Pulpal blood flow recorded from human premolar teeth with a laser Doppler flow meter using either red or infrared light

Objective

To compare red (635 nm) and infrared (780 nm) light for recording pulpal blood flow from human premolar teeth.

Design

Recordings were made from 11 healthy teeth in 9 subjects (aged 16–30 years) using a laser Doppler flow meter (Periflux 4001) equipped with both red and infrared lasers. Average blood flow signals were obtained with both light sources alternately from each tooth under five conditions: intact tooth without opaque rubber dam, intact tooth with dam, after injecting local anaesthetic (3% Mepivacaine) (LA) over the apex of the tooth and cavity preparation to almost expose the pulp, after removal and replacement of the pulp, and with the root canal empty.

Results

With infrared light, the dam significantly decreased the mean blood flow by 80%. Injecting LA and cavity preparation had no significant effect. Removal and replacement of the pulp reduced the mean blood flow by 58%. There was no further change when the pulp was removed. With red light, the dam reduced the signal from intact teeth by 60%. Injecting LA and cavity preparation had no significant effect. The signal fell by 67% after pulp removal and replacement and did not change significantly when the pulp was removed.

Conclusions

Opaque rubber dam minimises the contribution of non-pulpal tissues to the laser Doppler signal recorded from premolars. Using dam, the pulp contributed about 60% to the blood flow signal with both red and infrared light. The difference between them in this respect was not significant.     

A comparison between red and infrared light for recording pulpal blood flow from human anterior teeth with a laser Doppler flow meter

Objective

To compare red (635 nm) and infrared (780 nm) light for recording pulpal blood flow from human anterior teeth with a laser Doppler flow meter.

Design

Recordings were made from 7 healthy teeth in 5 subjects (aged 22–55 years) using a laser Doppler flow meter (Periflux 4001) equipped with both red and infrared lasers. Average blood flow signals were obtained with both light sources alternately from each tooth under five conditions: intact tooth without opaque rubber dam, intact tooth with dam, after injecting local anaesthetic (3% Mepivacaine) (LA) over the apex of the tooth and cavity preparation to almost expose the pulp, after removal and replacement of the pulp, and with the root canal empty.

Results

With infrared light, because of technical limitations, data were obtained for the first three conditions only. The dam significantly decreased the mean blood flow by 82%. Injecting LA and cavity preparation had no significant effect. With red light, dam produced a decrease of 56%, and the resulting signal was reduced by 33% after LA and cavity preparation. The remaining signal fell by 46% after pulp removal and replacement. This contribution of the pulp is similar to that recorded previously with infrared light. There was no significant further change when the pulp was finally removed.

Conclusions

The importance of using opaque rubber dam is confirmed. With dam, there is no advantage to using red rather than infrared light, and in each case the pulp contributes less than 50% to the blood flow signal.     

The effect of increasing sodium fluoride concentrations on erosion and attrition of enamel and dentine in vitro

Objectives

To investigate the effect of an aqueous sodium fluoride solution of increasing concentration on erosion and attrition of enamel and dentine in vitro.

Methods

Enamel and dentine sections from caries-free human third molars were polished flat and taped (exposing a 3 mm × 3 mm area) before being randomly allocated to 1 of 5 groups per substrate (n = 10/gp): G1 (distilled water control); G2 (225 ppm NaF); G3 (1450 ppm NaF); G4 (5000 ppm NaF); G5 (19,000 ppm NaF). All specimens were subjected to 5, 10 and 15 cycles of experimental wear [1 cycle = artificial saliva (2 h, pH 7.0) + erosion (0.3% citric acid, pH 3.2, 5 min) + fluoride/control (5 min) + attrition (60 linear strokes in artificial saliva from enamel antagonists loaded to 300 g)]. Following tape removal, step height (SH) in μm was measured using optical profilometry.

