Comparative analysis of self-cure and dual cure-dental composites on their physico-mechanical behaviour

Bonding Performance and Interfacial Ultra-Morphology/Nanoleakage of a Modern Self-Curing Bulk-Fill Restorative System: An In Vitro Study

OBJECTIVES

 The objective of this study was to evaluate the bonding performance and the interfacial ultramorphology of an innovative self-curing restorative system compared with a conventional light-curing resin composite applied on dentin in etch-and-rinse (ER) or self-etch (SE) mode.

MATERIALS AND METHODS

 Twenty cavities (class I) were prepared in sound dentin and restored using two materials: (1) CERAM (n = 10; CERAM.X ONE, Dentsply Sirona) in combination with a universal adhesive system (PBU [Prime & Bond Universal]), or (2) STELA (n = 10; Stela Automix, SDI) in combination with its adhesive primer. Half of the specimens from each group were bonded in ER or SE mode. Specimens underwent microtensile bond strength testing after 24 hours of storage in artificial saliva. Failure mode was determined using a stereomicroscope, and fractographic analysis was performed using scanning electron microscopy. The interfacial ultramorphology/nanoleakage of the resin-dentin slabs was analyzed through dye-assisted confocal microscopy.

STATISTICAL ANALYSIS

 For quantitative analysis, bond strength values (in MPa) were assessed for normality and variance using Kolmogorov-Smirnov and Levene's tests, followed by ANOVA based on restorative material and adhesive bonding protocol, with Fisher's least significant difference post hoc test (α = 5%).

RESULTS

 SE groups exhibited significantly lower bond strength (17.4 MPa for CERAM; 26.2 MPa for STELA) compared with ER groups (35.8 MPa for CERAM; 33.6 MPa for STELA) (p < 0.05). CERAM applied in SE mode showed significantly lower bond strength compared with STELA applied in SE mode. Furthermore, CERAM applied in SE mode was the only group presenting a pre-test failure rate (27%). The failure mode was predominantly mixed in ER groups and adhesive in SE groups. Nanoleakage was observed clearly in the CERAM groups applied in both ER and SE modes but was less evident in the STELA groups.

CONCLUSION

 The new self-curing material (STELA) used in SE or ER may represent a promising clinical option to provide adequate interfacial adaptation and strong bonding to dentin when restoring deep class I cavities. The use of conventional adhesives in deep class I cavities may generate resin-dentin interfaces characterized by gaps and leakages.

Proposal of a Modular Classification System for Direct Dental Resin Composites Based on Clinical Applications

The adhesive-resin composite pair has been the cornerstone of direct restorations in dentistry for many years. Resin composites are traditionally classified in three ways based on their inorganic structure, their organic composition and their viscosity. While these classifications have long been associated with the optical, mechanical, and clinical properties of resin composites, recent studies indicate that this classification is not always valid. In recent years, a significant expansion of the range of clinical resin composite families has occurred, each with varying degrees of validation through in vitro and clinical studies. As a result, new resin composites with distinct structures, viscosities, and clinical indications have emerged. Despite this progress, a formal classification of the clinical features of all resin composites is still lacking, leading to terminological inconsistencies in research and potential confusion among clinicians. This brief review, supported by an exhaustive search of the dental literature, proposes a new clinical classification system for resin composites based on their key clinical features to help clinicians and researchers easily identify the key clinical characteristics of formulations. This modular classification, encompassing eight main families and 14 characteristics, is particularly suited to future developments, as current trends aim to simplify procedures by integrating multiple formulations into single products.

Ability of a novel primer to enhance the polymerization of a self-cured resin composite

OBJECTIVE

This study evaluated the degree of conversion (DC), polymerization kinetics, and temperature of a new self-cure bulk-fill resin-based composite (Stela Automix, SDI).

METHODS

The study was divided into seven groups: (1) Stela Primer, (2) Stela Automix, (3) Stela Automix exposed to light for 20 s after 100 s, (4) Stela Primer with Stela Automix, (5) Stela Primer with Stela Automix and exposed to light for 20 s after 100 s, (6) Scotchbond Universal with Stela Automix, and (7) Scotchbond Universal with Stela Automix and exposed to light for 20 s after 100 s. The real-time reaction rates and DC at the bottom of 2 mm thick specimens at ∼32 °C were measured at 720 s after insertion using a spectrometer with an Attenuated Total Reflectance detector. The temperature of Stela, Stela exposed to light, Stela Primer with Stela, and Stela Primer with Stela exposed to light were measured by an infrared thermal camera in human molar teeth with Class I cavities. The temperature was recorded in real-time every 0.03 s for 720 s. The results were compared with ANOVA and Tukey's multiple comparison test (α = 0.05).

