The International Journal of Periodontics & Restorative ... · es and at the Department of Fixed...

The International Journal of Periodontics & Restorative Dentistry

Volume 34, Number 2, 2014

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In recent decades, several types of all-ceramic systems have been de-veloped to satisfy patients’ esthetic demands. All-ceramic materials can be divided into two groups: silica based (feldspathic and glass-ceramics) and polycrystalline ce-ramics (alumina and zirconia).1

Silica-based materials are charac-terized by etchability and translu-cency and ensure optimal esthetics, a natural appearance, and reliable clinical performances.2 Conversely, polycrystalline ceramics are char-acterized by outstanding mechani-cal properties.3 Such materials are mostly indicated to produce �xed dental prostheses (FDPs) with four or more units in anterior and poste-rior areas. The low translucency of polycrystalline materials facilitates the treatment of discolored abut-ments.3 Data on strength, color stability, precision of �t, and clinical performance of alumina and zirco-nia are available in the literature.4–7

1Private Practice, Cattolica, Italy.2 Professor and Chair, University “Federico II” of Naples, Naples, Italy.

3Private Practice, Rome, Italy.4Private Practice, Castagnola delle Lanze, Italy.5Private Practice, Padova, Italy.6Private Practice, Brescia, Italy.

7 Teaching and Research Assistant, University “Federico II” of Naples, Naples, Italy.

Correspondence to: Dr Giacomo Fabbri, Cattolica, Italy, Via del Porto 17 Cattolica (Rimini), 47841 Italy; fax + 39 0541 833322; email: [email protected].

©2014 by Quintessence Publishing Co Inc.

Giacomo Fabbri, DDS1/ Fernando Zarone, MD, DDS2 Gianluca Delli�corelli, DDS3/Giorgio Cannistraro, DDS4 Marco De Lorenzi, DDS5/Alberto Mosca, DDS6 Roberto Sorrentino, DDS, MSc, PhD7

This study aimed to assess the clinical performance of lithium disilicate restorations supported by natural teeth or implants. Eight hundred sixty lithium disilicate adhesive restorations, including crowns on natural teeth and implant abutments, veneers, and onlays, were made in 312 patients. Parafunctional patients were included, but subjects with uncontrolled periodontitis and gingival in�ammation were excluded. Veneers up to 0.5 mm thick were luted with �owable composite resin or light curing cements, while dual-curing composite systems were used with veneers up to 0.8 mm thick. Onlays up to 2 mm in thickness were luted with �owable composite resins or dual-curing composite cements. Crowns up to 1 mm in thickness were cemented with self-adhesive or dual-curing resin cements. The observational period ranged from 12 to 72 months, with a mean follow-up of 3 years. The mechanical and esthetic outcomes of the restorations were evaluated according to the modi�ed California Dental Association (CDA) criteria. Data were analyzed with descriptive statistics. Twenty-six mechanical complications were observed: 17 porcelain chippings, 5 fractures, and 4 losses of retention. Structural drawbacks occurred mainly in posterior segments, and monolithic restorations showed the lowest number of mechanical complications. The clinical ratings of the successful restorations, both monolithic and layered, were satisfactory according to the modi�ed CDA criteria for color match, porcelain surface, and marginal integrity. The cumulative survival rates of lithium disilicate restorations ranged from 95.46% to 100%, while cumulative success rates ranged from 95.39% to 100%. All restorations recorded very high survival and success rates. The use of lithium disilicate restorations in �xed prosthodontics proved to be effective and reliable in the short- and medium-term. (Int J Periodontics Restorative Dent 2014;34:XX–XX. doi: 10.11607/prd.1769)

Clinical Evaluation of 860 Anterior and Posterior Lithium Disilicate Restorations: Retrospective Study with a Mean Follow-up of 3 Years and a Maximum Observational Period of 6 Years


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Zirconia core fractures were not re-ported in three-unit FDPs.8,9 On the contrary, chipping of the veneering ceramics was described as the most frequent complication: chipping rates ranging from 8% to 25% after 24 to 38 months were observed for three-unit posterior FDPs.8,9

