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.

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.

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.

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.

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.

Effects of Alpha-tocopherol Antioxidant on Dentin-composite Microtensile Bond Strength after Sodium Perborate Bleaching.

It has been reported that bond strength can be reversed to prebleached levels with the application of 10% alpha-tocopherol in a 2-hour time frame or by delaying bonding for 2 weeks. This study evaluated the effectiveness of a 5-minute application of 20% alpha-tocopherol to reverse the deleterious effects of nonvital bleaching on consequent bond strength. Thirty third molars were assigned to the following 3 groups: unbleached, bleached, and bleached followed by treatment with alpha-tocopherol. The bleached groups were exposed to sodium perborate (2 g/mL) for 7 days. The postbleach treatment group was subsequently treated with 20% alpha-tocopherol for 5 minutes, and then all groups were restored with composite resin. After 24 hours of storage at 37°C and 100% humidity, restored tooth specimens were sectioned into 1-mm2 dentin-composite beams. Six beams from each tooth were subjected to microtensile bond strength testing. Representative beams were further evaluated with Raman microspectroscopy and scanning electron microscopy. The mean bond strength values (MPa) for each group were as follows: unbleached control group = 26.2, bleached control group = 20.3, and post-bleach treatment group = 18.5. A 1-factor analysis of variance and Tukey post hoc test (α = 0.05) indicated that bleaching had a detrimental effect on bond strength and that short-term alpha-tocopherol treatments did not improve postbleach bond strength. Raman microspectroscopy and scanning electron microscopy revealed no noted improvement for the post-bleach treatment group.The application of 20% alpha-tocopherol in a clinically relevant time frame was not effective in counteracting the deleterious effect of bleaching on bond strength. Bonding procedures should be delayed after tooth bleaching.

Stress analysis of irradiated human tooth enamel using finite element methods.

The objectives of this project were to use finite element methods to determine how changes in the elastic modulus due to oral cancer therapeutic radiation alter the distribution of mechanical stresses in teeth and to determine if observed failures in irradiated teeth correlate with changes in mechanical stresses. A thin slice section finite element (FE) model was constructed from micro CT sections of a molar tooth using MIMICS and 3-Matic software. This model divides the tooth into three enamel regions, the dentin-enamel junction (DEJ) and dentin. The enamel elastic modulus was determined in each region using nano indentation for three experimental groups namely - control (non-radiated), in vitro irradiated (simulated radiotherapy following tooth extraction) and in vivo irradiated (extracted subsequent to oral cancer patient radiotherapy) teeth. Physiological loads were applied to the tooth models at the buccal and lingual cusp regions for all three groups (control, in vitro and in vivo). The principal tensile stress and the maximum shear stress were used to compare the results from different groups since it has been observed in previous studies that delamination of enamel from the underlying dentin was one of the major reasons for the failure of teeth following therapeutic radiation. From the FE data, we observed an increase in the principal tensile stress within the inner enamel region of in vivo irradiated teeth (9.97 ± 1.32 MPa) as compared to control/non-irradiated teeth (8.44 ± 1.57 MPa). Our model predicts that failure occurs at the inner enamel/DEJ interface due to extremely high tensile and maximum shear stresses in in vivo irradiated teeth which could be a cause of enamel delamination due to radiotherapy.

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.

The interrelationship of microstructure and hardness of human coronal dentin using reference point indentation technique and micro-Raman spectroscopy.

OBJECTIVES: The aim of this paper is to determine the interrelationship between the microstructure - in terms of chemical composition and crystallinity - to the microhardness of coronal dentin. METHODS: Dentin microhardness was tested by a novel reference point indenter and compared to the traditional Knoop hardness method. Micro-Raman spectroscopy was used to determine the chemical composition and crystallinity of dentin. RESULTS: From the occlusal groove to the border of the coronal pulp chamber, dentin hardness decreased from superficial dentin (SD) to deep dentin (DD). Mineral/organic matrix ratios (phosphate/CH and phosphate/amide I) also decreased from SD to DD; however, this change was significant (P<0.05) in the phosphate/amide I ratio only. The phosphate/carbonate ratio decreased significantly by varying position from SD to DD. The degree of the crystallinity, as measured by the full width at half maximum (FWHM) of the peak at 960cm-1, decreased significantly going from superficial to deep dentin. SIGNIFICANCE: For the first time, the interrelationship between the microstructure and the mechanical properties of coronal dentin was determined by using the novel reference point indentation technique and micro-Raman spectroscopy. We hypothesize that the decrease in hardness from superficial to deep dentin can potentially be explained by decreased mineral content and increased carbonate content, which is also associated with decreased crystallinity. Collectively, there is a positive association between dentin hardness and mineral content and a negative association between dentin hardness and carbonate content.

