Effect of different grinding protocols on surface characteristics and fatigue behavior of yttria-stabilized zirconia polycrystalline: An in vitro study

STATEMENT OF PROBLEM

Zirconia frameworks milled by computer-aided design and computer-aided manufacturing (CAD-CAM) often require clinical adjustments. In addition, zirconia prefabricated abutments can also require customization to achieve an adequate emergence profile. However, the influence of grinding adjustment on the surface characteristics and mechanical behavior of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and the best grinding protocol is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of different grinding protocols on the surface characteristics, phase transformation, and mechanical behavior of Y-TZP for frameworks and implant abutments.

MATERIAL AND METHODS

Bar-shaped specimens were fabricated according to ISO 6872-2016 and divided into 3 groups: GC (control, untreated), GA (grinding and finishing with medium and fine diamond rotary instruments using high-speed handpiece under constant water cooling), and GB (grinding and finishing with coarse and medium diamond rotary instruments, respectively, using slow-speed handpiece without water cooling). After specimen grinding, the topography and surface roughness were evaluated by using a laser confocal microscope, the Young modulus was measured by the impulse excitation technique, and crystallographic phase transformation was analyzed by X-ray diffraction. Specimens were then submitted to step-stress accelerated life testing (n=18). The surface roughness and Young modulus results were analyzed by 1-way ANOVA and the Tukey honestly significant difference test (α=.05). The data of step-stress accelerated life testing were analyzed by the survival probability considering the number of cycles and force until fracture.

RESULTS

Statistically significant differences were found among groups considering surface roughness (GA>GB>GC) (P<.05) and Young modulus (GB>GA=GC) (P=.003). X-ray diffraction showed that grinding leads to phase transformation, GC showed only tetragonal phase, while GA and GB showed tetragonal and monoclinic phases. No statistically significant difference (P<.05) was found among groups submitted to the same loading profile when the survival probability was compared, but significant difference was found between the light and moderate loading (P=.002) and light and severe loading (P=.014) of GB when different loading profiles in each group were compared.

CONCLUSIONS

Although grinding protocols affected surface characteristics and promoted phase transformation, the mechanical behavior of Y-TZP was not impaired. Therefore, both the grinding protocols tested can be safely used based on the evaluated properties.

Efeitos de Diferentes Tratamentos de Superfície nas Características Superficiais e Resistência Adesiva da Zircônia Odontológica

O objetivo do estudo foi analisar características superficiais da zircônia, modificada superficialmente, por microscopia eletrônica de varredura (MEV), molhabilidade, energia de superfície, difração de raios x (DRX) e rugosidade superficial (Ra) e comparar      a efetividade dos tratamentos na qualidade adesiva do material. Discos de zircônia foram distribuídos em sete grupos (n6):          G1 (Rocatec), G2 (ácido hidrofluorídrico 40%, 210 segundos), G3 (ácido hidrofluorídrico 40%, 210 segundos + Rocatec), G4 (nanopartículas ZrO2), G5 (nanopartículas SiO2), G6 (nanopartículas SiO2 + ZrO2), G7 (nanopartículas SiO2 + ZrO2 + silano). Uma amostra por grupo (n1) foi analisada por DRX e MEV pós-tratamento e as demais, submetidas a microscopia confocal a laser (n5) para determinação da Ra. Sobre cada disco tratado foram cimentados 2 cilindros também de zircônia para teste de cisalhamento. Molhabilidade e energia de superfície foram desenvolvidas em triplicata (n3). G1, G3, G5 e G7 apresentaram valores de resistência ao cisalhamento superiores aos demais. (p<0,05). G5 e G7 apresentaram os maiores valores de Ra. Imagens em MEV mostraram modificações de superfície em todos os grupos. Em DRX, não houve alteração de fases da zircônia tratada. G1 e G3 apresentaram os menores ângulos de contato e G2, menor energia de superfície, sendo os demais estatisticamente semelhantes. Tratamentos   que depositam sílica superficial são eficazes para união adesiva da zircônia. Nanopartículas de sílica parecem promissoras para o favorecimento da adesão em zircônia.Palavras-chave: Zircônio. Materiais Dentários. Nanopartículas.

Nitric acid passivation does not affect in vitro biocompatibility of titanium

PURPOSE

In general, both chemical composition and surface features of implants affect cell response. The aim of this study was to evaluate the effect of titanium (Ti) passivation on the response of rat bone marrow cells, considering cell attachment, cell morphology, cell proliferation, total protein content, alkaline phosphatase (ALP) activity, and bonelike nodule formation.

MATERIALS AND METHODS

Cells were cultured on both commercially pure titanium (cpTi) and titanium-aluminium-vanadium alloy (Ti-6Al-4V) discs, either passivated or not. For attachment evaluation, cells were cultured for 4 and 24 hours. Cell morphology was evaluated after 4 days. After 7, 14, and 21 days, cell proliferation, total protein content, and ALP activity were evaluated. Bonelike nodule formation was evaluated after 21 days. Data were compared by analysis of variance and the Duncan multiple range test.

RESULTS

Cell attachment, cell morphology, cell proliferation, total protein content, ALP activity, and bonelike nodule formation all were unaffected by Ti composition or passivation.

DISCUSSION AND CONCLUSION

Although the protocol for passivation used here could interfere with the pattern of ions released from Ti-6Al-4V and cpTi surfaces, the present study did not show any effect of this surface treatment on in vitro biocompatibility of Ti as evaluated by osteoblast attachment, proliferation, and differentiation.