Clinical and histological evaluation of thermal injury thresholds in human teeth: a preliminary study

Dental health concerns for patients suffering from facial, peri-oral burns, and inhalation injury: A persistent yet underappreciated challenge

Demographic data reveal a correlative relationship between facial burns and profoundly impaired dental health, while inhalation injury correlates with a high Periodontal Screening and Recording Index, both of which significantly reduce quality of life for the burn injury patient. Despite these facts, few if any burn centers surveyed in the U.S. or Germany enlist specialized services and well-defined follow-up protocols for patients who might well be at risk. Facial burns represent a severe injury, the consequence of which may tragically lead to significant and long lasting functional, esthetic, and psychological sequelae such as perioral scarring, deformity and microstomia. Inhalation injury from inhaled heated air, gas, and chemical exposure are well-known causes of early as well as late airway injury, morbidity, and death. Thermal injury patterns to perioral-related and dental structures is increasingly being recognized. This review delineates current burn-related dental health pathology and when available the underlying causation. These findings may help guide future research as well as therapeutic strategies to improve dental health and outcome for our patients.

Effect of Rapid High-Intensity Light-Curing on Increasing Transdentinal Temperature and Cell Viability: An In Vitro Study

BACKGROUND

This study investigated effects of rapid high-intensity light-curing (3 s) on increasing transdentinal temperature and cell viability.

METHODS

A total of 40 dentin discs (0.5 mm) obtained from human molars were prepared, included in artificial pulp chambers (4.5 × 5 mm), and subjected to four light-curing protocols (n = 5), with a Valo Grand light curing unit: (i) 10 s protocol with a moderate intensity of 1000 mW/cm2 (Valo-10 s); (ii) 3 s protocol with a high intensity of 3200 mW/cm2 (Valo-3 s); (iii) adhesive system + Filtek Bulk-Fill Flow bulk-fill composite resin in 10 s (FBF-10 s); (iv) adhesive system + Tetric PowerFlow bulk-fill composite resin in 3 s (TPF-3 s). Transdentinal temperature changes were recorded with a type K thermocouple. Cell viability was assessed using the MTT assay. Data were analyzed using one-way ANOVA and Tukey tests for comparison between experimental groups (p < 0.05).

RESULTS

The 3 s high-intensity light-curing protocol generated a higher temperature than the 10 s moderate-intensity standard (p < 0.001). The Valo-10 s and Valo-3 s groups demonstrated greater cell viability than the FBF-10s and TPF-3 s groups and statistical differences were observed between the Valo-3 s and FBF-10 s groups (p = 0.023) and Valo-3 s and TPF-3 s (p = 0.025), with a potential cytotoxic effect for the FBF-10 s and TPF-3 s groups.

CONCLUSIONS

The 3 s rapid high-intensity light-curing protocol of bulk-fill composite resins caused a temperature increase greater than 10 s and showed cell viability similar to and comparable to the standard protocol.

A Finite Element Method Study on a Simulation of the Thermal Behaviour of Four Methods for the Restoration of Class II Cavities

The possibility of dental pulp damage during dental procedures is well known. According to studies, during finishing and polishing without cooling, temperatures of up to 140 °C or more can be generated. There are many studies that have analysed the influence of the finishing and polishing of fillings on the mechanical parameters, but the analysis of thermal parameters has led to uncertain results due to the difficulty of performing this in vivo. Background: We set out to conduct a study, using the finite element method, to determine the extent to which the type of class II cavity and the volume of the composite filling influence the duration of heat transfer to the pulp during finishing and polishing without cooling. Materials and Methods: A virtual model of an upper primary molar was used, with a caries process located on the distal aspect, in which four types of cavities were digitally prepared: direct access, horizontal slot, vertical slot and occlusal-proximal. All four cavity types were filled using a Filtek Supreme XT nanocomposite. Results: The study showed that the filling volume almost inversely proportionally influences the time at which the dental pulp reaches the critical temperature of irreversible damage. The lowest duration occurred in occlusal-distal restorations and the highest in direct access restorations. Conclusions: based on the results of the study, a working protocol can be issued so that finishing and polishing restorations without cooling are safe for pulpal health.

