In Vitro Models Used in the Formation of Root Caries Lesions-A Review of the Literature.

The management of root caries remains a challenge for clinicians due to its unique anatomical location and structure. There is increasing interest in utilising artificial root caries lesions to develop new strategies for remineralisation. An ideal protocol has not yet been agreed upon. The aim of this review is to provide a structured overview of previously reported in vitro root caries models. The literature was screened and mined for information mainly on substrate selection, model systems utilised, and variables used in the models. Human roots (60%) were the most frequently used substrates, followed by bovine roots (40%). Chemical models (69%) were the most frequently utilised model systems, followed by microbiological models (27%), to form root caries lesions. Acetate buffer solution (80%), pH 5.0 or above (40%), and a demineralisation time of five days (25%) were the common variables used in the chemical systems, while mono-species biofilm was most frequently used (73%) in microbiological models and Streptococcus mutans was the most common bacterial strain utilised in these models (80%). This review highlights the variability amongst the experimental approaches, discusses the advantages and limitations of these approaches, and emphasises that standardisation of experimental conditions along with sustained research will benefit root caries research.

Chapter 9.1: The Use of Fluorides in the Control of Coronal Caries.

Fluoride is the main agent used to control dental caries, with a very successful history after its widespread implementation worldwide, resulting in significant caries declines around the globe. In this chapter, the mechanism of action and peculiarities of different methods of fluoride use are revised. Fluoride controls caries progression by interfering with the processes of mineral exchanges (demineralization, remineralization) to which teeth are frequently subjected upon exposure to dental biofilm and a diet rich in fermentable sugars. Because caries is a ubiquitous disease of modern societies, different strategies have been developed to successfully keep fluoride available in oral fluids: (1) community-based approaches, such as water fluoridation, in which fluoride is delivered to communities at very low levels; (2) individual-based approaches, such as fluoride toothpastes, in which fluoride is delivered at higher concentrations, directly into the oral cavity, in a convenient combination with the act of brushing teeth to remove dental biofilm; (3) professionally-delivered approaches, such as fluoride gels and varnishes, in which very-high concentration products react with teeth resulting in local fluoride reservoirs that release the ion for weeks/months; and (4) combinations of these approaches, such as the concomitant use of fluoridated water and toothpaste, or the use of professional fluorides in caries-active patients. In conclusion, this chapter reviews the different modalities of fluoride use for coronal caries control, and summarizes the combined application of these methods according to the best evidence available.

Caries-arresting effects of silver diamine fluoride and sodium fluoride on dentine caries lesions.

OBJECTIVES: To investigate the remineralising effect and bacterial growth inhibition of 38% silver diamine fluoride (SDF) solution and 5% sodium fluoride (NaF) varnish on artificial dentine caries lesions. METHODS: Demineralised dentine blocks were treated with SDF + NaF (Group 1), SDF (Group 2), NaF (Group 3) and water (Group 4) and subjected to a Streptococcus mutans biofilm challenge. Lesion depth, precipitates' characteristics and matrix (collagen)-to-mineral ratio were evaluated by micro-computer tomography (micro-CT), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. The biofilm kinetics, viability and topography were assessed by counts of colony forming units (CFUs), confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM), respectively. Data were analysed by two-way ANOVA test. RESULTS: The lesion depths of Groups 1-4 were 170 ± 28 µm, 160 ± 32 µm, 353 ± 38 µm and 449 ± 24 µm, respectively. The addition of NaF to SDF did not show better remineralisation than SDF (p = 0.491). Metallic silver and silver chloride were found in Groups 1 and 2. The amide I-to-hydrogen phosphate ratios of the four groups were 0.14 ± 0.02, 0.14 ± 0.01, 0.29 ± 0.05 and 0.49 ± 0.16, respectively, and the addition of NaF to SDF did not offer better protection against collagen exposure than SDF (p = 0.986). The Log10 CFUs of Groups 1-4 were 5.75 ± 0.56, 4.49 ± 0.57, 6.55 ± 0.39 and 6.40 ± 0.38, respectively. The presence of NaF reduced the antibacterial effect of SDF (p < 0.001). The SEM and CLSM images supported the findings. CONCLUSION: Application of SDF with or without NaF reduced the demineralisation of dentine caries, but SDF exerted stronger inhibition of biofilm growth than SDF with NaF. CLINICAL SIGNIFICANCE: NaF varnish affects the antibacterialeffects of SDF, the adjunctive application of SDF solution and NaF varnish is not recommended to arrest dentine caries in clinic.

