In vitro comparison of mechanical properties and degree of cure of bulk fill composites

Objectives

The aim of our study was to measure and compare degree of conversion (DC) as well as micro- (indentation modulus, E; Vickers hardness, HV) and macromechanical properties (flexural strength, σ; flexural modulus, E _flexural) of two recently launched bulk fill resin-based composites (RBCs): Surefil® SDR? flow (SF) and Venus® bulk fill (VB).

Materials and methods

DC (n?=?6) was investigated by Fourier transform infrared spectroscopy (FTIR) in clinical relevant filling depths (0.1, 2, and 4 mm; 6 mm bulk, 6 mm incremental) and irradiation times (10, 20, 40 s). Micro- (n?=?6) and macromechanical (n?=?20) properties were measured by an automatic microhardness indenter and a three-point bending test device after storing the specimens in distilled water for 24 h at 37°C. Furthermore, on the 6-mm bulk samples, the depth of cure was determined. A field emission scanning electron microscope was used to assess filler size. Results were evaluated using one-way analysis of variance, Tukey’s honest significance test post hoc test, a multivariate analysis (α?=?0.05) and an independent t test. Weibull analysis was used to assess σ.

Results

VB showed, in all depth, significant higher DC (VB, 62.4–67.4 %; SF, 57.1–61.9 %), but significant lower macro- (VB, E _flexural?=?3.6 GPa; σ?=?122.7 MPa; SF, E _flexural?=?5.0 GPa; σ?=?131.8 MPa) and micromechanical properties (VB, E?=?7.3–8.8 GPa, HV?=?40.7–46.5 N/mm²; SF, E?=?10.6–12.2 GPa, HV?=?55.1–61.1 N/mm²). Both RBCs showed high reliability (VB, m?=?21.6; SF, m?=?26.7) and a depth of cure of at least 6 mm at all polymerization times. The factor “RBC” showed the strongest influence on the measured properties (η ²?=?0.35–0.80) followed by “measuring depth” (η ²?=?0.10–0.46) and “polymerization time” (η ²?=?0.03–0.12).

Conclusions

Significant differences between both RBCs were found for DC, E, σ, and E _flexural at all irradiation times and measuring depths.

Clinical relevance

Curing the RBCs in 4-mm bulks for 20 s can be recommended.     

Light transmittance and micro-mechanical properties of bulk fill vs. conventional resin based composites

Objectives

The aim of this study was to quantify the blue light that passes through different incremental thicknesses of bulk fill in comparison to conventional resin-based composites (RBCs) and to relate it to the induced mechanical properties.

Materials and methods

Seven bulk fill, five nanohybrid and two flowable RBCs were analysed. Specimens (n?=?5) of three incremental thicknesses (2, 4 and 6 mm) were cured from the top for 20 s, while at the bottom, a spectrometer monitored in real time the transmitted irradiance. Micro-mechanical properties (Vickers hardness, HV, and indentation modulus, E) were measured at the top and bottom after 24 h of storage in distilled water at 37 °C. Electron microscope images were taken for assessing the filler distribution and size.

Results

Bulk fill RBCs (except SonicFill) were more translucent than conventional RBCs. Low-viscosity bulk fill materials showed the lowest mechanical properties. HV depends highly on the following parameters: material (η_p ²?=?0.952), incremental thickness (0.826), filler volume (0.747), filler weight (0.746) and transmitted irradiance (0.491). The bottom-to-top HV ratio (HV_bt) was higher than 80 % in all materials in 2- and 4-mm increments (except for Premise), whereas in 6-mm increments, this is valid only in four bulk fill materials (Venus Bulk Fill, SDR, x-tra fil, Tetric EvoCeram Bulk Fill).

Conclusions

The depth of cure is dependent on the RBC’s translucency. Low-viscosity bulk fill RBCs have lower mechanical properties than all other types of analysed materials. All bulk fill RBCs (except SonicFill) are more translucent for blue light than conventional RBCs.

Significance

Although bulk fill RBCs are generally more translucent, the practitioner has to follow the manufacturer’s recommendations on curing technique and maximum incremental thickness.     

Degree of conversion of nano-hybrid resin-based composites with novel and conventional matrix formulation

Objectives

This study aimed to determine the degree of conversion (DC) of two nano-hybrid resin-based composites (RBCs) with novel monomer composition based on dimer acid derivates (hydrogenated dimer acid) and tricyclodecane–urethane structure compared to three nano-hybrid materials containing conventional matrices. DC was evaluated at 0.1, 2, and 6 mm depth at varying irradiation times (10, 20, and 40 s) and layering techniques (bulk and incremental).

