (maximum depth of composite to be polymerized in a single-layer step, as recommended by manufacturers).
Although the occlusal reproducibility achieved with such appliances has been widely studied,2–4 their effect on the physical properties of the polymerized restoration remains unknown.2 Microhardness describes the wear resistance of resin composite and its ability to abrade or be abraded by opposing teeth or restorative materials.5 To date, the evaluation of microhardness has been widely used for testing the quality of polymerization and thus the efficiency of different light sources for stimulating the photoinitiators of composite resins.5,6 To define the “depth of cure” of light-curing units (LCUs), it is also common to calculate the ratio of bottom/top surface microhardness.7 Minimum values of 0.8 are empirically accepted to consider the bottom composite surfaces adequately polymerized.8,9
Each group of composite samples was divided into five subgroups (N = 20) depending on the thickness of the preoperative occlusal matrix utilized: subgroup 1 (control: no matrix), subgroup 2 (0.5 mm), subgroup 3 (1 mm), subgroup 4 (2 mm), and subgroup 5 (3 mm).
This is the first study that investigates the Vickers microhardness (VMH) of a composite restorative material to indirectly assess the reliability of the preoperative occlusal matrix technique. Several clinical parameters (matrix thickness, LCU, composite film height, and post-curing period) were simulated and combined in the experiment.
The respective matrices were put over the composite discs contained in nylon washers before being polymerized. A microscope slide was used as a support to obtain a flat bottom surface. A mirror beneath the glass slide reproduced the clinical reflection of the dentine.10
Preparation of Specimens
Half the specimens per subgroup (N = 10) were randomly light-cured using a second-generation lamp (QTH: quartz-tungsten-halogen; output: 850 mW/cm2, 40 seconds) (Smartlite PS, Dentsply De-Trey Gmbh, Konstanz, Germany), and the remaining half were polymerized with a third-generation unit (LED: light-emitting diode; output: 950 mW/cm2, 40 seconds) (Ultra Lume 5, Ultradent Products Inc., South Jordan, UT). The operator checked the light source with a radiometer during the experiment and found the above-mentioned irradiance values. The light-curing tip was positioned in direct contact with the matrix surface in groups 2 to 5. When no matrix was used, the light-curing tip was positioned directly over and in contact with a mylar strip (group 1).
Two hundred microhybrid resin composite discs (Ø 8 mm) (Herculite XRV, KerrHawe S.A., Bioggio,
Composite cylinders were stored in the dark at 37°C and 100% relative humidity. The relevant data of the
The null hypotheses tested were that (1) the thickness of the preoperative occlusal matrix, the LCU, the height of the composite layer, and the storage period do not affect the top and bottom surface VMH of composite films, and that (2) the bottom/top microhardness ratios for the tested groups are within the empirically accepted limit (0.8).
MATERIALS AND METHODS
204
Matrices were prepared with vinylpolysiloxane bite registration material (Memosil 2, Heraeus Kulzer, Hanau, Germany) simulating the clinical procedure. This was delivered from the automix tips to customized silicon molds (which had different heights depending on the group of matrix thickness).
Vol 27 • No 4 • 203–212 • 2015
Journal of Esthetic and Restorative Dentistry
DOI 10.1111/jerd.12156
© 2015 Wiley Periodicals, Inc.
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
TABLE 1. Materials and equipment used in the study Material/equipment
Classification
Main features of composition and performance
Herculite XRV Batch No. 07-1179 KerrHawe S.A., P.O. Box 268, 6934 Bioggio, Switzerland
Microhybrid composite restorative material
• •
• Memosil 2, Batch No. 315485, Heraeus, Kulzer, Germany
Polyvinyl siloxane bite registration material
• •
Shade: A2 Chemical composition: Bis-GMA, Bis-EMA, TEGDMA, camphorquinone (photoinitiator), stabilizers, barium aluminium borosilicate (mean particle size 800 mW/cm2 • Peak wavelength range of 370–500 nm
LCU = light-curing unit; QTH = quartz-tungsten-halogen; LED = light-emitting diode.
materials and equipment employed in the experiment are outlined in Table 1.
