University of Birmingham

We are pleased to introduce the collection Frontiers in Dental Medicine: Highlights in Dental Materials 2021/22. This collection will welcome and showcase a selection of high impact articles authored by leaders in the field. The work presented here highlights the broad diversity of research performed across the Dental Materials section, and aims to put a spotlight on the main areas of interest. This collection aims to further support Frontiers’ strong community by shining a spotlight on our authors' highly impactful research.

Dean, Faculty of Dentistry ,The Hashemite University

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Frontiers in Dental Medicine

Dental Materials

Frontiers in Dental Medicine: Highlights in Dental Materials 2021/22

Editorial on the Research Topic <a href="https://www.frontiersin.org/research-topics/32302/frontiers-in-dental-medicine-highlights-in-dental-materials-202122">Frontiers in dental medicine: Highlights in dental materials 2021/22</a>The collection Highlights in Dental Materials 2021/22 was put together to showcase a selection of high-impact articles authored by leaders in the field. The work presented here highlights the broad diversity of research performed across articles published in the Dental Materials section, and the aim was to put a spotlight on the main areas of interest. The collection was skillfully edited by Prof Ziad Al-Dwairi from the Jordan University of Science and Technology.This collection includes two original research articles, two brief research reports, and a review. The topics covered include the susceptibility of teeth to develop caries irrespective of the restorative material used, assessment of a nano-hydroxyapatite for caries management, enamel bonding, assessment of implant coating materials, and droplet spread in the clinical environment.Caries research is key as dental caries is still a prevalent disease and is one of the main reasons for the loss of dental hard tissues, thus necessitating the use of dental materials. Secondary caries imposes a disease burden, as it results in the need to redo the restoration at a cost to the patient and requires further intervention and further movement along the restorative cycle of a tooth. In the study undertaken on patients attending the University of Pittsburgh School of Dental Medicine (as part of the Dental Registry and DNA Repository project), patients with secondary caries were identified and matched with patients with similar restorations that had not failed. Genomic DNA extracted from saliva was used to obtain genotypes in five markers of MMP2 and MMP3. The results obtained in this study demonstrate the role of MMP2 in failure of restorations due to secondary caries independent of the restorative material. This important research has been published by <a href="https://www.frontiersin.org/articles/10.3389/fdmed.2021.735535">Benli et al</a>. in an article entitled “Matrix metalloproteinase 2 is associated with secondary caries independent from the restorative material”. This research clearly provides proof that secondary caries is not material-dependent, as has been previously postulated.Another paper focusing on caries research and material interactions is the publication by Abo <a href="https://www.frontiersin.org/articles/10.3389/fdmed.2022.738326">El-Gar et al</a>. entitled “Potent antibacterial and antibiofilm activities of a synthetic remineralizing preparation of nano-hydroxyapatite against cariogenic Streptococcus mutans using an ex-vivo animal model”. This original research article investigates the use of a nano-hydroxyapatite in contact with bovine teeth and provides an evaluation of the bacterial inhibitory effect of the material, including the living tissue in this assessment. The use of tooth structure in the assessment of biological characteristics is important, as this leads to better clinical translation of the in vitro findings. The nanohydroxyapatite suspensions exhibited potential for remineralization and also exhibited antibiofilm characteristics.Another contribution to this collection is the review “Update on enamel bonding strategies” by <a href="https://www.frontiersin.org/articles/10.3389/fdmed.2021.666379">Sato et al</a>. This is a very timely review article highlighting the differences between enamel and dentine bonding and discussing the advances made in this field. This review is particularly helpful for clinicians, enabling them to choose their clinical strategy carefully based on scientific evidence.In an original scientific article on implant coatings by <a href="https://www.frontiersin.org/articles/10.3389/fdmed.2021.695417">Shokeen et al</a>. entitled “Surface characterization and assessment of biofilm formation on two titanium-based implant coating materials,” the authors investigate titanium nitride and titanium carbon nitride coatings over titanium implants. The surfaces were profiled and characterized, and it was shown that, in contrast with previous findings, there was no correlation between the surface roughness and hydrophobicity. The titanium carbon coating was hydrophilic and exhibited less microbial attachment when a well-established saliva-based oral microbial biofilm model was used, with growth conditions including relevant host components such as blood as well as the presence or absence of dietary carbohydrates.A brief research report by <a href="https://www.frontiersin.org/articles/10.3389/fdmed.2021.727111">Tsoi et al</a>. “The spread of droplets and aerosols of surgical motor handpiece irrigation using different suction systems,” reports on their investigation of the clinical environment with regard to aerosol spread. Aerosols have been the subject of much discussion during the COVID pandemic and in the post-pandemic period. Although spread of aerosols is a constant clinical problem. This research shows that both external oral suction and high-volume suction are effective in reducing aerosols and droplets generated by the irrigation of a surgical high-speed motor handpiece.These articles, all of which are published under the Research Topic Highlights in Dental Materials 2021/22, enrich our understanding of research in materials and its clinical translation. These publications break down barriers in relation to some of our beliefs that are based on practice rather than on scientific evidence. I wholeheartedly thank all the contributors and also the editorial team for putting together such an interesting collection.JC: sole author of editorial. All author contributed to the article and approved the submitted version.The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Editorial: Frontiers in dental medicine: Highlights in dental materials 2021/22

