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.

Incorporation of the microencapsulated antimicrobial agent phytoncide into denture base resin.

BACKGROUND: This study aimed to fabricate a denture base resin (DBR) containing phytoncide microcapsules (PTMCs) and determine the mechanical properties of the resin and antifungal activity. METHODS: Fifty-four heat-cured rectangular DBR specimens (64 × 10 × 3.3 ± 0.2 mm) containing nine concentrations of PTMC between 0 and 5% (wt/wt) were fabricated and subjected to a three-point bending test. A phytoncide release bioassay was developed using DBR containing 0% and 2.5% PTMCs (wt/wt) in a 24 well-plate assay with incubation of Porphyromonas gingivalis at 37 °C for 74 h. The antifungal activity of PTMCs against Candida albicans, in a pH 5.5 acidic environment was determined in a plate assay. RESULTS: Flexural strength decreased with increasing PTMC concentration from 97.58 ± 4.79 MPa for the DBR alone to 53.66 ± 2.46 MPa for DBR containing 5.0% PTMC. No release of phytoncide from the PTMCs in the DBR was detected at pH 7.4. The PTMCs had a minimal inhibitory concentration of 2.6% (wt/vol) against C. albicans at pH 5.5. CONCLUSIONS: PTMCs can be added to DBR 2.5% (wt/wt) without adversely affecting flexural strength. PTMCs released the antimicrobial agent at pH 5.5 at concentrations sufficient to inhibit the growth of the C. albicans.

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.

Effect of bulk-fill base material on fracture strength of root-filled teeth restored with laminate resin composite restorations.

OBJECTIVES: To evaluate the effect of using a bulk-fill flowable base material on fracture strength and fracture patterns of root-filled maxillary premolars with MOD preparations restored with laminate restorations. METHODS: Fifty extracted maxillary premolars were selected for the study. Standardized MOD cavities with endodontic treatment were prepared for all teeth, except for intact control. The teeth were divided randomly into five groups (n=10); (Group 1) sound teeth, (Group 2) unrestored teeth; (Group 3) MOD cavities with Vitrebond base and resin-based composite (Ceram. X One Universal); (Group 4) MOD cavities with 2mm GIC base (Fuji IX GP) and resin-based composite (Ceram. X One Universal) open laminate, (Group 5) MOD cavities were restored with 4mm of bulk-fill flowable base material (SDR) and resin-based composite (Ceram. X One Universal). All teeth were thermocycled and subjected to a 45° ramped oblique load in a universal testing machine. Fracture load and fracture patterns were recorded. Data were analyzed using one-way ANOVA and Dunnett's T3 test. RESULTS: Restoration in general increased the fracture strength compared to unrestored teeth. The fracture strength of group 5 (bulk-fill) was significantly higher than the fracture strength of the GIC laminate groups and not significantly different from the intact teeth (355±112N, P=0.118). The type of failure was unfavorable for most of the groups, with the majority being mixed failures. CONCLUSIONS: The use of a bulk-fill flowable base material significantly increased the fracture strength of extracted root-filled teeth with MOD cavities; however it did not improve fracture patterns to more favorable ones. CLINICAL SIGNIFICANCE: Investigating restorative techniques that may improve the longevity of root-filled premolar teeth restored with direct resin restorations.

Comparison between published clinical success of direct resin composite restorations in vital posterior teeth in 1995-2005 and 2006-2016 periods.

Composites are increasing in popularity as restorative materials. This growing role indicates the necessity of studies on their clinical outcome. In this study, clinical studies published on the performance of posterior composite restorations were included except those of less than a 24-month assessment period. Results of non-vital, anterior or primary teeth and cervical single-surface restorations were also excluded. Records about composite type, number of final recall restorations, failure/survival rate, assessment period and failure reasons were analysed for each decade. Overall survival/failure rates for studies in 1995-2005 were 89.41%/10.59% and for 2006-2016 were 86.87%/13.13%, respectively. In 1995-2005, the reasons for failure were secondary caries (29.47%) and composite fracture (28.84%) with low tooth fracture (3.45%) compared with reasons of failure in 2006-2016, which were secondary caries (25.68%), composite fracture (39.07%), and tooth fracture (23.76%). An increase in incidence of composite fracture, tooth fracture and need for endodontic treatment as failure reasons was noted in the latter decade in addition to a decrease in secondary caries, postoperative sensitivity, unsatisfactory marginal adaptation and wear. The overall rates of failure showed little difference, but the causes showed a notable change. This is believed to be a reflection of increased use of composites for larger restorations and possibly changes of material characteristics.

