1,721,357 research outputs found
Collagen degradation by host-derived enzymes during aging.
No full textIncompletely infiltrated collagen fibrils in acid-etched dentin are susceptible to degradation. We hypothesize that degradation can occur in the absence of bacteria. Partially demineralized collagen matrices (DCMs) prepared from human dentin were stored in artificial saliva. Control specimens were stored in artificial saliva containing proteolytic enzyme inhibitors, or pure mineral oil. We retrieved them at 24 hrs, 90 and 250 days to examine the extent of degradation of DCM. In the 24-hour experimental and 90- and 250-day control specimens, we observed 5- to 6-microm-thick layers of DCM containing banded collagen fibrils. DCMs were almost completely destroyed in the 250-day experimental specimens, but not when incubated with enzyme inhibitors or mineral oil. Functional enzyme analysis of dentin powder revealed low levels of collagenolytic activity that was inhibited by protease inhibitors or 0.2% chlorhexidine. We hypothesize that collagen degradation occurred over time, via host-derived matrix metalloproteinases that are released slowly over time
The use of sealants and fluoride varnish in preventing early childhood caries
No full textEarly Childhood Caries (ECC) is a completely preventable disease but still affecting around half of the preschool children worldwide. ECC often results in pain and infections, which significantly depreciate the children’s quality of life and overall wellbeing. The susceptibility of dental caries varies among children and teeth, and more target-specific and cost-effective caries-preventive measures are essential to combat the problem.
Systematic reviews and meta-analyses conducted in this thesis identified children with existing caries, poor oral hygiene and lower parental education attainment being more susceptible to future caries increment in their primary dentition. The consequence of ECC can be profound and lasting as children with ECC were shown to be 3 times more likely to develop caries in their mixed and permanent dentitions.
Among all primary teeth, the primary second molars (PSMs) have the longest service life for around 10 years. However, they are very vulnerable to caries as their occlusal fissures favour plaque accumulation. A meta-evaluation was performed as part of the thesis to evaluate different fissure sealants and preventive interventions to prevent occlusal caries in molars. Resin-based sealant (RBS) was found to be an effective and cost-saving preventive measure for permanent molars, but a clinically- and cost-effective treatment for the primary molars among preschool children is yet to be identified.
A randomised controlled trial was conducted to compare the clinical efficacies of 5% sodium fluoride varnish (NaFV) and glass-ionomer sealant (GIS) in preventing occlusal caries at PSMs. The cost effectiveness, children behaviours and acceptance towards these two preventive interventions were also evaluated. A total of 736 children were recruited from 18 kindergartens and randomised into either Group 1- receiving NaFV quarterly, or Group 2 - single placement of GIS at baseline. Interventions were performed on 1431 and 1264 PSMs, respectively. The primary outcome was the prevalence of dentinal caries developed at the occlusal surfaces of PSMs over time. By 18 months, 542 children with 1664 PSMs were reviewed. Despite a low GIS retention rate of 5.2% by 18 months, only 12.1% of PSM in GIS group developed dentinal occlusal caries. No significant difference was identified when compared to the proportion of occlusal dentinal decay among PSMs in the NaFV group (15.2%). Regression analysis with GEE revealed that only household income, baseline caries dft scores and plaque levels had a significant influence in the caries progression.
Further cost minimisation analysis suggested that single-placement of GIS is more cost-effective than quarterly-applied NaFV in prevention of occlusal caries. The children’s behaviours changed markedly within and between groups. Bivariate analyses at the 3 review timepoints consistently identified the child past anxiety and cooperation levels being the sole factors influencing their behaviours and cooperation towards upcoming dental examination and preventive treatments.
Quarterly-applied NaFV and single-placement of GIS demonstrated similar clinical efficacies in occlusal caries prevention among preschool children. However, GIS had a lower direct cost and thus being more cost-effective. Further research is required to forage a clinically- and cost-effective treatment to prevent occlusal caries among preschool children, and enhance children’s cooperation and behaviours.published_or_final_versionDentistryDoctoralDoctor of Philosoph
Development of a novel antibacterial quaternary ammonium silane cavity disinfectant
No full textDuring cavity preparations, clinicians have used various disinfectant materials for removal of surface contaminants and biofilms from dentine structure. This thesis consists of studies which examined antimicrobial, cytotoxic, and protease inhibitory properties of a partially condensed Quaternary Ammonium Silane (QAS) cavity disinfectant. The effect of QAS disinfectant on dentine bond durability and nanoleakage of simplified etch-and-rinse adhesives will also be evaluated.