VMH Test The top (T) and bottom (B) surfaces of the composite samples were tested for VMH at 1 hour and 24 hours post-curing. At each time point, five measurements were taken on each sample surface. These measurements were equally distributed along the circumference, being equidistant between the circle center and the periphery. Hence, the measuring points were previously marked on the discs’ surfaces halfway along their radius with an indelible marking pen in order to standardize the procedure and minimize the operator bias. This resulted in 50 top and 50 bottom VMH values per experimental subgroup of matrix thickness, LCU, disc height, and storage time (N = 10 specimens per subgroup). The VMH test was carried out using a calibrated Universal Vickers Microhardness indenter (Mitutoyo MVK-G1, Sakato, Kawasaki, Japan) with a load of 1 kg (1,249 MPa) and a dwell time of 15 seconds (Figure 1).
Sussex, UK) and observed under an SEM (JSM-6400LV, Jeol, Tokyo, Japan) at 20 kV, using a resolution of 4 nm and a working distance of 39 mm measured on the Z-axis. The T and B surfaces of the composite cylinders were examined for porosity and roughness at different magnifications (50×–1,000×) (Figures 1–3).
Statistical Analysis Since all structures were systematically fabricated under standardized procedures, an average VMH value was assigned to each subgroup of matrix thickness, LCU, disc height, storage period, and cylinder surface.11 Normal data distribution and homogeneity of variances were confirmed by the Kolmogorov–Smirnov and the Levene’s tests, respectively.
Scanning Electron Microscope (SEM) Evaluation
A multiple analysis of variance with repeated measurements for the “surface” factor (T/B) was performed for “Vickers microhardness (VMH),” which was considered the dependent variable. Matrix thickness, LCU, disc height, and storage time were the independent variables.12
Composite discs were coated using a special gold-sputtering machine (Emitech k550×, Emitech, East
The Student–Newman–Keuls test was run for further post-hoc comparisons.11
© 2015 Wiley Periodicals, Inc.
DOI 10.1111/jerd.12156
Journal of Esthetic and Restorative Dentistry
Vol 27 • No 4 • 203–212 • 2015
205
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
FIGURE 1. SEM images showing the mark left by the Vickers indenter on the T surface of a 2-mm high sample polymerized with QTH through a 0.5-mm thick matrix at 24 hours. A, 100 ×. B, 500 ×. C, 1K×. QTH = quartz-tungsten-halogen; SEM = scanning electron microscope.
FIGURE 2. SEM micrographs of the T surface of a 2-mm high sample cured with LED without a matrix at 24 hours. The microroughness is more evident at higher magnifications. A, 100 ×. B, 500 ×. C, 2K×. LED = light-emitting diode; SEM = scanning electron microscope.
RESULTS The microhardness ratios for the experimental groups were calculated as bottom/top VMH9 and compared with the empirically accepted limit of 0.8.8,9 Data were processed using the SPSS/PC+ v.20 statistical package software (SPSS Inc., Chicago, IL, USA) at α = 0.05.
206
Vol 27 • No 4 • 203–212 • 2015
Journal of Esthetic and Restorative Dentistry
The experimental results are presented in Tables 2 and 3. Matrix thickness, LCU, composite film height, and storage time were statistically significant predictors of composite surface VMH. Interactions among the factors were significant (p < 0.0001).
DOI 10.1111/jerd.12156
© 2015 Wiley Periodicals, Inc.
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
surfaces of 0.5-mm versus 3-mm thick matrix subgroups in all cases. Thus, the significantly lowest VMH values were associated with the use of 3-mm thick matrices (Table 2). Higher porosity was observed when these devices were utilized (Figure 3). Significant differences between 0.5-mm and 2-mm thick matrix subgroups were found among the T surfaces of 1.5-mm high discs cured with QTH at 1 hour among the T and B surfaces of QTH-cured samples and among the B surfaces of LED-polymerized cylinders at 24 hours, regardless of the disc height. The 1-mm and 3-mm thick matrix subgroups yielded significant VMH differences in the following cases: (1) T and B surfaces of 1.5-mm high QTH-cured samples at 1 hour and B surfaces of the same specimens at 24 hour, (2) T surfaces of 2-mm high QTH-cured samples at 1 hour and T and B surfaces of these samples at 24 hours, and (3) T and B surfaces of 2-mm high LED-cured discs at 1 hour. The thinnest matrices produced the highest VMH in all pair-wise comparisons, despite the lack of significant differences in several cases (Table 2). A higher porosity was detected in those samples that showed lower VMH values (Table 2, Figure 3).
FIGURE 3. SEM images of the B surface of a 1.5-mm high sample polymerized with QTH through a 3-mm thick matrix at 1 hour. Dispersed pores of different sizes may be observed on the flat surfaces of the composite discs. A, B, C, 100×. QTH = quartz-tungsten-halogen; SEM = scanning electron microscope.
