Matthias Frentzen

The possibility of detecting subgingival calculus by laser-fluorescence in vitro

Abstract The aim of the present study was to investigate laser-fluorescence effects on the root surface. The possibility of detecting subgingival calculus should be evaluated to control complete calculus removal after scaling and root planing. Twenty freshly extracted human teeth, partially covered with calculus on the root surface, were fixed on a translation stage. The specimens were irradiated by light from a laser source (diode laser, <1 mW) with a wavelength of 655 nm using the Diagnodent™-system. To simulate the conditions in a periodontal pocket during the measurement procedure, the teeth were covered by a layer of physiological saline solution or blood in order to determine the influence of different inflammatory fluids. The root surface was scanned on a line of about 1 cm in steps of 0.5 mm. The start and end was marked by a notch. The results of the laser-fluorescence detection were compared to clinical and histological findings. Clinically apparent calculus on the root surface was always accompanied with a statistically significant increase of laser-fluorescence values (p < 0.05). These values were not influenced by the different fluids (p < 0.05). The laser-fluorescence values were reproducible (p > 0.05). After scaling, when no debris remained at the root surface, laser-fluorescence values decreased significantly (p < 0.05). The histological findings supported the clinical results. In conclusion, the present study indicates that laser-fluorescence values on the root surface are strongly correlated to the presence of calculus. This fluorescence effect can basically be used to develop a new detecting system for subgingival calculus in periodontal pockets.

Osteotomy with 80-μs CO2 laser pulses: histological results

Haemostatic and aseptic effects and intricate cut geometry are beneficial aspects of non-contact laser osteotomy. Collateral thermal damage, however, has severely limited the use of conventional lasers. The purpose of this study was to test the side effects on bone after cutting it with short CO2 laser pulses and simultaneous application of a fine air–water spray. The 10.6 μm CO2 laser emitted 80-μs pulses of 46 mJ energy, f=100 Hz, focused to a spot diameter of 130 ìm. Scan rate amounted to 40 mm/s. To approximate live conditions 10 samples of cortical bone and 10 rib segments were prepared immediately after sacrificing of pigs. A reference cut with a bandsaw and three laser cuts with an increasing number of beam passes (4, 16, 64) were performed on each sample. Half of the samples were decalcified in EDTA. The others were embedded in plastic to cut non-decalcified sections. The laser incisions were not accompanied by carbonisation. The incisions with slightly convergent walls were 150 ìm wide. The depths of the cavities increased with the number of the beam passes from approximately 0.5 mm (4 passes) to 3 mm (64 passes). At the border of the incisions two narrow zones of damage were noted: an amorphous intensively stained zone of 1–3 μm width and a wider, also sharply demarcated but faintly stained zone of 7–10 μm. A broader zone of about 50 μm was characterised by empty lacunae and osteocyte damage. These effects were not predictable; intact osteocytes were also observed near to the cut surface. Polarised light microscopy showed no alterations in the inorganic structure of the bone at the cut borders. The histological results indicated only minimal damage to bone ablated at the specified parameters. The described laser procedure might have advantages over mechanical instruments.

3D analyses of interface voids in root canals filled with different sealer materials in combination with warm gutta-percha technique

ObjectivesThe aim of the present study was to analyze the formation of voids and gaps in root canals obturated with different sealer materials in combination with warm gutta-percha vertical compaction technique by using BeeFill® 2in1.Materials and methodsTwenty-four single-rooted teeth were collected, and root canals were prepared by using rotary files. All teeth were randomly allocated into three groups. Each group was obturated by using the BeeFill® 2in1 system in combination with Sealapex (non-eugenol, calcium hydroxide polymeric root canal sealer; Kerr Sybron, USA), RoekoSeal (polydimethylsiloxane-based sealer; Roeko, Germany), or 2Seal (epoxy-amine resin-based sealer; VDW, Germany). Following preparation, all teeth were scanned with a micro-computed tomography (CT) scanner, and a three-dimensional reconstruction of the obturated root canals was performed to analyze the volume of interface voids and gaps in the obturated teeth.ResultsStatistical analysis demonstrated that the silicon-based sealer RoekoSeal induced significantly less voids and gaps than other tested materials. The amount of voids and gaps significantly was higher in the apical region.ConclusionsThese data indicate that none of the root canal-filled teeth were free of gaps. Teeth obturated with RoekoSeal demonstrated to have the highest quality in terms of voids and gaps formation in combination with the BeeFill® 2in1 obturation system.Clinical relevanceThese findings point to the potential benefit of micro-CT analyses for in vitro evaluation of root canal obturation systems and provide further information about sealer materials used in combination with a warm gutta-percha vertical compaction technique.

