The Tunnel Wall Approach and Enamel Matrix Derivative to Cover Exposed Roots and Improve Clinical Attachment Levels in Cairo Class III Defects Associated with an Intrabony Lesion in the Anterior Area: Three Cases.

These case reports present a surgical technique to improve the clinical attachment level and cover the exposed root surface in Cairo Class III situations associated with a one- to two-wall combined intrabony defect in the anterior area. The tunnel wall approach combined previously described concepts and placed a CTG into a modified tunnel-type flap through a vertical releasing incision. The CTG acted both as a buccal soft tissue wall to stabilize the blood clot and as a space maintainer to coronally move the tissue. The decontaminated root surfaces were treated with enamel matrix derivative, and a bone filler material was placed from the bottom of the intrabony defect up to the cementoenamel junction to support the proximal soft tissue architecture. Healing of the four presented sites was uneventful. Clinical measurements up to 12 months showed significant probing depth reduction, clinical attachment gain, and coverage of the buccal recession in each case. Papilla improvement was reported in three cases. Radiographic examinations confirmed intrabony defect healing and the presence of embedded bone filler material in the soft tissue above the bone crest. The tunnel wall approach seems to be a valuable option to safely enhance the clinical attachment level and cover the exposed root in Cairo Class III situations associated with a one- to two-wall combined intrabony defect in the anterior area.

Caracterización morfológica de caninos en premolares, un caso de anodoncia parcial de caninos maxilares / Morphological characterization of canine teeth done in first bicuspid, a maxillary canine partial anodontia case report

En este informe de caso clínico se muestra el tratamiento exitoso de un paciente con anodoncia parcial de órganos dentales 13 y 23 debido a que fueron extraídos por presentar impactación y mal pronóstico de tracción. En este artículo se presenta un paciente masculino de 29 años clase I esquelética con un perfil convexo, maloclusión de clase III, overjet disminuido, ausencia de guías funcionales, discrepancia oseodentaria positiva en arcada superior y negativa en arcada inferior. El tratamiento se realizó con extracciones de los órganos dentales 34 y 44 para nivelar las discrepancias óseo dentarias interarcadas, se llevó a cabo mediante un cierre de espacios recíproco por medio de cadenas elásticas para ambas arcadas, con lo que se logró crear un overjet y overbite adecuados. La creación de las guías caninas funcionales se consiguió mediante el cambio de morfología de los órganos dentales 14 y 24, los cuales fueron llevados a la posición de los caninos ausentes. El tiempo total de tratamiento para este paciente fue de 24 meses. Se realizaron ameloplastias positivas, la aplicación de agregados de resina para mejorar la funcionalidad y proveer salud articular. Se sugiere que ante casos de anodoncia de caninos en la arcada superior, un tratamiento favorable se puede llevar a cabo mediante el cierre de espacios, la caracterización morfológica de los caninos ausentes mediante ameloplastias positivas en premolares (AU)

This case report shows the successful treatment of a patient with partial anodontia of dental organs 13 and 23 because they have been extracted due to present impactation and poor traction prognosis. This article presents a 29-year-old male class I skeletal patient with convex profile, class III malocclusion, overjet reduction, absence of functional guidance, positive bone-teeth discrepancy in the upper arch and negative in the lower arch. The treatment was carried out with the extractions of the dental organs 34 and 44 for correcting oral dental discrepancies between upper and lower arches; it was done using reciprocal closing of spaces by using elastic chains for both arches in order to achieve a suitable overjet and overbite. The creation of the canine guides was achieved by changing the morphology of the dental organs 14 and 24, which were taken to the position of the absent canines. The total treatment timing for this patient was 24 months. Positive ameloplasties were performed by application of resin aggregates to improve functionality and provide joint health. A favorable treatment for these kinds of cases of canine anodontics in the upper arch is carried out by closing spaces and the morphological characterization of the absent canines by positive in-premolar ameloplasties (AU)

