Fluid shifts across human dentine in vitro in response to hydrodynamic stimuli

Dentine surface modification and remineralization induced by bioactive toothpastes

OBJECTIVE

In this study, dentine surface was analysed through Environmental-scanning-electron-microscopy (ESEM) with energy-dispersive-X-ray-spectrometry (EDX) and Fourier-transform-infrared-spectroscopy (FTIR) with attenuated total-reflectance (ATR) to assess the morpho-chemical changes and variations in mineralization degree after demineralizing treatment, after five toothpastes application (HA & Citrate toothpaste, Zinc-HA toothpaste, Calcium Sodium Phosphosilicate toothpaste, Arginine & Calcium carbonate toothpaste, Colgate-Triple-Action, and Control toothpaste), after soaking in artificial saliva and after citric acid attack.

METHODS

Ca/P, Ca/N and P/N ratios were calculated from EDX atomic data to evaluate the mineralization degree of dentine surface. The IR calcium phosphate (CaP)/collagen and carbonate/collagen ratios has been evaluated to assess the remineralization changes in dentine; the carbonate/collagen IR ratio was calculated to identify the nucleation of B-type-carbonated apatite and calcium carbonate.

RESULTS

ESEM-EDX and ATR-FTIR showed residuals of toothpastes after the treatments in all cases, with a general increase in the mineralization degree after soaking in artificial saliva and a decrease after acid attack. Treatment with Arginine & Calcium carbonate toothpaste showed the highest Ca/P value after treatment (Ca/P 1.62) and acid attack (Ca/P 1.5) in confirmation, IR showed the highest amount of carbonate after treatment and soaking in artificial saliva. Arginine and calcium carbonate toothpaste and HA and citrate toothpaste remained to a higher extent on the dentine surface and revealed a higher remineralization activity. These formulations showed higher resistance to demineralization attack, as demonstrated by a higher ICaP/IAmide II intensity ratio than those obtained after EDTA treatment.

CONCLUSIONS

Toothpastes that remained to a higher extent on dentine surface (arginine and calcium carbonate toothpaste in particular) were more able to promote remineralization. The formed calcium phosphate (CaPs) phase was intimately bound to dentine rather than a simple deposit.

Nanoleakage of apical sealing using a calcium silicate-based sealer according to canal drying methods

Objectives

This study investigated the nanoleakage of root canal obturations using calcium silicate-based sealer according to different drying methods.

Materials and Methods

Fifty-two extracted mandibular premolars with a single root canal and straight root were selected for this study. After canal preparation with a nickel-titanium rotary file system, the specimens were randomly divided into 4 groups according to canal drying methods (1: complete drying, 2: blot drying/distilled water, 3: blot drying/NaOCl, 4: aspiration only). The root canals were obturated using a single-cone filling technique with a calcium silicate-based sealer. Nanoleakage was evaluated using a nanoflow device after 24 hours, 1 week, and 1 month. Data were collected twice per second at the nanoscale and measured in nanoliters per second. Data were statistically analyzed using the Kruskal-Wallis and Mann-Whitney U-tests (p < 0.05).

Results

The mean flow rate measured after 24 hours showed the highest value among the time periods in all groups. However, the difference in the flow rate between 1 week and 1 month was not significant. The mean flow rate of the complete drying group was the highest at all time points. After 1 month, the mean flow rate in the blot drying group and the aspiration group was not significantly different.

Conclusions

Within the limitations of this study, the canal drying method had a significant effect on leakage and sealing ability in root canal obturations using a calcium silicate-based sealer. Thus, a proper drying procedure is critical in endodontic treatment.

The anatomy, neurophysiology, and cellular mechanisms of intradental sensation

Somatosensory innervation of the oral cavity enables the detection of a range of environmental stimuli including minute and noxious mechanical forces. The trigeminal sensory neurons underlie sensation originating from the tooth. Prior work has provided important physiological and molecular characterization of dental pulp sensory innervation. Clinical dental experiences have informed our conception of the consequence of activating these neurons. However, the biological role of sensory innervation within the tooth is yet to be defined. Recent transcriptomic data, combined with mouse genetic tools, have the capacity to provide important cell-type resolution for the physiological and behavioral function of pulp-innervating sensory neurons. Importantly, these tools can be applied to determine the neuronal origin of acute dental pain that coincides with tooth damage as well as pain stemming from tissue inflammation (i.e., pulpitis) toward developing treatment strategies aimed at relieving these distinct forms of pain.

ISP Good Clinical Practice Recommendations for the management of Dentin Hypersensitivity

Dentin hypersensitivity (DH) is a rising concern in clinical dentistry that causes pain and discomfort and negatively affects the quality of life of patients. Indian Society of Periodontology conducted a nationwide survey, involving 3000 dentists in December 2020, which revealed significant knowledge gaps regarding DH, viz., under-diagnosis, incorrect differential diagnosis, and treatment strategies/recommendations for the management of DH patients in daily clinical practice. The current paper has been envisioned and conceptualized to update the practicing Indian dentists regarding the so-called enigma of dentistry "Dentin Hypersensitivity," based on the best available contemporary evidence. An expert panel was constituted comprising 30 subject experts from across the country, which after extensive literature review and group discussions formulated these recommendations. The panel advocated routine screening of all dentate patients for exposed dentin areas and DH to avoid under-diagnosis of the condition and suggested an early preventive management. Consensus guidelines/recommendations for the use of desensitizing agents (DAs) at home, including the use of herbal agents, are also provided within the backdrop of the Indian context. The guidelines recommend that active management of DH shall be accomplished by a combination of at home and in-office therapies, starting with the simplest and cost-effective home use of desensitizing toothpastes. A diagnostic decision tree and a flowchart for application in daily practice are designed to manage the patients suffering from DH or presenting with exposed dentin areas in dentition. Various treatment methods to manage DH have been discussed in the paper, including the insights from previously published treatment guidelines. Further, a novel system of classification of DH patients based on specific case definitions has been developed for the first time. Explicit charts regarding the available treatment options and the chronology of institution of the agent, for the management in different case categories of DH, have been provided for quick reference. The management strategy takes into account a decision algorithm based on hierarchy of complexity of treatment options and intends to improve the quality of life of the patient by long-term maintenance with an innovatively defined triple C's or 3Cs approach.

