Light-cured Composite Resin Research Articles

In vitro evaluation of the effect of two pediatric syrups on the microhardness and surface roughness of restoration materials.

The prolonged use of pediatric syrups without adequate control of oral hygiene can cause effects on the physical characteristics of the restoration materials, which in turn can cause deterioration of the material and subsequent carious recurrence. Aim: To evaluate the effect of two long-term use syrups in children on the microhardness and surface roughness of three restorative materials. Three study groups were formed, consisting of a conventional self-curing ionomer cement, a light-curing ionomer cement, and a light-curing composite resin. Each group had 40 specimens made with the respective restorative material; in addition, these were distributed in 2 subgroups with 20 specimens each, which were immersed in Paracetamol and Ferrous Sulfate in syrup following a protocol that consisted of 2 minutes each day for 28 days. Over time (0, 7, 14, 21, and 28 days), when evaluating microhardness, the composite resin subgroup exposed to ferrous sulfate (p = 0.027) and the Ketac Molar ionomeric cement subgroup (p = 0.002) exposed to Paracetamol showed statistically significant differences; while, when evaluating surface roughness, the composite resin subgroups (p = 0.032) and Ketac Molar ionomeric cement (p = 0.01) exposed to ferrous sulfate showed a statistically significant difference. The more days of exposure to ferrous sulphate syrup, the less the microhardness of the composite resin decreases; something similar occurs with the microhardness of Ketac Molar ionomeric cement when exposed to Paracetamol syrup. Meanwhile, the surface roughness of the composite resin and Ketac Molar ionomeric cement increases considerably when exposed to ferrous sulphate. Key words:Ionomeric cement, Microhardness, Composite resins, Surface roughness.

5-Year clinical performance of ceramic onlay and overlay restorations luted with light-cured composite resin

ObjectivesThis prospective clinical trial evaluated the clinical performance of ceramic partial coverage indirect adhesive restorations (PCIARs) in posterior teeth luted with a light-cured composite resin. MethodsFrom April 2016 to January 2017, a total of 60 patients (27 males, 33 females; mean age: 42.2 ± 10.86 years old) received 83 glass-ceramic PCIARs (26 onlay, 57 overlay) made of IPS Emax CAD (Ivoclar Vivadent). All restorations were luted with a light-cured composite resin (Filtek Z250, 3 M ESPE) by two operators. Two independent calibrated examiners blinded to the operators performing the treatment evaluated the restorations at baseline, 1-year, and 5-year following FDI World Dental Federation criteria including esthetic, functional, and biological properties. Data were analyzed with the Friedman test and the Wilcoxon sign test (p < 0.05). ResultsNone of the restorations failed due to fracture or retention loss. One restoration was clinically unsatisfactory because of secondary caries. Marginal staining (p:0.000), marginal adaptation (p:0.018) showed significant differences between 1-year and 5-year recall. ConclusionsThe PCIARs demonstrated excellent clinical performance at 1-year period. The degradation parameters appeared as minor staining and minor irregularities after 5-year, without any affect on the clinical performance. Clinical SignificanceOur findings provide evidence that the clinical performance of PCIARs luted with a light-cured composite resin was clinically acceptable after a five-year evaluation period. Due to secondary caries, only one restoration was considered clinically unsatisfactory. ClinicalTrials registration number: NCT04838483

Performance of two laser motion modes versus conventional orthodontic ceramic brackets debonding technique on enamel surface topography.

