Effect of fluoride varnish in combination with simulated oral environment on enamel-bracket shear bond strength.

To determine the effect of fluoride varnish application combined with a simulated oral environment prior to bracket bonding on the shear bond strength (SBS) between brackets and tooth enamel. Sixty de-identified, extracted teeth were grouped to either receive or not receive fluoride varnish and then stored for 7 days at 37 °C in phosphate-buffered saline (PBS) solution or PBS combined with three 15-min cycles/day in a demineralizing solution to simulate pH variation following meals. Subsequently, brackets were bonded and after 24-h dark cure at 37 °C, debonded using shear forces in a simulated oral environment. The maximum shear force was used to calculate SBS, and the adhesive remnant index (ARI) was determined by image analysis of photos of the bracket mesh pad after debonding. A statistically higher SBS (10.16 MPa) was observed when fluoride varnish was applied prior to storage in PBS + demineralizing solution compared to SBS (6.38 MPa) following storage in the same solution without varnish application. Based on 37% effect size, this difference is also clinically relevant. In contrast, no significant differences in SBS were observed with varnish application combined with PBS with no demineralizing solution or between storage solution alone. Moreover, there was no significant difference in ARI due to varnish combined with either storage method or storage solution only. Results suggest varnish application prior to bracket bonding in combination with simulated oral environment that included acid exposure is beneficial in maintaining higher SBS between bracket and enamel. Despite higher SBS, adhesive remaining on enamel did not increase.

Effectiveness of digital impressions in a predoctoral clinical curriculum.

AIM: The purpose of the present study was to investigate the effectiveness of digital impressions made by 3rd and 4th year dental students using a retrospective record review at one USA dental school during a 1-year period. MATERIALS AND METHODS: After reviewing patient records related to quality assurance, 125 digital impressions and the produced restorations were evaluated. Effectiveness and acceptability of digital impressions and restorations were associated with students' educational level, number of prepared teeth scanned, type of produced restoration, and restorative material used. Fisher's exact and chi-square tests were used for the statistical analysis. All dental students had previous experience of the digital curriculum in their preclinical education. RESULTS: A total of 91% of the digital impressions were acceptable, and 80% of the produced restorations had clinically acceptable margins. Impression approval and restoration acceptance were not affected by students' educational level, number of preparations or restoration type. Restoration acceptance was significantly affected by restorative material (P = 0.039), with higher rates of acceptable marginal integrity found with glass-ceramic and zirconia materials. CONCLUSIONS: Within the parameters of the present study, 3rd and 4th year dental students, after having extensive education in the preclinical curriculum, can utilize digital impressions effectively for clinical practice. The results show that with adequate educational experiences, dental students can use digital impressions effectively for clinically acceptable restorations. Dental schools can and should educate students in digital dentistry.

A survey of US dental schools on predoctoral implant curricula with emphasis on diagnosing and treating implant complications.

STATEMENT OF PROBLEM: Implant complications have been reported to occur at high rates and frequencies. Whether these high rates are observed in predoctoral implant programs and whether future dentists are educated to diagnose and treat implant complications is unknown. PURPOSE: The purpose of this study was to analyze and report the results of a survey on US predoctoral curricula related to implant treatment and with an emphasis on diagnosing and treating implant complications. MATERIAL AND METHODS: A 26-question survey was distributed to all (66) US dental schools. In addition to 3 questions regarding descriptive information about each school, 13 questions were used to calculate a curriculum composite score that was used to assess the quality of the school's implant curriculum. The remaining survey topics and number of questions included frequency of complications (2), tracking and types of complications (6), and school-reported student preparedness to identify or treat implant complications (2). A Kruskal-Wallis test was used to evaluate the relationship between the curriculum composite scores and student preparedness to diagnose and treat implant complications. RESULTS: Twenty-eight schools responded to the survey for a response rate of 42.4%, and 23 schools completed the entire survey (completion rate 34.8%). Fifteen schools (65.2%) reported methods of recording implant complications, and 8 of 23 schools (34.8%) reported methods of assessing student knowledge in recognizing implant complications. Only 2 schools reported methods of assessing student preparedness to treat implant complications. Most implant complications were mechanical (64.3%), followed by biological (28.6%) and esthetic (7.1%). The prostheses associated with the most complications were implant overdentures (39.1%), followed by single crowns (34.8%) and fixed partial dentures (4.3%). A positive relational trend was observed between reported student preparedness to recognize and treat implant complications and curriculum composite scores. CONCLUSIONS: Within the limitation of this survey-based study, implant curricula in US dental schools should consider improving the scope of teaching the diagnosis and treatment of implant complications. The implant complications observed at US dental schools showed similar trends to those reported in the literature.

