Pulpal temperature increase with high-speed handpiece, Er:YAG laser and ultrasound tips

Three-axis load analysis of high-speed handpiece on dental training teeth and computer-aided design/computer-aided manufacturing blocks

This study aimed to evaluate and compare the mechanical properties of dental training teeth with subtractive and additive computer-aided design/computer-aided manufacturing (CAD/CAM) materials used to fabricate dental simulation models. Therefore, the three-axis load generated during cutting movements, including drilling and milling performed using a dental handpiece, was measured and compared. The samples were cut vertically downward by 1.5 mm, horizontally by 6 mm, and vertically upward at a constant speed (1 mm/s), while the rotational speed of the bur was maintained at 200,000 rotations per minute. A three-axis load cell was used to measure the X-, Y-, and Z-axis loads on the specimen. The median value of the X-, Y-, and Z-axis measurements and the resultant load during the vertical-downward, horizontal, and vertical-upward movements were compared using a one-way analysis of variance and Tukey's post hoc test. For vertical downward movement, the drilling force of the dental training teeth was lower than that of Vita Enamic® and similar to that of Lava™ Ultimate. In contrast to subtractive CAD/CAM blocks, the drilling force of the dental training teeth was higher than that of 3D-printed resin blocks. Regarding horizontal movement, the milling force of dental training teeth was lower than that of Vita Enamic®. In contrast, the milling force of Nissin was similar to that of Lava™ Ultimate, while that of Frasaco was lower. Furthermore, compared to additive CAD/CAM blocks, the milling force of the dental training teeth was higher than that of 3D-printed resin blocks. Regarding vertical upward movement, the resultant loads of dental training teeth was lower than that of Vita Enamic®. Similarly, the resultant load of Nissin was similar to that of Lava™ Ultimate, while that of Frasaco was lower. Additionally, compared to additive CAD/CAM blocks, the resultant loads of the dental training teeth were similar to those of the 3D-printed resin blocks.

Pulp chamber temperature changes and enamel surface analysis during orthodontic composite removal using 3 different burs in a repeatable approach: an experimental study

BACKGROUND

During the debonding phase every clinician has to take care of preserving the enamel structure and tooth temperature. The objective of this study was to analyze in vitro the increase of the pulp chamber temperature and the wearing of enamel surface, during adhesive removal after debonding.

METHODS

Sixty extracted human teeth were selected. An orthodontic bracket was bonded on each tooth and after bracket removal, intraoral scanner pictures were used to evaluate ARI for each tooth. Three different burs were tested: tungsten-carbide multiple blades, arkansas stone and ceramic bur. A mechanical arm controlled by a dedicated software was used to reproduce a repeatable act of composite removal. To analyze in vitro the pulp chamber temperature during the composite removal procedure, teeth were treated endodontically placing a thermocouple through the root canal from the apex. A software registered temperature changes in a continuous manner. The enamel surface of every tooth was tested after the removal of composite with an optical stereoscopic microscope.

RESULTS

An association existed between maximum internal pulp chamber temperature variation and irrigation (P<0.0001) and between maximum internal pulp chamber temperature variation and bur type (P=0.0133), with a significantly lower temperature increase produced by the arkansas bur. A significant difference among groups was detected for ESI and EDI assessment (P=0.002, P=0.010).

CONCLUSIONS

Considering the initial setup, temperature variation analysis showed more conservative results using the arkansas burs with irrigation. ESI and EDI indexes showed significant enamel surface damage using tungsten-carbide burs.

Material removal and surface damage in high-speed grinding of enamel

Although high-speed grinding of the enamel surface is often required in restorative dentistry, the knowledge of grinding mechanics, material removal, and fracture damage mechanism related to this process is still relatively limited; therefore, it is important to perform relevant scientific and theoretical research. As per the occlusal surface and the buccal/lingual surface of the teeth, the experimental scheme of high-speed grinding of the enamel surface using a diamond grinding bur was designed, and the grinding force, force ratio, grinding temperature, chips, surface morphology, surface damage, and other important characteristics were tested and analyzed. Furthermore, the grinding geometry model, grinding mechanics, material fracture, and removal mechanism associated with the high-speed grinding of an enamel surface were considered. The results show that the grinding force, friction coefficient, grinding temperature, and surface damage achieved through buccal/lingual surface grinding are considerably greater, and the grinding quality is worse than that obtained via occlusal surface grinding under the same grinding conditions. With the increase in the feed rate, grinding force, friction coefficient, grinding temperature, and surface damage obviously increase, and the surface quality decreases. The embrittlement effect and the ironing mechanism are present during the process of high-speed grinding of enamel. Regardless of the feed rate, the three types of material fracture modes of the buccal/lingual surface are more serious than those of the occlusal surface (making it more likely to produce unstable large chips or tearing chips); moreover, the brittle fracture and damage of the final machined surface are more obvious. The cutting mechanics and cutting mechanism identified in this study will provide scientific guidance for dental grinding operations.