The risk of enamel deterioration that frequently coexists with debonding of orthodontic teeth brackets elevates the mandate for finding an optimum approach for debonding them without harmful effects. This in-vitro study is intended to compare the effects of two different laser modes (scanning and circular) and a conventional method on the enamel surface after debonding orthodontic brackets. 66 extracted premolars were assigned into 3 groups. After that, light-cure composite resin was used to attach the ceramic brackets to the teeth. Amongst the test groups, Group I: specimens that were debonded using conventional debonding using pliers; Group 2: specimens that were debonded using Er, Cr: YSGG laser applications using the circular motion method; and Group 3: specimens that were debonded using Er, Cr: YSGG laser applications using the scanning motion method. Adhesive Remnant Index (ARI) assessment, intra-pulpal temperature increase, enamel surface roughness after polishing, and assessment of the microstructure of enamel were carried out with scanning electron microscopy. The gathered information was examined statistically. The conventional debonding method had a significantly higher proportion of adhesive remnant index (ARI) scores of 2 and 3 in comparison to the circular (p < .004) and scanning laser groups (p < .001). There was no significant difference in ARI scores between the circular and scanning laser groups (p > .05). Moreover, the circular and scanning laser debonding methods resulted in a significantly higher proportion of Enamel Surface Roughness (ESR) scores of 0 and a lower proportion of ESR scores of 3 compared to the conventional technique group (p < .001). However, there was no significant difference in ESR scores between the circular and scanning laser methods (p = .945). Lastly, the average intra-pulpal temperature was significantly higher in the circular laser group (1.9 ± 0.5 ) compared to the scanning laser group (0.9 ± 0.2) with p < .001. Er, Cr: YSGG laser irradiation is a tool that shows promise for debonding ceramic brackets with minimal harm to the enamel surface. The scanning laser technique is more desirable due to the lower intra-pulpal temperature increase.

Characterization of dental light-curing resin composites incorporating multiple modified low-shrink monomers

ObjectivePolymerization shrinkage poses a significant challenge in dental resin composites. The objective of this study is to introduce spiroorthocarbonate monomer 3,9-dimethylene-1,3,5,7-tetraoxa-spiro[5,5]undecane (BMSOC) and epoxy resin monomer 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ECHM-ECHC) into bisphenol-S-bis(3-methacrylato-2-hydroxy propyl)ether (BisS-GMA) based resin composites to develop composites with reduced shrinkage properties. MethodsBMSOC and BisS-GMA were synthesized and thoroughly mixed with ECHM-ECHC, followed by inorganic fillers and photoinitiators. Based on the composition of the resin matrix, five groups of experimental composites were prepared, with traditional bisphenol A-dimethacrylate glycidyl ester (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) based composite serving as the control. The polymerization properties, including degree of conversion (DC) and polymerization shrinkage (PS), as well as marginal microleakage, wettability, flexural strength (FS), flexural modulus (FM), and biocompatibility were evaluated. ResultsThe results demonstrated that compared with the control group, the PS of BisS-GMA based composites containing BMSOC and ECHM-ECHC were significantly reduced (P < 0.05), and the lowest PS (0.96 ± 0.08 %) was observed when the ratio of BisS-GMA: (Epoxy + BMSOC) was 4:6. Additionally, the experimental composites also exhibited improved DC, minimal microleakage, low hydrophilicity, enhanced mechanical properties, qualified in vivo biocompatibility, and slight/moderate in vitro biocompatibility. SignificanceThe resin composites incorporating multiple modified low-shrink monomers are promising for dental applications to prevent various clinical problems caused by PS and extend restoration longevity.

An assessment of Brazilian dentists' knowledge about tooth fragment reattachment: A cross-sectional study.

Crown fractures are common traumatic dental injuries and tooth fragment reattachment is a viable option for restoring a fractured tooth. The aim of this study was to assess the knowledge and experience of dentists in the Federal District regarding the tooth fragment reattachment technique for enamel and dentin fractures. For the cross-sectional observational study, an electronic form was designed with objective and self-report questions for dentists. The data were analyzed using descriptive statistics, with their absolute and relative frequencies. For the analysis of categorical variables, the nonparametric chi-squared or Fisher exact association tests were used in the statistical software R (version 4.2.1). A total of 416 dentists participated in the study (58.9% female and 41.1% male). Of these, 70% declared they knew about fragment reattachment, but only 42.3% reported previous experience with this procedure. The most common storage medium used for the fractured fragment was milk (78.1%), and the bonding material used for reattachment was light-cured composite resin (86.3%). A majority (66.3%) reported that for a patient with enamel and dentin fracture, with the crown fragment in good condition, they would choose to do the reattachment. Dentists demonstrated that they had adequate knowledge about the tooth fragment technique, although many did not have previous experience with this procedure.

Cytotoxicity Evaluation of Various Composite Resin Materials: An In Vitro Study.