Results

When the number of cycles increased the amount of tooth surface loss increased significantly in enamel and dentine after attrition and erosion and for dentine after attrition. Attrition and erosion resulted in greater surface loss than attrition alone after 15 cycles of experimental wear of enamel. 5000 ppm and 19,000 ppm sodium fluoride solutions had a protective effect on erosive and attritional enamel tooth wear in vitro, however no other groups showed significant differences.

Conclusions

The more intensive the fluoride regime the more protection was afforded to enamel from attrition and erosion. However, in this study no such protective effect was demonstrated for dentine.     

Pulpal blood flow recorded from exposed dentine with a laser Doppler flow meter using red or infrared light

ObjectiveTo determine the percentage of the blood flow signal that is derived from dental pulp when recording from exposed dentine in a human premolar.DesignRecordings were made from 7 healthy teeth in 5 subjects (aged 22–33 yr.) with a laser Doppler flow meter (Periflux 4001) using either a red (635 nm) or an infrared (780 nm) laser. After exposing dentine above the buccal pulpal horn (cavity diam. 1.6 mm, depth 3 mm) and isolating the crown with opaque rubber dam, blood flow was recorded alternately with infrared or red light from the exposed dentine under four conditions: before and after injecting local anaesthetic (3% Mepivacaine without vasoconstrictor) (LA) over the apex of the root of the tooth; after exposing the pulp by cutting a buccal, class V cavity in the tooth; and after sectioning the coronal pulp transversely through the exposure.ResultsThere was no significant change in mean blood flow recorded with either light source when the tooth was anaesthetized or when the pulp was exposed. After the pulp had been sectioned, the blood flow recorded with infrared light fell by 67.8% and with red light, by 68.4%. The difference between these effects was not significant.ConclusionsWhen recording blood flow from exposed coronal dentine with either infrared or red light in a tooth isolated with opaque rubber dam, about 68% to the signal was contributed by the pulp. The signal:noise ratio was better with infrared than red light, and when recording from dentine than enamel.     

Effect of a 10% carbamide peroxide on wear resistance of enamel and dentine: In situ study

Objectives

This triple-blind, 2 × 2 crossover in situ study, was undertaken to verify whether the wear resistance of enamel and root dentine would be affected by bleaching with a 10% carbamide peroxide agent and a placebo agent.

Methods

Thirty slabs of each substrate (2 mm × 3 mm × 2 mm) were selected for each phase, after flattening and polishing procedures and microhardness test. After a 7-day lead-in period, one specimen of each substrate was randomly bonded on the facial surface of each one of 30 subject's upper second premolars. The volunteers received instructions on how to perform toothbrushing and application of gel in the tray. Fifteen volunteers bleached their maxillary arch with a 10% carbamide peroxide bleaching agent for a 2-week period, while the remainders used a placebo agent. After a 1-week washout period, a new set of enamel and root dentine slabs were bonded to the premolars and volunteers were crossed over to the alternate agent for 14 days. The resistance of enamel and root dentine to wear following bleaching, toothbrushing and intraoral exposure was measured with a profilometer, using reference areas.

Results

For enamel, ANOVA did not demonstrate significant difference between wear provided by placebo and bleaching agent (p = 0.3713), but higher wear depth was observed for bleached root dentine (p = 0.0346).

Conclusions

While overnight bleaching caused no alteration in wear resistance of enamel, root dentine showed increased tissue loss.     

Randomised in situ trial on the effect of milk and CPP-ACP on dental erosion

Objectives

This randomised in situ study aimed to analyse the effect of milk (with or without 5 ppm F) and CPP-ACP pastes (with or without 900 ppm F) on dental erosion.

