12-Month color stability of enamel,dentine, and enamel–dentine samples after bleaching

The study aimed to quantify the color regression of enamel (E), dentine (D), and combined enamel–dentine (ED) of differently bleached ED specimens over a period of 12 months in vitro. Two ED samples were obtained from the labial surfaces of bovine teeth and prepared to a standardized thickness with the enamel and dentine layer each 1 mm. The ED samples were distributed on four groups (each n = 80), in which the different bleaching products were applied on enamel (1, Whitestrips; 2, Illuminé 15%; 3, Opalescence Xtra Boost) or dentine surfaces (4, mixture of sodium perborate/distilled water). Eighty ED samples were not bleached (control). Color (L*a*b*) of ED was assessed at baseline, subsequently after bleaching and at 3, 6, and 12 months of storage after bleaching (each 20 samples/group). E and D samples were prepared by removing the dentine or enamel layer of ED samples to allow for separate color analysis. Bleaching resulted in a significant color change (ΔE) of ED specimens. Within the observation period, ΔL but not Δb declined to baseline. L* values of E and D samples also declined and were not significantly different from control samples after 12 months, while b* values did not decrease to baseline. Generally, no differences between the bleaching agents could be observed. Color change of enamel, dentine, and combined ED of in vitro bleached tooth samples is not stable over time with regard to lightness. However, yellowness did not return to baseline within 1 year.     

In vivo spectrophotometric evaluation of pure enamel and enamel–dentine complex in relationship with different age groups

Objective

The aim of this in vivo study was to investigate the influence of age on optical properties of pure enamel and enamel–dentine complex.

Methods

A spectrophotometric study was performed on two different age groups: young (10–35 years old) and adult (36–60 years old). In both groups, the tooth's total area of the upper right central incisor was recorded. Areas of 2 mm thick pure enamel and 3 mm enamel–dentine complex were detected and their L*a*b* and CR evaluated.

Results

For 2 mm pure enamel medians in the young group were L*74.8, a*3.1, b*15.1, against white background; and L*65.5, a*0.9, b*10.3 against black background. The correspondent opacity was 75%. In the adult group medians were L*70.0, a*4.1, b*15.4 against white background; and L*61.2, a*1.6, b*9.6, against black background. The correspondent opacity was 75%. For 3 mm enamel–dentine complex medians in the young group were L*77.8, a*3.0, b*19.8 against white background; and L*74.2, a*1.1, b*15.9, against black background. The correspondent opacity was 89%. In the adult group medians were L*73.4, a*4.0, b*18.5 against white background; and L*71.0, a*2.0, and b*15.3 against black background. The correspondent opacity was 90%.

Discussion

The application of this method on a larger group of subjects of different ages may serve as a database for a more exact characterization of optical properties of natural enamel and dentine.

Conclusions

L* values in enamel, as well as a* value of 3 mm thick enamel–dentine complex and 2 mm pure enamel were significantly higher in the young age group.

Clinical significance

L* and a* values of enamel over white and black backgrounds were statistically different within the 2 age groups considered. L* values over white background and a* values over black background of the enamel dentine complex seem to change with age. The opacity (CR) for enamel nor for enamel dentine complex does not change within the two age groups considered in this study.     

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 to dentin and enamel where does it stand in 2005?

Bonding to acid-etched enamel is well-known, effective, predictable and long-lasting. Bonding to dentin has had a less satisfactory history to date, but it has been highly recommended and researched. This article discusses the controversies in this subject and blends research and clinical observations to make some logical conclusions about how and when to use the various enamel and dentinal bonding materials that are available today.     

Shear bond strength and enamel fracture behavior of ceramic brackets Fascination? and Fascination?2

Objective

The purpose of this study was to compare the shear bond strength and incidence of enamel fractures of the ceramic brackets Fascination? and Fascination?2.

Materials and methods

A total of 360 teeth (180 first upper bicuspids and 180 lower incisors) were stored in 96% ethanol, while 360 other teeth (180 first upper bicuspids and 180 lower incisors) were stored in 0.1% thymol. All 720 teeth were bonded one-half each with Fascination? and Fascination?2 brackets using three different adhesives and three different light curing units. The teeth were debonded with a debonding-device according to DIN EN ISO 10477 using a universal testing machine with a crosshead speed of 1?mm per minute. The enamel surface was then examined stereomicroscopically (10x and 40x magnification). The non-parametric Mann?CWhitney U test was used, since the data were not normally distributed.

Results

The Fascination?2 brackets provided significantly lower shear bond strength than Fascination? brackets (p?=?0.003). Fascination? brackets demonstrated significantly fewer, smaller enamel fractures than Fascination?2 brackets (p?=?0.012).

