Reem Ajaj

The durability of the dentin–resin bonded interface remains a major challenge in adhesive dentistry, largely due to hydrolytic and enzymatic degradation of exposed collagen fibrils within the hybrid layer. Endogenous proteolytic enzymes, particularly matrix metalloproteinases and cysteine cathepsins, play a critical role in the progressive degradation of the exposed collagen matrix. Collagen crosslinking has emerged as a promising strategy to stabilize the dentin matrix, enhance resistance to endogenous proteases, and potentially improve the long-term durability of adhesive bonds; however, current evidence remains largely experimental, and its routine clinical application is still limited. This narrative review synthesizes current preclinical and emerging translational evidence on collagen crosslinking approaches investigated to reinforce the dentin–resin interface and the characterization techniques used to evaluate their effectiveness. Emphasis is placed on mechanisms of action, key evaluation approaches, and potential clinical relevance. While several crosslinking strategies, particularly carbodiimide-based systems and polyphenol-derived agents, demonstrate encouraging in vitro and laboratory-based outcomes, significant barriers to routine clinical translation persist. These include application time, penetration depth, esthetic concerns, biocompatibility, and integration within existing clinical adhesive workflows. Future research should prioritize clinically feasible formulations, standardized testing protocols, and long-term in vivo and clinical validation to facilitate the potential translation of collagen crosslinking strategies into clinically durable adhesive restorations.

Background: The aesthetic performance of single-shade polymer-based restorative materials (SPRs) can be compromised by extrinsic stains. Understanding the effects of novel whitening interventions on SPRs is crucial. Objective: This in vitro study aimed to evaluate the effects of different whitening interventions, including a novel purple tooth serum and charcoal-based whitening toothpaste with and without in-office bleaching, on the color of a new coffee-stained SPR. Materials and Methods: Seventy disc-shaped SPR specimens were prepared, stained, and then divided into seven groups (n = 10). Three groups were subjected directly to 2500 cycles of brushing simulation with regular toothpaste (control), charcoal toothpaste, or purple tooth serum. The rest were divided into bleaching groups, and the four groups underwent a simulation of bleaching and then brushing with the three products. The color parameters were recorded at the stained baseline, after brushing, after bleaching, and after post-bleaching brushing. The color change (ΔE00) was calculated, and the data were analyzed statistically using the Kruskal–Wallis test and Dunn–Bonferroni pairwise comparisons (p < 0.05). Results: In-office bleaching without brushing had a statistically significantly higher ΔE00 value than all other groups (p < 0.001). Post hoc tests indicated that the ΔE00 values of the brushed specimens were not significantly different from each other when assessed with and without bleaching (p > 0.05). When using the charcoal toothpaste, the post-bleaching brushed specimens had a noticeable color change above the PT. Conclusions: Bleaching improved the stained SPR color initially, but other treatments may offer longer-lasting aesthetics. The charcoal toothpaste showed promising results when combined with bleaching. The purple serum showed limited effectiveness.

During restoring class II and V cavities with resin composite, hemostatic agents are frequently used to control gingival bleeding and/or gingival fluid to provide a dry field which is crucial for efficient bonding. Hemostatic agents may adversely affect the bonding procedure, thus their removal prior to bonding is essential. The current study evaluates the effect of two hemostatic agents and different dentin cleansing protocols on the shear bond strength of resin composite to dentin using a universal adhesive. Ninety premolars were sectioned to expose coronal dentinal surfaces which were divided into 3 groups: control group, not treated with hemostatic agent (n = 10); a group treated with Viscostat “20% ferric sulphate” (n = 40); and a group treated with Viscostat clear “25% aluminum chloride” (n = 40). The groups treated with hemostatic agents were subdivided into 4 subgroups according to the cleansing protocol: water, phosphoric acid, katana cleaner, and air abrasion. Shear bond strength (SBS) of resin composite bonded to the treated dentin using a universal adhesive was measured after thermocycling. Two-way ANOVA showed that hemostatic agent, cleansing protocol and their interaction has significant effect on SBS (p < 0.0001). Viscostat (10 ± 3.3 MPa) exhibited lower SBS than Viscostat Clear (16.2 ± 5.5 MPa). Acid etching (17.3 ± 7.3 MPa) showed higher SBS compared to Katana Cleaner (12.6 ± 4.7 MPa), water (12.1 ± 4.8 MPa) and air abrasion (10.8 ± 2 MPa). The use of hemostatic agents can adversely affect the bond strength of universal adhesives to dentin. Phosphoric acid provided the best hemostatic agent-cleansing protocol while katana cleaner and air abrasion demonstrated inferior results.

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.

