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.

Long-term hybrid stability and matrix metalloproteinase inhibition by fucosterol in resin-dentin bonding biomechanics

Fucosterols have been widely studied for their antioxidant, anticancer, and anti-inflammatory properties. However, they have not yet been studied in the field of dentistry. This study aimed to determine whether pretreatment of dentin with fucosterol before resin restoration enhances bond stability in resin-dentin hybrid layers. After applying 0.1, 0.5, and 1.0 wt% fucosterol to demineralized dentin, microtensile bond strength (MTBS) and nanoleakage tests were performed before and after collagenase aging, and the surface was observed using scanning electron microscope (SEM). The fucosterol-treated group showed better bond strength and less nanoleakage both before and after collagenase aging, and the corresponding structures were confirmed using SEM. MMP zymography confirmed that the activity of MMPs was relatively low along the concentration gradient of fucosterol, and the FTIR analysis confirmed the production of collagen crosslinks. In addition, fucosterol exhibits cytotoxicity against Streptococcus mutans, the main cause of dental decay. The results of this study suggest that fucosterol pretreatment improves bond strength and reduces nanoleakage at the resin-dentin interface, possibly through a mechanism involving collagen cross-link formation via the inhibition of endogenous and exogenous MMP activity. This study demonstrates the potential of fucosterol as an MMP inhibitor in dentin, which contributes to long-term resin-dentin bond stability and can be used as a restorative material.

Light-curable urushiol enhanced bisphenol A glycidyl dimethacrylate dentin bonding agent

OBJECTIVES

The low durability of composite resin restorations can be attributed to the degradation of the resin dentin bonding interface. Owing to the presence of hydrophilic components in the adhesive, the integrity of the resin dentin bonding interface is easily compromised, which, in turn, leads to a reduction in bond strength. The hydrophilic nature of the adhesive leads to water sorption, phase separation, and leaching of the resin component. Therefore, hydrophobic adhesives could effectively be used to stabilize the integrity and durability of the resin dentin bonding interface.

METHODS

We synthesized a novel hydrophobic dentin adhesive by partially replacing bisphenol A glycidyl dimethacrylate (Bis-GMA) with a light-curable urushiol monomer. The properties of the produced adhesive, including the degree of conversion, viscosity, contact angle, water sorption/solubility, and mechanical strength, were comprehensively examined and compared to those of the commercially adhesive Adper Single Bond2 as a positive control. The adhesive properties were determined using microtensile bond strength measurements, laser confocal microscopy, scanning electron microscopy observations, and nanoleakage tests. Finally, the novel adhesive was subjected to biocompatibility testing to determine its potential cytotoxicity.

RESULTS

At a light-curable urushiol content of 20 %, the synthesized adhesive exhibited high degrees of conversion and hydrophobicity, low cytotoxicity, good mechanical properties, and outstanding adhesive strength.

CONCLUSIONS

The introduction of the light-curable urushiol into dentin adhesives can significantly enhance their hydrophobic, mechanical, and bonding properties, demonstrating potential to significantly improve restoration longevity.

CLINICAL SIGNIFICANCE

The integration of light-curable urushiol has endowed the experimental adhesives with several enhanced functionalities. These notable benefits underscore the suitability of this monomer for expanded applications in clinical practice.

Extrafibrillar demineralization: Yes or no?

OBJECTIVE

Extrafibrillar demineralization is considered to be an ideal solution for addressing the durability of resin-dentin bonding interfaces. However, its theoretical basis is contradictory to ionization equilibrium of hydroxyapatite dissolution. In this study, various calcium chelators were selected as dentin conditioners to explore the essence of dentin demineralization with chelators and its effect on resin-dentin adhesion.

METHODS

Polyethyleneimine grafted with EDTA and polyacrylic acid sodium (PAAN450k) larger than 40 kDa, as well as PAAN (PAAN3k) and EDTA smaller than 6 kDa, were prepared as dentin conditioners. The dentin powder was designed to characterize whether it would demineralize without contact with PAAN450k. Dentin demineralization effect with four conditioners was evaluated with field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy and quantification of hydroxyproline concentration after enzymatic degradation. Micro-tensile bond strength (µTBS) test and failure mode analysis were employed to assess the bonding effect of the four chelators in both wet and dry bonding, with H3PO4 wet bonding serving as the control group.

RESULTS

Demineralization occurs when PAAN450k was not in direct contact with the dentin powder. The extrafibrillar demineralization cannot be induced by any chelator regardless of its molecular weight. Complete demineralization including extrafibrillar and intrafibrillar demineralization would occur with sufficient interaction time. Moreover, chelators could not provide a reliable dentin bonding effect under a short interaction time.

SIGNIFICANCE

From the perspective of theory and application, extrafibrillar demineralization is not a reliable strategy, which provides a reminder for exploring new strategies in the future.

Effect of Instrument Lubricant on Mechanical Properties of Restorative Composite

OBJECTIVES

Using a wetting resin or adhesive system as an instrument lubricant when placing composite layers is commonly practiced to improve handling. This study investigated whether instrument lubricants affected strength, stiffness, or hardness.

METHODS

Composite beams (TPH Spectra) were fabricated using a stainless steel mold (25×2.5×2 mm) in two steps, where the second half (12.5 mm) was added and cured against a cured first half (n=15). The composite surface at the open end of the first half was smoothed using an instrument lubricated with wetting resin (Ultradent) or universal adhesive (ScotchBond Universal), enough to prevent sticking, or without lubrication. An additional beam of each group was characterized using scanning electron microscopy. Monolithic specimens were also fabricated. After 24 hour storage (37°C, 100% humidity), the beams' flexural strength and stiffness were determined by four-point bending. Vickers surface hardness was measured on 24-hour composite samples in 2 mm deep acrylic cavities, cured after the surface was smoothed with the two instrument lubricants or no lubricant (n=10). Hardness was remeasured after finishing with a series of contouring and polishing discs. Data were statistically analyzed using ANOVA followed by Student-Newman-Keuls post hoc test at 0.05 significance level.

RESULTS

There were significant differences (p<0.001) in flexural strength and stiffness among groups. While strength and stiffness were not affected by using a wetting resin as instrument lubricant, use of a universal adhesive increased strength and stiffness significantly, achieving monolithic values. Scanning electron micrographs showed less porosities at the interface when using instrument lubricants. Surface hardness was significantly reduced in groups in which instrument lubricants were used, but finishing/polishing restored original hardness (p<0.001).

CONCLUSIONS

Lubricating an instrument with a wetting agent did not adversely affect physical or surface properties, provided the surface was finished and polished. If a universal adhesive was used as lubricant, the strength and stiffness of a layered composite could be increased, reaching monolithic values.

Advances in ceramics for tooth repair: From bench to chairside

OBJECTIVES

To give a comprehensive review of advancement in dental ceramics, fabrication methods, and the challenges associated with clinical application.

DATA, SOURCES AND STUDY SELECTION

Researches on chemical composition, biomechanical behaviors, optical properties, bonding strategies and fabrication methods were included. The search of articles was independently conducted by two authors in the PubMed, Scopus, Medline and Web of Science.

CONCLUSIONS

Dental ceramics have shown significant advancements in terms of esthetics and function. However, improving fracture toughness without compromising optical properties remains a challenge. Repairing fractured zirconia or glass-matrix ceramic prostheses with the same material is difficult due to the sintering process. Developing innovative bonding techniques that provide strong and long-lasting bonding strength between ceramics and tooth structures poses a recurring obstacle.

CLINICAL SIGNIFICANCE

Despite the emergence of dental ceramics and fabrication techniques, certain limitations such as susceptibility to brittleness and fracture still exist. Therefore, the current review provided valuable information around the advanced dental ceramics in tooth repair. The laboratory test data and the clinical outcome are also presented in details, aiming to guide clinicians in making informed decisions regarding ceramic restorations.

A Historical Perspective on Dental Composite Restorative Materials

This review article will discuss the origin of resin-based dental composite materials and their adoption as potentially useful adjuncts to the primary material used by most dentists for direct restorations. The evolution of the materials, largely driven by the industry's response to the needs of dentists, has produced materials that are esthetic, strong, and versatile enough to be used in most areas of the oral cavity to replace or restore missing tooth structures. Significant advancements, such as the transition from chemical to light-curing materials, refinements in reinforcing particles to produce optimum polishing and wear resistance, formulating pastes with altered viscosities to create highly flowable and highly stiff materials, and creating materials with enhanced depth of cure to facilitate placement, will be highlighted. Future advancements will likely reflect the movement away from simply being a biocompatible material to one that is designed to produce some type of beneficial effect upon interaction within the oral environment. These new materials have been called "bioactive" by virtue of their potential effects on bacterial biofilms and their ability to promote mineralization of adjacent tooth structures.

