Purpose was to present the best available clinical evidence for successful bonding of oxide ceramic restorations.
PubMed database was searched for articles on clinical trials with resin-bonded alumina or zirconia ceramic restorations.
Overall only 10 articles reported on clinical trials with resin-bonded oxide ceramic restorations.
Clinically, using phosphate monomer containing luting agents after air-abrasion provided long-term durable bonding.
For most alternative bonding methods no clinical evidence of durable bonding could be found.
Despite a huge number of published laboratory bonding studies on dental oxide ceramics clinical long-term studies on resin bonded oxide ceramic restorations are rare. The purpose of this review is to present the best available clinical evidence for successful bonding of dental oxide ceramic restorations.
Clinical trials with resin-bonded restorations that had no or only limited mechanical retention and were made from alumina or zirconia ceramic were identified using an electronic search in PubMed database. Overall 10 publications with clinical trials could be identified. Their clinical outcome was compared with that laboratory bond strength studies.
Clinical data provide strong evidence that air-abrasion at a moderate pressure in combination with using phosphate monomer containing primers and/or luting resins provide long-term durable bonding to glass-infiltrated alumina and zirconia ceramic under the humid and stressful oral conditions.
As simple and clinically reliable bonding methods to oxide ceramics exist, the rationale for development of alternative bonding methods might be reconsidered especially when these methods are more time consuming or require rather complicated and/or technique sensitive procedures.
In recent years one of the most popular research subjects in dental materials science has been – and still is – all-ceramic materials and within that field bonding to zirconia and other oxide ceramics . Conducting a PubMed database search in May 2014 for articles dealing with the resin bond to dental zirconia ceramic reveals an astonishing increase of research being published in the last two decades years ( Table 1 ). While from 1990 to 1999 in total only 5 articles on this topic could be identified in the PubMed database, it increased to 15 articles in the years 2000–2004 und to 96 articles from 2005 to 2009 ( Fig. 1 ). This number has already been toped by 151 articles, which have been published from 2010 until May 2014.
|First author of most recent publication||Retainers||Location||N||Ceramic||Bonding method||Time in months||Failure and complication rates in %|
|Surface conditioning||Primer/luting resin||Failure||Debonding|
|Kern 2011||2 wings||Anterior||16||Alumina (In-Ceram Al)||Silica coating (Rocatec)||Espe Sil/Panavia||120||26.1||0|
|Kern 2011||1 wing||Anterior||21||Alumina In-Ceram Al/Zr||Air-abrasion with alumina||No primer/
|Galiatsatos 2014||2 wings||Anterior||54||Alumina (In-Ceram Al)||Air-abrasion with alumina||Monobond S/
|Sasse 2013||1 wing||Anterior||16||Zirconia (e.max ZirCAD)||Air-abrasion with alumina||No primer/
|Sasse 2013||1 wing||Anterior||14||Zirconia (e.max ZirCAD)||Air-abrasion with alumina||Metal/Zirconia Primer/Multilink automix||64||0||7.1 a|
|Sailer 2014||1 wing||Anterior||15||Zirconia (various)||As machined +
|Clearfil Porcelain Bond/Panavia 21||53||0||13.3|
|Sasse 2014||1 wing||Anterior||42||Zirconia (various)||Air-abrasion with alumina||No primer/
|Ohlmann 2008||2 inlays||Posterior||13||Zirconia (e.max ZirCAD)||Silica coating (Rocatec)||Monobond S/
|Abou Tara 2011||2 inlays with wings||Posterior||23||Zirconia
|Air-abrasion with alumina||No primer/
Unfortunately, the vast majority of the articles present laboratory research, reviews or case reports, while clinical trials are rare (7 out of 267 articles). The large number of articles dealing with bonding to zirconia and other oxide ceramics suggests that bonding to these ceramics would be an unsolved problem in dentistry. And in fact, most original laboratory research reports on bonding to zirconia ceramics start in their introduction with a statement pointing more or less out that achieving a reliable and predictable bond to this ceramic would be a major problem in dentistry or at least a limitation when restorations with limited or no mechanical retention such as occlusal veneers, partial coverage restorations or resin-bonded fixed dental prostheses (RBFDPs) are utilized .