Comparison of cone-beam computerized tomography and intraoral radiographs for determination of the periodontal ligament in a variable phantom

OBJECTIVES This in vitro study assessed the visualization quality of the periodontal ligament space in cone-beam computerized tomography (CBCT) compared with intraoral radiographs (CR). STUDY DESIGN A phantom mimicking variable periodontal ligament spaces (0-0.42 mm) was radiographed using CBCT and CR. Fifteen datasets of each modality were randomly mixed and presented twice to 19 experienced examiners and once to 19 inexperienced examiners. RESULTS Zero-millimeter gaps were recognized in 84.4% of CBCT and in 81.6% of CR images. On CBCT scans, gaps of 0.19 mm were identified with an accuracy of 93%-100% compared with 70.2%-81.7% using CR. Experienced examiners recognized gaps of >or=0.19 mm on CBCT repeatedly with nearly 100% accuracy. CONCLUSION Compared with CR, CBCT provides better visualization of simulated periodontal ligament space in this phantom.

YAG lasers in restorative dentistry: a histological investigation

An important indicator to prove the effectiveness of laser radiation and to control the side effects are histological studies of dental hard tissues. In our study, different pulsed, rare earth doped YAG-laser systems in the range from 1 micrometers to 3 micrometers were investigated. An improved plastic embedding technique based on a penetrating uv-activated PMMA-medium was developed to cut undecalcified sections of 15 micrometers thickness. The Nd:YAG laser showed wide zones of necrosis but little carbonization. The radiation of Holmium and Thullium-doped YAG lasers causes strong but well-defined zones of carbonization comparable to those of pulsed (ms) CO2 lasers. The Erbium-doped YAG-laser was the most effective system. As predominant side effects, residual zones of debris and microcracks were observed. In deeper cavities, the zones of damages increase. The side effects of the pulsed infrared laser types seem to be mainly influenced by the physical or chemical properties of the dental tissues and not by the selected laser parameters.

In vitro analysis of the effects of acid or laser etching on microleakage around composite resin restorations.

OBJECTIVES The aim of the present study was to determine the effect of two conditioning methods, phosphoric acid and XeCl laser application on microleakage at composite resin restorations. METHODS Class II MOD (mesio-occluso-distal) cavities were prepared on 90 extracted human wisdom teeth with one proximogingival margin on enamel and the other on dentin. Phosphoric acid (37%) and a XeCl excimer laser system were used for the etching procedure. The prepared teeth were randomly assigned to six groups: In group 1, acid-etching of the enamel margins was followed by application of enamel bonding, in group 2 additionally a dentin bonding system was used. In group 3, acid-etching of the enamel and dentin (total etch) was followed by the application of dentin bonding. In group 4, laser-etching of enamel margins was followed by the application of enamel bonding, in group 5 dentin bonding was used additionally. In group 6, laser-etching of enamel and dentin margins was followed by the application of dentin bonding. All restorations were placed incrementally and polymerized with a halogen light source. After restoration, all samples were thermocycled and stained in 0.5% basic fuchsin and sectioned longitudinally in a mesio-distal plane. Microleakage was scored by means of a stereomicroscope. The margins of the restorations at tooth-resin interface were examined with a scanning electron microscope. RESULTS In all groups, marginal leakage was more extensive at the gingival margin that was in dentin than at the gingival margin in enamel. Microleakage scores and the gap at the tooth-resin interface were significantly lower in all acid-etched groups than in laser-etched groups. CONCLUSION Acid-etch technique is more effective than the investigated laser-etch technique at 308nm concerning the reduction of marginal leakage in composite restorations.

Ghrelin promotes oral tumor cell proliferation by modifying GLUT1 expression

In our study, ghrelin was investigated with respect to its capacity on proliferative effects and molecular correlations on oral tumor cells. The presence of all molecular components of the ghrelin system, i.e., ghrelin and its receptors, was analyzed and could be detected using real-time PCR and immunohistochemistry. To examine cellular effects caused by ghrelin and to clarify downstream-regulatory mechanisms, two different oral tumor cell lines (BHY and HN) were used in cell culture experiments. Stimulation of either cell line with ghrelin led to a significantly increased proliferation. Signal transduction occurred through phosphorylation of GSK-3β and nuclear translocation of β-catenin. This effect could be inhibited by blocking protein kinase A. Glucose transporter1 (GLUT1), as an important factor for delivering sufficient amounts of glucose to tumor cells having high requirements for this carbohydrate (Warburg effect) was up-regulated by exogenous and endogenous ghrelin. Silencing intracellular ghrelin concentrations using siRNA led to a significant decreased expression of GLUT1 and proliferation. In conclusion, our study describes the role for the appetite-stimulating peptide hormone ghrelin in oral cancer proliferation under the particular aspect of glucose uptake: (1) tumor cells are a source of ghrelin. (2) Ghrelin affects tumor cell proliferation through autocrine and/or paracrine activity. (3) Ghrelin modulates GLUT1 expression and thus indirectly enhances tumor cell proliferation. These findings are of major relevance, because glucose uptake is assumed to be a promising target for cancer treatment.

