Effect of mold diameter on the depth of cure of a resin-based composite material

Ability of short exposures from laser and quad-wave curing lights to photo-cure bulk-fill resin-based composites

OBJECTIVE

This study investigated the ability of a laser, and a 'quad-wave' LCU, to photo-cure paste and flowable bulk-fill resin-based composites (RBCs).

METHODS

Five LCUs and nine exposure conditions were used. The laser LCU (Monet) used for 1 s and 3 s, the quad-wave LCU (PinkWave) used for 3 s in the Boost and 20 s in the Standard modes, the the multi-peak LCU (Valo X) used for 5 s in the Xtra and 20 s in the Standard modes, were compared to the polywave PowerCure used in the 3 s mode and for 20 s in the Standard mode, and to the mono-peak SmartLite Pro used for 20 s. Two paste consistency bulk-fill RBCs: Filtek One Bulk Fill Shade A2 (3 M), Tetric PowerFill Shade IVA (Ivoclar Vivadent), and two flowable RBCs: Filtek Bulk Fill Flowable Shade A2 (3 M), Tetric PowerFlow Shade IVA (Ivoclar Vivadent) were photo-cured in 4-mm deep x 4-mm diameter metal molds. The light received by these specimens was measured using a spectrometer (Flame-T, Ocean Insight), and the radiant exposure delivered to the top surface of the RBCs was mapped. The immediate degree of conversion (DC) at the bottom, and the 24-hour Vickers Hardness (VH) at the top and bottom of the RBCs were measured and compared.

RESULTS

The irradiance received by the 4-mm diameter specimens ranged from 1035 mW/cm² (SmartLite Pro) to 5303 mW/cm² (Monet). The radiant exposures between 350 and 500 nm delivered to the top surface of the RBCs ranged from 5.3 J/cm² (Monet in 1 s) to 26.4 J/cm² (Valo X), although the PinkWave delivered 32.1 J/cm² in 20 s 350 to 900 nm. All four RBCs achieved their maximum DC and VH values at the bottom when photo-cured for 20 s. The Monet used for 1 s and the PinkWave used for 3 s on the Boost setting delivered the lowest radiant exposures between 420 and 500 nm (5.3 J/cm² and 3.5 J/cm² respectively), and they produced the lowest DC and VH values.

CONCLUSIONS

Despite delivering a high irradiance, the short 1 or 3-s exposures delivered less energy to the RBC than 20-s exposures from LCUs that deliver> 1000 mW/cm². There was an excellent linear correlation (r > 0.98) between the DC and the VH at the bottom. There was a logarithmic relationship between the DC and the radiant exposure (Pearson's r = 0.87-97) and between the VH and the radiant exposure (Pearson's r = 0.92-0.96) delivered in the 420-500 nm range.

Impact of light-curing distance on the effectiveness of cure of bulk-fill resin-based composites

Objective

To investigate the effect of light-curing distance on the effectiveness of cure (EC) of bulk-fill resin-based composites (RBCs).

Materials and methods

Two bulk-fill RBCs (a Tetric N-Ceram Bulk Fill (TN) and a Filtek Bulk Fill (FK)) are evaluated. Specimens (4 mm high) are cured for 20 s at different distances (0 mm (D0), 2 mm (D2), 4 mm (D4), 6 mm (D6) and 8 mm (D8)) and stored for 24 h in 100% relative humidity at 37 °C. The top and bottom surface hardness (SH) (n = 12) are assessed using a Knoop microhardness tester and the EC is calculated. The EC is characterized by the hardness ratio (HR) (mean bottom: top SH). An HR of 0.8 is used as the benchmark for an effective/adequate cure. Data are analyzed using one-way analysis of variance and Tukey’s post hoc test (α = 0.05). Correlations between the top and bottom surfaces are examined using the Pearson correlation (α = 0.05).

Results

For the TN, the HR at D8 is significantly lower than all other light-curing distances, while for the FK, it is significantly lower than D0 only.