Methods

The study was a seven phase (5 days each) crossover design involving 15 participants wearing intraoral appliances with enamel and dentine specimens. Specimens were extraorally eroded (erosive soft drink, 6 × 90 s/day) and brushed (2 × 30 s/day, 2 N) using a non-fluoridated toothpaste (negative control). The test products were milk, milk + 5 ppm F (twice daily, each 100 ml/2 min), CPP-ACP paste, CPP-ACP paste + 900 ppm F (3 min/day) or a SnCl₂/AmF/NaF mouthrinse (positive control, 30 s/day), which were applied immediately after erosion with the appliances in the oral cavity. In an additional group, a fluoridated toothpaste was used without any additional test product. Tissue loss was determined profilometrically after 5 days and statistically analysed by linear mixed models methodologies (p < 0.05).

Results

Compared with the negative control (non-fluoridated toothpaste only, enamel: 2.2 ± 1.3 μm; dentine: 3.8 ± 2.2 μm), enamel and dentine loss was significantly reduced by the use of fluoridated toothpaste (enamel: 1.1 ± 1.0 μm; dentine: 2.4 ± 1.7 μm) and the SnCl₂/AmF/NaF mouthrinse (1.5 ± 1.5 μm; dentine: 1.8 ± 1.9 μm).

Conclusions

Milk and CPP-ACP were not effective in reducing enamel and dentine loss significantly, independently of the presence of fluoride.

Clinical significance

Enamel and dentine erosion were significantly reduced by the use of a fluoridated toothpaste or a SnCl₂/AmF/NaF mouthrinse, but not by milk or CPP-ACP under the conditions of the present study.

Clinical trials registration

NCT01566357.     

Effective tooth-bleaching protocols capable of reducing H2O2 diffusion through enamel and dentine

Objectives

To evaluate the effects of experimental protocols on bleaching effectiveness and hydrogen peroxide (HP) diffusion through enamel and dentine.

Methods

Enamel/dentine discs were subjected to six bleaching sessions, consisting of 1 or 3 applications of 17.5% or 35%-HP gel for 5/15 min, or 37% carbamide peroxide (CP) gel for 10/20 min. Discs undergoing the regular protocol (35%-HP; 3 × 15 min) constituted the positive control group. Colour change (ΔE) was assessed (CIE L*a*b* system) after each session. HP diffusion was quantified (sessions 1, 3, and 6) in enamel/dentine discs adapted to artificial pulp chambers. Data were analysed by Pillai's Trace and Bonferroni test, or by one-way ANOVA and SNK/Tamhane's test (α = 5%).

Results

All tooth-bleaching protocols significantly increased the ΔE values. A reduction in HP diffusion and no significant difference in ΔE compared with the positive control were observed for the following bleaching protocols: 17.5%-HP 3 × 15 min, at the 4th session; and 35%-HP 1 × 15 and 3 × 5 min, at the 5th session. HP diffusion in the 37%-CP 3 × 20 min bleaching protocol was statistically similar to that in the positive control. The other experimental bleaching protocols significantly decreased HP diffusion through enamel/dentine discs, but the ΔE values were statistically lower than those observed in the positive control, in all sessions.

Conclusion

Shortening the contact time of a 35%-HP gel or reducing its concentration produces gradual tooth colour change and reduced HP diffusion through enamel and dentine.

Clinical significance

A reduction in HP concentration, from 35% to 17.5%, in a bleaching gel or shortening its application time on enamel provides a significant tooth-bleaching improvement associated with decreased HP diffusion across hard dental tissues. Therefore, these protocols may be an interesting alternative to be tested in the clinical situation.     

Shear bond strength of porcelain laminate veneers to enamel,dentine and enamel–dentine complex bonded with different adhesive luting systems

Objectives

The aim of this study was to evaluate the shear bond strength of porcelain laminate veneers to 3 different surfaces by means of enamel, dentine, and enamel–dentine complex.

