Real-time Light Transmittance Monitoring for Determining Polymerization Completeness of Conventional and Bulk Fill Dental Composites.

OBJECTIVES: To monitor the real-time changes in light transmittance during composite curing and to use transmittance data to determine the curing times required for a complete polymerization. METHODS: Three conventional and three bulk fill composites were cured with two light-emitting diode curing units at layer thicknesses of 2 mm and 4 mm. The real-time light transmittance data were collected by a UV-Vis spectrometer in the wavelength range of 350-550 nm, plotted against time (t) and fitted to an exponential function f(t), whose first derivative ΔT(t) = df(t)/dt represented the rate of transmittance change. As the changing transmittance reflects structural changes that occur during polymerization, ΔT(t) > 0 was considered to indicate an ongoing polymerization, whereas ΔT(t) values approaching zero suggested a complete polymerization. This principle was used to determine times required for a complete polymerization (tcomplete) for each material/thickness/curing unit combination. RESULTS: Light transmittance was significantly influenced by the material type, sample thickness, and curing unit, amounting to 2.9%-27.0% for the bulk fill and 0.7%-16.7% for the conventional composites. The values of tcomplete amounted to 15.3-23.3 seconds for the bulk fill composites at 2 mm, 20.2-33.3 seconds for the conventional composites at 2 mm, 26.9-42.1 seconds for the bulk fill composites at 4 mm, and 40.1-59.8 seconds for the conventional composites at 4 mm. Additionally, an exponential relationship was discovered between the light transmittance and tcomplete. CONCLUSIONS: Some of the tcomplete values considerably exceeded the curing times recommended by the manufacturers.

Criteria for the Replacement of Restorations: Academy of Operative Dentistry European Section.

The replacement of a restoration is one of the most common procedures in dentistry. However, the criteria for such intervention, excluding catastrophic failure and persistent discomfort and pain, continue to be the subject of considerable debate. The decision-making process remains subjective on the part of the treating clinician, while the evidence base for refurbishment and repair rather than replacement for the management of defective and failing restorations continues to grow and strengthen. This article, prepared as an Academy of Operative Dentistry European Section consensus publication, reviews existing criteria for the replacement of restorations and encourages practitioners to shift, if not already doing so, to considering the replacement of a restoration as a last resort rather than as a prudent action to be taken if in any doubt about clinical acceptability. Further research in the area, spanning the risk assessment of defective and failing restorations and new diagnostic tools and processes, together with work to enhance the evidence base of restoration repair vs replacement, would be of immense value.

Enamel and Dentin Microhardness and Chemical Composition After Experimental Light-activated Bleaching.

OBJECTIVES: To evaluate 1) the influence of five bleaching agents (with additional light activation) on enamel and dentin surface microhardness and chemical composition and 2) the remineralizing potential of artificial saliva and amorphous calcium phosphate (ACP). METHODS AND MATERIALS: The study was conducted on 125 human third molars dissected into quarters for separate enamel and dentin measurements. The bleaching process was performed with 38% and 25% hydrogen peroxide (HP) and 30%, 16%, and 10% carbamide peroxide (CP) gels two times for 15 minutes each time. All bleaching gels were tested alone and in combination with ZOOM2, light-emitting diode (LED), organic LED, and femtosecond laser. A total of 25 bleaching combinations (n=10) were evaluated. Microhardness was measured by a Vickers diamond. Chemical analysis was performed using energy-dispersive X-ray spectroscopy. RESULTS: Bleaching agents used in the absence of light activation caused a significant reduction in enamel and dentin surface microhardness (p<0.001), ranging from 8% for 16% CP to 40% for 25% HP. The effects of different light activations were negligible. After two-week treatment with ACP and artificial saliva, maximum deviation from baseline microhardness was just 3%. Such treatment increased the concentrations of calcium, phosphorus, and fluorine. CONCLUSIONS: An increase in peroxide concentration and gel acidity negatively affected microhardness and concentrations of calcium and phosphorus in enamel and dentin. ACP and artificial saliva stimulated the remineralization of hard tissues.

