Longevity of extrinsic stains on monolithic zirconia restorations: An in vitro study.

STATEMENT OF PROBLEM: Three-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) has been commonly used for fixed prosthodontic restorations. The opacity of 3Y-TZP may be masked with external staining, although the longevity of extrinsic stains applied to monolithic zirconia is unclear. PURPOSE: The purpose of this in vitro study was to analyze the color and surface roughness of extrinsically stained zirconia specimens after thermocycling and toothbrushing. MATERIAL AND METHODS: Monolithic Ø12.5×1.25-mm zirconia disks were milled from 3Y-TZP blocks, sintered according to manufacturer instructions, and then divided into 3 groups (C, J, and O; n=16) for application of stain and glaze. All specimens underwent 10 000 thermocycles in distilled water before being further divided into 2 dentifrice groups (n=8): normal grit, low relative dentin abrasivity (RDA) (Subgroup N) and abrasive grit, high RDA (Subgroup A). Specimens were brushed in a multistation brushing machine under 1.47 N of force using a 5:8 toothpaste and distilled water slurry for 10 000 cycles with a straight (American Dental Association Standard) toothbrush to simulate 1 year of toothbrushing. Color and surface roughness measurements were obtained at 3 time points: baseline, after thermocycling, and after brushing. A 2-way repeated measures ANOVA was used to independently assess changes in color and surface roughness with respect to thermocycling and brushing (α=.05). RESULTS: Group J displayed no significant change in color for either dentifrice system (P>.05). However, a significant change in surface roughness was observed for both dentifrice subgroups (P<.001). Group C specimens displayed significant changes in color (P<.001) and surface roughness (P<.001) for both dentifrice systems. Group O specimens displayed significant changes in color (P<.025) for both dentifrice systems and significant changes in surface roughness (P<.004) for subgroup A, but no significant changes for subgroup N (P=.075). CONCLUSIONS: Artificial aging of monolithic zirconia resulted in changes in color and surface roughness that did not surpass the thresholds for perceptibility and acceptability. This study failed to establish durability limits for extrinsic stains applied to 3Y-TZP.

Surface Roughness of Prefabricated Pediatric Zirconia Crowns Following Simulated Toothbrushing.

Purpose: The purpose of this study was to evaluate the surface roughness of three different brands of prefabricated pediatric zirconia crowns (ZRCs) following simulated toothbrushing with a variety of dentifrices. Methods: Ninety-six total maxillary right central incisor prefabricated pediatric ZRCs (n equals 32 ZRCs/brand) were obtained from the manufacturers: Kinder Krowns®, NuSmile®, and Sprig®. ZRCs were equally assigned to dentifrices (n equals eight/dentifrice) with a variety of Relative Dentin Abrasion (RDA) values: Tom's of Maine Children's; Crest Kid's; Prevident 5000; and Crest® Pro-Health. ZRCs were brushed 10,000 strokes with a V-8 Toothbrushing Machine using the assigned dentifrices. Pre- and post-intervention data for the surface roughness of ZRCs, represented in Ra (average roughness) and Rz (mean roughness depth), were obtained using a stylus profilometer. Data were analyzed independently using two-way repeated measures analysis of variance with the Holm- Sidak method (α equals 0.05). Results: Baseline versus brushed Ra Kinder Krowns® with Prevident and Sprig® with Crest Kid's indicated statistically significant differences. Sprig® versus NuSmile® utilizing Crest Kid's were different in change in roughness. Both baseline and brushed NuSmile® dentifrice options were different versus all Sprig® and Kinder® ZRCs. Conclusions: Despite statistical significance, changes in surface roughness were small in scale. Although this study did not address toothbrushing and different dentifrices may affect the mechanical properties, durability, and/or retention properties of ZRCs, the study's results provide confidence to clinicians when using prefabricated pediatric ZRCs as a sustainable treatment option along with other restorative options, such as strip crowns and stainless steel crowns.

Color Stability of Prefabricated Pediatric Zirconia Crowns Following Sterilization.

