An application of finite element method in material selection for dental implant crowns

Materials used for dental crowns show a wide range of variety, and a dentist's choice can depend on several factors such as patient desires, esthetics, tooth factors, etc. One of the most important issues for implant surgery is the primary stability and it should be provided to minimize the risks of screw loosening, failed osseointegration, or nonunion. The current study aims to present the Finite Element Analysis (FEA)-based material selection strategy for a dental crown in terms of reducing the aforementioned risks of dental implants. A virtual surgery mandible model obtained using MIMICS software was transferred to the ANSYS and material candidates determined using CES software were compared using FEA. The results indicated that Zr0₂+Y₂O₃ (zirconia) has shown a 12.79% worse performance compared to Au83-88/Pt4-12/Pd4.5-6 alloy in terms of abutment loosening. On the other hand, zirconia is the most promising material for dental crowns in terms of the stability of the bone-implant complex. Therefore, it may show the best overall performance for clinical use. Moreover, as suggested in this study, a better outcome and more accurate predictions can be achieved using a patient-specific FEA approach for the material selection process.

Restoration's thickness and bonding tooth substrate are determining factors in minimally invasive adhesive dentistry

Purpose To explore fracture strength and failure behaviour of minimally invasive CAD-CAM composite resin overlay restorations.Methods Eighty bi- and tri-layer cylindrical overlay model including the restoration bonded over bovine tooth dentin (Groups D) and enamel-dentin (Groups E) were assembled (diameter 9 mm). Restorations were milled from CAD-CAM composite resin blocks (Brilliant Crios, Coltène/Whaledent AG) in different thicknesses (0.5mm, 1mm, 1.5mm, 2mm) and equally distributed in four Groups D and four Groups E (n=10). All specimens were submitted to an Hertzian load-to-failure contact test with spherical indenter. Critical loads were recorded in Newton and data were analysed using Kruskal-Wallis test for multiple and Mann-Whitney test for 2-samples comparisons (p < 0.05). Fragments were examined using SEM. The stress distribution for specimens with restorations of 0.5 mm and 2 mm was also investigated with FEA.Results For all specimens, the mean static loads in Newton increased with an increase in restoration thickness. On contrary, restorations with the same thickness displayed higher resistance values when bonded over enamel than dentin, except for the 2-mm thick restorations. A damage competition was detected between cone/median cracks originating at the loading contact area of the restorations and radial cracks beginning at their inner surface, with the former prevailing in restorations bonded on enamel and the latter being dominant for restorations bonded on dentin.Conclusions For bonded ultra-thin resin composite restorations (0.5 mm to 1.5 mm) enamel as bonding substrate assures higher critical loads to fracture than dentin. This influence gradually decreases as restoration thickened.

Enhancing the Mechanical Properties of Glass-Ionomer Dental Cements: A Review

This paper reviews the strategies that have been reported in the literature to attempt to reinforce glass-ionomer dental cements, both conventional and resin-modified. These cements are widely used in current clinical practice, but their use is limited to regions where loading is not high. Reinforcement might extend these applications, particularly to the posterior dentition. A variety of strategies have been identified, including the use of fibres, nanoparticles, and larger particle additives. One problem revealed by the literature survey is the limited extent to which researchers have used International Standard test methods. This makes comparison of results very difficult. However, it does seem possible to draw conclusions from this substantial body of work and these are (1) that powders with conventional particle sizes do not reinforce glass-ionomer cements, (2) certain fibres and certain nanoparticles give distinct improvements in strength, and (3) in the case of the nanoparticles these improvements are associated with differences in the morphology of the cement matrix, in particular, a reduction in the porosity. Despite these improvements, none of the developments has yet been translated into clinical use.

