C.-Y.S. Hsu

Effects of Low-energy CO2 Laser Irradiation and the Organic Matrix on Inhibition of Enamel Demineralization

In the past two decades, accumulated evidence has clearly demonstrated the inhibitory effects of laser irradiation on enamel demineralization, but the exact mechanisms of these effects remain unclear. The purpose of this study was to investigate the effects of low-energy CO2 laser irradiation on demineralization of both normal human enamel and human enamel with its organic matrix removed. Twenty-four human molars were collected, cleaned, and cut into two halves. One half of each tooth was randomly selected and its lipid and protein content extracted. The other half of each tooth was used as the matched control. Each tooth half had two window areas. All the left windows were treated with a low-energy laser irradiation, whereas the right windows served as the non-laser controls. After caries-like lesion formation in a pH-cycling environment, microradiographs of tooth sections were taken for quantification of demineralization. The mean mineral losses (with standard deviation) of the enamel control, the lased enamel, the non-organic enamel control, and the lased non-organic enamel subgroups were 3955 (1191), 52(49), 4565(1311), and 1191 (940), respectively. A factorial ANOVA showed significant effects of laser irradiation (p = 0.0001), organic matrix (p - 0.0125), and the laser-organic matrix interaction (p = 0.0377). The laser irradiation resulted in a greater than 98% reduction in mineral loss, but the laser effect dropped to about 70% when the organic matrix in the enamel was removed. The results suggest that clinically applicable CO2 laser irradiation may cause an almost complete inhibition of enamel demineralization.

Building Caries Risk Assessment Models for Children

Despite the well-recognized importance of caries risk assessment, practical models remain to be established. This study was designed to develop biopsychosocial models for caries risk assessment in various settings. With a questionnaire, an oral examination, and biological (salivary, microbiological, and plaque pH) tests, a prospective study was conducted among 1782 children aged 3-6 years, with 1576 (88.4%) participants followed in 12 months. Multiple risk factors, indicators, and protective factors were identified. Various risk assessment models were constructed by the random selection of 50% of the cases and further validated in the remaining cases. For the prediction of a “one-year caries increment”, screening models without biological tests achieved a sensitivity/specificity of 82%/73%; with biological tests, full-blown models achieved the sensitivity/specificity of 90%/90%. For identification of a quarter of the children with high caries burden (baseline dmft > 2), a community-screening model requiring only a questionnaire reached a sensitivity/specificity of 82%/81%. These models are promising tools for cost-effective caries control and evidence-based treatment planning. Abbreviations: decayed, missing, filled teeth in primary dentition (dmft); receiver operation characteristics (ROC); relative risk (RR); confidence interval (CI); National Institutes of Health (NIH); World Health Organization (WHO); US Department of Health and Human Services (US/DHHS); American Academy of Pediatric Dentistry (AAPD).

Laser-Matrix-Fluoride Effects on Enamel Demineralization

Laser and fluoride have been shown to inhibit enamel demineralization. However, the role of organic matrix and their interactions remains unclear. This study investigated the interaction among CO2 laser irradiation, fluoride, and the organic matrix on the demineralization of human enamel. Twenty-four molars were selected and cut into halves. One half of each tooth was depleted of its lipid and protein. The other half served as a matched control. Each tooth half had two window areas, treated with a 2.0% NaF gel. All left windows then received a laser treatment. Next, the tooth halves were subjected to a four-day pH-cycling procedure that created caries-like lesions. Tooth sections were cut from the windows, and microradiographs were used for quantification of the demineralization. The combined fluoride-laser treatment led to 98.3% and 95.1% reductions in mineral loss for enamel with and without organic matrix, respectively, when compared with sound enamel.

Behavioral Pathways Explaining Oral Health Disparity in Children

Policymakers’ understanding of and ability to reduce health disparities are pivotal for health promotion worldwide. This study aimed to verify the behavioral pathways leading to oral health disparities. Oral examinations were conducted for 1782 randomly selected preschoolers (3-6 yrs), and 1576 (88.4%) participants were followed up after 12 months. Parents were surveyed on their knowledge (K), attitude (A), and practices (P) regarding their children’s oral health homecare (infant feeding, diet, and oral hygiene) and dental attendance. Structural equation modeling substantiated the links between specific KAs and corresponding practices, while generic KA did not affect practices. KAP pathways partly explained the ethnic and socio-economic disparities in oral health. Deprivation had a direct effect (not mediated by KA) on dental attendance, but not on oral health homecare. Ethnicity directly influenced oral health homecare practices, but not dental attendance. These behavioral pathways, furthering our understanding of health disparity, may have practical implications for health promotion and policy-making.

