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MIND THE CROWN MARGINS.

Byline: NIDA OVAIS, BILAL AHMED, AZAD ALI AZAD and AYESHA ASLAM

ABSTRACT

Metal free ceramic restorations have increased in demand due to their superior esthetics and more resemblance to the natural teeth, more so now that metal-free biocompatible options are preferred.

Although porcelain fused to metal crowns are also used owing to less tooth structure loss in their preparation, the metal portion shows through the marginal area giving a blue-gray, cyanotic appearance to the tissue.

Margins are one of the most important components in the success of a ceramic restoration. Essential prerequisites for the clinical success of an all-ceramic restoration includes good esthetics, a high resistance to fracture and perfect marginal fit. A poor marginal design or one that is not prepared well may be a source of plaque accumulation, other than being esthetically unpleasing.

Different marginal designs have been proposed and the most acceptable ones for all-ceramic restorations are either the rounded shoulder or the large chamfer margin. A major part of the current literature and research done on this subject falls into two broad categories that are affected by the type of marginal finish line marginal fit and fracture resistance.

Key Words: Finish Lines, Shoulder Margins, Chamfer Margins.

INTRODUCTION

Better looking smiles have always had a growing importance for patients all over the world. This makes fabricating esthetic restorations the main objective for every dentist in any kind of treatment he performs.1

Multiple options are suggested when it comes to restoring teeth with crowns, ceramic being the foremost. Ceramics are a favorable option as regards to biocompatibility and unchangeable color over time, as well as their resistance to corrosion or wear.2

Ceramic restorations have increased in demand due to their superior esthetics3 and more resemblance to the natural teeth, more so now that metal-free biocompatible options are preferred.4 Although porcelain fused to metal crowns are also used owing to less tooth structure loss in their preparation, the metal portion shows through the marginal area giving a blue-gray, cyanotic appearance to the tissue.5,6

Margins are one of the most important components in the success of a ceramic restoration.7,8 Essential prerequisites for the clinical success of an all-ceramic restoration includes good esthetics, a high resistance to fracture and perfect marginal fit.9 A poor marginal design or one that is not prepared well may be a source of plaque accumulation10, other than being esthetically unpleasing.

Different marginal designs have been proposed and the most acceptable ones for all-ceramic restorations are either the rounded shoulder or the large chamfer margin.11 A major part of the current literature and research done on this subject falls into two broad categories that are affected by the type of marginal finish line marginal fit and fracture resistance.

LITERATURE REVIEW

Marginal and internal fit plays an essential role in clinically evaluating the long term success of a ceramic restoration in the oral cavity.12,13,14 Marginal fit has been shown to be clinically significant to the periodontal health and the development of secondary caries in the marginal area.15 A poor marginal adaptation may lead to marginal discoloration, exposure of the luting agent, dissolution of the cement, more gingival sulcular fluid flow, micro leakage, plaque accumulation, secondary decay, and eventually to bone loss and periodontal disease.16

Multiple in-vitro studies and clinical trials have been conducted to measure the marginal and internal gap sizes. However, there are no particular specifications in relation to the clinically acceptable marginal discrepancy.4 May et al18 evaluated that a marginal gap at the crown and die interface of an all ceramic crown in the posterior dentition was less than 70 micrometers. In one study19, the mean value was 28+/3.13 micrometers, while in another study20, it was 160 +/- 45.98 micrometers. According to Schaefer et al14, most acceptable marginal discrepancies have been reported in the range of 50-150 micrometers. A five year study conducted by McLean and Fraunhaufer21 on more than 1000 restorations revealed that 120 micrometers is the maximum tolerable marginal gap size. This value has been suggested in the current literature, to represent the maximum clinically acceptable gap size.13,17

Holmes et al22 defined the measurements of the misfit of crowns at different locations as internal gap, marginal gap, vertical marginal discrepancy, overextended margin, under extended margin, absolute marginal discrepancy and seating discrepancy. The recommended instrument for evaluation of absolute marginal discrepancy is the Profilometer, which provides a highly accurate and nondestructive method of measurement.23

Researchers have also evaluated changes in the marginal fit that may occur during various stages of fabrication.24 Euan et al25 found that during different stages of fabrication, differences in marginal fit were observed in the chamfer group (p=0.0042) but there were no differences in the crowns with shoulder margins (p=0.4335). Balkaya et al26 reported similar findings and also concluded that the marginal fit of the all ceramic crowns is affected by porcelain firing cycles. Miura et al24, as well as Vigolo and Fonzi27 differed in their results and found no such changes between the different marginal designs in the different CAD/CAM systems. These results were consistent with those found by Komine et al.28