Limited clinical data on the reli-ability of all-ceramic single crowns are available.10 Clinical retrospec-tive studies showed excellent per-formances of alumina crowns in anterior areas and good rates in posterior segments.5,11 In 2006, a pressable lithium disilicate glass-ceramic (IPS e.max Press, Ivoclar Vivadent) with improved physical properties and translucency was developed. Restorations can be produced either with a core subse-quently veneered with dedicated glass-ceramic �uoroapatite or in ful-ly anatomical restorations and then stained. More recently, a lithium di-silicate glass-ceramic designed for computer-aided design/computer-assisted manufacture (CAD/CAM) (IPS e.max Cad, Ivoclar Vivadent) was introduced, and preliminary investigations showed excellent biomechanic characteristics.7 Be-cause of its high strength (�400 MPa), etchability, translucency, and optimal esthetics, this material of-fers versatile applications and can be used in several types of restora-tions, ensuring a minimally invasive approach, excellent function, and esthetics. Lithium disilicate glass-ceramic represents a clinical option in the prosthetic treatment of single restorations such as veneers, inlays, onlays, and crowns. Monolithic res-torations with a staining technique

can be used to restore posterior segments.7,12–15 The same approach is paramount in anterior areas to manage extremely reduced thick-nesses, preserving as much dental tissue as possible and often avoid-ing preprosthetic endodontic treat-ments. Acid-etching techniques and resin luting procedures allow clini-cians to produce restorations with excellent clinical performances.16,17 Due to its high �exural strength, IPS e.max can be used for three-unit FDPs, particularly in anterior seg-ments where esthetics represent a fundamental parameter.15,18

CAD/CAM technologies pro-ducing zirconia and titanium frame-works have increasingly gained popularity in implant dentistry, combining optimal biologic and mechanical characteristics19,20 and showing values of �t comparable with those of conventional super-structures.20,21 Zirconia and titanium are generally used to produce cus-tomized abutments22; in such cas-es, lithium disilicate single crowns and three-unit FDPs can be used to �nalize the restoration. Titanium frameworks are usually indicated for full-arch prostheses using ve-neering acrylic or composite resin materials; the most common com-plication is chipping of the veneer-ing materials.23 Zirconia frameworks represent a promising restorative option for implant single crowns and FDPs.24–27 However, the clinical success of zirconia implant restora-tions appears to be limited by chip-ping of the veneering ceramic.25–27

The combination of lithium di-silicate restorations with zirconia or titanium frameworks represents a

valid option to combine mechani-cal effectiveness with excellent es-thetics, improving the long-term clinical outcomes of implant pros-theses. The adhesion between lithium disilicate and zirconia or titanium can be performed using resin cements.28

The present retrospective study aimed at assessing the clinical per-formance of anterior and posterior lithium disilicate restorations sup-ported by either natural teeth or implants. This observational analy-sis evaluated both the mechanics and esthetics of the prostheses over a maximum period of 6 years.

Method and materials

Study population

Between June 2006 and Decem-ber 2010, six expert prosthodon-tists made 860 lithium disilicate restorations in 312 patients (143 men, age range: 19 to 61 years; 169 women, age range: 19 to 71 years). Patients were in need of different prosthetic therapies and were selected from consecutive patients both at the authors’ of�c-es and at the Department of Fixed Prosthodontics of the University “Federico II” of Naples, Italy. The Ethical Committee of the university provided institutional review board approval, and all patients signed a written consent form to participate in the study.

The following inclusion criteria for abutment teeth were adopted9: good oral hygiene, periodontally healthy, vital or endodontically


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treated to a clinically sound state, and opposing natural teeth or �xed prostheses.

Patients not ful�lling the inclu-sion criteria were excluded from the study. All patients were in good general health, and 34% were smokers (more than 5 cigarettes per day). The gingival health was main-tained during the study period.

According to patients’ needs, single crowns on both teeth and implants and veneers and onlays were made in anterior and posteri-or areas as follows: 480 crowns (329 maxillary, 151 mandibular), 318 ve-neers (203 maxillary, 115 mandibu-lar), and 62 onlays (21 maxillary and 41 mandibular) (Table 1); 261 pros-theses were placed in patients with parafunctions (30.3%). The restora-tions were fabricated using pressed lithium disilicate using both mono-lithic and layered techniques.

