Elsevier

Journal of Dentistry

Volume 38, Issue 1, January 2010, Pages 16-22
Journal of Dentistry

A preliminary evaluation of the structural integrity and fracture mode of minimally prepared resin bonded CAD/CAM crowns

https://doi.org/10.1016/j.jdent.2009.07.003Get rights and content

Abstract

Purpose

This study was a preliminary evaluation of two minimal preparation designs proposed for ceramic and composite resin bonded CAD/CAM crowns. It compared the structural integrity and fracture mode of teeth restored with traditionally and minimally prepared resin bonded CAD/CAM crowns fabricated from the same material hypothesizing that teeth restored with minimal resin bonded crowns would demonstrate the same fracture strength to teeth restored with traditional resin bonded crowns.

Materials and methods

Forty intact maxillary molar teeth were used and divided in four groups. Two groups were prepared according to a traditional crown preparation design and two groups were prepared according to minimal preparation designs. A resin composite (Paradigm MZ100, 3M ESPE) and a leucite glass–ceramic (ProCAD, Ivoclar Vivadent) were used for the fabrication of the crowns using CEREC Scan. Crowns of ceramic were cemented using Variolink II (Ivoclar Vivadent) and crowns of composite with Rely X Unicem Aplicap™ (3M ESPE) and loaded until fracture. Load data was analysed using ANOVA comparing crowns of the same restorative material. The mode of fracture was also recorded and analysed (Kruskal–Wallis).

Results

For the composite system the mean fracture load and SD was 1682 N (±315) for the traditional and 1751 N (±338) for the minimal crowns. For the ceramic system the mean fracture load and SD was 1512 N (±373) for the traditional and 1837 (±356) for the minimal crowns. No statistically significant difference was found between the two designs for each system. Nonparametric analysis (Kruskal–Wallis) of the fracture mode showed no statistical significant difference between designs for either material (p > .05).

Conclusion

Within the limitations of this experimental design, it was found that minimally prepared resin bonded CEREC crowns demonstrated equal fracture resistance and mode of fracture to that of crowns bonded to traditionally prepared teeth.

Introduction

The continuous evolution in the dental materials industry with the introduction of new adhesive materials and techniques, and the scientific developments in cariology, have changed the way that dental diseases are treated and have led to the development of minimal invasive/ultraconservative dentistry.1 Minimally invasive approaches were first applied for the treatment of direct restorations. However, lately these principles are beginning to be applied to indirect restorations as well.2 The preservation of tooth tissue is very important, especially for cases where gross amount of tooth substance have already been lost for various reasons (e.g. tooth wear, trauma, etc.) or simply when the gross removal of tooth tissue cannot be justified for the replacing of the missing anatomy (i.e. hypoplastic defects).2, 3 Further to that an increasing demand from patients for aesthetic restorations and some wariness of amalgam hazards and mercury poisoning, have also increased the use of aesthetic restorations.4

All-ceramic restorations are some of the most aesthetically pleasing restorations. Due to the lack of metal core which blocks light transmission all-ceramic restorations can resemble natural tooth structure in terms of colour and light translucency better than any other restorative option. In that way restorations can be more easily “integrated” with tooth structure, since the bonding mechanism can establish optical continuity from tooth structure to restoration.5, 6, 7 In addition metal-free polymer crowns have been introduced as an alternative and inexpensive option offering restorations with high functional and aesthetic ratings.8, 9 The introduction of new ceramic and resin composite materials has improved some of the properties of both materials offering a new dimension to the application of aesthetic indirect restorations.2, 3, 10, 11, 12, 13, 14, 15

Another possible advantage of these restorations is the potential for a more conservative preparation due to the lack of a metal substructure.5 The use of materials that can be adhesively bonded to the tooth can make possible the application of even more minimal intervention procedures. Many in vitro and in vivo studies exist in the literature evaluating the fracture strength and clinical performance of dentine bonded crowns.2, 3, 8, 10, 11, 12, 13, 14, 15, 16, 17 These provide enough evidence to support the premise that the fracture strength of teeth restored with these restorations is increased significantly when the restoration is bonded to the tooth tissue.16, 18, 19, 20

Sintered feldspathic and leucite reinforced ceramic and filled polymers are used for the fabrication of metal-free restorations using traditional laboratory based fabrication techniques However, with the introduction of CAD/CAM technology, machinable versions of these materials can now be used for these applications.

