Reduced Periodontal Support for Lower Central Incisor - A 3D Finite Element Analysis of Compressive Stress in the Periodontium.

BACKGROUND: The aim of this study was to assess the stress concentration in simulated periodontal alveolar bone containing healthy teeth with and without attachment loss. METHODS: Six 3-D models of a lower central incisor were created simulating the teeth structure, cancellous and cortical bone and periodontal ligament. Each model presented a 1mm increasing distance between cement-enamel junction (CEJ) and alveolar bone crest (ABC) (1 to 6mm). A 100N, 45-degree load was applied to the buccal face of the lower central incisor. The effects of Minimum Principal Stress (MPS) on lamina dura (LD) and ABC were analyzed. RESULTS: The results showed an increase of MPS in the surrounding bone (ABC and LD) due to periodontal attachment loss. The 6mm attachment loss model showed the highest (p less than 0.001) magnitude in MPS. Each millimeter increase in CEJ-ABC distance generated a 12% pattern of attachment loss and an increase at least of 65.7% for ABC and 33.6% for LD. CONCLUSION: Under simulated conditions, attachment loss increases stress concentration in the surrounding bone suggesting a partly explanation regarding bone resorption risk for teeth with periodontal attachment loss.

Influence of surface sealant and erosive challenge on the color change of composite resin subjected to artificial staining.

The aim of this study was to evaluate the influence of surface sealant and erosive challenge on the color change of composite resin after artificial staining with coffee. Forty-eight composite specimens (8 × 1 mm) were prepared and divided into 4 groups (n = 12) based on the timing of sealant application (immediate vs delayed) and exposure to acid (erosive challenge vs no challenge). The groups were subjected to the procedures in the following order: 1, sealant application, erosive challenge, color measurement, coffee immersion, and color measurement; 2, sealant application, color measurement, coffee immersion, and color measurement; 3, erosive challenge, color measurement, sealant application, coffee immersion, and color measurement; and 4, color measurement, sealant application, coffee immersion, and color measurement. In groups 1 and 2, surface sealant was applied immediately after preparation of the specimens. In groups 3 and 4, sealant was applied after the first color measurement. Color was measured with a spectrophotometer using the CIE L*a*b* system. The erosive challenge (groups 1 and 3) was carried out in 0.01M hydrochloric acid, 150 mL/cycle, at room temperature (2-minute immersions 4 times a day for 5 days). After all specimens were immersed in coffee for 14 days, new color measurements were performed. For total color change (∆E*), groups 1 (21.01) and 2 (23.10) presented lower values than groups 3 (27.76) and 4 (26.57). For luminosity (∆L*), the opposite occurred (groups: 1, -16.84; 2, -17.72; 3, -22.62; and 4, -21.22). For ∆a* and ∆b*, the only statistically significant difference was the group 1 ∆b* value, which was the lowest among all groups. The opacity remained stable in all groups. The results suggest that resin luminosity decreases and color variation increases when surface sealant is applied after erosive cycling and storage.

Effect of the restorative technique on load-bearing capacity, cusp deflection, and stress distribution of endodontically-treated premolars with MOD restoration.

OBJECTIVES: To evaluate the influence of the restorative technique on the mechanical response of endodontically-treated upper premolars with mesio-occluso-distal (MOD) cavity. MATERIALS AND METHODS: Forty-eight premolars received MOD preparation (4 groups, n = 12) with different restorative techniques: glass ionomer cement + composite resin (the GIC group), a metallic post + composite resin (the MP group), a fiberglass post + composite resin (the FGP group), or no endodontic treatment + restoration with composite resin (the CR group). Cusp strain and load-bearing capacity were evaluated. One-way analysis of variance and the Tukey test were used with α = 5%. Finite element analysis (FEA) was used to calculate displacement and tensile stress for the teeth and restorations. RESULTS: MP showed the highest cusp (p = 0.027) deflection (24.28 ± 5.09 µm/µm), followed by FGP (20.61 ± 5.05 µm/µm), CR (17.72 ± 6.32 µm/µm), and GIC (17.62 ± 7.00 µm/µm). For load-bearing, CR (38.89 ± 3.24 N) showed the highest, followed by GIC (37.51 ± 6.69 N), FGP (29.80 ± 10.03 N), and MP (18.41 ± 4.15 N) (p = 0.001) value. FEA showed similar behavior in the restorations in all groups, while MP showed the highest stress concentration in the tooth and post. CONCLUSIONS: There is no mechanical advantage in using intraradicular posts for endodontically-treated premolars requiring MOD restoration. Filling the pulp chamber with GIC and restoring the tooth with only CR showed the most promising results for cusp deflection, failure load, and stress distribution.

Effect of different finishing times on surface roughness and maintenance of polish in nanoparticle and microhybrid composite resins.

The objective of the study was to evaluate the effect of immediate polishing, after 24 h and after 1 week, on the surface roughness of two micro-hybrid resins (Esthet-X; Opallis) and one nanoparticle resin (Filtek Z350), as well as verifying maintenance of the polish after 1 year, simulated by means of thermal cycling. Forty-three specimens of each material were made and divided into a control group and three experimental groups. The control group specimens received no surface treatment. Group 1 received finishing with an extra-fine diamond drill and posterior polishing with the systems Enhance and PoGo, immediately after polymerization. Group 2 received the same procedures; however, these were carried out after 24 h of storage. Group 3 received the surface treatment after 7 days of storage. After that, the surface roughness was evaluated by a profilometer. After the initial reading, the specimens were submitted to thermal cycling for 10,000 cycles. After thermal cycling, a new roughness reading was taken. The results showed a higher roughness value for the resin Esthet-X, and the resins Opallis and Z350 presented the same roughness values. As regards the time when polishing was performed, specimens polished immediately after polymerization presented higher roughness values in comparison with the other two periods. After thermal cycling, the statistical analysis showed that the Opallis resin polish had been maintained, whereas for the other two resins, there was a significant reduction in surface smoothness. The surface roughness was influenced by the material and also by the period of polishing; the surface roughness of all tested materials were at a clinically acceptable level.