Experimental pastes containing niobophosphate and 45S5 bioactive glasses for treatment of dentin hypersensitivity: dentin permeability and tubule obliteration

OBJECTIVES

This study tested the ability of bioactive pastes containing niobophosphate and 45S5 glasses to reduce dentin permeability and to obliterate dentinal tubules, as a mean of reducing human dentin hypersensitivity.

MATERIALS AND METHODS

Experimental pastes with concentrations of 10, 20, and 30 wt% of two bioactive glasses (45S5 or niobophosphate [NbG]) were formulated. A paste without bioactive glass (placebo) and a commercial paste (Nano P, FGM) were used as controls. Forty dentin disc specimens were obtained from caries-free extracted third human molars and divided in 8 groups (n = 5). Percentage of permeability (%Lp) was assessed in a dental permeability machine considering hydraulic conductance, immediately after pastes application and at day 7, day 14, and day 21. The precipitates formed on the surface of the dentin discs (and dentinal tubules) were analyzed by SEM/EDS and micro-Raman spectra. Data of dentin permeability (%) 2-way repeated-measures (ANOVA) and Holm-Sidak post-tests (α = 0.05). Dentinal tubule obliteration was visually (and elemental) evaluated and descriptively reported.

RESULTS

The experimental bioactive glass pastes containing NbG and 45S5, regardless of the concentration, reduced dentin permeability in comparison with pastes without bioactive glasses (P < 0.05). The formulated placebo and commercial paste did not reduce permeability over time (P < 0.05). SEM/EDS and micro-Raman analyses showed that both type of bioactive pastes (NbG or 45S5-based) presented mineral precipitates obliterating the dentinal tubules at day 21. NbG seems to offer a better initial effect than 45S5, while at 21 days there is no difference between both glasses.

CONCLUSION

Experimental bioactive pastes containing NbG and 45S5 (at concentrations of 10%, 20%, or 30%) have potential to reduce dentin permeability (over time) in comparison with pastes without bioactive glasses; and this occurs on behalf of obliteration of dentinal tubules by microparticle and precipitate formation.

CLINICAL RELEVANCE

Bioactive pastes containing NbG and 45S5 may benefit patients presenting dentin hypersensitivity, because these pastes can start acting fast after application and maintain their action up to 21 days.

Bioactive glass versus Arginine dentifrices on the reduction of dentin permeability and acid tolerance

Objectives

To compare the efficacy of calcium sodium phosphosilicate (CSPS) and arginine dentifrices on dentin permeability and acid tolerance.

Material and Methods

Sixty dentin discs were randomly assigned into 3 groups, then brushed for 1 min with CSPS, arginine, or fluoride (control) dentifrices. To test acid tolerance, each disc was soaked in 6% citric acid for 1 min. Dentin permeability was measured before, following brushing, and acid challenge. Ten discs per group were similarly treated and evaluated for tubule occlusion following a single dentifrice application, while other five discs per group were employed in an acid tolerance assay.

Results

The percentage reduction in dentin permeability was 39.26%, 32.27%, and 21.71% in the arginine, CSPS, and control groups, respectively. The differences in dentin permeability reduction between the arginine and CSPS groups following brushing and acid challenge were not significant (p = 0.398 and p = 0.211, respectively). The arginine dentifrice demonstrated a significant reduction in permeability compared with the control (p = 0.011). In addition, the occlusion exhibited by the arginine and CSPS dentifrices was more resistant to acid challenge compared with that of the control (p < 0.001). From SEM analysis, dentinal tubule occlusion was observed after a single application in all groups. Some open dentinal tubules were detected in the test groups, while almost all of the orifices were open in the fluoride group following acid challenge.

Conclusions

There is no significant difference between arginine and CSPS dentifrices in reducing dentin permeability following a single application and acid challenge. Following acid challenge, the reduced permeability generated by arginine and CSPS was more stable compared with the fluoride dentifrice.

Effect of tooth-brushing with a microcurrent on dentinal tubule occlusion

The purpose of this study was to investigate whether tooth-brushing with a microcurrent was effective in inducing dentinal tubule occlusion. The specific aims of the study were (1) to evaluate the effectiveness of tooth-brushing with a microcurrent on dentinal tubule occlusion by using scanning electron microscopy (SEM); and (2) to compare the dentinal fluid flow rate after tooth-brushing with a microcurrent by using a sub-nanoliter-scaled fluid flow measuring device (NFMD). All experimental groups showed partially occluded dentinal tubules and crystal-like structures at a specific microcurrent intensity indicated that tooth-brushing with a microcurrent could efficiently occlude dentinal tubules. The decrease in dentinal fluid flow rate in the tooth-brushing with microcurrents group indicated that dentinal tubules were occluded and the flow of dentinal fluid had decreased.

Laboratory evaluation of dentin tubule occlusion after use of dentifrices containing stannous fluoride

The purpose of this study was to examine the effect of desensitizing dentifrices containing stannous fluoride (SnF₂) on dentinal tubule occlusion. Two experimental dentifrices with the same ingredients but different SnF₂ concentrations (Group II, 0.4% w/w; Group III, 0.454% w/w) were used; distilled water was used in the control group (Group I). Third molars were collected from Japanese and American dental patients. The crowns were removed and sectioned to obtain dentin discs, which were further cut into quarters. Thirty-six specimens each from Japanese and American patients were divided into three sets (n = 12 each) and assigned to each of the three treatment groups. The specimens were brushed for 10 s twice per day for 4 days. After treatment, the discs were observed by scanning electron microscopy, and the extent of dentinal tubule occlusion in the images was expressed on a five-point categorical scale. Group II and III specimens from Japanese and American patients showed greater dentinal tube occlusion than those from Group I, but the differences were not statistically significant. The present results suggest that both SnF₂ concentrations mitigate dentin hypersensitivity, regardless of patient ethnicity.

