Composite cements benefit from light-curing

Objective

To investigate the effect of curing of composite cements and a new ceramic silanization pre-treatment on the micro-tensile bond strength (μTBS).

Methods

Feldspathic ceramic blocks were luted onto dentin using either Optibond XTR/Nexus 3 (XTR/NX3; Kerr), the silane-incorporated ‘universal’ adhesive Scotchbond Universal/RelyX Ultimate (SBU/RXU; 3M ESPE), or ED Primer II/Panavia F2.0 (ED/PAF; Kuraray Noritake). Besides ‘composite cement’, experimental variables were ‘curing mode’ (‘AA’: complete auto-cure at 21 °C; ‘AA*’: complete auto-cure at 37 °C; ‘LA’: light-curing of adhesive and auto-cure of cement; ‘LL’: complete light-curing) and ‘ceramic surface pre-treatment’ (‘HF/S/HB’: hydrofluoric acid (‘HF’: IPS Ceramic Etching Gel, Ivoclar-Vivadent), silanization (‘S’: Monobond Plus, Ivoclar-Vivadent) and application of an adhesive resin (‘HB’: Heliobond, Ivoclar-Vivadent); ‘HF/SBU’: ‘HF’ and application of the ‘universal’ adhesive Scotchbond Universal (‘SBU’; 3M ESPE, only for SBU/RXU)). After water storage (7 days at 37 °C), ceramic–dentin sticks were subjected to μTBS testing.

Results

Regarding the ‘composite cement’, the significantly lowest μTBSs were measured for ED/PAF. Regarding ‘curing mode’, the significantly highest μTBS was recorded when at least the adhesive was light-cured (‘LA’ and ‘LL’). Complete auto-cure (‘AA’) revealed the significantly lowest μTBS. The higher auto-curing temperature (‘AA*’) increased the μTBS only for ED/PAF. Regarding ‘ceramic surface pre-treatment’, only for ‘LA’ the μTBS was significantly higher for ‘HF/S/HB’ than for ‘HF/SBU’.

Significance

Complete auto-cure led to inferior μTBS than when either the adhesive (on dentin) or both adhesive and composite cement were light-cured. The use of a silane-incorporated adhesive did not decrease luting effectiveness when also the composite cement was light-cured.     

The repair potential of resin composite materials

Objectives

To measure the ‘repair’ strength of various combinations of composite using four manufacturers’ adhesive systems, to compare the bond strengths with the cohesive strength of the original, unrepaired products and to assess whether the chemical nature of the resin matrix influenced the repair strength.

Methods

Specimens were prepared of three composite materials Durafill, Heraeus Kulzer; P90 (Silorane) 3M ESPE; Z250 (3M ESPE) and aged in water at 60 °C for 1 month. One surface of each specimen was faced with 80-grit silicone carbide paper, one of four adhesives placed (Ecusit, DMG; Clearfil Repair, Kuraray; P90 System Adhesive; Single Bond 2, 3 M ESPE) and ‘repair’ composite added of the same type as above, such that all combinations of original and repair composite and adhesive were used. ‘Stick’ samples, approximately 6 mm × 0.8 mm × 4 mm were prepared from each repair specimen, a neck created at the junction of original and repair composites and the hour-glass sample tested in tension at 1 mm/min. The microtensile bond strength of the repair was calculated and the mode of failure (adhesive; cohesive in the original composite; cohesive in the repair composite) recorded.

Results

There was no significant difference between the cohesive strengths of Filtek P90 and Filtek Z250 (both ≈106 MPa); both were significantly stronger than Durafill (67.0 MPa). For bonding to Durafill the bond strengths ranged from 17.6 MPa to 50.9 MPa; for bonding to P90, the bond strengths ranged from 5.0 MPa to 54.2 MPa; for bonding to Z250, the bond strengths ranged from 17.2 MPa to 75.4 MPa. Clearfil Repair appeared to provide the most consistently high bond strengths, followed by the P90 System Adhesive, Single Bond 2 and Ecusit. Overall, the majority of failures (74%) was adhesive.

