Using Proanthocyanidin as a Root Dentin Conditioner for GIC Restorations.

Glass ionomer cements (GICs) are considered the material of choice for restoration of root carious lesions (RCLs). When bonding to demineralized dentin, the collapse of dentinal collagen during restorative treatment may pose challenges. Considering its acidic nature and collagen biomodification effects, proanthocyanidin (PAC) could be potentially used as a dentin conditioner to remove the smear layer while simultaneously acting to biomodify the dentinal collagen involved in the bonding interface. In this study, 6.5% w/v PAC was used as a conditioner for sound (SD) and laboratory demineralized (DD) root dentin before bonding to resin-modified GIC (FII), casein phosphopeptide-amorphous calcium phosphate (CPP-ACP)-modified GIC (FVII), or a high-viscosity GIC (FIX). Root dentin conditioned with deionized distilled water (DDW) or polyacrylic acid (PAA) served as controls. Results indicated FII showed higher shear bond strength (SBS) on SD than the other 2 GICs, especially in PAA-conditioned samples; FIX showed significantly higher SBS than FII and FVII on PAA- or PAC-conditioned DD. In each category of GIC, PAA and PAC did not have a significant influence on SBS in most cases compared to DDW except for a significant decrease in PAC-conditioned SD bonded to FII and a significant increase in PAA-conditioned DD bonded to FIX. The bonding interface between GIC and SD was generally more resistant to the acid-base challenge than DD. Although the alterations in failure modes indicated a compromised interfacial interaction between GICs and PAC-treated root dentin, biomodification effects of PAC on dentin were observed from Raman microspectroscopy analysis in terms of the changes in mineral-to-matrix ratio and hydroxyproline-to-proline ratio of dentin adjacent to the bonding interface, especially of DD. Results from this study also indicated the possibility of using in situ characterization such as Raman microspectroscopy as a complementary approach to SBS test to investigate the integrity of the bonding interface.

Effects of Collagen Crosslinkers on Dentine: A Literature Review.

This aim of this review is to explore the current research related to crosslinking agents used on dentine. A systematic search of publications in PubMed and Web of Science databases was performed. Further retrieval was conducted using the search terms of specific names of crosslinkers. Reviews, conference abstracts, dissertation and theses, non-English articles, studies of intrinsic crosslinking of dentine, studies of adhesives without specific crosslinker components, studies of crosslinker applications in other collagenous tissues or tooth-like structures and irrelevant studies were excluded. Manual screening was conducted on the bibliographies of remaining papers to identify other relevant articles. One hundred and one articles were included in this systematic review and full texts were retrieved. Both synthetic and naturally derived crosslinkers have been found to exhibit significant effects in biomodification of dentine via their multiple interactions with the dentine matrix. A stable matrix network or a durable hybrid layer in dentine bonding could be achieved, where the dentine collagen fibrils show improved biochemical and biomechanical properties and enzymatic biodegradation is reduced. Although no crosslinkers have been tested in clinical trials, extensive research has been conducted in laboratory studies to investigate their potential applicability for inhibition of demineralisation and/or promotion of remineralisation, caries prevention as well as improvement of bonding performance of adhesive systems. Further studies are needed to develop the feasibility for clinical use, reduce side effects as well as explore mechanisms of action and long-term effectiveness.

Ion release and physical properties of CPP-ACP modified GIC in acid solutions.