A study concluded that the marginal discrepancy in the rounded shoulder group was significantly lower than that in the large chamfer and tilted chamfer groups, whereas the rounded shoulder had the greatest internal discrepancy and large chamfer group had the least values (p=0.0014).29

METHODOLOGY

Electronic literature search of Medical Database, Pubmed and Google Scholar was carried out on a campus network by one author using specific search strategies which included combination of MeSH terms and keywords. Keywords used were crown margin", finish line", margin design", shoulder margin", chamfer margin", marginal discrepancy", marginal fit" and fracture resistance". A single author did the initial selection of studies and sent copies of each study to the other three authors for validation of the inclusion criteria. The titles and abstracts were filtered by one author according to the following inclusion and exclusion criteria.

Inclusion Criteria

In vitro and In vivo studies were chosen. At least one of the materials was chosen to be all ceramic and/ or metal ceramic. Only studies published in English language were included. Articles published between the last 20 years (1994 to 2014) were included.

Exclusion Criteria

Studies evaluating intracoronal restorations or implant supported restorations were excluded. Materials other than all ceramic or metal ceramic were excluded.

DISCUSSION

Majority of the researchers have agreed to the importance of fracture resistance and marginal fit in the longevity and success of all-ceramic restorations.47

Several different marginal configurations have been used to resolve problems related to esthetics but it has been difficult to devise a design that provides excellent esthetics, maintains good marginal seal, and promotes periodontal health.5 The marginal fit of crowns is a

References###Sample###Material###Margins eval-###Results###P Value

###Size###uated

Demir N et al###60###All Ceramics###Shoulder,###MG: Buccally, Shoulder greater than###N/A

(2014)###Chamfer###Chamfer

Miura S et al###15###All-Ceramic###Shoulder###MD: Lingually Chamfer greater than###N/A

(2014)###Shoulder

Yucel MT et al###80###All Ceramics (Cerec###Shoulder###No significant difference p less than 0.01

(2013)###3, IPS Empress 2, In###in MG before and after

###Ceram Alumina, Celay)###glazing

Euan R et al###20###All Ceramic###Shoulder,###MG: In Ceramgreater than Cerec 3greater than###N/A

(2012)###Chamfer###IPS Empress 2greater than Celay

Souza RO et al###30###All Ceramic###Tilted Chamfer, MG at different stages P less than 0.05

(2012)###Large Cham- of fabrication: Chamfer

###fer, Rounded (Significant) greater than Shoulder

###Shoulder###(Non-Significant)

Jalalian E et al###20###All Ceramic###Shoulder,###MG: Tilted Chamfer greater than P = 0.012

(2011)###Chamfer###Large Chamfer greater than Rounded

###Shoulder

Jalalian E et al###20###All Ceramic###Shoulder,###FR: Chamfer greater than Shoulder P = 0.001

(2011)###Chamfer

Polansky R et al###60###4 All Ceramic systems, 2 Shoulder###FR: Chamfer greater than Shoulder###N/A

(2010)###Metal ceramic systems

Baig MR et al###30###All Ceramics (Cercon, Shoulder,###MG: Vita Mark II greater than Em-###N/A

(2010)###IPS Empress 2), Full Chamfer###press greater than InCeram greater than Metal

###Metal###Ceramic greater than Galvano Ceram-

###ic greater than Procera

Giannetopoulos###30###All Ceramic###Shoulder, 30 MG: Shoulder = Chamfer P less than 0.05

S et al (2010)###bevel, 60 bevel

Michalakis KX et###24###Metal Ceramics###Shoulder,###FR: Shoulder greater than 30o bevel P less than 0.001

al (2009)###Chamfer###greater than 60o bevel

Limkangwalm-###16###All Ceramics###Shoulder,###FR: Chamfer greater than Shoulder p = 0.065

on-###Feather edge

kol P et al (2009)

Beuer F et al###50###All Ceramic###Shoulderless,###MG: Shoulder =###P less than 0.01

(2008)###slight chamfer,###Feather edge

###pronounced

###deep chamfer,

###beveled shoul-

###der, shoulder

Di lorio D et al###20###All Ceramic###Shoulder,###FR: Shoulder greater than Shoulder-###P less than 0.05