Aim This study aimed to determine and comparethe cytotoxicity of light-cured composite resin (Enlight light cure composite (Ormco, Glendora, California, USA)), light-cured acrylic resin (Orthocryl LC (Dentaurum, Ispringen, Germany)), and the self-cure acrylic (DPI RR cold cure acrylic (Dental Products of India, Bombay Burmah Trading Corporation Ltd., Mumbai, India)) material and to determine which component is best to be used for the purpose of nasal stent fabrication in the nasoalveolar molding (NAM) technique for cleft therapy. Methods Circular discs made from Enlight light cure composite, Orthocryl LC, and self-cure acrylic were submerged for 24 hours in gingival fibroblast media (three discs of each material) and control medium (three discs of each material) that were both contained in plates. After analyzing the optical densities of the plates, the cytotoxicity of the products was assessed by measuring cell viability using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The compiled data was analyzed using IBM SPSS Statistics for Windows, V. 23.0 (IBM Corp., Armonk, NY). The normality of the data was evaluated using the Shapiro-Wilk test.One-way analysis of variance (ANOVA) and pairwise comparison made with Tukey's honestly significant difference (HSD) post hoc test with a significance level (p) of 0.05 were considered. Results The percentage of cell viability was between 80% and 150%. A significantmean difference was noted in the cell viability between the three groups (p=0.009). High mean cell viability was seen in Orthocryl LC. However, there was no significant mean difference between Orthocryl LC and Enlight light cure composite material (p=0.854). Conclusion Both Orthocryl LC and Enlight light cure composite materials are less cytotoxic when compared to the self-cure acrylic resin material and can be used to fabricate the nasal stent component for infants with cleft defects, undergoing NAM procedure.

Knowledge and precautions of light-curing composite resin restorations by dental students

Composite resin is versatile material for performing several dental procedures in dentistry, and its use has already been consolidated in this field. The clinical success of adhesive restorations is directly related to the knowledge of restorative material properties and light-curing unit factors, among others. The aim of the study was to assess the knowledge about the technical characteristics of light-curing devices and the forms of use and maintenance employed by undergraduate dental students. A total of 230 students answered a questionnaire containing six questions on technical data, use, and maintenance of light-curing units. Of the total number of participants, the majority were students from private educational institutions attending the last two years. With 59.1% of them unaware of the ideal irradiance of a light-curing unit, 73.0% were careful to position the light-curing unit as close as possible to the restoration, and 42.6% followed the light-curing time recommended by textbooks and theoretical texts. As for use and maintenance, 50.4% used the protector attached to the light-curing unit, 57.4% used safety barriers, and 63.0% sanitized the light tip after use. The evaluation suggests that student’s knowledge of “light-curing resin materials” is incomplete. Therefore, it can be inferred that the students have a good understanding of biosafety precautions when using light-curing units, but more knowledge is needed about the technical and clinical aspects of the devices.

Orthodontic bracket bonding techniques and adhesion failures

The introduction of glass ionomer cements in orthodontics aimed to address the drawbacks of the acid-etch technique using composite resins, including demineralization, enamel damage, and potential allergic reactions. These cements release fluoride over time, potentially protecting against demineralization. Glass ionomer cements, despite their benefits in reducing adhesive residue and protecting against demineralization, showed higher bond failure rates compared to composite resins. This is attributed to their sensitivity to application techniques and moisture, along with a delayed setting time. In contrast, light-cured composite resins, preferred over chemically-cured resins in recent years, offer advantages such as ease of use, consistent handling, and controlled setting. However, early trials indicated higher bond failure rates for light-cured resins, a finding not consistently replicated in later studies. While glass ionomer cements offer certain advantages, their higher bond failure rate poses a significant limitation. Light-cured composite resins, with their user-friendly characteristics, have become the preferred choice in orthodontic bonding despite initial concerns about higher bond failure rates.