A new glass-ionomer cement (GIC) (Fuji VII™ EP) includes 3% (w/w) casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) to enhance ion release. OBJECTIVES: To assess this new GIC compared with a GIC without CPP-ACP (Fuji VII™) with respect to ion release, changes in surface hardness and in mass under a variety of acidic and neutral conditions. METHODS: Eighty blocks of Fuji VII™ (F7) and Fuji VII™ EP (F7EP) were subjected to three acidic solutions (lactic and citric acids pH 5.0, hydrochloric acid pH 2.0) and water (pH 6.9) over a three-day period. Ion release, surface hardness and weight measurements were carried out every 24h. RESULTS: Higher calcium ion release from F7EP was observed under all acidic conditions. Increased inorganic phosphate ion release was observed for F7EP in hydrochloric and citric acids. Fluoride ion release was similar between F7 and F7EP under all conditions but was significantly higher in acids compared with water. After three days there was no significant difference in surface hardness (p>0.05) between the two materials under all conditions except hydrochloric acid. Minimal change in mass was observed for F7 and F7EP in water, lactic and hydrochloric acids, however citric acid caused significantly more mass loss compared with water (p<0.001). CONCLUSION: Incorporation of 3% (w/w) CPP-ACP into F7 enhanced calcium and phosphate ion release, with no significant change in fluoride ion release and no adverse effects on surface hardness or change in mass. CLINICAL SIGNIFICANCE STATEMENT: GICs have the potential to release fluoride ions particularly under acidic conditions associated with dental caries and erosion. A new GIC containing CPP-ACP and fluoride releases not only fluoride ions but also calcium and phosphate ions under acidic conditions which should help to inhibit demineralisation associated with caries and erosion.

Mineralisation of developmentally hypomineralised human enamel in vitro.

Molar-incisor hypomineralisation (MIH) is a problematic and costly condition. Caries remineralising agents are often recommended for MIH management despite the lack of evidence that these lesions have the capacity for increasing their mineral content. Following surface layer removal ± NaOCl pre-treatment and 14-day exposure to a CPP-ACFP solution at pH 5.5, MIH lesions were analysed using transverse microradiography and polarised light microscopy. Lesions were highly variable but treatment with the remineralising solution increased mineral content (1,828 ± 461 vol% min · µm, %R = 17.7 ± 5.7) and porosity decreased demonstrating the proof of concept that the mineral content of developmentally hypomineralised enamel can be improved after eruption.

Bonding to glass ionomer cements using resin-based adhesives.

OBJECTIVE: This study compared the microshear bond strengths (MSBS) of four self-etching adhesives (Adper Scotchbond SE [SSE], Clearfil SE Bond [CSE], Clearfil S3 Bond [CS3] and One Coat 7.0 [OC]) and an etch-and-rinse adhesive (Adper Single Bond Plus [SB]) when bonded to two conventional glass ionomer cements (GICs) (Fuji IX GP EXTRA and Riva Self Cure). The null hypothesis tested was there is no difference in the adhesive ability of an etch-and-rinse adhesive and self-etching adhesives when bonded to GIC for up to 6 months. METHODS: The GICs were embedded in type III dental stone and wet ground with 1200-grit SiC paper. Twenty specimens were bonded for each adhesive according to manufacturers' instructions with a 1.5-mm bonding diameter. Specimens were stored at 100% humidity for 24 hours, 1 month, or 6 months. Microshear bond strengths were obtained using a crosshead speed of 1 mm/min. The results were calculated and analyzed using analysis of variance (ANOVA) and Tukey HSD test. RESULTS: SB had significantly lower MSBS than the four self-etching adhesives for all storage periods. MSBS at 6 months for SB was significantly lower than at 1 month. There were no significant differences in MSBS among the self-etching adhesives. Cohesive failure within GIC was the most common failure mode observed. CONCLUSIONS: SB showed a lower bond strength than the self-etching adhesives when bonded to conventional GICs for all storage periods. This might be a result of the phosphoric acid etching. However, cohesive strength of GIC was a limiting factor for the MSBS outcomes.

The effect of resin-based sealers on fracture properties of dentine.