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.

Cocaine-Mediated Autophagy in Astrocytes Involves Sigma 1 Receptor, PI3K, mTOR, Atg5/7, Beclin-1 and Induces Type II Programed Cell Death.

Cocaine, a commonly used drug of abuse, has been shown to cause neuropathological dysfunction and damage in the human brain. However, the role of autophagy in this process is not defined. Autophagy, generally protective in nature, can also be destructive leading to autophagic cell death. This study was designed to investigate whether cocaine induces autophagy in the cells of CNS origin. We employed astrocyte, the most abundant cell in the CNS, to define the effects of cocaine on autophagy. We measured levels of the autophagic marker protein LC3II in SVGA astrocytes after exposure with cocaine. The results showed that cocaine caused an increase in LC3II level in a dose- and time-dependent manner, with the peak observed at 1 mM cocaine after 6-h exposure. This result was also confirmed by detecting LC3II in SVGA astrocytes using confocal microscopy and transmission electron microscopy. Next, we sought to explore the mechanism by which cocaine induces the autophagic response. We found that cocaine-induced autophagy was mediated by sigma 1 receptor, and autophagy signaling proteins p-mTOR, Atg5, Atg7, and p-Bcl-2/Beclin-1 were also involved, and this was confirmed by using selective inhibitors and small interfering RNAs (siRNAs). In addition, we found that chronic treatment with cocaine resulted in cell death, which is caspase-3 independent and can be ameliorated by autophagy inhibitor. Therefore, this study demonstrated that cocaine induces autophagy in astrocytes and is associated with autophagic cell death.

Comparison of Accuracy of Calibration Ring Placement on 4 Different Endodontic Files.

INTRODUCTION: The purpose of the current study was to evaluate the accuracy and consistency of the placement of calibration rings on 4 file types: K3 (SybronEndo, Orange, CA), Vortex Blue (Tulsa Dentsply, Tulsa, OK), Kontrol Flex (Brasseler USA, Savannah, GA), and Lexicon (Tulsa Dentsply, Tulsa, OK). METHODS: Forty endodontic files, 10 of each type, were measured using a measuring microscope (Model W122; Gaertner Scientific Corp, Skokie, IL). Measurements were made from the file tip to the leading edge of 2 calibration rings and to the handle of each file. Each file measurement was performed 3 times by the same operator to ensure internal validity, and the 3 measurements were used to generate a mean for each file measurement. RESULTS: Based on a 1-factor analysis of variance and Tukey post hoc test (α = 0.05), K3 files displayed significantly greater accuracy and consistency in calibration ring and handle position. In contrast, Vortex Blue files were the least accurate, whereas both Kontrol Flex and Lexicon files were marked with similar precision. CONCLUSIONS: Calibration rings have been used by some operators to measure files during canal instrumentation. This study showed there was variation in placement of calibration rings and handles. Reliance on calibration rings and file handles as the sole means of measuring endodontic files may lead to inaccuracy in canal instrumentation.

Effect of 35% sodium ascorbate treatment on microtensile bond strength after nonvital bleaching.

UNLABELLED: According to previous reports, adverse effects of tooth bleaching on bond strength can be reversed by delaying bonding for 1-3 weeks or by applying 10% sodium ascorbate (SA) for 3 hours or more. This study evaluated the effectiveness of the short-term application of 35% SA to counteract the effects of a 7-day 35% hydrogen peroxide (H2O2) bleaching regimen on bond strength. METHODS: Forty extracted third molars were mounted and sectioned to obtain a flat dentin surface and then randomly assigned into 4 groups: group 1: restored, no bleach; group 2: bleached, bonded immediately; group 3: bleached, treated with two 1- minute 35% SA applications before bonding; and group 4: bleached, treated with two 5-minute 35% SA applications before bonding. For bleach treatment in groups 2-4, flattened dentin surfaces were exposed to H2O2 for 7 days at 37°C. Subsequent to respective treatments, dentin surfaces were built up with composite (TPH3 and Prime &Bond NT, Dentsply Caulk, Milford, DE). After 24 hours of storage (100% humidity, 37°C), the specimens were sectioned into 1-mm(2) dentin-composite beams. Four beams from each tooth (n = 40/group) were subjected to microtensile bond strength testing. RESULTS: Results were as follows: group 1: 18.1 ± 8.1MPa, group 2: 11.3 ± 5.7MPa, group 3: 11.2 ± 5.2MPa, and group 4: 12.6 ± 6.1MPa. A 1-factor analysis of variance and the Tukey post hoc test (α = 0.05) indicated that bleaching had a detrimental effect on bond strength and that short-term SA treatments after bleaching did not significantly improve bond strength. CONCLUSIONS: The application of 35% SA in a clinically relevant timeframe was not effective at reversing bleaching effects on bond strength. Bonding procedures should be delayed following tooth bleaching.