(2008)###Chamfer###less greater than Bevelled shoulder greater than

###Pronounced deep chamfer

###greater than Slight chamfer

Limkangwal-###32###Metal-Ceramic###Shoulder,###FR: Shoulder greater than Chamfer###p=

mongkol P et al###Feather edge###0.0045

(2007)

Kokubo Y et al###90###All Ceramics###Chamfer###MG: Feather edge greater than Shoul- N/A

(2005)###der

Yeo IS et al###120###All Ceramic: (Celay Shoulder###MG: At rounded slope of P less than 0.05

(2003)###InCeram, Conventional###chamfergreater than Margin MG:

###InCeram, IPS Empress###Conventional InCeram

###2) Metal-Ceramic###greater than Celay InCeram greater than IPS

###Empress 2; Metal-ceramic

###greater than IPS Empress 2

Huge concern for clinicians and there is no conclusive evidence of any one margin configuration that brings out better results than others in terms of marginal fit.12

The crown adaptation and the film thickness of the cement can influence dissolution of luting agent8,24 and hence marginal leakage.48 Therefore a good marginal fit is consistently emphasized during fabrication of all ceramic crowns.4-10

An excessive marginal gap leads to periodontal problems, plaque retention, recurrent caries and pulp lesions eventually leading to bone resorption.29 In addition, an excessive internal discrepancy leads to decreased fracture strength of an all ceramic restoration.49 However, it cannot be concluded that good marginal fit will influence the fracture resistance of an all ceramic restoration and the two properties may be interlinked. Foncesca et al50 conducted a study to identify a correlation between marginal fit and fracture resistance but did not get any statistically significant results.

Donovan T and Prince J5 suggested that the all ceramic margin should be close to a 90-degree angle so that the porcelain will be primarily under compressive forces, as the compressive strength of porcelain is much higher than its tensile strength.51 It was theoretically evaluated that the stress induced during seating of a restoration which has a porcelain margin angle of 33 degrees or less would result in fracture. Also, it was found that as the porcelain crown margin angle decreases in width, the angle of the margin, which is required to prevent failure of the restoration, increases.52 In another study,53 it was concluded that introducing a marginal angle increases the likelihood for marginal chipping of the all ceramic restoration.

Where the large chamfer produced micro cracks, Souza et al29 suggested that it may be because the chamfer finish line is more complicated to produce owing to the concave and convex areas in the tilted surfaces of this finish line. A study in support of chamfer margin, however suggested that there was a better marginal fitness due to the curve in the chamfer finishing line and that causes a better spread in the load.32

This is not the case in a 90 degree shoulder preparation. In addition, in the chamfer finishing line, there is an angled cut of enamel that brings a greater width of enamel in exposure to etch and bonding so there is a stronger bonding and unity between the restoration and teeth. This is in contrast to the shoulder margin that has a lesser width of enamel for exposure to etching and bonding.54

It was suggested that future researches should involve multiple evaluators to eliminate any examiner bias and increase the reliability of the research.

There is no agreement on the number and location of measuring sites that should be evaluated during measuring of marginal accuracy, although, this is one very important parameter because the marginal gap values can fluctuate greatly within the same sample.56

The profile meter is an accurate instrument for measurement of marginal gap but other more accurate methods should be discovered to evaluate marginal accuracy.13 X-ray micro tomography is a relatively more accurate and nondestructive method for measurement of marginal gaps as it allows easier recognition and measurement of critical distances but is not used by most researchers.56,57 It is recommended that future researches be conducted on the subject with the help of this instrument.

CONCLUSION

Shoulder or chamfer finishing lines can be selected for all ceramic crowns bonded to prepared teeth. There is no conclusive evidence about which marginal design is preferred over the other as both the margins have displayed different results in the studies and more research is suggested to evaluate their viability. The accuracy in measurements of the marginal fit depends on two factors.

1 The angle of the surface of the crown margin.

2 The profile readings during evaluation by the evaluator.

REFERENCES

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2 Bodereau EF. Aesthetic All-ceramic Restorations. CAD-CAM System. Int. J. Odontostomat. 2013; 7(1): 139-47.

3 Yucel MT, Aykent F, Avunduk MC. In vitro evaluation of the marginal fit of different all-ceramic crowns. Journal of Dental Sciences 2013; 8(3): 225-30.