AIM: To determine whether resin-based sealer cements are able to strengthen root dentine, as measured by work of fracture (Wf), micro-punch shear strength (MPSS) and resistance to vertical root fracture (VRF). METHODOLOGY: One hundred and twenty extracted premolar teeth were randomly assigned amongst four treatments before testing: intact, root canals prepared but unfilled, or root filled using epoxy- or urethane dimethacrylate (UDMA)-based sealer (plus core material). Samples were then prepared for measuring Wf, MPSS or VRF using standard test procedures. Data were analyzed using one-way anova with significance set at P < 0.05. RESULTS: For all three tests, root canals filled using epoxy resin-based sealer were not statistically significantly different compared with UDMA resin (P = 1 for Wf, P = 0.7 for MPSS and P = 0.12 for VRF), or different from both sound and prepared dentine (P > 0.05). There was also no significant difference between sound dentine and prepared dentine for both Wf (P = 0.92) and resistance to VRF (P = 1). CONCLUSIONS: Neither epoxy nor UDMA resins used as sealer cements enhanced fracture resistance of root dentine when placed within root canals of extracted teeth.

Push-out bond strengths of the dentine-sealer interface with and without a main cone.

AIM: To evaluate the push-out bond strength of the dentine-sealer interface with and without main cone for three resin sealers. METHODOLOGY: Thirty extracted maxillary premolar teeth with two separate canals were prepared using 0.04 taper Profile instruments to size 35-45. Teeth were divided into three groups for filling using AH Plus, EndoREZ or Resilon sealers. In each tooth, one canal was filled with a matching single-cone technique, and other was filled with sealer alone. A 1 mm slice of mid-root dentine was prepared for the push-out test. Failure modes after push-out were examined under microscopy and field emission-scanning electron microscopy. Data were analysed using two-way anova and paired t-tests, with significance set at P < 0.05. RESULTS: Overall, the epoxy resin-based sealer provided the highest push-out bond strengths. Push-out bond strengths were significantly higher (P < 0.001) when canals were filled with sealer alone than those filled with main cone and sealer (AH Plus 6.6 and 2.0 MPa, respectively; Resilon 3.4 and 0.4 MPa; EndoREZ 0.9 and 0.4 MPa). Sealers appeared to behave differently as thin films in association with a main cone, compared with bulk material. They failed in cohesive mode within the thin film, leaving a layer of sealer on the canal surface. Bulk sealer showed predominantly adhesive failure at the dentine-sealer interface, with a clean dentine wall and with resin tags either partially pulled out or sheared off at the interface. CONCLUSION: Push-out bond strengths of resin sealers were much lower when the sealer was present as a thin layer.

Temperature change, dentinal fluid flow and cuspal displacement during resin composite restoration.

Dentin-bonding agents and resin composite materials typically require light activation for polymerization. Light curing generates heat, which may influence dentinal fluid flow (DFF) and cuspal displacement. This study investigated the relationship among temperature increase, DFF and cuspal displacement in extracted human maxillary premolars with a mesial occlusal distal (MOD) cavity preparation. Two types of curing light were compared. Temperature changes were measured using thermocouples located on the occlusal cavity floor and at the pulp-dentine junction, during polymerization of bonding agent and resin composite material. DFF and cuspal displacement were measured simultaneously using automated flow measurement apparatus and direct current differential transformers respectively. Temperature increases of up to 15 degrees C were recorded during the restoration procedures. A quartz tungsten halogen (QTH) unit produced a significantly greater temperature increase than a light-emitting diode unit and curing of the bonding agent generated less temperature increase than curing of the resin composite. Heating due to exothermic reaction during polymerization of bonding agent and resin was not significantly different between light sources or between bonding and curing (P > 0.05). The QTH unit produced both greater inward fluid flow and cuspal displacement during the irradiation of bonding agent and resin composite than the light-emitting diode unit. There was not a simple relationship between temperature increase, fluid movement and cuspal displacement. From a clinical point of view, the light-emitting diode unit can be considered preferable to the QTH light, because it caused significantly smaller temperature increase, fluid shift and cuspal displacement.

An investigation of thermal stimulation in intact teeth.

