Polymerization and shrinkage stress formation of experimental resin composites doped with nano- vs. micron-sized bioactive glasses.

This study investigated the effect of adding bioactive glass 45S5 (BG) of different particle sizes to dental composite on resin polymerization and shrinkage stress formation. Commercial flowable composite was mixed with either 15 wt% BG fillers (nanometric, micrometric, or hybrid BG) or inert barium glass. Real-time linear polymerization shrinkage and shrinkage stress were recorded, and the degree of conversion was measured using FTIR spectroscopy. The commercial (unmodified) composite developed significantly higher linear shrinkage and shrinkage stress than the groups with 15 wt% added inert or BG fillers. After adding inert barium glass, the composite showed significantly higher linear shrinkage than when micrometric BG was added. The addition of bioactive or inert glass fillers did not affect the degree of conversion. Shrinkage stress can be reduced by adding inert or bioactive fillers (nano- and/or microparticulate BG) without affecting monomer conversion.

Effect of rapid high-intensity light-curing on polymerization shrinkage properties of conventional and bulk-fill composites.

OBJECTIVES: To compare the effect of high-intensity (3 s with 3440 mW/cm2) and conventional (10 s with 1340 mW/cm2) light-curing on shrinkage properties and degree of conversion of conventional and bulk-fill resin composites, including two composites specifically designed for high-intensity curing. METHODS: Real-time linear shrinkage and shrinkage force of 1.5 mm thick composite specimens were measured for 15 min after the start of light-curing using custom-made devices. From the shrinkage force data, maximum shrinkage force rate and time to achieve maximum shrinkage force rate were determined. Degree of conversion was measured using Fourier transform infrared spectrometry. RESULTS: Flowable composites showed significantly higher linear shrinkage compared to sculptable composites (1.93-2.91 % vs. 1.15-1.54 %), as well as significantly higher shrinkage forces (18.7-24.4 N vs. 13.5-17.0 N). Degree of conversion amounted to 45.8-60.1 %. For high-intensity curing, degree of conversion was significantly lower in three out of seven composites, whereas shrinkage forces were either increased, decreased, or unchanged compared to conventional curing. For high-intensity curing, maximum shrinkage rates were 6-61 % higher, whereas times to achieve maximum shrinkage force rate were 15-53 % shorter compared to conventional curing. Composites specifically designed for high-intensity curing showed shrinkage parameters comparable to other investigated composites. CONCLUSION: Shrinkage behavior under conditions of high-intensity light-curing was material-dependent. Shrinkage force kinetics were more strongly affected by high-intensity curing than absolute values of linear shrinkage and shrinkage force. CLINICAL SIGNIFICANCE: Despite being attractive for its convenience, high-intensity curing can lead to considerably faster development of shrinkage forces in the early stage of polymerization.

Effect of fiber incorporation on the contraction stress of composite materials.

OBJECTIVES: This study aimed to assess the effects of fiber incorporation on the contraction stress (CS), time to gelation (TG), and temperature rise (TR) features of two experimental resin-based composites (RBCs) in comparison to those of bulk-fill RBCs and conventional RBCs in simulated, clinically relevant cavities. MATERIALS AND METHODS: CS over 300 s, TG and TR were assessed by a stress-strain analyzer (SSA T80) in two cavity configurations (2 × 4 × 4 mm3/4 × 4 × 4 mm3/configuration value [Formula: see text] and [Formula: see text]) for two experimental RBCs, eight bulk-fill RBCs (EverX Posterior, Filtek Bulk Fill, SDR, SonicFill, Tetric EvoCeram Bulk Fill, Venus Bulk Fill, X-tra base, and X-tra Fill) and one RBC (Filtek Supreme XTE) by light curing (1200 mW/cm2) (n = 10). The experimental materials used were based on EverX Posterior with modifications made to the fiber and filler content. Statistical analyses were performed via ANOVA; multiple pair-wise comparisons were performed via Tukey's test, and homogeneous subsets were identified ("multcomp" package, R). RESULTS: CS values ranged from 1.00 to 4.07 MPa (2 × 4 × 4 mm3) and from 0.97 to 2.49 MPa (4 × 4 × 4 mm3); TG values ranged from 1.31 to 4.05 s (2 × 4 × 4 mm3) and from 1.39 to 3.84 s (4 × 4 × 4 mm3). SDR values showed lowest stress values in both cavity configurations. The experimental composite with fibers presented significantly higher stress values than did the experimental composite without fibers. CONCLUSION: Bulk-fill RBCs showed lower levels of stress than did conventional RBCs. The incorporation of fibers had no positive impact on the CS and TG. CLINICAL RELEVANCE: Appropriate material selection may be essential to clinical success because certain RBCs exhibit higher CS, TG, and TR values.

