Does the application of surface treatments in different sintering stages affect flexural strength and optical properties of zirconia?

Abstract

Objective: To investigate the influence of surface treatments conducted in presintering and postsintering stages on flexural strength and optical properties of zirconia.Materials and methods: Specimens were milled from partially sintered zirconia blocks in different geometries and divided into three main groups as presintered, postsintered, and control groups. Test groups were further divided into three subgroups (n = 10) according to the surface treatments conducted (grinding, Er,Cr:YSGG laser irradiation, air-borne particle abrasion [APA]). Four-point flexural strength (σ) test and Weibull analysis were conducted. Color differences (ΔE 00 ) and translucency parameter (TP ab ) were calculated with a spectrophotometer. Surfaces of specimens were scrutinized under FESEM. Data were statistically analyzed.Results: Postsintered groups exhibited higher σ values (P < .05). Within all groups, highest and lowest σ values were detected at postsintered and presintered APA groups, respectively (P < .05). All ΔE 00 values were above the perceptibility threshold (ΔE 00 > 0.8). Higher TP ab values were obtained and deeper scratches were observed in presintered groups.Conclusions: Surface treatments performed at postsintering stage had a favorable effect on the flexural strength of all specimens. Surface treatments performed before sintering increased translucency and caused higher ΔE 00 values.Clinical significance: Surface treatments performed at different sintering stages can alter mechanical and optical properties of zirconia.

Effect of air‐abrasion at pre‐ and/or post‐sintered stage and hydrothermal aging on surface roughness, phase transformation, and flexural strength of multilayered monolithic zirconia

“…The reason for the increased roughness may be highly dependent on the soft structure of the non‐sintered material. The observed microscopy images showed similar features to those published by Kurtulmus‐Yilmaz et al, 29 who stated that the BS group exhibited dramatically lower flexural strength values compared with the control. Passos et al 26 declared that air‐abrasion of Y‐TZP with 50‐ or 110‐μm Al 2 O 3 before sintering should not be preferred because this soft material might be visibly damaged.…”

“…Some studies have focused on the effects of sintering and air‐abrasion order 13,25‐29 . Moon et al 25 stated that although air‐abrasion of zirconia at pre‐sintered stage created blunt and melted‐round surfaces, the similar process applied after sintering generated coarse and needle‐like defects, which may trigger crack propagation.…”

“…After this treatment, some reports stated an increase in flexural strength, probably because of the residual compressive stress at the surface as a result of phase transformation, 17‐21 yet others concluded an unfavorable effect because of substantial surface damage 22‐24 . Unlike the earlier studies that concentrated on evaluating the effects of pretreatments after zirconia sintering, recent studies have focused on airborne‐particle abrasion before sintering 13,25‐29 . In one of these recent investigations, air‐abrasion after sintering was found to produce sharp‐edged irregularities, which might cause initiation of crack propagation, while these can be observed in rounded form by applying air‐abrasion before sintering 25 .…”

“…[22][23][24] Unlike the earlier studies that concentrated on evaluating the effects of pretreatments after zirconia sintering, recent studies have focused on airborne-particle abrasion before sintering. 13,[25][26][27][28][29] In one of these recent investigations, air-abrasion after sintering was found to produce sharp-edged irregularities, which might cause initiation of crack propagation, while these can be observed in rounded form by applying air-abrasion before sintering. 25 It has also been documented that performing air-abrasion at the pre-sintered rather than post-sintered stage yields higher surface roughness (Ra) values with lower monoclinic phase levels.…”

Combined application of femtosecond laser and air‐abrasion protocols to monolithic zirconia at different sintering stages: Effects on surface roughness and resin bond strength

“…Recently, several studies have focused on the sintering/surface treatment order. 10,[27][28][29][30][31][32] Applying pre-treatments in different sintering stages may lead to markedly different surface textures, 27,29 which may enhance both surface roughness and resin bond strength. 31 Previous studies concluded that higher surface roughness values could be obtained with lower m-phase levels by applying air-abrasion before sintering.…”