Immediate restoration after mineral trioxide aggregate pulpotomy with amalgam condensation: an in vitro study.

Mineral trioxide aggregate (MTA) pulpotomy may be an alternative to root canal therapy, with reported success rates as high as 85%. However, little technique-specific information has been reported regarding MTA placement in 1 visit. The purpose of this study was to evaluate different placement methods for MTA and resin-modified glass ionomer (RMGI) cement before immediate restoration with amalgam. Forty pulpotomized extracted third molars were randomly divided into 4 groups, and moist cotton was used to simulate pulp tissue in all teeth. In group 1, cotton was placed over the entire pulp chamber floor and in each canal orifice, and MTA was placed over the cotton. The procedure for group 2 was the same as that for group 1 except that a layer of RMGI was placed over the MTA. In group 3, cotton was placed in the canal orifices only, a layer of MTA was placed only over the cotton in the orifices, and RMGI was layered over the MTA and pulp chamber floor. The procedure for group 4 was the same as that for group 3 except that RMGI was placed over the MTA but not on the pulpal floor. Each of these procedures was followed by amalgam condensation. After a 7-day setting period, restored teeth were sectioned mesiodistally, photographed, measured, and evaluated for disturbance of the MTA-restoration junction. The study findings showed that the MTA layer was disturbed in 40% of the specimens in group 1, whereas 10%-20% of specimens in groups 2 through 4 demonstrated disturbed MTA. Analysis with a Pearson chi-square test indicated that the difference between group 1 and groups 2 through 4 was statistically significant (P < 0.05), but there was no significant difference (P > 0.05) between groups 2, 3, and 4. Group 3, in which MTA was placed over each canal orifice and RMGI was placed over the entire pulpal floor, performed best--only 10% of specimens exhibited deformed MTA. The findings suggest that RMGI may protect initially placed MTA during amalgam condensation.

Is histologic esophagitis associated with dental erosion: a cross-sectional observational study?

BACKGROUND: Gastroesophageal reflux disease (GERD) affects 15-25% of children and adolescents in the United States. The diagnosis of GERD in children is complex as reported symptoms or symptom profiles have been found to be unreliable. Frequently, the diagnosis must be confirmed by objective tests such as pH monitoring or histological evidence of esophagitis on an esophageal biopsy. Dental erosion has been shown to be associated with GERD as an atypical complication and has the potential to be a marker of GERD. The purposes of this study were to compare the frequency and patterns of dental erosion in children and adolescents with and without histologic esophagitis. METHODS: Twenty-five subjects were recruited from patients scheduled for an upper gastrointestinal endoscopy. Information regarding potential GERD symptoms, food habits, and dental hygiene habits were obtained. Intra-oral photographs were taken, and a dental exam for erosion was performed. The results of a standard biopsy taken from the lower third of the esophagus during an endoscopy were used to divide subjects into either the control group or the GERD group (i.e. those with histologic esophagitis). RESULTS: Twenty-two subjects yielded 586 evaluable teeth. No significant difference was found between frequency or erosion patterns of those with and without histologic esophagitis. Dental erosions were more frequent in primary teeth. CONCLUSIONS: Dental erosions do not appear to be associated with histologic esophagitis indicative of GERD.

Assessing the Effectiveness of a School-Based Dental Clinic on the Oral Health of Children Who Lack Access to Dental Care.

This program evaluation examines the effectiveness of a school-based dental clinic. A repeated-measures design was used to longitudinally examine secondary data from participants ( N = 293). Encounter intensity was developed to normalize data. Multivariate analysis of variance and Kruskal-Wallis test were used to investigate the effect of encounter intensity on the change in decay, restorations, and treatment urgency. A Pearson's correlation was used to measure the strengths of association. Encounter intensity had a statistically significant effect on change in decay ( p = .005), restorations ( p = .000), and treatment urgency ( p = .001). As encounter intensity increased, there was a significant association with the decrease in decay (-.167), increase in restorations (.221), and reduction in referral urgency (-.188). Incorporating dental care into a school-based health center resulted in improved oral health in underserved children while overcoming barriers that typically restrict access. The collaboration of school nurses with the school-based dental clinic was an important element for maximizing student access to dental care.