Polymerization shrinkage and shrinkage force kinetics of high- and low-viscosity dimethacrylate- and ormocer-based bulk-fill resin composites.

The aim of the present study was to investigate polymerization shrinkage, shrinkage force development, and degree of monomer conversion of high- and low-viscosity dimethacrylate- and ormocer-based bulk-fill resin composites. Two flowable bulk-fill composites (SDR, x-tra base), two high-viscosity bulk-fill composites (Bulk Ormocer, SonicFill), and two conventional composite materials (Esthet X flow, Esthet X HD) were photoactivated for 20 s at 1275 mW/cm2. Linear polymerization shrinkage and shrinkage force were recorded in real time using custom-made devices, and the force rate and time to achieve maximum force rate were determined. Degree of conversion was measured using Fourier-transform infrared spectroscopy. Data were analyzed with one-way ANOVA and Tukey's HSD post-hoc test, and bivariate correlations were computed (α = 0.05). The category of high-viscosity bulk-fill resin composites showed the significantly lowest polymerization shrinkage and force development. Within the tested flowable composite materials, SDR bulk-fill generated the significantly lowest shrinkage forces during polymerization and attained the significantly highest degree of conversion. Strong positive correlations were revealed between shrinkage force and both linear polymerization shrinkage (r = 0.902) and maximum force rate (r = 0.701). Linear shrinkage and shrinkage force both showed a negative correlation with filler volume content (r = - 0.832 and r = - 0.704, respectively). Bulk-fill resin composites develop lower shrinkage forces than their conventional flowable and high-viscosity counterparts, respectively, which supports their use for restoring high C-factor posterior cavities. Overall, bulk-fill composites with high filler amount and low force rate showed the most favorable shrinkage force characteristics.

Polymerization shrinkage and porosity profile of dual cure dental resin cements with different adhesion to dentin mechanisms.

This research aims to probe the porosity profile and polymerization shrinkage of two different dual cure resin cements with different dentin bonding systems. The self-adhesive resin cement RelyX U200 (named RU) and the conventional Allcem Core (named AC) were analyzed by x-ray microtomography (µCT) and Scanning Electron Microscopy (SEM). Each cement was divided into two groups (n = 5): dual-cured (RUD and ACD) and self-cured (RUC and ACC). µCT demonstrated that the method of polymerization does not influence the porosity profile but the polymerization shrinkage. Fewer concentration of pores was observed for the conventional resin cement (AC), independently the method used for curing the sample. In addition, SEM showed that AC has more uniform surface and smaller particle size. The method of polymerization influenced the polymerization shrinkage, since no contraction for both RUC and ACC was observed, in contrast with results from dual-cured samples. For RUD and ACD the polymerization shrinkage was greater in the lower third of the sample and minor in the upper third. This mechanical behavior is attributed to the polymerization toward the light. µCT showed to be a reliable technique to probe porosity and contraction due to polymerization of dental cements.