Mouthwashes: Surface Hardness and Accuracy of Dual-cured Visible Light-Cured Composite

In the oral environment, the longevity and durability of aesthetic composite resin restorative materials are critical considerations. However, many studies have been done on the effect of certain mouthwashes on the surface hardness and accuracy of composite resin. Therefore, this study aims to examine the effect of GUM® alcohol-free and Listerine alcohol-contained mouthwashes on the surface hardness and dimensional accuracy of cured and dual-cured visible light-cured composite.Methods: Thirty-disc specimens of Nanohybrid light-cured composite resin were prepared according to ISO standardization (4049/2000). The sample was divided into three groups (n=10), the Control non-treated in distilled water; Alcohol-free GUM® and Alcohol-contained Listerine mouthwashes. The surface hardness and dimensional accuracy of specimens were measured at different immersion intervals. These include initial immersion, after one and four weeks, and after the light dual-curing procedure. Data were analyzed via one-way ANOVA (post-hoc Tukey test) performed at a significant P-value of (p ≤.05) and confidence level of 95%.Conclusion: After the dual-curing process, the alcohol-free GUM® mouthwash showed a reduction in the surface hardness of the composite material. Listerine mouthwash had a static reduction in the composite specimen in diameters.

The effect of freezing on the fracture pattern of adhesive on debonding: an in-vitro study.

The purpose of this study was to quantitatively evaluate adhesive remnants on the enamel surface following bracket debonding using a freezing element. Thirty-six sound premolars were used in this study. In each case, a bracket was bonded onto each tooth with conventional light-cured composite resin and de-bonded after one week. Freezing of the underlying composite through the bracket was performed immediately before debonding with a portable cryosurgical system (-55 °C). Specimens were divided into three groups according to the duration of freezing: a control group without freezing was used as a reference and two interventional groups with different durations of freezing (15 or 40 s). Brackets were removed by using debonding pliers to squeeze the wings of the bracket in an occluso-gingival manner. Adhesive remnants on the tooth were then quantitatively evaluated by stereo-microscopy. Pearson's Chi-squared test was used to investigate the relationship between the proportion of remaining resin and the group of teeth. In the control group, 100% of the composite remained on the enamel surface of all specimens. Significantly less adhesive remnants were found in the intervention groups (p = 0.001 for the 15 s group and p = 0.043 for the 40 s group). There was no significant difference between the two interventions (p = 0.165) in terms of the proportion of remaining adhesive remnants. Freezing of the bracket and the underlying adhesive resin prior to bracket debonding may favorably alter the behavioral pattern of composite fracture, thus reducing the extent of adhesive remnants on the enamel. Increasing the freezing time from 15 to 40 s did not exert significant effects on adhesive remnants following debonding. Further research now needs to investigate the effect of freezing on the mechanical properties of the adhesive remnants and its in-vivo effect on pulp vitality over both short- and long-terms.

Dental restorative materials and special consideration for the elderly

With the global population aging, the oral health of elderly individuals faces unique challenges, particularly concerning dental caries. Root caries, in particular, have become a growing concern due to the significant number of retained teeth in older adults. This review delves into the frequency of root caries among older individuals and examines the limitations of existing dental restorative materials, including amalgam, glass ionomer cement, and light-cured composite resin, in meeting the unique requirements of the elderly. It underscores the urgent necessity for improving the antibacterial, bonding, remineralization, strength, and durability characteristics of these materials. Additionally, the study discusses factors related to aging, treatment planning, and special considerations in geriatric dental care. The review also delves into the challenges associated with providing dental care to elderly individuals, including depression, postural hypotension, prescribed drugs, delayed healing, adaptive potential, mucosal quality, and poor plaque control. Moreover, it addresses the role of xerostomia, bruxism, and certain medical conditions in exacerbating dental issues in the elderly. It also introduces novel anticariogenic restorative materials, such as antimicrobial materials, remineralization materials, and self-healing/low-shrinkage materials, highlighting their potential to improve oral health in older individuals.

Influence of abrasive dentifrices on polymeric reconstructive material properties after simulated toothbrushing