Effect of a Self-Etch Adhesive Containing Nanobioglass on Postoperative Sensitivity of Posterior Composite Restorations - A Randomized Trial

BACKGROUND

Postoperative sensitivity is one of the major problems regarding posterior resin composite restorations that causes patient discomfort, maybe a reason for replacement of the restoration with an additional office time.

AIM

To evaluate the effect of the addition of a Nanobioglass to a self-etch adhesive on the reduction of post-operative sensitivity following composite restorations versus a self-etch adhesive that is free of Nanobioglass agent.

MATERIALS AND METHODS

Sixteen patients having class II carious lesions were included in the study. After cavity preparation, each tooth was randomised to one of the following restorative treatments. Teeth in the control group were restored using self-etch adhesive (OptiBond All-In-One, Kerr) that is free of nanobioglass agent, and nano-hybrid resin composite (Herculite Ultra, Kerr). Restoration of teeth in the experimental group was similar to the control except that a nanobioglass agent was added to the self-etch adhesive. Patients were contacted for evaluation of postoperative sensitivity at 1 day, 1 week, 1 month, and 3 months. Data were analyzed using friedmann test followed by fisher exact test.

RESULTS

The experimental group (self-etch adhesive containing nanobioglass) showed a significantly less postoperative sensitivity compared with the control group (Self-etch adhesive free of nanobioglass) at 1 day, and 1-week evaluation periods. While both groups did not possess any significant difference at 1 month, and 3 months periods.

CONCLUSION

The problem of postoperative sensitivity following resin composite restorations could be solved by the addition of bioglass nanoparticles into dental adhesives.

The Effectiveness of Remineralizing Agents on Dentinal Permeability

The effectiveness of remineralizing agents in reducing dentine permeability by tubule occlusion using fluid filtration device functioning at 100 cmH₂O (1.4 psi) pressure and SEM/EDX analysis were evaluated and compared. Seventy (n = 70) dentine discs of 1±0.2 mm width were prepared from sound permanent human molars. Fifty (n = 50) dentine discs were randomly divided into 5 groups (n = 10): Group 1: GC Tooth Mousse Plus (Recaldent GC Corporation Tokyo, Japan), Group 2: Clinpro™ White Varnish (3M ESPE, USA), Group 3: Duraphat® Varnish (Pharbil Waltrop GmbH, Germany), Group 4: Colgate Sensitive Pro-Relief™ dentifrice (Colgate Palmolive, Thailand), and Group 5: Biodentine™ (Septodont/UK). Dentine permeability was measured after treatment application at 10 minutes, artificial saliva immersion at 7 days, and citric acid challenge for 3 minutes. Data were analyzed by two-way repeated measures ANOVA. Dentine specimens (n = 20) were used for SEM/EDX analyses to obtain qualitative results on dentine morphology and surface deposits. Each treatment agent significantly reduced dentine permeability immediately after treatment application and created precipitates on treated dentine surfaces. All agents increased permeability values after 7 days of artificial saliva immersion except Clinpro White Varnish and Biodentine. Clinpro White Varnish exhibited significant resistance to acid challenge compared to others. Colgate Sensitive Pro-Relief dentifrice has a dual mechanism of action in reducing the dentine sensitivity.

TRPM7 Mediates Mechanosensitivity in Adult Rat Odontoblasts

Odontoblasts, with their strategic arrangement along the outermost compartment of the dentin-pulp complex, have been suggested to have sensory function. In addition to their primary role in dentin formation, growing evidence shows that odontoblasts are capable of sensing mechanical stimulation. Previously, we found that most odontoblasts express TRPM7, the nonselective mechanosensitive ion channel reported to be critical in Mg²⁺ homeostasis and dentin mineralization. In line with this finding, we sought to elucidate the functional expression of TRPM7 in odontoblasts by pharmacological approaches and mechanical stimulation. Naltriben, a TRPM7-specific agonist, induced calcium transient in the majority of odontoblasts, which was blocked by TRPM7 blockers such as extracellular Mg²⁺ and FTY720 in a dose-dependent manner. Mechanical stretch of the odontoblastic membrane with hypotonic solution also induced calcium transient, which was blocked by Gd³⁺, a nonselective mechanosensitive channel blocker. Calcium transient induced by hypotonic solution was also blocked by high extracellular Mg²⁺ or FTY720. When TRPM7-mediated calcium transients in odontoblasts were analyzed on the subcellular level, remarkably larger transients were detected in the distal odontoblastic process compared with the soma, which was further verified with comparable immunocytochemical analysis. Our results demonstrate that TRPM7 in odontoblasts can serve as a mechanical sensor, with its distribution to facilitate intracellular Ca²⁺ signaling in the odontoblastic process. These findings suggest TRPM7 as a mechanical transducer in odontoblasts to mediate intracellular calcium dynamics under diverse pathophysiological conditions of the dentin.

Development of Epigallocatechin-3-gallate-Encapsulated Nanohydroxyapatite/Mesoporous Silica for Therapeutic Management of Dentin Surface

In dental clinic, unsatisfactory management of the dentin surface after dentin exposure often leads to the occurrence of dentin hypersensitivity and caries. Current approaches can occlude the tubules on the dentin surface to relieve dentin hypersensitivity; however, the blocked tubules are generally weak in combating daily tooth erosion and abrasion. Moreover, cariogenic bacteria, such as Streptococcus mutans, produce biofilm on the dentin surface, causing caries and compromising the tubules' sealing efficacy. To overcome this problem, the present study focused on establishing a versatile biomaterial, epigallocatechin-3-gallate-encapsulated nanohydroxyapatite/mesoporous silica nanoparticle (EGCG@nHAp@MSN), for therapeutic management of the dentin surface. The effectiveness of the biomaterial on dentinal tubule occlusion, including resistances against acid and abrasion, was evaluated by field-emission scanning electron microscopy (FESEM) and dentin permeability measurement. The inhibitory capability of the biomaterial on S. mutans biofilm formation was investigated by confocal laser scanning microscopy (CLSM), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, colony forming units (CFU) counts, and FESEM. Results demonstrated for the first time that the use of EGCG@nHAp@MSN on the dentin surface was capable of effectively occluding dentinal tubules, reducing dentin permeability, and achieving favorable acid- and abrasion-resistant stability. Furthermore, EGCG@nHAp@MSN held the capability to continuously release EGCG, Ca, and P, and significantly inhibit the formation and growth of S. mutans biofilm on the dentin surface. Thus, the development of EGCG@nHAp@MSN bridges the gap between multifunctional concept and dental clinical practice and is promising in providing dentists a therapeutic strategy for the management of the dentin surface to counter dentin hypersensitivity and caries.

