Periodontal pathogens promote cancer aggressivity via TLR/MyD88 triggered activation of Integrin/FAK signaling that is therapeutically reversible by a probiotic bacteriocin.

Epidemiological studies reveal significant associations between periodontitis and oral cancer. However, knowledge about the contribution of periodontal pathogens to oral cancer and potential regulatory mechanisms involved is limited. Previously, we showed that nisin, a bacteriocin and commonly used food preservative, reduced oral cancer tumorigenesis and extended the life expectancy in tumor-bearing mice. In addition, nisin has antimicrobial effects on key periodontal pathogens. Thus, the purpose of this study was to test the hypothesis that key periodontal pathogens (Porphyromonas gingivalis, Treponema denticola, and Fusobacterium nucleatum) promote oral cancer via specific host-bacterial interactions, and that bacteriocin/nisin therapy may modulate these responses. All three periodontal pathogens enhanced oral squamous cell carcinoma (OSCC) cell migration, invasion, tumorsphere formation, and tumorigenesis in vivo, without significantly affecting cell proliferation or apoptosis. In contrast, oral commensal bacteria did not affect OSCC cell migration. Pathogen-enhanced OSCC cell migration was mediated via integrin alpha V and FAK activation, since stably blocking alpha V or FAK expression abrogated these effects. Nisin inhibited these pathogen-mediated processes. Further, Treponema denticola induced TLR2 and 4 and MyD88 expression. Stable suppression of MyD88 significantly inhibited Treponema denticola-induced FAK activation and abrogated pathogen-induced migration. Together, these data demonstrate that periodontal pathogens contribute to a highly aggressive cancer phenotype via crosstalk between TLR/MyD88 and integrin/FAK signaling. Nisin can modulate these pathogen-mediated effects, and thus has therapeutic potential as an antimicrobial and anti-tumorigenic agent.

Demineralization prevention with a new antibacterial restorative composite containing QASi nanoparticles: an in situ study.

OBJECTIVES: To investigate whether a newly developed dental composite with quaternary ammonium silica dioxide (QASi) nanoparticles incorporated with other fillers into the restorative material demonstrates antibacterial activity by reducing enamel demineralization in an in situ gap model. MATERIALS AND METHODS: Twenty subjects wearing a lower removable partial denture (RPD) with acrylic flanges on both sides of the mouth were recruited into the 4-week in situ study. The gap model consisted of an enamel slab placed next to a composite, separated by a 38-µm space. In the split-mouth design on one side of the RPD, the composite was the Nobio Infinix composite (Nobio Ltd., Kadima, Israel), and the contralateral side used a control composite. Each participant received enamel slabs from one tooth. The gap model was recessed into the RPD buccal flange, allowing microbial plaque to accumulate within the gap. After 4 weeks of continuous wearing, decalcification (∆Z mineral loss) of the enamel slabs adjacent to the gap was determined by cross-sectional microhardness testing in the laboratory. RESULTS: The ∆Z for the antibacterial composite test side was 235±354 (mean±standard deviation [SD]; data reported from 17 participants) and statistically significantly lower compared to ∆Z of the control side (774±556; mean±SD) (paired t-test, P<0.0001; mean of test minus control -539 (SD=392), 95% confidence interval of difference: -741, -338). CONCLUSIONS: This in situ clinical study showed that composites with QASi antibacterial particles significantly reduced demineralization in enamel adjacent to a 38-µm gap over a 4-week period in comparison to a conventional composite. CLINICAL RELEVANCE: Composites with QASi nanoparticle technology have the potential to reduce the occurrence of secondary caries. TRIAL REGISTRATION: ClinicalTrials.gov #NCT04059250.

Caries inhibition with a CO2 9.3 µm laser: An in vitro study.

