In Vitro Microleakage and Fracture Resistance of "Infinity Edge" and Cusp Reduction Preparation Designs for Moderate-sized Class II Composites.

AIM: This study aimed to evaluate the marginal microleakage and maximum occlusal fracture loads and fracture modes of two novel class II preparation designs, "infinity edge" and the "2.5 mm cusp reduction" preparations as compared to a traditional class II preparation without cuspal involvement. MATERIALS AND METHODS: Thirty extracted human mandibular molars were prepared for moderate-sized class II restorations with extensions into all occlusal grooves. Of these, ten class II preparations served as control. Ten were modified for a 2.5 mm even reduction of the cusps adjacent to the interproximal box. An additional 10 preparations were modified with an "infinity edge" bevel on the interproximal and occlusal portions. All teeth were restored utilizing a flowable bulk-fill composite in the apical portion of the interproximal box and 2-4 mm of heated bulk-fill composite in one increment for the remainder. All groups were cyclic loaded and thermocycled, then imaged with microcomputed tomography (µCT) before and after infiltration with a silver nitrate solution. Images were subtracted to obtain volumetric measurements of microleakage and reported as a percentage of the total volume from the apical extent of the proximal box. All groups were loaded to failure and fracture load and mode were recorded. RESULTS: No significant differences were found in microleakage volume as a percentage of total tooth volume; however, the "infinity edge" group had significantly greater microleakage in the proximal box compared to the traditional class II group. No significant differences were found in fracture load or mode between the groups. CONCLUSION: Traditional class II, 2.5 mm cuspal reduction, and "infinity edge" preparation designs have similar fracture loads as well as volumes of microleakage; however, an "infinity edge" preparation has a higher ratio of microleakage in the proximal box. CLINICAL SIGNIFICANCE: Clinicians should carefully consider the use of "infinity edge" margins, particularly on dentin in the apical extent of the proximal box. How to cite this article: Watson JC, Lien W, Raimondi JC, et al. In Vitro Microleakage and Fracture Resistance of "Infinity Edge" and Cusp Reduction Preparation Designs for Moderate-sized Class II Composites. J Contemp Dent Pract 2024;25(1):3-9.

Effect of Milling Speed on the Properties of Zirconia Restorations.

Background: The purpose of this study was to evaluate the effect of milling speed on the surface roughness, marginal gap, marginal gap volume, marginal offset, and fracture load of zirconia restorations. Material and Methods: A mandibular molar #30 typodont tooth was digitally scanned and an ideal crown preparation for a zirconia restoration was digitally created. A single master model die of the crown preparation was milled out of a resin material. The master die was scanned, and a final restoration was designed using the bio-copy feature of the typodont tooth. Ten zirconia restorations were milled (CEREC Primemill, Dentsply Sirona) per each of three milling speeds (super-fast, fine, and extra-fine), sintered, and seated on the master die. Surface roughness, marginal gap, marginal gap volume, and marginal offset were measured using a non-contact profilometer. Then, all restorations were cemented to the dies and loaded to failure in a material testing device. Data were analyzed with one-way ANOVA and Tukey's post hoc tests per property (alpha=0.05). Results: Super-fast milling speed resulted in restorations with statistically significant greater surface roughness and marginal gap volume compared to fine and extra-fine milling speeds. No significant difference in marginal gap, marginal offset, and fracture load were found based on milling speed. Conclusions: Zirconia restorations milled at slower speeds may result in similar or slightly better properties compared to super-fast speed. Key words:Milling speed, properties, zirconia restorations.

Fracture strength of ceramic overlays with immediate dentin sealing and same-day delivery.