Fotopolimerización de resinas compuestas a través de diversos espesores de tejido dental / Light-polymerization of composite resins through different thicknesses of dental tissue

Objetivos: Determinar el espesor de tejido dental a través del cual se presente la fotopolimerización de la resina Prime Dent® con mínimo encogimiento y profundidad de curado adecuada. Método: Se obtuvieron 80 láminas de molares de 1, 2, 3 y 4 mm de espesor (20 por grupo). Se midió la contracción y se calculó el encogimiento de la resina polimerizando (Visilux 2, 3 M) a través de cada lámina (60 s, 400 mW/cm2). Se utilizó la técnica de bonded-disc. Se realizaron pruebas de profundidad de curado, midiendo el espesor de resina polimerizada de acuerdo con la especificación No. 27 ADA. Un grupo control sin tejido dental fue preparado para ambas propiedades. Los datos fueron analizados usando ANOVA con prueba de Tukey (p < 0.001). Resultados: Profundidad de curado: a medida que aumentó el espesor, ésta disminuyó, existiendo diferencia estadísticamente significativa en todos los grupos. El espesor que mostró menor encogimiento, cumpliendo con una profundidad de curado adecuada (ADA marca como valor mínimo, 1 mm) fue de 3 mm. Encogimiento: a medida que aumentó el espesor, éste disminuyó, no existiendo diferencia estadísticamente significativa entre los grupos de 2 y 3 mm. Conclusiones: De acuerdo con los resultados, es posible polimerizar a través de un espesor de 3 mm, por lo que no se recomienda polimerizar a través de un espesor de 4 mm. Es necesario obtener más propiedades mecánicas utilizando diferentes espesores de tejido dental.

Objectives: To determine the thickness of dental tissue through which Prime Dent Resin® might exhibit light-polymerization with minimum shrinkage and suitable curing depth. Method: 80 laminae measuring 1, 2, 3 and 4 mm thickness were obtained from molars (20 laminae per group). Contraction was measured and resin shrinkage was calculated by polymerization (Visilux 2, 3 M) though each lamina (60 s, 400 mW/cm2). Bonded-disk technique was used. Depth of curing tests were undertaken by measuring the thickness of polymerized resin according to ADA's specification number 27. A control group without dental tissue was prepared for both properties. Data were analyzed using ANOVA with Tukey test (p < 0.001). Results: Curing depth: curing depth decreased as thickness increased. All groups revealed statistically significant differences. The thickness that exhibited lesser shrinkage nonetheless meeting with suitable curing depth (ADA establishes minimum value of 1 mm) was the 3 mm group. Shrinkage: as thickness increased, shrinkage decreased; no statistically significant difference was reported for groups 2 and 3 mm. Conclusions: According to obtained results, it is possible to polymerize through a 3 mm thickness, therefore polymerization is not recommended through a 4 mm depth. It will be necessary to obtain further mechanical properties using different thicknesses of dental tissue.

Pre-heating of high-viscosity bulk-fill resin composites: effects on shrinkage force and monomer conversion.

OBJECTIVES: To investigate the influence of pre-heating of high-viscosity bulk-fill composite materials on their degree of conversion and shrinkage force formation. METHODS: Four bulk-fill composite materials (Tetric EvoCeram Bulk Fill-TECBF, x-tra fil-XF, QuixFil-QF, SonicFill-SF) and one conventional nano-hybrid resin composite (Tetric EvoCeram-TEC) were used. The test materials were either kept at room temperature or pre-heated to 68°C by means of a commercial heating device, before being photoactivated with a LED curing unit for 20s at 1170mW/cm(2). Shrinkage forces (n=5) of 1.5-mm-thick specimens were recorded in real-time for 15min inside a temperature-controlled chamber at 25°C (simulating intraoral temperature after rubber dam application) with a custom-made stress analyzer. Degree of conversion (n=5) was determined at the bottom of equally thick (1.5mm) specimens using Fourier transform infrared spectroscopy. Data were analyzed with Student's t-test, ANOVA and Tukey's HSD post-hoc test (α=0.05). RESULTS: Composite pre-heating significantly increased the degree of conversion of TECBF, but had no effect on monomer conversion of the other materials investigated. For each of the test materials, pre-heated composite generated significantly lower shrinkage forces than room-temperature composite. At both temperature levels, TECBF created the significantly highest shrinkage forces, and QF caused significantly higher shrinkage forces than both XF and TEC. CONCLUSIONS: Both the composite material and the pre-cure temperature affect shrinkage force formation. Pre-heating of bulk-fill and conventional restorative composites prior to photoactivation decreases polymerization-induced shrinkage forces without compromising the degree of conversion. CLINICAL SIGNIFICANCE: Composite pre-heating significantly reduces shrinkage force formation of high-viscosity bulk-fill and conventional resin composites, while maintaining or increasing the degree of monomer conversion, dependent upon the specific composite material used.