The Effect of Resin-modified Glass-ionomer Cement Base and Bulk-fill Resin Composite on Cuspal Deformation.

OBJECTIVES: This study investigated cuspal deformation in teeth restored with different types of adhesive materials with and without a base. METHODS: Mesio-occluso-distal slot cavities of moderately large dimension were prepared on extracted maxillary premolars (n=24). Teeth were assigned to one of four groups and restored with either a sonic-activated bulk-fill resin composite (RC) (SonicFill), or a conventional nanohybrid RC (Herculite Ultra). The base materials used were a flowable nanofilled RC (Premise Flowable) and a high-viscosity resin-modified glass-ionomer cement (RMGIC) (Riva Light-Cure HV). Cuspal deflection was measured with two direct current differential transformers, each contacting a buccal and palatal cusp. Cuspal movements were recorded during and after restoration placement. Data for the buccal and palatal cusp deflections were combined to give the net cuspal deflection. RESULTS: Data varied widely. All teeth experienced net inward cuspal movement. No statistically significant differences in cuspal deflection were found among the four test groups. CONCLUSIONS: The use of a flowable RC or an RMGIC in closed-laminate restorations produced the same degree of cuspal movement as restorations filled with only a conventional nanohybrid or bulk-fill RC.

Fracture strength and fracture patterns of root-filled teeth restored with direct resin composite restorations under static and fatigue loading.

AIM: To assess fracture strength and fracture patterns of root-filled teeth with direct resin composite restorations under static and fatigue loading. METHODOLOGY: MOD cavities plus endodontic access were prepared in 48 premolars. Teeth were root filled and divided into three restorative groups, as follows 1) resin composite; 2) glass ionomer cement (GIC) core and resin composite; and 3) open laminate technique with GIC and resin composite. Teeth were loaded in a servohydraulic material test system. Eight samples in each group were subjected to stepped fatigue loading: a preconditioning load of 100 N (5000 cycles) followed by 30,000 cycles each at 200 N and higher loads in 50-N increments until fracture. Noncycled teeth were subjected to a ramped load. Fracture load, number of cycles, and fracture patterns were recorded. Data were analyzed using two-way analysis of variance and Bonferroni tests. RESULTS: Fatigue cycling reduced fracture strength significantly (p<0.001). Teeth restored with a GIC core and a laminate technique were significantly weaker than the composite group (379±56 N, 352±67 N vs 490±78 N, p=0.001). Initial debonding occurred before the tooth underwent fracture. All failures were predominantly adhesive, with subcrestal fracture of the buccal cusp. CONCLUSIONS: Resin composite restorations had significantly higher fracture strength than did other restorations. Fatigue cycled teeth failed at lower load than did noncycled teeth.

The effect of laser irradiation on retention of full cast crowns.

The objective of this work was to determine the effect on the retention force of full cast crowns cemented on short tooth preparations after preparation of dentine with an erbium, chromium: yttrium scandium gallium garnet (Er, Cr:YSGG) laser at different sub-ablative power settings. Thirty teeth were prepared for full cast crowns using a milling machine. The surface area for all preparations was measured. The surfaces of the preparations were irradiated with 0 (control), 0.25 and 0.75 W laser. The crowns were cemented with self-cure resin cement and tested for retention on a Hounsfield Tensometer machine. The 0.75 W power setting produced the highest failure load value (346.2 +/- 86.1 N) and was significantly higher than the other groups. There were no significant differences between the 0.25 W and 0 W control groups

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.

