(1) To measure the marginal and internal adaptation of different prosthetic crowns infrastructures (IS); (2) to analyze two types of methodologies (replica and weight technique) used to evaluate the adaptation of indirect restorations.
Ceramic IS were fabricated using CAD/CAM technology and slip-casting technique, and metal IS were produced by casting ( n = 10). For each experimental group, the adaptation was evaluated with the replica (RT) and the weight technique (WT), using an impression material (low viscosity silicon) to simulate the luting agent. Cross-sectional images of the silicon replica were obtained and analyzed with Image J software to measure the low viscosity silicon layer thickness at pre-determined points. The silicon layer was also weighted. Results were statistically analyzed with ANOVA and Tukey’s test ( α = 0.05). Pearson correlation was used to analyze the relation between the two types of evaluation methods.
All IS evaluated showed clinically acceptable internal and marginal adaptation. Metal IS showed the best adaptation, irrespective of the measuring technique (RT and WT). The IS produced by CAD–CAM showed greater gap values at the occlusal area than at other evaluated regions. The IS produced by the dental laboratory technician showed similar gap values at all evaluated regions. There is no correlation between RT and WT ( p > 0.05).
Different levels of adaptation were found for the different experimental groups and for the different evaluation methods. However, all IS evaluated showed clinically acceptable values of marginal and internal adaptation.
The internal and marginal adaptation of ceramic restorations is an important factor for the clinical success and longevity of these restorations. The presence of a marginal gap can lead to dissolution of the luting agent, creating an area for biofilm development that may cause caries and periodontal diseases .
A marginal misfit can be considered acceptable when it is visually imperceptible or cannot be detected using a dental probe. Marginal gap values between 100 and 150 μm are considered clinically acceptable . In addition, the dimension of the internal gap is also important because internal gaps greater than 70 μm can reduce the fracture resistance of dental crowns .
Methods to evaluate the adaptation of prosthetic restorations have used laser videography , profile projector , micro-CT and CAD/CAM scanner . The replica technique (RT), or cement analog technique, has been widely used because of its ability to estimate the internal and marginal gap dimension of prosthetic restorations . This technique is non-destructive and uses an impression material instead of the cement to sit a restoration over the prepared die. After setting, the impression material and restoration are carefully separated from the die and the thickness of the cement layer analog is measured . Another non-destructive method that can be used to evaluate the gap dimension of prosthetic restorations is the “weight technique” (WT). It has lower cost and it is easier to execute than the RT. In the WT the impression material that simulates the cement layer is weighted instead of measuring the thickness in specific points as for the RT. The value obtained with the WT corresponds to the total internal gap thickness between the restoration and the prepared die .
Metal–ceramic restorations are widely studied and used worldwide, with most reported failures related to secondary caries. It is unusual to observe material structural failures . These restorations are considered the gold standard due to its clinical success and longevity. Advances in materials and technology contributed to the introduction of different techniques to produce dental restorations, such as the CAD/CAM system and the slip casting technique. The CAD/CAM systems imply none or minimal influence of the dental laboratory technician . On the contrary and as for the metal–ceramic restorations, the ceramic restorations fabricated by the slip casting technique depend on the ability of the technician .
Besides the claim that the use of pre-fabricated blocks and standardized scanning and milling procedures could minimize the influence of the dental laboratory technician in the production process and result in higher quality restorations , the first restorations produced by the CAD–CAM systems showed poor adaptation . Improvements were made in the CAD–CAM scanner and milling unit aiming to obtain better optical acquisitions and to produce restorations with finer details . However, it is not clear if the restorations produced by the more advanced CAD–CAM systems show comparable adaptation level to the restorations produced by the dental laboratory technician as the literature is usually limited to the comparison among different CAD–CAM systems and only few studies have a control group . In addition, different processing techniques (i.e. metal casting, slip casting, hot-pressing) are used depending on the choice of the restorative material. Thus, it is important to access the adaptation of CAD–CAM and technician-produced restorations to increase the knowledge on the advantages and limitations of each processing technique.
Therefore, this study evaluated the marginal and internal adaptation of prosthetic crown infrastructures (IS) produced by CAD–CAM technology and by the laboratory technician, using two measuring techniques (RT and WT), testing the hypotheses that all IS present clinically acceptable values of marginal and internal adaptation and that there is a positive correlation between the gap values produced by both measuring techniques (RT and WT).
Materials and methods
The materials used in this study are shown in Table 1 . Ten IS were produced for each experimental group.
|Vita In-Ceram YZ a /CAD–CAM||Yttria partially stabilized tetragonal zirconia polycrystal||YTZP|
|Vi In-Ceram Zirconia a /CAD–CAM||Alumina-based zirconia-reinforced glass-infiltrated ceramic||ICZ|
|Wironia ® light b /casting||NiCr metal alloy||MC|
|Vita In-Ceram Zirconia a / slip casting||Alumina-based zirconia-reinforced glass-infiltrated ceramic||SC|