Monomer release, cell adhesion, and cell viability of indirect restorative materials manufactured with additive, subtractive, and conventional methods

PURPOSE

The aim of this study was to measure residual monomer, cell adhesion, and cell viability of 3-dimensional printable permanent resin (PR), hybrid ceramic block (HCB), and indirect composite (IC) produced with additive, subtractive, and conventional techniques.

METHODS

Five 8 × 8 × 2 mm3 samples of each material were prepared for each experiment. In a 24-h period, monomer release was analyzed with high-performance liquid chromatography, and cell viability and adhesion were evaluated with the water-soluble tetrazolium salt test. Data were analyzed with IBM SPSS Statistics 26.0 statistical software, and results were regarded as significant at α = 0.05.

RESULTS

Monomer release (triethylene glycol dimethacrylate, urethane dimethacrylate, and Bisphenol A glycerolate dimethacrylate) was significantly higher in the IC group. Mean cell viability was significantly lower in the HCB group than in the IC group.

CONCLUSION

All monomers in the tested materials were released at rates that were below clinical significance. Cell adhesion rates in the groups were similar. Cytotoxic response was classified as minor in the HCB and PR groups and non-cytotoxic in the IC group.

Twelve-year longitudinal clinical evaluation of bonded indirect composite resin inlays

OBJECTIVE

This prospective clinical study evaluated the clinical performance of one-, two- and multi-surface composite resin inlays over a 12-year period on premolars and molars.

METHOD AND MATERIALS

One clinician placed 113 indirect composite resin inlays (Signum, Heraeus Kulzer) in 30 patients that were bonded using a three-step bonding system and composite resin luting cement. Evaluations were made at 3 and 12 years by another clinician who was not involved in the placement of the restorations, using the modified US Public Health Service (USPHS) criteria. Data were analyzed using a nonparametric statistical test (Mann-Whitney U test) followed by Bonferroni correction (alpha = .05).

RESULTS

Fourteen patients could not be followed, yielding to the follow-up of 99 restorations. After 12 years, compared to the 3-year follow-up, tooth integrity, secondary caries, and sensitivity criteria showed significant change, while other parameters did not show significant difference (P > .05). Parameters such as loss of marginal integrity, loss of restoration integrity, loss of surface polish, and secondary caries received more frequently delta scores. At the 3-year follow-up, the clinical performance of one- or two-surface inlays did not show significant difference from multi-surface ones (P = .6317), but at the 12-year follow-up, the results were more favorable for multi-surface inlays. Overall, the failure rate at 12 years was 12%.

CONCLUSIONS

Adhesively bonded indirect composite resin inlays showed acceptable long-term clinical results in terms of function, but surface and margin characteristics changed over time.

Properties of indirect composites polymerized with laboratory light-emitting diode units

This study evaluated the light intensity of light-emitting diode (LED) units and the effects of five laboratory polymerization units on hardness and flexural strength. Two indirect composite materials (Cesead N and Solidex Hardura) were polymerized with five units (α-Light II, Hyper LII, LED Cure Master, Twinkle LED, and α-Light V). The light intensity of the devices was measured with a spectroradiometer. After light exposure, Knoop hardness number, flexural strength, and elastic modulus were determined. Evaluation of light intensity, using a wavelength range of 400 to 500 nm, revealed that the α-Light V and Hyper LII units had the highest light intensity. For the top surface of the two composites, the Knoop hardness number was significantly higher for the α-Light V and Hyper LII. For the two composite materials, flexural strength did not differ among the five polymerizing units. The present results indicate that the Cesead N and Solidex Hardura composites can be adequately polymerized with laboratory LED units.

Microtensile strength of resin cement bond to indirect composite treated by different output powers of Er:YAG laser

The study aimed to evaluate the effect of different output powers of Er:YAG laser on microtensile bonding strength of indirect composite to resin cements.36 indirect composite blocks (GC Gradia DA2, Japan) size 15 × 10 × 10 mm(3) were constructed, and divided into 12 groups, as follows:G1: control group (no treatment); Groups G2 to G6: treated with Er:YAG laser (2,940 nm) in noncontact mode, frequency 20 Hz, pulse duration 470 µs, with output power ranging from 2W to 6W; Groups G7 sandblasting, Groups 8 to G12: as Groups G2 to G 6 with preparatory sandblasting. One specimen from each group was analyzed by SEM; each specimen was fixed to a specialized metal jig using cyanoacrylate (Mitreapel, Beta Kimya San. Ve TIC, Iran) and debonded under tension with a universal testing machine (Zwick, Germany) at a crosshead speed of 0.5 mm min(-1). Sandblasting and laser can improve bond strength above an energy level of 150 mJ. SEM evaluation of laser-treated specimens showed irregularities and deep undercuts. T test analysis showed no significant difference between sandblasted and non-sandblasted group, with laser output power of 0, 100, or 150 mJ (P = 0.666, P = 0.875, and P =  .069); in the specimens irradiated with energy output of 200, 250, or 300 mJ, sandblasted specimens showed higher bond strength than non-sandblasted ones. The results demonstrate that, in composite resin irradiated with laser at energy output of 200-300 mJ, sandblasting might be a suitable procedure to enhance bond strength of resin cement.