BACKGROUND AND OBJECTIVES: The caries preventive effects of different laser wavelengths have been studied in the laboratory as well as in pilot clinical trials. The objective of this in vitro study was to evaluate whether irradiation with a new 9.3 µm microsecond short-pulsed CO2 -laser could enhance enamel caries resistance with and without additional fluoride applications. STUDY DESIGN/MATERIALS AND METHODS: One hundred and one human tooth enamel samples were divided into seven groups. Each group was treated with different laser parameters (CO2 -laser, wavelength 9.3 µm, 43 Hz pulse-repetition rate, pulse duration between 3 µs at 1.5 mJ/pulse to 7 µs at 2.9 mJ/pulse). A laboratory pH-cycling model followed by cross-sectional microhardness testing determined the mean relative mineral loss delta Z (ΔZ) for each group to assess caries inhibition in tooth enamel by the CO2 9.3 µm short-pulsed laser irradiation. The pH-cycling was performed with or without additional fluoride. RESULTS: The non-laser control groups with additional fluoride had a relative mineral loss (ΔZ, vol% × µm) that ranged between 646 ± 215 and 773 ± 223 (mean ± SD). The laser irradiated and fluoride treated samples had a mean ΔZ ranging between 209 ± 133 and 403 ± 245 for an average 55% ± 9% reduction in mineral loss (ANOVA test, P < 0.0001). Increased mean mineral loss (ΔZ between 1166 ± 571 and 1339 ± 347) was found for the non-laser treated controls without additional fluoride. In contrast, the laser treated groups without additional fluoride showed a ΔZ between 470 ± 240 and 669 ± 209 (ANOVA test, P < 0.0001) representing an average 53% ± 11% reduction in mineral loss. Scanning electron microscopical assessment revealed that 3 µs pulses did not markedly change the enamel surface, while 7 µs pulses caused some enamel ablation. CONCLUSION: The CO2 9.3 µm short-pulsed laser energy renders enamel caries resistant with and without additional fluoride use. The observed enhanced acid resistance occurred with the laser irradiation parameters used without obvious melting of the enamel surface as well as after irradiation with energies causing cutting of the enamel. Lasers Surg. Med. 48:546-554, 2016. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Effects of CO2 laser irradiation on tooth enamel coated with biofilm.

BACKGROUND AND OBJECTIVES: CO2 laser irradiation of tooth enamel can inhibit demineralization of tooth enamel, by changing enamel composition and resistance to acid attack. The aim of this work was to examine these effects of CO2 laser irradiation on enamel covered by biofilm. MATERIALS AND METHODS: Streptococcus mutans was grown on bovine enamel surfaces for 48 hours to form a mature biofilm. Samples were irradiated by CO2 laser (wavelength of 10.6 µm) at a power of 0.08 W in a super-pulse mode for 1 second and 24 pulses/second, with an energy density of 0.77 J/cm(2) per pulse. Untreated controls and laser treated samples with and without biofilm were examined for the morphology of the biofilm and the enamel surface by scanning electron microscopy (SEM). Structural biofilm viability was assessed using confocal laser scanning microscopy with live/dead staining. The biofilm was removed in a sonication water bath and the non-treated and irradiated enamel samples were chemically analyzed using energy dispersive X-ray spectrometry (EDS) and Fourier transform infrared spectroscopy (FTIR). RESULTS: Irradiated samples showed a melt zone with micro-cracks in the center of the irradiating beam position, which was smaller when irradiated enamel was covered by biofilm. Confocal microscopy images demonstrated higher proportion of dead bacteria at the margins of the irradiated spot area, while at the spot center the bacteria were evaporated exposing the enamel surface to direct laser irradiation. EDS analysis showed an increase in Ca/P ratio after irradiation of enamel covered with biofilm. FTIR analysis showed an approximately 40% carbonate loss in the irradiated enamel samples, including those with biofilms. CONCLUSION: Biofilms protect enamel surfaces from possible morphological irradiation damage without interfering with the resultant chemical changes that may increase the enamel resistance to acid attack. Therefore, under certain exposure regimens that are thermally and mechanically safe for enamel, CO2 laser irradiation of biofilms on dental hard tissues is suggested as a potential novel preventive treatment for controlling dental caries.

Laser all-ceramic crown removal-a laboratory proof-of-principle study-phase 1 material characteristics.