Concerning the type of preoperative occlusal matrix, no significant differences were recorded among the T and B VMHs of the controls (Figure 2) and the samples polymerized through 0.5-mm thick matrices (except the B surfaces of 2-mm high discs cured with QTH at 24 hours). Scarce porosity was observed in these specimens (Figure 2). No significant differences were found in the comparison of the next subgroups of matrices: 0.5 mm/1 mm, 1 mm/2 mm and 2 mm/3 mm. Differences were significant among the T and B
© 2015 Wiley Periodicals, Inc.
DOI 10.1111/jerd.12156
Overall, the type of lamp (QTH or LED) did not affect the T and B VMH when the other variables were kept constant. Nevertheless, there were two exceptions in the control group in which the QTH showed significantly higher VMH than did the LED: B surfaces of 2-mm high samples at 24 hours, and T surfaces of 1.5-mm high samples at 1 hour. In the latter, the statistical differences disappeared in the 24-hour retest (Table 2). The composite T and B surface VMH values were not affected by the height of the composite cylinders within each experimental subgroup (Table 2). The T surfaces of the composite samples recorded higher VMH than their respective B surfaces within each experimental subgroup. Such differences were significant in 24 of the 40 possible pair-wise
Journal of Esthetic and Restorative Dentistry
Vol 27 • No 4 • 203–212 • 2015
207
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
TABLE 2. Mean and SD of Vickers microhardness (VMH) obtained in the experimental subgroups Matrix thickness No matrix Composite disc height
Lamp
1.5 mm
QTH
LED
2 mm
QTH
LED
0.5 mm
1 mm
2 mm
3 mm
Storage time
Vickers microhardness mean (SD) T
B
T
B
T
B
T
B
T
B
1 hour
84.75 (1.1) a34*
70.01 (1.63) bcd234
77.11 (1.33) ab23*
64.18 (1.47) def23
71.40 (1.54) bcd12
59.26 (1.58) ef23
66.01 (1.4) cde12
53 (1.58) fg234**
60.23 (1.58) ef123
45.32 (1.52) g23**
24 hours
95.14 (1.64) a12*
89.36 (1.42) ab1*
90.36 (1.39) ab1*
81.70 (0.96) bc1
81.1 (1.37) bc1
71.77 (1.97) cd1
76.08 (1.27) c1
63.60 (1.1) de12**
70.05 (1.42) cd1
56.01 (1.03) e12**
1 hour
73.01 (1.76) a5*
70.06 (1.79) a234*
71.05 (1.74) a3*
64.01 (1.34) ab23*
65.1 (1.33) ab2*
60.18 (1.72) bc123**
62.07 (1.71) abc2**
56.96 (1.66) bc123**
58.09 (1.57) bc23**
53.04 (1.74) c12**
24 hours
88.06 (1.40) a123*
80.07 (1.95)ab12*
82.52 (1.41) ab12*
77.05 (1.64) bc1
77.07 (1.73) bc1
71.97 (2.19) cd1
72.03 (1.82) bc12
67.04 (1.26) d1**
68.09 (1.34) cd12**
62.01 (1.77) d1**
1 hour
85.25 (1.46) a234*
60.40 (1.86) cd4
76.31 (1.33) ab23*
54.56 (1.48) cde3
72.04 (1.71) b12
50.59 (1.39) def3**
65.08 (1.37) bc2
45.17 (1.13) ef4**
59.78 (1.9) cd23
40.23 (1.67) f3**
24 hours
96.56 (1.19) a1*
85.60 (1.96) abc1*
89.5 (1.6) ab1*
72.59 (1.77) def12
82.07 (1.77) bcd1
62.71 (1.5) fg12
75.21 (2.01) cde1
54.24 (1.09) gh234**
67.10 (1.67) ef12
46.40 (1.29) h23**
1 hour
75.40 (1.33) a45*
63.32 (1.18) bcd34
70.26 (1.41) ab3*
59.52 (1.90) cd3
66.02 (1.8) abc2*
57 (1.7) d23
61.06 (1.98) bcd2
52.52 (1.43) de34**
56.28 (1.34) de3**
45.67 (1.64) e23**
24 hours
87 (1.82) a123*
73.94 (1.28) bc23
81.1 (1.23) ab123*
70.06 (1.48) bc12
76.08 (0.93) bc12
65.7 (1.29) cd12
71.02 (1.99) bc12
61.48 (1.96) d123**
66.43 (1.54) cd123
55.43 (1.54) d12**
T = top composite surface; B = bottom composite surface; QTH = quartz-tungsten-halogen; LED = light-emitting diode; LCU = light-curing unit. Different letters within the same row and different numbers within the same column indicate statistically significant differences (p < 0.05). Maximum (*) and minimum (**) top and bottom VMH values per experimental subgroup of LCU, composite-layer height, and post-curing time depending on the variation of the matrix thickness.
