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Journal of dentistry  2013;41(12):10.1016/j.jdent.2013.10.007.
Clinical data on survival rates reveal that all-ceramic dental prostheses are susceptible to fracture from repetitive occlusal loading. The objective of this review is to examine the underlying mechanisms of fatigue in current and future dental ceramics.
The nature of various fatigue modes is elucidated using fracture test data on ceramic layer specimens from the dental and biomechanics literature.
Failure modes can change over a lifetime, depending on restoration geometry, loading conditions and material properties. Modes that operate in single-cycle loading may be dominated by alternative modes in multi-cycle loading. While post-mortem examination of failed prostheses can determine the sources of certain fractures, the evolution of these fractures en route to failure remains poorly understood. Whereas it is commonly held that loss of load-bearing capacity of dental ceramics in repetitive loading is attributable to chemically-assisted 'slow crack growth' in the presence of water, we demonstrate the existence of more deleterious fatigue mechanisms, mechanical rather than chemical in nature. Neglecting to account for mechanical fatigue can lead to gross overestimates in predicted survival rates.
Clinical significance
Strategies for prolonging the clinical lifetimes of ceramic restorations are proposed based on a crack-containment philosophy.
PMCID: PMC3877306  PMID: 24135295
dental ceramics; fatigue; fracture modes; lifetime; crowns; fixed-partial dentures
2.  Reusing Electronic Patient Data for Dental Clinical Research: A Review of Current Status 
Journal of dentistry  2013;41(12):1148-1163.
PMCID: PMC4141471  PMID: 23603087
dental records; dental informatics; electronic health records; medical records systems; computerized; clinical research; review
3.  Purpose, structure, and function of the United States National Dental Practice-Based Research Network 
Journal of dentistry  2013;41(11):10.1016/j.jdent.2013.04.002.
Following a successful2005–2012 phase with three regional practice-based research networks (PBRNs), a single, unified national network called “The National Dental PBRN” was created in 2012 in the United States to improve oral health by conducting practice-based research and serving dental professionals through education and collegiality.
Central administration is based in Alabama. Regional centres are based in Alabama, Florida, Minnesota, Oregon, New York and Texas, with a Coordinating Centre in Maryland. Ideas for studies are prioritized by the Executive Committee, comprised mostly of full-time clinicians.
To date, 2736 persons have enrolled, from all six network regions; enrollment continues to expand. They represent a broad range of practitioners, practice types, and patient populations. Practitioners are actively improving every step of the research process, from idea generation, to study development, field testing, data collection, and presentation and publication.
Practitioners from diverse settings are partnering with fellow practitioners and academics to improve clinical practice and meet the needs of clinicians and their patients.
Clinical significance
This “nation’s network” aims to serve as a precious national resource to improve the scientific basis for clinical decision-making and foster movement of the latest evidence into routine practice.
PMCID: PMC3812393  PMID: 23597500
Practice-based research; Dentistry; Primary care; Health services research; Multi-centre studies
4.  Anatomy of Sodium Hypochlorite Accidents Involving Facial Ecchymosis – A Review 
Journal of dentistry  2013;41(11):10.1016/j.jdent.2013.08.012.
Root canal treatment forms an essential part of general dental practice. Sodium hypochlorite (NaOCl) is the most commonly used irrigant in endodontics due to its ability to dissolve organic soft tissues in the root canal system and its action as a potent antimicrobial agent. Although NaOCl accidents created by extrusion of the irrigant through root apices are relatively rare and are seldom life-threatening, they do create substantial morbidity when they occur.
To date, NaOCl accidents have only been published as isolated case reports. Although previous studies have attempted to summarise the symptoms involved in these case reports, there was no endeavor to analyse the distribution of soft tissue distribution in those reports. In this review, the anatomy of a classical NaOCl accident that involves facial swelling and ecchymosis is discussed.
By summarising the facial manifestations presented in previous case reports, a novel hypothesis that involves intravenous infusion of extruded NaOCl into the facial vein via non-collapsible venous sinusoids within the cancellous bone is presented.
Understanding the mechanism involved in precipitating a classic NaOCl accident will enable the profession to make the best decision regarding the choice of irrigant delivery techniques in root canal débridement, and for manufacturers to design and improve their irrigation systems to achieve maximum safety and efficient cleanliness of the root canal system.
PMCID: PMC3824250  PMID: 23994710
central venous pressure; ecchymosis; facial vein; intraosseous space; positive fluid pressure; root canal treatment; sodium hypochlorite
5.  Time-kill behavior against eight bacterial species and cytotoxicity of antibacterial monomers 
Journal of dentistry  2013;41(10):10.1016/j.jdent.2013.07.006.
The objectives of this study were to investigate: (1) the antibacterial activity of two antibacterial monomers, dimethylaminododecyl methacrylate (DMADDM) and dimethylammoniumethyl dimethacrylate (DMAEDM), against eight different species of oral pathogens for the first time; (2) the cytotoxicity of DMAEDM and DMADDM.
