Clinical Outcomes of Zirconium-Oxide Posts: Up-to-Date Systematic Review

The cast gold post and core has been considered the first choice among clinicians for many years due to its high success rate, favorable failure mode, and biocompatibility.^1,3 With the increasing demand for translucent all-ceramic restorations, a major concern has been the shading effect of the post-and-core restoration on the shade of all-ceramic crowns.^6,7

Zirconium-oxide posts were introduced by Meyenberg et al8 to provide esthetics and to maintain predictable long-term durability of the restorations. The essential approach is to deliver the prefabricated zirconia posts with either direct composite resin cores or indirect ceramic core materials. The root canal should be prepared in a specific manner to receive the prefabricated post.^8-11

The one-piece milled zirconia post-and-core approach was described as capable of providing the necessary esthetic requirement, increasing strength and toughness, and improving post adaptation to the canal walls. Yttrium-stabilized tetragonal zirconium polycrystalline (Y-TZP) posts and cores were designed and milled using computer-aided design/computer-aided manufacturing (CAD/CAM) technology. The resin pattern of the post and core was fabricated and scanned to mill the one-piece zirconia post and core.^12-14 The goal of this systematic review was to investigate the success rates and clinical outcomes of zirconium-oxide posts.

Material and Methods

The main question addressed was: Do zirconium-oxide posts maintain the long-term survival rate of endodontically treated teeth? A search was made among different databases, including PubMed/Medline, ISI Web of Knowledge, EMBASE, and Google Scholar, for articles from January 1995 to December 2014. The inclusion criteria were intended to be clinical studies, presence of success and failure rates, humans, and articles published in English language. All review articles, case reports, letters to the editor, and commentaries were excluded. The search was made with the following keywords in different combinations: “zirconia,” “zirconium oxide,” “dowel/dowels,” “post/posts,” and “post and core.” The initial search with different keywords showed 273 studies. After reviewing the titles, 22 studies that met the inclusion criteria were selected for abstract review. After the complete assessment of all the abstracts, 4 studies were included for full text review and data extraction (Figure 1).

Results

All studies were designed retrospectively and were performed either at private practices or universities. The participants’ numbers during the follow-up period were reported to be between 13 and 71 participants, in which 15 to 113 prefabricated zirconia posts were placed.^8-11 Bateli et al¹¹ reported the 89 patients who participated had 141 posts placed. However, 49.4% of the patients and 53.6% of the posts were dropped from the study.¹¹

In all studies, most posts were placed in anterior teeth.^8-11 In the two studies involving 120 posts placed in the anterior,^{9,10 21} posts were placed in premolars and two posts were placed in molars (Table 1). In three studies,^9-11 composite resin cores and heat-pressed ceramics were used as core materials, whereas in one study,⁸ only composite cores were used. In three studies, all posts were cemented with composite resin cements.^8,9,11 However, Nothdurft et al10 mentioned that resin-modified glass ionomer or glass-ionomer cements were used for post cementation.

In all studies, the range of the follow-up period was between 6 months and 14.5 years with mean between 11 months to 12.3 years (Figure 2).^8-11 In two studies, no failure of restorations was observed.^8,10 Paul et al9 found the failure was mainly in posts with Empress® cores due to loss of post retention, and they also observed that the failure rate ranged from 5% to 47%. Bateli et al¹¹ reported that 18.7% of posts failed due to teeth extraction (with unknown reason), periapical radiolucency, or loss of retention (Figure 3).

Discussion

The presented systematic review study was constructed to investigate the clinical performance of zirconia posts and their ability to maintain favorable long-term success. The cast post and core is considered as the gold standard in restoration of endodontically treated teeth. Ellner et al¹⁵ revealed an 80% success rate for titanium posts with direct composite cores after 5.5 years and a 92% to 100% success rate for metal posts with cast-gold cores. Creugers et al³ reported in a meta-analysis study the success rate ranging from 77.6% to 98.6% after a 5- to 10-year observation period.

Although clinical studies^8-11 showed that the evaluated zirconia posts had a comparable success rate to metal posts, in other studies^3,15 zirconia posts have showed either a short-term follow-up period or high dropout rate. Bateli et al reported that the success rate for more than 10 years of follow-up was 81.3%. The main drawback of this study was the high dropout rate of participants, which was more than 50%. Another shortcoming was the unknown reason for teeth extraction, which caused the type of failure of zirconia posts to be unknown. Additionally, the number of posts involved in the follow-up period was not linked to teeth type.¹¹ Paul et al reported that 34 of the 113 posts were not followed-up on. Twenty-four missing posts were in the indirect group, and 8 missing posts were in the direct group. If the missing posts were considered successful, the success rate would range from 95% to 100%. However, the success rate would range from 53% to 95% if the missing posts were considered as failures. The absence of this valuable information affected the overall success rate of the study, which is considered to be a major drawback.⁹

The common cause of failure of posts in two of the studies is loss of retention.^9,11 The reason for the loss of retention could be related to the type of cement or surface treatment of posts. Both studies used resin composite cements for post cementation. Bateli et al11 treated posts’ surfaces using either tribochemical silicatization with silanization or airborne-particle abrasion technique, while Paul et al⁹ sandblasted posts’ surfaces. Akgungor et al¹⁶ examined the different surface treatment protocols on zirconia posts in vitro. They concluded that the use of a mixture of silane coupling agent with MPD (10-methacryloyloxydecyl dihydrogen phosphate)-containing primer provided higher bond strength to silica-coated zirconium-oxide posts compared with airborne-particle-abraded post surfaces with the same mixture.

In the literature, all the clinical studies had investigated the prefabricated zirconia posts with indirect ceramic cores or direct composite cores. Although milled one-piece zirconia posts and cores were laboratory investigated,¹⁷ clinical investigation was needed as the clinical practice trends toward esthetic posts and cores.

Conclusion

Due to the limited number and major drawbacks of clinical studies on zirconia posts, it can be concluded that the long-term success rate was not identified. More clinical studies are needed to identify the durability of prefabricated zirconia posts. Moreover, milled one-piece zirconia posts and cores need to be clinically investigated.

About the Author

Ahmad M. Al-Thobity BDS, MDS, FRCD(C) Assistant Professor, Department of Substitutive Dental Sciences, College of Dentistry, University of Dammam, Dammam, Saudi Arabia