Thermography and conversion of fast-cure composite photocured with quad-wave and laser curing lights compared to a conventional curing light

OBJECTIVES

This study investigated effects of the different emittance-mode protocols from three light curing units (LCUs): (i) a Laser (Monet); (ii) a quad-wave (PinkWave); (iii) a conventional LED (Elipar S10) on the temperature rise (ΔT) and degree of conversion (DC) when photo-curing fast or conventional bulk-fill resin-based composites (RBC). The aim was to correlate ΔT and DC, and the radiant exposure delivered to RBC specimens.

METHODS

A 3D-printed resin mold of 4 mm depth was filled with two bulk-fill RBCs: Tetric PowerFill® (fast photo-polymerised composite) (TPF) or Tetric EvoCeram® Bulk-Fill (EVO). Three LCUs were used: (i) Monet laser for 1 s and 3 s (MONET-1 s, MONET-3 s); (ii) PinkWave quad-wave used for 3 s in Boost mode (PW-3 s) and for 20 s in standard mode (PW-20 s); (iii) Elipar S10 for 5 s (S10-5 s) and for 20 s in standard mode (S10-20 s). 2-dimensional temperature maps were obtained before, during and for 60 s after the LCU had turned off using a thermal imaging camera. Thermal changes were analysed at five depths: (0, 1, 2, 3, and 4 mm from the top surface of the RBC). The maximum temperature rise (Tmax) and the mean temperature rise (ΔT) were determined. Cylindrical-shaped specimens were prepared from each material using a stainless-steel split mold (4 × 4 mm) and light-cured with the same protocols. The DC was measured for 120 s and at 1 h after LCU had turned off using Fourier Transform Infrared Spectroscopy (FTIR). Data were analysed using Three-way ANOVA, One-way ANOVA, independent t-tests, and Tukey post-hoc tests (p < 0.05).

RESULTS

Radiant exposures delivered by the various irradiation protocols were between 4.5-30.3 J/cm2. Short exposure times from MONET-1 s and PW-3 s delivered the lowest radiant exposures (4.5 and 5.2 J/cm2, respectively) and produced the lowest ΔT and DC. The longer exposure times in the standard modes of PW-20 s, S10-20 s, and MONET-3 s produced the highest Tmax, ΔT, and DC for both composites. The ΔT range among composites at different depths varied significantly (31.7-49.9 °C). DC of TPF ranged between 30-65% and in EVO between 15.3-56%. TPF had higher Tmax, ΔT for all depths and DC compared to EVO, across the LCU protocols (p < 0.05), except for PW-20 s and MONET-3 s. The coronal part of the restorations (1-2 mm) had the highest ΔT. There was a positive correlation between ΔT and DC at 4-mm depth after 120 s SIGNIFICANCE: Longer, or standard, exposure times of the LCUs delivered greater radiant exposures and had higher DC and ΔT compared to shorter or high-irradiance protocols. The fast photo-polymerised RBC had comparatively superior thermal and conversion outcomes when it received a high irradiance for a short time (1-5 s) compared to the conventional Bulk-Fill RBC.

The Effect of Water Coolant and Bur Type on Pulp Temperature When Removing Tooth Structure and Restorative Dental Materials

OBJECTIVE

The aim was to compare intrapulp temperature (IPT) changes when flat-fissure diamond burs and pear-shaped tungsten carbide burs were used to cut tooth structure, amalgam, and composite resin with and without water coolant.

METHODS

Thermocouples were inserted into the pulp chamber of extracted intact mandibular molars. The thermocouples were connected to an electronic thermometer that detects temperature every second to an accuracy of 0.1°C. IPT changes were recorded while using a high-speed handpiece during MOD cavity preparations (n=40), composite resin removal (n=40), and amalgam removal (n=40). A two-way ANOVA was used for each procedure to test for the effect of bur (pear-shaped tungsten carbide vs flat-fissured diamond) and water coolant (on vs off), with significant main effects (α=0.05) further analyzed using Tukey's multiple comparison test.

RESULTS

During MOD cavity preparation, water coolant reduced changes in IPT (0.03±0.27°C) compared to no water coolant (1.27±0.29°C) when tungsten carbide burs were used (p<0.05) but not when diamond burs were used. During composite resin removal, tungsten carbide burs had less changes in IPT (0.55±0.18°C) compared to diamond burs (1.66±0.50°C) with no water coolant (p<0.05). Water coolant also reduced changes in IPT (0.09±0.14°C) compared to no water coolant (1.66±0.50°C) when diamond burs were used (p<0.01). Water coolant did not significantly affect IPT when tungsten carbide burs were used. During amalgam removal, tungsten carbide burs had lower changes in IPT (0.56±0.15°C) compared to diamond burs (1.88±0.43°C) with no water coolant (p<0.05). Water coolant also significantly reduced changes in IPT (0.71±0.2°C) compared to no water coolant (1.88±0.43°C) when diamond burs were used (p<0.05) but not when tungsten carbide burs were used.