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.

Enhancing the bond of a resin-based sealer to root dentine.

AIM: To evaluate whether application of a total-etch/separate adhesive layer can enhance the bond of a UDMA-based sealer to dentine. METHODOLOGY: The root canals of 20 decoronated maxillary premolar teeth with two canals were prepared to size 35-45, 0.04 taper using rotary NiTi instruments. The canals of each tooth were treated with application of either a total-etch/separate adhesive or the manufacturer-recommended primer, before root filling with sealer plus matching master cone using warm vertical compaction. After setting, roots were sectioned perpendicular to the long axis to obtain 1-mm-thick slices, and the root filling was subjected to the push-out test using a plunger closely matched to canal diameter. The roots of another 15 single-rooted premolars were sectioned in a bucco-lingual direction, and the cut surfaces were ground flat for microshear bond strength testing. One-half of the specimens were coated with a separate total-etch/adhesive layer, and then, a cylinder of sealer cement 1 mm diameter × 1.5 mm high was bonded to the prepared surface of all specimens. Microshear bond strength was measured in a universal testing machine after 48 h. Data were analysed using anova and paired t-tests, with significance set at P < 0.05. RESULTS: Use of a separate total-etch/adhesive markedly increased both microshear bond strength and push-out strengths compared with standard primer (P < 0.001). CONCLUSION: Application of a separate adhesive layer significantly increases bond strength of UDMA-based sealers to root dentine.

Assessment of laminate technique using glass ionomer and resin composite for restoration of root filled teeth.

OBJECTIVE: To evaluate the open laminate technique using glass ionomer cements (GIC) in association with a low shrink composite for restoring root filled premolars. METHODS: Extensive MOD cavities plus endodontic access and root filling were performed in intact extracted maxillary premolars. Three restoration types were evaluated: (1) resin composite alone; (2) resin-modified GIC (RM-GIC) open laminate plus resin composite; (3) conventional GIC open laminate plus resin composite (n=8 for all groups and tests). Three tests were conducted to assess restorations: (A) inward cusp deflection during light curing, using DCDTs; (B) fracture strength using a ramped oblique load at 45° to the long axis in a servohydraulic testing machine in comparison with intact and unrestored teeth; (C) proximal marginal leakage using methylene blue dye and the effect of thermocycling. Data were analysed using 1-way ANOVA for cuspal deflection and fracture strength and Fisher's exact test for leakage. RESULTS: Laminate restorations resulted in significantly less cuspal deflection compared with resin composite (4.2±1.2 µm for RM-GIC and 5.1±2.3 µm for conventional GIC vs. 12.2±2.6 µm for composite, P<0.001). Fracture strength was not significantly different among all groups. Failure with all restorations was predominantly adhesive at the tooth-restoration interface. The two laminate groups showed significantly better marginal seal than composite alone, but sealing ability of conventional GIC deteriorated after thermocycling. CONCLUSIONS: Laminate restoration of root filled teeth had beneficial effects in terms of reducing cuspal deflection and marginal seal, with acceptable fracture strength.

Effect of tooth surface preparation on the bonding of self-etching primer adhesives.

The aim of this study was to determine the bonding effectiveness of four self-etching primer adhesives after various tooth preparation protocols. Enamel/dentin specimens were prepared from 84 permanent molars, divided into three enamel preparation groups (silicon carbide paper [SiC1; erbium, chromium:yttri-um, scandium, gallium, garnet [Er,Cr:YSGG] laser [EL] and diamond bur [DB]) and five dentin preparation groups (SiC, EL, DB, steel[SB], and ceramic burs [CBs]). In each group,specimens were equally divided into four sub-groups and were bonded using Clearfil SEBond (CSE, Kuraray), Xeno IV (XE, Dentsply),Tokuyama Bond Force (TK, Tokuyama) and Filtek Silorane System Adhesive (FS, 3MESPE), as well as a hybrid resin composite(Clearfil Majesty Esthetic, Kuraray) for CSE,XE, and TK, and Filtek Posterior Restorative(3M ESPE) for FS). After 24 hours of water storage at 370C, microshear bond strength(iSBS) testing was carried out. Data were analyzed using analysis of variance (ANOVA)-Tukey test at a=0.05 and bond failure modes assessed. Representative debonded specimens were prepared and examined under the scanning electron microscope (SEM). All adhesives exhibited no significant differences in 1SBS on enamel and dentin under the clinical cavity preparation protocols, except for TK on den-tin. SEM revealed areas of altered subsurface enamel/dentin following EL ablation.