Raman spectroscopic assessment of degree of conversion of bulk-fill resin composites--changes at 24 hours post cure.

OBJECTIVE: The aim of this study was to determine degree of conversion (DC) of solid and flowable bulk-fill composites immediately and after 24 hours and investigate the variations of DC at surface and depths up to 4 mm. MATERIALS AND METHODS: Eight bulk-fill composites (Tetric EvoCeram Bulk Fill [shades IVA and IVB], Quixfil, X-tra fil, Venus Bulk Fill, X-tra Base, SDR, Filtek Bulk Fill) were investigated, and two conventional composites (GrandioSO, X-Flow) were used as controls. The samples (n = 5) were cured for 20 seconds with irradiance of 1090 mW/cm(2). Raman spectroscopic measurements were made immediately after curing on sample surfaces and after 24 hours of dark storage at surface and at incremental depths up to 4 mm. Mean DC values were compared using repeated measures analysis of variance (ANOVA) and t-test for dependent samples. RESULTS: Surface DC values immediately after curing ranged from 59.1%-71.8%, while the 24-hour postcure values ranged from 71.3%-86.1%. A significant increase of DC was observed 24 hours post cure for all bulk-fill composites, which amounted from 11.3% to 16.9%. Decrease of DC through depths up to 4 mm varied widely among bulk-fill composites and ranged from 2.9% to 19.7%. CONCLUSIONS: All bulk-fill composites presented a considerable 24-hour postcure DC increase and clinically acceptable DC at depths up to 4 mm. Conventional control composites were sufficiently cured only up to 2 mm, despite significant postcure polymerization.

Influence of irradiation time on subsurface degree of conversion and microhardness of high-viscosity bulk-fill resin composites.

OBJECTIVES: To evaluate the influence of irradiation time on degree of conversion (DC) and microhardness of high-viscosity bulk-fill resin composites in depths up to 6 mm. MATERIALS AND METHODS: Four bulk-fill materials (Tetric EvoCeram Bulk Fill--TECBF; x-tra fil--XF; QuixFil--QF; SonicFill-SF) and one conventional nano-hybrid resin composite (Tetric EvoCeram--TEC) were irradiated for 10, 20, or 30 s at 1,170 mW/cm(2). DC and Knoop microhardness (KHN) were recorded after 24-h dark storage at five depths: 0.1, 2, 4, 5, and 6 mm. Data were statistically analyzed using ANOVA and Bonferroni's post-hoc test (α = 0.05). RESULTS: With increasing bulk thickness, DC and KHN significantly decreased for TEC. TECBF and SF showed a significant decrease in DC and KHN at 4-mm depth after 10-s irradiation, but no decrease in DC after 30-s irradiation (p > 0.05). XF and QF demonstrated no significant DC decrease at depths up to 6 mm after irradiation of at least 20 s. At 4-mm depth, all materials tested achieved at least 80 % of their maximum DC value, irrespective of irradiation time. However, at the same depth (4 mm), only XF and QF irradiated for 30 s achieved at least 80 % of their maximum KHN value. CONCLUSIONS: Regarding DC, the tested bulk-fill resin composites can be safely used up to at least 4-mm incremental thickness. However, with respect to hardness, only XF and QF achieved acceptable results at 4-mm depth with 30 s of irradiation. CLINICAL RELEVANCE: Minimum irradiation times stated by the manufacturers cannot be recommended for placement of high-viscosity bulk-fill materials in 4-mm increments.

Risk factors for bruxism among Croatian navy employees.