The current project was designed to answer five research questions. The first research question aimed to analyze whether there is antimicrobial efficacy and potency of QAS against Streptococcus mutans with a systematic review. In conclusion, QAS showed antimicrobial efficacy to eliminate Streptococcus mutans.
The effect on host-derived proteases in dentine was conducted to answer the second research question of this project. The percentage of dry mass loss, used as an indirect measurement of dissolution of demineralized dentine matrix by endogenous matrix-bound proteases, increased with time and was significantly lower in the chlorhexidine (CHX) and QAS groups when compared to the control at 14 days. The rate of C-terminal cross-linked telopeptides (ICTP) and C-terminal peptide (CTX) release used to measure degradation of demineralized collagen matrix was lower in the CHX and QAS groups, when compared to the uninhibited control at 7 and 14 days. Dentinal MMP-2 and cathepsin-K activities of CHX and QAS groups were significantly reduced after demineralized dentine was pretreated with QAS. Hence, QAS was shown to be a good inhibitor of MMP and cathepsin-K activities in demineralized dentine.
The third research question investigated the application of QAS on cariogenic biofilm formation and dentine substrate changes onto which multi-species biofilms have been grown using Raman spectroscopy. Confocal laser scanning microscopy showed confluent biofilms in the control group, but increased dead cell count in the QAS groups. Log CFU (single/dual-species) biofilms was lower in the QAS groups than the control. Metabolic activities of biofilms also decreased with increasing QAS exposure time. Increased Raman shifts were seen in functional and aromatic groups of dentine with CH2-1450-1455 cm-1 bending, responding to treatment with shifts at 1450 cm-1, 1453 cm-1, 1457 cm-1, 1460 cm-1 and 1462 cm-1 for the control, 2% CHX, 2%, 5% and 10% QAS specimens. Thus, QAS was shown to possess antimicrobial activities and inhibit the growth of cariogenic biofilms.
The fourth research question was to evaluate the transdentinal cytotoxicity and macrophage phenotype response to QAS. The 2% QAS does not have a cytotoxic effect on 3T3 NIH mouse fibroblast cells and its application is associated with a constructive remodeling effect on macrophages.
The purpose of the last research question was to evaluate whether the application of QAS cavity disinfectant has any effect on long-term dentine bond strength and nanoleakage expression of two simplified etch-and-rinse adhesives. At the end of 12 months, 2% QAS was shown to preserve dentine bond stability and reduce interfacial nanoleakage.
In conclusion, the use of 2% QAS cavity disinfectant preserved dentine bond strength and enhanced bond durability. The cavity disinfectant is not cytotoxic and showed both antibacterial as well as anti-protease properties. (498 words)published_or_final_versionDentistryDoctoralDoctor of Philosoph
Stabilizing the resin : dentin interface of root canals using a novel approach : insights into interfacial integrity
No full textThe dentin is exposed to a wide variety of chemicals during treatment procedures. During root canal treatment, the dentin is exposed to proteolytic chemicals such as sodium hypochlorite and demineralizing chemicals such as ethylene diamine tetraacetic acid, in varying sequences. While these chemicals have largely beneficial effects in terms of dissolution of pulp tissue, hard tissue remnants and microbial biofilms, their non-specific nature is likely to result in untoward effects on the dentin itself.
The exact effects of different chemical sequences on dentin remains unknown: We first reviewed the effects of different clinically relevant chemical treatment sequences on dentin, and found that there was no consensus on how different sequences affect dentin structure and ultrastructure. More importantly, we identified that the effects of some chemical sequences on dentin were not known.
Chemical application sequences have differential effects on dentin collagen, but all sequences have detrimental effects on collagen: We first performed a comprehensive investigation on the effects of different chemical application sequences on the dentin collagen ultrastructure using several qualitative and quantitative analysis, and found that all sequences resulted in exposure of collagen, which was degraded and/or denatured when exposed to the proteolytic sodium hypochlorite.