DMAEDM and DMADDM were synthesized by reacting a tertiary amine group with an organo-halide. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against eight species of bacteria were tested. Time-kill determinations were performed to examine the bactericidal kinetics. Cytotoxicity of monomers on human gingival fibroblasts (HGF) was assessed using a methyl thiazolyltetrazolium assay and live/dead viability assay.
DMADDM showed strong bactericidal activity against all bacteria, with MIC of 1.2 to 9.8μg/mL. DMAEDM had MIC of 20 to 80mg/mL. Time-kill determinations indicated that DMADDM and DMAEDM had rapid killing effects against eight species of bacteria, and eliminated all bacteria in 30min at the concentration of 4-fold MBC. Median lethal concentration for DMADDM and DMAEDM was between 20 to 40μg/mL, which was 20-fold higher than 1 to 2μg/mL for BisGMA control.
DMAEDM and DMADDM were tested in time-kill assay against eight species of oral bacteria for the first time. Both were effective in bacteria-inhibition, but DMADDM had a higher potency than DMAEDM. Different killing efficacy was found against different bacteria species. DMAEDM and DMADDM had much lower cytotoxicity than BisGMA. Therefore, DMADDM and DMAEDM are promising for use in bonding agents and other restorative/preventive materials to combat a variety of oral pathogens.
PMCID: PMC3845446  PMID: 23876930
Antibacterial activity; cytotoxicity; oral bacteria; quaternary ammonium methacrylate; time-kill; human fibroblasts
6.  Agreement among dentists’ restorative treatment planning thresholds for primary occlusal caries, primary proximal caries, and existing restorations: Findings from The National Dental Practice-Based Research Network 
Journal of dentistry  2013;41(8):718-725.
The aim of this study was to quantify the agreement among individual National Dental Practice-Based Research Network dentists’ self-reported treatment decisions for primary occlusal caries, primary proximal caries, and existing restorations.
Five hypothetical clinical scenarios were presented: primary occlusal caries; primary proximal caries; and whether three existing restorations should be repaired or replaced. We quantified the probability that dentists who recommended later restorative intervention for primary caries were the same ones who recommended that existing restorations be repaired instead of replaced.
Dentists who recommended later restorative treatment of primary occlusal caries and proximal caries at a more-advanced stage were significantly more likely to recommend repair instead of replacement. Agreement among dentists on a threshold stage for the treatment of primary caries ranged from 40 to 68%, while that for repair or replacement of existing restorations was 36 to 43%.
Dentists who recommended repair rather than replacement of existing restorations were significantly more likely to recommend later treatment of primary caries. Conversely, dentists who recommended treatment of primary caries at an earlier stage were significantly more likely to recommend replacement of the entire restoration. Between-dentist agreement for primary caries treatment was better than between-dentist agreement for repair or replacement of existing restorations.
Clinical implications
These findings suggest consistency in how individual dentists approach the treatment of primary caries and existing restorations. However, substantial variation was found between dentists in their treatment decisions about the same teeth.
PMCID: PMC3788573  PMID: 23743181
Primary caries; Restoration repair/replacement; Decision-making; Health services research
7.  Cost-effectiveness of silicone and alginate impressions for complete dentures 
Journal of Dentistry  2014;42(8):902-907.
The aim of this study was to assess the cost effectiveness of silicone and alginate impressions for complete dentures.
Cost effectiveness analyses were undertaken alongside a UK single centre, double blind, controlled, crossover clinical trial. Taking the perspective of the healthcare sector, effectiveness is measured using the EuroQol (EQ-5D-3L) which provides a single index value for health status that may be combined with time to produce quality adjusted life years (QALYs); and Oral Health Impact Profile (OHIP-EDENT). Incremental cost effectiveness ratios are presented representing the additional cost per one unit gained.
Mean cost was higher in the silicone impression group (£388.57 vs. £363.18). Negligible between-group differences were observed in QALY gains; the silicone group had greater mean OHIP-EDENT gains. The additional cost using silicone was £3.41 per change of one point in the OHIP-EDENT.
The silicone group was more costly, driven by the cost of materials. Changes in the EQ-5D and QALY gains over time and between arms were not statistically significant. Change in OHIP-EDENT score showed greater improvement in the silicone group and the difference between arms was statistically significant. Given negligible QALY gains and low level of resource use, results must be treated with caution. It is difficult to make robust claims about the comparative cost-effectiveness.
Clinical significance
Silicone impressions for complete dentures improve patients’ quality of life (OHIP-EDENT score). The extra cost of silicone impressions is £30 per patient. Dentists, patients and health care funders need to consider the clinical and financial value of silicone impressions. Different patients, different dentists, different health funders will have individual perceptions and judgements.
NIHR-RfPB grant PB-PG-0408-16300.

This article forms part of a project for which the author (TPH) won the Senior Clinical Unilever Hatton Award of the International Assocation for Dental Research, Capetown, South Africa, June 2014.
PMCID: PMC4119300  PMID: 24995472
Prosthodontics; Quality-of life; Impression materials; Cost effectiveness; Cost; Resource
8.  A Randomised Controlled Trial of complete denture impression materials 
Journal of Dentistry  2014;42(8):895-901.