TABLE 3. Bottom/top microhardness ratios obtained in the experimental subgroups at 24 hours Bottom/top microhardness ratios for the experimental subgroups at 24 hours Composite disc height
Lamp
No matrix
0.5 mm
1 mm
2 mm
3 mm
1.5 mm
QTH
0.94
0.90
0.88
0.83
0.8
LED
0.91
0.93
0.93
0.93
0.91
QTH
0.89
0.81
0.76*
0.72*
0.69*
LED
0.85
0.86
0.86
0.86
0.83
2 mm
LED = light-emitting diode; QTH = quartz-tungsten-halogen. *Ratios below the accepted limit of 0.8.
208
Vol 27 • No 4 • 203–212 • 2015
Journal of Esthetic and Restorative Dentistry
DOI 10.1111/jerd.12156
© 2015 Wiley Periodicals, Inc.
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
FIGURE 4. Clinical application of the preoperative occlusal matrix technique. A, Occlusal surface of a molar before being restored. B, C, Impression of the molar occlusal surface, made with the matrix. D, Final composite restoration, with a perfect reproduction of the occlusal anatomy.
comparisons (Table 2). The T surfaces evidenced higher microroughness than the B surfaces in most groups (Figures 2 and 3).
clinical use of these matrices, which allow for obtaining a replica of the occlusal anatomy of a tooth that is going to be restored.1–3
The VMH of both the T and B surfaces was augmented within each subgroup at 24 hours, causing significant differences in 17 of the 40 possible pair-wise comparisons (Table 2).
The study results require the rejection of the first null hypothesis, as matrix thickness, LCU, composite film height, and time significantly affected the T and B surface VMHs (Table 2).
The B/T microhardness ratios are reported in Table 3. At 24 hours, all subgroups provided values within the empirically accepted limit of 0.8, except 2-mm high composite discs polymerized with the QTH LCU through 1-mm, 2-mm, and 3-mm thick occlusal matrices, which showed ratios below this limit (Table 3).
DISCUSSION
The thinnest matrices promoted the highest surface VMH values (Table 2). The matrix enlarges the distance from the light tip to the composite surface, which reduces the light intensity and hampers the physical properties of the composite resin.13,14 Moreover, the matrices were made of polyvinyl siloxane (Table 1), which is an addition-reaction silicon elastomer. All rubber polymers that were contained in the base material contracted during polymerization as they cross-linked.15
The goal of this investigation was to evaluate the reliability of the preoperative occlusal matrix technique in terms of the surface VMH of the underlying composite restorative material. Figure 4 illustrates the
The use of thin preoperative occlusal matrices may be recommended as a faster procedure that facilitates the reconstruction of the occlusal morphology without significantly decreasing the composite VMH when
© 2015 Wiley Periodicals, Inc.
DOI 10.1111/jerd.12156
Journal of Esthetic and Restorative Dentistry
Vol 27 • No 4 • 203–212 • 2015
209
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
compared with the no-matrix values (Table 2). Furthermore, matrices have the advantage of isolating the resin composite from oxygen in the air, which is beneficial because oxygen disturbs polymerization.16 This technique may also minimize direct handling, thus reducing possible porosities.17,18 Conversely, the utilization of occlusal matrices that are thicker than 1 mm would reduce the VMH of posterior composite restorations (Table 2). Moreover, low VMH scores appeared to be coupled with high porosity in this research (Figure 3), which could result in a weaker and more permeable composite construction that would lead to failure. Efficient curing may also depend on the irradiance and wavelength emitted by the lamp, such that the spectrum irradiated by the light source is higher than the absorption range of the composite photoinitiator.14,16,19 Until recently, QTH was the most commonly used LCU. Lamps of this type require fans and optical filters, which make them less energy-efficient.19 To overcome such drawbacks, blue LED LCUs with minor heat production and increased life expectancy were introduced.19 New LEDs have even higher light intensities (500–1,400 mW/cm2) and wavelengths coinciding with the absorption peak of camphorquinone (470 nm).6 Recently marketed LEDs are still compared with conventional QTHs, as the latter are considered the gold standard for LCUs. Whereas some studies attribute better top and bottom VMH values to resin composites polymerized with LEDs,7,20 other studies, including our experiment, confirm that the type of LCU does not affect the composite VMH.21,22 The QTH resulted in a higher B VMH than the LED only when polymerizing 2-mm high composite samples in the absence of a matrix (Table 2). Differences in the spectral emission of both lamps may produce variations in light scattering, which in turn may cause differences in the depth of penetration.23 However, methodological disparities among the study protocols make comparisons difficult. The fact that the VMH was not influenced by the height of the composite discs when the other variables were kept constant (Table 2) was somewhat predictable,
