Long termSurivival of direct vs. Indirect restorations
Today with the ever expanding range of restorative materials the dentist needs to be aware of how long these restorations are likely to survive and the possible reasons for failure. This will maximise longevity of restoration and prevent failure. The dentist must also have a knowledge of restorative materials advantages, disadvantages, indications and contraindications. All this information will allow the dentist to select the correct restorative material for specific clinical situations leading to long term clinical survival of restorations.
Long term survival of direct and indirect restorations is dependent on the restoration not failing
“failure occurs when a restoration reaches a level of degradation that preludes proper clinical performance for either aesthetic or functional reasons of because of inability to prevent new disease”1
Many factors contribute to the failure of a restoration these include patient, operator and restorative material factors. In this literature review I will address the failure of direct and indirect posterior restorations due to material factors independent of patient and operator factors such as clinical skill level of operator, tooth position and caries rate.
With regard to different materials for direct and indirect posterior restorations I hope to:
-Outline failure rates of direct and indirect posterior restorations
-Outline modes of failure of direct and indirect posterior restorations
-Outline briefly some advantages, disadvantages, indications and contraindications of direct and indirect posterior restorations.
-Outline in some cases the factors that operators should consider toreduce failure rates
-Compare long term survival of direct vs indirect posterior restoration failure
Direct posterior restorations
Both amalgam and resin composite are indicated as direct class 1 and 2 posterior restorations
Direct posterior amalgam
Amalgam is one of the most commonly used restorative materials worldwide in posterior direct restoration today. Amalgam doesn't bond to tooth structure, contains mercury and is not aesthetic, but its low cost, straightforward handling procedure, rapid application and good track record of clinical performance in the past mean it continues to be the most convenient restorative material in posterior teeth. In recent years there has been a decline in its popularity due to public health concerns over its mercury content. Failure of amalgams can be as high as 6% at seven years. 1 Failure of amalgam is mainly due to
1. Secondary caries
2. Tooth fracture
3. Gross amalgam fracture
4. Marginal breakdown
Secondary caries has been found to be the most common cause for amalgam failure accounting for 66% of all failures in amalgam restorations at seven years.1 Operative technique is of importance in prevention of secondary caries as contamination of the preparation by blood and saliva, poor matrix technique and poor condensation lead to poor adaption of restoration to the cavity wall and overhangs which predispose to secondary caries this can cause restoration failure due to tooth fracture and marginal breakdown.2
Tooth fracture can also cause amalgam failure. Amalgam doesn't bond to tooth structure and therefore doesn't reinforce the tooth, it is merely space filler and the tooth itself is weakened. It has been found that the bigger the restoration including depth and facial lingual width the more likely the tooth is to fracture.3The ability of a tooth with an amalgam restoration to resist fracture can be increased by preparing the enamel margins at an angle greater or equal to 90 degrees.4 This is because the enamel rods in the occlusal area of enamel are roughly parallel to the long axis of the tooth.5 it should be noted that flaws like subsurface cracks formed during cavity preparation contribute significantly to early restoration failure.6 It has been found that increased cusp fracture rates are linked to higher number of surfaces restored increased patient age.7
Amalgam failure can also arise as a result of gross amalgam fracture. This has been shown to account for approximately 33% amalgam failures in one study.1 Amalgam has a low tensile strength which predisposes it to fracture especially in load bearing areas. 1 Operator can reduce the chance of failure by having cavity preparations of adequate depth (2mm) and by creating round internal line angles.8
Marginal breakdown of amalgam can lead to failure. Incorrect cavo-surface angle can produce marginal surface breakdown and can lead to secondary caries causing failure. Marginal breakdown also occurs as a result of delayed expansion of amalgam but the addition of zinc and large amounts cooper to amalgam to increase mechanical properties has also lead to a decrease in marginal fracture and longer service by the restoration. 9 It should be noted that marginal breakdown of an amalgam isn't a definitive diagnosis of secondary caries or failure of an amalgam. Studies have shown that secondary caries is only present in approximately 58% of amalgams with ditched margins.10
Direct posterior Resin Composites
Resin composites are not currently the restoration of choice for posterior teeth because they are expensive, highly technique sensitive, take more time to place and their clinical track record of clinical performance hasn't been as good as amalgam in the past. This situation is changing as the public becomes more concerned by aesthetics and the health risks associated with the mercury in amalgam. Resin composite is also gaining popularity in the profession as the bonding systems improve and as the idea of conserving tooth structure becomes more important. Failure of resin composites can be as high as 14% at 7 years in posterior teeth.1 Assuming the correct type of composite was chosen e.g. hybrid or conventional. Failure of composites is mainly due to
1. Secondary caries
2. Gross resin composite fracture
With wear, tooth fracture and staining causing failure of a small percentage of resin composites.