Transforming smiles: Aesthetic rehabilitation with layered zirconia veneers and crowns for spaced dentition and faulty crowns-A case report

The objective of this case report was to provide a plan for aesthetic rehabilitation of a patient utilizing layered zirconia restorations to produce a homogeneous, pleasing smile. In this case, a female patient, aged 38 years, presented in dental clinic with a spaced dentition and faulty crowns that were causing functional and aesthetic concerns. She was a banker by profession and socially active. The treatment plan involved layered zirconia indirect restorations to enhance her natural teeth appearance. The aim of this case report was to propose an effective strategy for addressing her concerns, with the potential to achieve a desired aesthetic outcome. Additionally, the implementation of this treatment approach had a positive influence on self-esteem and confidence of the patient.

Remineralizing effects of hydroxypropyl methylcellulose film-loaded amorphous calcium phosphate nanoprecursors on enamel artificial caries lesions

OBJECTIVES

This study was to investigate hydroxypropyl methylcellulose (HPMC) film as a carrier for amorphous fluorinated calcium phosphate (AFCP) nanoprecursors to continuously deliver biomimetic remineralization of enamel artificial caries lesions (ACL).

MATERIALS AND METHODS

The AFCP/HPMC films were comprised of 25 wt% AFCP nanoparticles and 75 wt% HPMC. They were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and biocompatibility tests. Forty enamel ACL were prepared and randomly divided into four groups (n = 10): The enamel surfaces were covered with a pure HPMC film, Tooth Mousse Plus (contains 10% CPP-ACP and 0.2% NaF), and AFCP/HPMC film, or without any things (serving as negative control). Subsequently, all samples were alternatively kept in artificial saliva and a modified pH-cycling before they were characterized by Micro-CT, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), attenuated total reflectance (ATR)-FTIR, XRD, and nanoindentation.

RESULTS

After the enamel ACL was challenged by pH cycling, Tooth Mousse Plus and AFCP/HPMC film groups exhibited less lesion depth and mineral loss than the negative control and pure HPMC film groups. Additionally, the AFCP/HPMC film group revealed a highest remineralization rate of 55.34 ± 3.10 % among the all groups (p < 0.001). The SEM findings showed that the enamel ACL were densely deposited with minerals in the AFCP/HPMC film group, and the EDX results suggested a higher content of fluorine in the remineralized tissues. In particular, the AFCP/HPMC film group exhibited the best nanomechanical performance after 2 weeks of pH cycling (p < 0.05), with the hardness (H) restored from 0.29 ± 0.19 to 2.69 ± 0.70 GPa, and elastic modulus (Er) restored from 10.77 ± 5.30 to 68.83 ± 12.72 GPa.

CONCLUSION

The AFCP/HPMC film might be used as a promising strategy for arresting or reversing incipient enamel caries lesions.

Assessment of Prevalence and Causative Factors for Replacement of Composite and Amalgam Restorations: An Observational Study

Aim

This study intends to evaluate the frequency and causes of replacement for failed amalgam and composite dental restorations.

Methodology

A cross-sectional study comprising female patients with failed permanent composite and amalgam restorations aged 15-60 years old was carried out at the dental clinics of Qassim University. Using a self-structured proforma, demographic data and causes for restoration failure were recorded. The effectiveness of the restorations was assessed by using the Ryge criteria after performing clinical and radiographic examinations. The Statistical Package for Social Science was used for the statistical analysis.

Results

It is found that 84.6% of the 299 unsuccessful restorations examined were composite, and 15.4% were amalgam. The main reason for dental failure for both amalgam (95.6%) and composite (93.28%) restorations was secondary caries. Failure of amalgam restoration was largely caused by poor marginal adaptation. With varied incidences between amalgam and composite restorations, typical complaints included discomfort, sensitivity, pain, and food impaction with soreness. The main justification for replacement in amalgam restorations was sensitivity. Repair and replacement rates were similar for amalgam, composite, and mandibular/maxillary restorations. Moreover, 21.1% of individuals overall reported no symptoms, with 8.7% in the amalgam group and 23.3% in the composite group with significant differences (χ2 = 34.28, P = 0.001).

Conclusion

According to the current study, secondary caries was found to be the main reason for both amalgam and composite restoration failure. The main problems reported were sensitivity, discomfort, and pain with amalgam showing more sensitivity-related failures.

Novel antimicrobial and self-healing dental resin to combat secondary caries and restoration fracture

OBJECTIVE

Dental resin composites have been the most popular materials for repairing tooth decay in recent years. However, secondary caries and bulk fracture are the major hurdles that affect the lifetime of dental resin composites. This current study synthesized a novel antimicrobial and self-healing dental resin containing nanoparticle-modified self-healing microcapsules to combat secondary caries and restoration fracture.

METHODS

Multifunctional dental resins containing 0-20% nanoparticle-modified self-healing microcapsules were prepared. The water contact angle, antimicrobial properties, mechanical properties, cell toxicity, and self-healing capability of the dental resins were tested.

RESULTS

A novel multifunctional dental resin was synthesized. When the microcapsule mass fraction was 10%, the resin presented a strong bacteriostasis rate (80.3%) and excellent self-healing efficiency (66.1%), while the hydrophilicity, mechanical properties, and cell toxicity were not affected.

SIGNIFICANCE

The novel antimicrobial self-healing dental resin is a promising candidate for use in clinical practice, which provides a simple and highly efficient strategy to combat secondary caries and restoration fracture. This novel dental resin also gives the inspiration to prolong the service life of dental restorations.

Trends in dental expenditures in Japan with a universal health insurance system

BACKGROUND

The government of Japan has spent a significant amount on dental healthcare, but it remains unknown how the spending varies across age, type of service, and time. This study describes trends in dental expenditures in Japan.

METHODS

This descriptive study used two national data sources: Estimates of National Medical Care Expenditure and Survey on Economic Conditions in Health Care. We obtained annual total and average per capita dental expenditures by age in Japan from 1984 to 2020 and estimated the proportions of types of service from 1996 to 2021. All costs were adjusted for the 2020 Consumer Price Index (1 US dollar ≈ 100 yen in 2020).

RESULTS

Total dental expenditures increased from 1.96 trillion yen in 1984 to 3.00 trillion yen in 2020. In particular, total and average per capita dental spending for older persons showed a rapid increase (total: from 185 billion yen in 1984 to 1.18 trillion yen in 2020; average per capita: from 15,500 yen in 1984 to 32,800 yen in 2020), contributing to the total amount increase. The crown restoration and prosthesis category amounted to 50.3% of the total expenditure in 1996, and this proportion declined to 32.4% by 2021. In 0-14 years persons, expenses on the crown restoration and prosthesis category decreased while the medical management category (mainly including fees for a management plan for oral diseases or oral functions) increased. In persons aged 65 years or older, expenses on the crown restoration and prosthesis category decreased, with increasing expenses in the medical management and at-home treatment categories.

CONCLUSION

The amount of dental spending in Japan substantially increased from 1.96 trillion yen in 1984 to 3.00 trillion yen in 2020), a 1.53-fold increase. The observed changes in annual dental spending varied across age groups and types of service.

The germicidal effect, biosafety and mechanical properties of antibacterial resin composite in cavity filling

In recent years, dental resin materials have become increasingly popular for cavity filling. However, these materials can shrink during polymerization, leading to microleakages that enable bacteria to erode tooth tissue and cause secondary caries. As a result, there is great clinical demand for the development of antibacterial resins. The principle of antibacterial resin includes contact killing and filler-release killing of bacteria. For contact killing, quaternary ammonium salts (QACs) and antibacterial peptides (AMPs) can be added. For filler-release killing, chlorhexidine (CHX) and nanoparticles are used. These antibacterial agents are effective against gram-positive bacteria, gram-negative bacteria, fungi, and more. Among them, QACs has a lasting antibacterial effect, and silver nanoparticles even have a certain ability to kill viruses. Biocompatibility-wise, QACs, AMPs, and CHX have low cytotoxicity to cells when added into the resin. However, nanoparticles with smaller particle sizes have higher cytotoxicity. In terms of mechanical properties, QACs, AMPs, and CHX do not negatively affect the resin. However, the addition of magnesium oxide can have a negative impact. This paper reviews the types and antibacterial principles of commonly used antibacterial resins in recent years, evaluates their antibacterial effect, biological safety, and mechanical properties, and provides references for selecting clinical filling materials.

