Incremental Curing Research Articles

Study on the effects of incremental curing on the thermal conductivity, insulation, and mechanical properties of thermal conductive silicone rubber

With the development of fields such as electronics and telecommunications, electronic devices are becoming more integrated and powerful. Therefore, there is an increasing demand for high thermal conductive and insulating flexible materials. Silicone rubber (SR), as an excellent flexible substrate, is often combined with various thermal conductive fillers to enhance its thermal conductivity (TC). Carbon materials are commonly used as thermally conductive fillers. To improve the insulation performance while maintaining the TC of the material, uncured SR filled with boron nitride (BN) is used as an insulating layer on the same substrate. The TC of the once-cured BN/SR composite and the incremental cured BN/SR composite as a coating are 0.492 W/(mK) and 0.484 W/(mK), respectively, with a BN content of 10 vol%. The TC of carbon fiber (CF)/SR composites before and after surface treatment with BN/SR are 1.760 W/(mK) and 1.682 W/(mK), respectively, with a CF content of 20 vol%. The volume resistivity of the former is less than 104 Ω cm, while the latter is greater than 1014 Ω cm.

Thermally conductive silicone rubber used as insulation coating through incremental curing and the effects of thermal filler on its mechanical and thermal properties

Thermally conductive silicone rubber used as insulation coating through incremental curing and the effects of thermal filler on its mechanical and thermal properties

A comparison of the effects of incremental and snowplow techniques on the mechanical properties of composite restorations.

Glass fibre-reinforced composite (GFRC) has the potential to enhance the mechanical properties of resin-based restorations. Nevertheless, the application technique can influence the cervical margin porosity, potentially reducing the mechanical strength of restorations. In an in vitro setup, mould specimens underwent six different treatments to assess the effects of snowplow and incremental curing techniques on the properties of GFRC (EverX) and universal resin composite (Filtek). Mechanical properties, namely flexural strength (FS), compressive strength (CS) and Vickers hardness (VH), were evaluated following ISO 4049 standards. Data interpretation utilized the Kruskal-Wallis tests. No significant difference emerged across groups for FS. CS in the snowplow method with lesser EverX thickness (SnPl_1) was comparable with only EverX and Filtek (P > 0.05). The CS was reduced in the snowplow technique with greater EverX thickness (SnPl_2) (P < 0.05) and further decreased with the incremental method (P < 0.001). VH results showed that EverX Posterior was consistently softer than Filtek, with specific patterns of hardness variations among different application methods. Applying EverX and Filtek using the snowplow technique delivers superior CS and VH for restorations in contrast to the incremental method. Utilizing the snowplow approach in high-stress areas can make restorations more fracture-resistant.

Techniques Used by Dental Specialists for Extensive Posterior Composite Restorations

Objective: To assess the techniques used by dental specialists for placement of extensive posterior composite restorations. Methodology: A cross sectional descriptive was conducted in 150 dentists of College of Dentistry, SMDC, Lahore from June 2019 to July 2020 after obtaining ethical approval from Sharif Medical Research Centre (SMRC). Data was collected using a pre validated questionnaire Results: A statistically non-significant association between the specialty of the dentist the technique used for placement of the composite during restoration (p=0.08). The most commonly used techniques for the placement of posterior composite restorations by dentists of all specialties including Periodontology (88%), Prosthodontics (68.4%), Orthodontics (85.7%), Oral Surgery (91.3%), Oral Pathology (71.4%), Oral Biology (33.3%), Dental materials (75%), Community Dentistry (100%), Operative Dentistry (90.9%) and Oral Medicine (75%) is incremental curing. Practical implication: This study will give an insight on the various techniques used by dentists from various specialties for the placement of composite restorations in posterior teeth. This will in turn help them adopt new and revisit old techniques used by them while placing composite restorations. Conclusion: The most commonly used techniques for the placement of posterior composite restorations by dentists of all specialties is incremental curing followed by use of moisture control during the placement of composites both with and without rubber dam isolation. Keywords: Dental Specialists, Composite Restorations, Posterior Dental Restorations, Incremental Curing

Posterior composite restorations: Attitudes and knowledge of techniques and problems by dentists in government and private dental practices in Edo state

