Chairside vs. labside ceramic inlays: Effect of temporary restoration and adhesive luting on enamel cracks and marginal integrity

Abstract

Objectives

To assess the influence of different temporary restorations and luting techniques of labside and chairside ceramic inlays on enamel defects and marginal integrity.

Methods

120 extracted human third molars received MOD preparations with one proximal box each limited in either enamel or dentin. 64 Cerec 2 inlays and 56 IPS Empress I inlays were randomly assigned to the following groups (fabrication mode: chairside (CS) = no temporary restoration (TR), labside (LS) = TR with Luxatemp (L) inserted with TempBond NE, or Systemp.inlay (SI) without temporary cement), luting technique: SV = Syntac/Variolink II, RX = RelyX Unicem: A: Cerec inlays were luted with (1) CS/SV. (2) CS/SV/Heliobond separately light-cured. (3) CS/RX. (4) LS/L/SV. (5) LS/L/RX. (6) LS/SI/SV. (7) LS/SI/RX. (8) LS/SI/RX with selective enamel etching. B: Empress. (9) L/SV. (10) L/SV/Heliobond separately light-cured. (11) L/RX. (12) SI/SV. (13) SI/SV, Heliobond separately lightcured. (14) SI/RX. (15) SI/RX after selective enamel etching. Before and after thermomechanical loading (TML: loading time of TR 1000 × 50 N + 25 thermocycles (TC) between +5 °C and +55 °C; clinical simulation: 100,000 × 50 N + 2500 TC) luting gaps, enamel cracks, and marginal adaptation to enamel and dentin were determined under an SEM microscope (200×) using replicas.

Results

Loading time of temporary restorations negatively affected enamel integrity and enamel chipping ( p < 0.05). Luxatemp resulted in less enamel cracks than Systemp.inlay ( p < 0.05). Syntac/Variolink achieved better marginal enamel quality than RelyX Unicem in all groups ( p < 0.05). Marginal quality in dentin revealed no differences when no temporary cement was used ( p > 0.05). Temporary cement negatively affected dentin margins when RelyX Unicem was used ( p < 0.05).

Significance

Chairside-fabricated Cerec inlays reduce the risk of enamel cracks and marginal enamel chipping due to omitted temporary restorations. Syntac/Variolink revealed a significantly better performance than RelyX Unicem.

Introduction

Ceramic inlays are scientifically accepted based on numerous clinical studies . The majority of these studies investigated labside restorations having been successfully introduced on the market since the 1990s. Chairside-fabricated CAD/CAM inlays performed successfully as well , although marginal fit of these inlays was slightly inferior compared to labside restorations . Due to an increased risk for bulk fractures, however, Griggs estimated longevity of CAD/CAM inlays as inferior compared to labside ceramic inlays . On the other hand, long-term data of Reiss demonstrated superior long-term performance of Cerec CAD/CAM restorations over 18 years .

Despite a promising annual failure rate of 1–2%, fractures of ceramic inlays still represent the predominant reason for failure . Relating to cavity classes, Class I restorations show more marginal fractures in enamel and ceramic, and Class II restorations reveal more bulk fractures . However, there is always a certain loss of marginal quality over time, mainly without decreasing clinical survival probability .

Adhesive luting of all ceramic inlays still is a conditio sine qua non. Thus, the luting mechanism to both enamel and dentin is well investigated, whereby most studies used conservative methods and conventional luting scenarios e.g. with the etch-and-rinse approach . Regarding the simplification of luting strategies by reducing treatment steps or using self-adhesive cements there is only limited information found in the literature of the field . Today, conventional etch-and-rinse multi-step adhesives with dual-curing luting composites represent the gold standard but recent studies demonstrated that the factors curing depth, contamination, and cavity cleaning affect especially dentin adhesion beneath adhesive inlays .

Although it was repeatedly proven that Cerec inlays provide an acceptable marginal fit , it is often believed that labwork is more precise in terms of marginal adaptation.

The aim of the present study was to compare labside and chairside inlays with different fit in vitro and to assess the influence of temporary restoration, temporary cement, temporary material, and different adhesive luting procedures. The two-fold null hypothesis was that neither (1) the fabrication mode nor (2) the luting technique has an influence on enamel and marginal integrity.

Materials and methods

Preparation and evaluation of specimens

120 freshly extracted fully intact human third molars were stored for a maximum of 30 days in aqueous 0.5% chloramine T-solution. The teeth were cleaned and evaluated for defects under a stereomicroscope (50×). The number and total length of visual enamel cracks was noticed (stereomicroscope SV 11, Zeiss, Jena/WinMes 2.0 software).