210
Vol 27 • No 4 • 203–212 • 2015
Journal of Esthetic and Restorative Dentistry
since “1.5 mm” is the maximum desirable depth for the incremental curing of resin composites stated by the ISO-4049 (www.aenor.es), and manufacturers recommend polymerizing composite resin in layers of “2 mm.” These dimensions were selected to emulate the clinical procedure. Due to the lack of interference with light transmission,13 it is reasonable that the T surfaces of the composite discs registered significantly higher VMH values than did the respective B surfaces in most of the experimental subgroups, as occurred in previous research22 (Table 2). Since light passes through the mass of the matrix and the composite, its intensity is greatly decreased due to the light absorption and spreading by the restorative material, reducing its potential to cure.13 This is consistent with the gradual reduction in B surface microhardness produced when thicker matrices were used regardless of the type of LCU (Table 2). The SEM analysis revealed that the B surfaces (Figure 3) of the composite cylinders were flatter than the T surfaces (Figure 2), which may be due to the glass slide used as a support.10 The compression of the composite layer with the occlusal matrix generally resulted in higher surface microroughness of the T surfaces. However, this can be clinically solved by polishing the restoration. The T and B VMHs augmented after 24 hours in all subgroups; the differences were significant in almost half of the cases (Table 2). This supports previous findings, as the composite surface VMH is linearly correlated with the degree of conversion of the composite material;24 which successively increases over time.14 The second null hypothesis was rejected because not all the B/T microhardness ratios obtained were within the empirically accepted limit of 0.8 (Table 3). This limit may ensure adequate polymerization of the bottom surfaces of composite films.8,9 All samples verified this condition except 2-mm high composite discs cured with QTH when matrices of 1 mm to 3 mm were used (Table 3). The LED LCU demonstrated a better depth of penetration in the above-mentioned subgroups, probably due to differences in light intensity among both lamps.25
DOI 10.1111/jerd.12156
© 2015 Wiley Periodicals, Inc.
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
Future studies should analyze the influence of other relevant factors, such as resin composition, filler size and loading, shade, light intensity, and/or exposure time.14,23,24
5.
CONCLUSIONS
7.
Within the limitations of this research, it may be concluded that the entire polymerization process is somehow compromised when preoperative occlusal matrices are used. Despite the type of LCU, height of the composite layers, and storage period, the thinnest matrices are the most recommendable ones as they preserve the composite surface VMH and the curing depth more than do the thickest devices.
6.
8.
9.
10.
DISCLOSURE AND ACKNOWLEDGEMENTS The authors do not have any financial interest in the companies whose materials are included in this article. The authors would like to express their special and sincere gratitude to their friend, Dr. Carlos Oteo Calatayud, for selflessly offering them the clinical case of Figure 4 in order to illustrate and facilitate the understanding of this in vitro experiment. Dr. Carlos Oteo Calatayud is a professor at the Department of Restorative and Aesthetic Dentistry of the Faculty of Odontology of the Complutense University of Madrid (U.C.M., Spain).
2.
3.
4.
Lynch CD, Opdam NJ, Hickel R, et al. Guidance on posterior resin composites: Academy of Operative Dentistry—European section. J Dent 2014;42:377– 83. Hamilton JC, Krestik KE, Dennison JB. Evaluation of custom occlusal matrix technique for posterior light-cured composites. Oper Dent 1998;23:303–7. Geddes A, Craig J, Chadwick RG. Preoperative occlusal matrix aids the development of occlusal contour of posterior occlusal resin composite restorations—clinical rationale and technique. Br Dent J 2009;206:315–7. Trushkowsky RD. Use of a clear matrix to minimize finishing of a posterior resin composite. Am J Dent 1997;10:111–2.
© 2015 Wiley Periodicals, Inc.
12.
13.
14.
15.
REFERENCES 1.
11.
DOI 10.1111/jerd.12156
16. 17.
18. 19.
20.
