A prospective 15-year evaluation of extensive dentin–enamel-bonded pressed ceramic coverages

Abstract

Objectives

The purpose of this study was to investigate the durability of extensive dentin–enamel-bonded posterior ceramic coverages in a 15 years follow-up.

Methods

All extensive dentin–enamel-bonded posterior partial and complete all-ceramic coverages placed during the period November 1992–December 1998 were included. In 121 patients, 252 coverages (IPS Empress) were placed. The adhesive bonding to dentin and enamel was performed with three 3-step and one 2-step etch and rinse bonding. In 106 restorations the classic Syntac was used in combination with the dual-cured resin composite Variolink. The other restorations were luted with the chemically cured resin composite Bisfil 2B and bonded with 3-step etch and rinse systems, classic Gluma (37), Allbond 2 (57), Syntac (32) or the 2-step etch and rinse system, One step (20). The ceramics were evaluated yearly by modified USPHS criteria during 15 years.

Results

Postoperative sensitivity was registered in 4 patients during bite forces lasting for 2–4 weeks. Fifty-five of 228 coverages (24.1%) failed. The mean observation period of the acceptable coverages was 12.6 years (range 11–15 years). The main reasons for failure were lost restorations (18), ceramic fracture (16), and secondary caries (11). Significant differences in failure rate were observed between the dentin bonding agents but not between the two luting agents. Ceramic coverages placed on non-vital teeth failed in 39% and on vital teeth in 20.9% ( p = 0.014). Logistic regression indicated three significant predictors for failure of the coverages: gender and parafunctional habits of the patient and non-vitality of the tooth.

Significance

The technique investigated showed advantages like less destruction of healthy tissue, and avoiding of endodontic treatment and/or deep cervical placement of restoration margins to obtain retention.

Introduction

The popularity of tooth-colored posterior restorations has increased during the last years because of a growing demand for esthetics and concern about the biocompatibility of amalgam . Applying the adhesive bonding concept, several dental ceramic systems have been used during the last decades for veneer, inlay and onlay restorations . Most ceramic materials can be bonded to the underlying conditioned tooth surface after etching with hydrofluoric acid or ammonium bifluorid, mediated by use of an enamel/dentin bonding system and a resin composite luting material. Acid etching increase surface roughness and wetting of enamel, dentin and ceramic surfaces, which promote mechanical interlocking of resin bonding systems.

Bulk fracture and loss of restoration have been reported as the main reasons of failure in short-term evaluations of inlays and onlays . Leucite-reinforced glass–ceramic inlays showed improved clinical durability compared to fired ceramics . The advantage of bonded ceramics can be expected in the extremely non-retentive coverage situation . Traditional crown preparation techniques will in these cases occasionally result in extensive preparation and/or endodontic treatment in combination with a post and core placement in order to obtain retention. The minimal preparation for the bonded ceramic is less traumatic for the tooth, and pulp vitality can be preserved . There are few preparation design standards for the ideal dentin–enamel-bonded crowns, and Burke showed in vitro no differences between varying degrees of tooth preparation to enhance protection to fracture. The durability of the bonded ceramic will depend on the strength of the bond between tooth, luting system and ceramic and on the inherent strength of the ceramic. The use of chemically cured resin composite cements have been suggested to obtain optimal conversion and decreased stress formation during polymerization .

Few studies report the longevity of dentin–enamel-bonded all-ceramic crowns also defined as “partial or full coverage restorations in which an all-ceramic is bonded to the underlying dentin and any available enamel using a resin luting material” . In a systematic review assessing the 5-year survival rates of single crowns, densily sintered aluminum crowns and reinforced glass–ceramic crowns (Empress) showed survival rates comparable to those seen for porcelain-fused-to-metal (PFM) crowns . The short-term results of the extensive adhesively luted coverages are promising but clinical long-term data are not available . The aim of this study was to investigate the long-term durability of these extensive dentin–enamel-bonded posterior ceramic coverages. In addition the effect of luting cement, bonding system and preparation type was studied. The hypothesis tested was that there was (1) no difference in durability for the ceramic coverage placed with different luting agents and different bonding agents, and (2) no difference in durability between vital and endodontic treated teeth.