Materials and methods

DC was measured in real time by a Fourier transform infrared spectroscopy (FTIR) spectrometer with attenuated total reflectance accessory. The FTIR spectra were recorded on the bottom of the samples in real time for 5 min from photoinitiation. Results were compared using one- and multiple-way ANOVA, Tukey's HSD post hoc test (α?=?0.05), and partial eta-squared statistic.

Results

After 5 min of measurement, DC showed no significant difference by varying cure time for specimens of 0.1 mm thickness. At 2 mm depth, the DC significantly increased after a cure time of 20 s compared to 10 s, remaining equal after 40 s of irradiation. At 6 mm depth, bulk curing showed significantly lower DC compared to incremental curing for all polymerization times. Specimen geometry revealed a strong effect on DC (η ²?=?0.90) followed by curing time (η ²?=?0.39).

Conclusions

The RBCs containing the dimer acid and tricyclodecane–urethane structure showed a relatively low decrease of DC with increasing incremental thickness compared to the conventionally formulated materials. The former reached the highest DC among the tested materials.

Clinical relevance

For the tested RBCs, increments of 2 mm and irradiation time of at least 20 s may be recommended for clinical practice. The two materials containing novel monomer composition might be applied for enlarged increments because of the low decrease of DC they demonstrated for 6-mm increments.     

Effect of sonic-activated resin composites on the repair of aged substrates: an in vitro investigation

Objectives

This study aimed to evaluate whether sonic-activated resin-based composites (RBCs) used as repair materials might improve the repair bond strength of aged RBC substrates.

Materials and methods

Five RBCs were repaired by themselves and by all other materials. The repair was applied with and without sonic activation, resulting in 50 material application technique combinations (n?=?15) and 750 specimens. The cohesive strength of the five materials was used as control (n?=?15). Substrates were aged for 8 weeks in distilled water at 37 °C, roughened, cleaned with phosphoric acid, and repaired by using a silane primer and an adhesive as intermediate agents. The repair bond strength was assessed in a shear test. The modulus of elasticity (E) of the five RBCs was additionally evaluated in a three-point bending test.

Results

Results were compared using one- and multiple-way analyses of variance and Tukey’s honestly significant difference post hoc test (α?=?0.05), partial eta-square statistics, Pearson’s correlation, and Weibull’s analysis. No significant effect of sonic activation on the repair material was found in any material combination. The repair strength was 35.4–90.9 % of the cohesive strength of the original composites. E varied between 4.1 GPa (CLEARFIL MAJESTY Esthetic) and 9.7 GPa (CLEARFIL MAJESTY Posterior). The strongest influence on the shear bond strength was performed by E _repair (η ² _P?=?0.167), whereas the effect of E _substrate was significant but low (η ² _P?=?0.098). None of these parameters influenced the reliability of the repaired specimens (the Weibull parameter, m). The fracture pattern was mainly cohesive (93.3 %) in the control group and predominantly adhesive (89.2 %) in the repaired specimens.

Conclusions

Except for the material with the highest modulus of elasticity used as a substrate material, it was not detrimental to combine different RBCs in terms of repair.

Clinical relevance

If a substrate material is unknown, the recommendation for repairing would be in favor of a material with a high modulus of elasticity.     

Depth of cure and mechanical properties of nano-hybrid resin-based composites with novel and conventional matrix formulation

Objectives

This study’s purpose was to evaluate the depth of cure (DOC) and the variation of mechanical properties with depth of two nano-hybrid resin-based composites (RBCs) containing a novel monomer composition based on dimer-acid derivatives (h-Da) or rather tricyclodecane–urethane structure (TCD-urethane) compared to three conventionally formulated nano-hybrid RBCs based on hardness-profile measurements.

Materials and methods

Specimens were produced through different layering techniques (bulk, incremental) and curing times (10, 20, and 40?s). Mechanical properties (Vickers hardness (HV), modulus of elasticity (E)) were evaluated every 100?μm longitudinally throughout the bisected samples using an automatic micro-hardness indenter. DOC was determined as the depth at which the 80% hardness cutoff value in relation to the surface hardness was reached. Results were compared using one- and multiple-way ANOVA, Tukey HSD post-hoc test (α?=?0.05) and partial eta-squared statistic.

Results

Increasing curing time resulted in a significant increase in DOC. Generally, the novel-formulated materials showed higher DOC values. “Curing time” and “material” showed the strongest effect on DOC. Starting in 4?mm depth, significantly higher HV and E was reached for incremental compared to bulk-curing technique. Values in 0.1 and 2?mm depth (bulk, incremental) as well as in 4?mm depth (incremental) were independent from curing time, while in greater depths, values generally increased with curing time. “Filling technique” and “material” performed the strongest influence on mechanical properties.

