Impact of different adhesives on work of adhesion between CAD/CAM polymers and resin composite cements

Effects of different universal adhesives and surface treatments on repair bond strength between resin composites

OBJECTIVE

This study aimed to evaluate the effects of different universal adhesives and surface treatments on the repair bond strength between resin composites.

MATERIALS AND METHODS

A total of 220 composite samples were divided into three groups according to the adhesive resin to be applied: 1) Scotchbond Universal, 2) G-Premio Bond, and 3) Peak Universal Bond. They were then divided into seven subgroups according to surface treatments (n = 10): A) air abrasion, B) air abrasion+silane, C) hydrofluoric acid, D) hydrofluoric acid+silane, E) air abrasion+hydrofluoric acid+silane, F) silane, and G) no surface treatment (negative control). After surface treatment, a repair composite was applied. Samples aged in the thermocycle were subjected to micro-tensile bond strength testing. Cohesive strength values of 10 non-aged composite blocks were used as a positive control. Kruskal-Wallis and one-way ANOVA tests were used for statistical evaluation. Fractured surfaces were evaluated using a scanning electron microscope.

RESULTS

In Scotchbond Universal and G-Premio Bond, the mean micro-tensile bond strength value of the no surface treatment subgroup was significantly lower than that of the positive control. All subgroups of Peak Universal Bond showed similar values to the positive control.

CONCLUSION

While Scotchbond Universal and G-Premio Bond required mechanical roughening before adhesive application, Peak Universal Bond did not require any surface treatment.

CLINICAL SIGNIFICANCE

Different universal adhesives may show different repair bonding strengths with different surface treatments. Since achieving a standard in this regard can be associated with many independent factors, clinicians should determine how to apply the adhesive they use most effectively with the most appropriate surface treatment based on their own clinical experience.

Bond strength between titanium and polymer-based materials adhesively cemented

The aim was to evaluate the bond strength between titanium and polymer-based materials for prosthetic restorations, cemented with different adhesive cement systems. Eight groups with 13 specimens in each group were included. Each specimen consisted of two parts: a cylinder of titanium resembling a titanium base, and a cylinder of one of two polymer-based materials Micro Filled Hybrid (MFH) or Telio CAD and cemented with one of four adhesive cement systems, namely Multilink Hybrid Abutment, Panavia V5, RelyX Ultimate and G-Cem LinkAce. The titanium was sandblasted with 50 µm Al₂O₃ and treated according to each cement manufacturer's recommendations. The polymer-based materials were pre-treated according to the manufacturer's instructions including sandblasting for MFH. After cementation, the groups were water stored for one day before thermocycling: 5000 cycles in 5–55 °C. A shear bond strength test was performed (crosshead speed 0.5 mm/min) and data was analysed with one-way ANOVA, Tukey's test. Telio CAD cemented with Panavia V5 and G-Cem LinkAce showed significantly lower bond strength compared to all other groups, due to spontaneous debonding. The highest numerical bond strength was found in the group of MFH cemented with RelyX Ultimate or with G-Cem LinkAce. Generally, the Telio CAD groups showed lower bond strength values than the MFH groups. The conclusions are that pre-treatment methods and choice of cement system are of importance for polymer-based materials for prosthetic restorations. The bond strength is adequate for provisional cementation irrespective of cement system when pre-treating by sandblasting, but cement dependent without sandblasting.

Fracture resistance of additive manufactured and milled implant-supported interim crowns

STATEMENT OF PROBLEM

Interim dental prostheses can be fabricated by using subtractive or additive manufacturing technologies. However, the fracture resistance of implant-supported interim crowns fabricated by using vat-polymerization additive manufacturing methods remains unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the fracture resistance of anterior and posterior screw-retained implant-supported interim crowns fabricated by using subtractive and vat-polymerization direct light processing (DLP) additive manufacturing procedures.