There is continuing demand for non-implant prosthodontic treatment and yet there is a paucity of high quality Randomised Controlled Trial (RCT) evidence for best practice. The aim of this research was to provide evidence for best practice in prosthodontic impressions by comparing two impression materials in a double-blind, randomised, crossover, controlled, clinical trial.
Eighty-five patients were recruited, using published eligibility criteria, to the trial at Leeds Dental Institute, UK. Each patient received two sets of dentures; made using either alginate or silicone impressions. Randomisations determined the order of assessment and order of impressions. The primary outcome was patient blinded preference for unadjusted dentures. Secondary outcomes were patient preference for the adjusted dentures, rating of comfort, stability and chewing efficiency, experience of each impression, and an OHIP-EDENT questionnaire.
Seventy-eight (91.8%) patients completed the primary assessment. 53(67.9%) patients preferred dentures made from silicone impressions while 14(17.9%) preferred alginate impressions. 4(5.1%) patients found both dentures equally satisfactory and 7 (9.0%) found both equally unsatisfactory. There was a 50% difference in preference rates (in favour of silicone) (95%CI 32.7–67.3%, p < 0.0001).
There is significant evidence that dentures made from silicone impressions were preferred by patients.
Clinical significance
Given the strength of the clinical findings within this paper, dentists should consider choosing silicone rather than alginate as their material of choice for secondary impressions for complete dentures.
Trial Registration: ISRCTN 01528038.

This article forms part of a project for which the author (TPH) won the Senior Clinical Unilever Hatton Award of the International Assocation for Dental Research, Capetown, South Africa, June 2014.
PMCID: PMC4119301  PMID: 24995473
Prosthodontics; Quality-of life; Patient outcomes; Impression materials; Edentulous; Removable prosthodontics
9.  Effect of water-ageing on dentine bond strength and anti-biofilm activity of bonding agent containing new monomer dimethylaminododecyl methacrylate 
Journal of dentistry  2013;41(6):504-513.
The objectives of this study were to develop bonding agent containing a new antibacterial monomer dimethylaminododecyl methacrylate (DMADDM) as well as nanoparticles of silver (NAg) and nanoparticles of amorphous calcium phosphate (NACP), and to investigate the effects of water-ageing for 6 months on dentine bond strength and anti-biofilm properties for the first time.
Four bonding agents were tested: Scotchbond Multi-Purpose (SBMP) Primer and Adhesive control; SBMP + 5% DMADDM; SBMP + 5% DMADDM + 0.1% NAg; and SBMP + 5% DMADDM + 0.1% NAg with 20% NACP in adhesive. Specimens were water-aged for 1 d and 6 months at 37 °C. Then the dentine shear bond strengths were measured. A dental plaque microcosm biofilm model was used to inoculate bacteria on water-aged specimens and to measure metabolic activity, colony-forming units (CFUs), and lactic acid production.
Dentine bond strength showed a 35% loss in 6 months of water-ageing for SBMP control (mean ± sd; n = 10); in contrast, the new antibacterial bonding agents showed no strength loss. The DMADDM–NAg–NACP containing bonding agent imparted a strong antibacterial effect by greatly reducing biofilm viability, metabolic activity and acid production. The biofilm CFU was reduced by more than two orders of magnitude, compared to SBMP control. Furthermore, the DMADDM–NAg–NACP bonding agent exhibited a long-term antibacterial performance, with no significant difference between 1 d and 6 months (p > 0.1).
Incorporating DMADDM–NAg–NACP in bonding agent yielded potent and long-lasting antibacterial properties, and much stronger bond strength after 6 months of water-ageing than a commercial control. The new antibacterial bonding agent is promising to inhibit biofilms and caries at the margins. The method of DMADDM–NAg–NACP incorporation may have a wide applicability to other adhesives, cements and composites.
PMCID: PMC3751171  PMID: 23583528
Antibacterial primer and adhesive; Long-term water-ageing; Dentine bond strength; Quaternary ammonium; methacrylate; Human saliva microcosm biofilm; Caries inhibition
10.  Proanthocyanidins’ efficacy in stabilizing dentin collagen against enzymatic degradation: MALDI-TOF and FTIR analyses 
Journal of dentistry  2013;41(6):535-542.
To investigate grape seed extract proanthocyanidins’ (PA) capability in improving dentin collagen’s sustainability in an enzymatic environment, given that the size and shape of the collagen samples, and the manner to apply PA are both clinically relevant.
Human dentin was sectioned into 6-μm-thick films. After demineralization in 35 wt% phosphoric acid for 15 s, the films were subject to 30 s of treatment at PA concentrations of 0% (control), 0.5%, 1%, 2%, 3.75%, 7.5% and 15% (w/w), respectively. The films were then digested in 0.1 wt% collagenase for 1 h and 24 h. The amount of degraded collagen in the liquid digests was determined by MALDI-TOF mass spectroscopy. The trend of PA’s incorporation into dentin collagen was analyzed by ATR-FTIR.