Enamel organic matrix: potential structural role in enamel and relationship to residual basement membrane constituents at the dentin enamel junction.

Although mature enamel is predominantly composed of mineral, a previously uncharacterized organic matrix layer remains in the post-eruptive tissue that begins at the dentin enamel junction and extends 200-300 µm towards the outer tooth surface. Identification of the composition of this layer has been hampered by its insolubility; however, we have developed a single step method to isolate the organic enamel matrix relatively intact. After dissociative dissolution of the matrix with SDS and urea, initial characterization by Western blotting and gel zymography indicates the presence of type IV and type VII basement membrane collagens and active matrix metalloproteinase-20. When combined with data from transgenic knockout mice and from human mutations, these data suggest that the enamel organic matrix (EOM) and dentin enamel junction may have a structural and functional relationship with basement membranes, e.g. skin. To clarify this relationship, we hypothesize a "foundation" model which proposes that components of the EOM form a support structure that stabilizes the crystalline enamel layer, and bonds it to the underlying dentin along the dentin enamel junction. Since we have also co-localized an active matrix metalloproteinase to this layer, our hypothesis suggests that, under pathologic conditions, MMP-mediated degradation of the EOM could destabilize the enamel-dentin interface.

Social disparities in dentition status among American adults.

OBJECTIVES: To assess the overall dentition status of American adults, to investigate disparities and changes in dentition using the National Health and Nutrition Examination Surveys 2005-2006 and 2007-2008 and to study the effects of family poverty status, education, citizenship and language on dentition after adjusting for other demographics. METHODS: Descriptive statistics were used to explore and summarise dentition status. The prevalence of dentition markers over two surveys were compared using tests of proportions and a series of regressions were used to estimate the strength of association of family poverty status, education, citizenship and language with the four markers of dentition status. RESULTS: Overall, dentition status has improved in adults. However, gaps exist in that non-Hispanic Black and Mexican-Americans have a higher prevalence of dental decay and lower restoration rates than other races. After adjusting for selected demographics, adults with less education (<12 years) and lower family income had significantly higher dental decay rates, lower restoration rates and more missing teeth than those with more education (≥12 years) and those with higher family incomes. CONCLUSION: This study indicates that disparities in dentition associated with race/ethnicity, education and income still exist among adults in the USA. The results also indicate that to improve overall oral health and close the existing gaps in oral health, increased access to dental care would be needed for people who have low incomes and low levels of education.

Effect of Model Body Type and Print Angle on the Accuracy of 3D-Printed Orthodontic Models.

The assortment of low-cost 3D printers for "in-practice" use, e.g., for clear aligner therapies, is ever increasing. To address concerns about the accuracy of orthodontic models produced on such printers when cost-efficient modes of 3D printing are employed, this study examined the effect of print model body type and print angulation on accuracy. Six printing-configuration groups were included: two model types (solid or hollow shell) combined with three print angles (0°, 70°, or 90°) with 10 models/group; all models were printed with 100 µm layer thickness using a digital light processing-based three-dimensional printer. Eleven selected structures and distances were measured on the printed models with a digital microscope and compared to the same measures on a digitized master model. The clinically acceptable range was set at ±0.25 mm difference from the master model for single tooth measurements (intra-tooth) and ±0.5 mm for cross-arch measurements (inter-tooth). For individual measurements across all models, 98% fell within clinical acceptability. For mean measurements within each model group, only canine height for the shell-0° model had a mean difference (-0.26 mm ± 0.03) outside the clinically acceptable range for intra-tooth measurements. Standard deviations for all intra-tooth measurements were within 0.07 mm. While none of the mean inter-tooth measurements exceeded the acceptability range, the standard deviations were larger (0.04 to 0.30 mm). The accuracy of the orthodontic models for clear aligner therapies was not impacted beyond the clinically acceptable range when altering model body type and print angulation to improve efficiency of 3D printing. These findings suggest greater flexibility of the practitioner to alter print settings to address time and cost efficiency in various clinical scenarios and still maintain clinically acceptable model accuracy.

Correlation of impression removal force with elastomeric impression material rigidity and hardness.