Limited research is available evaluating whether the reported in vitro benefit of immediate dentin sealing (IDS)-namely, increased bond strength to tooth structure-can be acquired in the era of same-day (SD) dentistry. The purpose of this study was to compare the fracture strengths of ceramic overlays fabricated with a delayed dentin sealing (DDS) technique or an IDS technique under 1-hour SD or 2-week multiple-day (MD) delivery conditions. Forty extracted, healthy maxillary third molars were prepared for a lithium disilicate overlay restoration and divided into 4 groups of 10 teeth each. In the SD-DDS group, the teeth were prepared and then stored for 1 hour in artificial saliva, and the adhesion protocol (bonding agent and resin cement) was applied at the time of delivery of the ceramic overlay. In the SD-IDS group, the teeth were prepared, the adhesive protocol was applied immediately, and the teeth were stored for 1 hour before delivery of the overlay. The protocols for the MD-DDS and MD-IDS groups were identical to SD-DDS and SD-IDS, respectively, except that the teeth were provisionalized and stored for 2 weeks prior to delivery of the overlay. Specimens were thermocycled and subjected to cyclic functional loading before they were loaded to failure in a universal testing machine using a rod resting on the buccal incline of the palatal cusp. Two-way analysis of variance tests revealed no statistically significant differences in fracture strength between the groups based on dentin sealing (P = 0.331) or delivery time (P = 0.314). The specimens demonstrated 2 fracture types; either a portion of the ceramic cohesively fractured, leaving the tooth intact, or the ceramic and part of the tooth fractured. There were no instances in which the restoration itself delaminated during fracture testing. A Kruskal-Wallis test indicated there were no statistically significant differences in fracture modes between the groups. In this in vitro study, IDS did not provide a significant increase in the fracture strength of overlay restorations compared with DDS, regardless of whether the restorations were delivered the same day or after 2 weeks of storage.

Accuracy of an intraoral scanner based on sleeve type, decontamination, and calibration.

The purpose of this study was to evaluate the accuracy of an intraoral scanner based on camera sleeve type, decontamination protocol, and calibration status. Five extracted human teeth were set into a gypsum stone model and prepared for various indirect restorations. An optical impression was completed with a benchtop scanner to serve as a reference standard. A total of 160 optical impressions were completed using a sterilizable sleeve, an autoclavable sleeve with a single-use plastic window, or a single-use disposable plastic sleeve attached to a calibrated or an uncalibrated intraoral scanner. For the sterilizable sleeves, 2 decontamination protocols were used--high-level disinfection (HLD) or dry heat sterilization (DHS)--and scans were performed at baseline and after 25 and 50 cycles for each protocol. For the autoclavable (AS) and disposable single-use (SU) sleeves, scans were performed at baseline only. Thus, there were 10 optical impressions per test condition: sleeve type (HLD, DHS, AS, or SU) × decontamination status (baseline, 25 cycles [HLD or DHS], or 50 cycles [HLD or DHS]) × calibration status (calibrated or uncalibrated scanner). The individual optical impressions were compared to the reference standard impression by using 3-dimensional best-fit superimposition with the prepared tooth surfaces as reference points, and 3-dimensional linear differences were calculated for each superimposition. The median positive and absolute value median negative distance measurements were averaged for each impression to generate an average median discrepancy from baseline. The data were analyzed with Kruskal-Wallis and Mann-Whitney U tests (α = 0.05). No statistically significant differences in the median linear distance were found, regardless of sleeve type, decontamination protocol, or calibration status (P > 0.05). All groups demonstrated statistically similar linear disparities, ranging from 11.78 to 14.00 µm. The most precise sleeves were the single-use plastic sleeves, although their results were not significantly different from those of the multiuse sleeve. The results indicated that any of the currently available camera sleeves can provide similar accuracy in a clinical setting and that single-use disposable sleeves are a viable alternative to the currently accepted multiuse sleeves.

Efficacy of a chairside extraoral suction system in the reduction of aerosol contamination.