Methods

One hundred thirty-five extracted human maxillary central teeth were used, and the teeth were randomly divided into 9 groups (n = 15). The teeth were prepared with 3 different levels for bonding surfaces of enamel (E), dentine (D), and enamel–dentine complex (E–D). Porcelain discs (IPS e.max Press, Ivoclar Vivadent) of 2 mm in thickness and 4 mm in diameter were luted to the tooth surfaces by using 2 light-curing (RelyX Veneer [RV], 3M ESPE; Variolink Veneer [VV], Ivoclar Vivadent) and a dual-curing (Variolink II [V2], Ivoclar Vivadent) adhesive systems according to the manufacturers’ instructions. Shear bond strength test was performed in a universal testing machine at 0.5 mm/min until bonding failure. Failure modes were determined under a stereomicroscope, and fracture surfaces were evaluated with a scanning electron microscope. The data were statistically analysed (SPSS 17.0) (p = 0.05).

Results

Group RV-D exhibited the lowest bond strength value (5.42 ± 6.6 MPa). There was statistically no difference among RV-D, V2-D (13.78 ± 8.8 MPa) and VV-D (13.84 ± 6.2 MPa) groups (p > 0.05). Group VV-E exhibited the highest bond strength value (24.76 ± 8.8 MPa).

Conclusions

The type of tooth structure affected the shear bond strength of the porcelain laminate veneers to the 3 different types of tooth structures (enamel, dentine, and enamel–dentine complex).

Clinical significance

When dentine exposure is necessary during preparation, enough sound enamel must be protected as much as possible to maintain a good bonding; to obtain maximum bond strength, preparation margins should be on sound enamel.     

Bonding ability of 4-META self-etching primer used with 4-META/MMA-TBB resin to enamel and dentine: Primary vs permanent teeth

Objectives

The present study compared the efficacies of the self-etching Teeth Primer (TP: 4-META), and the etchants Red Activator (RA; 65% phosphoric acid) and Green Activator (GA; 10% citric acid with 3% ferric chloride), for bonding to enamel and dentine of human primary and permanent teeth, when used with 4-META/MMA-TBB resin (Bondfill SB).

Methods

Forty-eight non-carious primary canines and third molars were used. Eight groups were prepared: Group 1 (primary enamel with RA), Group 2 (permanent enamel with RA), Group 3 (primary enamel with TP), Group 4 (permanent enamel with TP), Group 5 (primary dentine with GA), Group 6 (permanent dentine with GA), Group 7 (primary dentine with TP) and Group 8 (permanent dentine with TP). Micro-tensile bond strengths (MTBS) were measured and analyzed statistically using ANOVAs and Tukey HSD tests at α = 0.05. Efficacy of etching/priming and the morphology of bonded interfaces were observed with SEM.

Results

Etching/priming efficacy of TP on enamel was low. The MTBS of Group 2 was significantly higher than the other groups (Groups 1, 3 and 4). For dentine, significant differences in MTBS were observed, in the order of Groups 6 > 8 > 7 = 5 (p < 0.05). The MTBSs of permanent dentine were significantly higher than primary dentine. For primary teeth, there was no significant difference in the MTBSs between enamel and dentine, irrespective of primer or etchant (p > 0.05).

Conclusion

TP primer/Bondfill SB may be used as an alternative to other adhesive/resin composite systems for bonding to enamel and dentine of primary teeth.     

Influence of the degree of dentine mineralization on pulp chamber temperature increase during resin-based composite (RBC) light-activation

Objectives

To analyse the influence of the degree of dentine mineralization on the pulp chamber temperature increase during composite light-activation.

Methods

Dentine discs (2 mm thick) obtained from recently extracted teeth or those with extensive dentine sclerosis were analysed by FT-IR spectrometry in order to choose the two discs with the greatest difference in the degree of mineralization. A model tooth was set up with the dentine discs between a molar with the pulp chamber exposed and a crown with a standardized class II cavity. A K-type thermocouple was introduced into the molar root until it came into contact with the dentine discs and the cavity was filled with P60 resin composite. The temperature rise was measured for 120 s after light-activation began: Standard (S) 600 mW/cm²/40 s; Ramp (R) 0 → 800 mW/cm²/10 s + 800 mW/cm²/10 s; Boost (B) 850 mW/cm²/10 s and LED (L) 1.300 mW/cm²/40 s (n = 10). The same protocol was repeated after grinding the dentine discs to 1.0 and 0.5 mm thickness.