Optimized Erbium-Doped Yttrium Aluminum Garnet (Er:YAG) Laser Parameters for the Removal of Dental Ceramic Restorations

OBJECTIVES

The use of lasers for debonding adhesively luted ceramic restorations is a rather recent oral laser application in dentistry. The removal of all-ceramic restorations in the mouth can often be a troublesome task. A novel method for the debonding of ceramic restorations without damaging the restorations is Er:YAG laser irradiation. The aim of this study was to evaluate the Er:YAG laser for debonding procedures of different dental ceramics and to identify appropriate laser settings.

MATERIAL AND METHODS

Lithium disilicate, zirconium-reinforced lithium silicate, feldspatic ceramic, and zirconium dioxide were investigated. Ten ceramic rectangular-shaped specimens with 1 and 2 mm thickness were produced from each material. All specimens were irradiated with four different power settings 1.5; 2.5; 3.5; 4.5 W, pulse duration 50 μs, laser repetition rate 10 Hz, time of irradiation 10 s. The transmitted energy was measured with a powermeter. Additionally the suitability of the Er:YAG laser to remove the adhesively bonded ceramic and the time until loss of retention was evaluated.

RESULTS

The transmission rate for 1 and 2 mm platelets was determined for zirconium-reinforced lithium silicate at 54.6%/35.6%, lithium disilicate at 53.2%/35.7%, zirconium dioxide at 40.6%/32.4%, and for the feldspathic ceramic at 19.4%/10.1%. For zirconium-reinforced lithium silicate and zirconium dioxide 2.5 W (250 mJ/10 Hz) was an appropriate energy level for effective debonding. Whereas for lithium disilicate and for feldspathic ceramic, 4.5 W (450 mJ/10 Hz) is required for efficient debonding.

CONCLUSIONS

There are differences regarding transmission rates between ceramic types for the Er:YAG laser light and additionally depending on the type of ceramic different energy settings should be used for adequate debonding. Based on our in-vitro experiments we recommend 2.5 W for zirconium-reinforced lithium silicate and zirconium dioxide and 4.5 W for lithium disilicate and feldspatic ceramic. Transmission rates of different ceramic types and varying influences of thicknesses and bonding materials should be considered to adjust the laser parameters during laser debonding of adhesively luted all-ceramic restorations.

Fracture Resistance of Class II MOD Cavities Restored by Direct and Indirect Techniques and Different Materials Combination

This study aimed to evaluate the fracture resistance of class II MOD cavities restored using different techniques and materials. Sixty extracted maxillary molars were selected and standardized class II MOD cavities were prepared using a custom-made paralleling device. The specimens were divided into four groups based on the restoration technique used: Group 1 (direct resin composite), Group 2 (short-fiber-reinforced composite resin), Group 3 (composite polyethylene fiber reinforcement), and Group 4 (CAD/CAM resin inlays). Fracture resistance was assessed for each group after thermocycling aging for 10,000 cycles. The mode of fracture was assigned to five types using Burke's classification. To compare the fracture force among the tested materials, a paired sample t-test was performed. The significance level for each test was set at p < 0.05. Significant differences in fracture resistance were observed among the different restoration techniques. CAD/CAM inlays (2166 ± 615 N), short-fiber-reinforced composite resin (2471 ± 761 N), and composite polyethylene fiber reinforcement (1923 ± 492 N) showed superior fracture resistance compared to the group restored with direct resin composite (1242 ± 436 N). The conventional resin composite group exhibited the lowest mean fracture resistance. The choice of restoration material plays a critical role in the clinical survival of large MOD cavities. CAD/CAM inlays and fiber-reinforced composites offer improved fracture resistance, which is essential for long-term success in extensive restorations.

A phenomenological study on East and Southeast Asian dental educators: perceived importance, challenges, and strategies in teaching dental materials science

BACKGROUND

Effective teaching of dental materials science is crucial for dental students to develop a comprehensive understanding of materials used in clinical practice. However, literature on educators' views on teaching this subject is still scarce. This qualitative study aimed to explore the lived experiences of dental educators in teaching dental materials science subjects, thereby addressing potential gaps and enhancing teaching practices.

METHODS

Thirteen dental educators from East and Southeast Asian countries (Malaysia, China, Indonesia, Thailand, South Korea, and Japan) participated in the present study. The present study adopted a transcendental phenomenological approach. One-to-one semi-structured online interviews were conducted. Interviews were recorded and transcribed verbatim. Thematic analysis was employed to identify patterns in the educators' experiences.

RESULTS

Three themes emerged from the present study. First, perceptions of the importance of dental materials science, highlighting its relevance in clinical practice, patient care, and lifelong learning. Second, the challenges faced in teaching dental materials science include limited instructional time, complex content, and insufficient resources. Third, specific strategies, such as applying interactive teaching methods, integrating clinical scenarios, and promoting critical thinking skills have been suggested to enhance teaching and learning.

CONCLUSION

Understanding dental educators' experiences can improve dental materials science education, curriculum development, teaching methods, and faculty training programmes, ultimately enhancing the knowledge and skills of dental students in this field.

Novel Dental Low-Shrinkage-Stress Composite with Antibacterial Dimethylaminododecyl Methacrylate Monomer

OBJECTIVES

Current dental resins exhibit polymerization shrinkage causing microleakage, which has the potential to cause recurrent caries. Our objectives were to create and characterize low-shrinkage-stress (LSS) composites with dimethylaminododecyl methacrylate (DMADDM) as an antibacterial agent to combat recurrent caries.

METHODS

Triethylene glycol divinylbenzyl ether and urethane dimethacrylate were used to reduce shrinkage stress. DMADDM was incorporated at different mass fractions (0%, 1.5%, 3%, and 5%). Flexural strength, elastic modulus, degree of conversion, polymerization stress, and antimicrobial activity were assessed.

RESULTS

The composite with 5% DMADDM demonstrated higher flexural strength than the commercial group (p < 0.05). The addition of DMADDM in BisGMA-TEGDMA resin and LSS resin achieved clinically acceptable degrees of conversion. However, LSS composites exhibited much lower polymerization shrinkage stress than BisGMA-TEGDMA composite groups (p < 0.05). The addition of 3% and 5% DMADDM showed a 6-log reduction in Streptococcus mutans (S. mutans) biofilm CFUs compared to commercial control (p < 0.001). Biofilm biomass and lactic acid were also substantially decreased via DMADDM (p < 0.05).

CONCLUSIONS

The novel LSS dental composite containing 3% DMADDM demonstrated potent antibacterial action against S. mutans biofilms and much lower polymerization shrinkage-stress, while maintaining excellent mechanical characteristics. The new composite is promising for dental applications to prevent secondary caries and increase restoration longevity.

Surface Properties and Streptococcus mutans Biofilm Adhesion of Ion-Releasing Resin-Based Composite Materials

OBJECTIVE

To evaluate the adhesion of Streptococcus mutans (S. mutans) and related surface properties of ion-releasing resin-based composite (RBC) restorative materials.

METHODS

Two ion-releasing RBCs, Activa (ACT) and Cention-N (CN), were compared to a conventional RBC (Z350) and a resin-modified glass ionomer cement (Fuji-II-LC). Ten disk-shaped specimens were fabricated for each material (n=40). After standardized surface polishing procedure, the surface properties of the specimens were evaluated using surface roughness measurements by a profilometer and hydrophobicity using water contact angle measurements. To assess bacterial adhesion, the number of S. mutans bacteria was calculated from colony-forming units (CFU). Confocal laser scanning microscope analysis was done for qualitative & quantitative assessment. The data were analyzed using One-way ANOVA followed by Tukey's post-hoc test to compare the mean values of surface roughness, water contact angle and CFU values. To compare the mean dead cell percentage Kruskal-Wallis rank test and Conover test were used. A p-value of ≤ 0.05 was used to report the statistical significance.