Conclusions

Within the limits of this study, the novel-formulated RBCs showed better performance concerning DOC compared to conventional materials.

Clinical relevance

For cavities deeper than 3?mm, all tested materials should be placed incrementally to ensure adequate polymerization. In large cavities (≥6?mm), the lowest increment should be cured at least 40?s. The novel-formulated RBCs might be cured in comparatively bigger increments.     

Effect of modulated irradiation time on the degree of conversion and the amount of elutable substances from nano-hybrid resin-based composites

Objectives

The aim of our study was to analyse whether the irradiation time and/or the modulation of irradiation time influence the degree of conversion (DC) and the amount of elutable substances from modern nano-hybrid resin-based composites (RBCs).

Materials and methods

The DC was recorded in real time for 5 min by means of attenuated total reflectance–Fourier transform infrared spectroscopy (n?=?5) on the lower surface of 2-mm-thick samples irradiated with continuous and modulated irradiation times for 20 s and 40 s. The modulated times comprise a short polymerisation (2 s or 5 s) followed by a rest period of 1 min and an additional polymerisation to complete 20 s and 40 s of polymerisation (2 s?+?18 s, 5 s?+?15 s, 2 s?+?38 s and 5 s?+?35 s). After storing the specimens in ethanol/water for 7 days at 37 °C, the eluates were analysed by gas chromatography–mass spectrometry. Results were statistically analyzed using a one-way ANOVA analysis (α?=?0.05).

Results

The effect of irradiation time on DC is similar in all three analyzed materials, showing a significant increase in DC by increasing irradiation time from 20 s to 40 s, while the DC is not influenced within one irradiation time (20 s or 40 s) by the modulation of time.

Conclusions

The type and amount of eluates are strongly dependent from the material and the irradiation protocol.

Clinical relevance

An interrupt irradiation of RBCs is clinically feasible, reducing in general the amount of elutable substances at similar DC as the corresponding continuous polymerisation.     

Investigations towards nano-hybrid resin-based composites

Objective

Clinical data indicate an increased trend in material fracture as reason for failure in composite restorations, questioning whether modern resin-based composites (RBCs) are able to fulfil the rising aesthetical demands and to provide at the same time a sufficient mechanical stability also in larger cavities. Nano-hybrid RBCs are promoted as materials with improved mechanical properties. The aim of this study was to analyse differences in mechanical properties within and between modern flowable and non-flowable nano-hybrid and micro-hybrid RBCs by measuring mechanical properties at macro- and micro-scale.

Methods

Thirty-four RBCs with traditional and new monomer formulation or photo-polymerization initiator technology—15 nano-hybrid, nine micro-hybrid and ten flowable—were therefore considered. Flexural strength, flexural modulus (E_flexural), indentation modulus, Vickers hardness (HV) and creep were measured after the samples had been stored in water for 24 h at 37°C. Differences within the materials as well as within material categories were statistically analysed using one-way ANOVA with Tukey HSD post hoc test (α?=?0.05) as well as partial eta-square statistics.

Results

The category of micro- and nano-hybrid RBCs performed in all properties superior compared to the flowable RBCs. The former two categories differ significantly only with regard to three parameters, with nano-hybrid RBCs showing higher HV respectively lower E_flexural and filler weight. The micro-mechanical parameters proved to be more sensitive to differences in filler amount and RBCs type than the macro-mechanical properties.

Clinical relevance

Only few differences were found between nano-hybrid and micro-hybrid RBCs as a material category and thus, from laboratory tests, no clear advantages in the mechanical stability in stress-bearing areas of nano-hybrid RBCs are expected clinically. Similar is valid for materials with new monomer formulation or photo-polymerization initiator technology. However, several of the measured nano-hybrid RBCs showed consistently higher mechanical properties than the mean values of the micro-hybrid RBCs.     

Effect of a daily dose of Lactobacillus brevis CD2 lozenges in high caries risk schoolchildren

Objectives

A double-blind, randomised, placebo-controlled clinical trial was performed to validate the hypothesis that the use of lozenges containing Lactobacillus brevis CD2 (Inersan®, CD Investments srl) may reduce plaque pH, salivary mutans streptococci (ms) and bleeding on probing, during a 6-week period, in a sample of high caries risk schoolchildren.