Context: Aesthetic considerations form a major aspect of dental material selection for tooth restorations. Anterior restorative materials exclusively used in anterior teeth. With the advances made, tooth-colored restorative materials are now used in posterior teeth restorations.Objective: The aim of this study was to evaluate the techniques employed, associated problems and the attitudes of dental practitioners to the placement of posterior compositesMethod: This was a questionnaire-based study conducted among sixty-eight (68) dentists practicing in public/government-owned and private hospitals.Results: The results show that 86.8% of the respondents considered the conservation of tooth substance as the most common factor influencing their choice of composite materials for posterior teeth. On their perceptions of posterior composites generally, 77.9% of the respondents agreed that posterior composites needed less destruction of sound tooth substance while 35.0% considered moisture control as the most difficult problem faced during placement of the restoration. Wooden wedges were the most popular wedges while ultraviolet curing light were the most commonly used by the respondents. Majority (82.4%) agreed that calcium hydroxide and glass ionomer cement should only be used in cases of operatively exposed dentine in deep cavities. The percentage that never used rubber dam was 47.1 while incremental curing was the most commonly used method. Sectional matrices were more commonly used by respondents while the most commonly encountered post-treatment problem was the fracture of restorationsConclusion: While more dental practitioners are embracing the use of composites for posterior restorations, there remains the need to get them to embrace the techniques of placement to ensure more satisfactory and predictable outcomes.

Towards mould free composites manufacturing of thermoset prepregs. Incremental curing with localised pressure-heat (ICULPH)

The use of composite materials is fundamental for high value added manufacturing industries such as automotive and aerospace. The major cost of producing composite parts is to produce moulds, however, mould wear over time. Therefore, a novel contribution towards eliminating the use of moulds is presented in this paper. A newly developed mechatronic system, to cure carbon fibre reinforced polymer (CFRP) samples, is described. The system is capable of curing thermoset composites through a localised pressure-heat that makes use of force feedback control to achieve a uniform curing pressure on the CFRP samples. The system was tested with 2-, 4-, 6- and 8-layer CFRP samples in a test matrix consisting of a pressure range of 70 to 310 KPa and a temperature range of 190°C to 220°C. The CFRP samples are benchmarked against standard production methods such as autoclave and hot press. These samples are analysed with three-point-bending and differential scanning calorimetry tests in order to obtain flexural strength and degree of cure, respectively. The results and implications of the tests are discussed and further developments towards mould free composites are highlighted.

A Comparative Evaluation of Time-dependent Changes on the Surface Hardness of Bulk Cure Composites: Anin vitroStudy

ObjectivesThe objective of this in vitro study was to assess the surface hardness through Vickers hardness (VH) test of one conventional hybrid resin composites (Filtek Z350), compared with that of two bulk cure resin composites (SDR™, Tetric N Ceram®).Materials and methodsTwenty specimens of each material were prepared in cylindrical aluminum molds with an internal diameter of 5 mm and depth of 4 mm, 10 (incremental curing) and 10 (bulk curing).The surface of each specimen was covered with a transparent plastic matrix strip before light curing with conventional visible light for 40 seconds. The specimens thus obtained were stored in deionized water and transferred to an incubator at 37°C for 24 hours to simulate clinical conditions. After 24 hours, the microhardness of each specimen was measured using a Vickers indenter, with a load of 100 gm and dwell time of 15 seconds (HV 0.2/40).The specimens were further subjected to VH test in an interval of 7, 30, and 90 days. The data were subjected to statistical analysis—Student’s t test, analysis of variance, and post hoc Tukey’s test.ResultsThe present study showed that SDR™ in bulk curing showed consistently greater value of hardness and was comparable to traditional incremental cured Filtek Z350, highlighting the advantages of the new SDR technology.How to cite this article: Sarma A, Nagar P. A Comparative Evaluation of Time-dependent Changes on the Surface Hardness of Bulk Cure Composites: An in vitro Study. Int J Clin Pediatr Dent 2018;11(3):183-187.

Comparison of the Amount of Temperature Rise in the Pulp Chamber of Teeth Treated With QTH, Second and Third Generation LED Light Curing Units: An In Vitro Study.

