**1. Introduction**

20 Will-be-set-by-IN-TECH

262 Reverse Engineering – Recent Advances and Applications

[2] Carslaw, H.S., and Jaeger, J.C. (2000). *Conduction of Heat in Solids*, Oxford University

[3] Comroe, J.H. (1962). *The lung; clinical physiology and pulmonary function tests*, Year Book

[4] Felici, M. and Filoche, M. and Sapoval, B. (2003). Diffusional screening in the human

[5] Felici, M. and Filoche, M. and Sapoval, B. (2004). Renormalized Random Walk Study of

[6] Gheorghiu, S., and Coppens, M.-O. (2004). Optimal bimodal pore networks for

[7] Grebenkov, D. S. and Filoche, M. and Sapoval, B. and Felici, M. (2005). Diffusion-Reaction in Branched Structures: Theory and Application to the Lung Acinus.

[8] Haefeli-Bleuer, B., and Weibel, E.R. (1998). Morphometry of the human pulmonary

[9] Hou, C. (2005). *Scaling laws for oxygen transport across the space-filling system of respiratory membranes in the human lung*, PhD thesis, University of Missouri, Columbia, MO. [10] Hou, C., Gheorghiu, S., Huxley, V.H., and Pfeifer, P. (2010). Reverse Engineering of Oxygen Transport in the Lung: Adaptation to Changing Demands and Resources

through Space-Filling Networks. *PLoS Comput. Biol.*, Vol. 6, No. 8, pp. e1000902. [11] Kjelstrup, S., Coppens, M.-O., Pharoah, J.G., and Pfeifer, P. (2010). Nature-Inspired Energy- and Material-Efficient Design of a Polymer Electrolyte Membrane Fuel Cell.

[12] Mayo, M. (2009). *Hierarchical Model of Gas-Exchange within the Acinar Airways of the*

[13] Mayo, M. Gheorghiu, S., and Pfeifer, P. (2011). *Diffusional Screening in Treelike Spaces: an*

[16] Pfeifer, P., and Sapoval, B. (1995). Optimization of diffusive transport to irregular surfaces with low sticking probability. *Mat. Res. Soc. Symp. Proc.*, Vol. 366, pp. 271. [17] Sapoval, B., Filoche, M., and Weibel, E.R. (2002). Smaller is better–but not too small: A physical scale for the design of the mammalian pulmonary acinus. *Proc. Natl. Acad. Sci.*

[18] Weibel, E.R. (1984). *The Pathway for Oxygen*, Harvard University Press, Cambridge, MA. [19] Weibel, E.R., Taylor, C.R., and Hoppeler, H. (1992). Variations in function and design: Testing symmorphosis in the respiratory system. *PLoS Comp. Biol.*, Vol. 6, No. 8, pp.

[20] Weibel, E.R., Sapoval, B., and Filoche, M. (2005). Design of peripheral airways for

*Human Lung*, PhD thesis, University of Missouri, Columbia, MO.

efficient gas exchange. *Respir. Physiol. Neurobiol.*, Vol. 148, pp. 3.

[14] Mandelbrot, B. (1982). *The Fractal Geometry of Nature*, W.H. Freeman, USA. [15] Needham, T. (2007). *Visual Complex Analysis*, Oxford University Press, USA.

*Exactly Solvable Diffusion-Reaction Model*, *Submitted*.

Oxygen Absorption in the Human Lung. *Phys. Rev. Lett.*, Vol. 92, pp.068101.

Press Inc., New York, NY.

Medical Publishers, Chicago, IL.

*Phys. Rev. Lett.*, Vol. 94, pp. 050602.

acinus *Anat. Rec.*, Vol. 220, pp. 401.

*Energy Fuels*, Vol. 24, pp. 5097.

*USA*, Vol. 99, No. 16, pp. 10411.

e1000902

pulmonary acinus. *J. Appl. Physiol.*, Vol. 94, pp. 2010.

heterogeneous catalysis. *AIChE J.*, Vol. 50, pp. 812.

