Abstract
Objectives
The objectives of the present study were to (1) retrospectively evaluate documented cases of ceramic and composite endocrowns performed using immediate dentin sealing (IDS); (2) correlate failures with clinical parameters such as tooth preparation characteristics and occlusal parameters.
Methods
99 documented cases of endocrowns were evaluated after a mean observation period of 44.7 ± 34.6 months. A classification of restorations was established in function of the level of damage of residual tooth tissues after preparation, from 1 to 3. Evaluation was performed according to FDI criteria and endodontic outcomes were analyzed. Occlusal risk factors were examined and fractographic analysis was performed in case of fracture.
Results
48.4% of patients were shown to present occlusal risk factors. 75.8% of restorations were Class 3 endocrowns. 56.6% were performed on molars, 41.4% on premolars and 2.0% on canines. 84.8% were performed in lithium-disilicate glass-ceramic and 12.1% in Polymer-Infiltrated Ceramic Network (PICN) material. The survival and success rates of endocrowns were 99.0% and 89.9% respectively, while the 10-year Kaplan-Meier estimated survival and success rates were 98.8% and 54.9% respectively. Ten failures were detected: periodontal disease (n = 3), endocrown debonding (n = 2), minor chipping (n = 2), caries recurrence (n = 2) and major fractures (n = 1). Due to the reduced amount of failures, no statistical correlation could be established with clinical parameters.
Conclusions
Endocrowns were shown to constitute a reliable approach to restore severely damaged molars and premolars, even in the presence of extensive coronal tissue loss or occlusal risk factors, such as bruxism or unfavorable occlusal relationships.
Clinical significance
Practitioners should consider the endocrown instead of the post and core approach to restore severely damaged non-vital posterior teeth. This minimally invasive solution reduces the risk of catastrophic failures and is easily performed. The use of IDS procedure and lithium-disilicate glass-ceramic as prosthesis material gave very good results.
1
Introduction
Nowadays, the development of adhesive dentistry has reduced the need of posts and cores to restore endodontically non-vital posterior teeth with extensive coronal tissue loss. Indeed, it has been more than 20 years since Pissis introduced the “mono-block porcelain technic” in which the retention of the restoration lies on the use of adhesive cementation and macromechanical retention in canal entrance. In 1999, Bindl and Mormann introduced the term “endocrown” to describe a mono-block ceramic crown bonded to a depulped posterior tooth. This minimally invasive approach is easily performed, less expensive and most of all could reduce failures related to post placement . Yet, surprisingly few in vitro and clinical studies have been dedicated to those restorations. Moreover, there is no exact definition of the endocrown, particularly regarding the amount of residual tooth tissues and the specific characteristics of the tooth preparation. Some authors define an endocrown as a preparation with “a circular equigingival butt margin and a central retention cavity of the entire pulp chamber” , others as “a total porcelain crown fixed to depulped posterior tooth, which is anchored to the internal portion of the pulp chamber and to the cavity margins” , while for Bernhart et al. , a preparation with a height reduction of only 2 mm is considered as an endocrown, if the tooth is non vital and there is at least a 2 mm of height retention in the pulp chamber. However, the amount of residual tooth walls, the creation of a peripheral butt margin (which can promote a ferrule effect) or the use of the pulp chamber cavity as macromechanical retention are variables which could influence restoration retention and performance.