Purpose: Since pediatric zirconia crowns (ZRCs) are prefabricated, they may be sterilized following try-in for re-use. Possible changes in color stability, gloss, and translucency were evaluated for four brands of prefabricated zirconia crowns following autoclave and cold sterilization. Methods: Sixteen maxillary right central incisor prefabricated ZRCs were obtained from NuSmile ®, Sprig, Cheng Crowns, and Kinder Krowns ® manufacturers and either autoclaved or cold sterilized. Gloss unit measurements were obtained with a small object Novo-Curve glossmeter. CIE-L*a*b* system values were measured with a CM-700d spectrophotometer under three different illuminants to calculate DE (quantitative representation of the perceived color). ΔE equals one was used for perceptibility threshold (PT) and ΔE equals 2.7 for acceptability threshold (AT). Results: All groups' baseline was ΔE less than one for all illuminants except Cheng Crowns to be autoclaved, indicating crowns are not identical in color from the manufacturer. For autoclaving, Cheng Crowns reached ΔE PT greater than one following the 10th sterilization cycle for all illuminants (D65 1.08±0.32 (standard deviation; P<0.001), A equals 1.07±0.32 (P<0.001), and F2 equals 1.25±0.38 (P<0.001). For cold sterilization, Sprig EZCrowns reached PT greater than one for all sterilization cycles, and Cheng Crowns reached ΔE PT greater than one for the sixth and 10th sterilization cycles. Gloss was not affected by either sterilization method. Spring EZcrowns had the highest mean translucency. Conclusions: Although each group may have a slight perceived difference, there was no clinically significant difference in color; all groups remained below the acceptability threshold of ΔE equals 2.7.

Effects of curing lights on human gingival epithelial cell proliferation.

BACKGROUND: Light-emitting diode (LED) and quartz-tungsten-halogen (QTH) curing lights are used commonly in clinics. The aim of this study was to assess the effect of these lights on the proliferation of human gingival epithelial cells. METHODS: Smulow-Glickman (S-G) cells were exposed to a VALO LED (Ultradent) or an XL3000 QTH (3M ESPE) light at 1 millimeter or 6 mm distance for 18, 39, 60, and 120 seconds. Untreated and Triton X-100 treated cells were used as controls. At 24, 48, and 72 hours after light exposure, cell proliferation was evaluated via a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. RESULTS: The authors first evaluated the performances of these 2 lights. Both LED and QTH lights generated heat. The LED light generated less heat than the QTH light and could save approximately two-thirds of the curing time. When used for 18 seconds at a 6 mm distance, the LED light did not inhibit the proliferation of S-G cells. However, if the exposure time was longer (for example, 39, 60, or 120 seconds), the LED light inhibited cell proliferation. The inhibitory effect increased when the exposure time was increased to 39, 60, or 120 seconds. The QTH light did not inhibit S-G cell proliferation if the exposure time was less than 120 seconds. CONCLUSIONS: Prolonged exposure to a blue curing light (both LED and QTH) inhibits the proliferation of gingival epithelial cells and may cause damages to oral soft tissues. PRACTICAL IMPLICATIONS: In dental practices, a balance should be struck in consideration of curing time not only to cure the composites completely but also to minimize unnecessarily prolonged light exposure.

Combination PROP: A Case Report of a Hybrid Flexible and Traditional Partial Removable Dental Prosthesis.

The need for partial removable dental prostheses (PRDP) is increasing as the over-65 partially edentulous population grows. The use of flexible materials in the fabrication of these prostheses has captured a large portion of the market once occupied by traditional cast metal PRDPs. While there are some clinical advantages to the use of flexible PRDPs, there are also disadvantages and contraindications that must be considered. This paper describes a clinical case in which a patient's dentition is restored with a hybrid partial removable dental prosthesis consisting of a traditional metal framework and flexible denture base and clasps. This design can result in achieving the benefits of each type of prosthesis in an effort to satisfy the needs of the patient.

Determination and Correlation of Depth of Cure of a New Composite Resin Delivery System.

