Surface properties of dental zirconia ceramics affected by ultrasonic scaling and low-temperature degradation

Abstract

Zirconia (3Y-TZP) dental prostheses are widely used in clinical dentistry. However, the effect of ultrasonic scaling performed as a part of professional tooth cleaning on 3Y-TZP dental prostheses, especially in conjunction with low-temperature degradation (LTD), has not been fully investigated. The present study aimed to evaluate the influence of ultrasonic scaling and LTD on the surface properties of 3Y-TZP in relation to bacterial adhesion on the treated surface. 3Y-TZP specimens (4 × 4 × 2 mm) were polished and then subjected to autoclaving at 134°C for 100 h to induce LTD, followed by 10 rounds of ultrasonic scaling using a steel scaler tip for 1 min each. Surface roughness, crystalline structure, wettability, and hardness were analyzed by optical interferometry, X-ray diffraction analysis, contact angle measurement, and nano-indentation technique, respectively. Subsequently, bacterial adhesion onto the treated 3Y-TZP surface was evaluated using Streptococcus mitis and S. oralis. The results demonstrated that the combination of ultrasonic scaling and LTD significantly increased the Sa value (surface roughness parameter) of the polished 3Y-TZP surface from 1.6 nm to 117 nm. LTD affected the crystalline structure, causing phase transformation from the tetragonal to the monoclinic phase, and decreased both the contact angle and surface hardness. However, bacterial adhesion was not influenced by these changes in surface properties. The present study suggests that ultrasonic scaling may be acceptable for debridement of 3Y-TZP dental prostheses because it did not facilitate bacterial adhesion even in the combination with LTD, although it did cause slight roughening of the surface.

Influence of Different Plaque Control Methods and Hydrothermal Aging on Structural Properties of Monolithic Zirconia

“…Another study examining bacterial adhesion on varied restorative materials after plaque removal via scaling both steel curette and ultrasonic scaler points to scalers did not affect zirconia surface roughness (34). In contrast to the present study, Nakazawa et al (25) reported that ultrasonic scaling increases the surface roughness with or without aging. They observed that small pits were formed on the zirconia surface instead of scratches, and they concluded that this occurred due to particle break off from the surface due to LTD. Vigolo, too, examined the effect of steel and titanium curettes on zirconia and lithium disilicate surfaces and concluded that the steel curette increased the zirconia surface roughness (35).…”

“…A previous study investigating the effect of ultrasonic scaling and LTD on phase transformation stated that ultrasonic scalers did not affect the phase transformation on the zirconia surface. But independent of the ultrasonic scaling processes, LTD increased the t→m phase transformation and decreased the material's surface hardness (25). Although our findings are partially compatible with the study mentioned above, the phase transformation percentages differed from ours due to the extended aging time for LTD. Sc and USc groups indicated lower surface hardness results, but there were no important changes in the other groups.…”

“…Besides, they said that LTD and surface treatment with ultrasonic scaling using a steel tip caused hydrophobic surface. Because of the aging time in that study, LTD may stimulate to release of hydroxyl groups due to the degradation of Zr-O-Zr bonds that specify the hydrophilicity may have been removed from the surface during ultrasonic scaling (25).…”

“…The ultrasonic scaler tip was placed on the zirconia surface to contact its lateral surface with an inclination of almost 0 degrees. Scaling motions were executed all over the surface of the specimens briefly, continuously, and equally in the same direction (25). Powders were applied using the standard unit (Air-Flow Master, EMS SA, Switzerland) by the same periodontal specialist.…”

The effects of physical decontamination methods on zirconia implant surfaces: a systematic review

“…After screening, 26 studies were selected for a full-text evaluation to assess their eligibility according to the selection criteria. After the evaluation, 11 studies [ 25 26 27 28 29 30 31 32 33 34 35 ] were included for the final review. Fifteen studies did not meet the inclusion criteria and were excluded for the following reasons: the study did not investigate interventions for decontamination purposes (n=9); the study did not use zirconia as an implant material (n=5); or there was no comparator or control group (n=1).…”