Patients with at least a 1-year follow-up were recalled for clinical and radiologic assessments. The observational period ranged from 12 to 72 months, with a mean fol-low-up of 3 years.

Veneers

A total of 318 veneers were made (203 in the maxilla and 115 in the mandible) (Table 2). Tooth prepa-rations were performed with a slight chamfer with a depth of 0.2 to 0.8 mm, an axial reduction of 0 to 0.8 mm, and an incisal reduc-tion of 0 to 1.5 mm in relation to the wax-up and the presence of discoloration on teeth. Transparent silicone templates derived from the wax-up were used to optimize the preparation.29 The axial reduc-tion was achieved using tapered

round-ended burs, preserving as much enamel as possible, to keep the �nish lines within enamel and achieve the best long-term reten-tion.30 The interproximal contact points between teeth were opened only in the presence of Class III composite restorations or in clini-cal situations such as diastema or interproximal black triangles. A palatal chamfer was made in 56 ve-neers, while a butt joint was made in 262 restorations. The buccal thickness ranged from 0.2 to 0.8 mm in the cervical third, 0.2 to 1.2 mm in the middle third, and 0.3 to 0.9 mm in the incisal third. Centric contacts at the interface were pre-vented through the localization of opposing contacts.29 The margins were preferably located supragin-givally, thus resulting in simpli�ed impression taking and evaluation of marginal adaptation while help-

Table 1 Descriptive characteristics of the study groups

GroupFollow-up range

(mo)Mean follow-up

(mo)Cumulative

survival rate (%)Cumulative

success rate (%)

Anterior crowns Veneered (n = 209)Monolithic (n = 22)

24–72 37.3 98.57 95.46

97.61 95.46

Posterior crowns Veneered (n = 65)Monolithic (n = 132)

12–61 33.4 96.92 96.21

95.39 96.21

Implant crowns Veneered (n = 7)Monolithic (n = 45)

12–61 28.3 100 97.78

100 97.78

Anterior veneers Veneered (n = 239)Monolithic (n = 40)

12–72 42.1 97.91 100

96.24 100

Posterior veneers Veneered (n = 26)Monolithic (n = 13)

24–61 37.5 100 100

100 100

Onlays Veneered (n = 16)Monolithic (n = 46)

12–57 32.5 100 97.83

100 97.83


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ing to maintain periodontal health. When the contour of the restora-tion needed to be changed, the margins were located at the gingi-val crest or slightly into the crevice. Speci�cally, 53 restorations were monolithic and 265 were layered. All veneers were cemented adhe-sively (Fig 1). The ceramic restora-tions were etched for 20 seconds with 4.5% hydro�uoric acid (IPS ce-ramic gel, Ivoclar Vivadent; Porce-lain Etch, Ultradent). The acid was then washed with water and dried.

A silane agent (Monobond S, Ivo-clar Vivadent; Ceramic Primer, 3M ESPE) was applied and blown dry on the veneer. Rubber dam was used for 139 veneers. In the re-maining 179 restorations, a gingival cord (N. 000 Ultrapak, Ultradent) was placed into the sulcus prior to luting. Concurrently, the tooth surface was etched for 30 seconds with 37% orthophosphoric acid gel (Ultra-Etch, Ultradent). After water rinsing of the tooth surface for 30 seconds, a bonding agent (Opti-

bond FL, Kerr) was applied to both the prepared tooth and the inter-nal surface of the veneers; a dentin primer (Optibond FL, Kerr) was ap-plied only in areas of exposed den-tin. Finally, luting procedures were performed as follows: veneers up to 0.5 mm in thickness were luted using �owable composites (Gradia Direct Flow, GC; Tetric EvoFlow, Ivoclar Vivadent) or light-curing ce-ment (Variolink Veneer, Ivoclar Viva-dent), while restorations up to 0.8 mm in thickness were cemented

Table 2 Anatomical distribution of lithium disilicate restorations

Teeth

Distribution of restored teeth Distribution of restored teeth

Layered veneers Monolithic veneers Layered crowns Monolithic crowns Layered onlays Monolithic onlays

