Circumferential root strains generated during lateral compaction with stainless steel vs. nickel-titanium finger spreaders.

The circumferential strains created in the radicular dentin by nickel-titanium (NiTi) and stainless steel (SS) finger spreaders (FSs) during a simulated clinical procedure of lateral compaction were compared after minimal (size 50) and extensive (size 100) canal preparations. Nineteen maxillary central incisors underwent minimal preparation, while 10 underwent an extra phase of extensive preparation. Four miniature strain gauges were bonded circumferentially in the apical third of the root (buccal, lingual, mesial, and distal). Lateral compaction was performed using either NiTi-FSs or SS-FSs. Force and strains were continuously recorded. The maximal strains (with and without normalization according to force) were recorded. The SS-FSs generated higher maximal strains normalized according to force compared with the NiTi-FSs. The maximal normalized strains were higher by 37%-43% for the mesial and distal aspects and by 6%-14% for the buccal and lingual aspects after the minimal preparation and by 24%-28% for the mesial and distal aspects and by 19%-20% for the buccal and lingual aspects after extensive preparation. The maximal normalized strains increased by 30%-70% from minimal to extensive preparations, with two teeth exhibiting vertical root fracture while compaction with SS-FS. The NiTi-FSs induce less strain in root dentin than the SS-FSs and thus may contribute less to the risk of vertical root fracture.

The Retentive Strength of Laser-Sintered Cobalt-Chromium-Based Crowns after Pretreatment with a Desensitizing Paste Containing 8% Arginine and Calcium Carbonate.

The retention of laser-sintered cobalt-chromium (Co-Cr)-based crowns were examined after dentin pretreatment with desensitizing paste containing 8% arginine and calcium carbonate (DP-ACC). Forty lower first molars were prepared using a standardized protocol. The Co-Cr crowns were produced using selective laser melting. The teeth were either pretreated with the desensitizing paste or not pretreated. After one week, each group was cemented with glass ionomer cement (GIC) or zinc phosphate cement (ZPC). Surface areas of the teeth were measured before cementation. After aging, a universal testing machine was used to test the retentive strength of the cemented crown-tooth assemblies. The debonded surfaces of the teeth and crowns were examined at 2.7× magnification. Pretreating the dentin surfaces with the desensitizing paste before cementation with GIC or ZPC did not affect the retention of the Co-Cr crowns. The retention of the GIC group (6.04 ± 1.10 MPa) was significantly higher than that of the ZPC group (2.75 ± 1.25 MPa). The predominant failure mode for the ZPC and the nontreated GIC group was adhesive cement-dentin failure; for the treated GIC group, it was adhesive cement-crown failure. The desensitizing paste can be safely used to reduce post-cementation sensitivity without reducing the retentive strength of Co-Cr crowns cemented with GIC or ZPC.

The effect of resin coating on the shear punch strength of restorative glass ionomer cements.

OBJECTIVE: The aim of the current study was to examine the shear punch strength (SPS) of high-strength glass ionomer cements (HSGICs) in relation to coating applications and duration of coating. MATERIALS AND METHODS: I-Ninety specimens each of Fuji IX GP Fast (FIX Fast), Ionofil Molar AC (IM), Riva Self Cure (R) and Ketac Molar (KM) were prepared and divided into uncoated and coated groups, sub-divided into three sub-groups and incubated for 24 h, 1 week or 8 weeks (distilled water, 37 °C) before SPS. II-Ninety specimens each of uncoated and coated Fuji IX GP Extra were similarly prepared, divided into six sub-groups and incubated for 2 h, 24 h, 1 week, 1 month, 2 months or 3 months (artificial saliva, 37 °C) before SPS. Another 90 specimens were coated for 2 h, 24 h, 1 week, 1 month or 2 months, after which the coating was removed. Specimens were re-incubated in artificial saliva until the end of the 3-month period and then subjected to SPS. RESULTS: None of the materials gained extra strength when coated. Uncoated KM, IM (at all times) and FIX Fast (at 24 h) were stronger. Fuji IX GP Extra achieved 11.5 MPa after 2 h, which increased to 56.7 MPa after 24 h. The highest strength after 3 months was achieved when the coating was retained for 2 h (71.7 MPa). CONCLUSION: A resin coating will not positively affect the SPS of HSGICs. CLINICAL RELEVANCE: There is no need to protect HSGICs from water to gain extra strength unless the coating is retained for 2 h.