Conclusion

The lower shear bond strength of the Fascination?2 brackets is clinically acceptable, but our study??s experimental design did not enable us to prove whether this is clinically associated with a lower risk of enamel fracture.     

Correlation of ultrasound microscopy and Vickers hardness measurements of human dentin and enamel — A pilot study

Objective

To investigate if Vickers microhardness of dentin and enamel correlated with acoustic velocity c(l) or acoustic reflection from the sample’s top (amplitude).

Is fluoride concentration in dentin and enamel a good indicator of dental fluorosis?

Despite some studies correlating dental fluorosis (DF) and fluoride (F) concentration in dental enamel, no information is available about DF and dentin F concentration. Our objective was to determine the correlation between teeth F concentration and DF severity in unerupted human 3rd molars, and the correlation between dentin and enamel F concentrations in the same tooth. Ninety-nine 3rd molars were studied-53 from Fortaleza, Brazil (F water, 0.7 ppm), 22 from Toronto (1.0 ppm), and 24 from Montreal (0.2 ppm). DF severity was evaluated according to the Thylstrup-Fejerskov Index, while F concentration was analyzed by Instrumental Neutron Activation Analysis. DF severity varied between TF0 and TF4, while F concentration ranged between 39 and 550 ppm in enamel and 101 and 860 ppm in dentin. Our results showed correlation between dentin F concentration and DF (r(S) = 0.316, p = 0.001), but no correlation between enamel F concentration and DF (r(S) = 0.154, p = 0.133). No correlation was observed between dentin and enamel F concentrations in the same tooth (r(S) = 0.064, p = 0.536).     

TGF-β autocrine signaling at secretory-stage enamel

Background

In recent years, transforming growth factor (TGF)-β has been found in the enamel matrix, and along with enamel protein, is thought to play an important role in the process of calcification of tooth enamel. The purpose of this study was to investigate the dynamics of TGF-β and its interactions with enamel proteins, through experiments at the genetic and protein levels.

Does the acidity of self-etching primers affect bond strength and surface morphology of enamel?

PURPOSE: This study examined the ultrastructure and microtensile bond strengths (TBS) of self-etching (with different acidity) and conventional adhesive systems bonded to unground enamel. MATERIALS AND METHODS: Resin composite (Filtek Z250) buildups were bonded to unground enamel surfaces of third molars after adhesive application with the following materials: Clearfil SE Bond (CSE); Optibond Solo Plus Self-Etch (OP); Tyrian Self Priming Etching (TY), and the controls Scotchbond Multi-Purpose Plus (SBMP) and Single Bond (SB). Six teeth were assigned to each material. After storage in waterfor 24 h at 37 degrees C, the bonded specimens were sectioned into beams of approximately 0.8 mm2 and subsequently subjected to microTBS testing at a crosshead speed of 0.5 mm/min. The average values were subjected to one-way ANOVA (alpha = 0.05). The effect of surface conditioning of each material was observed under scanning electron microscopy (SEM). RESULTS: The highest resin-enamel bond strength was observed for SBMP (22.7 +/- 5.2) and SB (26.7 +/- 5.2 MPa). The lowest mean bond strengths were 10.9 +/- 3.2 and 7.8 +/- 1.5 MPa for TY and OP, respectively. CSE showed an intermediate performance (18.7 +/- 4.6 MPa). An overall increase in porosity was evident along the entire enamel surface treated with the self-etching primers; however, no selective demineralization similar to that with 35% phosphoric acid was observed. CONCLUSION: The highest bond strength means and the more retentive etching pattern were observed for the two-step etch-and-rinse adhesives. Among the self-etching systems studied, Clearfil SE Bond should be preferred.     

Investigation of five α-hydroxy acids for enamel and dentin etching: Demineralization depth,resin adhesion and dentin enzymatic activity

ObjectivesSurface conditioning of enamel and dentin is a key step during adhesive restorative procedures and strategies. The aim of this study was to investigate the effectiveness of five α-hydroxy-acids (AHAs) as enamel and dentin surface etchants.MethodsEnamel and dentin specimens were prepared from human molars to determine the depth of demineralization by optical profilometry (Δz), the resin bond strength to enamel and dentin (μTBS), the micro-permeability of dentin–resin interfaces, and the gelatinolytic activity of dentin matrix induced by AHAs [glycolic (GA), lactic (LA), citric (CA), malic (MI) and tartaric (TA)] and controls [phosphoric (PA) and maleic (MA)]. All acids were prepared at 35% concentration. Adhesion studies employed Adper Single Bond Plus bonding system. Data were individually processed and analyzed by ANOVA, post-hoc tests and Pearson correlations (α = 0.05).ResultsAHA exhibited statistically lower depth of demineralization of enamel and dentin (average 4 fold) than controls (p < 0.001). In enamel, MA and PA etching resulted in higher μTBS than AHA groups (p < 0.001). In dentin, GA, TA, CI and LA etching resulted in statistically similar μTBS than PA (p < 0.05). The hybrid-layer (HL) thickness and interfacial micro-permeability intensity were statistically lower for AHA groups (p < 0.05). A significant positive correlation was observed between the intensity of micro-permeability and the thickness of HL (p < 0.05). AHA etchants elicited lower dentin enzymatic activity than controls (p < 0.05).SignificanceAHAs effectively etched enamel and dentin surfaces. In particular, GA and TA resulted in suitable μTBS and sealing ability as well as induced less gelatinolytic activity in dentin than PA and MA.     

