Marginal fit of endocrowns fabricated by three-dimensional printing and the conventional method: An in vitro study

Background

Marginal fit is a key factor in success of prosthetic restorations. This study aimed to assess and compare the marginal fit of endocrowns fabricated by three-dimensional (3D) printing and the conventional method.

Materials and Methods

This in vitro, experimental study evaluated 20 endocrowns, of which 10 were fabricated by 3D printing and 10 were fabricated by the conventional wax-up technique. The marginal gap was measured at 8 points under a stereomicroscope. The results were analyzed using the Shapiro-Wilk test, paired t-test, independent t-test, and one-way analysis of variance (α = 0.05).

Results

The mean marginal gap was maximum at the distal point, and minimum at the buccal point for the conventionally fabricated endocrowns with an overall mean marginal gap of 99.67 ± 4.59 μm. The mean marginal gap was maximum at the mesiobuccal and minimum at the buccal point before pressing (overall mean of 103.92 ± 2.19 μm) before pressing, and maximum at the distobuccal and minimum at the mesiobuccal point after pressing (overall mean of 117.67 ± 2.87 μm). According to paired t-test, the mean marginal gap of endocrowns fabricated by 3D printing significantly increased after pressing at all 8 points and also in general, compared with before pressing (P < 0.001). Furthermore, the mean marginal gap at all points was significantly greater in endocrowns fabricated by 3D printing compared with those fabricated by the conventional method (independent t-test, P < 0.001).

Conclusion

Within the limitations of this in vitro study, the results showed that endocrowns fabricated by the conventional method had significantly superior marginal fit than those fabricated by 3D printing.

Finite element analysis and experimental evaluation on stress distribution and sensitivity of dental implants to assess optimum length and thread pitch

BACKGROUND AND OBJECTIVE

The dental implant is one of the long term proper remedies to recover a missed tooth as a different prosthetic rehabilitation way. The finite element (FE) method and photoelasticity test are employed to achieve stress distribution and sensitivity in dental implants in order to obtain optimum length and thread pitch.

METHODS

The finite element method and experimental test are developed to evaluate stress distribution and sensitivity around dental implants. Three dimensional FE models of implant-abutment, cortical bone and cancellous bone are created by considering a variation of 0.6 to -1 mm on threads pitch while the implant lengths range from 8.5 mm to 13 mm. Then, axial and oblique forces are applied to the models to obtain the resultant stress contours.

RESULTS

The results indicate that the resultant von Mises stresses in the implant-abutment, cortical bones, and cancellous bones are different. The optimized setting for length and pitch is suggested according to maximum von Mises stress and sensitivity analysis.

CONCLUSIONS

It is concluded that the present FE model accurately predicts stress distribution pattern in dental implants. The results indicate that sensitivity of length play a more significant role in comparison with thread pitch. The accuracy of FEM results in comparison with those of the photoelasticity test recommends applying computation methods in medical practice as great potential in terms of future studies.