The aim of the study was to evaluate the relationship between bruxism, and sociodemographic parameters, symptoms of temporomandibular disorders (TMD), personality and war experience among Croatian navy employees. The sample included 1092 subjects, aged 20-60 years (mean age 37·06 ± 7·85). An individual's bruxism status was based on clinical oral examination and participants' report of bruxism. Subjects with bruxism index values ≥ 90th percentile were included in severe bruxism group (n = 111), and those with scores below 90th percentile were labelled as negligible bruxism group (n = 981). No differences were found in gender distribution between the two groups. The proportion of military personnel presenting with bruxism is double the proportion of administrative employees with bruxism. A total of 23·34% subjects in negligible bruxism group and 48·65% in severe bruxism group participated in the war. Subjects in severe bruxism group presented more TMD-related signs and symptoms than those in negligible bruxism group. Higher prevalence of neuroticism and psychoticism was found in severe bruxism group. According to logistic regression, the probability of severe bruxism was significantly associated with marital status [Odds ratio (OR) 6·859, 95% confidence interval (CI) 3·869-12·158 P < 0·001], neuroticism (OR 2·842, 95% CI 1·434-5·632 P = 0·003), psychoticism (OR 2·618, 95% CI 1·193-5·746 P = 0·016), military duty (OR 1·828, 95% CI 1·013-3·298 P = 0·045) and masticatory muscles tenderness (OR 9·372, 95% CI 4·923-17·841 P < 0·001). Smokers had a 2·72-fold (95% CI 1·706-4·335 P < 0·001) higher risk of bruxism than non-smokers. Subjects who participated in war were more represented in severe bruxism group. Further studies, including other potential risk factors, are required to clarify these relationships.

Influence of light intensity from different curing units upon composite temperature rise.

The unavoidable consequence of composite resin photopolymerization is temperature rise in tooth tissue. The temperature rise depends not only on the illumination time, but also on light intensity, distance of light guide tip from composite resin surface, composition and shade of composite resin and composite thickness. The most commonly used units for polymerization today are halogen curing units, which emit a large spectrum of wavelengths. A proportion of the spectrum has no influence on degree of conversion and therefore causes unnecessary temperature rise. Units based on light source - blue light emitting diodes (LED), as an alternative for halogen curing units, have been introduced in clinical practice. The aim of this study was to show the influence of the light intensity of curing units Elipar Trilight, Astralis 7 and Lux-o-Max unit on temperature rise in composite resin sample of Tetric Ceram. The temperature was measurement with Metex M-3850 D multimeter with the tip of temperature probe put into unpolymerized composite resin sample 1 mm depth. The highest temperature rise was recorded with standard curing mode for Elipar Trilight halogen curing unit (13.3 +/- 1.21 degrees C after 40 s illumination), while the lowest temperature rise was recorded for the Lux-o-Max unit based on LED technology (5.2 +/- 1.92 degrees C after 40 s illumination).

Photopolymerization of composite resins with plasma light.

Everyday improvements in components and characteristics of composite materials have induced faster development of curing units. Besides standard halogen curing units and soft-start photopolymerization light sources, some experiments with argon and pulsed laser light and low intensity blue superbright light emitting diodes have been made. On the other hand, rapid polymerization with strong plasma light is also clinically applicable. The aim of this study was to measure the degree of conversion and temperature rise for three restorative composite materials: Tetric Ceram (Vivadent, Schaan, Liechtenstein), Pertac II (ESPE, Seefeld, Germany) and Z100 (3M Dental Products, St Paul, MN, USA) during polymerization with plasma light Apollo 95E (DMDS, Dental/Medical Diagnostic Systems, Fleury d'Aude, France) and compare it with the results of polymerization with a halogen curing unit, Elipar Trilight (ESPE, Seefeld, Germany). The results revealed the degree of conversion values in the case of polymerization with plasma light to be almost equal to those obtained by curing with the halogen curing unit, whereas the temperature rise was almost negligible.

Composite conversion and temperature rise using a conventional, plasma arc, and an experimental blue LED curing unit.