In vivo analyses of the effects of polyamidoamine dendrimer on dentin biomineralization and dentinal tubules occlusion

This study evaluated the biomineralization and dentinal tubules occlusion abilities of the carboxyl-terminated polyamidoamine dendrimer (PAMAM-COOH) on human demineralized dentin in vivo at different time points. Demineralization dentin model with and without treated with PAMAM-COOH were sutured to the interior side of the rat's cheeks, that was incubated in the rats' saliva for 2, 4 and 6 weeks respectively. Finally, the newly formed precipitates were characterized by SEM, EDS, XRD and microhardness test. The hydroxyapatite (HA) on the dentin treated with PAMAM-COOH were formed gradually with the time going by, and the regenerated HA has a similar crystal structure with natural dentin, whereas the crystallites did not exist on the control group. The microhardness of PAMAM-COOH-applied specimens had a significantly higher than those without application. These results suggest that the PAMAM-COOH promoted the biomineralization of demineralized dentin and displayed favourable effects on blocking the open dentinal tubules.

A mesoporous silica biomaterial for dental biomimetic crystallization

The loss of overlying enamel or cementum exposes dentinal tubules and increases the risk of several dental diseases, such as dentin hypersensitivity (causing sharp pain and anxiety), caries, and pulp inflammation. This paper presents a fast-reacting, more reliable and biocompatible biomaterial that effectively occludes exposed dentinal tubules by forming a biomimetic crystalline dentin barrier. To generate this biomaterial, a gelatin-templated mesoporous silica biomaterial (CaCO3@mesoporous silica, CCMS) containing nanosized calcium carbonate particles is mixed with 30% H3PO4 at a 1/1 molar ratio of Ca/P (denoted as CCMS-HP), which enables Ca2+ and PO4(3-)/HPO4(2-) ions to permeate the dentinal tubules and form dicalcium phosphate dihydrate (DCPD), tricalcium phosphate (TCP) or hydroxyapatite (HAp) crystals at a depth of approximately 40 μm (sub-μ-CT and nano-SEM/EDS examinations). In vitro biocompatibility tests (WST-1 and lactate dehydrogenase) and ALP assays show high cell viability and mineralization ability in a transwell dentin disc model treated with CCMS-HP (p<0.05). The in vivo efficacy and biocompatibility analyses of the biomaterial in an animal model reveal significant crystal growth (DCPD, TCP or HAp-like) and no pulp irritation after 70 days (p<0.05). The developed CCMS-HP holds great promise for treating exposed dentin by growing biomimetic crystals within dentinal tubules. These findings demonstrate that the mesoporous silica biomaterials presented here have great potential for serving as both a catalyst and carrier in the repair or regeneration of dental hard tissue.

Influence of casein phosphopeptide-amorphous calcium phosphate application, smear layer removal, and storage time on resin-dentin bonding

The aim of this study is to evaluate the influence of Tooth Mousse (TM) application, smear layer removal, and storage time on resin-dentin microtensile bond strength (µTBS). Dentin specimens were divided into two groups: (1) smear layer covered; (2) smear layer removed using 15% EDTA for 90 s. In each group, half the specimens were treated once with TM for 60 min. After bonding procedures using a two-step self-etching adhesive (Clearfil SE Bond (CSE); Kuraray Medical, Tokyo, Japan), an all-in-one adhesive (G-Bond (GB); GC Corp, Tokyo, Japan), and a total-etch adhesive (Adper Single Bond 2 (SB); 3M ESPE, St. Paul, MN, USA), the specimens were stored for 3 d or 6 months in deionized water at 37 °C, and µTBS was tested and analyzed. With the exception of SB (no TM application) and GB, the μTBS was significantly increased for CSE and SB using EDTA pre-conditioning and 3 d of storage (P≤0.001). Bond strength of GB decreased significantly when using EDTA (3 d storage, P<0.05). TM application only increased the μTBS of GB (no EDTA) and SB (with EDTA) after 3 d (P≤0.02). Comparing the adhesives after 3 d of storage, CSE exhibited the greatest μTBS values followed by GB and SB (P≤0.02). The factors of adhesive, EDTA, and TM did not show any significant impact on μTBS when specimens were stored for 6 months (P>0.05). The additional application of TM and EDTA for cavity preparation seems only to have a short-term effect, and no influence on µTBS of dentin bonds after a period of 6 months.

Effect of different surface-cleaning techniques on the bond strength of composite resin restorations

STATEMENT OF PROBLEM

Different techniques have been suggested for cleaning dentin surfaces after the removal of an interim prosthesis and before the application of a bonding agent. How different surface-cleaning techniques affect the bond strength of the composite resin restorations is not clear.

PURPOSE

The purpose of this study was to investigate the effects of different surface-cleaning techniques on the bond strength of composite resin restorations and the surface topography of the prepared tooth surfaces.

