Journal of Dental Biomaterials
Volume:2 Issue: 3, 2015

This article aims to review various modes of fracture toughness of resin composites. Also, this study intends to review the papers on the fracture mode, namely “fractography”, under scanning electron microscopy finding fracture initiation site, and the effect of filler content on the fracture toughness of resin composites. It will also review the effect of aging on the fracture toughness of resin composites in different media, mainly distilled water, and acidic environment. In the review performed on fracture toughness of resin composites we used “fracture toughness (KIc)”, aging AND fracture toughness, AND fractography” of resin composites as the search strategy. The outcome of the review revealed that most of the studies investigated fracture toughness of resin composites under Mode I and less under mode II. However, some others looked at the fracture toughness of dental resin composites under mixed-mode loading conditions. It was also found that fracture toughness studies performed on the same types of resin composites resulted in different values of KIc. The differences were related to the method of performance that requires different specimen geometries.

Statement of Problem: Placement of mini-dental implants when single-tooth restorations are needed and the space is not sufficient to insert a standard diameter implant is indicated. There are many different mini-implant brands with various materials and surface characteristics; however, there are just few studies comparing them with each other. In this study, finite element analysis (FEA) was applied to evaluate stress distribution in two different types of bone (D2, D3) around three different mini-implant systems (Dio, Dentis, and Osteocare). Three different mini- implant systems consisting of Dentis (Dentis Co., Ltd., Dalseo-gu, Daegu, Korea), Dio (DIO Medical Co., Jungwon-gu Seongnam-si, Kyunggi-do, S.Korea) and Osteocare (OsteoCare™, Slough, Berkshire, UK) were evaluated using FEA. At the same time, a vertical loading of 100N and a lateral loading of 30N at an angle of 45° were applied on the coronal part of the abutment in 2 different bone qualities: D2 bone quality, a thick layer (2 mm) of the compact bone surrounding a core of dense trabecular bone; and D3 bone quality, a thin layer (1 mm) of the cortical bone surrounding a core of dense trabecular bone of favorable strength. Stress levels in the bone surrounding mini-implants were analyzed using Ansys software (Ver.14), which provides the ability to simulate every structural aspect of a product. Descriptive statistics were used to compare the results. After applying the loads and performing FEA, it was observed that in all three types of mini-implants for both static and dynamic analyses, the Von Mises stress values in D3 bone were more than those in D2 bone. The stresses in the cortical bone were obtained more than cancellous bone stresses. In all the studied systems, stress remained in the physiologic limits of the bone. In the cortical bone, stress distribution pattern in the three kinds of mini-implant was similar. Crestal bone stress, according to the amount of force applied, remained in acceptable levels.

Statement of Problem: Calcium hydroxide which is commonly used as an intracanal medicament, changes the pH of dentin and periradicular tissues to an alkaline pH. In some clinical situations, endodontic reparative cements like calcium enriched mixture cement are used after calcium hydroxide therapy. However, the alkaline pH may affect the physical properties of this cement.

This study was designed to evaluate the effect of alkaline pH on the push-out bond strength of calcium enriched mixture.

80 root slices were prepared from single-rooted human teeth and their lumens were instrumented to achieve a diameter of 1.3mm. Calcium enriched mixture (CEM) was mixed according to the manufacturer’s instruction and introduced into the lumens of root slices. The specimens were then randomly divided into 4 groups (n = 20) and wrapped in pieces of gauze soaked in synthetic tissue fluid (STF) buffered in potassium hydroxide at pH values of 7.4, 8.4, 9.4, or 10.4. The samples were incubated for 4 days at 37°C. The push-out bond strengths were then measured using a universal testing machine. Failure modes were examined under a light microscope at ×20 magnification. The data were analyzed using one-way analysis of variance and Tukey’s post hoc tests.

The greatest (1.41 ± 0.193 MPa) and lowest (0.8 ± 0.06 MPa) mean push-out bond strengths were observed after exposure to pH values of 7.4 and 8.4, respectively. There were significant differences between the neutral group and the groups with pH of 8.4 (p = 0.008) and 10.4 (p = 0.022). The bond failure was predominantly of cohesive type for all experimental groups.

Under the condition of this study, alkaline pH adversely affected the Push-out bond strength of CEM cement.

