Shape and Surface Design (dental lab technology articles Book 25)

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Embeds 0 No embeds. No notes for slide. Description High quality, efficiency and rationality should not be in contradiction with each other. Manual skills are still essential when it comes to the design and the aesthetic result of a restoration.

Designs created with rotary tools are still an essential part of any restoration fabrication. We will demonstrate how easy it is to use the Noritake Meister Point Set for the fabrication of aesthetic restorations. Keywords: shape, ceramic, morphology, grinding, grinding tool, ceramic facing 4.

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You just clipped your first slide! As a result of the controlled surface activation of the base glass by fine grinding and subsequently heat treating it, leucite crystals are precipitated. This block allows the optical properties of natural teeth to be closely imitated. This type of product is made up of a total of four to eight main and intermediate layers. Due to these highly esthetic properties, this glass-ceramic is mainly used to fabricate anterior crowns as well as inlays and onlays.

The digitally replicated denture technique: A case report

The entire process from the clinical pre-operative situation prepared tooth to the fabrication of the dental restoration with the apparatus Cerec 3 Sirona, Germany and ending with the adhesive cementation of the completed restoration takes about two hours. In order to extend the indication range of glass-ceramics beyond that of the anterior teeth, a glass-ceramic had to be developed that showed significantly higher strength and fracture toughness compared with the leucite type glass-ceramics.

Therefore, a new chemical system, based on a lithium disilicate glass-ceramic was developed to meet this need. Due to the high crystal content and the high degree of interlocking crystals, this glass-ceramic exhibits a strength of MPa and a fracture toughness of 2. This material IPS e. These products are subsequently coated with a fluoroapatite glass-ceramic in order to imitate the optical properties of natural teeth. The reliability of this material was shown by several in vitro and in vivo studies [ 19 , 20 ].

In a heat treatment process, lithium metasilicate was precipitated. The glass-ceramic produced in this way shows preferable machining properties. In its intermediate stage the material has a bluish color but exhibits very low chemical durability. Solid state reactions significantly improve the chemical durability of the material and impart the tooth-like optical properties.

Table 1 shows the main properties of the investigated lithium disilicate glass-ceramic and Figure 3 shows an SEM image of the interlocking microstructure and the high crystal content. Yttrium-stabilized zirconium oxide as polycrystalline sintered ceramic is applied in dentistry specially as crown and bridge frameworks [ 26 , 27 , 28 , 29 ].

Apart from being used to produce crown copings and bridge frameworks, this material is suitable for fabricating posts [ 30 ], abutments [ 31 ] and implants. Yttrium-stabilized zirconium oxide ceramics are characterized by high strength and fracture toughness. The reinforcement mechanism which is based on the stress-induced phase transformation of a tetragonal to a monocline crystal phase has been examined in various research projects [ 32 , 33 , 34 , 35 , 36 ].

Two different processes [ 29 ] are available for fabricating dental restorations using zirconium oxide: a machining of dense ceramics and b machining of presintered ceramics. The first method involves milling densely sintered or even hot isostatic pressed HIP zirconium oxide. This process is very time-consuming and the corresponding machining equipment is a large, heavy multi axis machining apparatus.

The second method is available in which zirconium oxide is milled in a porous state using a small desktop machining apparatus, like Cerec 3 Sirona, Germany. In fact, this way of producing ZrO 2 -based restorations has already become firmly established in dentistry. The porosity, hardness and strength of the material are coordinated to optimize the relationship between the machining time, the wear of the tools and the final properties of the zirconium oxide.

In Table 2 , the properties of these porous ZrO 2 blanks are shown. The processing of these porous blanks Figure 4 has to be very accurate, because the homogeneity of the density and the pore size distribution influences the properties of the final product. In Figure 5 the final microstructure of the zirconia material is demonstrated and the properties of this product are shown in Table 2.