MATERIAL AND METHODS

The occlusal surfaces of 25 molars were ground until the dentin was exposed. A bonding agent and interim cement were applied on the teeth. The teeth were divided into 5 groups (n=5) according to the method used for surface-cleaning (microairborne-particle abrasion, alcohol, rubber-rotary instrument, desiccating agent, and control). Once the surfaces of the teeth had been cleaned, the same bonding material was applied to the teeth. A 5-mm-thick composite resin layer was built up. Each specimen was sectioned to microbars, and 6 centrally located beams were selected for microtensile testing (n=30) (1.10 ±0.10 mm). The data were statistically analyzed with 1-way ANOVA (1-sample Kolmogorov-Smirnov test). The Bonferroni test was used for significantly different groups (α=.05). One specimen from each group was observed under a scanning electron microscope and an atomic force microscope. Energy dispersive x-ray analysis also was performed.

RESULTS

Bond strength values were in the following descending order: microairborne-particle abrasion, desiccating agent, alcohol, rubber-rotary instrument, control. Differences between the microairborne-particle abrasion group and the remainder of the groups, desiccating agent--rubber-rotary instrument, desiccating agent-control, alcohol--rubber-rotary instrument, and alcohol-control groups, were statistically significant (P<.05). The microairborne-particle abrasion group displayed the roughest surface and a different surface topography from the remainder of the groups. Increased aluminum was observed in the microairborne-particle abrasion group.

CONCLUSIONS

Surface-cleaning techniques, except for the rubber-rotary instrument, increased the bond strength of composite resin. The roughest dentin surfaces and highest bond strength were achieved with the microairborne-particle abrasion technique.

Evaluation of a calcium phosphate desensitizer using an ultrasonic device

This study evaluated the effect of a calcium phosphate desensitizer on the demineralization of bovine dentin by measuring changes in transmitted ultrasonic velocity. Bovine dentin specimens with and without application of desensitizer were immersed in 0.1 M lactic-acid buffer solution (pH 4.75) 10 min twice daily throughout the test period, and stored in artificial saliva solution (pH 7.0) between treatments. The propagation time of longitudinal ultrasonic waves was measured by a pulser-receiver. Data were evaluated using one-way ANOVA followed by Tukey HSD test (α=0.05). The ultrasonic velocity decreased over time in specimens stored in demineralizing solution (3,785-3,462 m/s); however, desensitizer-applied specimens had a significantly higher sonic velocity (3,945-3,990 m/s) than those without application. The calcium phosphate desensitizer appeared to reduce the demineralization of dentin and occluded dentinal tubules.

Development and validation of an in vitro model for measurements of cervical root dentine permeability

Objectives

The aim of this series of studies was the development and validation of a new model for evaluation of dentinal hypersensitivity (DH) therapies.

Materials and methods

Roots from extracted human teeth were sealed with a flowable composite. In the cervical area, a 3-mm-wide circular window was ground through the seal 1 mm deep into dentine. The pulp lumen was connected to a reservoir of artificial dentinal fluid (ADF) containing protein, mineral salts and methylene blue. At increased pulpal pressure, the ADF released through the said window was collected in containers each with 20 ml of physiologic saline for a consecutive series of 30-min intervals and ADF concentration (absorption) was determined photometrically. The model was verified by three experiments. In experiment 1, the lower limit of quantification (LLoQ, coefficient of variation = 20 % and difference of 5 standard deviations (SD) from blank) of ADF in physiologic saline was determined by measuring the absorption of 15 dilutions of ADF in physiologic saline (containing 0.625 ng to 12.5 μg methylene blue/ml) photometrically for ten times. In experiment 2, long-term linearity of ADF perfusion/outflow was investigated using 11 specimens. The ADF released through the window was collected in the said containers separately for each consecutive interval of 30 min for up to 240 min. Absorption was determined and analysed by linear regression over time. In experiment 3, perfusion before (2×) and after single treatment according to the following three groups was measured: BisGMA-based sealant (Seal&Protect®), an acidic fluoride solution (elmex fluid®) and control (no treatment).

Results

In experiment 1, the LLoQ was 0.005 μg methylene blue/ml. In experiment 2, permeability was different within the specimens and decreased highly linearly with time, allowing the prediction of future values. In experiment 3, Seal&Protect® completely occluded dentinal tubules. elmex fluid® increased tubular permeability by about 30 % compared to control.

Conclusions

A model comprising the use of artificial dentinal fluid was developed and validated allowing screening of therapeutic agents for the treatment of DH through reliable measurement of permeability of cervical root dentine.

Clinical relevance

The described in vitro model allows evaluation of potential agents for the treatment of DH at the clinically relevant cervical region of human teeth.

Laboratory validation of a new gas-enhanced dentine liquid permeation evaluation system

AIM

To validate a new automated dentine permeability testing platform based on pressure change measurements.

METHODOLOGY

A split chamber was designed allowing for concomitant measurement of fluid permeation and pressure difference. In a first test, system reliability was assessed by interposing a solid metal disk, embedded composite resin disks, or teeth by consecutively measuring eight times under standardized conditions. Secondly, the repeatability and applicability of the method was tested in a dentine wound model by using intact third molars: Class I (2 × 5 mm) and a full occlusal preparation as well a ceramic restoration were consecutively performed and repeatedly measured eight times each. In the last test, the system detection limit as well correlation between gas pressure difference and liquid permeation were evaluated: Again, third molars were used and occlusal preparations of increasing size (2 × 5, 3 × 5, 4 × 5, and 5 × 5 mm and full occlusal preparations, respectively) were made. Data was analyzed for the linearity of measurement, and R (2) values were calculated.

RESULTS

The embedding procedure allowed for perfect separation of the two chambers, and no significant variation in repeated measurements of evaluated samples for the respective treatments (p = 0.05) was found. The detection was 0.002 hPa/min for the pressure slope and 0.0225 μl/min for the fluid infiltration, respectively. The saline volume was highly correlating to the gas pressure changes (R (2) = 0.996, p < 0.0001).

CONCLUSIONS

The presented method is a reliable and exact tool to assess dentine permeability by nondestructive and repeatable measurements.

CLINICAL RELEVANCE

This method is suitable for measurements and comparison of the effectiveness of dentine wounds sealing materials.

Short-term response of three resin-based materials as desensitizing agents under oral environmental exposure

OBJECTIVE

This paper focuses on clinical responses after 7 days of oral exposure to two resin-based materials as desensitizing agents compared to a fluoride varnish and on morphological and analytical study as a means to elucidate the mechanism of action.