Anusavice JK. Phillip’s science of dental materials. 11th ed. St. Louis (MO): Elsevier Science; 2003. Gaglianone LA, Lima AF, Araújo LS, et al. Influence of different shades and LED irradiance on the degree of conversion of composite resins. Braz Oral Res 2012;26:165–9. Yaman BC, Efes BG, Dörter C, et al. The effects of halogen and light-emitting diode light curing on the depth of cure and surface microhardness of composite resins. J Conserv Dent 2011;14:136–9. Bala O, Olmez A, Kalayci S. Effect of LED and halogen light curing on polymerization of resin-based composites. J Oral Rehabil 2005;32:134–40. Lombardini M, Chiesa M, Scribante A, et al. Influence of polymerization time and depth of cure of resin composites determined by Vickers hardness. Dent Res J (Isfahan) 2012;9:735–40. Ray NJ, Lynch CD, Burke FM, et al. Early surface microhardness of a resin composite exposed to a pulse-delayed curing exposure: a comparison of a tungsten halogen and a plasma arc lamp, in vitro. Eur J Prosthodont Restor Dent 2005;13:177–81. Castillo Oyagüe R, Sánchez-Jorge MI, Sánchez Turrión A. Influence of CAD/CAM scanning method and tooth-preparation design on the vertical misfit of zirconia crown copings. Am J Dent 2010;23:341–6. Lucey S, Lynch CD, Ray NJ, et al. Effect of pre-heating on the viscosity and microhardness of a resin composite. J Oral Rehabil 2010;37:278–82. Rueggeberg FA, Jordan DM. Effect of light-tip distance on polymerization of resin composite. Int J Prosthodont 1993;6:364–70. Zhu S, Platt JA. Curing efficiency of three different curing lights at different distances for a hybrid composite. Am J Dent 2009;22:381–6. Mandikos MN. Polyvinyl siloxane impression materials: an update on clinical use. Aust Dent J 1998;43:428–34. Phillips RW. Skinner’s science of dental materials. 10th ed. Philadelphia (PA): WB Saunders; 1996. Jörgensen KD, Hisamitsu H. Porosity in microfill restorative composites cured by visible light. Scand J Dent Res 1983;91:396–405. Ironside JG, Makinson OF. Resin restorations: causes of porosities. Quintessence Int 1993;24:867–73. Rahiotis C, Kakaboura A, Loukidis M, et al. Curing efficiency of various types of light-curing units. Eur J Oral Sci 2004;112:89–94. Oberholzer TG, Du Preez IC, Kidd M. Effect of LED curing on the microleakage, shear bond strength and surface hardness of a resin-based composite restoration. Biomaterials 2005;26:3981–6.
Journal of Esthetic and Restorative Dentistry
Vol 27 • No 4 • 203–212 • 2015
211
EFFECT OF OCCLUSAL MATRICES ON COMPOSITE MICROHARDNESS Castillo-Oyagüe et al
21. Ritter AV, Cavalcante LM, Swift EJ Jr, et al. Effect of light-curing method on marginal adaptation, microleakage, and microhardness of composite restorations. J Biomed Mater Res B Appl Biomater 2006;78:302–11. 22. Lima AF, de Andrade KM, da Cruz Alves LE, et al. Influence of light source and extended time of curing on microhardness and degree of conversion of different regions of a nanofilled composite resin. Eur J Dent 2012;6:153–7. 23. Kumar CN, Gururaj M, Paul J. A comparative evaluation of curing depth and compressive strength of dental composite cured with halogen light curing unit and blue light emitting diode: an in vitro study. J Contemp Dent Pract 2012;13:834–7.
212
Vol 27 • No 4 • 203–212 • 2015
Journal of Esthetic and Restorative Dentistry
24. Santini A, Miletic V, Swift MD, et al. Degree of conversion and microhardness of TPO-containing resin-based composites cured by polywave and monowave LED units. J Dent 2012;40:577–84. 25. Tanthanuch S, Ruengsri P, Kukiattrakoon B. Optimal depth of cure for nanohybrid resin composite using quartz tungsten halogen and new high intensity light-emitting diode curing units. Gen Dent 2013;61:14–7.
Reprint requests: Raquel Castillo-Oyagüe, DDS, PhD, Department of Buccofacial Prostheses, Faculty of Dentistry, Complutense University of Madrid (U.C.M.)., Pza. Ramón y Cajal s/n, Madrid 28040, Spain; Tel.: 0034607367903; Fax: 0034913942029; email: [email protected]
DOI 10.1111/jerd.12156
© 2015 Wiley Periodicals, Inc.