Standardized cavities were prepared (MOD, oro-vestibular isthmus width 4 mm, 3 mm depth occlusally, 2 mm mesio-distal width of the proximal box). The proximal box ended mesially 1–2 mm above the cemento-enamel junction and distally 1–2 mm below the amelocemental junction in cementum. Preparation was performed using a diamond bur under sufficient water cooling (80 μm diamond, Two-Striper ® Prep-Set, Premier, St. Paul, USA), and finally with finishing diamonds (25 μm, Inlay Prep-Set, Intensiv, Viganello-Lugano, Switzerland). Internal cavity transitions were rounded, the enamel margins were not beveled.

Cerec scan

The teeth were powdered (Vita-Cerec-Powder, Vita Zahnfabrik, Bad Säckingen, Germany) and the optical impression was computed by a Cerec scanner (Cerec 2, Sirona, Bensheim). Vitablocs Mark II (Vita Zahnfabrik) were used as ceramic blocks. After the scan process the powder was removed with air–water spray for 30 s and the teeth were finally dried.

Impressions, temporary restorations and loading

Single-step impressions were taken from the cavities (Provil Novo, Heraeus Kulzer, Hanau, Germany) and impressions were filled with epoxy-resin die (Alpha Die MF, Schütz Dental, Rosbach, Germany). IPS Empress inlays were fabricated within one week. While the chairside-fabricated inlays were inserted immediately, the cavities of the labside-fabricated inlays were temporarily restored with either Luxatemp temporary inlays luted with temporary cement (TempBond NE) or Systemp.inlay inserted without temporary cement. All labside-fabricated inlay groups underwent a thermo-mechanical loading in order to simulate loading of the temporary restorations (1000 cycles á 50 N + 25 thermocycles between 5 °C and 55 °C + storage in distilled water at 37 °C, for 7 days). Thereafter, the temporary restorations were removed and cavities were cleaned with pumice powder. A repeated determination of enamel cracks and a control of the cavity margins for marginal fractures was carried out.

Fitting and adhesive luting

After fabrication of all inlays, their fit was checked and adjusted with finishing diamonds under water cooling in order to obtain a luting gap of 500 ± 50 μm for Cerec inlays and 200 ± 20 μm for IPS Empress inlays. At the bottom of the cervical boxes the luting gap width was determined prior to the luting process (100× magnification, SV 11, Zeiss, Jena, Germany).

The prepared and cleaned specimens were randomly assigned to 15 groups ( n = 8) ( Table 1 ). The bottom sides of the inlays were etched with hydrofluoric acid for 45 s (Ceramic Etch, Vita Zahnfabrik, Bad Säckingen), rinsed for 45 s with water spray and cleaned in an ultrasonically activated ethanol bath for 5 min. The inlays were silanated with Monobond S (Ivoclar Vivadent), dried after 60 s, coated with Heliobond which was air-thinned. Then the inlays were covered with a light shield (VivaPad, Ivoclar Vivadent, Schaan, Principality of Liechtenstein). Adhesive luting was performed with Syntac and Variolink or with RelyX Unicem according to the manufacturers’ recommendations or experimentally modified ( Tables 1 and 2 ). These modifications were a separate polymerization of Heliobond for 40 s and selective phosphoric acid etching of enamel margins when RelyX Unicem was used. After removal of excess luting composite, the luting gaps were covered with glycerol gel (Airblock, Dentsply DeTrey, Konstanz, Germany) in order to prevent the formation of an oxygen inhibition layer.

Table 1
Experimental groups.
Group Inlay material Temporary cement Temporary restorative material Luting system
1 Cerec 2 Syntac + Variolink II
2 Syntac + Variolinik II (Heliobond polymerized separately)
3 RelyX Unicem
4 Temp Bond NE Luxatemp Syntac + Variolink II
5 Temp Bond NE Luxatemp RelyX Unicem
6 Systemp.inlay Syntac + Variolink II
7 Systemp.inlay RelyX Unicem
8 Systemp.inlay RelyX Unicem (selective enamel etching)
9 Empress Temp Bond NE Luxatemp Syntac + Variolink II
10 Temp Bond NE Luxatemp Syntac + Variolinik II (Heliobond polymerized separately)
11 Temp Bond NE Luxatemp RelyX Unicem
12 Systemp.inlay Syntac + Variolink II
13 Systemp.inlay Syntac + Variolinik II (Heliobond polymerized separately)
14 Systemp.inlay RelyX Unicem
15 Systemp.inlay RelyX Unicem (selective enamel etching)