Oriented and Ordered Biomimetic Remineralization of the Surface of Demineralized Dental Enamel Using HAP@ACP Nanoparticles Guided by Glycine

Achieving oriented and ordered remineralization on the surface of demineralized dental enamel, thereby restoring the satisfactory mechanical properties approaching those of sound enamel, is still a challenge for dentists. To mimic the natural biomineralization approach for enamel remineralization, the biological process of enamel development proteins, such as amelogenin, was simulated in this study. In this work, carboxymethyl chitosan (CMC) conjugated with alendronate (ALN) was applied to stabilize amorphous calcium phosphate (ACP) to form CMC/ACP nanoparticles. Sodium hypochlorite (NaClO) functioned as the protease which decompose amelogenin in vivo to degrade the CMC-ALN matrix and generate HAP@ACP core-shell nanoparticles. Finally, when guided by 10 mM glycine (Gly), HAP@ACP nanoparticles can arrange orderly and subsequently transform from an amorphous phase to well-ordered rod-like apatite crystals to achieve oriented and ordered biomimetic remineralization on acid-etched enamel surfaces. This biomimetic remineralization process is achieved through the oriented attachment (OA) of nanoparticles based on non-classical crystallization theory. These results indicate that finding and developing analogues of natural proteins such as amelogenin involved in the biomineralization by natural macromolecular polymers and imitating the process of biomineralization would be an effective strategy for enamel remineralization. Furthermore, this method represents a promising method for the management of early caries in minimal invasive dentistry (MID).

On the importance of aging to the crack growth resistance of human enamel

With improvements in oral health and an overall increase in quality of life, the percentage of fully or largely dentate seniors is increasing. Understanding the effects of aging on the mechanical properties of teeth is essential to the maintenance of lifelong oral health. In this investigation the effects of aging on the fracture toughness of human enamel were evaluated from incremental crack growth experiments performed on tissue of donor teeth representing "young" (17 ⩽ age ⩽ 25) and "old" (age ⩾ 55) age groups. Results showed that the old enamel exhibited significantly lower resistance to fracture than that of the young tissue in two orthogonal directions of crack growth. For crack growth transverse to the enamel rods, the fracture toughness of the old enamel (0.37 ± 0.15 MPa m(0.5)) was nearly 70% lower than that of tissue from the young teeth (1.23 ± 0.20 MPa m(0.5)). Based on results from a mechanistic analysis of crack growth, the reduction in fracture resistance is attributed to a decrease in the degree of extrinsic toughening. The practice of restorative dentistry should account for these changes in tooth tissues in the treatment of senior patients.

STATEMENT OF SIGNIFICANCE

The mechanical behavior of enamel has been studied for over 3 decades. Due to the limited volume of tissue available for evaluation, past work has been largely based on indentation methods. In this investigation we have evaluated the resistance to fracture of human enamel using a conventional fracture mechanics approach and incremental crack growth. We compared the fracture resistance of cuspal enamel obtained from the teeth of representative "young" and "old" donor groups. Our results show that there is a substantial reduction in the resistance to fracture with age, that it is anisotropic, and that the degradation is more severe than that which occurs to dentin. As such, we feel this work is a significant contribution to the field.

Neonatal line on fetus and infant teeth: An indicator of live birth and mode of delivery

BACKGROUND

The neonatal line (NL) is an important issue in forensic odontology. It is the sign of a developmental birth defect, which is caused by the effect of metabolic stress on tooth structures when the fetus passes to extrauterine life.

AIMS

The aim of this research is to determine the existence and thickness of NL in teeth, as it is a legal necessity to indicate the signs of viability at birth in a forensic examination of a fetus or infant case.

STUDY DESIGN AND SUBJECTS

This research was conducted on 48 lower left and right lateral teeth, which were taken from 24 autopsy cases (46% female and 54% male). Left lateral teeth were sectioned in a vertical plane and right lateral teeth were sectioned in a horizontal plane. The NL thickness was measured with a scanning electron microscope (SEM). These cases comprised three conditions as: 70.3% normal birth, 16.7% caesarean sections, and 12.5% still birth cases under the legal and ethical permission.

OUTCOME MEASURES

The mean NL thickness of normal birth cases was higher than caesarean cases as 7.7μm and 2.5μm, respectively.

RESULTS AND CONCLUSIONS

The results showed a statistical significance between all birth conditions. NL does not exist in still birth cases (p<0.001). Not only is the presence of NL a sign of live birth, but also its thickness is an indicator of the delivery mode where NL thickness of normal birth was found thicker than the caesarean cases.