Since endocrown retention mainly lies on bonding, it is crucial to use prosthetic materials, which can be resin bonded to tooth tissues. Clinical studies about endocrowns usually refer to glass-ceramic materials, particularly feldspathic ceramic (Vita Mark II, Vita Zahnfabrik, Bad Säckingen, Germany) manufactured with a computer-aided design and manufacturing (CAD-CAM) process (Cerec system, Sirona, Benscheim, Germany) , except Bindl et al. who used In Ceram alumina or In Ceram spinell (Vita Mark II, Vita Zahnfabrik, Bad Säckingen, Germany) . Indeed glass-ceramic materials such as feldspathic ceramic are etchable ceramics, which can effectively bond to resin cement through the application of hydrofluoric acid and silane on their surface . Currently, the range of materials available for endocrowns also comprises lithium-disilicate reinforced glass-ceramics, which are popular materials with an excellent short clinical background for single unit restorations and a higher flexural strength than feldspathic ceramic . Yet, there are no clinical studies about the use of lithium-disilicate glass-ceramic for endocrowns. On the other hand, CAD-CAM composites appeared on the market a few years ago and are also recommended for single unit bonded restorations. CAD-CAM composites constitute a growing family of materials, which can be divided into two sub-classes: dispersed filler and Polymer Infiltrated Ceramic Network (PICN) materials . Particularly, PICNs (Vita Enamic, VITA, Vita Zahnfabrik, Bad Säckingen, Germany) represent a promising class of materials composed of a partially sintered glass-ceramic block (75% vol.) secondarily infiltrated with dimethacrylate monomers, which are polymerized under high temperature and high pressure . Currently there are very limited data about bonding properties and clinical behavior of current CAD-CAM composites. Finally, immediate dentin sealing (IDS) with a bonding agent directly after tooth preparation has been recommended for indirect bonded restorations . It is intended to improve bond strength, marginal adaptation and decrease bacterial leakage . Those arguments are based on in vitro studies and to author’s knowledge there are no clinical data about IDS.
Consequently, the objectives of the present study were to (1) retrospectively evaluate the documented cases of lithium-disilicate reinforced glass-ceramic, artisanal composite and CAD-CAM composite endocrowns performed in the Department of Fixed Prosthodontics of the University of Liège using the IDS procedure; (2) correlate failures with clinical parameters such as residual tooth tissue amount, tooth preparation characteristics and occlusal parameters.
2
Materials and methods
2.1
Study design
This is a retrospective record evaluation and a clinical examination of patients treated with posterior endocrowns, using IDS in the bonding protocol. The study received approval from the Ethics Committee of the University of Liège (Comité d’Ethique Hospitalo-Facultaire Universitaire de Liège, number B7072201524093, reference 2015/46). The patients were recruited in the Department of Fixed Prosthodontics of the University of Liege and were treated by four experienced practitioners or pre-graduated students. Only cases documented with photos and/or master casts highlighting the residual tooth tissue amount and the tooth preparation characteristics were included in this study. 94 patients (n = 137 endocrowns) were recalled. They were informed of the purposes of the study and consent was obtained before examinations. The endocrowns were performed during the follow-up period from July 2004 to July 2015.
2.2
Endocrown classification ( Fig. 1 )
Three classes of endocrowns were established on the basis of residual tooth tissue amount after preparation. Determination of the endocrown class was based on the analysis of clinical pictures and/or master casts by two independent evaluators. In case of discrepancy, an agreement was found between evaluators. Class 1 describes a tooth preparation where at least two cuspal walls have a height superior to the half of their original height. Class 2 describes a tooth preparation where maximum one cuspal wall has a height superior to the half of its original height. Class 3 describes a tooth preparation where all cuspal walls are reduced for more than the half of their original height ( Fig. 1 ). Moreover, the presence of a buccal chamfer or an extension in the pulp chamber were registered.
2.3
Patient record registrations
Specific data were collected regarding the following parameters: sex, age, prosthetic material brand, bonding protocol and associated products, and antagonistic teeth characteristics.
2.4
Clinical evaluation of restorations
Two independent evaluators clinically evaluated restorations following criteria of the World Dental Federation (FDI) . Three dimensions, which represent 18 items, are described: esthetic, functional and biological. The functional dimension includes the patient-reported satisfaction. Each item is assessed on a 5-point Likert scale (1 corresponding to an excellent restoration and 5 corresponding to a restoration that needs to be replaced). In case of discrepancy, an agreement was found between evaluators to determine the final score. Scores 4 and 5 were considered as failure. Additionally, periodontal probing of the restored tooth was performed in order to detect root fracture.
2.5
Endodontic evaluation
On the basis of pre-op and follow-up radiographs examination, the presence of a periapical lesion before treatment and at follow-up was detected. The realization of an endodontic retreatment before prosthodontic procedure was recorded. At follow-up, percussion pain of the restored tooth was tested.
