Restorative dentistry done digitally
Schepke, Ulf
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2018
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Schepke, U. (2018). Restorative dentistry done digitally: Implementation and evaluation of some digital
tools in contemporary implant dentistry. Rijksuniversiteit Groningen.
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CHAPTER
03
Adhesive failure of Lava Ultimate and
Lithium Disilicate crowns, bonded to zirconia
abutments: a prospective within-patient
comparison
• PART B •
This chapter is an edited version of:
Schepke U, Lohbauer U, Meijer HJA, Cune MS.
Adhesive failure of Lava Ultimate and Lithium Disilicate crowns, bonded to zirconia abutments: a prospective within-patient comparison.
Adhesive failure of Lava Ultimate and Lithium Disilicate
crowns, bonded to zirconia abutments: a prospective
within-patient comparison
96
Abstract
The purpose of this study is to demonstrate the importance of the choice of restorative material on the success of clinical bonding to zirconia.
Fifty participants seeking single implant treatment were included in a prospective study. All participants received screw-retained implant restorations. Lava Ultimate (LU) crowns were digitally manufactured and extraorally bonded to either a stock or a customized zirconia implant abutment by means of a resin composite cement. After 12 months, the treatment mode was changed. Lithium Disilicate (LDS) was used as an alternative restorative material in combination with geometrically and chemically identical abutments and bonding agents. These restorations were also followed up for 12 months. Primary outcome measures were clinical success and failure mode.
Forty LU restorations (80%) debonded and 3 restorations (6%) showed possible debonding related fractures within 12 months of clinical service, whereas no bonding failures at all occurred when LDS restorations were made.
The choice of restorative material for single crowns luted to zirconia implant abutments with an adhesive resin cement strongly influences the incidence of bonding failures after 12 months of clinical service.
97
Introduction
Zirconia is a popular restorative material in dentistry because of its favorable biological and mechanical properties.1 However, bonding to zirconia remains a challenge. Microtensile tests
for various bonding strategies reveal bond strengths varying from approximately 16 to 23 MPa, compared to 8 MPa in the untreated control group.2 Whereas some reviews are critically pessimistic,2
other authors consider this as acceptable bond strengths.3
There is consensus on the benefit of phosphate esther monomer 10-methacryloyloxydecyldihy-drogenphosphate (MDP) in resin cements to enhance the bond strength to zirconia.4 However,
all mentioned reviews focus on the interface between zirconia and the (adhesive) cement.2-4 The
influence of the mechanical and chemical properties of the restoration material on clinical bonding failures remains unclear.
The aim of this report is to emphasize the influence of the restorative material on the retention of full crowns to zirconia implant abutments after one year of clinical service by comparing the incidence and mode of clinical bonding failure when using two different restorative materials: a CAD/CAM polymer material (Lava Ultimate, LU) and lithium disilicate (LDS).
Materials and Methods
A single-center, clinical trial was designed for 50 participants missing a single mandibular or maxillary premolar. Permission from the Medical Ethics Committee of the University Medical Center Groningen, the Netherlands was granted (METc number 2012.388, ABR number NL 42288.042.12) and informed consent was obtained (Chapter 3, part A).
Implant surgery was performed using a standard protocol, and a screw-retained implant restoration was provided three weeks after impression-taking, consisting of a digitally designed and milled LU crown (Lava Ultimate, 3M ESPE, Seefeld, Germany), bonded to either a stock (ZirDesignTM, Dentsply
Sirona Implants, Mölndal, Sweden, n=25) or an individual zirconia abutment (AtlantisTM, Dentsply
Sirona Implants, Mölndal, Sweden, n=25),1* as described in detail in an earlier publication (chapter
3, part A).5
Due to an unexpected and unacceptably high number of debonding events, the treatment modality for all patients had to be changed at the regular follow-up appointment after one year.
The original CAD/CAM file of the LU restoration, as well as the original gypsum cast were used to manufacture a Lithium Disilicate (LDS) duplicate (e.max CAD, Ivoclar Vivadent AG, Schaan, Liechtenstein), which was subsequently bonded to a geometrically identical abutment. LDS crowns were etched for 20 seconds with 5% hydrofluoric acid (IPS Ceramic Etching Gel, Ivoclar Vivadent AG,
1* The present study was originally not designed to investigate a possible correlation between restoration material and bonding failures; randomization was therefore not applied to the choice of restorative material but to a third variable (i.e. abutment manufacturing).
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Schaan, Liechtenstein) and rinsed off under running water. The ceramic surfaces were dried before applying the bonding agent. The pretreatment of the abutments, as well as the bonding agent, cement and bonding procedure were kept unchanged.