PURPOSE: Difficult impression removal has been linked to high rigidity and hardness of elastomeric impression materials. In response to this concern, manufacturers have reformulated their materials to reduce rigidity and hardness to decrease removal difficulty; however, the relationship between impression removal and rigidity or hardness has not been evaluated. The purpose of this study was to determine if there is a positive correlation between impression removal difficulty and rigidity or hardness of current elastomeric impression materials. MATERIALS AND METHODS: Light- and medium-body polyether (PE), vinylpolysiloxane (VPS), and hybrid vinyl polyether siloxane (VPES) impression materials were tested (n = 5 for each material/consistency/test method). Rigidity (elastic modulus) was measured via tensile testing of dumbbell-shaped specimens (Die C, ASTM D412). Shore A hardness was measured using disc specimens according to ASTM D2240-05 test specifications. Impressions were also made of a custom stainless steel model using a custom metal tray that could be attached to a universal tester to measure associated removal force. Within each impression material consistency, one-factor ANOVA and Tukey's post hoc analyses (α = 0.05) were used to compare rigidity, hardness, and removal force of the three types of impression materials. A Pearson's correlation (α = 0.05) was used to evaluate the association between impression removal force and rigidity or hardness. RESULTS: With medium-body materials, VPS exhibited significantly higher (p ≤ 0.05) rigidity and hardness than VPES or PE, while PE impressions required significantly higher (p ≤ 0.05) removal force than VPS or VPES impressions. With light-body materials, VPS again demonstrated significantly higher (p ≤ 0.05) hardness than VPES or PE, while the rigidity of the light-body materials did not significantly differ between materials (p > 0.05); however, just as with the medium-body materials, light-body PE impressions required significantly higher (p ≤ 0.05) removal force than VPS or VPES. Moreover, there was no positive correlation (p > 0.05) between impression removal force and rigidity or hardness with either medium- or light-body materials. CONCLUSIONS: The evidence suggests that high impression material rigidity and hardness are not predictors of impression removal difficulty.

Surface characteristics and cell adhesion: a comparative study of four commercial dental implants.

PURPOSE: The aims of this study were to compare surface properties of four commercial dental implants and to compare those implant systems' cell adhesion, which may be affected by the surface properties, and to provide scientific information on the selection of implants for clinicians. MATERIALS AND METHODS: The surface properties of four commonly used dental implants (3i Nanotite™, Astra OsseoSpeed™, Nobel Biocare TiUnite®, and Straumann SLActive®) were studied using MicroSpy profiler, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, and Raman microspectroscopy. Primary mouse alveolar bone cells were cultured on the surface of implants from the four companies. After 48-hour culture, SEM in combination with a quantitative analysis of SEM images was used to examine the cell adhesion. Cell adhesion rates (ratios of cell surface to implant surface) among different systems were compared. RESULTS: Distinct differences were found among these implants. Comparisons of roughness among three locations: flank, top, and valley within the same implant system, or in the same location among different implants were made. Generally Astra and Straumann systems showed the roughest surface, whereas 3i showed the smoothest surface. Multiple cracks were found on the surface of the Nobel Biocare system, which also had a dramatically lower level of titanium. In addition, rutile phase of titanium oxide was found in 3i, Astra, and Straumann systems, and anatase phase of titanium oxide was only detected in the Nobel Biocare system. After 48-hour culture, Astra and Straumann systems displayed the highest cell adhesion at the areas of flank, top, and valley of the implant surface. Primary cells also reached confluence on the valley, but significantly less in the 3i system. Nobel Biocare showed the least cell adhesion on the flank and valley. CONCLUSION: Implant systems have distinct differences in surface properties, leading to different cell adhesion results. Further in vivo study is needed to study the impact of the surface characteristics and different cell adhesion on the osseointegration between implant and bone.

Effect of Different Crosslinkers on Denatured Dentin Collagen's Biostability, MMP Inhibition and Mechanical Properties.