Methods

A total of 191 children (aged 6–8 years), presenting two to three carious lesions and a salivary ms concentration of ≥10⁵ CFU/ml, were enrolled and divided into two groups, an L. brevis CD2 lozenge group and a no L. brevis lozenge group, and examined at baseline (t₀), after 3 weeks (t₁), after 6 weeks of lozenge use (t₂) and 2 weeks after the cessation of lozenge use (t₃). Plaque pH was assessed using the microtouch technique following a sucrose challenge. The area under the curve (AUC_5.7 and AUC_6.2) was recorded. Salivary ms were counted, and bleeding on probing was assessed.

Results

At t₀, the plaque-pH and ms concentration values were similar in both groups. Mean areas (AUC_5.7 and AUC_6.2) were significantly greater in the control group at t₁, t₂ and t₃. L. brevis CD2 lozenges significantly reduced salivary ms concentrations and bleeding. The subjects from the test group showed a statistically significant decrease (p?=?0.01) in salivary ms concentration. At t₂, a statistically significantly lower bleeding value was recorded in the test group compared with the control group (p?=?0.02).

Conclusions

Six weeks’ use of lozenges containing L. brevis CD2 had a beneficial effect on some important variables related to oral health, including a reduction in plaque acidogenicity, salivary ms and bleeding on probing. (Trial Registration Number NCT01601145 08/21/2012)     

Repair bond strength of microhybrid, nanohybrid and nanofilled resin composites: effect of substrate resin type, surface conditioning and ageing

Objectives

This study evaluated the microtensile bond strength (MTBS) of non-aged and aged resin-based composites (RBC) (nanohybrid and nanofilled) after two surface conditioning methods, repaired using the composite of the same kind or a microhybrid composite.

Materials and methods

Nanohybrid (Tetric EvoCeram—TE) and nanofilled (Filtek Supreme—FS) RBC blocks (5?×?5?×?6 mm) (N?=?128) were fabricated and randomly divided into two groups: (a) no ageing (control group) and (b) ageing (5.000 thermocycling, 5–55 °C). RBC surfaces were polished by up to 1,200-grit silicone carbide papers and conditioned with either (a) air abrasion with 30-μm SiO₂ particles (CoJet Sand) for 4 s + silane coupling agent (ESPE-Sil) + adhesive resin (VisioBond) (n?=?16) or (b) adhesive application only (Multilink A+B for TE; Adper ScotchBond 1XT for FS) (n?=?16). In half of the groups, repair resin of the same kind with the RBC and, in the other half, a different kind of composite (microhybrid, Quadrant Anterior Shine—AS) with its corresponding adhesive (Quadrant UniBond) was used. The specimens were submitted to MTBS test (0.5 mm/min). Data were analysed using three-way ANOVA and Tukey's tests. Degree of conversion (DC) of non-aged and aged resin composites (TE, FS) (n?=?3 per group) was measured by micro-Raman analyses.

Results

RBC type (p?=?0.001) and ageing affected the MTBS results significantly (p?=?0.001). Surface conditioning type did not show significant difference (p?=?0.726), but less number of pre-test failures was experienced with the CoJet system compared to adhesive resin application only. Repair strength on aged TE showed significantly less (p?<?0.05) MTBS than for FS. FS repaired with the same kind of RBC and adhesive resin presented the highest cohesive failures (43 %). DC was higher for TE (71 %) than for FS (58 %) before ageing.

Conclusion

On the aged RBCs, less favourable repair strength could be expected especially for nanohybrid composite. For repair actions, RBC surface conditioning could be accomplished with either adhesive resin application only or with CoJet system, providing that the latter resulted in less pre-test failures.

Clinical relevance

Clinicians could condition the resin surface prior to repair or relayering with either CoJet system or adhesive resin application only, depending on the availability of the system.     

Chemometric analysis of the consumption of oral rinse chlorite (ClO2 −) by human salivary biomolecules

Objectives

Oral rinse formulations containing chlorite anion (ClO₂ ^?) as an active agent exert a range of valuable oral healthcare activities. However, salivary biomolecules which chemically react with this oxidant can, at least in principle, serve as potentially significant barriers to these therapeutic properties in the oral environment. Therefore, in this investigation, we have explored the extent of ClO₂ ^? consumption by biomolecules which scavenge this agent in human salivary supernatants (HSSs) in vitro.

Materials and methods

HSS samples were equilibrated with oral rinse formulations containing this active agent (30 s at 35 °C in order to mimic oral rinsing episodes). Differential spectrophotometric and ion-pair reversed-phase high-performance liquid chromatographic analyses were employed to determine residual ClO₂ ^? in these admixtures.