MATERIAL AND METHODS

An implant (Zinic Implant RP ∅4.0×10 mm) was placed in a 15×15-mm polymethylmethacrylate block. An implant abutment (ZiaCam, nonrotatory RP) was positioned on each implant. The virtual implant abutment standard tessellation language (STL) file provided by the manufacturer was imported into a software program (Exocad v2.2 Valletta) to design 2 anatomic contour crowns, a maxillary right central incisor (anterior group) and a maxillary right premolar (posterior group). Each group was subdivided into 2 subgroups depending on the manufacturing method: milled (milled subgroup) and additive manufacturing (additive manufacturing subgroup). For the milled subgroup, an interim material (Vivodent CAD Multi) and a milling machine were used to fabricate all the specimens (N=40, n=10). For the additive manufacturing subgroup, a polymer interim material (SHERAprint-cb) and a DLP printer (SHERAprint 30) were used to manufacture all the specimens at a 50-μm layer thickness and 45-degree build orientation as per the manufacturer's instructions. Then, each specimen was cemented to an implant abutment by using composite resin cement (Multilink Hybrid Abutment HO) as per the manufacturer's instructions. A universal testing machine was used for fracture resistance analysis, and the failure mode was recorded. The Shapiro-Wilk test revealed that data were normally distributed. One-way ANOVA and Tukey multiple comparison were selected (α=.05).

RESULTS

One-way ANOVA revealed significant differences among the groups (P<.05). The anterior milled subgroup obtained a significantly higher fracture resistance mean ±standard deviation value of 988.4 ±54.8 N compared with the anterior additive manufacturing subgroup of 636.5 ±277.1 N (P<.001), and the posterior milled subgroup obtained significantly higher mean ±standard deviation of 423.8 ±68 N than the additive manufacturing subgroup of 321.3 ±128.6 N (P=.048). All groups presented crown fracture without abutment fracture.

CONCLUSIONS

Manufacturing procedures and tooth type influenced the fracture resistance of screw-retained implant-supported interim crowns. Milled specimens obtained higher fracture resistance compared with the DLP additive manufacturing groups. The anterior group was higher than the posterior group.

Effects of alumina airborne-particle abrasion on the surface properties of CAD/CAM composites and bond strength to resin cement

The purpose of this study is to clarify physical and chemical changes in surfaces of CAD/CAM composites caused by alumina airborne-particle abrasion and its effect on adhesive bonding. Our study involved three dispersed filler (DF)-based and a polymer-infiltrated ceramic network (PICN)-based CAD/CAM composites. Changes in the surface morphologies of the composites were examined, and surface free energy (SFE) analysis was performed based on Owens-Wendt theory. The influence of the abrasion on the bond strengths of CAD/CAM composites to the resin cement was characterized by shear bond strength (SBS) test. The abrasion increased the roughness of the composites. The SFE analysis showed that the abrasion significantly increased the dispersive component but decreased the polar component of the SFE associated with the DF-based composites, while no change occurred for those of the PICN-based composite. The abrasion slightly improved the SBSs for the DF-based composites but not that of the PICN-based composite.

Bonding performance of dispersed filler resin composite CAD/CAM blocks with different surface treatment protocols

The effect of various pretreatments on the bonding of a resin cement to resin-composite CAD/CAM blocks (RCBs) was examined. The surface of dispersed-filler RCBs (DF-RCBs) and a polymer infiltrated ceramic network RCB (PICN-RCB) was roughened using hydrofluoric acid etching (HF) or sandblasting, and followed by silanization and/or universal adhesive (UA) application. Microtensile bond strength (µTBS), surface roughness parameters (arithmetical mean height (Sa); developed interfacial area ratio (Sdr)), and critical surface energy (γ_c) were determined. For most DF-RCBs, the highest µTBS was obtained using HF+UA. UA application to DF-RCBs resulted in similar or higher µTBS compared to silanization, which indicates that silane treatment is not crucial for DF-RCBs, especially after HF. In contrast, the highest µTBS to PICN-RCB was obtained with silanization. Both roughening pretreatments significantly increased the surface roughness parameters and the γ_c of all RCBs. The γ_c was positively correlated with Sa (r=0.756, p<0.001) and Sdr (r=0.837, p<0.001).