RESULTS

The highest degree of conversion (DC) at the 2 mm depth was achieved when Stela Primer was combined with Stela (72.4 ± 3.5 % at 720 s). Stela could self-cure independently, but not as rapidly or effectively as when used with its Primer. The greatest temperature increase was for the light-cured Stela, followed by Stela Primer with Stela RBC exposed to light for 20 s. The Scotchbond Universal bonding system did not significantly increase the DC compared to Stela alone, except when exposed to light for 20 s, which slightly increased the final DC. Exposing Stela to light for 20 s did not improve the final DC of Stela as much as using the Stela Primer, but it did increase the temperature and prolonged the time taken to return to 37 °C.

SIGNIFICANCE

The Stela primer accelerates the degree of conversion of Stela. The reaction occurred rapidly and achieved a higher DC at the bottom of the specimens where the Stela was in contact with the Stela primer. Exposing Stela to light for 20 s is not recommended. Instead, Stela should be used with Stela Primer.

Clinical evaluation of a new chemically-cured bulk-fill composite in posterior restorations: 6-month multicenter double-blind randomized clinical trial

OBJECTIVE

To evaluate the postoperative sensitivity (POS), as well as the clinical performance of posterior restorations using a new chemically-cured bulk-fill composite (Stela Automix and Stela Capsule, SDI) comparing with a light-cured bulk-fill composite after 6 months.

METHODS

Fifty-five participants with at least three posterior teeth needing restoration were recruited. A total of 165 restorations were performed on Class I or Class II cavities. After the application of Stela primer, the chemically-cured composite (Stela Automix or Stela Capsule) was inserted. For the light-cured composite group, a universal adhesive (Scotchbond Universal) was applied with a bulk-fill composite (Filtek One). Participants were evaluated for spontaneous and stimulated POS in the baseline, after 48 h, 7 days, and 6 months. Additionally, each restoration was assessed using the updated version of FDI criteria after 6 months. The differences in the proportions of the groups were compared by Cochran test statistics (α = 0.05).

RESULTS

Both chemically-cured composites showed a lower risk of POS compared to the light-cured composite at baseline and up to 48 h (p < 0.04). A significantly lower surface luster and texture was observed for the Stela Capsule composite compared to the light-cured bulk-fill composite (baseline and 6 months; p = 0.03). A significant color mismatch was observed for the light-cured bulk-fill composite compared to the chemically-cured composites (baseline and 6 months; p = 0.03). No significant differences were observed in any other item evaluations (p > 0.05).

CONCLUSION

Chemically-cured composites exhibit lower postoperative sensitivity and less color mismatch compared to a light-cured bulk-fill composite after 6 months of clinical service.

CLINICAL SIGNIFICANCE

The chemically-cured composites appear to be an appealing option for restoring posterior teeth, as they exhibit lower postoperative sensitivity compared to a light-cured bulk-fill composite, both at baseline and up to 48 h, and less color mismatch.

Bonding performance and interfacial adaptation of modern bulk-fill restorative composites after aging in artificial saliva: an in vitro study

OBJECTIVES

This study aimed at comparing the microtensile bond strength (MTBS) and interfacial adaptation of a modern self-curing and a light-curing restorative bulk-fill composite to a conventional composite applied with the layering technique.

METHODS

Forty-eight occlusal cavities were divided in three main groups (16/group) based on tested materials: (i) STELA, bulk-fill self-curing restorative (STELA, SDI Ltd.); (ii) 3 M-BULK, bulk-fill composite (Filtek One Bulk-Fill, 3 M Oral Care); and (iii) 3 M-CTR, a conventional composite (Filtek Supreme XTE, 3 M Oral Care). These were used in combination with their adhesives in self-etch (SE) or etch-and-rinse (ER) mode. Specimens stored in artificial saliva (24 h or 12 months) were evaluated for MTBS and fractography. The interfacial analysis was performed through confocal microscopy. ANOVA and Fisher's LSD post hoc tests were performed with a level of significance of 5%.

RESULTS

All the tested materials applied in ER mode presented (24 h) greater bond strength than in SE mode. Although all materials showed a significant drop in the bond strength after prolonged storage, STELA showed the highest bonding performance and interfaces with few gaps. 3 M-BULK had the lowest bond strength and an interface with several voids and gaps.

CONCLUSIONS

All materials were affected by interface degradation and bonding reduction over prolonged aging. However, their use in combination with adhesives applied in ER mode may offer greater immediate bonding performance.

CLINICAL RELEVANCE

The use of restorative light-curing bulk-fill composites may generate gaps at the bonding interface and voids. STELA may represent a suitable alternative to avoid such issues.