Secondary caries has been found to be the most common cause of resin composite failure accounting for 88% of failures at seven years.1 However in another study secondary caries was found to be second to tooth fracture at 6 years after which it became the primary reason for failure between 6-17 years.11 The main reason for this is due to polymerisation shrinkage on setting of the resin composite which can range 2.6 to 7.1%12 this can form a marginal gap especially in dentine where bonding isn't as strong which can lead to an ingress bacteria (microleakage) which can cause secondary caries. The risk for secondary caries also increases with time11 and with the size of the cavity.1 The operator can reduce polymerization shrinkage and possibly secondary caries by using the incremental cure technique.
Gross resin composite fracture is responsible for high percentage of resin composite failures accounting for 12% of failures at 7 years.1 Resin composite is a brittle material and hence tensile strength is dependent on surface finish . It is for this reason that we always look at diametral tensile strength as a reference to fracture resistance. Its diametral tensile strength is low and as a result resin composites are prone to fracture.13 The fracture resistance is highly dependent on filler loading of resin composite with higher filler loading increasing fracture resistance14 so it is very important operator chooses of a resin composite with a high filler loading.
Tooth fracture doesn't account for a significant proportion of resin composite failure this is due to the fact that resin composites bond to tooth structure and reinforce it against fracture.15 Wear is only a factor for failure in bruxers in which case you probably wouldn't use resin composite if it was going to be subjected to high stresses. Colour is also no longer a major issue for failure with one study reporting 94% of resin composite with acceptable colour match to adjacent teeth after 17 years.16 This has also improved with decreased amines in the resin composites leading to less yellowing.
It should be noted that alot of studies of resin composites included older resin composites which dont reflect the current resin composites in use which have improved bonding which will lead to decreased failure in future studies.
Indirect posterior inlays and onlays
Indirect resin composite, gold and ceramic inlays are indicated as indirect class 1 and 2 posterior restorations. Indirect resin composite, gold and ceramic onlays are indicated as indirect class 1 and 2 posterior restorations involving one or more cusps.
Indirect posterior resin composite inlays/onlays
Indirect inlays and onlays were developed as an aesthetic alternative for medium and large posterior restorations. This was done to overcome some of the problems associated with direct posterior restorations. These restorations are expensive and time consuming to place but they have distinct advantages over direct posterior restorations which aim to reduce failure. Such advantages include:
1. They have improved proximal contacts as they are developed outside the mouth and even if incorrect can be adjusted easily.
2. They have decreased polymerisation shrinkage as it occurs outside the mouth. The only polymerization shrinkage which occurs in mouth is of the dual cured resin cement on cementation. This decreases microleakage and increases the strength of these restorations.17
No statistical differences in success rates at 5 years was seen between these and direct posterior restorations.18
With regards to failure of these restorations, in one study19 the failure rate of indirect resin composite inlays and onlays was 5% at 4-6 years. Fracture of the tooth or marginal ridge, and secondary caries are the most common modes of failure, with increased failure being seen with increased restoration size. Loss of marginal adaption, colour and anatomical form were also seen but did not cause restoration failure. In another study20 a failure rate of 6% at 1 year was seen. Failure was due to secondary caries and loss of pulp vitality. Again loss of anatomical form and marginal adaption were seen but did not cause failure of restorations.
The operator must ensure round internal line angles and depth of 2mm. Depth of less than 2mm can cause bulk fracture of restoration particularily in onlays.
Indirect posterior ceramic inlays/onlays
Indirect ceramic inlays/onlays are highly aesthetic and biocompatible indirect posterior restorations. They have the same indications and advantages as indirect posterior resin composite inlays/onlays but are more expensive and are seen as less user friendly. There is a very strong bond between the resin cement and the porelain making it a better material for an onlay than resin composite. Ceramic restorations have the potential to wear the opposing teeth, for this reason the operator shouldn't use them for patients with parafuntion and teeth under high stresses. Loss of anatomical form is not a problem with these restorations.
In one study21 eight out of fifty of the restorations failed due to fracture at 3 years it was found that adjustment to the fitting surface and polished surfaces seemed to predispose to failure. Another 6 year study22 found failure rate of 12%with resin cement and 26.3% with gic bonding techniques. Partial fracture and secondary caries were the most common reasons for failure. It was also noted that there was increased ditching in ceramic restoration which is probably due to differing wear rate between ceramic and tooth.
Operator must ensure adequate depth and round internal line angles. The operator must always make sure that with ceramic restorations there is contact only in maximum intercuspation and not in mandibular excursive movements.
