Removal Of Dental Hard Tissue Research Articles

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.

Sliding friction and wear of human teeth against biocompatible polyether ether ketone (PEEK) under various wear conditions

For the application in dentistry, the friction and wear behaviour of the thermoplastic polymer polyether ether ketone (PEEK) was analysed. Therefore, the friction coefficient and specific wear rate of PEEK against human enamel/dentine was investigated under various wet conditions. The tooth specimens consisting of enamel and dentine were prepared from nine mandibular molars. The sliding friction as well as the material loss of the counterparts was determined by using a block-on-ring rotational test configuration with a boundary film lubrication (deionised water). The material loss was measured by profilometry. The results were statistically analysed by one-way analysis of variance (ANOVA). As a result, the counter surfaces of the tooth samples showed a higher hardness and were stiffer than the polymeric specimens made of PEEK. The initial sliding friction coefficient varied in the range of μ = 0.23-0.44 for the three investigated rotational velocities from 1 m/s to 0.1 m/s and the stationary values were measured in the range of μ = 0.54-0.58 for the total sliding path of 1500 m. The resulting specific wear rate of PEEK was significantly higher ws = 80 ± 65.5 10-6 mm³/Nm than the coefficient of enamel/dentine ws = 0.9 ± 0.7 10-6 mm³/Nm (p < 0.01). In most cases, a significant increase of averaged surface roughness of the tooth samples was determined after tribological tests. In general, the investigations obtained a low removal of dental hard tissue (enamel, dentine) compared to the material loss of PEEK.

&lt;p&gt;Conservative Composite Resin Restoration for Proximal Caries – Two Case Reports&lt;/p&gt;

The paradigms of contemporary caries management have shifted to minimal intervention dentistry. Conservative restorative procedures are recommended to replace the complete removal of all carious tissues in the management of dental caries. This article reports two clinical cases of conservative restorations of proximal caries. Different conservative cavity designs and restorative techniques were performed in the two cases. Proximal caries in posterior teeth were prepared using the box-only preparation technique or the proximal tunnel preparation technique. The cavities were restored directly with resin composites. The advantages of using the box-only preparation with fissure sealant included the maximum conservation of tooth hard tissues and the prevention of unnecessary tissue removal in the occlusal surface. The tunnel preparation preserved the marginal ridge and protected the restored tooth from fracture. The filling of composites into the tunnel demonstrated a better marginal adaptation than other restorative materials. These two techniques allowed for the preservation of more healthy dental hard tissue compared with traditional techniques. Potential problems in the restoration included the high incidence of the inappropriate removal of dental hard tissue, damage of the vital pulp and the microleakage due to the polymerization shrinkage. The solutions to minimize the risk of these problems in the operative procedures were discussed.

Evaluating and comparing the morphological and histopathological changes induced by erbium:yttrium-aluminum-garnet laser and diamond bur on enamel, dentin and pulp tissue.

Lasers are used for different types of dental treatments. Using the erbium:yttrium-aluminum-garnet (Er:YAG) laser to remove dental hard tissue is simple, advantageous and influences the type of cavity preparation, whether conventional or conservative in nature. The aim of the present study was to evaluate and compare the morphological and histopathological changes in the enamel, dentin and pulp tissue of the teeth treated by Er:YAG laser and conventional burs. A conventional class I cavity was prepared in orthodontic patients by laser and bur. The teeth were extracted and analyzed for morphological changes using a scanning electron microscope, ground sections and histopathological changes under a light microscope. The time with laser was longer than the conventional methods. The lased cavity showed irregular appearance with absence of smear layer which is suitable for the resin restoration. The ground section and the histopathological study showed no differences between the groups. The Er:YAG laser is effective in the removal of dental hard tissue without damaging the pulp when coupled with ideal energy output. It is widely used in different dental fields. It needs time to be accepted by dentist and patients and further studies are required to explore its advantages.

Use of carbon dioxide lasers in dentistry

This paper aims to perform a descriptive analysis by reviewing publications concerned with the production of carbon dioxide (CO2) lasers and their technological advancement, optical properties, and parameters in relation to clinical applications in dentistry. This review was based on the literature search in Scopus, Google Scholar, and PubMed in English. The last search was made in December 2017 and there was no publication-year limit. : The 10,600-nm CO2 laser is a readily available dental laser on the market. It enables performance of a bloodless surgical procedure and reduces post-operative discomfort in soft tissue dental surgery. Due to the advancement of technology, CO2 lasers with short pulse duration and high peak power are available. This new-parameter CO2 laser causes less collateral thermal damage to soft tissue than conventional lasers with continuous wave mode. Recently, a 9,300-nm wavelength CO2 laser has been introduced for clinical use in dental hard tissue removal. These developments make CO2 lasers fitting for dental hard tissue preparation. The 10,600-nm CO2 laser is widely accepted for soft tissue surgery applications. Although CO2 lasers have been studied extensively in caries prevention, they have not been applied in clinical practice. The optical properties of 9,300-nm and 9,600-nm CO2 wavelengths are suitable for dental hard tissue treatment. Technological advancements in software and laser parameters will aid in new clinical application and technique development. CO2 lasers as hard tissue lasers will become more popular and more widely accessible to researchers and clinicians.