OBJECTIVES: To investigate the response of extracted intact teeth to thermal stimulation in terms of fluid movement, in relation to temperature change within tooth structure. METHODS: Dentinal fluid movement was measured in response to thermal stimuli applied to enamel. Freshly extracted teeth with intact crowns were investigated for the effects of thermal stimulation; namely, hot water (80 degrees C), iced water (2 degrees C) and carbon dioxide dry ice (-72 degrees C) for 5s application. Two capillary-based methods were used to measure fluid flow. To measure temperature changes at the dentino-enamel junction (DEJ) and pulpal wall in response to the same stimuli, fine J type thermocouples were used. RESULTS: Thermal stimuli caused fluid movement, which occurred before the temperature changed at the pulp wall. Sealing the dentinal tubules resulted in a delayed response time. In general, fluid movement occurred coincident with the temperature change detected at the DEJ. However, many teeth showed a "bidirectional" response to thermal stimulation. The initial fluid movement in the bidirectional response was detected before the earliest temperature change observed at the DEJ, and was in the opposite direction to the main fluid movement. CONCLUSION: Our results imply that thermal contraction and expansion of dentinal fluid may not be the complete explanation for dentinal fluid movement in intact teeth. Enamel may serve not only as a temperature transfer medium but may also expand or contract when subjected to thermal stimulation.

Effect of static loading of dentin beams at various pH levels.

Noncarious cervical lesions have a multifactorial etiology. Mechanical stress has been identified as one of the factors, but little evidence exists for its cause-effect relationship. This study was conducted at three different pH levels to observe the surface loss on dentin beams under tension and compression. Bovine dentin beams (10 x 3.75 x 1.45 mm) were fixed at one end and immersed in 0.1 M lactic acid solution at pH levels 4.5 (n = 20), 7 (n = 20), and 10 (n = 20) for 5 days under a load of 6.5 N (663 g). The mean surface loss was more on the surface under compression than that under tension at pH 4.5 and pH 7 than at pH 10. Also, the surface loss on the beams decreased as the distance from the fixed end increased. It was concluded that stress and lower pH both increase surface loss at the fixed end of the beam, which in a tooth represents the cervical region.

Minimizing dentinal fluid flow associated with gap formation.

The relationship between gap formation and outward fluid flow and procedures to minimize both phenomena were investigated in extracted human premolars restored in vitro with MOD composite restorations. We hypothesized that either glass-ionomer cement (GIC) liners or low-shrinkage composite could reduce fluid flow related to gap formation. Two groups restored with bonding agents with either high- or low-shrinkage resin composites, and 2 groups restored by either conventional or light-cured GIC liner plus resin composite were compared (8 teeth/group). Fluid flow was measured with an automated apparatus. Baseline fluid flow was low and unchanged after bonding, but increased sharply (though transiently) after teeth were lined with GIC. Outward flow was significantly greater with conventional than with light-cured GIC. Inward fluid flow occurred during light-curing, followed by extensive, prolonged outward flow after curing. Low-shrinkage composite or GIC liners reduced gap formation and limited outward fluid flow. GIC liners promoted outward fluid flow during their setting reactions.

Effect of loading and pH on the subsurface demineralization of dentin beams.

It is important to understand subsurface dentin demineralization and caries from the clinical perspective as dentin properties are modified under acidic conditions and mechanical loading. This study was conducted to observe the subsurface demineralization of dentin beams at three different pH levels under tension and compression. Bovine dentin beams (10 x 3.75 x 1.45 mm) were fixed at one end and immersed in 0.1 M lactic acid solution at pH levels 4.5, 7, and 10 for 5 days under a load of 6.5 N (663 g), and the subsurface demineralization depth was measured using a polarized light microscope. The mean subsurface demineralization depth was more subjacent to the surface under compression than that under tension at pH 4.5 and decreased as the distance from the fixed end increased. No subsurface demineralization was observed at pH 7 or 10. It was concluded that both stress and low pH are associated with increased subsurface demineralization at the fixed end of the beam.