To assess the influence of dentifrices with different abrasiveness levels on the properties of dental reconstructive materials. Forty-eight cylinders were obtained from four polymeric materials, being two CAD/CAM acrylic resins (Ivotion-Dent and Ivotion-Base), one injected acrylic resin (IvoBase-Hydrid) and one light-cured resin composite (Empress Direct). Specimens were allocated to four subgroups for toothbrushing simulation according to the dentifrice relative dentin abrasivity (RDA) and silica content: (i) RDA 0 = 0%; (ii) RDA 50 = 3%; (iii) RDA 100 = 10%; and (iv) RDA 120 = 25%. Specimens were then subjected to toothbrushing. Surface analyses [surface roughness Ra (SR) and scanning electron microscopy (SEM)] along with hardness and optical properties [translucency parameter (TP) and contrast ratio (CR)] were evaluated before and after toothbrushing. Statistical analyses were performed using ANOVA and Tukey test. A significant increase in SR was observed after toothbrushing with higher RDA toothpastes for Ivotion-Dent (100 and 120) and IvoBase-Hybrid (120). Ivotion-Base and Empress Direct presented no significant differences in SR when analyzed as a function of timepoint and RDA levels. Hardness was not influenced by toothbrushing with different RDA dentifrices, except for Empress Direct with RDA 0 toothpaste, where a decrease in the hardness was observed. TP of Ivotion-Dent and Empress Direct significantly decreased after toothbrushing with higher RDA dentifrices and CR of Ivotion-Dent, Empress Direct and IvoBase-Hybrid significantly increased with higher RDA dentifrices. The levels of dentifrice abrasiveness affected differently the SR, hardness and optical properties of polymeric reconstructive materials after toothbrushing.

Effects of ceramic microbeads on bonding between a zirconia framework and layered resin composite.

This study was conducted to evaluate the effects of ceramic microbeads on the bond strength between resin and zirconia. Microbeads made of zirconia (TZ) and zircon (ZS) were treated with and without hydrofluoric acid (HF). The microbeads were sintered to zirconia disks using intermediate feldspathic porcelains. Two control groups, NB (without microbeads) and AS (without porcelain and microbeads), were also prepared. All specimens were treated with a phosphate primer and veneered with a light-curing resin composite. The 24-h shear bond strengths were determined and analyzed by the Tukey-Kramer test (α=0.05, n=10). The TZ-HF specimen exhibited the highest bond strength, followed by TZ, ZS-HF, ZS, AS, and NB. Scanning electron microscopy observations revealed that the TZ-HF specimen had a complicated debonded surface, and it included microconcavities where the microbeads were detached. Sintering etched zirconia beads onto a zirconia framework with feldspathic porcelains is useful for bonding layered resin composite materials.

Accuracy of Indirect Veneer Mock-Up in Comparison to Diagnostic Wax-Up.

To evaluate the dimensional discrepancy between the diagnostic wax-up and the resulting mock-up. A maxillary model with misaligned teeth was scanned, and an initial cast was 3D printed. A total of 60 identical casts were 3D printed from the initial one after scanning. Based on a digital additive veneer wax-up on the six anterior teeth, 10 more casts were 3D printed. The specimens were allocated to seven groups (n = 10) as follows-group 1: transparent silicone matrix with a flowable light-cured composite resin; group 2: same as group 1 but with the addition of a prefabricated transparent tray; group 3: silicone impression putty (65 Shore A) and light-body silicone impression material with a dual-cured bisacryl resin; group 4: same as group 3 but without the light-body silicone; group 5: silicone laboratory putty (92 Shore A) with a dual-cured bisacryl resin; group 6: silicone laboratory putty (92 Shore A) with PMMA; group 7: wax-up casts (control). Scans from the mock-ups were coregistered, segmented, and superimposed with the scans from the wax-up. The difference between the mock-up and the wax-up was quantified by morphologic operations. Results were analyzed by Kruskal-Wallis test and Dunn post hoc test (P < .05). All mock-ups were larger than the wax-up. Significant differences were found for every labial surface third. The incisal third was the least accurate third while the middle third the most accurate. The most accurate were groups 2 and 5, and the largest discrepancy was observed in group 6. The analog mock-up differs dimensionally from the wax-up, regardless of the technique/materials used.