Dentin biomodification is a potent approach to reinforce and protect collagen: With the understanding that collagen fibres play a pivotal role in the structural integrity of the tooth, and that these fibres are exposed and degraded by the chemicals used during treatment, we reviewed the literature to identify strategies that can “protect” this collagen from future damage by host-derived and bacteria-derived collagenolytic enzymes. Our review showed that while dentin biomodifcation using collagen cross linkers was widely studied in restorative dentistry, a significant body of research was lacking with regards to dentin exposed to chemicals in root canal treatment.
Collagen cross linking and epoxy silanization can protect the dentin collagen from enzymatic damage: In this proof-of-concept study, we demonstrated that collagen cross linking with a common laboratory cross linker and an epoxy silane, can protect the collagen from the activity of collagenolytic enzyme and also maintain/improve the elastic modulus of dentin exposed to the enzyme.
Taken together, the results of our study will help in developing an innovative method that will protect the collagen that was subject to chemically-induced damages and potentially improve the integrity of the resin-dentin interface, which will be investigated in future studies.published_or_final_versionDentistryMasterMaster of Philosoph
Prevention of demineralization during multi-bracketed fixed orthodontic treatment
No full textEnamel demineralization, clinically manifesting as White Spot Lesion (WSL), is an undesirable but frequent after-effect of multi-bracketed fixed orthodontic treatment. The systematic reviews conducted as a part of this thesis identified the potential research gaps regarding the lack of well-controlled clinical trials that have assessed the prevention of WSLs. Thus, a randomized controlled clinical trial was conducted to investigate the efficacy of two different fluoride varnishes in prevention of WSLs during multi-bracketed fixed orthodontic treatment. Ninety-nine patients were randomly allocated into three intervention groups: Group A- routine oral hygiene instructions (OHI); Group B- 3-monthly topical application of 5% Sodium Fluoride (NaF) varnish with routine OHI; and Group C- 3-monthly application of 5% NaF plus tricalcium-phosphate (TCP) varnish with routine OHI. The outcome was assessed at 6-month intervals using quantitative laser fluorescence device, clinical evaluation, and photographic evaluation on six maxillary anterior teeth. Generalized estimating equations with intervention group, time, and their interaction were used to compare occurrence of WSLs, whereas Kruskal-Wallis independent-samples test to compare the means of fluorescent values among different groups at p=0.05. Generalized estimating equations showed that only the effect of time was found to be significant (p<0.001), whereas there was no significant difference among three intervention groups (p=0.305) using clinical assessment or photographic assessment (p=0.599). Three-monthly application of both the study varnishes with OHI has no additional benefit compared to standard OHI alone in preventing WSLs. There were higher odds of developing WSLs with increased duration of orthodontic treatment.
The secondary analysis of the data from the trial aimed to compare the validity of quantitative laser fluorescence and clinical photographs to the visual assessment of WSLs during multi-bracketed fixed orthodontic treatment. A total of 1607 observations of the clinical photographs, visual and laser fluorescent examination from 6-months, 12-months and 18-months follow-ups were used for this investigation. Receiver operating curves were constructed, and areas under the curve (AUC) were calculated for the outcomes at two levels: distinguishing presence/absence of WSLs and distinguishing slight and severe non-cavitated WSLs. Sensitivities and specificities were calculated and AUC for the outcomes at p<0.05 and 95% confidence intervals. The values of sensitivity and specificity of laser fluorescence were found to be good (0.78 and 0.82, respectively) to distinguish the presence/absence of WSLs (AUC= 0.855; 95% CI: 0.820-0.889) and for digital photographs was excellent (AUC= 0.973, 95% CI: 0.956-0.991) with sensitivity and specificity of 0.96 and 0.99, respectively. However, the sensitivity (0.31) and accuracy (AUC= 0.543, 95% CI: 0.418-0.668) of laser fluorescence was poor in delineating slight and severe WSLs; while the value of sensitivity and specificity for this outcome was good for clinical photographs (0.96 and 0.99, respectively) with an excellent accuracy (AUC=0.978, 95% CI: 0.936-1.000). Laser fluorescence and photographs can serve as helpful aid to identify the presence of WSLs around the brackets, although both have their limitations.published_or_final_versionDentistryDoctoralDoctor of Philosoph
Applications of proanthocyanidin in dentistry
No full textIn dentistry, repair and restoration of tooth structure to regain its mechanical properties is the ultimate aim of caries management. Currently, preventive therapies are preferred to operative interference. New preventive approaches are necessary to treat dental caries.