Indirect posterior gold inlays/onlays
Posterior cast gold inlays and onlays have an excellent clinical track record. These restorations have excellent wear resistance, don't wear the opposing teeth and have high strength. They have the same indications and contraindications as other inlays and onlays with the exception that they can be used in high stress areas, for example they can be used in bruxers. The disadvantage with this type of restoration is they are expensive, can cause hypersensitivity reactions and they aren't aesthetic. Posterior cast gold inlays weaken the remaining tooth structure and can lead to cusp fracture. The main mode of failure of these restorations is secondary caries and tooth fracture. One study showed a failure rate of 14.3% at 10 years with 2 and 3 surface restorations having lower failure rates that one surface restorations.24 When doing these restorations, particularily in bruxers, the operator must never place occlusal contact at enamel/gold margin, contacts must be in enamel or gold only.
Indirect posterior Crowns
Cast gold metal crowns
All metal crowns are generally made in the form of full coverage cast gold crown. This type of restoration has been around for over 100 years and has a reputation for giving the longest service of any dental restoration.25 These restorations are very strong and biocompatible. The preparation of full gold crowns is the most conservative of the full coverage crowns, and unlike ceramic crowns they cause no wear of opposing teeth. Their main drawback is their high cost and lack of aesthetics. These restorations are used in teeth with extensive tooth structure loss, root canal treated teeth and due to its high strength they can be placed in bruxers.
The main cause of failure for these restorations is wear of the metal and secondary caries.26 These restoration rarely fail by fracture and tend to protect tooth structure. Studies have shown that these restorations have the longest survival rates and conversely the lowest failure rates of any dental restoration. One long term study showed a failure rate as low as 4.6%27 while another study28 reported a 32% failure of these restorations over 10 years. Interestingly this study reported increased failure of cast gold crowns in root treated teeth. The operator must keep in mind resistance and retention when preparing the tooth for these types of restorations.
All ceramic crowns
All ceramic crown use in posterior teeth is increasing all the time. This trend will continue as patient's concern with aesthetics increases and development of improved strength in ceramics continues. These restorations are highly aesthetic, less expensive than other crown alternatives and biocompatible. Unfortunately all ceramic crowns have a non conservative tooth preparation, have very low tensile strength and cause wear of opposing teeth and as a result should not be used in bruxers or in teeth which undergo high biting forces as they will inevitably fail. These restoration are typically only used posteriorly teeth with loss of tooth structure or which have been root treated. In both cases they can only be used where aesthetics are paramount and they wont be subjected to high stresses.
The failure of thses restoration in posterior teeth is the highest for all crown restorations. Current evidence even suggests that clinicians shouldn't use all ceramic restorations in molars.29 Failure of these restorations is due to secondary caries and fracture of the crown restoration. One study showed a failure rate of 0.8%.30 Another study reported a 6% failure in all ceramic restorations after 3 years.31 Neither of these studys are longterm studys and the were set in private practice with single dentists carrying out work. Perhaps their exceptional clinical skill led to such high results because in a long term study over 10 years in general dental services the failure rate was 52%. This was higher that gold or ceramometal by a large fraction.28 Just like cast metal crowns the failure rate is increased in root treated teeth.
Porcelain fussed to metal crowns
Porcelain fused to metal crowns are the most common form of crown used in dentistry. They combine the strength of the cast metal with the aesthetics of porcelain. Their main disadvantage is their expense and the fact they wear opposing teeth so they cant be used in bruxers. Their biocompatibility is also questionable as a small percentage of people can have hypersensitivy reactions to the metal.
It is true to say that porcelain fused to metal have relatively long term service.32 When they fail it is usually due to recurrent caries or fracture of porcelain from the metal understructure.33 One study showed failure of 38% at 10 years.28 The rate of failure is increased with root treated teeth as was seen with the other two types of crowns.