Influence of surface treatment on bonding of resin luting cement to CAD/CAM composite blocks

The aim of this study was to determine the influence of different surface treatments of CAD/CAM composite blocks on bonding effectiveness of resin cements, based on the shear bond strength test and the surface science examination. Specimens were fabricated from two types of CAD/CAM composite blocks (Cerasmart and VITA Enamic), and the specimen surfaces were alumina sandblasted. Specimen surfaces were treated with i) silane, ii) primer, and iii) silane+primer, then two types of cements (Block HC Cem and Super Bond) were bonded. After 24 h storage, bond strengths were measured. Surface free energy measurements were performed of the treated CAD/CAM composite blocks surfaces. The groups ii) and iii) showed significantly higher bond strengths than the group i), apart from VITA Enamic with Block HC Cem. Although the total surface free energy showed different trends in different surface treatments, a similar trend was found in both CAD/CAM composite blocks.

Is the assumption of linear elasticity within prosthodontics valid for polymers? -An exemplary study of possible problems

As shown in previous studies within other scientific fields, the material behavior of polymethyl methacrylate (PMMA) is viscoelastic-viscoplastic. However, in dental biomaterial science it is mostly considered as linear elastic or elastic-plastic. The aim of the present study was to evaluate, whether the assumption of elastic or elastic-plastic material behavior for PMMA is a practicable simplification or a potential source of error, especially considering clinical loading conditions. Telio-CAD was tested in three-point bending tests with different test velocities to examine the material behavior at different initial loading rates. Additionally, a dynamic-mechanical-thermal-analysis at different frequencies and temperatures was used. Here, a significant influence of loading rate and temperature as well as stress relaxation and creep were observed. To describe the rate-dependency of the elastic modulus, a new model was created, from which the elastic modulus can be calculated with a given strain rate. This model was validated using linear elastic finite element analysis.

Effectiveness of current adhesive systems when bonding to CAD/CAM indirect resin materials: A review of 32 publications

The purpose of this review was to assess the available literature regarding bonding between current adhesive systems and computer-aided design/computer-aided manufacturing (CAD/CAM) indirect resin materials, to provide clinicians with a comparative overview of the relevant bonding procedures. An electronic search was performed through PubMed based on the keywords CAD/CAM and dental bonding. Additional relevant literature was obtained from the citations in the articles. A total of 313 papers were identified, of which 281 were excluded as being unsuitable, and an additional 3 papers were identified, giving a total of 32 articles that are included in this review. Based on this survey, it is recommended that microretentive surfaces should be generated by either blasting or hydrofluoric acid etching. This initial process should be followed by silanization to ensure chemical adhesion prior to bonding to CAD/CAM indirect resin composite materials (including Lava Ultimet, KATANA AVENCIA block, Gradia Block, Cerasmart, Paradigm, and Block HC) and CAD/CAM polymer-infiltrated ceramics (such as Vita Enamic). The use of materials containing methyl methacrylate (MMA) also appears to improve the bonding of CAD/CAM poly(methyl methacrylate) (PMMA) resin materials (including XHIPC-CAD/CAM, artBloc Temp, and Telio).

Biomechanical properties of polymer-infiltrated ceramic crowns on one-piece zirconia implants after long-term chewing simulation

Background

Implant and superstructure provide a complex system, which has to withstand oral conditions. Concerning the brittleness of many ceramics, fractures are a greatly feared issue. Therefore, polymer-infiltrated ceramic networks (PICNs) were developed. Because of its high elastic modulus, the PICN crown on a one-piece zirconia implant might absorb forces to prevent the system from fracturing in order to sustain oral forces. Recommendations for the material of superstructure on zirconia implants are lacking, and only one study investigates PICN crowns on these types of implants.

Accordingly, this study aimed to examine PICN crowns on one-piece zirconia implants regarding bond strength and surface wear after long-term chewing simulation (CS).

Methods

Twenty-five hybrid ceramic crowns (Vita Enamic, Vita Zahnfabrik) were produced using computer-aided design/computer-aided manufacturing (CAD/CAM) technology and adhesively bonded (RelyX™ Ultimate, 3M ESPE) to zirconia implants. Twenty of the specimens underwent simultaneous mechanical loading and thermocycling simulating a 5-year clinical situation (SD Mechatronik GmbH). Wear depth and wear volume, based on X-ray micro-computed tomography volume scans (Skyscan 1172-100-50, Bruker) before and after CS, were evaluated.