Ameloplastia positiva en relación céntrica como método auxiliar durante la finalización en el tratamiento de ortodoncia en un paciente bruxista / Positive ameloplasty in centric relationship as an auxiliary method during finalization in the orthodontic treatment in a bruxist patient

A continuación se presenta un caso de un paciente de 12 años de edad, con antecedente de bruxismo, con biotipo mesofacial, tercio inferior dolicofacial, hipertonicidad muscular en maseteros, cierre labial forzado con incompetencia labial de 4 milímetros con dolor en sinoviales anteriores inferiores. Los objetivos de tratamiento consistieron en lograr relajación muscular y promover un posicionamiento condilar ortopédicamente funcional y estable, realizar control vertical para disminuir gap interlabial, alinear líneas medias, mantener clase I molar bilateral, clase I canina bilateral y clase I incisiva, crear overjet y overbite adecuados, con recuperación estética y función del segmento anterior. Debido a eventos adversos durante la etapa de cierre de espacios, la clase molar y canina I no se logró, pero se aseguró mediante ameloplastias positivas la función y estética adecuadas para tener un tratamiento de ortodoncia estable a largo plazo (AU)

The following is a case of a 12-year-old patient, with a history of bruxism, with a mesofacial biotype, lower third of the facial area, muscular hypertonicity in the masseters, a forced labial closure with a 4-millimeter labial incompetence with pain in inferior anterior synoviums. Treatment objectives consisted of achieving muscle relaxation and promoting orthopedically functional and stable condylar positioning, perform vertical control to decrease interlabial gap, align midlines, maintain bilateral molar class I, bilateral canine class I and incisive class I, create adequate overjet and overbite, with aesthetic recovery and function of the anterior segment. Due to adverse events during the closing phase of spaces, the molar and canine I class was not achieved, but positive function and aesthetics were ensured by positive ameloplasties in order to have a long-term stable orthodontic treatment (AU)

Silicon-hydroxyapatite‒glycerohydrogel as a promising biomaterial for dental applications.

Nanocomposite silicon-hydroxyapatite‒glycerohydrogel (Si-HA‒glycerohydrogel) with different hydroxyapatite (HA) contents of 0.75 and 1.75 wt.% and the same Si content (2.04 wt.%) was obtained by the sol‒gel method. Silicon tetraglycerolate in the form of glycerol solution was used as a biocompatible precursor and HА in the form of aqueous colloidal suspension - as a template and property modifier. Transmission electron microscopy was applied to demonstrate that there are nanoscale HA particles that are in the crystalline state. For the first time, using the atomic force microscopy method, the remineralizing properties of Si-HA‒glycerohydrogel were studied on human teeth extracted for orthodontic reasons. It was found that Si-HA‒glycerohydrogel containing 1.75 wt.% HA has a pronounced remineralizing effect. Immersion of tooth enamel samples in the gel for one month significantly reduces roughness and makes the enamel surface more uniform. Silicon contained in glycerolates in a biologically active and accessible form exerts an additional positive effect on the process of remineralization of tooth enamel. By the energy dispersive X-ray analysis, it was demonstrated that the tooth enamel had an increased silicon content; and the Vickers microhardness test showed greater microhardness values. The obtained data analysis allows the remineralizing Si-HA‒glycerohydrogel to be considered as a promising biomaterial for dental applications.

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.

Prediction of femtosecond laser ablation profile on human teeth.

To predict the laser ablation profile on dental hard tissue which will enable the user to optimize laser parameters so as to carry out the laser treatment with minimal tissue damage. The present study constructs a mathematical model to predict the ablation profile based on Gaussian beam distribution of laser intensity and correlates the model with experimentally obtained ablation parameters (effective Gaussian beam radius, ablation threshold fluence, and effective energy penetration depth). To obtain the ablation parameters, laser ablation experiments were carried out on dental hard tissues using Ti:Sapphire femtosecond laser (800 nm, 100 fs, 10 kHz). The method is further extended to predict the ablation rate and efficiency as well. The profile predicted from the mathematical model is compared with that of experimental results. It is found that the predicted ablation profile agrees well with the experimental profile for both enamel and dentin except a slight deviation at higher fluence for dentin. The calculated ablation rate is comparable to that of experimental results whereas for ablation efficiency appreciable deviation is observed in the case of dentin. The model succinctly predicts the ablation profile, ablation rate, and ablation efficiency which will enable to perform dental surgery at optimized laser processing conditions with high precision thus reducing the tissue damage appreciably. Once the details of lesion are known through proper diagnostic tools, the method enables the user to readily obtain optimum laser parameters. It can be used as a handy reference for dentists to perform damage-free surgery, ensuring quicker healing.