CONCLUSIONS

Water coolant reduced IPT changes when drilling tooth structure with tungsten carbide burs, but not when removing amalgam or composite. Conversely, water coolant reduced IPT changes when drilling with flat fissure diamond burs to remove amalgam and composite, but not when removing tooth structure. When amalgam and composite were removed without water coolant, the tungsten carbide burs resulted in lower IPT changes than when flat fissure diamond burs were used in the same way.

Investigation of laser wavelength effect on the ablation of enamel and dentin using femtosecond laser pulses

We investigated the effect of femtosecond (fs) laser ablation of enamel and dentin for different pulse wavelengths: infrared (1030 nm), green (515 nm), and ultra-violet (343 nm) and for different pulse separations to determine the optimal irradiation conditions for the precise removal of dental hard tissues with the absence of structural and compositional damage. The ablation rates and efficiencies were established for all three laser wavelengths for both enamel and dentin at room temperature without using any irrigation or cooling system, and the surfaces were assessed with optical and scanning electron microscopy, optical profilometry, and Raman spectroscopy. We demonstrated that 515 nm fs irradiation provides the highest rate and efficiency for ablation, followed by infrared. Finally, we explored the temperature variations inside the dental pulp during the laser procedures for all three wavelengths and showed that the maximum increase at the optimum conditions for both infrared and green irradiations was 5.5 °C, within the acceptable limit of temperature increase during conventional dental treatments. Ultra-violet irradiation significantly increased the internal temperature of the teeth, well above the acceptable limit, and caused severe damage to tooth structures. Thus, ultra-violet is not a compatible laser wavelength for femtosecond teeth ablation.

Heat generated during dental treatments affecting intrapulpal temperature: a review

INTRODUCTION

Heat is generated and transferred to the dentine-pulp complex during various dental procedures, such as from friction during cavity preparations, exothermic reactions during the polymerisation of restorative materials and when polishing restorations. For in vitro studies, detrimental effects are possible when intra-pulpal temperature increases by more than 5.5°C (that is, the intra-pulpal temperature exceeds 42.4°C). This excessive heat transfer results in inflammation and necrosis of the pulp. Despite numerous studies stating the importance of heat transfer and control during dental procedures, there are limited studies that have quantified the significance. Past studies incorporated an experimental setup where a thermocouple is placed inside the pulp of an extracted human tooth and connected to an electronic digital thermometer.

METHODS

This review identified the opportunity for future research and develop both the understanding of various influencing factors on heat generation and the different sensor systems to measure the intrapulpal temperature.

CONCLUSION

Various steps of dental restorative procedures have the potential to generate considerable amounts of heat which can permanently damage the pulp, leading to pulp necrosis, discoloration of the tooth and eventually tooth loss. Thus, measures should be undertaken to limit pulp irritation and injury during procedures. This review highlighted the gap for future research and a need for an experimental setup which can simulate pulp blood flow, temperature, intraoral temperature and intraoral humidity to accurately simulate the intraoral conditions and record temperature changes during various dental procedures.

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 (β = − 4.26, 95%CI − 5.33 and β = − 4.47, 95%CI − 5.60, respectively). With air-cooling, the temperature increase in teeth with RBC was lower compared to teeth without RBC (β = − 0.42, 95%CI -0.79; − 0.05). Higher teeth volume resulted in lower temperature increase with air-cooling than without air-cooling (β = − 0.04, 95%CI -0.07; − 0.01 and β = − 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.

In Vitro Infrared Thermographic Assessment of Temperature Change in the Pulp Chamber during Provisionalization: Effect of Remaining Dentin Thickness