Results

The temperature increase was significantly higher in dentine with high degree of mineralization (p < 0.05). With respect to the dentine thickness, the following result was found: 2 mm < 1 mm < 0.5 mm (p < 0.05). The light-activation mode also presented significant difference as follows: S > R = L > B (p < 0.05).

Conclusions

The higher the degree of dentine mineralization the greater the increase in pulp chamber temperature. The temperature increase was influenced by the light-polymerization mode and dentine thickness.     

A photochemical method for in vitro evaluation of fluid flow in human dentine

Objective

To evaluate the flow dynamics of dentine fluid using a chemiluminescence method in vitro.

Materials and methods

Horizontally sliced coronal dentine specimens with thicknesses of 1.4, 1.6, 1.8, and 2.0 mm (n = 10 each) were prepared from extracted human third molars. After cleaning with EDTA, a mounted specimen was clamped between 2 acrylic chambers attached to both the occlusal and pulpal sides. The occlusal chamber, which was closed with a glass coverslip, was filled with a chemiluminescent solution (0.02% luminol and 1% sodium hydroxide in water). A trigger solution of 1% hydrogen peroxide and 1% potassium ferricyanide was injected into the pulpal chamber at a constant pressure of 2.5 kPa, and allowed to immediately flow into the patent dentinal tubules. Four consecutive measurements (T1–T4) were performed on each sample by recording the emission of chemiluminescence with a photodetector. The relationship between the crossing time of the liquid through the slice and dentine thickness was examined.

Results

An apparent time delay was detected between the starting points of the trigger solution run and photochemical emission at T1. Dt (Dt, s) values of each thickness group were 13.6 ± 4.25 for 1.4 mm, 18.1 ± 2.38 for 1.6 mm, 28.0 ± 2.46 for 1.8 mm, and 39.2 ± 8.61 for 2.0 mm, respectively. Dt significantly decreased as dentine became thinner towards the pulp chamber (P < 0.001).

Conclusions

The velocity of fluid flow increased both with increasing dentine depth or reduction of remaining dentine thickness.     

Erosion-inhibiting potential of a stannous chloride-containing fluoride solution under acid flow conditions in vitro

Objectives

This study aimed to analyse the erosion-inhibiting potential of a single application of stannous chloride-containing fluoride solution on pellicle-covered enamel and dentine under constant acid flow conditions in vitro.

Design

Bovine enamel (n = 60) and dentine (n = 60) samples were exposed 1 h to the oral cavity of 4 healthy volunteers to allow for in situ pellicle formation. Pellicle-covered samples were randomly assigned to three groups (each n = 20 enamel and n = 20 dentine samples; 5 enamel and 5 dentine samples/volunteer) and treated once with a SnCl2/AmF/NaF (800 ppm Sn(II), 500 ppm F, pH 4.5) or a NaF solution (500 ppm F, pH 4.5) for 2 min or remained untreated (controls). Samples were eroded with hydrochloric acid (pH 2.6) in a small erosion chamber at 60 μl/min for 25 min. Calcium release into the acid was monitored in consecutive 30 s intervals for 5 min, then at 1 min intervals up to a total erosion time of 25 min using the Arsenazo III procedure. Data were statistically analysed by random-effects linear models (p < 0.05).

Results

The stannous chloride-containing fluoride solution reduced calcium loss of enamel and dentine to up to 6 min and 3.5 min, respectively. Calcium loss (% of control) amounted from 24 ± 7 (30 s) up to 93 ± 14 (6 min) in enamel and from 38 ± 13 (30 s) to 87 ± 15 (3.5 min) in dentine. The sodium fluoride solution was unable to reduce enamel and dentine erosion at any time point.