Clinical Use of Silver Diamine Fluoride in Dental Treatment.

The use of a topical fluoride solution, namely silver diamine fluoride (SDF), in dental treatment has been drawing increasing attention. SDF has been used in some countries in Asia, including Japan and China, as a caries-arresting and anti-hypersensitivity agent. It was recently cleared by the Food and Drug Administration in the United States as a fluoride to manage hypersensitive teeth. Topical application of SDF is a noninvasive procedure that is quick and simple to use. Promising results of laboratory studies and clinical trials have suggested that SDF is more effective than other fluoride agents to halt the caries process. A review concluded that SDF is a safe, effective, efficient, and equitable caries control agent that has a potentially broad application in dentistry and may meet the criteria of both the WHO Millennium Development Goals and the US Institute of Medicine's criteria for 21st century medical care. This article provides an overview of the clinical use of SDF in dental treatment.

Effect of Heat Treatment on the Physical Properties of Provisional Crowns during Polymerization: An in Vitro Study.

This study concerned the effect of heat treatment during setting on the physical properties of four resin-based provisional restorative materials: Duralay (polymethyl methacrylate), Trim II (polyethyl methacrylate), Luxatemp (bis-acrylic composite), and Protemp 4 (bis-acrylic composite). Specimens were prepared at 23, 37, or 60 °C for evaluation of flexural strength, surface roughness, color change and marginal discrepancy. Flexural strength was determined by a three-point bending test. Surface profile was studied using atomic force microscopy. Color change was evaluated by comparing the color of the materials before and after placement in coffee. A travelling microscope helped prepare standardized crowns for assessment of marginal discrepancy. Flexural strength of all tested materials cured at 23 °C or 37 °C did not significantly change. The surface roughness and marginal discrepancy of the materials increased at 60 °C curing temperature. Marginal discrepancies, color stability, and other physical properties of materials cured at 23 °C or 37 °C did not significantly change. Flexural strength of certain provisional materials cured at 60 °C increased, but there was also an increase in surface roughness and marginal discrepancy.

Effect of laser irradiation on the fluoride uptake of silver diamine fluoride treated dentine.

This study aimed to evaluate the fluoride uptake of dentine treated with a 38 % silver diamine fluoride (SDF) solution and laser irradiation at sub-ablative energy levels. Fifteen human dentine slices were prepared and divided into four samples each. Four types of laser were chosen: CO2 (10,600 nm), Er:YAG (2,940 nm), Nd:YAG (1,064 nm) and Diode (810 nm). First, the four samples from 12 of the dentine slices were treated with SDF, and then irradiated by one of the four types of laser at three different settings. One sample was untreated and acted as a control. The setting that rendered the highest fluoride uptake was selected. Second, the remaining dentine slices were treated with SDF and irradiated by the four lasers with the selected settings. Fluoride uptake was assessed using Energy Dispersive X-ray Spectrometry at the dentine surface and up to 20 µm below the surface. The selected settings were CO2 irradiation at 1.0 W for 1 s, Er:YAG irradiation at 0.5 W for 20 s, Nd:YAG irradiation at 2.0 W for 1 s and diode irradiation at 3.0 W for 3 s. The fluoride content (weight %) at the dentine surface following CO2, Er:YAG, Nd:YAG and diode irradiation was 6.91 ± 3.15, 4.09 ± 1.19, 3.35 ± 2.29 and 1.73 ± 1.04, respectively. CO2 and Er:YAG irradiation resulted in higher fluoride uptake than Nd:YAG and diode irradiation at all levels (p < 0.05). CO2 laser and Er:YAG laser irradiation rendered higher fluoride uptake in the SDF-treated dentine than Nd:YAG laser and diode laser irradiation.

A survey of practices of tunnel preparation among dentists who attended the 100th FDI Annual World Dental Congress.

AIM: To study the practice of tunnel restoration (TR) among dentists who attended the 100th World Dental Federation (FDI) Annual World Dental Congress (AWDC). METHODS: An anonymous questionnaire was administered to a sample of 150 dentists who attended the 100th FDI AWDC in 2012. The participants were asked about TR and their practice of TR. They were also asked to provide their years of dental practice and the countries in which they received their dental training. RESULTS: Fifteen respondents were not performing restoration, and they were excluded from analysis. Most respondents (123/135) practiced general dentistry. Their basic dental training was from 46 countries and regions. Most of them (n = 117, 87%) knew about TR, and 53% (n = 71) practiced it. There were 12 dentists (9%) who had performed more than 10 TRs in the previous 12 months. Practice of TR among dentists who graduated more than 10 years previously was more common (odds ratio 5.87-5.98) than those who graduated <3 years previously. CONCLUSIONS: The current study found that about half of the surveyed dentists practiced TR, although most of them knew about it. Tunnel restoration was performed more frequently among dentists who had more than 10 years of clinical experience.