Maxilla Mandible Maxilla Mandible Maxilla Mandible Maxilla Mandible Maxilla Mandible Maxilla Mandible

Central incisors 64 27 13 2 43 3 12 4 – – – –

Lateral incisors 49 27 9 2 47 3 11 4 – – – –

Canines 41 24 10 4 28 9 8 11 – – – –

First premolars 12 8 5 4 40 18 28 23 2 2 8 3

Second premolars 5 8 2 2 38 23 29 29 3 1 8 8

First molars – – – – 13 8 17 10 2 2 3 7

Second molars – – – – 4 4 9 4 2 2 2 7

Total 171 94 39 14 213 68 114 85 9 7 21 25

Fig 1 Rehabilitation of the maxillary anterior teeth with six lithium disilicate veneers. (a) Preoperative view. (b) Five-year follow-up.


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with dual-curing composite sys-tems (Variolink II, Ivoclar Vivadent). Excess cement was removed with a brush and dental �oss interproxi-mally. The margins of the veneers were covered with glycerin gel, and resin luting agents were light polymerized for 30 seconds from each side. The margins were then �nished with a plastic scaler to re-move excess resin. The occlusal contacts were carefully evaluated and balanced.

Tooth-supported single crowns

A total of 428 tooth-supported single crowns were made (299 in the maxilla and 129 in the man-dible) (Table 2). Tooth preparation was performed following the di-agnostic wax-up. A general 0.3- to 1.0-mm overall reduction was per-formed, with the exception of the incisal/occlusal areas, which were

reduced by 1.5 mm. As to the mar-ginal design, a 0.4- to 1-mm slight circumferential chamfer prepara-tion was performed, with rounded internal angles. The taper of the preparations ranged from 5 to 10 degrees, depending on the abut-ment length.31 In posterior areas, the margins were located supra- or equigingivally to preserve enamel, facilitate impression making, and aid evaluation of marginal adapta-tion. In anterior areas, the margin was located at the gingival crest or slightly into the sulcus, depending on esthetic demands.

The thickness of the restora-tions ranged from 0.3 to 1.0 mm on interproximal and axial walls; the minimum thickness was 1.5 mm on the occlusal/incisal surfaces to achieve proper biomechanics. On a total of 428 single crowns (231 anterior and 197 posterior), 407 restorations were pressed (274 layered, 154 monolithic). Among these, 21 crowns were fabricated with CAD/CAM (8 layered and 13 monolithic). All restorations were cemented adhesively using self-adhesive (RelyX Unicem, 3M ESPE) or dual-curing resin cements (Mul-tilink Automix, Ivoclar Vivadent; Variolink II, Ivoclar Vivadent) in accordance with manufacturers’ instructions. The prepared teeth were isolated with a gingival cord (N. 000 Ultrapak), and the adhesive cementation was performed as previously described. The clinical conditions allowed for the cemen-tation of 68 crowns with rubber dam. The occlusion was re�ned, and any adjusted surface was pol-ished (Fig 2).

Onlays

A total of 62 onlays were made (21 in the maxilla and 41 in the mandible) (Table 2). Cavities were prepared with a minimum occlusal thickness of 2 mm, and an inter-proximal buildup was performed to facilitate impression making and cementation (Fig 3). On a total of 62 prostheses, 16 onlays were lay-ered while 64 restorations were produced fully anatomical with sub-sequent stain characterization. As to cementation, the prepared teeth were isolated with rubber dam and �owable composite resin (Gradia Direct Flow; Tetric EvoFlow) or dual-curing composite systems (Variolink II) used in accordance with the pro-tocol previously described. The oc-clusion was re�ned as needed, and any adjusted surface was polished.