The dental setting is regarded as a high-risk environment for aerosol concentrations and transmission of respiratory infectious agents, especially in relation to the COVID-19 pandemic. Although a number of approaches and practices have evolved to reduce the spread of pathogens in the dental setting, the risk of airborne infection remains a concern. Several new extraoral suction (EOS) devices have been marketed recently; further investigation is warranted to determine their clinical effectiveness. The aim of this study was to evaluate the efficacy of a chairside EOS device (PAX 2000 Extraoral Dental Suction System) in reducing aerosol contamination from patients receiving ultrasonic scaling by a registered hygienist as a part of initial or supportive periodontal therapy. The number of colony-forming units (CFUs) was measured with agar plates before, during, and after ultrasonic scaling at 3 different locations in the dental operatory (instrument table, patient chest area, and patient foot area). Forty subjects were randomly allocated into 2 test groups (n = 20) in which ultrasonic scaling was performed with or without the use of the EOS device. The CFUs retrieved after incubation were quantified and identified by their bacterial or fungal taxon. The use of the EOS device reduced the number of CFUs during scaling at all 3 locations, but the difference was only statistically significant (P = 0.018; Mann-Whitney U test) at the patient's chest area, where the highest number of CFUs was present. The aerosols consisted of 74 different taxa of human origin. The results suggest that the tested EOS system may reduce aerosol contamination in the clinical dental setting, especially in proximity to the patient's head, where most aerosols are generated.

Novel chairside spectrometer-trained system for measuring the irradiance of light-curing units.

The purpose of this study was to compare the performances of 5 different instruments in measuring the irradiance of light-curing units (LCUs). A novel spectrometer-trained radiometer (CheckUp), 2 conventional chairside radiometers (Bluephase Meter I and Bluephase Meter II), and 2 devices considered to be gold standards for measuring irradiance (an integrating sphere spectrometer and a thermopile sensor) were used to evaluate 7 LCUs. The irradiance of each LCU was measured 10 times with each meter. Data were analyzed using linear regression analysis and a 1-way analysis of variance with Tukey post hoc test (α = 0.05). The mean irradiance values of the LCUs differed significantly depending on which meter was used for measurement (P < 0.05). Bivariate regression analysis demonstrated that the highest correlations in the irradiance values were found between the CheckUp meter and both the integrating sphere (r2 = 0.980) and the thermopile (r2 = 0.933). The absolute mean (SD) percentage deviation between irradiance measured by the CheckUp instrument and irradiance measured by the other meters was 7.2% (2.0%) for the integrating sphere, 7.0% (3.6%) for the thermopile, 21.5% (16.1%) for Bluephase Meter I, and 13.1% (7.1%) for Bluephase Meter II. Compared with the 2 conventional chairside radiometers, the CheckUp meter provided the highest correlation with and lowest absolute percentage deviation from the irradiance measured by the gold standard spectrometers.

Evaluation of a Novel "Quad" Wavelength Light Curing Unit.

Background: This study investigated the properties (depth of cure, surface hardness, and volumetric shrinkage) of two composite restorative materials when polymerized with a novel "quad" spectrum (PinkWave) light-curing unit (LCU) compared to a tri-spectrum LCU (Valo Grand). Material and Methods: One Valo Grand LCU was modified to be similar in irradiance to the PinkWave, and a second Valo Grand was utilized at the manufacturer's standard irradiant settings. Depth of cure was evaluated using the scraping technique (ISO 4049). Top and bottom surface hardness and bottom/maximum hardness ratios were determined using a hardness tester. Volumetric shrinkage was determined using a video-imaging device. Additionally, the surface temperature of the light tips of the LCUs was measured using a K-type thermocouple. Results: No significant difference in depth of cure was found with either composite between the PinkWave LCU and the modified Valo Grand LCU at similar irradiance. The unadjusted Valo Grand LCU had slightly less depth of cure. There was no difference in top or bottom surface hardness, bottom/maximum hardness ratios, or volumetric shrinkage between any of the LCU curing modes per composite type. The PinkWave LCU had a significantly greater increase in heat at the tip compared to the modified Valo Grand LCU at similar irradiance and the unadjusted Valo Grand LCU. Conclusions: The new quad-spectrum LCU, PinkWave, had a significant increase in surface temperature without any improvement in the composite properties tested compared to the tri-spectrum LCU, Valo Grand, at similar irradiance. Key words:Light-curing unit, emission spectrum, composite resin, mechanical and physical properties.

Dental erosion as an indicator of gastroesophageal reflux disease.

