Application of organoselenium in inhibiting Candida albicans biofilm adhesion on 3D printed denture base material.

PURPOSE: Denture Stomatitis, a chronic mucosal inflammation associated with Candida albicans, is common among denture wearers. Several health conditions have been linked to chronic Candida infections. The complex, multifactorial nature of denture stomatitis requires the continuous pursuit of effective long-term solutions. The present in vitro study investigated the effect of incorporating organoselenium into 3D-printed denture base resin on C. albicans adhesion and biofilm formation. MATERIALS AND METHODS: Thirty disks were fabricated using 3D-printed denture base resin and assigned to three experimental groups (10/group): disks without organoselenium (control), disks with 0.5% organoselenium (0.5%SE), and disks with 1% organoselenium (1%SE). Each disk was incubated with approximately 1 × 106 cells/mL of C. albicans for 48 h. Microbial viability (CFU/mL) was quantified by the spread plate method, while Confocal laser scanning microscopy and scanning electron microscope were performed for quantifying the biofilm thickness and examining biofilm morphology, respectively. Data were analyzed using One-way ANOVA with Tukey's multiple comparisons test. RESULTS: CFU/mL was significantly (p < 0.05) higher in Control when compared with 0.5%SE and 1%SE, but no significant difference between 0.5%SE and 1%SE. A similar trend was observed with biofilm thickness except that there was no significant difference between the Control and 0.5%SE. There was C. albicans biofilm adhesion on the Control disks, with yeast cells and hyphae formation, whereas on 0.5%SE and 1%SE, there was inhibition of yeast cells transition to hyphae formation. CONCLUSIONS: Incorporation of organoselenium into 3D-printed denture base resin was effective in reducing C. albicans biofilm formation and growth on denture base material.

Bur Choice When Removing Zirconia Restorations.

PURPOSE: Removal of zirconia restorations can be challenging and time consuming, requiring dental burs with optimal cutting efficiency to minimize iatrogenic complications. Yet, there are very few burs marketed for this purpose and little evidence of their comparative benefit. This study evaluated one specialized bur and compared its cutting efficiency with three general-purpose burs (one single use and two multiple uses). MATERIALS AND METHODS: This study was designed to assess the cutting efficiency of 4 burs on a high-strength zirconia substrate. One of these burs is a multiple-use bur marketed for high-strength ceramics (Komet 4ZR), another is a single-use general-purpose bur (Piranha 837.012 coarse), and two are multiple-use general-purpose burs (Brassler 6837.31.012C coarse and Komet 6837.314.012 coarse). The cutting efficiency of each bur was determined by measuring the time taken to perform serial 2 mm cuts into a block of zirconia. Ten burs in each group were tested with repeated cuts until the time taken for a 2 mm cut was twice that of the first 2 mm cut (50% loss of efficiency). This study was performed under reproducible conditions using a custom-designed and fabricated rig assembly. RESULTS: The results demonstrated a statistically significant difference in the cutting efficiency between bur types. The single-use general-purpose bur (Piranha 837.012) was the most efficient for all cut numbers p <2.2 × 10-16 . The performance of all burs decreased with each cut, with cutting efficiency dependent on time point/cut number (p = 0.02). The rate of deterioration varied between burs, but this difference was not sufficient to be statistically significant. CONCLUSIONS: This study demonstrated that a single-use bur is more efficient than 3 multiple-use burs. The cutting efficiency of a single-use general-purpose bur (Piranha 837.012 coarse) on Cerec Zirconia Mono L was statistically superior to that of multiple patient use burs in this study, including one marketed for use on high-strength ceramics. Because single-use burs are comparatively inexpensive and require no sterilization, they should be strongly considered for the removal of zirconia restorations.

Fracture Resistance of Pressed and Milled Lithium Disilicate Anterior Complete Coverage Restorations Following Endodontic Access Preparation.