Implant-supported restorations

A total of 52 implant-supported restorations on 36 implants were made (30 in the maxilla and 22 in the mandible) (Table 2): 7 cement-ed crowns, 9 screwed crowns, 2 screwed zirconia full-arches (overall 26 restorations), 1 screwed zirco-nia four-unit FDP, and 2 screwed titanium three-unit FDPs. Lithium disilicate crowns were used in com-bination with zirconia or titanium frameworks and CAD/CAM abut-ments. Abutments and frameworks were designed with a minimum crown thickness of 1.5 mm circum-ferentially and at least 2 mm in oc-clusal/incisal aspects. In the case of titanium frameworks, a layer of

Table 2 Anatomical distribution of lithium disilicate restorations

Teeth

Distribution of restored teeth Distribution of restored teeth

Layered veneers Monolithic veneers Layered crowns Monolithic crowns Layered onlays Monolithic onlays

Maxilla Mandible Maxilla Mandible Maxilla Mandible Maxilla Mandible Maxilla Mandible Maxilla Mandible

Central incisors 64 27 13 2 43 3 12 4 – – – –

Lateral incisors 49 27 9 2 47 3 11 4 – – – –

Canines 41 24 10 4 28 9 8 11 – – – –

First premolars 12 8 5 4 40 18 28 23 2 2 8 3

Second premolars 5 8 2 2 38 23 29 29 3 1 8 8

First molars – – – – 13 8 17 10 2 2 3 7

Second molars – – – – 4 4 9 4 2 2 2 7

Total 171 94 39 14 213 68 114 85 9 7 21 25


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opaque mass was applied onto the structures to mask the grayish appearance of the metal. The lith-ium disilicate restorations were ce-mented onto zirconia and titanium using self-adhesive (RelyX Unicem) or dual-curing resin luting agent (Multilink Automix). The crowns were treated as in the case of nat-ural abutment restorations, and no procedures were performed on framework materials. As for screwed restorations, in all cases in which the screw access hole did not take up the buccal wall of the

restoration, an extraoral cementa-tion was carried out, avoiding the risk of subgingival residual cement. The screw access holes were then �lled with composite resin (Fig 4).

Clinical evaluation

Standardized photographs and ra-diographs were taken at all recall appointments. Data forms record-ing the mechanical and esthetic characteristics of each restoration were used as documentation tools.

Patients were examined at clin-ical recalls at least 1 year after ce-mentation and then annually; color match, porcelain surface, marginal discoloration, and integrity were evaluated following the modi-�ed California Dental Association (CDA) criteria.32 The patients’ satis-faction was assessed using nominal scores (nonacceptable, acceptable, good, and excellent). In the case of any mechanical complication, the restoration was considered a failure.

Fig 2 Full-mouth rehabilitation by means of lithium disilicate single crowns. (a) Finished and polished restorations on the master casts. (b) Five-year follow-up of the full-mouth rehabilitation onto natural teeth and implant abutments.

Fig 3 (left) Six-year follow-up of inlay and onlay monolithic restorations.

Fig 4 (below) Maxillary implant-supported full-arch rehabilitation. (a) Zirconia framework with 14 lithium disilicate single crowns. (b) Three-year follow-up.

a b


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Statistical analysis

Descriptive statistics were made with dedicated software (SPSS, ver-sion 17, IBM). The minimum, mean, and maximum follow-ups were calculated for all lithium disilicate prostheses. The cumulative survival and success rates were recorded in all groups using the Kaplan-Meier analysis; all groups were divided into veneered and monolithic pros-theses. Each mechanical complica-tion, both minor (loss of retention, minor chipping) and major (core fracture, support fracture, major chipping), was considered as a sta-tistical event. The log-rank test was performed to compare the survival curves of veneered and monolithic restorations. The level of signi�-cance was set at P = .05.

Results

All prostheses were fabricated by six expert dental technicians ac-cording to the manufacturers’ instructions. A total of 860 restor-ative units were evaluated from a minimum of 12 to a maximum of 72 months in 312 patients.

Veneers

Anterior layered veneers showed cumulative survival and success rates of 97.91% and 96.24%, re-spectively. Anterior monolithic ve-neers showed cumulative survival and success rates of 100% (Table 1). Both posterior layered and monolithic veneers showed cumu-

lative survival and success rates of 100% (Table 1).

Chipping was observed on �ve veneers, all at the maxillary arch. None of the minor cohesive fractures impaired function; the restorations were smoothed and �nished intraorally and remained in situ for further observation.