Table 2
Luting materials (components).
Luting system Components (Batch No.) Manufacturer
Syntac + Variolink I Etchant : 35% phosphoric acid (G07234) Ivoclar Vivadent
Primer : maleic acid 4%, TEGDMA, water, acetone (G19483) Schaan
Adhesive : water, PEGDMA, glutaraldehyde (J0076) Liechtenstein
Heliobond : bisGMA, UDMA, TEGDMA (H14837)
Variolink II :
Base : bisGMA, TEGDMA, UDMA, fillers, ytterbium trifluoride, stabilizer, pigments (H28532)
Catalyst : bisGMA, TEGDMA, UDMA, fillers, ytterbium trifluoride, stabilizer, pigments, benzoyl peroxide (H28532)
RelyX Unicem Powder : glass powder, silicic acid, calcium hydroxide, pigments, substituted pyrimidine, peroxide compound, initiator (205915) 3M Espe
Liquid : methacrylated phosphoric acic ester, dimethacrylate, acetate, stabilizer, initiator (205915) Seefeld
Germany

Light-curing components were light-cured with a polymerization lamp (Translux CL, Heraeus Kulzer, Hanau, Germany). The intensity of the light source was checked after each inlay insertion with a radiometer (Demetron Research Corp., Danbury, CT, USA) in order to ensure that 600 mW/cm 2 were exceeded. Heliobond was light-cured for 40 s if advised by the protocol, otherwise a combined polymerization of adhesive and luting composite for a total of 240 s was performed, starting from proximal aspects.

Visible overhangs were removed with a scaler (A8 S204S, Hu-Friedy, Leimen, Germany). The finish of the margins was performed with finishing diamonds (Two-Striper, Premier) and polishing disks (SofLex Pop-on, 3 M ESPE, Seefeld, Germany). High gloss polishing was performed with felt polishing cones (Dia-Finish E Filzscheiben, Renfert, Hilzingen, Germany) and diamond polishing paste (Brinell, Renfert, Hilzingen). Luting gap width of each inlay was again measured at the bottom of the cervical box.

Thermo-mechanical loading and SEM analysis

After repeated measurement of enamel cracks, all specimens were stored for 21 days in distilled water at 37 °C. Impressions of proximal enamel and dentin margins were taken and a first set of replicas for SEM evaluation of the marginal quality was made.

To simulate clinical service, specimens were fixed in a chewing simulator, with one tooth per chamber that was adjusted in oblique contact to the antagonist (steatite, 6 mm). Thermo-mechanical loading comprised 100,000 mechanical cycles @ 50 N at 0.5 Hz and 2500 thermocycles between 5 °C and 55 °C. Subsequently, another set of replicas was made. Replicas were sputtered with gold and evaluated under a SEM microscope (Leitz ISI 50, Akashi, Tokio, Japan) at 200-fold magnification with regard to marginal quality in enamel and dentin, with the percentage of perfect/gap-free margin serving as quality criterion . SEM examination was performed by one operator having experience with quantitative margin analysis who was blinded to the restorative procedures. Marginal integrity was expressed as a percentage of the entire margin length in enamel and dentin. Marginal qualities were classified according to the criteria “continuous margin”, “gap/irregularity” and “not judgeable/artifact” according to a well-proven protocol . Afterwards the percentage “continuous margin” in relation to the individual judgeable margin was calculated as marginal integrity.

Statistical appraisal

Statistical analysis was computed with SPSS 14.0 software package for Windows (SPSS Inc., Chicago, IL, USA). The Kolmogorov–Smirnov test was performed for testing of normal distribution, non-parametric tests (Wilcoxon matched-pairs-signed-ranks-test, Mann–Whitney- U -test) were applied for comparisons on the 95% level.

Materials and methods

Preparation and evaluation of specimens

120 freshly extracted fully intact human third molars were stored for a maximum of 30 days in aqueous 0.5% chloramine T-solution. The teeth were cleaned and evaluated for defects under a stereomicroscope (50×). The number and total length of visual enamel cracks was noticed (stereomicroscope SV 11, Zeiss, Jena/WinMes 2.0 software).

