Scientifically based rationale and protocol for use of modern indirect resin inlays and onlays

Effect of Adhesion Conditions on the Shear Bond Strength of 3D Printing Resins after Thermocycling Used for Definitive Prosthesis

Three-dimensional (3D) printing polymers such as urethane dimethacrylate (UDMA) and ethoxylated bisphenol A dimethacrylate (Bis-EMA) are typically used in definitive prosthesis and require surface treatments before bonding. However, surface treatment and adhesion conditions often affect long-term use. Herein, polymers were divided into Groups 1 and 2 for the UDMA and Bis-EMA components, respectively. The shear bond strength (SBS) between two types of 3D printing resins and resin cements was measured using Rely X Ultimate Cement and Rely X U200, according to adhesion conditions such as single bond universal (SBU) and airborne-particle abrasion (APA) treatments. Thermocycling was performed to evaluate the long-term stability. Sample surface changes were observed using a scanning electron microscope and surface roughness measuring instrument. The effect of interaction between the resin material and adhesion conditions on the SBS was analyzed via a two-way analysis of variance. The optimal adhesion condition for Group 1 was achieved when U200 was used after APA and SBU, whereas Group 2 was not significantly affected by the adhesion conditions. After thermocycling, the SBS significantly decreased in Group 1 without APA treatment and in the entire Group 2. Additionally, porosity, along with increased roughness, was observed on both material surfaces after APA.

Resin Bonding to a Hybrid Ceramic: Effects of Surface Treatments and Aging

The aim of this study was to verify the effects of different surface treatments on the microtensile bond strength between resin cement and a hybrid ceramic. Thirty-two hybrid ceramic slices (8 × 10 × 3 mm) were produced and allocated among four groups according to the surface treatment: Cont = no treatment, HA = 10% hydrofluoric acid applied for 60 seconds, PA = 37% phosphoric acid applied for 60 seconds and CJ = air abrasion with silica particle coated alumina (Cojet Sand, 3M ESPE, 30 μm/2.8 bar). As a control group, eight blocks of feldspathic ceramic (8 × 10 × 3 mm) were etched by hydrofluoric acid for 60 seconds (VMII). After the surface treatments, the ceramic slices were silanized (except the Cont group) and adhesively cemented to composite resin blocks (8 × 10 × 3 mm ) with a load of 750 g (polymerized for 40 seconds each side). The cemented blocks were cut into beams (bonded surface area of ∼1 mm2). Half of the beams were aged (thermocycling of 5°C-55°C/6000 cycles + water storage at 37°C/60 days), and the other half were tested immediately after being cut. Data were analyzed by Kruskal-Wallis and Dunn tests (non-aged groups) and by one-way analysis of variance and Tukey test (aged groups; α=0.05%). The mode of failure was classified by stereomicroscopy. The surface treatment significantly affected the bond strength in each set of groups: non-aged (p=0.001) and aged (p=0.001). Before being aged, samples in the CJ, HA, and PA groups achieved the highest bond strength values. However, after being aged, only those in the HA group remained with the highest bond strength values. Adhesive failure was found most often. In conclusion, hydrofluoric acid etching should be used for surface conditioning of the studied hybrid ceramic.

Colour stainability of indirect CAD-CAM processed composites vs. conventionally laboratory processed composites after immersion in staining solutions

OBJECTIVES

The aim of this study was to determine, by using a spectrophotometer device, the colour stainability of two indirect CAD/CAM processed composites in comparison with two conventionally laboratory-processed composites after being immersed 4 weeks in staining solutions such as coffee, black tea and red wine, using distilled water as control group.

METHODS

Two indirect CAD/CAM composites (Lava Ultimate and Paradigm MZ100) and two conventionally laboratory-processed composites (SR Adoro and Premise Indirect) of shade A2 were selected (160 disc samples). Colour stainability was measured after 4 weeks of immersion in three staining solutions (black tea, coffee, red wine) and distilled water. Specimen's colour was measured each week by means of a spectrophotometer (CIE L*a*b* system). Statistical analysis was carried out performing repeated ANOVA measurements and Tukey's HSD test to evaluate differences in ΔE00 measurements between groups; the interactions among composites, staining solutions and time duration were also evaluated.