Introduction: This in vitro study was designed to measure and compare the amount of temperature rise in the pulp chamber of the teeth exposed to different light curing units (LCU), which are being used for curing composite restorations. Methods: The study was performed in two settings; first, an in vitro and second was mimicking an in vivo situation. In the first setup of the study, three groups were formed according to the respective three light curing sources. i.e. quartz-tungsten-halogen (QTH) unit and two light-emitting diode (LED) units (second and third generations). In the in vitro setting, direct thermal emission from three light sources at 3 mm and 6 mm distances, was measured with a k-type thermocouple, and connected to a digital thermometer. For a simulation of an in vivo situation, 30 premolar teeth were used. Class I Occlusal cavity of all the teeth were prepared and they were restored with incremental curing of composite, after bonding agent application. While curing the bonding agent and composite in layers, the intrapulpal temperature rise was simultaneously measured with a k-type thermocouple. Results: The first setting of the study showed that the heat produced by irradiation with LCU was significantly less at 6 mm distance when compared to 3 mm distance. The second setting of the study showed that the rise of intrapulpal temperature was significantly less with third generation LED light cure units than with second generation LED and QTH light cure units. Conclusion: As the distance from the light source increases, less irradiation heat is produced. Third generation LED lights cause the least temperature change in the pulp chamber of single rooted teeth.

Evaluation of microleakage in hybrid composite restoration with different intermediate layers and curing cycles

Objective: To evaluate the impact of bulk or incremental curing of hybrid composite resin with different intermediate layers on interfacial microleakage. Materials and Methods: The recently extracted, sixty noncarious human mandibular molars were selected for the study. The standardized mesio-occluso-distal cavity with the occlusal cavity of 2 mm depth, 3 mm buccolingual width and proximal box dimension of 4 mm buccolingual width and 2 mm depth was prepared on all experimental teeth. The samples were divided into six groups of ten each. Group I was without an intermediate layer. Group II and III had 1 mm flowable composite liner, with incremental and bulk curing cycle, respectively. The Group IV, V, and VI had a self-cure composite liner with incremental and bulk curing. The teeth subjected to thermocycling and kept in 0.5% basic fuchsine dye for 24 h. The teeth were sectioned and observed under a stereomicroscope to grade them according to the extent of microleakage. The obtained data were statistically analyzed with Kruskal–Wallis and post hoc comparison test to understand the difference between the groups. Results: The Group II with flowable composite along incremental curing showed the least microleakage at both enamel (0.30) and cementum surface (0.50). The groups with self-cure composite liner were less effective than flowable composite. The microleakage at the enamel interface was less compared cementum interface across the groups. The groups with bulk curing were more prone to microleakage than incremental curing cycle. Conclusions: Within the limitation of the study, it was concluded that intermediate flowable composite with incremental curing was better suited to reduce microleakage.

Placement of Posterior Composite Restorations in Palestine Dental Practices: Techniques, Problems, and Attitudes

The management of posterior teeth damaged due to various factors has undergone considerable improvement over the years. Every year, dental technology and materials are advancing. One such advancement is steady replacement of amalgam with composites. This study was done to evaluate the attitude and techniques employed by general dental practitioners of Palestine during restoration of posterior teeth with composite. A questionnaire to evaluate the attitude of the Palestinian dental practitioners was distributed to 200 dentists in a local dental conference. The questionnaire consisted of general questions such as gender and years of experience as well as specific questions related to posterior composites placement such as techniques used while placement, problems encountered and factors affecting the placement of restoration in posterior teeth. 123 responses were obtained with a response rate of 61.5%. Esthetics seems to be the prime factor affecting the choice of material for posterior teeth restoration followed by patient’s preference. As per the study, moisture control is the most affecting factor of the placement of posterior composites and is suggested to be the most common problem encountered during placement of composites in the teeth. Incremental curing is a regularly used practice as per 63.4% participants. Mostly, universal matrix is used for the composite placement. For the wedging between the teeth, wooden wedges were preferred by majority of the general dental practitioners of Palestine. LED is found to be the most commonly used light cure source for the curing of composites. From this study, it can be concluded that more and more general dental practitioners in Palestine are using composites for the restoration of posterior teeth. Still there is a scope of continued improvement in this field.

