Effect Of Preparation Design Research Articles

Effect of the crown design and interface lute parameters on the stress-state of a machined crown–tooth system: A finite element analysis

The effect of preparation design and the physical properties of the interface lute on the restored machined ceramic crown–tooth complex are poorly understood. The aim of this work was to determine, by means of three-dimensional finite element analysis (3D FEA) the effect of the tooth preparation design and the elastic modulus of the cement on the stress state of the cemented machined ceramic crown–tooth complex.The three-dimensional structure of human premolar teeth, restored with adhesively cemented machined ceramic crowns, was digitized with a micro-CT scanner. An accurate, high resolution, digital replica model of a restored tooth was created. Two preparation designs, with different occlusal morphologies, were modeled with cements of 3 different elastic moduli. Interactive medical image processing software (mimics and professional CAD modeling software) was used to create sophisticated digital models that included the supporting structures; periodontal ligament and alveolar bone. The generated models were imported into an FEA software program (hypermesh version 10.0, Altair Engineering Inc.) with all degrees of freedom constrained at the outer surface of the supporting cortical bone of the crown–tooth complex. Five different elastic moduli values were given to the adhesive cement interface 1.8GPa, 4GPa, 8GPa, 18.3GPa and 40GPa; the four lower values are representative of currently used cementing lutes and 40GPa is set as an extreme high value. The stress distribution under simulated applied loads was determined. The preparation design demonstrated an effect on the stress state of the restored tooth system. The cement elastic modulus affected the stress state in the cement and dentin structures but not in the crown, the pulp, the periodontal ligament or the cancellous and cortical bone. The results of this study suggest that both the choice of the preparation design and the cement elastic modulus can affect the stress state within the restored crown–tooth complex.

Finite Element Stress Analysis of Cast Metal Inlays Restored Posterior Teeth

ABSTRACTCast metal inlays have overall characteristics unavailable in any other restorative procedure, including low restoration wear, low wear of opposing teeth, lack of breakage, burnishability, malleability, and proven long term service. They replace missing teeth structures, without doing anything to reinforce the remaining structures. Stress concentrations can manifest themselves in various forms of failures. The aim of the study was to investigate the effect of preparation design on stress distribution in molars with different class II preparations and restored with cast metal inlays.3D models of premolars and molars were created: intact teeth, unrestored teeth with class II preparations with different tapers (between 0 and 10 degree); the same teeth restored with metalic inlays. The geometries of the intact teeth were obtained by 3D scanning using a manufactured device. With Rhinoceros modeling program the preparations and the appropriately inlays were designed. These were exported in Ansys finite element analysis software for structural simulations. Stresses were registred around the occlusal contact areas. For the studied cases, the stress values were not significant influenced by the taper of the preparation. In the teeth restored with cast metal inlays, the von Mises equivalent stress values were similar to those in the intact tooth.From biomechanical point of view, it was demonstrated that class II cast metal inlays on posterior teeth restore the original strength of the teeth. Taking into account the other characteristics of these restorations, they remain the standard of care for long-term rehabilitations. A taper between 0 and 10 degree of the preparation is not decisive for the stress values.

Achievable Convergence Angle and the Effect of Preparation Design on the Clinical Outcome of Full Veneer Crowns in Dogs

It is widely accepted that the convergence angle of a full veneer crown preparation should be as close to parallel as possible to attain adequate retention/resistance. The shape of the dog's canine tooth limits the veterinary dentists' ability to achieve the recommended convergence angle. However, the clinically achievable convergence angle of the canine tooth in dogs has not been evaluated. In addition, the convergence angle and other physical properties of a preparation, such as height and base diameter, have been shown to affect the retention/resistance of full veneer crowns, in vitro. This effect has not been evaluated clinically in the dog. Physical properties of 32 stone dies from full veneer crowns of canine teeth were studied to evaluate the clinically achievable convergence angle and the potential effect physical properties of the preparation had on the clinical outcome of the restoration. The clinically achievable convergence angle was much higher than the current recommendation. There was an association, albeit not statistically significant, between physical properties of a preparation (convergence angle, height, base diameter) and the clinical outcome of the restoration.

The effect of preparation designs on the marginal and internal gaps in Cerec3 partial ceramic crowns

Objectives The purpose of this study was to evaluate the marginal and internal gaps in Cerec3 partial ceramic crowns (PCCs) of three different preparation designs in vitro using microcomputed tomography (μCT). Methods Cerec3 PCCs of three different preparation designs ( n = 20) were fabricated according to the following: Group I-conventional functional cusp capping/shoulder preparation, Group II-horizontal reduction of cusps and Group III-complete reduction of cusps/shoulder preparation. After fixation of PCCs, the μCT scanning was performed. For obtaining the average internal gap (AIG), the μCT sections were reconstructed 3-dimensionally, and then the total volume of the internal gap was divided by the contact surface area. The 2-dimensional (2D) μCT views were used to investigate the gaps at predetermined key positions in seven bucco-lingual sections and three mesio-distal cross sections. The gaps were measured using the μCT at each reference point. Statistical analysis was performed using one-way ANOVA and Tukey's test. Results For the 3D reconstruction technique, the AIGs were as followed: Group I 197.3 ± 48.2 μm, Group II 171.2 ± 45.1 μm, and Group III 152.7 ± 27.1 μm. For the 2D μCT views, the gaps of each group were the smallest on the margins ranging from 35.4 ± 32.2 to 128.4 ± 69.5 μm, and the largest on the horizontal or angle walls ranging from 184.5 ± 41.2 to 406.5 ± 176.1 μm. According to the results, Group I showed larger marginal and internal gaps compared with the other groups. Conclusions For the PCCs, the simplified designs (Groups II and III) demonstrated superior results compared to the traditional cusp capping design (Group I). The marginal gaps were smaller than the internal gaps in all groups.

Effect of Preparation Design on Marginal Gap of Metal-Ceramic Restorations

Effect of Preparation Design on Marginal Gap of Metal-Ceramic Restorations

Effect of Preparation Design on the Fracture Resistance of Zirconia Crown Copings

The aim of this in vitro study was to evaluate the effects of different preparation designs on the fracture resistance of single-crown zirconia frameworks. To this end, maxillary molar dies of CrCo alloy were fabricated with five different preparation designs: shoulderless, slight and pronounced deep chamfer, beveled and non-beveled shoulder. Ten zirconia copings with a wall thickness of 0.4 mm were fabricated for each type of preparation. After cementation by glass ionomer cement, they were loaded until fracture. There were significant differences in the breaking load of the experimental groups (ANOVA, p < 0.01). The shoulder preparation had a mean breaking load of 2286 N, the shoulderless preparation 2041 N, the beveled shoulder 1722 N, the pronounced deep chamfer 1752 N, and the slight chamfer 1624 N. Based on the results of this study, a shoulder preparation is highly recommended whenever possible. Moreover, for endodontically treated teeth that are structurally compromised or which have anatomically limited areas, the slight chamfer preparation is an optimal recommendation.