Marginal Adaptation of Flowable vs Sonically Activated or Preheated Resin Composites in Cervical Lesions

Marginal integrity of prototype bioactive glass-doped resin composites in class II cavities

OBJECTIVES

This in vitro study examined the marginal integrity of experimental composite materials doped with bioactive glass (BG).

MATERIALS AND METHODS

Class-II MOD cavities were prepared and restored with one of the following composite materials: a commercial composite material as a reference (Filtek Supreme XTE), an experimental composite doped with BG 45S5 (C-20), and an experimental composite doped with a fluoride-containing BG (F-20). Six experimental groups (n = 8) were used, as each of the three composites was applied with (+) or without (-) a universal adhesive (Adper Scotchbond Multipurpose). All specimens were subjected to thermocycling (10,000 x, 5-55 °C) and then additionally stored in artificial saliva for eight weeks. Scanning electron micrographs of the mesial and the distal box were taken at three time points (initial, after thermocycling, and after eight weeks of storage in artificial saliva). The margins were classified as "continuous" and "non-continuous" and the percentage of continuous margins (PCM) was statistically analyzed (α = 0.05).

RESULTS

In most experimental groups, thermocycling led to a significant decrease in PCM, while the additional 8-week aging had no significant effect. F-20 + performed significantly better (p = 0.005) after 8 weeks storage in artificial saliva than the reference material with adhesive, while no statistically significant differences were observed at the other two time points. C-20 + exhibited significantly better PCM than the reference material with adhesive after thermocycling (p = 0.026) and after 8 weeks (p = 0.003).

CONCLUSIONS

Overall, the experimental composites with BG showed at least as good marginal adaptation as the commercial reference, with an indication of possible re-sealing of marginal gaps.

CLINICAL RELEVANCE

Maintaining or improving the marginal integrity of composite restorations is important to prevent microleakage and its likely consequences such as pulp irritation and secondary caries.

Preheating and "snow-plow" composite application technique affect double bond conversion but not bond strength to dentine

OBJECTIVE

To measure degree of conversion (DC) of a flowable composite, microtensile bond strength (MTBS) to dentine in the snow-plow technique with/without preheating and temperature in the preheated composite.

MATERIALS AND METHODS

For DC, snow-plow specimens of Filtek Ultimate Flowable (Flow) and Filtek Bulk Fill (Bulk) (3M) were prepared by light-curing composites simultaneously in standardized molds while in control groups light-curing was separate. DC of Flow was measured using micro-Raman spectroscopy. For MTBS, specimens were prepared on dentine of human extracted molars by simultaneous (snow-plow) or separate (control) light-curing. MTBS was measured using a universal testing machine after 24 h and 6 months. Data were analyzed using ANOVA with Tukey's post hoc (α = 0.05).

RESULTS

Increased curing time significantly increased DC in snow-plow from 13.4% ± 11.6% (10 s) to 31.8% ± 4.4% (40 s) albeit significantly lower than controls (p < 0.05). Preheated Bulk improved conversion in snow-plow (44.3% ± 1.7%) and control (50.5% ± 2.6%) (p < 0.05). No significant differences occurred in MTBS between groups (p > 0.05). MTBS values ranged between 66.7 ± 8.4 MPa (snow-plow group_21°C_baseline) and 54.1 ± 15.8 MPa (control_21°C_long-term). Temperature in the preheated Bulk dropped to ~38°C after 30 s.

CONCLUSIONS

Snow-plow technique, irrespective of preheating, resulted in lower DC of Flow than separate light-curing of composite increments. Snow-plow, irrespective of preheating, resulted in similar initial and long-term MTBS to dentine.

CLINICAL SIGNIFICANCE

Clinicians with preference for flowable composite liners in Class II restorations should be aware that the snow-plow technique of simultaneous light-curing of flowable and bulk-fill composite increments affects monomer-to-polymer conversion, albeit no effect on immediate, and long-term bonding to dentine was detected. Preheating sculptable bulk-fill composite improves conversion of the flowable liner in the snow-plow technique but has no detectable effect on bond strength to dentine.

Optimizing fracture resistance of endodontically treated maxillary premolars restored with preheated thermos-viscous composite post-thermocycling, a comparative study. Part I

PURPOSE

This research aimed to investigate fracture resistance of endodontically treated maxillary premolars restored using preheated thermo-viscous and fiber-reinforced bulk fill resin composite, in vitro.

