A new in vitro model to study the relationship of gap size and secondary caries

The Impact of Open versus Closed Computer-Aided Design/Computer-Aided Manufacturing Systems on the Marginal Gap of Zirconia-Reinforced Lithium Silicate Single Crowns Evaluated by Scanning Electron Microscopy: A Comparative In Vitro Study

This study aimed to compare the impact of CAD/CAM closed systems and open systems on the marginal gap of monolithic zirconia-reinforced lithium silicate (ZLS) ceramic crowns, as both systems are used in everyday dentistry, both chair-side and laboratory. For the closed system, 20 plastic teeth were scanned by a Primescan intra-oral scanner (IOS), and for the open system, the same number of plastic teeth were scanned by Trios 4 IOS. For the closed system, CEREC software was used, and for the open system, EXOCAD software was used. All 40 ZLS crowns were grinded by the same four-axis machine and cemented with Temp-bond, followed by self-adhesive resin cement. For each type of cement, an evaluation of the marginal gap was conducted by scanning electron microscopy (SEM). Before comparisons between the groups, a Kolmogorov-Smirnov test was performed on the study variables showing a normal distribution (p > 0.05). Independent T tests (α = 0.05) and paired-sample T tests (α = 0.05) were used. The independent T test found no significant mean marginal gap differences in the zirconia-reinforced lithium silicate crowns bonded with Temp-bond and scanned by Primescan (28.09 μm ± 3.06) compared to Trios 4 (28.94 μm ± 3.30) (p = 0.401), and there was no significant mean marginal gap differences in zirconia-reinforced lithium silicate crowns bonded with self-adhesive resin cement (Gcem ONE) and scanned by Primescan (46.70 μm ± 3.80) compared to Trios 4 (47.79 μm ± 2.59) (p = 0.295). Paired-sample T tests showed significantly higher mean marginal gaps with Gcem ONE compared to Temp-bond for the total mean marginal gap when scanning with Primescan (p = 0.0005) or Trios 4 (p = 0.0005). In everyday dentistry, both closed systems (Primescan with Cerec) and open systems (Trios 4 with Exocad) can be used to achieve an acceptable (<120 µm) marginal gap for ZLS CELTRA® DUO single crowns. There is a significant difference between cementation with Temp-bond and Gcem ONE self-adhesive resin cement (p < 0.05).

Effect of surface roughness and biofilm formation on the color properties of resin-infiltrated ceramic and lithium disilicate glass-ceramic CAD-CAM materials

STATEMENT OF PROBLEM

Computer-aided design and computer-aided manufacturing (CAD-CAM) materials have become popular for dental restorations; however, which materials should be preferred in terms of surface properties after biofilm formation is unclear.

PURPOSE

The purpose of this in vitro study was to investigate the effect of biofilm formation on the discoloration properties of resin-infiltrated ceramic and glass-ceramic CAD-CAM materials and human teeth and to examine the effect of the brushing procedure on color change.

MATERIAL AND METHODS

One hundred and six 2-mm-thick specimens were prepared from IPS e.max CAD and Cerasmart, and a total of 53 intact human teeth were used. Five specimens from each group were used to measure the amount of live biomass in the biofilm. The remaining 48 specimens in each group were divided into 4 subgroups: kept in distilled water without the formation of dental biofilm (DW), kept in tea without the formation of dental biofilm (T), kept in distilled water after the formation of dental biofilm (DWB), and kept in tea after the formation of dental biofilm (TB) (n=12). After finishing and polishing the materials, initial color measurements were made using a spectrophotometer, and surface roughness measurements were made using noncontact profilometer. After creating a biofilm layer in DWB and TB, all specimens were kept in their solutions at 37 °C for 24 hours, and the color measurements were repeated. After the biofilm layer had been removed by brushing, a third color measurement was made. The data were statistically analyzed with one-way analysis of variance (ANOVA) and two-way ANOVA (α=.05).

RESULTS

The lowest roughness value was observed in Cerasmart. Tooth-IPS e.max CAD gave similar results. The Cerasmart material had the most viable biomass, whereas the IPS e.max CAD material had the least. TB had the highest ΔE1 value for all materials and DW had the lowest (P<.05). The brushing procedure caused the materials to return to their initial colors or reduce the color change in most groups.

CONCLUSIONS

The presence of biofilm on CAD-CAM materials immersed in distilled water caused an unacceptable degree of discoloration (ΔE>1.8), and immersion in tea led to greater color change. The adhesion of biofilm to restorative dental materials plays an important role in the coloring of these dental materials.

Effect of cervical margin relocation on marginal adaptation and microleakage of indirect ceramic restorations

PURPOSE

This study evaluated the effect of cervical margin relocation (CMR) with two different materials and contamination with hemostatic agents on the margin adaptation and microleakage of ceramic restorations.

MATERIALS AND METHODS

Mesial-occlusal-distal cavities were prepared in 60 human first molars and distributed to 3 groups (n = 20) according to the margin relocation procedure. The groups were: group F; flowable composite applied in two 2 mm increments, group B; bulk-fill flowable composite applied as a bulk increment of 4 mm thickness and group C (control); no CMR was done. Each group was subdivided into two subgroups (subgroup N; no hemostatic agent applied and subgroup H; hemostatic agent was applied). In all groups, ceramic inlays were prepared and cemented. The samples were subjected to thermocycling (10,000 cycles). The adaptation of the cervical margin was evaluated with scanning electron microscopy (200×). Samples were then assessed for microleakage analysis with the dye penetration method. Marginal adaptation data were normally distributed and analyzed using two-way ANOVA followed by Tukey's post hoc test. Ordinal microleakage score data were analyzed using cumulative link models followed by the analysis of deviance using Wald chi-square tests.

RESULTS

Both CMR and contamination with a hemostatic agent had significant effects on the margin adaptation of the cervical margin. Group C showed the highest adaptation with no significant difference from group F. The lowest adaptation was revealed in group B with a significant difference from group C. Subgroup N (in all groups) showed a statistically higher adaptation than subgroup H. Regarding microleakage assessment, CMR had no significant effect but hemostatic agent application showed a significantly higher microleakage score for all groups.

CONCLUSIONS

Both the CMR procedure and contamination with AlCl3 hemostatic agent had a negative effect on marginal adaptation. For microleakage assessment, only contamination with hemostatic agent negatively affected the microleakage with no effect on the margin relocation procedure.

Clinical performance of custom-milled polyetherketoneketone (PEKK) posts and cores: A 12-month follow-up randomized controlled pilot study

OBJECTIVES

Comparing the survival rate and the cumulative success rates of custom-milled polyetherketone ketone posts and cores (MPP) with prefabricated fiber posts (PFP) in restoring compromised endodontically treated premolars.

MATERIAL AND METHODS

This was a randomized, double-blind, parallel, two-arm controlled pilot study. A total of 24 patients (12 males, 12 females), each had a compromised lower premolar, needed a root canal treatment and to be restored with post and core. Patients were randomly allocated into two groups, MPP-group: restored with MPP, and PFP-group: restored with PFP and composite cores. After that, premolars were restored with single porcelain fused to metal (PFM) crowns. Clinical and radiographic follow-ups were conducted after 3, 6, and 12 months. The Kaplan-Meier, log-Rank, and χ2 tests were used to investigate differences between the two groups at the 0.05 significance level.

RESULTS

The survival rate after 12 months in the MPP and PFP groups was 66.7% and 100%, respectively. Meanwhile, the cumulative success rates were 63.6% and 100% in the same order. The log-rank test showed a significant difference between the two groups (p = .031). The difference in cumulative success rates was also significant, as the χ2 test revealed (p = .011).

CONCLUSION

The PFP group showed a higher success rate than the MPP group and according to the failure types, PEKK posts seem to be inferior to PFP in terms of the mechanical properties and bonding to resin mechanism.