AimThe aim to this study is to evaluate the biocompatibility and antibiofilm actions of two nano-hydroxy apatite (NHA).</sec>MethodologyNano-hydroxy apatites are biomaterials use in direct contact with living tissues. Therefore, they should be tested for their safety beside assessment of their minimum inhibitory (MIC) and minimum bactericidal concentration (MBC) using broth microdilution method. One hundred and twenty extracted bovine incisors were collected and cleaned to ensure the absence of any defects. Enamel blocks with different size (2 × 2 × 3 mm) and (5 × 5 × 2 mm) were prepared from their labial surfaces using an isomet saw. Enamel blocks are used for detecting the suitable concentration will be used in the following experiments using energy dispersive X-ray analysis (EDX). The remaining enamel blocks divided into 5 equal groups to detect inhibitory effect against bacterial adhesion to the initial enamel caries like lesions using viable count technique beside the antibiofilm activity against mature biofilm of Streptococcus mutans (S. mutans) using confocal laser microscopy. The remaining enamel blocks were used as a representing data for detecting surface topography for each group by using the scanning electron microscopy (SEM).</sec>ResultThe data showed safety of NHA suspensions. Additionally, only NHA suspension of large nanoparticle size (NHA-LPS) had MIC of 1.25 mg/ml against S. mutans. Also, have the higher percentages of Ca and P in the enamel blocks. Furthermore, the lowest level of bacterial adhesion was recorded in (group III) treated by NHA-LPS which was non-significantly different with the positive control group V. Biofilm thickness in group IV treated with NHA-small particle size (SPS) recorded high biofilm thickness followed by group III. Interestingly, group III showed greater killing effect against mature biofilm which is slightly higher than the positive control group V. In group III, surface topography revealed very smooth enamel surface with closed pores. Accordingly, NHA-LPS suspension had antiadhesive, antibacterial, and antibiofilm effect against cariogenic S. mutans representing a promising possibility to be recommended for safe effective remineralization.</sec>

Aim: The aim to this study is to evaluate the biocompatibility and antibiofilm actions of two nano-hydroxy apatite (NHA).Methodology: Nano-hydroxy apatites are biomaterials use in direct contact with living tissues. Therefore, they should be tested for their safety beside assessment of their minimum inhibitory (MIC) and minimum bactericidal concentration (MBC) using broth microdilution method. One hundred and twenty extracted bovine incisors were collected and cleaned to ensure the absence of any defects. Enamel blocks with different size (2 × 2 × 3 mm) and (5 × 5 × 2 mm) were prepared from their labial surfaces using an isomet saw. Enamel blocks are used for detecting the suitable concentration will be used in the following experiments using energy dispersive X-ray analysis (EDX). The remaining enamel blocks divided into 5 equal groups to detect inhibitory effect against bacterial adhesion to the initial enamel caries like lesions using viable count technique beside the antibiofilm activity against mature biofilm of Streptococcus mutans (S. mutans) using confocal laser microscopy. The remaining enamel blocks were used as a representing data for detecting surface topography for each group by using the scanning electron microscopy (SEM).Result: The data showed safety of NHA suspensions. Additionally, only NHA suspension of large nanoparticle size (NHA-LPS) had MIC of 1.25 mg/ml against S. mutans. Also, have the higher percentages of Ca and P in the enamel blocks. Furthermore, the lowest level of bacterial adhesion was recorded in (group III) treated by NHA-LPS which was non-significantly different with the positive control group V. Biofilm thickness in group IV treated with NHA-small particle size (SPS) recorded high biofilm thickness followed by group III. Interestingly, group III showed greater killing effect against mature biofilm which is slightly higher than the positive control group V. In group III, surface topography revealed very smooth enamel surface with closed pores. Accordingly, NHA-LPS suspension had antiadhesive, antibacterial, and antibiofilm effect against cariogenic S. mutans representing a promising possibility to be recommended for safe effective remineralization.