The control exhibited complete digestion in 1 h. In contrast, collagen treated with 0.5% and 1% PA afforded 13.84 ± 4.69% and an undetectable level of degradation, respectively in the first 1 h of digestion, and additional 17.48 ± 4.38% and 4.50 ± 1.68%, respectively in the following 23 h. Collagen treated with ≥2 wt% PA was not significantly digested regardless of digestion time. FTIR spectroscopy revealed that PA incorporation was saturated at ≥2 wt% PA.
Thirty seconds of PA treatment at 2 wt% and above could provide optimal protection for dentin collagen against collagenase digestion.
Clinical significance
This study demonstrated PA’s extraordinary efficiency in stabilizing demineralized dentin collagen when it is applied in a clinical relevant manner, and identified the optimal conditions for its utilization.
PMCID: PMC3661005  PMID: 23578472
Dentin collagen; Proanthocyanidins; Collagenase digestion; MALDI-TOF; ATR-FTIR
11.  Measuring the Impact of Practice-based Research Networks on Member Dentists in the Collaboration on Networked Dental and Oral Health Research, CONDOR 
Journal of dentistry  2013;41(5):10.1016/j.jdent.2013.03.005.
The National Institute of Dental and Craniofacial Research funded three practice-based research networks (PBRNs), NW-PRECEDENT, PEARL and DPBRN to conduct studies relevant to practicing general dentists. These PBRNs collaborated to develop a questionnaire to assess the impact of network participation on changes in practice patterns. This report presents results from the initial administration of the questionnaire.
Questionnaires were administered to network dentists and a non-network reference group. Practice patterns including caries diagnosis and treatment, pulp cap materials, third molar extraction, dentin hypersensitivity treatments and endodontic treatment and restoration were assessed by network, years in practice, and level of network participation.Test-retest reliability of the questionnaire was evaluated.
950 practitioners completed the questionnaire. Test-retest reliability was good-excellent (kappa>0.4) for most questions. Significant differences in responses by network were not observed. The use of caries risk assessment forms differed by both network participation (p<0.001) and years since dental degree (p=0.026). Recent dental graduates are more likely to recommend third molar removal for preventive reasons (p=0.003).
Practitioners in the CONDOR research networks are similar to their US colleagues. As a group, however, these practitioners show a more evidence-based approach to their practice. Dental PBRNs have the potential to improve the translation of evidence into daily practice. Designing methods to assess practice change and the associated factors is essential to addressing this important issue.
PMCID: PMC3825028  PMID: 23562351
dental practice-based research networks; behavior change; practice impact
12.  How can sensitive dentine become hypersensitive and can it be reversed? 
Journal of dentistry  2013;41(0 4):S49-S55.
This paper reviews a number of studies in oral biology and endodontics that deal with the reactivity of the pulpo-dentine complex in response to mechanical and immunological stimuli. It can be hypothesized that these reactions could also apply to changes in dentine sensitivity following periodontal procedures. Some of these changes involve neurogenic inflammation of the pulp under exposed open tubules; this increases the rate of outward fluid flow through the tubules, making the overlying exposed dentine more sensitive. Other changes may be due to inflammation-related nerve sprouting of pulpal nerves, which can lead to innervation ofmore tubules than normal. Changes may also involve upregulation of new, more sensitive ion channels in the membranes of these nerves.
The goal of the paper is to increase awareness of the issues involved in dentine sensitivity, so that future investigators may develop agents or techniques to stimulate mechanisms that mitigate dentine sensitivity or to block mechanisms that aggravate the condition, for therapeutic effect.
PMCID: PMC3988497  PMID: 23929645
Dentine sensitivity; pulpal reaction
13.  Effect of application mode on interfacial morphology and chemistry between dentin and self-etch adhesives 
Journal of dentistry  2012;41(3):231-240.
To investigate the influence of application mode on the interfacial morphology and chemistry between dentin and self-etch adhesives with different aggressiveness.
The occlusal one-third of the crown was removed from un-erupted human third molars, followed by abrading with 600 grit SiC under water. Rectangular dentin slabs were prepared by sectioning the tooth specimens perpendicular to the abraded surfaces. The obtained dentin slabs were treated with one of the two one-step self-etch adhesives: Adper Easy Bond (AEB, PH~2.5) and Adper Prompt L-Pop (APLP, PH~0.8) with (15s, active application) or without (15s, inactive application) agitation. The dentin slabs were fractured and the exposed adhesive/dentin (A/D) interfaces were examined with micro-Raman spectroscopy and scanning electron microscopy (SEM).
The interfacial morphology, degree of dentin demineralization (DD) and degree of conversion (DC) of the strong self-etch adhesive APLP showed more significant dependence on the application mode than the mild AEB. APLP exhibited inferior bonding at the A/D interface if applied without agitation, evidenced by debonding from the dentin substrate. The DDs and DCs of the APLP with agitation were higher than those of without agitation in the interface, in contrast to the comparable DD and DC values of two AEB specimen groups with different application modes. Raman spectral analysis revealed the important role of chemical interaction between acid monomers of self-etch adhesives and dentin in the above observations.