Whilst there is evidence of the clinical application of resin bonded indirect restorations with promising results,2, 8, 10, 11, 21, 22, 23 the work published so far on the fracture strength of resin bonded crowns has been carried out with traditional laboratory made crowns. It was therefore of interest to investigate the strength of these restorations when they are CAD/CAM fabricated. Previous studies indicate that the CEREC system is able to produce designs more conservative to that suggested by the manufacturer. However, the brittleness index of the materials and the software and hardware of the system can be determinant factors on the application of minimal designs.24, 25, 26 As a result minimal preparation designs were proposed for materials available for the CEREC 3 chairside system (Table 1).26

The aim of the present investigation was to evaluate the immediate post-operative structural integrity and the mode of fracture of CAD/CAM fabricated resin composite and ceramic crowns using minimal preparation designs, and compare this with traditionally prepared resin bonded CAD/CAM crowns. The null hypothesis was that the structural integrity of teeth restored with resin bonded CAD/CAM crowns using minimal preparation designs, whether made of ceramic or composite, is not compromised compared to teeth that have been restored using a traditional crown design.

Section snippets

Materials and methods

Two restorative materials were tested; namely a resin composite material (Paradigm MZ100, 3M/ESPE AG, ESPE Platz, Seefeld, Germany) and a leucite reinforced glass–ceramic (ProCAD, Ivoclar Vivadent Bendererstrasse 2, Schaan, Liechtenstein). Forty extracted caries-free and crack-free maxillary first molar teeth were used for this study. Four groups (A, B, C and D) of ten teeth in each were formed. Care was taken that all teeth had similar bucco-palatal widths (BPW—the distance from the maximum

Results

For the resin composite system the mean fracture loads and standard deviations (SD) reported were 1682 N (±315) for the traditional crowns (Group A) and 1751 N (±338) for the minimal crowns (Group C). One-way analysis of variance showed that there is no statistically significant difference between traditional/minimal preparation designs (p > .05). A bar graph of the mean fracture load and SD for the two designs is shown in Fig. 4.

For the ceramic system the mean fracture loads and standard

Discussion

This study was designed to compare the structural integrity of minimally prepared resin bonded CEREC crowns with traditional designs, in order to determine if there is any change in the fracture strength immediately post-operatively when a minimal intervention technique is employed. Crowns fabricated from the same restorative material were compared. Two materials, a resin composite (MZ100) and a ceramic (ProCAD), with the respective cementation technique proposed by their manufacturers were

Conclusions

The application of minimal intervention procedures for indirect restorations is another treatment modality, with the dentine bonded crowns being one representative. Recently CAD/CAM systems are also employed for the fabrication of indirect restorations. The structural integrity of teeth minimally prepared for crowns was compared to that of traditionally prepared teeth. Two restorative systems, a composite and a ceramic, and the CEREC system were used for the fabrication of the crowns. Within

Acknowledgements

The authors wish to thank Mrs. J. Russell, Department of Corporate Information and Computing Services, for her assistance in the statistical analysis of the results. The authors would also wish to thank 3M ESPE and Ivoclar Vivadent for supplying the materials.

References (37)

Cited by (41)

  • Fatigue resistance of ultrathin CAD/CAM complete crowns with a simplified cementation process

    2015, Journal of Prosthetic Dentistry
    Citation Excerpt :

    There was no significant difference among them. The results of these 2 studies indicate that the fatigue resistance of crowns made of RNC, LD, or FEL may be influenced by the thickness of those materials, which is in agreement with Schlichting et al9 and Federlin et al.12 Tsitrou et al,13 however, found that the use of minimal preparation design did not compromise the structural integrity of crown-restored teeth when a composite resin (Paradigm MZ100, 1.5 to 2 mm compared with 0.4 to 0.6 mm) cemented with a self-adhesive dual-polymerizing resin cement (RelyX Unicem II) or leucite glass-ceramic (Pro-CAD, 1.5 to 2 mm compared with 0.8 to 1.2 mm) cemented with a dual-polymerizing luting composite (Variolink II) was used. A probable explanation of this finding could be that no aging methods were used before the load to failure test.

View all citing articles on Scopus
View full text