Conclusion

A single application of a stannous chloride-containing fluoride solution reduced enamel and dentine erosion up to 6 min and 3.5 min of constant acid flow, respectively.     

Effect of open-sandwich vs. adhesive restorative techniques on enamel and dentine demineralization: An in situ study

Objectives

To assess in situ the effect of different restorative techniques used with fluoride-releasing materials on enamel and dentine demineralization in the presence of a cariogenic challenge.

Methods

Thirty human molars were prepared for 60 Class V cavities, with enamel and dentine margins. The teeth were divided into four groups (n = 15): L1 – open sandwich technique with a conventional glass ionomer cement (GIC), L2 – open sandwich technique with a resin-modified GIC, A1 – total-etch bonding with a fluoride-containing adhesive, A2 – total-etch bonding with a nonfluoride-containing adhesive. All the cavities were restored with a nanofilled composite. Fifteen volunteers used appliances containing one specimen from each group. The cariogenic challenge was carried out with a 20% sucrose solution 8×/day for 7 days. The specimens were sectioned for microhardness test and EDS analysis at different depths below the enamel and dentine margins (25, 50 and 100 μm) and distances from the tooth-restoration interfaces (25 and 75 μm). The data were analyzed by ANOVA and Games–Howell test (α = 5%).

Results

Both GICs produced higher hardness in enamel at all depth-and-distance combinations, but only L1 produced higher hardness in dentine (p < 0.05). L2 and A1 exhibited similar dentine hardness at 25 μm distance for all depths (p > 0.05). L1 demonstrated significantly higher amounts of calcium in dentine than the other groups, but had similar amounts in enamel to L2 and A1.

Conclusions

The open sandwich technique using conventional GIC proved more effective in reducing enamel and dentine demineralization at depths of up to 100 μm under a cariogenic challenge.

Clinical significance

Conventional GICs should be considered the materials of choice for lining of cavities not having all margins in enamel, particularly using the open sandwich technique.     

Resistance to degradation of resin-modified glass-ionomer cements dentine bonds

Objective

To evaluate the effect of EDTA pre-treatment of dentine on resistance to degradation of the bond between dentine and resin-modified glass-ionomer cements.

Methods

Sixty non-carious human molars underwent cavity preparations. Teeth were restored with Fuji II LC or Vitremer. Half of the cavities were restored following manufacturers’ instructions whereas the other half was pre-treated with EDTA (0.1 M, pH 7.4) for 60 s. Teeth were stored in water at 37 °C for 24 h, 3 months or submitted to 10% NaOCl immersion for 5 h. Teeth were sectioned into beams (1 ± 0.1 mm) and tested to failure in tension at 0.5 mm/min. Bond strength data (MPa) were analyzed by ANOVA and SNK multiple-comparisons tests (p < 0.05).

Results

When EDTA was used for pre-treatment of dentine, higher bond strengths were observed for both cements. Degradation challenges produced a decrease in bond strength values only in the Vitremer group. This decrease was avoided when EDTA was used for dentine treatment before restoring with Vitremer.

Conclusions

EDTA pre-treatment of dentine increases bond strength of resin modified glass-ionomers cements to dentine and improves resistance to degradation of the bond between Vitremer and dentine.     

Hydrolytic degradation of the resin–dentine interface induced by the simulated pulpal pressure,direct and indirect water ageing

Objectives

The aim of this study was to compare the hydrolytic effects induced by simulated pulpal pressure, direct or indirect water exposure within the resin–dentine interfaces created with three “simplified” resin bonding systems (RBSs).