RESULTS

All materials showed significant discoloration (p<0.01) when compared to control group. The highest ΔE00 observed was with red wine, whereas black tea showed the lowest one. Indirect laboratory-processed resin composites showed the highest colour stability compared with CAD/CAM resin blocks.

CONCLUSIONS

CAD/CAM processed composites immersed in staining solutions showed lower colour stability when compared to conventionally laboratory-processed resin composites.

CLINICAL SIGNIFICANCE

The demand for CAD/CAM restorations has been increasing; however, colour stainability for such material has been insufficiently studied. Moreover, this has not been performed comparing CAD/CAM processed composites versus laboratory-processed indirect composites by immersing in staining solutions for long immersion periods.

Color changes in staining solutions of four light-cured indirect resin composites

The purpose of this study was to investigate the effect of different staining solutions on the color coordinates of indirect light-cured resin composites. 112 discs were made using four indirect composites, Signum+/Haraeus-Kulzer, Sinfony/3M-Espe, GC Gradia/GC, Ena HRi/Micerium, and divided into four groups which immersed in tea, coffee, chocolate and distilled water, at 37 °C, for 4 weeks. The color, before and after immersion for 1, 2, 3 and 4 weeks, was measured according to CIELAB system and ΔL*, Δa*, Δb* and ΔE* values were calculated for all immersion periods. The effect of time, solution and material on primary and secondary color coordinates was estimated using two-way repeated ANOVAs and pairwise comparisons, at a = 0.05. The results showed that coffee strongly affected all the materials (p < 0.05), followed by tea and chocolate. Sinfony presented the highest color change (p < 0.05), due to changes in b* and L* coordinates. Color coordinates were affected differently by material type and solution. In conclusion, this study showed that the color of indirect resin composites was affected by all three examined factors (immersion time, staining solution and material type), in a clinically appreciable level (ΔΕ* > 2.7 U) even from the first week, and in an unacceptable level (ΔΕ* > 5.5 U) in the second, third and fourth week, depending on the staining solution and the material.

Difference in the color stability of direct and indirect resin composites

Indirect resin composites are generally regarded to have better color stability than direct resin composites since they possess higher conversion degree

Effect of different finishing techniques for restorative materials on surface roughness and bacterial adhesion

STATEMENT OF PROBLEM

The formation of biofilm and bacterial accumulation on dental materials may lead to the development of gingival inflammation and secondary caries.

PURPOSE

The purpose of this study was to examine the effect of different surface finishing and polishing methods on surface roughness and the adhesion of S. mutans bacteria to 2 new-generation indirect composite resins, 1 direct composite resin, and 1 ceramic material.

MATERIAL AND METHODS

Forty specimens (10 x 10 x 2 mm) of each material, indirect composite resins (SR Adoro, Estenia), direct composite resin (Tetric), and a ceramic material (VITABLOCS Mark II), were fabricated. Specimens were divided into 4 groups (n=10) that were treated with 1 of the following 4 surface finishing techniques: diamond rotary cutting instrument, sandpaper discs (Sof-Lex), silicone-carbide rubber points (Shofu), or a felt wheel with diamond paste. Surface roughness was measured with a profilometer. Test specimens were covered with artificial saliva and mucin to produce pellicle. Bacterial suspension (10(9) CFU/ml) was then added to the pellicle-coated specimens, and bacterial adhesion was determined using a confocal laser microscope and image analyzing program. Data were analyzed with 2-way ANOVA, followed by Tukey HSD test, Pearson correlation, and regression analysis (alpha=.05).

RESULTS

The highest surface roughness values were recorded in SR Adoro and diamond rotary cutting instrument groups. The lowest vital S. mutans adhesion was seen in the ceramic group and in SR Adoro indirect composite resin (P<.05).