OBJECTIVE: Sound, natural dentin collagen can be stabilized against enzymatic degradation through exogenous crosslinking treatment for durable bonding; however, the effect on denatured dentin (DD) collagen is unknown. Hence, the ability of different crosslinkers to enhance/restore the properties of DD collagen was assessed. METHODS: Demineralized natural and DD collagen films (7 mm × 7 mm × 7 µm) and beams (0.8 mm × 0.8 mm × 7 mm) were prepared. DD collagen was experimentally produced by heat or acid exposure, which was then assessed by various techniques. All specimens were then treated with 1 wt% of chemical crosslinker 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/n-hydroxysuccinimide (EDC/NHS) and two structurally different flavonoids-theaflavins (TF) from black tea and type-A proanthocyanidins from cranberry juice (CR) for either 30 s or 1 h. The controls were untreated. Dentin films were assessed for chemical interaction and cross-linking effect by FTIR, biostability against exogenous collagenase by weight loss (WL) and hydroxyproline release (HYP), and endogenous matrix metalloproteinases (MMPs) activity by confocal laser microscopy. Dentin beams were evaluated for tensile properties. Data were analyzed using ANOVA and Tukey's test (α = 0.05). RESULTS: Compared with natural collagen, DD collagen showed pronounced structural changes, altered biostability and decreased mechanical properties, which were then improved to various degrees that were dependent on the crosslinkers used, with EDC/NHS being the least effective. Surprisingly, the well-known MMP inhibitor EDC/NHS showed negligible effect on or even increased MMP activity in DD collagen. As compared with control, cross-linking induced by TF and CR significantly increased collagen biostability (reduced WL and HYP release, p < 0.05), MMP inhibition (p < 0.001) and mechanical properties (p < 0.05), regardless of denaturation. CONCLUSIONS: DD collagen cannot or can only minimally be stabilized via EDC/NHS crosslinking; however, the challenging substrate of DD collagen can be enhanced or restored using the promising flavonoids TF and CR.

Randomized clinical trials: is periodontal research good for patients?

Randomized controlled trials, in which randomization is used to allocate patients to a treatment arm, are a relatively new concept. Randomized controlled trials are increasingly high-stakes endeavors requiring a high level of planning and considerable financial support. Randomized controlled trials are the gold standard by which effectiveness of various treatments or interventions are determined. However, the methods involved in randomized controlled trials raise the question: is clinical research good for the participants? This paper discusses patient-centered issues relating to randomized controlled trials, for example, whether the informed-consent process results in subjects who are knowledgeable and informed about their participation, which, in turn, involves patient autonomy, health literacy and treatment preferences. Other issues discussed are those of statistical vs. clinical significance, professional ethics and ethical justification for randomized controlled trials, and differences in perceptions between patients and clinicians regarding the level of care being provided by the randomized controlled trials. Because our goal, as clinicians, is to provide treatment that improves the quality of life for the patient, it would seem logical that randomized controlled trials should include variables rated as important by patients as valid outcome measures. As clinicians and researchers, we can no longer afford to view randomized controlled trials from an ivory tower. Research participants, although autonomous agents, are inherently different from the patient seeking clinical care. Researchers have an ethical responsibility to consider the informed consent process as it relates to the subject's health literacy and potential for therapeutic and procedural misperceptions.

Archwire vibration and stick-slip behavior at the bracket-archwire interface.

INTRODUCTION: It is unknown whether or not intraoral vibrations affect stick-slip behavior at orthodontic bracket-archwire interfaces. In this study, we evaluated bracket-archwire stick-slip behavior as a function of ligation method and archwire vibration. METHODS: In-vivo archwire vibrations were measured to obtain frequencies and amplitudes for ex-vivo testing. A piezoresistive accelerometer ligated to the maxillary right canines of 6 subjects transduced the intraoral vibrations. All subjects gave informed consent to participate. Amplitude and frequency of the vibrations were quantified and used in a bench-top friction testing apparatus. Active and passive ligation methods were compared for 9 vibration scenarios. The amount of time to move the bracket along a stainless steel wire was recorded in 90 trials. Analysis of variance and post-hoc tests were used for statistical analyses of the data. RESULTS: During carrot biting, orthodontic wire vibrations had a mean frequency of 98 Hz and a peak-to-peak mean amplitude of 151 mV. The bench-top stick-slip measurement trials containing medium (150 mV) and high (190 mV) amplitude vibrations had significantly less friction (ln, s), 4.81 ± 2.08 and 4.67 ± 2.00, respectively, than those subjected to low (110 mV) amplitudes, 5.80 ± 1.39 (P = 0.04). There were no significant differences between passive and active ligation methods. CONCLUSIONS: Amplitudes of archwire vibrations affect stick-slip behavior at the bracket-archwire interfaces.

Effect of airborne-particle abrasion and aqueous storage on flexural properties of fiber-reinforced dowels.