Methods

A two-step/self-etching (CSE: Clearfil SE Bond), one-step/self-etching (S3: Clearfil S3) and etch-and-rinse/self-priming (SB: Single-bond 2) adhesives were applied onto dentine and submitted to three different prolonged (6 or 12 months) ageing strategies: (i) Simulated Pulpal Pressure (SPP); (ii) Indirect Water Exposure (IWE: intact bonded-teeth); (iii) Direct Water Exposure (DWE: resin–dentine sticks). Control and aged specimens were submitted to microtensile bond strength (μTBS) and nanoleakage evaluation. Water sorption (WS) survey was also performed on resin disks. Results were analysed with two-way ANOVA and Tukey's test (p < 0.05).

Results

The μTBS of CS3 and SB dropped significantly (p < 0.05) after 6 months of SPP and DWE. CSE showed a significant μTBS reduction only after 12 months of DWE (p = 0.038). IWE promoted no statistical change in μTBS (p > 0.05) and no evident change in nanoleakage. Conversely, SPP induced a clear formation of “water-trees” in CS3 and SB. WS outcomes were CS3 > SB = CSE.

Conclusion

The hydrolytic degradation of resin–dentine interfaces depend upon the type of the in vitro ageing strategy employed in the experimental design. Direct water exposure remains the quickest method to age the resin–dentine bonds. However, the use of SPP may better simulate the in vivo scenario. However, the application of a separate hydrophobic solvent-free adhesive layer may reduce the hydrolytic degradation and increase the longevity of resin–dentine interfaces created with simplified adhesives.     

Effect of a pulsed CO2 laser and fluoride on the prevention of enamel and dentine erosion

Objective

The hypotheses of this study was that pulsed CO₂ laser (λ = 10.6 μm) treatment in combination (or not) with previous fluoride gel application could increase the resistance of enamel and dentine to erosion, throughout successive erosive challenges.

Design

Thirty-two bovine specimens of enamel and of root dentine were flattened, polished and randomly assigned to the following treatments (n = 8): fluoride (F), laser (L), fluoride + laser (FL) or no treatment as negative control (C). The treated specimens were submitted to demineralization (0.3% citric acid, pH 2.45, for 5 min) and remineralization (artificial saliva, for 60 min) cycles, three times a day, for 3 days. Dental surface loss as well as the concentration of calcium, phosphorus and fluoride in the demineralizing solutions were determined after each cycling day. Enamel and dentine were analysed separately using repeated measures ANOVA for ranks (α = 0.05).

Results

The association between fluoride and laser (FL) resulted in the lowest enamel and dentine surface loss values throughout the cycles, differing significantly from the control group. No clear benefit of FL over the F or L treatments was observed. There was a non-significant trend (p > 0.05) for FL to release less calcium, phosphorus and fluoride into the demineralizing solutions when compared to the other groups.

Conclusions

Pulsed CO₂ laser (λ = 10.6 μm) alone was not able to prevent enamel or dentine surface losses due to erosion. Laser treatment in combination with fluoride showed some protection, but the effect does not appear to be synergistic.     

Inhibition of tooth erosion by milk containing different fluoride concentrations: An in vitro study

Objectives

This in vitro study assessed the effect of milk containing different fluoride concentrations on tooth erosion.

Methods

Bovine enamel and root dentine specimens were treated with: (1) bovine whole milk with 0 ppm F; (2) 2.5 ppm F; (3) 5 ppm F; (4) 10 ppm F (all after erosion); (5) whole milk with 0 ppm F (before erosion); (6) NaF (0.05% F, positive control, after erosion) or (7) 0.9% NaCl (negative control, after erosion). The specimens were submitted to pH cycles (4× 90 s in soft drink) and treatments for 5 days. The specimens were immersed in the treatment solutions for 1 min (only at the first cycle each day) with further exposition to 1:1 milk:saliva slurry for 10 min. The tooth loss was measured using a contact profilometer and statistically analysed (p < 0.05).