Interim crowns and partial fixed dental prosthesis materials generate exothermic heat during polymerization. The amount of heat transmitted to the pulp chamber can be a function of several factors, including the thickness and quality of the remaining dentin after crown preparation. The aim of this in vitro study was to measure with infrared thermography the temperature changes on the adjacent surface of the chamber roof of premolar teeth extracted from young and old patients (having different thicknesses of remaining dentin after crown preparation) during fabrication of provisional resinous restorations. Twenty extracted human first and second maxillary premolar teeth (10 from young patients, with a relatively large pulp chamber, and 10 from older patients, with a relatively small pulp chamber) were used. The roots were sectioned to expose the inner side of the chamber roof, and the crowns were provisionalized after preparation for a metal-ceramic crown. Two provisional materials, Turbo Temp 2 and Luxatemp Fluorescence, were used. Temperature changes on the inner side of the chamber roof were measured at 2-second intervals using an infrared thermal imaging camera. After completion of the temperature recordings, the teeth were sectioned and the remaining dentin thickness was determined. The older group (mean thickness: 2.82 mm) and younger group (mean thickness: 1.9 mm) differed significantly in dentin thickness (P < 0.014). The mean greatest temperature increases recorded on the chamber roof of teeth with less remaining dentin were 4.07°C for Turbo Temp 2 and 3.94°C for Luxatemp Fluorescence, while increases in the premolars with greater dentin thickness were 1.69°C for Turbo Temp 2 and 1.64°C for Luxatemp Fluorescence. Significant interactions were found between tooth groups (P < 0.000001for Turbo Temp 2 and for Luxatemp Fluorescence). No significant differences were found between assessed materials regardless of the thickness of the remaining dentin (P > 0.38for the older group and P > 0.29 for the younger group). Dentin had a significant effect in limiting the temperature increase generated during polymerization of provisional materials, indicating good thermal insulating properties of this tissue. A remaining dentin thickness of 1.9 mm or more is sufficient to protect the pulp from any temperature increase during provisionalization using tested materials.

Demineralization Inhibition by High-Speed Scanning of 9.3 µm CO2 Single Laser Pulses Over Enamel

BACKGROUND AND OBJECTIVE

In vitro studies were conducted to evaluate the use of an automated system for high-speed scanning of single 9.3 µm CO₂ laser pulses in the inhibition of caries-like lesion formation in the enamel of extracted human molars. The effect of the laser in generating an acid-resistant layer and the effect of the layer on inhibiting surface mineral loss during pH cycling was explored.

STUDY DESIGN/MATERIALS AND METHODS

Laser irradiation was performed with fluences of 0.6, 0.8, and 1.0 J/cm² for single pulses of 1 mm diameter (1/e² ), with pulse durations of 17, 22, and 27 microseconds, respectively. The laser was scanned at a 750 Hz pulse repetition rate in an automated pattern covering an area of 7 mm² in 0.3 sec. Six treatment groups were investigated: three groups for each fluence for laser-only and three for laser irradiation with additional fluoride from a toothpaste slurry (sodium fluoride at 1100 ppm). Each group used non-irradiated areas, which included untreated controls for the laser-only groups and a fluoride-only treatment for the groups with additional fluoride. pH cycling was performed on both groups, followed by microhardness testing to determine the relative mineral loss (∆Z) from a caries-like formation and surface mineral loss (∆S).

RESULTS

Laser irradiation with the 9.3 µm CO₂ laser generated an acid-resistant layer of about 15 µm in depth. For the laser-irradiated samples with additional fluoride application, the relative mineral loss (∆Z) was 113 ± 63 vol%-µm, while for those with only fluoride application ∆Z was 572 ± 172 vol%-µm. At the highest fluence (1.0 J/cm² ) used, an 80.2% inhibition of caries-like lesion was measured by ∆Z. Using only laser irradiation at the highest fluence resulted in an inhibition of caries-like lesion of 79.5% for the irradiated samples (∆Z = 374 ± 149 vol%-µm) relative to the control (∆Z = 1826 ± 325 vol%-µm). Surface microhardness tests resulted in an inhibition of surface softening, as measured by the Knoop Hardness Value (KHN) (108 ± 33 KHN for laser irradiated with additional fluoride, for non-irradiated controls with fluoride only 52 ± 16 KHN). Inhibition of surface loss was observed for all laser fluences, but the maximum surface loss for the untreated control group was only 2.2 ± 0.49 µm.