Tooth morphology and characteristics of non-carious cervical lesions.

OBJECTIVES: Two 3-dimensional models, one of a lower second premolar and one of a lower central incisor were used to investigate effects of load on the location and magnitude of cervical strains. METHODS: Point loads of 100 N were applied to the model premolar (at the cusp tip, parallel and 45 degrees to the long axis of the tooth) and incisor (at the mid-buccal point on incisal edge, parallel and 45 degrees to the long axis of the tooth). Outputs were presented in the form of tensile-strain contours and vector plots. RESULTS: Strains were concentrated near the cementoenamel junction (CEJ) regardless of load direction, and oblique loading showed higher tensile strains, opposite to the point of loading, than vertical loading for both models. For the premolar model, regardless of loading direction, strains were concentrated at the mid- buccal CEJ. In contrast, under vertical loading on the incisor model, tensile strains were concentrated at the line-angle of CEJ. From oblique loads, vector plots of both models showed tensile vectors in vertical directions while vertical loads showed tensile vectors in horizontal directions. CONCLUSION: Mechanisms of non-carious cervical lesions (NCCLs) may in part be due the changing orientation of tensile strains as well as their magnitude. Stress concentration at the CEJ related well to the common location of clinical NCCLs. The crown-root morphology may have an influence on the initial location of non-carious cervical lesions.

The effect of cleaning procedures on fracture properties and corrosion of NiTi files.

AIM: To evaluate the effect of repeated cleaning procedures on fracture properties and corrosion of nickel-titanium (NiTi) files. METHODOLOGY: New NiTi instruments were subjected to 2, 5 and 10 cleaning cycles with the use of either diluted bleach (1% NaOCl) or Milton's solution (1% NaOCl plus 19% NaCl) as disinfectant. Each cleaning cycle consisted of scrubbing, rinsing and immersing in NaOCl for 10 min followed by 5 min of ultrasonication. Files were then tested for torsional failure and flexural fatigue, and observed for evidence of corrosion using scanning electron microscope (SEM). Four brands of NiTi files were immersed in either Milton's solution or diluted bleach overnight and evaluated for corrosion. RESULTS: Up to 10 cleaning cycles did not significantly reduce the torque at fracture or number of revolutions to flexural fatigue (P > 0.05, two-way anova), although decreasing values were noted with increasing number of cleaning cycles using Milton's solution. No corrosion was detected on the surface of these files. Files immersed in 1% NaOCl overnight displayed a variety of corrosion patterns. The extent of corrosion was variable amongst different brands of files and amongst files in each brand. Overall, Milton's solution was much more corrosive than diluted bleach. Corrosion of file handles was often extreme. CONCLUSIONS: Files can be cleaned up to 10 times without affecting fracture susceptibility or corrosion, but should not be immersed in NaOCl overnight. Milton's solution is much more corrosive than bleach with the same NaOCl concentration.

Strains in the marginal ridge during occlusal loading.

BACKGROUND: The marginal ridge is considered fundamental to the ability of the tooth to resist functional and parafunctional occlusal loads without damage. Despite this role, very little is known of patterns of stress and strain in marginal ridges under load. This study investigated strains in proximal enamel of mandibular premolars using finite element analysis (FEA) and strain gauge measurements. METHODS: A three-dimensional FEA model of a human mandibular premolar was developed using commercial FEA software, and strains were computed in response to loads simulating clenching and chewing functions. Strains were measured in extracted premolars using strain gauges mounted on the proximal surfaces, under similar occlusal loading conditions. RESULTS: Strains in the vicinity of contact areas and marginal ridges were lower than near the cemento-enamel junction and on buccal and lingual surfaces. The magnitude of proximal strains increased with oblique loading on cuspal inclines. Finite element analysis results correlated well with strain gauge measurements and can be used to predict strain directions and magnitudes. CONCLUSIONS: At least for mandibular premolars, the marginal ridges are not highly stressed areas during simulated occlusal loading.