The ZrO 2 framework is subsequently covered with a fluoroapatite glass-ceramic using the build-up or press technique. Image of the presintered product IPS e. Properties of IPS e. In recent years, colored ZrO 2 ceramics have been developed for dental applications. Different procedures of coloring ZrO 2 frameworks are available. One possibility is the infiltration of porous ZrO 2 ceramic with special color solutions.

The dental color is visible after the infiltrated ZrO 2 frameworks have been densely sintered. A different possibility has opened up with the introduction of colored ZrO 2 blocks [ 28 ].

Why Choose SLA 3D Printing?

Restorations can now be fabricated without requiring infiltration. As a result, one working step is eliminated for the dental laboratory. These systems carry out machining processes with diamond tools. It is designed to machine glass-ceramic and ceramic restorations. The system is composed of three different modules, which are required in the fabrication of precision restorations.

With this system the dentist can scan the prepared teeth with an intraoral camera, which transmits the recorded information directly to the computer and transforms it into a digital image Figure 6 a and Figure 6 b. Subsequently, the surface of the model is optically recorded to produce a digital image Figure 6 c. Subsequently, the dentist chair-side or the dental technician lab-side can design the restoration using the CAD software Figure 7.

The data of the virtual model is used to mill a ceramic block to the desired shape with diamond tools. Zirconium oxide-based restorations that are fabricated in the dental laboratory have to be densely sintered to harden them. As the optical properties of zirconium oxide do not correspond to those of natural teeth, a fluoroapatite-based glass-ceramic has to be either built up on or pressed to the substructure. This additional and very time-consuming step can only be carried out by a dental technician in the dental laboratory.

The materials that are used to create a functional, long-lasting and esthetic restoration are dictated by the clinical pre-operative situation. The three types of materials that are commercially available today are discussed in Section 2. Highly esthetic glass-ceramics exhibiting strength values of MPa are mainly used to restore anterior teeth [ 29 ]. Figure 8 shows a clinical case in which leucite glass-ceramics were indicated. The tooth was prepared and the inlay created in one dentist appointment, in other words, chair-side. Due to the low strength of leucite glass-ceramics, the application of these materials is restricted to the fabrication of inlays, onlays and anterior crowns.

Application of a leucite-based glass-ceramic. Dentist: A. Peschke Ivoclar Vivadent AG.

1. Introduction

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The indication range of glass-ceramics has been considerably enlarged with the advent of lithium disilicate glass-ceramics. Figure 9 shows this material being used to create a full-anatomic crown for a posterior tooth. The worn gold crown, which had to be replaced, is shown in Figure 9 a.

The crown was removed and the remaining tooth structure was prepared to receive the new restoration. The dentist used an intraoral camera to capture a digital image of the prepared tooth. On the basis of this image, a virtual model of the final restoration was created with CAD software. Subsequently, the restoration was milled from a lithium metasilicate block. Figure 9 c shows the full-anatomic crown in a partially crystallized state lithium metasilicate during try-in.

Next, the dentist customized the crown with characterization stains and a glaze. The lithium metasilicate material was heat treated to transform it into its final high-strength lithium disilicate state. After the firing process, the restoration exhibited a natural tooth-color and was adhesively cemented.

A Guide to Materials, Equipment, and Clinical Procedures

The result is shown in Figure 9 d. Application of a lithium disilicate-based glass-ceramic. In the posterior region, the use of glass-ceramics is restricted to single-tooth restorations inlays, onlays and crowns , because of the high forces exerted in this part of the mouth. Consequently, long-span bridges in this region are usually fabricated with high-strength and tough oxide ceramics ZrO 2.

Subsequently, glass-ceramics are either built up on or pressed to these oxide ceramic substructures to imitate the optical and tribological properties of the natural dentine. Figure 10 shows a clinical case in which a damaged porcelain fused to metal PFM bridge had to be replaced. The dentist removed the old restoration and prepared the two remaining teeth to receive the new bridge. In this case, tooth 25 and 26 were missing. Because of restricted space, these two teeth were replaced by a single pontic.