Recent trends in bone tissue engineering: a review of materials, methods, and structures.

Bone tissue engineering (BTE) provides the treatment possibility for segmental long bone defects that are currently an orthopedic dilemma. This review explains different strategies, from biological, material, and preparation points of view, such as using different stem cells, ceramics, and metals, and their corresponding properties for BTE applications. In addition, factors such as porosity, surface chemistry, hydrophilicity and degradation behavior that affect scaffold success are introduced. Besides, the most widely used production methods that result in porous materials are discussed. Gene delivery and secretome-based therapies are also introduced as a new generation of therapies. This review outlines the positive results and important limitations remaining in the clinical application of novel BTE materials and methods for segmental defects.

Computational modeling of nickel-titanium orthopedic staples in the treatment of a fractured scaphoid: Effects of staple bridge configuration.

Internal fixation devices made of nickel-titanium (NiTi) staples have the advantage of producing compressive stress at the fracture site due to their unique shape memory effect and superelasticity. In the present study, a comparison was made between two commercial NiTi staples of the same size but with different bridge configurations, used for scaphoid fracture fixation. The staple and scaphoid anatomical configurations were modeled using SolidWorks, while ABAQUS software was used to analyze the stress and displacement caused by staples and distributed in the scaphoid waist. In the staple with a straight bridge, the regions under the tips of the staple legs underwent the largest stress, whereas there was negligible stress in the regions closer to the staple bridge. In the staple with an S-shaped bridge, the stress concentration was highly localized in the region close to the staple bridge, with a maximum stress that was over eight times higher than in the staple with a straight bridge. Considering the amount and distribution of stress in both staples, neither of the staples was able to create the ideal healing condition on the fracture surface.

All-trans retinoic acid effectively reduces atheroma plaque size in a rabbit model of high-fat-induced atherosclerosis.

BACKGROUND: Atherosclerosis (AS) is one of the most prevalent causes of death around the world. Since there are different types of risk factors, different types of medications focus on preventing atheromas and plaques from establishing or on preventing established plaques from growing. OBJECTIVES: The aim of this study was to evaluate the effect of all-trans retinoic acid (atRA) on AS in a rabbit model of fat-induced AS. MATERIAL AND METHODS: Atherosclerosis was induced by a high-fat diet (HFD) for 75 days. Thirty rabbits were randomly divided into 5 groups. Group 1 was the negative control group and received a normal diet. The animals in the other groups were fed a HFD. Group 2 (the AS positive control group) received no drugs, Group 3 received atorvastatin orally (20 mg/kg/day), Group 4 received atRA (5 mg/kg/day, orally), and Group 5 received both drugs. All medications were started on day 45 and continued until the end of the study. Fasting blood samples were obtained for lipid profile evaluation. The aorta sections were evaluated for maximum wall and intima thickness. RESULTS: Oral administration of atRA, atorvastatin or their combination significantly improved serum lipid profile (p < 0.001). Atorvastatin and atRA significantly decreased serum total cholesterol and LDL-cholesterol levels in HFD (p < 0.001). No difference was found in serum HDL-cholesterol levels among the studied groups. The HFD group (Group 2 - positive control) showed significant intima irregularities with fat deposition and foamy macrophage accumulation (atheroma). Administration of atRA and atorvastatin significantly decreased the size of atherosclerotic plaques (intima thickness). The maximum vessel wall and intima thickness were significantly decreased after atRA and atorvastatin administration (p < 0.001). No difference was found between atRA and atorvastatin effectiveness, but combination therapy significantly decreased AS size in comparison to using either of the drugs alone (p < 0.001). CONCLUSIONS: In reducing AS plaque size, atRA is as effective as atorvastatin. Additionally, the combination therapy of atRA and atorvastatin decreased AS size much more effectively, showing their synergistic effect. atRA can also improve the serum lipid profile.

Comparative Evaluation of the Effect of Different Post and Core Materials on Stress Distribution in Radicular Dentin by Three-Dimensional Finite Element Analysis.