THE EFFECT OF SERVISE LIFE ON THE WATER ABSORPTION PARAMETER OF LIGHT CURING COMPOSITE RESIN MATERIALS

Introduction. Water absorption is one of the important properties of light-curing composite resin materials used in dentistry for tooth restoration. Water absorption refers to the ability of a material to absorb water and can affect its mechanical and aesthetic properties.&#x0D; Aim. To find out whether the service life of the composite material has an effect on the water absorption parameter.&#x0D; Materials and methods. Light-curing composite resin Latelux (Latelux), manufactured by Latus, Ukraine, was chosen as the material for study. Two groups, test and control groups, were formed. The first group included samples of material with an expired service life (expired before 2018). The samples were dried in a desiccator and weighed, then placed into a thermostat with distilled water for 7 days, then removed and weighed to determine water absorption. Calculations were performed in MS Excel 2013 using the formula W: (m2-m3)/V (μg/mm3).&#x0D; Results. After calculating the obtained results, the water absorption of the samples with an expired shelf life was on average 3.55±0.9 µg/mm3, while the composite with a normal shelf life was 4.9±1.8 µg/mm3. All samples passed the test, i.e. their parameter did not exceed 40 μg/mm3 according to ISO standards. Statistically obtained data did not reveal a relationship between the shelf life of the composite and its water absorption (p=0.464). The thickness of the composite material also has no statistical significance on the water absorption of the composite either in the experimental (p=0.26) or in the control group (p=0.378).&#x0D; Conclusions. Based on the results of our own research, as well as data from literary sources, we can conclude that the shelf life does not have a significant impact on the water absorption rate of the Latelux composite material.

Streptococcus mutans levels in patients who received orthodontic brackets bonded using probiotic impregnated resin composite – a randomized clinical trial

To evaluate the effect of impregnating an orthodontic resin composite with probiotic bacteria (Lactobacillus rhamnosus GG) on the levels of Streptococcus mutans (S. mutans) in patients undergoing orthodontic treatment. Thirty patients were randomly selected and allotted by block randomization to two groups: an experimental group, who received brackets bonded with probiotic impregnated resin composite and a control group, who received brackets bonded with conventional light cure resin composite. Plaque samples were collected before (ET0 and CT0) and two months (ET1 and CT1) after bonding. Levels of S. mutans were assessed using the colony count method. Two months after bonding of the brackets, the S. mutans levels had decreased with statistical significance in the experimental group (p = 0.001), but not in the control group (p = 0.137). Impregnation of resin composite with probiotic bacteria for the purpose of preventing formation of white spot lesions on enamel holds promise. Long-term evaluation would be necessary to provide confirmatory results.

Toward Optimum Light Curing of Resin Composite Restorations: A survey on Current Awareness and Practice among General Dentists in Saudi Arabia

Introduction: This study aimed to assess the current awareness and practices of resin composite light curing of general dental practitioners (GDPs) in Saudi Arabia and to set several evidence-based recommendations to improve the quality of the outcome of concern. Methods: An online questionnaire was created. Two hundred and fifty email invitations were sent to GDPs appointed in general governmental hospitals in five main cities in Saudi Arabia to join the survey voluntarily and anonymously. The survey consisted of 24 questions classified into the following domains: 1-Demographic criteria 2- frequency and technical aspects of resin composites application 3- criteria of the currently used light curing units and curing light. Descriptive statistics and chi-square test were used to analyse the obtained responses. Results: One hundred and fifty-six responses were received. A significant number of GDPs are significantly satisfied with the quality of their light curing, not aware of the thermal hazards of light curing, and do not check power output of their LCUs (light curing units) (P&lt;0.05). An insignificant number of respondents use eye shields for eye protection during light curing. Conclusion: There was no uniform light curing protocol followed by respondent GDPs. GDPs in Saudi Arabia should improve their knowledge and clinical skills of light-curing resin composite.

Effects of Translucency and Thickness of Lithium Disilicate-Reinforced Glass-Ceramic Veneers on the Degree of Conversion of a Purely Light-Curing Bonding Resin: An In Vitro Study.

The objective of this study was to evaluate the variations in the degree of conversion (DC) of a light-curing composite resin when the thickness or the translucency of lithium disilicate-enriched glass-ceramic veneers are modified. IPS e. max® CAD blocks of the MT-A2, LT-A2 and MO1 types were cut to obtain four slices with thicknesses ranging from 0.6 mm to 1 mm. A strictly light-curing composite resin (G-aenial Universal Injectable) was injected in the empty part of a silicone mold so that the veneer could then be inserted under digital pressure to the stop. A 40 s light cure (1400 mW/cm2) was then performed. Resin samples were analyzed using Fourier transform infrared (FTIR) spectroscopy. When the degree of translucency of the ceramic was modified, a decrease in the resin conversion rate was noted, but with a non-significant global p-value (p = 0.062). Interestingly, the degree of conversion of the light-curing composite resin was also modified when the ceramic's thickness increased, especially when it was over 1 mm (DC0.6 > DC0.7 > DC0.8 > DC1; p < 0.0001). This confirms that the degree of conversion of a bonding material is very dependent on the ceramic's thickness. Contradictory data are, however, found in the literature, where there are reports of an absence of a difference between the DC obtained with thicknesses of ceramics of 0.7 and 2 mm.