All crowns were removed from the implants using a universal testing machine (Z010, Zwick GmbH&Co.KG). Subsequently, luting agent was light microscopically localized (Stemi 2000-C, Zeiss).

With a scanning electron microscope (SEM, Phenom™ G2 pro, Phenom World), the area of abrasion was assessed.

Results

After CS, none of the tested crowns were fractured or loosened.

The maximum vertical wear after CS was M = 0.31 ± 0.04 mm (mean ± standard deviation), and the surface wear was M = 0.74 ± 0.23 mm³.

The pull-off tests revealed a 1.8 times higher bond strength of the control group compared to the experimental group (t(23) = 8.69, p < 0.001).

Luting agent was mostly located in the crowns, not on the implants.

The area of abrasion showed avulsion and a rough surface.

Conclusions

PICN on one-piece zirconia implants showed high bond strength and high wear after CS.

Fractography of clinically fractured, implant-supported dental computer-aided design and computer-aided manufacturing crowns

Today, a substantial part of the dental crown production uses computer-aided design and computer-aided manufacturing (CAD/CAM) technology. A recent step in restorative dentistry is the replacement of natural tooth structure with pre-polymerized and machined resin-based methacrylic polymers. Recently, a new CAD/CAM composite was launched for the crown indication in the load-bearing area, but the clinical reality forced the manufacturer to withdraw this specific indication. In parallel, a randomized clinical trial of CAD/CAM composite crowns luted on zirconia implant abutments revealed a high incidence of failure within the first year of service. Fractured crowns of this clinical trial were retrieved and submitted to a fractographic examination. The aim of the case series presented in this article was to identify failure reasons for a new type of CAD/CAM composite crown material (Lava Ultimate; 3M Oral Care, St. Paul, Minnesota, USA) via fractographic examinations and analytical assessment of luting surfaces and water absorption behavior. As a result, the debonding of the composite crowns from the zirconia implant abutments was identified as the central reason for failure. The adhesive interface was found the weakest link. A lack of silica at the zirconia surface certainly has compromised the bonding potential of the adhesive system from the beginning. Additionally, the hydrolytic stress released from swelling of the resin-based crown (water absorption) and transfer to the luting interface further added to the interfacial stress and most probably contributed to a great extend to the debonding failure.

First clinical experiences with CAD/CAM-fabricated PMMA-based fixed dental prostheses as long-term temporaries

OBJECTIVE

The clinical performance of polymethylmethacrylate (PMMA)-based fixed dental prostheses (FDP) was evaluated in the indication of long-term temporaries.

MATERIALS AND METHODS

In the current indication of the applied machinable PMMA-based material (Vita CAD-Temp), i.e. temporary crowns and FDPs, 27 patients with compromised dentitions (uncertain dental prognosis or postponement of a removable treatment option) were recruited and 45 FDPs (3 or 4 units, 37 terminal-retained, 8 cantilevered) were inserted. Frameworks were computer-aided design (CAD)/computer-aided manufacturing (CAM)-manufactured after conventional impression taking and labside scanning of stone master casts. A resin-modified hybrid cement material (RelyX Unicem) was used for luting in a conventional protocol. Clinical follow-up was performed biannually.

RESULTS

Over an observation time from 2 to 26 months (median 13 months), 11 complications were found in 9 out of 45 PMMA restorations: 4 losses of retention, 5 complete fractures; two of these subsequent to a trepanation for endodontic treatment. Thereby, 3 out of 8 cantilevered FDPs had to be removed within 8 months. Thus, the statistical evaluation included FDPs with abutment at end, only. These standard design FDPs (n = 37) showed a 90.4 % survival rate with a complication-free rate of 88.3 % estimated for an observation time of 16 months.

CONCLUSION

Cantilevered FDPs and reconstructions on abutment teeth with markedly reduced biological prognosis or endodontic intervention yielded a high-failure rate. Terminal-retained FDPs performed clinically well in cases without compromised abutment teeth.

CLINICAL RELEVANCE

PMMA-based material might be used successfully for long-term temporization with 3- to 4-unit FDPs in a standard design over at least one year.