Effect of Silane Reaction Time on the Repair of a Nanofilled Composite Using Tribochemical Treatment.

PURPOSE: To investigate the influence of silane reaction time on the repair strength of an aged nanofilled composite and to characterize the bonding mechanism. MATERIALS AND METHODS: Nanofilled composite disks (n = 110, Filtek Supreme XT) were aged for 90 days in water. After tribochemical treatment (CoJet-Sand), the specimens were assigned to 5 groups (n = 22), primed with silane (Espe-Sil), and left to react for 1, 2, 3, 4, and 5 min. A thin layer of adhesive (Visio-Bond) was applied and a new composite with the same dimension was placed and cured. Non-aged specimens immediately layered and cured using the incremental technique served as controls. After aging (30 days in water plus 5000 thermal cycles), the interface was subjected to a shearing force until failure. Failure mode was evaluated under a stereomicroscope and scanning electron microscopy (SEM). Additional aged and treated surfaces were evaluated for morphology as well as elemental and molecular composition using SEM/EDX and ATR-FTIR. RESULTS: The mean shear bond strength (SBS) of the repaired specimens was 53.9 ± 8.6 MPa, with no significant difference among the various reaction times, but significantly lower compared to the control (88.1 ± 12.5 MPa). Tribochemical treatment created an irregular surface morphology with particles imbedded in the aged surface. Interfacial SEM/EDX analysis showed a 5-µm non-uniform high atomic number zone rich in Al and Si. CONCLUSION: Tribochemical treatments for repairing composite using a short silane reaction period (1 min) are equally effective as the prolonged reaction periods (2 to 5 min), yielding interfacial shear strength of ~60% of unrepaired material.

The Retentive Strength of Cemented Zirconium Oxide Crowns after Dentin Pretreatment with Desensitizing Paste Containing 8% Arginine and Calcium Carbonate.

The effect of dentin pretreatment with Desensitizing Paste containing 8% arginine and calcium carbonate on the retention of zirconium oxide (Y-TZP) crowns was tested. Forty molar teeth were mounted and prepared using a standardized protocol. Y-TZP crowns were produced using computer-aided design and computer-aided manufacturing (CAD-CAM) technology. The 40 prepared teeth were either pretreated with Desensitizing Paste or not pretreated. After two weeks, each group was subdivided into two groups, cemented with either Resin Modified Glass Ionomer Cement (RMGIC) or Self Adhesive Resin Cement (SARC)). Prior to cementation, the surface areas of the prepared teeth were measured. After aging, the cemented crown-tooth assemblies were tested for retentive strength using a universal testing machine. The debonded surfaces of the teeth and crowns were examined microscopically at 10× magnification. Pretreating the dentin surfaces with Desensitizing Paste prior to cementation did not affect the retention of the Y-TZP crowns. The retentive values for RMGIC (3.04 ± 0.77 MPa) were significantly higher than those for SARC (2.28 ± 0.58 MPa). The predominant failure modes for the RMGIC and SARC were adhesive cement-dentin and adhesive cement-crown, respectively. An 8.0% arginine and calcium carbonate in-office desensitizing paste can be safely used to reduce post-cementation sensitivity without reducing the retentive strength of Y-TZP crowns.

The effect of one-step vs. two-step impression techniques on long-term accuracy and dimensional stability when the finish line is within the gingival sulcular area.

PURPOSE: To evaluate the effect of two putty-wash impression techniques on the long-term accuracy and dimensional stability of poly(vinyl siloxane) (PVS) in the gingival sulcus area. MATERIALS AND METHODS: Impressions were taken from a master cast to simulate molar crown preparation. A space around the abutment served as the gingival sulcus. Fifteen impressions using the one- and two-step impression techniques were taken using Express Regular, Express Fast, and President impression materials with custom trays. Using a Toolmaker's microscope, the long (LD) and short distances (SD) of the abutment and the planar distance between two parallel lines (PL) at the circumference of the cast were taken at 0.5, 2, 24, 48, 72, 96, 120, and 144 hours after mixing. ANOVA was performed, with the discrepancy between the distances of the impressions and the master cast as the dependent variable. RESULTS: The differences when different materials and impression techniques were used were significant (p < 0.001) for LD, SD, and PL, as was the interaction between the material, time, and technique (p < 0.001). SD discrepancies were higher than those of LD for all materials and times. The two-step impression technique was more accurate, with smaller discrepancies than the one-step impression technique. For all materials, the PL discrepancy was deemed acceptable (less than 0.5%) for all tested times. President had higher discrepancies than the other materials. CONCLUSIONS: When using the two-step putty-wash impression technique, pouring of the impressions may be postponed up to 30 hours; however, when using the one-step impression technique, pouring should be performed within 2 hours.