RESULTS

Z350 and ACT had the smoothest surfaces, followed by CN, and the roughest surface was seen in FUJI-II-LC. The lowest water contact angles were seen in CN, and Z350, and the highest were in ACT. S. mutans counts were the highest in ACT and the lowest in Z350 and CN. CN and Fuji-II-LC registered the highest percentage of dead bacterial cells, while the lowest were in ACT.

SIGNIFICANCE

Surface properties did not significantly influence bacterial adhesion. More S. mutans bacteria accumulated on ACT than on the nanofilled composite and on CN. CN had antibacterial effects against Streptococcus mutans biofilms.

Prevalence and mean number of teeth with amalgam and nonamalgam restorations, United States, 2015 through 2018

BACKGROUND

Amalgam has been used for more than 150 years as a safe and reliable restorative material. The authors described the occurrence of amalgam and nonamalgam restorations in the United States in primary and permanent teeth across age groups and according to sociodemographic characteristics.

METHODS

The authors used clinical examination data from the National Health and Nutrition Examination Survey 2015-2018 for participants 2 years and older (n = 17,040). The authors estimated the prevalence and mean number of amalgam and nonamalgam restorations in primary and permanent teeth according to age groups (2-5 years, 6-11 years, 12-15 years, 16-19 years, 20-39 years, 40-59 years, 60-79 years, and ≥ 80 years), race and ethnicity, federal poverty guideline, education, and pregnancy status.

RESULTS

The prevalence of amalgam restorations ranged from 4% through 69%. Overall, amalgam restorations were more prevalent in children and adolescents from racial and ethnic minority groups and families at lower poverty levels and with lower education. The mean number of teeth with nonamalgam restorations was higher than those with amalgam restorations in primary teeth of children aged 6 through 11 years, permanent teeth of those 12 through 15 years and 20 through 39 years, and women aged 20 through 49 years, regardless of pregnancy status. The mean number of amalgam restorations was higher than that for nonamalgam restorations in older age groups.

CONCLUSIONS

Nonamalgam restorations were the most common in the primary teeth of children older than 5 years and in the permanent teeth of adults younger than 40 years. Amalgam restorations were more common in older adults. Amalgam and nonamalgam restorations were equally common in children younger than 5 years.

PRACTICAL IMPLICATIONS

The study findings suggest a shift from amalgam to alternative restorative materials in the United States.

Experimental Investigation of Dental Composites Degradation After Early Water Exposure

While dental composite long-term aging has already been studied in the past, no data exist about the early aging while it might be detrimental regarding the composites' longevity. This study aims to better understand the effects of early water exposure on dental composites. Dental resin composites with different fillers ratio were subjected to water exposure during 24 h, 1 week, or 1 month. After photopolymerization, the samples were stored at different conditions, whether in wet or dry condition (W, D, respectively) and in wet conditions after a first 24 h storage in dry conditions (DW). Three-point bending tests were performed to measure the flexural modulus. The samples were then subjected to a sorption/desorption protocol. While the matrix alone did not undergo any mechanical degradation with exposure time, the composites matrices presented a decrease in elastic modulus. This decrease was the highest for the matrix with nonsilanized fillers. Interestingly, the DW condition was detrimental for all the samples. Regarding the sample with nonsilanized fillers in DW for 1 month presented an elastic modulus lower than the matrix alone. These results were assigned to the sorption capacity of the polymer matrix, suggesting that the diffusion mechanisms and the nature of water molecules are determinant in the composite degradation. This study showed that dental composite early degradation mechanisms after water exposure are involved in the polymer matrix postpolymerization process as soon as after 24 h. Such mechanisms are detrimental in terms of the dental composite efficiency and have to be understood.

Identifying relevant topics and their competency levels for dental materials science: a fuzzy Delphi study

BACKGROUND

Dental materials science is an important core course in undergraduate dental programs which integrates foundational concepts of chemical engineering and materials science into clinical dentistry. The present study aimed to identify relevant dental materials science topics for Malaysian undergraduate dental curricula and to determine their appropriate competency levels in terms of cognitive and psychomotor taxonomies.

METHODS

Potential dental materials science topics were drafted in alignment with the revised national competency statement. The list of topics was further amended after comparing it with those recommended topics in the literature. Fuzzy Delphi method was applied. Experts were selected based on the different inclusion criteria. They ranked the topics using a five-point Likert scale and recommended the appropriate cognitive and psychomotor levels. Next, fuzzy evaluation was performed. Consensus was deemed for a topic to be included if (a) the average expert agreement was ≥ 75%, (b) the d-construct threshold value for each topic was ≤ 0.2 and (c) the average fuzzy number was ≥ 0.5.

RESULTS

Sixty-two experts participated in the study. They accepted 33 out of 36 potential dental materials science topics. The average Likert score and fuzzy number ranged from 3.63 to 4.92 and 0.526 to 0.784, respectively. Furthermore, "Endodontic materials" was ranked as the most significant topic. Meanwhile, many topics required dental students to demonstrate a cognitive level of "Apply" and a psychomotor level of "Guided response". Based on mean scores, "Impression materials" was rated as the most cognitively demanding topic, whilst "Temporary restorative materials" was the most demanding topic for psychomotor taxonomy.

CONCLUSION

The present study has identified relevant dental materials science topics and their appropriate cognitive and psychomotor levels using the Fuzzy Delphi approach. The findings of the present study form the basis for future studies to develop measurable learning outcomes, design corresponding innovative pedagogy and propose assessment criteria for each topic.

Time-dependent structural changes and hypermineralisation of artificially demineralised dentine following treatment with silver diammine fluoride and glass ionomer cement

OBJECTIVES

This study aimed to evaluate the change of mineral content in dentine lesions over time and examine the effectiveness of the combined treatment with silver diammine fluoride (SDF) and glass ionomer cement (GIC).

METHODS

Sixty bovine dentine specimens were divided into 4 groups: cont, Fuji, Safo, and Safo+Fuji. The specimens were imaged and measured using microcomputed tomography (microCT) at 7 time points: pre-demineralisation, after demineralisation for two weeks, immediately after treatment, 1 week, 2 weeks, 1 month, and 3 months after treatment. The 3-month group was evaluated with a light microscope, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and scanning electron microscope (SEM)/energy-dispersive X-ray spectroscopy (EDS). Data were analysed by Dunn's test and Wilcoxon signed rank test with Bonferroni correction for microCT, and Kruskal-Wallis test and two-way analysis of variance for EDS characterisation.

RESULTS

MicroCT images showed high mineral density beneath dentine lesions in Safo+Fuji. The mineral density at 600 μm in Safo+Fuji increased significantly over time, while Safo showed an opposite trend (adjusted p<0.005). In Safo+Fuji, EDS revealed significantly high energy of fluorine (p<0.05, at 300 μm) and a tendency towards high energy of calcium (p>0.05). However, Safo+Fuji showed lower energy of silver compared to Safo (p<0.001). ATR-FTIR revealed that phosphate groups had the highest peak at a depth between 300 and 400 μm in Safo+Fuji.

CONCLUSIONS

Safo+Fuji was effective in remineralising the deep lesion in dentine after one and three months, and a hypermineralisation zone generated beneath the lesion demonstrated additional benefit in this study.

CLINICAL SIGNIFICANCE

This long-term in vitro study showed that SDF+GIC treatment could strengthen the structure of decayed teeth when applied in the treatment of patients with advanced rampant caries.

Masking ability of resin composites: A scoping review

OBJECTIVE

To map the existing evidence regarding the masking ability of resin composites.

OVERVIEW

The literature search was conducted electronically, based on the PRISMA Extension for Scoping Reviews-online protocol at https://osf.io/m2h67/ with no language or time restrictions. Two independent reviewers conducted the screening, and a third reviewer was consulted in case of disagreement. Studies that evaluated resin composite masking ability regardless of background, application technique, thickness, or number of layers were selected. The search found 2995 potentially eligible studies. After removal of duplicates (657), irrelevant articles (2323), 15 citations met the eligibility criteria based on title and abstract, and eight studies were included based on full text analysis (seven in vitro, and one case report). Acceptable masking ability is obtained by one layer of opaque shade resin composite or by the layering technique. A black background is masked with 1.0- to 2.0 mm-thick layers of opaque shade resin composites. Masking of the C4 background is achieved with one layer of 0.5- to 1.5 mm-thick opaque shade resin composite or by the layering technique using different combinations of enamel body and dentin shades with a final thickness of 1.5 mm.