BACKGROUND AND OBJECTIVES: The removal of all-ceramic crowns is a time consuming and destructive procedure in the dental office. The removal of all-ceramic crowns using Er:YAG lasers has not been previously described in the scientific literature. The objective of this laboratory proof-of-principle study was to evaluate whether with regards to absorption and transmission characteristics of bonding cements and ceramics all-ceramic crowns can be removed from natural teeth using an Erbium laser. STUDY DESIGN/MATERIALS AND METHODS: The Fourier Transform Infrared Spectroscopy (FTIR) was used on flat ceramic samples (IPS Empress Esthetic (EE), E.max CAD, and E.max ZirCAD) to assess which infrared laser wavelengths transmit through the ceramics. Additionally, FTIR spectra for four bonding cements (Variolink Veneer, Variolink II, Multilink Automix, and SpeedCEM) were obtained. The Er:YAG laser energy transmission (wavelength 2,940 nm, 10 Hz repetition rate, pulse duration 100 µs at 126 mJ/pulse to 300 µs at 508 mJ/pulse) through different ceramic thicknesses was measured. Ablation thresholds for bonding cements were determined. Cement samples were directly irradiated or laser light was transmitted through ceramic samples. RESULTS: While the ceramics did not show any characteristic water absorption bands in the FTIR, all bonding cements showed a broad H2 O/OH absorption band. Some cements exhibited a distinct absorption peak at the Er:YAG laser emission wavelength. Depending on the ceramic thickness, EE and E.max CAD ceramics transmitted between 21 and 60% of the incident Er:YAG energy, with E.max CAD transmitting more energy than EE at comparable thicknesses. In contrast, E.max ZirCAD transmitted only 5-10% of the incident energy. Initial signs of cement deterioration occurred at 1.3-2.6 J/cm(2) . Multilink Automix, SpeedCEM, and Variolink II started ablation at 4.4-4.7 J/cm(2) . Variolink Veneer needed 44% less energy for ablation. CONCLUSION: Er:YAG laser energy can be transmitted through all-ceramic materials and those transmitted energies are sufficient for ablation of bonding cements.

Nisin lantibiotic prevents NAFLD liver steatosis and mitochondrial oxidative stress following periodontal disease by abrogating oral, gut and liver dysbiosis.

Oral microbiome dysbiosis mediates chronic periodontal disease, gut microbial dysbiosis, and mucosal barrier disfunction that leads to steatohepatitis via the enterohepatic circulation. Improving this dysbiosis towards health may improve liver disease. Treatment with antibiotics and probiotics have been used to modulate the microbial, immunological, and clinical landscape of periodontal disease with some success. The aim of the present investigation was to evaluate the potential for nisin, an antimicrobial peptide produced by Lactococcus lactis, to counteract the periodontitis-associated gut dysbiosis and to modulate the glycolipid-metabolism and inflammation in the liver. Periodontal pathogens, namely Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia and Fusobacterium nucleatum, were administrated topically onto the oral cavity to establish polymicrobial periodontal disease in mice. In the context of disease, nisin treatment significantly shifted the microbiome towards a new composition, commensurate with health while preventing the harmful inflammation in the small intestine concomitant with decreased villi structural integrity, and heightened hepatic exposure to bacteria and lipid and malondialdehyde accumulation in the liver. Validation with RNA Seq analyses, confirmed the significant infection-related alteration of several genes involved in mitochondrial dysregulation, oxidative phosphorylation, and metal/iron binding and their restitution following nisin treatment. In support of these in vivo findings indicating that periodontopathogens induce gastrointestinal and liver distant organ lesions, human autopsy specimens demonstrated a correlation between tooth loss and severity of liver disease. Nisin's ability to shift the gut and liver microbiome towards a new state commensurate with health while mitigating enteritis, represents a novel approach to treating NAFLD-steatohepatitis-associated periodontal disease.

In-vivo occlusal caries prevention by pulsed CO2 -laser and fluoride varnish treatment--a clinical pilot study.