TRIAL REGISTRATION

ISRCTN, ISRCTN13456471. October, 14, 2019. (https://doi.org/10.1186/ISRCTN13456471ISRCTN13456471).

Recurrent caries models to assess dental restorations: A scoping review

OBJECTIVES

To review the literature on recurrent caries models used to evaluate restorative materials, compare reported methodology and parameters, and devise specific recommendations to be considered in future investigations.

DATA

The following were extracted: study design, sample characteristics, source of teeth, name of restorations compared including controls, recurrent caries model type, type of demineralizing and remineralizing solutions, type of biofilm used, methods to detect recurrent caries.

SOURCES

Literature searches were performed in OVID Medline, EMBASE, SCOPUS, and Cochrane Library.

STUDY SELECTION

For a study to be included, it had to examine dental materials for tooth restoration purposes only with a valid control group and evaluate restorative dental materials regardless of the form of the teeth caries model used or nature of the tooth structure used. A total of 91 studies were included. Most of the studies presented were in vitro. Human teeth were the main source of specimens utilized. Around 88% of the studies used specimens without an artificial gap, and 44% used a chemical model. S. mutans was the main bacterial species used in microbial caries models.

CONCLUSION

The findings of this review provided an insight into the performance of available dental materials assessed using different recurrent caries models, yet this review cannot be used as a guideline for material selection. Selecting the appropriate restorative material relies on several patient-related factors such as microbiota, occlusion, and diet that are not comprehensively taken into consideration in recurrent caries models and thus hinder reliable comparison.

CLINICAL SIGNIFICANCE

Due to the heterogenicity of variables among studies on the performance of dental restorative materials, this scoping review aimed to provide insights for dental researchers concerning the available recurrent caries models, testing methods used, and aspects of comparison between these materials including their characteristics and limitations.

Composite plastering technique (CPT) for anterior and posterior restorations

Composite plastering technique (CPT) is a novel restoration improvement technique for eliminating and re-contouring the marginal defects. Restoration-related interproximal contour deficiencies such as dark triangles beneath the contact point following direct class II restorations, the gaps at the interproximal cavity step following indirect cementations, and the gaps at the interproximal wall following class III restoration layering procedures can be corrected using the CPT. The technique may also be used as a layering step during the free-hand layering in diastema closure restorations. Contour deficiencies on interproximal surfaces which lead to the renewal of restoration and periodontal damages can be prevented by additional direct composite build-up using the CPT. The technique can be performed either immediately after the restoration directly or long after by using the composite repair protocol. It focuses on filling and re-contouring the surface of the deficiency by using a mylar strip actively under rubberdam isolation. Composite is loaded between the strip and the tooth surface and the strip is pulled slightly in palato-buccal or the opposite direction depending on the location of the defect, to fill it by plastering the composite. It may contribute the longevity of the restoration by improving the emergence profile and correcting the interproximal contour. Re-contouring of the interproximal surface defects by CPT is a useful approach to improve the esthetics as well as the function of anterior and posterior direct and indirect restorations which may also prolong the longevity.

Preparation of Silica Aerogel/Resin Composites and Their Application in Dental Restorative Materials

As the most advanced aerogel material, silica aerogel has had transformative industrial impacts. However, the use of silica aerogel is currently limited to the field of thermal insulation materials, so it is urgent to expand its application into other fields. In this work, silica aerogel/resin composites were successfully prepared by combining silica aerogel with a resin matrix for dental restoration. The applications of this material in the field of dental restoration, as well as its performance, are discussed in depth. It was demonstrated that, when the ratio of the resin matrix Bis-GMA to TEGDMA was 1:1, and the content of silica aerogel with 50 μm particle size was 12.5%, the composite achieved excellent mechanical properties. The flexural strength of the silica aerogel/resin composite reached 62.9546 MPa, which was more than five times that of the pure resin. Due to the presence of the silica aerogel, the composite also demonstrated outstanding antibacterial capabilities, meeting the demand for antimicrobial properties in dental materials. This work successfully investigated the prospect of using commercially available silica aerogels in dental restorative materials; we provide an easy method for using silica aerogels as dental restorative materials, as well as a reference for their application in the field of biomedical materials.

Advances in biomineralization-inspired materials for hard tissue repair

Biomineralization is the process by which organisms form mineralized tissues with hierarchical structures and excellent properties, including the bones and teeth in vertebrates. The underlying mechanisms and pathways of biomineralization provide inspiration for designing and constructing materials to repair hard tissues. In particular, the formation processes of minerals can be partly replicated by utilizing bioinspired artificial materials to mimic the functions of biomolecules or stabilize intermediate mineral phases involved in biomineralization. Here, we review recent advances in biomineralization-inspired materials developed for hard tissue repair. Biomineralization-inspired materials are categorized into different types based on their specific applications, which include bone repair, dentin remineralization, and enamel remineralization. Finally, the advantages and limitations of these materials are summarized, and several perspectives on future directions are discussed.

A comprehensive review of the antibacterial activity of dimethylaminohexadecyl methacrylate (DMAHDM) and its influence on mechanical properties of resin-based dental materials

The repetitive restorative cycle should be avoided, aiming at the smallest number of restorations' replacements to ensure greater tooth longevity. Antibacterial materials associated with the control of caries etiological factors can help improve restoration's durability. This review aimed to analyze the results of in vitro studies that added Dimethylaminohexadecyl methacrylate (DMAHDM), an antibacterial monomer, to restorative materials. The PubMed, SCOPUS, Web of Science, and Biblioteca Virtual em Saúde databases were screened for studies published between 2015 and 2020. After full-text reading, 24 articles were included in the final sample. DMAHDM has demonstrated antibacterial efficacy against several bacteria related to dental caries and periodontal diseases, causing a transition in the biofilm balance without inducing resistance. When DMAHDM was included in acrylic resin, the material cytotoxicity increased, and changes in mechanical properties were observed. In contrast, resin composites had their mechanical properties maintained in most studies; however, toxicity was not examined. The association between DMAHDM and 2-methacryloyloxyethyl phosphorylcholine or silver nanoparticles improved the antibacterial effect. Besides, the association with nanoparticles of amorphous calcium phosphate or nanoparticles of calcium fluoride can provide remineralization capacity. There is a lack of information on the cytotoxicity and bacteria resistance induction, and further studies are needed to address this.

Comparison of microleakage between different restorative materials to restore marginal gap at crown margin

Background

An occurrence of secondary caries around the indirect restoration margin is reported to remain a leading cause of failures.

Objective

This study aimed to test the interfacial microleakage of conventional glass-ionomer (CGI), resin-modified glass ionomer (RMGI) and Nano-hybrid composite (CR) restorations at a full veneer margin crown.

Methods

Ninety human extracted molar teeth were divided into three groups (n = 30). Each group was subdivided into three subgroups (n = 10) according to the extent of the structural defects; The structural defect in G1 had a depth of 1.5 mm, width and length at 2 mm and 1 mm intrusion within the crown cervical margin. The corresponding structural defect dimension values for G2 were 2, 5, 4 and 2 mm with defects extending onto the root structure. Meanwhile, G3: structural deficiency of 2 mm depth, 3 mm width and 3 mm length and with 1.5 mm extension into the prepared teeth. These structural defects in each subgroup were restored with CGI, RMGI and CR. Artificial carious lesion formation was induced at the cervical finish line with a demineralizing solution. The artificial carious lesions were restored as per the group distribution. Subsequently, teeth samples were prepared and cemented with Nickel-chromium full coverage restorations utilizing glass-ionomer luting cement. Teeth samples were thermocycled, isolated with nail varnish, and immersed in 0.1% methylene blue for 24 h. The teeth samples were sectioned longitudinally, dye penetration was evaluated with a stereomicroscope. The data were analyzed with Kruskal–Wallis and Mann–Whitney U tests.