CONCLUSIONS

Acceptable masking of C4 shade background is achieved with one layer of opaque shade composite at least 0.5 mm-thick or by different combinations of the layering technique, with a final thickness of 1.5 mm. Acceptable masking of the black background of the oral cavity is achieved with a resin composite of at least 1.0 mm opaque shade.

CLINICAL SIGNIFICANCE

The thickness of the resin composite layer required to achieve adequate masking is variable and depends on the translucency/opacity of the tested resin composites and the background shade.

The Influence of Printing Layer Thickness and Orientation on the Mechanical Properties of DLP 3D-Printed Dental Resin

Technological advances are closely related to the development of new materials and their processing and manufacturing technologies. In the dental field, the high complexity of the geometrical designs of crowns, bridges and other applications of digital light processing 3D-printable biocompatible resins is the reason for the need for a deep understanding of the mechanical proprieties and behavior of these materials. The aim of the present study is to assess the influence of printing layer direction and thickness on the tensile and compression proprieties of a DLP 3D-printable dental resin. Using the NextDent C&B Micro-Filled Hybrid (MFH), 36 specimens (24 for tensile strength testing, 12 for compression testing) were printed at different layer angulations (0°, 45° and 90°) and layer thicknesses (0.1 mm and 0.05 mm). Brittle behavior was observed in all specimens regardless of the direction of printing and layer thickness for the tensile specimens. The highest tensile values were obtained for specimens printed with a layer thickness of 0.05 mm. In conclusion, both printing layer direction and thickness influence mechanical proprieties and can be used to alter the materials' characteristics and make the final printed product more suitable for its intended purposes.

Effect of thickness on the translucency of resin-based composites and glass-ceramics

This study was aimed to evaluate the effect of thickness (1, 2, 3, and 4 mm) on the translucency of resin-based composites (RBCs) and glass-ceramics, and compare the influence of the thickness of those materials on the translucency parameter (TP) value. The materials were divided into two groups, eight RBCs in Group 1 and five glass-ceramics in Group 2 and TP, ΔL*, Δa*, and Δb* were compared. Statistically significant differences were present in the 2, 3, and 4 mm in the TP, in the 2 and 4 mm in ΔL*, and in all thicknesses in Δa* and Δb* betweent the two groups. The TP of RBCs and glass-ceramics decreased as thickness increased, especially from 1 mm to 2 mm. The TP values of the RBCs were more significantly decreased as the thickness of the material increased from 2 mm to 4 mm than those of the glass-ceramics.

Influence of Thickness of Opaque Porcelain and Alloy Color on the Final Color of Porcelain-Fused-to-Metal Restorations

Despite the advent of metal-free solutions, porcelain-fused-to-metal restorations (PFM) are still widely used. Particularly for the latest ceramic systems, scarce information is present in the scientific literature about the ideal opaque layer thickness and the alloy color impact to achieve the desired final color of PFM restorations. This study aimed to evaluate the influence of opaque thickness variation layered on different metal alloys on the final color of PFM restorations. Opaque porcelain of one metal−ceramic system (VITA VM13) was layered in four different thicknesses (0.10 mm, 0.15 mm, 0.20 mm, and 0.25 mm) on three differently colored dental alloys: a gold−platinum alloy (yellowish), a gold−palladium alloy (light grayish), and a nickel−chromium alloy (dark grayish). The veneering porcelain layered over the opaque was kept constant (Base Dentine 0.45 mm, Transpa Dentine 0.50 mm, and Enamel 0.20 mm). Sixty specimens were fabricated, five samples for each combination of alloy/opaque thickness. The color difference (ΔE) between specimen and reference was measured using a clinical spectrophotometer. The two-way ANOVA revealed that the thickness of both the opaque (p < 0.001) and the metal alloy (p < 0.001) significantly influenced the ΔE values. Gray-colored alloys covered by a 0.10 mm thick opaque layer enabled the closest color match, whereas this occurred for yellow-color alloys covered by a 0.15 mm thick opaque layer. In contrast, the samples covered by a 0.25 mm thick opaque layer obtained the worst ΔE.

Monomers Release from Direct and Indirect Resin-Based Restorations after Immersion in Common Beverages

Impurities or degradation of the components of resin-based materials have been throughout investigated by the dental scientific community. The aim of this study is to examine if there is a release of monomers from resin-based materials when they are immersed in common beverage materials which are consumed by the population in large quantities. Three representative dental materials were used for this study, one resin composite indicated for direct restorations and two Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) materials with different methods of fabrication. Forty specimens were fabricated from each material using a low-speed precision sectioning blade 12 × 14 × 2 mm in size and immersed in wine, coffee or cola for 48 h and 12 days, equivalent to 1 month and 1 year of consumption. The materials released more monomers when the materials were immersed in the wine solution (p < 0.05). CAD/CAM materials release less monomers compared to the resin composite material indicated for direct restorations (p < 0.05). The CAD/CAM materials leach a limited quantity of monomers when they are immersed in common beverages due to the manufacturing process which includes high-temperature/high-pressure polymerization.

Effect of Fast High-Irradiance Photo-Polymerization of Resin Composites on the Dentin Bond Strength

This study investigated the influence of conventional (10 s at 1160 mW/cm²) and fast high-irradiance (3 s at 2850 mW/cm²) light curing on the micro-tensile bond strength (μTBS) of bulk-fill resin composites bonded to human dentin. Sixty-four extracted human molars were ground to dentin and randomly assigned into eight groups (n = 8 per group). After application of a three-step adhesive system (Optibond FL), four different bulk-fill composites (two sculptable and two flowable composites) were placed. Of these, one sculptable (Tetric PowerFill) and one flowable (Tetric PowerFlow) composite were specifically developed for fast high-irradiance light curing. Each composite was polymerized with the conventional or the fast high-irradiance light-curing protocol. The specimens were cut into dentin-composite sticks, μTBS was determined and failure modes were analyzed. Statistical analysis was performed using t-test for independent observations and one-way ANOVA. A statistical difference between the curing protocols was only found for Tetric PowerFlow, where the conventional protocol (23.8 ± 4.2 MPa) led to significantly higher values than the fast high-irradiance light-curing protocol (18.7 ± 3.7 MPa). All other composite materials showed statistically similar values for both polymerization protocols. In conclusion, the use of fast high-irradiation light curing has no negative influence on the μTBS of the investigated high-viscosity bulk-fill composites. However, it may reduce the dentin bond strength of flowable bulk-fill composite.

Resin-Based Composites for Direct and Indirect Restorations: Clinical Applications, Recent Advances, and Future Trends

Continuous advancements in resin-based composites can make selection of the appropriate system a daunting task for the clinician. This review aims to simplify this process and clarify some new or controversial topics. Various types of composites for direct and indirect applications are discussed, including microfilled and microhybrid composites, nanocomposites, single shade, bulk fill, fiber-reinforced, high temperature/high pressure processed, CAD/CAM, and three-dimensional printable composites. Recent material advancements that lead to improved seal and toughness, degradation resistance, antimicrobial and self-healing capabilities are presented. Future directions are highlighted, such as the development of "smart" materials that are able to interact with the host environment.

Dental Light-Curing-Assessing the Blue-Light Hazard

This article focuses on the current understanding and concerns over the blue-light hazard when using dental light-curing units. It also provides information and safety protocols to guide the practitioner in making important decisions regarding dental personnel's health and the quality of dental restorations.

TiO2 nanoparticles added to dense bovine hydroxyapatite bioceramics increase human osteoblast mineralization activity

OBJECTIVES

This study evaluated the effect of TiO₂ nanoparticles + dense hydroxyapatite (HA) on human osteoblast cells (SAOS-2).

METHODS

Particulate bovine HA powder with or without the addition of either 5 or 8 % TiO₂ (HA, HA/TiO₂Np5 % or HA/TiO₂Np8 %) were pressed into disks (Ø = 12.5 mm; thickness = 1.3 mm) uniaxially (100 MPa) and isostatically (200 MPa/1 min) and sintered at 1300 °C. Y-TZP disks were used as control. The following tests were performed: Scanning Electron Microscopy and Dispersive Energy Spectroscopy (SEM/EDS), Atomic Force Microscopy (AFM), cell viability assay (Alamar Blue-AB) and mineralized matrix deposition (Alizarin Red-AR). AB and AR data were submitted to 2-way ANOVA/Tukey tests and ANOVA/Tukey tests, respectively.