Machinability of high-speed enamel cutting with carbide bur

The cutting of tooth enamel using a high-speed air-turbine handpiece and carbide bur is a key procedure in oral surgeries, such as the minimally invasive extraction. However, presently little is known about the cutting mechanics and material removal mechanism related to tooth enamel machinability. In this study, the machinability of high-speed enamel cutting with carbide bur is studied by a computer-aided numerical control system. The dynamic cutting forces of enamel of the occlusal, buccal/lingual, and proximal surfaces were measured by the force measuring system. The force ratio, cutting torque, rotating speed, specific cutting energy, and bur wear were analyzed. The microstructure of enamel and carbide burs was observed by the scanning electron microscope, and the relationship between enamel microstructures and machinability was further analyzed. The results show that during the high-speed enamel cutting with carbide bur, the chip thickness is on the nano-scale, and the plastic deformation of the machined surface is obvious. With increased material removal rate, the cutting force, torque, specific cutting energy, and bur wear increases accordingly, whereas the rotating speed decelerates (p < 0.05). The different angles between the cutting direction and the axial direction of the enamel rods give rise to the large differences in the cutting mechanics and mechanism of the proximal, buccal/lingual, and occlusal surfaces of the teeth. When the cutting direction is parallel, vertical, and oblique 45° to the axial direction of the enamel rods, the force required for material fracture and crack propagation increases, and the cutting force increases as a consequence. Parallel and oblique 45° cutting are the main modes of tooth segmentation in the minimally invasive extraction. In comparison with the parallel cutting mode, the cutting force, torque, and cutting ratio of the oblique 45° cutting mode can be significantly increased, and the tool wear is obviously accelerated. This is the lowest priority in segmentation surgery, hence the problems of overload and temperature rise need to be considered. The cutting mechanics and cutting mechanism obtained in this study will provide scientific process guidance for dental cutting operations with the air-turbine handpiece driving bur.

Machinability of enamel under grinding process using diamond dental burrs

Enamel grinding is a critical dental surgery process. However, tooth damage during the process remains a significant problem. Grinding forces, burr wear, and surface quality were characterised in relation to grinding speed, enamel orientation, grinding depth, and burr grit grain size. Results indicated that enamel rod orientation, grinding depth, and grinding speed critically affected enamel grinding. Occlusal surface grinding resulted in significantly higher normal forces, surface roughness, and marginally greater tangential forces than axial surface grinding. Damage to enamel machined surfaces indicated the significant impact of diamond grit size and rod orientation. Burr wear was primarily diamond grit peeling off and breakage. Surface roughness of axial and occlusal sections was largely influenced by grinding speed and diamond grit size. Improving the surface quality of machined enamel surfaces could be realised using fine burrs, reducing the grinding speed and grinding depth, and adjusting the feed direction vertical to the rod orientation. Enamel surface quality and roughness could be improved by reducing brittle failure and circular runout during the grinding process, respectively.

Controlling In Vivo, Human Pulp Temperature Rise Caused by LED Curing Light Exposure

Objective:

The objective of this study was to evaluate the in vivo effectiveness of air spray to reduce pulp temperature rise during exposure of intact premolars to light emitted by a high-power LED light-curing unit (LCU).

Methods and Materials:

After local Ethics Committee approval (#255945), intact, upper first premolars requiring extraction for orthodontic reasons from five volunteers received infiltrative and intraligamental anesthesia. The teeth (n=9) were isolated using rubber dam, and a minute pulp exposure was attained. The sterile probe from a wireless, NIST-traceable, temperature acquisition system was inserted directly into the coronal pulp chamber. Real-time pulp temperature (PT) (°C) was continuously monitored, while the buccal surface was exposed to a polywave LED LCU (Bluephase 20i, Ivoclar Vivadent) for 30 seconds with simultaneous application of a lingually directed air spray (30s-H/AIR) or without (30s-H), with a seven-minute span between each exposure. Peak PT values were subjected to one-way, repeated-measures analysis of variance, and PT change from baseline (ΔT) during exposure was subjected to paired Student's t-test (α=0.05).

Results:

Peak PT values of the 30s-H group were significantly higher than those of 30s-H/AIR group and those from baseline temperature (p&lt;0.001), whereas peak PT values in the 30s-H/AIR group were significantly lower than the baseline temperature (p=0.003). The 30s-H/AIR group showed significantly lower ΔT values than did the 30s-H group (p&lt;0.001).

Conclusion:

Applying air flow simultaneously with LED exposure prevents in vivo pulp temperature rise.