Stainless steel bands in endodontics: effects on cuspal flexure and fracture resistance.

AIMS: This study investigated the effect of stainless steel bands on cuspal flexure and fracture resistance of extracted maxillary premolars. METHODOLOGY: Twenty extracted maxillary premolars (10 matched pairs) with mesio-occluso-distal (MOD) cavities and endodontic access were subjected to occlusal loading tests (100 N) using a servo-hydraulic testing machine. Cuspal deflections were measured by an extensometer, with and without the band present. Ten teeth (one of each pair) then had the band removed, and all teeth were subjected to loading until fracture. RESULTS: Mean cuspal flexure of teeth with bands was one-half of flexure without bands (P < 0.001). Teeth with bands fractured at higher load than their matched pairs with the band removed (P < 0.001), with mean loads at fracture of 1282 N and 729 N, respectively. CONCLUSIONS: The study showed that stainless steel bands used in endodontics reduce the cuspal flexure of maxillary premolars and increase their fracture resistance.

Measurement of strain on tooth roots during post removal with the Eggler post remover.

AIM: The aim was to measure root surface strains in teeth when removing cast post/cores with the Eggler post remover. METHODOLOGY: Two groups of 10 teeth each were tested: group 1 had 1 mm thickness of dentine coronally, and group 2 had 2 mm thickness of dentine. After root filling, 10 mm long cast post/cores were constructed and cemented with zinc phosphate cement, and strain gauges were applied to the roots. The post/cores were removed with the Eggler post remover whilst strain measurements were being recorded. Posts were removed twice: initially along the long axis of the tooth and then at a 10 degrees angle to the long axis. Comparisons between groups 1 and 2 were analysed statistically with the Mann-Whitney U-test whilst strains within each group were analysed with the Wilcoxon Signed Rank test at the 95% level of confidence. RESULTS: There was no significant difference in the strains measured between groups 1 and 2, and no significant difference within each group when removing posts along the long axis of the tooth and at a 10 degrees angle. Three teeth in group 1 and one tooth in group 2 fractured when removing posts at the 10 degrees angle. Three fractures were small slivers of dentine at the point where the Eggler's repeller arms contacted the tooth mesially and distally, whilst one tooth (from group 1) fractured obliquely. CONCLUSIONS: Post removal with the Eggler device is a relatively safe procedure but care must be taken when there is a possibility of pulling the post out in a nonaxial direction or when less than 1 mm of dentine surrounds the apical end of the post.

Pulpal space pressure and temperature changes from Nd:YAG laser irradiation of dentin.

OBJECTIVES: To investigate pulpal space pressure and temperature after application of Nd:YAG laser, and high-speed diamond bur on dentin surface. METHODS: One and 3 W Nd:YAG laser and high-speed diamond bur were used to remove dentine from twenty extracted premolars. The pulp chambers were monitored for pressure and temperature changes with a pressure transducer and thermocouple, respectively. RESULTS: Regardless of the remaining dentin thickness (RDT), laser irradiation and high-speed diamond bur use generated an increase in pulpal space pressure and temperature (ANOVA and Fisher's LSD tests, P < 0.001). Pressure and temperature increased with an increase in laser power. Three-Watt laser irradiation caused greater changes than 1 W (1.75 kPa and 1.31 degrees C, 0.53 kPa and 0.34 degrees C, respectively). Both pulpal space pressure (P < 0.001) and temperature (P < 0.005) increased as the RDT decreased. CONCLUSIONS: Laser irradiation and the use of a high-speed diamond bur generated an increase in pulpal space pressure and temperature. Pulpal space pressure and temperature increased with an increase in energy density of laser and a decrease in RDT.