Potential Mechanism for the Laser-Fluoride Effect on Enamel Demineralization

Laser-induced prevention of dental caries has been studied extensively. However, the cariostatic mechanisms of a combined fluoride-laser treatment are not well-understood. Using micro- computed tomography (micro-CT), we quantified the effect of fluoride and/or Er:YAG laser treatment on enamel demineralization. The mean mineral loss (%/V) for each group was 4,870 ± 1,434 (fluoride followed by laser treatment), 6,341 ± 2,204 (laser treatment), 7,669 ± 2,255 (fluoride treatment), and 10,779 ± 2,936 (control). The preventive effect of the laser (p < 0.001) and fluoride (p = 0.010) treatment was statistically significant. Characterized by micro-x-ray diffraction (XRD) analysis, the significant contraction in the a-axis after both laser and combined laser/fluoride treatment was revealed (both p < 0.05). In conclusion, subablative low-energy Er:YAG laser irradiation following fluoride treatment may instantaneously transform enamel hydroxyapatite into fluoridated hydroxyapatite to reduce enamel solubility as a preventive treatment for enamel demineralization.

Validity of caries risk assessment programmes in preschool children

OBJECTIVES Various programmes have been developed for caries risk assessment (CRA). Nevertheless, scientific evidence on their validity is lacking. This study aimed to compare the validity of 4 CRA programmes (CAT, CAMBRA, Cariogram, and NUS-CRA) in predicting early childhood caries. METHODS A total of 544 children aged 3 years underwent oral examination and biological tests (saliva flow rate, salivary buffering capacity and abundance of cariogenic bacteria mutans Streptococci and Lactobacilli). Their parents completed a questionnaire. Childrens caries risk was predicted using the 4 study programmes without biological tests (screening mode) and with biological tests (comprehensive mode). After 12 months, caries increment in 485 (89%) children was recorded and compared with the baseline risk predictions. RESULTS Reasoning-based programmes (CAT and CAMBRA screening) had high sensitivity (≥ 93.8%) but low specificity (≤ 43.6%) in predicting caries in children. CAMBRA comprehensive assessment reached a better balance (sensitivity/specificity of 83.7%/62.9%). Algorithm-based programmes (Cariogram and NUS-CRA) generated better predictions. The sensitivity/specificity of NUS-CRA screening and comprehensive models were 73.6%/84.7% and 78.1%/85.3%, respectively, higher than those of the Cariogram screening (62.9%/77.9%) and comprehensive assessment (64.6%/78.5%). NUS-CRA comprehensive model met the criteria for a useful CRA tool (sensitivity+specificity ≥ 160%), while its screening model approached that target. CONCLUSIONS Our results supported algorithm-based approach of caries risk modelling and the usefulness of NUS-CRA in identifying children susceptible to caries. CLINICAL SIGNIFICANCE This prospective study provided evidence for practitioners to select tools for assessing childrens caries risk, so that prevention measures can be tailored and treatment plan can be optimised.

Salivary biomarkers for dental caries

As a highly prevalent multifactorial disease, dental caries afflicts a large proportion of the worlds population. As teeth are constantly bathed in saliva, the constituents and properties of this oral fluid play an essential role in the occurrence and progression of dental caries. Various inorganic (water and electrolytes) and organic (proteins and peptides) components may protect teeth from dental caries. This occurs via several functions, such as clearance of food debris and sugar, aggregation and elimination of microorganisms, buffering actions to neutralize acid, maintaining supersaturation with respect to tooth mineral, participation in formation of the acquired pellicle and antimicrobial defense. Modest evidence is available on the associations between dental caries and several salivary parameters, including flow rate, buffering capacity and abundance of mutans streptococci. Despite some controversial findings, the main body of the literature supports an elevated caries prevalence and/or incidence among people with a pathologically low saliva flow rate, compromised buffering capacity and early colonization or high titer of mutans streptococci in saliva. The evidence remains weak and/or inconsistent on the association between dental caries and other saliva parameters, such as other possible cariogenic species (Lactobacillus spp., Streptococcus sanguis group, Streptococcus salivarius, Actinomyces spp. and Candida albicans), diversity of saliva microbiomes, inorganic and organic constituents (electrolytes, immunoglobulins, other proteins and peptides) and some functional properties (sugar clearance rate, etc.). The complex interactions between salivary components and functions suggest that saliva has to be considered in its entirety to account for its total effects on teeth.