The effect of contaminating media on the static and dynamic mechanical resilience of dental implant abutments' screws: In vitro study.

INTRODUCTION: This in vitro study aims to biomechanically evaluate the influence of medium contamination for example, saliva, blood, chlorhexidine (liquid and gel), and fluoride mouthwash on the biomechanical behavior of implant abutments' screws under static and dynamic loading. METHODS: Forty five Ti6Al4V commercial dental implants and abutments were tested in this study. Two main mechanical tests were carried out in the selected media. The first, static, aimed to evaluate the torque loss after the first tightening. The second, dynamic, involved a random cyclic load range between 0 and 200 N to evaluate torque loss due to mastication. In addition, metallographic longitudinal and cross-sections of the abutment-implant apparatus were examined to evaluate the abutment screw-abutment-implant interface. RESULTS: The static torque test showed that irrespective of the media, no statistical difference in static torque loss was found prior to dynamic loading. For the dynamic tests, torque-angle evolution analysis during tightening to 30 Ncm and after the spectrum loading, showed the same global mechanical behavior for all media, but the statistical analysis indicated a difference between the groups in reverse torque values (RTV) and in the torque loss due to dynamic loading. The medium groups CHX, CHX-gel, and Fluoride mouthwash, showed a meaningful torque loss due to loading, but the medium groups, control (no medium), blood and saliva showed an opposite trend and required a higher torque to open the abutment screws. The microstructural analysis revealed clear signs of cold-welding/galling, post-dynamic loading in these latter groups. CONCLUSIONS: The presence of lubrication/contamination media (CHX mouthwash/CHX-gel/Fluoride mouthwash) reduces the preload generated due to tightening but prevents damage due to galling. The observed reduction of RTV clearly emphasizes the need for frequent abutment screw retightening for implant-supported prosthetic long-term stability.

Effect of Silica-Modified Aluminum Oxide Abrasion on Adhesion to Dentin, Using Total-Etch and Self-Etch Systems.

This study compared the shear bond strength (SBS) and micromorphology of composite resin to human dentin after pre-treatment with silica-modified aluminum oxide air abrasion. Forty-six molar teeth were treated with either Scotchbond Multi-Purpose (SCMP) or Clearfil SE Bond (CLSE) adhesive. Buccal surfaces were pre-treated with the CoJet air abrasion system (SB), and lingual surfaces were controls. The adhesion of light-cured resin composite to the treated dentin surface was evaluated with SBS. After debonding, substrate surfaces were examined with an optical microscope for failure analysis. In addition, 15 molar teeth were sectioned and randomly assigned to one of five groups, according to the dentin surface pre-treatment and adhesive type, and examined with high-vacuum scanning electron microscopy/energy dispersive X-rays (SEM/EDS). The type of adhesive had a significant effect on SBS (p = 0.000); CLSE had the highest values. SB did not affect SBS (p = 0.090). SEM/EDS revealed residual aluminum and/or silicon on all dentin surfaces after SB, except for the control. Treatment with 32% phosphoric acid in the SCMP adhesive decreased the amounts of aluminum and silicon compared to SB dentin only, whereas CLSE resulted in similar quantities of aluminum and silicon as air-abraded dentin. The results of this study indicate that CLSE might have a higher bond strength to dentin than SCMP. Pre-treatment with SB does not appear to affect bonding strength.

Assessment of the modified O'Connor Tweezer Dexterity and Purdue Pegboard test for use among dental students.