PURPOSE: This in vitro study evaluated the fracture resistance and clinical prognosis of anterior lithium disilicate crowns (e.max Press and e.max CAD), following endodontic access and repair. The research design simulates intraoral loading conditions to produce clinically applicable results. MATERIALS AND METHODS: Monolithic anterior crowns, based on #8 anatomy, were fabricated from e.max Press ingots and e.max CAD blocks and adhesively bonded on identical dies milled out of a dentin analog material (NEMA G10). Specimens were divided into 4 groups: intact pressed, repaired pressed, intact milled, and repaired milled (n = 15/group). Repaired pressed and repaired milled were prepared with a standardized endodontic access and repaired using a porcelain repair system and composite resin. All crowns were cyclically loaded under simulated oral conditions and then loaded to failure in water, using a universal testing machine. Data were interpreted using ANOVA/Tukey post-hoc test (α = 0.05). RESULTS: Mean loads to failure ranged from 758.9 to 931.4 N for the 4 groups, indicating that both fabrication techniques, pressed and milled, yielded restorations that could reasonably withstand maximum masticatory forces. The pressed groups (923.7 N) exhibited significantly higher fracture resistance than the milled groups (797.5 N), p = 0.0002. When milled and pressed groups were categorized into intact and repaired subgroups, no difference was found in fracture resistance between the subgroups. Differences were noted in the modes of fracture, where the milled groups (intact and repaired) exhibited higher frequency of catastrophic fractures than the pressed groups. CONCLUSIONS: Endodontic access preparation does not appear to affect fracture resistance of an anterior lithium disilicate restoration, suggesting that replacement may not be necessary. Fabrication technique had a significant effect on fracture resistance and fracture mode of lithium disilicate restorations. The pressed fabrication technique resulted in significantly greater crown strength and fracture resistance than the milled technique.

Critical Thinking in Dental Students and Experienced Practitioners Assessed by the Health Sciences Reasoning Test.

To date, there has been a lack of published studies examining the validity of the Health Sciences Reasoning Test (HSRT) to assess critical thinking among dental students. The aim of this study was to examine the construct validity of the HSRT using a novice-expert model consisting of first-year dental students as novices and experienced general dentists as experts. Novice cohort subjects were recruited from all 105 students in the first-year dental school class at the University of Texas Health Science Center at San Antonio during a regularly scheduled course in August 2015. A total of 83 students participated, for a 79% response rate. Thirty individuals personally recruited from the same school's faculty and from private practitioners made up the expert cohort. The results showed that the adjusted mean overall score for the expert cohort (25.31) was significantly higher than that of the novice cohort (22.64) (p=0.04). The expert cohort achieved higher adjusted mean scores in all scales (Induction, Deduction, Analysis, Inference, and Evaluation), with the difference in the Analysis scale being significant (p=0.02). In this study, experienced general dentists achieved significantly better overall scores on the HSRT as compared to first-year dental students, suggesting the instrument was able to measure differences between novice and expert. Further efforts to validate the instrument in a dental education setting and to understand its correlation with strategies and practices aimed at developing critical thinking in dental students are warranted.

Management of Challenging Esthetic Anterior Cases with Limited Restorative Space: A Clinical Report.

With careful restorative planning and surgical placement, dental implants can be used to support and retain a wide range of esthetic prostheses. When implant planning or surgical executions are less than ideal, however, the resulting restorative space can be a significant obstacle to successful treatment. The aim of this article is to describe the use of a customized anterior bar to support a partial overdenture prosthesis for a youthful patient with a high smile line and a limited restorative space of 6 mm. Details of the treatment and an illustration of the customized design are also presented.

Marginal discrepancy of noble metal-ceramic fixed dental prosthesis frameworks fabricated by conventional and digital technologies.