Significance

It appears that bonding of new dimethacrylate-based composite to old dimethacrylate-based composite can be a viable clinical procedure. However, if the original composite is silorane-based (e.g., P90), then using the silane-based adhesive may be the best repair option, and similarly if it is planned to effect a repair with a silorane-based composite, using a silane-based adhesive may give the best outcome. The null hypotheses are thus rejected.     

Curing mode affects bond strength of adhesively luted composite CAD/CAM restorations to dentin

Objectives

To determine the effect of curing mode and restoration-surface pre-treatment on the micro-tensile bond strength (μTBS) to dentin.

Methods

Sandblasted CAD/CAM composite blocks (LAVA Ultimate, 3M ESPE) were cemented to bur-cut dentin using either the etch & rinse composite cement Nexus 3 (‘NX3’, Kerr) with Optibond XTR (‘XTR’, Kerr), or the self-etch composite cement RelyX Ultimate (‘RXU’, 3M ESPE) with Scotchbond Universal (‘SBU’, 3M ESPE). All experimental groups included different ‘curing modes’ (light-curing of adhesive and cement (‘LL’), light-curing of adhesive and auto-cure of cement (‘LA’), co-cure of adhesive through light-curing of cement (‘AL’), or complete auto-cure (‘AA’)) and different ‘restoration-surface pre-treatments’ of the composite block (NX3: either a silane primer (Kerr), or the XTR adhesive; RXU: either silane primer (RelyX Ceramic Primer, 3M ESPE) and SBU, or solely SBU). After water-storage (7 days, 37 °C), the μTBS was measured. Additionally, the degree of conversion (DC) of both cements was measured after 10 min and after 1 week, either auto-cured (21 °C/37 °C) or light-cured (directly/through 3-mm CAD/CAM composite).

Results

The linear mixed-effects model (α = 0.05) revealed a significant influence of the factors ‘curing mode’ and ‘composite cement’, and a less significant effect of the factor ‘restoration-surface pre-treatment’. Light-curing ‘LL’ revealed the highest μTBS, which decreased significantly for all other curing modes. For curing modes ‘AA’ and ‘AL’, the lowest μTBS and a high percentage of pre-testing failures were reported. Overall, DC increased with light-curing and incubation time.

Significance

The curing mode is decisive for the bonding effectiveness of adhesively luted composite CAD/CAM restorations to dentin.     

Durable bonding to mechanically and/or chemically pre-treated dental zirconia

Objectives

To evaluate the effect of mechanical and chemical surface pre-treatment on the bond durability of two composite cements to dental zirconia.

Methods

Fully sintered IPS e.max ZirCAD (Ivoclar-Vivadent) blocks were either subjected to tribochemical silica sandblasting (CoJet, 3M ESPE) or not mechanically pre-treated. Next, the zirconia samples were either additionally pre-treated using one of two silane/MDP-combined ceramic primers (Clearfil Ceramic Primer, Kuraray; Monobond Plus, Ivoclar-Vivadent), or not further chemically pre-treated. Finally, two identically pre-treated zirconia blocks were bonded together using either a conventional BisGMA-based (Clearfil Esthetic Cement, Kuraray) or an MDP-based (Panavia F2.0, Kuraray) ‘self-etch’ dual-cure composite cement. The specimens were trimmed at the interface to a cylindrical hour-glass shape and stored for 7 days in distilled water (37 °C), after which they were randomly exposed to one of three ageing protocols: (1) immersed in 37 °C water for 10 days (10 d); (2) subjected to 10,000 thermo-cycles (TC); or (3) immersed in 37 °C water for 6 months (6 m). After storage, the micro-tensile bond strength (μTBS) was determined in MPa (n = 15–21/group). Fractographic analysis was performed using SEM.

Results

Weibull analysis revealed the highest Weibull scale and shape parameters for the ‘CoJet/Clearfil Ceramic Primer/Panavia F2.0/10d’ combination. While the BisGMA-based composite cement Clearfil Esthetic Cement (Kuraray) bonded equally well to zirconia using either tribochemical silica sandblasting (CoJet, 3M ESPE) or not, sandblasting appeared indispensable for the MDP-based and more hydrophilic composite cement Panavia F2.0 (Kuraray).

Conclusions

Combined mechanical and chemical pre-treatment can best be recommended to durably bond to zirconia.