On the scheduled appointment after 12 months, clinical bonding of the LU crown to the zirconia abutments was evaluated with hand force. Subsequently, the occlusal restoration material was carefully removed from the screw access hole and the LU crown-abutment restoration was replaced by the identically designed LDS crown-abutment restoration and evaluated after yet another year. At that time, the implant had been in service for two years (figure 1). Fractured LU crowns were analyzed with Scanning Electron Microscopy (SEM).
Figure 1
Adapted consort flow diagram. Treatment Modality I consisted of LU crowns extraorally bonded to stock zirconia abutments (Intervention A) and customized zirconia abutments (Intervention B). Treatment modality II consisted of LDS crowns extraorally bonded to stock zirconia abutments (A) or customized zirconia abutments (B). Once a patient was allocated to an intervention (A or B), the abutment type remained unchanged. Also, the used cement and bonding agent was kept unchanged throughout the study for both Interventions as well as for both treatment modalities.
99
Results
In the LU group, 40 restorations (80%) debonded and three restorations (6%) fractured within one year of clinical service (figure 2). One patient reported that the LU crown debonded while chewing and was destroyed accidentally. SEM analysis of fractured LU crowns revealed a small space between the cement and the restoration material (figure 3). In all of the observed debonding cases, the residual cement was predominantly located in the LU crown and not on the abutment. This was not the case in all fractured crowns. Interestingly, no debonding occurred in the LDS group (figure 2). A fractographic analysis of the three fractured crowns was performed. All three crowns fractured in a mesiodistal direction indicating an occlusal stress concentration on the respective contact points on the premolar cusps. The fractographic analysis further showed a clear adhesive failure either at the interface between zirconia and the universal adhesive or between the restorative material and the universal adhesive. Shear chippings were observed at the margins, leading to the assumption that the crowns very likely delaminated from the abutment prior to fracture under an inclined shear loading situation.
Figure 2
Undisturbed survival according to Kaplan-Meier of 50 Lava Ultimate (LU) and Lithium Disilicate (LDS) crowns luted to zirconia abutments after a maximum of 12 months.
Lava Ultimate and Lithium Disilicate crowns
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Figure 3
SEM image of a fractured restoration. The cement remained in the Lava Ultimate (LU) crown. Delamination (arrow) is seen also between the cement and LU indicating week bond strengths also between cement and restoration material.
LavaUl&mate
Embedding Cement
101
Discussion
Failures in the LU group occurred unexpectedly and in a highly controlled environment (i.e. within a randomized controlled clinical trial). The manufacturer already reacted on those debonding issues with a change in indication.2*
The present study was originally not designed to show a possible correlation between restoration material and bonding failures; randomization was therefore not applied to the choice of restorative material, but to a third variable (i.e. abutment manufacturing).
Theoretically, it is possible that the first treatment modality (LU crowns) has influenced the participants to reduce chewing force on the implant side. This might have influenced the superior success rate of the second treatment modality (LDS crowns), but the effect seems to be negligible, given the big differences in performance between the two treatment modalities. However, the same cement was applied and most of the confounding issues could be erased due to the study design (i.e. within patient comparison).
Therefore, it seems evident that the choice of restoration material was of causal influence to the high difference of bonding failures.
Acknowledgments
This study was supported by a grant from Dentsply Sirona Implants, Mölndal, Sweden and by the authors’ institutions. Restorative materials were provided by Dentsply Sirona Implants, 3M and Ivoclar-Vivadent free of charge. The restorations were manufactured by Elysee Dental / Oosterwijk Dental labs, Utrecht, the Netherlands. The funding sources had no involvement in the study design, collection, analysis and interpretation of the data or in the decision to submit the article for publication.
2* Notice: Change in Indication — Lava™ Ultimate Restorative, 3M, 2016
Lava Ultimate and Lithium Disilicate crowns
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References
1. Denry I, Kelly JR. State of the art of zirconia for dental applications. Dent Mater. 2008;24(3):299-307.
2. Thompson JY, Stoner BR, Piascik JR, Smith R. Adhesion/cementation to zirconia and other non-silicate ceramics: Where are we now? Dent Mater. 2011;27(1):71-82.
3. Inokoshi M, De Munck J, Minakuchi S, Van Meerbeek B. Meta-analysis of bonding effectiveness to zirconia ceramics. J Dent Res. 2014;93(4):329-334.
4. Ozcan M, Bernasconi M. Adhesion to zirconia used for dental restorations: A systematic review and meta-analysis. J Adhes Dent. 2015;17(1):7-26.
5. Schepke U, Meijer HJ, Vermeulen KM, Raghoebar GM, Cune MS. Clinical bonding of resin nano ceramic restorations to zirconia abutments: A case series within a randomized clinical trial. Clin Implant Dent Relat Res. 2016;18(5):984-992.
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