Core fractures were noted on three veneers, one on a maxil-lary lateral incisor and two in the mandibular anterior segment; they all were layered. All fractured res-torations had ceramic materials in the opposite dentition and re-quired the replacement of the res-torations. The failed veneers were prepared with an incisal butt joint and fractures were observed 8 and 11 months after cementation, re-spectively; the replacements were performed with a new preparation design that involved the lingual aspect as well as a mini-chamfer. Loss of retention was observed on one mandibular veneer; the resto-ration was immediately rebonded and was still in function at the �nal follow-up.

Tooth-supported single crowns

Anterior layered tooth-supported crowns showed cumulative sur-vival and success rates of 98.57% and 97.61%, respectively. Anterior monolithic crowns showed cumu-lative survival and success rates of 95.46% (Table 1). Posterior layered crowns showed cumulative sur-vival and success rates of 96.92% and 95.39%, respectively. Posterior monolithic crowns showed cumu-

lative survival and success rates of 96.21% (Table 1).

Minor cohesive fractures of the veneering ceramic occurred on eight tooth-supported crowns, three in the maxilla and �ve in the mandible; two of these chipped crowns were monolithic, one per arch. Crown chippings occurred mostly in posterior segments (pre-molars and molars); only four of these needed a replacement, while the remaining chipped areas were simply smoothed and �nished. Core failures occurred 7 months after cementation on two maxil-lary crowns on central and lateral incisors in a single patient and required the replacement of the restorations. Both of the fractured restorations had ceramic materi-als in the opposite dentition. Loss of retention was observed on two mandibular crowns; the restora-tions were immediately rebonded and were still in function at the �nal follow-up. One mandibular crown needed root canal therapy because of a pulpitis occurring 18 months after cementation. The endodontic treatment was performed through the crown, and the access hole was then �lled with composite resin; the restoration was considered a fail-ure although it was still in function. Furthermore, one nonvital maxillary premolar restored with a crown was extracted because of root fracture.

Onlays

Layered onlays showed cumula-tive survival and success rates of 100% (Table 1). Monolithic onlays


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showed cumulative survival and success rates of 97.83% (Table 1).

Chipping was noticed on three onlays, all at the mandibular arch. Two of these chipped onlays were monolithic; both restorations were positioned on mandibular second premolars, and opposite denti-tion were represented by a natural tooth in one case and by a ceramic restoration in the other. The dam-aged area was intraorally repaired by means of composite resin. Loss of retention was observed on one maxillary onlay; the restoration was immediately rebonded and was still in function at the �nal follow-up.

Implant-supported restorations

Layered implant crowns showed cu-mulative survival and success rates of 100% (Table 1). Implant-support-

ed monolithic crowns reported cu-mulative survival and success rates of 97.78% (Table 1). Minor cohesive fractures of the veneering ceramic occurred on one monolithic im-plant crown on a maxillary canine. The chipping did not impair func-tion; consequently, the area was smoothed and �nished and the crown remained in situ.

Statistical analysis

Considering any complication as an event, the cumulative survival rates of lithium disilicate resto-rations ranged from 95.46% to 100%, while the cumulative suc-cess rates ranged from 95.39% to 100%, according to Kaplan-Meier survival analysis (Figs 5 to 10, Table 1). The log-rank test that compared the survival curves of veneered and monolithic restorations was not sta-

tistically signi�cant in any research group (P > .05) (Table 3).

Clinical evaluation

The clinical ratings of the success-ful restorations, both monolithic and layered, were satisfactory ac-cording to the modi�ed CDA crite-ria (Table 4). The color match of the monolithic restorations recorded the lowest proportion of A ratings (90.9%) but was considered abso-lutely acceptable both by clinicians and patients. With the exception of the previously reported failed pros-theses, no restoration was rated C or D for any of the evaluation crite-ria. The patient satisfaction scores were mainly excellent for all res-torations; a few prostheses were rated as good and none were re-ported to be nonacceptable or ac-ceptable (Table 5).

Fig 5 Kaplan-Meier graph of complication onset in relation to time for lithium disilicate anterior single crowns.

Fig 6 Kaplan-Meier graph of complication onset in relation to time for lithium disilicate posterior single crowns.

