Fatigue survival of endodontically treated teeth restored with different fiber-reinforced composite resin post strategies versus universal 2-piece fiber post system: An in vitro study.

STATEMENT OF PROBLEM: Various strategies have been proposed to reduce the cement space of foundation restorations for endodontically treated teeth. However, they may add more operative steps, or the dentist must keep different sizes of drills and posts in stock. A 2-piece universal adjustable post system has been developed to overcome this problem, but whether the system has acceptable fatigue survival performance is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the fatigue survival and stress distribution of endodontically treated teeth without a ferrule and restored with different glass fiber post strategies versus a recently introduced universal 2-piece fiber post system. MATERIAL AND METHODS: Bovine incisor roots were randomly assigned to 3 groups as per the post used (n=13): adapted glass fiber post with post space preparation of the same size, composite resin-custom glass fiber post (CTM), and universal 2-piece glass fiber-reinforced composite resin post (UNI). The posts were adhesively luted, the composite resin core was added, and a composite resin crown was produced with computer-aided design and computer-aided manufacturing (CAD-CAM), and then adhesively luted to each core. A fatigue test was performed with the stepwise stress method (10 000 cycles/step; 20 Hz; load=100 N to 750 N; step=50 N) until fracture, and the failure mode analyzed. The stress distribution was evaluated by finite element analysis with the maximum principal stress criteria by following the parameters of the in vitro test. The solids were considered homogeneous, linear, and isotropic, except for the glass fiber post (orthotropic), and a load of 450 N at 30 degrees was applied. The fatigue failure load and the number of cycles for failure were analyzed with Kaplan-Meier and Mantel-Cox (log rank test) (α=.05). The finite element analysis results were analyzed with colorimetric graphs. RESULTS: The highest fatigue failure load and the number of cycles for failure were found in the UNI system, whereas the lowest results were found in the CTM group. All groups exhibited repairable failures. The finite element analysis showed the lowest stress in root dentin in the UNI system. The CTM system had the largest stress regions at the dentin and dentin-core interface. CONCLUSIONS: The use of a 2-piece universal glass fiber post system resulted in more fatigue behavior compared with composite resin-custom glass fiber posts.

Assessment of patient and dentist preference between conventional and digital diagnostic waxing.

Patient expectations for rehabilitations of a high esthetic standard as well as the demand for fast but efficient care have provided new work perspectives in dentistry. Dentists also have to choose between conventional and digital workflows. The aim of the present randomized restorative trial was to compare diagnostic waxing (DW) performed conventionally with its digital counterpart and to assess the two approaches from the point of view of both patient and dentist. Twenty patients with esthetic complaints were selected to undergo molding processes to obtain conventional study models on the one hand, and intraoral scanning to obtain virtual models on the other. Both the 2D planning and 3D virtual models were sent to the laboratory for the performance of DW. The restorative trial was evaluated by one evaluator dentist, while patient opinion was determined through customized questionnaires. The results show that although 80% of patients rated the digital method to be more convenient in terms of execution time and comfort and indicated that scanning was the most reliable way to obtain an impression, 65% chose the conventional DW for their esthetic restoration after the mock-up tests were performed and analyzed. The evaluating dentist preferred the conventional DW technique in 50% of cases assessed. The conclusion is that although digital technology has its advantages, the final esthetic result does not always meet the expectations and demands of patients and dentists.

Mechanical behavior of implant assisted removable partial denture for Kennedy class II.