4 Limkangwalmongkol P, Kee E, Chiche GJ, Blatz MB. Comparison of marginal fit between all-porcelain margins versus alumina-supported margin on Procera Alumina crowns. J Prosthodont 2009; 18(2): 162-66.

5 Donovan T, Prince J. An analysis of margin configurations for metal-ceramic crowns. J Prosthet Dent. 1985; 53(2): 153-57.

6 Chatterjee U. Margin designs for esthetic restoration: An overview. Journal of Advanced Oral Research 2012; 3(1): 7-12.

7 Kokubo Y, Ohkubo C, Tsumita M, Miyashita A, Vult von Steyern P, Fukushima S.. Clinical marginal and internal gaps of Procera All Ceram crowns. J Oral Rehabil. 2005; 32(7): 526-30.

8 Tsitrou EA, Northeast SE, van Noort R. Evaluation of the marginal fit of three margin designs of resin composite crowns using CAD/CAM. J Dent. 2007; 35(1): 68-73.

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10 Polansky R, Heschl A, Arnetzl G, Haas M, Wegscheider W. Comparison of the marginal fit of different all-ceramic and metal-ceramic crown systems: an in vitro study. International Journal of Stomatology and Occlusion medicine 2010; 3(2):106-10.

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12 Baig MR, Tan KB, Nicholls JI. Evaluation of the marginal fit of a zirconia ceramic computer-aided machined (CAM) crown system. J Prosthet Dent 2010; 104(4): 216-27.

13 Limkangwalmongkol P, Chiche GJ, Blatz MB. Precision of fit of two margin designs for metal-ceramic crowns. J Prosthodont. 2007; 16(4): 233-37.

14 Schaefer O, Watts DC, Sigusch BW, Kuepper H, Guentsch A. Marginal and internal fit of pressed lithium disilicate partial crowns in vitro: A three-dimensional analysis of accuracy and reproducibility. Dent Mater 2012; 28(3): 320-26.

15 Bronson MR, Lindquist TJ, Dawson DV. Clinical acceptability of crown margins versus marginal gaps as determined by pre-doctoral students and prosthodontists. J Prosthodont 2005; 14(4): 226-32.

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17 WAlstmanna B, Rehmanna P, Trostb D, Balkenhola M. Effect of different retraction and impression techniques on the marginal fit of crowns. Journal of Dentistry 2008; 36(7): 508-12.

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20 Sulaiman F, Chai J, Jameson LM, Wozniak WT. A comparison of the marginal fit of In-Ceram, IPS Empress, and Procera crowns. Int J Prosthodont 1997; 10(5): 478-84.

21 McLean JW, Von Fraunhofer JA. The estimation of cement film thickness by an in vivo technique. Br Dent J 1971; 131(3): 107-11.

22 Holmes JR, Bayne SC, Holland GA, Sulik WD. Considerations in measurement of marginal fit. J Prosthet Dent 1989; 62(4): 405-08.

23 Mitchell CA, Pintado MR, Douglas WH. Nondestructive, in vitro quantification of crown margins. J Prosthet Dent 2001; 85(6): 575-84.

24 Miura S, Inagaki R, Kasahara S, Yoda M. Fit of zirconia all-ceramic crowns with different cervical margin designs, before and after porcelain firing and glazing. Dent Mater J. 2014; 33(4): 484-89.

25 Euan R, Figueras-Alvarez O, Cabratosa-Termes J, Brufau-de BarberA M, Gomes-Azevedo S. Comparison of the marginal adaptation of zirconium dioxide crowns in preparations with two different finish lines. J Prosthodont 2012; 21(4): 291-95.

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28 Komine F, Iwai T, Kobayashi K, Matsumura H. Marginal and internal adaptation of zirconium dioxide ceramic copings and crowns with different finish line designs. Dent Mater J 2007; 26(5): 659-64.

29 Souza RO, Ozcan M, Pavanelli CA, Buso L, Lombardo GH, Michida SM, Mesquita AM, Bottino MA. Marginal and internal discrepancies related to margin design of ceramic crowns fabricated by a CAD/CAM system. J Prosthodont 2012; 21(2): 94-100.
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Title Annotation:standards of ceramic restorations
Author:Ovais, Nida; Ahmed, Bilal; Azad, Azad Ali; Aslam, Ayesha
Publication:Pakistan Oral and Dental Journal
Article Type:Report
Date:Jun 30, 2015
Words:3050
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