While evidence shows that dental erosion (DE) is often caused by gastroesophageal reflux disease (GERD), the relationship of DE severity to a patient's symptoms and receipt of appropriate medical treatment for GERD is not clearly understood. The purpose of this study was to evaluate the association between DE and GERD. Eighty participants underwent a Basic Erosive Wear Examination for DE and completed the Patient-Reported Outcomes Measurement Information System (PROMIS) survey on symptoms of gastrointestinal reflux (PROMIS Scale v1.0, Gastrointestinal Gastroesophageal Reflux 13a) in English. Patients with observed erosive patterns were referred for gastroenterologic evaluation. The association between DE and GERD was assessed using multiple regression. The results showed that the extent of DE was positively associated with GERD symptoms (B = 0.585; 95% CI, 0.21-0.96), as measured by the PROMIS survey, in participants without a current diagnosis of GERD. Of the 80 patients in the study, 28 with more severe DE were evaluated in the gastroenterology department. A diagnosis of GERD was established for 27 of the 28, 9 of whom denied a past history of the disease. Twenty patients with GERD underwent upper endoscopy, and esophageal lesions were found in 6 patients (erosive esophagitis in 5 and Barrett esophagus in 1). Patients with clinically identified DE may benefit from medical evaluation and, if necessary, management of GERD. For a subset of patients, DE may be the only clinical indication of untreated or undertreated GERD, which could lead to serious esophageal changes. Dentists should consider referring patients with DE to primary care providers or gastrointestinal specialists to ensure that systemic conditions are identified and managed appropriately.

Fracture load of zirconia crowns based on preparation and cement type.

Limited research has been published evaluating the failure of zirconia crowns with less retentive tooth preparations. The purpose of this study was to evaluate the effect of axial wall height (AWH) and cement type on the fracture load of cubic phase-containing zirconia crowns. Standardized crown preparations with an AWH of 0, 2, or 4 mm (n = 10) were made in 90 extracted human maxillary third molars. The preparations were scanned, and crown restorations were designed. Cubic phase-containing zirconia crowns were milled and cemented with a resin-modified glass ionomer cement, a self-adhesive resin cement, or an adhesive resin cement. The specimens were subjected to thermocycling and cyclic loading. Each crown specimen was positioned in a universal testing machine so that the long axis of the tooth was at a 60° angle to the testing fixture and loaded until failure using a stainless steel rod resting on the buccal incline of the palatal cusp. Data were found to have a nonnormal distribution and were analyzed with Kruskal-Wallis and Mann-Whitney U tests (α = 0.05). Statistically significant differences in the median fracture loads of the groups were found based on both AWH and cement type (P < 0.05). Regardless of cement type, the median fracture loads were significantly lower in the 0-mm AWH groups than in the 2-mm and 4-mm AWH groups, which were not significantly different from each other. Compared to the other cement types, adhesive resin cement resulted in a significantly greater median fracture load when the AWH was 0 mm. The use of an adhesive resin cement with a cubic phase-containing zirconia crown may provide greater fracture resistance for preparations with minimal AWH.

Efficacy of various decontamination methods and sterilization on contaminated and inoculated diamond-coated burs.

The objective of this study was to evaluate the efficacy of various decontamination methods and subsequent sterilization on contaminated and inoculated diamond-coated burs. One hundred forty new diamond-coated burs and 120 extracted human molars were utilized in this study. The burs were divided into 7 groups (n = 20): 1, positive control; 2, negative control; 3, new, unused burs; and 4 to 7, burs subjected to various combinations of cleaning methods (manual cleaning, use of a cleaning stone, and/or ultrasonic cleaning) after contamination. In all of the groups except group 3, the burs were sterilized and used to abrade the enamel and dentin of the sterilized extracted teeth. In groups 1 and 4 to 7, the burs were subsequently inoculated with 1 of the following microorganisms: Enterococcus faecalis (ATCC 19433), Staphylococcus aureus (ATCC 6538), Pseudomonas aeruginosa (ATCC 15442), or Geobacillus stearothermophilus (ATCC 7953). Twenty-four hours after inoculation, the burs in group 2 and groups 4 to 7 were subjected to the cleaning treatments and sterilized with steam. The burs in all 7 groups were then cultured for bacterial contamination. No growth of any bacterial type was observed in any of the groups except the positive control group. The use of a cleaning stone in combination with manual or ultrasonic cleaning resulted in the least amount of remaining tooth debris on the diamond-coated burs. The contaminated and inoculated diamond-coated burs tested in this study were successfully sterilized, and the tested bacteria were eliminated. If using a diamond-coated bur multiple times, practitioners should consider utilizing debridement with a cleaning stone followed by either manual or ultrasonic cleaning and then by a single cycle of steam sterilization.