Clinical significance

As a standard procedure to durable bond zirconia to tooth tissue, both mechanical (tribochemical silica coating) and chemical (silane/MDP-combined ceramic primers) is clinically highly recommended.     

Is there one optimal repair technique for all composites?

Objectives

The aim of this study was to investigate the effectiveness of a variety of techniques to bond new composite to artificially aged composite of different compositions.

Methods

Composite resin blocks were made of five different commercially available composites (n = 30) (Clearfil AP-X, Clearfil PhotoPosterior, Photo Clearfil Bright, Filtek Supreme XT and HelioMolar). After aging the composite blocks (thermo-cycling 5000×), blocks were subjected to one of 9 repair procedures: no treatment (control), diamond bur, sandblasting alumina particles, CoJet™, phosphoric acid, 3% hydrofluoric acid 20 s or 120 s, 9.6% hydrofluoric acid 20 s or 120 s. In addition, the cohesive strength of the tested composites was measured. Two-phase sandwiches (‘repaired composite’) were prepared using each of the 9 repair protocols, successively followed by silane and adhesive (OptiBond FL) treatment, prior to the application of the same composite. Specimens were subjected to micro-tensile bond strength testing. Data were analyzed using ANOVA and Tukey's HSD (p < 0.05).

Results

For all composites the lowest bond strength was obtained when no specific repair protocol (control) was applied; the highest for the cohesive strength. Compared to the control for the microhybrid composite (Clearfil AP-X) five repair techniques resulted in a significantly higher repair strength (p < 0.05), whereas for the nano-hybrid composite (Filtek Supreme XT) and hybrid composite containing quartz (Clearfil PhotoPosterior) only one repair technique significantly increased the bond strength (p < 0.01).

Significance

None of the surface treatments can be recommended as a universally applicable repair technique for the different sorts of composites. To optimally repair composites, knowledge of the composition is helpful.     

Effect of ball milling on structures and properties of dispersed-type dental amalgam

Objectives

The purpose of the present study was to investigate the effect of ball milling on the initial mercury vapor release rate and mechanical properties such as compressive strength, diametral tensile strength and creep value, of the dispersed-type dental amalgam, and comparison was made with respect to two commercial amalgam alloys.

Methods

Ball milling was employed to modify the configuration of the originally spherical-shaped Ag-Cu-Pd dispersant alloy particles. Improvement in mechanical properties while maintaining a low early-stage mercury vapor release rate of the amalgam is attempted.

Results

The experimental results show that the amalgam (AmB10) which was made from Ag-Cu-Pd dispersant alloy particles that were ball-milled for 10 min and heat-treated at 300 °C for 2 days exhibited a low initial mercury vapor release rate of 69 pg/mm²/s, which was comparable with that of commercial amalgam alloy Tytin (68 pg/mm²/s), and was lower than that of Dispersalloy (73 pg/mm²/s). As for mechanical properties, amalgam AmB10 exhibited the highest 1 h compressive strength (228 MPa), which was higher than that of commercial amalgam alloy Dispersalloy by 72%; while its 24 h diametral tensile strength was also the highest (177 MPa), and was higher than that of Dispersalloy by 55%. Furthermore, the creep value of the amalgams made from Ag-Cu-Pd alloy particles with 10 min ball-milling and heat treatment at 300 °C for 2 days was measured to be 0.12%, which was about 20% that of Dispersalloy.

Significance

It is found that ball milling of the dispersant Ag-Cu-Pd alloy particles for 10 min was able to modify the configuration of the alloy particles into irregular-shapes. Subsequently, heat treatment at 300 °C significantly lowered the initial mercury vapor release rate, increased its 1 h compressive strength and 1 h diametral tensile strength, and lowered its creep value.     

Effect of 3-year water storage on the performance of one-step self-etch adhesives applied actively on dentine

Objectives

To evaluate the effect of the application method on the immediate and 3-year resin-dentine bond strength (μTBS) and nanoleakage (NL) for 3 one-step self-etch adhesives (Adper Prompt L-Pop; Clearfil S³ Bond and Xeno III).