Complete dentures are used in social healthcare of the seniors. These frequently deteriorate, due to the fragility and structural defects of the materials from which are realized, and also due to the accidents produced because of the patients disabilities. The loss of teeth impairs patients' appearance, mastication ability and speech, thus upsetting the quality of their social and personal life (Mack F., 2005). The selection of materials used in complete dentures technology is crucial, because this directly relates to its performance and life span. Generally, the complete dentures bases are made from acrylic resins – heat curing, light curing, casting, injection, microwaves technologies. Processing technology of these materials sometimes lead to complete dentures with small defects, which can initiate cracks; these are responsible for failure of the complete denture before the expected lifetime. The relative short lifetime of the complete dentures has led researchers to investigate the causes of fracture by studying the stress distribution upon mastication and to find ways to improve their mechanical performance. The finite element method (FEM) has been used for five decades for numerical stress analysis (N. Faur, 2002). The advent of 3D FEM further enables researchers to perform stress analysis on complicated geometries such as complete dentures, and provides a more detailed evaluation of the complete state of stress in their structures.

#### **1.1 The aim of the work**

Due to developing technologies of acrylic resins, the complete dentures have a high degree of porosity (defects). These defects in material structure, together with brittle fracture behavior, can cause failure of the complete denture before the expected lifetime.

The aim of this paper is to perform a numerical analysis which emphasize the high risk of denture degradation due to presence of defects. Numerical analysis was performed by applying finite elements method on a three-dimensional geometric model resulted by 3D scanning of a real denture. The scanned model, as a point cloud, has been processed and converted into a solid geometric model using "reverse engineering" techniques. Through the subject approached, this paper wants to inform about the reverse engineering tehniques and also presents their usefulness by a numerical analysis.

Reverse Engineering and FEM Analysis

**Brand Name Polymer: monomer**

Meliodent

Eclipse Prosthetic Resin System

a triangle, fig. 2.

**ratio** 

Base plate supplied as pre-packed material

Heat Cure 34g:17mL 64713213/64713308 Heat

Table 1. The characteristics of acrylic resins included in this study

**2.2 Geometric modeling of the upper complete denture** 

scanner and scanned with a scanning pitch of 0.1 x 0.1 mm.

Laser

Object

Fig. 2. Principle of laser triangulation sensor

DZ

and converted into a solid geometric model, fig. 5.

for Mechanical Strength Evaluation of Complete Dentures: A Case Study 265

**Batch No.** 

Finite element analysis was performed on geometric models, resulted after the complete dentures' 3D scanning (with 3D laser scanner LPX1200, Roland) and image processing by ,,reverse engineering'', taking into consideration the located defects. A thin layer of green dye (Okklean, Occlusion spray, DFS, Germany) was sprayed on the surface of the denture to increase its contrast for scanning. The denture was positioned on the rotating table of the 3D

Scanning technique used is that of triangulation which is based on using a 3D non-contact active scanner. Non-contact active scanners emit some kind of radiation or light and exploit a camera to look for the location of the laser dot. Depending on how far away the laser strikes a surface, the laser dot appears at different places in the camera's field of view. This technique is called triangulation because the laser dot, the camera and the laser emitter form

The results of scanning process may be a point cloud (fig. 3) or a polygon mesh (fig. 4) having the shape of the scanned object. In a polygonal representation, the registered points are connected by straight edges forming a network of small plane triangular facets. After 3D scanning, the point cloud or polygon mesh are processed by reverse engineering technique

**(polymer/monomer) Description Polymerization** 

polymerized

Lens

Dz

Sensor

<sup>030822</sup>Light –

**procedure** 

7 hrs at 70° C and 1 hr at 100° C

activated Visible blue light

Based on FEM analysis have been investigated the stress distribution and structural integrity of a maxillary complete denture. The study focused on fracture resistance evaluation of dentures, in the presence of structural defects of materials, which initiates denture's cracking or fracture, before the estimated lifetime. Also, was analysed, through defectoscopy method, the porosity degree of dentures depending on the material they are made, and the influence of the defect size and location in denture, on the stress and strain state.