BACKGROUND: This study evaluated the mechanical response of a removable partial denture (RPD) in Kennedy Class II according to being associated or not with implants. MATERIAL AND METHODS: Four RPDs were manufactured for a Kennedy Class II: CRPD - Conventional RPD, RPD+1M, RPD+2M and RPD+12M, respectively, signifying implant assisted RPDs with the implant installed in the first molar, second molar, and in the first and second molars. The finite element method was used to determine the most damaged support tooth under compressive load (300N, 10s) and strain gauge analysis was used to evaluate the microstrain. All groups were submitted to a retentive force analysis (0.5 mm/mm, 100kgf). Microstrain and retentive force data were submitted to One-way ANOVA and the Tukey test, all with α=5%. RESULTS: High microstrain was observed in the second premolar adjacent to the edentulous space under compression load (p< 0.01). RPD+12M presented lower microstrain, however being similar to RPD+2M. RPD+1M presented a higher mean value of retentive force, but similar to RPD+12M. FEM showed RPD assisted by implants concentrates less stress in the periodontal ligament. The association of two implants was sufficient to decrease the stress generated in the implants. The most stressed region for the o-ring abutment was the threads, and the group with two implants showed the lowest stress concentration. CONCLUSIONS: In cases of Kennedy Class II, the association of RPD with implants in the molar region is a favorable option for patient rehabilitation, reducing the movement of the direct retainer adjacent to the edentulous space, increasing the removal force and decreasing the stress magnitude in the periodontal ligament. Key words:Removable partial denture, Finite element analysis, Prosthetic dentistry, Implant-assisted RPD, Distal extension RPD considerations.

Effect of different materials and undercut on the removal force and stress distribution in circumferential clasps during direct retainer action in removable partial dentures.

OBJECTIVES: This study aimed to evaluate the effect of different materials and undercut on the removal force and stress distribution in the supporting tooth and in the circumferential clasp used in removable partial prosthesis. METHODS: Upper molars prepared for Akers circumferential clasp with retention and opposing arm were modeled, scanned, elaborated with CAD software and the geometries imported in FEA and analyzed. Six different materials were selected for the clasp (Polyamide, Polyoxymethylene, Polyetheretherketone - PEEK, Gold alloy, Titanium and CoCr) and 3 different undercuts (0.25, 0.50 and 0.75mm), totaling 18 groups. RESULTS: The clasps presented greater stress in their structure and potentially greater damage to the dental enamel when made with rigid materials and with more undercut; however, they presented greater ability to remain in position. SIGNIFICANCE: Polyamide with a higher undercut is an esthetic alternative to rigid metallic clasps. It showed promising behavior because it strongly reduces the damage to the enamel, and even with an undercut of 0.75, the retention is lower than for CoCr with a 0.25 undercut, and this retention might still be sufficient. Polyoxymethylene and Polyetheretherketone (PEEK) are not suitable materials for the clasps, because the maximum stress occurring during removal with higher undercuts is higher than the material strength.

Bond strength of a self-adhesive resin cement to enamel and dentin.

The purpose of this study was to evaluate the influence of surface treatments and thermocycling on the microtensile bond strength (µTBS) of self-adhesive resin cement to human enamel and dentin. Eighty human third molars were selected. The crowns of 40 teeth were transversally sectioned, exposing the mid-coronal dentin. The buccal surfaces of the other 40 teeth were grinded to obtain a 5 mm2 flat enamel area. Eighty resin blocks were produced and cemented to the dental surfaces with RelyX Unicem, then grouped according to the surface treatment (n=10): UnicemC with no conditioning, UnicemP with 37% phosphoric acid/15 s, and UnicemPA with 37% phosphoric acid/15 s plus adhesive bonding (Single Bond 2). There were two control groups, one for enamel and the other for dentin: VR with 37% phosphoric acid/15 s plus adhesive bonding (Single Bond 2) plus Variolink II. The enamel-dentin resin cement blocks were sectioned to produce non-trimmed bar specimens, which were divided into two storage conditions: dry, µTBS immediately after cutting; TC (5,000 x; 5°C/55°C). The samples were submitted to µTBS, and data were statistically analyzed by ANOVA and Tukey's test. The results showed statistical differences between UnicemC and the others. UnicemPA and VR showed better bond strength to dentin during the period before and after thermocycling, respectively. For the enamel, UnicemP showed better bond strength for both situations. Only for UnicemPA did the thermocycling significantly decrease the bond strength values. Within the limits of this study, it could be concluded that the bond strength is influenced by the surface treatments, and that thermocycling decreases the bond strength of all groups, but significantly only for UnicemPA.

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.