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Cum

ulat

ive

surv

ival

(%)

Veneered anterior crowns

Monolithic anterior crowns

Time to complication (mo)

0 8 12 24 29 36 40 48 60 7235 70

0.995

0.990

0.985

0.975


1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Cum

ulat

ive

surv

ival

(%)

Veneered posterior crowns

Monolithic posterior crowns

0 9 12 24 30 36 48 60 7225 3438 61

33

0.992 0.9840.976

0.9680.9610.969

0.985

0.954


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Monolithic restorations showed the lowest number of mechanical structural complications. No mono-lithic veneer failed. Conversely, three monolithic crowns located on

one implant and two natural teeth were affected by chipping. All failed crowns had ceramic restorations on the opposite dentition; two of these were placed in patients with

parafunctional habits. Unrestor-able fractures were observed only in layered restorations positioned in anterior segments in patients with uncontrolled parafunctions.

Fig 7 Kaplan-Meier graph of complication onset in relation to time for lithium disilicate implant-supported crowns.

Fig 8 Kaplan-Meier graph of complication onset in relation to time for lithium disilicate anterior veneers.

Fig 9 Kaplan-Meier graph of complication onset in relation to time for lithium disilicate posterior veneers.

Fig 10 Kaplan-Meier graph of complication onset in relation to time for lithium disilicate onlays.

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Cum

ulat

ive

surv

ival

(%)

Veneered implant crowns

0.978

Monolithic implant crowns

0 12 24 36 48 60 7261


0.996 0.9880.992

0.9800.984 0.976 0.967 0.963

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Cum

ulat

ive

surv

ival

(%)

Veneered anterior veneers

Monolithic anterior veneers

0 4 8 12 24 36 42 48 60 7210 3943 59 70


1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Cum

ulat

ive

surv

ival

(%)

Veneered onlays

Monolithic onlays

0 12 24 36 43 48 60 7257


1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Cum

ulat

ive

surv

ival

(%)

Veneered posterior veneers

Monolithic posterior veneers


0 12 24 36 48 60 7261


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Table 3 Results of the log-rank test comparing the survival curves

Groups Log-rank P

Veneered anterior crowns vs monolithic anterior crowns 0.381 > .05

Veneered posterior crowns vs monolithic posterior crowns 0.084 > .05

Veneered anterior veneers vs monolithic anterior veneers 1.062 > .05

Veneered posterior veneers vs monolithic posterior veneers 2.004 > .05

Veneered onlays vs monolithic onlays 0.345 > .05

Veneered implant crowns vs monolithic implant crowns 0.154 > .05

Table 4 Frequency distribution of clinical ratings in lithium disilicate restorations according to the modi�ed CDA criteria

Parameter

Modi�ed CDA rating

A B C D

Layered (%)

Monolithic (%)

Layered (%)

Monolithic (%)

Layered (%)

Monolithic (%)

Layered (%)

Monolithic (%)

Color match 97.9 90.9 2.1 7.4 0 1.7 0 0

Porcelain surface

96.7 97.1 3.3 2.9 0 0 0 0

Marginal discoloration

96.7 95.9 3.3 4.1 0 0 0 0

Marginal integrity

98.2 98.7 1.8 1.3 0 0 0 0

Table 5 Patients’ satisfaction scores for lithium disilicate restorations

Satisfaction score

Observational period (mo)

12 < x > 24 24 < x > 36 36 < x > 48 48 < x > 72

Veneers Crowns Onlays Veneers Crowns Onlays Veneers Crowns Onlays Veneers Crowns Onlays

Nonacceptable 0 0 0 0 0 0 0 0 0 0 0 0

Acceptable 0 0 0 0 0 0 0 0 0 0 0 0

Good 0 9 2 4 13 1 15 14 0 0 0 0

Excellent 31 99 10 95 159 25 90 116 22 83 70 2

x = observational period in months.


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Recurrent caries was not detected in any restoration, contour qual-ity was satisfactory, and proximal contacts were well maintained over time.