Standardized cavities were prepared (MOD, oro-vestibular isthmus width 4 mm, 3 mm depth occlusally, 2 mm mesio-distal width of the proximal box). The proximal box ended mesially 1–2 mm above the cemento-enamel junction and distally 1–2 mm below the amelocemental junction in cementum. Preparation was performed using a diamond bur under sufficient water cooling (80 μm diamond, Two-Striper ® Prep-Set, Premier, St. Paul, USA), and finally with finishing diamonds (25 μm, Inlay Prep-Set, Intensiv, Viganello-Lugano, Switzerland). Internal cavity transitions were rounded, the enamel margins were not beveled.

Cerec scan

The teeth were powdered (Vita-Cerec-Powder, Vita Zahnfabrik, Bad Säckingen, Germany) and the optical impression was computed by a Cerec scanner (Cerec 2, Sirona, Bensheim). Vitablocs Mark II (Vita Zahnfabrik) were used as ceramic blocks. After the scan process the powder was removed with air–water spray for 30 s and the teeth were finally dried.

Impressions, temporary restorations and loading

Single-step impressions were taken from the cavities (Provil Novo, Heraeus Kulzer, Hanau, Germany) and impressions were filled with epoxy-resin die (Alpha Die MF, Schütz Dental, Rosbach, Germany). IPS Empress inlays were fabricated within one week. While the chairside-fabricated inlays were inserted immediately, the cavities of the labside-fabricated inlays were temporarily restored with either Luxatemp temporary inlays luted with temporary cement (TempBond NE) or Systemp.inlay inserted without temporary cement. All labside-fabricated inlay groups underwent a thermo-mechanical loading in order to simulate loading of the temporary restorations (1000 cycles á 50 N + 25 thermocycles between 5 °C and 55 °C + storage in distilled water at 37 °C, for 7 days). Thereafter, the temporary restorations were removed and cavities were cleaned with pumice powder. A repeated determination of enamel cracks and a control of the cavity margins for marginal fractures was carried out.

Fitting and adhesive luting

After fabrication of all inlays, their fit was checked and adjusted with finishing diamonds under water cooling in order to obtain a luting gap of 500 ± 50 μm for Cerec inlays and 200 ± 20 μm for IPS Empress inlays. At the bottom of the cervical boxes the luting gap width was determined prior to the luting process (100× magnification, SV 11, Zeiss, Jena, Germany).

The prepared and cleaned specimens were randomly assigned to 15 groups ( n = 8) ( Table 1 ). The bottom sides of the inlays were etched with hydrofluoric acid for 45 s (Ceramic Etch, Vita Zahnfabrik, Bad Säckingen), rinsed for 45 s with water spray and cleaned in an ultrasonically activated ethanol bath for 5 min. The inlays were silanated with Monobond S (Ivoclar Vivadent), dried after 60 s, coated with Heliobond which was air-thinned. Then the inlays were covered with a light shield (VivaPad, Ivoclar Vivadent, Schaan, Principality of Liechtenstein). Adhesive luting was performed with Syntac and Variolink or with RelyX Unicem according to the manufacturers’ recommendations or experimentally modified ( Tables 1 and 2 ). These modifications were a separate polymerization of Heliobond for 40 s and selective phosphoric acid etching of enamel margins when RelyX Unicem was used. After removal of excess luting composite, the luting gaps were covered with glycerol gel (Airblock, Dentsply DeTrey, Konstanz, Germany) in order to prevent the formation of an oxygen inhibition layer.

Table 1
Experimental groups.
Group Inlay material Temporary cement Temporary restorative material Luting system
1 Cerec 2 Syntac + Variolink II
2 Syntac + Variolinik II (Heliobond polymerized separately)
3 RelyX Unicem
4 Temp Bond NE Luxatemp Syntac + Variolink II
5 Temp Bond NE Luxatemp RelyX Unicem
6 Systemp.inlay Syntac + Variolink II
7 Systemp.inlay RelyX Unicem
8 Systemp.inlay RelyX Unicem (selective enamel etching)
9 Empress Temp Bond NE Luxatemp Syntac + Variolink II
10 Temp Bond NE Luxatemp Syntac + Variolinik II (Heliobond polymerized separately)
11 Temp Bond NE Luxatemp RelyX Unicem
12 Systemp.inlay Syntac + Variolink II
13 Systemp.inlay Syntac + Variolinik II (Heliobond polymerized separately)
14 Systemp.inlay RelyX Unicem
15 Systemp.inlay RelyX Unicem (selective enamel etching)
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Nov 28, 2017 | Posted by in Dental Materials | Comments Off on Chairside vs. labside ceramic inlays: Effect of temporary restoration and adhesive luting on enamel cracks and marginal integrity
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