The effect of micro-mechanical signatures of constituent phases in modern dental restorative materials on their macro-mechanical property: A statistical nanoindentation approach.

This study utilized a statistical nanoindentation analysis technique (SNT) to measure the amount of organic and inorganic constituents of twenty different brands of dental resin-based composites (RBCs) and tested whether their macro-property such as flexural modulus could be approximated by the proportions of constituents' micromechanical signatures using various rules of mixtures. The probability density function (PDF) of constitutive moduli per RBC brand were measured for three groups, comprised of different indent arrays and inter-indent spacings. SNT was then applied to deconvolute each PDF, from which the effective filler (µF) and matrix (µM) moduli and filler (VF) and matrix (VM) volume fractions per RBC brand were computed. VF and VM values obtained via SNT were strongly correlated with VF and VM obtained via Thermogravimetric Analysis and Archimedes method. The "observed" flexural modulus (EcFS) measured under macro-experiment were well associated with "predicted" effective modulus (EcEff) measured under nano-experiment, thereby establishing that global modulus was strongly affected by the constituents' micromechanics. However, the "predicted" EcEff were proportionally higher than the "observed" EcFS. VF was a confounder to EcFS and EcEff, whereby the influence of VF on both modular ratios (EcFS/µM and EcEff/µM) was best modeled by an exponential regression.

Management of dental anxiety via distraction technique.

BACKGROUND: The purpose of this study was to evaluate the use of a stress ball as a distraction technique on stress levels of patients undergoing a dental procedure. MATERIAL AND METHODS: A randomized, split-mouth design was conducted using 20 adult subjects requiring scaling and root planing (Sc/RP) in all four quadrants. Each side of the mouth (maxillary/mandibular) received Sc/RP with local anesthetic with or without the use of a stress-ball distraction over two separate sessions. Subjects completed two pre-procedural questionnaires (Spielberger State-Trait Anxiety Inventory, STAI; Modified Dental Anxiety Scale, MDAS) before and after each treatment session. A Galvanic Skin Response (GSR) sensor (Neulog) was used throughout each session to measure skin conductance or sweat. RESULTS: No significant difference in GSR scores was found during treatment with or without the use of the stress ball. Also, no significant differences in the change in STAI or MDAS scores were found with or without the use of a stress ball. CONCLUSIONS: The results of this study found that the use of a stress ball as a distraction technique did not result in any significant reduction in stress levels in subjects undergoing scaling and root planing with local anesthesia. Key words:Anxiety, distraction, stress ball.

Repair of resin-veneered polyetheretherketone after veneer fracture.

STATEMENT OF PROBLEM: If a composite resin-veneered polyetheretherketone (PEEK) restoration chips or fractures, a repair may be indicated. However, the most appropriate repair protocol for a composite resin-veneered PEEK restoration is unclear. PURPOSE: The purpose of this in vitro study was to determine the efficacy of airborne-particle abrasion and/or a primer in the repair of composite resin-veneered PEEK prostheses. MATERIAL AND METHODS: PEEK specimens (N=80) were airborne-particle abraded with alumina before being conditioned with a methyl methacrylate-based primer. A thin layer of opaquer was applied, and a split mold was then filled with a veneering resin. The specimens underwent 5000 thermocycles, and then shear bond strength (SBS) was determined and used as the positive control group. Specimens that failed in either mixed or adhesive modes were contaminated with saliva and then exposed to 4 different repair treatment methods: no airborne-particle abrasion, bonded without a primer (negative control group); airborne-particle abrasion, bonded without a primer; no airborne-particle abrasion, bonded with a primer; and airborne-particle abrasion, bonded with a primer. All specimens had opaquer applied before being veneered. Repaired specimens then underwent thermocycling before SBS testing. Data were analyzed via ANOVA with a Newman-Keuls post hoc test (α=.05). RESULTS: The SBS values for the negative control were significantly lower than those of all other repair groups and the control group (P<.018). No significant differences in the SBS values were found among these other repair groups or the positive control group (P>.05). CONCLUSIONS: Composite resin-veneered PEEK restorations or prostheses repaired with airborne-particle abrasion and/or primer can provide SBS comparable with that of the initial SBS.