RESULTS

SEM revealed that the surface of HA/TiO₂Np5% resembles DPBHA surface, but also contains smaller granules. HA/TiO₂Np8% characteristics resembles HA/TiO₂Np5% surface, but with irregular topography. Y-TZP showed a typical oxide ceramic surface pattern. EDS revealed Ca, O, and P in all samples. C, O, and Zr appeared in Y-TZP samples. AFM data corroborates SEM analysis. AB test revealed excellent cellular viability for HA/TiO₂Np5% group. AR test showed that all groups containing TiO₂np had more mineralized matrix deposition than all other groups, with statistically differences between HA/TiO₂Np8% and HA cultivated in non-osteogenic medium. Culture in osteogenic medium exhibited much more mineralized matrix deposition by TiO₂np groups.

SIGNIFICANCE

In conclusion, the addition of TiO₂np showed chemical, superficial, and biological changes in the reinforced materials. HA/TiO₂Np5% showed the best results for cell viability and HA/TiO₂Np8% for mineralized matrix deposition.

Renewal MI Dental Composite Etch and Seal Properties

This study's aim was to assess whether the Renewal MI composite can self-etch enamel, seal sound cavities, and stabilize demineralized dentine. Etching was assessed using scanning electron microscopy (SEM). Cavity sealing was quantified using the ISO-11405 dye microleakage test. Demineralized dentine stabilization was evaluated by visualizing resin tag formation, enzyme activity and mineral precipitation at the adhesion interface. Renewal MI provided a mild etching of sound enamel in comparison with 37% phosphoric acid. It provided a comparable seal of sound cavities to Z250/Scotchbond Universal adhesive and a superior seal to Activa, Fuji IX and Fuji II LC. With demineralized dentine, Renewal MI formed 300-400 µm resin tags covering 63% of the adhesion interface compared with 55 and 39% for Z250/Scotchbond and Activa. Fuji IX and Fuji II LC formed no resin tags. A higher tag percentage correlated with lower surface enzyme activity. Unlike Activa and Fuji II LC, Renewal MI promoted mineral precipitation from simulated body fluid, occluding adjacent dentinal tubules within 6 months. These novel etching and sealing properties may facilitate Renewal MI's application in minimally invasive dentistry.

Effects of thermal cycling on mechanical and antibacterial durability of bioactive low-shrinkage-stress nanocomposite

OBJECTIVES

Recent studies developed low-shrinkage-stress composite with remineralizing and antibacterial properties to combat secondary caries and increase restoration longevity. However, their long-term durability in thermal cycling is unclear. The objectives of this study were to develop an antibacterial, remineralizing and low-shrinkage-stress composite, and to investigate its durability in thermal cycling for 20,000 cycles, equivalent to two years of clinical life.

METHODS

The resin consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE). Composites were made with 5% dimethylaminohexadecyl methacrylate (DMAHDM) and 20% of nanoparticles of amorphous calcium phosphate (NACP). Composites were thermal cycled at 5°C and 55°C for 20,000 cycles. A human salivary biofilm model was used to evaluate antibiofilm activity before and after thermal cycling.

RESULTS

After 20,000 cycles, the flexural strength of bioactive low-shrinkage-stress composite matched commercial control with no antibacterial activity (p > 0.05). Surface roughness was clinically acceptable at less than 0.2 μm. UV+NACP+DMAHDM composite reduced the total microorganisms, total streptococci, and mutans streptococci by 2-5 logs, compared to commercial composite. Biofilm lactic acid production was reduced by 11 folds. The antibacterial performance was maintained after thermal cycling, with no decrease after 20,000 cycles.

CONCLUSIONS

Bioactive low-shrinkage-stress composite possessed good mechanical properties that matched commercial composite both before and after thermal cycling. The new composite had potent antibacterial activity, which was maintained and did not decrease after thermal cycling.

CLINICAL SIGNIFICANCE

The new bioactive low-shrinkage-stress composite could reduce polymerization shrinkage stress and release calcium and phosphate ions, with good mechanical properties and strong antibacterial function that were durable after thermal cycling. These properties indicate great potential for inhibiting recurrent caries and increasing the restoration longevity.

Performance of PROPELLER FSE T2WI in reducing metal artifacts of material porcelain fused to metal crown: a clinical preliminary study

This study aimed to compare MRI quality between conventional fast spin echo T₂ weighted imaging (FSE T₂WI) with periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) FSE T₂WI for patients with various porcelain fused to metal (PFM) crown and analyze the value of PROPELLER technique in reducing metal artifacts. Conventional FSE T₂WI and PROPELLER FSE T₂WI sequences for axial imaging of head were applied in participants with different PFM crowns: cobalt-chromium (Co–Cr) alloy, pure titanium (Ti), gold–palladium (Au–Pd) alloy. Two radiologists evaluated overall image quality of section in PFM using a 5-point scale qualitatively and measured the maximum artifact area and artifact signal-to-noise ratio (SNR) quantitatively. Fifty-nine participants were evaluated. The metal crown with the least artifacts and the optimum image quality shown in conventional FSE T₂WI and PROPELLER FSE T₂WI were in Au–Pd alloy, Ti, and Co–Cr alloy order. PROPELLER FSE T₂WI was superior to conventional FSE T₂WI in improving image quality and reducing artifact area for Co-Cr alloy (17.0 ± 0.2% smaller artifact area, p < 0.001) and Ti (11.6 ± 0.7% smaller artifact area, p = 0.005), but had similar performance compared to FSE T₂WI for Au–Pd alloy. The SNRs of the tongue and masseter muscle were significantly higher on PROPELLER FSE T₂WI compared with conventional FSE T₂WI (tongue: 29.76 ± 8.45 vs. 21.54 ± 9.31, p = 0.007; masseter muscle: 19.11 ± 8.24 vs. 15.26 ± 6.08, p = 0.016). Therefore, the different PFM crown generate varying degrees of metal artifacts in MRI, and the PROPELLER can effectively reduce metal artifacts especially in the PFM crown of Co-Cr alloy.

Low-Shrinkage Resin Matrices in Restorative Dentistry-Narrative Review

Dimethacrylate-based resin composites restorations have become widely-used intraoral materials in daily dental practice. The increasing use of composites has greatly enhanced modern preventive and conservative dentistry. They have many superior features, especially esthetic properties, bondability, and elimination of mercury and galvanic currents. However, polymeric materials are highly susceptible to polymerization shrinkage and stresses that lead to microleakage, biofilm formation, secondary caries, and restoration loss. Several techniques have been investigated to minimize the side effects of these shrinkage stresses. The primary approach is through fabrications and modification of the resin matrices. Therefore, this review article focuses on the methods for testing the shrinkage, as well as formulations of resinous matrices available to reduce polymerization shrinkage and its associated stress. Furthermore, this article reviews recent cutting-edge developments on bioactive low-shrinkage-stress nanocomposites to effectively inhibit the growth and activities of cariogenic pathogens and enhance the remineralization process.

Chemical and mechanical properties of dual-polymerizing core build-up materials

OBJECTIVES

To investigate the chemical (degree of conversion (DC)) and mechanical properties (Martens hardness (HM), elastic indentation modulus (E_IT), and biaxial flexural strength (BFS)) of four dual-polymerizing resin composite core build-up materials after light- and self-polymerization.

MATERIALS AND METHODS

Round specimens with a diameter of 12 mm and a thickness of 1.5 mm were manufactured from CLEARFIL DC CORE PLUS (CLE; Kuraray), core·X flow (COR; Dentsply Sirona), MultiCore Flow (MUL; Ivoclar Vivadent), and Rebilda DC (REB; VOCO) (N = 96, n = 24/material). Half of the specimens were light-polymerized (Elipar DeepCure-S, 3 M), while the other half cured by self-polymerization (n = 12/group). Immediately after fabrication, the DC, HM, E_IT, and BFS were determined. Data was analyzed using Kolmogorov-Smirnov, Mann-Whitney U, and Kruskal-Wallis tests, Spearman's correlation, and Weibull statistics (p < 0.05).