Subablative Er:YAG Laser Effect on Enamel Demineralization

Objectives: To characterize the cariostatic potential of a low-energy Er:YAG laser treatment. Methods: Twelve sound premolars were selected. Two 2 × 1 mm windows were created on each tooth and randomly assigned to L1 and L2 groups. Three sites in each window were chosen with the middle site as the control and the left and right ones receiving Er:YAG laser treatment of 5.1 J/cm2 (L1) or 2.0 J/cm2 (L2), respectively. The teeth were further subjected to 4-day pH cycling to create caries-like lesions. After mineral quantification using a micro-computed tomography scanner, the preventive effects (ΔML = mineral loss of the control area minus that of the lased area) of L1 and L2 treatments were calculated based on the difference in the gray value of the control and lased sites. Results: Significant inhibitory effects of L1 and L2 on enamel demineralization were demonstrated (both p ≤ 0.001), with the L1 treatment having a greater effect (45.2%) than the L2 treatment (25.2%, p = 0.004). Conclusions: Subablative low-energy Er:YAG laser irradiation can significantly prevent enamel demineralization potentially through the retardation of enamel diffusion. This study confirmed that high-energy laser treatment, which may damage the peripheral and underlying tissues, may not be needed for caries prevention.

Polarization-resolved hyperspectral stimulated Raman scattering microscopy for label-free biomolecular imaging of the tooth

We report the development and implementation of a rapid polarization-resolved hyperspectral stimulated Raman scattering (SRS) microscopy technique for label-free biomolecular imaging of the tooth. The hyperspectral SRS imaging technique developed covers both fingerprint (800–1800 cm−1) and high-wavenumber (2800–3600 cm−1) regions for tooth Raman imaging without fluorescence background interference with an imaging speed of 106 faster than confocal Raman imaging. Significant differences of hyperspectral SRS spectra among different tooth locations (e.g., dentin, enamel, and dentin-enamel junction) are observed, revealing the biochemical distribution differences across the tooth. Further polarization-resolved SRS imaging shows different polarization dependences related to the molecular orientation differences of various tooth locations. This work demonstrates the potential of polarization-resolved hyperspectral SRS imaging technique developed i...

Thermal Treatments Modulate Bacterial Adhesion to Dental Enamel

Numerous studies have demonstrated the effects of laser-induced heat on demineralization of enamel; however, no studies have investigated the link between heat/laser-induced changes in physicochemical properties and bacterial adhesion. In this study, we investigated the effects of thermal treatment on surface properties of enamel such as hydrophobicity and zeta potential. Bacterial adhesion to treated surfaces was characterized by confocal laser scanning microscopy, and adhesion force was quantified by atomic force microscopy. The hydrophobicity of enamel increased after heating (p < 0.05), and the zeta potential of heated enamel became more negative than that of the control (p < 0.01). Streptococcus oralis and S. mitis were more hydrophilic than S. sanguis, with more negative zeta potential (all p < 0.01). S. mitis and S. oralis occupied significantly less area on enamel after being heated (p < 0.05). Heating reduced the adhesion force of both S. mitis and S. oralis to enamel with or without saliva coating. Reduction of adhesion force was statistically significant for S. mitis (p < 0.01), whereas that of S. oralis was not statistically significant (p > 0.05). Heating did not affect the adhesion of S. sanguis with or without saliva coating. In conclusion, thermal treatment and photothermal/laser treatments may modulate the physicochemical properties of enamel, preventing the adhesion of some bacterial species.