BACKGROUND AND OBJECTIVES: High caries prevalence in occlusal pits and fissures warrants novel prevention methods. An 86% reduction in dental enamel smooth surface demineralization in-vivo following short-pulsed 9.6 µm-CO(2) -laser irradiation was recently reported. The objective of this study was to conduct a blinded 12-month-pilot clinical trial of occlusal pit and fissure caries inhibition using the same CO(2) -laser irradiation conditions. STUDY DESIGN/MATERIALS AND METHODS: Twenty subjects, average age 14 years, were recruited. At baseline, second molars were randomized into test and control groups, assessed by International Caries Detection & Assessment System (ICDAS-II), SOPROLIFE light-induced fluorescence evaluator in daylight and blue-fluorescence mode and DIAGNOdent. An independent investigator irradiated test molars with a CO(2) -laser, wavelength 9.6 µm, pulse-duration 20 µs, pulse-repetition-rate 20 Hz, beam diameter 800 µm, average fluence 4.5 ± 0.5 J/cm(2), 20 laser pulses per spot. At 3-, 6- and 12-month recall teeth were assessed by ICDAS, SOPROLIFE and DIAGNOdent. All subjects received fluoride varnish applications at baseline and 6-month recall. RESULTS: All subjects completed the 3-month, 19 the 6-month and 16 the 12-month recall. At all recalls average ICDAS scores had decreased for the test and increased for the control fissures (laser vs. control, 3-month: -0.10 ± 0.14, 0.30 ± 0.18, P > 0.05; 6-month: -0.26 ± 0.13, 0.47 ± 0.16, P = 0.001; 12-month: -0.31 ± 0.15, 0.75 ± 0.17, P < 0.0001; mean ± SE, unpaired t-test) being statistically significantly different at 6- and 12-month recalls. SOPROLIFE daylight evaluation revealed at 6- and 12-months statistically significant differences in changes between baseline and recall for test and control molars, respectively (laser vs. control, 6-month: 0.22 ± 0.13, 0.17 ± 0.09, P = 0.02; 12-month: 0.28 ± 0.19, 0.25 ± 0.17, P = 0.03). For SOPROLIFE blue-fluorescence evaluation mean changes in comparison to baseline for the control and the laser treated teeth were also statistically significant for the 6- and 12-month recall. CONCLUSION: Specific microsecond short-pulsed 9.6 µm CO(2) -laser irradiation markedly inhibits caries progression in pits and fissures in comparison to fluoride varnish alone over 12 months.

Nisin probiotic prevents inflammatory bone loss while promoting reparative proliferation and a healthy microbiome.

Dysbiosis of the oral microbiome mediates chronic periodontal disease. Realignment of microbial dysbiosis towards health may prevent disease. Treatment with antibiotics and probiotics can modulate the microbial, immunological, and clinical landscape of periodontal disease with some success. Antibacterial peptides or bacteriocins, such as nisin, and a nisin-producing probiotic, Lactococcus lactis, have not been examined in this context, yet warrant examination because of their biomedical benefits in eradicating biofilms and pathogenic bacteria, modulating immune mechanisms, and their safety profile in humans. This study's goal was to examine the potential for nisin and a nisin-producing probiotic to abrogate periodontal bone loss, the host inflammatory response, and changes in oral microbiome composition in a polymicrobial mouse model of periodontal disease. Nisin and a nisin-producing Lactococcus lactis probiotic significantly decreased the levels of several periodontal pathogens, alveolar bone loss, and the oral and systemic inflammatory host response. Surprisingly, nisin and/or the nisin-producing L. lactis probiotic enhanced the population of fibroblasts and osteoblasts despite the polymicrobial infection. Nisin mediated human periodontal ligament cell proliferation dose-dependently by increasing the proliferation marker, Ki-67. Nisin and probiotic treatment significantly shifted the oral microbiome towards the healthy control state; health was associated with Proteobacteria, whereas 3 retroviruses were associated with disease. Disease-associated microbial species were correlated with IL-6 levels. Nisin or nisin-producing probiotic's ability to shift the oral microbiome towards health, mitigate periodontal destruction and the host immune response, and promote a novel proliferative phenotype in reparative connective tissue cells, addresses key aspects of the pathogenesis of periodontal disease and reveals a new biomedical application for nisin in treatment of periodontitis and reparative medicine.

Polymicrobial periodontal disease triggers a wide radius of effect and unique virome.