The chemical interaction with dentin is especially important for improving the DC of the strong self-etching adhesive at the A/D interface. Agitation could benefit polymerization efficacy of the strong self-etch adhesive through enhancing the chemical interaction with tooth substrate.
PMCID: PMC3593798  PMID: 23153573
self-etch adhesives; degree of conversion; micro-Raman; agitation; adhesive/dentin interface
14.  Effect of proanthocyanidins and photo-initiators on photo-polymerization of a dental adhesive 
Journal of dentistry  2012;41(1):71-79.
To evaluate the effects of proanthocyanidins (PA) and photoinitiator type on the degree of conversion (DC) and polymerization rate (PR) of a model dental adhesive.
Three types of photo-initiation systems were introduced into the Bis-GMA/HEMA co-monomer mixture, resulting in four resin formulations including CQ/A (0.5 wt% CQ and EDMAB), CQ/A/I-1 (0.5 wt% CQ, EDMAB and DPIHP), CQ/A/I-2 (1.0 wt% CQ, EDMAB and DPIHP), and TPO (2.1 wt% TPO). For each resin formulation, adhesives containing 0, 2.5%, 5% and 10% of PA with respect to the weight of resin were produced after mixing the resin with various amount of PA/ethanol solution. When light-cured, the RP and DC of each adhesive was determined using ATR- FTIR spectroscopy.
Across and within the initiator groups, the DC followed the general trend of CQ/A < CQ/A/I-1 < CQ/A/I-2 < TPO and 0-PA > 2.5-PA > 5-PA > 10-PA, respectively. The change of PR with respect to photo-initiation systems and PA content was in a similar but less pronounced pattern.
PA hampered the polymerization of all adhesives regardless of photoinitiators used. The initiator formulations CQ/A/I-2 and TPO are better fit for PA-containing adhesives, both leading to > 65% DC in the presence of 5% PA.
Clinical significance
The inclusion of PA in dental adhesives has been limited by its interference with the light-curing of adhesive resins. This study found photo-initiation formulations that could maintain a satisfactory degree of monomer conversion while a significant amount of PA is incorporated.
PMCID: PMC3570613  PMID: 23079281
Dental adhesive; Proanthocyanidins; Degree of conversion; ATR-FTIR
15.  The anti-MMP activity of benzalkonium chloride 
Journal of dentistry  2010;39(1):10.1016/j.jdent.2010.10.003.
This study evaluated the ability of benzalkonium chloride (BAC) to bind to dentine and to inhibit soluble recombinant MMPs and bound dentine matrix metalloproteinases (MMPs).
Dentine powder was prepared from extracted human molars. Half was left mineralized; the other half was completely demineralized. The binding of BAC to dentine powder was followed by measuring changes in the supernatant concentration using UV spectrometry. The inhibitory effects of BAC on rhMMP-2, -8 and -9 were followed using a commercially available in vitro proteolytic assay. Matrix-bound endogenous MMP-activity was evaluated in completely demineralized beams. Each beam was either dipped into BAC and then dropped into 1 mL of a complete medium (CM) or they were placed in 1 mL of CM containing BAC for 30 d. After 30 d, changes in the dry mass of the beams or in the hydroxyproline (HYP) content of hydrolyzates of the media were quantitated as indirect measures of matrix collagen hydrolysis by MMPs.
Demineralized dentine powder took up 10-times more BAC than did mineralized powder. Water rinsing removed about 50% of the bound BAC, while rinsing with 0.5 M NaCl removed more than 90% of the bound BAC. BAC concentrations 0.5 wt% produced 100% inhibition of soluble recombinant MMP-2, -8 or -9, and inhibited matrix-bound MMPs between 55-66% when measured as mass loss or 76-81% when measured as solubilization of collagen peptide fragments.
BAC is effective at inhibiting both soluble recombinant MMPs and matrix-bound dentine MMPs in the absence of resins.
PMCID: PMC3866626  PMID: 20951183
MMPs; dentine; benzalkonium chloride; binding
16.  Zinc reduces collagen degradation in demineralized human dentin explants 
Journal of dentistry  2010;39(2):10.1016/j.jdent.2010.11.005.
PMCID: PMC3847813  PMID: 21108986
17.  Dental plaque microcosm response to bonding agents containing quaternary ammonium methacrylates with different chain lengths and charge densities 
Journal of dentistry  2013;41(11):10.1016/j.jdent.2013.08.003.
Antibacterial bonding agents are promising to combat bacteria and caries at tooth-restoration margins. The objectives of this study were to incorporate new quaternary ammonium methacrylates (QAMs) to bonding agent and determine the effects of alkyl chain length (CL) and quaternary amine charge density on dental plaque microcosm bacteria response for the first time.