PURPOSE: A great range of clinical failures have been observed with fiber-reinforced dowels, often attributed to fracture or bending of the dowels. This study investigated flexural properties of fiber-reinforced dowels, with and without airborne-particle abrasion, after storage in aqueous environments over time. Scanning electron microscopy (SEM) was used to analyze the mode of failure of dowels. MATERIALS AND METHODS: Two dowel systems (ParaPost Fiber Lux and FibreKor) were evaluated. Ten dowels of each system were randomly assigned to one of six experimental groups: 1--control, dry condition; 2--dowels airborne-particle abraded and then stored dry; 3--dowels stored for 24 hours in aqueous solution at 37°C; 4--dowels airborne-particle abraded followed by 24-hour aqueous storage at 37°C; 5--dowels stored for 30 days in aqueous solution at 37°C; 6--dowels airborne-particle abraded followed by 30-day aqueous storage at 37°C. Flexural strength and flexural modulus were tested for all groups according to American Society of Testing and Materials (ASTM) standard D4476. One failed dowel from each group was randomly selected to be evaluated with SEM equipped with energy dispersive spectroscopy (EDS) to characterize the failure pattern. One intact dowel of each system was also analyzed with SEM and EDS for baseline information. RESULTS: Mean flexural modulus and strength of ParaPost Fiber Lux dowels across all conditions were 29.59 ± 2.89 GPa and 789.11 ± 89.88 MPa, respectively. Mean flexural modulus and strength of FibreKor dowels across all conditions were 25.58 ± 1.48 GPa and 742.68 ± 89.81 MPa, respectively. One-way ANOVA and a post hoc Dunnett's t-test showed a statistically significant decrease in flexural strength as compared to the dry control group for all experimental groups stored in water, for both dowel systems (p < 0.05). Flexural modulus for both dowel systems showed a statistically significant decrease only for dowels stored in aqueous solutions for 30 days (p < 0.05). Airborne-particle abrasion did not have an effect on flexural properties for either dowel system (p > 0.05). SEM and EDS analyses revealed differences in composition and failure mode of the two dowel systems. Failed dowels of each system revealed similar failure patterns, irrespective of the experimental group. CONCLUSIONS: Aqueous storage had a negative effect on flexural properties of fiber-reinforced dowels, and this negative effect appeared to increase with longer storage times. The fiber/resin matrix interface was the weak structure for the dowel systems tested.

Comparison of flexural properties and surface roughness of nanohybrid and microhybrid dental composites.

Recently introduced nanohybrid dental composites have promised a smoother surface finish and strength, comparable to that of microhybrid composites. This study compared the mechanical properties and surface finish of nanohybrid and microhybrid composites by measuring the flexural strength and modulus (four-point bend) and surface roughness after polishing (using atomic force microscopy) of six commercial dental composites (three nanohybrid, three microhybrid). Scanning electron microscopy (SEM) was used to qualitatively characterize filler morphology and size. The flexural strength and modulus were significantly higher among the microhybrid composites, while the nanohybrid composites exhibited significantly lower surface roughness. SEM characterization revealed differences in filler particle size and shape that could affect the flexural properties and surface roughness. Composites containing spherical filler particles exhibited higher flexural properties and lower roughness values compared to composites with irregular fillers. These results did not support the premise that nanohybrid composites offer similar mechanical properties to microhybrids in addition to a better surface finish.

Distinct effects of polyphenols and solvents on dentin collagen crosslinking interactions and biostability.

OBJECTIVE: To evaluate the effects of different polyphenols and solvents on dentin collagen's crosslinking interactions and biostabilization against MMPs and collagenase degradation. METHODS: Two polyphenols [proanthocyanidin (PA) and quercetin (QC)] with different water solubility were prepared as treatment solutions using ethanol (EtOH) or dimethyl sulfoxide (DMSO) as solvents. 6-um-thick dentin films were microtomed from dentin slabs of third molars. Following demineralization, films or slabs were subject to 60-s treatment (PA or QC) or no treatment (control) with subsequent extended-rinse with original solvent (EtOH or DMSO) or distilled water (DW). Collagen crosslinking interactions were assessed by FTIR. Biostability was assessed through endogenous MMPs activity via confocal laser scanning microscopy, and exogenous collagenase degradation via weight loss, hydroxyproline release and SEM. Finally, direct collagenase inactivation was also evaluated. Data were analyzed by three-way ANOVA and post-hoc tests (α=0.05%). RESULTS: Distinct effects of two polyphenols and solvents on collagen crosslinking and biostabilization were observed. Higher crosslinking and biostability efficacy occurred with PA than QC (p<0.001) that demonstrated negligible collagen interactions. With DMSO solvent, efficacy results were significantly reduced with both polyphenols (p<0.05). DMSO-rinse further weakened interactions of PA with collagen, diminishing biostability (p<0.05). Low biostability was detected with QC and DW-rinse, suggesting direct enzymatic inhibition due to physical presence in collagen. SIGNIFICANCE: Collagen crosslinking interactions and biostability depend on polyphenol chemical characteristics. Treatment-solution solvents may affect interactions between polyphenols and collagen, specifically, DMSO showed detrimental effects on collagen crosslinking and biostability and should be used with caution.