Potent Antibacterial and Antibiofilm Activities of a Synthetic Remineralizing Preparation of Nano-Hydroxyapatite Against Cariogenic Streptococcus mutans Using an Ex-vivo Animal Model

Objective: This study aimed to compare the effectiveness of various combinations of dental suction devices in reducing the amount and distance of spread of aerosols and droplets using an electrical surgical motor model with a self-irrigation system.Materials and Methods: In a standard single-chaired air-conditioned ventilated dental clinic, an electrical dental surgical motor with a high-speed handpiece (Implantmed) cooled with 0.2% fluorescein containing normal saline was used to drill a gypsum block mounted on a phantom head in a supine position. A single operator performed thrice each of the following suction settings: (a) no suction, (b) low-volume suction, (c) low-volume + high-volume suctions, and (d) low-volume + external oral suctions. Aerosols (0.1–5 μm) were measured with a particle counter at the mouth opening of the phantom head, and droplet sizes and distances were analyzed via a machine learning algorithm by identifying fluorescence droplets on pre-loaded pieces of paper on the floor for each group.Results: The different suction systems have different performances in terms of droplet distance (p = 0.007), whereas using (c) high volume suctions (41.1 ± 22.9 cm) and (d) external oral suction unit (39 ± 18.2 cm) had significantly reduced the spread of droplets when compared with (a) without suction (58.9 ± 17.1 cm). Using (d) external oral suction or (c) high volume suction could reduce the number for all droplet sizes. The use of (c) high volume suction was most effective in reducing aerosol count of 0.3–1 μm, while (d) external oral suction was most effective in reducing aerosol count of 3–5 μm.Conclusions: Both external oral suction and high-volume suction were effective in reducing aerosols and droplets generated by the irrigation of a surgical high-speed motor handpiece. External oral suction could be an effective alternative to high volume suction in dental surgical procedures to reduce the spread of aerosols and droplets.Clinical Relevance: External oral suction or high-volume suction should be used in conjunction with low-volume suction in surgical procedure to reduce the spread of aerosols and droplets in a dental clinic environment.

Objective: This study aimed to compare the effectiveness of various combinations of dental suction devices in reducing the amount and distance of spread of aerosols and droplets using an electrical surgical motor model with a self-irrigation system.Materials and Methods: In a standard single-chaired air-conditioned ventilated dental clinic, an electrical dental surgical motor with a high-speed handpiece (Implantmed) cooled with 0.2% fluorescein containing normal saline was used to drill a gypsum block mounted on a phantom head in a supine position. A single operator performed thrice each of the following suction settings: (a) no suction, (b) low-volume suction, (c) low-volume + high-volume suctions, and (d) low-volume + external oral suctions. Aerosols (0.1–5 μm) were measured with a particle counter at the mouth opening of the phantom head, and droplet sizes and distances were analyzed via a machine learning algorithm by identifying fluorescence droplets on pre-loaded pieces of paper on the floor for each group.Results: The different suction systems have different performances in terms of droplet distance (p = 0.007), whereas using (c) high volume suctions (41.1 ± 22.9 cm) and (d) external oral suction unit (39 ± 18.2 cm) had significantly reduced the spread of droplets when compared with (a) without suction (58.9 ± 17.1 cm). Using (d) external oral suction or (c) high volume suction could reduce the number for all droplet sizes. The use of (c) high volume suction was most effective in reducing aerosol count of 0.3–1 μm, while (d) external oral suction was most effective in reducing aerosol count of 3–5 μm.Conclusions: Both external oral suction and high-volume suction were effective in reducing aerosols and droplets generated by the irrigation of a surgical high-speed motor handpiece. External oral suction could be an effective alternative to high volume suction in dental surgical procedures to reduce the spread of aerosols and droplets.Clinical Relevance: External oral suction or high-volume suction should be used in conjunction with low-volume suction in surgical procedure to reduce the spread of aerosols and droplets in a dental clinic environment.