Six QAMs were synthesized with CL = 3, 6, 9, 12, 16, 18. Each QAM was incorporated into Scotchbond Multi-purpose (SBMP). To determine the charge density effect, dimethylaminododecyl methacrylate (DMAHDM, CL = 16) was mixed into SBMP at mass fraction = 0%, 2.5%, 5%, 7.5%, 10%. Charge density was measured using a fluorescein dye method. Dental plaque microcosm using saliva from ten donors was tested. Bacteria were inoculated on resins. Early-attachment was tested at 4 hours. Biofilm colony-forming units (CFU) were measured at 2 days.
Incorporating QAMs into SBMP reduced bacteria early-attachment. Microcosm biofilm CFU for CL = 16 was 4 log lower than SBMP control. Charge density of bonding agent increased with DMAHDM content. Bacteria early-attachment decreased with increasing charge density. Biofilm CFU at 10% DMAHDM was reduced by 4 log. The killing effect was similarly-strong against total microorganisms, total streptococci, and mutans streptococci.
Increasing alkyl chain length and charge density of bonding agent was shown for the first time to decrease microcosm bacteria attachment and reduce biofilm CFU by 4 orders of magnitude. Novel antibacterial resins with tailored chain length and charge density are promising for wide applications in bonding, cements, sealants and composites to inhibit biofilms and caries.
PMCID: PMC3845448  PMID: 23948394
Antibacterial bonding agent; Alkyl chain length; Quaternary amine charge density; Dental plaque microcosm biofilm; Caries inhibition
18.  Immunohistochemical and biochemical assay of MMP-3 in human dentin 
Journal of dentistry  2011;39(3):10.1016/j.jdent.2011.01.001.
The function of endogenous MMP-3 and its distribution within the human dentin is unclear. Thus, the aim of the present study was to assay the presence and distribution of MMP-3 within human sound dentin by means of biochemical and immunohistochemical assays.
Powdered dentin from extracted human teeth was prepared and 1) partially demineralized with 1% H3PO4 for 10 min or 2) untreated (control). The presence of MMP-3 was measured using a colorimetric assay system (QuantisirTM, Epigentek, USA). Additional cryo-fractured dentin fragments were processed for immunohistochemical identification of MMP-3 under FEI-SEM. Casein-zymography was used to investigate MMP-3 activity.
MMP-3 detected level was 2.732 ng/µL in partially demineralized dentin powder, while it increased to 3.280 ng/µL in mineralized dentin. The FEI-SEM analysis revealed positive immunolabeling patterns for MMP-3, predominantly localized on the intertubular collagen fibrillar network showing MMP-3 directly or indirectly bound to the collagen fibrils. Casein-zymograms showed positive proteolytic activity for MMP-3 in demineralized dentin powder.
The results of the study clearly revealed the presence and distribution of MMP3 in human sound dentin. While the presence was verified, its role is still unclear. Future studies are needed to investigate the possible involvement of MMP-3 in physiological and pathological condition of the dentin-pulp complex.
PMCID: PMC3815524  PMID: 21215789
MMP-3; dentin; dentin bonding agent; biochemical assay; immunohistochemistry
19.  Hydroxyapatite Effect on Photopolymerization of Self-etching Adhesives with Different Aggressiveness 
Journal of Dentistry  2012;40(7):564-570.
To understand the correlation of the acidic monomer/hydroxyapatite (HAp) reaction with the photopolymerization behavior of self-etching adhesives with different aggressiveness.
Two commercial self-etching adhesives the strong Adper Prompt L-Pop (APLP, pH~0.8) and the mild Adper Easy Bond (AEB, pH~2.5) were used. HAp powders were incorporated into both adhesives to acquire solutions with concentrations of 0, 1, 3, 5, 7 wt%. The attenuated total reflectance Fourier transform infrared (ATR/FT-IR) technique was employed to collect the in-situ spectra during light-curing, from which the degree of conversion (DC) and polymerization rate (PR) were calculated. The pH of each tested solution was also measured.
Without HAp incorporation, the DC and PR of the strong APLP (7.8% and 0.12%/s, respectively) were much lower than those of the mild AEB (85.5% and 5.7%/s, respectively). The DC and PR of APLP displayed an apparent increasing trend with the HAp content. For example, the DC increased from 7.8% to 58.4% and the PR increased from 0.12 to 3.8%/s when the HAp content increased from 0 to 7 wt%. In contrast, the DC and PR of AEB were much less affected by the HAp content. The observations were correlated well with the spectral and pH changes, which indicated that APLP underwent a higher extent of chemical reaction with HAp than AEB.
The results disclosed the important role of the acidic monomer/HAp chemical reaction in improving the photopolymerization of the strong (low-pH) self-etching adhesives such as APLP. The phenomenon of polymerization improvement strongly depended on the adhesive aggressiveness.
PMCID: PMC3367082  PMID: 22445789
Self-etching; hydroxyapatite; FTIR; photo-polymerization; degree of conversion
20.  Effects of dual antibacterial agents MDPB and nano-silver in primer on microcosm biofilm, cytotoxicity and dentin bond properties 
Journal of dentistry  2013;41(5):464-474.