Materials and methods

During the period November 1992–December 1998, 262 enamel–dentin-bonded ceramic partial and complete coverages (IPS Empress, Ivoclar, Schaan, Liechtenstein) were placed by four operators in 121 patients, 75 women and 46 men with a mean age of 52 years (range 26–81). The study was randomized in a way that all patients, which did need an extensive posterior all-ceramic restoration, during this period, were included in the study after giving their agreement. No patient or patient group was excluded. The participants were treated on a regular basis at the operator’s Public Dental Health Service clinics in Umeå and Visby, Sweden or the Umeå dental school clinic. The study was approved by the local ethics committee at the University of Umeå. The socio-economic status of the participants was varying from low to high. The reasons for placement were filling- or tooth fracture, secondary caries and replacement of extensive amalgam restorations. Preparations with retention obtained as for conventional metallic crowns by parallel walls and increased height of the walls were not included. The evaluated ceramics were distributed as follows: in the lower arch 20 premolars and 120 molars, in the upper arch 44 premolars and 68 molars. All teeth were in occlusion and had at least one proximal contact. The cavities were prepared with butt-joint margins using tapered diamond burs. Sharp internal and external preparation angles were rounded to assure optimum strength of the ceramic. The occlusal thickness of the coverage was at least 1.5 mm. To increase the enamel surface of the preparations minimal shoulder or chamfer preparations were made in part of the teeth in case of enough thickness of the remaining cusp(s). The thickness of the remaining cusp was estimated by the operator to be at risk for fracture or not before a preparation was performed. In case of risk, the remaining cusp(s) were left unprepared. The different forms of preparations evaluated have been reported earlier . Preparation group 1: partial coverage with no shoulder preparation of thin remaining cusp wall (premolars, n = 4; molars, n = 25); Preparation group 2: minimal retentive partial coverage preparation, with a combination of unprepared thin remaining cusp wall(s), and cusps which have been prepared with a shoulder or chamfer (premolars (with one remaining unprepared cusp wall), n = 18; molars (with one or two remaining unprepared cusp walls), n = 70); Preparation group 3: minimal retentive full coverage crowns with shoulder or chamfer preparation of all remaining cusps (premolars, n = 21; molars, n = 63); Preparation group 4: non-retentive endodontic treated teeth, no post and core treatment (premolars, n = 13; molars, n = 14). The numbers given are excluded the drop out restorations. Undercuts were blocked with resin-modified glass ionomer cement or dentin-bonded resin composite material or removed by preparation. A full arch impression was made with a custom-made acrylic resin tray with polyvinyl-siloxane impression materials (President, Coltène, Altstätten, Switzerland; Provil, Bayer, Leverkussen, Germany; or similar materials). Temporary restorations were cemented with an eugenol-free cement (Fermit, Vivadent, Schaan, Liechtenstein; Tempbond-NE, Kerr, Karlsruhe, Germany), or phosphate cement was used to cover the non-retentive preparations. All-ceramics were processed by four experienced technicians. The internal surfaces of the ceramic coverages were etched with hydrofluoric acid in the laboratory. At the second appointment, the operation field was isolated with cotton rolls and a conventional saliva suction device or rubber dam. At the try-in of the coverages, anatomical form, marginal adaptation and color were evaluated. After this the fitting surface of the ceramic restoration was cleaned by a 2–3 s etching with 9.5% hydrofluoric acid or 20 s etching with 36% phosphoric acid to remove any possible contaminants during the try-in like saliva or crevicular fluid. The etching times were based on internal SEM observations of cleaning methods of saliva contaminated with hydrofluoric acid pre-etched ceramic surfaces. A silan coupling agent (Ultradent, Salt lake City, UT, USA; Monobond S, Vivadent) was then applied for 2 min. The teeth were etched with 36% phosphoric acid for 15 s, enamel 10 s followed by an enamel and dentin etch for another 5 s. The 15 s etching time for enamel has been proven to give good longevity in our long-term evaluations, while the 5 s dentin etch is considered to optimize penetration of the demineralized dentin and minimize the risk for nanoleakage. The cavity was thoroughly rinsed with water for 20 s, and carefully dried taking care not to dry out the surface (wet technique introduced by J. Kanca). Four different dentin bonding systems used were applied according to the manufactureŕs instructions. In 106 restorations the classic Syntac adhesive system (Vivadent) was used in combination with a dual-cured resin composite (Variolink, Vivadent) systematically by one of the operators. In the other center restorations were luted with a chemically cured resin composite (Bisfil 2B, Bisco Inc., Itasca IL, USA). Three 3-step etch and rinse systems were used systematically in different time periods by the other operators. 37 were bonded with the Gluma system (original Gluma, Bayer, Dormhagen, Germany), 57 with the Allbond 2 system (Allbond 2, Bisco Inc.), 32 with the classic Syntac system (Vivadent). Another 20 coverages were placed at the end of the study with the simplified 2-step etch and rinse system One step (Bisco Inc.) as a comparison with the 3-step system of the same manufacturer. The distribution of the adhesive systems for the different preparation groups is shown in Table 1 . The luting materials were applied to the fitting surface of the coverages. Excess cement was removed immediately after placement with probe or brush-tips and proximal floss. The dual-cured agent was light cured from all directions for 40–60 s per location (VRC 400, Dentronic, USA; 1000 mW/cm 2 ).