Veneer or Interproximal Enamel Reduction?

BACKGROUND: Clinicians often ask, "Veneer or no to veneer?" Clinicians usually think of porcelain veneers for cases in which patients are dissatisfied with their teeth shape. Interproximal reduction can change teeth's shape and appearance within the enamel to improve gingival contour, eliminate black gingival triangles, and correct the Curve of Spee. AIM: Our aim is to present to clinicians the option of reshaping and interproximal reduction (IPR) as a valid alternative to porcelain veneers. CASE REPORT: A male patient with round bulbous-shaped anterior maxillary teeth sought a better masculine smile. Interproximal reduction with thin bur size was performed to reshape the anterior teeth in order to achieve a proportional teeth width to height and give a more rectangular rather than square shape. Finally, the orthodontist closed the multiple diastemas using round wires in order to reduce anterior teeth proclination. The patient received bleaching treatment and minor composite fillings. CONCLUSION: Not every cosmetic case should be treated with veneers and crowns. Conservative minimal intervention, such as IPR was more than sufficient in treating such cases. It is the right of the patients to be informed and educated about all possible treatment options. CLINICAL SIGNIFICANCE: Minor reshaping and IPR preserving teeth structures can be helpful in achieving esthetic results and patients' confidence.

Antimicrobial Photodynamic Therapy as an Adjunct for Clinical Partial Removal of Deciduous Carious Tissue: A Minimally Invasive Approach.

This study aimed to evaluate the use of antimicrobial photodynamic therapy (aPDT) as an adjunct for minimally invasive treatment (partial removal of carious tissue-PRCT) of deciduous carious tissue evaluating its efficacy in reducing microorganisms. For that, a clinical study was design including children with deciduous molars with active deep caries lesions (DCL). PRCT was performed and remaining dentin was treated with 100 µg mL-1 methylene blue solution (5 min) and than irradiated with a low power laser emitting red light (InGaAIP-indium gallium aluminum phosphide; λ = 660 nm; 100 mW; 300 J cm-2 ; 90 s; 9 J). The colony forming units (CFU) count after PRCT and after PRCT + aPDT/mg of dentin were compared for total microorganisms, including Candida spp., the mutans streptococci group, Streptococcus spp. and Lactobacillus spp. The dentin was classified (color, consistency and humidity). The microbial reduction varied from 69.88% to 86.29% and was significantly observed for total microorganisms, mutans streptococci, Streptococcus spp. and Lactobacillus spp (P < 0.001). The dentin type did not influence reduction of microorganisms (P > 0.05). The aPDT presents a promising future for clinical use as an adjunct for the reduction of microorganisms in PRCT of DCL in all kinds of dentin.

Influence on interradicular bone volume of Invisalign treatment for adult crowding with interproximal enamel reduction: a retrospective three-dimensional cone-beam computed tomography study.