Methods

The occlusal enamel of 42 human molars were removed to expose a flat dentine surface. The adhesives were applied under inactive or active application. After light-curing (600 mW/cm² for 10 s), composite buildups were constructed incrementally and sectioned to obtain bonded sticks (0.8 mm²) to be tested in tension immediately or after 3 years of water storage of water storage. For NL, 2 bonded sticks from each tooth at each time were coated with nail varnish, placed in silver nitrate and polished down with SiC paper. The μTBS data was submitted to a two-way repetead mesures ANOVA and Tukey's test for each adhesive (α = 0.05).

Results

The active application showed higher immediate and 3-year μTBS than the inactive application (p < 0.05). An increase in the silver nitrate deposition was seen for all conditions after 3 years; however this was more pronounced for all materials under inactive application (p < 0.05).

Conclusions

The active application improves the immediate bonding performance of the adhesive systems. Reductions of the bond strength were observed for all materials after 3 years, however reduced degradation rate was observed when the materials are applied actively in dentine.     

Non-destructive examination of interfacial debonding using acoustic emission

Objectives

This study aims to assess the viability of using the acoustic emission (AE) measurement technique to detect and monitor in situ the interfacial debonding in resin composite restorations due to build-up of shrinkage stresses during polymerization of the composite.

Materials and methods

The non-destructive testing technique that measures acoustic emission (AE) was used to detect and monitor the interfacial debonding in resin composite during curing of the composite. Four groups of specimens, n = 4 each, were tested: (1) intact human molars with Class-I cavities restored with the composite Z100 (3M ESPE, USA); (2) intact human molars with Class-I cavities restored with the composite Filtek™ P90 (3M ESPE, USA); (3) ring samples prepared from the root of a single bovine tooth and ‘restored’ with Z100; (4) freestanding pea-size specimens of Z100 directly placed on the AE sensor. The restorations in Groups (1)-(3) were bonded to the tooth tissues with the adhesive Adper™ Scotchbond™ SE Self-Etch (3M ESPE, USA). The composites in all the specimens were cured with a blue light (3M ESPE, USA) for 40 s. The AE signals were recorded continuously for 10 min from the start of curing. Non-destructive 3D imaging was performed using X-ray micro-computed tomography (micro-CT) to examine the bonding condition at the tooth-restoration interface.

Results

The development of AE events followed roughly that of the shrinkage stress, which was determined separately by the cantilever beam method. The number of AE events in the real human tooth samples was more than that in the ring samples, and no AE events were detected in the pea-size specimens placed directly on the AE sensor. The number of AE events recorded in the specimens restored using Z100 was more than that found in specimens restored with Filtek P90. The micro-CT imaging results showed clear interfacial debondings in the tooth specimens restored with Z100 after curing, but no clear debonding was found in the P90 specimens.

Conclusions

The AE technique is an effective tool for detecting and monitoring in situ the interfacial debonding of composite restorations during curing. It can potentially be employed to evaluate the development of shrinkage stress and the quality of interfacial bonds in teeth restored with different composite materials, cavity geometries, and restorative techniques.     

Relationships of beta-blockers and anxiolytics intake and salivary secretion, masticatory performance and taste perception

Objective

Assess the influence of salivary flow on physiological parameters of the stomatognathic system in patients who take beta-blockers or anxiolytic medications.

Design

Sixty patients were divided into three groups based on the following criteria: Group 1, control (n = 20; no use of medication); Group 2, use of antihypertensive beta-blockers (n = 20); and Group 3, use of benzodiazepine anxiolytics (n = 20). Salivary flow was assessed by determining stimulated and non-stimulated flow/minute. The quantification of the sense of taste was determined on a visual analogue scale (VAS) using solutions of 0.9% NaCl (salty), 50% sucrose (sweet), 20% unsweetened coffee (bitter) and 4.2% vinegar (sour). The DMFT index (number of decayed/missing/filled teeth) was determined by a calibrated examination, following the criteria of the World Health Organization (WHO). Masticatory performance was assessed with an Optosil comminution test and Rosim-Ramler equation.

Results

The results did not reveal a significant correlation between salivary flow and masticatory performance (p > 0.05). We observed significant decreased non-stimulated salivary flow for Group 2 (p = 0.05) when compared to controls. However, taste perception was not influenced by salivary secretion amongst groups. Furthermore, we observed a significant negative correlation between non-stimulated salivary flow and DMFT in Group 1 (p = 0.02; r = −0.52).

