The use of different adhesive filling material and mass combinations to restore class II cavities under loading and shrinkage effects: a 3D-FEA.

3D tooth models were virtually restored: flowable composite resin + bulk-fill composite (A), glass ionomer cement + bulk-fill composite (B) or adhesive + bulk-fill composite (C). Polymerization shrinkage and masticatory loads were simulated. All models exhibited the highest stress concentration at the enamel-restoration interfaces. A and C showed similar pattern with lower magnitude in A in comparison to C. B showed lower stress in dentine and C the highest cusps displacement. The use of glass ionomer cement or flowable composite resin in combination with a bulk-fill composite improved the biomechanical behavior of deep class II MO cavities.

Accuracy evaluation of surgical guides in implant dentistry by non-contact reverse engineering techniques.

OBJECTIVE: In the paper laser scanning was used to evaluate, by indirect methods, the accuracy of computer-designed surgical guides in the oral implant supported rehabilitation of partially or completely edentulous patients. MATERIALS AND METHODS: Five implant supported rehabilitations for a total of twenty-three implants were carried out by computer-designed surgical guides, performed with the master model developed by muco-compressive and muco-static impressions. For all cases the surgical virtual planning, starting from 3D models obtained by dental scan DICOM data, was performed. The implants were inserted on the pre-surgical casts in the position defined in the virtual planning. These positions were acquired by three-dimensional optical laser scanning and compared with the laser scans of the intraoral impressions taken post-operatively. RESULTS: The comparison between the post-surgical implant replica positions and the positions in the pre-operative cast, for the five patients, shows a maximum distance in the range 1.02-1.25 mm, an average distance in the range 0.21-0.41 mm and a standard deviation in the range 0.21-0.29 mm. SIGNIFICANCE: The results of this research demonstrate accurate transfer of implant replica position by virtual implant insertion into a pre-operative cast and a post-operative cast obtained from impressioning. In previous studies the evaluation of the implant positions have required a post-surgical CT scan. With the indirect methods by laser scanning technique, proposed in the paper, this extra radiation exposure of the patient can be eliminated.

Cell fate following ER stress: just a matter of "quo ante" recovery or death?

The endoplasmic reticulum (ER) is a complex and multifunctional organelle. It is the intracellular compartment of protein folding, a complex task, both facilitated and monitored by ER folding enzymes and molecular chaperones. The ER is also a stress-sensing organelle. It senses stress caused by disequilibrium between ER load and folding capacity and responds by activating signal transduction pathways, known as unfolded protein response (UPR). Three major classes of transducer are known, inositol-requiring protein-1 (IRE1), activating transcription factor-6 (ATF6), and protein kinase RNA (PKR)-like endoplasmic reticulum kinase (PERK), which sense with their endoluminal domain the state of protein folding, although the exact mechanism(s) involved is not entirely clear. Depending on whether the homeostatic response of the UPR is successful in restoring an equilibrium between ER load and protein folding or not, the two possible outcomes of the UPR so far considered have been life or death. Indeed, recent efforts have been devoted to understand the life/death switch mechanisms. However, recent data suggest that what appears to be a pure binary decision may in fact be more complex, and survival may be achieved at the expenses of luxury cell functions, such as expression of differentiation genes.

3D-finite element analyses of cusp movements in a human upper premolar, restored with adhesive resin-based composites.

The combination of diverse materials and complex geometry makes stress distribution analysis in teeth very complicated. Simulation in a computerized model might enable a study of the simultaneous interaction of the many variables. A 3D solid model of a human maxillary premolar was prepared and exported into a 3D-finite element model (FEM). Additionally, a generic class II MOD cavity preparation and restoration was simulated in the FEM model by a proper choice of the mesh volumes. A validation procedure of the FEM model was executed based on a comparison of theoretical calculations and experimental data. Different rigidities were assigned to the adhesive system and restorative materials. Two different stress conditions were simulated: (a) stresses arising from the polymerization shrinkage and (b) stresses resulting from shrinkage stress in combination with vertical occlusal loading. Three different cases were analyzed: a sound tooth, a tooth with a class II MOD cavity, adhesively restored with a high (25 GPa) and one with a low (12.5GPa) elastic modulus composite. The cusp movements induced by polymerization stress and (over)-functional occlusal loading were evaluated. While cusp displacement was higher for the more rigid composites due to the pre-stressing from polymerization shrinkage, cusp movements turned out to be lower for the more flexible composites in case the restored tooth which was stressed by the occlusal loading. This preliminary study by 3D FEA on adhesively restored teeth with a class II MOD cavity indicated that Young's modulus values of the restorative materials play an essential role in the success of the restoration. Premature failure due to stresses arising from polymerization shrinkage and occlusal loading can be prevented by proper selection and combination of materials.