BACKGROUND: The aim of this study was to use three-dimensional datasets to identify associations between treatment for adult crowding, using Invisalign aligner and interproximal enamel reduction (IER), and changes in the volume of interradicular bone. METHODS: A total of 60 cone-beam computed tomography (CBCT) scans from 30 adult patients (28 women, two men; 30 CBCTs pre-treatment, 30 post-treatment) were examined retrospectively in order to measure bone volume three-dimensionally. The patients' average age was 36.03 ± 9.7 years. The interradicular bone volume was measured with OsiriX at four levels in the anterior tooth areas of the maxilla and mandible. Differences in bone between T0 and T1 were analyzed with IBM SPSS 21.0 using the Wilcoxon test for paired samples. RESULTS: Overall, a slight increase in the quantity of bone was found (0.12 ± 0.73 mm). There was a highly significant increase in bone in the mandible (0.40 ± 0.62 mm; P <  0.001), while in the maxilla there was a slight loss of bone, which was highly significant in the apical third (- 0.16 ± 0.77 mm; P = 0.001). CONCLUSIONS: Overall, treatment for adult crowding using an aligner and IER appears to have a positive effect on interradicular bone volume, particularly in patients with severe grades of the condition (periodontally high-risk dentition). This effect is apparently independent of IER. This is extremely important with regard to the treatment outcome, since IER and root proximity have been matters of debate in the literature and teeth should remain firmly embedded in their alveolar sockets.

Does ErbiumiYttrium-Aluminum-Garnet Laser to Enamel improve the Performance of Etch-and-rinse and Universal Adhesives?

AIM: This study aims to evaluate the effect of erbium: Yttrium-aluminum-garnet (Er:YAG) laser irradiation on the enamel microshear bond strength (µSBS), followed by the utilization of etch-and-rinse and universal adhesive systems. MATERIALS AND METHODS: A total of 32 molars were sectioned in the mesiodistal direction producing 64 samples that were randomized into two groups (n = 32): single bond 2 (SB2) (etch-and-rinse system; 3M), SB universal (SBU) (universal etching system; The SB2 and SBU groups were then divided into two subgroups (n = 16): (i) enamel was irradiated with an Er:YAG laser (λ = 2.94 µm, 60 mJ, 10 Hz), and (ii) enamel served as a control. The samples were restored with TPH3 (Dentsply), stored in artificial saliva for 24 hours, and subjected to a micro-shear test. RESULTS: Kruskal-Wallis (p < 0.05) and Mann-Whitney U tests indicated no significant differences in uSBS between the groups, and the fractures were predominately at the resin-enamel interface. CONCLUSION: The previous irradiation of enamel with Er:YAG laser does not interfere with the performance of simplified two-step etch-and-rinse and universal adhesive systems. CLINICAL SIGNIFICANCE: The increasing use of Er:YAG laser is important to evaluate the influence of this irradiation on the adhesion of restorative materials. Thus, to obtain the longevity of the restorative procedures, it is necessary to know the result of the association of the present adhesive systems to the irradiated substrate.

Effectiveness of Enamel Matrix Derivative in Conjunction with Particulate Autologous Bone in the Treatment of Noncontained Intrabony Defects: A 2-Year Prospective Case Series.

This case series evaluated the healing of deep intrabony defects treated with a combination of enamel matrix derivative and autologous particulate bone harvested from the buccal and lingual/palatal cortical plate with a Piezosurgery device. A total of 15 defects with a predominantly one- or two-wall component were consecutively treated in 15 patients with advanced chronic periodontitis. In all selected sites, the three-wall component was ≤ 25% of the total defect depth. Clinical and radiographic parameters were recorded at baseline and 12 and 24 months postoperatively. All defects showed favorable clinical and radiographic outcomes at the 24-month follow-up. The probing depth reduction was 4.4 ± 1.6 mm, and more than 50% of the defects presented clinical attachment level gain of at least 5 mm. The bone fill was 3.1 ± 1.6 mm.

Influence of multi-wavelength laser irradiation of enamel and dentin surfaces at 0.355, 2.94, and 9.4 µm on surface morphology, permeability, and acid resistance.