Heat generation caused by ablation of dental hard tissues with an ultrashort pulse laser (USPL) system

Heat generation during the removal of dental hard tissues may lead to a temperature increase and cause painful sensations or damage dental tissues. The aim of this study was to assess heat generation in dental hard tissues following laser ablation using an ultrashort pulse laser (USPL) system. A total of 85 specimens of dental hard tissues were used, comprising 45 specimens of human dentine evaluating a thickness of 1, 2, and 3mm (15 samples each) and 40 specimens of human enamel with a thickness of 1 and 2mm (20 samples each). Ablation was performed with an Nd:YVO4 laser at 1,064nm, a pulse duration of 9ps, and a repetition rate of 500kHz with an average output power of 6W. Specimens were irradiated for 0.8s. Employing a scanner system, rectangular cavities of 1-mm edge length were generated. A temperature sensor was placed at the back of the specimens, recording the temperature during the ablation process. All measurements were made employing a heat-conductive paste without any additional cooling or spray. Heat generation during laser ablation depended on the dental hard tissue (enamel or dentine) and the thickness of the respective tissue (p < 0.05). Highest temperature increase could be observed in the 1-mm thickness group for enamel. Evaluating the 1-mm group for dentine, a significantly lower temperature increase could be measured (p < 0.05) with lowest values in the 3-mm group (p < 0.05). A time delay for temperature increase during the ablation process depending on the material thickness was observed for both hard tissues (p < 0.05). Employing the USPL system to remove dental hard tissues, heat generation has to be considered. Especially during laser ablation next to pulpal tissues, painful sensations and potential thermal injury of pulp tissue might occur.

Selective Removal of Natural Occlusal Caries by Coupling Near-infrared Imaging with a CO(2) Laser.

Laser removal of dental hard tissue can be combined with optical, spectral or acoustic feedback systems to selectively ablate dental caries and restorative materials. Near-infrared (NIR) imaging has considerable potential for the optical discrimination of sound and demineralized tissue. Last year we successfully demonstrated that near-IR images can be used to guide a CO(2) laser ablation system for the selective removal of artificial caries lesions on smooth surfaces. The objective of this study was to test the hypothesis that two-dimensional near-infrared images of natural occlusal caries can be used to guide a CO(2) laser for selective removal. Two-dimensional NIR images were acquired at 1310-nm of extracted human molar teeth with occlusal caries. Polarization sensitive optical coherence tomography (PS-OCT) was also used to acquire depth-resolved images of the lesion areas. An imaging processing module was developed to analyze the NIR imaging output and generate optical maps that were used to guide a CO(2) laser to selectively remove the lesions at a uniform depth. Post-ablation NIR images were acquired to verify caries removal. Based on the analysis of the NIR images, caries lesions were selectively removed with a CO(2) laser while sound tissues were conserved. However, the removal rate varied markedly with the severity of decay and multiple passes were required for caries removal. These initial results are promising but indicate that the selective removal of natural caries is more challenging than the selective removal of artificial lesions due to varying tooth geometry, the highly variable organic/mineral ratio in natural lesions and more complicated lesion structure.

Near-infrared image-guided laser ablation of artificial caries lesions.

Laser removal of dental hard tissue can be combined with optical, spectral or acoustic feedback systems to selectively ablate dental caries and restorative materials. Near-infrared (NIR) imaging has considerable potential for the optical discrimination of sound and demineralized tissue. The objective of this study was to test the hypothesis that two-dimensional NIR images of demineralized tooth surfaces can be used to guide CO(2) laser ablation for the selective removal of artificial caries lesions. Highly patterned artificial lesions were produced by submerging 5 × 5 mm(2) bovine enamel samples in demineralized solution for a 9-day period while sound areas were protected with acid resistant varnish. NIR imaging and polarization sensitive optical coherence tomography (PS-OCT) were used to acquire depth-resolved images at a wavelength of 1310-nm. An imaging processing module was developed to analyze the NIR images and to generate optical maps. The optical maps were used to control a CO(2) laser for the selective removal of the lesions at a uniform depth. This experiment showed that the patterned artificial lesions were removed selectively using the optical maps with minimal damage to sound enamel areas. Post-ablation NIR and PS-OCT imaging confirmed that demineralized areas were removed while sound enamel was conserved. This study successfully demonstrated that near-IR imaging can be integrated with a CO(2) laser ablation system for the selective removal of dental caries.