Periodontal disease is a microbially-mediated inflammatory disease of tooth-supporting tissues that leads to bone and tissue loss around teeth. Although bacterially-mediated mechanisms of alveolar bone destruction have been widely studied, the effects of a polymicrobial infection on the periodontal ligament and microbiome/virome have not been well explored. Therefore, the current investigation introduced a new mouse model of periodontal disease to examine the effects of a polymicrobial infection on periodontal ligament (PDL) properties, changes in bone loss, the host immune response, and the microbiome/virome using shotgun sequencing. Periodontal pathogens, namely Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia, and Fusobacterium nucleatum were used as the polymicrobial oral inoculum in BALB/cByJ mice. The polymicrobial infection triggered significant alveolar bone loss, a heightened antibody response, an elevated cytokine immune response, a significant shift in viral diversity and virome composition, and a widening of the PDL space; the latter two findings have not been previously reported in periodontal disease models. Changes in the PDL space were present at sites far away from the site of insult, indicating that the polymicrobial radius of effect extends beyond the bone loss areas and site of initial infection and wider than previously appreciated. Associations were found between bone loss, specific viral and bacterial species, immune genes, and PDL space changes. These findings may have significant implications for the pathogenesis of periodontal disease and biomechanical properties of the periodontium. This new polymicrobial mouse model of periodontal disease in a common mouse strain is useful for evaluating the features of periodontal disease.

Adhesion of composite to enamel and dentin surfaces irradiated by IR laser pulses of 0.5-35 micros duration.

The characteristics of laser-treated tooth surfaces depend on the laser wavelength, pulse duration, spatial and temporal laser beam quality, incident fluence, surface roughness, and the presence of water during irradiation. Ablated surfaces are most commonly restored with adhesive dental materials and the characteristics of the ablated surfaces influence adhesion of restorative materials. Previous studies suggest that high bond strengths can be achieved using shorter laser pulses that minimize peripheral thermal damage. In this study, Er:YSGG, Er:YAG, and CO(2) lasers were used at irradiation intensities sufficient to simulate efficient clinical caries removal to uniformly irradiate bovine enamel and human dentin surfaces using a motion control system with a microprocessor-controlled water spray. The degree of spatial overlap of adjacent pulses was varied so as to investigate the influence of irradiation uniformity and surface roughness on the bond strength. Composite resin was bonded to the irradiated surfaces and shear bond tests were used to obtain bond strengths in MPa. The highest results were obtained using the Er:YAG pulses with pulse durations less than 35 mus without the necessity for postirradiation acid etching. Some of these groups were not significantly different from nonirradiated, acid-etch-only positive control groups.

Imaging caries lesions and lesion progression with polarization sensitive optical coherence tomography.

New diagnostic tools are needed for the characterization of dental caries in the early stages of development. If carious lesions are detected early enough, they can be arrested without the need for surgical intervention. The objective of this study was to demonstrate that polarization sensitive optical coherence tomography (PS-OCT) can be used for the imaging of early caries lesions and for the monitoring of lesion progression over time. High-resolution polarization resolved images were acquired of natural caries lesions and simulated caries lesions of varying severity created over time periods of 1 to 14 days. Linearly polarized light was incident on the tooth samples and the reflected intensity in both orthogonal polarizations was measured. PS-OCT was invaluable for removing the confounding influence of surface reflections and native birefringence necessary for the enhanced resolution of the surface structure of caries lesions. This study demonstrated that PS-OCT is well suited for the imaging of interproximal and occlusal caries, early root caries, and for imaging decay under composite fillings. Longitudinal measurements of the reflected light intensity in the orthogonal polarization state from the area of simulated caries lesions linearly correlated with the square root of time of demineralization indicating that PS-OCT is well suited for monitoring changes in enamel mineralization over time.

Caries inhibition in vital teeth using 9.6-µm CO2-laser irradiation.

The aim of this study was to test the hypothesis that in a short-term clinical pilot trial short-pulsed 9.6 µm CO(2)-laser irradiation significantly inhibits demineralization in vivo. Twenty-four subjects scheduled for extraction of bicuspids for orthodontic reasons (age 14.9 ± 2.2 years) were recruited. Orthodontic brackets were placed on bicuspids (Transbond XT, 3M). An area next to the bracket was irradiated with a CO(2)-laser (Pulse System Inc, Los Alamos, New Mexico), wavelength 9.6 µm, pulse duration 20 µs, pulse repetition rate 20 Hz, beam diameter 1100 µm, average fluence 4.1 ± 0.3J∕cm(2), 20 laser pulses per spot. An adjacent nonirradiated area served as control. Bicuspids were extracted after four and twelve weeks, respectively, for a quantitative assessment of demineralization by cross-sectional microhardness testing. For the 4-week arm the mean relative mineral loss ΔZ (vol% × µm) for the laser treated enamel was 402 ± 85 (mean ± SE), while the control showed significantly higher mineral loss (ΔZ 738 ± 131; P = 0.04, t-test). The difference was even larger after twelve weeks (laser arm ΔZ 135 ± 98; control 1067 ± 254; P = 0.002). The laser treatment produced 46% demineralization inhibition for the 4-week and a marked 87% inhibition for the 12-week arm. This study shows, for the first time in vivo, that the short-pulsed 9.6 µm CO(2)-laser irradiation successfully inhibits demineralization of tooth enamel in humans.