Protein content of molar–incisor hypomineralisation enamel

Objectives

The aim of the study was to compare the relative amounts and nature of the proteinous content of sound and molar–incisor hypomineralisation (MIH) enamel.

Methods

TCA (20%) was used to dissolve the mineral phase and precipitate the proteins from enamel pieces sectioned from sound and MIH enamel. The protein content was estimated using a miniaturized version of the method of Lowry et al. Samples of the solubilised protein were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), stained with Coomassie Blue R250 and tryptic fingerprint/mass spectrometry (MS/MS) of bands in excised gel pieces used for protein identification.

Results

Compared to sound enamel, brown enamel showed a 15–21-fold higher protein content, and yellow and chalky enamel showed about 8-fold higher protein content. Tryptic fingerprint/MS performed on excised 50–70 kDa areas demonstrated serum albumin, type I collagen and antitrypsin to be common to all types of enamel. Yellow and brown enamel showed more abundant serum albumin and antitrypsin, and the presence of serum antithrombin. Albumin is reported to be an inhibitor of crystal growth, and antitrypsin and antithrombin inhibit kallikrein 4 proteolytic activity.

Conclusions

The combination of the effects of serum proteins on developing enamel may result in elevated proteinous content and reduced mineral content as seen in MIH enamel.     

Efficacy of TiF4 and NaF varnish and solution: a randomized in situ study on enamel erosive–abrasive wear

Objectives

This in situ/ex vivo study analysed the anti-erosive/abrasive effect of TiF₄ and NaF varnish and solution on enamel wear.

Materials and methods

Twelve subjects took part in this study which was performed in three periods (phases) with the duration of 5 days each. Each two human enamel specimens per subject were pretreated with experimental NaF varnish or solution (phase A), experimental-TiF₄ varnish or solution (phase B) and placebo varnish or untreated control (phase C). The specimens were worn in palatal appliances; one enamel specimen, from each treatment, was subjected to erosion (ERO; cola soft drink, 4?×?90 s/day), and the other specimen was subjected to erosion plus abrasion (ERO + ABR; tooth brushing, 2?×?10 s/day). The tooth wear was quantified by a contact profilometer (micrometre) and analysed using two-way repeated measures ANOVA and Bonferroni’s test (n?=?12 subjects, p?<?0.05).

Results

All fluoride varnishes and solutions reduced the enamel wear (around 25 %) significantly compared to the control and placebo varnish. There were no significant differences among the fluoride formulations and between the conditions ERO and ERO + ABR.

Conclusions

Therefore, it can be concluded that TiF₄ has the same protective potential as NaF formulations to reduce human enamel wear under this experimental in situ model.

Clinical significance

In vitro studies have indicated a better anti-erosive/abrasive effect of TiF₄ compared to NaF varnish. The present in situ study does not support the previous findings. Therefore, any of the tested professional fluoride varnishes in principle could be able to partially reduce enamel wear.     

Combined effect of a fluoride-, stannous- and chitosan-containing toothpaste and stannous-containing rinse on the prevention of initial enamel erosion–abrasion

Objectives

The aim of this study was to assess the preventive effect of a fluoride-, stannous- and chitosan-containing (F/Sn/chitosan-) toothpaste (TP) on initial enamel erosion and abrasion.

Methods

In total, 150 human premolar enamel specimens were ground, polished and divided into 5 toothpaste/rinse groups (n = 30): (G1) placebo-TP/tap water, (G2) sodium fluoride (NaF-) TP/tap water, (G3) F/Sn/chitosan-TP/tap water, (G4) F/Sn/chitosan-TP/Sn-rinse, (G5) NaF-TP/NaF-rinse. The 8-day erosion–abrasion cyclic treatment (one cycle/day) consisted of incubating the samples in artificial saliva (30 min), then submitting the samples to toothbrush abrasion (2 min incubation in toothpaste slurry; brushing with 20 toothbrush strokes) and rinsing (2 min; 10 ml) with the respective solution: tap water (G1–G3), Sn-rinse (G4) or NaF-rinse (G5). Afterwards, the samples were submitted to erosion (2 min; 30 ml 1% citric acid, pH = 3.6). Surface microhardness (SMH) was measured initially and after every abrasion and erosion treatment. Enamel substance loss was calculated after each abrasion. Non-parametric ANOVA followed by Wilcoxon rank tests were used for analysis.