2.6
Occlusal risk factors evaluation
Occlusal relationships were characterized as favorable or unfavorable based on the clinical examination by the two independent evaluators. Class III or class II.2 malocclusion, anterior or posterior crossbite, edge to edge or open bite, were considered as unfavorable occlusal relationships. The presence of parafunctional habits was recorded if the patient related grinding or clenching habits, masticatory muscle discomfort, or if abnormal wear facets were observed on teeth. The use of an occlusal nightguard was noted. Finally, when a material fracture was detected, the occlusal contact points and facets were examined in order to determine whether the fracture was located on an occlusal contact or guidance.
2.7
Replica preparation and fractographic analysis
If a fracture of the prosthetic material was detected, a double-mix impression of the endocrown surface was performed with a high- and a low-viscous A-silicone impression material. The fractured surface was first cleaned with a cotton pellet and alcohol and was then rinsed and thoroughly air-dried . The replicas were produced using a quadrafunctional hydrophilic siloxane impression material (Aquasil ULV, Dentsply De Trey, Konstanz, Germany), the low viscosity material being syringed onto the fractured surface and over the occlusal surface of the endocrown. The impressions were cast with filled polyurethane (Alpha Die MF, Schütz, Rosbach, Germany). After setting, the model was sectioned to isolate the restoration replica to be analyzed, which was gold-coated for scanning electron microscopy (SEM). The fractographic analysis was performed using an Environmental Scanning Electron Microscope with a Field Emission Gun (ESEM-FEG XL-30, FEI, Hillsboro, Oregon USA) used in high vacuum mode. The interpretation of fracture patterns was based on the descriptions by Scherrer et al. , particularly to determine the origin and direction of the crack propagation.
2.8
Statistical analysis
Results are presented as means and standard deviations (SD) or as medians and quartiles (Q1 and Q3) for continuous variables and as frequency tables for categorical variables. Survival of dental crowns was represented by Kaplan-Meier curve. Results were considered significant at the 5% critical level (P < 0.05). Statistical calculations always used the maximum number of data available and were carried out with the SAS (SAS Institute, Cary, NC, version 9.4) package and R (version 3.2.3).
2
Materials and methods
2.1
Study design
This is a retrospective record evaluation and a clinical examination of patients treated with posterior endocrowns, using IDS in the bonding protocol. The study received approval from the Ethics Committee of the University of Liège (Comité d’Ethique Hospitalo-Facultaire Universitaire de Liège, number B7072201524093, reference 2015/46). The patients were recruited in the Department of Fixed Prosthodontics of the University of Liege and were treated by four experienced practitioners or pre-graduated students. Only cases documented with photos and/or master casts highlighting the residual tooth tissue amount and the tooth preparation characteristics were included in this study. 94 patients (n = 137 endocrowns) were recalled. They were informed of the purposes of the study and consent was obtained before examinations. The endocrowns were performed during the follow-up period from July 2004 to July 2015.
2.2
Endocrown classification ( Fig. 1 )
Three classes of endocrowns were established on the basis of residual tooth tissue amount after preparation. Determination of the endocrown class was based on the analysis of clinical pictures and/or master casts by two independent evaluators. In case of discrepancy, an agreement was found between evaluators. Class 1 describes a tooth preparation where at least two cuspal walls have a height superior to the half of their original height. Class 2 describes a tooth preparation where maximum one cuspal wall has a height superior to the half of its original height. Class 3 describes a tooth preparation where all cuspal walls are reduced for more than the half of their original height ( Fig. 1 ). Moreover, the presence of a buccal chamfer or an extension in the pulp chamber were registered.
2.3
Patient record registrations
Specific data were collected regarding the following parameters: sex, age, prosthetic material brand, bonding protocol and associated products, and antagonistic teeth characteristics.
2.4
Clinical evaluation of restorations
Two independent evaluators clinically evaluated restorations following criteria of the World Dental Federation (FDI) . Three dimensions, which represent 18 items, are described: esthetic, functional and biological. The functional dimension includes the patient-reported satisfaction. Each item is assessed on a 5-point Likert scale (1 corresponding to an excellent restoration and 5 corresponding to a restoration that needs to be replaced). In case of discrepancy, an agreement was found between evaluators to determine the final score. Scores 4 and 5 were considered as failure. Additionally, periodontal probing of the restored tooth was performed in order to detect root fracture.
2.5
Endodontic evaluation
On the basis of pre-op and follow-up radiographs examination, the presence of a periapical lesion before treatment and at follow-up was detected. The realization of an endodontic retreatment before prosthodontic procedure was recorded. At follow-up, percussion pain of the restored tooth was tested.