OBJECTIVES: To quantify the depth of cure (DOC) of a composite resin system using two different testing criteria. METHOD AND MATERIALS: The DOC testing employed two different experimental protocol: 1) Forty-eight previously extracted human molars were randomly assigned to four groups of twelve each (n = 12): Group 1 SonicFill composite resin system, shade A1; Group 2 SonicFill, shade A3; Group 3 Herculite Ultra composite resin, shade A1; Group 4 Herculite Ultra, shade A3. Cylindrical cavities (4.0 mm diameter and 10 mm depth) were prepared at the tooth CEJ, in a mesiodistal direction. The preparations were filled with each composite resin material in one bulk increment and polymerized with a LED light for 20 seconds. After 5 minutes, the occlusal surfaces of the teeth (specimens) were ground flat until the composite was exposed in a transverse plane. The uncured (soft) composite was scraped away, using a "modified" ISO 4049 DOC specification, and the remaining cured (hard) material was measured. Three measurements, at different positions of the specimen, were performed, for a total of thirty-six measurements per specimen group. The measurements were averaged and divided by fifty percent, arriving at the final DOC for each specimen. 2) A DOC testing protocol was performed using a two-piece (4.0 mm x 10.0 mm) custom-made Teflon device (mold). The groupings duplicated the previous experimental protocol. The mold was filled with each composite resin material in one bulk increment to a 10 mm length (depth). Excess composite material was removed, followed by placement of a Mylar strip over the external orifice. The composite resin specimen was light-polymerized for 20 seconds. Again, the uncured (soft) composite was scraped away, with the same measurement protocol followed as in method 1. Statistical analyses were conducted using ANOVA tests at a p < .05 level of significance. RESULTS: Statistical differences were exhibited between the two different DOC methodologies, extracted teeth versus the Teflon device. Considering each method, the SonicFilTM composite revealed significantly greater DOC compared to the Herculite Ultra composite resin. Also, significant differences were displayed between the Al compared to the A3 shades, with the A1 (lighter) shades exhibiting greater DOC. CONCLUSION: The prepped teeth seemed a more realistic DOC testing approach due to the variables of light interaction of the composite resin to either tooth substance (enamel/dentin) versus using the Tefion mold, although greater DOCs were recorded using the manufactured device. The SonicFill composite system did reveal greater DOC compared to the Herculite Ultra composite regardless of experimental method or material shade.

Design and evaluation of a filter-based chairside amalgam separation system.

This study evaluated the ability of a chairside filtration system to remove particulate-based mercury (Hg) from dental-unit wastewater. Prototypes of the chairside filtration system were designed and fabricated using reusable filter chambers with disposable filter elements. The system was installed in five dental operatories utilizing filter elements with nominal pore sizes of 50 microm, 15 microm, 1 microm, 0.5 microm, or with no system installed (control). Daily chairside wastewater samples were collected on ten consecutive days from each room and brought to the laboratory for processing. After processing the wastewater samples, Hg concentrations were determined with cold vapor atomic absorption spectrometry (USEPA method 7470A). Filter systems were exchanged after ten samples were collected so that all five of the configurations were evaluated in each room (with assignment order balanced by a Latin Square). The numbers of surfaces of amalgam placed and removed per day were tracked in each room. In part two, new filter systems with the 0.5 microm filter elements were installed in the five dental operatories and vacuum levels at the high-velocity evacuation cannula tip were measured with a vacuum gauge. In part three of the study, the chairside filtration system utilizing 0.5 microm and 15 microm filter elements was evaluated utilizing the ISO 11143 testing protocol, a laboratory test of amalgam separator efficiency utilizing amalgam samples of known particle size distribution. Mean Hg per chair per day (no filter installed) was 1087.38 mg (SD = 993.92 mg). Mean Hg per chair per day for the 50 microm, 15 microm, 1 microm, 0.5 microm filter configurations was 79.13 mg (SD = 71.40 mg), 23.55 mg (SD = 23.25 mg), 17.68 mg (SD = 17.35 mg), and 4.25 mg (SD = 6.35 mg), respectively (n = 50 for all groups). Calculated removal efficiencies from the clinical samples were 92.7%, 97.8%, 98.4%, and 99.6%, respectively. ANCOVA on data from the four filter groups, with amalgam-surfaces-removed included as a significant covariate, was statistically significant (P < 0.0001). Tukey post-hoc comparisons (P < or = 0.05) indicated that the 50 microm filter removed less mercury than all other filters and the 0.5 microm removed more mercury than the 50 microm and 15 microm filters. Chairside vacuum measured on chairs with the 0.5 microm filters installed were minimally affected at the time of installation, and then gradually diminished as the filters became loaded with debris. The 0.5 microm configuration passed the ISO 11143 testing protocol at 96.8% efficiency.

Development and testing of a novel forward-deployable dental dressing.

The purpose of this study was to measure select properties of four temporary filling materials suitable for use in treating minor dental emergencies in the field. Specimens were made of each of the following four materials: intermediate restorative material, Fuji IX GP Fast, Ketac-Molar Quick, and the forward-deployable dental dressing recently developed by the Naval Institute for Dental and Biomedical Research. Twenty-fours hours after specimen fabrication, five properties (hardness, compressive strength, diametral tensile strength, flexural strength, and flexural modulus) were measured for each of the materials and compared using analysis of variance and Tukey-Kramer tests to determine whether significant differences existed among the materials (alpha = 0.05). Data analysis revealed that significant differences existed among the products for all of the properties tested. The forward-deployable dental dressing's properties compared favorable with and, in many cases exceeded those of intermediate restorative material, Fuji IX GP Fast, and Ketac-Molar Aplicap Quick.