OBJECTIVE: Ultraviolet (UV) and infrared (IR) lasers can be used to specifically target protein, water, and mineral, respectively, in dental hard tissues to produce varying changes in surface morphology, permeability, reflectivity, and acid resistance. The purpose of this study was to explore the influence of laser irradiation and topical fluoride application on the surface morphology, permeability, reflectivity, and acid resistance of enamel and dentin to shed light on the mechanism of interaction and develop more effective treatments. METHODS: Twelve bovine enamel surfaces and twelve bovine dentin surfaces were irradiated with various combinations of lasers operating at 0.355 (Freq.-tripled Nd:YAG (UV) laser), 2.94 (Er:YAG laser), and 9.4 µm (CO2 laser), and surfaces were exposed to an acidulated phosphate fluoride gel and an acid challenge. Changes in the surface morphology, acid resistance, and permeability were measured using digital microscopy, polarized light microscopy, near-IR reflectance, fluorescence, polarization sensitive-optical coherence tomography (PS-OCT), and surface dehydration rate measurements. RESULTS: Different laser treatments dramatically influenced the surface morphology and permeability of both enamel and dentin. CO2 laser irradiation melted tooth surfaces. Er:YAG and UV lasers, while not melting tooth surfaces, showed markedly different surface roughness. Er:YAG irradiation led to significantly rougher enamel and dentin surfaces and led to higher permeability. There were significant differences in acid resistance among the various treatment groups. CONCLUSION: Surface dehydration measurements showed significant changes in permeability after laser treatments, application of fluoride and after exposure to demineralization. CO2 laser irradiation was most effective in inhibiting demineralization on enamel while topical fluoride was most effective for dentin surfaces. Lasers Surg. Med. 49:913-927, 2017. © 2017 Wiley Periodicals, Inc.

Atomic force microscopy analysis of enamel nanotopography after interproximal reduction.

INTRODUCTION: Interproximal reduction (IPR) removes enamel and leaves grooves and furrows on the tooth surface, which may increase the risk of caries. The aims of this study were to assess the nanotopography of enamel surfaces produced by the most commonly used IPR instruments and to evaluate the effect of polishing after IPR. METHODS: Enamel slabs were cut from the interproximal surfaces of healthy premolars and then treated with diamond burs, strips, or discs, or Sof-Lex polishing discs (3M ESPE, St Paul, Minn). All samples were cleaned by sonication in distilled water. The control group had no IPR performed and was subjected only to cleaning by sonication. The enamel surfaces were assessed using atomic force microscopy. RESULTS: The IPR instruments all produced surfaces rougher than the control sample; however, the samples that received polishing with Sof-Lex discs after enamel reduction were smoother than untreated enamel (P <0.05 for all comparisons). The larger grit medium diamond burs and medium strips generated rougher enamel surfaces than their smaller grit counterparts: fine diamond burs and fine strips (P <0.001). The difference in roughness generated by mesh and curved disks was not statistically significant (P = 0.122), nor was the difference caused by fine strips and mesh discs (P = 0.811) or by fine strips and curved discs (P = 0.076) (surface roughness values for medium bur, 702 ± 134 nm; medium strip, 501 ± 115 nm; mesh disc, 307 ± 107 nm; fine bur, 407 ± 95 nm; fine strip, 318 ± 50 nm; curved disc, 224 ± 65 nm). The smoothest surfaces were created by use of the entire series of Sof-Lex polishing discs after the enamel reduction (surface roughness, 37 ± 14 nm), and these surfaces were significantly smoother than the control surfaces (surface roughness, 149 ± 39 nm; P = 0.017). CONCLUSIONS: Different IPR instruments produced enamel surfaces with varied nanotopography and different degrees of roughness. Enamel surfaces treated with diamond-coated burs were the roughest, followed by diamond-coated strips and diamond coated discs. Polishing with Sof-Lex polishing discs after IPR reduced the enamel surface roughness, and this surface was even smoother than untreated enamel.

In vitro performance of ultrasound enamel preparation compared with classical bur preparation on pit and fissure sealing.