OBJECTIVES: The current study aimed to assess criteria validity and test-retest reliability of the modified O'Connor Tweezer Dexterity (O'Connor) and the Purdue Pegboard test (PPT) for use among dental students. Occupational therapists were asked to assess dentist-related skills due to the high percentage of students who failed the dental school exams that year. The O'Connor and the PPT are suitable for these purposes, they aim to evaluate fine motor skills requirements. The original tests were modified for use under indirect visualization conditions (through a mirror) to mimic the typical dentists' work environment. MATERIALS AND METHODS: A total of 110 dentists were included in the present study (50 dentists for the O'Connor test and 60 for the PPT). Both tests were conducted twice. Initially, the original version of the tests was followed by the modified versions (through a mirror). For the test-retest reliability assessment, 21 participants (10 participants from the O'Connor group and 11 participants from the PPT group) repeated the evaluation within a 1-week interval using the same settings (original followed by modified versions). RESULTS: Both versions of the O'Connor tests were significantly correlated (r = 0.54, p < 0.01), as were the two PPT versions (r = 0.640, p < 0.01). Significantly test-retest reliability was found for both tests. The interclass correlation ranged between 0.883 and 0.997, p < 0.000. CONCLUSION: The results confirmed our hypothesis, demonstrating a criteria validity and test-retest reliability assessment of the modified O'Connor and the modified PPT for assessing dentists.

Influence of periodontal ligament simulation and splints on strains developing at the cervical area of a tooth crown.

Many in vitro tooth models do not incorporate periodontal ligament (PDL) simulation. This study presents the influence of physiologically loaded occlusal splints on cervical strains in a model incorporating roots and PDL. Four sets (N = 10) of occlusal splints differing in material (hard/soft) and location (upper/lower) were prepared for first maxillary and mandibular anatomic molars. Two strain gauges were bonded to the buccal and lingual aspects of the lower molar. Teeth were embedded in acrylic resin with/without a PDL-simulating material. Force vs. strain data were acquired during loading and the maximal strains at 500 N were analyzed. When PDL was incorporated into the model without splints, buccal compressive strains were significantly decreased. Usage of a soft splint resulted in compressive strains on both tooth aspects. Usage of a hard splint on the lower tooth resulted in higher compressive strains on the lingual side compared with the buccal side, whereas usage of this splint on the upper tooth resulted in tensile strains on the lingual side. Bending towards the buccal side occurred when the splints were located on the upper tooth. Soft splints reduce buccal bending, but do not reduce cervical strains. Periodontal ligament stimulation materials should therefore be incorporated in models involving teeth.

Survival and Success Rates of Monolithic Zirconia Restorations Supported by Teeth and Implants in Bruxer versus Non-Bruxer Patients: A Retrospective Study.

The aim of this study was to assess retrospectively the survival and success rates of monolithic zirconia restorations supported by teeth and implants in bruxer versus non-bruxer patients. Methods: A total of 15 bruxer and 25 non-bruxer patients attended the recall appointment. The bruxer group (mean age of 61.2 ± 13.3 years and follow-up of 58.7 ± 16.8 months) were treated with 331 monolithic zirconia restorations, while the non-bruxer group, with a comparable mean age and follow-up time, were treated with 306 monolithic zirconia restorations. Clinical data were retrieved from the patients' files. At the recall appointment, all supporting teeth and implants were examined for biological and technical complications, and the restorations were evaluated using modified California Dental Association (CDA) criteria. Data were statistically analyzed using survival analysis methods. A significance level of p < 0.05 was used. A total of 31 versus 27 biologic and technical complications were recorded in the bruxer and non-bruxer groups, respectively. No significant differences were found between the two groups regarding overall complications and survival rate. Regarding the type of complication, a significantly higher rate of veneered porcelain chipping (p = 0.045) was observed in the bruxer group. With regard to biological complications, the only complications that exhibited a borderline, although not significant, difference were three fractured teeth exclusively in the bruxer group (p = 0.051), which were replaced with implant-supported restorations. Within the limitations of this study, we conclude that there were no significant differences in the overall survival and success rates of the monolithic zirconia restorations in bruxer versus non-bruxer patients, although veneered zirconia restorations and single tooth abutments exhibited a higher rate of complications in the bruxer group.

The Accuracy of Open-Tray vs. Snap on Impression Techniques in A 6-Implant Model: An In Vitro 3D Study.