Evaluation of field dental equipment in a deployment environment.

Dental officers and technicians must have reliable, durable, well-performing field dental equipment to enable them to provide dental care to deployed troops in operational environments. Unfortunately, no organized program exists to test such equipment before its purchase and use in the field. This article presents the results of a project conducted by the Naval Institute for Dental and Biomedical Research and the Air Force Dental Evaluation and Consultation Service to evaluate commercially available field dental equipment through laboratory testing and clinical-user evaluations in theater. The purpose of this 2-year project was to identify the best-performing and most cost-effective field dental equipment for possible future procurement. Initial laboratory testing was performed at the Naval Institute for Dental and Biomedical Research, and the equipment was then shipped to Kuwait for in-theater environmental and clinical-user testing. A seven-member scientific team of military dental officers and technicians was deployed for 1 month to perform in-theater testing under regional environmental conditions and to coordinate clinical-user evaluations. The testing provided beneficial results by identifying equipment that performed properly and equipment that exhibited shortcomings serious enough to render it inadequate for operational use. It is recommended that the project serve as a model for future testing and evaluation of medical/dental equipment by all of the military services.

Comparison of two video-imaging instruments for measuring volumetric shrinkage of dental resin composites.

OBJECTIVES: The purpose of this study was to measure the polymerization shrinkage of three dental resin composites using two commercially available video-imaging devices to determine if the devices produced equivalent results. METHODS: Small, semi-spherical specimens of a microhybrid (Venus), microfill (Filtek A110), and flowable (Esthet*X Flow) resin composite were manually formed and light activated for 40s using a light-curing unit. The volumetric polymerization shrinkage of fifteen specimens of each brand of resin composite was measured using the AcuVol and the Drop Shape Analysis System model DSA10 Mk2 (DSAS) video-imaging devices. Mean volumetric shrinkage values were calculated for each resin composite and equivalence was evaluated using the two one-sided tests approach. Differences between the means that were less than approximately 5% of the observed shrinkage were considered indicative of clinical equivalence. RESULTS: Mean volumetric shrinkage values measured for the resin composites were: Venus (AcuVol, 3.07+/-0.07%; DSAS, 2.90+/-0.07%); Filtek A110 (AcuVol, 2.26+/-0.10%; DSAS, 2.25+/-0.09%); and Esthet*X Flow (AcuVol, 5.01+/-0.17%; DSAS, 5.14+/-0.11%). Statistical analysis revealed that the two imaging devices produced equivalent results for Filtek A110 and Esthet*X Flow but not for Venus. CONCLUSIONS: Video-imaging systems provide an easy method for measuring volumetric shrinkage of resin composites. As with other methods for measuring volumetric shrinkage, however, they are best used to comparatively measure different materials within the same laboratory.

Disinfectants' effect on mercury release from amalgam.

BACKGROUND: Mercury environmental discharge is under increased scrutiny by the U.S. Environmental Protection Agency (EPA). Dental amalgam should be processed properly to prevent an additional environmental burden. Some processing agencies require that submitted amalgam be noninfectious. Investigations have demonstrated that oxidizing disinfectants mobilize mercury from amalgam into solution and add mercury to the environmental burden if it is disposed of improperly. The authors conducted a study to evaluate the effect of representative disinfectants on amalgam mercury release. METHODS: The authors sized a high-copper spherical amalgam alloy to match that typically found in dental unit suction traps. They exposed 20 grams of the alloy to several disinfectant solutions and evaluated the filtered supernatant solution for mercury content. RESULTS: Chlorine disinfectant materials discharged the most mercury ions, followed by bromide, iodophor, peroxide/peracetic acid and phenolic disinfectants. The quaternary ammonium compound did not discharge mercury ions above the detection limit (0.2 parts per billion) into solution. CONCLUSIONS: A quaternary ammonium compound did not mobilize mercury ions into solution when used as a disinfectant agent for amalgam. Chlorine disinfectants mobilized mercury ions the most, followed by bromide, iodophor, peroxide/peracetic acid and phenolic disinfectants. CLINICAL IMPLICATIONS: Dentists are obligated to be good environmental stewards and should follow practices that reduce environmental mercury release. Dental personnel should be aware that oxidizing disinfectants mobilize mercury ions into solution, which will be added to the environment if they are processed improperly. If required by processing, dental personnel should consider the different oxidizing effects of commonly used disinfectants.

Dental sealant longevity in a cohort of young U.S. naval personnel.