CONCLUSIONS

Bacterial adhesion to indirect composite resin materials differed from that to ceramic material after surface treatments. A positive correlation was observed between surface roughness and the vital S. mutans adhesion.

The Influence of Luting Systems on the Microtensile Bond Strength of Dentin to Indirect Resin-based Composite and Ceramic Restorations

Compared to self-etch and self-adhesive luting systems, the two etch-and-rinse luting agents evaluated in the current study provided more reliable bonding when used to bond indirect resin-based composite restorations to sound dentin. On the contrary, the self-adhesive luting system showed the highest mean bond strength for the cementation of glass ceramic restorations.

Opalescence and fluorescence properties of indirect and direct resin materials

OBJECTIVE

To measure the opalescence and fluorescence properties of indirect and direct resin materials before and after polymerization, and to determine the influence of the material and shade group combination on these properties.

MATERIAL AND METHODS

BelleGlass NG (BG, indirect resin) and Estelite Sigma (ES, direct resin), each composed in 3 shade groups (EN, OD and TL for BG; BS, AS and OP for ES) out of a total of 16 shades were investigated. Resin material was packed into a mold (the BEC condition) and polymerized with a light-polymerization unit (CWL). Secondary polymerization (CIC) was performed for BG. Color was measured in the BEC, CWL, and CIC conditions, and the opalescence parameter (OP) and fluorescence parameter (FL) were calculated.

RESULTS

For the OP, the mean for BG material was 24.3 before polymerization, which changed to 19.9 after polymerization (CIC). In the case of ES, the mean OP before polymerization was 25.6, which changed to 12.4 after polymerization (CWL). For the FL, the mean FL for BG was 2.5 before polymerization, which changed to 0.7 after polymerization. In the case of ES, the mean FL before polymerization was 1.2, which did not change after polymerization. Material and shade group combination influenced the OP and FL values (p<0.05).

CONCLUSIONS

The opalescence and fluorescence properties of resin materials varied depending on the material, shade group, and polymerization. Clinically, these properties should be considered when neighboring teeth are restored with different types of material.

Changes in color and color coordinates of an indirect resin composite during curing cycle

OBJECTIVES

To measure the color changes of indirect resin composites during curing cycle and to determine the influence of shade group on these changes.

METHODS

One brand (belleGlass NG), divided into three shade groups (EN, OD and TL), was investigated. Resin composite was packed into a mold (BC) and was cured with a light-curing unit (C1). Secondary curing was performed in the proprietary curing chamber (C2). Color was measured at BC, C1 and C2 conditions. Changes in color and color coordinates were calculated and repeated measures three-way ANOVA was performed. Each pair of compared-condition in the curing cycle was set as a repeated variable.

RESULTS

Net curing color change (C2-BC) was in the range of 1.0-10.1DeltaEab* units. Based on ANOVA for the color changes, DeltaEab* was influenced by the compared-condition, the shade group and the shade designation (p<0.01). Changes in color coordinates varied by the shade group.

CONCLUSION

Changes in color during curing cycle were perceptible in several shades by the condition (DeltaEab*>3.7); therefore, clinical practice of shade matching should consider these color changes.

Degree of conversion of dual-cure luting resins light-polymerized through various materials

OBJECTIVE

The aim of this study was to investigate the degree of monomer conversion of four dual-cure luting resins irradiated through various restorative materials or dentin.

MATERIAL AND METHODS

RelyX ARC (3M-ESPE), RelyX Unicem (3M-ESPE), Variolink 2 (Ivoclar,Vivadent), and Panavia F 2.0 (Kuraray) were mixed in accordance with the manufacturer's instructions. They were placed under the disks (thickness 1.5 mm) representing a metal restoration, a composite restoration (Sinfony D A3), a fiber-reinforced composite (EverStick 0.5 mm + 1.0 mm Sinfony D A3) restoration, and dentin. Five specimens (thickness 0.6 mm) in each group were irradiated through the disks for 40 s (Optilux-501, 800 mW/cm(2)). Light polymerization of the dual-cure luting resin without the covering disk was used as control. The degree of monomer conversion (DC%) was determined by Fourier transform infrared spectroscopy (FT-IR)/ATR spectrometry from the bottom of the resin. The infrared spectra were recorded at every 5.2 s for 15 min beginning from the mixing of the resin.