The objective of this study was to investigate the effects of dentin primer containing dual antibacterial agents, namely, 12-methacryloyloxydodecylpyridinium bromide (MDPB) and nanoparticles of silver (NAg), on dentin bond strength, dental plaque microcosm biofilm response, and fibroblast cytotoxicity for the first time.
Scotchbond Multi-Purpose (SBMP) was used as the parent bonding agent. Four primers were tested: SBMP primer control (referred to as “P”), P+5%MDPB, P+0.05%NAg, and P+5%MDPB+0.05%NAg. Dentin shear bond strengths were measured using extracted human teeth. Biofilms from the mixed saliva of 10 donors were cultured to investigate metabolic activity, colony-forming units (CFU), and lactic acid production. Human fibroblast cytotoxicity of the four primers was tested in vitro.
Incorporating MDPB and NAg into primer did not reduce dentin bond strength compared to control (p>0.1). SEM revealed well-bonded adhesive-dentin interfaces with numerous resin tags. MDPB or NAg each greatly reduced biofilm viability and acid production, compared to control. Dual agents MDPB+NAg had a much stronger effect than either agent alone (p<0.05), increasing inhibition zone size and reducing metabolic activity, CFU and lactic acid by an order of magnitude, compared to control. There was no difference in cytotoxicity between commercial control and antibacterial primers (p>0.1).
The method of using dual agents MDPB+NAg in the primer yielded potent antibacterial properties. Hence, this method may be promising to combat residual bacteria in tooth cavity and invading bacteria at the margins. The dual agents MDPB+NAg may have wide applicability to other adhesives, composites, sealants and cements to inhibit biofilms and caries.
PMCID: PMC3654025  PMID: 23402889
Antibacterial primer; dentin bond strength; silver nanoparticles; MDPB; human saliva microcosm biofilm; caries inhibition
21.  Restorative material and other tooth-specific variables associated with the decision to repair or replace defective restorations: findings from The Dental PBRN 
Journal of Dentistry  2012;40(5):397-405.
Using data from dentists participating in The Dental Practice-Based Research Network (DPBRN), the study had 2 main objectives: (1) to identify and quantify the types of restorative materials in the existing failed restorations; and (2) to identify and quantify the materials used to repair or replace those failed restorations.
This cross-sectional study used a consecutive patient/restoration recruitment design. Practitioner-investigators recorded data on consecutive restorations in permanent teeth that needed repair or replacement. Data included the primary reason for repair or replacement, tooth surface(s) involved, restorative materials used, and patient demographics.
Data for 9,875 restorations were collected from 7,502 patients in 197 practices for which 75% of restorations were replaced and 25% repaired. Most of the restorations that were either repaired or replaced were amalgam (56%) for which most (56%) of the material used was direct tooth-colored. The restorative material was 5 times more likely to be changed when the original restoration was amalgam (OR=5.2, p<.001). The likelihood of changing an amalgam restoration differed as a function of the tooth type (OR=3.0, p<.001), arch (OR=6.6, p<.001); and number of surfaces in the original restoration (OR=12.2, p<.001).
The probability of changing from amalgam to another restorative material differed with several characteristics of the original restoration. The change was most likely to take place when (1) the treatment was a replacement; (2) the tooth was not a molar; (3) the tooth was in the maxillary arch; and (4) the original restoration involved a single surface.
PMCID: PMC3322253  PMID: 22342563
practice-based research; repair; replacement; decision; defective; restorations
22.  Dental primer and adhesive containing a new antibacterial quaternary ammonium monomer dimethylaminododecyl methacrylate 
Journal of dentistry  2013;41(4):345-355.
The main reason for restoration failure is secondary caries caused by biofilm acids. Replacing the failed restorations accounts for 50–70% of all operative work. The objectives of this study were to incorporate a new quaternary ammonium monomer (dimethylaminododecyl methacrylate, DMADDM) and nanoparticles of silver (NAg) into a primer and an adhesive, and to investigate their effects on antibacterial and dentin bonding properties.
Scotchbond Multi-Purpose (SBMP) served as control. DMADDM was synthesized and incorporated with NAg into primer/adhesive. A dental plaque microcosm biofilm model with human saliva was used to investigate metabolic activity, colony-forming units (CFU), and lactic acid. Dentin shear bond strengths were measured.
Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the new DMADDM were orders of magnitude lower than those of a previous quaternary ammonium dimethacrylate (QADM). Uncured primer with DMADDM had much larger inhibition zones than QADM (p<0.05). Cured primer/adhesive with DMADDM-NAg greatly reduced biofilm metabolic activity (p<0.05). Combining DMADDM with NAg in primer/adhesive resulted in less CFU than DMADDM alone (p<0.05). Lactic acid production by biofilms was reduced by 20-fold via DMADDM-NAg, compared to control. Incorporation of DMADDM and NAg into primer/adhesive did not adversely affect dentin bond strength.
A new antibacterial monomer DMADDM was synthesized and incorporated into primer/adhesive for the first time. The bonding agents are promising to combat residual bacteria in tooth cavity and invading bacteria at tooth-restoration margins to inhibit caries. DMADDM and NAg are promising for use into a wide range of dental adhesive systems and restoratives.