STATEMENT OF PROBLEM: Studies evaluating the marginal adaptation of available computer-aided design and computer-aided manufacturing (CAD-CAM) noble alloys for metal-ceramic prostheses are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the vertical marginal adaptation of cast, milled, and direct metal laser sintered (DMLS) noble metal-ceramic 3-unit fixed partial denture (FDP) frameworks before and after fit adjustments. MATERIAL AND METHODS: Two typodont teeth were prepared for metal-ceramic FDP abutments. An acrylic resin pattern of the prepared teeth was fabricated and cast in nickel-chromium (Ni-Cr) alloy. Each specimen group (cast, milled, DMLS) was composed of 12 casts made from 12 impressions (n=12). A single design for the FDP substructure was created on a laboratory scanner and used for designing the specimens in the 3 groups. Each specimen was fitted to its corresponding cast by using up to 5 adjustment cycles, and marginal discrepancies were measured on the master Ni-Cr model before and after laboratory fit adjustments. RESULTS: The milled and DMLS groups had smaller marginal discrepancy measurements than those of the cast group (P<.001). Significant differences were found in the number of adjustments among the groups, with the milled group requiring the minimum number of adjustments, followed by the DMLS and cast groups (F=30.643, P<.001). CONCLUSIONS: Metal-ceramic noble alloy frameworks fabricated by using a CAD-CAM workflow had significantly smaller marginal discrepancies compared with those with a traditional cast workflow, with the milled group demonstrating the best marginal fit among the 3 test groups. Manual refining significantly enhanced the marginal fit of all groups. All 3 groups demonstrated marginal discrepancies within the range of clinical acceptability.

Effect of Split-File Digital Workflow on Crown Margin Adaptation.

PURPOSE: Computer-aided design/computer-aided manufacturing (CAD/CAM) is becoming increasingly integrated into dental practice workflow at a pace that exceeds scientific validation. The aim of this study is to evaluate a complete digital split-file protocol relative to segmental digital and analog techniques for restoring a single maxillary anterior edentulous space with custom abutment and crown. MATERIALS AND METHODS: Four treatment workflows were assessed: complete digital (CD), segmental digital (SD), milled wax (AM), and heat pressed and hand waxed (AH) and heat pressed. The CD workflow "split" an abutment and crown into separate files to fabricate a zirconia abutment and both zirconia/lithium disilicate crown restorations. The SD workflow scanned the existing abutment for design of segmental restorations in zirconia, lithium disilicate, and milled wax (AM). The AH specimens were conventionally hand waxed. Both the AM and AH specimens were heat pressed with lithium disilicate. All restorations were evaluated with standardized measurements using scanning electron microscopy (SEM) as manufactured without internal adjustments and after manual adjustment. The number of adjustments, adjustment time, and location of adjustments were recorded. One-way ANOVA with repeated measures was used to report geometric means with 95% confidence intervals. RESULTS: The mean marginal gap after adjustment of the CD group was 69 µm, with an upper bound (UB) of 79 µm and a lower bound (LB) of 60 µm. SD group mean was 26 µm with an UB of 31 µm and LB of 22 µm. The AM group mean was 32 µm, with an UB of 49 µm and a LB of 20 µm; AH group mean of 26 µm with an UB of 34 µm and a LB of 20 µm. The SD, AM, and AH workflows were statistically similar (p = 1.000), and the CD workflow was statistically greater than the other three (p < 0.001). CONCLUSIONS: The split-file (CD) protocol results in marginal gap size within clinical standards after adjustment; however, 52 of the 60 digitally produced restorations showed a horizontal marginal offset that required adjustment for proper contours.

Marginal Gap of Milled versus Cast Gold Restorations.