AIM: Fissure sealants are effective in preventing caries. The aim of this in vitro study was to evaluate the effects of two different enamel surface preparation techniques for pit and fissure sealing. MATERIALS AND METHODS: Sixty extracted sound third molars were used. For each tooth, the mesial half of the occlusal fissures was treated with ultrasound diamond tip T1 mounted on an ultrasonic handpiece, while the distal half with conventional diamond bur. The teeth were randomly divided into 2 groups (n = 30/each). Group 1 samples were stored in distilled water at 4 °C. For group 2 samples, sealing of occlusal fissures was performed according to standard procedures. Bucco-lingual cuts parallel to the long axis of the tooth were made in order to separate the two different types of preparations. The effects of the executed procedures were assessed with SEM. RESULTS: Surfaces prepared with ultrasound system showed the presence of residual debris and appeared more irregular than surfaces prepared with traditional bur system. Furthermore, images showed the presence of cracks on the bottom and on the walls of the ultrasound prepared fissures. CONCLUSION: Conventional bur surface treatment showed a better performance when compared to ultrasound preparation and could probably ensure superior sealant retention.

In situ effect of titanium tetrafluoride varnish on enamel demineralization

Abstract The effect of a 4% titanium tetrafluoride (TiF 4 ) varnish on enamel demineralization was evaluated. Twelve volunteers participated in this double-blind, randomized crossover study. Six enamel specimens were positioned in intraoral appliances throughout four treatment stages: 4% TiF 4 varnish (experimental varnish), 5% sodium fluoride (NaF) varnish (Duraphat ® ), placebo varnish, and negative control (deionized water). After 24 h, the varnishes were removed and plaques were allowed to accumulate. A 20% sucrose solution was dripped onto enamel blocks (10x/day). Enamel alterations were analyzed by surface microhardness (SMH), percentage of surface loss (%SML), cross-sectional microhardness (CSMH), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometry (EDS). Student's paired t-test was used for SMH analysis and repeated-measures analysis of variance (ANOVA) for %SML and CSMH (∆Z) analyses (p-value=0.05). The TiF 4 varnish group had lower %SML than the placebo and control groups (p=0.044 and p=0.003, respectively), thus showing its capacity to inhibit surface demineralization. TiF 4 and NaF varnishes demonstrated a protective effect against mineral loss on the enamel subsurface. Both were statistically different from the control group when CSMH was analyzed (p=0.000). A titanium dioxide film was observed on enamel surfaces of the TiF 4 group SEM images. EDS confirmed the presence of titanium in all TiF 4 samples. The 4% TiF 4 varnish is a promising compound capable of reacting with enamel to protect it against surface and subsurface demineralization.

Dental hard tissue ablation using mid-infrared tunable nanosecond pulsed Cr:CdSe laser.

BACKGROUND AND OBJECTIVE: Mid-infrared erbium: yttrium-aluminum-garnet (Er:YAG) and erbium, chromium: yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers (2.94- and 2.78-µm, respectively) are utilized for effective dental hard tissue treatment because of their high absorption in water, hydroxide ion, or both. Recently, a mid-infrared tunable, nanosecond pulsed, all-solid-state chromium-doped: cadmium-selenide (Cr:CdSe) laser system was developed, which enables laser oscillation in the broad spectral range around 2.9 µm. The purpose of this study was to evaluate the ablation of dental hard tissue by the nanosecond pulsed Cr:CdSe laser at a wavelength range of 2.76-3.00 µm. STUDY DESIGN/MATERIALS AND METHODS: Enamel, dentin, and cementum tissue were irradiated at a spot or line at a fluence of 0-11.20 J/cm2 /pulse (energy output: 0-2.00 mJ/pulse) with a repetition rate of 10 Hz and beam diameter of ∼150 µm on the target (pulse width ∼250 ns). After irradiation, morphological changes, ablation threshold, depth, and efficiency, and thickness of the structurally and thermally affected layer of irradiated surfaces were analyzed using stereomicroscopy, scanning electron microscopy (SEM), and light microscopy of non-decalcified histological sections. RESULTS: The nanosecond pulsed irradiation without water spray effectively ablated dental hard tissue with no visible thermal damage such as carbonization. The SEM analysis revealed characteristic micro-irregularities without major melting and cracks in the lased tissue. The ablation threshold of dentin was the lowest at 2.76 µm and the highest at 3.00 µm. The histological analysis revealed minimal thermal and structural changes ∼20 µm wide on the irradiated dentin surfaces with no significant differences between wavelengths. The efficiency of dentin ablation gradually increased from 3.00 to 2.76 µm, at which point the highest ablation efficiency was observed. CONCLUSION: The nanosecond pulsed Cr:CdSe laser demonstrated an effective ablation ability of hard dental tissues, which was remarkably wavelength-dependent on dentin at the spectral range of 2.76-3.00 µm. These results demonstrate the potential feasibility of the use of pulsed Cr:CdSe laser as a novel laser system for dental treatment. Lasers Surg. Med. 48:965-977, 2016. © 2016 Wiley Periodicals, Inc.