The objective of this study was to evaluate the degree of conversion and temperature rise in three different composite materials when illuminated by an experimental light source [blue superbright light emitting diodes (LEDs)] and compared with plasma light and traditional photopolymerization unit. The degree of conversion and temperature rise were measured using Fourier transform infrared (FTIR) spectroscopy and digital multimeter, respectively. The results revealed significantly higher degree of conversion values in case of conventional curing than with other two light sources whereas temperature rise was significantly lower when blue LEDs and plasma light were used. There were great differences in light intensities between blue LEDs of only 9 mW cm-2 compared with plasma light of 1370 mW cm-2 and Elipar II of 560 mW cm-2. Better match of LED spectral distribution peak to camphorquinone absorption distribution peak probably explains much lower intensities used for similar photopolymerization effect like in the case of rapid plasma lamp curing.

Double tooth.

The form of primary and permanent teeth can differ morphologically from that which is considered normal, completely or in some parts. The changes in tooth form can be hereditary or caused by some disease or trauma. Fusion is a union of one or more teeth during development. Gemination means that two separate morphological units were created by division of the tooth germ. The intention of this study was to state the prevalence of double teeth (fusion and gemination) among the persons tested, as to gender, distribution in the maxilla or mandible, and whether the anomaly occurred bilaterally or unilaterally. The results of this investigation have shown that in a total of examined 3,517 plaster models, a prevalence of double teeth was 0.2%. 57.2% of them were fusioned and 42.9% geminated.

Degree of conversion and temperature rise during polymerization of composite resin samples with blue diodes.

To ensure an adequate clinical composite filling light source for photopolymerization is of great importance. In everyday clinical conditions commonly used unit for polymerization of composite material is halogen curing unit. The development of new blue superbright light emitting diodes (LED) of 470 nm wavelengths comes as an alternative to standard halogen curing unit of 450-470 nm wavelengths. The purpose of this study was to compare the degree of conversion (DC) and temperature rise of four hybrid composite materials: Tetric Ceram, Pertac II, Valux Plus and Degufill Mineral during 40 s illumination with standard halogen curing unit Heliolux GTE of 600 mW cm(-2) intensity, Elipar Highlight soft-start curing unit of 100 mW cm(-2) (10 s) and 700 mW cm(-2) (30 s) intensity and 16 blue superbright LED of minimal intensity of 12 mW cm(-2) on the surface and 1 mm depth. The results revealed only a little bit higher DC values in case of polymerization with even 66 times stronger halogen curing units which showed twice higher temperature than blue diodes. Temperature and DC obtained are higher on the surface than on 1 mm depth regardless on the light source used.

The efficiency of dentine adhesives in treating non-caries cervical lesions.

The aim of this study was to prove the hypothesis that dentine adhesives can be used as therapeutic material in treating dentine hypersensitivity, regardless of aetiology. The research was conducted on 492 students of Zagreb University School of Dental Medicine (154 male, 338 female), 20-25-years-old. The defects of the tooth neck were found in 38 patients, on 133 teeth (38 of male patients, 95 of female) and dentine hypersensitivity was recorded according to the subjective sensations of patients. Therapeutic characteristics of three adhesive materials were examined simultaneously: All Bond 2, fourth generation adhesive, Syntac Single Component and One Step, fifth generation adhesives. Teeth treated with dentine lacquer Cervitec were used as a control group. Tooth necks were treated with selected materials according to instructions of a manufacturer. A completed statistical survey of the results has clearly shown that dentine adhesives can be used in symptomatic therapy of dentine hypersensitivity of the non-caries cervical lesions (NCCL). The survey has also shown that dentine adhesives of the fifth generation (Syntac Single Component and One Step) have much higher efficiency rate than dentine adhesives of the fourth generation (All Bond 2) and dentine lacquer (Cervitec). According to data complied through this study the conclusion can be brought forward that dentine adhesives are not a final solution to the problem of dentine hypersensitivity, because their efficiency decreases with time.

The effect of the photopolymerization method on the quality of composite resin samples.