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.

Fracture strength and fracture patterns of root filled teeth restored with direct resin restorations.

OBJECTIVE: To compare fracture characteristics of root-filled teeth with variable cavity design and resin composite restoration. METHODS: 80 extracted intact maxillary premolars were divided randomly into eight groups; (1) intact teeth; (2) unrestored MOD cavity; (3) unrestored MOD cavity plus endodontic access through the occlusal floor; (4) unrestored MOD plus endodontic access with axial walls removed; (5) MOD restored with resin composite; (6) MOD plus endodontic access, resin composite; (7) MOD plus extensive endodontic access, resin composite; (8) MOD plus extensive endodontic access, GIC core and resin composite. A ramped oblique load was applied to the buccal cusp in a servohydraulic testing machine. Fracture load and fracture patterns were recorded. Fracture loads were compared statistically using 1-way ANOVA, with Dunnett test for multiple comparisons. RESULTS: Unrestored teeth became progressively weaker with more extensive preparations. Endodontic access confined within the occlusal floor did not significantly affect strength compared to an MOD cavity. Loss of axial walls weakened teeth considerably [292+80N vs 747+130N for intact teeth]. Restoration increased the strength of prepared teeth particularly in teeth without axial walls. Teeth with a GIC core were not significantly weaker than intact teeth [560+167N]. Failures were mostly adhesive at the buccal interface, with the fracture propagating from the buccal line angle of the occlusal floor (MOD and MOD plus access groups) or of the proximal box (axial wall removed). CONCLUSIONS: Direct restorations increased fracture resistance of root filled teeth with extensive endodontic access. Both restored and unrestored teeth showed similar fracture patterns.

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.

Thermal transfer in extracted incisors during thermal pulp sensitivity testing.

AIM: To measure the temperature distribution within tooth structure during and after application of thermal stimuli used during pulp sensitivity testing. METHODOLOGY: Extracted intact human maxillary anterior teeth were investigated for temperature changes at the labial enamel, the dentino-enamel junction (DEJ) and pulpal surface during and after a 5-s application of six different thermal stimuli: hot water (80 degrees C), heated gutta-percha (140 degrees C), carbon dioxide dry ice (-72 degrees C), refrigerant spray (-50 degrees C), ice stick (0 degrees C) and cold water (2 degrees C). J-type thermocouples and heat conduction paste were used to detect temperature changes, together with a data acquisition system (Labview). Data were analysed using analysis of variance, with a confidence level of P < 0.05. RESULTS: Temperature change was detected more quickly at the DEJ and pulpal surface with the application of hot water, heated gutta-percha and refrigerant spray than with carbon dioxide dry ice and ice (P < 0.05). Cold water and refrigerant spray were in the same range in terms of time to detect temperature change at both the DEJ and pulpal surface. Thermal stimuli with greater temperature difference from tooth temperature created a greater thermal gradient initially, followed by a greater temperature change at the DEJ and the pulpal surface. In this regard, ice and cold water were weaker stimuli than others (P < 0.05). CONCLUSIONS: Thermal stimuli used in pulp testing are highly variable in terms of temperature of the stimulus, rate of thermal transfer to the tooth and extent of temperature change within tooth structure. Overall, dry ice and refrigerant spray provide the most consistent stimuli, whereas heated gutta-percha and hot water were highly variable. Ice was a weak stimulus.

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.