Debonding of adhesively restored deep Class II MOD restorations after functional loading.

PURPOSE: To assess debonding due to functional loading at the cervical dentin margins of deep Class II MOD restorations prepared with a variety of adhesive restoratives in endodontically-treated teeth. MATERIALS AND METHODS: MOD preparations and endodontic treatment were carried out on extracted sound maxillary premolars. The cavities were restored with seven material combinations: Three different resin-based composites (RBC) (Z100, Herculite XRV or Clearfil RP with their respective bonding systems); two bonded amalgam combinations (Valiant with Superbond D or with Panavia 21) and two sandwich combinations [the RBC Tetric with the polyacid-modified RBC (compomer) Compoglass or Z100 with the resin-modified glass ionomer Fuji II LC]. For each group, half of the samples were exposed to mechanical functional loading and the other half served as control. Imperfect bond formation and debonding due to loading was determined by dye penetration. In addition, the dye penetration scores were correlated with the cusp fracture strengths of similarly prepared restorations of a previous study. RESULTS: After functional loading, the RBC in combination with hybridizing dentin bonding agents showed better preservation of marginal integrity than the sandwich restorations, which in turn performed better than the amalgam restorations (P < 0.05). Debonding correlated with reduction in fracture resistance. Under the conditions of this study, debonding of adhesive MOD restorations by functional loading can best be prevented by using RBC in combination with hybridizing dentin-bonding systems.

Fracture resistance of endodontically-treated premolars adhesively restored.

PURPOSE: To investigate the cusp fracture resistance of endodontically treated teeth, adhesively restored with various materials. MATERIALS AND METHODS: MOD preparations and endodontic treatment was carried out on extracted sound maxillary premolars. The cavities were restored with the amalgam Valiant in combination with Superbond or Panavia bonding, the resin composites Z100, Herculite XRV or Clearfil RP with their respective bonding systems, Z100 in combination with the glass ionomers Ketac Fil, Fuji II and Vitremer, and Tetric in combination with Compoglass. Fracture resistance was measured by axial loading in an Instron testing machine. RESULTS: One of the restorative methods, resin composites in combination with dentin bonding systems in beveled MOD preparations rendered the tooth a cusp fracture resistance which did not differ significantly from that of sound natural teeth. Two other restorative methods, bonded amalgam and a sandwich of glass ionomer cement/resin composite in beveled preparations were significantly weaker in resisting cusp fracture than sound natural teeth, but still significantly stronger than the unrestored tooth with a MOD preparation. It was statistically apparent that several adhesive restorative systems could satisfactorily be used to restore teeth after endodontic therapy.

[Finishing and polishing of an anterior hybrid composite--Herculite XR. SEM evaluation]. / Rifinitura e lucidatura di un composito ibrido per anteriori--HERCULITE XR. Valutazioni al SEM.

A study was a conducted in order to discover finishing and polishing effectiveness, by particular operative method, on HERCULITE XR, sub-micron hybrid composite. The study was realized on 35 incisors extracted for periodontal reasons, treated with "labial veneers" according to Jordan (1987), divided into 7 groups each containing 5, and finished with different technique. After treatment, the teeth were subjected to SEM examination. The results showed that the high speed finishing technique by twelve and thirty fluted carbide burs and final polishing with Command Ultrafine Luster Paste produces the smoothest and flatest surface of HERCULITE XR. Furthermore the HERCULITE XR/enamel margin doesn't appear fractured or disrupted. Since finishing and polishing rotary techniques in accordance with the characteristic of each type of composite resins.