Knowledge of risk factors and the periodontal disease-systemic link in dental students' clinical decisions.

This study evaluated second-, third-, and fourth-year dental students' ability to identify systemic conditions associated with periodontal disease, risk factors most important for referral, and medications with an effect on the periodontium and their ability to apply this knowledge to make clinical decisions regarding treatment and referral of periodontal patients. A twenty-one question survey was administered at one U.S. dental school in the spring semester of 2012 to elicit the students' knowledge and confidence regarding clinical reasoning. The response rate was 86 percent. Periodontal risk factors were accurately selected by at least 50 percent of students in all three classes; these were poorly controlled diabetes, ≥6 mm pockets posteriorly, and lack of response to previous non-surgical therapy. Confidence in knowledge, knowledge of risk factors, and knowledge of medications with an effect on the periodontium improved with training and were predictive of better referral decision making. The greatest impact of training was seen on the students' ability to make correct decisions about referral and treatment for seven clinical scenarios. Although the study found a large increase in the students' abilities from the second through fourth years, the mean of 4.6 (out of 7) for the fourth-year students shows that, on average, those students missed correct treatment or referral on more than two of seven clinical cases. These results suggest that dental curricula should emphasize more critical decision making with respect to referral and treatment criteria in managing the periodontal patient.

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.

Factors influencing patients seeking oral health care in the oncology dental support clinic at an urban university dental school setting.

The purpose of this study was to identify predictors and/or factors associated with medically compromised patients seeking dental care in the oncology dental support clinic (ODSC) at the University of Missouri-Kansas City (UMKC) School of Dentistry. An 18-item survey was mailed to 2,541 patients who were new patients to the clinic from 2006 to 2011. The response rate was approximately 18% (n = 450). Analyses included descriptive statistics of percentages/frequencies as well as predictors based on correlations. Fifty percent of participants, 100 females and 119 males, identified their primary medical diagnosis as cancer. Total household income (p < .001) and the importance of receiving dental care (p < .001) were significant factors in relation to self-rated dental health. Perceived overall health (p < .001) also had a significant association with cancer status and the need for organ transplants. This study provided the ODSC at UMKC and other specialty clinics with vital information that can contribute to future planning efforts.

Type VII collagen is enriched in the enamel organic matrix associated with the dentin-enamel junction of mature human teeth.

The inner enamel region of erupted teeth is known to exhibit higher fracture toughness and crack growth resistance than bulk phase enamel. However, an explanation for this behavior has been hampered by the lack of compositional information for the residual enamel organic matrix. Since enamel-forming ameloblasts are known to express type VII collagen and type VII collagen null mice display abnormal amelogenesis, the aim of this study was to determine whether type VII collagen is a component of the enamel organic matrix at the dentin-enamel junction (DEJ) of mature human teeth. Immunofluorescent confocal microscopy of demineralized tooth sections localized type VII collagen to the organic matrix surrounding individual enamel rods near the DEJ. Morphologically, immunoreactive type VII collagen helical-bundles resembled the gnarled-pattern of enamel rods detected by Coomassie Blue staining. Western blotting of whole crown or enamel matrix extracts also identified characteristic Mr=280 and 230 kDa type VII dimeric forms, which resolved into 75 and 25 kDa bands upon reduction. As expected, the collagenous domain of type VII collagen was resistant to pepsin digestion, but was susceptible to purified bacterial collagenase. These results demonstrate the inner enamel organic matrix in mature teeth contains macromolecular type VII collagen. Based on its physical association with the DEJ and its well-appreciated capacity to complex with other collagens, we hypothesize that enamel embedded type VII collagen fibrils may contribute not only to the structural resilience of enamel, but may also play a role in bonding enamel to dentin.

A preliminary three-dimensional finite element analysis of mandibular implant overdentures.

A treatment protocol that may lead to reduced mandibular posterior residual ridge resorption in patients with overdentures retained and supported by two interforaminal implants was investigated. The treatment included the addition of short implants in the posterior edentulous mandible for the presumed purpose of favorable provision of mechanical load stimulus to alveolar bone. Three-dimensional finite element analysis was used to model cited effective strains that may stimulate bone remodeling in two selected models. Based on this laboratory study, the addition of posterior short implants has a favorable effect in maintaining bone mass under implant retained overdentures.