Dental Bulk-Fill Composites (BFCs) and Bulk-Fill Flowables (BFFs) were introduced in the market to facilitate efficient bulk filling of cavities up to 5 mm. The aim of this study was to synthesize the literature investigating their polymerization efficiency. A comprehensive search of PubMed and the Cochrane Library from 2010 to January 2019 was performed using the medical subject headings. Screening of the titles, abstracts and full text was performed. Data extraction for relevant information was done on the included studies. Clinically relevant parameters were selected to present the study estimates (meta-analysis) using a random effects model for polymerization efficiency (Degree of Conversion (DC) and Depth of Cure (DoC)). Twenty one studies fulfilled the inclusion criteria and were included in the analysis reporting seven BFCs and nine BFFs. Ten materials reported acceptable DC values of above 55% and ten materials reported adequate DoC values. Most of the stated materials reported adequate DC and DoC values in at least one investigation with BFFs showing higher and more acceptable values compared to packable BFCs. It is suggested that future studies be carried out using a standard methodology following the ISO 4049 standard and manufacturer’s instructions to compare results.

Objective: The objective of the study is to investigate the effect of infection control barrier (ICB) and curing time on irradiance of light cure units (LCUs). Methods: Irradiance (mW/cm²) of the LCUs at a government dental school were recorded with and without ICB at 0 (T₀), 10 (T₁₀), and 20 (T₂₀) seconds using a digital radiometer. Data were analyzed using IBM^® SPSS^® Statistics Version 17 for Windows software for the analysis of variance and Bonferroni methods at 0.05 significance level. Results: Using ICB resulted in a statistically significant effect on the irradiance mean (P < 0.01). A significant difference existed between the four different brands of LCUs at different time intervals, irrespective of the use of ICB. At T₀ and T₁₀, the mean output of Acteon mini-light-emitting diode (LED) was significantly higher than that of either the Kerr Demi Ultra or the Kavo Polylux II. At T₂₀, E-Morlit's mean irradiance was significantly higher than that of Kerr Demi Ultra, which in turn was significantly higher than that of the Kavo PolyLux II. The mean irradiance of the LEDs was significantly higher than that of the halogens irrespective of barrier placement and at all-time points. Conclusion: The ICB used in this study resulted in a statistically significant reduction in the irradiance output. No significant difference in the irradiance was found at different curing time intervals for the tested units regardless of ICB usage.

Introduction: This study aims to evaluate the effects of different curing units and modes on the degree of conversion (DC) and microhardness (MH) of two different resin composites [ESTELITE ∑ QUICK (EQ), and Z350 XT (Z3)]. Materials and Methods: One hundred (100) discs of each tested material were made and divided into two subgroups (n = 50) according to the discs' dimensions: 5 mm diameter × 2 mm thickness, and 2 mm diameter × 2 mm thickness. Each subgroup was further subdivided into the following five classes (n = 10): I) cured with halogen light curing-unit; II) cured with light-emitting diode (LED) unit; III) cured with argon laser; IV) cured with halogen light-curing unit for 5 s, 10 s rest followed by 20 s curing; and V) cured with halogen light-curing unit for 10 s, then 10 s rest, followed by 10 s curing. The first subgroup was tested for MH using the Vickers Microhardness tester and the second subgroup was tested for DC using Fourier transform infrared spectroscopy (FTIR). Data were statistically analyzed using two-way analysis of variance (ANOVA) and Tukey's post hoc test P < 0.05. Results: Specimens in class IV showed the highest mean DC and MH, followed by class III, then class II. Class I showed significantly lower mean values for both DC and MH. On the other hand, Z3 showed statistically significantly higher mean DC and MH than EQ. Conclusion: Although the two tested composites did not perform similarly under the test conditions, curing with halogen unit for 5 s, then 10 s rest, followed by 10 s curing improved the DC and the MH of both the tested materials.

This study compares the FEA-calculated stresses generated within the supporting periodontal structure of a mandibular second molar restored with a full ceramic crown and with a porcelain-fused-to-metal (PFM) crown, each resisting occlusal forces acting at different inclinations. Three-dimensional finite element models representing the crown of an unrestored mandibular second molar and two relevant restoration designs were constructed. Two designs represented the molar restored with a full ceramic crown and with a PFM crown, each cemented with the same resin cement. Occlusion was assumed at three contact areas, which equally shared a 100 N force. The analysis was carried out for forces located in the bucco-axial-lingual plane at five inclinations, 0, 22.5°, 45°, 67.5°, and 90°, measured from the axial direction of the tooth. The magnitudes and sites of the maximum equivalent stress (MES) generated within the supporting periodontium of each analyzed model were collected. Generally, there were no significant differences in the site and magnitude of MES in the regions of the supporting structure for the analyzed models. The MES was located at the tooth periodontal ligament (PDL) bifurcation area and distal root apex, crestal bone at the junction between cortical and cancellous bone, and the distal wall of the mesial root socket of cancellous bone. The highest stresses corresponded to a horizontal load, followed by the axial load in the PDL and cortical zones. The results show opposite observations for the cancellous bone. The lowest stresses were generated under a load inclination between 22.5° and 45°. Considering the stresses generated within the supporting structures, the present work validates, by calculation, the proposed clinical use of either a full ceramic crown or a PFM crown as a restoration for mandibular second molars.