An Automated Digital Microradiography System for Assessing Tooth Demineralization.

Digital Transverse microradiography (TMR) offers several advantages over film based methods including real-time image acquisition, excellent linearity with exposure, and it does not require expensive specialized film. The purpose of this work was to demonstrate that a high-resolution digital microradiography system can be used to measure the volume percent mineral loss for sound and demineralized enamel and dentin thin sections from 150-350-µm in thickness. A custom fabricated digital microradiography system with ~ 2-µm spatial resolution consisting of a digital x-ray imaging camera, a computerized high-speed motion control system and a high-intensity copper Kα; x-ray source was used to determine the volume percent mineral content of sound and demineralized tooth sections. The volume percent mineral loss was compared with cross-sectional microhardness measurements on sound extracted human teeth. The correlation between microhardness and microradiography was excellent (Pr=0.99) for section thickness ranging from 59-319-µm (n=13). The attenuation was linear with varying exposure time from 1-10 seconds. Digital TMR is an effective and rapid method for the assessment of the mineral content of enamel and dentin thin sections.

Dissolution studies of bovine dental enamel surfaces modified by high-speed scanning ablation with a lambda = 9.3-microm TEA CO(2) laser.

BACKGROUND AND OBJECTIVES: Previous studies have demonstrated that lasers can be used to modify the chemical composition of dental enamel to render the mineral phase more resistant to acid dissolution with minimal peripheral thermal damage. Transverse excited atmospheric (TEA) CO(2) lasers tuned to the strong mineral absorption of hydroxyapatite (HAP) near lambda = 9 microm are well-suited for the efficient ablation of dental hard tissues if the laser-pulse is stretched to greater than 5-10 microseconds to avoid plasma shielding phenomena. Moreover, TEA CO(2) lasers can be operated at very high repetition rates and are inherently less expensive and more versatile than Er:YAG and Er:YSGG solid-state lasers. In this study a lambda = 9.3-microm TEA CO(2) with a pulse duration of 8 microseconds and a repetition rate of 300 Hz was used to uniformly treat bovine enamel surfaces at ablative irradiation intensities. We hypothesized that a uniform surface layer of modified enamel of improved crystallinity and CaP phase composition would be formed with an enhanced resistance to acid-dissolution in the ablated areas at higher scanning rates used with the water spray. Such a modified layer of enamel formed at the base and walls of a cavity preparation under the irradiation conditions employed in this study have the potential to inhibit secondary caries under sealants and restorations. STUDY DESIGN/MATERIALS AND METHODS: The surfaces of bovine enamel blocks (3 x 3 mm(2)) were rapidly scanned across the laser beam at rates of 2, 3, and 6 mm/second with and without a water-spray at an incident fluence of 30 J/cm(2). The resistance to acid dissolution was evaluated using controlled surface dissolution experiments on laser-irradiated and control samples. RESULTS: The groups irradiated at a fluence of 30 J/cm(2) with a repetition rate of 300 Hz and a high scan rate of 6 mm/second with and without water-cooling significantly reduced the overall surface dissolution rates (P < 0.001). At low scan rates (2-3 mm/second) excessive heat deposition resulted in the formation of an outer layer of asperities containing non-apatitic CaP phases that were more susceptible to acid-dissolution. At a scanning rate of 6 mm/second even without the water spray a layer of purer phase HAP was formed without thermal damage, indicating that a high scanning rate can be used to avoid excessive thermal damage during ablation. The best results (80% inhibition) were attained for the higher scanning speed 6-mm/second combined with a water spray. CONCLUSION: This study demonstrates that an enamel surface with enhanced resistance to acid dissolution is produced after ablation with lambda = 9.3-microm TEA CO(2) laser pulses delivered at high-repetition rates if sufficiently high scanning rates are used with or without a water-spray.

Influence of an optically thick water layer on the bond-strength of composite resin to dental enamel after IR laser ablation.