RESULTS

ANOVA revealed significant differences in DC% between the luting resins tested (p<0.001) and the different restorations (p<0.001). RelyX ARC showed the highest degree of conversion 15 min after the start of polymerization, whereas Panavia F 2.0 and RelyX Unicem showed the lowest.

CONCLUSIONS

The degree of conversion of dual-cured luting resins differed significantly. Furthermore, the restorative material significantly influenced the DC% of the dual-cure luting resin underneath.

In vitro biological response to a light-cured composite when used for cementation of composite inlays

OBJECTIVE

To define the cytotoxicity of a photo-cured composite when used as a bonding system under a composite inlay.

METHODS

Composite specimens were photo-cured with or without a 2 mm composite inlay interposed between them and the light source. Samples were extracted in complete cell culture medium and the obtained eluates applied to primary cultures of human pulp and gingival fibroblasts. After 72 h of incubation, cell viability was evaluated by MTT assay. Survival rates were calculated with respect to negative controls.

RESULTS

Both shielded and unshielded composite samples were cytotoxic to pulp and gingival cells. The inlay shielded composite samples reached a significantly higher level of cytotoxicity compared to the unshielded ones.

SIGNIFICANCE

The results suggested that the cytotoxicity of a light-cured composite resin used as a bonding system for indirect composite restorations may be significantly increased as a result of an inlay light-shielding effect.

Influence of light-activated and auto- and dual-polymerizing adhesive systems on bond strength of indirect composite resin to dentin

STATEMENT OF PROBLEM

Clinicians must be aware of the bonding effectiveness of auto- and dual- polymerizing adhesive systems before choosing the material and technique of cementing inlay/onlays to dentin. An inadequate choice may compromise the success of indirect restorations.

PURPOSE

This study compared the microtensile bond strength (MTBS) of indirect composite resin bonded to dentin by light-activated, autopolymerizing, and dual-polymerizing adhesive systems.

MATERIAL AND METHODS

Occlusal dentin surfaces of 36 human third molars were exposed and flattened. Teeth were assigned to 1 of the following 6 groups (n=6) of adhesive luting systems: 2 dual-polymerizing systems (Scotchbond Multipurpose Plus/Rely X [SBMP] and Prime & Bond NT Dual Cure/Enforce [PBDC]); 1 autopolymerizing system (ED Primer/Panavia F [EDP]); and 3 light-activated systems (control groups) (Adper Single Bond/Rely X [SB], Prime & Bond NT/Enforce [PB], and Clearfil SE Bond/Panavia F [CF]). The restorative materials were applied according to manufacturer's directions. A 2-mm-thick prepolymerized composite resin (Clearfil APX) disc was cemented with the resin cements on the bonded dentin. Teeth were stored in water at 37 degrees C for 24 hours. Afterwards, teeth were sectioned both mesial-distally and buccal-lingually to obtain multiple bonded beam specimens with 0.8 mm(2) of cross-sectional area. Each specimen was tested in tension at a crosshead speed of 0.5 mm/min until failure. Data (MPa) were analyzed by 1-way analysis of variance and the Tukey post hoc test (alpha=.05). Failure patterns of tested specimens were analyzed using scanning electron microscopy.

RESULTS

Mean MTBS values (MPa) for experimental groups were as follows: SBMP, 32.89 +/- 3.26(a); SB, 26.74 +/- 7.45(ab); PB, 26.11 +/- 4.48(ab); CF, 25.30 +/- 6.42(ab); EDP, 16.82 +/- 5.53(bc); PBDC, 11.20 +/- 5.89(c) (P<.001). Groups with similar lowercase letters were not significantly different. Failure pattern of fractured specimens varied according to the polymerization mode.