CONCLUSIONS

The results demonstrate a significant benefit of the 9.3 µm CO₂ laser at fluences of 0.6, 0.8, and 1.0 J/cm² in caries-like lesion inhibition as measured by the relative mineral loss in depth and surface mineral loss, without significant damage to the enamel. Additionally, inhibition of surface softening and surface loss during pH cycling was observed. The surface loss was small compared with the overall lesion depth and thickness of the generated acid-resistant layer. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Evaluation of photopolymerization efficacy and temperature rise of a composite resin using a blue diode laser (445 nm)

The purpose of this study was to evaluate the photopolymerization efficacy of a diode laser (445 nm) for use with a composite containing camphorquinone and to estimate the safety of the method related to the temperature rise. Five cylindrical composite specimens were prepared for each thickness: 1, 2, and 3 mm. Three light-curing modes were investigated: a light emitting diode (LED) unit and a diode laser (445 nm) with output powers at 0.7 W or 3 W. Evaluation of the polymerization efficacy was based on Vickers hardness measurements, and the highest temperatures at the bottom of the specimens were recorded using a K-type thermocouple. The highest microhardness was observed after the diode laser curing operating at 3 W. A comparison of the microhardness of the 0.7 W laser cured specimens with the LED cured specimens showed a statistically significant difference in favor of the laser curing. Laser curing operating at 3 W resulted in extremely high temperatures. Laser curing at 0.7 W resulted in statistically significantly higher maximum temperatures than did LED curing for both 1 mm thick (52.9°C against 45.4°C) and 3 mm thick (43.6°C against 40.9°C) specimens. Diode laser (445 nm) may be an alternative for photopolymerization of composite materials and may result in a higher degree of conversion and depth of cure of composites than what has been seen with LED curing units when they emit at the same energy density.

Effect of different dry-polishing regimens on the intrapulpal temperature assessed with pulpal blood microcirculation model

OBJECTIVE

The aim of the study was to evaluate the effect of different dry-polishing regimens on the intrapulpal temperature assessed using a pulpal blood microcirculation model.

MATERIALS AND METHODS

Eighty extracted human mandibular premolar teeth were used. Standardized class V cavity preparations were performed and were then restored. Teeth were divided into four main groups (n = 20): Fine polishing disc (SSF; 3M Sof-Lex, 3M ESPE, Minnesota); Super-fine polishing disc (SSS; 3M Sof-Lex); Spiral finishing wheel (SSW; 3M Sof-Lex); Enhance PoGo-One step diamond micro-polisher cup (EPO; Dentsply Sirona, Inc, Delaware). The main groups were divided: the low-load pressure (0.4N) and the high-load pressure (0.8N). The average change in intrachamber temperatures (Δt), from initial to highest, were measured.

RESULTS

The highest temperature increase was recorded in SSF08 (9.55°C). The lowest value was recorded in EPO04 (1.9°C). SSS08, SSW08, and EPO08 demonstrated significantly higher Δt values than the low-load mode in SSS04, SSW04, and EPO04, respectively (P < .0001).

CONCLUSIONS

Temperature was the least affected by the diamond cup in both pressure modes, and it was also less affected by the spiral finishing wheel in the low-load mode than in the high-load mode. Fine and super-fine discs had the greatest effect on intrachamber temperatures.

CLINICAL SIGNIFICANCE

The present study suggests intrachamber temperature can rise among different dry-polishing regimes. Dental practitioners should pay attention to dry-polishing regimens and pressures for reducing heat-related dental problems.

Comparative clinical and psychosocial benefits of tooth bleaching: different light activation of a 38% peroxide gel in a preliminary case-control study

Tooth bleaching is a widespread dental treatment with important psychosocial antecedents and outcomes involved. In the activation of in-office bleaching agents, a selective light radiation, that is, a diode laser seems to be a positive choice to decrease the time of bleaching without surface modification and with no residual tooth sensitivity for maximum effect and minimal clinical and psychological side effects.

Postcementation hypersensitivity: scientific data versus dentists' perceptions

PURPOSE

The purpose of this article was to obtain dentists' opinions via an Internet survey as to the prevalence, causes, and prevention of postcementation sensitivity and compare their responses with published data on the problem.

MATERIALS AND METHODS

Information as to respondents opinions of postcementation sensitivity was obtained from an Internet survey asking about their experience and for a ranking of the importance of each of 15 factors.

RESULTS

A total of 466 valid responses were received. The incidence of postcementation sensitivity was estimated to be less than 2% by more than 2/3 of the dentists. The factors considered "very important" in reducing sensitivity by more than 50% of the respondents were desiccation, luting agent, occlusion, provisional, and water spray.

CONCLUSIONS

Comparing respondents' opinions with published clinical studies, the incidence of postcementation sensitivity appears to be underestimated. There is little published evidence to support the importance of antimicrobials, desensitizing, or bonding agents, although these are considered effective by some dentists. Many respondents consider luting agent to be an important variable.