Results

G1 presented the greatest SMH decrease, while G4 presented the least SMH decrease (p < 0.001). G3 had a similar SMH decrease to G2 and G5. Substance loss was significantly lower in G4 than all other groups (p < 0.05), closely followed by G3. Both G2 and G5 showed similar calculated enamel substance loss to G1.

Conclusion

The treatment with F/Sn/chitosan-TP and tap water provided a similar SMH decrease to both NaF-TP groups, but significantly lower substance loss. F/Sn/Chitosan-TP and Sn-rinse showed a better preventive effect, which promoted less SMH decrease and reduced substance loss.

Clinical significance

The toothpaste containing fluoride, stannous and chitosan shows promising results in reducing substance loss from erosion and abrasion. The combination of this toothpaste with the stannous-containing rinse showed even better prevention against erosion–abrasion.     

Interfacial and surface characterization of two self-etching adhesive systems and a total-etch adhesive after bonding to ground and unground bovine enamel—a qualitative study

The purpose of the study was to evaluate the enamel surface and interface morphology of two self-etching adhesive systems (SAS) vs a total-etch control, after bonding to ground and unground enamel using field emission scanning electron microscopy (FESEM). Thirty bovine incisors were used in this study. The buccal enamel surface of 15 teeth was ground flat to resemble freshly cut enamel. The rest of the teeth were left intact. Two SAS, Clearfil SE Bond (CSE, Kuraray) and Prompt L-Pop (3M-ESPE), and a conventional adhesive system, Scotchbond Multipurpose (3M-ESPE, control), were used to condition the surface of unground and ground enamel on 12 teeth. A composite button was bonded to the remaining 18 teeth; a cross-section (1 mm thick) was obtained from each and the bonded interface was polished. All specimens were dehydrated in ascending grades of ethanol, gold-sputter-coated, and observed under FESEM (Hitachi S-4000) to evaluate the ultrastructural morphology of the enamel surface and the enamel–dentin interface. The etching patterns and adhesive penetration varied according to the aggressiveness of the SAS, with CSE being the mildest and H₃PO₄ being the most aggressive. There were no significant differences on the ultrastructural morphology of the enamel surface between unground and ground specimens. It appears that microporosities within enamel prisms provide sufficient enamel–resin hybridization in unground enamel. The enamel dissolution pattern and depth of infiltration depend on the type of SAS used, with no significant differences in unground and ground enamel.     

Cellular viability and genetic expression of human gingival fibroblasts to zirconia with enamel matrix derivative (Emdogain?)

PURPOSE

The objective of this study was to investigate the biologic effects of enamel matrix derivative (EMD) with different concentrations on cell viability and the genetic expression of human gingival fibroblasts (HGF) to zirconia surfaces.

MATERIALS AND METHODS

Immortalized human gingival fibroblasts (HGF) were cultured (1) without EMD, (2) with EMD 25 µg/mL, and (3) with EMD 100 µg/mL on zirconia discs. MTT assay was performed to evaluate the cell proliferation activity and SEM was carried out to examine the cellular morphology and attachment. The mRNA expression of collagen type I, osteopontin, fibronectin, and TGF-β1 was evaluated with the real-time polymerase chain reaction (RT-PCR).

RESULTS

From MTT assay, HGF showed more proliferation in EMD 25 µg/mL group than control and EMD 100 µg/mL group (P<.05). HGFs showed more flattened cellular morphology on the experimental groups than on the control group after 4h culture and more cellular attachments were observed on EMD 25 µg/mL group and EMD 100 µg/mL group after 24h culture. After 48h of culture, cellular attachment was similar in all groups. The mRNA expression of type I collagen increased in a concentration dependent manner. The genetic expression of osteopontin, fibronectin, and TGF-β1 was increased at EMD 100 µg/mL. However, the mRNA expression of proteins associated with cellular attachment was decreased at EMD 25 µg/mL.

CONCLUSION

Through this short term culture of HGF on zirconium discs, we conclude that EMD affects the proliferation, attachment, and cell morphology of HGF cells. Also, EMD stimulates production of extracellular matrix collagen, osteopontin, and TGF-β1 in high concentration levels.

CLINICAL RELEVANCE

With the use of EMD, protective barrier between attached gingiva and transmucosal zirconia abutment may be enhanced leading to final esthetic results with implants.