Results

Bioanalytical data acquired revealed the rapid consumption of ClO₂ ^? by biomolecular electron donors and/or antioxidants present in HSS samples. Mean?±?95 % confidence interval (CI) consumption levels of 7.14?±?0.69 and 5.34?±?0.69 % of the total ClO₂ ^? available were found for oral rinse products containing 0.10 and 0.40 % (w/v) ClO₂ ^?, respectively. A mixed model analysis-of-variance performed on experimental data acquired demonstrated highly-significant differences between oral rinse ClO₂ ^? contents (p?<?0.0001), trial participants (p?<?0.001) and sampling days–within-participants (p?<?0.001), and also revealed non-additive ClO₂ ^?-scavenging responses of participants’ HSSs to increases in the oral rinse content of this oxidant (p?<?0.0001). A slower, second phase of the reaction process (t _1/2?=?1.7–2.8 h) involved the oxidative consumption of salivary urate.

Conclusions

These data clearly demonstrate that for recommended 30 s oral rinsing episodes performed at physiological temperature, <10 % of the total oral rinse ClO₂ ^? available is chemically and/or reductively consumed by HSS biomolecules for both oral rinse formulations investigated.

Clinical relevance

These observations are of much clinical significance in view of the retention of these products’ active agent, i.e. <10 % of ClO₂ ^? is consumed by HSS biomolecules within recommended 30 s oral rinsing episodes, and hence, the bulk of this oxyhalogen oxidant (>90 %) may effectively exert its essential microbicidal, anti-periodontal and oral malodour-neutralising actions.     

Effectiveness and mode of action of whitening dentifrices on enamel extrinsic stains

Objectives

This study was conducted in order to investigate the mode of action and the whitening effect of whitening dentifrices.

Material and methods

Two hundred fifty-six bovine enamel specimens (10?×?10 mm²) were prepared, partially stained, and assigned into eight groups (n?=?32): six whitening dentifrices, one nonwhitening and deionized water (negative control), and further divided in two subgroups (n?=?16), according to the test model: chemical (dentifrice slurry treatment only) or chemo-mechanical (slurry?+?toothbrushing). Specimens were treated with dentifrice slurries 2×/day for 1 min and toothbrushed or not, according to each model. In between dentifrice treatments, specimens were artificially stained for 5 h. This protocol was repeated for 5 days and enamel color changes (?E) were measured after each day (days 1–5). The abrasive level of the dentifrices was determined following the ISO11609 guidelines.

Results

In the chemo-mechanical model, the whitening action of all dentifrices was observed after day 1, being higher than the negative control group (p?<?0.05). In days 2–5, nonsignificant changes in color were observed for all groups (p?>?0.05). Differences on ?E among dentifrices were observed, and they seemed to correlate well with their abrasive level (r ²?=?0.80). In the chemical model, no significant differences were observed among groups (p?>?0.05), with ?E remaining constant throughout the study. Higher ?E values were observed in the chemo-mechanical model compared to the chemical (p?<?0.05).

Conclusions

All tested dentifrices were effective in whitening stained enamel and their mode of action showed to be mainly mechanical (toothbrushing abrasion).

Clinical relevance

The abrasive level of dentifrices seems to determine its whitening effectiveness.     

Blue light kills Aggregatibacter actinomycetemcomitans due to its endogenous photosensitizers

Objectives

The aim of this study was to demonstrate that the periodontal pathogen Aggregatibacter actinomycetemcomitans (AA) can be killed by irradiation with blue light derived from a LED light-curing unit due to its endogenous photosensitizers.

Materials and methods

Planktonic cultures of AA and Escherichia coli were irradiated with blue light from a bluephase® C8 light-curing unit with an emission peak at 460 nm, which is usually applied for polymerization of dental resins. A CFU-assay was performed for the analysis of viable bacteria after treatment. Moreover, bacterial cells were lysed and the lysed AA and E. coli were investigated for generation of singlet oxygen. Spectroscopic measurements of lysed AA and E. coli were performed and analyzed for characteristic absorption and emission peaks.

Results

A light dose of 150 J/cm² induced a reduction of ≥5 log₁₀ steps of viable AA, whereas no effect of blue light was found against E. coli. Spectrally resolved measurements of singlet oxygen luminescence showed clearly that a singlet oxygen signal is generated from lysed AA upon excitation at 460 nm. Spectroscopic measurements of lysed AA exhibited characteristic absorption and emission peaks similar to those of known porphyrins and flavins.

Conclusions

AA can be inactivated by irradiation with blue light only, without application of an exogenous photosensitizer.

Clinical relevance

These results encourage further studies on the potential use of these blue light-mediated auto-photosensitization processes in the treatment of periodontitis for the successful inactivation of Aggregatibacter actinomycetemcomitans.     

