Comparison of the indentation strength and single-edge-v-notched beam methods for dental ceramic fracture toughness testing

Aim: To study influence of the cooling rate after sintering a veneering porcelain (Vita VM9) on fracture toughness by indentation strength (IS) and single-edge-v-notched beam (SEVNB) methods. Methods: Vita VM9 bars were sintered according to the manufacturer's recommendation and cooled under three conditions: Slow (inside the furnace from sintering temperature to room temperature); Normal (inside the furnace from sintering temperature to 500 ºC and outside the furnace from 500 ºC to room temperature); and Fast (outside the furnace from sintering temperature to room temperature). Fracture toughness was measured by IS (n=10) and SEVNB (n=10) methods. Data were analyzed by two-way ANOVA (α=0.05). Results: The fracture toughness obtained from SEVNB (slow - 1.02±0.10; normal - 1.09±0.13; and fast - 1,02±0.18 MPa.m1/2 cooling techniques) was significantly lower than IS (slow - 1.19±0.13; normal - 1.17±0.07; and fast - 1.16±0.06 MPa. m1/2 cooling techniques). There was no significant influence of the cooling technique (p=0.012). Conclusions: The measurement technique influenced the fracture toughness values . IS method overestimated the fracture toughness values. Irrespective of the measuring method, cooling rate did not influence the Vita VM9 veneering porcelain fracture toughness (Au)

Strength of 3Y-TZP and feldspathic porcelain subjected to different cooling methods

AIM: To investigate the effect of the cooling rate on flexural strength of monolayer and bilayer porcelain/zirconia (Y-TZP) bars. METHODS: Forty-five specimens were made for each design group: (PM) monolithic specimens of veneer porcelain Vita VM9 (Vita, Germany); (ZM) monolithic specimens of zirconia (ZiHP; ProtMat, Brazil); (PB) bilayer specimens zirconia/porcelain with porcelain on lower surface; and (ZB) bilayer specimens porcelain/zirconia with zirconia on lower surface. Each group was cooled by three different methods after porcelain sintering: slow specimens were cooled inside the turned-off furnace; normal specimens were removed from the furnace and cooled in air at room temperature; and fast specimens were removed from the furnace at 910°C and cooled by compressed air for 10 s. Specimens were polished and flexural strength was measured in water at 37 °C (n=15). Maximum load at fracture was recorded, and equations for simple (monolayer) and composite (bilayer) structures were used to calculate the flexural strength. RESULTS were analyzed using one-way ANOVA (p<0.05) and Tukey test separately for each design. RESULTS: The results of one-way ANOVA were statistically significant only for the PB group. The post-hoc Tukey test showed the highest flexural strength for fast cooling and the lowest for slow cooling; the normal cooling was statistically similar to both. CONCLUSIONS: Cooling methods affected only the flexural strength of bilayer specimens with porcelain on low surface (under tension) when the slow cooling method was used...

Clinical fractures of veneered zirconia single crowns.

Crowns made from an yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) core with a porcelain veneer have shown high clinical failure rates. Manifestations of clinical failure in veneering ceramic ranges from a single chip to an extended fracture. Core failures are uncommon but usually are catastrophic. This article examines the possible causes of failure in zirconia systems and presents a case report involving the diagnosis and repair of three different types of failure in six 3Y-TZP/porcelain crowns.

White enamel lesions and their progression from childhood to adolescence: a prospective study.

PURPOSE: To assess the current situation of white enamel lesions on vestibular surfaces of permanent maxillary incisors, diagnosed 6 years ago, without clinical intervention. MATERIALS AND METHODS: The prospective study reassessed 53 students of both sexes, aged between 13 and 18 years old, all attending the public school system in Natal, Brazil. Data collection was performed by calibrated examiners, and a clinical chart consisting of demographic data on dental caries, oral hygiene and gingival condition was prepared. A tactile-visual examination was conducted using a clinical mirror and periodontal probe. Data compilation and analysis were carried out using SPSS software. In this analysis, the chi-square test was used for qualitative independent variables. To identify the net effect of treatment, multiple logistic analysis with forward stepwise model selection was performed. RESULTS: The final sample was composed of 106 lesions in the 53 individuals, with mean age of 15.02 years, visible plaque index (VPI) of 23.34%, and gingival blood indices (GBI) of 25.92%. A statistically significant relationship (P = 0.003) was found between initial DMFS and the prognosis of white enamel lesions. CONCLUSION: It was observed that past caries experience and dental plaque were the main predictive factors for negative lesion outcomes, demonstrating the need for oral hygiene control through continuing preventive measures.

Restauração cerâmica estética com o sistema In-Ceram: relato de caso / Esthetic ceramic restoration using the In-Ceram system: a case report

A busca crescente de pacientes por estética e opções restauradoras ametálicas tem conduzido à procura por alternativas para a reconstrução dentária, por meio de restaurações que simulem as características de um dente natural. Dentre os materiais restauradores odontológicos, as cerâmicas se destacam, tanto do ponto de vista estético-funcional como em relação à durabilidade e resistência. Atualmente, existe no mercado ampla variedade de sistemas totalmente cerâmicos, dentre os quais aparece o sistema In-Ceram, com suas variações In-Ceram Alumina, In-Ceram Spinell e In-Ceram Zircônia, que ainda necessitam de ser investigados minuciosamente. Assim, este artigo apresenta um caso clínico que demonstra a confecção de uma coroa sem metal para um elemento canino superior direito. Foi utilizado como material para infra-estrutura o sistema In-Ceram Alumina e a porcelana convencional Vitadur Alpha para revestimento, o que acarretou estética satisfatória, que mimetiza aspectos de um dente natural.

The increasing search patients for esthetic restorative options lead to the search for alternatives fot the dental reconstruction which simulate the features of a natural tooth. Between the restorative dental materials, the dental ceramics present extraordinary durability and resistance. Currently, there are a large variety of total ceramics systems in the dental market, i.e. In-Ceram system (Alumina, Spinell and Zirconia). This article has the objective to present a clinical case demonstrating the restoration of a right canine with a metal free crown using In-Ceram Alumina as the infrastructure and the conventional porcelain Vitadur Alpha as a veneering material. However, these all-ceramic systems should be submitted to longitudinal clinical evaluations, to be considered more reliable and safe, provided that the correct indications of each variation of the In-Ceramic ceramic system is respected.