PMCID: PMC3631010  PMID: 23353068
Antibacterial dental adhesive; dentin bond strength; silver nanoparticles; quaternary ammonium methacrylate; human saliva microcosm biofilm; caries inhibition
23.  Association between caries location and restorative material treatment provided 
Journal of dentistry  2011;39(4):302-308.
This cross-sectional study by the Northwest PRECEDENT practitioners correlated the location of caries diagnosed in the past 12 months with treatment provided.
An oral health survey was conducted on up to 20 patients per practice for 101 practices in the Northwest PRECEDENT network. A total of 1943 eligible patients were randomly assessed for the location of and treatment provided for caries lesions diagnosed within the past 12 months. Regression analysis using Generalized Estimating Equations (GEE) was performed to assess association of treatment to tooth location and surface characterization, adjusting for age, practice location (urban/rural), dentist gender, and experience level. The analysis accounts for clustering by practice using robust variance estimates.
Overall, 55.4% of patients exhibited recent caries and 42.8% received treatment for at least one permanent tooth. 18% of treated teeth were treated with amalgam, and 72% were treated with composite. This percentage varied as a function of tooth surface characteristics, patient characteristics, and dentist characteristics. The results suggest that restoration selection does depend on tooth type and which surfaces are being restored. The odds of a molar receiving an amalgam restoration are 2.44 (95% CI=1.81–3.30) times higher as compared to a bicuspid, adjusting for all other covariates. When the restoration includes the occlusal surface of a tooth the odds are 0.42 (95% CI=0.20–0.89) times as great that amalgam will be placed. When the restoration includes the mesial or distal surface of the tooth the odds for amalgam restoration are 2.49 (95% CI=1.25–4.95) times higher compared to when it does not include these surfaces.
Restorative material choice varied based on caries location and practitioner gender.
PMCID: PMC3606693  PMID: 21256915
24.  Differences Between Reported And Actual Restored Caries Lesion Depths: Results From The Dental PBRN 
Journal of Dentistry  2011;40(3):248-254.
The objectives of this research were to (1) quantify the discordance between the caries lesion depth at which dentists restored initial lesions during a clinical study (“actual depth”) and the lesion depth that they reported during a hypothetical clinical scenario (“reported depth”); (2) test the hypothesis that certain practitioner, practice, patient, and caries lesion characteristics are significantly associated with this discordance.
Practitioner-investigators who perform restorative dentistry in their practices completed an enrollment questionnaire and participated in two consecutive studies on caries diagnosis and treatment. The first study was a survey asking about caries treatment. The second study collected data on restorations placed in routine clinical practice due to caries in patients over 19 years of age on occlusal surfaces only or proximal surfaces only. We report results on 2691 restorations placed by 205 dentists in 1930 patients with complete data.
Discordance between actual depth and reported depth occurred in only about 2% of the restorations done due to proximal caries, but about 49% of the restorations done due to occlusal caries. Practice type, restorative material used and the diagnostic methods used were significantly associated with discordance.
Dentists frequently restored occlusal caries at a shallower depth as compared to their reported depth, but the discordance was very small for proximal lesions. Discordance for occlusal caries was more common when radiographs were not taken or if a resin restoration was placed.
PMCID: PMC3279178  PMID: 22245444
Caries; threshold; restoration; remineralization; decision making
25.  Improved degree of conversion of model self-etching adhesives through their interaction with dentin 
Journal of dentistry  2011;40(1):57-63.
To investigate the correlation of the chemical interaction between model self-etching adhesives and dentin with the degree of conversion (DC) of the adhesives.
The model self-etching adhesives contained bis[2-methacryloyloxy)ethyl] phosphate (2MP) and 2-hydroxyethyl methacrylate (HEMA) with a mass ratio of 1/1, and 0-40% water contents, respectively. The adhesives were applied either onto the prepared dentin surface or unreactive substrates (such as glass slides), agitated for 15s, then light-cured for 40s. The DCs of the adhesives were determined using micro-Raman spectral and mapping analysis.
The DCs of the adhesives cured on the dentin substrate were found to be significantly higher than those on the unreactive glass substrate. Moreover, the DCs of the adhesives displayed a decreasing trend as the distance from the dentin surface became greater. The chemical interaction of the acidic 2MP/HEMA adhesives with the mineral apatite in dentin was proposed to play a significant role for the observations. The chemical interaction could be validated by the spectral comparison in the phosphate regions of 1100 cm−1 and 960 cm−1 in the Raman spectra. The results also revealed a notable influence of water content on the DC of adhesives. The DCs of the adhesive at 10% water content exhibited the highest DC level for both substrates.
Interaction with dentin dramatically improved the degree of conversion of self-etching adhesives. Our ability to chemically characterize the a/d interface including in situ detection of the DC distribution is very important in understanding self-etching adhesive bonding under in vivo conditions.
PMCID: PMC3246068  PMID: 22024375
Self-etching; dentin; micro-Raman spectroscopy; photo-polymerization; degree of conversion

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