Prevention of dentine caries using silver diamine fluoride application followed by Er:YAG laser irradiation: an in vitro study.

To evaluate the preventive effect of Er:YAG laser (EYL) irradiation followed by silver diamine fluoride (SDF) application on dentine with cariogenic biofilm challenge. Twenty-four dentine slices were prepared from extracted sound human third molars. Each slice was cut into four parts for SDF application, followed by EYL irradiation (group SL), SDF application (group S), EYL irradiation (group L) and water (group W). The specimens were subjected to cariogenic biofilm challenge for 12 h, followed by immersion in a buffered remineralising solution containing calcium chloride and sodium hypophosphate for 12 h at 37 °C. Surface morphological changes in the specimens were examined using scanning electronic microscopy. Elemental analysis was performed using energy-dispersive X-ray spectrometry. Micro-mechanical properties were investigated by nano-indentation. The specimen surfaces of groups SL and L showed laser melting contours with narrowed dentinal orifices. Group S showed a partial tubular occlusion. A porous surface was observed in group W, indicating demineralisation. The mean (SD) fluoride weight percentages were 3.93 (0.91), 3.10 (0.61), 0.17 (0.09) and 0.32 (0.07) in groups SL, S, L and W, respectively, (p < 0.001; SL, S > L, W). The mean (SD) micro-hardness values in GPa were 1.84 (0.22), 0.49 (0.13), 0.41 (0.11) and 0.30 (0.06) in groups SL, S, L and W, respectively, (p < 0.001; SL > S > L, W). The mean (SD) elastic moduli in GPa were 75.1 (7.2), 20.0 (1.3), 24.3 (5.2) and 20.2 (2.8) in groups SL, S, L and W, respectively, (p < 0.001; SL > S, L, W). SDF application followed by EYL irradiation on a dentine surface increased its resistance to cariogenic biofilm challenge.

The inhibitory effects of silver diamine fluorides on cysteine cathepsins.

AIM: The expression of cysteine cathepsins in human carious dentine suggests that this enzyme contributes to the collagen degradation in caries progress. This study investigated whether silver diamine fluoride (SDF) inhibited the activity of cysteine cathepsins. METHODS: Three commercial SDF solutions with concentrations at 38%, 30% and 12% were studied. Two fluoride solutions with the same fluoride ion (F(-)) concentrations as the 38% and 12% SDF solutions, and 2 silver solutions with the same silver ion (Ag(+)) concentrations as the 38% and 12% SDF solutions were prepared. Five samples of each experimental solution were used to study their inhibitory effect on two cathepsins (B and K) using cathepsin assay kits. Positive control contained assay buffer and cathepsins dilution was used to calculate the percentage inhibition (difference between the mean readings of the test solution and control solution divided by that of the control group). RESULTS: The percentage inhibition of 38%, 30% and 12% SDF on cathepsin B were 92.0%, 91.5% and 90.3%, respectively (p<0.001); on cathepsin K were 80.6%, 78.5% and 77.9%, respectively (p<0.001). Ag(+) exhibited the inhibitory effect against both cathepsin B and K with or without the presence of F(-) (p<0.01). The solutions containing Ag(+) have significantly higher inhibitory effect than the solutions containing F(-) only (p<0.01). CONCLUSION: According to this study, SDF solution at all 3 tested concentrations significantly inhibited the activity of cathepsin B and K.

A novel oligopeptide simulating dentine matrix protein 1 for biomimetic mineralization of dentine.