OBJECTIVES: The aim of this study was to investigate the stress distribution of different post and core materials in radicular dentin by three-dimensional finite element analysis (3D FEA). MATERIALS AND METHODS: Twelve 3D models of a maxillary central incisor were simulated in the ANSYS 5.4 software program. The models were divided into three groups; the first group included: 1-Gold post and core and 2-Nickel-chromium (Ni-Cr) post and core restored with metal-ceramic restorations (MCRs). The second group included: 1-Stainless steel post, 2-Titanium post, 3-Carbon fiber post, 4-Glass fiber post, and 5-Quartz fiber post with composite cores and MCRs. The third group included: 1-Zirconia post and core, 2-Zirconia post, 3-Carbon fiber post, 4-Glass fiber post, and 5-Quartz fiber post; the last four models had composite cores restored with all-ceramic restorations (ACRs). Each specimen was subjected to a compressive load at a 45-degree angle relative to its longitudinal axis at a constant intensity of 100 N. The models were analyzed with regard to the stress distribution in dentin. RESULTS: Two stress concentration sites were detected in the models. The first group showed the lowest stress levels in the cervical region, while the stress levels detected in the second group were higher than those in the first group and lower than those found in the third group. Fiber-reinforced posts induced a higher stress concentration between the middle and cervical thirds of the root compared to other posts. CONCLUSIONS: According to the results, since cast posts induce lower stresses in dentin, they are recommended for clinical use. Fiber-reinforced posts and ACRs caused the maximum stresses in dentin.

Comparative Evaluation of Retentive Properties of Two Compatible Ball Attachments in Mandibular Implant-Retained Overdentures: An In Vitro Study.

OBJECTIVES: The retentive properties of implant-retained overdentures (IRO) may be influenced by the type of attachments. The aim of this research was to compare the retention of two dental implant systems with compatible ball attachments, namely Straumann® system (SS) and Rhein83 SRL system (RS) after fatigue testing. MATERIALS AND METHODS: Two laboratory models consisting of two parallel Straumann® fixtures at a distance of 22 mm were prepared. Five pairs of each systems' ball attachments were examined (n=5). The samples were soaked in artificial saliva. The retention strength values (RSV) were recorded before the fatigue test and after 1100, 2200, 3300, 4400, and 5500 insertion and removal cycles at a speed of 51 mm/minute with a 50-N load cell in a universal testing machine. The data were analyzed by repeated measures analysis of variance (ANOVA) followed by independent sample t-test with Bonferroni corrections. RESULTS: There was a decrease in the RSV in both systems after 5500 cycles of insertion and removal. There was a significant statistical difference between the RSV of the normal Sphero Block of the RS (17.52±0.68 N) and that of the Spare Lamella retention inserts of the SS (19.72±0.74 N, P=0.001). CONCLUSIONS: Although the RSVs of the RS and SS were almost similar before the fatigue test, as the number of insertion and removal cycles increased, the RSV decreased more significantly in the RS compared to the SS.

Comprehensive Treatments for Congenitally Missing Teeth and Generalized Diastema.

Congenitally missing teeth and/or hypodontia is a prevalent dental anomaly. There are different treatment options available for these conditions such as space maintenance, restoring the space by resin-bonded-fixed-partial-dentures (RBFPDs), and dental implants. This study addresses the comprehensive treatments for congenitally missing tooth and diastema using interdisciplinary approaches. One patient was treated with small-diameter-implants and the other one was treated using an intraoral scanner to make digital impression and fabricating RBFPDs with CAD/CAM system. Both patients were completely satisfied.

Full Mouth Reconstruction of a Skeletal Class II Division 1 Patient with Adenoid Cystic Carcinoma Using an Interim Immediate Obturator and a Definitive Obturator.

A 61-year-old female patient with adenoid cystic carcinoma (ACC) of the right maxilla and Angle class II division 1 malocclusion had received a subtotal maxillectomy in right side and used a conventional clasp-retained obturator. After implants placement, a maxillary interim immediate obturator (IIO) and then a definitive obturator using six endosseous implants were fabricated. During one-year follow-up, the patient was completely satisfied. Ideally, after implants placement in edentulous patients suffering from hemimaxillectomy, an implant-supported obturator (ISO) is designed in order to prevent nasal reflux and to improve speech and swallowing. However, in the following case, because of skeletal class II division 1 malocclusion and implants insertion in the premaxilla, using an ISO was impossible because it would cause excessive upper lip protrusion and lack of anterior teeth contact. Therefore, a five-unit implant-supported fixed partial denture (FPD) was fabricated in the maxillary anterior segment so that anterior teeth contacts were possible and the patient's normal lip support was achieved. A bar and three ball attachments were used in the maxillary posterior segment. A closed-hollow-bulb ISO was preferred. Conventional ISO in these patients results in several problems. Using a maxillary anterior FPD along with ISO caused satisfactory results in the current patient.

Using Bar and Ball Attachments in Maxillary and Mandibular Implant-Supported Overdentures in a Patient with Adenoid Cystic Carcinoma Associated with Microstomia: A Clinical Report.