Results

Rinsing with milk before erosive challenge significantly reduced tooth loss compared to negative control (67% and 24% reduction in dentine and enamel loss, respectively) and to milk after erosive challenge, only for dentine. The addition of fluoride to milk also reduced tooth loss compared to negative control, but with no significant differences among fluoride concentrations for enamel and dentine (μm), respectively: 0 ppm (3.63 ± 0.04 and 2.51 ± 0.53), 2.5 ppm F (2.86 ± 0.42 and 1.96 ± 0.47), 5 ppm F (2.81 ± 0.27 and 1.77 ± 0.44), 10 ppm F (2.03 ± 0.49 and 1.68 ± 0.59). There was a negative and significant correlation between [F] and the tooth loss.

Conclusions

Daily rinse with milk containing F is able to reduce both enamel and dentine erosion in vitro.

Clinical significance

Since the prevalence of dental erosion is steadily increasing, rinse with milk or its derivate might be an important strategy to reduce the progression of tooth erosion.     

Effect of simulated pulpal microcirculation on intrachamber temperature changes following application of various curing units on tooth surface

Objective

The purpose of this study was to evaluate ex vivo the rise in intrachamber temperature induced by the application of various curing units on tooth surface, under conditions of continuous water flow inside the pulp chamber simulating pulp microcirculation.

Methods

Fifteen extracted intact human teeth were selected. Intrachamber temperature increases were induced by applying the following curing units to the buccal aspect of the tested teeth: a conventional halogen lamp, two high-intensity halogen lamps, a plasma arc curing light, a mercury/metal-halide lamp, and a diode laser. Temperature changes on the tooth surfaces were recorded using thermocouples connected to a data logger. The Greenhouse–Geisser and Bonferroni tests in the SPSS software package were used for analysis of the data. The level of significance was set at 0.05.

Results

Under conditions of water flow the average intrachamber temperature rise was less than 6 °C, for all curing units. Without water flow, the increase in pulp temperature exceeded 6 °C for all units except the conventional halogen lamp. The diode laser produced a significantly greater temperature increase than any other curing unit. Application of the diode laser and the two high-intensity halogen lamps to lateral incisor specimens produced significantly greater temperature increases than other teeth.

Conclusions

When the simulated pulp microcirculation was absent, the temperature increases produced by all curing units except the conventional halogen lamp were large enough to be potentially harmful to the pulp. On the contrary, with the cooling effect of water flow inside the pulp chamber, all units proved to be safe for use.     

Extracts of irradiated mature human tooth crowns contain MMP-20 protein and activity

Objectives

We recently demonstrated a significant correlation between enamel delamination and tooth-level radiation dose in oral cancer patients. Since radiation can induce the synthesis and activation of matrix metalloproteinases, we hypothesized that irradiated teeth may contain active matrix metalloproteinases.

Materials and methods

Extracted teeth from oral cancer patients treated with radiotherapy and from healthy subjects were compared. Extracted mature third molars from healthy subjects were irradiated in vitro and/or incubated for 0–6 months at 37 °C. All teeth were then pulverized, extracted, and extracts subjected to proteomic and enzymatic analyses.

Results

Screening of irradiated crown extracts using mass spectrometry identified MMP-20 (enamelysin) which is expressed developmentally in dentine and enamel but believed to be removed prior to tooth eruption. MMP-20 was composed of catalytically active forms at Mr = 43, 41, 24 and 22 kDa and was immunolocalized predominantly to the morphological dentine enamel junction. The proportion of different sized MMP-20 forms changed with incubation and irradiation. While the pattern was not altered directly by irradiation of healthy teeth with 70 Gy, subsequent incubation at 37 °C for 3–6 months with or without prior irradiation caused the proportion of Mr = 24–22 kDa MMP-20 bands to increase dramatically. Extracts of teeth from oral cancer patients who received >70 Gy radiation also contained relatively more 24 and 22 kDa MMP-20 than those of healthy age-related teeth.

Conclusion

MMP-20 is a radiation-resistant component of mature tooth crowns enriched in the dentine–enamel. We speculate that MMP-20 catalyzed degradation of organic matrix at this site could lead to enamel delamination associated with oral cancer radiotherapy.