OBJECTIVE: The objectives were to design and fabricate an oligopeptide that simulates dentine matrix protein 1 (DMP1) to study its ability to bind to dentine collagen fibrils and induce biomimetic mineralization for the management of dentine hypersensitivity. MATERIALS AND METHODS: A novel oligopeptide was developed by connecting the collagen-binding domain of DMP1 to the hydrophilic C-terminal of amelogenin. Fluorescein isothiocyanate-coupled oligopeptide was applied to the completely demineralized dentine collagen and examined using fluorescent microscopy. The nucleation and growth of hydroxyapatite were initiated by immersing oligopeptide into calcium chloride and sodium hydrogen phosphate solutions. Scanning electron microscopy (SEM), transmission electron microscopy, and selected area electron diffraction (SAED) were used to examine the formation. Dentine slices were acid-etched, coated with oligopeptide, and immersed into a metastable calcium phosphate solution. Dentine mineralization was evaluated by SEM, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). RESULTS: Fluorescent dentine collagen was identified in the specimens. The nucleation and growth of crystals were detected after immersing the oligopeptide into calcium chloride and sodium hydrogen phosphate solutions. Under SEM, crystals were observed covering the oligopeptide-coated dentine surface, within the demineralized dentine collagen matrix and occluding dentinal tubules. SAED, XRD, and FTIR confirmed that the crystals were hydroxyapatite. CONCLUSION: A novel oligopeptide-simulating DMP1 was developed, that can bind to collagen fibrils, initiate mineralization, and induce biomimetic mineralization of dentine. CLINICAL RELEVANCE: Biomimetic mineralization of dentine facilitated by this oligopeptide is a potential therapeutic technique for the management of dentine hypersensitivity.

An ex vivo study of arrested primary teeth caries with silver diamine fluoride therapy.

OBJECTIVES: This ex vivo study compared the physico-chemical structural differences between primary carious teeth biannually treated with silver diamine fluoride (SDF) and carious teeth without such treatment. METHOD: Twelve carious primary upper-central incisors were collected from 6-year-old children. Six teeth had arrested caries after 24-month biannual SDF applications and 6 had active caries when there was no topical fluoride treatment. The mineral density, elemental contents, surface morphology, and crystal characteristics were assessed by micro-computed tomography (micro-CT), energy-dispersive X-ray spectrometry (EDX), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). RESULTS: Micro-CT examination revealed a superficial opaque band approximately 150µm on the arrested cavitated dentinal lesion. This band was limited in the active carious lesion. EDX examination detected a higher intensity of calcium and phosphate of 150µm in the surface zone than in the inner zone, but this zone was restricted in the active cavitated dentinal lesion. SEM examination indicated that the collagens were protected from being exposed in the arrested cavitated dentinal lesion, but were exposed in the active cavitated dentinal lesion. TEM examination suggested that remineralised hydroxyapatites were well aligned in the arrested cavitated dentinal lesion, while those in the active cavitated dentinal lesion indicated a random apatite arrangement. CONCLUSIONS: A highly remineralised zone rich in calcium and phosphate was found on the arrested cavitated dentinal lesion of primary teeth with an SDF application. The collagens were protected from being exposed in the arrested cavitated dentinal lesion. CLINICAL SIGNIFICANCE: Clinical SDF application positively influences dentine remineralisation.

Restoring proximal caries lesions conservatively with tunnel restorations.

The tunnel restoration has been suggested as a conservative alternative to the conventional box preparation for treating proximal caries. The main advantage of tunnel restoration over the conventional box or slot preparation includes being more conservative and increasing tooth integrity and strength by preserving the marginal ridge. However, tunnel restoration is technique-sensitive and can be particularly challenging for inexperienced restorative dentists. Recent advances in technology, such as the contemporary design of dental handpieces with advanced light-emitting diode (LED) and handheld comfort, offer operative dentists better vision, illumination, and maneuverability. The use of magnifying loupes also enhances the visibility of the preparation. The advent of digital radiographic imaging has improved dental imaging and reduced radiation. The new generation of restorative materials has improved mechanical properties. Tunnel restoration can be an option to restore proximal caries if the dentist performs proper case selection and pays attention to the details of the restorative procedures. This paper describes the clinical technique of tunnel restoration and reviews the studies of tunnel restorations.

Biomimetic mineralisation of phosphorylated dentine by CPP-ACP.