BACKGROUND: The U.S. Navy emphasizes caries prevention and encourages the placement of dental sealants on the caries-susceptible teeth of patients at risk of developing caries. The authors analyzed dental records to assess the longevity of dental sealants placed in naval personnel. METHODS: A cluster sample of dental records from 1,123 personnel who entered naval service in 1997 was drawn from eight Navy dental treatment facilities. The authors determined the number of sealants provided, the number of sealants that failed over the observation period (1997-2001), the dates of sealant failure and the longevity of sealants placed during and after recruit training. RESULTS: A total of 319 personnel received sealants during their first two years of service. The authors evaluated 1,467 sealed teeth. They followed the sealants for an average of 35 months. They noted 179 sealant failures in 102 subjects; 69 previously sealed teeth required sealant replacement, and 110 sealed teeth required restoration of the occlusal surface. Among those sealants that failed, the mean length of time from placement to failure was 26 months. Sealant failure rates were significantly higher among subjects at moderate risk or high risk of developing caries than among subjects at low risk. CONCLUSIONS: After an average of 35 months, 87.8 percent of the sealants placed in this population were retained and functional. Subjects who were at moderate or high risk of developing caries demonstrated significantly higher sealant failure rates than those at low risk of developing caries. CLINICAL IMPLICATIONS: Dental sealants can be retained successfully in adults. They should be considered a viable treatment alternative for adult patients who are susceptible to caries; however, patients at elevated risk of developing caries may require more frequent re-evaluation and maintenance to achieve maximum benefit.

Statistical estimation of resin composite polymerization sufficiency using microhardness.

With respect to determining sub-surface resin polymerization sufficiency, this study compared a traditional method of applying linear regression to bottom- to top-surface Knoop hardness ratios to an alternative method based on nonlinear regression. Inverse linear regression on ratios was used to estimate the exposure duration required for 80% bottom-surface hardness with respect to the top, in six light-by-material groups. Alternatively, a one-phase, two-parameter, exponential association of the form Y=Y(max)(1-e(-kt)) (where Y(max) is maximum hardness, k is a rate constant, and t is exposure duration), was used to model hardness. Inverse nonlinear regression estimated, for each condition, the exposure duration required for the bottom surface to achieve 80% of corresponding condition (light and material) top-surface Y(max). Mathematically, analysis of ratios was demonstrated to yield potentially less precise and biased estimates. Nonlinear regression yielded better statistical fit and provided easily accessible tests for differences in k across light-system groups. Another recently proposed nonlinear model for polymerization, Y=Y(max)kt(n)/(1+kt(n)), was also considered. While this new model has substantially greater phenomenological and mechanistic justification, we found that the model-fitting process was more sensitive to initial parameter values and sometimes yielded untenable results when applied to our data. However, we believe that these problems would not occur if sample points are well distributed across a wide range of exposure durations, and that the model, Y=Y(max)kt(n)/(1+kt(n)), should be considered for such data sets.

Diagnosis of militarily relevant diseases using oral fluid and saliva antibodies: fluorescence polarization immunoassay.

This laboratory is developing fluorescence polarization (FP) methods as diagnostic tools to assay antibodies in saliva and other oral fluids. FP provides quantitation of molecular interaction, such as antigen-antibody binding, of a single, small-volume sample in real time and without prior separation of components such as blood cells. There is potential for wide-spread use of these homogeneous assays as noninvasive tests, especially as more compact, simplified fluorescence polarimeters become available. FP tests can be designed that are applicable to a wide spectrum of microorganisms and may be used in a clinic or far-forward deployed setting to aid in diagnosis of disease or verification of vaccination. Rapid salivary diagnostics, including FP, have been identified by the Office of Naval Research as requirements for future naval capabilities in basic and applied medical research for warfighter protection in casualty prevention. The applications of FP salivary diagnostics for determination of tuberculosis exposure and of anthrax immunization status are discussed as examples.

Waterline biofilm and the dental treatment facility: a review.

Biofilms are well-organized communities of cooperating microorganisms that can include bacteria, protozoa, diatoms, and fungi. Surveys of dental unit waterlines (DUWLs) indicate that biofilm formation is a universal problem and that environmental and human-derived opportunistic pathogens can be cultured consistently from biofilms retrieved from DUWLs and other dental devices. Although the health risks presented by waterline bacterial colonization have yet to be adequately addressed, professional and ethical considerations indicate that steps should be taken to improve the quality of DUWLs. To address these concerns, the Council on Scientific Affairs of the ADA recently published a list of products cleared by the FDA to control dental waterline contamination. The goal of this article is to increase the awareness of potential health risks posed by biofilm formation and provide information on techniques and devices designed to control the microbial contamination of DUWLs.