A recently published systematic review nicely summarized the huge variety of bonding methods used on dental oxide ceramics and their results in laboratory bond strength testing . Overall, they identified 23 different surface treatments that had been tested still with a wide variation of specific conditions. However, the authors of this systematic review concluded, that promising laboratory test results still need to be confirmed by clinical studies before clinical recommendation could be given. However unfortunately in this systematic review obviously no attempt was made to correlate laboratory and clinical findings.
So the question might be raised whether despite the vast amount of laboratory research it really is still a significant problem in dentistry to bond reliably to oxide ceramics such as alumina and zirconia ceramics. This article will not attempt to replicate the above mentioned reviews but will summarize published clinical trials on bonded oxide ceramic restorations and correlate their results with that of laboratory bond strength testing using the same bonding methods as in the clinical trials. Therefore, the purpose of this review is to present the best available clinical evidence for successful bonding of dental oxide ceramic restorations.
Clinical trials on bonding to oxide ceramics
When aiming to truly test the bonding capacity of bonding systems to oxide ceramics clinically it will be best to use non-retentive restorations such as resin-bonded fixed dental prostheses (RBFDFs) which rely solely on adhesion. As these restorations undergo substantial loading on their pontics and their long-term function depends completely on the durability of the resin bond they seem to be the ideal in vivo test system. Second best might be to use restorations with limited mechanical retention but which need to withstand high loading forces such as RBFDFs with a retentive design in the anterior region and inlay-retained fixed dental prostheses (IRFDFs) in the posterior region.
Conventional retentive restorations such as crowns and crown-retained fixed dental prostheses are considered not suitable to truly test the bonding capacity of bonding systems to oxide ceramics clinically as they do not require adhesive luting because they are successfully retained by conventional cements .
Therefore only clinical trials with RBFDFs and IRFDFs made from alumina and zirconia ceramics have been included in the current comparison of clinical and laboratory bond strength data. Using in the PubMed database the search terms “resin-bonded AND fixed dental prosthesis (FDP) AND all-ceramic”, “resin-bonded AND fixed partial denture (FPD) AND all-ceramic”, “inlay-retained AND fixed dental prosthesis (FDP) AND all-ceramic”, and “inlay-retained AND fixed partial denture (FPD) AND all-ceramic” overall 94 articles were found. Excluding case reports and laboratory research 10 publications could be identified, 4 reporting on clinical bonding to alumina ceramic and 6 on clinical bonding to zirconia ceramic ( Table 1 ). However, 3 and 2 publications reported follow-ups of the same patient cohort each. Overall, 6 different bonding methods have been tested in these trials, 3 methods were used with alumina ceramic and 4 with zirconia ceramic.
Clinical bonding to alumina ceramic
All clinical trials were on all-ceramic RBFDPs made from glass-infiltrated alumina ceramic (In-Ceram alumina or In-Ceram zirconia, both Vita, Bad Säckingen, Germany) . No clinical trials with alumina ceramic IRFDFs or with RBFDPs made from densely sintered alumina ceramic were found.
Method 1 tested on glass-infiltrated alumina ceramic
Silica-coating by air-abrasion with 110 μm silica-containing alumina particles at 2.5 bars (Rocatec Plus, 3M Espe, Seefeld, Gerrmany), then silane application (Espe Sil, 3M Espe) and using a methacryloyloxydecyldihydrogenphosphate (MDP) containing luting resin (Panavia, Kuraray, Osaka, Japan). No RBFDPs debonded during 10 years observation time, which shows that this bonding method provides long-term durable bonding to glass-infiltrated alumina ceramic under clinical conditions. It confirms various laboratory studies that also showed durable bonding after long-term thermal cycling and water storage independent whether a MDP containing luting resin was used .
Method 2 tested on glass-infiltrated alumina ceramic
Air-abrasion with 50 μm alumina particles at 2.5 bars and using a MDP containing luting resin (Panavia 21, Kuraray). No RBFDPs debonded during 10 years observation time, which shows that this bonding method provides long-term durable bonding to glass-infiltrated alumina ceramic under clinical conditions. It confirms various laboratory studies that also showed durable bonding after long-term thermal cycling and water storage when a MDP containing luting resin was used after air-abrasion with alumina particles .