Repair of dental resin-based composites

Objectives

The study analyzed the reparability and compatibility of light-curing resin-based composites (RBCs) of the categories “microhybrid,” “nanohybrid,” and “packable.”

Materials and methods

Six RBCs with different matrix and filler formulation—purely methacrylate-based composites (MBCs), ormocer-based composites (OBCs), and silorane-based composites (SBCs)—were used for the specimens. Every material was combined with itself and with the other five RBCs, resulting in a total of 36 combination groups (n?=?20). The specimens were polymerized, aged for 8 weeks in distilled water at 37 °C, and then repaired by means of a repair kit. Shear bond strength and fracture mode were measured after aging of the specimens, undergoing storage for 24 h in distilled water at 37 °C followed by thermocycling (5,000 cycles, 5–55 °C) and an additional 4-week storage in distilled water at 37 °C.

Results

Data were statistically analyzed using ANOVA with TUKEY HSD post hoc test (α?=?0.05). On average, the OBC Admira reached the highest value as a substrate material (30.41 MPa), and the SBC Filtek Silorane reached the lowest value (8.14 MPa). Filtek Silorane was identified as the repair material with the highest bond strength value (28.70 MPa), while a packable composite reached the lowest bond strength value (15.55 MPa). The analysis of the break modes showed that adhesive breaks are typical when strength is at its lowest (6.27 MPa). A large number of cohesive fractures are conspicuous when identical materials are used for repair, except Filtek Silorane (2 % cohesive fractures).

Conclusions

The study demonstrated that the effect of the different materials on bond strength varies strongly, depending on whether the material is used as filling or as repair material.

Clinical relevance

It is generally advisable but not compulsory to combine identical RBCs.     

Clinical longevity of ceramic laminate veneers bonded to teeth with and without existing composite restorations up to 40 months

Objectives

This study evaluated the survival rate of ceramic laminate veneers bonded to teeth with and without existing composite restorations (ECR).

Materials and methods

Twenty patients (mean age: 49.7 years) received 92 feldspathic ceramic laminate veneers (Shofu Vintage AL) on the maxillary teeth (intact teeth: n?=?26; teeth with ECR: n?=?66). Preparations with incisal overlap were made, and ECR of good quality were not removed but conditioned using silica coating (CoJet) and silanization (ESPE-Sil). Enamel and dentin were etched with 38 % H₃PO₄ for 15–30 s and rinsed 30 s; adhesive resin (Excite) was applied, and laminate veneers were then cemented (Variolink Veneer). Restorations were evaluated at baseline and thereafter every 6 months using modified United States Public Health Service criteria.

Results

Mean observation period was 21.6 months. Overall, five absolute failures were encountered (fractures: n?=?3; chipping: n?=?1; debonding: n?=?1), resulting in a survival rate of 94.6 % (Kaplan–Meier). Survival rates of the laminates bonded to teeth without (96 %) and with ECR (93.5 %) did not show significant differences (p?>?0.05). Slight marginal defects (16 of 87 laminates) and slight marginal discoloration at the margins were noted (12 of 87 laminates) until the final recall. Secondary caries and endodontic complications were not detected in any of the teeth.

Conclusion

The clinical survival of ceramic laminate veneers up to 40 months was not significantly influenced when they were bonded onto intact teeth or onto teeth with ECR.

Clinical relevance

When no caries is present, it may not be necessary to replace existing composite restorations prior to cementation of ceramic laminate veneers.     

Six months of high-dose xylitol in high-risk caries subjects—a 2-year randomised, clinical trial

Objectives

The hypothesis was that the daily use of a high dose of a xylitol chewing gum for 6 months would reduce the increment of decayed permanent first molar surfaces (ΔD₆S) in high-risk schoolchildren after 2 years.

Methods

In this randomised, clinical trial, 204 schoolchildren with a high caries risk were assigned to two experimental groups, xylitol and non-xylitol. Caries status, salivary mutans streptococci, and lactobacilli were re-evaluated 2 years later in 74 xylitol-treated and 83 non-xylitol-treated schoolchildren. Differences in mean ?D₆S between groups registered at baseline and at follow-up were evaluated using the nonparametric Mann–Whitney U test.

Results

Outcome was the development of detectable carious lesions initial (D₁–D₂) and manifest (D₃) in the permanent first molars. In the xylitol group, the difference in proportion of children with decayed first permanent molars at baseline and follow-up was 1.43 % for manifest lesion and 2.86 % for initial lesions; while in the non-xylitol group was 10.26 % (p?<?0.01) and 16.66 % (p?<?0.01), respectively. A statistically significant difference regarding means was also observed in the non-xylitol group: the ?D₆S for manifest lesion was 0.18 (p?=?0.03) and 0.67 (p?=?0.02) for initial lesion.