MATERIALS AND METHODS

The elemental composition of Vertise™ Flow (VF), Universal Dentine Sealant (UDS) and Flor-Opal® Varnish (FOV) were investigated by using an X-ray energy dispersive spectrometer (EDX) in conjunction with a scanning electron microscope (SEM). SEM morphology of the material-treated dentine surfaces and pain reduction ability according to the Visual Analogue Scale (VAS) were evaluated in selected hypersensitive teeth. Post treatments and 7 day controls were recorded with SEM and VAS measurements. Clinical data was analysed with the Student's t-test for paired data, with a 5% significance level.

RESULTS

Silicon, ytterbium and alumina were the most present elements in VF, whilst calcium, chloride, silicon and alumina were highest in UDS. Within a 7 day oral environment all the tested materials modified the treated-dentine surfaces showing tubular occlusion of different morphology. Clinically, the efficacy of all materials was similar after a 7-day examination. However, VAS scores were significantly reduced if compared with the baseline (p < 0.05).

CONCLUSIONS

Within the limits of this study, data indicate that both resins are effective in sealing tubules and reducing VAS. A resin-related effect on the dentine's morphology was observed, which may influence the long-term response of the resins in the treatment of dental hypersensitivity, which requires further investigation.

Evaluation of dentinal fluid flow behaviours: a fluid-structure interaction simulation

This study uses the fluid-structure interaction (FSI) method to investigate the fluid flow in dental pulp. First, the FSI method is used for the biomechanical simulation of dental intrapulpal responses during force loading (50, 100 and 150 N) on a tooth. The results are validated by comparison with experimental outcomes. Second, the FSI method is used to investigate an intact tooth subjected to a mechanical stimulus during loading at various loading rates. Force loading (0-100 N) is applied gradually to an intact tooth surface with loading rates of 125, 62.5, 25 and 12.5 N/s, respectively, and the fluid flow changes in the pulp are evaluated. FSI analysis is found to be suitable for examining intrapulpal biomechanics. An external force applied to a tooth with a low loading rate leads to a low fluid flow velocity in the pulp chamber, thus avoiding tooth pain.

Effect of Er,Cr:YSGG laser on human dentin fluid flow

The aim of the current investigation was to assess the rate and magnitude of dentin fluid flow of dentinal surfaces irradiated with Er,Cr:YSGG laser. Twenty extracted third molars were sectioned, mounted, and irradiated with Er,Cr:YSGG laser at 3.5 and 4.5 W power settings. Specimens were connected to an automated fluid flow measurement apparatus (Flodec). The rate, magnitude, and direction of dentin fluid flow were recorded at baseline and after irradiation. Nonparametric Wilcoxon signed ranks repeated measure t test revealed a statistically significant reduction in fluid flow for all the power settings. The 4.5-W power output reduced the flow significantly more than the 3.5 W. The samples showed a baseline outward flow followed by inward flow due to irradiation then followed by decreased outward flow. It was concluded that Er,Cr:YSGG laser irradiation at 3.5 and 4.5 W significantly reduced dentinal fluid flow rate. The reduction was directly proportional to power output.

Effects of common dental materials used in preventive or operative dentistry on dentin permeability and remineralization

The aim of this study was to evaluate the dentin remineralization induced by bioactive substances contained in common dental materials used in preventive and operative dentistry. Several materials were applied on human dentin segments. Dentin permeability was quantified using a fluid filtration system working at 20 cm H(2)O. Micro-Raman, SEM-EDX, and microhardness calculation were used to evaluate changes in the mineralization of dentin. Dentin treated with the prophylactic materials showed different dentin permeability values, in particular subsequent to immersion in remineralizing solutions (RSS). The bioactive glass (Sylc) was the only substance able to reduce dentin permeability after immersion in remineralizing solution and to show hydroxyapatite precipitation as a sign of dentin remineralization. The reduction in dentin permeability obtained after the application of the other prophylactic materials used in this study was due to the presence of the remnant material in the dentinal tubules, with no remineralization effect after storage in remineralizing solution. In conclusion, the results indicated that bioactive glass prophy powder may induce immediate remineralization of dentin.

Effect of a new desensitizing material on human dentin permeability

OBJECTIVES

Resin-modified glass ionomers (RMGI) have demonstrated clinical success providing immediate and long-term relief from root sensitivity. RMGIs have been recently introduced as paste-liquid systems for convenience of clinical usage. The objective of this study was to measure the ability of a new paste-liquid RMGI to reduce fluid flow through human dentin, compared to an established single-bottle nanofilled total etch resin adhesive indicated for root desensitization.

METHODS

Dentin permeability was measured on human crown sections on etched dentin, presenting a model for the exposed tubules typical of root sensitivity, and permitting measurement of the maximum permeability. In the first two groups, the etched dentin was coated with either the RMGI or adhesive, and permeability measured on the coated dentin. In a third group, a smear layer was created on the dentin with sandpaper, then the specimens were coated with the RMGI; permeability was measured on the smeared and coated dentin. Specimens from each group were sectioned and examined via scanning electron microscopy (SEM).

RESULTS

Both the resin adhesive and the new paste-liquid RMGI protective material significantly reduced fluid flow through dentin, and exhibited excellent seal on dentin with either open tubules or smear-layer occluded tubules. The RMGI infiltrated the smear layer with resin during placement, penetrated dentin tubules, and formed resin tags.

SIGNIFICANCE

The RMGI was equivalent to the adhesive in its ability to reduce fluid flow and seal dentin. It is therefore concluded that the new RMGI and the adhesive show the potential to offer excellent sensitivity relief on exposed root dentin.

Effect of desensitising toothpastes on dentinal tubule occlusion: a dentine permeability measurement and SEM in vitro study

OBJECTIVES

The purpose of this study was to evaluate the in vitro effectiveness of a new bioglass-containing and two commercial desensitising toothpastes on dentinal tubule occlusion after citric acid challenge or artificial saliva (AS) immersion.