Traumatic Dental Injury: A Case Report

difficulties regarding treatment cost, psychological and emotional factors, and the fact that the treatment may continue for the rest of the patient’s life. The current paper reports the case of an 8-year-old girl who sought the pediatric dentistry clinic at the Catholic University of Brasilia with coronal fracture in tooth 11. During the interview, the patient reported that she had fallen during a leisure activity, fact that caused the fracture. She was firstly assisted in a private practice, where she received emergency care. Clinical and radiographic examination found that the patient had a fracture involving enamel and dentin, but not the pulpal. Class IV composite resin restoration was the proposed treatment. After selecting the colors, the cavity preparation was completed according to parameters in recent conservative guidelines. Rubber dam restoration was used to avoid contamination. The dentin and enamel surfaces were then treated according to the protocol of the chosen adhesive agent. The composite resin was inserted by incremental technique and light curing. The smoothest surfaces were obtained using the complete sequence of Sof-Lex discs. Systematic follow-ups were performed to check the periapical conditions, restoration integrity, as well as the color stability. Thus, the patient aesthetic, phonetic and mastication functions were restored, and she resumed her social activities.

Effect of Incremental Curing Agent Additions on Thermal Degradation of Polydimethylsiloxane in Air: A Kinetic Study

Effect of Incremental Curing Agent Additions on Thermal Degradation of Polydimethylsiloxane in Air: A Kinetic Study

Thermographic analysis of temperature rise in the pulp chamber with LED and QTH light curing units: Anin vitroinvestigation

Aims: To compare the temperature rise in the pulp chamber with light-emitting diode (LED) and Quartz-Tungsten-Halogen (QTH) light curing units by infrared thermography. Materials and Methods: Class V cavity was prepared in 20 freshly extracted maxillary first premolars measuring 2 mm depth, 4 mm width, and 1 mm above the cement enamel junction. The samples were divided into two groups (n = 10). Cavity was etched with 37% phosphoric acid, rinsed and bonding agent was applied over the etched cavity surface on both the groups. In group I the samples were cured with LED curing unit, whereas group II were cured with QTH unit, which was followed by two incremental curing of composite. Thermal emission for QTH and LED (fast mode) light curing units were noted by Fluke Ti32 infrared thermography after 20 s bonding agent curing and first and second increment composite curing for 40 s each. Statistical Analysis: Data were analyzed with Student t-test and Friedman test using SPSS version 11.5 software. Results: The statistical analysis revealed that the temperature rise was significantly minimal with LED fast mode (Group I) in all stages of curing compared with QTH unit (Group II). There is significant rise of temperature during first incremental curing of composite, whereas insignificant increase of temperature during curing of second increment of composite (P < 0.001%). Conclusions: Temperature rise caused due to both QTH and LED light curing units does not result in irreversible pulpal damage and thermography is a viable means of quantifying the temperature changes during photo polymerization.

Degree of conversion of nano-hybrid resin-based composites with novel and conventional matrix formulation

This study aimed to determine the degree of conversion (DC) of two nano-hybrid resin-based composites (RBCs) with novel monomer composition based on dimer acid derivates (hydrogenated dimer acid) and tricyclodecane-urethane structure compared to three nano-hybrid materials containing conventional matrices. DC was evaluated at 0.1, 2, and 6 mm depth at varying irradiation times (10, 20, and 40 s) and layering techniques (bulk and incremental). DC was measured in real time by a Fourier transform infrared spectroscopy (FTIR) spectrometer with attenuated total reflectance accessory. The FTIR spectra were recorded on the bottom of the samples in real time for 5 min from photoinitiation. Results were compared using one- and multiple-way ANOVA, Tukey's HSD post hoc test (α = 0.05), and partial eta-squared statistic. After 5 min of measurement, DC showed no significant difference by varying cure time for specimens of 0.1 mm thickness. At 2 mm depth, the DC significantly increased after a cure time of 20 s compared to 10 s, remaining equal after 40 s of irradiation. At 6 mm depth, bulk curing showed significantly lower DC compared to incremental curing for all polymerization times. Specimen geometry revealed a strong effect on DC (η (2) = 0.90) followed by curing time (η (2) = 0.39). The RBCs containing the dimer acid and tricyclodecane-urethane structure showed a relatively low decrease of DC with increasing incremental thickness compared to the conventionally formulated materials. The former reached the highest DC among the tested materials. For the tested RBCs, increments of 2 mm and irradiation time of at least 20 s may be recommended for clinical practice. The two materials containing novel monomer composition might be applied for enlarged increments because of the low decrease of DC they demonstrated for 6-mm increments.