Results

CGI-G1 recorded the highest micro-leakage score at 1.450; while CR-G3 recorded the least score (0.350). At a cementum-restoration interface, CR-G1 (0.850) documented the lowest micro-leakage; RMGI-G3 had a greater value at 1.700.

Conclusions

The hybrid CR could be effectively used to restore the restoration of a marginal gap around crown margins.

Relevance of Biofilm Models in Periodontal Research: From Static to Dynamic Systems

Microbial biofilm modeling has improved in sophistication and scope, although only a limited number of standardized protocols are available. This review presents an example of a biofilm model, along with its evolution and application in studying periodontal and peri-implant diseases. In 2011, the ETEP (Etiology and Therapy of Periodontal and Peri-Implant Diseases) research group at the University Complutense of Madrid developed an in vitro biofilm static model using representative bacteria from the subgingival microbiota, demonstrating a pattern of bacterial colonization and maturation similar to in vivo subgingival biofilms. When the model and its methodology were standardized, the ETEP research group employed the validated in vitro biofilm model for testing in different applications. The evolution of this model is described in this manuscript, from the mere observation of biofilm growth and maturation on static models on hydroxyapatite or titanium discs, to the evaluation of the impact of dental implant surface composition and micro-structure using the dynamic biofilm model. This evolution was based on reproducing the ideal microenvironmental conditions for bacterial growth within a bioreactor and reaching the target surfaces using the fluid dynamics mimicking the salivary flow. The development of this relevant biofilm model has become a powerful tool to study the essential processes that regulate the formation and maturation of these important microbial communities, as well as their behavior when exposed to different antimicrobial compounds.

Impact of Different Etching Strategies on Margin Integrity of Conservative Composite Restorations in Demineralized Enamel

Good margin integrity with a tight seal of the adhesive interface is considered one of the key factors for the clinical success of composite restorations. This study investigated the effect of enamel etching with phosphoric acid on the margin integrity of self-etch bonded composite restorations in demineralized enamel. Crowns of bovine incisors were assigned into 14 groups (n = 10 per group) of which ten groups (groups 1–5 and 8–12) were demineralized (21 days, acid buffer, pH 4.95) to create artificial carious lesions. Standardized Class V cavities were prepared in all specimens. Demineralized groups were either etched with phosphoric acid for 10, 30, 60, or 120 s (groups 2–5 and 9–12), or no etching was performed (groups 1 and 8). The non-demineralized (sound) groups were etched for 10 s (groups 7 and 14) or remained non-etched (groups 6 and 13). Resin composite restorations were then placed using either a one-step (iBond Self Etch, groups 1–7) or two-step self-etch adhesive (Clearfil SE Bond, groups 8–14). Margin integrity of the restorations was assessed after thermocycling (5000×, 5–55 °C) using scanning electron microscopy, and the percentage of continuous margins (%CM) was statistically analyzed (α = 0.05). Phosphoric acid etching significantly increased %CM in both demineralized and sound enamel. For iBond Self Etch, a significant increase in %CM in demineralized enamel was observed with increased etching times. All etched groups treated with Clearfil SE Bond and those etched for 60 or 120 s and treated with iBond Self Etch showed similar %CM in demineralized enamel as in etched sound enamel, and significantly higher %CM than in non-etched sound enamel. In conclusion, enamel etching with phosphoric acid improves margin integrity of composite restorations in demineralized enamel when bonded with the examined adhesives.

Fit of tooth-supported zirconia single crowns-A systematic review of the literature

PURPOSE

The purpose of this study is to systematically map all the factors that influence the fit and adaptation of zirconia crowns and/or copings.

MATERIALS AND METHODS

The investigational strategy involved carrying out an electronic search between December 1, 2009 and September 1, 2019 through the Embase and Medline databases using Boolean operators to locate appropriate articles.

RESULTS

A total of 637 articles were discovered after the removal of duplicates, and 46 of these were selected for evaluation. Further, a quality assessment was performed using GRADE evaluation criteria.

CONCLUSIONS

Shoulder finish line preparations had slightly better marginal fit compared to chamfer finish lines. Crowns obtained from digital impressions had comparable to superior marginal adaptation compared to conventional impressions. Increasing cement space showed to improve zirconia crown adaptation. Cementation and veneering zirconia frameworks found to increase the marginal and internal gaps. Limited information is available on the effect of the alteration of sintering time/Temperature and/or sintering techniques on the adaptation of zirconia crowns. Most of the selected studies had a moderate quality assessment evaluation. Future studies could investigate the chair-side, ultra-fast sintering effect on the marginal gap of zirconia crowns.

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

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

Margin Integrity of Bulk-Fill Composite Restorations in Primary Teeth

This in vitro study examined the margin integrity of sculptable and flowable bulk-fill resin composites in Class II cavities of primary molars. Standardized Class II cavities were prepared in human primary molars and restored with the following resin composite materials after application of a universal adhesive: a sculptable bulk-fill composite (Tetric EvoCeram Bulk Fill (TEC) or Admira Fusion x-tra (AFX)), a flowable bulk-fill composite (Venus Bulk Fill (VBF) or SDR), or a conventional composite (Filtek Supreme XTE (FS)). The bulk-fill materials were applied in 4 mm layers, while the conventional composite was applied in either 2 mm (FS2, positive control) or 4 mm layers (FS4, negative control). The specimens were exposed to thermo-mechanical loading (TML) in a computer-controlled masticator. A quantitative margin analysis was performed both before and after TML using scanning electron microscopy, and the percentage of continuous margins (margin integrity) was statistically analyzed (α = 0.05). All composites showed a significant decline in margin integrity after TML. AFX exhibited the significantly highest margin integrity of all materials after TML (97.5 ± 2.3%), followed by FS2 (79.2 ± 10.8%), TEC (73.0 ± 9.1%), and FS4 (71.3 ± 14.6%). SDR (43.6 ± 22.3%) and VBF (25.0 ± 8.5%) revealed the lowest margin integrity. In conclusion, the tested sculptable bulk-fill materials show similar or better margin integrity in primary molars than the conventional resin composite placed in 2 mm increments.

Nanoparticles as Anti-Microbial, Anti-Inflammatory, and Remineralizing Agents in Oral Care Cosmetics: A Review of the Current Situation

Many investigations have pointed out widespread use of medical nanosystems in various domains of dentistry such as prevention, prognosis, care, tissue regeneration, and restoration. The progress of oral medicine nanosystems for individual prophylaxis is significant for ensuring bacterial symbiosis and high-quality oral health. Nanomaterials in oral cosmetics are used in toothpaste and other mouthwash to improve oral healthcare performance. These processes cover nanoparticles and nanoparticle-based materials, especially domains of application related to biofilm management in cariology and periodontology. Likewise, nanoparticles have been integrated in diverse cosmetic produces for the care of enamel remineralization and dental hypersensitivity. This review summarizes the indications and applications of several widely employed nanoparticles in oral cosmetics, and describes the potential clinical implementation of nanoparticles as anti-microbial, anti-inflammatory, and remineralizing agents in the prevention of dental caries, hypersensitivity, and periodontitis.

A universal adhesive incorporating antimicrobial peptide nisin: effects on Streptococcus mutans and saliva-derived multispecies biofilms

For purpose of enhancing the antibacterial activity of a universal adhesive, the antimicrobial peptide nisin was incorporated into Single Bond Universal and its antibacterial effect on Streptococcus mutans monospecific biofilms and saliva-derived multispecies biofilms was studied. Nisin was incorporated into Single Bond Universal and the antibacterial activity was examined by confocal laser scanning microscopy (CLSM), reverse transcription-quantitative polymerase chain reaction (qRT-PCR), phenol-sulfuric acid method and lactate dehydrogenase enzymatic method. The bonding properties were tested by microtensile bond strength (μTBS) and degree of conversion (DC). Data were analyzed by one-way analysis of variance (ANOVA) and least significant difference multiple comparison tests (P < 0.05). The Single Bond Universal incorporated with 3% (w/v) nisin could significantly inhibit the growth of the S. mutans monospecific biofilms (P< 0.01) and decrease the expression of genes related to extracellular polysaccharide (EPS) synthesis (gtfB, gtfC, gtfD and spaP) and acidogenicity (ldh) (P < 0.05). 3% (w/v) nisin-incorporated Single Bond Universal could also inhibit the growth of saliva-derived multispecies biofilms and decrease the excretion of EPS and lactic acid ( P< 0.05). μTBS and DC of 3% (w/v) nisin-incorporated Single Bond Universal did not deteriorate obviously (P > 0.05). In conclusion, 3% (w/v) nisin-incorporated Single Bond Universal substantially inhibited the growth of both S. mutans monospecific and saliva-derived multispecies biofilms without compromising the bonding properties.