PURPOSE: This in vitro study evaluated and compared the vertical marginal gap of cast and milled full coverage gold copings using two margin designs (chamfer and chamfer bevel) before and after fitting adjustments. MATERIALS AND METHODS: Ten impressions were made of two metal master dies (one chamfer margin, one chamfer-bevel margin) and poured twice in Type IV stone. The 20 subsequent casts with 40 dies were split into four groups (n = 10); cast gold bevel, cast gold chamfer, milled gold bevel, and milled gold chamfer groups. The cast specimens received approximately 40 µm die relief no closer than 1 mm from the finish line. Cast copings were hand waxed, cast in a high noble gold alloy, chemically divested, and the sprues were removed. For milled gold copings, casts were scanned and copings designed using 3shape D900 scanner and software. Parameters were set to approximate analog fabrication (cement gap = 0.01 mm; extra cement gap = 0.04 mm, drill radius = 0.65 mm). Copings were milled from the same high noble alloy. All copings were seated on their respective master die in a custom scanning jig and measured using a measuring microscope at 90× (60 measurements per specimen, 15 per surface). Following initial measurements, all copings were adjusted on stone dies. The number of adjustment cycles was recorded and post-adjustment measurements were made using the same method. Data were analyzed using independent and paired t-tests. RESULTS: Milled gold copings with a beveled margin (11.7 ± 20.4 µm) had a significantly (p < 0.05) smaller marginal gap than cast gold copings with a beveled margin (43.6 ± 46.8 µm) after adjustment. Cast gold copings with a chamfer margin (22.7 ± 24.7 µm) had a significantly (p < 0.05) smaller marginal gap than milled gold copings with a chamfer margin (27.9 ± 31.6 µm) following adjustments. Adjustments significantly decreased marginal gap for both cast groups (p < 0.05) and the milled chamfer bevel group (p < 0.05) but had no significant effect on the milled chamfer group. CONCLUSIONS: Within the limitations of this study, results indicate that gold restorations milled with the tested parameters provide a vertical marginal gap that is an acceptable alternative to traditional gold crown casting techniques.

Enhancing Fracture and Wear Resistance of Dentures/Overdentures Utilizing Digital Technology: A Case Series Report.

Since it was first introduced into the dental world, computer-aided design/computer-aided manufacturing (CAD/CAM) technology has improved dramatically in regards to both data acquisition and fabrication abilities. CAD/CAM is capable of providing well-fitting intra- and extraoral prostheses when sound guidelines are followed. As CAD/CAM technology encompasses both surgical and prosthetic dental applications as well as fixed and removable aspects, it could improve the average quality of dental prostheses compared with the results obtained by conventional manufacturing methods. The purpose of this article is to provide an introduction into the methods in which this technology may be used to enhance the wear and fracture resistance of dentures and overdentures. This article will also showcase two clinical reports in which CAD/CAM technology has been implemented.

Precision of fit between implant impression coping and implant replica pairs for three implant systems.

STATEMENT OF PROBLEM: The fabrication of an accurately fitting implant-supported fixed prosthesis requires multiple steps, the first of which is assembling the impression coping on the implant. An imprecise fit of the impression coping on the implant will cause errors that will be magnified in subsequent steps of prosthesis fabrication. PURPOSE: The purpose of this study was to characterize the 3-dimensional (3D) precision of fit between impression coping and implant replica pairs for 3 implant systems. The selected implant systems represent the 3 main joint types used in implant dentistry: external hexagonal, internal trilobe, and internal conical. MATERIAL AND METHODS: Ten impression copings and 10 implant replicas from each of the 3 systems, B (Brånemark System), R (NobelReplace Select), and A (NobelActive) were paired. A standardized aluminum test body was luted to each impression coping, and the corresponding implant replica was embedded in a stone base. A coordinate measuring machine was used to quantify the maximum range of displacement in a vertical direction as a function of the tightening force applied to the guide pin. Maximum angular displacement in a horizontal plane was measured as a function of manual clockwise or counterclockwise rotation. Vertical and rotational positioning was analyzed by using 1-way analysis of variance (ANOVA). The Fisher protected least significant difference (PLSD) multiple comparisons test of the means was applied when the F-test in the ANOVA was significant (α=.05). RESULTS: The mean and standard deviation for change in the vertical positioning of impression copings was 4.3 ±2.1 µm for implant system B, 2.8 ±4.2 µm for implant system R, and 20.6 ±8.8 µm for implant system A. The mean and standard deviation for rotational positioning was 3.21 ±0.98 degrees for system B, 2.58 ±1.03 degrees for system R, and 5.30 ±0.79 degrees for system A. The P-value for vertical positioning between groups A and B and between groups A and R was <.001. No significant differences were found for vertical positioning between groups B and R. The P-value for rotational positioning between groups A and B and between groups A and R was <.001. No significant differences were found for rotational positioning between groups B and R. CONCLUSIONS: The results of the study confirmed that implant systems differ in precision of fit. Vertical precision between paired implant components is a function of joint type and the tightening force applied to the guide pin. The magnitude of vertical displacement with applied torque is greater for conical connections than for butt joint connections. The rotational freedom between paired components is unique to the implant system and is presumably related to the machining tolerances specified by the manufacturer.