Effect of modulated photo-activation on polymerization shrinkage behavior of dental restorative resin composites.

This study investigated the influence of modulated photo-activation on axial polymerization shrinkage, shrinkage force, and hardening of light- and dual-curing resin-based composites. Three light-curing resin composites (SDR bulk-fill, Esthet X flow, and Esthet X HD) and one dual-curing material (Rebilda DC) were subjected to different irradiation protocols with identical energy density (27 J cm(-2) ): high-intensity continuous light (HIC), low-intensity continuous light (LIC), soft-start (SS), and pulse-delay curing (PD). Axial shrinkage and shrinkage force of 1.5-mm-thick specimens were recorded in real time for 15 min using custom-made devices. Knoop hardness was determined at the end of the observation period. Statistical analysis revealed no significant differences among the curing protocols for both Knoop hardness and axial shrinkage, irrespective of the composite material. Pulse-delay curing generated the significantly lowest shrinkage forces within the three light-curing materials SDR bulk-fill, Esthet X flow, and Esthet X HD. High-intensity continuous light created the significantly highest shrinkage forces within Esthet X HD and Rebilda DC, and caused significantly higher forces than LIC within Esthet X flow. In conclusion, both the composite material and the applied curing protocol control shrinkage force formation. Pulse-delay curing decreases shrinkage forces compared with high-intensity continuous irradiation without affecting hardening and axial polymerization shrinkage.

Resin composites: Modulus of elasticity and marginal quality.

OBJECTIVE: To investigate how the modulus of elasticity of resin composites influences marginal quality in restorations submitted to thermocyclic and mechanical loading. METHODS: Charisma, Filtek Supreme XTE and Grandio were selected as they were found to possess different moduli of elasticity but quite similar polymerization contraction. MOD cavities (n=30) were prepared in extracted premolars, restored and then subjected to thermocyclic and mechanical loading. Marginal quality of the restorations before and after loading was analyzed on epoxy replicas under a scanning electron microscope. The percentage of gap-free margins and occurrence of paramarginal fractures were registered. Modulus of elasticity and polymerization contraction were analyzed with parametric and margins with nonparametric ANOVA and post hoc Tukey HSD or Wilcoxon rank-sum tests, respectively. The number of paramarginal fractures was analyzed with exact Fisher tests (α=0.05). RESULTS: Grandio demonstrated significantly more gap-free enamel margins than Charisma and Filtek Supreme XTE, before and after loading (p<0.01), whereas there was no difference between Charisma and Filtek Supreme XTE (p>0.05). No significant effect of resin composite (p=0.81) on the quality of dentine margins was observed, before or after loading. Deterioration of all margins was evident after loading (p<0.0001). More paramarginal enamel fractures were observed after loading in teeth restored with Grandio when compared to Charisma (p=0.008). CONCLUSIONS: The resin composite with the highest modulus of elasticity resulted in the highest number of gap-free enamel margins but with an increased incidence of paramarginal enamel fractures. CLINICAL SIGNIFICANCE: The results from this study suggest that the marginal quality of restorations can be improved by the selection of a resin composite with modulus of elasticity close to that of dentine, although an increase in paramarginal enamel fractures can result as a consequence.