Antibacterial and thermomechanical properties of experimental dental resins containing quaternary ammonium monomers with two or four methacrylate groups

Resins with strong antibacterial and thermomechanical properties are critical for application in oral cavities. In this study, we first evaluated the antibacterial effect of an unfilled resin incorporating 1, 4, and 7 mass% of quaternary ammonium salt (QAS) monomers containing two methacrylate groups (MAE-DB) and four methacrylate groups (TMH-DB) against Streptococcus mutans, and tested the cytotoxicity and thermomechanical properties of the 4 mass% MAE-DB and TMH-DB modified resin materials. A neat resin without a QAS monomer served as the control. As the concentration of both QAS monomers increases, the formation of a Streptococcus mutans biofilm on the experimental material is increasingly inhibited. The results of colony forming unit counts and the metabolic activity showed that both the MAE-DB and TMH-DB modified resins have a strong bactericidal effect on the bacteria in a biofilm, but no bactericidal effect on the bacteria in a solution. The viability-staining and morphology results also demonstrate that the bacteria deform, lyse, shrink, and die on the surface of the two QAS-modified resins. Cytotoxicity results show that the addition of TMH-DB can reduce the cytotoxicity of the resin, while the addition of MAE-DB increases the cytotoxicity of the resin. DMA results show that a TMH-DB modified resin has a higher storage modulus than a MAE-DB modified resin owing to its better crosslink density. The two groups of experimental resins showed a similar glass transition temperature. These data indicate that the two QAS monomers can impart similar antibacterial properties upon contact with a dental resin, whereas TMH-DB can endow the resin with a higher crosslink density and storage modulus than MAE-DB because it has more polymerizable groups.

Resins with strong antibacterial and thermomechanical properties are critical for application in oral cavities.

Experimental composites containing quaternary ammonium methacrylates reduce demineralization at enamel-restoration margins after cariogenic challenge

OBJECTIVE

This study evaluated the influence of experimental composites containing quaternary ammonium monomers (QAM) at different concentrations and alkyl chains on demineralization at enamel-composite margins after cariogenic challenge.

METHODS

Standardized 4×4mm cavities were cut into 35 bovine enamel blocks, which were randomly divided into seven groups (n=5) and restored with the following experimental composites and commercial materials: (G12.5) - 5% dimethylaminododecyl methacrylate (DMADDM) with a 12-carbon alkyl chain (G12.10) - 10% DMADDM, (G16.5) - 5% dimethylaminohexadecyl methacrylate (DMAHDM) with a 16-carbon alkyl chain (G16.10) - 10% DMAHDM, (CG) - control group (without QAM), (GZ250) - commercial composite (Filtek Z250^®), and (GIC) - glass ionomer cement (Maxxion R^®). After restorative procedures, initial microhardness was measured and experimental composites were subjected to Streptococcus mutans biofilm formation for 48h. After cariogenic challenge, the samples were washed and microhardness was reassessed. A 3D non-contact profilometer was used to determine surface roughness and enamel demineralization was assessed by micro-CT. Microhardness results were analyzed by the Kruskal-Wallis and Mann-Whitney tests and micro-CT results were analyzed by Tukey's HSD test (95% confidence interval).

RESULTS

None of the materials could prevent mineral loss at the enamel-restoration margins. The addition of 10% DMAHDM yielded the lowest, albeit statistically significant, mineral loss (p<0.05). 3D non-contact profilometry showed enamel surface roughness modification after biofilm exposure. The CG had the highest roughness values. Micro-CT analysis revealed mineral loss, except for GIC.

SIGNIFICANCE

The addition of 10% QAM with a 16-carbon chain in experimental composites reduced mineral loss at the enamel-restoration margins after cariogenic challenge.

Marginal Discrepancies of Monolithic Zirconia Crowns: The Influence of Preparation Designs and Sintering Techniques

PURPOSE

The marginal fit is an essential component for the clinical success of prosthodontic restorations. The aim of this study was to investigate the influence of different abutment finish line widths and crown thicknesses on the marginal fit of zirconia crowns fabricated using either standard or fast sintering protocols.

MATERIALS AND METHODS

Six titanium abutments were fabricated for receiving zirconia molar crowns. Crowns were designed virtually and milled from partially sintered zirconia blanks and divided into 12 groups (n = 10/group). Crowns in groups 1 to 6 were sintered by standard sintering, while those in groups 7 to 12 were sintered by fast sintering. Groups were further categorized according to abutment finish line and crown thickness: G1/G7 (0.5 mm chamfer, 0.8 mm thick); G2/G8 (0.5 mm chamfer, 1.5 mm thick); G3/G9 (1.0 mm chamfer, 0.8 mm thick); G4/10 (1.0 mm chamfer, 1.5 mm thick); G5/G11 (1.2 mm chamfer, 0.8 mm thick); G6/G12 (1.2 mm chamfer, 1.5 mm thick). The marginal gaps were assessed at 8 locations using digital microscopy. The linear mixed effect model analysis was performed at a significance level of 0.05.

RESULTS

All vertical marginal gaps were within the clinically acceptable range (∼11-52 μm). G8 (FS, 0.5 mm chamfer, 1.5 mm thick) demonstrated the largest gaps (47.95 μm, 95% CI: 44.57-51.23), whereas G3 (SS, 1.0 mm chamfer, 0.8 thick) had the smallest marginal gap (14.43 μm, 95% CI: 11.15-17.71). A linear mixed effect models showed significant differences for the interaction between finish line × crown thickness × sintering (F = 18.96, p < 0.001). The lingual surfaces showed the largest gaps in both sintering protocols, while the mesial and mesiobuccal surfaces demonstrated the smallest gaps.

CONCLUSIONS

There was a significant interaction between finish line widths, crown thickness, and sintering protocol on the marginal gaps in both sintering protocols; 1.0 mm finish line preparations with either 0.8 mm or 1.5 mm occlusal reduction had better marginal fit in both sintering protocols compared to 0.5 mm or 1.2 mm finish lines. Smaller marginal discrepancies were observed for standard sintering crowns with a 0.5 mm finish line and 1.5 mm occlusal reduction. Conservative occlusal reduction should be accompanied with a 1.2 mm finish line to obtain better marginal fit for full-contoured zirconia crowns.

Preparation of a highly crosslinked biosafe dental nanocomposite resin with a tetrafunctional methacrylate quaternary ammonium salt monomer

The design of antimicrobial dental nanocomposite resin to prevent secondary dental caries and minimize biosafety problems is an important endeavor with both fundamental and practical implications.

A threshold gap size for in situ secondary caries lesion development

OBJECTIVES

This study investigated the influence of very small gaps in secondary caries (SC) development and additionally linked the threshold gap size with the caries activity level from volunteers.

METHODS

For 21 days, 15 volunteers wore a modified occlusal splint loaded with dentin-composite samples restored with different interfaces: bonded (B = samples restored with complete adhesive procedure), no-bonded (NB = restored with composite resin without adhesive procedure), and 30, 60 and 90 μm (no adhesive procedure and with intentional gap). The splint was dipped in a 20% sucrose solution (10 min) 8 x per day. Samples were imaged with transversal wavelength independent microradiography (T-WIM) and lesion depth and mineral loss were calculated. Average wall lesion depth from each volunteer was determined and according to the values the volunteers were grouped as high, mid and low caries activity levels.