Finite Element Analysis of the Mechanical Performance of Non-Restorable Crownless Primary Molars Restored with Intracoronal Core-Supported Crowns: A Proposed Treatment Alternative to Extraction for Severe Early Childhood Caries

Early childhood caries (ECC) involve extensive coronal tooth structure loss, and tooth reconstruction remains highly challenging. To fulfill preclinical assessment, the present study investigated the biomechanics of non-restorable crownless primary molars that were restored by stainless steel crowns (SSC) using different composite core build-up materials. Computer-aided design-integrated 3D finite element and modified Goodman fatigue analyses were performed to determine stress distribution, risk of failure, fatigue life and dentine-material interfacial strength for the restored crownless primary molars. A dual-cured resin composite (MultiCore Flow), a light-cured bulk-fill resin composite (Filtek Bulk Fill posterior), a resin-modified glass-ionomer cement (Fuji II LC) and a nano-filled resin-modified glass-ionomer cement (NRMGIC; Ketac N100) were used as core build-up composite materials in the simulated models. The finite element analysis showed that types of core build-up materials affected the maximum von Mises stress only in the core materials (p-value = 0.0339). NRMGIC demonstrated the lowest von Mises stresses and revealed the highest minimum safety factor. The weakest sites were along the central grooves regardless of type of material, and the ratio of shear bond strength to maximum shear stress at the core-dentine interface of the NRMGIC group was lowest among the tested composite cores. However, all groups provided lifetime longevity from the fatigue analysis. In conclusion, core build-up materials differentially influenced the von Mises stress (magnitude and distribution) and the safety factor in crownless primary molars restored with core-supported SSC. However, all materials and the remaining dentine of crownless primary molars provided lifetime longevity. The reconstruction by core-supported SSC, as an alternative to tooth extraction, may successfully restore non-restorable crownless primary molars without unfavorable failures throughout their lifespan. Further clinical studies are required to evaluate the clinical performance and suitability of this proposed method.

Conditional Mitigation of Dental-Composite Material-Induced Cytotoxicity by Increasing the Cure Time

Light-cured composite resins are widely used in dental restorations to fill cavities and fabricate temporary crowns. After curing, the residual monomer is a known to be cytotoxic, but increasing the curing time should improve biocompatibility. However, a biologically optimized cure time has not been determined through systematic experimentation. The objective of this study was to examine the behavior and function of human gingival fibroblasts cultured with flowable and bulk-fill composites cured for different periods of time, while considering the physical location of the cells with regard to the materials. Biological effects were separately evaluated for cells in direct contact with, and in close proximity to, the two composite materials. Curing time varied from the recommended 20 s to 40, 60, and 80 s. Pre-cured, milled-acrylic resin was used as a control. No cell survived and attached to or around the flowable composite, regardless of curing time. Some cells survived and attached close to (but not on) the bulk-fill composite, with survival increasing with a longer curing time, albeit to <20% of the numbers growing on milled acrylic even after 80 s of curing. A few cells (<5% of milled acrylic) survived and attached around the flowable composite after removal of the surface layer, but attachment was not cure-time dependent. Removing the surface layer increased cell survival and attachment around the bulk-fill composite after a 20-s cure, but survival was reduced after an 80-s cure. Dental-composite materials are lethal to contacting fibroblasts, regardless of curing time. However, longer curing times mitigated material cytotoxicity exclusively for bulk-fill composites when the cells were not in direct contact. Removing the surface layer slightly improved biocompatibility for cells in proximity to the materials, but not in proportion to cure time. In conclusion, mitigating the cytotoxicity of composite materials by increasing cure time is conditional on the physical location of cells, the type of material, and the finish of the surface layer. This study provides valuable information for clinical decision making and novel insights into the polymerization behavior of composite materials.