Composite depth of cure obtained with QTH and LED units assessed by microhardness and micro-Raman spectroscopy

This study analyzed the depth of cure of a composite assessed by microhardness and the degree of conversion as a function of the light cure unit (LCU) used. Two light cure units, one LED (Ultraled-Dabi Atlante) and one quartz-tungsten-halogen (QTH, Optilux 401-Demetron) unit were used to cure 4.0 x 4.0 mm and 5.0 mm deep composite specimens (Filtek Z250, 3M ESPE). After 24 hours storage at 37 degrees C, Knoop microhardness and degree of conversion were measured on the irradiated surface and at each millimeter of the sample's depth. The degree of conversion was determined by using micro-Raman spectroscopy. The specimens cured with the QTH unit presented uniform decay in microhardness up to 4 mm in depth. Beyond 4 mm, the drop was abrupt. With LED photoactivation, uniform decay was observed only up to 2 mm. At higher depths, the decay in microhardness increased rapidly, especially beyond 3 mm. Depth of cure assessed by micro-Raman revealed that the degree of conversion behaved similarly to microhardness for both LCUs. A strong linear regression between microhardness and the degree of conversion, including both LCUs, was established with R2 = 0.980.     

The importance of dentin collagen fibrils on the marginal sealing of adhesive restorations

This study evaluated the importance of the union between dentin collagen and three different adhesive materials. Sixty Class V restorations were prepared on the buccal and lingual surfaces of 30 recently extracted human premolars, with the cervical margins in dentin and the occlusal margins in enamel. These restorations were distributed to three groups of 20 cavities each based on the employed adhesive system used: Group A: Single Bond; Group B: Prime&Bond NT; Group C: One Coat Bond. Each group was subdivided according to dentin treatment: (1) manufacturers' adhesive protocol and (2) removal of the collagens fibers (total etch + sodium hypochlorite 5% for two minutes) + adhesive protocol. After the restorations were completed, the teeth were stored in saline solution (24 hours/37 degrees C), subjected to thermal cycling, washing and scoring according to dye penetration. Dye penetration was evaluated, with the numbers ranging from 0 (no infiltration) to 3 (greatest infiltration). When the dentin microleakage scores were compared in subgroups A1XA2, B1XB2 and C1XC2, the Mann-Whitney Test revealed significant differences between groups B and C (p < 5%). The better results were shown in subgroups B2 (p = 0.0345) and C2 (p = 0.0029). The results showed that the collagen fibrils were not necessary for adhesion, and their removal positively influenced the marginal sealing of Prime&Bond NT and One Coat Bond.     

The influence of C-factor, flexural modulus and viscous flow on gap formation in resin composite restorations

This study analyzed the influence of C-factor, flexural modulus and viscous flow on gap formation in resin composite restorations. Two resin composites, a mini-filled hybrid (P 60) and a nanofilled (Supreme), were used. The flexural modulus was obtained from bar-shaped specimens submitted to three-point bending. Viscous flow was obtained from the difference between the initial and final diameter of resin composite disks submitted to a load of 10 N for 120 seconds. Gap analysis was conducted in three types of cylindrical cavities (C-factor of 1.8, 2.6 and 3.4) that were prepared on the occlusal surfaces of human molars. The gap width at the dentin-resin composite interface was measured using a 3D scanning system (Talyscan 150). The data were analyzed by ANOVA and Student-Newman-Keuls' test, t-test and linear regression analysis (alpha = 0.05). The cavities with C-factor 3.4 presented the highest Gap formation (p < 0.0001). The lowest Gap formation was found in cavities restored with Supreme resin composite (p < 0.0001). P 60 presented significantly higher flexural modulus and lower viscous flow than Supreme (p < 0.0001). Regression analyses detected a significant influence of flexural modulus and viscous flow on gap formation (p < 0.05).     

Bond strength of acrylic teeth to denture base resin after various surface conditioning methods before and after thermocycling

This study aimed to evaluate the durability of adhesion between acrylic teeth and denture base acrylic resin. The base surfaces of 24 acrylic teeth were flatted and submitted to 4 surface treatment methods: SM1 (control): No SM; SM2: application of a methyl methacrylate-based bonding agent (Vitacol); SM3: air abrasion with 30-microm silicone oxide plus silane; SM4: SM3 plus SM2. A heat-polymerized acrylic resin was applied to the teeth. Thereafter, bar specimens were produced for the microtensile test at dry and thermocyled conditions (60 days water storage followed by 12,000 cycles). The results showed that bond strength was significantly affected by the SM (P < .0001) (SM4 = SM2 > SM3 > SM1) and storage regimens (P < .0001) (dry > thermocycled). The methyl methacrylate-based adhesive showed the highest bond strength.     

Prevalence of human papillomavirus in squamous cell carcinoma of the tongue

Oncogenic human papillomaviruses (HPVs) are important agents in the genesis of gynecological cancer, and have also been implied in the genesis of oral cancer. With the purpose of evaluating the relationship between HPV and squamous cell carcinoma (SCC) of the tongue, a case-control study was performed. Fifty white male patients who were smokers and had the histological diagnosis of SCC of the tongue were selected. The control group was composed of 10 matched patients with no clinical evidence of tongue lesions. Polymerase chain reaction (PCR) was used to detect the presence of HPV genome in fresh-frozen tissue specimens from SCC of the tongue margin. Thirty-seven patients (74%) had a positive PCR for oncogenic papillomavirus, and only 1 specimen (10%) of the control group was positive for nononcogenic papillomavirus. Based on the statistical analysis of this study there was a 25.6% higher risk for SCC of the tongue to harbor oncogenic HPV than the healthy control tongue tissue.