Method 3 tested on glass-infiltrated alumina ceramic
Air-abrasion with 250 μm alumina particles at 2.5 bars pressure, then silane application (Monobond S, Ivoclar Vivadent, Schaan, Liechtenstein) and using a dual curing luting resin (Variolink II, Ivoclar Vivadent). Within 8 years observation time 3.7% of the RBFDPs debonded. These clinical results are supported by laboratory studies which showed that silanating air-abraded alumina ceramic improved the bond strength of luting resins without MDP monomer compared to the control without silane application . However it confirms laboratory results that silane application is inferior to using silica coating and silane application or using MDP containing luting resins without prior silica coating . This is in agreement with the above clinical studies as only with method 3 debondings occurred clinically but not with methods 1–2.
Clinical bonding to zirconia ceramic
Overall five clinical trials with zirconia ceramic using either RBFDPs (3) or IRFDFs (2) could be identified . In two trials with RBFDPs a non-retentive preparation design was used, so that the retention of the restoration depended solely on adhesion , while in the other three trials the preparation design involved also some mechanical retention, so that the bonding interface might have been stressed to a lesser extend . In these clinical trials 4 different bonding methods have been tested during an observation time of 1–5 years.
Method 1 tested on zirconia ceramic
Air-abrasion with 50 μm alumina particles at 2.5 bars pressure and using a MDP containing luting resin (Panavia 21, Kuraray). During normal function no RBFDPs and IRFDFs debonded during an observation time of 20–64 months. However, a debonding rate of 4.8–6.3% occurred in RBFDPs whereas all debondings were caused by traumatic incidents as reported by the patients and failure modes were mixed, i.e. resin remained at both, the enamel and the zirconia ceramic bonding surfaces. These clinical results reveal that using a MDP containing resin after air-abrasion provides long-term durable bonding to zirconia ceramic under clinical conditions. It confirms various laboratory studies that also showed durable bonding after long-term thermal cycling and water storage when a MDP containing luting resin was used after air-abrasion with alumina particles .
Method 2 tested on zirconia ceramic
Air-abrasion with 50 μm alumina particles at 2.5 bars pressure and using a phosphoric acid methacrylate-containing primer (Metal/Zirconia Primer, Ivoclar Vivadent) in combination with a dual-curing luting resin (Multilink Automix, Ivoclar Vivadent). During normal function no RBFDPs debonded during an observation time of 64 months. However, a debonding rate of 7.1% occurred that again were caused by traumatic incidents . The mixed failure mode reveals that this bonding method also provides long-term durable bonding to zirconia ceramic under clinical conditions. It confirms also various laboratory studies that also showed high bond strength after long-term thermal cycling and water storage when this bonding system was used after air-abrasion with alumina particles .
Method 3 tested on zirconia ceramic
The bonding surfaces were not air-abraded but only cleaned with ethanol. Then a MDP containing primer (Clearfil Porcelain Bond or Clearfil Ceramic Primer, both Kuraray) was used in combination with a MDP containing luting resin (Panavia 21, Kuraray). During an observation time of 53 months 13.3% of the RBFDPs debonded during normal function despite the retentive preparation design. These results are also supported by various laboratory studies that showed a reasonable bond strength was achieved with MDP containing primers on not air-abraded zirconia ceramic but although a significant decrease in bond strength was observed after longer-term aging with water storage and/or thermal cycling . Based on the limited durability of the bond of MDP primers to not air-abraded zirconia it might be assumed that the debonding rate in this clinical study would have been considerably higher if a non-retentive preparation design had been chosen as in other clinical trials with zirconia ceramic RBFDPs .
Method 4 tested on zirconia ceramic
Tribochemical silica coating (Rocatec, 3M Espe) of the zirconia ceramic bonding surfaces and using a silane (Monobond S, Ivoclar Vivadent) in combination with a MDP containing dual curing luting resin (Panavia F, Kuraray). During an observation time of only 12 months 46.2% of the IRFDFs with two inlay-retainers debonded during normal function despite a retentive inlay preparation design. These clinical results are also supported by various laboratory studies that showed that the bond strength to silica-coated zirconia ceramic decreased significantly after a few months of artificial aging . Although MDP containing luting resins were able to produce durable bonding to air-abraded zirconia ceramic clinically obviously the silica layer between on the zirconia ceramic prevented the MDP containing luting resin from directly bonding to the zirconia surface thus explaining the high rate of debonded IRFDFs within only one year.
However it should be mentioned that there are various laboratory studies that reported durable resin bonding on some silica coated zirconia ceramics . Nevertheless no clinical trials could be identified that confirm durable bonding to silica-coated zirconia ceramic in vivo.