Rapid and conservative ablation and modification of enamel, dentin, and alveolar bone using a high repetition rate transverse excited atmospheric pressure CO[sub 2] laser operating at λ=9.3 μm

Transverse excited atmospheric pressure (TEA) CO(2) lasers tuned to the strong mineral absorption of hydroxyapatite near lambda=9 microm are well suited for the efficient ablation of dental hard tissues if the laser pulse is stretched to greater than 5 to 10 micros to avoid plasma shielding phenomena. Such CO(2) lasers are capable of operating at high repetition rates for the rapid removal of dental hard tissues. The purpose of this study was to test the hypothesis that stretched lambda=9.3-microA CO(2) laser pulses can produce lateral incisions in enamel, dentin, and alveolar bone for dental restorations and implants at repetition rates as high as 400 Hz without peripheral thermal damage. The single pulse ablation rates through enamel, dentin, and bone were determined for incident fluence ranging from (1 to 160 J/m(2)) for laser pulses from 5 to 18 mus in duration. Lateral incisions were produced in hard tissue samples using a computer-controlled scanning stage and water spray, and the crater morphology and chemical composition were measured using optical microscopy and high-resolution synchrotron radiation infrared spectromicroscopy. The residual energy remaining in tooth samples was measured to be 30 to 40% for enamel and 20 to 30% for dentin without water cooling, under optimum irradiation intensities, significantly lower than for longer CO(2) laser pulses. The transmission through 2-m length 300-, 500-, 750-, and 1000-microm silica hollow waveguides was measured and 80% transmission was achieved with 40 mJ per pulse. These results suggest that high repetition rate TEA CO(2) laser systems operating at lambda=9.3 microm with pulse durations of 10 to 20 micros are well suited for dental applications.

Removal of root substance with the Vector™‐system compared with conventional debridement in vitro

The aim of the present study was to assess the removal of root substance with the Vector-system depending on different irrigation fluids and to compare the results with conventional methods for root debridement. Forty extracted human teeth were treated using four different methods: Vector-system with polishing fluid and metal curette (VP), Vector-system with abrasive fluid and metal curette (VA), conventional ultrasonic system (U) with insert tip "P" and hand instrument. Treatment of the calculus-free root surfaces was carried out for a total of 12 min. using an artificial periodontal pocket. At intervals of 120 s, the removal of dental hard tissues was assessed using a three-dimensional (3D) laser scanning device and the Match 3D software with an accuracy of 0.00001 mm(3). No difference in the removal of root substance with the hand instrument (0.0055 mm(3)/s) and the Vector-system using the abrasive fluid (0.0044 mm(3)/s) could be observed (p=0.51). Using these two systems, a larger amount of root substance (p<0.05) was removed compared with the other methods (U: 0.0023 mm(3)/s, VP: 0.0022 mm(3)/s), which did not differ from each other (p=0.76). The present study indicates that the Vector-system in combination with polishing fluid or conventional ultrasonics might be used for root debridement without extensive root substance removal.

Use of infra-red and ultra-violet lasers in the removal of dental hard tissue

Lasers have been evaluated as a means of removing dental hard tissue. There are distinctly different effects which are attributable to the laser wavelength used and the substrate which is being irradiated. This leads to a number of different modes of tissue removal including photothermal and photoablative changes. The different changes are described and the significance of these in terms of tissue damage are discussed.

Dye-enhanced Ablation of Enamel by Pulsed Lasers

Laser removal of dental hard tissue has been proposed as a replacement for or augmented approach to the dental handpiece. The main limitation for widespread usage of lasers in dentistry has been inefficient ablation of dental hard tissue, accompanied by potential laser-induced damage to the surrounding tissue. The research focuses on a novel approach for enhancement of tissue ablation and confinement of laser interaction to a small tissue volume by controlled placement of an exogenous dye on the enamel surface. Studies were done with both pulsed alexandrite and pulsed Nd:YAG lasers, with indocyanine green and India ink, respectively, used as photo-absorbers. These dye-enhanced laser processes demonstrated the feasibility of this technique for cavity preparation. While control studies produced little or no appreciable crater, average preparation depth for the dye-enhanced ablation was from 1 to 1.5 mm, with a diameter of approximately 0.6 mm. Knoop hardness measurements show that, surrounding the crater, there is small annular region slightly softened by the laser action. SEM studies of the interior structure of the tooth did not show significant damage to the surrounding tissue. Temperature measurement studies indicated that the pulsed nature of the laser, combined with the photo-absorbing dye, effectively prevented significant temperature rise at the pulp. The remarkable effectiveness of this technique in creating cavity preparations and the absence of any notable collateral damage to the surrounding tissue suggest that dye-enhanced pulsed-laser ablation could be used as an alternative to the dental handpiece in selected procedures.