Dentine is composed of an organic matrix, consisting of type 1. Degradation of collagen matrix is the main reason for breakdown of resin-dentine bonds and development of secondary caries over time. Hence, preservation of collagen fibrils is essential for preventive and reparative procedures in minimum intervention dentistry. Proanthocyanidin (PA) is a natural collagen cross-linker, which can be obtained from grape seeds, pine bark or elm tree. It has a high affinity to proline-rich proteins, like collagen. Cross-linking of the collagen fibrils increases their mechanical properties and their resistance to breakdown by proteolytic enzymes.
Thus, in the first part of the study, with the aim of discovering other possible natural dentine collagen cross-linkers, the effect of two smaller molecular size flavonoids, naringin and quercetin, on the mechanical properties of demineralized dentine was compared to PA. Demineralized dentine treated with PA showed the greatest increase in mechanical properties, followed by quercetin and naringin. The protease inhibitory effect of PA was evaluated by examining its actions on soluble and collagen-bound matrix metalloproteinases and cysteine cathepsins. Proanthocyanidin, even at low concentration of 1%, exhibited excellent inhibitory effects on soluble and matrix-bound proteases.
Secondly, PA was incorporated in a dental adhesive to facilitate its application in clinical situations. The effect of PA incorporation on durability of resin-dentine bond was evaluated. Up to 2% of PA could be added to dental adhesive with no adverse effects on immediate resin-dentine bond strength. However, the bond strengths of PA-incorporated adhesives dropped significantly following ageing. This could be attributed to the free radical scavenging effect of PA, which might also have interfered with polymerization of dental adhesive.
The mechanical properties of PA-incorporated adhesive were evaluated and it was shown that up to 1% PA could be incorporated into an adhesive resin. With the addition of higher concentration of PA, the mechanical properties of the adhesive resin were reduced with increased solubility. Proanthocyanidin release from the cured resin showed an initial burst for 48 hours and was stabilized after five days.
Finally, the remineralization potential of PA on artificial root caries was also compared with quercetin and naringin. All three flavonoids showed remineralization potential; however, their effects were inferior to fluoride. Proanthocyanidin formed a precipitate band on the superficial layer of carious lesion, preventing further mineral deposition. Subsequently, PA was incorporated in a CPP-ACFP (casein phosphoproteins amorphous calcium fluorophosphates) containing-paste to increase the mineral uptake in subsurface layer of caries lesion. Simultaneous application of PA and CPP-ACFP was shown to have a favourable outcome on mineral deposition in root caries lesion.published_or_final_versionDentistryDoctoralDoctor of Philosoph
Influence of chemomechanical caries removal methods on dentine
No full textChemomechanical caries excavation is an excellent example of conservative caries removal methods due to its ability to reliably preserve a greater thickness of caries-affected dentine (CAD). Chemomechanical caries removal (CMCR) agents dissolve the denatured collagen fibrils leaving the sound and partially degraded fibrils intact. Also, one of the main advantages of the CMCR method is its characteristic visual excavation end point sign, after this point, the solution fails to become turbid. Chemomechanical caries removal agents are classified based on their chemistry into sodium hypochlorite (NaOCl)- or enzyme-based CMCR agents.
The aim of this project was to evaluate the efficacy of currently available chemomechanical caries removal methods and their effects on tooth substrate, residual bacteria, and bonding to dentine with either resin- or resin-modified glass ionomer (RM-GIC)-based adhesives. The current project was designed to answer five research questions. The first research question aimed to compare the caries excavation time between CMCR and rotary caries removal methods. According to the outcome of this study, the NaOCl-based CMCR method is more time consuming compared with the enzyme-based CMCR method. Furthermore, no significant difference in caries excavation time was found between the enzymebased CMCR and the caries-detector guided rotary caries excavation method.