Influência da técnica de inserção de resina composta sobre o selamento marginal em restaurações estéticas oclusais / The influence of the insertion technique of composite resin on the microleaakage of occlusal esthetic restorations

Este trabalho objetiva avaliar a influência da técnica de inserção de resina composta sobre o selamento marginal de restaurações oclusais. Cavidades oclusais em 60 molares humanos foram restauradas de acordo com os grupos: 1 - Filtek Z350/3M ESPE; 2 - Ice®/SDI e 3 - Concept Advantage®/Vigodent, subdivididos em: A - Técnica de inserção incremental e B - Técnica de Inserção cruciforme. Os corpos de prova sofreram: estresse térmico (500 ciclos; 5ºC +/- 1 e 55ºC +/-1); exposição ao agente químico traçador (AQT); seccionamento e análise (lupa estereoscópica 25X) para atribuição de escores de 0 (sem penetração do AQT) a 2 (penetração máxima do AQT). Os resultados evidenciaram os maiores percentuais para o escore 0 para 3-B (80,0%), 2-A (75,0%), 2-B (75,0%), 1-A (70,0%). Houve diferenças estatisticamente significantes nos grupos 1 e 3, não ocorrendo no grupo 2 (testes de Mann-Whiteny e Kruskal-Wallis / nível de significância de 5%). Concluiu-se que nenhuma técnica de inserção foi capaz de impedir a microinfiltração e que a técnica cruciforme representa uma alternativa à técnica incremental, considerando o tipo de resina composta empregado.

The aim of this study was to evaluate the influence of the insertion technique of composite resin on the microleakage of occlusal restorations. Occlusal cavities in 60 human molars were restored according to the following groups: 1 - Filtek Z350?/3M ESPE; 2 - Ice?/ SDI and 3 - Concept Advantage ? / Vigodent; subdivided into: A - Technique of incremental insertion and B - cruciform Insertion Technique. The specimens were toexposed: heat stress (500 cycles, 5 ? C + / - 1 and 55 ? C + / -1); exposure to the chemical tracer (AQT); sectioning and examination (25X stereomicroscope) for assigning scores from 0 (no penetration of AQT) to 2 (maximum penetration of AQT). The results showed the highest percentages for the score 0 for 3-B (80.0%), 2-A (75.0%), 2-B (75.0%), 1-A (70.0%). There were statistically significant differences in groups 1 and 3, which did not occur in group 2 (Mann-Whiteny and Kruskal-Wallis / significance level of 5%). It was concluded that no technique of insertion was able to prevent microleakage and the cruciform technique represents an alternative to the incremental technique depending on the type of composite resin used.

Influencia de la fotopolimerización gradual en el estrés de contracción en restauraciones de resina compuesta / Influence of gradual polymerization contraction stress of composite restorations

Cuando el factor estética es primordial, las resinas compuestas continúan siendo la opción restauradora más utilizada. Sin embargo, a pesar de su constante evolución aún presentan algunos inconvenientes, tales como: desgaste, contracción de polimerización e infiltración marginal. Actualmente, nuevos conceptos relacionados a técnicas de fotopolimerización desarrollaron una mejor adaptación marginal asociada a la permanencia de sus propiedades mecánicas. La polimerización gradual, es decir, reducción inicial de la intensidad de luz, seguida por fotoactivación con mayor intensidad han demostrado ser una alternativa con buenos resultados clínicos. Este trabajo propone discutir las principales variables que pueden interferir en el proceso de fotopolimerización, con el objetivo de alertar a los odontólogos en cuanto a la necesidad de un constante control clínico, no solamente por la observación de la técnica incremental, sino principalmente, a través de la monitorización de la cantidad de energía luminosa empleada en el proceso de fotopolimerización. En este contexto, son presentados, mediante revisión de literatura, los principales factores relacionados a la contracción de polimerización y las técnicas de fotopolimerización disponibles para minimizar sus efectos