Conclusions

Patients under beta-blockers therapy presented reduced non-stimulated salivary flow when compared to controls, without influencing the sense of taste or masticatory performance. The use of anxiolytics did not affect salivary flow and taste perception in the studied sample.     

Monomer-to-polymer conversion and micro-tensile bond strength to dentine of experimental and commercial adhesives containing diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide or a camphorquinone/amine photo-initiator system

Objectives

To compare the degree of conversion (DC) of adhesives initiated by diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) or a camphorquinone/tertiary amine system (CQ/Amine) as well as their ‘immediate’ micro-tensile bond strength (μTBS) to bur-cut dentine.

Methods

DC of Scotchbond Universal (‘SBU’; 3M ESPE), its experimental counterpart containing TPO as photo-initiator system, an experimental G-aenial Bond (‘Ga-B’; GC) adhesive formulation, and an experimental LUB-102 adhesive formulation (‘LUB’, Kuraray Noritake), containing as photo-initiatior system either 2 wt% CQ along with 2 wt% tertiary amine (‘SBU_CQ/Amine’; ‘Ga-B_CQ/Amine’; ‘LUB_CQ/Amine’), or 2 wt% TPO (‘SBU_TPO’; ‘Ga-B_TPO’; ‘LUB_TPO’), was determined using Fourier-transform infrared spectroscopy (FTIR), after being cured with a dual-wavelength light-curing unit (bluephase 20i, Ivoclar Vivadent). The same adhesive formulations were applied to bur-cut mid-coronal dentine of intact human molars, and subjected to a μTBS test after 1-week water storage. Besides being applied following a self-etch (SE) application mode, the adhesive formulations SBU_CQ/Amine and SBU_TPO were also applied following an etch-and-rinse (E&R) mode, this both for DS and μTBS measurement.

Results

No significant difference in DC was found for any of the adhesive formulations, except for SBU_CQ/Amine_SE and SBU_TPO_SE. For both SBU formulations, a significantly higher DC was reached for the E&R than the SE approach. Regarding μTBS, no significant differences were recorded, except for the significantly higher μTBS measured for SBU_CQ/Amine_E&R and SBU_TPO_E&R.

Conclusions

In self-etch adhesives, the photo-initiator TPO may be used instead of CQ/Amine. The curing and ‘immediate’ bonding efficiency depended on the application protocol (E&R versus SE), but not on the photo-initiator system.

Clinical significance

The photo-initiator TPO may be used in self-etch adhesives instead of CQ/Amine with similar curing and ‘immediate’ bonding efficiency.     

Influence of tooth-surface hydration conditions on optical coherence-tomography imaging

Objectives

This study examined the influence of tooth-surface hydration conditions on optical coherence tomography (OCT) imaging.

Methods

Emitted light was coupled in a single-mode fibre-optic Michelson interferometer, and delivered to a sample and a reference mirror mounted on a linearly translating galvanometer driven by a triangular voltage waveform at a fringe-modulation frequency of 1 kHz. Backscattered light from the sample was coupled back to the system, digitised and used to create two-dimensional images together with beam scanning. OCT imaging of the occlusal surfaces of 10 extracted human teeth was performed soon after mounting (‘wet’ condition), immediately after air blowing for 10 s (‘air-blow’ condition), and at intervals thereafter (‘1-min’, ‘5-min’ and ‘10-min’ conditions, respectively).

Results

For the wet condition, three distinct peaks indicated the water surface, tooth surface and dentino-enamel junction. Backscattered light was detected at levels above noise, possibly causing grainy OCT images. By contrast, two distinct peaks indicating the tooth surface and dentino-enamel junction were observed for the air-blow and 10-min conditions, with greater signal intensities for the latter. The intensity was lower for the air-blow condition than the wet condition. The signal intensities decreased during storage in air at room temperature.

Conclusion

Tooth-substrate hydration conditions thus appeared to influence time domain-OCT imaging.     

Hygroscopic dimensional changes of self-adhering and new resin-matrix composites during water sorption/desorption cycles

Objectives

To study hygroscopic dimensional changes in new resin-matrix composites during water sorption/desorption cycles.