The second research question investigated the effects of CMCR methods on surface topography, hardness and chemical structure of dentine. The morphological analysis showed that there was no smear layer formed following enzyme-based CMCR; while it was partially absent after the NaOCl-based CMCR method. Also, the Vickers hardness of residual dentine following both CMCR methods was lower than the hardness of dentine following the rotary caries removal method. Moreover, the outcome of this study also revealed that the CMCR methods investigated had no adverse effect on the chemical structure of dentine.
The third research question was regarding the evaluation of the antibacterial effects of CMCR agents. Accordingly, a study was conducted on coronal cariesfree dentine discs using a modified non-invasive protocol. This confocal laser scanning microscopy study reported that the enzyme-based CMCR agent (Papacarie) showed an antimicrobial effect similar to 2% chlorhexidine gluconate solution (gold standard antibacterial solution). The NaOCl-based CMCR agent (Carisolv) showed a weak antibacterial activity, which could be improved by subsequent application of a silver diamine fluoride and potassium iodide agent.
The ‘adhesion studies section’ of this project consists of three studies and was conducted to answer the fourth and fifth research questions of this project. The outcomes of the first and second studies showed that surface treatment of dentine with 37% phosphoric acid for 5 seconds had no adverse effect on bonding of RMGIC adhesives to both sound and caries-affected dentine, which addressed the fourth research question.
The purpose of the last research question was to evaluate the effect of CMCR method on bonding of MDP-containing self-etch and RM-GIC adhesives to residual caries-affected dentine. It was concluded that CMCR methods had no adverse effects on bonding to dentine and both adhesive systems showed good bond strengths to caries-affected dentine.published_or_final_versionDentistryDoctoralDoctor of Philosoph
Co-accomplishing satisfaction : a multivariate investigation into dentist-patient communication
No full textOBJECTIVES: This thesis adopts a multivariate approach to examine perceptions and practices regarding routine dentist-patient interactions in initial consultations.
METHODS: A 16-item Dental Patient Feedback on Consultation skills (DPFC) questionnaire was adapted for use in the dental setting through face, content, and construct validity. A cross-sectional survey (n=389) of patients’ perceptions of their dentist’s clinical performances was conducted in a teaching hospital. Test-retest reliability (n=42) was assessed. Variations in DPFC responses (scale and item level) were examined in relation to socio-demographics and dental attendance patterns in bivariate and regression analyses.
Second tier data was collected in the form of 70 audio-visual recordings (~15 hours) which were transcribed and sequentially analyzed to identify internal structures. Corpus-based discourse and sociolinguistic analysis drawing on traditions of Conversation Analysis, was used to identify dental consultation stages and sequential patterns across turn-taking systems. Transcribed recordings from the top quartile of survey results (n=18) were examined to reveal how dentists and their patients co-accomplished ‘successful’ consultations.
RESULTS: Face validity of the DPFC questionnaire ranged 81.1-100%. Content Validity Index ranged 0.73-1.00. Variations across DPFC scores regarding global ratings of satisfaction were apparent (p<0.001). Cronbach’s alpha value was 0.94 and Intraclass Coefficient Correlation value was 0.89. Results identified that dental attendance pattern was a factor associated with DPFC (p<0.05); but no significant differences were observed regarding socio-demographics.
Corpus-based discourse and sociolinguistic analysis indicated seven specific consultation stages across the 70 recordings. This was divided into two parts by radiographic imaging, namely Part A: Opening, Oral Problem Presentation, Medical History Taking, Oral Examination, Post-examination; and Part B: Diagnosis and Explanation, and Closing.
Sequential analysis of Turn-Constructional Units in the Oral Problem Presentation Stage across the 70 recordings indicated patterns for dentists’ soliciting and patients’ presenting. Dentists solicited patient problems through open-ended questions (n=68) and closed-ended questions (n=2). Patients adopted two oral problem presentation types either using talk with gestures (n=61) or without gestures (n=9). Sequential analysis of the top quartile of recordings (n=18) revealed that patients perceived higher satisfaction with clinical communication if dentists re-visited their oral problems in the Diagnosis and Explanation Stage through a stepwise formulation. This presented as re-visiting patients’ oral problems through either repeating patients’ own terms or repairing patients’ prior talk. Finally, a case is analyzed to examine how a patient perceived effective dentist communication despite receiving a less-than-satisfactory admission outcome.