1. Survival and reason for failure of amalgam versus composite posterior restorations placed in a randomized clinical trial. Mario Bernardo, Henrique Luis, Michael D. Martin, Brian G. Leroux, Tessa Rue, Jorge Leitao and timothy A. DeRouen. J Am Dent Assoc 2007; 138;775-783
2. Introduction to dental materials. Richard van Noort. Mosby 3rd edition 2007. Page 94-95
3. Relationship of restoration width, tooth postion, and alloy to fracture at the margins of 13-14 year old amalgams. Osbourne JW and Gale EN. J Dent Res 1990;69;1599-1601
4.Fundamentals of Operative Dentistry: A Contemporary Approach. James B. Summit, J. Williams Robins, Thomas J. Hilton, Richard S. Schwartz. Quintessence Publishing Co Inc.,U.S.; 3rd Revised edition edition (Feb 2006) pg 344
5. Fernandes DP, Chevitarese O. The orientation and direction of rods in dental enamel. J Prosthet Dent 1991;65:793-800
6. The failure of amalgam dental restorations due to cyclic fatigue crack growth. D. Arola, M.P Huang and M. B Sultan. Journal of materials in medicine 10 1999;319-327
7. Prevalence of cusp fractures in teeth restored with amalgam and with resin-based composite. Michael J. Wahl, Margaret M. Schmitt, Donald A. Overton and M. Kathleen Gordon. J Am Dent Assoc. 2004;135;1127-1132
8. Introduction to dental materials. Richard van Noort. Mosby 3rd edition 2007. Page 95
9. 13 year clinical assessment of 10 amalgam alloys. Osborne JW, Norman RD. Dent mater 1990;6;189-194
10. Secondary caries around amalgam restorations. Luiz Andre Freire Pimenta, Maria Fidela de Lima Navarro and Alberto Consolaro. Journal of prosthetic dentistry. 1995; colume 74 no.3;219-222
11Longevity of direct resin composite restorations in posterior teeth: a review . A. Brunthaler, F. Konig, T. Lucas, W. Sperr and A. Schelle. Clinical oral investigations (2003) 7;63-70
12. Curing contraction of composites and glass-ionomer cements. AG Feilaer, AJ de Gee, CL Davidson. J prosthetic Dent 1988;59;297-300
13. Introduction to dental materials. Richard van Noort. Mosby 3rd edition 2007. Page 118-119
14. Can a single resin composite serve all purposes? JJM Roeters, ACC Shortall and NJM Opdam. British dental journal 2005;199;73-79
15. Reinforcement of weakened cusps by adhesive restorative materials:an in vitro study. LC Macpherson and BG Smith. Br Dent 1995;178;341-344
16. Seventeen year clinical study of ultraviolet cured posterior composite class 1 and 2restorations. AD Wilder, KN Jr May, SC Bayne, DF Taylor and KF Leinfelder. J Esthet Dent 1999;11;135-142
17. Fundamentals of Operative Dentistry: A Contemporary Approach. James B. Summit, J. Williams Robins, Thomas J. Hilton, Richard S. Schwartz. Quintessence Publishing Co Inc.,U.S.; 3rd Revised edition edition (Feb 2006) pg519
18. Composite filling and inlays. An 11 year evaluation. U. Pallesen and V. Quist. Clin Oral Investig 2003;7;71-79
19.A four to six years follow-up of indirect resin composite inlays/onlays. J. Leirskar, H. Nordbo, N. Ryhe Thoresen, T. Henaug and F. Ramm von der Fehr. Acta Odontal Scand 2003;61;247-251
20. One year clinical evaluation of composite and ceramic inlays in posterior teeth. A. Scheibenbogen, J. Manhart, K.H. Kunzelmann and R. Hickel. J Prosthet Dent 1998;80;410-6
21. A 3-year clinical evaluation of a porcelain inlay system. A.J.E. Qualtrough and N.H.F. Wilson. J. Dent. 1996;24;317-323
22. Fired ceramic inlays: a 6-year follow up. J.W.V. van Dijken, C. Hoglund-Aberg and A-L. Olofsson. J. Dent. 1998;26;219-215
23. A Review of Metals Used in Dentistry. Norman RD. (1991): Prepared for Committee to Coordinate Environmental Health and Related Progratns, PHS, DHHS.
24. Longevity of cast god inlays and partial crowns- a retrospective study at a dental school clinic.R. Stoll, M Sieweke, K Pieper, V Stachniss and A Schulte. Clin Oral Invest (1999)3:100-104
25. Intarcoronal and Extracoronal tooth restorations. Gordon J. Christensen. JADA 1999;130;557-560
26. Longevity of posterior tooth dental restorations. Gordon J. Christensen. JADA2005;136;201-203
27. helen retrospective srown
28. Ten year outcome of crowns placed within the General Dental Services in England and Wales. FJT Burke and PSK Lucarotti. Journal of Dentistry 2009;37;12-24
29. Factors essential for Successful All-ceramic Restorations. TE Donovan. JADA 2008;139(4):14s
30. Retrospective assessment of 546 all ceramic anterior and posterior crowns in a general practice.BS Segal. J Prosthet Dent 2001;85;544-50.
31. Survival of In-Ceramcrowns in private practice:a propective clinical trial. EA McLaren and SN White. J of Prosthet Dent 2000;83(2):216-222.
32. Porcelain-fused-to-metal vs. Non-metal crowns. GJ Christensen. JADA 1999;130;409-410
33. Longevity of posterior tooth dental restorations. GJ Christensen. JADA 2005;136;201-203