The Spread of Droplets and Aerosols of Surgical Motor Handpiece Irrigation Using Different Suction Systems

Certain patients, despite receiving proper treatment, still show higher failure rates of restorative dental treatments. The aim of this work was to test if MMP2 and MMP3 alleles are overrepresented in individuals with secondary caries. A total of 1,089 individuals from the University of Pittsburgh School of Dental Medicine Dental Registry and DNA Repository project were selected for this study. From this total, 341 individuals were selected for having a record of secondary caries in any type of restoration and were matched with 748 individuals by sex, age, ethnicity, and restorative work in the same teeth that did not fail. Genomic DNA extracted from saliva was used to obtain genotypes in five markers of MMP2 and MMP3 using TaqMan chemistry and end-point analysis. Chi-square was used to test if differences in allele and genotype distributions were statistically different at an alpha of 0.05. The less common allele and homozygote genotype of MMP2 rs9923304 were less commonly found among individuals with secondary caries. The less common allele of MMP2 rs2287074 was also less frequent among individuals with secondary caries. These results provide statistical evidence for the role of MMP2 in failure of restorations due to secondary caries. We can conclude that MMP2 variation impacts the risk of having secondary caries, independent of the restorative material.

Certain patients, despite receiving proper treatment, still show higher failure rates of restorative dental treatments. The aim of this work was to test if MMP2 and MMP3 alleles are overrepresented in individuals with secondary caries. A total of 1,089 individuals from the University of Pittsburgh School of Dental Medicine Dental Registry and DNA Repository project were selected for this study. From this total, 341 individuals were selected for having a record of secondary caries in any type of restoration and were matched with 748 individuals by sex, age, ethnicity, and restorative work in the same teeth that did not fail. Genomic DNA extracted from saliva was used to obtain genotypes in five markers of MMP2 and MMP3 using TaqMan chemistry and end-point analysis. Chi-square was used to test if differences in allele and genotype distributions were statistically different at an alpha of 0.05. The less common allele and homozygote genotype of MMP2 rs9923304 were less commonly found among individuals with secondary caries. The less common allele of MMP2 rs2287074 was also less frequent among individuals with secondary caries. These results provide statistical evidence for the role of MMP2 in failure of restorations due to secondary caries. We can conclude that MMP2 variation impacts the risk of having secondary caries, independent of the restorative material.

Matrix Metalloproteinase 2 Is Associated With Secondary Caries Independent From the Restorative Material

Implant-related oral diseases such as peri-implantitis and peri-mucositis are largely initiated by bacterial colonization on artificial implant surfaces. Therefore, implant and abutment material characteristics that minimize bacterial attachment and subsequent biofilm formation are important factors in reducing the risk of infection-related implant failure. This study compares the properties of two different titanium-based implant coating materials, titanium nitride (TiN) and titanium carbon nitride (TiCN). Surface hydrophilicity/ hydrophobicity and roughness were evaluated via contact angle measurements and surface profiling with white light interferometry, respectively. TiN-coated surfaces were hydrophobic according to its contact angle higher than 72.7°, whereas TiCN-coated surfaces were hydrophilic with its contact angle of 53.6°. The average roughness (Ra) was greater for TiCN than TiN with the root mean square roughness (Rq) being significantly higher. These findings are in contrast to the common understanding for titanium-based materials that surface roughness and hydrophobicity are positively correlated. A well-established saliva-based oral microbial biofilm model was employed to compare bacterial attachment and biofilm formation on TiN and TiCN. Growth conditions included relevant host components such as blood as well as the presence or absence of dietary carbohydrates. The accumulated biomass was measured by crystal violet staining and the bacterial community profiles of the attached biofilms were determined via 16S rRNA gene microbiome sequencing at different time points over a 7-day period. At all time points, TiCN showed significantly less bacterial attachment and biofilm formation compared to TiN. This implied the importance of the hydrophilic state over surface roughness as parameter for the prevention of oral microbial attachment. Although, the biofilm community composition was very similar on both materials, environmental growth conditions resulted in significantly different bacterial profiles independent of the surface. In conclusion, TiCN coating produced a unique titanium surface which is rougher but more hydrophilic. TiCN-coated surfaces exhibited reduced bacterial attachment and biofilm formation in comparison to TiN coating. This coating technique can be further explored to improve implant and abutment success.