To compare the three-dimensional accuracy of an open-tray and two snap on impression techniques (with and without connecting the plastic caps of the snap on impression transfers) in a full arch 6-implant model, a reference acrylic resin model of the maxilla with six implants was fabricated. Prominent geometrical triangles, in the palate area, served as reference points for a digital overlap between scans. Three impression transfer techniques were evaluated and compared: open-tray direct impression (DI), snap on impression (SpO), and connected snap on impression (SpOC). Polyether impression material was used to make 30 impressions (n = 10), and the master model and all casts were digitally scanned with a laboratory optical scanner. The obtained 3D data were converted and recorded as STL files, which were imported to a 3D inspection software program. Angular deviations (buccal, occlusal and interproximal planes) between the study casts and the reference model were measured. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey post hoc test, with 0.05 used as the level of significance. The 3D angular deviations from the master model revealed no significant differences between the DI and SpO impression groups, but there were significant differences in the SpOC impression group, particularly in the buccal and occlusal planes. In all groups, the 3D angular deviation between the most distal scan abutments on each side of the model was significantly different from all other areas when compared to the master model. Within the limits of this study, it is possible to conclude that the indirect closed tray snap on impression technique with unconnected plastic caps exhibited the same three-dimensional accuracies as the direct open tray technique. The indirect closed tray snap on impression technique with connected plastic caps was less accurate than either the indirect closed tray snap on impression technique with unconnected plastic caps or the direct open tray technique. In the case of full arch implant supported prostheses, inaccuracies may be expected in the most distal implants for all the three impression techniques evaluated in this study. Further in vitro and in vivo research is required.

Influence of Practitioner-Related Placement Variables on the Compressive Properties of Bulk-Fill Composite Resins-An In Vitro Clinical Simulation Study.

Aims: To determine if restoration location and/or execution behavior force parameters have an influence on the mechanical properties of bulk-fill composite dental restorations. Methods: Pressure transducers were placed within each quadrant of dental mannequin jaws. Cylindrical molds were placed above the transducers and filled with two bulk-fill composite materials, Filtek and Tetric, by four experienced dentists. Each dentist prepared five specimens per quadrant and material. The total placement time, mean force, number of peak forces (above 25 N), and mean peak(s) force during placement were measured. Then, the stiffness and maximal compressive strength of the specimens were determined while loading the specimens up to failure using a universal loading machine. Results: Placement time was affected by jaw (p < 0.004) and side (p < 0.029), with the shortest time demonstrated for the left side of the mandible. Force exerted during restoration placement was not normally distributed without differences in location (jaw) or material. A higher application force was found on the right side (p < 0.01). The number of peak forces was affected by side (p < 0.03), with less peaks on the left side. No significant differences were found in compressive strength when correlated to restoration location, participant, or material (p = 0.431). The stiffness values of Filtek (3729 ± 228 N/mm) were found to be 15% higher than Tetric (3248 ± 227 N/mm) (p < 0.005). No correlations were found between the compressive strength or stiffness and the amount of force applied during placement. Conclusions: The individual restoration material placement parameters did influence practitioner performance; however, these differences did not affect the mechanical properties of the final restoration.

Effect of Different Surface Treatments of Lithium Disilicate on the Adhesive Properties of Resin Cements.

The aim of the current study was to evaluate the influence of hydrofluoric (HF) acid concentration and conditioning time on the shear bond strength (SBS) of dual cure resin cement to pressed lithium disilicate ceramic compared to treatment with an Etch and Prime self-etching glass-ceramic primer (EP). A total of 100 samples of pressed lithium disilicate (IPS e.max Press, Ivoclar Vivadent) were randomly divided into five groups (n = 20) according to surface treatment: two different concentrations of HF (5% or 9%), for different durations (20 or 90 s), or treatment with EP. Adhesion of light-cured resin cement to the treated surface was tested by the SBS test. The substrate surfaces of the specimen after failures were examined by SEM. Data were analyzed using Weibull distribution. The highest cumulative failure probability of 63.2% of the shear bond strength (η parameter) values was in the 9% HF -90 s group (17.71 MPa), while the lowest values were observed in the 5% HF -20 s group (7.94 MPa). SBS values were not affected significantly by the conditioning time (20 s or 90 s). However, compared to treatment with 5% HF, surface treatment with 9% HF showed a significantly higher η (MPa) as well as ß (reliability parameter). Moreover, while compared to 9% HF for 20 s, EP treatment did not differ significantly in SBS values. Examination of the failure mode revealed a mixed mode of failure in all the groups. Within the limits of this study, it is possible to assume that IPS e.max Press surface treatment with 9% HF acid for only 20 s will provide a better bonding strength with resin cement than using 5% HF acid.