Conclusion

The use of a chewing gum containing a high dose of xylitol for a period of 6 months has been shown to produce a long-term effect on caries development in high caries-risk children.

Clinical relevance

A school-based preventive programme based on 6 months’ administration of a high dose of xylitol via chewing gum proved to be efficacious in controlling caries increment in high-risk children.     

Effect of seating forces on cement–ceramic adhesion in microtensile bond tests

Objectives

The aim of this study was to evaluate the effect of different seating forces during cementation in cement–ceramic microtensile bond strength (μTBS).

Materials and methods

Forty-five blocks (5?×?5?×?4 mm³) of a glass-infiltrated alumina-based ceramic (In-Ceram Alumina) were fabricated according to the manufacturer’s instructions and duplicated in resin composite. Ceramic surfaces were polished, cleaned for 10 min in an ultrasonic bath, silica coated using a laboratory type of air abrasion device, and silanized. Each treated ceramic block was then randomly assigned to five groups (n?=?9) and cemented to a composite block under five seating forces (10 g, 50 g, 100 g, 500 g, and 750 g) using a dual-cured resin cement (Panavia F). The ceramic–cement–composite assemblies were cut under coolant water to obtain bar specimens (1 mm?×?0.8 mm²). The μTBS tests were performed in a universal testing machine (1 mm/min). The mean bond strengths values were statistically analyzed using one-way ANOVA (α?≤?0.05).

Results

Different seating forces resulted in no significant difference in the μTBS results ranging between 13.1?±?4.7 and 18.8?±?2.1 MPa (p?=?0.13) and no significant differences among cement thickness.

Conclusions

Excessive seating forces during cementation seem not to affect the μTBS results.

Clinical relevance

Excessive forces during the seating of single all-ceramic restorations cementation seem to display the same tensile bond strength to the resin cement.     

The effect of aging on the mechanical properties of nanohybrid composites based on new monomer formulations

Objectives

Nanohybrid resin-based composites (RBCs) containing new types of matrix monomers such as dimer acid-based dimethacrylate or tricyclodecane-urethane are assumed to show decreased water uptake and therefore better resistance to hydrolytic degradation than RBCs using bisphenol A diglycidyl methacrylate (BisGMA) due to their hydropobic nature. Our study aimed to analyze the effect of aging on six nanohybrid RBCs, of which two are using these new types of monomers, with regard to differences in the mechanical properties of the materials.

Materials and methods

Diametral tensile strength (DTS), Vickers hardness (HV), and creep were measured. Mechanical tests were performed after storing samples for 24 h in distilled water, as well as after aging (thermocycling for 5,000 cycles at 5–55°C and storage for 4 weeks either in distilled water, artificial saliva, or ethanol).

Results

The effect of aging on all test parameters was lower than the effect of the material. This information was provided by a general linear model, showing higher partial η² values for the influence factor material than for the factor aging. The influence of aging on the micromechanical properties HV and creep was proven to be more sensitive than on the macromechanical property (DTS). This was also illustrated by lower η² values for the variable aging for DTS. An increase of the creep of all materials was observed after storage in alcohol.

Conclusions

The use of new types of monomers could not be shown to be a significant advantage to the other examined materials containing BisGMA.

Clinical relevance

Nanohybrid composites can be recommended as universal filling materials, whether based on new or conventional monomers.     

Apparent diffusion coefficient-based differentiation of cystic lesions of the mandible

Objective

To evaluate the apparent diffusion coefficient (ADC) for differentiation of cystic lesions of the mandible.

Methods

We retrospectively evaluated 27 cystic lesions of the mandible. We determined the overall ADCs and the pixel-based ADC profiles (ADC mapping) of the fluid areas using two b values (500 and 1000?s/mm²).

Results

The overall ADCs of the fluid areas of ameloblastomas (2.45?±?0.27?×?10^?3?mm²/s) and simple bone cysts (2.52?±?0.14?×?10^?3?mm²/s) were significantly larger than those of dentigerous cysts (1.50?±?0.49?×?10^?3?mm²/s; p?=?0.047 and p?=?0.041, respectively), radicular cysts (0.90?±?0.21?×?10^?3?mm²/s; p?=?0.048 and p?=?0.042, respectively), and keratocystic odontogenic tumors (0.87?±?0.13?×?10^?3?mm²/s; p?=?0.032 and p?=?0.021, respectively). However, the overall ADCs were similar between ameloblastomas and simple bone cysts and among dentigerous cysts, radicular cysts, and keratocystic odontogenic tumors. ADC mapping demonstrated that ameloblastomas and simple bone cysts had 80?C99?% fluid areas with high ADC levels, whereas radicular cysts and keratocystic odontogenic tumors had 66?C100?% fluid areas with low or extremely low ADC levels. However, the ADC mapping profiles of dentigerous cysts differed substantially among the cases. The ADC-based criteria did not effectively differentiate between ameloblastomas and simple bone cysts or between radicular cysts and keratocystic odontogenic tumors.