Implant-related oral diseases such as peri-implantitis and peri-mucositis are largely initiated by bacterial colonization on artificial implant surfaces. Therefore, implant and abutment material characteristics that minimize bacterial attachment and subsequent biofilm formation are important factors in reducing the risk of infection-related implant failure. This study compares the properties of two different titanium-based implant coating materials, titanium nitride (TiN) and titanium carbon nitride (TiCN). Surface hydrophilicity/ hydrophobicity and roughness were evaluated via contact angle measurements and surface profiling with white light interferometry, respectively. TiN-coated surfaces were hydrophobic according to its contact angle higher than 72.7°, whereas TiCN-coated surfaces were hydrophilic with its contact angle of 53.6°. The average roughness (Ra) was greater for TiCN than TiN with the root mean square roughness (Rq) being significantly higher. These findings are in contrast to the common understanding for titanium-based materials that surface roughness and hydrophobicity are positively correlated. A well-established saliva-based oral microbial biofilm model was employed to compare bacterial attachment and biofilm formation on TiN and TiCN. Growth conditions included relevant host components such as blood as well as the presence or absence of dietary carbohydrates. The accumulated biomass was measured by crystal violet staining and the bacterial community profiles of the attached biofilms were determined via 16S rRNA gene microbiome sequencing at different time points over a 7-day period. At all time points, TiCN showed significantly less bacterial attachment and biofilm formation compared to TiN. This implied the importance of the hydrophilic state over surface roughness as parameter for the prevention of oral microbial attachment. Although, the biofilm community composition was very similar on both materials, environmental growth conditions resulted in significantly different bacterial profiles independent of the surface. In conclusion, TiCN coating produced a unique titanium surface which is rougher but more hydrophilic. TiCN-coated surfaces exhibited reduced bacterial attachment and biofilm formation in comparison to TiN coating. This coating technique can be further explored to improve implant and abutment success.

Surface Characterization and Assessment of Biofilm Formation on Two Titanium-Based Implant Coating Materials

Optimal strategies for the application of an adhesive differ between enamel and dentin because of the differences in their composition. The development of adhesive systems has mainly focused on the bonding of dentin, rather than on the enamel, by etching with phosphoric acid (PA). Dental adhesive technologies continue to rapidly advance, and various adhesive systems have been developed since the study of Buonocore in 1955. He introduced the enamel acid-etch technique. Then, the etch-and-rinse (ER) system was developed, and subsequently, the self-etch (SE) system. Universal adhesives are a new generation of one-bottle SE adhesives that can be applied with either ER mode or SE mode, or a combined system involving selective enamel etching mode. Since the combination of PA etching and the SE system differs from conventional ER systems, the enamel bonding strategy should be carefully considered. This concise review of the literature on reliable enamel bonding strategies should prove helpful to clinicians to choose an appropriate adhesive system to achieve optimal clinical outcomes.

Optimal strategies for the application of an adhesive differ between enamel and dentin because of the differences in their composition. The development of adhesive systems has mainly focused on the bonding of dentin, rather than on the enamel, by etching with phosphoric acid (PA). Dental adhesive technologies continue to rapidly advance, and various adhesive systems have been developed since the study of Buonocore in 1955. He introduced the enamel acid-etch technique. Then, the etch-and-rinse (ER) system was developed, and subsequently, the self-etch (SE) system. Universal adhesives are a new generation of one-bottle SE adhesives that can be applied with either ER mode or SE mode, or a combined system involving selective enamel etching mode. Since the combination of PA etching and the SE system differs from conventional ER systems, the enamel bonding strategy should be carefully considered. This concise review of the literature on reliable enamel bonding strategies should prove helpful to clinicians to choose an appropriate adhesive system to achieve optimal clinical outcomes.