Does Augmented Visual Feedback from Novel, Multicolored, Three-Dimensional-Printed Teeth Affect Dental Students' Acquisition of Manual Skills?

Although three-dimensional (3D) printing technology is increasingly used in dental education, its application regarding the provision of online visual augmented feedback has not been tested. Thus, this study aimed to: (1) develop two generations of multicolored 3D-printed teeth that provide visual augmented feedback for students conducting the cavity preparation process, (2) assess students' clinical performance after training on the 3D models, and (3) acquire student feedback. For the first-generation model, augmented feedback was obtained from five 3D-printed teeth models for five cavity preparation procedures. Each model comprised three layers printed in green, yellow, and red indicating whether preparation was acceptable, limited, or unacceptable, respectively. The study used a crossover design in which the experimental group trained on five multicolored models and 10 standard plastic teeth, and the control group trained on 15 standard plastic teeth. Students gave positive feedback of the methodology but complained about the printed material's hardness. Therefore, a second-generation model was developed: the model's occlusal plane was replaced with a harder printed acrylic material, and the experiment was repeated. During training, instructors provided external terminal feedback only for performance on standard plastic teeth. Manual grades for cavity preparations on standard plastic teeth were compared. No significant differences were found between the control and experimental groups in both generations' models. However, less instructor time was needed, and similar clinical results were obtained after training with both generations. Thus, multicolored 3D-printed teeth models promote self-learning during the process of acquiring manual skills and reduce student dependency on instructors.

The Retentive Strength of Zirconium Oxide Crowns Cemented by Self-Adhesive Resin Cements before and after 6 Months of Aging.

The aim of this study was to evaluate the retentive strength of zirconium oxide (yttria-stabilized tetragonal zirconia polycrystals (Y-TZP)) crown-copings treated by combined mechanical and chemical treatments and cemented by four types of self-adhesive resin cements (SARCs) to human prepared teeth, before and after six months of aging in water and thermocycling. A total of 120 molar teeth were mounted, prepared using a standardized protocol and digitally scanned, and Y-TZP copings were produced. Teeth were randomly assigned to four SARC groups. Prior to cementation, the intaglio surfaces of all crowns were sandblasted and then coated with Z-Prime™ Plus (Bisco Dental, Schaumburg, IL, USA). Post cementation, each cement group was subdivided into aged and non-aged groups. After aging, the cemented assemblies were tested for retentive strength using a universal testing machine. Failure analysis was conducted by inspecting all matched debonded surfaces of the teeth and crowns at 3× magnification. Aging treatment did not affect the retentive strength of the Y-TZP crown-copings (p = 0.918). The interaction between cement and aging was statistically significant (p = 0.024). No significant differences in the retentive strengths between the different SARCs were observed pre-aging (p = 0.776), whereas post-aging, Panavia SA (PAN; Kuraray Dental Co Ltd., Osaka, Japan) showed significantly higher strength than RelyX U-200 (RU200; 3M ESPE, Seefeld, Germany). The predominant failure mode was adhesive between the cement and dentin, followed by mixed mode failure.

Load-Bearing Capacity of Zirconia Crowns Screwed to Multi-Unit Abutments with and without a Titanium Base: An In Vitro Pilot Study.

The static and dynamic load-bearing capacities and failure modes of zirconia crowns screwed to multi-unit abutments (MUAs) with and without a titanium base (T-base) were determined. Thirty-six monolithic zirconia crowns screwed to straight MUAs torqued to laboratory analogs (30 Ncm) were assigned to two groups (n = 18). In group A, the zirconia crowns were screwed directly to the MUAs; in group B, the zirconia crowns were cemented to the T-base and screwed to the MUAs. All specimens were aged in 100% humidity (37 °C) for one month and subjected to thermocycling (20,000 cycles). Afterwards, the specimens underwent static and dynamic loading tests following ISO 14801. The failure modes were evaluated by stereomicroscopy (20×). There was an unequivocally similar trend in the S-N plots of both specimen groups. The load at which the specimens survived 5,000,000 cycles was 250 N for both groups. Group A failed mainly within the metal, and zirconia failure occurred only at a high loading force. Group B exhibited failure within the metal mostly in conjunction with adhesive failure between the zirconia and T-base. Zirconia restoration screwed directly to an MUA is a viable option, but further studies with larger sample sizes are warranted.