RESULTS

No wall lesion formation was observed in B and NB groups. In general, intentional gaps led to SC lesion depth progression independent of caries activity level of volunteers. No substantial wall lesions were found for two volunteers. A trend for deeper lesion in larger gaps was observed for the high activity group.

CONCLUSION

Very small gaps around or wider than 30 μm develop SC independent of the caries activity level of the patient and SC wall lesion progression seemed to be related to individual factors even in this standardized in situ model.

SIGNIFICANCE

Independently of caries activity level of the patient, the threshold gap size for secondary caries wall lesion seems to be 30 μm at most.

Advanced smart biomaterials and constructs for hard tissue engineering and regeneration

Hard tissue repair and regeneration cost hundreds of billions of dollars annually worldwide, and the need has substantially increased as the population has aged. Hard tissues include bone and tooth structures that contain calcium phosphate minerals. Smart biomaterial-based tissue engineering and regenerative medicine methods have the exciting potential to meet this urgent need. Smart biomaterials and constructs refer to biomaterials and constructs that possess instructive/inductive or triggering/stimulating effects on cells and tissues by engineering the material's responsiveness to internal or external stimuli or have intelligently tailored properties and functions that can promote tissue repair and regeneration. The smart material-based approaches include smart scaffolds and stem cell constructs for bone tissue engineering; smart drug delivery systems to enhance bone regeneration; smart dental resins that respond to pH to protect tooth structures; smart pH-sensitive dental materials to selectively inhibit acid-producing bacteria; smart polymers to modulate biofilm species away from a pathogenic composition and shift towards a healthy composition; and smart materials to suppress biofilms and avoid drug resistance. These smart biomaterials can not only deliver and guide stem cells to improve tissue regeneration and deliver drugs and bioactive agents with spatially and temporarily controlled releases but can also modulate/suppress biofilms and combat infections in wound sites. The new generation of smart biomaterials provides exciting potential and is a promising opportunity to substantially enhance hard tissue engineering and regenerative medicine efficacy.

Developing a New Generation of Therapeutic Dental Polymers to Inhibit Oral Biofilms and Protect Teeth

Polymeric tooth-colored restorations are increasingly popular in dentistry. However, restoration failures remain a major challenge, and more than 50% of all operative work was devoted to removing and replacing the failed restorations. This is a heavy burden, with the expense for restoring dental cavities in the U.S. exceeding $46 billion annually. In addition, the need is increasing dramatically as the population ages with increasing tooth retention in seniors. Traditional materials for cavity restorations are usually bioinert and replace the decayed tooth volumes. This article reviews cutting-edge research on the synthesis and evaluation of a new generation of bioactive dental polymers that not only restore the decayed tooth structures, but also have therapeutic functions. These materials include polymeric composites and bonding agents for tooth cavity restorations that inhibit saliva-based microcosm biofilms, bioactive resins for tooth root caries treatments, polymers that can suppress periodontal pathogens, and root canal sealers that can kill endodontic biofilms. These novel compositions substantially inhibit biofilm growth, greatly reduce acid production and polysaccharide synthesis of biofilms, and reduce biofilm colony-forming units by three to four orders of magnitude. This new class of bioactive and therapeutic polymeric materials is promising to inhibit tooth decay, suppress recurrent caries, control oral biofilms and acid production, protect the periodontium, and heal endodontic infections.

Retentive strength and marginal discrepancies of a ceramic-reinforced calcium phosphate luting agent: An in vitro pilot study

STATEMENT OF PROBLEM

Information on the properties of a relatively new luting agent with a unique formulation (ceramic-reinforced calcium phosphate) is limited.

PURPOSE

The purpose of this in vitro study was to compare the retentive strengths and marginal discrepancies of a ceramic-reinforced calcium phosphate luting agent (CM) with a self-adhesive resin luting agent (RX) and to determine and compare the mode of failure of dislodged cemented copings.

MATERIAL AND METHODS

Forty extracted human molar teeth were prepared to receive zirconia copings. After cementation, the specimens were divided into 4 subgroups (n=10): CM A (axial loading), CM OA (off-axis loading), RX A (axial loading), and RX OA (off-axis loading). For each subgroup, 9 of the specimens received experimental treatment (thermocycling and dynamic loading), and the tenth received no experimental treatment. Eight copings were pulled off in a universal testing machine (MTS Insight; MTS). The ninth specimen was treated experimentally but was not pull tested. The marginal discrepancy and the dentin interface of the specimens that were not pull tested were analyzed with scanning electron microscopy and energy dispersion spectroscopy. The mode of failure of the dislodged copings was also subjectively evaluated.

RESULTS

The mean retentive strengths were 5.92 MPa for CM A, 5.81 MPa for CM OA, 5.75 MPa for RX A, and 5.69 MPa for RX OA. The marginal discrepancy recorded for both CM and RX ranged from 30 to 45 μm, (mean, 36 ±4.6 μm). Energy dispersion spectroscopy analysis showed the presence of calcium, phosphorus, silicon, and aluminum for the CM marginal discrepancy and the presence of aluminum in the dentinal tubules adjacent to the CM. Calcium and phosphorus were detected in lesser amounts adjacent to the RX marginal discrepancy. The mode of failure for CM was primarily adhesive to the tooth preparation, and, for RX, the failure mode was predominantly adhesive to the coping.

CONCLUSIONS

CM had statistically significantly higher mean retentive strength compared with RX. Subgroups loaded axially had statistically significantly higher retentive strengths compared with those loaded off axis.

Bioactive Dental Composites and Bonding Agents Having Remineralizing and Antibacterial Characteristics

Current dental restorative materials are typically inert and replace missing tooth structures. This article reviews efforts in the development of a new generation of bioactive materials designed to not only replace the missing tooth volume but also possess therapeutic functions. Composites and bonding agents with remineralizing and antibacterial characteristics have shown promise in replacing lost minerals, inhibiting recurrent caries, neutralizing acids, repelling proteins, and suppressing biofilms and acid production. Furthermore, they have demonstrated a low cytotoxicity similar to current resins, with additional benefits to protect the dental pulp and promote tertiary dentin formation. This new class of bioactive materials shows promise in reversing lesions and inhibiting caries.

Determination of Caries Lesion Activity: Reflection and Roughness for Characterization of Caries Progression

Caries lesion progression is difficult to determine with visual and tactile examinations. The hypothesis of this study was that reflection and roughness measurements could determine caries progression. Ground/polished sound human enamel specimens were analyzed at baseline (sound) and after two four-day demineralization periods for reflection using optical reflectometry (ORef) and for roughness using optical surface profilometry (SPro). Specimens were demineralized using a microbial- Streptococcus mutans aries model. Comparisons among the periods for ORef and SPro were performed using repeated measures analysis of variance. Two-sample t-tests were used for differences in transverse microradiography. The integrated mineral loss and depth of the four-day demineralization period were significantly smaller than those for the eight-day demineralization period ( p<0.01). With increased demineralization time, reflection was significantly decreased and roughness was significantly increased ( p<0.01). Correlation between ORef and SPro was moderate ( r=-0.63). Both reflection and roughness can be characterized for nondestructive longitudinal assessment of caries lesion progression.

Natural saliva as an adjuvant in a secondary caries model based on Streptococcus mutans

OBJECTIVE

Two factors for secondary caries formation were evaluated using an artificial biofilm model, saliva as additive in culture medium and bonding procedures of composite materials for artificial gap creation.

DESIGN

Standardized cavities were prepared in bovine tooth samples (n = 44), treated with two different bonding pretreatments, restored and after artificial ageing incubated with Streptococcus mutans in a Mueller-Hinton-Broth-Sugar medium with or without human saliva for seven days. Secondary caries formation was analyzed using confocal laser scanning microscopy and transversal microradiography.