Fracture strength of various titanium-based, CAD-CAM and PFM implant crowns.

OBJECTIVE: CAD-CAM has dramatically advanced dental restorative procedures to include implant-supported crowns. The purpose of this study was to compare the fracture resistance following mechanical loading and thermocycling of various screw-retained and cement-retained ceramic and polymethylmethacrylate material combinations using the TiBase abutment compared to PFM implant-supported crowns. OVERVIEW: Twelve implant restorations were fabricated for each of eight groups. Three groups were screw-retained and five groups were cement-retained implant restorations. The ceramic and polymethylmethacrylate restorations were fabricated on the TiBase abutment while the PFM restorations were fabricated on an UCLA abutment. Data were analyzed with a one way Analysis of Variance and Tukey's post-hoc test to evaluate the effect of abutment and crown type on fracture load (alpha = 0.05). A significant difference was found in the maximum fracture load between groups (P < 0.001). CONCLUSIONS: The screw-retained implant restorations demonstrated higher fracture loads than their cement-retained counterparts. The TiBase abutment compared favorably to the UCLA abutment. CLINICAL SIGNIFICANCE: The TiBase abutment is a titanium insert which combines the esthetics of a ceramic abutment with the mechanical properties of a titanium abutment and should be considered a viable clinical alternative to the conventional implant-supported PFM crown based on theses in vitro results and in context of in vivo studies. The lithium disilicate hybrid abutment/crown implant-supported restoration utilizing the TiBase abutment may be an ideal clinical choice due to simplicity, single appointment CAD-CAM, and esthetics.

Assessing the Effects of Air Abrasion with Aluminum Oxide or Glass Beads to Zirconia on the Bond Strength of Cement.

AIM: The purpose of this study was to evaluate the effects of air abrasion with aluminum oxide or glass beads to three types of zirconia containing various levels of cubic crystalline phases (3Y-TZP, Katana ML; 4Y-PSZ, Katana STML; and 5Y-PSZ, Katana UTML, Noritake) on the shear bond strength of resin cement. MATERIALS AND METHODS: Thirty block specimens (8 × 8 × 3.5 mm) were milled out of each zirconia material and mounted in plastic pipe. Ten specimens of each of the zirconia materials were air-abraded using 50 µm aluminum oxide particles, ten specimens were abraded using 80 µm glass beads, and ten specimens served as a control and received no surface treatment. A zirconia primer was applied to the surface of the zirconia specimens. Composite disks were bonded using a resin cement and light-cured. The specimens were stored in 37°C distilled water for 24 hours and thermocycled for 2,500 cycles. The specimens were loaded in shear on a universal testing machine. Data were analyzed with one-way and two-way ANOVAs and Tukey's post hoc tests (α = 0.05). RESULTS: A significant difference in shear bond strength was found based on the surface treatment (p < 0.001), but not on the type of zirconia (p = 0.132). CONCLUSION: Air abrasion with glass beads or no surface treatment resulted in significantly lower bond strength of the resin cement to all three zirconia types compared to air abrasion with aluminum oxide. CLINICAL SIGNIFICANCE: Although air abrasion with aluminum oxide may reportedly be more likely to weaken cubic-containing zirconia compared to air abrasion with glass beads, the use of aluminum oxide results in greater bond strength of the resin cement.

An Investigation of the Effect of Modifying and Reusing Impression Copings on Transfer of Implant Analog Position and Angulation.

