How does indirect air-cooling influence pulp chamber temperature in different volume teeth and absence/presence of resin-based composite during light curing?

BACKGROUND: Light-curing of materials during restorative dental procedures poses a risk for pulp tissue overheating. Therefore, the aim of this study was to investigate the effect of indirect air-cooling on pulp chamber temperatures during light-curing of varying volume teeth and absence/presence of resin-based composite (RBC) at different exposure time. METHODS: The volume of 11 human teeth was measured by micro computed tomograph. An experimental rig controlled the thermal environment of the teeth and a thermocouple inserted retrograde into the root canal measured temperature changes. Pulp chamber temperature was measured with and without air-cooling on teeth without and with RBC at 15 s, 30 s and 60 s intervals. Generalized estimating equations were used for statistical analysis. RESULTS: The temperature increase with air-cooling (versus no air-cooling) was lower in teeth despite absence/presence of RBC (ß = - 4.26, 95%CI - 5.33 and ß = - 4.47, 95%CI - 5.60, respectively). With air-cooling, the temperature increase in teeth with RBC was lower compared to teeth without RBC (ß = - 0.42, 95%CI -0.79; - 0.05). Higher teeth volume resulted in lower temperature increase with air-cooling than without air-cooling (ß = - 0.04, 95%CI -0.07; - 0.01 and ß = - 0.17, 95%CI -0.30; - 0.05, respectively). CONCLUSIONS: Air-cooling resulted in lower pulp chamber temperature increase. Using air-cooling, the temperature increase was lower in teeth with RBC compared to teeth without RBC. Lower volume teeth resulted in higher temperature increase, thus they seemed to benefit more from air-cooling compared to higher volume teeth. Air-cooling could be an effective tool in controlling pulp temperature increase during light-curing, especially when the tooth volume is small.

Light-curing units used in dentistry: Effect of their characteristics on temperature development in teeth.

This study aimed to investigate pulp chamber and surface temperature development using different LED light curing units (LCUs). Eight brands of LED-LCUs were tested in a laboratory bench model. The pulp chamber and surface temperature were recorded with a type T thermocouple and infrared cameras, respectively. The highest pulp chamber and surface temperature increase was 6.1±0.3°C and 20.1±1.7°C, respectively. Wide-spectrum LED-LCUs produced higher pulp chamber temperature increase at 0 mm and 2 mm but lower at 4 mm. Narrow-spectrum LED-LCUs produced higher surface temperature increase. LED-LCU featuring modulated output mode resulted in lower increase in pulp chamber temperature but higher on surface temperature. LED-LCU with light guide tip delivering an inhomogeneous beam caused higher increase in temperature on the surface and in the pulp chamber. LED-LCUs with different spectral emission, output mode and light guide tip design contributed to different temperature development in the pulp chamber and at the surface of teeth.

In vitro Candida albicans biofilm formation on different titanium surface topographies.

OBJECTIVES: To investigate if differences in titanium implant surface topography influence Candida albicans biofilm formation. MATERIALS AND METHODS: Titanium discs were prepared and characterized using a profilometer: Group A (R a 0.15 µm, smooth), Group B (R a 0.64 µm, minimally rough) and Group C (R a 1.3 µm, moderately rough). Contact angle and surface free energy (SFE) were determined for each group. Non-preconditioned titanium discs were incubated with C. albicans for 24 h. In additional experiments, the titanium discs were initially coated with human saliva, bovine serum albumin or phosphate-buffered saline for 2 h before incubation with C. albicans for 24 h. The amount of fungal biofilm formation was quantified using a colorimetric assay. RESULTS: C. albicans biofilm formation was significantly lower (p < 0.05) on the minimally rough titanium surface compared to smooth and moderately rough surfaces. The titanium surface displaying the lowest SFE (Group B) was associated with significantly lower (p < 0.05) C. albicans biofilm formation than the other two groups. Salivary coating resulted in greater adherence of C. albicans with increased surface roughness. CONCLUSIONS: The minimally rough titanium discs displayed lowest SFE compared to smooth and moderately rough surfaces and showed the least C. albicans biofilm formation. This study demonstrated that C. albicans biofilm formation increased in a SFE-dependent manner. These findings suggest that SFE might be a more explanatory factor for C. albicans biofilm formation on titanium surfaces than roughness. The presence of a pellicle coating may negate the impact of SFE on C. albicans biofilm formation on titanium surfaces.

Heat Development in the Pulp Chamber During Curing Process of Resin-Based Composite Using Multi-Wave LED Light Curing Unit.

