Carboxylic acid functionalized polyethyleneglycol resin, High Load

Purpose: This in vitro study investigated the null hypothesis that metal-free crowns induce fracture loads and mechanical behavior similar to metal ceramic systems and to study the fracture pattern of ceramic crowns under compressive loads using finite element and fractography analyses. Materials and methods: Six groups (n = 8) with crowns from different systems were compared: conventional metal ceramic (Noritake) (CMC); modified metal ceramic (Noritake) (MMC); lithium disilicate-reinforced ceramic (IPS Empress II) (EMP); leucite-reinforced ceramic (Cergogold) (CERG); leucite fluoride-apatite reinforced ceramic (IPS d.Sign) (SIGN); and polymer crowns (Targis) (TARG). Standardized crown preparations were performed on bovine roots containing NiCr metal dowels and resin cores. Crowns were fabricated using the ceramics listed, cemented with dual-cure resin cement, and submitted to compressive loads in a mechanical testing machine at a 0.5-mm/min crosshead speed. Data were submitted to one-way ANOVA and Tukey tests, and fractured specimens were visually inspected under a stereomicroscope (20×) to determine the type of fracture. Maximum principal stress (MPS) distributions were calculated using finite element analysis, and fracture origin and the correlation with the fracture type were determined using fractography. Results: Mean values of fracture resistance (N) for all groups were: CMC: 1383 ± 298 (a); MMC: 1691 ± 236 (a); EMP: 657 ± 153 (b); CERG: 546 ± 149 (bc); SIGN: 443 ± 126 (c); TARG: 749 ± 113 (b). Statistical results showed significant differences among groups (p < 0.05) represented by different lowercase letters. Metal ceramic crowns presented fracture loads significantly higher than the others. Ceramic specimens presented high incidence of fractures involving either the core or the tooth, and all fractures of polymer crown specimens involved the tooth in a catastrophic way. Based on stress and fractographic analyses it was determined that fracture occurred from the occlusal to the cervical direction. Conclusions: Within the limitations of this study, the results indicated that the use of ceramic and polymer crowns without a core reinforcement should be carefully evaluated before clinical use due to the high incidence of failure with tooth involvement. This mainly occurred for the polymer crown group, although the fracture load was higher than normal occlusal forces. High tensile stress concentrations were found around and between the occlusal loading points. Fractographic analysis indicated fracture originating from the load point and propagating from the occlusal surface toward the cervical area, which is the opposite direction of that observed in clinical situations.

Objectives: This study aimed to analyze interactions between oral biofilms and a dental triethylene glycol dimethacrylate (TEGDMA)-based resin infiltration material on enamel. Methods: Demineralized enamel specimens (14 days, acidic buffer, pH 5.0) were either infiltrated with a commercial TEGDMA resin and subjected to a three-species biofilm (Streptococcus mutans UAB 159, Streptococcus oralis OMZ 607 and Actinomyces oris OMZ 745) (group 1), applied to the biofilm (group 2), or merely resin infiltrated (group 3). A control group received no treatment (4). Biofilm formation and metabolic activity of biofilms were measured for group (1) and (2) after 24h CFU and a resazurin assay. Resin biodegradation was measured for group (1) and (3) by high performance liquid chromatography (HPLC) coupled with mass spectrometry after 6 and 24h incubation. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) images were taken to study the biofilm and material's autofluorescence in groups (1-4) after 24h. Results: SEM and CLSM images showed reduced biofilm formation on resin-infiltrated specimens (group 1) compared to group 2, while no biofilm was detectable on groups 3 and 4. CFU data (log10 CFU per mL) of group 1 showed significantly reduced bacterial numbers (p<0.05) compared to group 2. However, HPLC analysis of TEGDMA leakage after 6h and 24h revealed no differences between group 1 and group 3. Conclusions: The results of the current study indicate that freshly resin-infiltrated enamel surfaces show a biofilm reducing effect, while monomer leakage was not affected by bacterial presence. Clinical significance: Resin infiltrated enamel surfaces are constantly exposed to the oral microflora. Yet, it is not known how biofilms interact with enamel-penetrated resins and if and to which extent accessory alignments in oral hygiene are needed.

Objective: The main objective of this study was to evaluate the wear characteristics of fiber-reinforced dental composites. Variables under investigation include the fiber weight percent added to the matrix as well as fiber length. Methods: Dental specimens with glass fiber content of 2, 5.1, 5.7, and 7.6 wt% with fiber length of either 1.5 or 3 mm, were prepared by mixing an activated dental resin with commercial glass fibers. The specimens were then tested on a pin on disc setup, where the antagonist disc was manufactured of a similar fiber-reinforced composite with 5.1 wt% fiber and fiber length of 3 mm. The volume loss and coefficient of friction of the specimens was monitored periodically throughout testing. In addition, the wear surfaces of all specimens were evaluated using a scanning electron microscope. Results: The specimens with 5.7 wt% fibers and fiber length of 3 mm performed better in this study compared to all other fiber-reinforced specimens under all load conditions. In fact, this specimen had a comparable wear rate to a particle-filled dental composite. For the fiber lengths considered, increasing the length of the fibers increased the wear resistance of the specimen. The coefficient of friction showed a good correlation with the wear resistance of specimens. Significance: Fiber-reinforced composites demonstrated a high resistance to wear and may therefore be advantageous for dental applications, where high wear resistance is essential to functionality.