RESULTS

Lesions were significantly pronounced in groups using saliva, but were not influenced by the bonding pretreatments.

CONCLUSIONS

The results indicate that the addition of saliva, but not the type of bonding procedure influences the outcome in the present biofilm-based secondary caries model.

Calcium phosphate precipitation in experimental gaps between fluoride-containing fast-setting calcium silicate cement and dentin

A novel fast-setting calcium silicate cement containing fluoride (novel-CSC) has been developed for applications in tooth crowns. The aim of this study was to assess the ability of the novel-CSC to close the experimental gaps at the dentin-cement interface. The novel-CSC was tested against Vitrebond and GC Fuji II LC. Experimental gaps of 50 or 300 μm width were created between the materials and dentin. Specimens with the 300-μm-wide gap were immersed in phosphate-buffered saline and the closed gap area was measured during 96 h. All specimens with 50 or 300 μm gap width were analyzed by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM/EDX) to assess the morphology and chemical composition of the precipitates after 96 h immersion in phosphate-buffered saline. High-resolution micro-computed tomography (μCT) was used to evaluate the integrity and continuity of the precipitiates after 96 h and 180 d. In all novel-CSC samples, precipitates closed the gap area completely after 96 h. The SEM/EDX revealed that the globular precipitates closing the gap area were mainly composed of calcium and phosphorus. After 180 d, μCT indicated thicker precipitates compared with initial precipitates only in the novel-CSC group, whereas no precipitates were observed in resin-modified glass ionomers. Novel-CSC promoted continuous precipitation of calcium phosphate, including apatite, and closed the experimental gaps.

Calibration of a lactic-acid model for simulating biofilm-induced degradation of the dentin-composite interface

OBJECTIVE

To verify and calibrate a chemical model for simulating the degradation of the dentin-composite interface induced by multi-species oral biofilms in vitro.

METHODS

Dentin-composite disks (5-mm dia.×2-mm thick) were made from bovine incisor roots and filled with either Z100™ (Z100) or Filtek™ LS (LS) composite. The disks, which were covered with nail varnish, but with one of the dentin-composite margins exposed, were immersed in lactic acid solution at pH 4.5 for up to 48h. Diametral compression was performed to measure the reduction in bond strength of the dentin-composite disks following acid challenge. Scanning electron microscopy (SEM) was used to examine decalcification of dentin and fracture modes of the disks. To better understand the degradation process, micro-computed tomography, in combination with a radiopaque dye (AgNO3), was used to assess interfacial leakage in 3D longitudinally, while SEM was used to determine the path of leakage. One-way analysis of variance (ANOVA) was used to analyze the results, with the level of statistical significance set at p<0.05. The results were compared with those obtained previously using multi-species biofilms for verification and calibration purposes.

RESULTS

After 48h of acid challenge, the debonding load of both the LS- and Z100-filled disks reduced significantly (p<0.05). In the Z100-filled disks, debonding mostly occurred at the adhesive-dentin interface, while in the LS-filled disks, this happened at the adhesive-composite interface, instead. The degree of dentin demineralization, the reduction in debonding load and the modes of failure observed were very similar to those induced by multi-species oral biofilms found in the previous work. Leakage of AgNO3 occurred mainly along the hybrid layer. The specimens filled with Z100 had a thicker hybrid layer (∼6.5μm), which exhibited more interfacial leakage than those filled with LS.

SIGNIFICANCE

The chemical model with lactic acid used in this study can induce degradation to the dentin-composite interface similar to those produced by multi-species biofilms. With appropriate calibration, this could provide an effective in vitro method for ageing composite restorations in assessing their potential clinical performance.

In vitro biofilm models to study dental caries: a systematic review

The aim of this systematic review is to characterize and discuss key methodological aspects of in vitro biofilm models for caries-related research and to verify the reproducibility and dose-response of models considering the response to anti-caries and/or antimicrobial substances. Inclusion criteria were divided into Part I (PI): an in vitro biofilm model that produces a cariogenic biofilm and/or caries-like lesions and allows pH fluctuations; and Part II (PII): models showing an effect of anti-caries and/or antimicrobial substances. Within PI, 72.9% consisted of dynamic biofilm models, while 27.1% consisted of batch models. Within PII, 75.5% corresponded to dynamic models, whereas 24.5% corresponded to batch models. Respectively, 20.4 and 14.3% of the studies reported dose-response validations and reproducibility, and 32.7% were classified as having a high risk of bias. Several in vitro biofilm models are available for caries-related research; however, most models lack validation by dose-response and reproducibility experiments for each proposed protocol.

Minimal Gap Size and Dentin Wall Lesion Development Next to Resin Composite in a Microcosm Biofilm Model

This in vitro study investigated the development of dentin wall lesions next to resin composite containing very small gap sizes using an in vitro biofilm model, and evaluated whether a relevant threshold for the gap size could be established. Microcosm biofilms were grown for 14 days within small interfacial gaps between dentin-resin composite discs under intermittent cariogenic challenge. The factor under study was gap size: samples were either restored with composite resin without adhesive procedure (no intentional gap; no bonding [NB] group) or with intentional gaps of 30, 60, or 90 µm, or with complete adhesive procedure (no gap; bonding [B] group). Secondary caries wall lesion progression was measured in lesion depth (LD) and mineral loss (ML) using transversal wavelength independent microradiography at 3 locations: outer surface lesion and wall lesions at 200 and 500 µm distance from gap entrance. Results from linear regression analysis showed that the presence of an intentional gap (30, 60, and 90 µm) affected the secondary caries progression at 200 µm from the gap entrance (p ≤ 0.013). The NB group did not show significant wall lesion development (ML and LD, p ≥ 0.529). At 500 µm distance almost no wall caries development was observed. In conclusion, dentin wall lesions developed in minimal gap sizes, and the threshold for secondary wall lesion development was a gap of around 30 µm in this microcosm biofilm model.

Interfacial degradation of adhesive composite restorations mediated by oral biofilms and mechanical challenge in an extracted tooth model of secondary caries

OBJECTIVE

To study the combined effect of simulated occlusal loading and plaque-derived biofilm on the interfacial integrity of dental composite restorations, and to explore whether the effects are modulated by the incorporation of sucrose.

METHODS

MOD-class-II restorations were prepared in third molars. Half of the specimens (n=27) were subjected to 200,000 cycles of mechanical loading using an artificial oral environment (ART). Then, both groups of specimens (fatigued and non-fatigued) were divided into three subgroups for testing in CDC-reactors under the following conditions: no biofilm (Control), biofilm with no sucrose (BNS) and biofilm pulsed with sucrose (BWS). BNS and BWS reactors were incubated with a multispecies inoculum from a single plaque donor whereas the control reactor was not. The BWS reactor was pulsed with sucrose five times a day. The biofilm challenges were repeated sequentially for 12 weeks. pH was recorded for each run. Specimens were examined for demineralization with micro-CT and load capacity by fast fracture test.

RESULTS

Demineralization next to the restorations was only detectable in BWS teeth. Fracture loads were significantly reduced by the concomitant presence of biofilm and sucrose, regardless of whether cyclic mechanical loading was applied. Cyclic loading reduced fracture loads under all reactor conditions, but the reduction was not statistically significant.

CONCLUSIONS

Sucrose pulsing was required to induce biofilm-mediated degradation of the adhesive interface. We have presented a comprehensive and clinically relevant model to study the effects of mechanical loading and microbial challenge on the interfacial integrity of dental restorations.