Conclusions

The ADC-based differentiation was effective for discriminating some types of cystic lesion of the mandible.     

Polymerization kinetic calculations in dental composites: a method comparison analysis

Objectives

This study aimed to describe the polymerization process and to quantify the parameters of influence in two bulk-fill resin-based composites by comparing two real-time methods: the Fourier transform infrared (FTIR) spectroscopy and the visible light transmission spectrometry.

Materials and methods

The degree of conversion (DC) was recorded in real time for 5 min using the attenuated total reflectance FTIR spectroscopy (n?=?6) on the lower surface of 2, 4, and 6 mm thick samples irradiated for 20 s. The variation in irradiance was recorded during material irradiation at the bottom of the samples (n?=?5). Results were statistically analyzed using one-way and multiple-way ANOVAs with Tukey HSD post hoc test (α?=?0.05), partial eta-squared statistics, and Pearson correlation.

Results

No significant difference was found in DC in any materials as a function of incremental thickness, whereas the irradiance passing the specimens differed consistently within both analyzed increments and materials. These data could be described by the superposition of two exponential functions, the first being attributed to the gel phase and the second to the glass phase, resulting in an exponential sum function. DC data were able to calculate the end of the gel phase and the beginning of the glass phase, whereas irradiance measurements were able to detect only the last phase. The polymerization kinetics in the glass phase was less material-dependent as in the gel phase.

Conclusions

The irradiance measurements were more sensitive to variation in thickness, meaning that translucency is continuing to change as a function of thickness at a higher extent than DC.

Clinical relevance

Knowing the impact of the modulation factors describing the calculated sum exponential function allows the manipulation of the polymerization process at different stages to tailor material properties.     

In vitro fracture load of monolithic lithium disilicate ceramic molar crowns with different wall thicknesses

Objectives

The objective of this in vitro study was to assess the effect of wall thickness on the fracture loads of monolithic lithium disilicate molar crowns.

Material and methods

Forty-eight extracted molars were prepared by use of a standardized preparation design. Lithium disilicate crowns (e.max CAD, Ivoclar/Vivadent, Schaan, Liechtenstein) of different wall thicknesses (d?=?0.5, 1.0, and 1.5 mm; n?=?16 for each series) were then constructed and milled (Cerec MC-XL, Sirona, Bensheim, Germany). After placement of the teeth in acrylic blocks (Technovit, Heraeus Kulzer, Hanau, Germany), the crowns were adhesively luted (Multilink, Ivoclar Vivadent). In each series, eight crowns were loaded without artificial aging whereas another eight crowns underwent thermocycling (10,000 cycles, THE-1100, SD Mechatronik) and chewing simulation (1.2 million cycles, Willytec CS3, SD Mechatronik, F _max?=?108 N). All specimens were loaded until fracture on one cusp with a tilt of 30° to the tooth axis in a universal testing machine (Z005, Zwick/Roell). Statistical assessment was performed by use of SPSS 19.0.

Results

Crowns with d?=?1.0 and 1.5 mm wall thickness did not crack during artificial aging whereas two of the crowns with d?=?0.5 mm wall thickness did. The loads to failure (F _u) of the crowns without aging (with aging) were 470.2?±?80.3 N (369.2?±?117.8 N) for d?=?0.5 mm, 801.4?±?123.1 N (889.1?±?154.6 N) for d?=?1.0 mm, and 1107.6?±?131.3 N (980.8?±?115.3 N) for d?=?1.5 mm. For aged crowns with d?=?0.5 mm wall thickness, load to failure was significantly lower than for the others. However, differences between crowns with d?=?1.0 mm and d?=?1.5 mm wall thickness were not significant.

Conclusions

Fracture loads for posterior lithium disilicate crowns with 0.5 mm wall thickness were too low (F _u?<?500 N) to guarantee a low complication rate in vivo, whereas all crowns with 1.0 and 1.5 mm wall thicknesses showed appropriate fracture resistances F _u?>?600 N.

Clinical relevance

The wall thickness of posterior lithium disilicate crowns might be reduced to 1 mm, thus reducing the invasiveness of the preparation, which is essential for young patients.