OBJECTIVES: Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) has the potential to induce the biomimetic mineralisation of dentine collagen fibrils. This study aimed to demonstrate in vitro the ability of CPP-ACP to form apatite crystals on phosphorylated dentine collagen fibrils. METHODS: Dentine slices with a 2-mm thickness were prepared from sound human third molars. The slices were etched with phosphoric acid to expose the collagen fibres. Sodium trimetaphosphate was then used to phosphorylate the exposed collagen fibres. CPP-ACP paste was topically applied to the surface of the phosphorylated slices, which were then immersed in a metastable calcium phosphate remineralising solution and incubated at 37°C for 10 days. The CPP-ACP paste and the remineralising solution were replaced every two days. Phosphorylated dentine slices without a CPP-ACP application and non-phosphorylated dentine slices with a CPP-ACP application were prepared and used for comparison. The slices were examined using scanning electron microscope (SEM), diffuse reflectance-Fourier transform infrared spectroscopy (DR-FTIR) and X-ray diffraction (XRD). RESULTS: The SEM results revealed the presence of intrafibrillar and interfibrillar crystal nucleation and growth along the phosphorylated dentine collagen fibres. The DR-FTIR and XRD confirmed that the crystals were hydroxyapatite. No apatite crystal nucleation and growth were observed in either the slices that had no non-phosphorylation or those without CPP-ACP application. CONCLUSIONS: CPP-ACP can induce the biomimetic mineralisation of dentine through apatite formation along and between the phosphorylated dentine collagen fibres. CLINICAL SIGNIFICANCE: The in vitro study imitated the application of CPP-ACP to exposed dentine tooth surfaces in the mouth. This could lead to the development of a new therapeutic technique for the treatment of tooth hypersensitivity.

Inhibitory effect of silver diamine fluoride on dentine demineralisation and collagen degradation.

OBJECTIVE: To investigate the inhibitory effects of 38% silver diamine fluoride (SDF) on demineralised dentine. METHODS: Human dentine blocks were demineralised and allocated to four groups: SF, F, S and W. The blocks in group SF received a topical application of 38% SDF solution (253,900ppm Ag, 44,800ppm F), group F received a 10% sodium fluoride solution (44,800ppm F), group S received a 42% silver nitrate solution (253,900ppm Ag) and group W received deionised water (control). They were subjected to pH cycling using demineralisation solution (pH 5) and remineralisation solution (pH 7) for 8 days. The surface morphology, crystal characteristics, lesion depth and collagen matrix degradation of the specimens were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-CT testing and spectrophotometry with a hydroxyproline assay. RESULTS: The surface morphology under SEM showed evident demineralisation with exposed collagen in groups S and W, but not in group SF. Clusters of granular spherical grains were observed in the cross-sections of specimens in groups SF and F. XRD revealed precipitates of silver chloride in groups SF and S. The mean lesion depths (±SD) of groups SF, F, S and W were 182 ± 32µm, 204 ± 26µm, 259 ± 42µm and 265 ± 40µm, respectively (SDF, F

The inhibitory effects of silver diamine fluoride at different concentrations on matrix metalloproteinases.

OBJECTIVE: To study the inhibitory effect of various commercially available concentrations of silver diamine fluoride (SDF) solutions on matrix metalloproteinases (MMPs). METHODS: Three SDF solutions with concentrations at 38%, 30% and 12% were studied. Two sodium fluoride (NaF) solutions at 10% and 3% were prepared, and they had the same fluoride ion concentrations as 38% and 12% SDF, respectively. Two silver nitrate (AgNO(3)) solutions at 42% and 13% were also prepared, and they had the same silver ion concentrations as 38% and 12% SDF, respectively. Ten samples of each experimental solution were used to study their inhibitory effect on three MMPs, which were MMP-2 (gelatinase A), MMP-8 (neutrophil collagenase) and MMP-9 (gelatinase B) using MMP assay kits. Positive control containing assay buffer at pH 9 and MMPs dilution was used to calculate the percentage inhibition. RESULTS: The percentage inhibition of 38%, 30% and 12% SDF on MMP-2 were 79%, 60% and 17%, respectively (p<0.001); on MMP-8 were 94%, 85% and 77%, respectively (p<0.001); on MMP-9 were 82%, 65% and 60%, respectively (p<0.001). The percentage inhibition on MMP-2, MMP-8 and MMP-9 by 38% SDF was significantly higher than the corresponding percentage inhibition by 10% NaF and 42% AgNO(3). SIGNIFICANCE: Greater inhibitory effect on MMPs was found with higher concentration of SDF solution. SDF had more inhibition on MMPs than solutions of NaF and AgNO(3) containing equivalent concentration of fluoride and silver ions, respectively.

Use of fluorides in dental caries management.

Fluoride is commonly and widely used to prevent and even arrest caries. The clinical effects of fluorides depend on the chemical compounds utilized and the methods used to apply the fluoride ion to the surface of the tooth. Fluorosis has been reported in conjunction with increased doses of fluoride. A coordinated approach to fluoride delivery is essential to avoid the risk of fluorosis.