Finite element analysis of adhesive endo-crowns of molars at different height levels of buccally applied load

This study aimed to evaluate the biomechanical behaviour of adhesive endo-crowns and the influence of their design on the restoration prognosis when four loading positions are applied from the restoration–tooth junction. Two three-dimensional finite element models for the lower first molar were developed: endo-crown as a monobloc and endo-crown of a primary abutment and a full crown. Four crown loading positions were considered: 5, 6, 7 and 8 mm. A force of 1400 N was applied buccally on the middle of the mesiodistal width. No differences were observed for the two endo-crowns concerning restoration displacement and the distribution of equivalent von Mises stress and total equivalent strain. Shifting the position of the applied load to 8 mm resulted in an increase in the displacement from 25 to 42 µm and an increase of equivalent von Mises stress concentration at the tooth. The height of load application on the restoration has a significant role in the prognosis of endo-crowns.

Pulsed lasers in dentistry: sense or nonsense?

The great interest in the field of laser applications in dentistry provokes the question, if all these new techniques may really fulfill advantages, which are expected after initial in-vitro studies. Whereas laser surgery of soft oral tissues has been developed to a standard method, laser treatment of dental hard tissues and the bone are attended with many unsolved problems. Different laser types, especially pulsed lasers in a wide spectrum of wavelengths have been proofed for dental use. Today neither the excimer lasers, emitting in the far uv-range from 193 to 351 nm, nor the mid-infrared lasers like Nd:YAG (1,064 μm), Ho:YAG (2,1 μm) and Er:YAG (2,96 μm) or the C02-laser (10,6 μm) show mechanism of interaction more carefully and faster than a preparation of teeth with diamond drillers. The laser type with the most precise and considerate treatment effects in the moment is the short pulsed (15 ns) ArF-excimer laser with a wavelength of 193 nm. However this laser type has not yet the effectivity of mechanical instruments and it needs a mirror system to deliver the radiation. Histological results point out, that this laser shows no significant pathological alterations in the adjacent tissues. Another interesting excimer laser, filled with XeCI and emitting at a wavelength of 308 nm has the advantage to be good to deliver through quartz fibers. A little more thermal influence is to be seen according to the longer wavelength. Yet the energy density, necessary to cut dental hard tissues will not be reached with the laser systems available now. Both the pulsed Er:YAG- (2,94 μm, pulse duration 250 s) and the Ho:YAG -laser (2,1 μm, pulse duration 250 μs) have an effective coupling of the laser energy to hydrogeneous tissues, but they do not work sufficient on healthy enamel and dentine. The influence to adjacent healthy tissue is not tolerable, especially in regard of the thermal damage dentine and pulp tissues. Moreover, like the 193 nm ArF-excimer laser radiation the Er:YAG-laser radiation could also only be delivered via mirror systems, while the radiation of the Ho:YAG-Laser can be well transmitted through quartz fibers. The energy of the well known and in other medical disciplines often used Nd:YAG - laser (1,064 μm, pulse duration 150 us) laser can be transmitted through fiber systems without problems, but this laser has not the effectivity to work sufficient on healthy hard dental tissues due to the high transmission in mineralized dental tissues. The thermal injuries of this laser type are not tolerable. The short pulsed TEA-C02-laser (9,6 and 10,6 μm, pulse duration 200-300 ns), which has an excellent coupling not only to the hydrogeneous tissues but also to the mineralized tissues could be an alternative system to prepare dental tissues. The greatest disadvantage of this system is the noneffective delivery of the light energy through flexible fiber systems, which are still in development. Another good chance perhaps will have the q-switched Neodym, Erbium and Holmium:- YAG lasers with pulse durations of about some hundred ns. Both, possible thermal influences and possible disruptive effects should be small enough to let the adjacent tissues undamaged.

Indocyanine green (ICG) as a new adjuvant for the antimicrobial photo-dynamic therapy (aPDT) in dentistry

Clinical surveys show a continuous increase of antimicrobial resistance related to the frequency of the administrated medication. The antimicrobial photodynamic therapy (aPDT) is an effective adjuvant to reduce the need of antibiotics in dentistry, especially in periodontics. The antimicrobial effect of lightactivated photosensitizers in periodontics is demonstrated in clinical studies and case reports. Indocyanine green (ICG) as a new adjuvant shows the high potential of antiphlogistic and antimicrobial effects in combination with laser-light activation. In trying to answer the question of just how far the influence of temperature is acting on bacteria, this study was carried out. The influences of ICG at different concentrations (0.01 up to 1 mg/ml) in combination with a culture medium (brain-heart-infusion) and a bacteria culture (Streptococcus salivarius) at different optical densities (OD600 0.5 and 0.1) were investigated under laser-light activation. Laser activation was carried out with diode laser at 810 nm and two different power settings (100 mW/300 mW). The pulse repetition rate was 2 kHz. Taking account of the fiber diameter, distance and spot size on the sample surface, the applicated intensities were 6.2 and 18.7 W/cm2. Total irradiation time was 20 s for all meaurements. Transmitted laser power and temperature increase in the culture medium as well as in the bacteria culture were determined. Additionally the influence of ICG regarding bacterial growth and bactericidal effect was investigated in the bacteria culture without laser irradiation. Without laser, no bactericidal effect of ICG was observed. Only a bacteriostatic effect could be proved. In dependence of the ICG concentration and the applied intensities a temperature increase of ΔT up to 80°C was measured.