Conclusion

The effect of light-curing distance on the EC of bulk-fill RBCs is material dependent. Notwithstanding the light-curing distance, the EC of the FK and TN is below the threshold HR value of 0.8 when photopolymerized for 20 s in 4 mm increments in black opaque molds.

Comparisons of ISO depth of cure for a resin composite in stainless-steel and natural-tooth molds

The purpose of this study was to compare the depth of cure (DOC) of a resin-based composite (RBC) using the ISO DOC protocol with stainless-steel and molar-tooth molds (4 mm cylindrical cavity). The tooth mold included testing with and without the occlusal surface being covered with black tape around the cavity opening. The RBC was cured with either halogen (HAL) or light-emitting diode (LED) light. The results showed that specimens made in the non-taped tooth mold had DOCs that were significantly greater (28%-35%) than those in the stainless-steel mold. The taped tooth mold also produced significantly greater DOCs, but only by 6%-8%. Knoop hardness (KNH) measurements along the central axis of the RBC specimens showed that depths for 80% of maximum hardness were substantially greater than those determined by the ISO DOC protocol but were limited to the center and quickly dropped below 80% in a lateral direction. The KHN mapping for each of the three molds found that the ISO DOCs could validate a KHN of ≥80% across the RBC to the periphery, only for the non-taped tooth mold. This was due to light incident on the tooth surrounding the RBC being scattered into the RBC.

Depth of cure of high-viscosity bulk-fill and conventional resin composites using varying irradiance exposures with a light-emitting diode curing unit

The purpose of this study was to determine the depth of cure (DOC) of three resin-based composites (RBCs) using varying irradiance exposures with a corded light-emitting diode curing unit. DOCs for Filtek Z250, TPH Spectra, and Tetric EvoCeram Bulk Fill were determined using the International Organization for Standardization (ISO) Standard 4049. The RBCs were light-polymerized using three different power modes and manufacturer-recommended curing times. Irradiance was determined using a spectrometer sensor and the total energy density was calculated for each power mode and concomitant polymerization time. The DOC data were analyzed with a two-way analysis of variance and Tukey's post hoc test. Tetric EvoCeram Bulk Fill produced significantly greater DOCs than TPH and Z250 (P < 0.05) for all three power mode settings. Overall, the DOC of Tetric EvoCeram Bulk Fill was greater than those of TPH and Z250 at all power settings, but the individual RBCs did not show a significant DOC difference among the three power settings (P > 0.05).

The Influence of Distance on Radiant Exposure and Degree of Conversion Using Different Light-Emitting-Diode Curing Units

Objectives:

To investigate the influence of curing distance on the degree of conversion (DC) of a resin-based composite (RBC) when similar radiant exposure was achieved using six different light-curing units (LCUs) and to explore the correlation among irradiance, radiant exposure, and DC.

Methods and Materials:

A managing accurate resin curing-resin calibrator system was used to collect irradiance data for both top and bottom specimen surfaces with a curing distance of 2 mm and 8 mm while targeting a consistent top surface radiant exposure. Square nanohybrid-dual-photoinitiator RBC specimens (5 × 5 × 2 mm) were cured at each distance (n=6/LCU/distance). Irradiance and DC (micro-Raman spectroscopy) were determined for the top and bottom surfaces. The effect of distance and LCU on irradiance, radiant exposure, and DC as well as their linear associations were analyzed using analysis of variance and Pearson correlation coefficients, respectively (α=0.05).

Results:

While maintaining a similar radiant exposure, each LCU exhibited distinctive patterns in decreased irradiance and increased curing time. No significant differences in DC values (63.21%-70.28%) were observed between the 2- and 8-mm distances, except for a multiple-emission peak LCU. Significant differences in DC were detected among the LCUs. As expected, irradiance and radiant exposure were significantly lower on the bottom surfaces. However, a strong correlation between irradiance and radiant exposure did not necessarily result in a strong correlation with DC.

Conclusions:

The RBC exhibited DC values &gt;63% when the top surface radiant exposure was maintained, although the same values were not reached for all lights. A moderate-strong correlation existed among irradiance, radiant exposure, and DC.