Biomimetic Enamel Regeneration Mediated by Leucine-Rich Amelogenin Peptide

We report here a novel biomimetic approach to the regeneration of human enamel. The approach combines the use of inorganic pyrophosphate (PPi) to control the onset and rate of enamel regeneration and the use of leucine-rich amelogenin peptide (LRAP), a nonphosphorylated 56-amino acid alternative splice product of amelogenin, to regulate the shape and orientation of growing enamel crystals. This study builds on our previous findings that show LRAP can effectively guide the formation of ordered arrays of needle-like hydroxyapatite (HA) crystals in vitro and on the known role mineralization inhibitors, like PPi, play in the regulation of mineralized tissue formation. Acid-etched enamel surfaces of extracted human molars, cut perpendicular or parallel to the direction of the enamel rods, were exposed to a PPi-stabilized supersaturated calcium phosphate (CaP) solution containing 0 to 0.06 mg/mL LRAP for 20 h. In the absence of LRAP, PPi inhibition was reversed by the presence of etched enamel surfaces and led to the formation of large, randomly distributed plate-like HA crystals that were weakly attached, regardless of rod orientation. In the presence of 0.04 mg/mL LRAP, however, densely packed mineral layers, comprising bundles of small needle-like HA crystals, formed on etched surfaces that were cut perpendicular to the enamel rods. These crystals were strongly attached, and their arrangement reflected to a significant degree the underlying enamel prism pattern. In contrast, under the same conditions with LRAP, little to no crystal formation was found on enamel surfaces that were cut parallel to the direction of the enamel rods. These results suggest that LRAP preferentially interacts with ab surfaces of mature enamel crystals, inhibiting their directional growth, thus selectively promoting linear growth along the c-axis of enamel crystals. The present findings demonstrate a potential for the development of a new approach to regenerate enamel structure and properties.

The role of copper nanoparticles in an etch-and-rinse adhesive on antimicrobial activity, mechanical properties and the durability of resin-dentine interfaces

OBJECTIVES

To evaluate the effect of addition of copper nanoparticles at different concentrations into an etch-and-rinse adhesive (ER) on antimicrobial activity, Knoop microhardness (KHN), in vitro and in situ degree of conversion (DC), as well as the immediate (IM) and 2-year (2Y) resin-dentine bond strength (μTBS) and nanoleakage (NL).

METHODS

Seven experimental ER adhesives were formulated according to the amount of copper nanoparticles incorporated into the adhesives (0 [control], 0.0075 to 1wt.%). We tested the antimicrobial activity of adhesives against Streptococcus mutans using agar diffusion assay after IM and 2Y. The Knoop microhardness and in vitro DC were tested after IM and 2Y. The adhesives were applied to flat occlusal dentine surfaces after acid etching. After resin build-ups, specimens were longitudinally sectioned to obtain beam-like resin-dentine specimens (0.8mm²), which were used for evaluation of μTBS and nanoleakage at the IM and 2Y periods. In situ DC was evaluated at the IM period in these beam-like specimens. Data were submitted to appropriate statistical analyses (α=0.05).

RESULTS

The addition of copper nanoparticles provided antimicrobial activity to the adhesives only in the IM evaluation and slightly reduced the KHN, the in vitro and in situ DC (copper concentrations of 1wt.%). However, KHN increase for all concentrations after 2Y. After 2Y, no significant reductions of μTBS (0.06 to 1% wt.%) and increases of nanoleakage were observed for copper containing adhesives compared to the control group.

CONCLUSION

Copper nanoparticles addition up to 0.5wt.% may provide antimicrobial properties to ER adhesives and prevent the degradation of the adhesive interface, without reducing the mechanical properties of the formulations.

Quaternary ammonium-based biomedical materials: State-of-the-art, toxicological aspects and antimicrobial resistance

Microbial infections affect humans worldwide. Many quaternary ammonium compounds have been synthesized that are not only antibacterial, but also possess antifungal, antiviral and anti-matrix metalloproteinase capabilities. Incorporation of quaternary ammonium moieties into polymers represents one of the most promising strategies for preparation of antimicrobial biomaterials. Various polymerization techniques have been employed to prepare antimicrobial surfaces with quaternary ammonium functionalities; in particular, syntheses involving controlled radical polymerization techniques enable precise control over macromolecular structure, order and functionality. Although recent publications report exciting advances in the biomedical field, some of these technological developments have also been accompanied by potential toxicological and antimicrobial resistance challenges. Recent evidenced-based data on the biomedical applications of antimicrobial quaternary ammonium-containing biomaterials that are based on randomized human clinical trials, the golden standard in contemporary medicinal science, are included in the present review. This should help increase visibility, stimulate debates and spur conversations within a wider scientific community on the implications and plausibility for future developments of quaternary ammonium-based antimicrobial biomaterials.

Models of Caries Formation around Dental Composite Restorations

The main reason cited for the replacement of dental composite restorations is the recurrence of caries. Numerous models-both in vitro, with acid gels or bacterial biofilms, and in situ, with dental appliances-have been used to study caries formation around dental composites. The literature shows that many factors may affect caries formation, including marginal gap formation, gap size, the local chemical environment, the durability of the bonded interface, the extent of bacterial penetration, and the presence of mechanical loading. Studies have also shown that what have been called wall lesions may form independent of surface lesions, though not likely due to microleakage through very small gap spaces in the clinical situation. Gap size and mechanical loading have been shown to be related to lesion severity within in vitro models, but these results do not correspond exactly with those obtained from in situ studies using restorations in dental appliances. Though not conclusive, some in vitro models have shown that certain materials possessing antimicrobial characteristics may reduce the severity of lesion formation, suggesting possible pathways for developing new composite and adhesive materials for restorations with potentially enhanced longevity.

Effect of Bioactive Primers on Bacterial-Induced Secondary Caries at the Tooth-Resin Interface

Secondary caries at the tooth-resin interface is the primary reason for replacement of resin composite restorations. The tooth-resin interface is formed by the interlocking of resin material with hydroxyapatite crystals in enamel and collagen mesh structure in dentin. Efforts to strengthen the tooth-resin interface have identified chemical agents with dentin collagen cross-linking potential and antimicrobial activities. The purpose of the present study was to assess protective effects of bioactive primer against secondary caries development around enamel and dentin margins of class V restorations, using an in vitro bacterial caries model. Class V composite restorations were prepared on 60 bovine teeth (n=15) with pretreatment of the cavity walls with control buffer solution, an enriched fraction of grape seed extract (e-GSE), 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide/N-hydroxysuccinimide, or chlorhexidine digluconate. After incubating specimens in a bacterial model with Streptococcus mutans for four days, dentin and enamel were assessed by fluorescence microscopy. Results revealed that only the naturally occurring product, e-GSE, significantly inhibited the development of secondary caries immediately adjacent to the dentin-resin interface, as indicated by the caries inhibition zone. No inhibitory effects were observed in enamel margins. The results suggest that the incorporation of e-GSE into components of the adhesive system may inhibit secondary caries and potentially contribute to the protection of highly vulnerable dentin-resin margins.

Caries-resistant bonding layer in dentin

The present study examined the mechanism for caries resistance and the pulp responses in vital teeth following the use of the augmented-pressure adhesive displacement technique. Dentin adhesives were applied to the surface of sound dentin disks in 4 experimental groups: non-antibacterial adhesive and gentle adhesive displacement (N-G), non-antibacterial adhesive and augmented-pressure adhesive displacement (N-H), antibacterial adhesive and gentle adhesive displacement (A-G), antibacterial adhesive and augmented-pressure adhesive displacement (A-H). The depth of demineralization induced by biological or chemical demineralization models was measured using confocal laser scanning microscopy and analyzed with two-way ANOVA. Pulp responses of vital dog's teeth to the augmented-pressure adhesive displacement technique were evaluated using light microscopy. Depth of demineralization was significantly affected by "adhesive type" and "intensity of adhesive displacement" for biological demineralization. For chemical demineralization, only "intensity of adhesive displacement" showed significant influence on lesion depth. Pulp response of 0.1, 0.2 and 0.3 MPa groups showed only moderate disorganization of the odontoblast layer at 24 hours that completely re-organized after 3 weeks. Augmented-pressure adhesive displacement improves the caries resistance property of bonded dentin and does not cause irreversible pulpal damage to vital teeth when the air pressure employed is equal or smaller than 0.3 MPa.