BACKGROUND AND OBJECTIVES: Several studies of hard tissue ablation with Er:YAG lasers have shown that the addition of an optically thick water layer ( approximately 1 mm) added to the surface of dental enamel before each incident laser pulse, profoundly influences the rate and efficiency of ablation and the resulting surface morphology. The objective of this study was the determination of laser parameters which result in clinically useful bond strengths without the need for phosphoric acid etching. The hypothesis to be tested was that laser irradiation through a relatively thick layer of water would result in a surface to which composite could be bonded with bond strength similar to surfaces etched with phosphoric acid. This hypothesis is predicated on the assumption that the water prevents the formation of non-apatite calcium phosphate phases on the enamel surface. MATERIALS AND METHODS: In this study, a calibrated syringe pump and a motion control system were used to uniformly treat flat enamel surfaces using free-running Er:YAG laser pulses with and without water, and 9.6 mum CO(2) laser pulses on a dry surface for comparison. The rate of water delivery that resulted in the most efficient ablation was determined by profiling the resulting laser incisions using optical coherence tomography. In addition, enamel surfaces of 5 x 5 mm(2) were uniformly treated and the resulting surface morphology was examined using synchrotron radiation-fourier transform infrared spectroscopy (SR-FTIR), and optical and electron microscopy. The influence of the modified surface morphology on the adhesion of composite resin was investigated. RESULTS: The shear-bond strength of composite bonded to enamel surfaces irradiated at intensities clinically relevant for caries removal approached values measured for conventional acid etching when the water delivery rate was optimized. CONCLUSIONS: This study demonstrates that composite restorative materials can be directly bonded to laser prepared surfaces without the necessity of further surface preparation and acid etching and that the addition of a thick water layer ( approximately 1 mm) prevents the formation of undesirable CaP phases that compromise adhesion to restorative materials. 2003.

Peripheral thermal and mechanical damage to dentin with microsecond and sub-microsecond 9.6 microm, 2.79 microm, and 0.355 microm laser pulses.

BACKGROUND AND OBJECTIVES: It is desirable to minimize peripheral thermal damage during laser irradiation, since thermal damage to collagen and mineral compromises the bond strength to restorative materials in dentin and inhibits healing and osteointegration in bone. There were two primary objectives of this study. The first objective was to measure the degree of thermal damage peripheral to incisions in dentin produced with lasers resonant to the specific absorption bands of water, collagen, and hydroxyapatite with varying pulse duration using polarized-light microscopy (PLM). The second objective was to use synchrotron radiation infrared spectromicroscopy (SR-FTIR) to identify the specific chemical nature of the optical changes observed under PLM in the respective zones of thermal damage peripheral to the laser incisions. STUDY DESIGN/MATERIALS AND METHODS: Precise incisions were produced in 3 x 3 mm2 blocks of human dentin using CO2 (9.6 microm), Er:YSGG (2.79 microm), and Nd:YAG (355 nm) lasers with and without a computer controlled water-spray. Optical coherence tomography (OCT) was used to obtain optical cross-sections of each incision to determine the rate of ablation. The peripheral thermal damage zone around each incision was analyzed using PLM and SR-FTIR. RESULTS: Thermally induced chemical changes to both mineral and the collagen matrix were observed with SR-FTIR with a 10 microm spatial resolution and those changes were correlated with optical changes observed with PLM. Minimal (<10 microm) thermal damage was observed for pulse durations less than the thermal relaxation time (Tr) of the deposited laser energy, with and without applied water at 9.6 microm and with only applied water at 2.79 microm. For pulse durations greater than Tr, greater peripheral thermal damage was observed for both IR laser wavelengths with and without the water-spray. There was minimal thermal damage for 355 nm laser pulses less than Tr with and without applied water; however, extensive mechanical damage (cracks) was observed. CONCLUSIONS: High resolution SR-FTIR is well suited for characterization of the chemical changes that occur due to thermal damage peripheral to laser incisions in proteinaceous hard tissues. Sub-microsecond pulsed IR lasers resonant with water and mineral absorption bands ablate dentin efficiently with minimal thermal damage. Similar laser parameters are expected to apply to the ablation of alveolar bone.

Thermal and chemical modification of dentin by 9-11-microm CO2 laser pulses of 5-100-micros duration.