Discussion

In this study, lithium disilicate res-torations were associated with very high success rates (95.39% to 100% at 72 months), comparable with results reported in previous studies.2,11 Several variables con-tribute to the clinical effectiveness of such restorations; particularly, lithium disilicate prostheses have to be bonded with correct adhesive techniques to achieve the reported success rates. Moreover, the quan-tity and quality of tooth structure is paramount, especially the enamel at the �nish lines: the more the enamel is preserved, the better the adhesion and the more limited ag-ing of the bonding interfaces will be over time.2,17,30 An estimated survival probability of 93.5% after

10 years was reported for porcelain laminate veneers.33 Moreover, a recent systematic review reported that glass-ceramic veneers present an adequate clinical survival for at least 5 years of function with very low complication rates.34

Accordingly to the clinical situ-ations, the authors transferred the concept of adhesion to enamel to improve restoration longevity from veneers to crowns (Fig 11), produc-ing very thin restorations and pre-serving as much enamel as possible.

All fractures and mechani-cal complications occurred in restorations with thicknesses in accordance or even superior to manufacturing instructions but ap-plied on teeth where the majority of supporting substrate was dentin or composite. Conversely, no me-chanical complications were ob-served in restorations cemented on teeth where enamel represented at least 50% of the bonding substrate. As regards technical drawbacks, 63% of mechanical complications (fractures and chipping) were ob-

served on restorations that had porcelain as opponent and 33% of these occurred in patients with parafunctions. The remaining 37% of the mechanical complications were noticed in patients that had natural teeth as antagonist denti-tion and were not affected by brux-ism or clenching. Considering the high rate of parafunctional patients (30.3%) and the high success rate in this study, lithium disilicate may be considered a valid option to treat such patients, especially us-ing monolithic restorations, as they did not show any structural compli-cations.

According to the CDA quality evaluation system, all of the resto-rations were classi�ed as satisfacto-ry for marginal integrity, color, and surface, with the only exception of monolithic crowns and onlays, which did not show an optimal re-sult in color match in some cases (9.1%). Case selection is a crucial factor for achieving natural appear-ance with a monolithic approach, as several variables contribute to

Fig 11 Minimally invasive preparations for lithium disilicate crowns.


14

the successful esthetic of a resto-ration, such as color of the natural abutment, ceramic thickness, cor-rect choice of ingots, and color and value of adjacent teeth.

The combination of lithium di-silicate restorations with zirconia and titanium frameworks or abut-ments showed excellent results in terms of esthetics, function, and loss of retention. Only one mono-lithic crown placed on a zirconia framework was affected by chip-ping 6 days after cementation. This restoration fractured in a patient treated with an implant-supported full-arch prosthesis, and the prema-ture fracture was probably due to an uneven occlusal control in cen-tric relation; the fractured fragment was immediately rebonded with an adhesive technique, occlusion was re�ned, and the crown was still in function after 3 years.

Lithium disilicate technology demonstrates unique features to be used in different clinical situations; the possibility to choose between ingots with different opacity and translucency allows the clinician to select the ideal core, even in cases in which severe discolorations make it very dif�cult to obtain satisfactory esthetics.3 The etchability of lithium disilicate improves the clinical per-formance of adhesive cementa-tion and eases the management of clinical complications. Especially in cases of chipping or fractures, the possibility of applying an effective adhesive by means of the etching technique allows the clinician to re-pair any mechanical complication with easy handling procedures and a favorable prognosis.

As to the study’s limitations, the present investigation is a ret-rospective, clinical, multipractice study; consequently, although the same rigorous approach was re-spected, different operators and several clinical variables (restora-tion type, intraoral distribution, multiunit prostheses in a single pa-tient) could act as confounders in the clinical and statistical results. Considering these limitations, fur-ther in vivo investigations would be necessary to validate the clinical re-liability of lithium disilicate restora-tions in the long-term, con�rming the effectiveness of the proposed prosthetic approach.

Conclusion

According to the results of this study and within its limitations, the use of lithium disilicate in �xed prosthodontics proved to be effec-tive and reliable in the short- and medium-term. The choice of this material may represent a valid op-tion in many clinical situations, offering biologic, technical, and es-thetic advantages.

Acknowledgment

The authors reported no con�icts of interest related to this study.

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