Methods

Five materials were examined: a self-adhering flowable composite: Vertise^® Flow (VF), a universal composite: GC Kalore (GCK), two micro-fine hybrid composites: GC Gradia Direct Anterior (GDA) and GC Gradia Direct Posterior (GDP), and a posterior restorative composite: Filtek^® Silorane (FS). Five disk-shaped specimens of each material were prepared (15 mm diameter × 2 mm thickness) according to ISO 4049. The mean diameter of each specimen was measured by a custom-built laser micrometer (to a resolution of 200 nm) periodically over 150 d water immersion and 40 d recondition periods at (37 ± 1) °C. Perspex controls were used. Data analysis was performed by repeated measures ANOVA, one-way ANOVA and Tukey's post hoc test (p < 0.05).

Results

Differences in hygroscopic expansion were found for all test materials during sorption, ranging from 0.74% (±0.05) for FS to 4.82% (±0.13) for VF. The differences were significant for all materials (p < 0.001), except between GCK and GDA. The mathematical relationship between diametral expansion and square root of time was non-linear. VF exhibited significant dehydration shrinkage.

Significance

The silorane composite FS had the lowest hygroscopic expansion. The extent of compensation of polymerization shrinkage by hygroscopic expansion depends on materials, specimen dimensions and time-scale. So the clinical situation must be taken into consideration in the application of these findings.     

High volume individual fibre post versus low volume fibre post: the fracture load of the restored tooth

Objectives

The purpose of this study was to evaluate the fracture loads of post-and-core systems with two different individually formed fibre post designs and polymerization conditions.

Methods

Totally seventy-two (n = 8/group) bovine teeth were cut and made up the root length of 15.0 mm. They were divided into 3 main groups (Group A, B, C). A: one glass fibre post was light-cured before cementation, B: fibres were bundled to fill the entire root canal opening and light-cured before cementation, C: one unpolymerized glass fibre post was inserted into cement-filled root canal and light-cured with luting cement (ParaCem). Moreover specimens of each group were divided into 3 subgroups according to the post length: subgroup 1: 10 mm; subgroup 2: 7.5 mm; subgroup 3: 5.0 mm. After cementation, the core was built up, and then made the composite resin crown (Filtek Z250). Fabricated specimen was loaded from 45° of palatal side at a crosshead speed of 1.0 mm/min. The first load drop and maximum fracture loads were statistically analyzed by ANOVA and Tukey's test.

Results

Maximum fracture load of Group B (433 N) and C (418 N) are significantly higher than Group A (284 N) (p < 0.01). Short post (5 mm) provided higher fracture loads in all main groups, especially in Group C.

Conclusions

Using short and thick fibre post system (the same diameter as the root canal) showed higher strength than one fibre post only. In addition, by curing the cement and the fibre material simultaneously, the strength of the restored tooth was increased.     

Influence of matrix systems on proximal contact tightness of 2- and 3-surface posterior composite restorations in vivo

Objectives

To investigate the influence of cavity preparation (MO/DO/MOD) and type of matrix system on proximal contact tightness of direct posterior composite restorations.

Materials and methods

85 patients in need of a two- or three surface Class II direct composite restoration were randomly divided into two treatment groups. Group 1 was treated with a sectional matrix system combined with a separation ring (Palodent); Group 2 was treated with a circumferential matrix system in combination with a retainer (Tofflemire). Proximal contact tightness was recorded before treatment and directly after finishing the restoration.

Results

For the two-surface cavities use of the separation ring resulted in a statistically significantly tighter proximal contacts at both the mesial and distal site (MO: 2.51 ± 0.81 N; DO: 2.82 ± 1.14 N) compared to the use of the circumferential (MO: −1.08 ± 1.04 N; DO: −0.22 ± 0.87 N) (p = 0.01). Regarding the three-surface (MOD) cavities no statistically significant differences were found between the mesial and distal site, nor was there an effect of the used matrix system. No statistically significant influence of cavity design (mesially/distally) was recorded for all cavities (MO, DO and MOD).

Conclusions

Use of the sectional matrix system in two-surface Class II cavities resulted in statistically significantly tighter proximal contacts than the use of the circumferential matrix system.For the three-surface no statistically significant differences in contact tightness were found between the different matrix systems.Location of the cavity (mesially or distally) did not show to have any statistically significant effect on the obtained proximal contact tightness.     