BACKGROUND AND OBJECTIVES: Previous studies have shown that dentin can be thermally modified by pulsed CO(2) laser irradiation to form a more highly mineralized tissue. The implications are important for the potential laser modification or removal of dentinal and root caries and the transformation of dentin to a more acid resistant mineralized tissue. STUDY DESIGN/MATERIALS AND METHODS: Time resolved radiometry measurements with TEA CO(2) laser pulses were used to determine the magnitude of the absorption coefficients of dentin at the highly absorbed CO(2) laser wavelengths and to measure the temperature excursions during lambda = 9.3, 9.6, 10.3, and 10.6 microm laser irradiation at irradiation intensities of 0.1-8 J/cm(2) per pulse. In addition, photoacoustic and transient reflectance measurements were used to monitor the loss of water and organics and to detect the thresholds for surface modification and tissue ablation. RESULTS: The absorption coefficients were measured to be 5,000; 6,500; 1,200; and 800 cm(-1) at lambda = 9.3, 9.6, 10.3, and 10.6 microm, respectively. The surface temperatures of dentin were markedly higher than those measured on enamel for similar irradiation intensities due to the lower reflectance losses of dentin and the lower thermal diffusivity of dentin at the respective wavelengths. Hence, lower fluences are required for the thermal decomposition of dentin. Ablation typically occurred with the first few laser-pulses during multiple pulse irradiation and eventually ceased after modification of dentin to a more highly mineralized enamel-like tissue. The debris ejected during the initial laser pulses shielded the surface by as much as 60% at the low fluences employed in this study. Optical and electron microscopy and IR spectroscopy indicated that incident laser pulses with incident fluence as low as 0.5 J/cm(2) at 9.3 and 9.6 microm wavelengths with a duration of 5-8-micros were sufficient to induce chemical and morphological changes in dentin. CONCLUSIONS: In this study, the laser parameters for the efficient thermal modification of dentin with minimum heat deposition at CO(2) laser wavelengths were firmly established.

Irradiation of dental enamel with Q-switched lambda = 355-nm laser pulses: surface morphology, fluoride adsorption, and adhesion to composite resin.

BACKGROUND AND OBJECTIVES: Lasers can be used to modify the chemical composition of dental enamel to increase the bond strength to restorative materials and to render the mineral phase more resistant to acid dissolution. Previous studies have suggested a synergistic relationship between CO(2) laser irradiation and fluoride treatment on increased resistance to acid dissolution. In this study a near-UV laser operating with lambda = 355-nm laser pulses of 3-5 nanoseconds duration was used to modify the surface morphology of dental enamel to increase the bond strength to restorative materials and increase the uptake of topical fluoride to render the surface more resistant to acid dissolution. We hypothesize that the short UV laser pulses are primarily absorbed by protein and lipid localized between the enamel prisms resulting in removal of intact mineral effectively etching the surface without thermal modification of the mineral phase. Such modification is likely to increase the permeability of the enamel surface and the subsequent absorption of fluoride. In addition, there is an increase in surface roughness without the formation of a layer of loosely adherent, thermally modified enamel that increases the bond strength to composite restorative materials. STUDY DESIGN/MATERIALS AND METHODS: The surfaces of blocks of bovine enamel, 5 x 5 mm(2), were uniformly irradiated by 355-nm laser pulses and subsequently bonded to composite. The shear bond test was used to assess the bond strength of non-irradiated blocks (negative control), acid etched blocks (positive control), and laser irradiated blocks. The resistance to acid dissolution was evaluated using controlled surface dissolution experiments on irradiated samples, irradiated samples exposed to topical fluoride, and non-irradiated control samples with and without fluoride. RESULTS: The laser surface treatments significantly increased the shear-bond strength of enamel to composite, to a level exceeding 20 MPa which was significantly more than the non-irradiated control samples and significantly less than the acid etch. Laser irradiation alone and topical fluoride application alone did not significantly increase the resistance to acid dissolution. The laser treatment followed by topical application of fluoride significantly increased the resistance to acid dissolution to a level of over 50% versus the control samples. CONCLUSIONS: We present a novel method for increasing bond strength to restorative materials and enhancing fluoride delivery to enamel surfaces and shed some light on the underlying mechanisms of caries inhibition via laser treatment and topical application of fluoride.