2.6
Occlusal risk factors evaluation
Occlusal relationships were characterized as favorable or unfavorable based on the clinical examination by the two independent evaluators. Class III or class II.2 malocclusion, anterior or posterior crossbite, edge to edge or open bite, were considered as unfavorable occlusal relationships. The presence of parafunctional habits was recorded if the patient related grinding or clenching habits, masticatory muscle discomfort, or if abnormal wear facets were observed on teeth. The use of an occlusal nightguard was noted. Finally, when a material fracture was detected, the occlusal contact points and facets were examined in order to determine whether the fracture was located on an occlusal contact or guidance.
2.7
Replica preparation and fractographic analysis
If a fracture of the prosthetic material was detected, a double-mix impression of the endocrown surface was performed with a high- and a low-viscous A-silicone impression material. The fractured surface was first cleaned with a cotton pellet and alcohol and was then rinsed and thoroughly air-dried . The replicas were produced using a quadrafunctional hydrophilic siloxane impression material (Aquasil ULV, Dentsply De Trey, Konstanz, Germany), the low viscosity material being syringed onto the fractured surface and over the occlusal surface of the endocrown. The impressions were cast with filled polyurethane (Alpha Die MF, Schütz, Rosbach, Germany). After setting, the model was sectioned to isolate the restoration replica to be analyzed, which was gold-coated for scanning electron microscopy (SEM). The fractographic analysis was performed using an Environmental Scanning Electron Microscope with a Field Emission Gun (ESEM-FEG XL-30, FEI, Hillsboro, Oregon USA) used in high vacuum mode. The interpretation of fracture patterns was based on the descriptions by Scherrer et al. , particularly to determine the origin and direction of the crack propagation.
2.8
Statistical analysis
Results are presented as means and standard deviations (SD) or as medians and quartiles (Q1 and Q3) for continuous variables and as frequency tables for categorical variables. Survival of dental crowns was represented by Kaplan-Meier curve. Results were considered significant at the 5% critical level (P < 0.05). Statistical calculations always used the maximum number of data available and were carried out with the SAS (SAS Institute, Cary, NC, version 9.4) package and R (version 3.2.3).
3
Results
3.1
Clinical data about patients, procedures and endocrowns
Among the 94 patients (n = 137 endocrowns) recalled, 64 (n = 99 endocrowns) agreed to participate in the study. Among them, 38 were women. The mean age was 55.2 ± 12.6 years with a range from 29 to 84 years at the time of examination. 8.1% of endocrowns were performed by pre-graduated students. Data about distribution of restorations in function of endocrown class, localisation and material brand are summarized in Table 1 . Immediate dentin sealing (IDS) procedure was performed in all cases with Optibond FL (Kerr, Bioggio, Swiss), a 3-step etch-and-rinse bonding agent, which was polymerized on dentin directly after preparation. All restorations were bonded with Variolink 2 (Ivoclar, Schaan, Liechtenstein) following manufacturer recommendations and after air abrasion treatment of the IDS with Cojet (3 M, Saint-Paul, USA) followed by the application of Excite DSC (Ivoclar, Schaan, Liechtenstein), a 2-step etch-and-rinse and dual cure bonding agent. Glass-ceramic restoration intaglio was chair-side pretreated as follows: etched with 9.0% hydrofluoric acid (Ultradent, Cologne, Germany) for 20 s, rinsed with water, etched with phosphoric acid (Ultra-Etch, Ultradent, Cologne, Germany) for one minute as an additional surface cleaning procedure, rinsed with water, cleaned in an ultrasonic bath with 90° ethanol for 5 min, dried with an air spray and recovered by a silane layer (Monobond S, Ivoclar, Schaan, Liechtenstein) following manufacturer recommendations. PICN restorations were etched with hydrofluoric acid for 60 s, rinsed with water, cleaned in an ultrasonic bath with 90° ethanol for 5 min, dried with an air spray and recovered by a Monobond S layer, as recommended by manufacturer. Artisanal composite restorations (brand was unknown) were sandblasted with Cojet, rinsed with water, cleaned in an ultrasonic bath with 90° ethanol for 5 min, dried with an air spray and recovered by a Monobond S layer.