AIM: The aim of this research was to determine whether sterilization and reutilization of impression copings had an impact on the accuracy of casts made for multiimplant restorations. MATERIALS AND METHODS: Four master casts embedded with five implant analogs were fabricated. Polyvinyl siloxane (PVS) impressions of the master cast with copings attached to the analogs were made and poured in dental stone. The impression copings were subjected to cleaning and sterilization. These processes were repeated 30 cycles for each of the two groups of five impression copings: one without modification and one with modification that included air abrasion and PVS adhesive. A coordinate measuring machine (CMM) was used to measure relative angles and distances between the reference analog and analogs. The relative angles and distances measured on the stone casts were compared to the master resin cast to obtain positional and angular displacements. RESULTS: For impression copings that were not modified, a significant difference was detected for both positional and angular displacements. For impression copings that were modified, a significant change was observed only for positional displacement. The maximum discrepancies measured for positional and angular displacements after 30 cycles of reuse were only 81 µm and 0.46°, respectively, regardless of the modification. CONCLUSION: Within the limitations of this study, unmodified impression copings that have undergone 30 cycles of cleaning and sterilization appeared to incur more impression inaccuracy than those impression copings that were modified by airborne-particle abrasion and PVS adhesive. CLINICAL SIGNIFICANCE: Impression copings used in this study can likely be recycled up to 30 times without reducing the accuracy of the impression to a level that may be considered clinically significant.

A Survey of US Air Force General Dentists Regarding Computer-aided Design/Computer-aided Manufacturing Usage.

AIM: The purpose of this study was to survey all United States Air Force (USAF) general dentists regarding their experience with computer-aided design/computer-aided manufacturing (CAD/CAM) while in a dental school. Dental school graduation year and location was compared to the type and amount of CAD/CAM training and clinical experience during dental school to better understand the differences and influence of this technology. MATERIALS AND METHODS: A survey consisting of six questions was sent through e-mail to 546 general dentists in the AF Dental Corps in 2018 of which 306 replied (56% response rate). RESULTS: Dentists who graduated in 2005 or earlier and between 2006 and 2009 stated they did not receive CAD/CAM training in dental school, while more respondents in the group of graduation years 2014-2017 stated that they did receive training. About 11% of the respondents who graduated in 2014-2017 completed 6-10 restorations and 9% completed 11 or more restorations compared to the other year groups. More respondents who graduated from a dental school in the southwest and southeast regions of the United States reported completing more restorations compared to other school regions. CONCLUSION: Computer-aided design/computer-aided manufacturing is now becoming a prevalent curriculum in US dental schools, both as a core requirement and an elective. Its training platforms varied from lectures and literature reviews to preclinical laboratory. CLINICAL SIGNIFICANCE: More respondents in the groups of graduation years 2014-2017 had completed more CAD/CAM restorations compared to other year groups; however, most of the respondents did not feel their training was sufficient enough to use CAD/CAM technology independently.

Assessing Flexural Strength Degradation of New Cubic Containing Zirconia Materials.

AIM: Newer zirconia materials may have greater strength degradation under cyclic fatigue with increased yttria and cubic content. The purpose of this study was to evaluate the flexural strength (FS) degradation of newer zirconia materials compared to more traditional tetragonal zirconia materials. MATERIALS AND METHODS: The following materials were tested: two 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) materials (Lava Plus, 3M ESPE; Katana ML, Kuraray), one 4 mol% partially stabilized zirconia (4Y-PSZ) material (Katana STML, Kuraray), two 5 mol% partially stabilized zirconia (5Y-PSZ) materials (Katana STML, Kuraray; Lava Esthetic, 3M ESPE), and one lithium disilicate material (IPS e.max CAD LT, Ivoclar Vivadent). Thirty beams were milled for each ceramic material with final dimensions of 4.0 × 1.3 × 18.0 mm after sintering or crystallization. Each specimen was placed on a 3-point bend test device on a universal testing machine (Instron, Norwood, MA). Flexural strength was determined on 10 beam specimens per group with a central load applied until fracture. Flexural fatigue strength was then measured on the remaining 20 beam specimens per group using the staircase method for 6,000 cycles at 2 Hz. Data were analyzed with one-way ANOVAs/Tukey post hoc tests (α = 0.05). RESULTS: A significant difference was found between groups (p < 0.001) per property. The 3Y-TZP zirconia materials had the greatest flexural and flexural fatigue strength. The cubic containing zirconia materials performed more moderately. The lithium disilicate material had the lowest strength values. The percent degradation in flexural fatigue strength of the 3Y-TZP zirconia materials was less than the 5Y-PSZ, Katana UTML, and the 4Y-PSZ, Katana STML, cubic containing materials, but similar to the 5Y-PSZ cubic containing material, Lava Esthetic. CONCLUSION: The amount of strength degradation was material dependent, with the 4Y-PSZ or 5Y-PSZ cubic containing zirconia materials demonstrating greater or similar strength degradation compared to the primarily tetragonal 3Y-TZP zirconia materials. CLINICAL SIGNIFICANCE: The differences in FS degradation between cubic containing materials and traditional zirconia materials could significantly impact the long-term success of these newer materials. Clinicians should be aware that these cubic containing materials may perform differently long-term than the very strong traditional 3Y-TZP materials and to follow manufacturer instructions on required material thickness and indications for use to prevent premature failure of the restoration.