An optimal degree of conversion and minimal polymerization shrinkage are generally antagonistic goals, as increased monomer conversion invariably leads to elevated polymerization shrinkage values. However, both parameters are indispensable for an optimal resin composite restoration. A number of approaches have been used to reduce the stress on the restoration cavity wall interface, such as dentine bonding agents to counteract polymerization shrinkage, stress-absorbing lining materials and low-intensity curing lights to control the flow capacity of the material during polymerization. However, the configuration of the cavity and cohesive fractures of the material and surrounding tooth tissues are still a problem in day-to-day clinical practice. A new photopolymerization light source, pulsed laser, ensures a higher degree of conversion and lower polymerization shrinkage, and differentiates this technique from standard polymerization methods and continuous-wave argon laser polymerization. The coherence and monochromacity of pulsed laser light set at 468 nm and the far greater intensity of laser nanopulses produce a saturation effect in the depths of the composite, thus resulting in higher monomer conversion. The total amount of energy illuminating the sample surface, which is only one-fifth of that of conventional methods, and the cooling and relaxation of the material between nanopulses may be responsible for the reduced net polymerization shrinkage.

"C"-shaped canal configuration of mandibular second permanent molar.

Roots of the second mandibular molar often fuse so the purpose of this investigation was to examine the appearance of "C"-shaped root canals and to classify different root canal types. A hundred and twelve randomly chosen second lower permanent molars-after extraction due to periodontal disease-were prepared and then analysed. Contrast liquid (methylene blue) was injected into prepared teeth. Each tooth was cut into slices to view the root canal morphology. Results of the analysis revealed fusion, either total or partial in 14 cases (12.5%). As a conclusion various appearances were classified into 5 types according to the fused canal shapes and the frequency of different types varied from 0.89%-6.25%.

Pulsed blue laser curing of hybrid composite resins.

Clinical performance of light-curing composite restorations is greatly influenced by the quality of the curing-light. Currently used photopolymerization units have some important drawbacks, such as decreasing light output with time and distance, which results in a relatively low degree of conversion and shallow depth of cure, particularly of darker shades. Experiments with continuous argon laser polymerization showed overheating of the composite sample, as well as increased shrinkage of the material. In this study a pulsed laser, set at 468 nm (the maximum of the camphorquinone absorption coefficient), with 20-ns pulse duration, repetition rate of 10 Hz and energy of 10 mJ per pulse, was used as a light source. The aim of the study was to evaluate the effect of polymerization of light and dark shades of three different hybrid composites cured by pulsed laser at the surface and at 3.0 mm depth. The degree of conversion was measured by Fourier transform infrared spectroscopy (FTIR). Applying pulsed blue laser, significantly better results were obtained for both shades compared to standard polymerization values. Very weak dependence of the degree of conversion, between the surface measurements and those at 3.0 mm, were observed in the case of pulsed laser polymerization due to the piercing nanopulses and the monochromatic light at 468 nm.

Polymerization of composites using pulsed laser.

The quality of visible-light-cured composites depends on the capability of the light source to properly polymerize the material within a specified exposure time. In this study, the degree of conversion of different composite materials (hybrid and microfilled) of light and dark shades was compared after illumination by a standard curing unit and pulsed laser (lambda=468) respectively. The degree of conversion was measured by Fourier transform infrared spectroscopy. Results obtained by the analysis of the pulsed laser-induced polymerization were significantly higher for all the materials and shades observed. All values of the degree of conversion were lower for dark shades of all types of composites, regardless of the photopolymerization technique used. Besides the surface, better polymerization was recorded also at depths of 1.0, 2.0 and 3.0 mm, respectively. These values varied from 59.7%+/-2.14 to 84.5%+/-0.33 for pulsed laser (including all depths) caused by the saturation effect induced by high power laser pulses and from 42.7%+/-1.48 to 74.7%+/-0.99 for standard polymerization.