Chemical/molecular structure of the dentin-enamel junction is dependent on the intratooth location.

The dentin-enamel junction (DEJ) plays an important role in preventing crack propagation from enamel into dentin. This function stems from its complex structure and materials properties that are different from either dentin or enamel. The molecular structural differences in both mineral and organic matrix across the DEJ zone were investigated by two-dimensional confocal Raman microspectroscopic mapping/imaging technique. The intensity ratios of 1450 (CH, matrix)/960 (P-O, mineral) decreased gradually to nearly zero across the DEJ. The width of this transition zone was dependent on the intratooth location, with 12.9 +/- 3.2 microm width at occlusal positions and 6.2 +/- 1.3 microm at cervical positions. The difference in width was significant (P < 0.001). Concurrently, spectral differences in both organic and inorganic matrices across the DEJ were also noted. For example, the ratios of 1243 (amide III)/1450 (CH) within the DEJ were lower than the values in dentin; however, the ratios of 1665 (amide I)/1450 (CH) within the DEJ were higher than those values in dentin. In addition, the ratios of 1070 (carbonate)/960 (phosphate) within the dentin were lower than the values in the DEJ. Raman images indicated that the distribution of the above ratios across the DEJ zone were also different at occlusal and cervical positions. The results suggest that the intratooth-location-dependent structure of the DEJ may be related to its function. Micro-Raman spectroscopic/imaging analysis of the DEJ provides a powerful means of identifying the functional width and molecular structural differences across the DEJ.

Vertical dimensional stability and rigidity of occlusal registration materials.

Dimensionally accurate occlusal registration records are essential for restorative dentistry; moreover, since records are not used immediately or may be used more than once, the registration material should exhibit accuracy over time (a concept known as dimensional stability). It has been speculated that materials with increased hardness or rigidity should produce more accurate registration records due to an increased resistance to distortion. This study compared the rigidity and associated dimensional accuracy of a recently marketed bisacrylic occlusal registration material and a vinyl polysiloxane (VPS). Maxillary and mandibular typodont arches were mounted on a plasterless articulator from which teeth No. 3, 13, and 15 had been removed to simulate edentulous spaces. After preparing teeth No. 2, 4, 12, and 14 as bridge abutments, the remaining teeth were equilibrated selectively to produce even anterior contact. Four digital photographs were taken to make vertical interarch measurements at four locations (teeth No. 3, 7, 10, and 14). Following initial photos (controls), 10 interocclusal records were made using each registration material, with material placed only in the segments in which teeth were prepared. The records were used for mounting the maxillary arch against the mandibular arch after 48, 72, and 120 hours. There were significant effects on vertical dimensional change related to arch location, material, and mounting time. Both materials demonstrated significantly larger posterior vertical openings than anterior vertical openings, while the bisacrylate produced a larger posterior opening than VPS at 48 and 72 hours and a larger anterior opening at all mounting times. There also was a significant difference in hardness/rigidity due to material and measurement time; at all measurement times, bisacrylate exhibited a significantly higher hardness number.

Assessment of the accuracy of two gutta-percha gauges used to alter gutta-percha tip diameter.

This study sought to compare the accuracy of two gauges used to alter gutta-percha (GP) cone tips. Randomly selected size 20 cones (with tapers of 0.02, 0.06, 0.10, or 0.12) were trimmed to size 50 (N= 10/taper/gauge) for an overall sample of 80 cones. Accuracy of the altered cone tips was determined by calculating the difference (in %) between the altered tip diameter and the expected tip diameter (0.50 mm). A two-factor ANOVA revealed significant differences (p < or = 0.05) in altered tip accuracy as a result of GP gauge and cone taper. The results suggest that the SybronEndo gauge performs accurately regardless of the cone taper, while the Maillefer gauge was accurate only when used to alter cones with a 0.02 taper.