Table 1
Distribution of the adhesive systems for the preparation groups.
Bonding Total
Gluma Allbond 2 Syntac One step
Preparation group
1 1 7 11 10 29
2 10 16 58 4 88
3 20 20 39 5 84
4 2 10 14 1 27
Total 33 53 122 20 228

Occlusion was checked and adjusted as necessary after placement based on a dynamic occlusion. The reconstructions were finished with diamond or carbide finishing burs, polishing stones and the Profin finishing system (Dentatus, Hägersten, Sweden) under water cooling followed by polishing stones.

Evaluation

Each coverage was evaluated after insertion (baseline) and then every year during the follow-up regularly by two calibrated investigators. Evaluations at the Visby clinic were performed by the operator and at the end of the study by two other investigators. All were well familiar with the evaluation system. Disagreement was resolved by consensus. A slight modification of the United States Public Health System (USPHS) criteria was used to evaluate the quality of the restorations ( Table 2 ; ). At the yearly recalls, none of the evaluators did know the adhesive luting technique used for the restorations to be evaluated.

Table 2
Slightly modified USPHS criteria according to van Dijken et al. .
Category Score Criteria
Acceptable Unacceptable
Anatomical form 0 The restoration is continuous with tooth anatomy
1 Slightly under- or over-contoured restoration; marginal ridges slightly undercontoured; contact slightly open (may be self-correcting); occlusal height reduced locally
2 Restoration is undercontoured, dentin or base exposed; contact is faulty, not self-correcting; occlusal height reduced; occlusion affected
3 Restoration is missing partially or totally; fracture of tooth structure; shows traumatic occlusion; restoration causes pain in tooth or adjacent tissue
Marginal adaptation 0 Restoration is continuous with existing anatomic form, explorer does not catch
1 Explorer catches, no crevice is visible into which explorer will penetrate
2 Crevice at margin, enamel exposed
3 Obvious crevice at margin, dentin or base exposed
4 Restoration mobile, fractured or missing
Color match 0 Excellent color match
1 Good color match
2 Slight mismatch in color, shade or translucency
3 Obvious mismatch, outside the normal range
4 Gross mismatch
Marginal discoloration 0 No discoloration evident
1 Slight staining, can be polished away
2 Obvious staining cannot be polished away
3 Gross staining
Surface roughness 0 Smooth surface
1 Slightly rough or pitted
2 Rough, cannot be refinished
3 Surface deeply pitted, irregular grooves
Caries 0 No evidence of caries contiguous with the margin of the restoration
1 Caries is evident contiguous with the margin of the restoration

Postoperative sensitivity was analyzed according with the system used by Borgmeijer et al. . Bite-wing radiographs were taken regularly and in addition color slides were made of selected cases.

The follow-up was considered as a drop out when a participant was not evaluated during 3 years. The restorations were recorded as in function, censored if the participants dropped out, or failed if they were repaired or replaced or the tooth was indicated for extraction.