A novel array chip to monitor in situ composite degradation using electrochemical impedance spectroscopy

Objectives

This paper presents a novel array-chip technology used to monitor the physical properties of dental composites in situ. The DECAY chip (Degradation via Electrochemical Array) leverages microfabrication techniques to construct a uniform array of recessed wells that may be filled with dental restorative materials (e.g. composite or amalgam) and analyzed electrochemically in solution.

Methods

The array enables the uniform preparation of multiple specimens and reference controls on a common substrate, all of which may be simultaneously evaluated. The DECAY-chip presented here consists of a 3 × 3 array of 100 μm deep wells, and is used to monitor the degradation of a common dental composite as a function of time.

Results

The data correlate changes in the measured dielectric properties to surface and bulk changes as the composite is exposed to an ethanol:DI mixture (75% ethanol). A model for the system is presented, as are future plans to simplify the methodology for rapid materials screening and in vitro analyses.

Significance

This in situdiagnostic chip will enable evaluation of composite specimens, tested under a wide range of simulated oral environments. It may also serve as a screening platform for new composite formulations and aid in the study of materials degradation and failure mechanisms.     

Surface alteration of human tooth enamel subjected to acidic and neutral 30% hydrogen peroxide

Objectives

To investigate the effects of acidic and neutral 30% hydrogen peroxide (HP) on human tooth enamel in terms of chemical structure, mechanical property, surface morphology and tooth colour.

Methods

Twenty-seven human dental blocks were obtained from premolars and randomly divided into three groups (n = 9): Group acidic HP (30% HP, pH ≈ 3.6), Group neutral HP (30% HP, pH ≈ 7.0) and Group DW (distilled water, pH ≈ 6.8). Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, atomic force microscopy (AFM) investigation, microhardness test and colour measurements were carried out before and after treatments. ATR-FTIR and Raman spectroscopy were analysed and then the carbonate:mineral ratio (C:M), Raman absolute intensity (RAI), Raman relative intensity (RRI), and laser-induced fluorescence intensity (FI) were obtained for evaluation.

Results

The C:M, percentage microhardness and percentage RRI of group acidic HP decreased more significantly than those of group neutral HP (P = 0.02, P = 0.001, P < 0.001, respectively) and group DW (P = 0.01, P = 0.008, P < 0.001, respectively). Whilst group neutral HP and group DW had no statistical difference in above terms (P = 0.818, P = 0.528, P = 0.158, respectively). Significant morphological alterations were observed in group acidic HP. Group acidic HP and neutral HP had no significant difference in percentage FI (P = 0.652) and ΔE (P = 0.906).

Conclusions

This study suggested that neutral 30% HP had the same efficiency in tooth bleaching and it caused less deleterious effects on enamel than acidic 30% HP.     

Prevention of toothbrushing abrasion of acid-softened enamel by CO(2) laser irradiation

Objective

The aim of the present study was to evaluate the effect of CO₂ laser irradiation (10.6 μm) at 0.3 J/cm² (0.5 μs; 226 Hz) on the resistance of softened enamel to toothbrushing abrasion, in vitro.

Methods

Sixty human enamel samples were obtained, polished with silicon carbide papers and randomly divided into five groups (n = 12), receiving 5 different surface treatments: laser irradiation (L), fluoride (AmF/NaF gel) application (F), laser prior to fluoride (LF), fluoride prior to laser (FL), non-treated control (C). After surface treatment they were submitted to a 25-day erosive-abrasive cycle in 100 ml sprite light (90 s) and brushed twice daily with an electric toothbrush. Between the demineralization periods samples were immersed in supersaturated mineral solution. At the end of the experiments enamel surface loss was determined using a contact profilometer and morphological analysis was performed using scanning electron microscopy (SEM). For SEM analysis of demineralization pattern, cross-sectional cuts of cycled samples were prepared. The data were statistically analysed by one-way ANOVA model with subsequent pairwise comparison of treatments.

Results

Abrasive surface loss was significantly lower in all laser groups compared to both control and fluoride groups (p < 0.0001 in all cases). Amongst the laser groups no significant difference was observed. Softened enamel layer underneath lesions was less pronounced in laser-irradiated samples.