Evidence provided for the use of oscillating instruments in restorative dentistry: A systematic review

Oscillating diamond instruments are considered gentle sources for the removal of demineralized tooth hard tissues and the preparation of cavity angles and margins needed in minimally invasive dentistry. However, there is a question if literature provides enough evidence for their efficacy in restorative dentistry procedures. A literature search until May 2016 was conducted, using PubMed, Scopus, and The Cochrane Central Register of Controlled Trials databases. The quality of the studies was assessed using the recommendation of the Oxford Centre for Evidence-based Medicine. Fifty-five studies were finally included in the study. Of which, 78.2% of them were laboratory studies and only 21.8% were clinical studies. The strength of recommendation was 5 for most of them and D their grade of evidence. Bond strength of adhesives on surfaces prepared with these instruments, effective caries removal and cutting characteristics of the oscillating instruments were the main targets of the studies. Conventional diamond, steel, and chemical vapor deposition diamond tips and systems based on abrasive slurry were the oscillating tips, used in different studies. The strength of recommendation and grade of evidence of the studies were low. Although these devices seem to be useful for many clinical situations, there is a need for more well-structured evidence-based studies with more widely accepted procedures and common devices, to have more meaningful results and conclusions of higher strength.

Temperature rises during application of Er:YAG laser under different primary dentin thicknesses

OBJECTIVE

The present study investigated the effects of the Er:YAG laser's different pulse repetition rates on temperature rise under various primary dentin thicknesses.

BACKGROUND DATA

The Er:YAG laser can be used for restorative approaches in clinics and is used to treat dental caries. There are some reports that explain the temperature rise effect of the Er:YAG laser. Recently, the Er:YAG laser has been found to play an important role in temperature rises during the application on dentin.

METHODS

Caries-free primary mandibular molars were prepared to obtain dentin discs with 0.5, 1, 1.5, and 2 mm thicknesses (n=10). These discs were placed between the Teflon mold cylinders of a temperature test apparatus. We preferred three pulse repetition rates of 10, 15, and 20 Hz with an energy density of 12.7 J/cm2 and a 230 μs pulse duration. All dentin discs were irradiated for 30 sec by the Er:YAG laser. Temperature rises were recorded using an L-type thermocouple and universal data loggers/scanners (E-680, Elimko Co., Turkey). Data were analyzed by two-way ANOVA and Tukey tests.

RESULTS

Whereas the lowest temperature rise (0.44±0.09 °C) was measured from a 10 Hz pulse repetition rate at a dentin thickness of 2 mm, the highest temperature rise (3.86±0.43 °C) was measured from a 20 Hz pulse repetition rate at a 0.5 mm dentin thickness.

CONCLUSIONS

Temperature rise did not reach critical value for pulpal injury in any primary dentin thicknesses irradiated by a high repetition rate of the Er:YAG laser.

Ultrasonic cavity preparation using CVD coated diamond bur: A case report

Before any restorative procedure can be undertaken a proper cavity preparation is required. This clinical step is the mechanical alteration of the tooth to receive a restorative material with which a satisfactory form, function and the esthetics of the tooth will be established. In recent years improvements in materials and techniques have been devised and new technologies are now available for this purpose. The aim of the present study is to report two clinical cases in which a CVD coated diamond bur coupled to an ultrasonic handpiece is used in dental preparation. This technique provides an accurate and conservative tooth preparation with ideal access and visibility and because of enhanced efficiency can also play a role in eliminating some of the patient discomfort of the dental treatment.

Thermal irritation of teeth during dental treatment procedures

While it is reasonably well known that certain dental procedures increase the temperature of the tooth's surface, of greater interest is their potential damaging effect on the pulp and tooth-supporting tissues. Previous studies have investigated the responses of the pulp, periodontal ligament, and alveolar bone to thermal irritation and the temperature at which thermal damage is initiated. There are also many in vitro studies that have measured the temperature increase of the pulp and tooth-supporting tissues during restorative and endodontic procedures. This review article provides an overview of studies measuring temperature increases in tooth structures during several restorative and endodontic procedures, and proposes clinical guidelines for reducing potential thermal hazards to the pulp and supporting tissues.

Influence of various polishing methods on pulp temperature : an in vitro study

OBJECTIVE

After orthodontic debonding, adhesive removal can lead to rises in pulp temperature, causing histological changes or pulp necrosis. The objective of this study was to measure increases in pulp temperature during adhesive removal using different instruments and various cooling procedures.

MATERIALS AND METHODS

A thermoelement was introduced into the pulp chamber of 10 human incisors. The teeth were immersed in a 36°C water bath up to the cementoenamel junction. Two carbide burs, one polishing disk and two rubber points were used for polishing. All measurements were taken over a 10 s period by a single investigator, under slight pressure and with constant motion. Three cooling procedures were examined: no cooling, air cooling and water cooling. Pulp temperatures were measured before polishing and after 10 s of polishing.

RESULTS

Without cooling, the two rubber points revealed clinically relevant temperature increases of 6.1°C and 12.4°C. Cooling with air and with water reduced pulp temperature in conjunction with all polishing methods. Air cooling was most efficient, except in combination with the polishing disk.

CONCLUSION

Under these study conditions, carbide burs and polishing disks can be used safely and without risk to the pulp, even without cooling. On the other hand, rubber points cause a marked increase in pulp temperature when used without cooling.