Statistical analysis

The SPSS (Statistical Package for the Social Sciences; SPSS Inc., Chicago, IL, USA) version 17.1 was used to process the data. The characteristics of the restorations were described by descriptive statistics using frequency distributions of the scores. The number of failed restorations observed during the 15 years and the survival age of all-ceramics vs. gender, age of the participants, luting agent and bonding system, vitality of the teeth, preparation type and modified Ryge criteria scores at the final recalls were tested with non-parametric tests (Kruskal–Wallis, Mann–Whitney, Monte Carlo exact test, univariate analysis of variance test and post hoc Bonferrini test) . Kaplan–Meier was used to describe survival functions. To determine the individual contribution of the different factors to predict the outcome of the bonded coverage, a logistic regression was performed. As dependent variable the failure of the coverage and as predictor variables all factors which could influence the outcome with the 5- and 10-year evaluations as endpoint: gender, parafunctional habits, jaw, tooth type, vitality of the tooth, preparation type, luting agent, bonding agent. The null hypothesis was rejected at 5% level.

Materials and methods

During the period November 1992–December 1998, 262 enamel–dentin-bonded ceramic partial and complete coverages (IPS Empress, Ivoclar, Schaan, Liechtenstein) were placed by four operators in 121 patients, 75 women and 46 men with a mean age of 52 years (range 26–81). The study was randomized in a way that all patients, which did need an extensive posterior all-ceramic restoration, during this period, were included in the study after giving their agreement. No patient or patient group was excluded. The participants were treated on a regular basis at the operator’s Public Dental Health Service clinics in Umeå and Visby, Sweden or the Umeå dental school clinic. The study was approved by the local ethics committee at the University of Umeå. The socio-economic status of the participants was varying from low to high. The reasons for placement were filling- or tooth fracture, secondary caries and replacement of extensive amalgam restorations. Preparations with retention obtained as for conventional metallic crowns by parallel walls and increased height of the walls were not included. The evaluated ceramics were distributed as follows: in the lower arch 20 premolars and 120 molars, in the upper arch 44 premolars and 68 molars. All teeth were in occlusion and had at least one proximal contact. The cavities were prepared with butt-joint margins using tapered diamond burs. Sharp internal and external preparation angles were rounded to assure optimum strength of the ceramic. The occlusal thickness of the coverage was at least 1.5 mm. To increase the enamel surface of the preparations minimal shoulder or chamfer preparations were made in part of the teeth in case of enough thickness of the remaining cusp(s). The thickness of the remaining cusp was estimated by the operator to be at risk for fracture or not before a preparation was performed. In case of risk, the remaining cusp(s) were left unprepared. The different forms of preparations evaluated have been reported earlier . Preparation group 1: partial coverage with no shoulder preparation of thin remaining cusp wall (premolars, n = 4; molars, n = 25); Preparation group 2: minimal retentive partial coverage preparation, with a combination of unprepared thin remaining cusp wall(s), and cusps which have been prepared with a shoulder or chamfer (premolars (with one remaining unprepared cusp wall), n = 18; molars (with one or two remaining unprepared cusp walls), n = 70); Preparation group 3: minimal retentive full coverage crowns with shoulder or chamfer preparation of all remaining cusps (premolars, n = 21; molars, n = 63); Preparation group 4: non-retentive endodontic treated teeth, no post and core treatment (premolars, n = 13; molars, n = 14). The numbers given are excluded the drop out restorations. Undercuts were blocked with resin-modified glass ionomer cement or dentin-bonded resin composite material or removed by preparation. A full arch impression was made with a custom-made acrylic resin tray with polyvinyl-siloxane impression materials (President, Coltène, Altstätten, Switzerland; Provil, Bayer, Leverkussen, Germany; or similar materials). Temporary restorations were cemented with an eugenol-free cement (Fermit, Vivadent, Schaan, Liechtenstein; Tempbond-NE, Kerr, Karlsruhe, Germany), or phosphate cement was used to cover the non-retentive preparations. All-ceramics were processed by four experienced technicians. The internal surfaces of the ceramic coverages were etched with hydrofluoric acid in the laboratory. At the second appointment, the operation field was isolated with cotton rolls and a conventional saliva suction device or rubber dam. At the try-in of the coverages, anatomical form, marginal adaptation and color were evaluated. After this the fitting surface of the ceramic restoration was cleaned by a 2–3 s etching with 9.5% hydrofluoric acid or 20 s etching with 36% phosphoric acid to remove any possible contaminants during the try-in like saliva or crevicular fluid. The etching times were based on internal SEM observations of cleaning methods of saliva contaminated with hydrofluoric acid pre-etched ceramic surfaces. A silan coupling agent (Ultradent, Salt lake City, UT, USA; Monobond S, Vivadent) was then applied for 2 min. The teeth were etched with 36% phosphoric acid for 15 s, enamel 10 s followed by an enamel and dentin etch for another 5 s. The 15 s etching time for enamel has been proven to give good longevity in our long-term evaluations, while the 5 s dentin etch is considered to optimize penetration of the demineralized dentin and minimize the risk for nanoleakage. The cavity was thoroughly rinsed with water for 20 s, and carefully dried taking care not to dry out the surface (wet technique introduced by J. Kanca). Four different dentin bonding systems used were applied according to the manufactureŕs instructions. In 106 restorations the classic Syntac adhesive system (Vivadent) was used in combination with a dual-cured resin composite (Variolink, Vivadent) systematically by one of the operators. In the other center restorations were luted with a chemically cured resin composite (Bisfil 2B, Bisco Inc., Itasca IL, USA). Three 3-step etch and rinse systems were used systematically in different time periods by the other operators. 37 were bonded with the Gluma system (original Gluma, Bayer, Dormhagen, Germany), 57 with the Allbond 2 system (Allbond 2, Bisco Inc.), 32 with the classic Syntac system (Vivadent). Another 20 coverages were placed at the end of the study with the simplified 2-step etch and rinse system One step (Bisco Inc.) as a comparison with the 3-step system of the same manufacturer. The distribution of the adhesive systems for the different preparation groups is shown in Table 1 . The luting materials were applied to the fitting surface of the coverages. Excess cement was removed immediately after placement with probe or brush-tips and proximal floss. The dual-cured agent was light cured from all directions for 40–60 s per location (VRC 400, Dentronic, USA; 1000 mW/cm 2 ).