Many clinical studies and literature reviews have suggested that bar and ball attachments in maxillary and mandibular implant-supported overdentures (ISOs) should be indicated only when there is sufficient interocclusal space (IOS; minimum = 30 mm). The aim of this clinical report was to present the prosthetic rehabilitation of a patient with adenoid cystic carcinoma associated with microstomia due to radiotherapy (IOS = 23 mm). ISOs offer superior retention and greater stability than conventional obturators, so that base extensions were kept to the minimum. Placing the balls parallel to the prosthesis path of insertion is much easier with this treatment modality.

Three Dimensional Finite Element Analysis of Distal Abutment Stresses of Removable Partial Dentures with Different Retainer Designs.

OBJECTIVES: This finite element method study aimed to compare the amount of stress on an isolated mandibular second premolar in two conventional reciprocal parallel interface designs of removable partial dentures (RPDs) and the same RPD abutment tooth (not isolated). MATERIALS AND METHODS: A Kennedy Class 1, modification 1 RPD framework was simulated on a 3D model of mandible with three different designs: an isolated tooth with a mesial rest, an isolated tooth with mesial and distal rests and an abutment with a mesial rest (which was not isolated); 26 N occlusal forces were exerted bilaterally on the first molar sites. Stress on the abutment teeth was analyzed using Cosmos Works 2009 Software. RESULTS: In all designs, the abutment tooth stress concentration was located in the buccal alveolar crest. In the first model, the von Mises stress distribution in the contact area of I-bar clasp and cervical portion of the tooth was 19 MPa and the maximum stress was 30 MPa. In the second model, the maximum von Mises stress distribution was 15 MPa in the cervical of the tooth. In the third model, the maximum von Mises stress was located in the cervical of the tooth and the distal proximal plate. CONCLUSION: We recommend using both mesial and distal rests on the distal abutment teeth of distal extension RPDs. The abutment of an extension base RPD, which is not isolated in presence of its neighboring more anterior tooth, may have a better biomechanical prognosis.

Effect of Abutment Height on Retention of Single Cement-retained, Wide- and Narrow-platform Implant-supported Restorations.

BACKGROUND AND AIMS: In contrast to prepared natural dentin abutments,little is known concerning factors influencing the retention of fixed prostheses cemented to implant abutments. The aim of this study was to investigate the effect of im-plant abutment height on the retention of single castings cemented to wide and narrow platform implant abutments. MATERIALS AND METHODS: Thirty-six parallel-sided abutments (Biohorizon Straight Abutment) of narrow platform (NP) and wide platform (WP) sizes with their analogs were used. In each group of platform size, abutments were prepared with axial wall heights of 5, 4, 3, 2 mm (n=9). On the whole 72 castings were constructed, which incorporated an attachment to allow removal. Castings were cemented to abutments with TempBond®. A uniaxial tensile force was applied to the crown using an Instron machine until cement failure occurred. Analysis of variance of the models were fit to determine the effect of height of abutment of the restorations on the mean tensile strength (α=0.05). RESULTS: The mean peak removal force for corresponding abutments was significantly different (P < 0.05): (1) with plat-form sizes: WP > NP; (2) with alteration of axial wall height for NP: 5 mm > 4 mm > 3 mm = 2 mm and for WP: 5 mm > 4 mm = 3 mm = 2 mm. CONCLUSION: The retention of NP cement-retained restorations is influenced by the wall height but not in same manner as WP. Restorations of narrow-platform size with longer abutment exhibited higher tensile resistance to dislodgement.

The effect of recasting on bond strength between porcelain and base-metal alloys.

PURPOSE: Long-term success of metal ceramic restorations depends on metal ceramic bond strength. The purpose of this study was to determine whether recasting of base-metal alloys has any effect on metal ceramic bond strength. MATERIALS AND METHODS: Super Cast and Verabond base-metal alloys were used to cast 260 wax patterns. The alloy specimens were equally divided into five groups and cast as: group A 0.0%, B 25%, C 50%, D 75%, and E 100% once-cast alloy. Each group was divided into two subgroups: the first group was cast with Super Cast and the second with Verabond. In each subgroup half of the cast alloys were veneered with Vita VMK 68 and the others with Ceramco 3. RESULTS: Recasting decreased bond strength (p < 0.006) when used for 50% once-cast alloy. Group E with 100% new Super Cast alloy veneered with Vita VMK 68 porcelain had the highest bond strength (30.75 ± 9.58 MPa), and group B including 25% new and 75% recast Super Cast alloy veneered with the same porcelain had the lowest bond strength (21.72 ± 5.19 MPa). CONCLUSIONS: By adding over 50% once-cast alloy in base-metal alloys, metal-ceramic bond strength decreases significantly.