Rubrics 101: a primer for rubric development in dental education.

Identifying and implementing effective methods for assessing dental student performance are ongoing challenges for dental educators. Questions related to grading and assessment are common among faculty and students alike. Faculty members who are well-trained clinicians or scientists often have little formal training in education. In addition, assessment of performance brings with it an element of subjectivity. Questions about assessment and grading are most likely to arise when expectations are unclear or the rationale for the grade awarded is not articulated. The authors propose that one solution to assessment dilemmas can be found in the use of rubrics: scaled tools with levels of achievement and clearly defined criteria placed in a grid. Rubrics establish clear rules for evaluation and define the criteria for performance. Rubrics speak to both teaching and learning expectations and outcomes and can provide faculty members with a tool that can be useful in evaluating dental student performance. Rubrics can also provide students with clear expectations of performance, an opportunity to self-assess, and timely, detailed feedback. The purpose of this article is to define a rubric, apply the steps of rubric development as described in the educational literature to dental student assessment, present two examples of rubric implementation for assessing student progress toward competence, and recommend electronic resources for rubric development.

The chamfer finish line: preclinical student performance using different bur designs.

The primary purposes of this investigation were to evaluate sophomore dental student performance in the production of a chamfer finish line using two diamond bur types-a round-ended bur and a torpedo-shaped bur-and to gain student feedback about their preferences for bur type. Fifty students took part in the study, each of whom prepared the buccal surfaces of two mandibular molar typodont teeth, producing chamfer finish lines. Students prepared both teeth in the same laboratory session and were randomly assigned to two groups that were required to prepare the first of the two molars with a specific bur type. The prepared chamfer finish lines were scored and the data analyzed using the Wilcoxon signed-rank test. Student performance was significantly better when the round-ended bur was used (p=0.005). Student feedback was collected with a survey that consisted of four questions and the opportunity to provide write-in comments. In response to the question "Overall, was one bur type better?" 58 percent of the students preferred the round-ended bur for creating a chamfer finish line. The most frequent write-in comment, made by twelve of the fifty students, criticized the torpedo-shaped bur for creating finish lines that were too shallow or too long.

Functional impressions for complete denture fabrication. A modified jump technique.

Tissue conditioners are used with great success in dentistry as functional impression materials for rebasing removable prostheses. In the rebase procedure, a functional impression is made in an existing denture to create a master cast. The orientation of the occlusal surface to the underlying tissue surface is captured with a reline jig or denture flask and transferred to the new denture base in what is called a "jump" in laboratory jargon. Functional impression methods are not commonly considered, however, for the fabrication of new dentures despite their popularity and ease of use. This article describes a modified jump technique for remaking complete dentures. The method uses functional impressions in existing maxillary and mandibular dentures to create master casts and to act as stabilized carriers for jaw relation records. More precise esthetic and phonetic assessments of the existing prostheses are accommodated, and prescriptive changes may be referenced to the current tooth arrangement.