METHODS

One hundred dentin discs from human third molars were used. Specimens were randomly divided into five groups (n=20), Group 1: EDTA-treated dentin; Group 2: brushing with distilled water; Group 3: brushing with Novamin; Group 4: brushing with Sensodyne Freshmint; Group 5: brushing with Colgate Sensitive. In each group, samples were then equally split into two subgroups (n=10) to test two post-treatments: 6% citric acid challenge or 24h immersion in artificial saliva. Dentine permeability of each specimen was measured before and after each treatment using a hydrostatic device working at 20cm H(2)O pressure. Data were analysed by two-way repeated measures ANOVA to determine if there were any significant differences within or between groups. Dentine morphology and surface deposits were observed by SEM.

RESULTS

All three desensitising toothpastes significantly reduced dentine permeability and created precipitates on the treated dentine surfaces. Moreover, the reductions in dentine permeability showed partial recovery after a citric acid and artificial saliva immersion. Sensodyne showed significant resistant to acid attack and Novamin exhibited the lowest permeability after artificial saliva immersion for 24h.

CONCLUSIONS

The application of the three toothpastes resulted in effective dentinal tubule occlusion. However, the new bioglass-containing toothpaste (Novamin) represented excellent occlusion effects after brushing treatment and AS immersion, while Sensodyne demonstrated more reduction in permeability when citric acid challenged.

Real-time measurement of dentinal fluid flow during amalgam and composite restoration

OBJECTIVES

This study examined changes in the dentinal fluid flow (DFF) during restorative procedures and compared permeability after restoration among restorative materials and adhesives.

METHODS

A class 1 cavity was prepared and restored with either amalgam (Bestaloy), or composite (Z-250) with one of two etch-and-rinse adhesives (Scotchbond MultiPurpose: MP and Single Bond 2: SB) or one of two self-etch adhesives (Clearfil SE Bond: CE and Easy Bond: EB) on an extracted human third molar which was connected to a sub-nanoliter fluid flow measuring device (NFMD) under 20 cm water pressure. DFF was measured from the intact tooth state through the restoration procedures to 30 min after restoration, and re-measured at 3 and 7 days post-restoration.

RESULTS

Inward flow during cavity preparation was followed by outward flow after preparation. In amalgam restoration, the outward flow changed into an inward flow during amalgam filling, which was followed by a slight outward flow after finishing. In composite restoration, MP and SB showed an inward flow and outward flow for the rinsing and drying steps, respectively. Application of a hydrophobic bonding resin in the MP and CE systems caused a decrease in the flow rate. Air-drying of solvent for the CE and EB systems caused a sudden outward flow, whereas light-curing of the adhesive and composite caused an abrupt inward flow.

CONCLUSIONS

Each restorative step clearly changed the direction and the rate of the DFF during restoration, which could be well identified with NFMD.

Effect of a new liner/base on human dentin permeability

OBJECTIVES

Resin-modified glass ionomers (RMGI) have demonstrated clinical success in their ability to minimize post-operative sensitivity of restorations. RMGIs have been recently introduced as paste-liquid systems for convenience of clinical usage. The objective of this study was to measure the ability of a new paste-liquid RMGI liner/base to reduce fluid flow through human dentin.

METHODS

Dentin permeability was measured on human crown sections on etched dentin, using etched dentin as a model for the exposed tubules typical of root sensitivity, and permitting measurement of the maximum permeability. In the one group, the etched dentin was coated with the RMGI, and pre- and post-treatment permeability was measured on the coated dentin. In the second group, a smear layer was created on the dentin with sandpaper, then the samples were coated with the RMGI; permeability was measured on the smeared and coated dentin. Samples from each group were sectioned and examined via scanning electron microscopy (SEM).

RESULTS

The new paste-liquid RMGI liner/base significantly reduced fluid flow through dentin, and exhibited excellent seal on dentin with either a smear layer or open tubules. SEM images show evidence that the RMGI infiltrated the smear layer with resin during placement, penetrated dentin tubules, and formed resin tags in acid-etched dentin.

CONCLUSIONS

Based on these results, combined with previous research on adhesion and microleakage, it is concluded that the new RMGI liner/base should minimize post-operative sensitivity in restorations.

Fluoropolymers as low-surface-energy tooth coatings for oral care

A range of low-surface-energy fluoropolymers has been synthesised and their effectiveness as dental-care coatings for plaque, stain and erosion prevention has been evaluated using a series of oral care models employing pressed discs of calcium hydroxyapatite or sections of human teeth. Since the blocking of dentinal tubules is a key mechanistic strategy in the treatment of dentine hypersensitivity, the capability of these non-permanent fluoropolymer coatings to occlude the pore structure of human dentine and to reduce the outward flow of simulated dentinal fluid has also been investigated. Several of the fluoropolymer coatings have been found to inhibit bacterial adhesion but no correlation has been established between anti-adhesion efficacy and fluorine content or surface energy. All the fluoropolymers have been seen to reduce stain uptake by pellicle-coated HA discs, with homopolymers being considerably more effective than copolymers. Some fluoropolymer coatings have also been shown to inhibit the acid demineralisation of hydroxyapatite discs and to reduce dentine permeability. Coatings of the 2:1 copolymer of 1H,1H,2H,2H-perfluorodecyl acrylate and 2-hydroxyethyl acrylate are most promising, exhibiting significant anti-adhesion and anti-erosion efficacy and reducing dentine permeability to a level that is comparable with that achieved with the standard treatment employed in commercial anti-sensitivity formulations.

Thermal stimulation causes tooth deformation: a possible alternative to the hydrodynamic theory?

OBJECTIVES

To investigate the relationship between temperature distribution and tooth structure deformation during and after localised application of thermal stimuli used during pulp vitality testing.