The composite resins are still the most used restorative option when the esthetic aspect is primordial. However, even their constant evolution they present some inconvenients like: wear, polymerization contraction and marginal leakage. Today, new concepts related to light curing have developed a better marginal adaptation associated to the permanency of their mechanical properties. The gradual polymerization, which means, initial reduction at the light intensity, followed by the photoactivation with more intensity has demonstrated to be an alternative with good clinical results. This paper proposes to discuss the principal variables that could interfere at the light curing process, with the aim to alert the dentists about the necessity of a constant clinical control, not just by the observation of the incremental technique, but principally, through monitoring the quantity of light energy used at the polymerization process. In this context, are presented, by a literature revision, the principal factors related to the polymerization contraction and the available light curing techniques to minimize their effects

Comparative analysis of the shrinkage stress of composite resins

The aim of this study was to compare the shrinkage stress of composite resins by three methods. In the first method, composites were inserted between two stainless steel plates. One of the plates was connected to a 20 kgf load cell of a universal testing machine (EMIC-DL-500). In the second method, disk-shaped cavities were prepared in 2-mm-thick Teflon molds and filled with the different composites. Gaps between the composites and molds formed after polymerization were evaluated microscopically. In the third method, the wall-to-wall shrinkage stress of the resins that were placed in bovine dentin cavities was evaluated. The gaps were measured microscopically. Data were analyzed by one-way ANOVA and Tukey's test (alpha=0.05). The obtained contraction forces were: Grandio = 12.18 ± 0.428N; Filtek Z 250 = 11.80 ± 0.760N; Filtek Supreme = 11.80 ± 0.707 N; and Admira = 11.89 ± 0.647 N. The gaps obtained between composites and Teflon molds were: Filtek Z 250 = 0.51 ± 0.0357 percent; Filtek Supreme = 0.36 ± 0.0438 percent; Admira = 0.25 ± 0.0346 percent and Grandio = 0.16 ± 0.008 percent. The gaps obtained in wall-to-wall contraction were: Filtek Z 250 = 11.33 ± 2.160 µm; Filtek Supreme = 10.66 ± 1.211µm; Admira = 11.16 ± 2.041 µm and Grandio = 10.50 ± 1.224 µm. There were no significant differences among the composite resins obtained with the first (shrinkage stress generated during polymerization) and third method (wall-to-wall shrinkage). The composite resins obtained with the second method (Teflon method) differed significantly regarding gap formation.

Transmission of composite polymerization contraction force through a flowable composite and a resin-modified glass ionomer cement

The purpose of this study was to evaluate the individual contraction force during polymerization of a composite resin (Z-250), a flowable composite (Filtek Flow, FF) and a resin-modified glass ionomer cement (Vitrebond, VB), and the transmission of Z-250 composite resin polymerization contraction force through different thicknesses of FF and VB. The experiment setup consisted of two identical parallel steel plates connected to a universal testing machine. One was fixed to a transversal base and the other to the equipment's cross head. The evaluated materials were inserted into a 1-mm space between the steel plates or between the inferior steel plate and a previously polymerized layer of an intermediate material (either FF or VB) adhered to the upper steel plate. The composite resin was light-cured with a halogen lamp with light intensity of 500 mW/cm² for 60 s. A force/time graph was obtained for each sample for up to 120 s. Seven groups of 10 specimens each were evaluated: G1: Z-250; G2: FF; G3: VB; G4: Z-250 through a 0.5-mm layer of FF; G5: Z-250 through a 1-mm layer of FF; G6: Z-250 through a 0.5-mm of VB; G7: Z-250 through a 1-mm layer of VB. They were averaged and compared using one-way ANOVA and Tukey test at a = 0.05. The obtained contraction forces were: G1: 6.3N + 0.2N; G2: 9.8 + 0.2N; G3: 1.8 + 0.2N; G4: 6.8N + 0.2N; G5: 6.9N + 0.3N; G6: 4.0N + 0.4N and G7: 2.8N + 0.4N. The use of VB as an intermediate layer promoted a significant decrease in polymerization contraction force values of the restorative system, regardless of material thickness. The use of FF as an intermediate layer promoted an increase in polymerization contraction force values with both material thicknesses.