Comparative evaluation of residual monomer content and polymerization shrinkage of a packable composite and an ormocer

Aim:The aim of this study is to evaluate the residual monomer content and polymerization shrinkage of a packable composite (Surefil) and an ormocer (Admira).Materials and Methods:The study was conducted in two parts. In Part I, 10 samples of each material were prepared in a standardized split brass mould, using incremental curing technique. The residual monomer content was measured by observing change in weight before and after Soxhlet Extraction procedure. In part II, the volumetric polymerization shrinkage was calculated by measuring the difference in specific gravities of 10 uncured and 10 cured samples of each material using a modified version of ASTM D-792 method. The data obtained was put to statistical analysis using student's ‘t’ test.Results:Part I - The percentage change in weight for Surefil was 0.525% while that for Admira was 0.374%, which was found to be statistically significant. Part II - The volumetric percentage shrinkage for Surefil ranged between 1.04-3.42% and that for Admira between 1.01-2.31%, which was not found to be significant statistically.Conclusion:Admira may be considered more biocompatible than Surefil due to the lower residual monomer content in the former; however, both are comparable with regards to their polymerization shrinkage.

Comparison of temperature rise in the pulp chamber with different light curing units: An in-vitro study

Aims/Objectives:This in vitro study was designed to measure and compare the temperature rise in the pulp chamber with different light curing units.Materials and Methods:The study was done in two settings-in-vitro and in-vivo simulation. In in-vitro setting, 3mm and 6mm acrylic spacers with 4mm tip diameter thermocouple was used and six groups were formed according to the light curing source- 3 Quartz-Tungsten-Halogen (QTH) units and 3 Light-Emitting-Diode (LED) units. For the LED units, three modes of curing like pulse-cure mode, fast mode and ramp mode were used. For in-vivo simulation, 12 caries free human third molar tooth with fused root were used. K-type thermocouple with 1 mm tip diameter was used. Occlusal cavity was prepared, etched, rinsed with water and blot dried; bonding agent was applied and incremental curing of composite was done. Thermal emission for each light curing agent was noted.Results:Temperature rise was very minimal in LED light cure units than in QTH light cure units in both the settings. Temperature rise was minimal at 6mm distance when compared to 3 mm distance. Among the various modes, fast mode produces the less temperature rise. Temperature rise in all the light curing units was well within the normal range of pulpal physiology.Conclusion:Temperature rise caused due to light curing units does not result in irreversible pulpal damage.

The influence of different composite placement techniques on microleakage in preparations with high C- factor: Anin vitrostudy

Objective:This study evaluated the marginal leakage around class-I cavity preparations restored with Nanofilled composite (Filtek Z-350 A2 shade, 3M ESPE, USA) and a self-etch adhesive (Xeno III, DENTSPLY/Caulk) using different composite placement techniques.Materials and Methods:Standardized class-I cavities were prepared on 36 caries-free, extracted human premolars and were randomly assigned to three groups: (1) Horizontal incremental curing was done; each increment of thickness 1.5 mm was cured one after the other using curing unit (T-LED, Elca Technology, Italy). (2) Concave surface was obtained with a ball burnisher on the first increment and cured for 20 seconds; subsequently, the next increment was placed and similarly cured. (3) Cavities were filled with resin, short of the occlusal surface; two cuts (mesiodistal and buccolingual) were made through the condensed resin and cured for 20 seconds, followed by addition of resin in the gaps created by the cuts and additional curing for 20 seconds. The specimens were stored in distilled water for three months and then subjected to thermocycling, followed by immersion in 0.5% methylene blue dye for 24 hours. The teeth were sectioned longitudinally and evaluated for microleakage under stereomicroscope, and the scores obtained were analysed with Fisher Exact test and Kruskal-Wallis nonparametric test.Results:There was no statistically significant difference among three groups.Conclusion:None of the techniques was capable of eliminating the microleakage in preparations with a high C-factor.

Factors influencing shear strength of incrementally cured composite resins.

Factors influencing the shear strength of incremental curing of three different composite resins were examined. The first increment was cured under different surface conditions, in air, or under a coverglass. A separate experiment studied the effect of curing in nitrogen atmosphere. There was no difference in the shear strength of the specimens if the first increment was created in air or under a coverglass. One material (Heliomolar RO) showed higher shear strength when cured in increments and one when bulk-cured (Herculite XR). Curing increments in a nitrogen atmosphere increased the shear strength for two of the three materials tested (P50 and Heliomolar). The results showed that the bond strength between the increments of composites was influenced by the surface properties of the composites themselves after they had been cured under the different conditions; it was also affected by the inherent chemical and physical properties of the materials utilized.