CONCLUSIONS: The lack of socio-demographic variations in DPFC indicates similar treatment across groups and standardized communication practices by dentists in this public hospital context. Patients with prior dental visits within one year require greater attention in first encounters, possibly due to their recently unresolved oral problems. To enhance the quality of dentist-patient communication, dentists need to attend to patients’ non-verbal signals during talk when presenting oral problems. In identifying how patients and dentists co-accomplish ‘successful’ communication, a clear topical thread connecting patients’ oral problem presentation with the final dentist explanation stages emerged. Empirical findings suggest re-visiting of patients’ oral problems before delivering diagnosis may enhance patient perceptions of ‘successful’ communication in initial consultations.published_or_final_versionDentistryDoctoralDoctor of Philosoph
Arginine-based prebiotic measures for caries prevention
No full textDental caries, a chronic biofilm-mediated disease, is prevalent worldwide. Prevention of oral biofilm-related microbial dysbiosis would probably reduce this disease and its associated global burden. Fluorides (F) have been the mainstay for caries control for decades, inhibiting demineralization and facilitating remineralization. However, it has limited effect on oral biofilms. Wide spread use of F has developed F-resistant strains of S. mutans that further limits its effect on cariogenic biofilms. Prebiotics like arginine exhibits endogenous caries-protective benefits by restoring oral biofilm homeostasis. A novel integrated therapy, by combining the biofilm-modulatory effect of arginine with F, may have a synergistic effect for caries prevention; hence, a series of studies were undertaken to examine the caries-preventive potential of arginine in fluoridated vehicles or with F.
Eight studies were conducted based on findings from 5 systematically conducted reviews. A preliminary study evaluated the reliability of different methods for F detection in low F-containing child-formula dentifrices prior to examining the effect of L-arginine/ L-arginine monohydrochloride (Arg.HCl) on F bioavailability. Three studies comprehensively examined the caries-preventive potential of Arg.HCl in 1100-ppm and 600-ppm NaF dentifrices, respectively. The fifth study examined the effect of incorporating L-arginine/Arg.HCl in 5% NaF varnish on its physical-chemical properties, F/arginine release, remineralization potential and HGF-1 cytotoxicity. The effect of a novel synbiotic utilizing L-arginine and Lactobacillus rhamnosus GG on S. mutans was investigated in the sixth study. Further, the possibility of appending F to the synbiotic for developing synbiotic-F therapy was discerned in the seventh study. Finally, L-arginine was incorporated in glass ionomer cement (GIC) to evaluate the effect on its mechanical properties and antibacterial potential in the eighth study.
The first study showed that 2% arginine improved F bioavailability of the low F-containing child-formula dentifrices. The second and third studies concluded that incorporation of 2% Arg.HCl in 1100-ppm NaF toothpaste enhanced its caries remineralization potential on incipient caries-like lesions and its antimicrobial effect against S. mutans compared to 1100-ppm NaF toothpaste. The fourth study reported that 2% Arg.HCl enhanced the remineralization potential of 600-ppm NaF dentifrice, to a level comparable to 1100-ppm NaF dentifrice. The fifth study showed that incorporation of 2% L-arginine in 5% NaF varnish exhibited good biocompatibility, periodic perennial Arg/F release, with significantly higher F release and remineralization potential than 5% NaF varnish. The sixth study indicated that L-arginine enhanced the growth of L. rhamnosus GG and the combined synbiotic (2% L-arginine and L. rhamnosus GG) synergistically inhibited the growth of S. mutans. Further, the seventh study revealed that the combined synbiotic (2% L-arginine and L. rhamnosus GG) with 2000-ppm NaF provided optimum synbiotic-F synergism for restoring ecological homeostasis. Finally, the eighth study concluded that the addition of 4% L-arginine in GIC enhanced its antibacterial activity via a biofilm modulatory effect for bacterial homeostasis, with no detrimental effect on its mechanical properties.
In conclusion, adding arginine to fluoridated vehicles and probiotics (to develop as a synbiotics) appears a promising ecological-based caries preventive measure.published_or_final_versionPaediatric DentistryDoctoralDoctor of Philosoph
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