An interventional study for improving the manual dexterity of dentistry students.

OBJECTIVES: Traditionally, the acquisition of manual skills in most dental schools worldwide is based on exercises on plastic teeth placed in a "phantom head simulator". No manual trainings are done at home. Studies revealed that preliminary training of one motoric task leads to significant improvement in performance of the required motoric task that has similar components. Performing tasks indirectly via a dental mirror are complicated for the young dental students. We hypothesized that instructed training of basic skills required in dentistry at home on a tool simulating the phantom laboratory will improve the capabilities of the students and will be reflected by their clinical grades. METHODS: We developed a portable tool PhantHome which is composed of jaws, gingival tissue, rubber cover and a compatible stand. Specific teeth produced by a 3D printer with drills in different directions were placed in both jaws. Students were requested to insert pins by using tweezers and dental mirror according to instructions initiating with easy tasks and continue to ones that are more complicated. 106 first clinical year dental students participated in the study; 65 trained only in the traditional phantom lab (control). 41 trained at home by the PhantHome tool two weeks before and 2 months during the initial stage of phantom lab. The students grades routinely provided in the phantom laboratory at different stages were compared. RESULTS: Students who trained with the portable tool performed better than the control group in the first direct and second indirect preparations (p<0.05). These exams were taken when the PhantHome was available to the students. Then, the tool was returned and the phantom course continued regularly. We believe that this is why no differences between the grades of the groups were observed further on. CONCLUSIONS: Training by the PhantHome improves motor skills and consequently the clinical performances.

Enhanced Nanoassembly-Incorporated Antibacterial Composite Materials.

The rapid advancement of peptide- and amino-acid-based nanotechnology offers new approaches for the development of biomedical materials. The utilization of fluorenylmethyloxycarbonyl (Fmoc)-decorated self-assembling building blocks for antibacterial and anti-inflammatory purposes represents promising advancements in this field. Here, we present the antibacterial capabilities of the nanoassemblies formed by Fmoc-pentafluoro-l-phenylalanine-OH, their substantial effect on bacterial morphology, as well as new methods developed for the functional incorporation of these nanoassemblies within resin-based composites. These amalgamated materials inhibit and hinder bacterial growth and viability and are not cytotoxic toward mammalian cell lines. Importantly, due to the low dosage required to confer antibacterial activity, the integration of the nanoassemblies does not affect their mechanical and optical properties. This approach expands on the growing number of accounts on the intrinsic antibacterial capabilities of self-assembling building blocks and serves as a basis for further design and development of enhanced composite materials for biomedical applications.

The influence of dentin and/or metal surface treatment on the retention of cemented crowns in teeth with an increased taper.

OBJECTIVES: To evaluate the effect of dentin and/or metal surface treatments on retention of cast crowns cemented to preparations with compromised retention. METHODS: Cast crowns (n=105) were fabricated on extracted molars prepared to 40 degrees convergence and standard height. 60 teeth were randomly divided into: (A) cemented with zinc phosphate cement; (B-D) cemented with resin cement (Compolute, 3M) with either no surface treatment (B), dentin etched and bonded (EBS multi, 3M) (C), or dentin etched and bonded, and metal tribochemically treated (Co-Jet, 3M) (D); 45 teeth were randomly divided and crowns cemented with another resin cement (Rely-X Arc, 3M) with either no surface treatment (E), dentin etched and bonded (Single Bond, 3M) (F), or dentin etched and bonded and metal tribochemically treated (G). Teeth were stored in 100% humidity for 3 months and thermocycled 5000 cycles. Crowns were dislodged from the preparations and retention (MPa) was calculated. RESULTS: Group D showed significantly higher retention (3.52+/-1.3 MPa) compared to Group C (2.26+/-0.9 MPa), Group B (0.85+/-0.4 MPa), and Group A (1.22+/-0.4 MPa). Group G exhibited significantly higher retention (5.4+/-1.4 MPa) compared to F (2.6+/-1.2 MPa) and E (2.0+/-0.6 MPa). Higher retention corresponded with more cohesive cement type of failure. SIGNIFICANCE: Cast crowns with compromised retention cemented by resin cement should undergo combined tribochemical metal treatment and dentin bonding. The crucial link is the interaction of different brands of resin cements with the metal tribochemically treated.