Bond strength of dual-cured resin cement used with dual-cured adhesives.

The reported advantage of new dual-cured adhesive agents is that they do not require light curing, resulting in a reduced film thickness and improved seating of bonded all-ceramic restorations. The purpose of this study was to determine the effect of dual-cured adhesives on the bond strength of dual-cured resin cement to dentin under different polymerization conditions: with or without light curing of the dual-cured adhesive as well as with or without light curing of the dual-cured resin cement through a lithium disilicate ceramic material. Human molars were sectioned to remove the coronal tooth structure and randomly divided into 3 adhesive groups: Clearfil SE Bond 2, ExciTE F DSC, and Universal Primer. The adhesive agents were applied to the dentin surface with or without light activation. A dual-cured resin cement was applied, and discs of lithium disilicate were cemented to the dentin surface. Half of the discs were light cured from the top surface, and the other half were allowed to self-cure. Shear bond strength was tested after storage in distilled water for 24 hours. The effect of light curing of the adhesive or cement on the shear bond strength of the lithium disilicate discs to dentin was product dependent. Clearfil SE Bond 2 performed significantly better with light curing of both the adhesive and cement. Less significant effects of the various light-curing and self-curing combinations were observed with ExciTE F DSC or Universal Primer. When neither the adhesive nor the cement was light cured, all 3 adhesives performed poorly and had a significant loss in bond strength.

Effect of Toothbrushing on Surface Color of Ceramic-polymer Materials: An In Vitro Study.

AIM AND OBJECTIVE: The purpose of this study was to examine the effects of toothbrushing on the change in color of extrinsic characterization of ceramic-polymer materials. MATERIALS AND METHODS: Two ceramic-polymer materials (CeraSmart, GC; Enamic, VITA) and one lithium-disilicate material (IPS e.max CAD; Ivoclar Vivadent) were tested. Specimens of each material were prepared, characterized, and glazed per manufacturer's instructions. The treated surface of the blocks were then brushed in a toothpaste slurry with artificial saliva using a toothbrush machine with a soft toothbrush. Commission Internationale de L'Eclairage (CIE) L*a*b* values were recorded with a spectrophotometer at baseline and at 3, 6, 9, and 12 simulated years of brushing (7,300 strokes/year). A mean change in color (ΔE*) and standard deviation was determined for each group and brushing interval. Data were analyzed with a two-way repeated measures ANOVA examining the effects of toothbrushing the ceramic materials on ΔE* over time (α = 0.05). RESULTS: The difference in the ΔE* between CeraSmart and Enamic was significant at 3 years, while the differences between them were not significant at 6, 9, and 12 years of simulated brushing. The ΔE* of IPS e.max CAD was significantly lower than CeraSmart and Enamic at all time points (all p < 0.0001) except for the comparison with Enamic at 3 years. CONCLUSION: The extrinsic stains on the ceramic-polymer materials may be more susceptible to change from simulated toothbrushing compared to the lithium-disilicate material. CLINICAL SIGNIFICANCE: Toothbrushing may change the color of extrinsic characterization of ceramic-polymer materials. However, the change may remain clinically imperceptible to the naked eye (ΔE* > 1.0) for nearly 6 equivalent years of brushing.