CONCLUSION

The autopolymerizing system and one of the dual-polymerizing systems were as effective as the light-activated systems in bonding indirect composite restorations to dentin.

Influence of cavity dimension and restoration methods on the cusp deflection of premolars in composite restoration

OBJECTIVES

The aim of this study was to measure the cusp deflection by polymerization shrinkage during composite restoration for mesio-occluso-distal (MOD) cavities in premolars, and to examine the influence of cavity dimension, C-factor and restoration method on the cusp deflection.

METHODS

Thirty extracted maxillary premolars of similar size were prepared with four different sizes of MOD cavity, and divided into six groups. The width and depth of the pulpal wall of the cavity were as follows: group 1: 1.5x1 mm, group 2: 1.5x2 mm, group 3: 3x1 mm, and groups 4-6: 3x2 mm. Groups 1-4 were restored using a bulk filling with a composite. Group 5 was restored incrementally, and group 6 was restored with an indirect composite inlay. Cusp deflections were measured using LVDT transducers. The cusp deflections were compared between groups using ANOVA and Scheffe tests, and a correlation analysis was done.

RESULTS

The cusp deflections of groups 1-4 were 12.1 (2.2), 17.2 (1.9), 16.2 (0.8) and 26.4 (4.2) microm, respectively. There was a strong positive correlation between the length cubed divided by the thickness cubed of the remaining cusp (L3/T3) and cusp deflection. The C-factor was related to the % flexure (100xcusp deflection/cavity width). The cusp deflections of groups 5 and 6 were 17.4 (2.0) and 17.9 (1.4) microm, respectively, which were much lower values than those of group 4.

SIGNIFICANCE

The cusp deflection increased with increasing cavity dimension and C-factor. Use of an incremental filling technique or an indirect composite inlay restoration could reduce the cuspal strain.

Increasing occlusal vertical dimension--why, when and how

Cosmetic dentistry has evolved with the advent of more robust porcelain materials and ever-stronger bonding agents. This series of three articles aims to provide a practical overview of what is now possible both functionally and cosmetically from the preparation of a small number of teeth, through a whole smile, to full mouth rehabilitation. A complete diagnosis is the starting point to planning any cosmetic or functional changes. Guidance is given on the techniques used but adequate training must be considered essential before embarking upon modification in occlusal schemes or even minor adjustments in smile design. Understanding vertical dimension and how and when it can be changed has always been a challenging prospect for the general dental practitioner. This article aims to discuss the rationale behind changes in vertical dimension and demonstrate how it can be achieved in general practice assuming adequate hands-on postgraduate training has been completed.

Inlay shading effect on the photopolymerization kinetic of a dental composite material used as bonding system in an indirect restoration technique

OBJECTIVES

To define the inlay shading effect on the polymerization levels and kinetics of a light activated bonding system for an indirect restoration technique.

MATERIALS AND METHODS

For the bonding system, an adhesive: Excite (Ivoclar-vivadent) and a composite: Z250 (3M-ESPE, St Paul Minnesota, USA) were investigated. A Demetron (Kerr USA) light curing unit was used. The composite inlay blocks of 2 mm thick were used for the experiment (Artglass A2 Heraeus, Kulzer, Dormagen, Germany). The bonding composite was photocured using a 2 mm composite inlay block as a shielding system while the adhesive was shielded by a 2.3 mm thick wafer, composed of the inlay material and the previously cured bonding composite. The kinetics and levels of polymerization were measured by a differential scanning calorimeter technique (DSC 25, Mettler, Orange, CA, Toledoh, küsnacht, switzerland).

RESULTS

The inlay shielded dental composite reaches a significantly lower level of polymerization compared to the unshielded composite. Inlay shielded composite, has a slower polymerization kinetic compared to unshielded composite. The resin adhesive shielded by the inlay-composite wafer reaches polymerization values not significantly different from those of the unshielded adhesive.

SIGNIFICANCES

The degree of cure of the light-cured composite resins for use as a base for indirect composite restorations, may be severely reduced as a result of inlay shielding.