RESULTS

Light-polymerization either led to similar E_IT (MUL; p = 0.119) and BFS (MUL and REB; p = 0.094-0.326) values or higher DC, HM, E_IT, and BFS results (all other groups; p < 0.001-0.009). When compared with the other materials, COR showed a high DC (p < 0.001) and HM (p < 0.001) after self-polymerization and the highest BFS (p = 0.020) and Weibull modulus after light-polymerization. Positive correlations between all four tested parameters (R = 0.527-0.963, p < 0.001) were found.

CONCLUSIONS

For the tested resin composite core build-up materials, light-polymerization led to similar or superior values for the degree of conversion, Martens hardness, elastic indentation modulus, and biaxial flexural strength than observed after self-polymerization. Among the tested materials, COR should represent the resin composite core build-up material of choice due to its high chemical (degree of conversion) and mechanical (Martens hardness, elastic indentation modulus, and biaxial flexural strength) properties and its high reliability after light-polymerization. The examined chemical and mechanical properties showed a positive correlation.

CLINICAL RELEVANCE

The chemical and mechanical performance of dual-polymerizing resin composite core build-up materials is significantly affected by the chosen polymerization mode.

Ceramic Toughening Strategies for Biomedical Applications

Aiming at shortage of metal materials, ceramic is increasingly applied in biomedicine due to its high strength, pleasing esthetics and good biocompatibility, especially for dental restorations and implants, artificial joints, as well as synthetic bone substitutes. However, the inherent brittleness of ceramic could lead to serious complications, such as fracture and disfunction of biomedical devices, which impede their clinical applications. Herein, several toughening strategies have been summarized in this review, including reinforcing phase addition, surface modification, and manufacturing processes improvement. Doping metal and/or non-metal reinforcing fillers modifies toughness of bulk ceramic, while surface modifications, mainly coating, chemical and thermal methods, regulate toughness on the surface layer. During fabrication, optimization should be practiced in powder preparation, green forming and densification processes. Various toughening strategies utilize mechanisms involving fine-grained, stress-induced phase transformation, and microcrack toughening, as well as crack deflection, bifurcation, bridging and pull-out. This review hopes to shed light on systematic combination of different toughening strategies and mechanisms to drive progress in biomedical devices.

Characteristics of wastewater originating from dental practices using predominantly mercury-free dental materials

Dental materials are currently undergoing a revolution. Mercury use, including traditional amalgam (mercury-containing) material used in dental fillings, is now being widely regulated under the Minamata convention, and dental amalgam is currently being replaced by resin formulations in dentistry. These resin-based materials can be tuned to offer varying material properties by incorporation of a range of nano- and micro-particle based 'fillers' for different dental properties and applications. However, these innovations may have a concomitant effect on the waste streams associated with common dental applications, in particular the potential for higher concentrations of novel micro- and nanomaterials within wastewater streams, and a potential route for novel nanomaterials into the wider Environment. These new materials may also mean that wastewater filtering apparatus commonly deployed at present, such as amalgam separators, may be less efficient or insufficient to capture these new filler materials in dental facility wastewater. In this work, we analyse dental wastewater streams from three dental facilities in Ireland with differing amalgam separators in place. The potential overall toxicity, particulate load and physicochemical properties are analysed. The overall risk posed by these new materials is also discussed.

Comparative Evaluation of Compressive Strength and Flexural Strength of Self-cured Cention N with Dual-cured Cention N: An In Vitro Study

Aim and objective

This study aimed to investigate and compare compressive strength and flexural strength of self-cured Cention N with dual-cured Cention N.

Materials and methods

Cention N is mixed according to the proportions, as mentioned by the manufacturer. Dual cured samples are cured using a diode that emits blue light. Cylindrical plexiglass split mold of dimension 6 mm height, and 4 mm diameter used to fabricate samples for compressive strength. Compressive strength tested using Instron universal testing machine. Rectangular plexiglass split mold of dimension 25 mm length, 2 mm height, and 2 mm width were used to fabricate samples for flexural strength. Flexural strength tested using Instron universal testing machine. To compare the mean values independent t-test was used and the significance of the study was measured by calculating a p-value.

Result

There is no statistically significant difference between compressive strength and flexural strength of self-cured Cention N with dual-cured Cention N.

Conclusion

The type of polymerization does not affect flexural strength and compressive strength of Cention N.

Clinical Significance

Self-curing polymerization alone is sufficient for Cention N to achieve adequate compressive strength and flexural strength. So it can be inserted as a single layer on a prepared cavity and to fasten curing additional light curing can be used.

How to cite this article

Fousiya Ks, Balagopal VR, Suresh KJ, et al. Comparative Evaluation of Compressive Strength and Flexural Strength of Self-cured Cention N with Dual-cured Cention N: An In Vitro Study. Int J Clin Pediatr Dent 2022;15(2):210-214.

Effect of Light Curing Distance on Microhardness Profiles of Bulk-Fill Resin Composites

Bulk-fill (BF) dental resin composites are made to be polymerized in increments of up to 5 mm rather than the 2 mm increment recommended for conventional composites. This project aimed to determine microhardness (MH) profiles of BF resin composites at different depths and varying light cure (LC) distances from the light source in an attempt to mimic varying clinical situations. Forty-eight cylindrical specimens (4 mm diameter and 6 mm height) were prepared from 3 BF composites: Tetric N-Ceram Bulk-Fill (TBF), Filtek One Bulk-Fill (FBF), and Sonic-Fill 2 (SF2). Four different distances (0, 2, 4, and 6 mm) from the LC unit were investigated. Vickers MH was measured at the top and bottom of the samples and at every 1 mm, by creating 3 indentations at each depth. The bottom-top microhardness ratio (MHR) and percentage reduction in MHR were also measured. Data was analyzed using mixed-model repeated-measure ANOVA at 0.05 significance level. The main variables effects “material, LC distance, and depth” were significant (p < 0.001). Increasing LC distance and the depth of the tested BF significantly affected Vickers MH and MHR. None of the tested BF materials had sufficient MHR at the depths of 4–6 mm. SF2 showed the least MHR reduction.

Mechanical Properties of Bisacryl-, Composite-, and Ceramic-resin Restorative Materials

OBJECTIVE

Resin-based materials used in restorative dentistry are introduced at a fast pace with limited knowledge about their properties. Comparing properties of these materials from different restorative categories is lacking but can help the clinician in material selection. This study aimed to compare mechanical properties and wear resistance of bis-acryl-, composite-, and ceramic-resin restorative materials.

METHODS AND MATERIALS

Bisacryl-resin (Bis-R, LuxaCrown, DMG), composite-resin (Com-R, Filtek Supreme Ultra, 3M Oral Care), and ceramic-resin (Cer-R, Enamic, VITA Zahnfabrik) specimens were prepared for mechanical tests: fracture toughness (FT) with and without initial thermomechanical loading using a mastication simulator, flexural strength (FS), and flexural modulus (FM), compressive strength (CS), and volumetric wear loss measurement. The datasets for FT and wear resistance were each analyzed using two-way ANOVA followed by pairwise comparisons or Tukey testing as appropriate. The datasets for FS, FM, and CS were analyzed using one-way ANOVA followed by the Tukey test.

RESULTS

Analysis of FS, FM, and CS showed significant differences between materials, with all pairwise comparisons between materials showing significance. Analysis of FT resulted in a significant interaction between the material and treatment, with analysis of wear loss showing a significant interaction between the material and the number of cycles.

CONCLUSIONS

Cer-R demonstrated superior FT, CS, and wear resistance compared to Bis-R and Comp-R materials. Fracture toughness of Bis-R increased after thermomechanical loading.

Physicochemical and biological properties of experimental dental adhesives doped with a guanidine-based polymer: an in vitro study

OBJECTIVES

The objective of this study is to formulate experimental dental adhesives with different polyhexamethylene guanidine hydrochloride concentrations (PHMGH) and evaluate their physical, chemical, and biological properties.

MATERIALS AND METHODS

The experimental adhesives were formulated with 0 (control, G_CTRL), 0.5 (G_0.5%), 1 (G_1%), or 2 (G_2%) wt.% into the adhesive. The adhesives were analyzed for degree of conversion (DC%), softening in solvent (ΔKHN%), ultimate tensile strength (UTS), microtensile bond strength (μTBS) immediately and after 1 year of aging, antibacterial activity, and cytotoxicity.