Conclusion

Irradiation of dental enamel with a CO₂ laser at 0.3 J/cm² (5 μs, 226 Hz) either alone or in combination with amine fluoride gel significantly decreases toothbrushing abrasion of softened-enamel, in vitro.     

Novel methods of balancing covariates for the assessment of dental erosion: a contribution to validation of a synthetic scoring system for erosive wear

Objectives

The purpose of the study was to balance several potential erosive covariates, using traditional and novel epidemiological approaches, in order to assess the relative risks of dental erosion more precisely.

Methods

Traditional (univariate and logistic regression analysis) and novel techniques (propensity scores and Inverse Probability Weighting—IPW) were applied for evaluating the effect of twenty covariates on dental erosion among 502 adolescents.

Results

Different approaches gave different estimates of the relative risks of dental erosion. The increased consumption of carbonated soft drinks had the major erosive effect, when traditional analyses were used (unadjusted: OR = 3.475 and CI: 1.499-8.052, logistic regression: OR = 3.219 and CI: 1.373-7.547). On the other hand, IPW method indicated that the consumption of erosion drinks immediately after intense physical exercise had the highest odds ratio (OR = 1.363 and CI: 0.963-1.929), followed by the increased consumption of citrus fruit juice (OR = 1.326 and CI: 1.004-1.752). This method also demonstrated a marked improvement in balance, with the 95% CIs for each OR being considerably narrower than those reported in the initial analysis.

Conclusions

Standardization of the potential aetiological criteria of erosive wear is a considerably difficult process. Nevertheless, novel methods revealed that the increased consumption of carbonated soft drinks and citrus fruit juices could be included as aetiologic factors in a synthetic scoring system for erosion. Parameters which are related to salivary protective mechanisms (e.g. consumption of erosion drinks immediately after intense physical exercise) could also be a part of such an index. Further research is required in order to achieve the maximum validation of the potential erosive risk factors.     

The influence of visible dental caries on social judgements and overall facial attractiveness amongst undergraduates

Objectives

Where previous work has suggested that the presence of caries alone may influence social judgements, this study investigated whether overall facial attractiveness and caries influence ratings of social and intellectual competence and the extent to which any effect may be the result of facial attractiveness alone.

Methods

Three photos of young males who were reliably rated as ‘unattractive’, ‘attractive’ or ‘neither unattractive nor attractive’, were selected and were digitally modified by a dentist to have caries or not, to give a total of 6 vignettes. In a cross-sectional study of N = 263 undergraduates, each participant appraised one single colour photograph for the following characteristics: social competence, intellectual ability, psychological adjustment, care of own appearance and attractiveness, using a 5 point Likert scale.

Results

The data were analysed using two-way ANOVA where factor 1 was attractiveness and factor 2 was the presence or absence of caries. Faces of higher attractiveness received significantly more positive appraisals than those of lower attractiveness on all measures, irrespective of caries. Presence of caries only resulted in significant decreases in measures of attractiveness and care of own appearance, but none of the other measures.

Conclusions

Individuals’ overall level of attractiveness is more important to a social judgement than their dental condition. Previous research in this area may have found significant effects for dental condition due to using a single face with more marked differences in caries, which affected facial attractiveness. Future research should focus on factors that affect attractiveness and how these compete to affect social judgments.     

Selective masking for thin indirect restorations: can the use of opaque resin affect the dentine bond strength of immediately sealed preparations?

Purpose

Evaluate the dentine bond strength using different methods of application of opaque resins to mask dentine discoloration.

Materials and methods

Dentine was exposed on 21 extracted molars which were assigned to 3 groups: G1: immediate dentine sealing (IDS). G2: IDS + opaque. G3: IDS with adhesive resin mixed with opaque. After 1 week, teeth were restored and beams were fabricated for microtensile testing. Optical microscopy was used to analyse the failure mode.

Results

Bond strength mean values were statistically different: G1 55.20 MPa > G2 45.79 MPa > G3 18.96 MPa. Failure modes were mostly adhesive for G1 and G3. G2 presented mostly mixed failures.

Conclusion

The use of opaque resin to mask discoloured dentine results in a decrease of bond strength.