Failed bonded interfaces submitted to microcosm biofilm caries development

OBJECTIVES

This study aimed to evaluate the dentin wall carious lesion development of different composite-dentin interfaces in the presence of two adhesive bonding materials in the gaps, using a microcosm biofilm model.

METHODS

Dentin samples were prepared (10.4mm(2)) and restored with a composite resin using two adhesive systems (etch-and-rinse and self-etch techniques). Different conditions with respect to composite-dentin interfaces were produced with a 200μm gap: failed bonded without ageing or after mechanical ageing, or non-bonded with or without the presence of adhesive material on the dentin wall. For cariogenic challenge, specimens were subjected to a biofilm microcosm model for 14days to create caries-like wall lesions. Before and after caries development, transverse wavelength-independent microradiography images were taken, and lesion depth and mineral loss were measured. Data were analysed with linear regression models (p<0.05).

RESULTS

The composite-dentin interface conditions significant influenced the caries development: lesion development was reduced by the presence of the adhesive material on dentin wall, while lesion development was increased by the mechanical ageing (p=0.019). There was no difference between the adhesive materials (p values>0.05).

CONCLUSION

Different composite-dentin interfaces influence wall lesion development in gaps, with the interfaces submitted to ageing showing less carious protection than those interfaces with the presence of adhesive covering the dentin.

CLINICAL SIGNIFICANCE

The presence of adhesive bonding material in the gaps plays a role on the wall caries lesion development.

Methacryloxylethyl Cetyl Ammonium Chloride Induces DNA Damage and Apoptosis in Human Dental Pulp Cells via Generation of Oxidative Stress

The polymerizable antibacterial monomer methacryloxylethyl cetyl ammonium chloride (DMAE-CB) has provided an effective strategy to combat dental caries. However, the application of such material raises the question about the biological safety and the question remains open. The mechanism of this toxic action, however, is not yet clearly understood. The present study aims at providing novel insight into the possible causal link between cellular oxidative stress and DNA damage, as well as apoptosis in human dental pulp cells exposed to DMAE-CB. The enhanced formation of reactive oxygen species and depletion of glutathione, as well as differential changes in activities of superoxide dismutase, glutathione peroxidase, and catalase in DMAE-CB-treated cells indicated oxidative stress. By using substances that can alter GSH synthesis, we found that GSH was the key component in the regulation of cell response towards oxidative stress induced by DMAE-CB. The increase in oxidative stress-sensitive 8-Oxo-2'-deoxyguanosine (8-OHdG) content, formation of γ-H2AX and cell cycle G1 phase arrest indicated that DNA damage occurred as a result of the interaction between DNA base and ROS beyond the capacities of antioxidant mechanisms in cells exposed to DMAE-CB. Such oxidative DNA damage thus triggers the activation of ataxia telangiectasia-mutated (ATM) signaling, the intrinsic apoptotic pathway, and destruction of mitochondrial morphology and function.

Caries Detection around Restorations Using ICDAS and Optical Devices

PURPOSE

Secondary caries is the major reason for replacement of restorations in operative dentistry. New detection methods and technology have the potential to improve the accuracy for diagnosis of secondary carious lesions. This in vitro study evaluated the performance of the ICDAS (International Caries Detection and Assessment System) visual criteria and optical devices for detecting secondary caries around amalgam and composite resin restorations in permanent teeth.

MATERIALS AND METHODS

A total of 180 extracted teeth with Class I amalgam (N = 90) and resin composite (N = 90) restorations were selected. Two examiners analyzed the teeth twice using the visual criteria (ICDAS), laser fluorescence (LF), light-emitting diode device (MID), quantitative light-induced fluorescence system (QLF), and a prototype system based on the Fluorescence Enamel Imaging technique (Professional Caries Detection System, PCDS). The gold standard was determined by means of confocal laser scanning microscopy.

RESULTS

High-reproducibility values were shown for all methods, except for MID in the amalgam group. For both groups the QLF and PCDS were the most sensitive methods, whereas the other methods presented better specificity (p < 0.05).

CONCLUSION

All methods, except the MID device appeared to be potential methods for detecting secondary caries only around resin composite restorations, whereas around amalgam restorations all methods seemed to be questionable.

CLINICAL SIGNIFICANCE

Using Internal Caries Detection and Assessment System (ICDAS), an LF device, quantitative light-induced fluorescence and a novel method based on Fluorescence Enamel Imaging technique may be effective for evaluating secondary caries around composite resin restorations.

Improved secondary caries resistance via augmented pressure displacement of antibacterial adhesive

The present in vitro study evaluated the secondary caries resistance potential of acid-etched human coronal dentin bonded using augmented pressure adhesive displacement in conjunction with an experimental antibacterial adhesive. One hundred and twenty class I cavities were restored with a commercial non-antibacterial etch-and-rinse adhesive (N) or an experimental antibacterial adhesive (A) which was displaced by gentle air-blow (G) or augmented pressure air-blow (H). After bonding and restoration with resin composite, the resulted 4 groups (N-G, N-H, A-G and A-H) were exposed to Streptococcus mutans biofilm for 4, 8, 15, 20 or 25 days. The development of secondary caries in the bonding interface was then examined by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Data acquired from 15, 20 and 25 days of artificial caries induction were analyzed with three-way ANOVA at α = 0.05. The depth of the artificial carious lesions was significantly affected by “adhesive type” (Single Bond 2 vs experimental antibacterial adhesive p = 0.003), “intensity of adhesive displacement” (gentle vs augmented-pressure adhesive displacement; p < 0.001), as well as “artificial caries induction time” (p < 0.001). The combined use of augmented pressure adhesive displacement and experimental antibacterial adhesive reduces the progression of secondary caries.

Novel rechargeable calcium phosphate dental nanocomposite

OBJECTIVES

Calcium phosphate (CaP) composites with Ca and P ion release can remineralize tooth lesions and inhibit caries. But the ion release lasts only a few months. The objectives of this study were to develop rechargeable CaP dental composite for the first time, and investigate the Ca and P recharge and re-release of composites with nanoparticles of amorphous calcium phosphate (NACP) to achieve long-term inhibition of caries.

METHODS

Three NACP nanocomposites were fabricated with resin matrix of: (1) bisphenol A glycidyl dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) at 1:1 mass ratio (referred to as BT group); (2) pyromellitic glycerol dimethacrylate (PMGDM) and ethoxylated bisphenol A dimethacrylate (EBPADMA) at 1:1 ratio (PE group); (3) BisGMA, TEGDMA, and Bis[2-(methacryloyloxy)ethyl] phosphate (BisMEP) at 2:1:1 ratio (BTM group). Each resin was filled with 20% NACP and 50% glass particles, and the composite was photo-cured. Specimens were tested for flexural strength and elastic modulus, Ca and P ion release, and Ca and P ion recharge and re-release.

RESULTS

NACP nanocomposites had strengths 3-fold of, and elastic moduli similar to, commercial resin-modified glass ionomer controls. CaP ion recharge capability was the greatest for PE group, followed by BTM group, with BT group being the lowest (p<0.05). For each recharge cycle, CaP re-release reached similarly high levels, showing that CaP re-release did not decrease with more recharge cycles. After six recharge/re-release cycles, NACP nanocomposites without further recharge had continuous CaP ion release for 42 d.

SIGNIFICANCE

Novel rechargeable CaP composites achieved long-term and sustained Ca and P ion release. Rechargeable NACP nanocomposite is promising for caries-inhibiting restorations, and the Ca and P ion recharge and re-release method has wide applicability to dental composites, adhesives, cements and sealants to achieve long-term caries-inhibition.