RESULTS

There were no differences among groups for DC%, ΔKHN%, and UTS (p > 0.05%). There were no differences between each PHMGH-doped adhesive compared to G_CTRL in the immediate μ-TBS (p > 0.05). Adhesives with at least 1 wt.% of PHMGH presented better stability of μ-TBS. PHMGH-doped adhesives showed improved longitudinal μ-TBS compared to G_CTRL (p < 0.05). Lower Streptococcus mutans biofilm formation was observed for PHMGH-doped adhesives (p < 0.05). There was lower viability of planktonic S. mutans in the media in contact with the samples when at least 1 wt.% of PHGMGH was incorporated (p < 0.05). The formulated adhesives showed no cytotoxicity against pulp cells (p > 0.05).

CONCLUSIONS

The adhesive with 2 wt.% of PHMGH showed the highest antibacterial activity, without affecting the physicochemical properties and cytotoxicity, besides conferring stability for the dental adhesion.

CLINICAL RELEVANCE

PHMGH, a positively charged polymer, conveyed antibacterial activity to dental adhesives. Furthermore, it did not negatively affect the essential physicochemical and biocompatibility properties of the adhesives. More importantly, the incorporation of PHMGH provided stability for the μ-TBS compared to the control group without this additive.

Reconstruction of a Demineralized Dentin Matrix via Rapid Deposition of CaF2 Nanoparticles In Situ Promotes Dentin Bonding

Dentin bonding based on a wet-bonding technique is the fundamental technique used daily in clinics for tooth-restoration fixation and clinical treatment of tooth-related diseases. Limited bonding durability led by insufficient adhesive infiltration in the demineralized dentin (DD) matrix is the biggest concern in contemporary adhesive dentistry. This study proposes that the highly hydrated noncollagenous protein (NCP)-formed interfacial microenvironment of the DD matrix is the root cause of this problem. Meanwhile, the endogenous phosphate groups of the NCPs are used as pseudonuclei to rapidly induce the formation of amorphous CaF₂ nanoparticles in situ in the interfacial microenvironment. The DD matrix is thus reconstructed into a novel porous structure. It markedly facilitates the infiltration of dentin adhesives in the DD matrix and also endows the DD matrix with anticollapsing capability when water evaporates. Whether using a wet-bonding or air-drying mode, the bonding effectiveness is greatly promoted, with the 12 month bonding strength being about twice that of the corresponding control groups. This suggests that the nanoreinforced DD matrix eliminates the dependence of bonding effectiveness on the moisture status of the DD surface controlled only by experiences of dentists. Consequently, this bonding strategy not only greatly improves bonding durability but also overcomes the technical sensitivity of bonding operations of the total-etched bonding pattern. This exhibits the potential to promote dentin bonding and is of great significance to dentistry.

On the behaviour of zirconia-based dental materials: A review

Zirconia-based dental materials are extensively used in clinical practice due to their tooth-like appearance, biofunctionality, biocompatibility, and affordability. However, premature clinical failures of veneering porcelains raise a concern about their integrity. Extensive studies have been performed over a decade to resolve this issue, but it is challenging to reference all information effectively. A single source identifying the significance of potential parameters on material performance has not previously been available. An evidence-based meta-narrative review technique was used to review the characteristic parameters that can affect the overall behaviour of zirconia-based materials. Keywords were chosen to assess manuscripts based on scientific coherence with this paper's research objective. Online keyword searches were carried out on ScienceDirect, PubMed, and SAGE databases for relevant published manuscripts from year 1985-2020.261 out of 3170 identified manuscripts were included. A total of 10 parameters were identified and classified into the material, manufacturing, and geometric aspects. The effect of every parameter was reviewed on the performance of the material. A discrepancy in findings was observed and is attributed to the fact that there is no standard methodology. This review acts as a single source that summarizes various parameters' contribution to zirconia-based dental materials' performance. This review facilitates manufacturing improvements by accounting for every parameter's effect on overall performance.

Direct Restorations for Anterior Esthetic Rehabilitation and Smile Symmetry Recovery: Two Case Reports

Esthetics is an increasing concern for patients, particularly in anterior teeth. The current approaches to manage the esthetic demands include options such as prosthodontic rehabilitation, orthodontic treatment, and direct restorations. Direct restorative procedures for anterior teeth have become a reliable alternative, since current composite materials can mimic teeth’s esthetics and function perfectly. This article describes two clinical cases of anterior esthetic rehabilitations where the direct reshaping of the four maxillary incisors was performed using the buccolingual layering technique with the help of a silicone index. In Case 1, a diastema closure was also performed, whereas in Case 2, the replacement of old restorations was also carried out. It was possible to achieve excellent final esthetic results in both cases, recovering the smile symmetry, and both patients were satisfied. The literature supports the use of direct restorations in the anterior region with very good long-term prognosis. It is a minimally invasive approach that is reversible, repairable, cost-effective, and when combined with layering techniques and adequate restorative materials, it is possible to achieve good esthetic and functional outcomes. However, regular maintenance appointments are mandatory, and all cases should be carefully planned to ensure predictable and long-lasting results.

Novel low-shrinkage-stress bioactive nanocomposite with anti-biofilm and remineralization capabilities to inhibit caries

Background/purpose

A common reason for dental composite restoration failure is recurrent caries at the margins. Our objectives were to: (1) develop a novel low-shrinkage-stress, antibacterial and remineralizing resin composite; (2) evaluate the effects of dimethylaminohexadecyl methacrylate (DMAHDM) on mechanical properties, biofilm inhibition, calcium (Ca) and phosphate (P) ion release, degree of conversion, and shrinkage stress on the new low-shrinkage-stress resin composite for the first time.

Material and methods

The resin consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE) with high resistance to salivary hydrolytic degradation. Composites were made with 0%–8% of DMAHDM for antibacterial activity, and 20% of nanoparticles of amorphous calcium phosphate (NACP) for remineralization. Mechanical properties and Streptococcus mutans biofilm growth on composites were assessed. Ca and P ion releases, degree of conversion and shrinkage stress were evaluated.

Results

Adding 2–5% DMAHDM and 20% NACP into the low-shrinkage-stress composite did not compromise the mechanical properties (p > 0.05). The incorporation of DMAHDM greatly reduced S. mutans biofilm colony-forming units by 2–5 log and lactic acid production by 7 folds, compared to a commercial composite (p < 0.05). Adding 5% DMAHDM did not compromise the Ca and P ion release. The low-shrinkage-stress composite maintained a high degree of conversion of approximately 70%, while reducing the shrinkage stress by 37%, compared to a commercial control (p < 0.05).

Conclusion

The bioactive low-shrinkage-stress composite reduced the polymerization shrinkage stress, without compromising other properties. Increasing the DMAHDM content increased the antibacterial effect in a dose-dependent manner.

Effect of wetting agent coverage on the surface properties of resin composite submitted to brushing and staining cycles

Background

Wetting agents facilitate the composites handling, acting as a lubricant and decreasing their stickness to spatula. The effects of these materials on the properties of composites are not completely clear. This study aimed to evaluate Gloss, Color, Roughness and Microhardness of a composite (Filtek Z250 XT, 3M Oral Care) covered by a wetting agent (Modeling Resin, Bisco), submitted to brushing and staining cycles with red wine.

Material and Methods

Cylinder-shaped samples (8 mm ø x 2 mm height) were divided into 4 groups, according to application of wetting agent and brushing cycles (n = 20). The composite was placed in the orifice of a polytetrafluoroethylene mold, received wetting agent coverage, and was light-cured. Gloss, Color, Roughness and Microhardness were evaluated in two times: after samples confection and after brushing + staining cycles. Data were submitted to one-way ANOVA and Tukey’s test (ΔL, Δa, Δb and ΔE) and two-way repeated measures ANOVA and Bonferronis’s test (gloss, roughness and microhardness).

Results

In general, the composite showed higher gloss values when added by the wetting agent. No statistical differences were observed regarding colors’ groups. Roughness increased after brushing cycles, regardless of wetting agent application. The only group which presented decreased Microhardness after cycles was the group without wetting agent, only submitted to staining with red wine.

Conclusions

The application of wetting agent on the composite did not interfere negatively with its properties of Gloss, Color, Roughness and Microhardness.

Key words:Resin composite, wetting agent, surface properties, gloss, color, esthetic dentistry.