Femtosecond laser for cavity preparation in enamel and dentin: ablation efficiency related factors.

To study the effects of laser fluence (laser energy density), scanning line spacing and ablation depth on the efficiency of a femtosecond laser for three-dimensional ablation of enamel and dentin. A diode-pumped, thin-disk femtosecond laser (wavelength 1025 nm, pulse width 400 fs) was used for the ablation of enamel and dentin. The laser spot was guided in a series of overlapping parallel lines on enamel and dentin surfaces to form a three-dimensional cavity. The depth and volume of the ablated cavity was then measured under a 3D measurement microscope to determine the ablation efficiency. Different values of fluence, scanning line spacing and ablation depth were used to assess the effects of each variable on ablation efficiency. Ablation efficiencies for enamel and dentin were maximized at different laser fluences and number of scanning lines and decreased with increases in laser fluence or with increases in scanning line spacing beyond spot diameter or with increases in ablation depth. Laser fluence, scanning line spacing and ablation depth all significantly affected femtosecond laser ablation efficiency. Use of a reasonable control for each of these parameters will improve future clinical application.

Quantitative assessment of the enamel machinability in tooth preparation with dental diamond burs.

Enamel cutting using dental handpieces is a critical process in tooth preparation for dental restorations and treatment but the machinability of enamel is poorly understood. This paper reports on the first quantitative assessment of the enamel machinability using computer-assisted numerical control, high-speed data acquisition, and force sensing systems. The enamel machinability in terms of cutting forces, force ratio, cutting torque, cutting speed and specific cutting energy were characterized in relation to enamel surface orientation, specific material removal rate and diamond bur grit size. The results show that enamel surface orientation, specific material removal rate and diamond bur grit size critically affected the enamel cutting capability. Cutting buccal/lingual surfaces resulted in significantly higher tangential and normal forces, torques and specific energy (p<0.05) but lower cutting speeds than occlusal surfaces (p<0.05). Increasing material removal rate for high cutting efficiencies using coarse burs yielded remarkable rises in cutting forces and torque (p<0.05) but significant reductions in cutting speed and specific cutting energy (p<0.05). In particular, great variations in cutting forces, torques and specific energy were observed at the specific material removal rate of 3mm(3)/min/mm using coarse burs, indicating the cutting limit. This work provides fundamental data and the scientific understanding of the enamel machinability for clinical dental practice.

Simulation of temperature and thermally induced stress of human tooth under CO2 pulsed laser beams using finite element method.

The authors report the simulation of temperature distribution and thermally induced stresses of human tooth under CO2 pulsed laser beam. A detailed tooth structure comprising enamel, dentin, and pulp with realistic shapes and thicknesses were considered, and a numerical method of finite element was adopted to solve time-dependent bio-heat and stress equations. The realistic boundary conditions of constant temperature for those parts embedded in the gingiva and heat flux condition for those parts out of the gingiva were applied. The results which were achieved as a function of energy density (J/cm(2)) showed when laser beam is irradiated downward (from the top of the tooth), the temperature and thermal stresses decrease quickly as a function of depth that is a result of strong absorption of CO2 beams by enamel. This effect is so influential that one can use CO2 beams to remove micrometer layers while underlying tissues, especially the pulp, are safe from thermal effects.