OBJECTIVE: The study aimed to investigate factors contributing to heat development during light curing of a flowable bulk-fill resin-based composite (SDRTM, Lot # 602000876, Dentsply Sirona, Konstanz, Germany) (RBC). MATERIALS AND METHODS: Temperatures were measured with calibrated thermocouples. A multi-wave light-emitting diode (LED) light curing unit (LCU) was used (Ivoclar Vivadent, Schaan, Lichtenstein). In all experiments, the RBC was first cured (cured) for 30 s and, after 5 min of recovery time, received a second LCU irradiation (post-cured) for 30 s. The exothermic reaction was measured by calculating the Δ temperature between cured and post-cured RBC. In a cylinder-shaped polymer mold, temperature was recorded inside of RBC during curing (part 1) and light transmission through RBC during curing was investigated (part 2). Pulpal temperatures were assessed in an extracted third molar during light curing (part 3). Data were statistically analyzed using one-way ANOVA (α=0.05). RESULTS: Increased thickness of RBC led to decreased pulp chamber temperatures. Inside RBC, there was a large variation in heat development between the cured and post-cured groups (p<0.05). The cured group absorbed more LCU irradiation than the post-cured group. CONCLUSION: The irradiance of the LCU seemed to be a more important factor than exothermic reaction of RBCs for pulp chamber heat development. Flowable bulk-fill RBCs can act as a pulpal insulator against LCU irradiation, despite their exothermic curing reaction.

Quantification of porosity in composite resins delivered by injectable syringes using X-ray microtomography.

OBJECTIVE: To assess whether composite polymer resin delivered in compules include pores and the possible effect on the amount of porosity in dental restorations. METHOD AND MATERIALS: Original compules containing unpolymerised composite polymer resin (CPR) were scanned in a micro-CT. Four products were examined, which comprised universal composites (Herculite XRV Ultra, Ceram.X Universal, Tetric Evo Ceram) and a flowable bulk-fill composite (SDR) (n = 10 per group). The pore size distribution and amount of porosity (vol.%) were estimated for the unpolymerized and polymerized material used to restore a standardised cavity in a typodont tooth. Manufacturers' instructions were followed regarding material handling, and polymerisation by use of a calibrated light-curing unit. The pore characteristics and their size distribution, and the amount of porosity in the dental restoration were contrasted with the values measured in the compule. Non-parametric tests were used to analyse differences between the four products. RESULTS: All the composite polymer resin compules contained unpolymerised material that included pores. The universal composite compules included pores predominantly in the sub-100 µm sizes. In contrast, the flowable bulk-fill compules included a few pores with a diameter >100 µm, which were assumed to be air-bubbles. The unpolymerised material within the compule included consistently more pores compared to the extruded portion from the compule tip, and in the final restoration (p < .001). The amount of porosity in the restorations differed amongst the tested materials, with the flowable bulk-fill composite showing the lowest amount of porosity (p < .01).

Light-curing units used in dentistry: factors associated with heat development-potential risk for patients.

OBJECTIVES: To investigate how heat development in the pulp chamber and coronal surface of natural teeth with and without cusps subjected to irradiance using light-emitting diode (LED)-light-curing units (LCUs) is associated with (i) irradiance, (ii) time, (iii) distance, and (iv) radiant exposure. MATERIALS AND METHODS: Three different LED-LCUs were used. Their irradiance was measured with a calibrated spectrometer (BlueLight Analytics Inc., Halifax, Canada). An experimental rig was constructed to control the thermal environment of the teeth. The LED-LCU tip position was accurately controlled by a gantry system. Tooth surface temperature was measured by thermography (ThermaCAM S65 HS, FLIR Systems, Wilsonville, USA) and pulp chamber temperature with a thermocouple. LED-LCU tip distance and irradiation times tested were 0, 2, and 4 mm and 10, 20, and 30 s, respectively. Ethical permission was not required for the use of extracted teeth. RESULTS: Maximum surface and pulp chamber temperatures were recorded in tooth without cusps (58.1 °C  ± 0.9 °C and 43.1 °C ± 0.9 °C, respectively). Radiant exposure explained the largest amount of variance in temperature, being more affected by time than irradiance. CONCLUSIONS: At all combinations of variables tested, repeated measurements produced consistent results indicating the reliability of the method used. Increased exposure time seems to be the factor most likely to cause tissue damage. CLINICAL RELEVANCE: Risk of superficial tissue damage at irradiances >1200 mW/cm2 is evident. There is a risk of pulp damage when only thin dentin is left at higher irradiances (>1200 mW/cm2). Clinicians should be aware of LED-LCU settings and possible high temperature generated.

Effect of cements on fracture resistance of monolithic zirconia crowns.

Objectives The present study investigated the effect of cements on fracture resistance of monolithic zirconia crowns in relation to their compressive strength. Materials and methods Four different cements were tested: zinc phosphate cement (ZPC), glass-ionomer cement (GIC), self-adhesive resin-based cement (SRC) and resin-based cement (RC). RC was used in both dual cure mode (RC-D) and chemical cure mode (RC-C). First, the compressive strength of each cement was tested according to a standard (ISO 9917-1:2004). Second, load-to-failure test was performed to analyze the crown fracture resistance. CAD/CAM-produced monolithic zirconia crowns with a minimal thickness of 0.5 mm were prepared and cemented to dies with each cement. The crown-die samples were loaded until fracture. Results The compressive strength of SRC, RC-D and RC-C was significantly higher than those of ZPC and GIC (p < 0.05). However, there was no significant difference in the fracture load of the crown between the groups. Conclusion The values achieved in the load-to-failure test suggest that monolithic zirconia crowns with a minimal thickness of 0.5 mm may have good resistance against fracture regardless of types of cements.