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.

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.

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.

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.

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.