Table 1
Distribution of the adhesive systems for the preparation groups.
Bonding Total
Gluma Allbond 2 Syntac One step
Preparation group
1 1 7 11 10 29
2 10 16 58 4 88
3 20 20 39 5 84
4 2 10 14 1 27
Total 33 53 122 20 228

Occlusion was checked and adjusted as necessary after placement based on a dynamic occlusion. The reconstructions were finished with diamond or carbide finishing burs, polishing stones and the Profin finishing system (Dentatus, Hägersten, Sweden) under water cooling followed by polishing stones.

Evaluation

Each coverage was evaluated after insertion (baseline) and then every year during the follow-up regularly by two calibrated investigators. Evaluations at the Visby clinic were performed by the operator and at the end of the study by two other investigators. All were well familiar with the evaluation system. Disagreement was resolved by consensus. A slight modification of the United States Public Health System (USPHS) criteria was used to evaluate the quality of the restorations ( Table 2 ; ). At the yearly recalls, none of the evaluators did know the adhesive luting technique used for the restorations to be evaluated.

Table 2
Slightly modified USPHS criteria according to van Dijken et al. .
Category Score Criteria
Acceptable Unacceptable
Anatomical form 0 The restoration is continuous with tooth anatomy
1 Slightly under- or over-contoured restoration; marginal ridges slightly undercontoured; contact slightly open (may be self-correcting); occlusal height reduced locally
2 Restoration is undercontoured, dentin or base exposed; contact is faulty, not self-correcting; occlusal height reduced; occlusion affected
3 Restoration is missing partially or totally; fracture of tooth structure; shows traumatic occlusion; restoration causes pain in tooth or adjacent tissue
Marginal adaptation 0 Restoration is continuous with existing anatomic form, explorer does not catch
1 Explorer catches, no crevice is visible into which explorer will penetrate
2 Crevice at margin, enamel exposed
3 Obvious crevice at margin, dentin or base exposed
4 Restoration mobile, fractured or missing
Color match 0 Excellent color match
1 Good color match
2 Slight mismatch in color, shade or translucency
3 Obvious mismatch, outside the normal range
4 Gross mismatch
Marginal discoloration 0 No discoloration evident
1 Slight staining, can be polished away
2 Obvious staining cannot be polished away
3 Gross staining
Surface roughness 0 Smooth surface
1 Slightly rough or pitted
2 Rough, cannot be refinished
3 Surface deeply pitted, irregular grooves
Caries 0 No evidence of caries contiguous with the margin of the restoration
1 Caries is evident contiguous with the margin of the restoration
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Nov 30, 2017 | Posted by in Dental Materials | Comments Off on A prospective 15-year evaluation of extensive dentin–enamel-bonded pressed ceramic coverages
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