METHODS

Strains and temperature changes within tooth structures were recorded when three different thermal stimuli, namely heated gutta percha (120-140 degrees C), carbon dioxide dry ice (-72 degrees C) and refrigerant spray (-50 degrees C), were applied to extracted bovine incisors. Each stimulus was applied for 5s on the labial enamel surface in a random order, with a 30-min interval between tests. Finite element analysis was performed on basic geometrical shapes to investigate structural deformation in relation to temperature change.

RESULTS

Application of thermal stimuli to the labial enamel surface resulted in rapid development of strain at the pulpal dentine surface before any temperature change was detected at the dentino-enamel junction. The strain pattern was biphasic; heat produced an initial contraction of the pulpal surface, followed by an expansion, and the reverse pattern was found with cold stimulation. Finite element analysis confirmed that the initially pronounced thermal gradient across the enamel and dentine caused rapid flexural deformation before temperature changes reached the dentino-enamel junction. When the temperature changes reached the pulpal dentine and thus reduced the thermal gradient, the direction of the strain was reversed.

CONCLUSION

These results indicate possible alternatives to the hydrodynamic theory for thermal stimuli applied to intact teeth. Mechanically induced dentine deformation may trigger nerve impulses directly, or may exert mechanically induced dentinal fluid flow that triggers nerve activity.

Influence of previous provisional cementation on the bond strength between two definitive resin-based luting and dentin bonding agents and human dentin

This study evaluated the effect of two different types of provisional luting agents (RelyX Temp E, eugenol-based; RelyX Temp NE, eugenol-free) on the shear bond strengths between human dentin and two different resin-based luting systems (RelyXARC-Single Bond and Duo Link-One Step) after cementation with two different techniques (dual bonding and conventional technique). One hundred human molars were trimmed parallel to the original long axis, to expose flat dentin surfaces, and were divided into three groups. After related surface treatments for each specimen, the resin-based luting agent was applied in a silicone cylindrical mold (3.5 x 4 mm), placed on the bonding-agent-treated dentin surfaces and polymerized. In the control group (n = 20), the specimens were further divided into two groups (n = 10), and two different resin-based luting systems were immediately applied following the manufacturer's protocols: RelyX ARC-Single Bond (Group I C) and Duo Link-One Step (Group II C). In the provisionalization group (n = 40), the specimens were further divided into four subgroups of 10 specimens each (Group I N, I E and Group II N, II E). In Groups I N and II N, eugenol-free (RelyX NE), and in groups I E and II E, eugenol-based (RelyX E) provisional luting agents (PLA), were applied on the dentin surface. The dentin surfaces were cleaned with a flour-free pumice, and the resin-based luting systems RelyX ARC (Group I N and E) and Duo Link (Group II N and E) were applied. In the Dual bonding groups (n = 40), the specimens were divided into four subgroups of 10 specimens each (Group I ND, ED and Group II ND, ED). The specimens were treated with Single Bond (Groups I ND and ED) or One Step (Groups II ND and ED). After the dentin bonding agent treatment, RelyX Temp NE was applied to Groups I ND and II ND, and RelyX Temp E was applied to Groups I ED and II ED. The dentin surfaces were then cleaned as described in the provisionalization group, and the resin-based luting systems were applied: RelyX ARC-Single Bond (Group I ND and ED) and Duo Link-One Step (Group II ND and ED). After 1,000 thermal cycles between 5 degrees C and 55 degrees C, shear bond testing was conducted at a crosshead speed of 0.5 mm/minutes. One-way ANOVA, followed by a post hoc Tukey test (alpha = 0.05) was done. The dentin-resin-based luting system interfaces were evaluated under a scanning electron microscope. There was a significant reduction in the mean shear bond strength values of groups subjected to the provisionalization compared to the control and dual bonding technique groups (p < 0.05). The composition of provisional luting did not create a significant difference with regard to reducing shear bond strength values (p > 0.05). With regard to resin based luting systems, the shear bond strength values of the double-bond technique groups were not significantly different from the controls (p > 0.05).

Clinical and scanning electron microscopic features of invasive cervical resorption in a maxillary molar

This case report presents clinical and morphological features of severe invasive cervical resorption (ICR) involving a maxillary first molar. Surface morphology of the ICR defect that extended into enamel was studied using a scanning electron microscope. The topography and morphology of resorbed enamel and pulpal surfaces are described. The pulpal space was characterized by proliferation of fibrovascular tissue invaded by a number of > or = 15-microm-large dentinoclastlike cells. The vertical orientation and hexagonal geometric outlines of enamel rods indicated that the resorptive defect had extended into the outer surface of enamel. Preferential odontoclastic dissolution of interprismatic enamel was noted. Deposits of a cementumlike substance were noticed on enamel surfaces, indicating that resorptive process was coupled with repair. Complete destruction of dentin was associated with no response by the tooth to cold stimulus, supporting the hydrodynamic theory of dentinal sensitivity. The results of this study indicate that in addition to predentin and cementum, the outer surface enamel may be resistant to the resorptive process as well.

Technique sensitivity associated with air-drying of HEMA-free, single-bottle, one-step self-etch adhesives

OBJECTIVES

This study examined the effect of air-drying on bond strength to dentin and nanoleakage in resin-dentin interfaces using HEMA-free one-step self-etch adhesives.

METHODS

Twelve teeth had their occlusal dentin exposed and split in half. In the group of G-BOND (GB), the adhesive was dried gently or vigorously on each slit half tooth, and then light-cured. In the group of the experimental adhesive (EX), three coats of adhesive were dried using a single air-drying process prior to light-curing or dried after each of three coats of adhesive before light-curing. The split specimens were built-up with resin composite and then subjected to microtensile bond strength testing and TEM examination.

RESULTS

GB showed significantly higher bond strength after vigorous drying than after gentle drying. Three teeth of from EX group showed higher bond strength after triple drying than after single drying, while two teeth showed no significant difference. Droplets were revealed in the adhesive layer after gentle drying with GB, and silver deposits existed along the interfaces in all groups.

SIGNIFICANCE

The bonding quality to dentin may be improved by using an accelerated air-drying technique; although it is impossible to remove intrinsic dentin moisture that is drawn upwards from dentin tubules.