METHODOLOGY

Sixty sound human maxillary premolars were selected and divided randomly into 6 groups of ten teeth each (n = 10). Group 1; is the positive control with sound unprepared teeth (P), Group 2; is the negative control in which Mesio-occluso-distal (MOD) cavities were left unrestored (N), Group 3; includes the teeth restored by incremental packing with conventional nanohybrid composite (ChP), Group 4; includes teeth restored with short fiber reinforced bulk fill composite (EF), Group 5; includes teeth restored with preheated thermo-viscous bulk fill composite (VB), and Group 6; includes teeth restored using packable bulk fill composite (XF) Tested restorative materials were bonded with a universal adhesive in self-etch mode. Teeth were kept in distilled water for 24 h at 37 °C proceeded by thermocycling (5- 55 °C, 1200×). Teeth were then exposed to compressive load till fracture at a crosshead speed of 1 mm/min. One-way ANOVA followed by Tukey post-hoc test was implemented to compare between more than two groups in non-related samples. The significance level was established at α = 0.05 for both tests.

RESULTS

Intact teeth significantly recorded the highest fracture resistance values among all groups. A significant difference was recorded among all the tested groups, with the EF recording the highest values, followed by the VB group then the XF group and ChP that recorded the lowest data. Negative control premolars significantly recorded the lowest fracture.

CONCLUSIONS

After thermocycling, endodontically treated maxillary premolars restored with pre-heated thermos-viscous composite did not exhibit an increase in fracture resistance. Notably, our findings indicate that short fiber-reinforced composite demonstrated significantly higher fracture resistance compared to other types of composites assessed in this study. This suggests the potential superiority of short fiber-reinforced composite in enhancing the overall structural integrity of endodontically treated teeth subjected to occlusal forces.

Various ways of pre-heating a bulk-fill thermoviscous composite in restoration in non-carious cervical lesions: 12-month randomized clinical trial

OBJECTIVE

The objective of the study is to evaluate through a randomized clinical trial the best method to preheat a composite resin, if using a Caps dispenser device associated with Caps Warmer (CD) or with a VisCalor Caps dispenser/warmer (VD) for restorations in non-carious cervical lesions (NCCLs).

MATERIAL AND METHODS

One hundred and twenty restorations were distributed to two groups (n = 60) according to the pre-heating way of thermoviscous bulk-fill composite resin. For the CD group, pre-heating was carried at 68 °C using a heating bench for 3 min. For the VD group, pre-heating was performed at 68 °C using a heating gun for 30 s. After that, pre-heated bulk-fill composites were directly inserted in the NCCLs. The total working time was recorded. The restorations were evaluated after 6 and 12 months of clinical performance according to the FDI criteria. Statistical analysis was performed using the Student's t test for unpaired samples for working time, and the Chi-square test for restoration clinical performance (α = 0.05).

RESULTS

Working time was shorter for VD with a statistically significant difference compared to CD (p = 0.01). Few restorations were lost or fractured after 12 months of clinical evaluation (p > 0.05). The retention rates were 96.7% (CI 95 %: 88.6-99.1%) for CD and 98.3% (CI 95 %: 91.1-99.7%) for VD. The other FDI parameters were considered clinically acceptable.

CONCLUSIONS

The different pre-heating ways did not influence the clinical performance of thermoviscous bulk-fill composite restorations in NCCLs after 12 months.

CLINICAL RELEVANCE

Regardless of the bulk-fill thermoviscous composite resin pre-heating ways, the restorations are clinically acceptable after 12 months.

Improved Flexural Properties of Experimental Resin Composites Functionalized with a Customized Low-Sodium Bioactive Glass

This study evaluated the flexural properties of an experimental composite series functionalized with 5-40 wt% of a low-Na F-containing bioactive glass (F-series) and compared it to another experimental composite series containing the same amounts of the conventional bioactive glass 45S5 (C-series). Flexural strength and modulus were evaluated using a three-point bending test. Degree of conversion was measured using Fourier-transform infrared spectroscopy. Weibull analysis was performed to evaluate material reliability. The control material with 0 wt% of bioactive glass demonstrated flexural strength values of 105.1-126.8 MPa). In the C-series, flexural strength ranged between 17.1 and 121.5 MPa and was considerably more diminished by the increasing amounts of bioactive glass than flexural strength in the F-series (83.8-130.2 MPa). Analogously, flexural modulus in the C-series (0.56-6.66 GPa) was more reduced by the increase in bioactive glass amount than in the F-series (5.24-7.56 GPa). The ISO-recommended "minimum acceptable" flexural strength for restorative resin composites of 80 MPa was achieved for all materials in the F-series, while in the C-series, the materials with higher bioactive glass amounts (20 and 40 wt%) failed to meet the requirement of 80 MPa. The degree of conversion in the F-series was statistically similar or higher compared to that of the control composite with no bioactive glass, while the C-series showed a declining degree of conversion with increasing bioactive glass amounts. In summary, the negative effect of the addition of bioactive glass on mechanical properties was notably less pronounced for the customized bioactive glass than for the bioactive glass 45S5; additionally, mechanical properties of the composites functionalized with the customized bioactive glass were significantly less diminished by artificial aging. Hence, the customized bioactive glass investigated in the present study represents a promising candidate for functionalizing ion-releasing resin composites.