Statement of Problem: Recent literatures show that accelerated Portland cement (APC) and calcium hydroxide Ca (OH)2 may have the potential to promote the bone regeneration. However, certain clinical studies reveal consistency of Ca (OH)2, as one of the practical drawbacks of the material when used alone. To overcome such inconvenience, the combination of the Ca (OH)2 with a bone replacement material could offer a convenient solution. To evaluate the soft tissue healing and bone regeneration in the periodontal intrabony osseous defects using accelerated Portland cement (APC) in combination with calcium hydroxide Ca (OH)2, as a filling material. Five healthy adult mongrel dogs aged 2-3 years old (approximately 20 kg in weight) with intact dentition and healthy periodontium were selected for this study. Two one-wall defects in both mesial and distal aspects of the 3rd premolars of both sides of the mandible were created. Therefore, four defects were prepared in each dog. Three defects in each dog were randomly filled with one of the following materials: APC alone, APC mixed with Ca (OH)2, and Ca (OH)2 alone. The fourth defect was left empty (control). Upon clinical examination of the sutured sites, the amount of dehiscence from the adjacent tooth was measured after two and eight weeks, using a periodontal probe mesiodistally. For histometric analysis, the degree of new bone formation was estimated at the end of the eighth postoperative week, by a differential point-counting method. The percentage of the defect volume occupied by new osteoid or trabecular bone was recorded. Measurement of wound dehiscence during the second week revealed that all five APCs had an exposure of 1-2 mm and at the end of the study all samples showed 3-4 mm exposure across the surface of the graft material, whereas the Ca (OH)2, control, and APC + Ca (OH)2 groups did not show any exposure at the end of the eighth week of the study. The most amount of bone formation was observed in APC group which was significantly different with all other groups (p < 0.05). Despite acceptable soft tissue response of Ca (OH)2, this additive material could not be suggested because of negative effects on bone formation results.

Statement of Problem: Thermal injury during dental implant placement and restoration is a clinical concern as it may cause bone damage and compromise osseointegration. The threshold level for heat-induced cortical bone necrosis is 47°C for 60 seconds. To measure the amount of heat transferred to the implant-bone interface when a two-piece or one-piece abutment was prepared in vertical and horizontal direction using various time intervals. Three groups of samples (n = 24), one-piece and two-piece implant and natural teeth, were used in this study to compare the amount of heat transferred to the implant-bone interface. This study used cooling system in the 10, 20, 30, and 60 seconds time intervals. The Thermocouples (K type) were attached to each sample at the crestal, middle and apical points. To have a similar condition with the oral cavity, each implant was embedded separately in transparent acrylic resin in a 37°C water bath. To have a constant cutting pressure, the turbine was fixed on the stable stand and a 100 g counterweight hanged to it. Then, the bath was fixed in front of it and cutting started at vertical and horizontal directions for 10, 20, 30, 60 seconds. The maximum decrease from 37°C was observed in two-piece implant at the apical point (3.95°C) after 60 seconds and the minimum decrease was seen in one-piece implant at the crestal point (0.6°C) after 60 seconds. Also the minimum increase was observed in the natural teeth at the apical point (0.15°C) at 10 seconds and the maximum temperature increase was seen in one-piece implant at the apical point (1.95°C) at 20 seconds. Within the limitation of this study, it was concluded that to reduce the thermal damage on the bone tissue, an intermittent cut up to 20 seconds is acceptable. Cutting one-piece implant caused more heat transfer than that of two-piece implant.

Statement of Problem: There are limited histomorphometric studies on biologic efficacy of high density tetrafluoroethylen (d-PTFE) membrane. To investigate the healing of surgically induced grade II furcation defects in dogs following the use of dense polytetrafluoroethylene as the barrier membrane and to compare the results with the contra lateral control teeth without the application of any membrane. Mandibular and maxillary 3rd premolar teeth of 18 young adult male mongrel dogs were used for the experiment. The furcation defects were created during the surgery. 5 weeks later, regenerative surgery was performed. The third premolar teeth were assigned randomly to control and test groups. In the test group, after a full thickness flap reflection, the d-PTFE membrane was placed over furcation defects. In the control group, no membrane was placed over the defect. 37 tissue blocks containing the teeth and surrounding hard and soft tissues were obtained three months post-regenerative surgery. The specimens were demineralized, serially sectioned, mounted and stained with Hematoxylin and Eosin staining technique. From each tissue block, 35-45 sections of 10 µm thickness within 60µm interval captured the entire surgically created defect. The histological images were transferred to computer and then the linear measurement ranges of the defects area, interadicular alveolar bone, epithelial attachment and coronal extension of the new cementum were done. Then, the volume and area of afore-mentioned parameters were calculated considering the thickness and interval of the sections. To compare the parameters between the control and test teeth, we calculated the amount of each one proportionally to the original amount of defects. The mean interradicular root surface areas of original defects covered with new cementum was 74.46% and 29.59% for the membrane and control defects, respectively (p < 0.0001). Corresponding values for epithelial attachment were 16.03% and 48.93% for the membrane and control defects, respectively (p < 0.005). The mean volume of the new bone formed in the inter-radicular defects was 61.80% and 35.93% for the membrane and control defects, respectively (p < 0.02). The present study provided a biological rationale for high density polytetrafluoroethylen (d-PTFE, n-PTFE) as a barrier membrane for enhancement of the bone and cementum regeneration in grade II furcation defects subjected to regeneration therapy.